Composite positive pole piece, preparation method thereof and sulfide all-solid-state battery

Abstract

The invention provides a composite positive pole piece and a preparation method thereof and a sulfide all-solid-state battery, the composite positive pole piece comprises a current collector, a composite positive pole layer is attached to the surface of the current collector, the composite positive pole layer comprises a positive pole active material, the positive pole active material comprises a mono-polycrystal ternary compound material, the mono-polycrystal ternary compound material comprises a single crystal ternary material and a polycrystal ternary material, and the mass ratio of the single crystal ternary material to the polycrystal ternary material is 1: 3-3: 1. The composite positive pole piece provided by the invention not only can effectively inhibit the structural damage and interface side reaction of the battery in the cycle process and remarkably improve the cycle stability of the battery, but also increases the contact area of the positive active material and the electrolyte layer, improves the interface compatibility between the positive pole piece and the electrolyte layer, reduces the interface resistance, and improves the service life of the battery. And rapid transmission of lithium ions at an interface is promoted, so that the composite positive pole piece can have excellent cycling stability while the capacitance is improved.

Description

Technical Field

[0001] This application relates to the field of all-solid-state batteries, and more specifically, to a composite positive electrode sheet, its preparation method, and a sulfide all-solid-state battery. Background Technology

[0002] Solid-state batteries are currently the most promising type of power / energy storage battery due to their high energy density and safety. Solid-state batteries are currently mainly divided into three categories: oxide, sulfide, and polymer. Among them, sulfide solid-state batteries possess ultra-high ionic conductivity and excellent mechanical properties, and are considered a highly promising technology route for the commercial application of solid-state batteries. However, sulfide solid-state batteries face pressing issues in their commercialization process, including the stability of the positive and negative electrode interface with the electrolyte, the compatibility of electrolyte and electrode materials, and high cost. The stability of the sulfide electrolyte-positive electrode interface is one of the hot research topics in solid-state batteries.

[0003] High-nickel ternary material Li[Ni x Co y Mn 1-x-y O2 (x≥0.8) is the preferred cathode material for high-energy-density batteries. From a particle state perspective, it can be divided into monocrystalline and polycrystalline. Monocrystalline ternary materials are directly grown from small primary crystals, offering advantages such as structural stability and good cycle performance. Polycrystalline ternary materials are formed from the agglomeration of small monocrystalline particles into larger secondary particles, exhibiting advantages such as high specific capacity and high initial cycle efficiency. However, when using a single monocrystalline material as the cathode active material, an active material content exceeding 50% in the electrode significantly reduces the specific capacity of the solid-state battery, leading to a decrease in discharge capacity. Conversely, when using a single polycrystalline ternary material as the cathode active material, the active material content can be significantly increased, benefiting battery capacity utilization, but resulting in poorer cycle stability.

[0004] Therefore, it is necessary to develop a positive electrode to solve the problem that high-nickel ternary positive electrode materials cannot simultaneously achieve excellent capacity and cycle stability in sulfide batteries. Summary of the Invention

[0005] The main objective of this application is to provide a composite cathode electrode, its preparation method, and a sulfide all-solid-state battery, in order to solve the problem that high-nickel ternary cathode materials in existing technologies cannot simultaneously achieve excellent capacity and cycle stability in sulfide all-solid-state batteries.

[0006] According to the first aspect of this application, a composite positive electrode sheet is provided, the composite positive electrode sheet including a current collector, the surface of the current collector being coated with a composite positive electrode layer, the composite positive electrode layer including a positive electrode active material, the positive electrode active material including a monocrystalline-polycrystalline ternary composite material, wherein the monocrystalline-polycrystalline ternary composite material includes a monocrystalline ternary material and a polycrystalline ternary material, and the mass ratio of the monocrystalline ternary material to the polycrystalline ternary material is 1:3 to 3:1.

[0007] Furthermore, the chemical formula of the single-crystal ternary material is Li[Ni] x Co y Mn 1-x-y O2, where 0.8≤x≤0.95, 0.02≤y≤0.1, and x+y<1.

[0008] Furthermore, the chemical formula of the polycrystalline ternary material is Li[Ni] a Co b Mn 1-a-b O2, where 0.8≤a≤0.95, 0.02≤b≤0.1, and a+b<1.

[0009] Furthermore, the average grain size of the single-crystal ternary material is 0.5~5μm.

[0010] Furthermore, the average grain size of the polycrystalline ternary material is 5~15μm.

[0011] Furthermore, the composite cathode layer also includes a sulfide electrolyte. With the total mass of the mono-polycrystalline ternary composite material and the sulfide solid electrolyte as 100%, the mass content of the mono-polycrystalline ternary composite material is 75%~85%, and the mass content of the sulfide solid electrolyte is 15%~25%.

[0012] Furthermore, the sulfide solid electrolyte is an aluminum-modified sulfide solid electrolyte.

[0013] Furthermore, in aluminum-modified sulfide solid electrolytes, the mass content of aluminum doping is 0.5wt%~2.5wt%.

[0014] Furthermore, the preparation method of aluminum-modified sulfide solid electrolyte includes: uniformly mixing sulfide with aluminum-containing compound and calcining to obtain modified sulfide solid electrolyte.

[0015] Furthermore, the molar ratio of the aluminum-containing compound to the mass ratio of the sulfide solid electrolyte is (0.03~0.1) mol: 100g.

[0016] Furthermore, the sulfides are selected from Li6PS5Cl, Li3PS4, Li4SnS4, and Li7P3S. 11 Li 10 GeP2S12 Li7P2S8I, Li 10 SiP2S 12 At least one of them.

[0017] Furthermore, the aluminum compound is selected from at least one of Al(CH3COO)3, Al2O3, and Al(OH)3.

[0018] Furthermore, the composite positive electrode layer also includes a conductive agent and a binder.

[0019] Furthermore, the ratio of the mass of the conductive agent to the total mass of the mono-polycrystalline ternary composite material and the aluminum-modified sulfide solid electrolyte is (3~7):100.

[0020] Furthermore, the ratio of the mass of the adhesive to the total mass of the mono-polycrystalline ternary composite material and the aluminum-modified sulfide solid electrolyte is (1~5):100.

[0021] Furthermore, the conductive agent is selected from at least one of conductive graphite, conductive carbon black, conductive carbon fiber, graphene, Super P, VGCF, and carbon nanotubes.

[0022] Furthermore, the adhesive is selected from at least one of polytetrafluoroethylene, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, and polyimide.

[0023] According to a second aspect of this application, a method for preparing a composite positive electrode sheet is provided, the method comprising:

[0024] Step S1: Mix the monocrystalline ternary material with the polycrystalline ternary material to obtain a mono-polycrystalline ternary composite material;

[0025] Step S2: Disperse the mono-polycrystalline ternary composite material, optional aluminum-modified sulfide solid electrolyte, optional conductive agent and optional binder in an ester solvent to form a positive electrode slurry. Coat the positive electrode slurry on the surface of the current collector and dry it. The positive electrode slurry forms a positive electrode active material layer attached to the surface of the current collector to obtain a composite positive electrode sheet.

[0026] Furthermore, the ester solvent includes at least one of isobutyl isobutyrate, isoamyl isovalerate, petroleum ether, and N-methylpyrrolidone.

[0027] According to a third aspect of this application, a sulfide all-solid-state battery is provided, the sulfide all-solid-state battery including a positive electrode, the positive electrode being a composite positive electrode provided in the first aspect of this application, and the composite positive electrode being prepared by the method for preparing a composite positive electrode provided in the second aspect of this application.

[0028] By applying the technical solution of this application, the composite positive electrode sheet provided by this application uses a single-polycrystalline ternary composite material formed by combining single-crystal ternary materials and polycrystalline ternary materials as the positive electrode active material. It makes full use of the structural stability of single-crystal ternary materials and the excellent capacity of polycrystalline ternary materials, so that the composite positive electrode sheet can improve the capacity while also having excellent cycle stability. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0030] As described in the background section of this application, existing technologies suffer from the problem that high-nickel ternary cathode materials cannot simultaneously achieve excellent capacity and cycle stability in sulfide all-solid-state batteries. To address this issue, this application provides a composite cathode sheet, its preparation method, and a sulfide all-solid-state battery.

[0031] In a first typical embodiment of this application, a composite positive electrode sheet is provided, which includes a current collector, a composite positive electrode layer is attached to the surface of the current collector, the composite positive electrode layer includes a positive electrode active material, the positive electrode active material includes a monocrystalline-polycrystalline ternary composite material, wherein the monocrystalline-polycrystalline ternary composite material includes a monocrystalline ternary material and a polycrystalline ternary material, and the mass ratio of the monocrystalline ternary material to the polycrystalline ternary material is 1:3 to 3:1.

[0032] In this application, a mono-polycrystalline ternary composite material formed by combining monocrystalline ternary materials and polycrystalline ternary materials is used as the positive electrode active material. This material can not only effectively suppress structural damage and interfacial side reactions during battery cycling and significantly improve the cycle stability of the battery, but also increase the contact area between the positive electrode active material and the electrolyte layer, greatly improve the interfacial compatibility between the positive electrode sheet and the electrolyte layer, reduce the interfacial resistance, and promote the rapid transport of lithium ions at the interface.

[0033] In this application, the mass ratio of monocrystalline ternary material to polycrystalline ternary material in the aforementioned monocrystalline-polycrystalline ternary composite material is 1:3 to 3:1. Specifically, the mass ratio of monocrystalline ternary material to polycrystalline ternary material is any value from 1:3, 2:5, 3:7, 1:1, 7:3, 5:2, 3:2, 3:1, or any range between two. When the amount of monocrystalline ternary material in the monocrystalline-polycrystalline ternary composite material is too small, the structural stability of the monocrystalline-polycrystalline ternary composite material is poor, which is not conducive to improving the cycle stability of the all-solid-state battery; when the amount of polycrystalline ternary material in the monocrystalline-polycrystalline ternary composite material is too small, it is not conducive to improving the capacity utilization of the all-solid-state battery.

[0034] In some embodiments of this application, the chemical formula of the above-mentioned single-crystal ternary material is Li[Ni]x Co y Mn 1-x-y O2, where 0.8≤x≤0.95, 0.02≤y≤0.1, and x+y<1, is used to further improve the energy density of single-crystal ternary materials. Specifically, x is any value or a range between any two of 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, and 0.95; and y is any value or a range between any two of 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1.

[0035] In some embodiments of this application, the chemical formula of the above-mentioned polycrystalline ternary material is Li[Ni] a Co b Mn 1-a-b O2, where 0.8≤a≤0.95, 0.02≤b≤0.1, a+b<1; to further improve the energy density of polycrystalline ternary materials. Specifically, a is any value or a range between any two of 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95; b is any value or a range between any two of 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0036] In some embodiments, the grain size of the monocrystalline ternary material is 0.5~5μm, and the grain size of the polycrystalline ternary material is 5~15μm, which facilitates a tighter bond between the monocrystalline and polycrystalline ternary materials in the monocrystalline-polycrystalline composite material, thereby improving the energy density of the all-solid-state battery. Specifically, the grain size of the monocrystalline ternary material is any value or a range between 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, and 5μm; the grain size of the polycrystalline ternary material is any value or a range between 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, and 15μm.

[0037] In some embodiments, the composite positive electrode layer further includes a sulfide electrolyte. Based on the total mass of the mono- and polycrystalline ternary composite material and the sulfide solid electrolyte (100%), the mass content of the mono- and polycrystalline ternary composite material is 75%–85%, and the mass content of the sulfide solid electrolyte is 15%–25%, to further improve the interfacial compatibility between the positive electrode and the electrolyte layer and reduce the interfacial resistance. Specifically, based on the total mass of the mono- and polycrystalline ternary composite material and the sulfide solid electrolyte (100%), the mass content of the mono- and polycrystalline ternary composite material is any value from 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, and 85%, or a range between any two; the mass content of the sulfide solid electrolyte is any value from 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%, or a range between any two. The mono-polycrystalline ternary composite material formed by combining monocrystalline ternary materials and polycrystalline ternary materials fully leverages the advantages of both materials. Furthermore, by combining the mono-polycrystalline ternary composite material with aluminum-modified sulfide solid electrolyte, it is more effective in improving the energy density of the battery while reducing the interfacial resistance between the positive electrode and the electrolyte layer, thereby improving the lithium-ion transport efficiency.

[0038] In some embodiments, the sulfide solid electrolyte is an aluminum-modified sulfide solid electrolyte, which further enhances the interfacial compatibility between the positive electrode and the electrolyte layer and suppresses interfacial side reactions through the interaction between the aluminum-modified sulfide solid electrolyte and the monocrystalline-polycrystalline ternary composite material. Preferably, the aluminum doping content in the aluminum-modified sulfide solid electrolyte is 0.5wt% to 2.5wt% to further improve the compatibility between the positive electrode and the electrolyte layer. Specifically, the aluminum doping content is any value from 0.5wt%, 1wt%, 1.5wt%, 2wt%, and 2.5wt%, or any value within a range of two.

[0039] In some specific embodiments, the preparation method of aluminum-modified sulfide solid electrolyte includes: mixing sulfide with aluminum-containing compound and calcining to obtain aluminum-modified sulfide solid electrolyte, so as to further improve the structural stability of aluminum-modified sulfide.

[0040] In some specific embodiments, the sulfides mentioned above are commonly used sulfide electrolytes in the art, including but not limited to Li6PS5Cl, Li3PS4, Li4SnS4, and Li7P3S. 11 Li 10 GeP2S 12 Li7P2S8I, Li 10 SiP2S 12 Any one or more mixtures thereof;

[0041] In some specific embodiments, the molar ratio of aluminum-containing compound salt to sulfide is 0.03 to 0.1:1, in order to further improve the modification effect of aluminum-modified sulfide solid electrolyte while saving the amount of aluminum-containing compound, thereby improving the interfacial compatibility between the positive electrode and the electrolyte layer. Specifically, the molar ratio of aluminum salt to sulfide is any value from 0.03:1, 0.05:1, 0.07:1, 0.09:1, 0.1:1, or any value in between.

[0042] In some specific embodiments, in order to avoid the introduction of impurities by aluminum-containing compounds that affect the performance of aluminum-modified sulfide solid electrolytes, the aluminum-containing compounds are preferably selected from any one or any mixture of Al(CH3COO)3, Al2O3, and Al(OH)3.

[0043] In some specific embodiments, the calcination temperature is 500~700℃ and the calcination time is 3~5h to further improve the calcination efficiency.

[0044] Specifically, the calcination temperature is any value among 500℃, 550℃, 600℃, 650℃, and 700℃, or a range between any two; the calcination time is any value among 3h, 3.5h, 4h, 4.5h, and 5h, or a range between any two.

[0045] In some embodiments, the aluminum-modified sulfide solid electrolyte is prepared according to the following steps:

[0046] After the sulfide was mixed evenly with Al(CH3COO)3 ethanol solution, it was dried and calcined to obtain aluminum-modified sulfide solid electrolyte.

[0047] In some specific embodiments, the concentration of the Al(CH3COO)3 ethanol solution is preferably 0.8-1.5 mol / L to improve the preparation efficiency of the aluminum-modified sulfide solid electrolyte. Specifically, the concentration of the Al(CH3COO)3 ethanol solution is any value or a range of any two values ​​selected from 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, and 1.5 mol / L.

[0048] In some specific embodiments, the preferred molar ratio of Al(CH3COO)3 to sulfide is (0.03~0.1) mol:100g to further reduce the interfacial resistance between the positive electrode and the electrolyte layer. Specifically, the molar ratio of Al(CH3COO)3 to sulfide is 0.03 mol:100g, 0.04 mol:100g, 0.05 mol:100g, 0.08 mol:100g, 0.1 mol / 100g, or any range of two such values.

[0049] In some embodiments, the composite positive electrode layer further includes a conductive agent and a binder. Preferably, the mass ratio of the conductive agent to the total mass of the mono-polycrystalline ternary composite material and the sulfide solid electrolyte is (3~7):100, and the mass ratio of the binder to the total mass of the mono-polycrystalline ternary composite material and the sulfide solid electrolyte is (1~5):100, so as to improve the electronic conduction efficiency and structural stability of the positive electrode by reasonably adding the mass of the conductive agent and the binder.

[0050] Specifically, in the aforementioned composite positive electrode layer, the mass ratio of the conductive agent to the total mass of the mono-polycrystalline ternary composite material and the sulfide solid electrolyte is any value among 3:100, 3.5:100, 4:100, 4.5:100, 5:100, 5.5:100, 6:100, 6.5:100, and 7:100, or any value between any two; the mass ratio of the binder to the total mass of the mono-polycrystalline ternary composite material and the sulfide solid electrolyte is any value among 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, and 5:100, or any value between any two.

[0051] The aforementioned conductive agents are commonly used conductive agents in this field, including but not limited to any one or more mixtures of conductive graphite, conductive carbon black, conductive carbon fiber, graphene, Super P, VGCF, and carbon nanotubes. Super P is amorphous carbon black; VGCF is graphitized carbon fiber.

[0052] The adhesives mentioned above are commonly used adhesives in the art, including but not limited to any one or any mixture of polytetrafluoroethylene, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, and polyimide.

[0053] In a second typical embodiment of this application, a method for preparing a composite positive electrode sheet is provided, the method comprising:

[0054] Step S1: Mix the monocrystalline ternary material with the polycrystalline ternary material to obtain a mono-polycrystalline ternary composite material;

[0055] Step S2: Disperse the mono-polycrystalline ternary composite material, optional sulfide electrolyte, optional conductive agent and optional binder in an ester solvent to form a positive electrode slurry. Coat the positive electrode slurry on the surface of the current collector and dry it. The positive electrode slurry forms a positive electrode active material layer attached to the surface of the current collector to obtain a composite positive electrode sheet.

[0056] In some specific embodiments, the ester solvents mentioned above include any one or a mixture of any of isobutyl isobutyrate, isoamyl isovalerate, petroleum ether, and N-methylpyrrolidone, which further improves the dispersion stability of the positive electrode slurry.

[0057] In some embodiments, in step S1 above, single-crystal ternary materials and polycrystalline ternary materials are mixed by ball milling to form a single-polycrystalline ternary composite material.

[0058] In some specific embodiments, the ball milling speed is 250~400 r / min, and the ball milling time is 2~5 h, in order to further make the bonding between the single-crystal ternary material and the polycrystalline ternary material tighter and improve the structural stability of the single-polycrystalline ternary composite material. Specifically, the ball milling speed is any value or any two values ​​from 250 r / min, 280, 300 r / min, 320 r / min, 350 r / min, 380 r / min, and 400 r / min; the ball milling time is any value or any two values ​​from 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, and 5 h.

[0059] In a third typical embodiment of this application, a sulfide all-solid-state battery is provided, wherein the sulfide all-solid-state battery includes a positive electrode sheet, which is a composite positive electrode sheet prepared according to the second typical embodiment.

[0060] The sulfide all-solid-state battery provided in this application uses the composite positive electrode sheet provided in the first typical embodiment or the composite positive electrode sheet obtained according to the preparation method provided in the second typical embodiment as the positive electrode sheet, and uses a single-polycrystalline ternary composite material formed by combining single-crystal ternary materials and polycrystalline ternary materials as the positive electrode active material. It makes full use of the structural stability of single-crystal ternary materials and the excellent capacity of polycrystalline ternary materials, so that the sulfide solid-state battery has both excellent energy density and cycle stability.

[0061] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0062] Example 1

[0063] This embodiment provides a composite positive electrode sheet, which includes an aluminum foil and a composite positive electrode layer attached to the aluminum foil. The composite positive electrode layer is made of a mono-polycrystalline ternary composite material, an aluminum-modified sulfide solid electrolyte, a carbon nanotube conductive agent, and a polyvinylidene fluoride binder.

[0064] It is prepared according to the following steps:

[0065] (1) Preparation of single-polycrystalline ternary composite materials: 30g of single-crystal ternary material LiNi 0.85 Co0.1 Mn 0.05 O2 and 70g of polycrystalline ternary material LiNi 0.85 Co 0.1 Mn 0.05 O2 was added to a ball mill for the first ball milling and mixing to obtain a mono-polycrystalline ternary composite material. The first ball milling speed was 300 r / min, and the first ball milling time was 3 h.

[0066] (2) Preparation of aluminum-modified sulfide solid electrolyte: 100g Li6PS5Cl was added to 500mL of 0.1mol / L Al(CH3COO)3 ethanol solution and mixed. The mixture was stirred at 40℃ for 3h to obtain a mixed solution. The solution was then vacuum dried at 100℃ for 18h to obtain a dried aluminum-modified Li6PS5Cl solid electrolyte precursor. The dried aluminum-modified Li6PS5Cl solid electrolyte precursor was calcined at 600℃ for 4h to obtain modified Li6PS5Cl.

[0067] (3) Preparation of composite positive electrode sheet: 80g of mono-polycrystalline ternary composite material, 20g of aluminum modified sulfide solid electrolyte, 5g of carbon nanotube conductive agent and 3g of polyvinylidene fluoride binder are added to a ball mill, and an appropriate amount of isobutyl isobutyrate dispersant is added. The ball mill is run at 400r / min for 2h to form a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil positive electrode current collector and vacuum dried at 80℃ for 18h. Then, it is cold-pressed under a pressure of 15MPa to obtain a composite positive electrode sheet.

[0068] Example 2

[0069] The only difference between this embodiment and embodiment 1 is that the amount of single-crystal ternary material used in step (1) is adjusted to 25g and the amount of polycrystalline ternary material used to 75g.

[0070] Example 3

[0071] The only difference between this embodiment and embodiment 1 is that the amount of single-crystal ternary material used in step (1) is adjusted to 75g and the amount of polycrystalline ternary material used to 25g.

[0072] Example 4

[0073] The only difference between this embodiment and Embodiment 1 is that the single-crystal ternary material in step (1) is LiNi. 0.9 Co 0.05 Mn 0.05 O2.

[0074] Example 5

[0075] The only difference between this embodiment and Embodiment 1 is that the polycrystalline ternary material in step (1) is LiNi. 0.9 Co0.05 Mn 0.05 O2.

[0076] Example 6

[0077] The only difference between this embodiment and embodiment 1 is that the molar amount of Al(CH3COO)3 is adjusted in step (2) so that the mass ratio of the molar amount of Al(CH3COO)3 to Li6PS5Cl is 0.03mol:100g.

[0078] Example 7

[0079] The only difference between this embodiment and embodiment 1 is that the molar amount of Al(CH3COO)3 is adjusted in step (2) so that the mass ratio of the molar amount of Al(CH3COO)3 to the mass of Li6PS5Cl is 0.1mol:100g.

[0080] Example 8

[0081] The only difference between this embodiment and embodiment 1 is that in step (3), the mass of the mono-polycrystalline ternary composite material is adjusted to 75g, and the mass of the aluminum-modified Li6PS5Cl is adjusted to 25g.

[0082] Example 9

[0083] The only difference between this embodiment and embodiment 1 is that in step (3), the mass of the mono-polycrystalline ternary composite material is adjusted to 85g, and the mass of the aluminum-modified Li6PS5Cl is adjusted to 15g.

[0084] Example 10

[0085] The only difference between this embodiment and embodiment 1 is that the amount of carbon nanotube conductive agent used in step (3) is 3g.

[0086] Example 11

[0087] The only difference between this embodiment and embodiment 1 is that the amount of carbon nanotube conductive agent used in step (3) is 7g.

[0088] Example 12

[0089] The only difference between this embodiment and embodiment 1 is that the amount of polyvinylidene fluoride adhesive used in step (3) is 1g.

[0090] Example 13

[0091] The only difference between this embodiment and embodiment 1 is that the amount of polyvinylidene fluoride adhesive used in step (3) is 5g.

[0092] Example 14

[0093] The only difference between this embodiment and embodiment 1 is that in step (1), the amount of single-crystal ternary material is adjusted to 20g and the amount of polycrystalline ternary material is adjusted to 80g.

[0094] Example 15

[0095] The only difference between this embodiment and embodiment 1 is that in step (1), the amount of single-crystal ternary material is adjusted to 80g and the amount of polycrystalline ternary material is adjusted to 20g.

[0096] Example 16

[0097] The only difference between this embodiment and embodiment 1 is that in step (2), the molar amount of Al(CH3COO)3 is adjusted so that the mass ratio of the molar amount of Al(CH3COO)3 to Li6PS5Cl is 0.01mol:100g.

[0098] Example 17

[0099] The only difference between this embodiment and embodiment 1 is that in step (1), the molar amount of Al(CH3COO)3 is adjusted so that the mass ratio of the molar amount of Al(CH3COO)3 to the mass of Li6PS5Cl is 0.2mol:100g.

[0100] Example 18

[0101] The only difference between this embodiment and embodiment 1 is that in step (3), the mass of the mono-polycrystalline ternary composite material is adjusted to 70g and the mass of the aluminum-modified Li6PS5Cl is adjusted to 30g.

[0102] Example 19

[0103] The only difference between this embodiment and embodiment 1 is that in step (3), the mass of the mono-polycrystalline ternary composite material is adjusted to 90g and the mass of the aluminum-modified Li6PS5Cl is adjusted to 10g.

[0104] Comparative Example 1

[0105] The only difference between this comparative example and Example 1 is that, in step (1), no single-crystal ternary material was added; instead, a polycrystalline ternary material, LiNi, was used. 0.9 Co 0.05 Mn 0.05 O2 replaces mono- and polycrystalline ternary composite materials as positive electrode active materials.

[0106] Comparative Example 2

[0107] The only difference between this comparative example and Example 1 is that, in step (1), no polycrystalline ternary material was added; instead, a single-crystal ternary material, LiNi, was used.0.9 Co 0.05 Mn 0.05 O2 replaces mono- and polycrystalline ternary composite materials as positive electrode active materials.

[0108] Experimental Example 1

[0109] The composite positive electrode sheet provided in the examples and comparative examples, together with the sulfide solid electrolyte layer (Li6PS5Cl), the copper foil negative electrode current collector and the lithium metal negative electrode material layer, are stacked in sequence, placed in a mold, and cold-pressed under a pressure of 80MPa to obtain a solid sulfide battery with a single-polycrystalline high-nickel positive electrode composite.

[0110] The all-solid-state battery was subjected to electrochemical performance testing. The test conditions were: constant current charge-discharge, with a constant current range of 0.1C to 0.5C; test voltage range of 2.0 to 4.25V (vs. Li+ / Li); and test pressure of 30 MPa. The test results are shown in Table 1.

[0111] Table 1

[0112]

[0113] As shown in Table 1, compared with Comparative Examples 1-2, the positive electrode active materials prepared in Examples 1-19 exhibit higher specific capacitance and excellent cycle stability. A comparison between Examples 1-19 and Comparative Example 1 shows that the mono-polycrystalline ternary composite material significantly increases the contact area between the active material and the electrolyte, improves the interfacial compatibility between the positive electrode and the electrolyte, reduces interfacial resistance, and promotes rapid lithium-ion transport at the interface. A comparison between Examples 1-19 and Comparative Example 2 shows that the addition of monocrystalline ternary material incorporates the structural stability inherent in monocrystalline ternary material into the mono-polycrystalline composite ternary material, effectively suppressing structural damage and interfacial side reactions during battery cycling, and significantly improving the battery's cycle stability.

[0114] A comparison of Examples 1-3 and Examples 14-15 shows that when the mass ratio of single-crystal ternary material to polycrystalline ternary material is adjusted to 1:3 to 3:1 in Examples 1-3, the prepared positive electrode active material has high specific capacitance and excellent cycle stability.

[0115] A comparison of Examples 6-7 and Examples 16-17 shows that, in Examples 6-7, by adjusting the molar amount of Al(CH3COO)3 to keep the mass ratio of Al(CH3COO)3 to Li6PS5Cl within a suitable range, the prepared positive electrode active material has high specific capacitance and excellent cycle stability.

[0116] A comparison of Examples 8-9 with Examples 18-19 shows that the positive electrode active material prepared in Examples 8-9 by adjusting the mass of the mono-polycrystalline ternary composite material and the mass of aluminum-modified Li6PS5Cl has a higher specific capacitance and excellent cycle stability.

[0117] As can be seen from the above description, the embodiments of this application achieve the following technical effects: The composite positive electrode sheet provided by this application uses a single-polycrystalline ternary composite material formed by combining single-crystal ternary materials and polycrystalline ternary materials as the positive electrode active material. It makes full use of the structural stability of single-crystal ternary materials and the excellent capacity of polycrystalline ternary materials, combined with high-performance sulfide solid electrolyte, to effectively improve the energy density of the battery, so that the composite positive electrode sheet can improve the capacity while also having excellent cycle stability.

[0118] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite positive electrode sheet, characterized in that, The composite positive electrode includes a current collector, the surface of which is coated with a composite positive electrode layer. The composite positive electrode layer includes a positive electrode active material, which includes a monocrystalline-polycrystalline ternary composite material. The monocrystalline-polycrystalline ternary composite material includes a monocrystalline ternary material and a polycrystalline ternary material, and the mass ratio of the monocrystalline ternary material to the polycrystalline ternary material is 1:3 to 3:

1.

2. The composite positive electrode sheet according to claim 1, characterized in that, The chemical formula of the single-crystal ternary material is Li[Ni] x Co y Mn 1-x-y O2, where 0.8≤x≤0.95, 0.02≤y≤0.1, x+y<1; And / or, the chemical formula of the polycrystalline ternary material is Li[Ni] a Co b Mn 1-a-b O2, where 0.8≤a≤0.95, 0.02≤b≤0.1, and a+b<1.

3. The composite positive electrode sheet according to claim 1, characterized in that, The average grain size of the single-crystal ternary material is 0.5~5μm; And / or, the average grain size of the polycrystalline ternary material is 5~15μm.

4. The composite positive electrode sheet according to claim 1, characterized in that, The composite cathode layer also includes a sulfide electrolyte. Based on the total mass of the mono-polycrystalline ternary composite material and the sulfide solid electrolyte as 100%, the mass content of the mono-polycrystalline ternary composite material is 75%~85%, and the mass content of the sulfide solid electrolyte is 15%~25%.

5. The composite positive electrode sheet according to claim 4, characterized in that, The sulfide solid electrolyte is an aluminum-modified sulfide solid electrolyte. Preferably, the aluminum doping content in the aluminum-modified sulfide solid electrolyte is 0.5wt%~2.5wt%. Preferably, the preparation method of the aluminum-modified sulfide solid electrolyte includes: The sulfide and aluminum-containing compound were mixed evenly and calcined to obtain the modified sulfide solid electrolyte. Preferably, the molar ratio of the aluminum-containing compound to the mass ratio of the sulfide solid electrolyte is (0.03~0.1) mol: 100g; Preferably, the sulfide is selected from Li6PS5Cl, Li3PS4, Li4SnS4, and Li7P3S. 11 Li 10 GeP2S 12 Li7P2S8I, Li 10 SiP2S 12 At least one of them; Preferably, the aluminum-containing compound is selected from at least one of Al(CH3COO)3, Al2O3, and Al(OH)3; Preferably, the calcination temperature is 500~700℃.

6. The composite positive electrode sheet according to any one of claims 1 to 5, characterized in that, The composite positive electrode layer also includes a conductive agent and a binder; Preferably, the mass ratio of the conductive agent to the total mass of the mono-polycrystalline ternary composite material and the aluminum-modified sulfide solid electrolyte is (3~7):100; Preferably, the mass ratio of the adhesive to the total mass of the mono-polycrystalline ternary composite material and the aluminum-modified sulfide solid electrolyte is (1~5):

100.

7. The composite positive electrode sheet according to claim 6, characterized in that, The conductive agent is selected from at least one of conductive graphite, conductive carbon black, conductive carbon fiber, graphene, Super P, VGCF, and carbon nanotubes. And / or, the adhesive is selected from at least one of polytetrafluoroethylene, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, and polyimide.

8. The method for preparing the composite positive electrode sheet according to any one of claims 1 to 7, characterized in that, include: Step S1: Mix the single-crystal ternary material with the polycrystalline ternary material to obtain the single-polycrystalline ternary composite material; Step S2: The mono-polycrystalline ternary composite material, the optional aluminum-modified sulfide solid electrolyte, the optional conductive agent, and the optional binder are dispersed in an ester solvent to form a positive electrode slurry. The positive electrode slurry is coated on the surface of the current collector and dried. The positive electrode slurry forms the positive electrode active material layer attached to the surface of the current collector, thus obtaining the composite positive electrode sheet.

9. The preparation method according to claim 8, characterized in that, The ester solvent includes at least one of isobutyl isobutyrate, isoamyl isovalerate, petroleum ether, and N-methylpyrrolidone.

10. A sulfide all-solid-state battery, characterized in that, The sulfide all-solid-state battery includes a positive electrode sheet, which is a composite positive electrode sheet according to any one of claims 1 to 7 or a composite positive electrode sheet obtained by the preparation method according to claim 8 or 9.

Images