A positive electrode sheet based on a gradient structure, and a preparation method and application thereof

Abstract

The application discloses a kind of positive pole piece based on gradient structure and its preparation method and application, it is related to electrochemistry technical field, positive pole piece includes bottom layer, middle layer, surface layer;Bottom layer, middle layer, surface layer all include the positive active material prepared using different proportions of transition metal material;Transition metal material includes Ni, Co, Mn, from bottom layer to surface layer, Ni content gradually reduces, Mn, Co content gradually increases.Through design three-layer gradient positive pole structure, not only optimize the composition of positive material, improve the energy density of battery, also through reasonable configuration solid electrolyte and the proportion of conductive agent, improve the electronic and ionic conductivity of battery under high load, to enhance the cycle stability and conventional rate capability of battery, also can effectively balance multiple performance requirements of battery under high load condition, improve the comprehensive performance of solid-state battery, provide a feasible technical path for high energy density and long life solid-state lithium battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, in particular to a positive electrode sheet based on a gradient structure and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for new energy, solid-state batteries, as the next generation of battery technology, have attracted widespread attention due to their high safety, long cycle life and excellent energy density. In the field of solid-state sulfurized physical batteries, the performance of the positive electrode material has an important influence on the overall performance of the battery, especially the key parameters such as energy density, cycle life and rate performance. In order to improve the performance of the battery, researchers have adopted various optimization strategies, such as high-load positive electrode, ternary positive electrode material and gradient positive electrode material design. These technologies can effectively improve the electrical conductivity and structural stability of the electrode, especially in high-load positive electrode batteries, which can effectively improve the energy density of the battery.

[0003] Although the current technology has made some progress in improving the performance of the positive electrode, under high load conditions, the ion and electron transport paths of the battery are lengthened, resulting in a decrease in battery reaction kinetics, and the capacity and power density of the battery cannot be fully utilized. Although the structural stability and cycle life of the positive electrode are improved by adjusting the gradient structure design, the contact between the solid-state electrolyte and the positive electrode material under high load is not complete, which limits the ion conductivity of the battery. Moreover, although the use of conductive agents can improve the electronic conductivity, their uneven distribution or insufficient to meet the needs of high-load batteries, resulting in a decrease in cycle performance.

[0004] Overall, the existing technology still has some deficiencies in balancing high-load performance, cycle life and excellent electronic and ionic conductivity. SUMMARY

[0005] Based on the problem that the current positive electrode sheet still has some deficiencies in balancing high-load performance, cycle life and excellent electronic and ionic conductivity, the purpose of the present application is to provide a positive electrode sheet based on a gradient structure and a preparation method and application thereof, which can effectively balance the multiple performance requirements of the battery under high load conditions and improve the comprehensive performance of the solid-state battery, providing a feasible technical path for high-energy-density and long-life solid-state lithium batteries.

[0006] The present application is realized by the following technical solutions:

[0007] In a first aspect, the application provides a positive electrode sheet based on a gradient structure, comprising a bottom layer, an intermediate layer and a surface layer; the bottom layer, the intermediate layer and the surface layer all comprise positive electrode active materials prepared from transition metal materials in different proportions; the transition metal materials include Ni, Co and Mn, and the content of Ni gradually decreases and the contents of Mn and Co gradually increase from the bottom layer to the surface layer.

[0008] The application ensures that the energy density, structural stability and long cycle life of the battery can be considered under high load conditions by regulating the composition and structure of the materials of each layer of the positive electrode. Specifically, the first layer uses a high-nickel ternary positive electrode material to improve the energy density; the second layer, as a transition layer, gradually reduces the content of nickel and gradually increases the content of manganese, thereby improving the structural stability; the third layer uses a high-manganese material to further improve the oxidation resistance and cycle life of the battery. The proportion of solid-state electrolyte and conductive agent of each layer of material changes with the transmission distance of ions and electrons, ensuring that the ion conductivity and electronic conductivity between different layers are optimized, thereby enhancing the battery performance under high load.

[0009] The application designs a three-layer gradient positive electrode structure, not only optimizes the composition of the positive electrode material and improves the energy density of the battery, but also improves the electronic and ionic conductivity of the battery under high load by reasonably configuring the proportion of solid-state electrolyte and conductive agent, thereby enhancing the cycle stability and conventional rate performance of the battery. The three-layer gradient positive electrode structure of the application can effectively balance the multiple performance requirements of the battery under high load conditions, improve the comprehensive performance of the solid-state battery, and provide a feasible technical path for high-energy-density and long-life solid-state lithium batteries.

[0010] In a specific embodiment, the positive electrode active material of the bottom layer comprises Li(Ni 0.83 Co 0.11 Mn 0.06 )O2; the positive electrode active material of the intermediate layer comprises Li(Ni 0.6 Co 0.2 Mn 0.2 )O2; and the positive electrode active material of the surface layer comprises Li(Ni 0.33 Co 0.33 Mn 0.33 )O2.

[0011] In a specific embodiment, the raw material components for preparing the positive electrode sheet further include a solid-state electrolyte, conductive carbon black, a binder and a solvent.

[0012] In a specific embodiment, the solid-state electrolyte comprises Li6PS5Cl. Its excellent ionic conductivity and better interface stability help to reduce the interface resistance.

[0013] In a specific embodiment, the conductive carbon black includes Super P conductive carbon black. The conductive carbon black can enhance the electronic conductivity.

[0014] In a specific embodiment, the binder includes polyvinylidene fluoride. The polyvinylidene fluoride binder can ensure the stable combination of the electrode material and the conductive carbon black.

[0015] In a specific embodiment, the solvent includes N,N,N-trimethyl-2-aminoethanol. The N,N,N-trimethyl-2-aminoethanol can improve the solubility and dispersibility of the slurry, ensuring its uniformity.

[0016] In a specific embodiment, in the bottom layer, the mass ratio of positive electrode active material: solid-state electrolyte: conductive carbon black is 70:(20-24):(6-10); in the middle layer, the mass ratio of positive electrode active material: solid-state electrolyte: conductive carbon black is 70:(24-26):(4-6); and in the surface layer, the mass ratio of positive electrode active material: solid-state electrolyte: conductive carbon black is 70:(18-22):(8-12).

[0017] The positive electrode tab design of the present application adopts a gradient structure, which optimizes the ratio of positive electrode material, solid-state electrolyte and conductive carbon black layer by layer, aiming to balance the ion conductivity and electronic conductivity of the battery. Considering the characteristics of the ion and electron transmission path changing with the level, the following is further explained for this design:

[0018] Bottom layer (close to the current collector side): Since the interface between the current collector and the coating is crucial to the internal resistance and cycle performance, increasing the proportion of conductive carbon black in the bottom layer can effectively reduce the contact resistance of this interface and improve the internal resistance and cycle stability of the battery. At the same time, in order to enhance the ion conductivity of the bottom layer, the proportion of solid-state electrolyte is appropriately increased, and the design of this layer ensures good ion and electronic conductivity, especially the performance under high load and fast discharge.

[0019] Middle layer: As the distance from the current collector increases, the proportion of solid-state electrolyte is moderately increased to maintain sufficient ion conductivity to support efficient charging and discharging of the battery. In this layer, the proportion of conductive carbon black is slightly reduced to gradually transition to a structure configuration more suitable for optimizing electronic conductivity.

[0020] Surface layer (far from the current collector side) reduces the proportion of solid-state electrolyte and significantly increases the content of conductive carbon black, the main purpose is to optimize the electronic conductivity to reduce the internal resistance and improve the energy release efficiency of the battery. Under this design, the discharge performance of the battery is improved, especially at the conventional rate.

[0021] In a second aspect, the present application provides a method for preparing a positive electrode tab, comprising the following steps:

[0022] Preparation of the composite cathode material: the cathode active material, solid electrolyte and conductive carbon black are mixed in proportion, and then the binder and solvent are added to the composite cathode powder, and pre-mixed in a vacuum zirconia ball mill jar;

[0023] Layer-by-layer coating:

[0024] First layer coating: the slurry of the bottom layer cathode material is coated on the aluminum foil;

[0025] Second layer coating: the slurry of the middle layer cathode material is coated on the surface of the first layer;

[0026] Third layer coating: the slurry of the surface layer cathode material is coated on the surface of the second layer;

[0027] After each layer is coated, drying treatment is performed, and heat treatment is performed by low-temperature annealing.

[0028] In a specific embodiment, the loadings of the three layers are the same.

[0029] In a specific embodiment, the total loading of the three layers is 45 mg / cm 2 .

[0030] In a specific embodiment, the mass ratio of the composite cathode powder to the binder is 100:(1-5).

[0031] In a third aspect, the application provides a battery, which comprises the above-mentioned cathode sheet or the cathode sheet prepared by the above-mentioned preparation method.

[0032] In a specific embodiment, the preparation method of the battery comprises the following steps:

[0033] The cathode sheet is cut into a circular sheet and placed at the bottom of a mold;

[0034] The electrolyte powder or electrolyte film is uniformly laid on the cathode sheet, and the electrolyte surface is compacted;

[0035] The graphite composite negative electrode powder is uniformly spread on the surface layer of the electrolyte;

[0036] The entire battery assembly is placed under a stacking pressure of 50 MPa-80 MPa for pressing, to ensure that the layers of materials are tightly combined, thereby preparing the battery.

[0037] In a fourth aspect, the application provides an electronic device comprising the above-mentioned battery. The battery described herein comprises a high-performance lithium ion battery, which can be widely used in electric vehicles, electric tools, energy storage systems, and portable electronic devices.

[0038] Compared with the prior art, the application has the following advantages and beneficial effects:

[0039] (1) The positive electrode tab of the present application solves the problem of the difficulty of simultaneously optimizing the ion conductivity and electronic conductivity of the battery in the prior art by designing a gradient structure and adjusting the proportion of the positive electrode material, solid-state electrolyte and conductive carbon black layer by layer.

[0040] (2) The present application solves the problem of material performance degradation in traditional batteries, especially under high load conditions, by placing high-nickel content in the bottom layer to improve energy density, and increasing manganese content in the middle and surface layers to improve the oxidation resistance and stability of the battery material, thereby significantly extending the service life and cycle stability of the battery.

[0041] (3) The present application increases the amount of conductive agent in the bottom layer, enhances the contact between the coating and the current collector, thereby effectively reducing the internal resistance and improving the charge and discharge efficiency of the battery, solving the problem of high internal resistance of the battery in the prior art, which limits its performance under high load conditions.

[0042] (4) The present application optimizes the energy density, conductivity and stability of the battery through the gradient design of the bottom, middle and surface layers, and exhibits good comprehensive performance under high load and long cycle conditions, having strong market application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed in the examples, it should be understood that the following drawings only show some embodiments of the present application, therefore should not be considered as limiting the scope, for those skilled in the art, without creative labor, other related drawings can also be obtained from these drawings. In the drawings:

[0044] Figure 1 The structure of the positive electrode tab based on the gradient structure and the corresponding solid-state battery in the present application. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the following will further explain the present application with examples, the exemplary embodiments of the present application and their explanations are only used to explain the present application, and not as a limitation of the present application.

[0046] In the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present application.

[0047] Reference throughout this specification to "one embodiment", "an embodiment", "one example", or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the application. Thus, appearances of the phrases "one embodiment", "an embodiment", "one example", or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics can be combined in any suitable

[0048] "ranges" disclosed herein are defined by both a lower and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and a range of 80-110 are listed, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] If not otherwise specified, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0050] Example 1

[0051] The present embodiment provides a preparation method of a positive electrode tab based on a gradient structure and a method of preparing a battery using the positive electrode tab, and the specific steps are as follows:

[0052] S1, material selection and gradient design

[0053] The bottom layer uses a positive electrode material of high nickel content (Li(Ni 0.83 Co 0.11 Mn 0.06 )O2), aiming to improve the energy density of the battery; the middle layer uses a positive electrode material of moderate nickel content and increased manganese content ((Li(Ni 0.6 Co 0.2 Mn 0.2 )O2), to enhance the structural stability of the battery; the surface layer selects a positive electrode material of high manganese content (Li(Ni 0.33 Co 0.33 Mn 0.33 )O2), to improve the cycle life and oxidation resistance. The solid-state electrolyte selects Li6PS5Cl, which has excellent ionic conductivity and good interface stability, which helps to reduce the interface resistance. The conductive carbon black uses Super P, which can effectively enhance the electronic conductivity of the electrode. As a binder, polyvinylidene fluoride (PVDF) is used to ensure good combination of the positive electrode material and the conductive carbon black. In addition, N,N,N-trimethyl-2-aminoethanol (TNMP) is selected as a solvent to improve the solubility and dispersibility of the slurry and ensure its uniformity.

[0054] S2, gradient structure design and proportion optimization

[0055] According to the design idea of the gradient structure, the proportion of the solid-state electrolyte and the conductive carbon black in each layer of the positive electrode material is optimized according to the ion and electron conductivity requirements of the battery.

[0056] The bottom layer (close to the current collector side) is designed as positive active material: solid-state electrolyte: conductive carbon black = 70:24:6, increasing the proportion of conductive carbon black to effectively reduce the contact resistance between the current collector and the coating layer, improve the internal resistance and cycle stability, and enhance the ionic conductivity by appropriately increasing the proportion of solid-state electrolyte.

[0057] The middle layer (away from the current collector side) is designed as positive active material: solid-state electrolyte: conductive carbon black = 70:25:5, with a moderate proportion of solid-state electrolyte, aiming to balance ionic and electronic conductivity, supporting efficient charging and discharging of the battery.

[0058] The surface layer (away from the current collector side) is designed as positive active material: solid-state electrolyte: conductive carbon black = 70:20:10, reducing the proportion of solid-state electrolyte and significantly increasing the content of conductive carbon black, optimizing electronic conductivity to meet high load requirements.

[0059] S3, Preparation of composite positive electrode material

[0060] Mix the positive active material, solid-state electrolyte, and conductive carbon black according to the above design ratio. The powder is pre-mixed in a vacuum zirconium oxide ball mill tank with a ball-to-powder ratio of 10:1 and pre-mixed at 150 rpm for 1 h. Use polyvinylidene fluoride (PVDF) as the binder and TNMP as the solvent, and control the mass ratio of composite positive electrode material and polyvinylidene fluoride to be 100:3. Finally, the following three kinds of composite positive electrode powders are prepared:

[0061] Li(Ni 0.83 Co 0.11 Mn 0.06 )O2: Li6PS5Cl: Super P = 70:24:6;

[0062] Li(Ni 0.6 Co 0.2 Mn 0.2 )O2: Li6PS5Cl: Super P = 70:25:5;

[0063] Li(Ni 0.33 Co 0.33 Mn 0.33 )O2: Li6PS5Cl: Super P = 70:20:10.

[0064] S4, Layer-by-layer coating

[0065] S4-1, coat the prepared slurry containing positive material Li(Ni 0.83 Co 0.11 Mn 0.06 )O2 on aluminum foil. After completing the first layer of coating, place the electrode piece in a vacuum drying oven and set the temperature to 100°C for drying to remove the solvent.

[0066] S4-2, coating the second layer of Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 slurry, after completing the drying process, annealing.

[0067] S4-3, coating the third layer of Li(Ni 0.33 Co 0.33 Mn 0.33 )O2 slurry, also drying and annealing.

[0068] After each layer is coated, low-temperature annealing at 250° (1 hour) is used to promote the stability of the crystal structure of the positive electrode material and improve the adhesion between the layers, ensuring good interfacial bonding. By adjusting the gap between the doctor blades, the load of the three layers is controlled, and finally the positive electrode sheet with a load of 45 mg / cm 2 is obtained.

[0069] S5, assembly and pressing

[0070] The coated sheet is cut into a circular sheet with a diameter of 10 mm and placed at the bottom of a self-made mold to ensure stable positioning. 110 mg of Li6PS5Cl solid-state electrolyte powder is evenly laid, or a Li6PS5Cl electrolyte film is used to ensure the flatness and uniform distribution of the electrolyte layer. The electrolyte surface is compacted using slight pressure to ensure full contact with the positive electrode material. Then, graphite composite negative electrode powder (Gr: Li6PS5Cl = 6:4) is evenly scattered on the surface layer of the electrolyte according to the N / P ratio of 1.3. To improve the density of the electrolyte layer and ensure good contact between different layers, an axial pressure of 450 MPa is applied. Finally, the entire battery assembly is placed under a stacking pressure of 60 MPa for pressing to ensure tight bonding between the materials in each layer. As Figure 1 shown is a structure diagram of a positive electrode sheet based on a gradient structure and its corresponding solid-state battery.

[0071] After completing the battery assembly, packaging is performed, and charge-discharge cycle tests, conventional rate performance tests, and total impedance tests are conducted.

[0072] Example 2

[0073] This example provides a preparation method of a positive electrode sheet based on a gradient structure and a method of preparing a battery using the positive electrode sheet. Unlike Example 1, in this example, the proportion of the solid-state electrolyte in the bottom layer is adjusted to positive electrode active material: solid-state electrolyte: conductive carbon black = 70:22:8, and the proportions of the middle layer (positive electrode active material: solid-state electrolyte: conductive carbon black = 70:25:5) and the surface layer (positive electrode active material: solid-state electrolyte: conductive carbon black = 70:20:10) remain unchanged.

[0074] The specific steps are as follows:

[0075] S1, Material selection and gradient design

[0076] The bottom layer uses a high-nickel-content (Li(Ni 0.83 Co 0.11 Mn 0.06 )O2) cathode material to increase the energy density of the battery; the middle layer uses a cathode material with moderate nickel content and increased manganese content ((Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) to enhance the structural stability of the battery; the surface layer selects a high-manganese-content cathode material (Li(Ni 0.33 Co 0.33 Mn 0.33 )O2) to improve the cycle life and oxidation resistance. The solid-state electrolyte is selected as Li6PS5Cl, which has excellent ion conductivity and good interface stability, helping to reduce the interface resistance. Super P is used as conductive carbon black, which can effectively enhance the electronic conductivity of the electrode. As a binder, polyvinylidene fluoride (PVDF) is used to ensure good bonding of the cathode material and conductive carbon black. In addition, N,N,N-trimethyl-2-aminoethanol (TNMP) is selected as the solvent to improve the solubility and dispersibility of the slurry, ensuring its uniformity.

[0077] S2, Gradient structure design and proportion optimization

[0078] According to the design idea of the gradient structure, the proportion of solid-state electrolyte and conductive carbon black in each layer of cathode material is optimized according to the ion and electronic conductivity requirements of the battery.

[0079] The bottom layer (close to the current collector side) is designed as cathode active material: solid-state electrolyte: conductive carbon black = 70:22:8, increasing the proportion of conductive carbon black to effectively reduce the contact resistance between the current collector and the coating interface, improve the internal resistance and cycle stability, and increase the ion conductivity by appropriately increasing the proportion of solid-state electrolyte.

[0080] The middle layer (far from the current collector side) is designed as cathode active material: solid-state electrolyte: conductive carbon black = 70:25:5, with a moderate proportion of solid-state electrolyte, aiming to balance the ion and electronic conductivity, supporting efficient charging and discharging of the battery.

[0081] The surface layer (far from the current collector side) is designed as cathode active material: solid-state electrolyte: conductive carbon black = 70:20:10, reducing the proportion of solid-state electrolyte and significantly increasing the content of conductive carbon black to optimize the electronic conductivity to meet the high load demand.

[0082] S3, Preparation of composite cathode material

[0083] The positive active material, solid-state electrolyte and conductive carbon black are mixed according to the above design ratio, the powder is pre-mixed in a vacuum zirconia ball mill jar, the ball-to-powder ratio is 10:1, pre-mixed at 150 rpm for 1 h, polyvinylidene fluoride (PVDF) is used as the binder, TNMP is used as the solvent, and the mass ratio of the composite positive electrode material and polyvinylidene fluoride is controlled to be 100:3. Finally, the following three kinds of composite positive electrode powders are prepared:

[0084] Li(Ni 0.83 Co 0.11 Mn 0.06 )O2: Li6PS5Cl: Super P = 70:22:8;

[0085] Li(Ni 0.6 Co 0.2 Mn 0.2 )O2: Li6PS5Cl: Super P = 70:25:5;

[0086] Li(Ni 0.33 Co 0.33 Mn 0.33 )O2: Li6PS5Cl: Super P = 70:20:10.

[0087] S4, layer-by-layer coating

[0088] S4-1, the prepared slurry containing positive material Li(Ni 0.83 Co 0.11 Mn 0.06 )O2 is coated on the aluminum foil, after the first layer of coating is completed, the electrode piece is placed in a vacuum drying oven, and the temperature is set to 100°C for drying to remove the solvent.

[0089] S4-2, coating the second layer of Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 slurry, after drying treatment, annealing is performed.

[0090] S4-3, coating the third layer of Li(Ni 0.33 Co 0.33 Mn 0.33 )O2 slurry, and the same drying and annealing treatment is performed.

[0091] After each layer is coated, low-temperature annealing at 250° is used (1 hour) to promote the stability of the crystal structure of the positive material and improve the adhesion between the layers, ensuring good bonding between the layers. By adjusting the gap between the doctor blades, the load of the three layers is controlled, and finally the positive electrode piece with a load of 45 mg / cm 2 is obtained.

[0092] S5, assembly and pressing

[0093] The coated electrode sheet was cut into a 10mm diameter circular sheet and placed on the bottom of a self-made mold, ensuring stable positioning. 110mg of Li6PS5Cl solid electrolyte powder was evenly laid, or a Li6PS5Cl electrolyte film was used, ensuring the flatness and uniform distribution of the electrolyte layer. The electrolyte surface was compacted using slight pressure to ensure full contact with the positive electrode material. Then, graphite composite negative electrode powder (Gr: Li6PS5Cl = 6:4) was evenly scattered on the electrolyte surface layer according to the N / P ratio of 1.3. To improve the density of the electrolyte layer and ensure good contact between different layers, an axial pressure of 450MPa was applied. Finally, the entire battery assembly was placed under a stacking pressure of 60MPa for pressing, ensuring the tight bonding between the layers of materials.

[0094] After completing the battery assembly, it was packaged and subjected to charge-discharge cycle tests, conventional rate performance tests, and total impedance tests.

[0095] Example 3

[0096] This example provides a preparation method of a positive electrode sheet based on a gradient structure and a method of preparing a battery using the positive electrode sheet. Unlike Example 1, in this example: the surface layer is positive electrode active material: solid electrolyte: conductive carbon black = 70:24:6, and the bottom layer and the middle layer remain unchanged (positive electrode active material: solid electrolyte: conductive carbon black = 70:25:5 and 70:22:8, respectively).

[0097] The specific steps are as follows:

[0098] S1, material selection and gradient design

[0099] The bottom layer uses a positive electrode material with high nickel content (Li(Ni 0.83 Co 0.11 Mn 0.06 )O2) to improve the energy density of the battery; the middle layer uses a positive electrode material with moderate nickel content and increased manganese content ((Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) to enhance the structural stability of the battery; and the surface layer uses a positive electrode material with high manganese content (Li(Ni 0.33 Co 0.33 Mn 0.33)O2), improve cycle life and oxidation resistance. The solid-state electrolyte is selected as Li6PS5Cl, which has excellent ionic conductivity and good interface stability, which helps to reduce the interface resistance. The conductive carbon black uses Super P, which can effectively enhance the electronic conductivity of the electrode. As the binder, polyvinylidene fluoride (PVDF) is used to ensure good bonding of the positive electrode material and conductive carbon black. In addition, N,N,N-trimethyl-2-aminoethanol (TNMP) is selected as the solvent to improve the solubility and dispersibility of the slurry, ensuring its uniformity.

[0100] S2, gradient structure design and proportion optimization

[0101] According to the design idea of gradient structure, the proportion of solid-state electrolyte and conductive carbon black in each layer of positive electrode material is optimized according to the ion and electron conductivity requirements of the battery.

[0102] The bottom layer (close to the current collector side) is designed as positive electrode active material: solid-state electrolyte: conductive carbon black = 70:24:6, increasing the proportion of conductive carbon black to effectively reduce the contact resistance between the current collector and the coating interface, improve the internal resistance and cycle stability, and increase the ion conductivity by appropriately increasing the proportion of solid-state electrolyte.

[0103] The middle layer (away from the current collector side) is designed as positive electrode active material: solid-state electrolyte: conductive carbon black = 70:25:5, the proportion of solid-state electrolyte is moderate, aiming to balance the ion and electron conductivity, supporting the high efficiency of the battery charging and discharging.

[0104] The surface layer (away from the current collector side) is designed as positive electrode active material: solid-state electrolyte: conductive carbon black = 70:22:8, reducing the proportion of solid-state electrolyte and significantly increasing the content of conductive carbon black, optimizing the electronic conductivity to meet the high load demand.

[0105] S3, preparation of composite positive electrode material

[0106] The positive electrode active material, solid-state electrolyte and conductive carbon black are mixed according to the above design proportion, and the powder is pre-mixed in a vacuum zirconia ball mill tank, with a ball-to-powder ratio of 10:1, pre-mixed at 150 rpm for 1 h, with polyvinylidene fluoride (PVDF) as the binder and TNMP as the solvent, the mass ratio of composite positive electrode material and polyvinylidene fluoride is controlled at 100:3. Finally, the following three kinds of composite positive electrode powders are prepared:

[0107] Li(Ni 0.83 Co 0.11 Mn 0.06 )O2: Li6PS5Cl: Super P = 70:24:6;

[0108] Li(Ni 0.6 Co 0.2 Mn0.2 )O2: Li6PS5Cl: Super P = 70:25:5;

[0109] Li(Ni 0.33 Co 0.33 Mn 0.33 )O2: Li6PS5Cl: Super P = 70:22:8.

[0110] S4, Layer-by-layer coating

[0111] S4-1, The prepared slurry containing cathode material Li(Ni 0.83 Co 0.11 Mn 0.06 )O2 is coated on the aluminum foil. After completing the first layer coating, the electrode piece is placed in a vacuum drying oven, and the temperature is set to 100°C for drying to remove the solvent.

[0112] S4-2, Coating the second layer of Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 slurry, and after completing the drying process, annealing.

[0113] S4-3, Coating the third layer of Li(Ni 0.33 Co 0.33 Mn 0.33 )O2 slurry, and similarly, drying and annealing are performed.

[0114] After each layer is coated, low-temperature annealing at 250°C (1 hour) is used to promote the stability of the crystal structure of the cathode material and improve the adhesion between the layers, ensuring good interfacial bonding. By adjusting the scraper gap to control the load of the three layers, the final cathode electrode piece with a load of 45 mg / cm 2 is obtained.

[0115] S5, Assembly and pressing

[0116] The coated electrode piece is cut into a circular piece with a diameter of 10 mm and placed at the bottom of a self-made mold to ensure stable positioning. 110 mg of Li6PS5Cl solid-state electrolyte powder is evenly laid, or a Li6PS5Cl electrolyte film is used to ensure the flatness and uniform distribution of the electrolyte layer. The electrolyte surface is compacted using slight pressure to ensure full contact with the cathode material. Then, graphite composite anode powder (Gr: Li6PS5Cl = 6:4) is evenly spread on the surface of the electrolyte according to the N / P ratio of 1.3. To improve the density of the electrolyte layer and ensure good contact between different layers, an axial pressure of 450 MPa is applied. Finally, the entire battery assembly is placed under a stacking pressure of 60 MPa for pressing to ensure tight bonding between the layers of materials.

[0117] After the battery assembly is completed, encapsulation is performed, and charge-discharge cycle tests, conventional rate performance tests, and total impedance tests are performed.

[0118] Comparative Example 1

[0119] This comparative example provides a method for preparing a positive electrode tab and a method for preparing a battery using the positive electrode tab, which is different from Example 1 in that a standard positive electrode material and a ratio design are used in the comparative example, the ratio of the solid-state electrolyte in the bottom layer is positive electrode active material: solid-state electrolyte: conductive carbon black = 70:25:5, and the ratio of all layers remains consistent, and the ratio of the middle layer and the surface layer is not optimized.

[0120] The specific steps are as follows:

[0121] S1, material selection and gradient design

[0122] The bottom layer uses a positive electrode material with high nickel content (Li(Ni 0.83 Co 0.11 Mn 0.06 )O2), aiming to improve the energy density of the battery; the middle layer uses a positive electrode material with moderate nickel content and increased manganese content ((Li(Ni 0.6 Co 0.2 Mn 0.2 )O2), to enhance the structural stability of the battery; the surface layer selects a positive electrode material with high manganese content (Li(Ni 0.33 Co 0.33 Mn 0.33 )O2), to improve the cycle life and oxidation resistance. The solid-state electrolyte is selected as Li6PS5Cl, which has excellent ionic conductivity and good interface stability, which helps to reduce the interface resistance. The conductive carbon black uses Super P, which can effectively enhance the electronic conductivity of the electrode. As a binder, polyvinylidene fluoride (PVDF) is used to ensure good bonding of the positive electrode material and conductive carbon black. In addition, N,N,N-trimethyl-2-aminoethanol (TNMP) is selected as a solvent to improve the solubility and dispersibility of the slurry and ensure its uniformity.

[0123] S2, gradient structure design and ratio optimization

[0124] According to the design idea of the gradient structure, the ratio of the solid-state electrolyte and the conductive carbon black in each layer of the positive electrode material is optimized according to the ion and electron conductivity requirements of the battery.

[0125] The bottom layer (close to the current collector side) is designed as positive electrode active material: solid-state electrolyte: conductive carbon black = 70:25:5, increasing the ratio of conductive carbon black to effectively reduce the contact resistance between the current collector and the coating interface, improve the internal resistance and cycle stability, and increase the ionic conductivity by appropriately increasing the ratio of the solid-state electrolyte.

[0126] The middle layer (far from the current collector side) is designed as positive active material: solid-state electrolyte: conductive carbon black = 70:25:5, the proportion of solid-state electrolyte is moderate, aiming to balance the ion and electron conductivity, supporting the high efficiency of the battery charging and discharging.

[0127] The surface layer (far from the current collector side) is designed as positive active material: solid-state electrolyte: conductive carbon black = 70:25:5, the proportion of solid-state electrolyte is reduced, and the content of conductive carbon black is significantly increased, optimizing the electron conductivity to meet the high load demand.

[0128] S3, preparation of a composite positive electrode material

[0129] The positive active material, solid-state electrolyte and conductive carbon black are mixed according to the above design ratio, the powder is pre-mixed in a vacuum zirconium oxide ball mill tank, the ball-to-powder ratio is 10:1, pre-mixed at 150 rpm for 1 h, polyvinylidene fluoride (PVDF) is used as the binder, TNMP is used as the solvent, and the mass ratio of the composite positive electrode material and polyvinylidene fluoride is controlled to be 100:3. The following three kinds of composite positive electrode powders are finally prepared:

[0130] Li(Ni 0.83 Co 0.11 Mn 0.06 )O2: Li6PS5Cl: Super P = 70:25:5;

[0131] Li(Ni 0.6 Co 0.2 Mn 0.2 )O2: Li6PS5Cl: Super P = 70:25:5;

[0132] Li(Ni 0.33 Co 0.33 Mn 0.33 )O2: Li6PS5Cl: Super P = 70:25:5.

[0133] S4, layer-by-layer coating

[0134] S4-1, the prepared slurry containing positive electrode material Li(Ni 0.83 Co 0.11 Mn 0.06 )O2 is coated on the aluminum foil, after completing the first layer coating, the electrode piece is placed in a vacuum drying oven, and the temperature is set to 100°C for drying to remove the solvent.

[0135] S4-2, coating the second layer of Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 slurry, after completing the drying process, annealing is performed.

[0136] S4-3, coating the third layer of Li(Ni 0.33 Co 0.33 Mn 0.33 )O2 slurry, also drying and annealing treatment.

[0137] After each layer is coated, low-temperature annealing at 250° (1 hour) is used to promote the stability of the crystal structure of the positive electrode material and improve the adhesion between the layers, ensuring good interfacial bonding. By adjusting the scraper gap to control the load of the three layers, the final positive electrode sheet with a load of 45 mg / cm 2 is obtained.

[0138] S5, assembly and pressing

[0139] The coated electrode sheet is cut into a circular sheet with a diameter of 10 mm and placed at the bottom of a self-made mold to ensure stable positioning. 110 mg of Li6PS5Cl solid-state electrolyte powder is evenly laid, or a Li6PS5Cl electrolyte film is used to ensure the flatness and uniform distribution of the electrolyte layer. The electrolyte surface is compacted using slight pressure to ensure full contact with the positive electrode material. Then, graphite composite negative electrode powder (Gr: Li6PS5Cl = 6:4) is evenly spread on the surface of the electrolyte according to the N / P ratio of 1.3. To improve the density of the electrolyte layer and ensure good contact between different layers, an axial pressure of 450 MPa is applied. Finally, the entire battery assembly is placed under a stacking pressure of 60 MPa for pressing to ensure tight bonding between the materials in each layer.

[0140] After completing the battery assembly, it is packaged for charge-discharge cycle testing, conventional rate performance testing, and total impedance testing.

[0141] Comparative Example 2

[0142] This comparative example provides a method for preparing a positive electrode sheet and a method for preparing a battery using the positive electrode sheet. Unlike Example 1, the positive electrode active material of this comparative example only contains a layer of Li(Ni 0.83 Co 0.11 Mn 0.06 )O2, where the positive electrode active material: solid-state electrolyte: conductive carbon black = 70:25:5.

[0143] The specific steps are as follows:

[0144] S1, material selection

[0145] A high nickel content (Li(Ni 0.83 Co 0.11 Mn 0.06)O2) is used as the positive electrode material. Li6PS5Cl is used as the solid electrolyte. Super P is used as the conductive carbon black. Polyvinylidene fluoride (PVDF) is used as the binder, and N,N,N-trimethyl-2-aminoethanol (TNMP) is used as the solvent.

[0146] S2. Proportional design

[0147] Positive electrode active material: solid electrolyte: conductive carbon black = 70:25:5.

[0148] S3. Preparation of positive electrode materials

[0149] The positive electrode active material, solid electrolyte, and conductive carbon black were mixed according to the above-designed ratio. The powders were premixed in a vacuum zirconia ball mill with a ball-to-material ratio of 10:1. The premixing was performed at 150 rpm for 1 hour. Polyvinylidene fluoride (PVDF) was used as a binder and TNMP was used as a solvent. The mass ratio of the composite positive electrode material to polyvinylidene fluoride was controlled to be 100:3. The composite positive electrode powder was finally prepared:

[0150] Li(Ni 0.83 Co 0.11 Mn 0.06 )O2: Li6PS5Cl: Super P=70:25:5.

[0151] S4, coating

[0152] Prepared containing positive electrode material Li (Ni 0.83 Co 0.11 Mn 0.06 )O2 slurry is coated on aluminum foil. After coating, the electrode is placed in a vacuum drying oven and the temperature is set to 100℃ for drying to remove the solvent.

[0153] After coating, low-temperature annealing at 250°C (1 hour) was used to promote the stability of the crystal structure of the positive electrode material and improve the adhesion between the layers to ensure good bonding between the interlayer interfaces. The loading amount was controlled by adjusting the scraper gap, and the final loading amount was 45 mg / cm 2 The positive electrode.

[0154] S5. Assembly and pressing

[0155] The coated electrode sheet was cut into a circular sheet with a diameter of 10 mm and placed on the bottom of a self-made mold, ensuring stable positioning. 110 mg of Li6PS5Cl solid-state electrolyte powder was evenly laid, or a Li6PS5Cl electrolyte film was used, ensuring the flatness and uniform distribution of the electrolyte layer. A slight pressure was used to compact the electrolyte surface, ensuring full contact with the positive electrode material. Then, graphite composite negative electrode powder (Gr: Li6PS5Cl = 6:4) was evenly scattered on the surface layer of the electrolyte according to the N / P ratio of 1.3. To improve the density of the electrolyte layer, an axial pressure of 450 MPa was applied. Finally, the entire battery assembly was placed under a stacking pressure of 60 MPa for compression, ensuring tight bonding between the layers of materials.

[0156] After completing the battery assembly, packaging was performed, and charge-discharge cycle tests, conventional rate performance tests, and total impedance tests were conducted.

[0157] The batteries prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to electrochemical performance tests, and the test results are shown in Table 1.

[0158] Table 1: Electrochemical performance test results of Examples 1-3 and Comparative Examples 1-2

[0159]

[0160] According to the test data in the table, compared to Example 1, the proportion of the bottom layer conductive carbon black in Example 2 is higher, thereby enhancing the electron transmission between the coating and the current collector, revealing the importance of the interface between the coating and the current collector, and increasing the amount of the bottom layer conductive agent can reduce the contact resistance of the interface, improving the internal resistance and cycle performance of the battery. The established optimized gradient structure can reduce the polarization inside the positive electrode sheet and reduce the charge carrier transmission barrier in the transmission direction; compared to Example 3, the surface layer of Example 1 has reduced solid-state electrolyte and increased conductive carbon black, which is in line with the requirements of ion and electron conductivity with thickness changes, so the overall performance is improved; Comparative Example 1 is a completely homogeneous positive electrode material: solid-state electrolyte: conductive carbon black ratio, which does not change the requirements of ion and electron conductivity compared to Examples 1-3, so the performance is poor; Comparative Example 2 does not use a three-layer structure and proportion change, and the overall performance is reduced, proving that the positive electrode sheet prepared using the technical solution of the present application can effectively balance the multiple performance requirements of the battery under high load conditions, improving the comprehensive performance of the solid-state battery, and providing a feasible technical path for high-energy density and long-life solid-state lithium batteries.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part or all of the technical features; 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 present application, and they should be covered in the scope of the claims and the description of the present application.

Claims

1. A positive electrode sheet based on a gradient structure, characterized in that: The invention comprises a bottom layer, an intermediate layer and a surface layer; the bottom layer, the intermediate layer and the surface layer all comprise positive electrode active materials prepared using transition metal materials in different proportions; the transition metal materials include Ni, Co and Mn; from the bottom layer to the surface layer, the Ni content gradually decreases, and the Mn and Co contents gradually increase; In terms of mass ratio, in the bottom layer, the positive electrode active material: solid electrolyte: conductive carbon black = 70: (20-24): (6-10); in the middle layer, the positive electrode active material: solid electrolyte: conductive carbon black = 70: (25-26): (4-5); in the surface layer, the positive electrode active material: solid electrolyte: conductive carbon black = 70: (18-22): (8-12).

2. The positive electrode sheet based on a gradient structure according to claim 1, characterized in that: The positive electrode active material of the bottom layer includes Li(Ni 0.83 Co 0.11 Mn 0.06 )O2; the positive electrode active material of the intermediate layer includes Li(Ni 0.6 Co 0.2 Mn 0.2 )O2; the positive electrode active material of the surface layer includes Li(Ni 0.33 Co 0.33 Mn 0.33 )O2.

3. The positive electrode sheet based on a gradient structure according to claim 1, characterized in that: The raw material components for preparing the positive electrode plate also include solid electrolyte, conductive carbon black, binder and solvent.

4. The positive electrode sheet based on a gradient structure according to claim 3, characterized in that: The solid electrolyte includes Li6PS5Cl.

5. The positive electrode sheet based on a gradient structure according to claim 3, characterized in that: The conductive carbon black includes Super P conductive carbon black.

6. The positive electrode sheet based on a gradient structure according to claim 3, characterized in that: The binder includes polyvinylidene fluoride.

7. The positive electrode sheet based on a gradient structure according to claim 3, characterized in that: The solvent includes N,N,N-trimethyl-2-aminoethanol.

8. A method for preparing a positive electrode sheet according to any one of claims 1 to 7, characterized in that: The following steps are involved: Preparation of composite cathode material: The cathode active material, solid electrolyte and conductive carbon black are mixed in proportion, and then a binder and a solvent are added to the composite cathode powder and pre-mixed in a vacuum zirconia ball mill; Layer by layer: The first coating layer is to coat the bottom cathode material slurry on the aluminum foil; The second layer coating is to coat the slurry of the intermediate layer positive electrode material on the surface of the first layer; The third layer coating is to coat the surface cathode material slurry on the second layer surface; Each layer is dried after coating and heat treated by low temperature annealing.

9. The method for preparing a positive electrode sheet according to claim 8, characterized in that: The load capacity of the three layers is the same.

10. The method for preparing a positive electrode sheet according to claim 9, characterized in that: The total loading of the three layers is 45 mg / cm 2 .

11. The method for preparing a positive electrode sheet according to claim 8, characterized in that: The mass ratio of the composite positive electrode powder to the binder is 100:(1-5).

12. A battery, characterized in that: The battery comprises the positive electrode sheet according to any one of claims 1 to 7 or the positive electrode sheet prepared by the preparation method according to any one of claims 8 to 11.

13. A battery according to claim 12, characterized in that: The preparation method of the battery comprises the following steps: Cut the positive electrode into round pieces and place them at the bottom of the mold; Evenly spread electrolyte powder or electrolyte film on the positive electrode sheet and compact the electrolyte surface; Spreading the graphite composite negative electrode powder evenly on the surface of the electrolyte; The entire battery assembly is placed under a stacking pressure of 50MPa to 80MPa for pressing to ensure that each layer of material is tightly bonded to prepare a battery.

14. An electronic device, characterized in that: A battery comprising the battery according to claim 12 or 13.

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