Composite conductive agent, method for preparing the same, positive electrode sheet, and dry battery

Abstract

The application relates to the technical field of batteries, in particular to a composite conductive agent, a preparation method thereof, a positive electrode diaphragm and a dry battery. The composite conductive agent comprises a plurality of modified conductive agents; the modified conductive agent is obtained by annealing treatment of a conductive agent. The modified conductive agent is obtained by annealing means to regulate the surface functional groups of the conductive agent, can be in-situ reacted with a sulfide electrolyte to generate a stable CEI interface layer in the battery charging and discharging process, the interface layer can effectively isolate the direct contact of the electrolyte and the positive electrode material and the conductive agent, and block the continuous occurrence of side reactions such as reduction of transition metals and oxidation of sulfides. 2‑ ​

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite conductive agent and its preparation method, a positive electrode film, and a dry-process battery. Background Technology

[0002] With the upgrading of new energy vehicles towards longer range and faster charging, and the surge in demand for miniaturization and longer range in consumer electronics, the application scenarios of lithium-ion batteries are becoming increasingly widespread, making them a core energy device supporting the development of the new energy industry. However, current mainstream traditional liquid lithium-ion batteries are limited by their core component, the flammable liquid organic electrolyte. This not only poses safety hazards such as electrolyte leakage, combustion, and even explosion at high temperatures, but also means that energy density improvement is approaching its theoretical limit, making it difficult to meet the needs of next-generation high-safety, high-energy-density energy storage devices.

[0003] To overcome the safety and energy density bottlenecks of traditional liquid lithium-ion batteries, all-solid-state lithium-ion batteries have become a focus of industry research due to their technological characteristics. This technology completely replaces liquid electrolytes with solid electrolytes, eliminating the risks of flammability and leakage inherent in liquid electrolytes, significantly improving the thermal stability and safety performance of batteries, and becoming the core development direction for next-generation lithium-ion batteries. Dry-process all-solid-state batteries have significant advantages over traditional wet-process batteries: they require no organic solvents, are environmentally friendly and safe, have simplified processes, good material compatibility, maintain the stability of solid electrolytes, and can be adapted to high-capacity, thick electrode designs, thus improving energy density. However, in the development of high-power, long-cycle dry-process all-solid-state batteries, the stability of the solid-solid interface remains a key bottleneck restricting its technological development. Sulfide electrolytes can react directly with or electrochemically degrade with positive electrode active material particles in the positive electrode. In sulfide all-solid-state batteries, the addition of conductive agents promotes the redox kinetics of sulfide electrolytes, leading to the degradation of sulfides into polysulfides, thereby consuming the positive electrode active material. Furthermore, the polysulfides produced by the side reaction are insulators, which will greatly affect the ionic conductivity at the interface. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a composite conductive agent and its preparation method, a positive electrode film, and a dry battery.

[0005] To achieve the above objectives, this application adopts the following solution: A composite conductive agent includes multiple modified conductive agents; the modified conductive agents are obtained by annealing the conductive agents.

[0006] The conductive agent is oil furnace black, acetylene black, Ketjen black, graphene, carbon fiber, or carbon nanotubes; preferably acetylene black, graphene, or carbon fiber. The modified conductive agent includes modified furnace black, modified acetylene black, modified Ketjen black, modified graphene, modified carbon fiber, or modified carbon nanotubes; preferably modified acetylene black, modified graphene, or modified carbon fiber.

[0007] The annealing conditions are as follows: annealing at 200℃-800℃ for 0.5-3 hours under argon atmosphere; preferably annealing at 600℃ for 1 hour.

[0008] The composite conductive agent includes at least two of the following: modified acetylene black, modified graphene, or modified carbon fiber.

[0009] Preferably, the composite conductive agent comprises modified acetylene black and modified graphene; preferably, the mass ratio of modified acetylene black to modified graphene is (1-2):(1-2).

[0010] Preferably, the composite conductive agent comprises modified acetylene black and modified carbon fiber; preferably, the mass ratio of modified acetylene black to modified graphene is (0.5-2):(0.5-2); more preferably, it is 1:1.

[0011] Preferably, the composite conductive agent comprises a mixture of three: modified acetylene black, modified graphene, or modified carbon fiber; preferably, the mass ratio of the modified acetylene black, modified graphene, or modified carbon fiber is (0.5-2):(0.5-2):(0.5-2); more preferably, it is 1:1:1.

[0012] The present invention also includes a method for preparing the composite conductive agent, comprising the following steps: mixing at least two modified conductive agents to obtain the composite conductive agent.

[0013] The present invention also includes a positive electrode film, comprising the aforementioned composite conductive agent, positive electrode material, solid electrolyte, and binder; preferably, the mass ratio of positive electrode material, solid electrolyte, composite conductive agent, and binder is (70-90):(10-20):(1-5):(1-5); more preferably 80:15:3:2; Preferably, the cathode material is one or more of the following: nickel-cobalt-manganese ternary, lithium-rich manganese-based, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel manganese oxide. Preferably, the cathode material is one or more of the following: nickel-cobalt-manganese ternary, lithium-rich manganese-based, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel manganese oxide. The solid electrolyte is a sulfide electrolyte or a halide electrolyte; Preferably, the sulfide electrolyte is Li (6-m) PS (5-m) X (1+m) Li 10 GeP2S 12; 0 ≤ m ≤ 1.0, X is selected from at least one of Cl, Br, and I; Preferably, the halide electrolyte is Li x MB6, wherein M is at least one of Y, Zr, In, Sc, Ta, and La, and B is at least one of Cl, Br, and I; 2≤x≤4; Preferably, the adhesive is at least one of PTFE, PVDF, PAN, PMMA, PAA, and PE, with PTFE being the most preferred.

[0014] Preferably, the positive electrode film is prepared in the following manner: 1) Place the positive electrode material, solid electrolyte, and composite conductive agent in the mixing tank of a high-speed disperser. After simple mixing with a stirring rod, stir at 500-1000 rpm for 5-20 minutes, controlling the temperature between -20℃ and 10℃. Scrape the wall 1-2 times during stirring. Stir at 1500-2500 rpm for 3-10 minutes, controlling the temperature between -40℃ and 10℃. Add the binder and stir at 500-1000 rpm for 3-10 minutes, controlling the temperature between -40℃ and 10℃. Scrape the wall 1-2 times during stirring. 2) Pre-fiberization: Stir the mixed powder obtained in step 1) at 7000-10000 rpm for 1-5 min. No cooling treatment is performed during this process, and the temperature of the mixing tank is controlled between 30℃ and 80℃ during high-speed dispersion. 3) Kneading and crushing: The pre-fiberized powder obtained in step 2) is mechanically / manually kneaded into a ball, then crushed with tweezers and placed into the mixing tank of a mixer for high-speed dispersion and granulation at a speed of 1000-8000 rpm for 2-20 seconds. 4) Powder mixing and toughening: Control the temperature of the two rollers of the differential speed roller mill at 80-120℃; adjust the roller gap to 800-1400um; put the powder obtained in step 3) between the two rollers for rolling and mixing, collect the material, and repeat this process 3-5 times; wherein the speed ratio of roller 1 to roller 2 is controlled between 4:20-4:32 (mm / s); Folding and toughening: Fold the thick film electrode sheet obtained after powder mixing and pass it through the rollers, control the temperature at 80-120℃, and control the number of times 3-8; wherein the speed ratio of roller 1 to roller 2 is controlled between 4:20-4:32 (mm / s); 5) Membrane thinning: The thick film electrode sheet, which has been repeatedly folded and toughened, is thinned by continuously reducing the roller gap to gradually reduce the film thickness. The temperature is controlled at 80-120℃, and the thickness is controlled at 150-200 μm. The ratio of roller speed 1 to roller speed 2 is controlled between 4:20 and 4:32 (mm / s) to obtain the dry cathode film. 6) Foil composite: Place the dry-process positive electrode film on the carbon-coated aluminum foil, adjust the roller gap thickness to be lower than the composite film + foil thickness, adjust the temperature to 80-120℃, first perform single-sided composite, and then perform double-sided composite. 7) Compaction: The electrode sheet after composite foil is compacted under a pressure of 0.3-0.5MPa to control the compaction density of the positive electrode layer itself to 2.6-3.0 g / cc; 8) Composite electrode punching: The compacted composite electrode is die-cut or cut into the required size for use in assembling battery cells.

[0015] The present invention also includes a dry cell comprising the aforementioned positive electrode membrane.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: Firstly, there is the interface stabilization mechanism. By modifying the functional groups on the surface of the conductive agent through annealing, a modified conductive agent is obtained. This modified agent can react in situ with the sulfide electrolyte during battery charging and discharging to generate a stable CEI interface layer. This interface layer can effectively isolate the electrolyte from direct contact with the positive electrode material and the conductive agent, blocking the reduction of sulfur by transition metals. 2- And the continuous occurrence of side reactions such as sulfide oxidation.

[0017] Secondly, the three-dimensional conduction enhancement mechanism, as a preferred form, achieves the construction of a dual continuous conduction channel for electrons / ions within the positive electrode system through the combination of various modified conductive agents. A three-dimensional interconnected network can be spontaneously formed in the dry positive electrode sheet, which completely improves the imbalance problem of the single component having the advantage of conduction while the other component has the lag in conduction in the existing technology, and greatly improves the rate performance and capacity utilization efficiency of the battery.

[0018] Thirdly, the comprehensive performance improvement mechanism relies on a stable interface and a highly efficient multi-conduction network to reduce the battery Rct by more than 30%, while achieving improved rate charge and discharge performance and long cycle life (capacity retention rate improved by more than 10% after 100 cycles). At the same time, by suppressing heat generation from interface side reactions and lithium dendrite growth, the thermal stability and safety of the entire battery are significantly improved.

[0019] Fourthly, a low-cost, large-scale technology path is proposed, which modifies existing carbon-based conductive agents and achieves full-process cost control from raw material selection to preparation process (such as avoiding precious metals and high-energy-consuming steps). This overcomes the cost bottleneck of materials such as silver nanowires, while ensuring the performance stability of the modified conductive agent, and has the potential for commercial application. Attached Figure Description

[0020] Figure 1 This is a graph showing the cycling test results of the all-solid-state mold half-cell prepared by this invention at a current of 0.2C.

[0021] Figure 2This is an EIS test result diagram of the all-solid-state mold half-cell prepared by the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] Example 1: 1. A method for preparing a composite conductive agent, comprising the following steps: Step S1, Raw material preparation: Acetylene black and graphene are surface annealed separately at 600℃ in argon atmosphere for 1 hour to obtain modified acetylene black and modified graphene. The modified conductive agent materials obtained after treatment are mixed evenly in a 1:1 ratio to form a composite modified conductive agent; 2. Preparation of dry-process positive electrode film: Step S2, Electrode raw material preparation: Mix ternary cathode material, LPSC sulfide solid electrolyte, composite modified conductive agent (prepared in step S1) and PTFE binder in a mass ratio of 80%:15%:3%:2%; Step S3: Place the positive electrode material, electrolyte material, and composite modified conductive agent described in step S2 into a high-speed disperser mixing tank. After simple mixing with a stirring rod, stir at 800 rpm for 10 minutes, controlling the temperature at 0°C. Scrape the wall once during stirring. Stir at 2000 rpm for 5 minutes, controlling the temperature at 0°C. Add PTFE binder, stir at 800 rpm for 8 minutes, controlling the temperature at 0°C. Scrape the wall once during stirring. Step S4, Pre-fiberization: Stir the mixed powder obtained in step S3 at 8000 rpm for 3 minutes. No cooling is performed during this process. During high-speed dispersion, the temperature of the mixing tank is controlled between 30℃ and 50℃. If the heating rate is too fast, natural cooling is required as appropriate, followed by continued high-speed dispersion. The tank wall is scraped once during the pre-fiberization process. Step S5, kneading and crushing: The pre-fiberized powder obtained in step S4 is mechanically / manually kneaded into a ball, then crushed with tweezers and placed into the mixing tank of a mixer for high-speed dispersion and granulation at 2500 rpm for 10 seconds. Step S6, Powder mixing and toughening: Control the temperature of the two rollers of the differential speed roller mill at 100℃; adjust the roller gap to 1200um; put the powder obtained in step S4 between the two rollers for rolling and mixing, collect the material and repeat this process 4 times; wherein the speed ratio of roller 1 to roller 2 is controlled at 4:32 (mm / s); Folding and toughening: Fold the thick film electrode sheet obtained after powder mixing and pass it through the rollers, control the temperature at 120℃, and control the number of times 8 times; wherein the speed ratio of roller 1 to roller 2 is controlled at 4:32 (mm / s); Step S7, membrane thinning: The thick film electrode sheet after repeated folding and toughening is thinned by continuously reducing the roller gap to gradually thin the film, controlling the temperature at 100℃ and the thickness to 200 μm; wherein the speed ratio of roller 1 to roller 2 is controlled at 4:32 (mm / s); Step S8, Foil Composite: Place the dry-process positive electrode film on top of the carbon-coated aluminum foil (the positive electrode side is close to the foil), adjust the roller gap thickness to be lower than the thickness of the composite film + foil, adjust the temperature to 100℃, perform single-sided composite first, and then perform double-sided composite. Step S9, Compaction: The electrode sheet after composite foil is compacted under a pressure of 0.5 MPa to control the compaction density of the positive electrode layer itself to 3.0 g / cc; Step S10, Composite electrode punching: The compacted composite electrode is die-cut or cut into the required size for use in assembling battery cells.

[0024] Example 2: The difference between Example 2 and Example 1 lies in the preparation of the composite conductive agent. Step S1 is as follows: Raw material preparation: Acetylene black and graphene are surface annealed at 600℃ in argon atmosphere for 1 hour to obtain modified acetylene black and modified graphene. The modified conductive agent materials obtained after treatment are mixed evenly in a 2:1 ratio to form a composite modified conductive agent; Example 3: The difference between Example 3 and Example 1 lies in the preparation of the composite conductive agent. Step S1 is as follows: Raw material preparation: Acetylene black and graphene are surface annealed at 600℃ in argon atmosphere for 1 hour to obtain modified acetylene black and modified graphene. The modified conductive agent materials obtained after treatment are mixed evenly in a 1:2 ratio to form a composite modified conductive agent; Example 4: The difference between Example 4 and Example 1 lies in the preparation of the composite conductive agent. Step S1 is as follows: Raw material preparation: Acetylene black, VGCF, and graphene are surface-annealed at 600°C in argon atmosphere for 1 hour to obtain modified acetylene black, modified VGCF, and modified graphene. The modified conductive agent materials obtained after treatment are mixed evenly in a 1:1:1 ratio to form a composite modified conductive agent. Example 5: The difference between Example 5 and Example 1 lies in the preparation of the composite conductive agent. Step S1 is as follows: Raw material preparation: Acetylene black and VGCF are surface annealed at 600°C in argon atmosphere for 1 hour to obtain modified acetylene black and modified VGCF. The modified conductive agent materials obtained after treatment are mixed evenly in a 1:1 ratio to form a composite modified conductive agent; Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that step S1 is omitted, i.e. the conductive agent is not modified, and the conductive agent acetylene black and graphene are directly used for electrode raw material preparation in step S2; Step S2: Electrode raw material preparation: The ternary cathode material, LPSC sulfide solid electrolyte, conductive agent (acetylene black and graphene in a mass ratio of 1:1) and PTFE binder are mixed in a mass ratio of 80%:15%:3%:2%; Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that step S1 is omitted, i.e. the conductive agent is not modified, and the conductive agent acetylene black and graphene are directly used for electrode raw material preparation in step S2; Step S2: Electrode raw material preparation: The ternary cathode material, LPSC sulfide solid electrolyte, conductive agent (acetylene black: graphene mass ratio of 2:1) and PTFE binder are mixed in a mass ratio of 80%:15%:3%:2%; Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that step S1 is omitted, i.e. the conductive agent is not modified, and the conductive agent acetylene black and graphene are directly used for electrode raw material preparation in step S2; Step S2: Electrode raw material preparation: The ternary cathode material, LPSC sulfide solid electrolyte, conductive agent (acetylene black: graphene mass ratio of 1:2) and PTFE binder are mixed in a mass ratio of 80%:15%:3%:2%; Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that step S1 is omitted, i.e. the conductive agent is not modified, and the conductive agent carbon fiber VGCF, acetylene black, and graphene are directly used for electrode raw material preparation in step S2; Step S2: Electrode raw material preparation: Ternary cathode material, LPSC sulfide solid electrolyte, conductive agent (VGCF, acetylene black, and graphene are mixed in a mass ratio of 1:1:1) and PTFE binder are mixed in a mass ratio of 80%:15%:3%:2%; The positive electrode films of the examples and comparative examples were used to prepare sulfide all-solid-state molded half-cells and tested: After the LPSC electrolyte was pressed into a disc, the die-cut positive electrode film was placed in the mold from above and compacted, and the lithium indium sheet was placed in the mold from below. Finally, the mold was tightened and pressurized to obtain a full cell. The preferred mass of the sulfide solid electrolyte was 100-150 mg, the pressure range was 0.9-1.2 T, and the holding time was 1-2 min; the pressure range of the positive electrode film was 1.8-2.2 T, and the holding time was 1-2 min; the pressure range of the lithium indium sheet was 0.5-1 T, and the holding time was 5-10 min.

[0025] Table 1 shows a comparison of battery Rct, cycle performance, and rate performance.

[0026] Table 1

[0027] Meanwhile, exemplary illustrations of typical Examples 4 and 5, as well as Comparative Examples 3 and 4, are provided, and the results are shown in Figures 1 and 2. The results demonstrate that the modified composite conductive agent can react in situ with the sulfide electrolyte during battery charging and discharging to generate a stable CEI interface layer. This interface layer effectively isolates the electrolyte from direct contact with the positive electrode material and the conductive agent, blocking the reduction of transition metal S. 2- And the continued occurrence of side reactions such as sulfide oxidation. As a preferred option, the composite system can play a synergistic role. The modified acetylene black material provides a continuous conductive framework, the modified graphene enhances in-plane electron transport, and the modified carbon fiber can improve network toughness. The uniform mixing ratio can balance electron conduction and ion transport channels. Compared with the unmodified material, the battery cycle and rate performance are also improved, and the RCT is reduced. Figure 2 However, the battery performance plummeted after 50 cycles due to side reactions. The modified composite material showed significantly improved long-cycle stability. The modified conductive agent material systematically solved the interfacial compatibility problem between traditional carbon-based conductive agents and sulfide electrolytes, while optimizing the mass transfer and conduction pathways within the cathode, ultimately achieving... Figure 1 The capacity retention rate of the all-solid-state dry-process battery is improved by more than 10% after 100 cycles, and the capacity retention rate at 0.5C / 0.1C rate is improved by 6.6%.

[0028] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0029] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A composite conductive agent, characterized in that, It includes various modified conductive agents; the modified conductive agents are obtained by annealing conductive agents.

2. The composite conductive agent according to claim 1, characterized in that, The conductive agent is oil furnace black, acetylene black, Ketjen black, graphene, carbon fiber, or carbon nanotubes; preferably acetylene black, graphene, or carbon fiber. The modified conductive agent includes modified furnace black, modified acetylene black, modified Ketjen black, modified graphene, modified carbon fiber, or modified carbon nanotubes; preferably modified acetylene black, modified graphene, or modified carbon fiber.

3. The composite conductive agent according to claim 1, characterized in that, The annealing conditions are as follows: annealing at 200℃-800℃ for 0.5-3 hours under argon atmosphere; preferably annealing at 600℃ for 1 hour.

4. The composite conductive agent according to claim 2, characterized in that, Including at least two of the following: modified acetylene black, modified graphene, or modified carbon fiber.

5. The composite conductive agent according to claim 2, characterized in that, It includes modified acetylene black and modified graphene; preferably, the mass ratio of modified acetylene black to modified graphene is (1-2):(1-2).

6. The composite conductive agent according to claim 2, characterized in that, It includes modified acetylene black and modified carbon fiber; preferably, the mass ratio of modified acetylene black to modified graphene is (0.5-2):(0.5-2); more preferably, it is 1:

1.

7. The composite conductive agent according to claim 2, characterized in that, The mixture includes three components: modified acetylene black, modified graphene, or modified carbon fiber; preferably, the mass ratio of the modified acetylene black, modified graphene, or modified carbon fiber is (0.5-2):(0.5-2):(0.5-2); more preferably, it is 1:1:

1.

8. A method for preparing the composite conductive agent according to any one of claims 1-7, characterized in that, The process includes the following steps: mixing at least two modified conductive agents.

9. A positive electrode membrane, characterized in that, Includes the composite conductive agent as described in any one of claims 1-7, the positive electrode material, the solid electrolyte, and the binder; Preferably, the mass ratio of the positive electrode material, solid electrolyte, composite conductive agent, and binder is (70-90):(10-20):(1-5):(1-5); more preferably, it is 80:15:3:

2. Preferably, the cathode material is one or more of the following: nickel-cobalt-manganese ternary, lithium-rich manganese-based, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel manganese oxide. The solid electrolyte is a sulfide electrolyte or a halide electrolyte; Preferably, the sulfide electrolyte is Li (6-m) PS (5-m) X (1+m) Li 10 GeP2S 12 ; 0 ≤ m ≤ 1.0, X is selected from at least one of Cl, Br, and I; Preferably, the halide electrolyte is Li x MB6, wherein M is at least one of Y, Zr, In, Sc, Ta, and La, and B is at least one of Cl, Br, and I; 2≤x≤4; Preferably, the adhesive is at least one of PTFE, PVDF, PAN, PMMA, PAA, and PE, with PTFE being the most preferred.

10. A dry-process battery, characterized in that, Includes the positive electrode film as described in claim 9.

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