Positive electrode for solid-state battery, and preparation method therefor and use thereof

Abstract

The present application relates to the technical field of solid-state batteries, and provides a positive electrode for a solid-state battery, and a preparation method therefor and a use thereof. Specifically, the positive electrode comprises a current collector layer and a composite positive electrode layer; the composite positive electrode layer comprises a positive electrode material, a conductive agent and a sulfide solid-state electrolyte; the positive electrode material comprises a positive electrode active material, and a polymer and a lithium salt that coat the surface of the positive electrode active material; and the polymer comprises at least one of an ester group, a cyano group or a carbon-fluorine bond. In the present application, by uniformly providing on the surface of the positive electrode active material an ion-conducting polymer coating layer resistant to decomposition at high voltages, interfacial side reactions between the positive electrode active substance and the sulfide electrolyte and the formation of interfacial ion depletion layers can be reduced, and good ion transport capability and volume change adaptability are achieved, thereby obtaining solid-state battery products having high electrochemical and mechanical properties.

Description

A positive electrode for solid-state batteries and a preparation method and application thereof

[0001] Cross-reference to Related Applications

[0002] The present application claims priority to the Chinese patent application No. CN2024111307712, filed on August 16, 2024, and entitled "A positive electrode for solid-state batteries and a preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of solid-state batteries, in particular to a positive electrode for solid-state batteries and a preparation method and application thereof. BACKGROUND

[0004] With the gradual penetration of new energy vehicles in the market, safety and range are widely concerned by users. However, the current commercialized liquid lithium-ion battery has approached the limit of its energy density, and the organic liquid electrolyte has a series of safety problems such as easy leakage and easy combustion. Due to the advantages of intrinsic safety and high energy density, all-solid-state batteries are known as one of the most promising electrochemical energy storage devices in the next generation.

[0005] According to the difference of solid-state electrolyte composition, the currently widely studied solid-state batteries are mainly divided into polymer, oxide and sulfide-based solid-state batteries. Among them, sulfide solid-state electrolyte has good forming plasticity and high room temperature ionic conductivity (>10 -3 S / cm), and has great application prospect in solid-state batteries. However, the chemical stability and air stability of sulfide electrolyte are poor, and the reaction activity with polar solvents is high, which is difficult to be made into an electrode sheet by a wet homogenate coating process; therefore, in order to avoid the failure of sulfide electrolyte, a dry film forming method is usually used to make the electrode sheet; that is, by mixing and dispersing the active material, conductive agent, binder and sulfide solid-state electrolyte, then hot rolling is performed to realize the film forming of the electrode sheet.

[0006] For example, CN202011173589.7 discloses a positive electrode material layer for all-solid-state batteries and a preparation method thereof, by pre-mixing and fiberizing the active material, sulfide solid-state electrolyte, conductive agent and fiberizable polymer binder under the action of shear force, and then realizing a self-supporting composite positive electrode sheet through hot rolling. However, the fiberized PTFE cannot conduct ion transmission, which often becomes an obstacle to ion transmission inside the composite positive electrode, affecting its large current charge and discharge performance. At the same time, the one-dimensional linear structure PTFE cannot adapt to the shrinkage and expansion of the positive electrode material caused by the charge and discharge process, which is easy to cause adhesion failure, and further leads to the failure of physical contact between the sulfide electrolyte and the positive electrode particles and blocks the effective ion transmission.

[0007] In addition, due to the narrow electrochemical stability window of sulfide solid-state electrolyte, when it is directly in contact with the positive electrode material, it often triggers interface side reactions, leading to deterioration of the interface environment and increase of impedance. Therefore, in similar technical solutions, the positive electrode material often needs to be coated and modified; for example, the positive electrode active material is coated and modified in CN202011173589.7, and the material of the coating and modification layer is a conductive polymer, an oxide solid-state electrolyte, a metal oxide, a metal fluoride, and a lithium-containing metal oxide. In CN202311365075.5, the surface of the positive electrode material is coated with a halide solid-state electrolyte with a component gradient. In the above coating process, the internal stress generated by the rigid active material contacting each other can be reduced, and the contact between the electrolyte and the active material in the composite positive electrode can be increased. However, the inorganic particle-coated positive electrode material is still in rigid contact with the sulfide electrolyte, and during the charging and discharging process, it still faces the problem of stress accumulation and contact failure caused by volume change; and the polymer-coated positive electrode material has poor ion transport performance and is easy to oxidize and degrade.

[0008] Therefore, the present application is proposed.

[0009] Content of the application

[0010] In a first aspect, the present application provides a positive electrode for a solid-state battery, which mainly solves the technical defects of poor ion transport capacity, poor volume change adaptability, and poor contact between active material and solid-state electrolyte.

[0011] The positive electrode for a solid-state battery provided by the present application comprises a current collector layer and a composite positive electrode layer.

[0012] The composite positive electrode layer comprises a positive electrode material, a conductive agent, and a sulfide solid-state electrolyte.

[0013] The positive electrode material comprises a positive electrode active material, and a polymer and a lithium salt coated on the surface of the positive electrode active material; the polymer comprises at least one of an ester group, a cyano group, or a carbon-fluorine bond.

[0014] Beneficial effects: uniformly coating the surface of the positive electrode active material with an ion-conducting polymer layer (polymer matrix-lithium salt) having high-voltage decomposition resistance reduces the interface side reaction between the positive electrode active material and the sulfide electrolyte and the formation of the interface ion dissipation layer, improves the interface ion transmission capacity, and effectively alleviates the problems of poor solid-solid contact and space charge layer between the two. The fibrous polymer binder introduced in the conventional solid-state composite positive electrode cannot adapt to the volume expansion or contraction of the positive electrode active material, resulting in reduced contact between the positive electrode active material and the sulfide electrolyte during the cycle process, hindering the effective transmission of ions in the positive electrode. The solid-state positive electrode of the present application effectively solves the above defects; specifically, the ion-conducting polymer coating layer in the present application can uniformly penetrate into the gap between the positive electrode active material and the sulfide electrolyte, on the one hand, it can alleviate the solid-solid rigid contact between the two, on the other hand, it can well adapt to the volume expansion and contraction of the active material; the polymer with certain adhesion can alleviate the mechanical stress concentration and particle breakage caused by volume change, effectively avoid micro-cracks and voids in the electrode, thereby effectively enhancing the ion transmission area between the active material and the sulfide electrolyte, realizing the effective transmission of ions inside the electrode, and improving the discharge capacity and cycle stability of the solid-state battery.

[0015] In an alternative embodiment, the positive electrode active material comprises one of a layered metal oxide material, a spinel oxide material, or a polyanion material;

[0016] And / or, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisdifluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium bis-oxalate borate, or lithium difluoro-oxalate borate;

[0017] And / or, the conductive agent comprises at least one of conductive carbon black, ketjen black, nano-carbon fiber, carbon nanotube, or conductive graphite;

[0018] And / or, the sulfide solid-state electrolyte comprises one of a glass phase electrolyte, a crystal phase electrolyte, or a lithium-sulfur argyrodite.

[0019] In an alternative embodiment, when the polymer comprises an ester group, the polymer comprises at least one of poly(ethylene carbonate), poly(propylene carbonate), poly(trimethylene carbonate), poly(vinylidene carbonate), polycaprolactone, poly-β-propiolactone, poly(methyl methacrylate), poly(ethyl acrylate), and poly(cyanoacrylate);

[0020] When the polymer comprises a cyano group, the polymer comprises poly(acrylonitrile);

[0021] When the polymer comprises a carbon-fluorine bond, the polymer comprises at least one of poly(vinylidene fluoride) or poly(vinylidene fluoride-hexafluoropropylene).

[0022] In an alternative embodiment, in the composite cathode layer, the mass ratio of the cathode material, the sulfide solid electrolyte and the conductive agent is (80-85) : (10-15) : (1.5-2.5).

[0023] In an alternative embodiment, in the cathode material, the mass ratio of the cathode active material, the polymer and the lithium salt is (20-30) : (1-8) : (1-8).

[0024] In a second aspect, the application provides a preparation method of the cathode for solid-state batteries, comprising the following steps:

[0025] (1) preparing a suspension comprising a polymer, a lithium salt, a cathode active material and an organic solvent, and then performing spray drying treatment to obtain cathode material particles;

[0026] (2) mixing the cathode material particles, the sulfide solid electrolyte and the conductive agent, and performing dry ball milling treatment to obtain a composite cathode powder;

[0027] (3) performing hot roller pressing treatment on the composite cathode powder to obtain a composite cathode film; and compounding the composite cathode film with a current collector to obtain a cathode for solid-state batteries.

[0028] Advantages: First, the spray drying of the precursor mixed solution can coat a uniform ion-conducting polymer layer on the surface of the cathode active material, reducing the non-uniform mixing of the conventional dry electrode, which can cause non-uniform composition of the electrode sheet; at the same time, no additional non-ionic conductive binder is needed in the mixing process, which effectively avoids the obstruction of ion transmission in the electrode sheet, thereby facilitating the electrode sheet to exhibit higher energy density; second, through the hot rolling method, the molten polymer can penetrate and fill into the gap between the active material and the solid electrolyte, improving the density of the electrode sheet, thereby achieving good ion transmission performance; in addition, the polymer coating layer is thin and has a low content in the composite cathode, and the penetration and filling in the hot rolling process make it fully integrated with each component and have good electrical conductivity.

[0029] In an alternative embodiment, in the suspension, the mass concentration of the polymer is 1-8%.

[0030] In an alternative embodiment, the spray drying comprises: an inlet air pressure of 3-5 MPa, an inlet material flow rate of 20-30 mL / min, a hot air temperature at the inlet of 240-260°C, and a hot air temperature at the outlet of 110-130°C.

[0031] In an alternative embodiment, the dry ball milling process has a ball-to-material mass ratio of (1.8-2.2):1, a rotation speed of 250-350 rpm, and a ball milling time of 1-2 h.

[0032] In an alternative embodiment, the hot rolling process has a rolling pressure of 10-200 MPa and a rolling temperature of 80-400℃.

[0033] In a third aspect, the application provides a solid-state battery comprising the positive electrode.

[0034] In a fourth aspect, the application provides an electrical equipment comprising the solid-state battery. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the description of the embodiments or the prior art. Obviously, the drawings described below are some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0036] FIG. 1 provides a preparation process flowchart of the embodiment 1 of the application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the application more clear, the following will combine the drawings in the embodiments of the application to clearly and completely describe the technical solutions in the embodiments of the application. Obviously, the described embodiments are some embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0038] The first aspect of the application is to provide a positive electrode for a solid-state battery.

[0039] The positive electrode of the application comprises a current collector layer and a composite positive electrode layer; the composite positive electrode layer comprises a positive electrode material, a conductive agent and a sulfide solid-state electrolyte; the positive electrode material comprises a positive electrode active material, and a polymer and a lithium salt coated on the surface of the positive electrode active material; the polymer comprises at least one of an ester group, a cyano group or a carbon-fluorine bond.

[0040] As a preferred embodiment, the current collector layer comprises but is not limited to a carbon-coated aluminum foil, a stainless steel foil, etc.

[0041] As a preferred embodiment, the positive active material is one of a layered metal oxide material, a spinel oxide material, or a polyanion material; specifically, the layered metal oxide material includes, but is not limited to, lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), a nickel-cobalt-manganese ternary material (LiNi x Co y Mn 1-x-y O2) or a lithium-rich manganese-based material (xLi2MnO3·(1-x)LiMO2), etc., the spinel oxide material includes, but is not limited to, lithium manganate (LiMn2O4) or lithium nickel manganate (LiNi 0.5 Mn 1.5 O4) or the like, and the polyanion material includes, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), or lithium manganese iron phosphate (LiMn x Fe 1-x PO4) or the like; it can be understood that the values of x and y in the above molecular formula are assigned in a conventional ratio in the art, between 0 and 1.

[0042] As a preferred embodiment, when the polymer includes an ester group, the ester group includes, but is not limited to, a carbonate group, a polyester group, or a polyacrylate group, etc., and specifically, the polymer includes polyethylene carbonate (PEC), polypropylene carbonate (PPC), polytrimethylene carbonate (PTMC), polyvinyl carbonate (PVC), polycaprolactone (PCL), poly-beta-propiolactone, polymethyl methacrylate (PMMA), polyethyl acrylate (PEA), and polycyanoacrylate (PCA); as a preferred embodiment, when the polymer includes a cyano group, the polymer includes polyacrylonitrile (PAN); as a preferred embodiment, when the polymer includes a carbon-fluorine bond, the polymer includes a polyvinylidene fluoride group, such as polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0043] As a preferred embodiment, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisdifluorosulfonimide (LiFSI), lithium bis-trifluoromethylsulfonimide (LiTFSI), lithium bisoxalate borate (LiBOB), or lithium difluoro oxalate borate (LiDFOB).

[0044] As a preferred embodiment, the conductive agent includes at least one of conductive carbon black SP, Ketjen black, nano-carbon fiber VGCF, carbon nanotube CNT, or conductive graphite; in some more preferred embodiments, the conductive agent is a combination of SP and VGCF, i.e., a combination of fiber-shaped and particulate conductive agents, to achieve interstitial filling of the positive active material and the sulfide solid electrolyte.

[0045] As a preferred embodiment, the sulfide solid-state electrolyte comprises one of a glass phase electrolyte, a crystal phase electrolyte or a lithium argyrodite; wherein the glass phase electrolyte is generally sulfide, including but not limited to Li2S, P2S5, SiS2, B2S3, GeS3, etc., the crystal phase electrolyte includes but is not limited to LGPS (LiGeP2S6), etc., and the lithium argyrodite includes but is not limited to LiPS5X (X = Cl, Br or I), etc. 12 ) and the like.

[0046] As a preferred embodiment, in the composite cathode layer, the mass ratio of the cathode material, the sulfide solid-state electrolyte and the conductive agent is (80%~85%):(10%~15%):(1.5%~2.5%).

[0047] As a preferred embodiment, in the cathode material, the mass ratio of the cathode active material, the polymer and the lithium salt is (20~30):(1~8):(1~8); in some more preferred embodiments, the mass ratio of the polymer and the lithium salt is 1:1.

[0048] As a preferred embodiment, the overall thickness of the solid-state battery cathode is 200 μm~500 μm.

[0049] As a preferred embodiment, the thickness ratio of the current collector layer to the composite cathode layer is (10~25):1.

[0050] As a preferred embodiment, the particle size of the cathode material is 2 μm~10 μm.

[0051] As a preferred embodiment, the area density of the composite cathode layer is 20 mg / cm2~30 mg / cm2.

[0052] The second aspect of the present application is to provide a preparation method of the solid-state battery cathode, mainly comprising the following steps (1)~(3).

[0053] (1) preparing a suspension containing a polymer, a lithium salt, a cathode active material and an organic solvent, and then performing spray drying treatment to obtain cathode material particles.

[0054] As a preferred embodiment, the organic solvent includes at least one of dimethylformamide (DMF), N-methylpyrrolidone (NMP), acetone (AC), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), ethyl acetate, dimethylbenzene, isobutyl isobutyrate or ethanol.

[0055] As a preferred embodiment, the amount of the organic solvent added can be 1% to 8% by mass of the polymer in the suspension.

[0056] As a preferred embodiment, during the preparation of the suspension, means for achieving sufficient dispersion of the solute components include, but are not limited to, oscillation, stirring, centrifugation, ultrasonic treatment, heat treatment, etc. In some more preferred embodiments, the suspension is stirred for 12 to 24 hours, the stirring frequency is 300 to 800 rpm, and the temperature of the suspension during stirring is 25 to 80°C.

[0057] As a preferred embodiment, the carrier gas for the spray drying is high-purity nitrogen, and the parameters for the spray drying include: the inlet gas pressure is 3 to 5 MPa, the feed rate is 20 to 30 mL / min, the hot air temperature at the inlet is 240 to 260°C, and the hot air temperature at the outlet is 110 to 130°C.

[0058] As a preferred embodiment, during the spray drying, the suspension that is not fed into the spray drying device is continuously subjected to dispersion treatment to avoid the settlement of the positive electrode particles, which would result in poor uniformity of the coating; the dispersion treatment includes, but is not limited to, oscillation, stirring, centrifugation, ultrasonic treatment, etc.

[0059] (2) The positive electrode material particles, the sulfide solid-state electrolyte, and the conductive agent are mixed and subjected to dry ball milling to obtain a composite positive electrode powder.

[0060] As a preferred embodiment, the ball-to-material mass ratio for the dry ball milling is (1.8 to 2.2):1, the rotation speed is 250 to 350 rpm, and the ball milling time is 1 to 2 hours.

[0061] (3) The composite positive electrode powder is subjected to hot roller pressing to obtain a composite positive electrode film; the composite positive electrode film is combined with a current collector to obtain a positive electrode for a solid-state battery.

[0062] As a preferred embodiment, the roller pressure for the hot roller pressing is 10 to 200 MPa, and the roller temperature for the hot roller pressing is 80 to 400°C. Those skilled in the art can adapt the roller temperature to be higher than or equal to the melting point of the polymer.

[0063] In the preparation method of the positive electrode for solid-state batteries provided in the present application, firstly, the polymer and the lithium salt are uniformly coated on the surface of the particles of the positive electrode active material to form an ion-conducting coating layer; and then, in the process of dry preparation of the positive electrode sheet, the heat roller pressing step causes the ion-conducting coating layer to partially melt and uniformly penetrate into the interstices between the positive electrode material and the sulfide solid-state electrolyte. Therefore, the ion-conducting polymer component of the present application exists on the surface of the positive electrode particles on the one hand, and in the interstices between the positive electrode material and the electrolyte on the other hand.

[0064] In addition, the polymer used in the present application has a polar group and has strong lithium salt dissociation capacity; therefore, the lithium salt component introduced in step (1) will be distributed in the polymer in the form of anions and cations (i.e., in the ion-conducting coating layer); and the polymer will provide a lithium source and improve ion transmission.

[0065] The third aspect of the present application is to provide a solid-state battery comprising the positive electrode for solid-state batteries. It can be understood that the solid-state battery should also include a solid-state negative electrode, and optionally a solid-state electrolyte layer, necessary or non-necessary functional elements or packaging components, etc., which can be selected and combined by those skilled in the art; when the solid-state battery comprises the positive electrode for solid-state batteries provided in the present application, regardless of the structure or components of the solid-state battery, it can be regarded as an embodiment of the present application.

[0066] The fourth aspect of the present application is to provide an electrical equipment comprising the solid-state battery. The electrical equipment can be any equipment or device that converts electrical energy into other forms of energy, including but not limited to new energy vehicles, building electrical equipment, industrial electrical equipment, household and agricultural electrical equipment, etc.; when comprising the solid-state battery, any electrical equipment equipped with the solid-state battery can belong to an embodiment of the present application.

[0067] Example 1

[0068] The preparation flowchart of the present embodiment is shown in FIG. 1.

[0069] S1: 2 g of polyvinylidene fluoride-hexafluoropropylene (Sigma-Aldrich, 427187) and 2 g of lithium salt LiTFSI were dispersed in 98 g of N-methylpyrrolidone solvent, and stirred and dissolved at 80°C to form a suspension solution with a polymer content of 2% by mass. Then, single-crystal Ni90 ternary positive electrode material was added to the above suspension solution (the solid content of the positive electrode active material was 20%), and fully stirred and dispersed to obtain a uniformly dispersed suspension solution.

[0070] S2: The suspension prepared in S1 is transported to a small spray dryer through a diaphragm pump for spray drying and coating of the positive electrode material; the carrier gas for spray drying is high-purity nitrogen, the inlet pressure is 4 MPa, the feeding amount is 25 mL / min, the hot air temperature at the air inlet is 250℃, the hot air temperature at the air outlet is 120℃, and the ion-conducting polymer-coated positive electrode material powder is obtained.

[0071] S3: The ion-conducting polymer-coated positive electrode material prepared in S2, the LPSC sulfide electrolyte, and the conductive additive are weighed, and the mass ratio of the three is 85:13:2; the conductive additive includes SP and VGCF (mass ratio 1:1). The weighed raw material components are mechanically ball-milled and uniformly mixed, wherein the ball-to-material mass ratio is 2:1, the rotation speed is 300 r / min, and the ball-milling time is 1.5 h.

[0072] S4: The composite powder after ball-milling in S3 is hot-rolled into a film, the rolling pressure is 50 MPa, the roller temperature is 180℃, and the surface density is 20 mg / cm 2 ; the film layer obtained by rolling is compounded on one side of the carbon-coated aluminum foil current collector, and the composite positive electrode sheet of the present embodiment is obtained.

[0073] Example 2

[0074] The same as Example 1, except that the mass of the N-methylpyrrolidone solvent in step S1 is adjusted to 95 g, and the mass of the polyvinylidene hexafluoropropylene is adjusted to 5 g.

[0075] Example 3

[0076] The same as Example 1, except that the solid content of the positive electrode active material in step S1 is adjusted to 25%.

[0077] Example 4

[0078] The same as Example 1, except that the polyvinylidene hexafluoropropylene in step S1 is replaced by polyacrylonitrile.

[0079] Example 5

[0080] The same as Example 1, except that the polyvinylidene hexafluoropropylene in step S1 is replaced by polyvinyl alcohol.

[0081] Example 6

[0082] The same as Example 1, except that LiTFSI in step S1 is replaced by LiDFOB.

[0083] Example 7

[0084] The same as example 1, the only difference is that the single crystal Ni90 ternary positive electrode material in step S1 is replaced by a lithium-rich manganese-based positive electrode material.

[0085] Example 8

[0086] The same as example 1, the only difference is that the LPSC sulfide electrolyte in step S3 is replaced by LGPS.

[0087] Comparative example 1

[0088] The same as example 1, the only difference is that step S3 is replaced by: weighing the ion-conducting polymer-coated positive electrode material prepared in S2, the LPSC sulfide electrolyte, the conductive additive (SP: VGCF = mass ratio 1:1), and the binder PTFE, the mass ratio of the four is 83.5%, 14%, 0.5%, 2%, and the weighed raw material components are mechanically ball-milled and uniformly mixed, wherein the ball-to-material mass ratio is 2:1, the rotation speed is 300 r / min, and the ball-milling time is 1.5 h.

[0089] Comparative example 2

[0090] The same as example 1, the only difference is that the addition of lithium salt in step S1 is cancelled.

[0091] Comparative example 3

[0092] The same as example 1, the only difference is that the polyvinylidene fluoride-hexafluoropropylene in step S1 is replaced by low-oxidation-stable polyethylene oxide PEO.

[0093] Comparative example 4

[0094] The same as example 1, the only difference is that the polyvinylidene fluoride-hexafluoropropylene in step S1 is replaced by inorganic material LiNbO3.

[0095] Comparative example 5

[0096] The same as example 1, the only difference is that step S2 is replaced by: the suspension prepared in S1 is subjected to a solvothermal reaction, and then washed, dried and obtained as an ion-conducting polymer-positive electrode material mixed powder.

[0097] Comparative example 6

[0098] The same as example 1, the only difference is that step S4 is replaced by: the composite powder after ball-milling in S3 is prepared into a slurry with a solid content of 45% (the solvent is xylene), the slurry is coated onto one side of the carbon-coated aluminum foil current collector, and then dried to obtain the composite positive electrode sheet of this comparative example.

[0099] Test example

[0100] The positive electrode plate prepared by each embodiment and the comparative example is prepared into a solid-state battery; the specific method is as follows: the negative electrode is selected to be lithium-indium alloy, and the electrolyte is selected to be sulfide electrolyte LPSCl; first, the positive electrode plate is cut into a circular plate with a diameter of 10 mm using a cutting machine, and is placed in a glove box for standby; then, the assembly of a mold battery is carried out, and the solid-state mold battery corresponding to different test examples is assembled in an argon atmosphere glove box.

[0101] (1) Ion conductivity test: by assembling a Li|LPSCl|composite positive electrode|LPSCl|Li solid-state mold battery, electrochemical impedance spectroscopy test is carried out at an ambient temperature of 30°C, and finally the ion conductivity of the composite positive electrode is obtained. The test results are shown in Table 1.

[0102] (2) Electronic conductivity test: by assembling a Ti|composite positive electrode|Ti blocking battery, direct current polarization test is carried out at an ambient temperature of 30°C, and finally the electronic conductivity of the composite positive electrode is obtained. The test results are shown in Table 1.

[0103] Table 1

[0104] As can be seen from Table 1, the ion-conducting polymer coating layer provided by the application can effectively penetrate and fill the internal gaps of the electrode plate during hot rolling, improve the density of the electrode plate, and make the composite positive electrode have good ion transmission performance. Compared with the ordinary PTFE dry method positive electrode (Comparative Example 1), the ion conductivity of Example 1 is increased by nearly 3 times, and due to the electronic insulation property of the polymer coating layer, the electronic conductivity of the dry method positive electrode in Example 1 is slightly reduced. However, overall, due to the low content of the polymer and the good uniformity in the composite positive electrode, the dry method positive electrode obtained in Example 1 can basically maintain good electronic transmission performance.

[0105] (3) Galvanostatic Charge-Discharge (GCD) test: by constant current charging and discharging test of the battery, the charge and discharge performance of the battery is studied, mainly including charge and discharge voltage platform, charge and discharge specific capacity, charge and discharge efficiency and cycle stability and other information. By assembling a composite positive electrode|LPSCl|lithium-indium alloy, the charge and discharge voltage interval is 1.9V-3.7V (vs Li + / Li-In), the test temperature is 30°C, the constant current charge and discharge rate is 1C (1C=220mA / g), and the capacity retention rate after 100 cycles is recorded. The test results are shown in Table 2.

[0106] Table 2

[0107] As can be seen from Table 2, the solid-state battery based on the positive electrode sheet of the application has higher initial discharge capacity, good rate performance and excellent cycle stability. Specifically, the linear PTFE binder of Comparative Example 1 cannot adapt to the expansion and shrinkage of the active material, resulting in the failure of the active material and sulfide electrolyte interface to separate during the cycle process, hindering the effective transmission of ions inside; the polymer layer of Comparative Example 2 has no lithium salt added, and the polymer ion transmission performance is poor, resulting in blocked effective ion transmission inside the electrode; the low oxidation potential PEO polymer is selected in Comparative Example 3, and the polymer is easily oxidized and decomposed during the cycle process, producing undesirable interface products, resulting in rapid capacity decay of the solid-state battery; the inorganic material coated positive electrode strategy is selected in Comparative Example 4, and the positive electrode-electrolyte interface is still rigid contact, which still faces stress accumulation caused by volume change during charging and discharging, resulting in contact failure. In contrast, the strategy of coating the positive electrode with ion-conducting and high-voltage-resistant polymer in the application, the polymer coating layer has high-voltage-resistant groups such as cyano group / ester group, which effectively avoids its oxidation and decomposition at high potential; under the coating of ion-conducting polymer electrolyte layer, the direct contact of positive active material and sulfide electrolyte is reduced, thereby relieving the interface side reaction between the two. At the same time, the ion-conducting polymer can uniformly penetrate into the gap between the two, on the one hand, it can relieve the rigid contact between the two solid-solid, on the other hand, it can well adapt to the volume expansion and shrinkage of the active material, realizing the effective transmission of ions inside the electrode, thereby improving the charge-discharge performance and cycle stability of the solid-state battery.

[0108] Although the application has been illustrated and described with reference to specific embodiments, it is realized that the above embodiments are merely for illustration of the technical solutions of the application, and are not limiting thereof; it should be understood by those skilled in the art that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features thereof can be replaced by equivalents, without departing from the spirit and scope of the application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application; therefore, it means that all these replacements and modifications within the scope of the application are included in the appended claims. Industrial applicability

[0109] By uniformly setting the ion-conducting polymer coating layer with high-voltage-resistant decomposition characteristics on the surface of the positive active material, the application can reduce the interface side reaction and the formation of the interface ion dissipation layer between the positive active material and the sulfide electrolyte, has good ion transmission capacity and volume change adaptability, and further obtains a solid-state battery product with high electrochemical performance and mechanical performance.

Claims

1. A positive electrode for a solid-state battery, characterized in that, The positive electrode comprises a current collector layer and a composite positive electrode layer; The composite positive electrode layer comprises a positive electrode material, a conductive agent and a sulfide solid-state electrolyte; The positive electrode material comprises a positive electrode active material, and a polymer and a lithium salt coated on the surface of the positive electrode active material; the polymer comprises at least one of an ester group, a cyano group or a carbon-fluorine bond.

2. The positive electrode for a solid-state battery according to claim 1, characterized by The positive electrode active material comprises one of a layered metal oxide material, a spinel oxide material or a polyanion material; The lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisdifluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium bis-oxalate borate or lithium difluoro-oxalate borate; The conductive agent comprises at least one of conductive carbon black, ketjen black, nano-carbon fiber, carbon nanotube or conductive graphite; The sulfide solid-state electrolyte comprises one of a glass phase electrolyte, a crystal phase electrolyte or a lithium thiogermanate.

3. The positive electrode for solid-state batteries according to claim 1, characterized by When the polymer comprises an ester group, the polymer comprises at least one of polyethylene carbonate, polypropylene carbonate, polytrimethylene carbonate, polyvinyl carbonate, polycaprolactone, poly-beta-propiolactone, polymethyl methacrylate, polyethyl acrylate and polycyano acrylate; When the polymer comprises a cyano group, the polymer comprises polyacrylonitrile; When the polymer comprises a carbon-fluorine bond, the polymer comprises at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene.

4. The positive electrode for solid-state batteries according to claim 1, characterized by In the composite positive electrode layer, the mass ratio of the positive electrode material, the sulfide solid-state electrolyte and the conductive agent is (80%-85%):(10%-15%):(1.5%-2.5%).

5. The positive electrode for solid-state batteries according to claim 1, characterized by In the positive electrode material, the mass ratio of the positive electrode active material, the polymer and the lithium salt is (20-30):(1-8):(1-8).

6. The method for producing a positive electrode for a solid-state battery according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: (1) preparing a suspension comprising a polymer, a lithium salt, a positive electrode active material and an organic solvent, and then performing spray drying treatment to obtain positive electrode material particles; (2) mixing the positive electrode material particles, a sulfide solid-state electrolyte and a conductive agent, and performing dry ball milling treatment to obtain a composite positive electrode powder; (3) performing hot roller pressing treatment on the composite positive electrode powder to obtain a composite positive electrode film; and compounding the composite positive electrode film with a current collector to obtain a solid-state battery positive electrode.

7. The method for producing a positive electrode for a solid-state battery according to claim 6, characterized by, In the suspension, the mass concentration of the polymer is 1%-8%.

8. The method for producing a positive electrode for a solid-state battery according to claim 6, characterized by, The spray drying comprises: an inlet air pressure of 3-5 MPa, an inlet material flow rate of 20-30 mL / min, an inlet air temperature of 240-260°C, and an outlet air temperature of 110-130°C.

9. The method for producing a positive electrode for a solid-state battery according to claim 6, characterized by, The dry ball milling treatment comprises: a ball-to-material mass ratio of (1.8-2.2):1, a rotation speed of 250-350 rpm, and a ball milling time of 1-2 h.

10. The method for producing a positive electrode for a solid-state battery according to claim 6, characterized by, The hot roller pressing treatment comprises: a roller pressure of 10-200 MPa, and a roller temperature of 80-400°C.

11. A solid state battery, characterized by The solid-state battery comprises the solid-state battery positive electrode according to any one of claims 1-5.

12. An electrical device, characterized by The power-using device includes the solid-state battery as claimed in claim 11. The power-using device includes the solid-state battery as claimed in claim 11.

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