中文   |   English   |   Email Alert
Fig/Tab
Advanced Search
image

Electrode Materials for Flexible Lithium-Ion Battery

Changhuan Zhang , Nianwu Li , Xiuqin Zhang

Progress in Chemistry ›› 2021, Vol. 33 ›› Issue (4) : 633 -648.

PDF
Progress in Chemistry ›› 2021, Vol. 33 ›› Issue (4) : 633-648 DOI: 10.7536/PC200528
review-article
Scan to read & Share
Electrode Materials for Flexible Lithium-Ion Battery
Author information +
History +
PDF

Abstract

With the development of science and technology, great progress has been made in portable electronic products, especially in wearable devices. Flexible battery, as the core component of portable electronic products, has attracted attention of more and more researchers. Lithium-ion battery is used as the main power source in a variety of products because of its good cycle performance and long life span. In order to make portable electronic products flexible and miniaturized, the development of flexible lithium-ion batteries with high energy density can be an urgent issue. Flexible electrode materials are regarded as the important research direction because they are key materials for flexible lithium-ion battery. The article describes recent progress on researches about electrode materials for flexible lithium-ion battery, including integrated flexible electrode and new macro-flexibility electrode structure design. The carbon-based materials and Mxene-based materials all belong to integrated flexible electrode with electrochemical activity. The polymer-based materials, textile-based materials and metal-based materials all belong to integrated flexible electrode based on non-electrochemical activity. The new macro-flexibility electrode structure design meets the needs that wearable devices are woven and tolerable of large scale deformation. This paper analyzes and discusses existing problems of flexible electrodes in order to provide new ideas for researches about flexible lithium-ion battery with high energy density in future.

Contents

1 Introduction

2 Integrated flexible electrode design

2.1 Based material with electrochemical active

2.2 Other non-electrochemical activity based material

3 Macro-flexible electrode structure design

3.1 Kirigami structure

3.2 Fiber structure

4 Conclusion and outlook

Graphical abstract

Keywords

flexible lithium-ion battery / flexible electrode / macro-flexible structure / electrode material / wearable

Cite this article

Download citation ▾
Changhuan Zhang, Nianwu Li, Xiuqin Zhang. Electrode Materials for Flexible Lithium-Ion Battery. Progress in Chemistry, 2021, 33(4): 633-648 DOI:10.7536/PC200528

登录浏览全文

4963

注册一个新账户 忘记密码

1 Introduction

With the rapid development of modern science and technology, portable electronic products are gradually developing in the direction of flexibility, lightweight and miniaturization. Flexible wearable electronic devices have broad application prospects in communication, health care, smart clothing and other fields, and batteries, as their core components, have attracted more and more attention[1,2]. The choice of battery directly affects the design and function of products. Lithium-ion battery has become the main power source of all kinds of electronic equipment because of its good cycle performance, high energy density and long service life[3,4]. However, due to the limitations of materials and manufacturing processes, traditional lithium-ion batteries can not meet the needs of complex deformation conditions such as bending, folding and even stretching.Moreover, the volume and mass of traditional batteries account for a large proportion, which reduces their energy density. Therefore, the research of flexible lithium-ion batteries with high energy density has become one of the research hotspots to promote the development of flexible electronic products[5,6]. As a key material of flexible battery, flexible electrode is a research hotspot in the field of flexible lithium-ion battery.
The traditional electrode is generally prepared by mixing active material, binder and conductive agent, grinding them evenly, and then coating them on the metal current collector. The main disadvantages are: (1) the surface of the metal current collector is smooth, and the active layer is easy to fall off when the electrode prepared by the traditional coating method undergoes repeated bending, folding, twisting or stretching deformation; (2) the prepared electrode is a rigid material, which can cause short circuit or failure of the battery when subjected to severe deformation; (3) that mas proportion of the metal current collector is large, and the energy density of the battery is reduced. The development of flexible lithium-ion batteries requires electrode materials with high conductivity, high capacity and high flexibility. In view of the above problems, researchers usually abandon the conventional metal current collector and adopt the integrated electrode design method in the design and research of flexible lithium-ion battery electrodes.According to the topology principle, the overall structure of the electrode can also be designed with the help of traditional paper-cut art, textile fiber structure concept and so on, and the electrode with flexible macro-structure can be prepared. In this paper, some achievements in the research of electrode flexibility of lithium-ion batteries in recent years are summarized from two aspects of integrated flexible electrode design and macroscopic flexible electrode structure design, and the existing problems are analyzed and discussed, in order to provide new ideas for the future research of flexible lithium-ion batteries with high energy density.

2 Integrated flexible electrode design

The integrated flexible electrode design mainly adopts the conductive flexible self-supporting electrode directly or loads the active substance on the flexible conductive material[7]. The integrated flexible electrode needs to have the following conditions: (1) high enough electron conductivity to facilitate electron conduction; (2) high enough flexibility to meet the needs of deformation use; (3) the substrate/current collector material can provide a relatively high loading rate of the active material and has a sufficiently high adhesive force with the active material; (4) having good electrochemical performance[8]. Self-supporting flexible carbon-based, Mxene-based negative electrodes or flexible electrodes with flexible substrates/current collectors loaded with positive or negative active materials are mainly able to meet the above requirements, and the flexible substrates/current collectors are mainly made of carbon-based materials, Mxene materials, polymer materials, textile materials and metal-based materials[7,8]. The integrated electrode not only meets the requirement of the battery on mechanical flexibility, but also has the structural characteristics of a porous structure, a higher specific surface area and the like which are beneficial to improving the ion migration speed, reducing the interface impedance and the like, thereby finally improving the mechanical flexibility and electrochemical performance of the flexible lithium ion battery.

2.1 Lectrode with its own electrochemically active substrate material

2.1.1 Carbon material base flexible electrode

Carbon material is an ancient and young material,which is one of the elements most closely related to human life in nature.Carbon has three hybrid States of sp,sp2and sp3,and different hybrid States can form different allotropes.In addition,the anisotropy of sp2leads to the anisotropy of crystals.Carbon can form zero-dimensional fullerene molecules,one-dimensional carbenes and carbon nanotubes,two-dimensional graphene and three-dimensional diamond crystals.Carbon nanotubes,graphene and other materials have high electrical and thermal conductivity,special surface and interface characteristics,which can significantly promote the diffusion of electrons and ions,improve safety,and are widely used in the field of flexible energy storage[8⇓~10]。 the rough surface of carbon-based materials can also increase the contact area and reduce the contact resistance,so flexible electrodes based on carbon-based materials are very attractive.carbon fiber,carbon nanotubes(CNTs),graphite,graphene,graphyne,carbon cloth/carbon paper and so on are the main carbon materials used for flexible lithium-ion battery electrodes[11,12]。
(1)Carbon fiber based flexible electrode
carbon fiber is a one-dimensional carbon material formed by the growth of graphite crystallites along the fiber axis.the diameter of carbon fiber is usually between tens of nanometers and tens of microns.It has good conductivity and has been widely used in flexible energy storage devices.Electrospinning technology is a simple and easy method to prepare carbon fiber materials with uniform structure and mechanical deformation,which can control the diameter of the fiber and the morphology of the material(such as hollow,porous structure,etc.)[13]。 the results show that the self-supporting flexible electrode materials without binder and conductive agent can be prepared by the combination of electrospinning and heat treatment,and good electrochemical properties can be obtained[14,15]。 Cao and Liu et al.Prepared a self-supporting SnS/N-doped carbon nanofibers(CNFs)composite electrode with good mechanical flexibility by combining electrospinning and heat treatment.When the size of the electrode is the size of five one-dollar coins,it can hang five one-dollar coins(weighing about 30 G)[16]。 When SnS/N-doped CNFs are used as the negative electrode of the flexible lithium-ion battery and lithium sheet is used as the counter electrode,the cycle stability of the assembled half-cell can reach more than 1000 cycles,the specific capacity is 648 mAh·g-1after 500 cycles at a current density of 200 mA·g-1,and the specific capacity is 548 mAh·g-1after 500 cycles at a current density of 500 mA·g-1.In the composite electrode system,the SnS nanoparticles are uniformly dispersed in the one-dimensional porous nanofibers with uniform diameter,which shortens the migration path of ions and electrons and improves the conductivity.The carbon nanofibers can effectively alleviate the volume change of SnS during charge and discharge while improving the electronic conductivity 。
the structure of the material determines its performance.It has been proved that the heterostructure material has high charge transfer ability,which is formed by depositing more than two layers of different materials on the same substrate in turn.These materials have different band gaps,and have internal electric field coupling effect at their heterointerfaces,which promotes the reaction kinetics of heterostructure materials and improves the ability of charge transfer,so they are widely used in the field of energy storage[17,18]。 Ren and Li et al.Used a combination of electrospinning and solvothermal methods to grow CuOx-Co3O4heterostructure nanowires on three-dimensional porous nitrogen-doped carbon nanofibers(PNCNF),as shown in Figure 1[19]。 The active material loading of the composite electrode is about 1.0 mg·cm-2,and the synergistic effect of the one-dimensional CuOx-Co3O4heterogeneous array and the three-dimensional PNCNF substrate material can effectively shorten the diffusion path of lithium ions,The interface contact performance is improved,and more electrochemical active sites are provided,so that the self-supporting CuOx-Co3O4@PNCNF composite anode material has higher discharge specific capacity and excellent cycle stability.The half cell assembled with lithium sheet as counter electrode has a cycle stability of more than 1000 cycles.After 100 cycles of charge and discharge at a current density of 200 mA·g-1,the half cell still has a discharge specific capacity of 1122 mAh·g-1,and after 1000 cycles of charge and discharge at a current density of 2 A·g-1,the reversible specific capacity is 668 mAh·g-1.The CuOx-Co3O4@PNCNF/LiFePO4battery was charged and discharged in the range of 0.01~3.0 V with the current density as the 5 A·g-1.The specific capacities of the first cycle were 1065 and 780 mAh·g-1,respectively,and the specific discharge capacity was 726 mAh·g-1after 90 cycles.The whole battery can still light up an LED lamp after being bent into a 180 degree state 。
Due to the limitations of electrospinning technology in industrial application,Hu and Lei used commercial carbon fibers to prepare nitrogen-doped porous carbon fibers(NCF)by electrochemical deposition followed by calcination,and then the NCF was subjected to azide hydrothermal treatment to obtain a free-standing NNCF flexible anode[20]。 The flexible half cell assembled with NNCF still has a capacity retention of 97.32%after 200 cycles.The full cell with NNCF-LiCoO2as positive electrode and NNCF as negative electrode has an operating voltage of 2.6 V and a discharge capacity of 0.2 mAh·cm-2at a current density of 0.2 mA·cm-2.The research of carbon nanofiber-based flexible electrode has made some progress,but its mechanical flexibility is very limited,and it is difficult to meet the needs of complex deformation when it is used as current collector or host material.The introduction of carbon nanotubes or graphene with high strength and modulus can effectively improve the mechanical strength of the flexible electrode on the basis of ensuring the electrochemical performance of the material 。
(2)Carbon nanotube-based flexible electrode
Carbon nanotubes(CNTs)are one-dimensional nanomaterials with a radial dimension of nanometer and an axial dimension of micron.The sp2hybrid structure of carbon atoms in CNTs leads to the delocalization of p orbital electrons,which can form delocalized largeπbonds.Because of its significant conjugation effect,CNTs have some special electrical properties[21]。 CNTs have a large length-to-diameter ratio,and can have good heat transfer performance along the length direction.CNTs have higher capacity than graphitized carbon and can improve the kinetic characteristics of the electrode.Therefore,in the design of flexible electrodes,CNTs are widely used as a substrate/current collector material for the negative electrode or active material of flexible lithium ion batteries[22]。
Wang et al.prepared a nitrogen-doped carbon nanofibers/CNTs(CNFs/CNTs)composite film with a layered structure by combining electrospinning and heat treatment,and used it as a self-supporting anode for flexible lithium-ion batteries,which has the advantages of both CNFs and CNTs[23]。 By comparing the morphology of CNFs and CNFs/CNTs,it was found that pure CNFs had some small damage to the morphology,and the addition of CNTs could improve the defects in the morphology and improve the mechanical properties of the composite electrode.The half cell assembled with CNFs/CNTs has a specific discharge capacity of 2459 and a specific charge capacity of 1500.5 mAh·g-1at the first cycle at a current density of 0.05 A·g-1in the voltage range of 0.001 to 3.0 V.The specific discharge capacity is 1099.5 mAh·g-1after 100 cycles,and the specific capacity is 545 mAh·g-1after 400 cycles at a current density of 0.2 A·g-1.At the same voltage range and the current density of 0.05 A·g-1,the first discharge and charge specific capacities of the half cell assembled by CNFs were 1655.8 and 942.4 mAh·g-1,respectively,and the reversible discharge specific capacity was 490.7 mAh·g-1after 100 cycles.The results show that the addition of CNTs can effectively improve the mechanical flexibility and electrochemical performance of the electrode.The half cell with electrode size of 1.5×2.5 cm was folded at 0°,45°,90°,135°and 180°,and the voltage plateaus were almost the same,and the discharge capacities under different deformation conditions had little difference.Using 1.2~1.5 mg·cm-2CNFs/CNTs as negative electrode and about 6.5 mg·cm-2LiNi0.5Co0.2Mn0.3O2(theoretical specific capacity is about 280 mAh·g-1)as positive electrode,The assembled battery was tested in the range of 2.5~4.4 V,and the discharge capacity was 629.6 mAh·g-1at a current density of 0.1 A·g-1.After 10 cycles at 0.1,0.2,0.5 and 1 A·g-1,respectively,and 100 cycles at 0.1 A·g-1,the specific discharge capacity was maintained at 359.7 mAh·g-1,and 12 LED lamps could be lit when the whole battery was bent at 0°,90°,180°and 360°.Yang et al.prepared V2O5nanobelts(VNTs)/CNTs composite cathode material by mixing Na2V6O16·xH2O precursor and commercial CNTs through hydrothermal reaction,and prepared three-dimensional interwoven porous VNTs VNTs Ts CNTs-x(X is the content of CNTs)self-supporting composite cathode by vacuum filtration[24]。 The structural design of the electrode material establishes a path beneficial to electron transmission and buffers the volume expansion generated in the process of charging and discharging,and the flexible lithium ion battery assembled by using the electrode material as a positive electrode is tested for electrochemical performance.The specific discharge capacity is 295.8 mAh·g-1in the first cycle,223.5 mAh·g-1after 200 cycles,156.2 mAh·g-1when the current density is increased to 2000 mA·g-1,and 110 mAh·g-1after 1000 cycles.Yuan and Cao et al.prepared a three-dimensional porous spongy carbon nanotube/mesoporous silicon/carbon(CNT/meso-Si/C)composite material through sol-gel and magnesium thermal reduction reaction,as shown in Figure 2.Using lithium foil as the negative electrode and CNT/meso-Si/C as the positive electrode,the assembled battery had a discharge specific capacity of 2100 mAh·g-1in the first cycle at a current density of 0.5 A·g-1,and a specific capacity of 1800 mAh·g-1after 500 cycles,with good rate capability[25]。 the network structure of CNT improves the conductivity of the material,and the three-dimensional porous sponge structure constructed by the mesoporous silicon layer is beneficial to the transport of lithium ions.the pressure test shows that the electrode can withstand more than 60%compression,and the structure can still maintain integrity after 1000 cycles when the electrode is subjected to 40%compression。
In addition to being used as positive and negative electrode additives and positive electrode substrate materials,CNTs can also be directly used as active materials to construct flexible negative electrodes[26,27]。 However,materials will show some nano-size effect after reaching the nano-scale,and nano-powder will show strong agglomeration effect.CNTs have strong van der Waals force,single CNTs is fibrous,and its nano-powder materials are easy to entangle together to form agglomerates.In practical applications,the agglomeration state often destroys the excellent performance of single CNTs,which limits its application in flexible electrodes.Ozkan et al.prepared a three-dimensional superstructure anode composed of vertically arrayed CNTs and three-dimensional graphite foam by chemical vapor deposition using nickel foam as a template[28]。 The three-dimensional superstructure material containing the vertical array CNTs has high specific surface area,high conductivity and excellent electrochemical stability,the current density is 500 mA·g-1,the specific capacity is larger than 800 mAh·g-1after 120 cycles,and the specific capacity of the material containing the agglomerated CNTs is only 500 mAh·g-1.Therefore,the agglomeration phenomenon caused by the size effect of nanomaterials has a great impact on the electrochemical performance of the electrode 。
(3)Graphite based flexible electrode
Graphite and carbon nanotubes are allotropes of carbon element,which have excellent electrical and thermal conductivity.Cui et al.Found that flexible polyimide pyrolytic graphite film(GF)has a highly oriented crystalline structure,excellent electrochemical corrosion resistance,high conductivity and certain mechanical strength,so it has good electrochemical activity and is an ideal material for flexible current collector of lithium ion batteries[29]。 On the basis of this research,they used laser drilling(laser beam diameter is about 80μm)to prepare flexible porous graphite film(PGF),which still has good mechanical flexibility after bending 360°,and can maintain flexibility and integrity after bending 180°and cycling 200 times[30]。 Flexible PGF has high voltage resistance and very light weight.The gram weight of conventional 15μm copper foil current collector is 8.7 mg·cm-2,while the gram weight of PGF with a thickness of about 40μm is about 4.3 mg·cm-2,which is an ideal substitute for traditional battery current collector.The half cell assembled with PGF as the current collector of the LiNi0.5Mn1.5O4and lithium sheet has a specific discharge capacity of 127.5 mAh·g-1at a current density of 1 C(1 C=130 mA·g-1),and the specific capacity remains at 106.2 mAh·g-1after 400 cycles,with an average coulombic efficiency of 99.3%.As that PGF has a flexible self-support structure and lithium ions can be normally intercalate and deintercalated,the PGF can be directly used as the negative electrode of a lithium ion battery;when the half battery assembled by use the PGF as the negative electrode is charged and discharged at a current of 15 mA·g-1,the initial discharge specific capacity is 275.0 mAh·g-1,and the coulombic efficiency is 95.5%;and after 99 cycles,the discharge specific capacity is improved to 359.2 mAh·g-1,and the coulombic efficiency is improved to 99.6%.The flexible PGF/PGF-LiNi0.5Mn1.5O4battery assembled with PGF as the negative and positive current collectors respectively can withstand a high voltage of 5 V,and its electrochemical performance was tested in the voltage range of 3.5-4.9 V.At a current density of 0.5 C,the specific discharge capacity is 111.9 mAh·g-1,and the specific discharge capacity after 400 cycles is 90.8 mAh·g-1,with an average coulombic efficiency of 99.6%.The above research results show that the flexible battery based on flexible PGF has the characteristics of light weight,light and thin,simple manufacturing process and high energy density,and is an ideal material for flexible wearable electronic products 。
(4)Graphene-based flexible electrode
Graphite,as the anode material of lithium ion batteries,has a theoretical specific capacity of 372 mAh·g-1/818 mAh·cm-3,while metal oxides as anode materials have a higher specific capacity than graphite.The disadvantage is that metal oxides will produce a huge volume change during charging and discharging,resulting in the reduction of the cycle capacity of batteries.In 2004,Andre Geim and Konstantin Novoselov,physicists at the University of Manchester,UK,successfully separated graphene with a single atomic layer thickness from graphite by micromechanical peeling[31]。 The high electrical conductivity(106S·m-1)of graphene can provide a good electron transport channel,the high thermal conductivity can improve the thermal stability of the battery,the high specific surface area(2630 m2·g-1)can provide more electrochemical active sites,and the high mechanical strength(42 N·m-1)can improve the mechanical performance of the battery.In addition,the lamellar distance of graphene is in the order of micro-nanometer,which is much smaller than that of bulk graphite,and can shorten the diffusion path of lithium ions,which is conducive to improving the power performance of lithium ion batteries[32]。
Wang et al.Proposed an electrode design method combining nano-three-dimensional conductive network self-support and sandwich structure to prepare flexible metal oxide and redox graphene composite anode[33]。 Firstly,the cellulose paper is prepared into a porous flexible carbon paper(CP)with a three-dimensional network structure with high specific surface area(2443 m2·g-1),high conductivity(1500 S·m-1)and bending resistance(bending resistance times are more than 85,000 times)by utilizing the reaction that the cellulose fiber is subjected to oxygen-ammonia combined pyrolysis to prepare the twisted ultra-thin graphite sheet,Then,CP is used as a carrier to prepare a CP@Fe3O4by a self-assembly method,and finally,reduced graphene oxide(RGO)is used for coating to prepare a flexible CP@Fe3O4@RGO composite electrode with a three-dimensional conductive network self-supporting sandwich structure,as shown in Figure 3.The content of the Fe3O4in the CP@Fe3O4@RGO is about 53 wt percent,and when the CP@Fe3O4@RGO is used as a negative electrode of a lithium ion battery,the flexibility and the electronic conductivity can be improved,the volume expansion of the Fe3O4in the charging and discharging process can be effectively relieved,and the cycle life of the battery is improved,wherein the specific capacity is 1160 mAh·g-1when more than 2000 cycles are carried out.Due to the low price of biomass cellulose raw materials,the preparation method using cellulose as raw materials for pyrolysis is expected to realize the large-scale preparation of three-dimensional network structure graphene paper,which has a good development prospect 。
Based on the advantages of graphene,Yang et al.Prepared a self-supporting flexible anode film material containing graphene by combining chemical vapor deposition and electrochemical deposition[34]。 The structure of the material is a three-dimensional cross-linked porous N-doped graphene foam(NGF)/N-doped graphene core-shell structure(Ge-QD@NG/NGF),and the Ge content in the composite material is about 73.76%.In order to test the flexibility and electrochemical performance of the composite electrode,the Ge-QD@NG/NGF was coated with PDMS by spraying method.The material was not damaged after many times of free bending,and the stress-strain curve was basically linear,and the stress it could withstand was about 0.9 MPa.The half cell assembled with the composite material was tested in the range of 0.01~1.5 V at 1 C current density,and the discharge and charge specific capacities were 1597 and 1220 mAh·g-1,1000,respectively.The discharge reversible capacity retention rate was 96%after several cycles.The battery was tested in the state of 90°bending,and the capacity was not affected basically.The method is simple to operate and provides important theoretical guidance for the research of the three-dimensional cross-linked graphene-based high-capacity material system for the flexible battery.Du et al.prepared a lamellar graphene/nanocellulose/silicon(GN/NC/Si)sandwich film by using a simple vacuum filtration method and covalent crosslinking effect[35]。 As a current collector material,the hydroxylated Si nanoparticles are regularly embedded in the GN lamellae,and NC acts as an adhesive for the covalent cross-linking of the GN and Si nanoparticles.The electrical conductivity of GN/NC/Si with different Si content is similar to that of GN/NC,which is about 38.39~52.08 S·cm-1and much higher than that of Si anode.The half cell assembled by using Si as the negative electrode shows high reversible capacity,good cycle stability and excellent rate capability.When the Si content is 68%,the voltage range is 0.005~2.0 V,the current density is 100 mA·g-1,and the reversible capacity is 1251 mAh·g-1after 100 cycles.The stress-strain test results show that the film has strong mechanical properties,the average strength of the film with 68%Si is 7.9 MPa at 2.2%strain,and no fracture is observed after severe deformation,which indicates that the film can not only provide good flexibility,but also buffer the volume change of Si during cycling.The full cell assembled with LiCoO2as the positive electrode has a specific discharge capacity of about 80~90 mAh·g-1in the first cycle and a voltage plateau of 3.4 V at a current density of 100 mA·g-1in the voltage range of 1.8 to 4.2 V.The full cell can light an LED lamp under the conditions of bending and folding 。
Graphene is widely used as electrode materials for batteries because of its excellent electrical and thermal conductivity.Due to the limitation of preparation process,it brings some challenges in large-scale application.Hu et al.Designed and prepared a free-standing composite electrode containing porous graphene(hG)without binder and solvent by using an environmentally friendly and large-scale dry pressing method,as shown in Figure 4[36]。 the inherent nano-pores of hG facilitate the escape of gas during dry pressing,and at the same time,it can accommodate the positive or negative active materials that can not be compressed.A variety of self-supporting electrodes can be prepared by selecting the pressure,the compression time,and the type of active material.the results show that there is no significant difference in the rate capability of the free-standing cathode prepared by using lithium iron phosphate(LFP)as the active material and holding the pressure at 500,200 and 20 MPa for 10 min and 20 MPa for 10 s,respectively.the preparation process greatly improves the production efficiency。
(5)Graphylene-based flexible electrode
Graphyne(GDY)Is a new type of carbon allotrope discovered after carbon nanotubes,graphene and fullerenes.3-diacetylene bonds are conjugated with benzene rings to form a two-dimensional planar network structure of lamellar carbon materials,which has unique structure and properties conducive to the rapid diffusion and transport of lithium ions in and out of plane,and has a theoretical mass specific capacity of 744 mAh·g-1,so it is an ideal lithium storage material[37,38]。 Li and Huang et al.prepared a yellow transparent film of carbon framework hydrogen substituted graphyne(HsGDY)by in situ triethynylbenzene cross-coupling reaction,and used it as a flexible self-supporting electrode for lithium-ion batteries at a current density of 0.1 A·g-1.The reversible mass specific capacity and volume specific capacity of the electrode can reach 1012 mAh·g-1and 1447 mAh·cm-3,respectively,and the mass specific capacity after 100 cycles is 1050 mAh·g-1.The excellent bendability of the electrode makes it have broad application prospects in flexible energy storage systems[39]。 On the basis of this research,they prepared a yellow transparent film of fluorinated graphene(F-GDY).Through theoretical calculation and experimental verification,it is proved that F-GDY is an ultra-stable two-dimensional material for flexible batteries.The half cell assembled with F-GDY film has a reversible capacity of about 1700 mAh·g-1at a current density of 50 mA·g-1,and has a stable cycle performance of 9000 cycles at a current density of 2 A·g-1[40]。 GDY is mainly prepared by catalytic coupling reaction.Because of its two-dimensional planar structure,it is easy to produce small molecular oligomers in the chemical reaction process,which affects its crystalline phase,and then affects its interfacial properties and electrochemical properties.Huang et al.Found that pure GDY thin films with high conductivity and uniform morphology can be prepared by heat treatment by controlling the temperature and time of heat treatment[41]。 The reversible discharge specific capacity of the half cell assembled by the GDY film heat-treated at 400℃is 901 mAh·g-1at a current density of 100 mA·g-1and 430 mAh·g-1at a current density of 5 A·g-1.On the basis of this study,they found that GDY doped with heteroatoms had better electrochemical performance,and designed and synthesized pyridine graphyne containing pyridine nitrogen(PY-GDY)and pyrimidine graphyne containing pyrimidine nitrogen(PM-GDY),as shown in Figure 5[42]。 The electronic structure of GDY doped with heteroatoms is different from that of pure GDY,and the existence of heteroatoms improves the conductivity of the material.The doped nitrogen heteroatoms are uniformly distributed in the GDY to generate extra space around the doping sites,which is more beneficial to the storage and diffusion of lithium,thereby improving the storage capacity.It was found that the electrochemical performance of the PM-GDY electrode was related to the chemical structure of the repeat unit.At the current density of 50 mA·g-1,the PM-GDY electrode had a higher capacity than the PY-GDY electrode,but the rate capability of the PY-GDY was better than that of the PM-GD.Studies have shown that the doping of heteroatoms can adjust the properties of materials,but in general,precise doping is needed,and precise doping of heteroatoms is of great significance.Compared with other carbon materials,graphyne,as a new two-dimensional planar carbon material,has a broader application prospect in the field of flexible lithium ion electrode materials,and the research process of industrialization should be accelerated in the progress of basic research 。
(6)Carbon cloth/carbon paper based flexible electrode
the carbon cloth/carbon paper has outstanding electronic conductivity and excellent mechanical flexibility,the network structure of the fiber can form a conductive network which is beneficial to the transmission of ions and electrons,the surface of the carbon cloth/carbon paper is rough,and the adhesion force is strong,so that the carbon fabric/carbon paper is used as a substrate/current collector material of a flexible electrode and is beneficial to improving the electrochemical performance of a flexible battery。
Lee et al.Used conductive carbon cloth as current collector,mixed nano-sized LiFePO4(LFP)and Li4Ti5O12(LTO)active materials with flexible two-dimensional redox graphene respectively,and adhered them to carbon cloth by rolling to prepare flexible positive and negative electrodes[43]。 The LTO/LFP full battery assembled by the flexible electrode prepared by the method has high flexibility and area capacity,and can bear mechanical fatigue.The area capacity of the LTO/LFP battery reached the 1.2 mAh·cm-2,and the battery could maintain a stable open-circuit voltage after 1000 times of repeated bending with a bending radius of 10 mm,and the battery still retained a certain capacity after 100 times of bending with bending radii of 30,20 and 10 mm,respectively.The use of carbon cloth as the current collector enhances the flexibility and conductivity of the electrode material,and can effectively prevent the flexible battery from delamination or damage during repeated deformation and use 。
In order to improve the material performance,the hydrothermal method can be used to grow nano-arrays on carbon cloth,increase the specific surface area and improve the reactive sites.Sun and Zhang et al.Used a template-free hydrothermal method to grow V3O7hydrate on flexible carbon cloth,and then calcined it to prepare an N-doped carbon-coated V2O5nanoribbon/carbon cloth(V2O5@N-C)composite cathode with high flexibility,as shown in Figure 6[44]。 The specific capacity of the flexible battery assembled with the composite material is 215 mAh·g-1after 50 cycles at a current density of 0.5 C(1 C=294 mAh·g-1).Li and Jiang et al.modified commercial carbon cloth with dopamine and in-situ grown V2O5array nanosheets on it.After heat treatment,they prepared V2O5NAs/CC cathode materials for flexible lithium-ion batteries[45]。 It was found that the conductivity of the V2O5NAs/CC was about 0.45 S·cm-1,and the conductivity remained unchanged after 250 times of bending.The flexible half cell assembled with the V2O5NAs/CC was tested at a current density of 15 C(1 C=300 mA·g-1).When the loading of the V2O5was 2.1 mg,the specific capacity was 120 mAh·g-1,and the capacity loss rate was 0.18%after 100 cycles at 2.5~4.0 V with 1 C current density.The flexible full cell assembled with V2O5NAs/CC as positive electrode and pre-lithiated carbon fiber as negative electrode showed high mechanical properties(more than 250 cycles)and good electrochemical performance(specific capacity was about 250 mAh·g-1 )。
The carbon cloth can be used as a substrate/current collector material of a positive electrode,and can also be used for preparing a flexible self-supporting negative electrode material through hydrothermal treatment.Liu et al.Prepared a self-supporting flexible anode material without binder by hydrothermal growth of Zn2SnO4on functionalized flexible carbon cloth[46]。 The Zn2SnO4is uniformly fixed on the surface of the carbon cloth fiber,which provides a fast diffusion path for lithium ions and electrons,relieves the volume change caused by the lithium ion insertion/extraction process,and significantly improves the electrochemical performance.The reversible specific capacity is 1510 mAh·g-1after 60 cycles of charge and discharge at a current density of 100 mA·g-1,while the reversible specific capacity of the conventional electrode is only 668 mAh·g-1after 60 cycles of charge and discharge at a current density of 100 mA·g-1.Du and Su et al.Prepared a self-supporting MoSe2nanoflower@carbon cloth(MoSe2@CC)composite by a combination of hydrothermal and heat treatment methods[47]。 The anode material of the MoSe2@CC used for the lithium ion battery shows good rate capability and excellent cycle stability,the specific capacities are 1337,1092,952,831 and 749 mAh·g-1at the current densities of 0.1,0.2,0.5,1.0 and 2.0 A·g-1respectively,and the specific capacity is 638 mAh·g-1after 1200 cycles at the current density of 5.0 A·g-1 。
the carbon cloth/carbon paper as the positive and negative electrode substrate/current collector material has good operability,the preparation method is simple,and the prepared electrode has good flexibility,but the load of the active material is difficult to be greatly improved,so that the energy density of the battery is reduced。

2.1.2 MXene-based flexible electrode

MXene is a two-dimensional layered inorganic material composed of transition metal carbides,nitrides,or carbonitrides with a thickness of several atomic layers and has the formula Mn+1XnTx,where M represents a transition metal,X is carbon and/or nitrogen(n=1,2,or 3),and T represents oxygen,hydroxyl,fluorine,etc[48]。 Because of its unique structure and surface chemical properties,it has metal-like conductivity and good ion transport channels,and has broad application prospects in the field of energy storage materials.MXene is an ideal material for flexible energy storage electrode due to its high volume specific capacity and high conductivity[49]。
Feng et al.prepared a flexible free-standing Si/MXene composite electrode by liquid phase mixing and vacuum filtration,as shown in Fig.7A,with an active material loading of 1.1~1.3 mg·cm-2[50]。 The MXene layered material can effectively alleviate the volume change of Si particles in the electrochemical reaction process and improve the conductivity of the composite material.The flexible half battery assembled by using the MXene layered material as a negative electrode has a capacity of 2118 mAh·g-1after 100 cycles at a current density of 200 mA·g-1and a capacity of 1672 mAh·g-1after 200 cycles at a current density of 1000 mA·g-1.The good performance of the material is attributed to the fact that the three-dimensional structure of the material contributes to the transport of lithium ions/electrons and the infiltration of electrolyte,and increases the active sites of MXene for lithium storage.Xu et al.Used sulfur particles with low price and controllable structure as templates to prepare a flexible self-supporting three-dimensional porous MXene foam electrode through vacuum filtration and de-templating,as shown in Figure 7B[51]。 The material has high specific capacity,stable cycle performance and excellent rate capability.When the current density is 50 mA·g-1,the specific capacity is 455.5 mAh·g-1,and after 3500 cycles of 1 A·g-1,The capacity is 220 mAh·g-1,and the capacity can be kept 101 mAh·g-1when the current density is 18 A·g-1.The preparation of three-dimensional porous MXene foam electrode by sulfur template method provides a research idea to construct 3D porous foam from 2D nanosheets.The basic research work of MXene-based flexible electrode needs to be further carried out,and the area specific capacity and the performance of the whole battery need to be further explored 。

2.2 Flexible electrodes of other substrate material

2.2.1 Polymer-based flexible electrode

macromolecular polymer is a kind of macromolecular compound which is composed of specific structural units repeatedly connected by covalent bonds.Due to the multi-layer structure of long-chain molecules and the special movement mode of macromolecular chains,they have excellent mechanical properties,such as high elasticity and high strength,and can be used as substrate materials for flexible electrodes by coating conductive layers on the surface or introducing conductive materials to improve the conductivity of polymers.In addition,polypyrrole,polyaniline,polythiophene and other polymers have the ability to transport charges,which are good intrinsic conductive materials and can be directly used as conductive current collectors。
Li et al.Prepared self-supporting polyurethane/copper/silicon(PU/Cu/Si)flexible nanocomposites by layer-by-layer self-assembly method[52]。 PU as the base material of the composite electrode can provide good tensile properties,nano-Cu as the conductive material can establish a three-dimensional conductive network to improve the conductivity of the composite electrode,and nano-Si as the lithium storage material.The deformation of the PU/Cu/Si composite film was 125.1%under the stress of 8.2 MPa,and the half cell assembled with the PU/Cu/Si composite film as a flexible anode still had a capacity of 574 mAh·g-1after 300 cycles at 1 C.The method of layer-by-layer self-assembly effectively alleviates the agglomeration of nano-Cu and nano-Si materials,and the composite anode can also effectively alleviate the volume expansion of Si in the reaction process,but the layer-by-layer self-assembly method takes a long time to prepare the material,and the process is more complex.Li et al.prepared the redox graphene/cellulose nanofiber/redox graphene(RGO/CNF/RGO)flexible composite conductive paper with sandwich structure by vacuum filtration and chemical reduction method,as shown in Figure 8[53]。 The tensile strength and modulus of the composite were 72.7 MPa and 4.8 GPa,respectively,when the content of RGO was 4 wt%.Due to the special structure of the sandwich,RGO/CNF/RGO has high conductivity,and the conductivity of the material can reach 4382 S·m-1when the content of RGO is only 4 wt%.In addition,the method for preparing the electrode by suction filtration is simple and easy to operate,and is a path easy to industrialize and apply 。
the above studies show that the polymer substrate/current collector plays a driving role in the development of flexible lithium-ion battery electrodes,and the modified non-conductive polymer materials have broad application space in the future.However,due to the low conductivity of polymers,their application in high specific energy flexible batteries is limited,and further exploration is needed。

2.2.2 Textile material-based flexible electrode

textile materials with three-dimensional structure have become the ideal choice of substrate/current collector materials for flexible batteries because of their low cost,large specific surface area,excellent flexibility and high wearing comfort.the flexible electrode structure based on textile material is to attach the active material to the textile material,which can improve the performance of the flexible battery and make it have a certain tensile property。
Wang et al.used nickel-coated Cotton fabric(Ni-Cotton)as conductive current collector and flexible substrate material to load single-shell or multi-shell hollow structure V2O5(nS-V2O5,n is the number of shells)active materials,and the active material loading of the 3S-V2O5/Ni-cotton cathode prepared by Wang et al.was as high as 2.5 mg·cm-2[7]。 Because the 3S-V2O5has larger specific surface area and more lithium storage active sites,the electrode specific capacity and the battery rate performance of the fabric-based flexible battery are greatly improved,The electrode/electrolyte contact interface is improved,the migration path of lithium ions and electrons is shortened,and the structure can also effectively relieve the volume expansion and stress strain caused by the deintercalation of lithium ions,After 500 charge-discharge cycles,the capacity is 222.4 mAh·g-1,and the specific capacity of the 2 cm×2 cm soft pack battery prepared by the method is 144.3 mAh·g-1.The voltage is almost unchanged when the battery is bent at 180°,and the capacity is not significantly reduced after hundreds of bending and folding cycles.The battery can light a 1 m long LED lamp.The preparation methods of the Ni-cotton current collector,the V2O5hollow structure material and the V2O5hollow structure/Ni-cotton composite electrode are relatively simple and have certain advantages in large-scale application 。
in addition to the cotton fabric used in the above study,nylon fabric can also be used as a substrate material for the preparation of flexible electrodes.Tang et al.used the flexible nylon fabric as the substrate material,and used the magnetron sputtering method to construct the silicon(Si)anode on the nylon fabric deposited with Cu and Ni metal layers(Fig.9).Can obviously relieve the stress concentration phenomenon of the material interface and overcome the damage caused by the volume expansion of the Si nano particles in the charge and discharge process,and is a flexible interface design strategy for effectively regulating and controlling the interface stress of a silicon(Si)negative electrode[54]。 The results show that the material can still maintain good flexibility and structural integrity after 50 000 bending cycles。

2.2.3 Metal substrate flexible electrode

One of the key materials of flexible lithium-ion batteries is the self-supporting flexible electrode materials.In the selection of substrate materials for electrode materials,carbon materials,textile materials and polymers are used as substrate materials.Compared with metal substrate materials,the electronic conductivity is relatively low,which limits the rapid commercialization process of flexible lithium-ion batteries to a certain extent[8,9]。 By using the metal substrate with high conductivity,the three-dimensional array nano material with larger specific surface area can be grown in situ,the electrochemical active site of the material is improved,and the porosity of the material is higher.O that the wettability of the electrolyte is improved,the rapid diffusion path of electrons/ions is realized,the volume change of an active material in an electrochemical reaction process is relieved,and the structural stability of the flexible battery is improved。
Xia et al.Found that a self-supporting porous three-dimensional nanosheet array can be prepared by using gold-plated stainless steel foil as a substrate and using a combination of hydrothermal,calcination and lithiation methods,as shown in Figure 10[55]。 The half-cell assembled by using the composite material as a positive electrode of a lithium ion battery still has high reversible specific capacity and good cycle stability at a high rate.The reversible specific capacity measured at 10 C was 104.6 mAh·g-1,0.1 C and the capacity retention was 81.8%after 1000 cycles.The reversible specific capacity of the battery assembled by using the LiCoO2nanosheet array as a positive electrode and the Li4Ti5O12nanosheet array as a negative electrode at 0.1 C is 130.7 mAh·g-1,10 C,the reversible specific capacity is 85.3 mAh·g-1,0.1 C,and the capacity retention rate is 80.5%after 1000 cycles.The design of flexible three-dimensional nano-array materials provides a new idea for the design of high-performance flexible cathode materials for lithium-ion batteries 。
The structure of three-dimensional nanoarrays can also be used to design and prepare flexible anode materials.Zhu et al synthesized self-supporting CSTAs@MoS2@PPy sandwich-like nanotube arrays(SNTAs)on steel foil by template hydrothermal method[56]。 In the structure,MoS2nanosheets are uniformly grown on the conductive PPy,and at the same time,they are deposited on the vertically aligned submicron-sized tubular carbon.CSTAs@MoS2@PPy SNTAs as flexible lithium-ion battery electrodes can not only improve the conductivity of ions and electrons,but also effectively alleviate the volume expansion of MoS2during charging and discharging.The specific capacity of the half-cell assembled with the lithium sheet is 1050 mAh·g-1after 600 cycles at a current density of 200μA·cm-2/805 mA·g-1,and the specific capacity is 630 mAh·g-1at a current density of 1000μA·cm-2/4027 mA·g-1.The battery with CSTAs@MoS2@PPy SNTAs as negative electrode and LiCoO2as positive electrode has a specific capacity of 1000.3 mAh·g-1and a coulombic efficiency of 93.5%at a current density of 50μA·cm-2/100 mA·g-1.Nickel foam(NF)as a substrate material has excellent electronic conductivity,large specific surface area can provide sites for the growth of active materials,and the cost is low.Zhu et al.controllably synthesized a micron-scale sea urchin-shaped composite anode material composed of highly loaded NiCo2O4array nanowires with NF as the substrate through a surfactant-assisted hydrothermal method and calcination treatment,and the loading capacity of the(NiCo2O4HNAs/NF),NiCo2O4HNAs/NF was as high as 7 mg·cm-2,as shown in fig.11[57]。 The NiCo2O4HNAs/NF has large specific surface area and uniform porous structure,and the NiCo2O4active substance and the NF have strong adhesive force,When the current density is 500 mA·g-1,the reversible specific capacity is 1094 mAh·g-1,and when the current density is 1000 mA·g-1,the specific capacity is 875 mAh·g-1.The high electrical conductivity of metal substrate/current collector materials improves the electrochemical performance of the materials,but there are still some problems to be solved in meeting the mechanical flexibility requirements of flexible batteries 。

3 Design of Macroscopically Flexible Electrode Structure

An electrode using a flexible material with intrinsic electrochemical activity as the negative electrode or a flexible conductive material as the substrate/current collector can meet the general bending or folding requirements of flexible batteries, but it is urgent to further improve its ability to work normally under large deformation conditions[58]. For wearable electronic devices, problems such as the weavability and breathability of batteries also need to be solved. Therefore, according to the topological principle, inspired by the traditional paper-cut art and the concept of textile fiber structure, researchers have prepared paper-cut structure, fibrous structure and other electrodes with macro-flexible structure, which provides the possibility for flexible lithium-ion batteries to be used under complex deformation conditions such as stretching and compression, or to be woven[59].

3.1 Paper-cut structure electrode

Inspired by the traditional paper-cut process,Fang et al.prepared a paper-cut structure electrode suitable for flexible lithium-ion batteries by coating and printing with a customizable PDMS soft template,as shown in Figure 12[60]。 The electrode uses CNTs as a conductive material and nano LFP or LTO as a positive electrode or a negative electrode active material,viscous ink is prepared,and the electrode is coated on a PDMS soft template to realize the electrode design of a flexible paper-cut structure which can bear large deformation.Finite element analysis and corresponding experimental tests reveal the ultra-low strain in the material,which is less than 3%at 100%tensile ratio.The flexible full cell assembled with the flexible LFP positive electrode and the flexible LTO negative electrode has good electrochemical performance.During 500 cycles of dynamic stretching,the average discharge capacity of the assembled full cell at 0.3 C is 94.5 mAh·g-1.The flexible and stretchable paper-cut structure electrode can effectively alleviate the stress concentration of the battery in the stretching/bending process,improve the performance of the battery,and meet the use requirements under large deformation conditions,but the paper-cut structure battery needs to be accurately aligned during assembly,which brings some challenges to the battery assembly 。

3.2 Fiber structured electrode

In order to meet the weaving needs of wearable devices,the fibrous one-dimensional energy storage devices with coaxial,parallel and twisted structures have become a hot research topic[61]。 Inspired by traditional textile fiber materials,Geng et al.prepared fibrous TiO2/rGO flexible electrodes by wet-spinning method using redox graphene(rGO)and titanium dioxide(TiO2)nanosheets,and assembled them with lithium wires to form a coaxial fibrous flexible lithium ion half cell,as shown in Figure 13(a )[62]。 The TiO2/rGO fiber flexible electrode has high conductivity(1.12×104S·m-1),and the stress-strain test shows that the TiO2/rGO fiber can bear the maximum strain of nearly 8%and the stress of 150~160 MPa.A 3 cm long half cell was assembled with the composite,and the specific discharge capacity was 168 mAh·g-1at the current of 0.0085 mA,which was very close to the theoretical specific capacity 170 mAh·g-1.The capacity retention rate was 70%after 200 cycles,and the specific capacity was 89 mAh·g-1at the test current of 0.0425 mA.A 10 cm long full cell assembled with LiMn2O4as the positive electrode can continuously illuminate LEDs(2.0 V,60 mW)for more than 5 H.Hu and Zhao et al.used low-cost and high-efficiency 3D printing technology to prepare flexible fiber electrodes,which can be twisted to assemble flexible all-fiber lithium-ion batteries,as shown in Figure 13(B )[63]。
The electrode is prepared by using high-viscosity polymer ink containing carbon nanotubes and active substances,which is made into one-dimensional fibers by 3D printing,and the flexible battery assembled by twisting can be woven,which meets the requirements of wearable electronic devices for flexibility and air permeability.The Volume specific capacity of the LFP/Li half cell is 68.8 mAh·cm-3,LTO/Li and the volume specific capacity of the LFP/Li half cell is 65.5 mAh·cm-3at the current density of 50 mA·g-1with the active material loading of 7.6 mg and 8.2 mg·cm-1,respectively.The all-fiber Li-ion battery with gel polymer as quasi-solid electrolyte was assembled by twisting,which had good electrochemical performance.The average discharge plateau voltage was 1.9 V,the specific discharge capacity was 110 mAh·g-1at the current density of 50 mA·g-1,and the capacity retention rate was 81%after 30 cycles.Advanced 3D printing technology has realized the design and manufacture of flexible lithium-ion batteries that can be woven and woven in fibrous form,which will open up a new way for the research of flexible wearable all-fiber energy storage devices 。
the fiber-shaped battery has the advantages of small size,easy twisting,knotting and weaving,but its low active material loading greatly reduces the energy density of the battery.in order to improve its energy density,small size cells can be stacked and combined.However,the assembly of small size cells is not only expensive,but also difficult to ensure the consistency and stability of the battery pack.Therefore,there are still some challenges In the research of high energy density fiber-shaped structure batteries。

4 Conclusion and prospect

As a key component of flexible electronic products, flexible energy storage devices have broad prospects for development. A series of progress has been made in the research of electrode materials for flexible lithium-ion batteries, but there is still a huge space for development. Most of the studies on the integrated flexible electrode use carbon materials or MXene materials as the flexible negative electrode and flexible substrate/current collector materials to load the positive and negative active materials to achieve the flexibility of the electrode. Carbon nanofibers, CNTs, graphite, graphene, graphyne, carbon cloth and other carbon-based nanomaterials can be directly used as cathode materials of flexible lithium batteries, and are also more widely used materials in the research of flexible non-metallic substrates/current collectors. As flexible cathodes of batteries, graphene and graphyne have higher specific capacity than other carbon materials. As substrate materials,The use of carbon nanofibers and carbon cloth is easier to achieve the preparation of flexible batteries, but the tensile properties of carbon-based materials can not fully meet the needs of flexible wearable devices.Moreover, there are still some technical problems to be solved in industrial application, especially the emerging material graphyne, which has broad application prospects in the field of energy storage, but the progress of its basic research should be accelerated in the process of industrialization. In recent years, the basic research of MXene flexible anode or MXene substrate/current collector materials has gradually increased, which has gradually promoted the development of MXene-based flexible electrode materials. Non-metallic substrates/current collectors such as polymers and textile materials can improve the tensile properties to a certain extent, but the conductivity is relatively low, which requires additional conductive layers or composite use with carbon-based materials, and the active material loading needs to be further improved. Metal substrate/current collector materials can improve the conductivity of materials, but the preparation methods are mostly in-situ growth methods, which brings some challenges to industrial applications, and the flexibility can not fully meet the needs of use. In addition, the adhesion properties and interface properties between the active material and the substrate/current collector material have a great impact on the electrochemical performance of flexible lithium-ion batteries, and the relationship between material structure and performance needs to be further studied and discussed. At present, the research of integrated flexible electrodes has promoted the commercialization of flexible lithium-ion batteries to a certain extent, in order to meet the needs of large-scale deformation or weaving technology.Some novel electrode structure designs, such as paper-cut structure and fiber structure, emerge as the times require, and their simple and ingenious manufacturing process provides new opportunities for the application of flexible lithium-ion batteries in flexible portable electronic products.
The development of flexible lithium-ion batteries is both opportunities and challenges. In the future research of flexible electrodes, the combination of new materials and new structures, and the increase of research on key properties such as area specific capacity and flexibility of batteries will accelerate the application process of flexible lithium-ion batteries, thus promoting the development of flexible wearable electronic products.

References

Publishing order | Descend order by publishing year | Descend order by cited within
[1]

Wang X F, Lu X H, Liu B, Chen D, Tong Y X, Shen G Z. Adv. Mater., 2014, 26(28): 4763.

[2]

Zhu Y H, Yang X Y, Liu T, Zhang X B. Adv. Mater., 2020, 32(5): 1901961.
[3]

Chen D, Lou Z, Jiang K, Shen G Z. Adv. Funct. Mater., 2018, 28(51): 1805596.
[4]

Li J, Jiang Q, Yuan N, Tang J G. Materials, 2018, 11(11): 2280.
[5]

Tarascon J M, Armand M. Nature, 2001, 414(6861): 359.

[6]

Gwon H, Hong J, Kim H, Seo D H, Jeon S, Kang K. Energy Environ. Sci., 2014, 7(2): 538.
[7]

Zhu Y J, Yang M, Huang Q Y, Wang D R, Yu R B, Wang J Y, Zheng Z J, Wang D. Adv. Mater., 2020, 32(7): 1906205.
[8]

Zhang Y, Jiao Y D, Liao M, Wang B J, Peng H S. Carbon, 2017, 124: 79.
[9]

Wen L, Li F, Cheng H M. Adv. Mater., 2016, 28: 4306.

[10]

Zhang C H, Li N W, Yao H R, Liu L, Yin Y X, Guo Y G. Acta Chim. Sinica, 2017, 75(2): 206.
[11]

Yousaf M, Shi H T H, Wang Y S, Chen Y J, Ma Z M, Cao A Y, Naguib H E, Han R P S. Adv. Energy Mater., 2016, 6(17): 1600490.
[12]

Ma Y, Asfaw H D, Edström K. Chem. Mater., 2015, 27(11): 3957.
[13]

Wang J F, Xu H J, Huo Y P, Wang Y T, Dong M D. Nanotechnology, 2020, 31(13): 132001.

[14]

Zhang C, Liang Y, Yao L, Qiu Y. Solid State Ion., 2014, 267: 74.
[15]

Li W H, Zeng L C, Wu Y, Yu Y. Sci. China Mater., 2016, 59(4): 287.
[16]

Xia J, Liu L, Jamil S, Xie J, Yan H X, Yuan Y T, Zhang Y, Nie S, Pan J, Wang X Y, Cao G Z. Energy Storage Mater., 2019, 17: 1.
[17]

Chang X, Wang T, Zhang P, Zhang J, Li A, Gong J L. J. Am. Chem. Soc., 2015, 137(26): 8356.

[18]

Hao J N, Zhang J, Xia G L, Liu Y J, Zheng Y, Zhang W C, Tang Y B, Pang W K, Guo Z P. ACS Nano, 2018, 12(10): 10430.
[19]

Chen H, He J, Li Y L, Luo S, Sun L N, Ren X Z, Deng L B, Zhang P X, Gao Y, Liu J H. J. Mater. Chem. A, 2019, 7(13): 7691.
[20]

Zhang Q, Zhou K, Lei J H, Hu W C. Appl. Surf. Sci., 2019, 467/468: 992.
[21]

Baughman R H, Zakhidov A, de Heer W A. Science, 2002, 297: 787.

[22]

Park S, Vosguerichian M, Bao Z N. Nanoscale, 2013, 5(5): 1727.

[23]

Huang L, Guan Q, Cheng J L, Li C, Ni W, Wang Z P, Zhang Y, Wang B. Chem. Eng. J., 2018, 334: 682.
[24]

Yang H, Xu G B, Wei X L, Cao J X, Yang L W, Chu P K. J. Power Sources, 2018, 395: 295.
[25]

Yang Y B, Yang X D, Chen S, Zou M C, Li Z H, Cao A Y, Yuan Q. ACS Appl. Mater. Interfaces, 2017, 9(27): 22819.
[26]

Zhang C, Yao L, Qiu Y. J. Appl. Polym. Sci., 2016, 133(9): 43001.
[27]

Zhang M, Lu R C, Yuan H X, Amin K, Mao L J, Yan W, Wei Z X. ACS Appl. Mater. Interfaces, 2019, 11(23): 20873.

[28]

Yan Y R, Li C L, Liu C, Mutlu Z, Dong B, Liu J, Ozkan C S, Ozkan M. Carbon, 2019, 142: 238.
[29]

Han P X, Zhang B, Huang C S, Gu L, Li H, Cui G L. Electrochem. Commun., 2014, 44: 70.
[30]

Xu G, Han P, Wang X, Zhou X, Han X, Lu D, Liu H, Zhao J, Ma J, Cui G. ACS Appl. Mater. Interfaces, 2020, 12: 9468.

[31]

Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A. Science, 2004, 306: 666.

[32]

Zhang M W, Hou C Y, Halder A, Wang H Z, Chi Q J. Mater. Chem. Front., 2017, 1(1): 37.
[33]

Gao T, Xu C Y, Li R Q, Zhang R, Wang B L, Jiang X F, Hu M, Bando Y, Kong D S, Dai P C, Wang X B. ACS Nano, 2019, 13(10): 11901.
[34]

Mo R W, Rooney D, Sun K N, Yang H Y. Nat. Commun., 2017, 8: 13949.

[35]

Zhou X M, Liu Y, Du C Y, Ren Y, Li X L, Zuo P J, Yin G P, Ma Y L, Cheng X Q, Gao Y Z. ACS Appl. Mater. Interfaces, 2018, 10(35): 29638.

[36]

Kirsch D J, Lacey S D, Kuang Y D, Pastel G, Xie H, Connell J W, Lin Y, Hu L B. ACS Appl. Energy Mater., 2019, 2(5): 2990.
[37]

Cranford S W, Buehler M J. Carbon, 2011, 49(13): 4111.
[38]

Li Y J, Xu L, Liu H B, Li Y L. Chem. Soc. Rev., 2014, 43(8): 2572.
[39]

He J, Wang N, Cui Z L, Du H P, Fu L, Huang C S, Yang Z, Shen X Y, Yi Y P, Tu Z Y, Li Y L. Nat. Commun., 2017, 8: 1172.
[40]

He J, Wang N, Yang Z, Shen X Y, Wang K, Huang C S, Yi Y P, Tu Z Y, Li Y L. Energy Environ. Sci., 2018, 11(10): 2893.
[41]

He J, Bao K J, Cui W, Yu J, Huang C S, Shen X Y, Cui Z L, Wang N. Chem. Eur. J., 2018, 24(5): 1187.
[42]

Yang Z, Shen X Y, Wang N, He J, Li X D, Wang X, Hou Z F, Wang K, Gao J, Jiu T G, Huang C S. ACS Appl. Mater. Interfaces, 2019, 11(3): 2608.

[43]

Ha S H, Shin K H, Park H W, Lee Y J. Small, 2018, 14(43): 1703418.
[44]

Wu L J, Zhang Y, Li B J, Wang P X, Fan L S, Zhang N Q, Sun K N. RSC Adv., 2018, 8(12): 6540.
[45]

Ma K, Liu X, Cheng Q L, Saha P, Jiang H, Li C Z. J. Power Sources, 2017, 357: 71.
[46]

Xia J, Tian R, Guo Y P, Du Q, Dong W, Guo R J, Fu X W, Guan L, Liu H Z. Mater. Des., 2018, 156: 272.
[47]

Kang J W, Su Q M, Feng H G, Huang P, Du G H, Xu B S. Electrochimica Acta, 2019, 301: 29.
[48]

Naguib M, Mochalin V N, Barsoum M W, Gogotsi Y. Adv. Mater., 2014, 26(7): 992.

[49]

Yang Q, Wang Y K, Li X L, Li H F, Wang Z F, Tang Z J, Ma L T, Mo F N, Zhi C Y. Energy Environ. Mater., 2018, 1(4): 183.
[50]

Tian Y, An Y L, Feng J K. ACS Appl. Mater. Interfaces, 2019, 11(10): 10004.

[51]

Zhao Q, Zhu Q Z, Miao J W, Zhang P, Wan P B, He L Z, Xu B. Small, 2019, 15(51): 1904293.
[52]

Liu L, Li M, Chu L, Jiang B, Lin R. Appl. Surf. Sci., 2019, 476: 501.
[53]

Hou M J, Xu M J, Li B. ACS Sustainable Chem. Eng., 2018, 6(3): 2983.
[54]

Jiang C L, Xiang L, Miao S J, Shi L, Xie D H, Yan J X, Zheng Z J, Zhang X M, Tang Y B. Adv. Mater., 2020, 32(17): 2070135.
[55]

Xue L, Savilov S V, Lunin V, Xia H. Adv. Funct. Mater., 2018, 28(7): 1705836.
[56]

Lu B, Liu J, Hu R Z, Wang H, Liu J W, Zhu M. Energy Storage Mater., 2018, 14: 118.
[57]

Wang Y, Liu P C, Zhu K J, Wang J, Liu J S. Nanoscale, 2017, 9(39): 14979.

[58]

Xie K Y, Wei B Q. Adv. Mater., 2014, 26(22): 3592.

[59]

Kaltenbrunner M, Sekitani T, Reeder J, Yokota T, Kuribara K, Tokuhara T, Drack M, Schwödiauer R, Graz I, Bauer-Gogonea S, Bauer S, Someya T. Nature, 2013, 499(7459): 458.

[60]

Bao Y H, Hong G Q, Chen Y, Chen J, Chen H S, Song W L, Fang D N. ACS Appl. Mater. Interfaces, 2020, 12(1): 780.

[61]

Sun H, Zhang Y, Zhang J, Sun X M, Peng H S. Nat. Rev. Mater., 2017, 2(6): 17023.
[62]

Hoshide T, Zheng Y C, Hou J Y, Wang Z Q, Li Q W, Zhao Z G, Ma R Z, Sasaki T, Geng F X. Nano Lett., 2017, 17(6): 3543.

[63]

Wang Y B, Chen C J, Xie H, Gao T, Yao Y G, Pastel G, Han X G, Li Y J, Zhao J P, Fu K, Hu L B. Adv. Funct. Mater., 2017, 27(43): 1703140.

Funding

the Key Project of Science for Beijing Institute of Fashion Technology(2020A-04)

the Special Fund for High-Level Teachers of Beijing Institute of Fashion Technology(BIFTXJ201917)

the Beijing Great Wall Scholars Incubator Program(CTT&TCD20180321)

and the Research of High-Performance Multi-Functional Winter Olympic Clothing(Z181100005918005)

PDF (28423KB)

3087

Accesses

0

Citation

Detail
Sections
Recommended

/

〈 〉

Address of Editorial Office: No. 33 Beisihuan Xilu, Zhongguancun , Beijing 100190, China
Tel: +86 10 8262 7757
Fax: +86 10 8262 7757
E-mail: progchem@mail.las.ac.cn
http://www.progchem.ac.cn
    • 　
    Copyright © Editorial Office of Progress in Chemistry