1 Introduction
The development of energy resources has promoted social progress, while the rapid development of society and the economy has brought about significant transformations in energy technology, leading to an increasing demand for energy in industrial production and daily life
[1]. However, the combustion of traditional fossil fuels such as coal, oil, and natural gas leads to massive carbon dioxide emissions, triggering a series of environmental problems including global warming
[2]. To reduce dependence on fossil fuels and lower greenhouse gas emissions and pollutant generation, the development and utilization of renewable energy have become a new trend in global energy development. Currently, the mainstream approach is to develop renewable clean energy technologies such as solar, geothermal, and wind power; however, these energy sources are limited by extraction technologies, climate, and geographical location, resulting in high costs, making it essential to develop stable and reliable renewable energy
[3-6]. As one of the most widely applied and highly commercialized energy storage devices, lithium-ion batteries (LIBs) play a crucial role in alleviating energy shortages, reducing environmental pollution, and achieving the "dual carbon" goals
[7]. With the development of the information age, LIBs are widely used in fields such as portable electronic devices, power tools, energy storage, aerospace, and new energy vehicles
[8-11]. In recent years, due to increasingly stringent requirements for energy and power density, LIBs have gradually occupied the main market share of secondary batteries (including electric vehicles, energy storage, and 3C electronic products), and demand continues to grow. As
shown in Fig. 1a, b, it is projected that by 2030, the demand for LIBs across different regions and sectors globally will continue to increase significantly
[12]. As the update and iteration speed of products in the new energy sector accelerates, people are continuously optimizing LIB performance. However, the service life of power batteries is generally 5–8 years, which will lead to a large number of LIBs facing retirement (
Fig. 1c). Since retired LIBs contain large amounts of metal components and organic pollutants, if they are not scientifically and reasonably recycled and treated, it will not only cause a waste of resources but also pose a huge threat to the environment
[13-15].
Currently, the recycling of retired LIBs focuses more on the comprehensive utilization of valuable metals in cathodes, and a mature process system has been established. Metals such as lithium, cobalt, nickel, and manganese in cathode materials are highly scarce and economically valuable, and their recycling technologies are becoming increasingly perfected. However, more critically, focusing solely on cathode recycling cannot achieve full-component battery circulation: on one hand, graphite recycling can offset profit fluctuations caused by volatility in cathode metal prices; on the other hand, a complete recycling system covering both cathode and anode materials can reduce environmental burdens and enhance the economic value of solid waste. Meanwhile, the high-value regeneration of graphite can significantly improve the overall value and sustainability of the entire recycling industry chain.
However, attention to the recycling and application of graphite anodes from retired LIBs remains limited. Considering the risks associated with limited resource supply and environmental pressure, recycling and reusing graphite anodes from retired LIBs has become an urgent issue to be addressed.
[16]. Commercial graphite mainly consists of artificial graphite and natural graphite, accounting for 43% and 46% of the lithium battery anode market share, respectively.
[17]. In response to the shortage of natural graphite and the high price of artificial graphite, recycling waste graphite anodes can significantly alleviate pressure on the supply chain of graphite materials for lithium-ion battery anodes and meet the growing demand for lithium batteries. The recycling process for waste graphite anodes includes electrode separation, layer exfoliation and purification, and regeneration.
[18](
Figure 1d). Furthermore, as an anode for lithium-ion batteries, maintaining the crystallinity and layered structure of regenerated graphite is crucial. During long-term charge-discharge cycles, lithium ions intercalate into and deintercalate from the graphite, while inactive lithium intrudes into the channels, leading to the destruction of the structural integrity of the graphite and damage to its pore structure.
[19]. Therefore, purified graphite still requires further regeneration; common methods include high-temperature catalytic graphitization, carbon coating, element doping, and material compositing.
[20].
Starting from the exfoliation and purification of spent lithium-ion battery graphite anodes, this paper reviews and summarizes the methods and benefits of recycling waste graphite, providing important data support and directional guidance for its resource utilization. Meanwhile, it compiles the current status of waste graphite recycling, including secondary applications in other energy storage fields such as regenerated anodes, raw materials for high-value graphene-based materials, catalysts, and functional composite materials. On this basis, this paper focuses on analyzing the problems and challenges faced in the recycling and utilization of spent lithium-ion battery graphite anodes, and prospects the future of waste graphite anode recycling.
2 Peeling and purification of graphite anodes from retired lithium-ion batteries
During long-term cycling, the graphite anode in spent lithium-ion batteries often suffers significant performance degradation due to coverage by electrolyte decomposition byproducts, residual electrode binders, and the accumulation of lattice defects
[21](
Figure 2a). To address this issue, current strategies for the exfoliation and purification of graphite primarily rely on two approaches: thermal treatment and chemical repair
[22](
Figure 2b). Thermal treatment typically involves high-temperature annealing under an inert atmosphere (such as nitrogen or argon), utilizing high heat to decompose and remove residual polyvinylidene fluoride (PVDF) and electrolyte decomposition products from the graphite surface, while simultaneously promoting the ordering of the graphite lattice and partially repairing defects
[23-24]. Existing research indicates that annealing within the range of 700–1200 °C can not only effectively strip impurity layers and byproduct carbon films but also improve the specific surface area and electrochemical cycling stability of graphite
[25-26]. However, excessively high temperatures or prolonged holding times can cause the collapse of the graphite structure and agglomeration of particles; controlling these two variables is key to improving efficiency
[27]. Although the thermal treatment method is simple, convenient, and suitable for large-scale operations, it is often accompanied by health and environmental risks. This is because incomplete combustion of waste graphite and binder residues can release toxic gases, smoke, and particulate matter
[28]. Additional health and safety protection measures are required to handle these byproducts, which significantly increases the cost of spent graphite recycling and subsequent regeneration processes, as
Table 1shows
[29].
In contrast, chemical repair focuses more on the regulation of interfaces and structures. For instance, using chemical reducing agents to remove oxide layers from the graphite surface can restore its electrical conductivity and lithium-ion intercalation capability; regeneration strategies based on asphalt or organic carbon sources form graphitic-like carbon layers through high-temperature carbonization or surface coating, thereby compensating for lattice defects and improving cycle life and rate performance. Furthermore, heat treatment and chemical repair can be combined, such as first removing impurities via high-temperature annealing, followed by asphalt coating and re-carbonization to strengthen structural and interfacial stability. This composite approach not only achieves deep purification but also effectively enhances the electrochemical performance of regenerated graphite. In summary, the individual or synergistic application of heat treatment and chemical repair provides a reliable technical pathway for the efficient regeneration of waste graphite anodes and lays a solid foundation for their promotion in secondary applications within power batteries.
2.1 Heat treatment process
Thermo-mechanical dissociation combined with flotation can promote partial reduction of metal oxides during pyrolysis, helping to improve their leaching efficiency and reduce the amount of reducing agents required for hydrometallurgical processing. Meanwhile, the removal of binders enables foam flotation to efficiently separate lithium metal oxides (LMOs) from graphite, which is why the thermo-mechanical crushing process has become the preferred method for the selective separation of graphite and LMOs. Vanderbruggen et al.
[30]systematically compared the effects of three upstream treatment methods—mechanical dissociation (Mechanical), thermo-mechanical dissociation (Thermal-mechanical, TM), and electro-hydraulic fragmentation (EHF)—on the separation efficiency of battery active components. The process flow is as shown in
Figure 3a. The study shows that while simple mechanical crushing can achieve partial delamination of electrode layers, the incomplete removal of binders results in only 5.1% (by mass) of the black mass entering the fine fraction (<63 µm). This indicates insufficient dissociation of the actual active components, leading to low recovery rates in subsequent flotation, at only around 60% (
Figure 3b). In contrast, thermo-mechanical treatment significantly improves dissociation efficiency: the mass fraction of fine black mass increases from 36% to 51%, binders are effectively removed, and graphite and cathode oxide particles are fully dissociated. In flotation separation experiments, the products obtained via the TM process exhibited the highest selectivity. The overflow recovery rate for graphite reached 94.4%, while the underflow recovery rate for LMOs reached 89.4% (
Figure 3c). Heat treatment not only removes binders and improves particle dissociation but also provides higher-purity raw materials for downstream sorting, thereby creating fundamental conditions for graphite performance restoration. It should be noted that when batteries undergo direct heat treatment, due to dense structures and localized temperature rises, PVDF may only partially decompose, while side reactions such as Al melting and HF generation may occur. Among these, Al melting leads to graphite agglomeration and introduces metallic impurities; meanwhile, HF generation damages the graphite structure and corrodes equipment, posing safety and environmental risks. Both factors significantly deteriorate the morphology, structure, and electrochemical performance of regenerated graphite, while increasing process costs and safety hazards. Therefore, electrolyte cleaning and electrode disassembly should be performed prior to pyrolysis to obtain regenerated graphite with more complete morphology and stable structure.
Furthermore, the pyrolysis combined with oxidation/acid leaching remediation strategy is also noteworthy. This process can promote the decomposition of binders and the solid electrolyte interphase (SEI) film, accelerate the efficient separation of graphite from metal foils, and enable the selective oxidation and separation of impurity metals, thereby avoiding interference in subsequent metal recovery. Yang et al.
[31]proposed a remediation route combining a "two-step" heat treatment with wet purification (
Figure 3d). First, the electrode was treated at 400 °C under an Ar atmosphere, successfully detaching the graphite anode from the copper foil to obtain a pure copper current collector. Subsequently, heat treatment at 500 °C in air selectively oxidized copper impurities remaining in the graphite into CuO for subsequent removal via acid leaching. In the wet purification process, metals such as Li, Cu, and Al were almost 100% leached out. Then, through pH control and sodium carbonate precipitation, Li
2CO
3with a purity greater than 99% was obtained. Meanwhile, the finally obtained regenerated graphite also exhibited excellent electrochemical performance (
Figure 3e, f): within a voltage window of 0.01–2 V, the initial specific capacities were 591, 510, and 335 mAh/g, respectively, with a Coulombic efficiency close to 100%, and the capacity retention rate remained as high as 97.9% after 100 cycles at 1 C. Heat treatment combined with acid leaching can not only thoroughly remove binders and impurities but also restore the lattice order and interfacial electrochemical stability of graphite. Furthermore, this study evaluated the process economics: treating 1 ton of waste graphite requires consuming 1.644 tons of HCl, 0.602 tons of NaOH, and approximately 10,000 kWh of electricity, with a total cost of about 13,364.2 yuan. Considering the revenue from by-product recovery of metallic copper and lithium carbonate, and given that the market price of regenerated graphite is approximately 15,000 yuan/ton, this process is proven to be economically feasible.
Noting that HF and organic volatiles are generated during the heat treatment process, to avoid strong corrosion of equipment by HF, alkali washing combined with activated carbon adsorption can be employed to treat exhaust gases, and a closed-loop circulation system can be implemented for acid-base waste liquids to further enhance environmental friendliness. Additionally, adding alkaline treatment agents during the heat treatment process can also effectively reduce HF content. Wang et al.
[32]used calcium oxide as a reaction medium to achieve in-situ decomposition heat treatment of PVDF binders at a lower temperature of 300 °C. The experimental procedure is as
shown in Figure 3g. Herein, CaO forms solid-phase contact with PVDF, promoting interaction between CaO and the C—F bonds in PVDF. Meanwhile, HF generated from PVDF is immediately captured by CaO, forming CaF
2, thereby achieving defluorination (
Figure 3h). Compared with traditional pyrolysis, CaO-assisted pyrolysis requires lower temperatures and reduces hydrogen fluoride emissions, demonstrating superior economic and environmental benefits.
The thermal treatment method has low reagent costs, requiring only inert gas or CaO additives. However, it has high equipment thresholds, needing high-temperature furnaces and exhaust gas treatment systems, along with facilities for handling HF and organic volatiles, resulting in a comprehensive cost of approximately 13,364 yuan/ton. The products produced by this method have high value; the purity of regenerated graphite can reach over 99%, with a market price of about 15,000 yuan/ton, plus additional revenue from by-product Cu and Li.2CO3recovery benefits, demonstrating economic feasibility. In terms of environmental benefits, although there is a risk of toxic gas emissions, compliant discharge can be achieved through alkali washing and activated carbon adsorption, supplemented by closed-loop wastewater circulation, showing strong adaptability for large-scale application.
2.2 Electrochemical exfoliation
Aqueous electrolysis enables rapid decoupling of the "graphite-copper foil" interface, directly yielding usable regenerated graphite and high-purity copper foil
[33]. In terms of process, the copper foil coated with graphite serves as the cathode, and waste graphite as the anode; these are immersed in a Na
2SO
4 aqueous solution to undergo electrochemical exfoliation under constant voltage conditions (
Figure 4a). Under the intensifying effect of the electric field, ion migration and interfacial reactions cause binder failure and detachment of graphite from the current collector (
Figure 4b). Regarding electrochemical performance, as shown in
Figure 4c, the capacity of regenerated graphite decreases with increasing C-rates from 0.2 to 5 C, but recovers to 374 mAh/g when returning to 0.2 C, demonstrating good reversibility. Cyclic voltammetry (CV) tests show that the broad reduction peak at 0.5–0.7 V during the first scan corresponds to the in-situ formation of the solid electrolyte interphase (SEI), with stable peak shapes in subsequent cycles (
Figure 4d). The shrinking of the high-frequency semicircle in the electrochemical impedance spectroscopy (EIS) indicates reduced charge transfer impedance and polarization, while the low-frequency Warburg line approaching 45° suggests that Li
+ diffusion is more unobstructed, corroborating the pore structure characterization (
Figure 4e). More importantly, under 0.1 C conditions, the first-cycle discharge capacity of regenerated graphite reaches 427.8 mAh/g, and the capacity retention rate remains at 87.4% after 100 cycles (
Figure 4f). Although the high specific surface area leads to a thicker SEI and some initial lithium loss, the material exhibits overall cycling stability and high capacity, possessing application potential competitive with pristine graphite. In the economic evaluation, energy consumption costs were calculated based on actual electricity prices, combined with revenue from copper foil and graphite output. The results show a profit of $10.1430 per kilogram of processed waste anode material. Since the electrolyte can be recycled, the actual profit per kilogram will be higher than this value. Meanwhile, the potential value of electrochemical exfoliation lies in the secondary recovery of lithium ions once they are enriched to a certain concentration in the electrolyte. Therefore, it offers positive economic returns and scalability, providing an engineering basis for the "repair-and-reuse" of waste graphite.
Electrochemical exfoliation has moderate energy consumption, with a unit processing energy of 3000~5000 kWh/t. Since the electrolyte is recyclable and reagent consumption is low, the equipment only requires an "electrolytic cell + separation unit," yielding significant economic returns. Meanwhile, the product value is high; the first-cycle discharge capacity of regenerated graphite can reach 427.8 mAh/g, approaching that of pristine graphite, while the synchronous recovery of high-purity copper foil further enhances profits. Furthermore, this method offers excellent environmental benefits, with no toxic gas emissions, minimal waste liquid that is easy to treat harmlessly. However, its scalability is limited by electrolytic cell layout, necessitating optimization of electrode structures to improve processing efficiency.
2.3 Chemical remediation
The core of chemical repair lies in the selective dissolution of electrode binders to achieve complete separation of graphite from the current collector under mild conditions, while preserving its microstructure and electrochemical activity as much as possible. For water-insoluble PVDF, studies typically employ high-polarity organic solvents (such as dimethylformamide (DMF), dimethyl carbonate (DMC), etc.) to disrupt the interactions between the binder and active materials through penetration and swelling-dissolution effects. If water-soluble binders are used instead, aqueous systems can be directly applied for desorption, further reducing energy consumption and the risk of secondary pollution. Review evidence also indicates that N-methylpyrrolidone (NMP) is commonly used in PVDF systems
[34], DMC
[35], DMF
[36], dimethylacetamide (DMAC)
[37], and other polar solvents for chemical separation, whereas when using water-soluble binders, direct aqueous separation can be performed; however, residual electrolyte LiPF must be thoroughly removed during the pretreatment stage
6to prevent HF generation.
Zuo et al.
[35]utilized pre-cleaning of spent anodes to remove residual electrolyte and strip graphite particles. As
shown in Fig. 4g, combining improved Hummers oxidation with ultrasonic fragmentation converted nearly all spent graphite into graphene-like carbon nanofragments (ox-CNFs). Their size distribution ranges from 15 nm to 2 μm (
Fig. 4h, i), exhibiting excellent hydrophilicity and good dispersibility. Reduced carbon nanofragments (re-CNFs) were obtained via hydrothermal/chemical reduction. X-ray diffraction (XRD) and transmission electron microscopy (TEM) corroborated that cycled graphite can be effectively "deconstructed-reconstructed" through a coupled chemical-physical pathway, achieving upcycling from spent graphite to high-value-added carbon nanomaterials. Furthermore, after adding carboxylated ox-CNFs to aniline, the resulting CNFs/polyaniline composite achieved a discharge capacitance of 356.4 F/g at a scan rate of 2 mV/s, representing an 80.5% improvement compared to pure polyaniline materials (
Fig. 4j).
The chemical solvent exfoliation route, centered on the directional dissolution of electrode binders, enables complete detachment of graphite anodes from current collectors under relatively mild conditions, providing high-purity carbon sources and a scalable process window for subsequent "regeneration-application." Natarajan et al.
[36]employed DMF to dissolve PVDF, removing graphite from Cu foil in spent batteries. After filtration and vacuum drying at 150 °C, recovered graphite was obtained, as
shown in Fig. 4k. The same process also involved acetone cleaning of polyethylene (PE) and polypropylene (PP) separators to remove surface impurities, providing a clean raw material basis for composite reuse. Subsequently, PP and PE separator films with varying graphite loadings (PP/GRx, PE/GRx) were prepared via solution intercalation. Their micro-morphology, thermal, mechanical, and electrical properties were systematically characterized, demonstrating the feasibility of direct engineering reuse of recovered graphite. As
shown in Fig. 4l, m, taking PP as an example, the tensile strength increased from 3.4 MPa to 33.9 MPa with increasing filler content. When using PE as the matrix, the tensile strength rose from 3.0 MPa to 38.1 MPa, while the electrical conductivity exhibited a jump of 5–6 orders of magnitude. The conductive performance of the recovered graphite is comparable to that of commercial graphite, thereby completing a closed-loop demonstration of "chemical solvent exfoliation–material regeneration (polymer composites)."
From the perspective of "regenerative design," Jeschull et al.
[38]Their systematic research on water-soluble binder systems has laid the material and process foundation for future aqueous chemical delamination and green regeneration. Compared to the PVDF-NMP system, sodium carboxymethyl cellulose/styrene-butadiene rubber composite films (CMC-Na/SBR) and sodium polyacrylate (PAA-Na) offer lower costs and more environmentally and health-friendly characteristics, while facilitating the formation of a more stable and thinner SEI. At both laboratory and pilot scales, graphite electrode preparation and electrochemical evaluation were completed using aqueous slurries with a low binder content of 4% (by mass) and solid contents of 37%~38% and 48%~50%. This demonstrates that aqueous formulations can achieve scaled-up production without compromising electrochemical performance, thereby enhancing the operability and environmental performance of subsequent aqueous/low-toxicity solvent delamination and regeneration from the source.
Polar solvents such as DMF/DMC enable low-temperature delamination of PVDF-based electrodes and directly guide composite material regeneration. For graphite anodes subjected to cycling degradation, chemical oxidation coupled with ultrasonic deconstruction provides an efficient upgrading pathway from macroscopic particles to nanofragments. Furthermore, the forward-looking application of water-soluble binders reduces reliance on organic solvents and mitigates health/emission burdens from a material design perspective, thereby enhancing the overall sustainability and scalability of the chemical solvent delamination-regeneration chain.
Chemical repair methods offer advantages such as low energy consumption, operation at ambient or moderate temperatures, high product purity, and intact preservation of the graphite microstructure. They can be directly applied in high-end scenarios like polymer composites, yielding products with high added value. However, their core limitation lies in high reagent costs, relying on high-polarity solvents such as DMF and NMP. The ratio of reagent consumption to processing volume reaches 1:1 to 1:2, and waste liquid treatment costs account for over 60%. Scaling up requires supporting efficient solvent recovery systems. Furthermore, this process generally necessitates integrated equipment including dissolution tanks, filtration, and drying units. Environmental risks are concentrated in organic solvent volatilization and waste liquid contamination, requiring strict control of exhaust gas collection and wastewater treatment. Overall economic viability depends on large-scale solvent recycling.
3 Regeneration Strategies for Waste Graphite Anodes
3.1 Surface treatment technology
To address issues such as defects, polarization by-products, and insufficient wettability on the surface of spent graphite anodes caused by cycling and aging, oxidation and fluorization treatments are widely used for the "refurbishment" of interfaces and active sites. Acidic oxidation, such as in nitric acid or perchloric acid systems, can selectively etch surface defects and amorphous carbon, forming nanoscale micropores and introducing oxygen-containing functional groups like carboxyl, hydroxyl, and carbonyl groups on the surface. This enhances electrolyte wettability and controllability of initial film formation without significantly damaging the host layered structure.
[39]</sup>transport. Furthermore, oxygen-containing functional groups serve as preferential nucleation sites for the SEI film, rapidly undergoing interfacial reactions with decomposition products in the electrolyte, such as carbonate solvent molecules, to accelerate SEI film formation. Meanwhile, a uniform and dense oxygen-containing SEI film can suppress continuous electrolyte decomposition and graphite exfoliation. The weak interaction between functional groups and lithium ions avoids strong adsorption traps during the lithium intercalation process, reducing irreversible lithium fixation. In terms of the capacity-rate trade-off, this is more beneficial for Li
+transport and uniform SEI nucleation.
Fluorination treatment involves using C
4F
8 and other fluorine-containing precursors to in situ construct an ultra-thin C-F
x functional layer in low-temperature plasma, which can significantly suppress initial side reactions and reduce polarization. Taking synthetic and natural graphite treated with C
4F
8 plasma as examples, the rate performance and cycling stability are significantly improved while maintaining the integrity of the main structure
[40-41]. Surface C—F bonds impart a denser and more stable interface layer, reducing electrolyte decomposition and irreversible lithium loss. Graphite treated with C
4F
8 exhibits superior reversible capacity and reduced voltage hysteresis in high-rate regions compared to untreated samples, demonstrating the feasibility of plasma fluorination as a "low-temperature mild" repair-modification pathway for aged graphite.
Surface treatment technologies feature low reagent costs, simple equipment, and straightforward operating procedures, making them suitable for integration with exfoliation processes. Their product value is reflected in enhanced electrochemical performance; for instance, oxidation treatment improves the rate capability of graphite by 20%–30%, while fluorination treatment significantly optimizes cycling stability. These materials can be directly reused as anodes for power batteries, offering higher added value than ordinary recycled graphite. In terms of environmental benefits, acid oxidation generates small amounts of acidic waste liquid requiring neutralization, yet overall pollution remains controllable. Plasma fluorination produces no secondary pollution, representing a more promising green modification pathway with strong scalability and no apparent capacity constraints.
3.2 Coating Technology
In recent years, carbon coating has been proven to be an efficient and low-cost method for enhancing the electrochemical performance of graphite. This method involves spraying or impregnating recycled graphite with carbon sources such as phenolic resin or pitch, followed by pyrolysis to form a uniform and dense graphitized carbon layer. This layer not only fills surface micro-defects and suppresses side reactions with the electrolyte but also provides a continuous electron phase at high rates, thereby balancing cycling stability and rate capability.
[42-43]. Li et al.
[44]used carboxymethyl cellulose and glucose as raw materials, carbonized them at 800 °C for 5 h, and prepared carbon-coated graphite (
Figure 5a). As shown in
Figure 5b, after 270 cycles at a 1 C rate, this modified graphite still maintained a high specific capacity of 424.7 mAh/g. In addition, other carbon sources, such as reaction compounds of polyethylene glycol and monoolein
[45], phenolic resin
[46], and pitch
[47]have also been used to prepare carbon-coated graphite. The aforementioned carbon coating processes typically require pre-treatment of waste graphite via leaching and heating to remove impurities, followed by high-temperature sintering to achieve simultaneous structural reconstruction of the graphite and carbon coating.
Ruan et al.
[48]proposed a feasible, environmentally friendly, and economical method for regenerating graphite anodes from spent lithium-ion batteries. As
shown in Figure 5c, this method treats waste graphite (SGT) through pyrolysis, acid leaching, graphitization, and amorphous carbon coating processes, ultimately yielding regenerated graphite (G-A-T-SGT@C). The results indicate that, compared to SGT, G-A-T-SGT@C exhibits extremely low impurity content, smaller specific surface area, reduced pore defects, and significantly improved degree of graphitization. Lithium-ion batteries using G-A-T-SGT@C as the anode demonstrate excellent performance: an initial Coulombic efficiency as high as 90.64% (
Figure 5d), a specific capacity reaching 344 mAh/g at 0.2 C (
Figure 5e), and outstanding cycling stability maintained over 250 cycles at 0.5 C (
Figure 5f). Compared to lithium-ion batteries using commercial graphite as the anode, the performance of these regenerated graphite batteries is equally remarkable. To investigate the carbon coating process and reveal its repair mechanism, Da et al.
[49]employed in-situ transmission electron microscopy (
in-situ TEM) technology to observe the evolution of the graphite surface structure from room temperature to 1100 °C. Under controlled heating conditions, amorphous carbon transforms into graphitized carbon on existing graphite layers, as
shown in Figure 5g. High-resolution transmission electron microscopy (HRTEM) images indicate (
Figures 5h and i) that during the high-temperature coating regeneration process, the gradual graphitization of the carbon coating layer follows an epitaxial growth mechanism (
Figure 5i).
In addition to carbon coating, metal oxide coating and conductive polymer coating methods can also be applied to regeneration strategies. Metal oxide coating is mainly achieved through sol-gel methods, precipitation methods, atomic layer deposition (ALD), and other techniques to deposit ultra-thin coatings, enabling them to act as an "artificial SEI" without significantly sacrificing electron and ion flux, effectively reducing irreversible consumption in the first cycle, suppressing interfacial side reactions, and preventing crosstalk between particle-side reactions. Among these, the sol-gel method uses metal alkoxides or inorganic salts as precursors; through hydrolysis and condensation reactions in a solvent, a uniformly dispersed sol is formed. After immersing the substrate material in the sol, colloidal particles adsorb onto the substrate surface, aggregate, and gelate. Following drying and calcination, a dense metal oxide coating layer is formed. This coating layer is uniform and dense, with strong interfacial bonding to the substrate. In contrast, the precipitation method involves dispersing the substrate material in a metal salt solution and adjusting the system's pH by adding a precipitating agent dropwise, causing metal ions to generate precipitates in situ on the substrate surface. After filtration, washing, and calcination, the precipitates are converted into a metal oxide coating layer. The coating layer obtained by this method has a high loading capacity, and its thickness can be easily regulated by adjusting the metal salt concentration. Furthermore, studies have shown that utilizing ALD for nanoscale uniform oxide layer surface modification of composite electrodes can significantly enhance rate capability and cycling stability, providing a refined engineering approach for the interfacial "re-passivation" of recycled graphite.
[50]. Meanwhile, using conductive polymers such as polyaniline (PANI) as a coating layer can form a conductive network on the graphite surface while improving interfacial flexibility and film-forming stability, thereby reducing initial polarization and the risk of particle contact failure. This strategy has been confirmed in multiple studies to synergize with carbon coating/oxidation pretreatment.
[51].
The product obtained through coating technology demonstrates outstanding value. The initial coulombic efficiency of carbon-coated regenerated graphite can reach 90.64%, with excellent capacity retention after 250 cycles. Its performance approaches that of commercial graphite, offering strong market competitiveness. Energy consumption is primarily concentrated in the sintering stage, generating only a small amount of carbon oxide exhaust gas that can be directly emitted.
3.3 Doping technology
Non-metal doping (e.g., N, B, S elements) can effectively modulate local electronic states, create reversible adsorption/intercalation sites, and improve material wettability, thereby enhancing the reversible capacity and rate performance of graphite anodes. However, excessive doping may weaken structural stability and introduce side reaction sites, necessitating a balance between defect density and conductive pathways.
[52-54].
Among these, boric acid pretreatment combined with short-time annealing not only repairs compositional and structural defects in waste graphite but also achieves boron doping on its surface. Boron doping can introduce electron holes, enhance the electronic state density and conductivity of graphite, accelerate charge transport, and reduce interfacial impedance; it can also expand the graphite interlayer spacing and lower the energy barriers for lithium-ion insertion and extraction. Meanwhile, stable B—C bonds formed on the surface inhibit excessive growth and peeling of the SEI film during charging and discharging, thereby significantly improving cycling stability. Markey et al.
[55]achieved a specific capacity of up to 332 mAh/g by pretreating waste graphite with boric acid and sintering it at 1050 °C. Moreover, excellent cycling stability was maintained after 100 cycles, outperforming the original waste graphite. In addition, Xu et al.
[56]used acid-treated waste graphite and urea as raw materials to produce regenerated graphite with nitrogen doping and expanded interlayer spacing through a process involving simultaneous vapor-phase exfoliation and elemental doping (
Fig. 6a). During heating, ammonia gas generated from urea decomposition etches and exfoliates the graphite edges, further inserting into the graphite interlayers to cause exfoliation. Under high-temperature conditions of 800 °C, the interlayer g-C
3N
4serves as a nitrogen source and undergoes complete pyrolysis, thereby achieving nitrogen doping of the graphite. After 200 cycles at a current density of 0.1 A/g, the specific capacity of this regenerated graphite remained at 465.8 mAh/g (
Fig. 6b); even at a high current density of 4 A/g, this nitrogen-doped graphite exhibited a high specific capacity of 143.5 mAh/g, approximately twice that of commercial graphite (
Fig. 6c). This improvement in specific capacity can be attributed to nitrogen doping, the exfoliated structure, and the expanded interlayer spacing.
To investigate the mechanism by which nitrogen doping and vacancies introduced by the nitrogen doping process enhance volumetric capacity, Hai et al.
[57]precisely controlled the depth and concentration of the introduced dopant elements by regulating the incident energy and fluence of the injected ions to fabricate nitrogen-doped graphite (
Figure 6d). As
shown in Figures 6e~h, after nitrogen ion implantation, the number of graphite nanocrystals increased, disordered graphite structures appeared, and the graphite lattice spacing expanded. These structural changes can provide sufficient accommodation space and transport channels for lithium ion intercalation and deintercalation. Meanwhile, nitrogen doping on the graphite surface formed pyridinic nitrogen and pyrrolic nitrogen, constructing a three-dimensional structure on the pure graphite surface. Pyridinic and pyrrolic nitrogen can increase the electron state density at the Fermi level of the graphite layers and open the band gap, thereby improving the electrochemical performance of graphite. These four structural changes in graphite formed during the nitrogen ion implantation process can synergistically enhance its electrochemical performance.
Therefore, the essence of structural regulation via non-metal element doping is to enhance electron state density and conduction rate through "charge injection, hole introduction, and heterojunction formation," addressing the bottleneck of insufficient electronic conductivity in graphite and improving the rate performance of the electrode. Meanwhile, it also expands the interlayer spacing through atomic substitution and particle embedding, reducing Li+migration energy barriers, thereby simultaneously enhancing capacity and rate performance.
3.4 Composite modification
Si anodes possess high theoretical capacity and low operating voltage, making them one of the most promising anode materials for LIBs. Si/C composites combine the high specific capacity of Si with the structural stability of graphite, representing a mainstream approach that balances energy density and lifespan.
[58]By designing structures such as core-shell, hierarchical porous architectures, and elastic binders, the volume expansion effect of Si can be mitigated, the SEI stabilized, and high areal loading performance maintained. Regarding engineering details on Si content windows, composite structures, and binder/electrolyte synergy, recent research has provided a clear roadmap that can directly offer a modular transformation paradigm for the high-value utilization of recycled graphite.
[59-64].
Xu et al.
[65]prepared Si-graphite anodes using mechanical ball milling combined with a carbonization process (
Figure 6i). Under the action of electrostatic forces, the waste graphite matrix can achieve tighter bonding with Si nanoparticles, thereby suppressing the volume expansion of Si. Among these, defective graphite enhances the conductivity of the material, while oxygen-containing functional groups improve the mechanical toughness of the solid electrolyte interphase (SEI) film. The results show that the initial discharge capacity of this composite anode at a current density of 0.05 A/g is 1321.8 mAh/g (
Figure 6j). The composite material exhibits excellent rate performance at different current densities; in sharp contrast, the capacity of the Si/AG electrode decays significantly as the current density increases, retaining only 430 mAh/g at a current density of 3 A/g (
Figure 6k). Meanwhile, after 400 cycles at a current density of 1 A/g, the capacity retention rate of this composite anode still reaches 69% (
Figure 6l).
Furthermore, the composite modification method can fully utilize the cathode and anode of spent lithium-ion batteries to prepare novel battery anode materials. Ye et al.
[66]Using cathode and anode materials from spent lithium-ion batteries as raw materials, expanded graphite (CoO/CoFe
2O
4/EG) composite anode materials were successfully prepared through reduction-acid leaching, oxidation-intercalation, and solvent heat treatment (
Fig. 6m). After 700 cycles at a current density of 1 A/g, the CoO/CoFe
2O
4/EG electrode maintained a capacity of 890 mAh/g, with performance comparable to materials synthesized from pure reagents (
Fig. 6n). In addition, the research team also prepared metal sulfides and graphite anodes from spent lithium-ion batteries via a gas sulfidation process
[67]. After pretreatment, spent LiNi
xCo
yMn
1-x-γO
2 (NCM), LiNi
xCo
yAl
1-x-γO
2 (NCA) cathode materials and graphite were obtained; subsequently, a mixture of graphite, cathode materials (NCM/NCA), and sublimed sulfur was sintered in an Ar/H
2 mixed atmosphere, then transferred to deionized water to leach out lithium elements, ultimately yielding carbon-based metal sulfide composites (NCMS/C and NCAS/C). Benefiting from the synergistic effect generated by the close contact between metal sulfides and reconstructed graphite, the composite exhibits excellent electrochemical performance for lithium storage. This study achieved full-component recovery of both spent cathode and anode materials through a short-process solid-solid reaction, avoiding the use of multi-step acid-base neutralization reactions.
The modification of composite materials is achieved by introducing secondary phases such as Si and metal oxides to generate stable covalent Si—C bonds and physical protective layers, thereby realizing a tight combination between graphite and the secondary phase and suppressing the expansion effect of Si itself. Meanwhile, the introduction of the secondary phase also provides a larger theoretical capacity, demonstrating excellent electrochemical performance for lithium storage.
4 Functionalized Application of Waste Graphite
4.1 Graphene
Recycled graphite can not only be repaired and reused but also serves as a precursor for high-value-added carbon materials such as graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO), achieving an "upcycling" of materials. Using spent lithium-ion battery graphite anodes as a carbon source, graphene with uniform layer structure and good conductivity can be prepared via one-step or multi-step strategies involving chemical oxidation, exfoliation, and reduction. Studies show that this process maintains a high yield while obtaining layer size and electrical performance comparable to commercial graphene, verifying the feasibility and scaling potential of converting recycled graphite into graphene.
[68]. Zhang et al.
[69]proposed a process integrating calcination with oxidation-reduction to prepare graphene from waste graphite of lithium-ion batteries. As
shown in Figure 7a, the process first calcines the waste graphite at 600 °C to remove organic coatings on the graphite surface. Subsequently, an improved Hummers method (KMnO
4+H
2SO
4) is used to synthesize graphite oxide, which is then exfoliated by ultrasound to obtain GO. Finally, rGO is produced through reduction with N
2H
4·H
2O (hydrazine hydrate). Compared with commercial graphite, preparing graphene from waste graphite reduces the consumption of KMnO
4by 40% and H
2SO
4by 28.6% (
Figure 7b).
In the direction of electrochemical exfoliation, direct "in-situ intercalation-gas expansion-layer-by-layer exfoliation" under constant voltage/current conditions using inexpensive electrolyte systems enables mild and scalable graphene preparation. This technology offers advantages such as low energy consumption and tunable defect density and oxygen-containing functional groups, facilitating the on-demand acquisition of flake graphene for conductive, catalytic, and composite reinforcement applications.
[70]. He et al.
[71]achieved direct exfoliation of bulk graphite layers by recharging spent lithium-ion batteries to obtain lithiated graphite (
Figure 7c). When spent lithium-ion batteries are recharged to a capacity exceeding 50%, the waste graphite electrodes are completely converted into lithium-intercalated graphite compounds (LiC
6and LiC
12), as shown in
Figure 7d. After hydrolysis and ultrasonic treatment, 58.8% of the graphene precipitated, while 41.2% remained in suspension. In this regard, researchers characterized the suspended graphene using HRTEM and selected area electron diffraction (SAED), finding that the suspended graphene consists of single-layer structures or overlapping single-layer graphene. The six-fold symmetric patterns indicate that the single-layer graphene crystals possess a hexagonal structure, proving that fully lithiated graphite has been successfully exfoliated into few-layer graphene (
Figure 7e, f). Raman spectroscopy results (
Figure 7g, h) show that for graphene prepared from graphite electrodes at 100% state of charge (SOC), the 2D peaks of precipitated graphene and suspended graphene exhibit different shapes and positions: the 2D peak of suspended graphene shows good symmetry and a larger redshift, with the peak position concentrated at 2688 cm
-1, confirming it as single-layer or bilayer graphene. In contrast, the 2D peak of precipitated graphene exhibits an asymmetric shape, with the peak position concentrated at 2705 cm
-1, indicating a lower degree of exfoliation compared to suspended graphene, with a layer count of 2~4 layers. Meanwhile, the lithium in the intercalation compounds dissolves and is recovered in the form of Li
2CO
3. Economic analysis indicates that the total production cost of this process is $6025/t, with by-product revenue of $5485/t. Consequently, the calculated production cost for graphene is only $540/t, which is far lower than the cost and selling price of commercial graphene produced by current mainstream processes.
Furthermore, combining clean pretreatment of recycled graphite (salt removal, binder removal) with electrochemical or mechanochemical exfoliation can further enhance product purity and size uniformity. This process also demonstrates good coupling potential with physical intensification methods such as microwaves and ultrasound, providing new degrees of freedom and an economic basis for scalable preparation.
[72-73]. Chen et al.
[74]proposed an ultrasonic-assisted exfoliation method for preparing few-layer graphene from waste graphite (
Fig. 7i). Since the interlayer forces in waste graphite are weakened after multiple charge-discharge cycles, its exfoliation efficiency is 3–10 times that of commercial graphite. Similarly, TEM and Raman spectroscopy detected the prepared graphene sheets with sizes exceeding 1 μm and thicknesses less than 1.5 nm (corresponding to 1–4 layers of graphene) (
Fig. 7j–k). After annealing at 500 °C, its electrical conductivity reached 9100 S/m.
In summary, chemical oxidation and reduction methods are the most promising processes for preparing graphene from waste graphite. This process can efficiently remove organic and inorganic impurities from waste graphite, thereby obtaining high-quality graphene. Furthermore, since waste graphite itself has a higher degree of oxidation and structural defects, its oxidation and exfoliation efficiencies are both higher than those of commercial graphite. At the same time, the price of waste graphite is also far lower than that of commercial graphite.
4.2 Catalyst
Due to the abundant surface functional groups and excellent carbon matrix structure of waste graphite, research on preparing catalysts from waste graphite has received widespread attention. In graphite-based catalysts, waste graphite typically serves as both the active substance and the catalyst support. Such graphite-based catalysts can be used for the degradation of organic compounds via advanced oxidation-reduction, electrochemical oxygen reduction reactions, and the capture and catalysis of polysulfides. Guan et al.
[75]used ferric chloride and waste graphite as raw materials to prepare an expanded graphite-supported zero-valent iron composite catalyst via carbothermal reduction (
Figure 8a). Through heterogeneous Fenton reactions, this composite catalyst demonstrated excellent removal efficiency for 4-chlorophenol in water. This research team, Chen et al.
[74]used waste graphite, copper from LIB anodes, and iron oxide from rolling mill scale waste as raw materials to synthesize a graphite-supported zero-valent iron-copper bimetallic catalyst, also via carbothermal reduction. These catalysts exhibit good stability and can efficiently degrade 4-chlorophenol through the synergistic action of reduction reactions and heterogeneous Fenton reactions.
Through a one-step calcination process, copper-containing waste graphite anode materials can also be used to prepare CuO/C catalysts, which activate peroxymonosulfate (PMS) to degrade organic pollutants
[76]. Among them, the Cu(II)/Cu(I) redox cycle promotes PMS activation, thereby generating reactive oxygen species (HO·, SO
4·
-, ·O
4-and
1O
2), these reactive oxygen species are key to achieving pollutant degradation (
Figure 8b). Similarly, using waste lithium-ion battery anodes as raw materials, graphene oxide (GO) is prepared from waste graphite via a simplified Hummer's method; copper sulfate (CuSO
2SO
4) is prepared by reacting copper foil with sulfuric acid (H
4), and finally, a GO/CuO composite catalyst is obtained through adsorption and bonding reactions, as shown in
Figure 8c[77]. Compared with single CuO, this composite catalyst exhibits superior photocatalytic degradation activity for methylene blue, and its photocatalytic efficiency can be further enhanced under an applied electric field (
Figure 8d).
Waste graphite, leveraging its cost advantages and inherent characteristics such as porous structure, defects, abundant functional groups, and metal impurities, has become a highly promising raw material for catalyst preparation. These inherent traits not only facilitate catalyst synthesis but also enhance catalytic performance. However, in-depth analysis of the mechanisms by which these characteristics influence catalyst preparation and catalytic activity has not yet been conducted. Furthermore, due to differences among lithium-ion battery manufacturers and varying states of deactivation, the inherent properties of waste graphite may differ significantly, thereby exerting a substantial impact on catalytic performance.
4.3 Capacitor
Waste graphite is also applied in the field of capacitors, such as supercapacitors
[78], lithium-ion capacitors
[79]and sodium-ion capacitors
[80]. Natarajan et al.
[81]utilized waste lithium-ion battery cathodes and graphite produced by different manufacturers to fabricate an asymmetric supercapacitor. As
shown in Figure 8e, after leaching and hydrothermal treatment, the waste cathode was converted into spherical cobalt manganese oxide (MnCo
2O
4) particles. Meanwhile, using waste anode graphite and aluminum foil as raw materials, reduced graphene oxide (RGO) was prepared via the Hamer method and an aluminum reduction process. The assembled MnCo
2O
4//RGO supercapacitor in 1 mol/L sodium sulfate (Na
2SO
4) electrolyte achieved an operating voltage of up to 1.8 V (
Figure 8f). Its performance characterization, as
shown in Figures 8g and h, demonstrated a maximum energy density of 23.9 Wh/kg at a power density of 450 W/kg, with a capacitance retention of 94.4% after 8000 cycles, a performance superior to some devices previously fabricated using commercial raw materials. Aravindan et al.
[79]systematically investigated the feasibility of using waste graphite as an anode material for preparing lithium-ion capacitors and sodium-ion capacitors. When commercial activated carbon was used as the cathode, dual-carbon lithium/sodium-ion capacitors could be assembled. In lithium-ion capacitors, the waste graphite requires pre-lithiation treatment to form a graphite intercalation compound (LiC
6), enabling lithium ion supply; in a carbonate solution system at room temperature, the maximum energy density of this dual-carbon lithium-ion capacitor reached 185.54 Wh/kg. Similarly, in sodium-ion capacitor research, using sodium hexafluorophosphate (NaPF
6) in tetraethylene glycol dimethyl ether as the electrolyte, a "solvent co-intercalation" mechanism was proposed to achieve high reversibility. After assembling pre-sodiated waste graphite with commercial activated carbon into a capacitor, this structure achieved a maximum energy density of 59.93 Wh/kg and a maximum power density of 6.8 kW/kg at room temperature. Even after 5000 cycles at room temperature, the capacity remained at approximately 98%
[78].
5 Technical Comparison, Engineering Challenges, and Current Status
5.1 Engineering challenges of various technical processes
The specific process flow for the recycling, regeneration, and application of graphite anodes from retired LIBs includes: mechanical physical treatment, stripping-purification, regeneration, and functional application. Core technical bottlenecks still faced during the scale-up of each step, such as
Figure 1dshown.
In the mechanical-physical processing stage, there are challenges in efficient separation and pretreatment. The primary bottleneck for large-scale recycling is the efficient separation of electrode materials and the homogenization of pretreatment. Retired batteries come in mixed models, making automated disassembly equipment difficult to adapt to different battery structures, resulting in low efficiency in separating electrode sheets. Currently, large-scale disassembly efficiency is only 60%~70%, and the peeling of copper/aluminum foils from active materials is incomplete; residual metal impurities significantly affect subsequent purification effects. Furthermore, insufficient removal of residual electrolyte during the pretreatment stage generates HF during the peeling process, causing equipment corrosion and damage to the graphite structure. The inconsistent impurity content and lattice defect levels of waste graphite from different sources make it difficult to standardize pretreatment processes, increasing the difficulty of subsequent purification.
The stripping and purification of graphite anodes from retired LIBs is a core prerequisite step for resource utilization. Thermal treatment, electrochemical methods, and chemical solvent methods, as three mainstream technologies, exhibit differences in process characteristics, performance, and environmental economics; the basis for technology selection and process optimization can refer to
Table 2.
In the stripping and purification stage, all three methods face challenges in equipment adaptability and pollution control. During scale-up of the thermal treatment method, maintaining temperature uniformity within the high-temperature furnace is difficult, easily leading to local agglomeration of graphite particles or structural collapse. Meanwhile, HF generated from PVDF decomposition is highly corrosive to furnace materials, necessitating the use of expensive corrosion-resistant alloys, which increases equipment investment costs. Furthermore, efficient treatment of HF and organic volatiles in the exhaust gas requires a complex "alkali washing + activated carbon adsorption system," significantly increasing operating costs. In contrast, the electrochemical method faces issues with uneven electrode polarization that must be resolved in the scaled design of electrolytic cells. Currently, constant-voltage electrolysis systems at the laboratory scale exhibit low current density in edge regions after scale-up, resulting in reduced graphite desorption rates. Simultaneously, controlling lithium ion enrichment and fluorine residue during electrolysis becomes more difficult; without developing efficient electrolyte purification and recovery systems, the electrochemical performance of regenerated graphite will be compromised. In the chemical solvent process, solvent recovery is the core bottleneck for scale-up. Distillation recovery of solvents such as DMF and NMP consumes significant energy, and solvent loss rates are high during recovery. The separation efficiency between solvents and binders is low, and PVDF degradation products remaining in the waste liquid are difficult to remove completely, limiting the number of times solvents can be recycled and significantly increasing reagent costs.
In the scaled-up production of the regeneration process, ensuring the performance consistency of regenerated graphite is challenging. Variations in the initial properties of waste graphite from different sources, such as changes in interlayer spacing caused by differing cycle counts and differences in surface functional group types, lead to significant fluctuations in the specific capacity of products under the same regeneration process, thereby increasing the difficulty of precise control over the regeneration process. For instance, non-uniform control of coating thickness during carbon coating and uneven distribution of doping element concentrations both result in increased dispersion of the electrochemical performance of regenerated graphite, failing to meet the stringent requirements for anode materials in power batteries.
Scaling up in functional application scenarios faces a gap between "laboratory performance and industrial-grade products." For example, when preparing graphene via chemical oxidation, the degree of oxidation is easy to control at the laboratory scale. However, in large-scale production, KMnO4 and H2SO4 exhibit insufficient mixing uniformity, leading to uneven graphene sheet sizes and low product yield rates. In the preparation of graphite-based catalysts, the binding stability between surface functional groups of waste graphite and metal active components decreases during the large-scale loading process, shortening the cyclic service life of the catalysts. Furthermore, there is inadequate alignment with downstream applications for functionalized products; for instance, the electrode molding process for regenerated graphite-based capacitors has poor compatibility with existing energy storage equipment production lines, requiring additional equipment modifications, which limits large-scale promotion.
Finally, challenges also exist in the integrated synchronous recovery of cathodes and anodes. Currently, most large-scale recycling processes focus solely on the separate recovery of graphite anodes or cathode metals, failing to achieve collaborative recovery of all components from both electrodes. For instance, when recovering graphite via thermal treatment, metals such as Li, Co, and Ni in the cathode material form alloy phases that are difficult to separate; when stripping graphite using chemical solvents, cathode active materials tend to dissolve in the solvent, causing secondary pollution and resource waste. Full-process collaborative recovery requires developing an integrated "stripping-leaching-separation" process to address the selective separation of cathode and anode materials; otherwise, resource utilization rates will decline, compromising the overall economic viability of recycling.
5.2 Current Status of Engineering Implementation for Various Technical Processes
Various technologies differ in their focus on process characteristics, economic feasibility, and environmental benefits. To further clarify the direction for technological industrialization, a Technology Readiness Level (TRL) evaluation system is introduced (levels 1–9, where level 1 represents basic research and level 9 indicates full commercialization).
[82], the maturity of core technologies, their stage characteristics, and bottlenecks to industrialization are analyzed as follows.
In the exfoliation-purification technology field, the TRL of the thermal treatment method has reached levels 5~6, placing it at the pilot scale-up stage. Its laboratory processes have matured, with some enterprises already conducting pilot work, achieving single-batch processing capacities of 1~5 tons. The core bottlenecks for industrialization focus on controlling temperature uniformity within high-temperature furnaces, the high-cost equipment investment required for HF exhaust gas treatment, and the tendency of graphite particles to agglomerate. The TRL of the electrochemical exfoliation method is at levels 4~5, representing a transition stage from laboratory to pilot scale; laboratory validation has confirmed its feasibility, and small-scale test units can operate stably. However, large-scale pilot testing has not yet been conducted. The core challenges for industrialization lie in the scalable design of electrolytic cells, recovery technologies for lithium ions enriched in the electrolyte, and purification processes for fluorine residues in graphite. The TRL of the chemical solvent method is at levels 3~4, having only completed laboratory validation and optimization; while product performance meets standards, pilot scale-up has not been performed. Its industrialization bottlenecks mainly involve establishing efficient solvent recovery systems, treating degradation products of binders in waste liquids, and designing and adapting scalable dissolution tanks.
Regarding regeneration strategies, the TRL level for surface treatment technology is 5, indicating a pilot stage. The pilot line operates stably, regenerated graphite shows good performance consistency, and small-batch supply has been achieved. Core bottlenecks to be overcome for industrialization include cost control for neutralizing acid oxidation waste liquid, increasing the capacity of plasma fluorination equipment, and adaptability regulation for raw materials from different sources. The TRL level for carbon coating technology is 5, also at the pilot stage. Coating uniformity meets standards at the pilot scale, and the cycle performance of the product approaches that of commercial graphite. Core bottlenecks for industrialization are cost control of carbon sources, development of continuous sintering equipment, and precise control of coating thickness. The TRL level for doping technology is 3-4, at the laboratory verification stage. Doping uniformity is controllable with excellent performance in the laboratory, but no pilot testing has been conducted. Industrialization requires resolving issues such as the high cost of large-scale doping equipment (e.g., ion implanters), performance dispersion caused by fluctuations in raw material characteristics, and optimization and adaptation of doping amounts. The TRL level for composite modification technology is 5-6. The composite structure is stable with outstanding electrochemical performance in the laboratory; small samples meet standards, and pilot-scale amplification has been achieved. Core bottlenecks for industrialization lie in the uniform dispersion of secondary phase materials, suppression of Si volume expansion, and integration of cathode-anode synergistic recycling processes.
In the field of functional applications, the Technology Readiness Level (TRL) of graphene preparation technology is at levels 4–5, in the transition stage from laboratory to pilot scale. Under pilot scale conditions, the production yield reaches 40%–50%, and product quality approaches that of commercial graphene. Industrialization requires breakthroughs in large-scale process control, ensuring uniformity of graphene sheet dimensions, and reducing production costs (currently approximately $540/ton). The TRL of graphite-based catalysts is at level 3, having completed only laboratory validation; in the lab, they exhibit excellent catalytic activity (degradation rate of 4-chlorophenol >90%). Core bottlenecks for industrialization include the loading stability of active catalyst components, consistency issues in catalytic performance caused by graphite from different sources, and adaptability to industrial wastewater treatment scenarios. The TRL of energy storage capacitors is at level 5, currently in the pilot stage. Pilot devices achieve an energy density of 23.9 Wh/kg and a cycle life of up to 8,000 cycles, with small-batch applications already realized. Industrialization necessitates resolving compatibility between electrode forming processes and existing production lines, optimizing electrolyte systems, and perfecting large-scale assembly processes.
6 Conclusion and Outlook
Current research on the recycling and application of graphite anodes from retired lithium-ion batteries has established a technical framework of "exfoliation and purification - performance regeneration - functional application." It demonstrates significant advantages in process integrity, technological diversity, economic feasibility, and environmental benefits, laying a solid foundation for future development.
Although existing research has achieved phased results, there are still three major core shortcomings in transitioning from the laboratory to industrialization and from "feasible" to "efficient," which constrain the large-scale promotion of graphite anode recycling, such as
Figure 9shows. In addition, bottlenecks still exist in the performance of some technologies, the processes are not green and efficient enough, and current technologies still have obvious defects.
(1) Recycling methods have significant limitations. Thermal treatment consumes high energy and easily causes graphite particle agglomeration. Chemical solvent exfoliation relies on organic solvents such as DMF, resulting in high reagent consumption and costly waste liquid treatment. Although electrochemical exfoliation is mild, fluorine elements remain in the graphite, requiring additional purification steps.
(2) Significant fluctuations in material characteristics make performance stability difficult to control, resulting in "source inconsistency" of waste graphite. Graphite anodes from batteries of different manufacturers and varying end-of-life states (cycle count, operating environment) exhibit significant differences in impurity content (e.g., Cu, Al residues), lattice defect levels, and surface functional group types. This leads to inconsistencies in electrochemical performance (e.g., specific capacity fluctuating by ±15%) and catalytic activity (e.g., up to 20% variation in 4-chlorophenol degradation rates) under identical regeneration processes, posing major challenges for quality control in large-scale production. Currently, there is no universal regeneration solution for such "heterogeneous graphite."
(3) Low level of industrialization and lack of engineering technology support. Current research mostly remains at the stage of small-scale laboratory verification. On one hand, there is a lack of continuous and automated production equipment (such as integrated devices for graphite exfoliation, purification, and regeneration); existing processes are mostly batch operations, resulting in low efficiency and high costs. On the other hand, complete industry standards (such as indicators for regenerated graphite purity and electrochemical performance) have not yet been established, and synergy with cathode recycling is insufficient. Most processes target only the graphite anode, failing to achieve "synchronous recycling of anodes and cathodes and full resource utilization," which limits the overall economic viability of recycling.
Addressing existing shortcomings, future research on the recycling of spent graphite anodes needs to break through in three dimensions: "technology optimization, industrial implementation, and value enhancement," to drive the transformation from "laboratory results" to a "green industry."
(1) Develop green and efficient processes to reduce energy consumption and pollution, improve economic viability, and focus on "low-toxicity to non-toxic" exfoliation systems. For instance, promote aqueous-based exfoliation processes using water-soluble binders (CMC-Na/SBR) to replace organic solvents such as DMF, thereby reducing wastewater treatment burdens. Develop low-energy pyrolysis technologies assisted by microwaves and enhanced by ultrasound, lowering heat treatment temperatures from 700 °C to below 400 °C, while optimizing parameters like temperature and holding time to achieve a balance between energy consumption and graphite crystallinity. Explore integrated "in-situ purification-regeneration" processes, such as combining plasma fluorination (surface modification) with electrochemical exfoliation, to simultaneously address fluorine residue and lattice defect issues, enhancing process efficiency.
(2) Achieve precise regulation of material performance. To address fluctuations in material characteristics and enable customized regeneration, establish a "Waste Graphite Characteristic Database." Use characterization techniques such as spectroscopy (XRD, XPS) and electron microscopy (SEM, TEM) to categorically record impurity and defect information for graphite from different sources, thereby designing targeted regeneration schemes. For instance, intensify acid leaching steps for high-impurity graphite and employ directional nitrogen doping for repair in high-defect graphite; deepen composite modification technologies, such as designing a "core-shell-buffer layer" Si/C composite structure to mitigate Si volume expansion; develop precise "graphite-metal sulfide" composite processes utilizing Ni/Co/Mn elements from waste cathodes to prepare high-performance integrated energy storage-catalysis materials, solving the problem of synergistic anode and cathode recycling.
(3) Expand into high-value-added applications. Go beyond "battery reuse" to open up new scenarios in the energy storage field, developing anodes for sodium-ion batteries and carbon-based electrolytes for solid-state batteries based on regenerated graphite. Leverage the layered structure and defect characteristics of regenerated graphite to enhance ion conduction efficiency. In the environmental protection field, deepen the application of graphite-based catalysts, such as preparing "regenerated graphite@Fe"0-Cu" bimetallic catalysts for the efficient degradation of organic pollutants in industrial wastewater (such as 4-chlorophenol and methylene blue), realizing the value upgrade from "waste to environmental materials." Explore interdisciplinary integration, such as combining with flexible electronic technology to composite regenerated graphite with polymers, preparing flexible energy storage films for wearable devices, thereby expanding application boundaries.
In summary, the recycling and regeneration of waste graphite anodes is not only a cutting-edge topic in materials science but also a crucial component of energy strategy and sustainable development. Through interdisciplinary collaboration and technological breakthroughs, it is expected that value conversion from "waste" to "strategic resource" will be achieved in the future, providing solid support for the construction of a global green energy system.
National Natural Science Foundation of China(52104302)
National Natural Science Foundation of China(52064031)
Yunnan Fundamental Research Projects(202401AS070069)
Yunnan Fundamental Research Projects(202402AF080003)
“Xingdian Talent Support Plan” Programs of Yunnan Province(KKXX202452031)
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