Composite layer coated positive electrode material and preparation method thereof, positive electrode plate and solid-state battery

Abstract

The invention relates to a composite layer coated positive electrode material and a preparation method thereof, a positive electrode plate and a solid-state battery. The positive electrode material comprises a main material, and further comprises a first coating layer which contains an ion diffusion material and coats the outer surface of the main material, and a second coating layer which contains an ion diffusion material and coats the outer surface of the first coating layer, the second coating layer is a polymer electrolyte coating layer and comprises a polymer formed by polymerizing a polymerizable oligomer and a solid electrolyte, and the second coating layer is coated outside the first coating layer through in-situ polymerization; and the third coating layer comprises a grafted conductive agent, the grafted conductive agent is coated outside the second coating layer, and the grafted conductive agent is at least partially grafted and connected with the solid electrolyte in the polymer electrolyte coating layer. According to the positive electrode material disclosed by the invention, the problem that the impedance between the electrode material and electrolyte particles is too large is solved, and the positive electrode material can show higher power, fast charging performance and cycling stability under the working condition of lower pressure.

Description

Technical Field

[0001] This invention relates to the field of solid-state batteries, and more specifically, to a composite-coated cathode material and its preparation method, a cathode electrode containing the cathode material, and a solid-state battery. Background Technology

[0002] Solid-state lithium-ion batteries (hereinafter referred to as solid-state batteries) are considered the main development direction of next-generation lithium-ion batteries due to their high energy density and high safety. However, current research shows that the internal resistance of solid-state batteries is much greater than that of liquid batteries, and their performance requires extremely high pressure support. Due to their non-rheological physical properties, the internal solid electrolyte cannot wet into the gaps between the electrode materials, and the effective transfer of Li-ion energy at the solid-solid interface is limited. + Insufficient pathways severely limit the performance of solid-state batteries in practical applications. Furthermore, uneven particle distribution can lead to problems such as localized short circuits and lithium dendrite formation, all of which negatively impact the performance of solid-state batteries.

[0003] Sulfide solid electrolytes possess excellent mechanical properties and superior ionic conductivity. Many researchers have used nanotechnology to increase the specific surface area of ​​particles, thereby reducing interfacial impedance. However, the rigid contact between the cathode material and the electrolyte in solid-state batteries remains poor, limiting the improvement of lithium-ion transport efficiency. Some studies have used polymer solid electrolytes doped or filled with ionic liquids to improve the interfacial contact between electrodes and electrolytes. However, the intrinsic conductivity of polymer solid electrolytes is insufficient, and the filling with ionic liquids will aggravate interfacial side reactions and reduce the intrinsic safety advantages of solid batteries due to the risk of leakage. While optimizing the ion conductivity of the electrolyte membrane can reduce the impedance of solid-state batteries, it does not solve the problem of excessive impedance between electrode materials and electrolyte particles.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One object of the present invention is to provide a positive electrode material for composite layer coating in solid-state batteries, comprising a main positive electrode material and further comprising: A first coating layer comprising an ion-diffusing material is applied to the outside of the cathode material. The second coating layer is an interface buffer layer and a polymer electrolyte coating layer, which contains a polymer formed by polymerizable oligomer polymerization and a solid electrolyte. The second coating layer is coated on the outside of the first coating layer by in-situ polymerization. A third coating layer comprising a grafted conductive agent is coated on the outside of the second coating layer, wherein the grafted conductive agent is at least partially grafted to the solid electrolyte in the polymer electrolyte coating layer.

[0006] According to the cathode material of this application, the ion diffusion material in the first coating layer is an inorganic lithium salt; the second coating layer includes a polymer formed by in-situ polymerization of polymerizable oligomers, an inorganic ceramic filler, a solid electrolyte lithium salt, and a crosslinking agent; the grafted conductive agent in the third coating layer is graphitized carbon fiber, which is sintered and grafted onto the polymer electrolyte coating layer.

[0007] According to the cathode material of this application, the inorganic lithium salt in the first coating layer is selected from at least one of lithium phosphate (Li3PO4), lithium aluminate (LiAlO2), and lithium zirconate (LiZrO3). Preferably, the thickness of the first coating layer is 10-40 nm. Optionally, the polymerizable oligomer contained in the second coating layer is selected from vinyl alcohol, ethylene oxide, propylene oxide, etc., and the molecular weight of the polymerizable oligomer is 500-1000. The inorganic ceramic filler is selected from lithium lanthanum zirconium oxide (LLZO) and / or oxide. Titanium (TiO2); the solid electrolyte lithium salt is selected from lithium hexafluorophosphate (LiPF6) and / or lithium bisfluorosulfonyl imide (LiTFSI); the crosslinking agent is a photoinitiator, selected from photoinitiator TPO, photoinitiator 1173, etc.; the thickness of the second coating layer is 80~120nm; optionally, the grafted conductive agent in the third coating layer is graphitized carbon fiber with a length dimension of 500nm~3μm, which is grafted onto the polymer electrolyte coating layer after being sintered at 150℃ for 30min.

[0008] Another objective of this invention is to provide a method for preparing a composite-coated cathode material for solid-state batteries, characterized by comprising: preparing a cathode material main material; coating a first coating layer by immersing the cathode material main material in a salt solution of the diffusion material, stirring, heating, settling, and filtering to obtain a cathode material coated with the first coating layer; coating a second coating layer, wherein the second coating layer is a polymer electrolyte coating layer, obtained by mixing a solvent, a polymerizable oligomer, an optional filler, a crosslinking agent, and a solid electrolyte in a certain proportion to obtain a second coating layer precursor solution; mixing the cathode material coated with the first coating layer and the precursor solution in a certain proportion, performing in-situ polymerization by photoinitiation, and filtering to obtain a cathode material further coated with the second coating layer; and coating a third coating layer by mixing a grafted conductive agent with the cathode material coated with the second coating layer in a certain proportion, calcining the grafted agent to obtain a cathode material further coated with the third coating layer.

[0009] According to the preparation method of this application, the ion diffusion material in the first coating layer is an inorganic lithium salt; the precursor solution of the second coating layer includes a solvent, a polymerizable oligomer, an inorganic ceramic filler, a crosslinking agent, and a solid electrolyte lithium salt; the grafted conductive agent in the third coating layer is graphitized carbon fiber, which is sintered and grafted onto the polymer electrolyte coating layer, and the grafted conductive agent is at least partially grafted and connected to the solid electrolyte lithium salt in the second coating layer.

[0010] According to the preparation method of this application, the inorganic lithium salt in the first coating layer is selected from at least one of lithium phosphate (Li3PO4), lithium aluminate (LiAlO2) and lithium zirconate (LiZrO3), and preferably, the thickness of the first coating layer is 10~40 nm. The polymerizable oligomer contained in the second coating layer precursor solution is selected from vinyl alcohol, ethylene oxide, propylene oxide, etc., and the molecular weight of the polymerizable oligomer is 500~1000; the inorganic ceramic filler is selected from lithium lanthanum zirconium oxide (LLZO), titanium dioxide (TiO2), etc.; the solid electrolyte lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonyl imide (LiTFSI), etc.; the crosslinking agent is a photoinitiator, and the photoinitiator is selected from photoinitiator TPO, photoinitiator 1173, etc.; the thickness of the second coating layer is 80~120nm; The grafted conductive agent in the third coating layer is a graphitized carbon fiber with a length dimension of 500 nm to 3 μm, which is grafted onto the polymer electrolyte coating layer after being sintered at 150°C for 30 min.

[0011] According to the preparation method of this application, after the coating step of the first coating layer and before the coating step of the second coating layer, i.e., between the two, an initiator pretreatment step may be optionally included: mixing an amino-rich coupling agent compound with a solvent to prepare a coupling agent solution, immersing the cathode material coated with the first coating layer into the initiator solution, allowing it to stand, filtering, and drying to obtain a pretreated cathode material with an amino-rich surface; preferably, the coupling agent is a silane coupling agent, and optionally, the coupling agent is 3-aminopropyltriethoxysilane (APTES).

[0012] Another objective of this application is to provide a positive electrode sheet, wherein the positive electrode sheet comprises the aforementioned positive electrode material or the positive electrode material prepared by the aforementioned preparation method; preferably, the positive electrode sheet comprises the positive electrode material, a sulfide solid electrolyte as a positive electrode mixed electrolyte, a conductive agent, and a binder; more preferably, the sulfide solid electrolyte is selected from lithium germanium phosphorus sulfide (Li2S·P2S5), lithium silicon phosphorus sulfide chloride (Li2S·P2S5·SiS2), and lithium phosphorus sulfide chloride (Li3PS4).

[0013] Another objective of this application is to provide a solid-state battery comprising the aforementioned positive electrode, negative electrode, and sulfide electrolyte membrane.

[0014] Another objective of this application is to provide a solid-state battery in which, after assembling a positive electrode, a negative electrode, and a sulfide electrolyte membrane into a battery, hot isostatic pressing is applied to allow the positive electrode material and the sulfide electrolyte particles to form dense contact sites through the elastic deformation of the polymer interface buffer layer, and a three-dimensional conductive network is formed by a conductive agent.

[0015] Compared with existing technologies, the beneficial effects of this invention are: it provides a cathode material with a high ion conductivity and high stability electrode-electrolyte interface structure, and its preparation method. Solid-state batteries assembled using electrode sheets with this interface structure cathode material exhibit higher power, fast-charging performance, and cycle stability under lower pressure conditions than current technologies, thus overcoming the shortcomings of solid-state batteries. Attached Figure Description

[0016] 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.

[0017] Figure 1 This is a schematic diagram of a cathode material and its gradient coating layer according to one embodiment of this application; Figure 2 This is a schematic diagram of the positive electrode structure of one embodiment of this application, which has a low-impedance positive electrode-electrolyte interface. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0019] The inventors of this application, through electrochemical impedance spectroscopy (EIS) combined with the relaxation time stepwise method (DRT) experimental analysis, discovered that for solid-state batteries, the impedance peaks are mainly concentrated in the ultra-high frequency / high frequency region (relaxation time 10). -6 -10 -4 This indicates that the grain boundary response of the solid electrolyte (including ohmic impedance) and the electrode-electrolyte contact interface impedance of the positive and negative electrodes are the main reasons for the excessive internal resistance of solid batteries.

[0020] This invention improves the low intrinsic ionic conductivity of solid electrolytes and the poor electrode-electrolyte interface by modifying materials and designing electrode material structures, thereby enhancing their performance and accelerating the industrial application of solid-state batteries.

[0021] Based on solid-state batteries, this invention designs a positive electrode material with a high ion conductivity and high stability electrode-electrolyte interface structure. Solid-state batteries are assembled using electrode sheets with this interface structure positive electrode material, which can exhibit higher power, fast charging performance and cycle stability under lower pressure conditions than current batteries, thus making up for the shortcomings of solid-state batteries.

[0022] The present invention provides a positive electrode material for composite layer coating in solid-state batteries, including a positive electrode base material and further including: a first coating layer, the first coating layer comprising an ion diffusion material, the first coating layer covering the outside of the positive electrode base material to improve the ion diffusion rate on the surface of the positive electrode base material; the ion diffusion material in the first coating layer is an inorganic lithium salt. The second coating layer is an interface buffer layer and a polymer electrolyte coating layer. It comprises a polymer formed by polymerizing polymerizable oligomers and a solid electrolyte. The second coating layer is coated on the outside of the first coating layer through in-situ polymerization. Through the ion diffusion material and the solid electrolyte, good solid-solid interface contact sites can be provided, reducing the ion resistance of the electrode electrolyte interface. The second coating layer includes a polymer formed by in-situ polymerization of polymerizable oligomers, inorganic ceramic filler, solid electrolyte lithium salt, and crosslinking agent. The third coating layer contains a grafted conductive agent that coats the outside of the second coating layer. The grafted conductive agent is at least partially grafted to the solid electrolyte in the polymer electrolyte coating layer, thereby providing a good conductive network and further reducing electrode impedance.

[0023] The grafted conductive agent in the third coating layer is graphitized carbon fiber, which is sintered and grafted onto the polymer electrolyte coating layer.

[0024] One embodiment of the present invention provides a material design and structure for a gradient coating layer at the positive electrode-electrolyte interface. For example... Figure 1 As shown, the positive electrode-electrolyte interface structure includes a positive electrode main material and a three-dimensional interface coating layer, including: a first coating layer (ion diffusion layer), a second coating layer (interface buffer layer), and a third coating layer (conductive layer); wherein the positive electrode main material is preferably a single-crystal high-nickel ternary material Li(NiaCobMnc)O2 (90%≤a≤96%), and the particle size D90≤8μm is controlled by mechanical crushing and sieving. The first coating layer is an inorganic lithium salt layer, such as lithium phosphate (Li3PO4), lithium aluminate (LiAlO2), or lithium zirconate (LiZrO3), with a thickness of 10-40 nm. Its function is to increase the ion diffusion rate on the material surface. The second coating layer is a polymer electrolyte coating layer, and the electrolyte is a solid electrolyte. This polymer electrolyte coating layer is formed by in-situ polymerization of solid electrolyte oligomers (ethylene alcohol, ethylene oxide, propylene oxide, etc. with a molecular weight of 500-1000), inorganic ceramic fillers (lithium lanthanum zirconium oxide (LLZO), titanium dioxide (TiO2), etc.), lithium salts (lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonyl imide (LiTFSI), etc.), and crosslinking agents (photoinitiator TPO, photoinitiator 1173, etc.), with a coating layer thickness of 80-120 nm. Its function is to provide good solid-solid interface contact sites and reduce the ionic impedance at the electrode-electrolyte interface.

[0025] The third coating layer is a conductive agent graft layer, which is a graphitized carbon fiber with a length dimension of 500 nm to 3 μm, grafted onto the polymer solid electrolyte layer via hydrogen bonds after sintering at 150 °C for 30 min. Its function is to provide a good conductive network and further reduce electrode impedance.

[0026] The second aspect of the present invention provides a method for preparing a positive electrode material with a composite layer coating for a solid-state battery, characterized in that it includes: preparing a positive electrode material; The first coating layer is formed by dissolving the salt of the ion diffusion material in a solvent to form a salt solution, immersing the positive electrode material in the salt solution, stirring, heating, settling, and filtering to obtain the positive electrode material coated with the first coating layer. The second coating layer is a polymer electrolyte coating layer. It is obtained by mixing solvent, polymerizable oligomer, optional filler, crosslinking agent and solid electrolyte in a certain proportion to obtain a precursor solution for the second coating layer. The cathode material coated with the first coating layer and the precursor solution are mixed in a certain proportion, and in-situ polymerization is carried out by photo-initiated polymerization. After filtration, a cathode material coated with the second coating layer is obtained. The third coating layer is formed by mixing the grafted conductive agent with the positive electrode material coated with the second coating layer in a certain proportion, calcining the grafting process, and then obtaining a positive electrode material coated with the third coating layer.

[0027] According to one embodiment of this application, the inorganic lithium salt in the first coating layer is selected from at least one of lithium phosphate (Li3PO4), lithium aluminate (LiAlO2), and lithium zirconate (LiZrO3), and the thickness of the first coating layer is 10~40 nm. The polymerizable oligomers contained in the precursor solution of the second coating layer are selected from vinyl alcohol, ethylene oxide, propylene oxide, etc.; the inorganic ceramic filler is selected from lithium lanthanum zirconium oxide (LLZO), titanium dioxide (TiO2), etc.; the solid electrolyte lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonyl imide (LiTFSI), etc.; the crosslinking agent is a photoinitiator, and the photoinitiator is selected from photoinitiator TPO, photoinitiator 1173, etc.; the thickness of the second coating layer is 80~120nm; The grafted conductive agent in the third coating layer is a graphitized carbon fiber with a length dimension of 500 nm to 3 μm, which is grafted onto the polymer electrolyte coating layer after being sintered at 150°C for 30 min.

[0028] According to another embodiment of the present invention, based on the previous embodiment, after the aforementioned coating step of the first coating layer and before the coating step of the second coating layer, i.e., between the two, an initiator pretreatment step may be optionally included: preparing a coupling agent solution by mixing an amino-rich coupling agent with a solvent, immersing the cathode material coated with the first coating layer into the initiator solution, allowing it to stand, filtering, and drying to obtain a pretreated cathode material with an amino-rich surface; preferably, the coupling agent is a silane coupling agent, and optionally, the coupling agent is 3-aminopropyltriethoxysilane (APTES).

[0029] The present invention also provides a positive electrode sheet, wherein the positive electrode sheet comprises the aforementioned positive electrode material or the positive electrode material prepared by the aforementioned preparation method; preferably, the positive electrode sheet comprises the positive electrode material, a sulfide solid electrolyte as a positive electrode mixed electrolyte, a conductive agent, and a binder; more preferably, the sulfide solid electrolyte is selected from lithium germanium phosphorus sulfide (Li2S·P2S5), lithium silicon phosphorus sulfide chloride (Li2S·P2S5·SiS2), and lithium phosphorus sulfide chloride (Li3PS4).

[0030] According to one embodiment of the present invention, a low-impedance positive electrode is provided. The low-impedance positive electrode structure designed by the present invention is as follows: Figure 2 The aforementioned positive electrode material with composite coating, electrolyte (positive electrode mixed with electrolyte), conductive agent, and binder.

[0031] In this embodiment, the electrolyte used is a sulfide electrolyte, including one of lithium germanium phosphorus sulfide (LGPS), lithium silicon phosphorus sulfide chloride (LSiPSCl), lithium phosphorus sulfide chloride (LPSCl), and lithium phosphorus sulfide (LPS), which is ball-milled to maintain a particle size D90 of 80~150nm; the conductive agent is preferably graphitized carbon fiber, including VGCF, which is ball-milled to control the length dimension of 500nm~3μm to construct a three-dimensional electron transport network between particles; The preferred binders are polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0032] The electrode structure consists of four parts: 1) a shaped nano-sized positive electrode material and a coating layer containing ion diffusion material; 2) an elastic coating layer constructed from polymer electrolyte; 3) a carbon fiber conductive layer grafted onto the surface of the coating layer; and 4) an ion and electron transport network constructed from sulfide electrolyte and free conductive agent.

[0033] The effect of this structure is that the surface coating layer constructed from the polymer electrolyte can form dense contact sites with the positive electrode material, reducing the interfacial impedance of electrode ion conduction.

[0034] The present invention also provides a solid-state battery comprising the aforementioned positive electrode, negative electrode, and sulfide electrolyte membrane; further, after assembling the positive electrode, negative electrode, and sulfide electrolyte membrane into a battery, hot isostatic pressing is used to cause the positive electrode material and sulfide electrolyte particles to form dense contact sites through the elastic deformation of the polymer interface buffer layer, and a three-dimensional conductive network is formed by the conductive agent.

[0035] According to one embodiment of the present invention, a solid-state battery using the positive electrode sheet described in the present invention is provided. In this embodiment, a sulfide electrolyte membrane with a thickness of 20-30 μm and a pure silicon negative electrode with a particle size D50 of 50-200 nm are preferably assembled with the positive electrode sheet to obtain a solid-state mold battery or a pouch battery.

[0036] Sulfide solid electrolytes possess high intrinsic ionic conductivity, which is beneficial for improving the charge and discharge efficiency of solid-state batteries. According to one embodiment of the present invention, a sulfide-based solid electrolyte is preferably used as the positive electrode co-electrolyte, including but not limited to lithium germanium phosphorus sulfide (Li₂S·P₂S₅), lithium silicon phosphorus sulfide chloride (Li₂S·P₂S₅·SiS₂), and lithium phosphorus sulfide chloride (Li₃PS₄), etc. Dry planetary ball milling is employed at 300~500 r / min for 1.5~2 h to obtain electrolyte a with a D0. 90 The size is 80~150nm.

[0037] Polymer-based solid electrolytes possess excellent mechanical properties and electrochemical stability, and can be used to improve interfacial contact and battery life. According to this embodiment, a polymer electrolyte is preferably used to construct the interface gradient modification layer of the cathode material. The detailed steps of implementing the technical solution are as follows: 1) Inorganic lithium salt layer coating: The preferred cathode material of this invention is single-crystal high-nickel ternary material Li(Ni) a Co b Mn cO2 (90%≤a≤96%), and the particle size D is controlled by mechanical crushing and sieving. 90 ≤8μm; The preferred first coating layer material of this invention is an inorganic lithium salt material, including lithium phosphate (Li3PO4), lithium aluminate (LiAlO2), lithium zirconate (LiZrO3), etc., preferably a carbonate solvent, and the lithium salt concentration is controlled at 0.8~1.2mol / L. The lithium salt solution is prepared by stirring for 15~20min.

[0038] The cathode material is immersed in the above lithium salt solution, and magnetically stirred at 150~200 r / min for 20~30 min at room temperature. Then, it is heated to 45℃~60℃ and allowed to stand for 1 h. After filtering out the cathode material, it is placed in an oven at 60~80℃ to dry, and the pretreated cathode material is obtained.

[0039] 2) Preparation of polymer coating precursor: In this invention, aminosilane coupling agents such as 3-aminopropyltriethoxysilane (APTES) are preferred as initiators. An ethanol solution with an initiator concentration of 0.8~1.0 mol / L is prepared. The pretreated cathode material is immersed in the solution and allowed to stand at room temperature for 45~60 min. The cathode material is then filtered out and dried in an oven at 60~80℃ to obtain a pretreated cathode material with an amino-rich surface.

[0040] The polymer electrolyte coating layer of this invention comprises polymer oligomers, nano-ceramic fillers, crosslinking agents, and lithium salts as raw materials. Preferred polymer oligomers include those containing ether, hydroxyl, and carboxyl groups, including but not limited to vinyl alcohol oligomers, ethylene oxide oligomers, and propylene oxide oligomers (the molecular weight of the polymerizable oligomers is 500-1000). Preferred nano-ceramic fillers include lithium lanthanum zirconium oxide (LLZO) and titanium dioxide (TiO2) with particle sizes of 50-80 nm. Preferred crosslinking agents include photoinitiators such as TPO and 1173 (C6H5COC(CH3)2OH). Preferred lithium salts include lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiTFSI). Preferred solvents include ethyl acetate, xylene, and dichloromethane.

[0041] The precursor solution was obtained by mixing solvent, oligomer, ceramic filler, crosslinking agent and lithium salt in a mass ratio of 80:18:0.7:0.3:1, stirring magnetically at 200~300 r / min for 40~60 min at room temperature, and then letting it stand for 30 min.

[0042] 3) Preparation of cathode material with interfacial coating: The pretreated cathode material and precursor solution were immersed in the mixture at a mass ratio of 1:3, and magnetically stirred at 200-300 r / min for 45-60 min at room temperature to ensure thorough mixing. In-situ polymerization was initiated by irradiation with ultraviolet light at room temperature for 15-20 min. After removing the light source, the cathode material was filtered out and dried in an oven at 60-80℃ for 60-80 min to obtain the cathode material coated with a polymer electrolyte layer.

[0043] 3) Conductive agent coating: The present invention preferably uses carbon fiber raw materials (VGCF, etc.) with a carbon content of 96%~98%, and uses dry planetary ball milling at room temperature at 300~500 r / min for 2~3 h to obtain graphitized carbon fibers with a length dimension of 500nm~3μm. The dried sample is placed in a muffle furnace and the graphitized carbon fibers mentioned above are mixed in at a mass ratio of 90:10. The sample is then calcined at 150℃ for 30 min to obtain a positive electrode material with an interface coating layer.

[0044] 4) Preparation of the positive electrode sheet: The positive electrode sheet of this invention comprises the positive electrode main material prepared in step 2), the sulfide solid electrolyte described in step 1), a conductive agent, and a binder, which are coated and rolled in a mass ratio of 85:12:1.5:1.5 to obtain the positive electrode sheet. Solid-state battery preparation: Preferably, a sulfide electrolyte film with a thickness of 20~30μm and a particle size D 50 Using pure silicon of 50~200nm as the negative electrode, after assembling soft-pack batteries or mold batteries, hot isostatic pressing at 250~300MPa for 10min at 60℃ promotes the formation of dense contact sites between the positive electrode main material and sulfide electrolyte particles through the elastic deformation of the polymer interface buffer layer. A three-dimensional conductive network is constructed by carbon fiber conductive agent. The resulting battery has significantly reduced ohmic internal resistance and polarization internal resistance.

[0045] The following explanation, combined with specific embodiments and comparative examples, further illustrates the point.

[0046] Example 1 The positive electrode-electrolyte interface, electrode, and solid-state battery fabrication process designed in this invention are as follows: Inorganic lithium salt coating: S1: Take Li(Ni) 0.9 Co 0.05 Mn 0.05 100g of O2 cathode material was mechanically crushed and sieved to obtain a particle size D. 90 It is 7.46 μm; S2: Take 50g of lithium phosphate (Li3PO4) and an appropriate amount of propylene carbonate, and mechanically stir at 200r / min for 20min at room temperature to prepare a 1mol / L inorganic lithium salt solution. S3: Immerse the positive electrode material in the above lithium salt solution, stir magnetically at 200 r / min for 30 min at room temperature, then heat to 50°C and let stand for 1 h to obtain the precursor solution; S4: After filtering the precursor solution to obtain the cathode material, dry it in an oven at 70°C under an argon atmosphere to obtain the pretreated cathode material. Polymer solid electrolyte coating: S5: Take 10g of 3-aminopropyltriethoxysilane (APTES) coupling agent, add it to an appropriate amount of ethanol, and mechanically stir at 200r / min for 10min to prepare a 0.8mol / L crosslinking agent solution; S6: Take the pretreated positive electrode material, immerse it in the solution, let it stand at room temperature for 60 minutes, filter out the positive electrode material, and dry it in a 70℃ oven to make its surface rich in amino functional groups. S7: Take 54g of vinyl alcohol oligomer, particle size D 90 2.1 g of lithium lanthanum zirconium oxide (71.4 nm), 0.9 g of TPO crosslinking agent, and 3 g of lithium difluorosulfonyl imide were added to 240 g of ethyl acetate solvent. The mixture was magnetically stirred at 200 r / min for 60 min at room temperature and then allowed to stand for 30 min to obtain a polymer electrolyte precursor solution. S8: Take the pretreated positive electrode material from S6 and add it to the polymer electrolyte precursor solution at a mass ratio of 1:3. Stir magnetically at 200 r / min for 60 min at room temperature, then irradiate with ultraviolet light for 20 min to initiate in-situ polymerization. After removing the light source, filter out the positive electrode material and dry it in an 80℃ oven to obtain the positive electrode material coated with the polymer electrolyte layer. Conductive layer coating: S9: Take VGCF conductive agent with a carbon content of 98%, dry planetary ball mill at 500 r / min for 3 h at room temperature to obtain carbon fiber with a length dimension of 1.5 μm; S10: Take 100g of the sample obtained from S8 and 11g of ball-milled carbon fiber, place them in a muffle furnace and calcine at 150℃ for 30min to obtain the positive electrode material with grafted conductive layer. Electrode and battery fabrication: S11: Lithium-phosphorus-sulfur-chlorine electrolyte was processed by dry planetary ball milling at 300 r / min for 2 h to obtain sulfide electrolyte size D. 90 It is 125nm; S12: Take 85g of the positive electrode material described in S10, 12g of the pretreated sulfide electrolyte, 1.5g of VGCF conductive agent, and 1.5g of polyvinylidene fluoride-chlorotrifluoroethylene copolymer binder. Use NMP as a solvent to adjust the viscosity of the positive electrode slurry to 4000cps at 25℃. S13: Control coating weight to 0.3g / 1000mm 2 Compacted density 3g / cm³3 Prepare the positive electrode sheet; select D 50 The negative electrode was prepared using pure silicon particles with a thickness of 100 nm; a sulfide electrolyte membrane with a thickness of 30 μm was selected to assemble a mold battery for performance testing.

[0047] Examples 2-4: The positive electrode-electrolyte interface, electrode, and solid-state battery fabrication process designed in this invention are as follows (some raw materials were replaced during the experiment): Example 2: The cathode material in S1 of Example 1 is replaced with Li(Ni) 0.92 Co 0.06 Mn 0.02 O2, the remaining components and steps are the same as in Example 1.

[0048] Example 3: The lithium salt solution solute in S2 of Example 1 was replaced with lithium zirconate (LiZrO3), and the remaining components and steps were the same as in Example 1.

[0049] Example 4: The polymer electrolyte oligomer in S7 of Example 1 was replaced with ethylene oxide oligomer, and the remaining components and steps were the same as in Example 1.

[0050] Examples 5-6 The cathode-electrolyte interface, electrode, and solid-state battery fabrication process designed in this invention are as follows (some parameters in the fabrication process have been changed). Example 5: The conditions for immersing the positive electrode material in the inorganic lithium salt solution in S3 of Example 1 were changed to immersion at 60°C for 1 hour, and the remaining components and steps were the same as in Example 1.

[0051] Example 6: The UV-initiated polymerization time in S8 of Example 1 was adjusted to 15 min, and the remaining components and steps were the same as in Example 1.

[0052] Comparative Example Comparative Examples 1-2: The design of the positive electrode-electrolyte interface, electrode, and solid-state battery fabrication process are as follows (one layer in the gradient coating layer is omitted).

[0053] Comparative Example 1 Without setting an ion diffusion layer, without performing inorganic lithium salt coating in S2, S3, and S4, the process directly proceeds to the polymer electrolyte coating process in S5. The remaining components and steps are the same as in Example 1.

[0054] Comparative Example 2 Without setting an outer conductive layer, without performing the carbon fiber conductive agent grafting process in S9 and S10, the process directly proceeds to the electrode preparation process in S11. The remaining components and steps are the same as in Example 1.

[0055] Comparative Examples 3-5 The fabrication process of the designed positive electrode-electrolyte interface, electrodes, and solid-state battery is as follows (selecting components / preparation conditions outside the preferred range).

[0056] Comparative Example 3: The carbon fiber conductive agent selected in this invention was replaced with conductive carbon black, and the remaining components and steps were the same as in Example 1.

[0057] Comparative Example 4: The steps of immersing the material in the silane coupling agent in S5 and S6 are omitted, and S7 is carried out directly. The remaining components and steps are the same as in Example 1.

[0058] Comparative Example 5: The calcination temperature of the positive electrode material grafted with the conductive layer in S10 was adjusted to 200℃, and the remaining components and steps were the same as in Example 1.

[0059] Test case The materials obtained in each embodiment and each comparative example were tested as follows: The initial coulombic efficiency test refers to the process of charging the assembled mold battery at a constant current of 0.1C under an ambient temperature of 25℃ and a set pressure of 20MPa. Charging is stopped once the upper limit voltage is reached, and the initial charge capacity C1 is recorded. After resting for 30 minutes, a constant current discharge of 0.1C is performed, stopping the discharge once the lower limit voltage is reached, and the initial discharge capacity C2 is recorded. The battery voltage range is 2.0 ~ 4.25V. The initial coulombic efficiency = initial discharge capacity C2 / initial charge capacity C1.

[0060] The [Material Specification Capacity Performance Test] involves charging the mold battery at a constant current of 0.1C under an ambient temperature of 25℃ and a set pressure of 20MPa. Once the upper limit voltage is reached, charging is switched to constant voltage until the current reaches 0.05C, at which point charging is stopped. After resting for 30 minutes, a constant current discharge of 0.1C is performed, stopping the discharge once the lower limit voltage is reached. This charge-discharge process is repeated three times, and the average discharge capacity is recorded as C0. Therefore, the material specification capacity performance = average discharge capacity C0 / mass of positive electrode active material used in the assembled battery.

[0061]

Short-term power test

[0062] [Rate Performance 1C / 0.1C] The battery was tested at different rates of 1C and 0.2C using the LAND battery testing system (CT2001A) charge and discharge tester. The constant current charge and discharge test conditions were 25℃ constant temperature, and the voltage range was 2.0~4.25V. The rate performance of 2C / 0.2C was tested.

[0063] [Number of Cycles] In a 25℃ ambient chamber, the mold battery is cyclically charged and discharged within a specified potential range at a current of 1 / 3C. The discharge capacity of each cycle is recorded. The test ends when the battery capacity reaches 80% of the capacity of the first cycle, and the number of cycles at this time is recorded as the number of cycles corresponding to 80% SOH.

[0064] Table 1 Test data for each embodiment / comparative example

[0065] 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 therein. Such 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 positive electrode material for composite layer coating in solid-state batteries, comprising a main positive electrode material, characterized in that, Also includes: A first coating layer comprising an ion-diffusing material is applied to the outside of the cathode material. The second coating layer is an interface buffer layer and a polymer electrolyte coating layer, which contains a polymer formed by polymerizable oligomer polymerization and a solid electrolyte. The second coating layer is coated on the outside of the first coating layer by in-situ polymerization. A third coating layer comprising a grafted conductive agent is coated on the outside of the second coating layer, wherein the grafted conductive agent is at least partially grafted to the solid electrolyte in the polymer electrolyte coating layer.

2. The positive electrode material with composite layer coating according to claim 1, characterized in that, The ion diffusion material in the first coating layer is an inorganic lithium salt; The second coating layer comprises a polymer formed by in-situ polymerization of polymerizable oligomers, an inorganic ceramic filler, a solid electrolyte lithium salt, and a crosslinking agent; The grafted conductive agent in the third coating layer includes graphitized carbon fibers, which are sintered and grafted onto the polymer electrolyte coating layer.

3. The positive electrode material with composite layer coating according to claim 2, characterized in that, The inorganic lithium salt in the first coating layer is selected from at least one of lithium phosphate, lithium aluminate, and lithium zirconate; preferably, the thickness of the first coating layer is 10-40 nm; optionally, The second coating layer contains polymerizable oligomers selected from vinyl alcohol, ethylene oxide, and propylene oxide, wherein the molecular weight of the polymerizable oligomers is 500-1000; the inorganic ceramic filler is selected from lithium lanthanum zirconium oxide and / or titanium dioxide; the solid electrolyte lithium salt is selected from lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide, etc.; the crosslinking agent is a photoinitiator, wherein the photoinitiator is selected from photoinitiator TPO and / or photoinitiator 1173; the thickness of the second coating layer is 80-120 nm; optionally, the grafted conductive agent in the third coating layer is graphitized carbon fiber with a length dimension of 500 nm-3 μm.

4. A method for preparing a positive electrode material with a composite layer coating for solid-state batteries, characterized in that, include: Prepare the main materials for the positive electrode; The first coating layer is applied by immersing the main cathode material in a salt solution of the diffusion material, stirring, heating, settling, and filtering to obtain a cathode material coated with the first coating layer. The second coating layer is a polymer electrolyte coating layer. It is obtained by mixing solvent, polymerizable oligomer, optional filler, crosslinking agent and solid electrolyte in a certain proportion to obtain a precursor solution for the second coating layer. The cathode material coated with the first coating layer and the precursor solution are mixed in a certain proportion, and in-situ polymerization is carried out by photo-initiated polymerization. After filtration, a cathode material coated with the second coating layer is obtained. The third coating layer is formed by mixing the grafted conductive agent with the positive electrode material coated with the second coating layer in a certain proportion, calcining the grafting process, and then obtaining a positive electrode material coated with the third coating layer.

5. The preparation method according to claim 4, characterized in that, The ion diffusion material in the first coating layer is an inorganic lithium salt; The second coating layer precursor solution includes a solvent, a polymerizable oligomer, an inorganic ceramic filler, a crosslinking agent, and a solid electrolyte lithium salt; The grafted conductive agent in the third coating layer is graphitized carbon fiber, which is sintered and grafted onto the polymer electrolyte coating layer. The grafted conductive agent is at least partially grafted and connected to the solid electrolyte lithium salt in the second coating layer.

6. The preparation method according to claim 5, characterized in that, The inorganic lithium salt in the first coating layer is selected from at least one of lithium phosphate, lithium aluminate, and lithium zirconate (LiZrO3). Preferably, the thickness of the first coating layer is 10~40 nm. The polymerizable oligomer contained in the precursor solution of the second coating layer is selected from at least one of vinyl alcohol, ethylene oxide, and propylene oxide; the inorganic ceramic filler is selected from lithium lanthanum zirconium oxide and / or titanium dioxide; the solid electrolyte lithium salt is selected from lithium hexafluorophosphate and / or lithium bisfluorosulfonyl imide; the crosslinking agent is a photoinitiator, and the photoinitiator is selected from photoinitiator TPO and / or photoinitiator 1173; preferably, the thickness of the second coating layer is 80~120 nm; The grafted conductive agent in the third coating layer is graphitized carbon fiber with a length dimension of 500 nm to 3 μm, which is grafted onto the polymer electrolyte coating layer after being sintered at 150 to 180 °C for 30 to 40 minutes.

7. The preparation method according to claim 5, characterized in that, After the coating step of the first coating layer and before the coating step of the second coating layer, i.e., between the two, an initiator pretreatment step may be included: preparing a coupling agent solution by mixing an amino-rich coupling agent with a solvent, immersing the cathode material coated with the first coating layer into the coupling agent solution, allowing it to stand, filtering, and drying to obtain a pretreated cathode material with an amino-rich surface; preferably, the coupling agent is a silane coupling agent, and optionally, the silane coupling agent is 3-aminopropyltriethoxysilane.

8. A positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to any one of claims 1-3 or the positive electrode material prepared by the preparation method according to any one of claims 4-7; preferably, the positive electrode sheet comprises the positive electrode material, a sulfide solid electrolyte as a positive electrode mixed electrolyte, a conductive agent, and a binder; more preferably, the sulfide solid electrolyte is selected from at least one of lithium germanium phosphorus sulfide, lithium silicon phosphorus sulfide chloride, and lithium phosphorus sulfide chloride.

9. A solid-state battery comprising the positive electrode, negative electrode, and sulfide electrolyte membrane as described in claim 8.

10. The solid-state battery according to claim 9, characterized in that, After assembling the positive electrode, negative electrode, and sulfide electrolyte membrane into a battery, hot isostatic pressing is used to make the positive electrode material and sulfide electrolyte particles form dense contact sites through the elastic deformation of the polymer interface buffer layer, and a three-dimensional conductive network is formed by the conductive agent.

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