1 Introduction
In the context of "dual carbon" goals, electrochemical devices have gradually evolved into an emerging field, widely applied in transportation, power grids, energy storage, and other sectors. Among these, batteries and supercapacitors have garnered significant attention due to their inherent advantages. While batteries and supercapacitors differ to some extent—batteries offering higher energy density and supercapacitors providing higher power density—they share identical components: electrodes, electrolytes, and separators. Currently, both batteries and supercapacitors have achieved successful commercialization with broad market applications. In the progression from laboratory research to industrialization, process technology stands as the key factor for successful product commercialization; therefore, improving and optimizing process technology holds crucial significance for product commercialization.
The manufacturing processes for batteries and supercapacitors are quite similar
[1-3], as
shown in Figure 1. The process typically includes
[4]: mixing, coating, drying, calendering, slitting and sheeting, vacuum drying, stacking/winding, welding, encapsulation, formation, and aging. Each process step has a significant impact on the final product performance. Among these, as the initial stage processes, the effects of mixing, coating, drying, and calendering greatly influence the subsequent cell preparation and performance. Currently, the existing slurry preparation processes are mainly wet methods, generally using
N-methyl-2-pyrrolidone (NMP) or water as solvents. The active material, conductive agent, binder, and other dry powder materials are stirred and dispersed uniformly; the electrode obtained after wet coating and drying is called a wet electrode. The preparation of wet electrodes requires evaporating the solvent at a certain temperature and configuring a solvent recovery system. Studies have shown that the energy consumption of the solvent evaporation and recovery system accounts for about 47% of the total energy in the preparation process, while the costs of wet mixing, coating, and solvent evaporation/recovery processes account for about 20% of the total manufacturing cost
[5]. At the same time, the reproductive toxicity of NMP also has certain impacts on human health; therefore, the industry is actively seeking alternatives to NMP. Unlike wet electrodes, the dry process disperses powder materials uniformly and then presses them into electrodes of a certain thickness under hot pressing conditions. No solvent is required from powder mixing to electrode sheet pressing, which can reduce solvent costs by 1.9%
[6], and can also reduce the harm of NMP to the human body. Dry electrode preparation includes three processes: physical mixing, film formation (or coating/deposition), and calendering. The core equipment required includes high-speed mixing equipment, film formation-related equipment (fibrillation, dry powder film formation), and high-precision calendering equipment (high-temperature rolling). There is no need to equip solvent evaporation and recovery devices, which can significantly reduce equipment costs and floor space. It is estimated that after adopting the dry electrode process, material costs will decrease by 1.9%, energy consumption by 38%, direct labor costs by 16.2%~21.6%, equipment costs by about 14.2%~19.0%, and factory floor space by 13.1%~16.5%
[1]. Therefore, dry electrodes have advantages such as low cost and environmental friendliness
[1,7], making them suitable for producing thick electrodes with high compaction density, low porosity, high ion/electron transport, and high mechanical properties
[5,8-9]. Replacing the wet process with the dry process can effectively improve energy density, meeting the growing practical application demands for high energy, among others.
The preparation of dry electrodes highly depends on the performance level of core equipment; the operational stability of the equipment and key process parameters have a decisive impact on the microstructure and macroscopic performance of the electrodes. (1) In the physical mixing stage, mainstream equipment includes high-speed mixers and ball mills. Addressing the solid-phase mixing characteristics of the dry process, the mixing system typically requires drive motors with higher power density, stirring components with excellent wear resistance, and high-precision speed control systems to ensure stable and uniform dispersion under conditions of high solid content and high shear load. Notably, high-speed mixers also demonstrate compatibility with wet mixing processes, exhibiting good process adaptability. Furthermore, the duration of dry mixing is typically on the order of minutes, significantly lower than the hour-long mixing cycles of wet processes; therefore, despite higher unit power requirements, the proportion of comprehensive energy consumption remains low. (2) In the film formation (or coating/deposition) stage, common equipment encompasses airflow crushers, screw extruders, twin-screw fibrillators, and open mills. Among these, airflow crushers offer the highest production efficiency, while screw extruders demonstrate superior product yield. Open mills generate strong shear forces by adjusting the speed ratio between rollers, thereby achieving binder fibrillation and film formation. Twin-screw fibrillators possess inherent advantages for continuous production and can control the fibrillation process under cooling conditions, showing significant potential for process scale-up. (3) Core equipment for the calendering process includes hot calenders and precision calenders; this stage plays a decisive role in the electrode's compacted density, pore structure, and distribution uniformity. The dry process imposes higher requirements on calendering equipment, necessitating powerful compaction under higher linear loads, stricter thickness tolerance control, and higher material throughput, while simultaneously ensuring consistency in film thickness and structure during roll-to-roll continuous operation. Consequently, the requirements for the pressure output capability, control precision, and gap uniformity of calenders in the dry process are significantly higher than those in traditional wet coating processes.
As early as the late 20th century, Whittingham
[10]and the Goodenough research group
[11]respectively proposed LiTiS-based dry electrodes prepared using polytetrafluoroethylene (PTFE) binders
2dry electrodes and LiFePO
4dry electrodes. In the early 21st century, Maxwell successfully applied dry electrode technology to the mass production of supercapacitors and used it to manufacture lithium-ion battery electrodes in 2016. Maxwell's electrode production demonstrated the industrial manufacturability of dry electrodes. Subsequently, Tesla, building on Maxwell's existing patents, announced the 4680 cylindrical lithium battery featuring a dry anode based on PTFE binders
[12]. This not only improved energy density but also reduced costs and environmental impact. Dry electrode technology has garnered significant attention in the battery and capacitor fields in recent years
[3,13-19]. In terms of academic research, Ruan Jingjing et al.
[13]prepared graphite dry electrodes for lithium-ion batteries using a binder fibrillation method. Scanning electron microscopy (SEM) images showed that the electrodes formed branched fibers with a hierarchical structure, constructing a continuous network architecture within the electrode. Pameté et al.
[16]compared the performance of dry and wet electrode supercapacitors in organic, ionic liquid, and quasi-solid-state electrolytes. Supercapacitors based on dry electrodes exhibited significant performance improvements, with lifespans extended by 45%, 192%, and 84% in organic, ionic liquid, and quasi-solid electrolytes, respectively.
In addition to academic research achievements, the engineering and industrialization of dry electrode processes are also advancing actively. Major enterprises are continuously increasing investment and R&D in processes and equipment, achieving significant breakthroughs. For example, Tesla publicly unveiled its new structural 4680 cylindrical battery in 2020, whose positive electrode sheet was manufactured using dry electrode technology. Compared with conventional 18650 batteries, the energy density of the 4680 battery increased from 240 Wh/kg to 300 Wh/kg, and the cost decreased from 185
$/kWh to 75 $/kWh, representing a 59.46% reduction in unit cost
[20]. Tesla has successfully established a dry electrode production line and is the only enterprise capable of balancing performance with mass production. Shenzhen Qingyan Electronics focuses on tackling dry process challenges, breaking through technical barriers, successfully producing commercial dry electrode sheets, and developing a series of manufacturing equipment and mass production lines for dry electrodes. Among these, the developed dry electrode forming and compounding integrated machine achieves key parameters of up to 800 mm in width and a maximum speed of 50 m/min. Wuxi Lead Intelligent Equipment Corporation launched a dry continuous coating and cold rolling production line in 2025, achieving speeds of 60 m/min for positive electrodes and 80 m/min for negative electrodes, supporting electrode thicknesses ranging from 40 to 300 μm, with a market share exceeding 70%. These breakthroughs have laid a solid foundation for large-scale preparation and establishing a complete industrial chain, propelling domestic dry electrode technology into the international advanced ranks and facilitating the accelerated development of domestic battery industry clusters.
Although dry electrode technology has received widespread attention and made significant progress, it still faces some non-negligible challenges and technical bottlenecks. For example, the forming process of dry electrodes often leads to insufficient uniformity of electrode materials, thereby affecting the overall performance and cycle stability of the battery.
[21-22]At the same time, due to the low surface energy of the binders used in dry electrodes, their interaction with the current collector is weak. This results in insufficient mechanical strength and structural stability of the electrode, making it prone to deformation or detachment during charge and discharge cycles.
[23]In addition, the conductivity of dry electrodes still struggles to match that of wet electrodes in certain scenarios.
[24], which limits their application in high-power-density batteries. Finally, the selection and optimization of dry electrode materials require further research to achieve higher energy conversion efficiency, longer service life, and product commercialization.
[21,25-26]. Scaling laboratory processes to production lines also presents significant challenges. While steps such as powder formulation, tablet pressing, compaction density, coating uniformity, and electrode winding can be optimized in the lab, each step may encounter issues during large-scale manufacturing, leading to reduced product yield. For instance, Tesla's dry cathode loss rate reached as high as 70%–80%, equipment repair cycles lasted up to 45 days, and initial product yield was only 20%, resulting in high total costs. These factors represent urgent problems that must be addressed for the process chain. Dry electrode technology is currently at a critical stage of breakthrough from laboratory to industrialization. Its core advantages lie in simplified processes, cost-effectiveness, and environmental friendliness. However, it also faces technical bottlenecks, such as electrode performance (material distribution uniformity, conductivity, adhesion) being inferior to wet electrodes, the need for optimization of material systems, and challenges like low yield, high loss, and difficult cost control during industrial scale-up. Therefore, to achieve industrialization and commercialization of dry electrodes, systematic breakthroughs in materials and mass production processes are required; this is key to promoting the widespread application of dry electrode technology.
Based on this, it is necessary to conduct an in-depth discussion and research on dry electrode technology to comprehensively understand its application and development requirements. This paper aims to comprehensively explore the current development status and challenges faced by dry electrode technology, and propose effective solution strategies by analyzing research achievements in recent years. First, various types of dry electrode technology are briefly introduced. Second, the challenges encountered by this technology in practical applications are deeply analyzed to more effectively identify and understand its bottlenecks. Finally, combining the latest research trends, a series of innovative solutions are outlined, aiming to provide theoretical support and practical guidance for the future development of dry electrode technology. Through this research, it is hoped that more attention and discussion will be stimulated, promoting the widespread application and continuous progress of dry electrode technology in the field of energy storage.
2 Classification of Dry Electrode Technology
The manufacturing process of dry electrodes consists of three steps: physical mixing, film formation (or coating, deposition), and calendering. During the final calendering step, the thickness of the required electrode and its dense structure can be adjusted. As
shown in Figure 2, based on the process characteristics of electrode technology, dry electrode processing methods can be classified into six types
[7]: polymer fibrillation
[27], spray deposition
[28], vapor deposition
[29], hot melt extrusion
[22], powder compaction
[30], and 3D printing
[31].
Polymer fibrillation refers to the process where a fibrillatable binder undergoes fibrillation under high shear forces, connecting active material particles and conductive agents together. This mixture is then repeatedly rolled and laminated onto a current collector under heat and pressure to produce a dry electrode. In 2019, after acquiring Maxwell, Tesla pioneered the application of this technology in the research and commercial production of dry-processed lithium battery electrodes. Current fibrillation methods primarily include mortar grinding and high-speed airflow impact.
[32]. This process can be applied to both cathode and anode materials and is compatible with existing commercial lithium-ion battery production facilities. Therefore, fibrillated dry electrodes hold significant potential to replace current wet electrode technologies in future developments. However, current research indicates that the primary fibrillatable polymer binders are PTFE. Since PTFE has a low Lowest Unoccupied Molecular Orbital (LUMO) level, it readily accepts electrons, undergoing reduction reactions when used in anodes, which leads to stability issues in the electrode.
[33]. Therefore, future research needs to focus on the exploration and study of fibrillatable binders.
Spraying deposition refers to attaching uniformly mixed powder materials onto the surface of a current collector via spraying deposition technology, followed by hot pressing to form an electrode sheet of a certain thickness. Common spraying deposition methods include air spraying and electrostatic spraying.
[32], suitable for electrodes with tunable active material areal density. However, research on the spraying deposition process is currently still at the laboratory stage; complex high-pressure equipment, operating costs, and slow deposition rates limit its industrial application.
[34].
Vapor deposition refers to the process of evaporating and vaporizing raw materials through various methods and depositing them onto a current collector. Vapor deposition includes magnetron sputtering, thermal evaporation, pulsed laser deposition, atomic layer deposition, etc.
[35]. Classified by whether the structure changes, vapor deposition can be divided into physical vapor deposition and chemical vapor deposition. Vapor deposition is typically used to fabricate thin-film electrodes, such as those in microelectronic devices and highly integrated circuits. It is not suitable for ultra-thick electrodes, such as those in electric vehicles and 3C consumer electronics products. Furthermore, vapor deposition requires high equipment configuration standards, such as complex machinery, vacuum operating environments, and small production scales, which are unfavorable for industrial mass production.
Melt extrusion refers to the process where uniformly mixed powder materials undergo shear compounding and dispersion within a twin-screw extruder. As the temperature rises, the binder gradually melts and is extruded through the die opening; electrodes are then obtained by cold or hot pressing onto the current collector. The melt extrusion process requires the binder to possess suitable thermal stability and mechanical processing characteristics to remain stable during melting and extrusion. Currently reported binders include polyvinylidene fluoride (PVDF), polypropylene (PP), and poly(propylene carbonate) (PPC).
[34]. However, the melt extrusion process is influenced by extrusion temperature, shear force, and extrusion duration.
[36], necessitating research into various key factors to achieve optimal electrode performance. Furthermore, factors such as excessive polymer consumption, manufacturing complexity, and elevated sintering temperatures hinder its widespread industrial application.
Powder compression refers to the process where uniformly mixed powder materials are directly pressed in a mold under hot pressing or hydraulic equipment to achieve material densification. Compared with other dry electrode technologies, the powder compression method requires little or no binder and is a simple process, thus also known as the direct pressing method. Powder compression can effectively increase the proportion of active material and reduce binder costs, offering advantages such as a simple process, scalability, solvent-free operation, and being binder-free. However, the rigid mold pressing required by the powder compression method has disadvantages of uneven stress and density, which may lead to inconsistent compaction density and densification across the dry electrode. Therefore, future research needs to further optimize the powder compression process technology.
3D printing is a rapid prototyping technology, which can be divided into Stereolithography (SLA), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), Direct Ink Writing (DIW), Inkjet Printing (IJP), and other printing technologies.
[37]. Currently, the 3D printing technology applied in dry electrodes is FDM, which refers to the extrusion and deposition of binders at melting temperatures together with active materials and conductive agent powder materials onto the current collector. 3D printing technology can precisely customize personalized electrode shapes, morphologies, thicknesses, etc., according to specific application scenarios. However, due to cost and efficiency issues, 3D printing technology is not suitable for large-scale electrode production and is only applicable to specific fields such as microelectronics and wearable devices.
3 Challenges Facing Dry Electrode Technology
The powder materials required for dry electrodes include active materials, conductive agents, and binders. This section mainly analyzes the existing problems and challenges faced by dry electrodes (
Figure 3), mainly including uneven material distribution, low electrode conductivity, low electrode adhesion, poor electrode wettability, and difficulties in scaling up.
3.1 Uneven material distribution
In an ideal state, the active material, conductive agent, and binder in the electrode should be uniformly dispersed, with particles of various powder materials able to contact each other. The active material directly determines the battery's capacity, the conductive agent is key to influencing power performance, and the binder ensures the structural integrity of the electrode. On one hand, the absence of added solvents means there is no medium for dispersion and flow, resulting in relatively poor dispersibility and fluidity of the powder materials. On the other hand, agglomeration of particles between powder materials easily occurs, leading to uneven mixing.
[33]. This is mainly due to differences in polarity and surface energy between particles of different materials, resulting in poor chemical affinity.
[20]. Influenced by the above factors, powder materials cannot be fully dispersed under the inertial action of the stirring medium during the mixing process and tend to aggregate with similar materials. When the mixed powder materials are pressed into a film on the current collector, situations of local excess or local deficiency of the same material may occur, preventing each material from fully exerting its function. Taking active material as an example, when locally excessive, the internal active material becomes electrochemically isolated due to blocked electron conduction paths and cannot effectively participate in lithium ion intercalation/deintercalation reactions; conversely, if locally deficient, the active material in that region will bear a higher local current density, causing the particles to undergo abnormally strong electrochemical polarization.
[20]. The aforementioned phenomena will continue to intensify during long-term cycling, accelerating the deterioration of the structural stability of local active materials. Ultimately, uneven material distribution affects electrode performance.
[38], for example: blocked electron and ion transport channels lead to increased internal resistance; uneven binder dispersion results in low adhesion, causing powder shedding; uneven distribution of active material leads to fluctuations in capacity and cycling stability. Future research needs to explore the characteristics and mechanisms of powder material mixing, analyze gas-solid phase kinetics, and develop equipment with higher rotational speeds to meet dispersion requirements.
3.2 Low electrode conductivity
Both dry mixing and wet mixing require the addition of conductive agents. Conductive agents are typically carbon materials used to construct a divergent conductive network with multiple pathways. However, due to the sp
2orbitals of carbon atoms, strong π-π interactions exist between them. In the dry mixing state, these interactions promote the formation of aggregates by the conductive agents
[39]. This results in an uneven distribution of conductive agents, affecting the construction of the conductive network within the electrode. This directly causes obstruction in some electron transmission paths, forcing electrons to choose adjacent paths with lower resistance. This leads to excessive local current
[40], causing intense intercalation/deintercalation behavior in the active material in that region. Under prolonged charge-discharge cycles, this induces significant stress within the active material particles, leading to cracking and pulverization of the active material. These cracks and pulverization exacerbate side reactions with the electrolyte, continuously forming LiF on the surface of the active material. This reduces the active Li
+in the electrolyte, accelerating the deterioration of the device's cycle life
[41]. Meanwhile, portions of the active material through which no electrons pass fail to fully participate in charge-discharge processes, forming electrochemical dead zones that directly impact capacity and energy release. The role of the binder is to firmly adhere the active material and conductive agents, preventing material detachment from the electrode. As a binder commonly used in dry processes, PVDF possesses two C—H and C—F bonds, whereas PTFE has four C—F structures. Compared to C—H structures, C—F structures exhibit relatively higher density and greater covalent bond energy, increasing their electronegativity and resulting in reduced electron mobility
[42], thereby reducing the conductivity of the electrode. Furthermore, the solvent in wet coating exhibits a larger contact angle with the current collector, enabling close contact between the slurry and the current collector. In contrast, dry electrodes typically involve laminating a self-supporting electrode film onto the current collector; certain interfacial voids exist between the film and the current collector, preventing the formation of tight contact via solvent action. This causes obstruction in electron transmission, leading to increased internal resistance
[43]. The device generates significant Ohmic heat, ultimately reducing electrochemical conversion efficiency and affecting lifespan performance.
3.3 Poor electrode adhesion
Currently, the binders mainly applied to dry electrodes are PTFE and PVDF
[44]. The different characteristics of these two binders, such as molecular weight and melting point, determine the need to select different dry electrode processes. PTFE remains the binder used for preparing dry electrodes via the polymer fibrillation method. In contrast, PVDF possesses thermoplasticity and is commonly used in spray deposition, 3D printing, and melt extrusion processes
[32]. Both PTFE and PVDF (α-phase) binders have non-polar structures with highly symmetric molecular architectures and specifically arranged C—F chemical bonds; the centers of positive and negative charges in the entire molecule coincide, resulting in a zero dipole moment. Due to the uniform charge distribution of non-polar structures, they typically do not easily participate in chemical reactions and thus primarily bond through weak intermolecular electrostatic interactions (van der Waals forces). For dry electrodes prepared based on PTFE and PVDF binders, the electrode material and current collector are mainly bonded through weak van der Waals forces
[20], leading to poor adhesion between the electrode film and the current collector. Furthermore, the loose connection between materials can easily cause electrode delamination
[20,23], damaging the electron transport channels. This may result in obstructed electron transport in some areas, increasing the internal resistance at the interfaces to a certain extent. Additionally, electrode delamination may also lead to the detachment of active materials during electrochemical charging and discharging processes
[19]. As the sole substance providing capacity, the detachment and loss of active materials will reduce capacity or energy. Therefore, the weak adhesion of electrodes caused by binders ultimately leads to problems such as capacity fading and increased internal resistance.
3.4 Poor electrode wettability
As a crucial medium for active ion transport, the electrolyte is vital for electrochemical performance. Dry electrode processes tend toward designs with high loading and large areas
[43]; increasing electrode thickness and area extends the time required for wetting. Therefore, under identical production cycles, the issue of poor electrolyte wettability in dry electrodes becomes more pronounced. Furthermore, PTFE and PVDF, commonly used binders in dry electrodes, are both non-polar molecules. Non-polar molecules have low surface energy
[20], exhibiting large contact angles and difficulty dissolving in various solvents. Consequently, dry electrodes prepared thereby also exhibit large contact angles with the electrolyte, reducing the wetting effect of the electrolyte on the electrode. Moreover, both binders contain highly electronegative fluorine (F) elements, resulting in strong hydrophobicity and oleophobicity of the binders, which reduces the affinity between the electrode and the electrolyte
[38,45]. The type of binder also significantly affects electrode wettability. From the perspective of ion transport, PTFE binders exhibit a much larger contact angle with polar solvents compared to PVDF and other polar binders. Poor wettability between dry electrodes and the electrolyte leads to hindered active ion transport
[20], increasing internal resistance and reducing electrode performance. Additionally, studies have found that as the proportion of PTFE increases, the contact angle between the electrode surface and the electrolyte becomes larger
[46], further demonstrating the poor affinity between PTFE-based electrodes and the electrolyte. Rate performance is closely related to the mobility of ions within the electrode; better wetting effects facilitate improved ion transport rates
[47-48]. Therefore, it is necessary to comprehensively consider various factors to balance electrode adhesiveness and wettability in order to obtain dry electrode sheets with excellent performance.
3.5 Scaling difficulties
During the mixing process of dry electrodes, friction between powder material particles generates heat, and greater force is required to stir and evenly disperse the powder materials. The existence of these issues imposes certain technical requirements on equipment for dry mixing. Furthermore, due to variations in material density and particle size, it is difficult to obtain a uniform powder mixture.
[7,42]. In large-scale production processes, the continuous preparation of dry electrode films is a challenge that cannot be ignored.
[49]. Furthermore, to achieve large-scale production, it is necessary to further explore mixing equipment suitable for dry blending, conduct in-depth research on the compatibility of equipment types (such as high-speed shear mixers, double-cone mixers, etc.) with specific powder raw materials, and achieve uniform dispersion at the microscale.
4 Solution strategies for dry electrode technology
Addressing issues such as uneven material distribution, low electrode conductivity, poor adhesion, inadequate electrode wettability, and difficulties in scaling up,
Figure 4briefly summarizes the corresponding solution strategies for dry electrode technology. This section will outline recent research progress in dry electrode technology from the perspectives of materials and processes.
4.1 Key Materials
4.1.1 Adhesive
The physicochemical properties and thermal performance of binders are crucial for electrode manufacturing and also determine equipment requirements and process parameters. Currently, binders used in dry electrodes include materials such as PTFE, PVDF, polyethylene oxide (PEO), polypropylene (PP), paraffin wax, and stearic acid.
[50]. Researchers are dedicated to improving existing binder characteristics and exploring novel binders to enhance various electrode performances.
[23,33,51-55].
Currently used binders each have their own advantages; therefore, researchers have combined different binders to enhance electrode adhesion by integrating various strengths through physicochemical interactions. To address the issue of poor adhesion, Sung et al.
[23]introduced polyacrylic acid (PAA) and PTFE as a composite binder. Through hydrogen bonding between the —COOH groups in PAA and the —OH groups on the Al
2O
3of the aluminum foil current collector, the adhesion between the dry electrode and the aluminum foil current collector was improved, reducing contact internal resistance. The adhesion strength of using PTFE binder alone is close to zero, whereas the adhesion strength of the PAA/PTFE composite binder significantly increased to 40.0 gf·20 mm
-1, and the use of the PAA/PTFE composite binder exhibits excellent rate performance and cycling stability. Kang et al.
[33]prepared a PAA-CMC polymer (PC) by graft polymerization and crosslinking reactions of PAA and sodium carboxymethyl cellulose (CMC), and combined it with PTFE to form a PC-PTFE dual-binder system. As
shown in Figure 5a,
b, PC acts as a "micro bollard" to form a tighter connecting force with PTFE, thereby enhancing electrode adhesion. A 180° peel test revealed that the adhesion force between PC-PTFE and the aluminum foil current collector (0.9615 N/cm) is stronger than that of PTFE (0.5733 N/cm). Most existing binders are fluorinated polymers, which have deficiencies in adhesion, conductivity, and recyclability. Based on this, Leibetseder et al.
[56]developed a fluorine-free water-soluble surfactant polymer. Polymers based on 11-aminoundecanoic acid can be modified via various copolymer monomers, significantly enhancing adhesion. Furthermore, they maintain good thermal stability at temperatures up to 350 ℃ and offer environmental friendliness in recycling processes.
Developing novel binders in the field of dry electrode technology is also a major research hotspot. Regarding the issue of uneven distribution of electrode materials, Kim et al.
[51]used phenoxy resin as a binder to prepare dry NCM811 cathodes. The glass transition temperature (
Tg) of the PVDF binder is 187.58 °C, while that of the phenoxy resin
Tgis only 79.68 °C (
Figure 5c). This indicates that at a certain temperature, phenoxy resin has better ductility than PVDF, making it easier to generate a uniform network structure connecting active materials during the hot-pressing process, resulting in lower internal resistance (
Figure 5d), thereby improving electrochemical stability. In addition, the particle size of the binder also affects the uniformity of material mixing. Schälicke et al.
[52]prepared electrode materials based on binders with different particle sizes and found that large-particle binders lead to instability in the electrode active material layer, whereas using binders with smaller particles, such as tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV) and fluorinated ethylene propylene copolymer (FEP), can obtain stable electrodes; small-particle binders are distributed relatively more uniformly across the entire electrode.
To address the issue of poor conductivity, Yuan et al.
[57]utilized the conductive polymer polyaniline (PANI) as a binder to investigate the performance of graphite electrodes. PANI, in its intermediate oxidation state, exhibits optimal conductivity after doping. A hot-pressing method was employed to adhere polyaniline and active materials to the current collector, obtaining dry electrodes via a heated roll-to-roll process. The results indicate that PANI can simultaneously function as both a binder and a conductive agent, offering stable cycling performance while reducing the content of non-active electrode components. These findings on PANI provide new insights for the preparation and cost reduction of dry electrodes. Furthermore, Jang et al.
[53]prepared a fluorine-free, hydroxyl-rich nanohybrid siloxane (Siloxane nanohybrid, SNH) binder through a simple sol-gel reaction of two silane precursors for application in cathode materials. Compared with PVDF, the capacity retention of the full cell based on SNH increased from 61.24% to approximately 87.82% after 200 cycles. Benefiting from silanol (Si—OH) groups, the SNH binder significantly enhanced affinity for active materials and conductive agents, forming uniform electron/ion conduction pathways.
4.1.2 Conductive agent
Conductive agents primarily provide a conductive network for electrons, reduce internal resistance, and achieve high-rate performance. In dry electrodes, agglomeration and uneven distribution of conductive agents lead to reduced conductivity. To address this issue, existing research has approached the improvement of material dispersion uniformity and conductivity in dry electrodes from various aspects, such as surface treatment of conductive agents
[58], studying different types of conductive agents
[59-60], and adding surfactants to improve the dispersion uniformity of conductive agents
[61]. Meanwhile, composite binders and conductive agents can also serve as dual-functional materials to realize the construction of multi-path conductive networks
[62], ultimately enhancing the conductivity of the electrode.
Kim et al.
[58]prepared surface-treated O-SWCNT conductive agents by treating single-walled carbon nanotube (SWCNT) conductive agent materials with ozone (O
3), introducing oxygen-containing groups such as hydroxyl, carbonyl, and carboxylic acid (
Figure 6a). By comparing the charge transfer resistance (
Rct) of dry electrodes based on SP, SWCNT, and O-SWCNT conductive agents, it was found that the
Rct values for those based on SP and SWCNT conductive agents were 202 and 67 Ω, respectively, while the
Rct for the one based on O-SWCNT decreased to 43 Ω (
Figure 6b). The conductive agent treated with O
3 exhibited a denser microstructure in the composite material and could also protect the CEI film formed on the cathode surface, preventing side reactions. This not only helps mitigate microcracks in NCM811 particles but also improves the stability of the active material. Improving the pore structure of the conductive agent can also effectively enhance its electronic conductivity. Oh et al.
[60]introduced porous spherical carbon black with high porosity and high specific surface area as a conductive agent to prepare dry electrodes. Compared with graphene and carbon nanotube materials, porous spherical carbon black can improve electrical performance and lithium-ion transport characteristics, exhibiting excellent rate performance and cycle life. Furthermore, it was found that optimizing the content of the porous spherical conductive agent within the range of 2–3 wt% enabled the cathode to achieve higher energy density. Other researchers have also added multi-walled carbon nanotubes (MWNT) during the preparation of an epoxy resin-based (EP) binder to form a composite conductive binder
[62].
Figure 6c shows a schematic diagram of the preparation process of the conductive binder, where a 3D network is formed under the action of the conductive agent and the binder, significantly improving the electrode's conductivity. The abundant ether oxygen groups and nitrogen elements in EP promote Li
+ ion transport, increasing the migration rate of reversible ions. As
shown in Figure 6d, electrodes based on the composite conductive binder exhibit lower charge transfer resistance compared to PVDF (3.6 Ω vs. 32 Ω). This indicates that dual-functional composite conductive binder materials possess superior electrical performance compared to single-functional materials.
4.1.3 Current collector
As the substrate supporting electrode materials, using an appropriate current collector can effectively reduce internal resistance and improve electrochemical performance.
Researchers evaluated the impact of different current collectors on the electrochemical performance of dry electrodes, such as corroded aluminum foil and aluminum mesh. Wang et al.
[63]investigated three different current collectors (aluminum foil, corroded aluminum foil, and carbon-coated aluminum foil), revealing the significant influence of current collectors on electronic conductivity and interfacial adhesion strength. Among them, carbon-coated current collectors exhibited superior electrochemical performance. Sul et al.
[27]compared the performance of solvent-free dry electrodes with wet slurry electrodes and also introduced a novel aluminum mesh as a current collector to prepare high-loading sulfur anodes. Ryu et al.
[30]reported dry electrodes using etched aluminum foil as the current collector. The dry cathode exhibited strong adhesion and cohesion, anchoring onto the submicron pores of the etched aluminum foil, enabling seamless compaction of the active material within its network structure.
However, most current studies still use aluminum foil as the positive current collector and copper foil as the negative current collector. Compared to binders and conductive agents, researchers have paid less attention to current collectors.
4.2 Process Technology
4.2.1 Process Parameter Optimization
The experimental parameters of the process also have a non-negligible impact on the final performance of the electrode, such as stirring speed, stirring time, addition sequence, and pressing temperature.
[64-69].
Yonaga et al.
[66]Dry electrode materials were prepared based on three different rotation speeds (1000, 3000, and 10000 r/min), comprehensively evaluating the impact of electrode powder mixture morphology on electrode structure and battery performance. It was found that controlling the distribution of conductive agents and binders can improve the rate performance of batteries. Low-speed dry mixing results in poor dispersibility, forming long-range conductive pathways with low tortuosity; high-speed dry mixing leads to excessive dispersion, causing high tortuosity in both long-range and short-range conductive pathways. In contrast, medium-speed dry mixing effectively forms short-range and long-range conductive paths, improving electrode capacity and stability. Tao et al.
[67]Investigated the direct impact of dry mixing time (10, 30, and 60 min) on powder mixtures and dry electrode performance. The results showed that electrodes mixed for 30 min exhibited superior performance. Insufficient mixing time leads to a low degree of PTFE fibrillation, while excessive mixing time causes PTFE fiber breakage and the formation of PTFE-carbon black films. Appropriate mixing time can enhance PTFE fibrillation, mechanical properties, and electrochemical performance. Generally, the contact between active material particles and conductive agent particles in dry electrodes is point-to-point. To ensure interfacial contact and uniformity between materials, researchers employ stepwise mixing of active materials, conductive agents, and binders to achieve this goal. Choi et al.
[68]A composite of PTFE and carbon black (CB) was prepared via pre-mixing through the electrostatic action of an ionic surfactant, and then mixed with the active material NCMA to prepare a dry electrode (
Figure 7a). CP-SEM/EDS analysis indicated that the cathode microstructure based on the PTFE/CB composite was more uniformly distributed than that of electrodes prepared by wet mixing. Pre-compositing PTFE/CB also enhances lithium-ion transport kinetics within the electrode.
Figure 7bshows the ionic resistance of a 96:2:2 PVDF binder electrode (2% CB content), a 98:0:2 electrode (0% CB content), and a 98:1:1 PTFE/CB composite binder electrode (1% CB content).
Rion. The
Rion of the dry electrode 98:1:1 PTFE/CB composite electrode is significantly lower than that of the wet electrode 96:2:2 PVDF binder electrode. Uniformly distributed powder materials can be obtained through the pre-compositing of binders and conductive agents under the electrostatic action of surfactants, resulting in electrodes with excellent cycling performance (
Figure 7c).
Compared to laboratory preparation, large-scale industrial production focuses more on process parameters during manufacturing. Strong coupling relationships exist among these parameters, having a significant impact on product yield and production efficiency. For instance, during the fibrillation of PTFE binders, appropriate stirring speed and time must be controlled to form a uniform spider-web-like network structure; insufficient fibrillation can lead to weak bonding strength, while excessive fibrillation causes the electrode to become too hard and brittle, affecting electrode consistency and product yield. Similarly, increasing the calendering speed can reduce the required calendering time and shorten the production cycle; however, excessively high calendering speeds may cause cracks or inadequate compaction, compromising the mechanical properties of the electrode and product yield. Furthermore, raising the pressing temperature facilitates the melting of the binder, promoting its dispersion between powder materials and enhancing bonding strength; nevertheless, higher temperatures entail longer heating times and increased energy consumption, which not only reduce production efficiency but also raise production costs. Therefore, in scaled-up manufacturing, it is essential to comprehensively consider various process parameters to optimize both dry electrode performance and production efficiency.
4.2.2 Development of New Process Technology
In addition to optimizing process parameters, researchers have also proposed novel process technologies to enhance the performance of dry electrodes. These novel process technologies include roll-to-roll dry printing methods based on corona electrostatic spraying
[47], cold plasma process powder coating manufacturing technology
[70], nanoparticle deposition system technology
[71], and pulse mixing strategies
[72].
Liang et al.
[70]reported an electrode manufacturing technology using a cold plasma process powder coating (CPC), with principles and steps as
shown in Figure 8a. Cold plasma is utilized to create conductive and binding networks between particles, such as the aluminum (Al) particles used in this study. By forming a 3D metal network of highly conductive electrodes in situ, conductive additives and polymer binders are replaced, improving the electronic conductivity of the electrode. Cold plasma replaces conductive additives and polymer binders, effectively enhancing the power performance of devices, which is crucial for high-power automotive and energy storage applications. Meanwhile, CPC technology can reduce electrode processing costs by approximately 40%, and costs related to capital investment, facilities, and maintenance by 70%, representing a novel, highly scalable, low-cost manufacturing technology. Kim et al.
[71]first proposed a nanoparticle deposition system (NPDS) for preparing binder-free dry electrodes (
Figure 8b). By accelerating powder at supersonic speeds to collide with the substrate, a thin film is formed using a simple pressure difference between the nozzle and the deposition chamber, directly depositing particles onto the substrate. Based on NPDS technology, a binder-free dry cathode of LiNi
0.9Co
0.05Mn
0.05O
2was successfully prepared, exhibiting superior adhesion and cycle life compared to wet slurry-coated electrodes. This demonstrates that NPDS has significant development potential in preparing binder-free dry cathodes, laying the foundation for developing advanced binder-free dry anodes. Li et al.
[72]To promote uniform mixing of powder materials in dry electrodes, a pulsed mixing strategy was proposed starting from shear force regulation. Based on the pulsed mixing method, ultra-thick dry LiMn
2O
4electrodes with excellent stability, high mechanical strength, and superior 3D charge transfer kinetics were constructed. The pulsed mixing method improved the mechanical strength of the electrode and created a uniform pore structure, establishing a 3D multi-directional charge transfer pathway that accelerates charge transfer kinetics in ultra-thick dry electrodes.
Table 1Summarizes the performance and key technical indicators of dry electrodes reported in recent years, providing an intuitive and clear comparison of technical parameters. Currently, most studies have adopted the fibrillation method for preparing dry electrodes, followed by powder compaction and spray deposition. Fibrillation is more suitable for scaled-up preparation and applicable in production line manufacturing. In lithium-ion batteries, dry electrodes can be applied to either the cathode or the anode, effectively enhancing electrode performance in both cases.
Based on the above discussion, this paper summarizes the current challenges facing dry electrodes and corresponding solution strategies. As
shown in Figure 9, recent research directions have focused on the uniformity of material distribution, electrode conductivity, and binder properties of dry electrodes, significantly improving their performance and providing a certain research foundation for their development. However, research on electrode wettability and scalability remains relatively limited. Wettability has a significant impact on the power performance of electrodes, while the scalability of dry electrodes is crucial for achieving commercialization. To promote further development of dry electrodes, future efforts need to focus more on research related to electrode wettability and scalable development.
5 Conclusion and Outlook
Dry electrode technology, as a promising process technique, has received widespread attention and is suitable for producing thick electrodes with high compaction density, low porosity, high ion/electron transport, and superior mechanical properties. This paper first introduces six classifications of dry electrode technology: polymer fibrillation, spray deposition, vapor deposition, hot melt extrusion, powder compaction, and 3D printing. The type of binder is closely related to the process technology; therefore, appropriate process methods must be selected based on the binder type and characteristics. However, dry electrode technology still faces numerous challenges in practical applications, including uneven material distribution, low electrode conductivity, poor electrode adhesion, inadequate electrode wettability, and difficulties in scaling up. These factors significantly affect the internal resistance and stability of the electrodes, leading to a decline in electrochemical performance. To address these challenges, recent research has proposed various solution strategies covering both materials and processes, aiming to enhance electrode performance. Certain progress has been made, particularly in uniform material dispersion, conductivity, and adhesion. Nevertheless, research on electrolyte wetting effects and large-scale production remains insufficient. Future research needs to explore effective solutions systematically from multiple dimensions to promote further advancements in dry electrode technology, especially in applications involving solid-state batteries, ultra-high loading electrodes, and sodium-ion battery systems. Based on current research progress, the following key research directions are proposed:
(1) In terms of material system optimization, breakthroughs in the development of functional binders are a key priority. Parameters such as thermal properties, interfacial compatibility, and mechanical strength of the binder directly affect the structural stability and electrochemical performance of the electrode. PTFE binders exhibit instability issues in negative electrodes; therefore, PTFE needs to be modified to increase its LUMO value, or materials with strong chemical stability should be adopted as negative electrode binders. Dry electrodes based on high-molecular-weight polymer binders possess strong binding forces but suffer from poor electrolyte wetting. By compounding the binder with a surfactant to create a functional binder, the contact angle can be increased to promote electrolyte infiltration. Consequently, developing novel binder materials with multiple functional characteristics to balance various performance parameters and optimize electrode sheet performance is the key to achieving stability in the dry electrode process.
(2) At the level of preparation process optimization, a mapping relationship between material characteristics and process parameters should be established. First, clarify the performance of single material characteristics under different processes; second, comprehensively analyze test data based on orthogonal experimental design and test results. Finally, based on all results, establish an influence model of material characteristics and process parameters on electrode performance to screen out the process parameters with optimal comprehensive performance. By systematically studying the physicochemical characteristics of different material systems (such as active materials, conductive agents, etc.) and combining them with key processes like dry film formation and rolling, a process parameter optimization model is constructed to achieve precise control of electrode performance.
(3) In terms of equipment development, there is an urgent need to address the technical challenges of uniform powder dispersion and continuous production. Develop high-efficiency, low-energy-consumption dry powder mixing equipment to improve operating parameters (stirring speed, dispersion speed) and break the agglomeration forces between particles. To achieve continuous production, processes such as mixing and calendering can be designed for automatic feeding, optimizing the stability of the powder conveying system. Integrate online quality monitoring systems and adopt roll-to-roll transmission and winding/unwinding technologies to reduce interruptions and promote the fluency of continuous production equipment. These technological innovations in equipment will directly determine the industrialization process of dry electrodes.
(4) It is recommended to adopt a research paradigm of multidisciplinary collaborative innovation, integrating professional knowledge from fields such as materials science, mechanical engineering, and automatic control, to establish a full-chain R&D system ranging from material development to equipment design. Deep communication among various disciplines should break down disciplinary barriers and construct a scientific linkage for collaborative innovation. Simultaneously, professional deep integration must be conducted with product requirements as the orientation and manufacturing processes as the axis. For instance, experts from multiple fields may propose different requirements for the same process; they should thoroughly analyze existing problems in current solutions and jointly discuss and propose optimal solutions.
(5) Accelerate the formulation of industry standards, build a systematic standard system, and speed up the establishment of standardization regulations. The industry should expedite the development of unified technical standards, clearly specifying requirements for dry electrodes regarding raw material ratios, preparation processes, and performance testing to ensure the standardization and consistency of technical pathways. Meanwhile, it is necessary to establish and improve standardized production systems, regulating the entire chain from process flows and equipment parameters to quality control, laying the foundation for large-scale production and jointly promoting the commercial application of dry electrode technology.
In the future, with breakthroughs in the aforementioned key technologies, dry electrode technology is expected to play an important role in next-generation electrochemical devices, providing new technical support for the development of the new energy industry.
National Key Research and Development Program of China(2024YFB2408500)
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