Multi-gradient positive electrode and preparation method thereof, and full-solid-state battery and preparation method thereof

Abstract

The application relates to a multi-gradient positive electrode and a preparation method thereof, a full-solid-state battery and a preparation method thereof. The multi-gradient positive electrode comprises a current collector, a high-electron-channel layer and a high-ion-channel layer arranged in sequence, the mass proportion of positive electrode active substances in the high-electron-channel layer and the high-ion-channel layer is the same, the mass proportion of a conductive agent in the high-electron-channel layer is higher than that in the high-ion-channel layer, and the mass proportion of a solid-state electrolyte in the high-electron-channel layer is lower than that in the high-ion-channel layer. The application keeps the mass proportion of the positive electrode active substances in the positive electrode, builds the composition gradient of the electrode by changing the content of the conductive agent and the solid-state electrolyte, realizes the optimized distribution of the electrode components, increases the contact between the solid-state electrolyte and the active material, keeps the high energy density, makes the solid battery consider the energy density and the rate performance, and improves the cycle stability and the capacity retention rate of the solid battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a multi-gradient cathode and its preparation method, and an all-solid-state battery and its preparation method. Background Technology

[0002] Solid-state lithium batteries are used in various fields, with high energy density and power density being their core performance indicators. However, the rigid solid-solid interface between the solid electrolyte and electrodes in solid-state lithium battery design limits ion diffusion efficiency. Simultaneously, during charge-discharge cycles, chemical reactions can increase the contact resistance between the current collector and electrode materials, leading to increased interfacial impedance and affecting electron transport. These factors further contribute to rapid capacity decay and poor cycle stability. However, reducing the content of active electrode materials to improve ion and electron transport rates inevitably affects the battery's energy density, while increasing the amount of active electrode materials increases plate resistance and significantly reduces capacity. Therefore, balancing high energy density, power density, and cycle life remains a significant technical challenge. Summary of the Invention

[0003] Based on this, this application provides a multi-gradient cathode and its preparation method, and an all-solid-state battery and its preparation method, to solve the above-mentioned technical problems.

[0004] The first aspect of this application provides a multi-gradient positive electrode, comprising a current collector, a high electron channel layer, and a high ion channel layer arranged sequentially, wherein the mass percentage of the positive electrode active material is the same in the high electron channel layer and the high ion channel layer.

[0005] The mass percentage of conductive agent in the high electron channel layer is higher than that in the high ion channel layer;

[0006] The mass percentage of solid electrolyte in the high electron channel layer is lower than that in the high ion channel layer.

[0007] In some implementations, the conductive agent in the high electron channel layer accounts for 2% to 5% of the mass, and the solid electrolyte accounts for 10% to 15% of the mass.

[0008] In some implementations, the conductive agent in the high ion channel layer accounts for 1% to 3% of the mass, and the solid electrolyte accounts for 14% to 20% of the mass.

[0009] In some implementations, the thickness of the high electron channel layer is 15 μm to 40 μm.

[0010] In some implementations, the thickness of the high ion channel layer is 15 μm to 40 μm.

[0011] The second aspect of this application provides a method for preparing a multi-gradient cathode as described in the first aspect above, comprising the following steps:

[0012] S1. The positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling to obtain the first mixture;

[0013] S2. The first mixture is coated on the surface of the current collector to form a high electron channel layer on the surface of the current collector;

[0014] S3. The positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling to obtain the second mixture;

[0015] S4. Coat the surface of the high electron channel layer with the second mixture to form a high ion channel layer on the surface of the high electron channel layer;

[0016] S5, roll forming process, to produce multi-gradient positive electrodes.

[0017] In some embodiments, dry spraying or electrostatic spraying is used for coating in steps S2 and S4.

[0018] In some implementations, the adhesive is polytetrafluoroethylene (PTFE).

[0019] The third aspect of this application provides an all-solid-state battery, which includes the multi-gradient cathode provided in the first aspect or the multi-gradient cathode prepared by the preparation method provided in the second aspect.

[0020] The fourth aspect of this application provides a method for preparing an all-solid-state battery as described in the third aspect above, comprising the following steps:

[0021] A solid electrolyte mixture consisting of a solid electrolyte and a binder is coated onto the surface of the high-ion channel in a multi-gradient cathode to form a solid electrolyte film on the surface of the high-ion channel.

[0022] Roll forming process is performed on multi-gradient positive electrode and solid electrolyte membrane.

[0023] In this application, the positive electrode of a solid-state battery is composed of two composite films with different composition gradients. The composition gradient between the two films is achieved by changing the ratio of conductive agent to solid electrolyte, thereby optimizing electrode performance. Specifically, a high electron channel layer is located near the current collector, while a high ion channel layer is located near the solid electrolyte. The conductive agent content in the high electron channel layer is higher than that in the high ion channel layer, creating a conductive agent composition gradient, constructing electron channels, facilitating electron transport on the current collector side, and reducing its interfacial impedance. Similarly, the solid electrolyte content in the high ion channel layer is higher than that in the high electron channel layer, creating a solid electrolyte composition gradient, constructing ion channels, and facilitating ion transport. Without changing the mass ratio of the positive electrode active material in the positive electrode sheet, the composition gradient of the electrode is constructed by varying the content of the conductive agent and solid electrolyte, achieving optimized distribution of electrode components. This not only increases the contact between the solid electrolyte and the active material but also maintains high energy density, enabling the solid-state battery to balance energy density and rate performance, and improving the cycle stability and capacity retention of the solid-state battery. Attached Figure Description

[0024] Figure 1 This is a flowchart of a method for preparing a multi-gradient cathode in one embodiment of this application. Detailed Implementation

[0025] A detailed reference is now provided to embodiments of this application, one or more of which are described below. Each embodiment is provided for explanation and not for limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0026] Therefore, this application is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of this application are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this application.

[0027] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0028] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it means that the units for the left and right endpoints are the same. For example, 100~150 nm means that the units for the left endpoint "100" and the right endpoint "150" are both nm (nanometers).

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0034] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] In the development of all-solid-state batteries, the positive and negative electrode plates adopted the design of traditional lithium-ion liquid batteries, replacing the liquid electrolyte with a solid electrolyte layer. In this structure, the electrolyte between the electrodes is actually compressed to the thickness of the solid electrolyte layer, resulting in uneven distribution of the electrolyte between the thicker electrode plates. It becomes difficult for the electrolyte to penetrate to the bottom of the electrode, thus limiting the capacity of the battery.

[0036] Traditional technologies have improved solid-state batteries by adding solid electrolytes to the electrodes to create ion channels. However, this design increases the resistance of the electrode plates when increasing the active material loading, thus significantly reducing the battery's energy storage capacity. It also affects the ratio of solid electrolyte to conductive agent, thereby impacting the overall battery performance.

[0037] Furthermore, as is well known, lithium-ion battery electrodes generally exhibit two competing charge transport processes that determine electrical performance: ion transport within the electrolyte and electron transport through the active materials and conductive agents connected together within the electrode itself. During both discharge and charge processes, the electron current density is highest at the current collector, while the ion current density is zero; at the interface of the separator, the electron current density is zero, while the ion current density is highest. Therefore, electrodes with high porosity exhibit good ion transport characteristics but poor electronic conductivity; while highly dense electrodes exhibit poor ion transport characteristics but good electronic conductivity. In traditional technologies, liquid batteries achieve a balance between rate capability and energy density through electrode construction with a porous gradient; however, in all-solid-state batteries, a solid electrolyte is generally required to fill the voids to form ion channels, thus eliminating the so-called porous gradient.

[0038] Therefore, how to provide a solid-state battery that balances energy density, rate performance, and cycle performance has become an urgent technical problem to be solved.

[0039] To address the aforementioned technical problems, the first aspect of this application provides a multi-gradient positive electrode, comprising a current collector, a high electron channel layer, and a high ion channel layer arranged sequentially, wherein the mass percentage of the positive electrode active material in the high electron channel layer and the high ion channel layer is the same; the mass percentage of the conductive agent in the high electron channel layer is higher than that in the high ion channel layer; and the mass percentage of the solid electrolyte in the high electron channel layer is lower than that in the high ion channel layer.

[0040] In some embodiments, the mass percentage of the conductive agent in the high electron channel layer is 2% to 5%, including but not limited to 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0041] In some embodiments, the mass percentage of the solid electrolyte in the high electron channel layer is 10% to 15%, including but not limited to 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 14%, and 15%.

[0042] In some embodiments, the mass percentage of the conductive agent in the high ion channel layer is 1% to 3%, including but not limited to 1%, 1.5%, 2%, 2.5%, and 3%.

[0043] In some embodiments, the mass percentage of the solid electrolyte in the high ion channel layer is 14% to 20%, including but not limited to 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, and 20%.

[0044] In some embodiments, the thickness of the high electron channel layer is 15μm to 40μm, including but not limited to 15μm, 20μm, 25μm, 30μm, 35μm, and 40μm.

[0045] In some embodiments, the thickness of the high ion channel layer is 15 μm to 40 μm, including but not limited to 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, and 40 μm.

[0046] This application, based on the distribution patterns of ion and electron current densities, adjusts the content of conductive agent and solid electrolyte in the electrode to form a multi-gradient electrode structure with electron and ion channels. By configuring the solid-state battery positive electrode as a composite of two layers with different compositional gradients, the compositional gradient between the two layers is achieved by changing the ratio of conductive agent to solid electrolyte, thus optimizing electrode performance. Specifically, the layer closer to the current collector is a high-electron-channel layer, and the layer closer to the solid electrolyte is a high-ion-channel layer. The conductive agent content in the high-electron-channel layer is higher than that in the high-ion-channel layer, forming a conductive agent compositional gradient, constructing electron channels, facilitating electron transport on the current collector side, and reducing its interfacial impedance. The solid electrolyte content in the high-ion-channel layer is higher than that in the high-electron-channel layer, forming a solid electrolyte compositional gradient, constructing ion channels, and facilitating ion transport. Without changing the mass ratio of the positive electrode active material in the positive electrode sheet, the composition gradient of the electrode is constructed by changing the content of conductive agent and solid electrolyte, thereby achieving the optimized distribution of electrode components. This not only increases the contact between the solid electrolyte and the active material, but also maintains high energy density, enabling solid batteries to balance energy density and rate performance, and improving the cycle stability and capacity retention of solid batteries.

[0047] like Figure 1 As shown, the second aspect of this application provides a method for preparing a multi-gradient cathode as described in the first aspect above, comprising the following steps:

[0048] S1. The positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling to obtain the first mixture;

[0049] S2. The first mixture is coated on the surface of the current collector to form a high electron channel layer on the surface of the current collector;

[0050] S3. The positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling to obtain the second mixture;

[0051] S4. Coat the surface of the high electron channel layer with the second mixture to form a high ion channel layer on the surface of the high electron channel layer;

[0052] S5, roll forming process, to produce multi-gradient positive electrodes.

[0053] In multi-gradient cathodes, the positive electrode active material can be any material suitable for use as a positive electrode active material in lithium-ion secondary batteries, without any restrictions on its application. For example, the positive electrode active material can include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; Li 1+x Mn 2-x Lithium manganese oxides such as O4 (x is 0~0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and LiNi 1-x M X O2 represents lithium nickel oxide (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, including at least one of the above elements, and x is 0.01~0.3); molecular formula LiMn 2-x M x O2 (where M is Co, Ni, Fe, Cr, Zn, or Ta and x is 0.01~0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn) lithium manganese composite oxide; with LiNi x Mn 2-x Spinel-type lithium-manganese composite oxides represented by O4; the Li portion in the formula LiMn2O4 is replaced by alkaline earth metal ions; LiNi x Co y Mn (1-x-y) O2 (where x=0.8, y=0.1); disulfide compounds; Fe2(MoO4)3; lithium cobalt oxide; lithium iron phosphate; elemental sulfur (S8); Li2S n(n=1), organic sulfur compounds or carbon-sulfur polymers (C2S) x ) n (x is 2.5 ~ 50, n is 2); may include sulfur-based compounds, etc.

[0054] The conductive agent in the multi-gradient cathode only needs to be conductive without causing a chemical change in the all-solid-state battery, and there are no particular limitations. This includes, but is not limited to, natural graphite, artificial graphite, and other graphites; conductive carbon black (Super-P), acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black. Conductive fibers, such as carbon fibers and metal fibers, such as VGCF (vapor-grown carbon fiber); fluorinated carbon, aluminum, nickel powder, and other metal powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; it can also include one or a mixture of two or more conductive materials selected from polyphenylene derivatives.

[0055] The binder in the multi-gradient cathode is polytetrafluoroethylene (PTFE) and related derivatives.

[0056] Solid electrolyte materials in multigradient cathodes can be halides; however, depending on the design, other known materials such as sulfide-based solid electrolyte materials, polymer-based solid electrolyte materials, and oxide-based solid electrolyte materials can be used as solid electrolyte materials.

[0057] In some embodiments, dry spraying or electrostatic spraying is used for coating in steps S2 and S4.

[0058] In some embodiments, the binder is polytetrafluoroethylene (PTFE).

[0059] In this application, the positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling, which promotes the fibrillation of polytetrafluoroethylene (PTFE) and then binds the positive electrode active material, conductive agent and solid electrolyte. No solvent is required, which is more environmentally friendly.

[0060] This application achieves a tighter bond between the current collector, the high electron channel layer, and the high ion channel layer through the rolling process in step S5; at the same time, it reduces the porosity of the high electron channel layer and the high ion channel layer.

[0061] The third aspect of this application provides an all-solid-state battery, which includes the multi-gradient cathode provided in the first aspect or the multi-gradient cathode prepared by the preparation method provided in the second aspect.

[0062] The fourth aspect of this application provides a method for preparing an all-solid-state battery as described in the third aspect above, comprising the following steps:

[0063] A solid electrolyte mixture consisting of a solid electrolyte and a binder is coated onto the surface of the high-ion channel in a multi-gradient cathode to form a solid electrolyte film on the surface of the high-ion channel.

[0064] Roll forming process is performed on multi-gradient positive electrode and solid electrolyte membrane.

[0065] In some embodiments, the preparation method of an all-solid-state battery further includes the following steps:

[0066] A fully solid-state battery is prepared by sequentially stacking a multi-gradient positive electrode, a solid electrolyte membrane, and a negative electrode sheet that have undergone roll forming, and then assembling them under pressure.

[0067] It is understood that the process for assembling the positive and negative electrode sheets and the solid electrolyte membrane is not particularly limited in this application. Any known assembly method can be used in this application without departing from the inventive concept of this application.

[0068] The present application will be further described below with reference to specific embodiments and comparative examples.

[0069] Example 1

[0070] The positive electrode active material NCM811 (LiNi) with a mass ratio of 80:5:2:13 was used. 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 are mixed by air jet milling, which promotes the fibrillation of PTFE and binds the positive electrode active material, conductive agent and solid electrolyte to obtain the first mixture.

[0071] The first mixture is applied to the surface of the current collector by dry spraying, forming a high electron channel layer on the surface of the current collector. The thickness of the high electron channel layer is 30 μm.

[0072] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 80:2:2:16 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain a second mixture.

[0073] The second mixture is applied to the surface of the high electron channel layer by dry spraying, forming a high ion channel layer on the surface of the high electron channel layer. The thickness of the high ion channel layer is 30 μm.

[0074] By reducing porosity through roll pressing, multi-gradient cathodes can be produced.

[0075] Example 2

[0076] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 80:4:2:14 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain the first mixture.

[0077] The first mixture is applied to the surface of the current collector by dry spraying, forming a high electron channel layer on the surface of the current collector. The thickness of the high electron channel layer is 30 μm.

[0078] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 80:2:2:16 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain a second mixture.

[0079] The second mixture is applied to the surface of the high electron channel layer by dry spraying, forming a high ion channel layer on the surface of the high electron channel layer. The thickness of the high ion channel layer is 30 μm.

[0080] By reducing porosity through roll pressing, multi-gradient cathodes can be produced.

[0081] Example 3

[0082] The positive electrode active material NCM811, the conductive agent Super-P, the binder PTFE, and the solid electrolyte Li3InCl6 in a mass ratio of 80:3:2:15 were mixed by an air jet mill to promote the fibrillation of PTFE and bind the positive electrode active material, the conductive agent, and the solid electrolyte, thus obtaining the first mixture.

[0083] The first mixture is applied to the surface of the current collector by dry spraying, forming a high electron channel layer on the surface of the current collector. The thickness of the high electron channel layer is 30 μm.

[0084] The positive electrode active material NCM811, the conductive agent Super-P, the binder PTFE, and the solid electrolyte Li3InCl6 in a mass ratio of 80:1:2:17 were mixed by an air jet mill to promote the fibrillation of PTFE and bind the positive electrode active material, the conductive agent, and the solid electrolyte, thus obtaining a second mixture.

[0085] The second mixture is applied to the surface of the high electron channel layer by dry spraying, forming a high ion channel layer on the surface of the high electron channel layer. The thickness of the high ion channel layer is 30 μm.

[0086] By reducing porosity through roll pressing, multi-gradient cathodes can be produced.

[0087] Example 4

[0088] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 78:5:2:15 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain the first mixture.

[0089] The first mixture is electrostatically sprayed onto the surface of the current collector to form a high electron channel layer. The thickness of the high electron channel layer is 30 μm.

[0090] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 78:2:2:18 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain a second mixture.

[0091] The second mixture is applied to the surface of the high electron channel layer by dry spraying, forming a high ion channel layer on the surface of the high electron channel layer. The thickness of the high ion channel layer is 30 μm.

[0092] By reducing porosity through roll pressing, multi-gradient cathodes can be produced.

[0093] Comparative Example 1

[0094] The positive electrode active material NCM811, the conductive agent Super-P, the binder PTFE, and the solid electrolyte Li3InCl6 in a mass ratio of 80:2:2:16 were mixed by an air jet mill to promote the fibrillation of PTFE and bind the positive electrode active material, the conductive agent, and the solid electrolyte, thus obtaining the first mixture.

[0095] The first mixture is applied to the surface of the current collector by dry spraying, and the thickness of the first coating layer is 30 μm.

[0096] The positive electrode active material NCM811, the conductive agent Super-P, the binder PTFE, and the solid electrolyte Li3InCl6 in a mass ratio of 80:5:2:13 were mixed by an air jet mill to promote the fibrillation of PTFE and bind the positive electrode active material, the conductive agent, and the solid electrolyte, thus obtaining a second mixture.

[0097] The second mixture is applied to the surface of the first coating layer by dry spraying to form a second coating layer with a thickness of 30 μm.

[0098] By reducing porosity through roll pressing, multi-gradient cathodes can be produced.

[0099] Comparative Example 2

[0100] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE, and solid electrolyte Li3InCl6 in a mass ratio of 80:5:2:13 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain a mixture. The mixture was then coated on the surface of the current collector by dry spraying and the porosity was reduced by roll pressing to obtain the positive electrode.

[0101] Comparative Example 3

[0102] The positive electrode active material NCM811, the conductive agent Super-P, the binder PTFE, and the solid electrolyte Li3InCl6 in a mass ratio of 83:2:2:13 were mixed by an air jet mill to promote the fibrillation of PTFE and bind the positive electrode active material, the conductive agent, and the solid electrolyte, thus obtaining the first mixture.

[0103] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 80:2:2:16 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain a second mixture.

[0104] The first mixture and the second mixture are sequentially coated onto the surface of the current collector by dry spraying, and the porosity is reduced by roller pressing to obtain the positive electrode.

[0105] Comparative Example 4

[0106] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 78:5:2:15 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain the first mixture.

[0107] The positive electrode active material NCM811, conductive agent Super-P, binder PTFE and solid electrolyte Li3InCl6 in a mass ratio of 81:2:2:15 were mixed by air jet milling to promote the fibrillation of PTFE and bind the positive electrode active material, conductive agent and solid electrolyte to obtain a second mixture.

[0108] The first mixture and the second mixture are sequentially coated onto the surface of the current collector by dry spraying, and the porosity is reduced by roller pressing to obtain the positive electrode.

[0109] Fabrication of all-solid-state batteries:

[0110] A solid electrolyte mixture, prepared by combining PTFE binder and Li3InCl6 in a mass ratio of 5:95, was coated onto the surface of the positive electrode prepared in the above examples and comparative examples. The porosity was reduced by roll pressing to complete the preparation of the solid electrolyte membrane. The roll-pressed positive electrode, the solid electrolyte membrane, and a lithium metal sheet were then stacked sequentially and assembled under pressure to obtain an all-solid-state battery. Its 3C discharge capacity retention and 100-cycle cycle retention were tested. The experimental parameters of the examples and comparative examples are summarized in Table 1 below:

[0111] Table 1

[0112] 100-cycle retention rate 3C discharge capacity retention rate Example 1 90% 95% Example 2 89% 94% Example 3 88% 93% Example 4 91% 94% Comparative Example 1 74% 87% Comparative Example 2 80% 91% Comparative Example 3 77% 88% Comparative Example 4 85% 90%

[0113] The technical solution adopted in this application improves the electron transport rate and ion transport rate of the all-solid-state battery, thus resulting in better rate performance. Furthermore, experimental results show that the 3C discharge capacity retention rate and 100-cycle retention rate of the battery in this embodiment are significantly improved compared to the comparative example, thereby enhancing the cycle stability and capacity retention of the solid-state battery.

[0114] In the technical solution adopted in this application, the mass ratio of the positive electrode active material in the positive electrode remains unchanged. Therefore, compared with the technical solution that achieves electrode gradient design by changing the content of active material and solid electrolyte, this application has a higher energy density.

[0115] The multi-gradient cathode provided in this application is simpler to prepare, simplifies the process, reduces manufacturing costs, and is more suitable for large-scale mass production of solid-state batteries.

[0116] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0117] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A multi-gradient positive electrode, characterized in that, It includes a current collector, a high electron channel layer, and a high ion channel layer arranged sequentially, wherein the mass ratio of the positive electrode active material in the high electron channel layer and the high ion channel layer is the same, and the types of the positive electrode active material in the high electron channel layer and the high ion channel layer are the same; The mass percentage of the conductive agent in the high electron channel layer is higher than that in the high ion channel layer. The mass percentage of solid electrolyte in the high electron channel layer is lower than the mass percentage of solid electrolyte in the high ion channel layer. The conductive agent in the high electron channel layer accounts for 2% to 5% of the mass, and the solid electrolyte accounts for 10% to 15% of the mass. The conductive agent in the high ion channel layer accounts for 1% to 3% of the mass, and the solid electrolyte accounts for 14% to 20% of the mass.

2. The multi-gradient positive electrode according to claim 1, characterized in that, The thickness of the high electron channel layer is 15μm~40μm.

3. The multi-gradient positive electrode according to claim 1, characterized in that, The thickness of the high-ion channel layer is 15μm~40μm.

4. A method for preparing a multi-gradient cathode as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. The positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling to obtain the first mixture; S2. The first mixture is coated on the surface of the current collector to form a high electron channel layer on the surface of the current collector; S3. The positive electrode active material, conductive agent, binder and solid electrolyte are mixed by air jet milling to obtain the second mixture; S4. The second mixture is coated on the surface of the high electron channel layer to form a high ion channel layer on the surface of the high electron channel layer. S5, roll forming process, to produce multi-gradient positive electrodes.

5. The preparation method according to claim 4, characterized in that, In steps S2 and S4, coating is performed using either dry spraying or electrostatic spraying.

6. The preparation method according to claim 4, characterized in that, The adhesive is polytetrafluoroethylene.

7. An all-solid-state battery, characterized in that, The all-solid-state battery includes a multi-gradient cathode as described in any one of claims 1 to 3 or a multi-gradient cathode prepared by any one of claims 4 to 6.

8. A method for preparing an all-solid-state battery as described in claim 7, characterized in that, Includes the following steps: A solid electrolyte mixture consisting of a solid electrolyte and a binder is coated onto the surface of a high-ion channel in a multi-gradient cathode to form a solid electrolyte film on the surface of the high-ion channel. The multi-gradient positive electrode and the solid electrolyte membrane are subjected to roll forming.

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