Composite positive electrode material and preparation method and application thereof

Abstract

The invention provides a composite positive electrode material as well as a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The composite positive electrode material comprises nickel cobalt lithium manganate, polyvinylidene fluoride, a conductive agent, a lithium salt and N-methyl pyrrolidone, wherein the lithium salt comprises any one or a combination of at least two of lithium bis (fluorosulfonyl) imide, lithium difluorophosphate, lithium difluoro (oxalato) borate, lithium bis (trifluoromethanesulfonyl) imide, lithium trifluoroacetate or lithium nitrate. The lithium salt, polyvinylidene fluoride and N-methyl pyrrolidone form PVDF (Polyvinylidene Fluoride) polymer electrolyte particles, and the particles can form an active particle-PVDF polymer electrolyte chain-active particle ion transmission path in the positive electrode, so that the intrinsic impedance of the positive electrode is remarkably reduced, and the rate performance is improved; meanwhile, anions dissociated from the lithium salt can be decomposed on the surfaces of the positive electrode particles in the charging and discharging process to form an inorganic CEI layer, so that the cycle performance and the high-voltage stability are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a composite cathode material, its preparation method and application, and more particularly to a composite cathode material, its preparation method and its application in the preparation of sulfide solid-state batteries. Background Technology

[0002] With the rapid development of solid-state battery technology, research on composite cathode systems that can be adapted to high-capacity cathode materials and have excellent ion conduction performance has received increasing attention. Currently, the theoretical specific capacity of mainstream cathode materials has exceeded 200 mAh / g, and some nickel-rich ternary materials can even reach over 250 mAh / g, which places higher demands on the ion transport capabilities of composite cathodes. Sulfide-based composite cathodes, due to their high ionic conductivity (up to 10 mAh / g at room temperature), are particularly promising. -2 The S / cm ratio is on the order of magnitude, far exceeding the 10 of polymer electrolytes. -4 ~10 -5 Solid-state batteries (S / cm) and good interface compatibility continue to be research hotspots, occupying a core position in the research and development of all-solid-state battery energy density exceeding 400Wh / kg.

[0003] However, this system suffers from severe charge transfer impedance at the interface between the positive electrode active material and the sulfide electrolyte. Furthermore, traditional solid-state battery composite cathode preparation methods using solid-phase milling result in uneven component distribution and active material agglomerates with particle sizes reaching 5-10 μm, further hindering lithium-ion transport. Consequently, the composite cathode exhibits a capacity retention of less than 60% at 1C rate, and a capacity decay rate exceeding 30% after 50 cycles. In composite cathodes prepared using liquid-phase milling, the treated sulfide electrolyte reacts with the solvent, causing the ionic conductivity to drop to 10. -4 A conductivity below S / cm leads to a deterioration in battery rate performance. Therefore, the incorporation of sulfide electrolytes into composite cathodes generally results in insufficient ionic conductivity. Furthermore, sulfides themselves have a narrow electrochemical window, and are easily oxidized on the cathode side, generating byproducts that simultaneously impair battery electrochemical performance.

[0004] Therefore, it is of great significance to improve the performance of sulfide battery composite cathodes by constructing efficient ion conduction networks through other means to improve interfacial dynamics.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a composite cathode material, its preparation method, and its application. The composite cathode material of this invention incorporates lithium salt, polyvinylidene fluoride (PVDF), and the solvent NMP to form polymer electrolyte particles. This creates an ion transport path within the cathode consisting of active particles, polymer electrolyte particles, and active particles, reducing intrinsic impedance. Simultaneously, it forms an inorganic-rich CEI layer on the surface of the cathode particles, significantly improving the rate capability and cycle performance of the composite cathode.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a composite cathode material, the composite cathode material comprising: lithium nickel cobalt manganese oxide, polyvinylidene fluoride, a conductive agent, a lithium salt, and... N 1-Methylpyrrolidone; The lithium salt includes any one or a combination of at least two of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoroacetate, or lithium nitrate.

[0008] Furthermore, the mass ratio of lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive agent, and lithium salt is (7~9):(0.5~2):(0.5~2):(0.5~2).

[0009] Furthermore, the aforementioned N The content of methylpyrrolidone accounts for 10-15% of the mass of the polyvinylidene fluoride, and the N The content of methylpyrrolidone accounts for 1 to 1.5% of the total mass of the composite cathode material.

[0010] Furthermore, the lithium nickel cobalt manganese oxide is selected from any one or a combination of at least two of lithium nickel cobalt manganese oxide NCM811, NCM523 or NCM622, preferably lithium nickel cobalt manganese oxide NCM811.

[0011] Furthermore, the lithium salt is composed of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium nitrate.

[0012] Furthermore, the molar ratio of lithium difluorosulfonylimide, lithium difluorophosphate, and lithium nitrate is (8~10):(2~4):(1~4).

[0013] Furthermore, the conductive agent is selected from any one or a combination of at least two of carbon black, carbon nanotubes, graphene or carbon fiber, preferably carbon black.

[0014] In a second aspect, the present invention provides a composite cathode material as described in the first aspect, wherein the preparation method of the composite cathode material includes: Lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive agent and lithium salt are placed in NIn methylpyrrolidone, after reaction and degassing, a slurry is obtained; The slurry is coated and dried to obtain the composite cathode material.

[0015] Furthermore, the aforementioned N The amount of methylpyrrolidone added is 0.429 to 1 times the total mass of the lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive agent and lithium salt.

[0016] Furthermore, the reaction temperature is 40~65℃, and the reaction time is 2~6 h.

[0017] Furthermore, the reaction is carried out under stirring conditions, with the stirring speed being 3000~5000 rpm.

[0018] Furthermore, the degassing method is vacuum degassing.

[0019] Furthermore, the vacuum degree of the vacuum degassing is -1.5 to -0.5 bar.

[0020] Furthermore, the coating speed is 10~40 m / min.

[0021] Furthermore, the coating thickness of the slurry is 80~200 μm.

[0022] Furthermore, the preparation method also includes rolling, wherein the areal density after rolling is 10~30 mg / cm³. 2 .

[0023] Furthermore, the drying is vacuum drying, the vacuum drying temperature is 70~90℃, and the vacuum drying time is 12~36 h.

[0024] Thirdly, the present invention provides an application of the composite cathode material as described in the first aspect in the preparation of sulfide solid-state batteries.

[0025] Fourthly, the present invention provides a sulfide solid-state battery positive electrode sheet, the sulfide solid-state battery positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; The positive electrode active material layer includes the composite positive electrode material as described in the first aspect.

[0026] Fifthly, the present invention provides a sulfide solid-state battery, the sulfide solid-state battery comprising a positive electrode, an electrolyte layer and a negative electrode layer stacked sequentially; The positive electrode includes the sulfide solid-state battery positive electrode as described in the fourth aspect.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The composite cathode material of the present invention introduces specific lithium salts, polyvinylidene fluoride (PVDF) binder, and solvents. N 1,3-methylpyrrolidone (NMP) binds them to form polymer electrolyte particles, thereby forming an ion transport path of active particles-polymer electrolyte particles-active particles inside the positive electrode, which significantly improves ionic conductivity.

[0028] (2) The composite cathode material described in this invention can form an inorganic-rich CEI layer on the surface of cathode particles, thereby significantly improving the rate capability and cycle performance of the composite cathode. In addition, this invention can also prepare high-performance composite cathodes by optimizing the type and proportion of lithium salts. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a scanning electron microscope image of the composite cathode material prepared in Example 1.

[0031] Figure 2 This is a scanning electron microscope image of the composite cathode material prepared in Example 4. Detailed Implementation

[0032] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0033] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the shown orientation or positional relationship, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] It should be noted that specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many ways other than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In a first aspect, the present invention provides a composite cathode material, the composite cathode material comprising: lithium nickel cobalt manganese oxide, polyvinylidene fluoride (PVDF), a conductive agent, and a lithium salt. N 2-Methylpyrrolidone (NMP); The lithium salt includes any one or a combination of at least two of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiMTFSI), lithium trifluoroacetate (LiTFA), or lithium nitrate (LiNO3).

[0037] It should be noted that this invention introduces lithium salt into the composite cathode material, and through subsequent coating drying temperature and time, leaves a certain amount of NMP in the composite cathode material. This allows the lithium ions dissociated from the lithium salt in the NMP to complex with the NMP to form [Li]. + The -NMP] complex group, together with the anion, forms a solvation-like sheath structure. This structure facilitates lithium-ion transport between F atoms in the long PVDF polymer chain, as well as between PVDF chains, with lithium ions at the core. This bound NMP significantly enhances the lithium-ion transport performance along the PVDF chains, resulting in an ionic conductivity of 10 for the PVDF binder itself. -4S / cm or higher. Furthermore, by adding the specific lithium salts described above, this invention can improve the ion transport performance of PVDF while simultaneously forming an inorganic interface layer rich in fluorides, nitrides, and phosphides—an excellent ion conductor—through the decomposition of anions.

[0038] As an optional implementation, the mass ratio of lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive agent, and lithium salt is (7~9):(0.5~2):(0.5~2):(0.5~2); Among them, lithium nickel cobalt manganese oxide: "7~9" can be, for example, 7, 7.5, 8, 8.5, 9, etc.; Among them, polyvinylidene fluoride: "0.5~2" can be, for example, 0.5, 0.8, 1, 1.2, 1.5, 2, etc.; The conductive agent is specified as "0.5~2", for example, it can be 0.5, 0.8, 1, 1.2, 1.5, 2, etc. Among them, lithium salt: "0.5~2" can be, for example, 0.5, 0.8, 1, 1.2, 1.5, 2, etc.

[0039] As an optional implementation, the N The content of methylpyrrolidone accounts for 10 to 15% of the mass of the polyvinylidene fluoride, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0040] As an optional implementation, the N The content of methylpyrrolidone accounts for 1 to 1.5% of the total mass of the composite cathode material, for example, it can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0041] As an optional implementation, the lithium nickel cobalt manganese oxide is selected from any one or a combination of at least two of lithium nickel cobalt manganese oxide NCM811, NCM523 or NCM622.

[0042] In a preferred embodiment, the lithium nickel cobalt manganese oxide is lithium nickel cobalt manganese oxide NCM811.

[0043] As an optional implementation, the lithium salt is composed of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), and lithium nitrate (LiNO3).

[0044] It should be noted that the addition of LiFSI to the lithium salt can significantly improve the rate performance of the cathode by constructing ion transport channels on the PVDF; while the addition of LiDFP can improve the high-voltage stability of the cathode; and the addition of LiNO3 can improve the cycle stability of the cathode material. Therefore, the combination of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), and lithium nitrate (LiNO3) can more significantly improve the performance of the composite cathode material.

[0045] As an optional implementation, the molar ratio of lithium difluorosulfonylimide, lithium difluorophosphate, and lithium nitrate is (8~10):(2~4):(1~4); Among them, "8~10" can be, for example, 8, 8.5, 9, 9.5, 10, etc.; Among them, "2~4" can be, for example, 2, 2.5, 3, 3.5, 4, etc.; Among them, "1~4" can be, for example, 1, 1.5, 2, 2.5, 3, 3, 3.5, 4, etc.

[0046] As an optional implementation, the conductive agent is selected from any one or a combination of at least two of carbon black, carbon nanotubes, graphene or carbon fiber.

[0047] In a preferred embodiment, the conductive agent is carbon black.

[0048] In a second aspect, the present invention provides a composite cathode material as described in the first aspect, wherein the preparation method of the composite cathode material includes: Lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive agent and lithium salt are placed in N In methylpyrrolidone, after reaction and degassing, a slurry is obtained; The slurry is coated and dried to obtain the composite cathode material.

[0049] It should be noted that, using the preparation method provided by the present invention, a composite cathode with multiple lithium salts can significantly reduce the intrinsic impedance of the cathode and improve rate performance because the PVDF polymer electrolyte particles formed by the lithium salt, binder PVDF and solvent NMP can form an ion transport path of active particles-PVDF polymer electrolyte chain-active particles inside the cathode. At the same time, the anions dissociated from the lithium salt will decompose on the surface of the cathode particles during charging and discharging to form an inorganic CEI layer, thereby significantly improving cycle performance and high voltage stability.

[0050] As an optional implementation, the NThe amount of methylpyrrolidone added is 0.429 to 1 times the total mass of the lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive agent and lithium salt, for example, it can be 0.429 times, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, etc.

[0051] As an optional implementation, the solid content of the slurry is 50-70%, for example, it can be 50%, 52%, 54%, 55%, 56%, 58%, 60%, 62%, 64%, 65%, 66%, 68%, 70%, etc.

[0052] As an optional implementation, the reaction temperature is 40~65℃, for example, 40℃, 42℃, 44℃, 45℃, 46℃, 48℃, 50℃, 52℃, 54℃, 55℃, 56℃, 58℃, 60℃, 62℃, 64℃, 65℃, etc., and the reaction time is 2~6 h, for example, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc.

[0053] As an optional implementation, the reaction is carried out under stirring conditions, and the stirring speed is 3000~5000 rpm, for example, 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 5000 rpm, etc.

[0054] As an optional implementation, the degassing method is vacuum degassing.

[0055] As an optional implementation, the vacuum degree of the vacuum degassing is -1.5 to -0.5 bar, for example, it can be -1.5 bar, -1.2 bar, -1.0 bar, -0.8 bar, -0.5 bar, etc.

[0056] As an optional implementation, the coating speed is 10~40 m / min, for example, it can be 10 m / min, 15 m / min, 20 m / min, 25 m / min, 30 m / min, 35 m / min, 40 m / min, etc.

[0057] As an optional implementation, the coating thickness of the slurry is 80~200 μm, for example, it can be 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, etc.

[0058] As an optional implementation, the drying is vacuum drying.

[0059] As an optional implementation, the vacuum drying temperature is 70~90℃, for example, it can be 70℃, 72℃, 74℃, 75℃, 76℃, 78℃, 80℃, 82℃, 84℃, 85℃, 86℃, 88℃, 90℃, etc., and the vacuum drying time is 12~36 h, for example, it can be 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h, etc.

[0060] Thirdly, the present invention provides an application of the composite cathode material as described in the first aspect in the preparation of sulfide solid-state batteries.

[0061] Fourthly, the present invention provides a sulfide solid-state battery positive electrode sheet, the sulfide solid-state battery positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; The positive electrode active material layer includes the composite positive electrode material as described in the first aspect.

[0062] Fifthly, the present invention provides a sulfide solid-state battery, the sulfide solid-state battery comprising a positive electrode, an electrolyte layer and a negative electrode layer stacked sequentially; The positive electrode includes the sulfide solid-state battery positive electrode as described in the fourth aspect.

[0063] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0064] Example 1 This embodiment provides a sulfide solid-state battery composite cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium bis(fluorosulfonyl)imide (LiFSI), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent with a mass ratio of 1:1:1:8. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the sulfide solid-state battery composite cathode material; wherein, the final prepared sulfide solid-state battery composite cathode material retains 1.5 wt% of N-Methylpyrrolidone NMP.

[0065] The prepared sulfide solid-state battery composite cathode was imaged using scanning electron microscopy (SEM), such as... Figure 1 As shown, the composite cathode prepared in this embodiment has good interface integrity and is relatively flat, with active particles and PVDF polymer electrolyte particles evenly distributed.

[0066] Example 2 This embodiment provides a sulfide solid-state battery composite cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium salts (lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorophosphate (LiDFP), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. The mass ratio of NCM811 to PVDF and carbon black is 8:1:1, the mass ratio of PVDF to LiFSI is 1:1, and the molar ratio of LiFSI to LiDFP is 3:1. (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the sulfide solid-state battery composite cathode material; wherein, the final prepared sulfide solid-state battery composite cathode material retains 1.5 wt% of N -Methylpyrrolidone NMP.

[0067] Example 3 This embodiment provides a sulfide solid-state battery composite cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium salts (lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), and lithium nitrate (LiNO3), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. The mass ratio of NCM811 to PVDF and carbon black is 8:1:1, the mass ratio of PVDF to LiFSI is 1:1, and the molar ratio of LiFSI to LiDFP and LiNO3 is 9:3:1.

[0068] (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the sulfide solid-state battery composite cathode material; wherein, the final prepared sulfide solid-state battery composite cathode material retains 1.5 wt% of N -Methylpyrrolidone NMP.

[0069] Example 4 This embodiment provides a sulfide solid-state battery composite cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium salts (lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), and lithium nitrate (LiNO3), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. The mass ratio of NCM811 to PVDF and carbon black is 8:1:1, the mass ratio of PVDF to LiFSI is 1:1, and the molar ratio of LiFSI to LiDFP and LiNO3 is 9:3:2.

[0070] (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the sulfide solid-state battery composite cathode material (e.g. Figure 2 (as shown); wherein, the final prepared sulfide solid-state battery composite cathode material also retains 1.5 wt% of... N -Methylpyrrolidone NMP.

[0071] Example 5 This embodiment provides a sulfide solid-state battery composite cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium salts (lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), and lithium nitrate (LiNO3), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. The mass ratio of NCM811 to PVDF and carbon black is 8:1:1, the mass ratio of PVDF to LiFSI is 1:1, and the molar ratio of LiFSI to LiDFP and LiNO3 is 9:3:3.

[0072] (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the sulfide solid-state battery composite cathode material; wherein, the final prepared sulfide solid-state battery composite cathode material retains 1.5 wt% of N -Methylpyrrolidone NMP.

[0073] Example 6 This embodiment provides a sulfide solid-state battery composite cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium salts (lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), and lithium nitrate (LiNO3), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. The mass ratio of NCM811 to PVDF and carbon black is 8:1:1, the mass ratio of PVDF to LiFSI is 1:1, and the molar ratio of LiFSI to LiDFP and LiNO3 is 9:3:4.

[0074] (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the sulfide solid-state battery composite cathode material; wherein, the final prepared sulfide solid-state battery composite cathode material retains 1.5 wt% of N -Methylpyrrolidone NMP.

[0075] Comparative Example 1 This comparative example provides a cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent with a mass ratio of 1:1:8. NThe mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the cathode material; wherein, the cathode material finally prepared retains 0 wt% of N -Methylpyrrolidone NMP.

[0076] Comparative Example 2 This comparative example provides a cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium permanganate, carbon black, and nickel cobalt manganese oxide (NCM811) in a solvent with a mass ratio of 1:1:1:8. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min to a thickness of 100 μm; then vacuum dried at 80°C for 24 h to obtain the cathode material; wherein, the cathode material finally prepared still retains 1.5 wt% of N -Methylpyrrolidone NMP.

[0077] Comparative Example 3 This comparative example provides a cathode material, which is prepared by the following steps: (1) Place polyvinylidene fluoride (PVDF), lithium bis(fluorosulfonyl)imide (LiFSI), carbon black, and lithium nickel cobalt manganese oxide (NCM811) in a solvent with a mass ratio of 1:1:1:8. N The mixture was stirred in 3000 rpm in methylpyrrolidone NMP and reacted at 60°C for 2 h. The mixture was then connected to a vacuum system (0.05 mbar) and the bubbles were removed at -1.5 bar to obtain a slurry with a solid content of 70 wt%. (2) The slurry obtained in step (1) is coated on a coating machine at a speed of 40 m / min and the coating thickness is 100 μm; then it is vacuum dried at 120℃ for 24 h to obtain the cathode material; wherein, the cathode material finally prepared has no NMP residue.

[0078] Test Example 1 Ionic conductivity Test samples: sulfide solid-state battery composite cathode materials provided in Examples 1-6, and cathode materials provided in Comparative Examples 1-3.

[0079] Test method: Assemble a mold battery with an internal structure of Li|LPSCl|NCM811|LPSCl|Li, and then perform constant current polarization test to calculate the lithium-ion conductivity of the composite cathode NCM811.

[0080] The specific test results are shown in Table 1 below: Table 1

[0081] As shown in Table 1, the lithium ions dissociated from lithium salts upon dissolution in NMP complex with NMP to form [Li] + The -NMP] complex group, together with the anion, forms a solvation-like sheath structure. This structure enables lithium-ion transport between F atoms in the long PVDF polymer chain, as well as between PVDF chains, with lithium ions as the core. This partially bound NMP significantly enhances the lithium-ion transport performance on the PVDF chain, resulting in a final ionic conductivity of 10. -4 S / cm or higher.

[0082] Test Example 2 Battery performance test Test samples: sulfide solid-state battery composite cathode materials provided in Examples 1-6, and cathode materials provided in Comparative Examples 1-3.

[0083] Battery assembly method: All powders (positive / negative electrode materials, sulfide electrolyte, conductive agent, etc.) are mixed in a glove box and directly dry-pressed into robust electrode sheets and electrolyte films. The sulfide electrolyte is then transferred onto the negative electrode sheet. The negative electrode and electrolyte film composite electrode, and the positive electrode are stacked in sequence, first with a printing frame, then isostatically pressed into a single unit, ensuring tight contact between the solid and solid interfaces. The pressed battery cells are then placed in an aluminum-plastic film bag in an inert atmosphere, vacuumed, and heat-sealed to completely isolate them from external water and oxygen.

[0084] Battery performance testing methods: (1) Rate capability: 2 C / 0.1 C; 200 cycles; (2) High voltage stability: 4.25 V; (3) Cyclic stability: 200 cycles.

[0085] The specific test results are shown in Table 2 below: Table 2

[0086] As shown in Table 2, when the composite positive electrode prepared in this embodiment is assembled with a sulfide solid electrolyte and a lithium metal negative electrode and subjected to constant current charge-discharge cycle testing, the PVDF polymer electrolyte particles formed by the novel lithium salt, binder PVDF, and binding solvent NMP act as a bridge, effectively promoting lithium-ion transport between active material particles. At the same time, the three lithium salts have different anionic groups that can decompose on the surface of the positive electrode particles to generate an excellent interface layer rich in various inorganic substances, which can effectively promote ion transport, reduce interfacial side reactions between the positive electrode and the sulfide electrolyte, and improve the cycle performance of the battery.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material comprises: lithium nickel cobalt manganese oxide, polyvinylidene fluoride, a conductive agent, a lithium salt, and N - methylpyrrolidone; The lithium salt comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium difluoro oxalate borate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoroacetate or lithium nitrate.

2. The composite cathode material of claim 1, wherein, The mass ratio of the lithium nickel cobalt manganese oxide, the polyvinylidene fluoride, the conductive agent and the lithium salt is (7-9):(0.5-2):(0.5-2):(0.5-2). Preferably, said N - the content of methylpyrrolidone is comprised between 10 and 15% by mass of the polyvinylidene fluoride, and said N - the content of methylpyrrolidone is comprised between 1 and 1.5% by mass of the total mass of the composite cathode material.

3. The composite cathode material of claim 1 or 2, wherein, The lithium nickel cobalt manganese oxide is selected from any one or a combination of at least two of lithium nickel cobalt manganese oxide NCM811, NCM523 or NCM622, and preferably is lithium nickel cobalt manganese oxide NCM811.

4. The composite cathode material of claim 1 or 2, wherein, The lithium salt is composed of lithium bisfluorosulfonylimide, lithium difluorophosphate and lithium nitrate. Preferably, the molar ratio of the lithium bisfluorosulfonylimide, the lithium difluorophosphate and the lithium nitrate is (8-10):(2-4):(1-4).

5. The composite cathode material of claim 1 or 2, wherein, The conductive agent is selected from any one or a combination of at least two of carbon black, carbon nanotube, graphene or carbon fiber, and preferably is carbon black.

6. A method of producing the composite cathode material according to any one of claims 1 to 5, characterized by, The preparation method of the composite positive electrode material comprises: The lithium nickel cobalt manganese oxide, the polyvinylidene fluoride, the conductive agent, and the lithium salt are placed in N - methylpyrrolidone, reacted, and deaerated to obtain a slurry; The slurry is coated and dried to obtain the composite positive electrode material.

7. The composite cathode material of claim 6, wherein, The N - the methylpyrrolidone is added in an amount of 0.429 to 1 times the total mass of the lithium nickel cobalt manganese oxide, the polyvinylidene fluoride, the conductive agent, and the lithium salt; Preferably, the temperature of the reaction is 40-65°C, and the time of the reaction is 2-6 h. Preferably, the reaction is carried out under stirring, and the stirring speed is 3000-5000 rpm. Preferably, the defoaming method is vacuum defoaming. Preferably, the vacuum degree of the vacuum defoaming is -1.5 to -0.5 bar. Preferably, the coating speed is 10-40 m / min. Preferably, the coating thickness of the slurry is 80-200 μm. Preferably, the production method further comprises roll-pressing, the face density after the roll-pressing being 10 to 30 mg / cm 2 ; Preferably, the drying is vacuum drying, the temperature of the vacuum drying is 70-90°C, and the time of the vacuum drying is 12-36 h.

8. Use of the composite positive electrode material according to any one of claims 1-5 in the preparation of a sulfide solid-state battery.

9. A sulfide solid-state battery positive electrode sheet, characterized by, The sulfide solid-state battery positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector. The positive electrode active material layer comprises the composite positive electrode material according to any one of claims 1-5.

10. A sulfide solid-state battery, characterized by, The sulfide solid-state battery comprises a positive electrode sheet, an electrolyte layer and a negative electrode sheet which are sequentially laminated. The positive electrode sheet comprises the sulfide solid-state battery positive electrode sheet according to claim 9.

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