Lithium vanadium phosphate dry-method self-supporting electrode membrane as well as preparation method and application thereof

Abstract

The invention relates to a lithium vanadium phosphate dry-process self-supporting electrode membrane and a preparation method and application thereof, the preparation method comprises the following steps: shearing PTFE and a binder at a rotating speed of 5000rpm-8000rpm in an environment of lower than 20 DEG C to form a three-dimensional network structure so as to obtain a first mixture; according to a batch feeding operation mode, adding a conductive agent into the first mixture, stirring to obtain a uniformly mixed second mixture, adding LVP into the second mixture, continuously stirring to obtain a uniformly mixed third mixture, adding an electrode processing aid into the third mixture, and continuously stirring to obtain a uniformly mixed fourth mixture; differential rolling is adopted, the fourth mixture is rolled through a first roller pair under the condition of a first linear speed to complete preliminary compaction, a self-supporting electrode film initial pressing forming body is obtained, the self-supporting electrode film initial pressing forming body is rolled through a second roller pair under the condition of a second wire harness to complete hot pressing forming, and the self-supporting electrode film is obtained.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a dry-process self-supporting electrode film of lithium vanadium phosphate, its preparation method, and its application. Background Technology

[0002] Over the past few decades, global industrialization and urbanization have driven a surge in energy demand. However, this enormous global demand has led to massive consumption of fossil fuels and greenhouse gas emissions, causing environmental problems. Under the dual pressure of increasing fossil fuel consumption and environmental protection worldwide, policies and regulations in various countries and regions are imposing increasingly stringent requirements on vehicle emissions and fuel consumption. Therefore, the development of clean energy (such as solar, wind, hydro, and nuclear power) has become particularly urgent. my country has a vast territory, and its clean energy resources are unevenly distributed and unstable, necessitating conversion into electrical energy storage, which presents challenges to energy storage technology.

[0003] Lithium-ion batteries have become the mainstream energy storage technology due to their advantages such as long lifespan and high energy density, and are widely used in electronic products, electric vehicles, and other fields. However, lithium-ion batteries experience significant capacity decay at low temperatures, limiting their application in extremely cold regions, extreme operating conditions, and winter scenarios for electric vehicles. Therefore, the development of low-temperature lithium-ion batteries is urgently needed.

[0004] Lithium vanadium phosphate (Li3V2(PO4)3, LVP) possesses a dual voltage plateau of 3.6V / 4.1V, a high ion diffusion coefficient, and excellent low-temperature power characteristics, making it an ideal cathode material for next-generation high-power, low-temperature lithium-ion batteries. However, current research on LVP primarily focuses on wet processes, which require organic solvents (such as N-methylpyrrolidone). Therefore, wet processes suffer from problems such as volatile organic compound emissions, high drying energy consumption, and interfacial side reactions caused by solvent residues, contradicting the current "dual-carbon" policy. Existing dry electrode research mainly focuses on lithium iron phosphate (LiFePO4, LEP) or lithium nickel cobalt manganese oxide (NCM) systems; research on dry processes for LVP is currently lacking. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a dry-process self-supporting electrode film of lithium vanadium phosphate, its preparation method, and its applications.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a dry-process self-supporting electrode film of lithium vanadium phosphate, the method comprising:

[0007] Polytetrafluoroethylene (PTFE) and binder are sheared at a speed of 5000 rpm to 8000 rpm in an environment below 20°C, so that the PTFE molecular chains are stretched under shear force to form fibrils, which are then interwoven into a three-dimensional network structure to obtain the first mixture.

[0008] Following the batch feeding method, the conductive agent is added to the first mixture, and a uniformly mixed second mixture is obtained by stirring. Lithium vanadium phosphate (LVP) is added to the second mixture, and the mixture is stirred continuously to obtain a uniformly mixed third mixture. The electrode processing aid is added to the third mixture, and the mixture is stirred continuously to obtain a uniformly mixed fourth mixture.

[0009] Using differential speed rolling, the fourth mixture is initially compacted by the first roller-to-roll pressing under the first linear speed condition to obtain a self-supporting electrode film initial pressing body. The self-supporting electrode film initial pressing body is then hot-pressed and shaped by the second roller-to-roll pressing under the second wire harness condition to obtain a self-supporting electrode film.

[0010] Preferably, the mass ratio of the polytetrafluoroethylene, the binder, the conductive agent, the LVP, and the electrode processing aid is 2-3:1-2:1.5-4:92-94:0.1-0.5.

[0011] Preferably, the adhesive comprises one or more of the following: acrylate-methyl acrylate copolymer P (AA-MA), polyacrylate PAA, or polyvinylidene fluoride PVDF;

[0012] The conductive agent includes one or more of the following: conductive carbon black, carbon nanotubes, graphene, or graphite.

[0013] The electrode processing aids include one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt EMIM-TFSI or 1-butyl-3-methylimidazolium tetrafluoroborate BMIM-BF4.

[0014] Preferably, the environment below 20°C is specifically 0°C-20°C.

[0015] Preferably, during the batch feeding process, the stirring speed of each batch is 3000rpm-5000rpm, and the stirring time of each batch is 5min-10min.

[0016] Preferably, during the differential rolling process,

[0017] The first linear velocity is 1.3-1.5:1, and the second linear velocity is 1.1-1.2:1;

[0018] The pressure of the first roller during roller pressing is 5T-20T, and the temperature is 80℃-100℃.

[0019] The pressure of the second roller pair during rolling is 5T-20T, and the temperature is 100℃-120℃.

[0020] Preferably, the self-supporting electrode film has a thickness of 100μm-120μm and a compaction density of 2g / cm³. 3 -2.5g / cm 3 .

[0021] In a second aspect, the present invention provides a lithium vanadium phosphate dry self-supporting electrode film, wherein the lithium vanadium phosphate dry self-supporting electrode film comprises the lithium vanadium phosphate dry self-supporting electrode film prepared by the preparation method described in the first aspect above.

[0022] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a lithium vanadium phosphate dry self-supporting electrode film prepared by the preparation method described in the first aspect above, or comprising the lithium vanadium phosphate dry self-supporting electrode film described in the second aspect 8 above.

[0023] Fourthly, the present invention provides an energy storage device, the energy storage device comprising: for a lithium-ion battery or a lithium-ion capacitor;

[0024] The energy storage device includes a lithium vanadium phosphate dry self-supporting electrode film prepared by the preparation method described in the first aspect, or includes a lithium vanadium phosphate dry self-supporting electrode film described in the second aspect, or includes a positive electrode sheet described in the third aspect.

[0025] The method for preparing a dry-process self-supporting electrode film of lithium vanadium phosphate provided in this invention fills a gap in research on LVP dry-process technology. On one hand, during the PTFE fiberization process, this invention employs low-temperature shearing to suppress the thermal motion of PTFE molecular chains, preventing fibril breakage and promoting the formation of a uniform fibril network. Furthermore, the synergistic effect of PTFE with other binders controls fibril size and prevents agglomeration or breakage. The uniform three-dimensional network structure formed by interlacing significantly improves the mechanical strength of the self-supporting electrode film through the dual effects of physical entanglement and chemical bonding. Simultaneously, the nanoscale fibril network effectively disperses rolling stress, preventing crack propagation during rolling and providing structural support for subsequent high-pressure compaction. On the other hand, during the preparation of the self-supporting electrode film, this invention uses a batch feeding method to add conductive agents, LVP, and electrode processing aids, gradually forming conductive pathways and self-supporting electrodes. The membrane forms a hierarchical nested structure: a three-dimensional network structure provides mechanical support and ion transport pathways, a conductive agent constructs a continuous electron transport network, and LVP particles are uniformly distributed as active materials. This structure ensures rapid electron and ion transport while maintaining the mechanical stability of the self-supporting electrode membrane. Simultaneously, during subsequent rolling, the hardness of the LVP particles generates significant mechanical stress on the electrode structure. The synergistic effect of PTFE fibrils and electrode processing aids absorbs and disperses this stress, ensuring the stability of the electrode structure and preventing rolling cracks due to stress concentration. Furthermore, this invention employs differential rolling, which not only generates radial crushing and extrusion pressure but also uses shear stress to grind the material. This dual action causes the particles to crack and eventually pulverize after being squeezed, sheared, and bent, significantly increasing the compaction density of the electrode membrane. It also helps eliminate internal stress, reduces rebound, and improves the mechanical strength of the electrode membrane. Two-stage rolling avoids stress concentration caused by single high pressure, and the three-dimensional mesh structure disperses pressure, solving the cracking problem caused by the high hardness of LVP. Furthermore, by using it in combination with other binders, this invention can improve the electrochemical stability of PTFE at low voltages, reduce its reaction with lithium, thereby improving battery cycle stability. It also improves process conditions, reduces agglomerate formation, and increases production efficiency and product quality. The added electrode processing aid acts as a lubricant, enabling synergistic control to achieve optimal film formation, reducing energy consumption, reducing rolling passes, improving product thickness accuracy, and increasing rolling efficiency.

[0026] The self-supporting electrode film prepared by the method of this invention has uniform thickness, dense structure, and good mechanical properties. The battery using the self-supporting electrode film provided by this invention has excellent performance, with a capacity retention rate of ≥90% at -40℃, which can meet the application requirements in extremely cold regions, extreme working conditions, and winter scenarios for electric vehicles. Attached Figure Description

[0027] Figure 1 A flowchart illustrating the preparation method of a dry self-supporting electrode film of lithium vanadium phosphate provided in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the stacking of the separator and positive and negative electrodes during the battery assembly process according to an embodiment of the present invention;

[0029] Figure 3 A scanning electron microscope (SEM) image of the lithium vanadium phosphate material provided in Embodiment 1 of the present invention;

[0030] Figure 4 This is a SEM image of the dry-process self-supporting electrode film of lithium vanadium phosphate provided in Embodiment 1 of the present invention;

[0031] Figure 5 The charge-discharge curves of the lithium-ion battery provided in Embodiment 1 of the present invention at 25°C and 0.2C and -40°C and 0.2C current density are shown. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] The reagents and materials used in the following examples and comparative examples are all commercially available conventional reagent products, or can be prepared by conventional methods. Where specific experimental steps or conditions are not specified in the examples, they were performed according to conventional experimental steps and conditions in the art. Unless otherwise specified, all equipment used is conventional equipment currently available in the art.

[0034] Existing research on lithium vanadium phosphate (LVP) mainly focuses on wet processes, while research on dry processes for LVP is still lacking. Furthermore, in dry process studies of other systems, the degree of fiberization of polytetrafluoroethylene (PTFE) is uncontrollable, easily leading to high electrode brittleness and low compaction density. In addition, the high hardness of LVP easily punctures PTFE fibers during rolling, forming microcracks. Uneven fiberization leads to uneven stress distribution within the electrode, easily causing structural defects. The high hardness of LVP exacerbates interfacial stress, thus easily causing rolling cracking and other phenomena in dry processes. To solve the problems of rolling cracking, electrode structural defects, and low compaction density caused by uneven PTFE fiberization and high LVP hardness, this invention provides a solvent-free, high-compact, and highly flexible LVP dry-process electrode film, which can achieve 2 g / cm³. 3 -2.5g / cm 3 The compacted density has a volume retention rate of ≥90% at -40℃.

[0035] Specifically, this invention provides a method for preparing a dry-process self-supporting LVP electrode film, the main steps of which are as follows: Figure 1 As shown, it includes:

[0036] Step 110: Polytetrafluoroethylene (PTFE) and binder are sheared at a speed of 5000 rpm to 8000 rpm in an environment below 20°C, so that the PTFE molecular chains are stretched under shear force to form fibrils, and then interwoven into a three-dimensional network structure to obtain the first mixture.

[0037] This invention involves low-temperature shearing and fiberization. Specifically, in a low-temperature environment below 20°C, PTFE molecular chains are stretched along the shear direction under high-speed shear force to form nanoscale fibrils (≤200nm), which then interweave into a three-dimensional network structure, i.e., a fibril network. This not only provides self-support for the electrode film, but also provides diffusion pathways for ions through the pores in the three-dimensional network structure. The low-temperature environment suppresses the thermal motion of the molecular chains, prevents fibril breakage, and promotes the formation of a uniform fibril network. Preferably, the environment below 20°C is specifically 0°C-20°C. Controlling the shearing temperature within this range not only suppresses the thermal motion of the PTFE molecular chains and promotes the formation of a uniform fibril network through low temperature, but also avoids process risks such as equipment icing and binder degradation.

[0038] In the low-temperature fiberization process, other binders are required as aids. These binders can form weak interactions (such as hydrogen bonding, van der Waals forces, and dipole-dipole interactions) with the PTFE surface through polar groups (such as carboxyl groups, ester groups, or fluorine atoms). This reduces the shear force required for PTFE molecular chain sliding, thereby lowering fiberization energy consumption and promoting fibril formation, allowing the fiberization process to be completed at lower temperatures or under lower mechanical forces. Furthermore, the binders can also interact with the subsequently added active material LVP surface through polar groups, enhancing the interfacial bonding with LVP. Preferably, the binders include one or more of the following: acrylate-methyl acrylate copolymer P (AA-MA), polyacrylic acid (PAA), and polyvinylidene fluoride (PVDF).

[0039] This step achieves directional stretching and fibrillation of PTFE molecular chains through low-temperature high-speed shearing. At the same time, hydrogen bonds are formed between the carboxyl groups in other binders and the residual hydroxyl groups on the PTFE surface, which synergistically controls the fibril size (nanoscale) and avoids agglomeration or breakage. The uniform three-dimensional network structure formed by interweaving significantly improves the mechanical strength of the self-supporting electrode film through the dual effects of physical entanglement and chemical bonding. Meanwhile, the nanoscale fibril network can effectively disperse the rolling stress, prevent crack propagation during rolling, and provide structural support for subsequent high compaction.

[0040] Preferably, in this invention, the content of each component used satisfies the following condition: the mass ratio of PTFE, binder, conductive agent, LVP and electrode processing aid is 2-3:1-2:1.5-4:92-94:0.1-0.5.

[0041] Step 120: Following the batch feeding method, the conductive agent is added to the first mixture, and a uniformly mixed second mixture is obtained by stirring. LVP is added to the second mixture, and the mixture is stirred continuously to obtain a uniformly mixed third mixture. Electrode processing aid is added to the third mixture, and the mixture is stirred continuously to obtain a uniformly mixed fourth mixture.

[0042] Step 120 involves adding other components in batches. Specifically, the conductive agent, LVP, and electrode processing aid are added in batches, with each batch stirred thoroughly before adding the next batch. Therefore, step 120 can also be called gradient loading dry mixing, which reduces agglomeration during the dry mixing process. Preferably, during the batch addition process, the stirring speed for each batch is 3000rpm-5000rpm, and the stirring time for each batch is 5min-10min. The stirring speed and stirring time for the three batches can be the same or different, depending on the specific stirring conditions after adding the components.

[0043] First, the conductive agent is mixed with the first mixture. Under shear force, PTFE forms a three-dimensional network structure. Its fibril surface has high surface energy, which can adsorb conductive particles. The conductive agent is physically coated by the three-dimensional network structure due to van der Waals forces or electrostatic interactions, forming a "PTFE fibril-conductive agent" composite unit. When the conductive agent is stirred with the first mixture, the three-dimensional network structure has not yet solidified, and the conductive agent can embed into the fibril pores, forming a uniformly dispersed primary conductive network. The conductive agent adsorbed on the fibril surface acts as "connection points," while the conductive agent in the pores forms "conductive bridges." The two work together to construct the primary conductive framework, forming a continuous electron conduction path.

[0044] Preferably, the conductive agent includes one or more of conductive carbon black (SP), carbon nanotubes (CNT), graphene, or graphite.

[0045] Under shear force, PTFE forms a three-dimensional network structure. Its flexibility comes from the stretching and interweaving of PTFE molecular chains. When the conductive agent and the first mixture are stirred and mixed to form a primary conductive framework, the three-dimensional network structure still maintains a certain degree of flexibility, which can buffer the mechanical impact when the active material LVP particles are added. After the active material LVP particles are added, the LVP particles fill the pores of the primary conductive framework and form a "point-to-surface" contact with the conductive agent. This contact method not only increases the contact area for electron conduction, but also enables electrons to be transferred more effectively between the LVP particles and the conductive agent, thus forming part of the secondary conductive pathway. At the same time, the LVP particles are mechanically fixed by being wrapped by the PTFE fibrils to prevent them from falling off or agglomerating during the cycling process.

[0046] Adding the electrical discharge machining (EDM) aid in the final stage provides lubrication, improving the smoothness of the mixture. On one hand, lubrication reduces friction. In the rolling process, this lubrication not only reduces the friction between LVP particles and the rollers, ensuring the fourth mixture can pass smoothly through the roller gap and preventing electrode film cracking or uneven thickness due to excessive viscosity or friction, but also improves the flowability of the rolling process in step 130, preventing roller sticking. During the hot pressing and setting stage, it reduces the adhesion of the fourth mixture to the roller surface, improving the surface quality of the electrode film. Roller sticking leads to uneven stress on the electrode film, making it prone to cracking. The lubrication and anti-sticking properties of the ionic liquid effectively avoid this problem, ensuring the integrity and stability of the electrode film during the rolling process.

[0047] Preferably, the electrode processing aid is an ionic liquid, comprising one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt EMIM-TFSI or 1-butyl-3-methylimidazolium tetrafluoroborate BMIM-BF4. Compared with traditional lubricants, ionic liquids have advantages such as high thermal stability (withstanding temperatures above 200°C), good electrochemical compatibility, and high ionic conductivity. Therefore, this invention not only avoids electrode film defects caused by lubricant volatilization or carbonization, but also allows the electrode processing aid to act as an ionic conductor, improving electrode rate performance.

[0048] The electrode processing aid in this invention can also adjust the contact mode between the active material LVP and the conductive agent. For example, by partially coating the LVP surface with ionic liquid, it forms a more stable "point-to-surface" contact with the conductive agent, further optimizing the electron conduction path and improving electron conduction efficiency, while preventing LVP from detaching or agglomerating during cycling. Furthermore, the electrode processing aid in this invention works synergistically with PTFE fibrils to enhance the mechanical fixation of LVP. For instance, by adsorbing onto the fibril surface, the ionic liquid improves its flexibility, buffers the mechanical impact of the added LVP particles, and ensures structural stability.

[0049] In addition, the electrode processing aids of ionic liquids have high surface energy, which can be adsorbed on the surface of conductive agents, changing their surface charge distribution and making them negatively charged. This causes electrostatic repulsion with the positively charged LVP, thereby preventing agglomeration. Furthermore, the long-chain cations of ionic liquids can form a steric hindrance layer on the surface of conductive agents, hindering close contact between particles. This not only ensures the continuity and stability of the primary conductive pathway, but also, in synergy with surface charge regulation, can significantly improve the dispersion stability of the fourth mixture.

[0050] In this invention, the conductive agent, LVP, and electrode processing aid are added in batches. If the conductive agent is added to the first mixture along with other components, for example, if LVP particles are added to the first mixture at the same time as the conductive agent, the PTFE fibrils will preferentially adsorb LVP (because LVP has a high mass ratio), which will prevent the conductive agent from being effectively captured by the three-network structure. Furthermore, the conductive agent has a relatively small particle size and a large specific surface area, which makes it easy to agglomerate due to its high surface energy, leading to the breakage of the conductive network.

[0051] In summary, in step 120, after the conductive agent is mixed with the first mixture, the PTFE fibrils form a three-dimensional network structure under shear force. The high surface energy of the PTFE fibrils adsorbs conductive agent particles, while the conductive agent embeds itself in the gaps between the fibrils, forming a "PTFE fibril-conductive agent" composite unit. This composite unit constitutes the primary conductive framework, which can buffer the mechanical impact when LVP particles are added subsequently. After the addition of LVP, the active LVP particles fill the gaps in the conductive framework, forming a "point-to-surface" contact with the conductive agent, laying the foundation for the construction of secondary conductive pathways, and achieving mechanical fixation through the encapsulation effect of the PTFE fibrils. The electrode processing aid further adjusts the contact mode between LVP and the conductive agent, optimizing the electron conduction path and making the secondary conductive pathway more complete. Simultaneously, the synergistic effect of the electrode processing aid and PTFE fibrils enhances the mechanical fixation of LVP. During the rolling process, the hardness of the LVP particles will generate significant mechanical stress on the electrode structure. The synergistic effect of the PTFE fibrils and ionic liquid can absorb and disperse these stresses, ensuring the stability of the electrode structure and preventing rolling cracking due to stress concentration. Ultimately, the self-supporting electrode film forms a hierarchical nested structure: a three-dimensional network provides mechanical support and ion transport pathways, a conductive agent constructs a continuous electron transport network, and LVP particles are uniformly distributed as the active material. This structure ensures rapid electron and ion transport while maintaining the mechanical stability of the self-supporting electrode film.

[0052] Step 130: Using differential speed rolling, the fourth mixture is initially compacted by the first roller-to-roll pressing under the first linear speed condition to obtain a self-supporting electrode film initial pressing body. The self-supporting electrode film initial pressing body is then hot-pressed and shaped by the second roller-to-roll pressing under the second wire harness condition to obtain a self-supporting electrode film.

[0053] During differential rolling, the initial linear speed of the first roller pair is 1.3-1.5:1. The differential speed generates shear force, stretching the three-dimensional network structure and causing the LVP particles to align along the rolling direction, thus increasing the compaction density. The temperature during the initial compaction stage is 80℃-100℃, which softens the binder near its glass transition temperature, enhancing its viscoelasticity and aiding in the rearrangement of PTFE fibrils.

[0054] During differential rolling, the second linear speed of the second roller pair is 1.1-1.2:1. Slight shearing can maintain the three-dimensional network structure, while the high temperature of 100℃-120℃ can partially crystallize PTFE and fix the compaction state.

[0055] The pressure during the first roller press is 5T-20T, and the pressure during the second roller press is also 5T-20T. This high pressure can achieve a pressure of 2g / cm³. 3 -2.5g / cm 3 The compaction density is adjusted to avoid excessive compression that could cause the conductive network to break.

[0056] Differential roller pressing generates a difference in linear velocity between two rollers, simultaneously producing radial crushing and extrusion force while using shear stress to grind the material. This dual action causes the particles to crack and eventually pulverize after being squeezed, sheared, and bent, thereby significantly improving the compaction density of the electrode film. Preferably, the self-supporting electrode film obtained by this invention has a thickness of 100μm-120μm.

[0057] Differential rolling presses progressively compact and shape the electrode film by controlling the difference in linear speed and temperature of the rollers. This process helps eliminate internal stress, reduce rebound, and improve the mechanical strength of the electrode film. The two-stage rolling process avoids stress concentration caused by a single high-pressure press, and the three-dimensional mesh structure disperses pressure, solving the cracking problem caused by the high hardness of LVP.

[0058] The method for preparing a dry-process self-supporting electrode film of lithium vanadium phosphate provided in this invention fills a gap in research on LVP dry-process technology. On one hand, during the PTFE fiberization process, this invention employs low-temperature shearing to suppress the thermal motion of PTFE molecular chains, preventing fibril breakage and promoting the formation of a uniform fibril network. Furthermore, the synergistic effect of PTFE with other binders controls fibril size and prevents agglomeration or breakage. The uniform three-dimensional network structure formed by interlacing significantly improves the mechanical strength of the self-supporting electrode film through the dual effects of physical entanglement and chemical bonding. Simultaneously, the nanoscale fibril network effectively disperses rolling stress, preventing crack propagation during rolling and providing structural support for subsequent high-pressure compaction. On the other hand, during the preparation of the self-supporting electrode film, this invention uses a batch feeding method to add conductive agents, LVP, and electrode processing aids, gradually forming conductive pathways and self-supporting electrodes. The membrane forms a hierarchical nested structure: a three-dimensional network structure provides mechanical support and ion transport pathways, a conductive agent constructs a continuous electron transport network, and LVP particles are uniformly distributed as active materials. This structure ensures rapid electron and ion transport while maintaining the mechanical stability of the self-supporting electrode membrane. Simultaneously, during subsequent rolling, the hardness of the LVP particles generates significant mechanical stress on the electrode structure. The synergistic effect of PTFE fibrils and electrode processing aids absorbs and disperses this stress, ensuring the stability of the electrode structure and preventing rolling cracks due to stress concentration. Furthermore, this invention employs differential rolling, which not only generates radial crushing and extrusion pressure but also uses shear stress to grind the material. This dual action causes the particles to crack and eventually pulverize after being squeezed, sheared, and bent, significantly increasing the compaction density of the electrode membrane. It also helps eliminate internal stress, reduces rebound, and improves the mechanical strength of the electrode membrane. Two-stage rolling avoids stress concentration caused by single high pressure, and the three-dimensional mesh structure disperses pressure, solving the cracking problem caused by the high hardness of LVP. Furthermore, by using it in combination with other binders, this invention can improve the electrochemical stability of PTFE at low voltages, reduce its reaction with lithium, thereby improving battery cycle stability. It also improves process conditions, reduces agglomerate formation, and increases production efficiency and product quality. The added electrode processing aid acts as a lubricant, enabling synergistic control to achieve optimal film formation, reducing energy consumption, reducing rolling passes, improving product thickness accuracy, and increasing rolling efficiency.

[0059] The self-supporting electrode film prepared by this invention can be used in positive electrode sheets, and further applied in lithium-ion batteries or lithium-ion capacitors. For example, firstly, following the method described above, the self-supporting film is laminated onto both sides of a 12μm carbon-coated aluminum foil. After winding, it is rolled under pressure of 5T-20T and temperature of 100℃-120℃ to obtain an LVP dry-process electrode sheet, which is used as the positive electrode sheet. Then, the negative electrode sheet is prepared, specifically:

[0060] The graphite anode material, conductive carbon black, and binder PTFE are mixed in a mass ratio of 97:2:1 and then mixed evenly using a dry mixing mixer under solvent-free conditions to form a dry anode powder mixture.

[0061] The negative electrode dry mixture is pressed into a film using a film forming machine. The initial film thickness is 130μm-150μm, thus obtaining the initial film.

[0062] The initial membrane is thinned multiple times using a film forming machine until the membrane thickness reaches 80μm-90μm, resulting in a graphite dry membrane, i.e., a negative electrode membrane.

[0063] Then, the negative electrode film is laminated onto both sides of a 12μm carbon-coated copper foil (the preparation process is the same as that of the positive electrode), and finally a graphite dry electrode sheet is obtained, which is used as a negative electrode sheet.

[0064] Using a film cutting machine, positive electrode sheets (54mm*122mm) and negative electrode sheets (56mm*124mm) are sliced ​​according to the designed electrode sheet dimensions to produce positive and negative electrode sheets that can be used in soft-pack battery cells. Figure 2 This is a schematic diagram illustrating the stacking of the separator and positive and negative electrodes during battery assembly in an embodiment of the present invention. The positive electrode, negative electrode, and separator are then stacked in a dry room with a dew point ≤ -40°C. Figure 2 The cells are stacked alternately in the sequence of "separator → negative electrode → separator → positive electrode," and the four corners are fixed with high-temperature resistant tape after stacking. The separator used is a 12μm wet-process PE + ceramic coating. Then, the cells undergo pre-welding of the tabs, tab welding, baking, and moisture testing. After passing these tests, they are encapsulated using aluminum-plastic film, injected with electrolyte, and packaged into lithium-ion cells. After encapsulation, the soft-pack cells undergo high-temperature aging, formation, and capacity testing to produce qualified soft-pack cells. The resulting battery has a rated capacity of 5.5Ah. The materials and methods used in the above process are commonly used in this field and will not be described in detail here.

[0065] The self-supporting electrode film prepared by the method of this invention has uniform thickness, dense structure, and good mechanical properties. The battery using the self-supporting electrode film provided by this invention has excellent performance, with a capacity retention rate of ≥90% at -40℃, which can meet the application requirements in extremely cold regions, extreme working conditions, and winter scenarios for electric vehicles.

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0067] Example 1

[0068] In this embodiment, a dry-process self-supporting electrode film of lithium vanadium phosphate was prepared, then it was used to prepare a positive electrode sheet and assembled into a lithium-ion battery.

[0069] In this embodiment, the mass ratio of PTFE, P(AA-MA), conductive carbon black, LVP and EMIM-TFSI is 3:1:3.5:92:0.5.

[0070] (1) Preparation of dry self-supporting electrode film of lithium vanadium phosphate

[0071] Step 1: Fibrosis.

[0072] PTFE and P(AA-MA) were subjected to high-speed shearing at 20°C and then thoroughly mixed in a mixer. The parameters were set as follows: speed 6000 rpm and time 5 min.

[0073] Step 2: Gradient loading dry mixing.

[0074] The process involves batch feeding, with conductive carbon black, LVP, and EMIM-TFSI added in three batches. Each batch is mixed thoroughly before the next batch is added. The parameters are set as follows: the stirring speed for each batch is 5000 rpm and the stirring time is 8 minutes.

[0075] Step 3: Differential speed roller pressing to form film.

[0076] The dry-mixed material is rolled under a roller press. First, the dry-mixed material is initially compacted under the first pair of rollers, and then hot-pressed and shaped under the second pair of rollers to obtain a self-supporting electrode film with a thickness of 100μm. The parameters are set as follows: the linear velocity ratio of the first pair of rollers is 1.3:1, the pressure is 20T, and the temperature is 100℃; the linear velocity ratio of the second pair of rollers is 1.1:1, the pressure is 20T, and the temperature is 120℃.

[0077] Step 4: Prepare LVP dry electrode sheet.

[0078] The obtained self-supporting electrode film was hot-pressed with carbon-coated aluminum foil to obtain LVP dry electrode sheet, which was used as a positive electrode sheet. The parameters were set as follows: the thickness of the carbon-coated aluminum foil was 12μm, the pressure during the hot-pressing process was 20T, and the temperature was 100℃.

[0079] (2) Negative electrode sheet fabrication

[0080] Graphite anode material, conductive graphite, and PTFE binder were mixed in a mass ratio of 97:2:1 using a dry mixing machine under solvent-free conditions to form a dry anode powder mixture. The dry anode powder mixture was then pressed into a film using a film-forming machine, with an initial film thickness of 140 μm to ensure successful film formation. The initial film was repeatedly thinned using the film-forming machine until a thickness of 85 μm was achieved. This anode film was then laminated with a 12 μm thick carbon-coated copper foil to obtain a graphite dry electrode sheet, which was then used as a backup anode electrode.

[0081] (3) Battery assembly

[0082] Using a membrane cutting machine, positive electrode sheets (54mm*122mm) and negative electrode sheets (56mm*124mm) were sliced ​​according to the designed electrode dimensions to produce positive and negative electrode sheets suitable for use in pouch cells. In a drying room with a dew point ≤-40℃, the positive and negative electrode sheets and the separator were then alternately stacked in the order of "separator → negative electrode → separator → positive electrode," and the four corners were fixed with high-temperature resistant tape. The separator used was a 12μm wet-process PE + ceramic coating. After pre-soldering of the tabs, tab welding, baking, and moisture content testing, the cells were encapsulated using aluminum-plastic film, injected with electrolyte, and sealed into lithium-ion cells. After encapsulation, the pouch cells underwent high-temperature aging, formation, and capacity testing processes to produce qualified pouch cells.

[0083] Figure 3 This is a scanning electron microscope (SEM) image of the LVP material used in Embodiment 1 of the present invention. Figure 4 This is a SEM image of the self-supporting electrode film prepared in Example 1 of the present invention. Figure 5 The self-supporting electrode film prepared in Example 1 of this invention, after being applied to a lithium-ion battery, shows the charge-discharge curves of the lithium-ion battery at 25°C and 0.2C current density and -40°C and 0.2C current density. Figure 3 As can be seen, the LVP material used in this invention consists of spherical particles, which is beneficial for the dry film formation of PTFE fibers. Figure 4 It can also be clearly seen that after gradient dry mixing, the fibrillated PTFE network uniformly coats LVP and conductive carbon black, resulting in a self-supporting electrode film with uniform thickness and dense structure. Figure 5 It is evident that the battery using the self-supporting electrode film provided in this embodiment of the invention exhibits excellent performance. Even at -40℃, its capacity retention rate remains ≥90%, enabling it to operate in low-temperature environments and meet the application requirements in extremely cold regions, extreme working conditions, and winter scenarios for electric vehicles.

[0084] Example 2

[0085] In this embodiment, a dry-process self-supporting electrode film of lithium vanadium phosphate was prepared, then it was used to prepare a positive electrode sheet and assembled into a lithium-ion battery.

[0086] In this embodiment, the mass ratio of PTFE, PAA, conductive carbon black, LVP, and EMIM-TFSI is 2.5:1:4:92.4:0.1.

[0087] (1) Preparation of dry self-supporting electrode film of lithium vanadium phosphate

[0088] Step 1: Fibrosis.

[0089] PTFE and PAA were sheared at high speed at 10°C and then thoroughly mixed in a mixer. The parameters were set as follows: speed 5000 rpm and time 10 min.

[0090] Step 2: Gradient loading dry mixing.

[0091] The process involves batch feeding, with conductive carbon black, LVP, and EMIM-TFSI added in three batches. Each batch is mixed thoroughly before the next batch is added. The parameters are set as follows: the stirring speed for each batch is 5000 rpm and the stirring time is 5 minutes.

[0092] Step 3: Differential speed roller pressing to form film.

[0093] The dry-mixed material is rolled under a roller press. First, the dry-mixed material is initially compacted under the first pair of rollers, and then hot-pressed and shaped under the second pair of rollers to obtain a self-supporting electrode film with a thickness of 100μm. The parameters are set as follows: the linear velocity ratio of the first pair of rollers is 1.5:1, the pressure is 5T, and the temperature is 80℃; the linear velocity ratio of the second pair of rollers is 1.1:1, the pressure is 20T, and the temperature is 120℃.

[0094] Step 4: Prepare LVP dry electrode sheet.

[0095] The obtained self-supporting electrode film was hot-pressed with carbon-coated aluminum foil to obtain an LVP dry electrode sheet, which was used as a positive electrode sheet. The parameters were set as follows: the thickness of the carbon-coated aluminum foil was 12 μm, the pressure during the hot-pressing process was 10T, and the temperature was 100℃.

[0096] (2) Negative electrode sheet fabrication

[0097] Graphite anode material, conductive graphite, and PTFE binder were mixed in a mass ratio of 97:2:1 using a dry mixing machine under solvent-free conditions to form a dry anode powder mixture. The dry anode powder mixture was then pressed into a film using a film-forming machine, with an initial film thickness of 130 μm to ensure successful film formation. The initial film was repeatedly thinned using the film-forming machine until a thickness of 80 μm was achieved. This anode film was then laminated with a 12 μm thick carbon-coated copper foil to obtain a dry graphite electrode sheet, which was then used as a backup anode electrode.

[0098] (3) Battery assembly

[0099] The battery assembly method is the same as in Example 1, and will not be elaborated here.

[0100] Example 3

[0101] In this embodiment, a dry-process self-supporting electrode film of lithium vanadium phosphate was prepared, then it was used to prepare a positive electrode sheet and assembled into a lithium-ion battery.

[0102] In this embodiment, the mass ratio of PTFE, PVDF, carbon nanotubes, LVP and BMIM-BF4 is 2:2:1.5:94:0.5.

[0103] (1) Preparation of dry self-supporting electrode film of lithium vanadium phosphate

[0104] Step 1: Fibrosis.

[0105] PTFE and PVDF were sheared at high speed at 0℃ and then thoroughly mixed in a mixer. The parameters were set as follows: speed 8000 rpm and time 10 min.

[0106] Step 2: Gradient loading dry mixing.

[0107] The process involves batch feeding, with conductive carbon black, LVP, and processing aids added in three batches. Each batch is mixed thoroughly before the next batch is added. The parameters are set as follows: the stirring speed for each batch is 3000 rpm, and the stirring time is 10 minutes.

[0108] Step 3: Differential speed roller pressing to form film.

[0109] The dry-mixed material is rolled under a roller press. First, the dry-mixed material is initially compacted under the first pair of rollers, and then hot-pressed and shaped under the second pair of rollers to obtain a self-supporting electrode film with a thickness of 100μm. The parameters are set as follows: the linear velocity ratio of the first pair of rollers is 1.4:1, the pressure is 5T, and the temperature is 100℃; the linear velocity ratio of the second pair of rollers is 1.2:1, the pressure is 10T, and the temperature is 100℃.

[0110] Step 4: Prepare LVP dry electrode sheet.

[0111] The obtained self-supporting electrode film was hot-pressed with carbon-coated aluminum foil to obtain an LVP dry electrode sheet, which was used as a positive electrode sheet. The parameters were set as follows: the thickness of the carbon-coated aluminum foil was 12 μm, the pressure during the hot-pressing process was 5T, and the temperature was 120℃.

[0112] (2) Negative electrode sheet fabrication

[0113] Graphite anode material, conductive graphite, and PTFE binder were mixed in a mass ratio of 97:2:1 using a dry mixing machine under solvent-free conditions to form a dry anode powder mixture. The dry anode powder mixture was then pressed into a film using a film-forming machine, with an initial film thickness of 150 μm to ensure successful film formation. The initial film was repeatedly thinned using the film-forming machine until a thickness of 90 μm was achieved. This anode film was then laminated with a 12 μm thick carbon-coated copper foil to obtain a graphite dry electrode sheet, which was then used as a backup anode electrode.

[0114] (3) Battery assembly

[0115] The battery assembly method is the same as in Example 1, and will not be elaborated here.

[0116] Comparative Example 1

[0117] Comparative Example 1 prepared a dry-process self-supporting electrode film of lithium vanadium phosphate, which was then used to prepare a positive electrode sheet and assembled into a lithium-ion battery.

[0118] The difference from Example 1 is that only PTFE was used, and P(AA-MA) was not used.

[0119] Comparative Example 2

[0120] Comparative Example 2 prepared a dry self-supporting electrode film of lithium vanadium phosphate, which was then used to prepare a positive electrode sheet and assembled into a lithium-ion battery.

[0121] The difference from Example 1 is that the electrode processing aid EMIM-TFSI was not used.

[0122] The performance of the self-supporting electrode films or positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-2 was characterized, and the measured data are listed in Table 1.

[0123] The compaction density test method and operation steps are as follows:

[0124] 1. Use a circular die to cut the self-supporting electrode film, ensuring an area of ​​10cm². 2 The error shall not exceed ±0.5cm 2 , to be used as samples for testing.

[0125] 2. Measure the thickness of the sample to be tested using a micrometer, and weigh the mass of the sample to be tested using a precision balance (accuracy of 0.1 mg).

[0126] 3. Calculate the compacted density using the following formula:

[0127] Compacted density = Electrode mass / Electrode area * Electrode thickness.

[0128] The resistivity testing method and operating steps are as follows:

[0129] 1. Use a circular die to cut the positive electrode sheet, ensuring an area of ​​10 cm². 2 The error shall not exceed ±0.5cm 2 , to be used as samples for testing.

[0130] 2. Place the sample to be tested on the metal terminals of the resistivity meter. Apply a pressure of 5 MPa to both sides of the sample using the upper metal terminals and maintain the pressure for 5 seconds. Click "Start Resistivity Test" to measure the resistance R and thickness d. Calculate the resistivity using the following formula:

[0131] ρ = R·A / d, where R is the measured resistance value, A is the contact area, i.e. the area of ​​the sample to be tested, and d is the thickness of the positive electrode.

[0132] The peel strength test method and operation steps are as follows:

[0133] 1. Cut the sample:

[0134] Cut a 25mm wide sample on the positive electrode sheet, with a length that meets the clamping requirements (usually ≥150mm).

[0135] 2. Instrument calibration:

[0136] Use standard weights or calibration devices to calibrate the force sensor or displacement sensor of the tensile testing machine to ensure accurate test data.

[0137] 3. Fixture installation:

[0138] Fix one end of the specimen in the fixture on the tensile testing machine and the other end in the lower fixture, ensuring that the specimen axis is aligned with the tensile direction to avoid skewing.

[0139] 4. Start the test:

[0140] Start the tensile testing machine. The upper clamp moves upward at a set speed, while the lower clamp remains fixed. Record the force-displacement curve during the peeling process. Observe the peeling phenomenon to see if uniform peeling, localized debonding, or material fracture occurs.

[0141] 5. Data Processing:

[0142] Extract the average peel force from the force-displacement curve and calculate the peel strength per unit width: Peel strength = F / w, where F is the average peel force (N) and w is the sample width (m).

[0143] Repeat the measurement 3-5 times and take the average value.

[0144] serial number <![CDATA[Compaction density (g / cm 3 )]]> Resistivity (Ω*cm) Peel strength (N / m) Example 1 2.45 9.809 12.62 Example 2 2.30 9.952 12.41 Example 3 2.25 9.852 12.21 Comparative Example 1 2.05 10.086 11.61 Comparative Example 2 2.00 10.147 11.42

[0145] Table 1

[0146] Comparing the data of Examples 1-3 and Comparative Examples 1-2 in Table 1, it can be seen that the dry self-supporting electrode film of lithium vanadium phosphate prepared by the preparation method provided by the present invention has a higher compaction density, and the positive electrode sheet using the self-supporting electrode film prepared by the present invention has low resistivity and higher peel strength.

[0147] Comparing the data in Example 1 and Comparative Example 1 in Table 1, it can be seen that Example 1 has a higher compaction density, lower resistivity, and higher peel strength. This is because Example 1 used additional binders besides PTFE. On the one hand, after PTFE is mixed with other binders, it forms a three-dimensional network structure under shear force. The addition of other binders can optimize the lubrication and bonding strength between particles, making the active material LVP particles more tightly arranged. During the rolling process, this structure can better withstand pressure, reduce particle breakage and binder network damage, thereby increasing the compaction density. On the other hand, the additional binders can enhance the adhesion to the current collector, reduce the interfacial resistance, enhance the bonding force between the self-supporting electrode film and the current collector, and improve its peel strength. Furthermore, the additional binders can also coat the conductive agent particles to form a conductive agent-binder composite, reducing the contact resistance between conductive agent particles. At the same time, the binder can fill the gaps between the conductive agents to form a more continuous conductive network, reducing electron transport resistance and lowering the resistivity of the electrode sheet. In contrast, Comparative Example 1 used only PTFE without adding any other binders, resulting in a lower conductivity of the prepared electrode sheet compared to Example 1, making it difficult to form an effective conductive network and leading to a decrease in resistivity.

[0148] Comparing the data in Example 1 and Comparative Example 1 in Table 1, it can be seen that the example exhibits higher compaction density, lower resistivity, and higher peel strength. This is because, on the one hand, the electrode processing aid significantly improves the rheological properties of the slurry. Its high solubility and dispersibility enable the active material LVP, conductive agent, and binder (PTFE + other binders) to form a uniform mixture system, reducing particle agglomeration and voids. During differential rolling, the uniform slurry is more likely to achieve a tight arrangement under pressure, increasing the compaction density. On the other hand, PTFE and other binders form a three-dimensional network structure through fibrillation, while the electrode processing aid promotes the wetting and spreading of the binder on the current collector surface, forming a stronger adhesion layer, further enhancing the interfacial bonding between the binder and the current collector, and improving the peel strength. Furthermore, the electrode processing aid can also adjust the contact mode between the active material LVP and the conductive agent. By partially coating the LVP surface, it forms a more stable "point-to-surface" contact with the conductive agent, optimizing the electron conduction path, improving electron conduction efficiency, and reducing resistivity.

[0149] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a dry-process self-supporting electrode film of lithium vanadium phosphate, characterized in that, The preparation method includes: Polytetrafluoroethylene (PTFE) and binder are sheared at a speed of 5000 rpm to 8000 rpm in an environment below 20°C, so that the PTFE molecular chains are stretched under shear force to form fibrils, which are then interwoven into a three-dimensional network structure to obtain the first mixture. Following the batch feeding method, the conductive agent is added to the first mixture, and a uniformly mixed second mixture is obtained by stirring. Lithium vanadium phosphate (LVP) is added to the second mixture, and the mixture is stirred continuously to obtain a uniformly mixed third mixture. The electrode processing aid is added to the third mixture, and the mixture is stirred continuously to obtain a uniformly mixed fourth mixture. Using differential speed rolling, the fourth mixture is initially compacted by the first roller-to-roll pressing under the first linear speed condition to obtain a self-supporting electrode film initial pressing body. The self-supporting electrode film initial pressing body is then hot-pressed and shaped by the second roller-to-roll pressing under the second wire harness condition to obtain a self-supporting electrode film.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the polytetrafluoroethylene, the binder, the conductive agent, the LVP, and the electrode processing aid is 2-3:1-2:1.5-4:92-94:0.1-0.

5.

3. The preparation method according to claim 1, characterized in that, The adhesive comprises one or more of the following: acrylate-methyl acrylate copolymer P(AA-MA)), polyacrylate PAA, or polyvinylidene fluoride PVDF; The conductive agent includes one or more of the following: conductive carbon black, carbon nanotubes, graphene, or graphite. The electrode processing aids include one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt EMIM-TFSI or 1-butyl-3-methylimidazolium tetrafluoroborate BMIM-BF4.

4. The preparation method according to claim 1, characterized in that, An environment below 20℃ specifically refers to 0℃-20℃.

5. The preparation method according to claim 1, characterized in that, During the batch feeding process, the mixing speed of each batch is 3000rpm-5000rpm, and the mixing time of each batch is 5min-10min.

6. The preparation method according to claim 1, characterized in that, During differential roller pressing... The first linear velocity is 1.3-1.5:1, and the second linear velocity is 1.1-1.2:1; The pressure of the first roller during roller pressing is 5T-20T, and the temperature is 80℃-100℃. The pressure of the second roller pair during rolling is 5T-20T, and the temperature is 100℃-120℃.

7. The preparation method according to claim 1, characterized in that, The self-supporting electrode film has a thickness of 100μm-120μm and a compaction density of 2g / cm³. 3 -2.5g / cm 3 .

8. A dry-process self-supporting electrode film of lithium vanadium phosphate, characterized in that, The lithium vanadium phosphate dry self-supporting electrode film includes the lithium vanadium phosphate dry self-supporting electrode film prepared by any of the preparation methods described in claims 1-7.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises a dry self-supporting electrode film of lithium vanadium phosphate prepared by any of the preparation methods described in claims 1-7, or comprises the dry self-supporting electrode film of lithium vanadium phosphate as described in claim 8.

10. An energy storage device, characterized in that, The energy storage device includes: for lithium-ion batteries or lithium-ion capacitors; The energy storage device includes a lithium vanadium phosphate dry self-supporting electrode film prepared by any of the preparation methods described in claims 1-7, or includes the lithium vanadium phosphate dry self-supporting electrode film described in claim 8, or includes the positive electrode sheet described in claim 9.

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