Lithium-rich positive electrode sheet, method for manufacturing same, and secondary battery

Abstract

The application discloses a lithium-rich positive electrode sheet, a preparation method thereof, and a secondary battery. The lithium-rich positive electrode sheet comprises a current collector and a functional layer arranged on the current collector. The functional layer comprises a lithium-rich positive electrode material and a composite material. The composite material comprises an inorganic material and a polymer material. The lithium-rich positive electrode material and the inorganic material are connected through the polymer material. The lithium-rich positive electrode sheet provided by the application can reduce the phenomenon of powdering and falling of the lithium-rich positive electrode material.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a lithium-rich positive electrode sheet and its preparation method, and a secondary battery. Background Technology

[0002] The lithium-rich positive electrode sheet of a lithium battery is made by mixing lithium-rich positive electrode material, conductive agent and binder in a solvent, coating it on a current collector and drying it. During the drying process, due to poor adhesion, the lithium-rich positive electrode material is easy to fall off the current collector. At the same time, after the battery ages at high temperature and after long-term cycling, the lithium-rich positive electrode sheet is more likely to experience severe pulverization, which leads to poor contact between active particles in the positive electrode sheet, increases the internal resistance of the battery, and ultimately reduces the electrochemical performance of the battery.

[0003] Therefore, how to solve the problem of lithium-rich cathode material pulverization and shedding in lithium-rich cathode sheets has become a key issue. Summary of the Invention

[0004] The purpose of this application is to provide a lithium-rich positive electrode sheet, its preparation method, and a secondary battery.

[0005] To achieve the objectives of this application, the following technical solution is provided:

[0006] In a first aspect, this application provides a lithium-rich positive electrode sheet, which includes a current collector and a functional layer; the functional layer is disposed on the current collector, and the functional layer includes a lithium-rich positive electrode material and a composite material, wherein the composite material includes an inorganic material and a polymer material, and the lithium-rich positive electrode material and the inorganic material are connected through the polymer material.

[0007] This application introduces composite materials into the lithium-rich cathode sheet, using polymer materials in the composite material to connect the lithium-rich cathode material and inorganic materials. This improves the bonding force between the lithium-rich cathode material, the current collector, and the composite material, thereby preventing the lithium-rich cathode material from pulverizing and falling off during the coating, drying, and high-temperature formation of the battery, thus ensuring the electrical performance of the lithium-rich cathode sheet. At the same time, since inorganic materials have good conductivity and thermal stability, using inorganic materials to make composite materials can improve the conductivity and structural stability of the lithium-rich cathode sheet.

[0008] In one embodiment, the inorganic material is a hydrophobic material; the hydrophobic material has a porous structure, and the polymer material is contained within the pores of the hydrophobic material. By setting the hydrophobic material to a porous structure, the polymer material can be contained within the mesopores of the hydrophobic material, increasing the bonding area between the polymer material and the hydrophobic material, thereby improving the bonding strength between the hydrophobic material and the polymer material and ensuring that the composite material does not pulverize and detach. Furthermore, by allowing the polymer material to flow out from the pores of the hydrophobic material and combine with the lithium-rich cathode material, the bonding force between the polymer material and both the hydrophobic material and the lithium-rich cathode material can be enhanced, thereby further reducing the pulverization and detachment of the lithium-rich cathode material.

[0009] In one embodiment, the glass transition temperature of the polymer material is -20°C to 150°C.

[0010] In one embodiment, the mass ratio of the inorganic material to the polymer material is (80-90):(10-20). Controlling the mass ratio of the hydrophobic material to the polymer material within the above range is beneficial for balancing the electrical performance and structural stability of the lithium-rich cathode electrode.

[0011] In one embodiment, the porosity of the hydrophobic material is 60% to 90%. Controlling the porosity of the hydrophobic material within this range provides ample space for the polymer material and also ensures the structural stability of the hydrophobic material.

[0012] In one embodiment, the particle size D50 of the hydrophobic material is 50 nm to 10 μm. Controlling the particle size of the hydrophobic material within this range is beneficial for processing and ensures the lithium-ion transport rate in the lithium-rich cathode electrode.

[0013] In one embodiment, the lithium-rich cathode material includes the lithium-rich compound Li. 1+x M y O z , where M is one or more elements selected from Fe, Mn, Cu, Zn, Co, Cr, Zr, Ni, Sb, Ti, V, Mo, and Sn, and 0 < x ≤ 1, 0 < y, 0 < z < 10.

[0014] In one embodiment, the lithium-rich cathode material comprises a cathode active material and a lithium supplement agent dispersed in the cathode active material, wherein the particle size D50 of the lithium supplement agent is 0.1 μm to 15 μm. Controlling the particle size of the lithium supplement agent within the above range is beneficial for processing and ensures the lithium ion transport rate in the lithium-rich cathode sheet.

[0015] In one embodiment, the particle size D50 of the positive electrode active material is 0.5 μm to 100 μm. Controlling the particle size of the positive electrode active material within this range is beneficial for processing and ensures the lithium ion transport rate in the lithium-rich positive electrode sheet.

[0016] In one embodiment, the functional layer includes a lithium-rich cathode material layer and a composite material layer; the lithium-rich cathode material layer includes the lithium-rich cathode material, and the composite material layer includes the composite material.

[0017] In one embodiment, the lithium-rich cathode material layer is disposed between the current collector and the composite material layer. By disposing the lithium-rich cathode material layer between the current collector and the composite material layer, the exposed side of the original lithium-rich cathode material layer can be covered by the composite material, thereby protecting the opposite sides of the lithium-rich cathode material layer from both the current collector and the composite material layer, thus reducing pulverization and detachment.

[0018] In one embodiment, the composite material layer is disposed between the current collector and the lithium-rich cathode material layer. By disposing the composite material layer between the current collector and the lithium-rich cathode material layer, the strong adhesion of the composite material layer can be used to fix the lithium-rich cathode material layer onto the current collector, and the exposed side of the lithium-rich cathode material layer can also improve the lithium-ion transport efficiency.

[0019] In one embodiment, the thickness of the lithium-rich cathode material layer is 0.1 μm to 200 μm, and the thickness of the composite material layer is 0.1 μm to 100 μm.

[0020] In one embodiment, the lithium-rich cathode material and the composite material are uniformly mixed in the functional layer. Coating the lithium-rich cathode material and composite material after mixing them improves the bonding strength between them. Because, compared to the above method, all lithium-rich cathode materials can come into contact with the composite material, allowing for a tight bond between all lithium-rich cathode materials and the polymer material. This prevents the lithium-rich cathode material in the lithium-rich cathode sheet from pulverizing and detaching during electrode coating drying and high-temperature battery formation.

[0021] In one embodiment, the mass ratio of the lithium-rich cathode material to the composite material is (99.1–90):(0.9–10). Controlling the mass ratio of the lithium-rich cathode material to the composite material within the above range helps to ensure the battery energy density while suppressing the pulverization and shedding of the lithium-rich cathode material.

[0022] In one embodiment, the thickness of the lithium-rich positive electrode sheet is 0.2 μm to 300 μm. Controlling the thickness of the lithium-rich positive electrode sheet within this range helps to ensure the energy density of the battery.

[0023] Secondly, this application also provides a method for preparing a lithium-rich positive electrode sheet, comprising: mixing inorganic materials and polymer materials in a certain proportion to obtain a composite material; fabricating the composite material and the lithium-rich positive electrode material in a certain proportion on a current collector, and obtaining a lithium-rich positive electrode sheet after drying and rolling.

[0024] Thirdly, this application also provides a secondary battery, the secondary battery comprising a negative electrode, a separator, and a lithium-rich positive electrode as described in any one of the embodiments of the first aspect. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of a lithium-rich positive electrode sheet according to one embodiment;

[0027] Figure 2 This is a schematic diagram of the structure of a composite material in one embodiment;

[0028] Figure 3 This is a schematic diagram of the structure of a lithium-rich positive electrode sheet in another embodiment;

[0029] Figure 4 This is a schematic diagram of the structure of a lithium-rich positive electrode sheet in another embodiment;

[0030] Figure 5 This is a schematic diagram of the preparation process of a lithium-rich positive electrode sheet according to one embodiment;

[0031] Figure 6 This is a schematic diagram of the preparation process of a lithium-rich positive electrode sheet with a multilayer structure, according to one embodiment.

[0032] Figure 7 This is a schematic diagram of the preparation process of a lithium-rich positive electrode sheet with a multilayer structure, which is another embodiment of the invention.

[0033] Figure 8 This is a schematic diagram of the preparation process of a lithium-rich positive electrode sheet with a single functional layer, according to one embodiment. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0036] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0037] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0038] Firstly, this application provides a lithium-rich positive electrode sheet, please refer to... Figure 1 and Figure 2 The lithium-rich cathode electrode includes a current collector 10 and a functional layer 20 disposed on the current collector 10; the functional layer 20 includes a lithium-rich cathode material A and a composite material B, the composite material B includes an inorganic material B1 and a polymer material B2, and the lithium-rich cathode material A and the inorganic material B1 are connected by the polymer material B2.

[0039] Specifically, the current collector 10 of the positive electrode includes, but is not limited to, any one of copper foil or aluminum foil.

[0040] Functional layer 20 includes lithium-rich cathode material A and composite material B. Both lithium-rich cathode material A and composite material B can be granular structures. For example, lithium-rich cathode material A can be spherical, near-spherical, or other irregular shapes. Composite material B can also be spherical, near-spherical, or other irregular shapes. It can be understood that lithium-rich cathode material A is a general term for particles of the same material, and composite material B is also a general term for particles of the same material. Functional layer 20 contains countless particles of lithium-rich cathode material A and particles of composite material B.

[0041] In one embodiment, the structural formula of the lithium-rich cathode material A can be Li 2+x My O z Wherein, M is one or more elements selected from Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, and Sn, and 0 < x ≤ 1, 0 < y, 0 < z < 10, preferably 0 < y < 3, 0 < z < 5.

[0042] In another embodiment, the lithium-rich cathode material includes a cathode active material and a lithium supplement agent dispersed in the cathode active material. Optionally, the cathode active material can be a phosphate cathode active material or a ternary cathode active material. In specific embodiments, it includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The lithium supplement agent includes, but is not limited to, one or more of lithium iron phosphate, lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. It should be noted that some lithium supplement agents can be directly used as cathode active materials, such as lithium nickel oxide.

[0043] Optionally, in lithium-rich cathode materials, the ratio of cathode active material to lithium supplementer is 90-99:1-10. If the proportion of lithium supplementer is too high, it will affect the proportion of cathode active material; if the proportion of lithium supplementer is too low, the battery energy density will be low.

[0044] Composite material B can be prepared by combining inorganic material B1 and polymer material B2. Optionally, inorganic material B1 may include one or more of oxides such as titanium dioxide, silicon dioxide, and zinc dioxide, and carbon materials such as fluorinated graphene, fluorinated hard carbon, and fluorinated graphite.

[0045] Polymer material B2 may include one or more of guar gum, acrylate, polystyrene, gum arabic, polymethyl methacrylate, 2-methoxyethyl 2-acrylate, and polyethylene glycol diacrylate.

[0046] Optionally, the inorganic material B1 and polymer material B2 in composite material B can be bonded in the following ways: polymer material B2 coats the outer surface of inorganic material B1. Alternatively, inorganic material B1 can have a porous structure, and polymer material B2 can be embedded in the pores of inorganic material B1.

[0047] Optionally, during the preparation of functional layer 20, lithium-rich cathode material A and pre-prepared composite material B can be provided in advance. Then, by heating, polymer material B2 in composite material B is molten, thereby partially combining polymer material B2 with a portion of lithium-rich cathode material A. Therefore, composite material B can be tightly bonded to lithium-rich cathode material A through polymer material B2.

[0048] Optionally, the glass transition temperature of polymer material B2 is -20℃ to 150℃. It is understood that controlling the glass transition temperature of polymer material B2 within this range is to ensure that, during the preparation of the lithium-rich cathode electrode, polymer material B2 exhibits fluid dynamics at high temperatures. This fluid dynamics of polymer material B2 allows it to capture the lithium-rich cathode material A, so that after cooling and solidification, polymer material B2 can connect the lithium-rich cathode material A and the inorganic material B1. Therefore, even after cooling, polymer material B2 can still connect the lithium-rich cathode material A, preventing the lithium-rich cathode material A from pulverizing and falling off.

[0049] This application introduces composite materials into the lithium-rich cathode sheet, using polymer materials in the composite material to connect the lithium-rich cathode material and inorganic materials. This improves the bonding force between the lithium-rich cathode material and the current collector, as well as the composite materials, thereby preventing the lithium-rich cathode material from pulverizing and falling off during the coating, drying, and high-temperature formation of the battery, thus ensuring the electrical performance of the lithium-rich cathode sheet. At the same time, since inorganic materials have good conductivity and thermal stability, using inorganic materials to make composite materials can improve the conductivity and structural stability of the lithium-rich cathode sheet.

[0050] In one embodiment, the functional layer may further include a binder and a conductive agent. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. The binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0051] Optionally, during the preparation of the functional layer, the lithium-rich cathode material, binder, and conductive agent can be mixed together to obtain a slurry containing the lithium-rich cathode material. Then, the slurry of the lithium-rich cathode material and the slurry of the composite material are placed on the current collector.

[0052] In one embodiment, the mass ratio of lithium-rich cathode material, binder and conductive agent can be (75-95):(2-25):(5-25).

[0053] In one implementation method, please refer to Figure 2 Inorganic material B1 is a hydrophobic material with a porous structure, and polymer material B2 is contained in the pores of the hydrophobic material (inorganic material B1).

[0054] Specifically, the hydrophobic material can be an oxide with a porous structure, such as titanium dioxide, silicon dioxide, zinc dioxide, or carbon materials (e.g., fluorinated graphene, fluorinated hard carbon, fluorinated graphite). The polymer material B2 can flow into the porous structure of the hydrophobic material while maintaining its own fluidity, and be contained within the pores of the hydrophobic material after cooling and solidification.

[0055] Preferably, the hydrophobic material is spherical and can have an open porous structure. An open porous structure can be understood as the hydrophobic material forming pores from its outer surface. Furthermore, the pores on the hydrophobic material are uniformly distributed.

[0056] Optionally, the polymer material B2 is contained within the pores of the hydrophobic material. Furthermore, after the functional layer is prepared, at least part of the polymer material B2 in the pores extends out of the pores and connects to the lithium-rich cathode material A.

[0057] By using hydrophobic inorganic materials, the corrosion of lithium-rich cathode materials by external moisture can be reduced. Simultaneously, the porous structure of the hydrophobic material allows for the inclusion of polymer materials within its mesopores, increasing the bonding area between the polymer and hydrophobic materials and thus enhancing their bonding strength. This ensures the composite material does not pulverize or detach. Furthermore, the polymer material flows out from the pores of the hydrophobic material and bonds with the lithium-rich cathode material, further strengthening the adhesion between the polymer and both materials and further reducing the pulverization and detachment of the lithium-rich cathode material.

[0058] In one embodiment, the mass ratio of inorganic material to polymer material is (80-90):(10-20). Specifically, the mass ratio of inorganic material (hydrophobic material) to polymer material can be, but is not limited to, 80:20, 82:18, 84:16, 86:14, 88:12, or 90:10. Controlling the mass ratio of inorganic material to polymer material within the above range is beneficial for balancing the electrical performance and structural stability of the lithium-rich cathode electrode.

[0059] When the mass ratio of inorganic to polymer materials is below the above range, it indicates that the polymer content is too high. However, since polymer materials neither contribute electrons nor conduct electricity, they are not conducive to lithium-ion transport. When the mass ratio of inorganic to polymer materials is above the above range, it indicates that the polymer content is too low, resulting in a weaker adhesive effect from the polymer material and poorer structural stability of the lithium-rich cathode electrode.

[0060] In one embodiment, the porosity of the hydrophobic material is 60% to 90%. Specifically, the porosity of the hydrophobic material can be, but is not limited to, 60%, 65%, 70%, 75%, 80%, 85%, and 90%. Controlling the porosity of the hydrophobic material within the above range can provide a relatively abundant space for the polymer material and can also ensure the structural stability of the hydrophobic material.

[0061] When the porosity of the hydrophobic material is below the above range, the porosity of individual hydrophobic particles is poor, resulting in poor capacity to accommodate polymer materials. This may cause most of the polymer material to remain outside the hydrophobic material, and it will also reduce the lithium-ion transport efficiency in lithium-rich cathode materials. When the porosity of the hydrophobic material is above the above range, the hydrophobic material has abundant pores, but its structural strength is weak, making it prone to breakage after rolling.

[0062] In one embodiment, the particle size D50 of the hydrophobic material is 50 nm to 10 μm. Specifically, the particle size D50 of the hydrophobic material can be, but is not limited to, 50 nm, 60 nm, 80 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1 μm, 5 μm, and 10 μm. Controlling the particle size of the hydrophobic material within the above range is beneficial for processing and ensures the lithium ion transport rate in the lithium-rich cathode electrode.

[0063] When the particle size of the hydrophobic material is below the above range, its dispersibility is poor, easily leading to particle agglomeration, which makes it difficult to encapsulate polymer materials. When the particle size of the hydrophobic material is above the above range, the particles are too large, increasing the transport path of lithium ions in the composite material and resulting in a decrease in the lithium ion transport rate.

[0064] In one embodiment, the lithium-rich cathode material includes a cathode active material and a lithium supplement agent dispersed in the cathode active material. The particle size D50 of the cathode active material is 0.5 μm to 100 μm. Specifically, the particle size D50 of the cathode active material can be, but is not limited to, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 5 μm, 10 μm, 20 μm, 50 μm, 80 μm, and 100 μm. Controlling the particle size of the cathode active material within the above range is beneficial for processing and ensures the lithium-ion transport rate in the lithium-rich cathode sheet.

[0065] When the particle size of the positive electrode active material is below the above range, its dispersibility is poor, easily leading to particle agglomeration, which is detrimental to the mixing of the positive electrode active material with binders and conductive agents. When the particle size of the positive electrode active material is above the above range, the particles are too large, increasing the transport path of lithium ions in the positive electrode active material and resulting in a decrease in the lithium ion transport rate.

[0066] In one embodiment, the particle size D50 of the lithium replenishing agent is 0.1 μm to 15 μm. Specifically, the particle size D50 of the lithium replenishing agent can be, but is not limited to, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, and 15 μm. Controlling the particle size of the lithium replenishing agent within the above range is beneficial for processing and ensures the lithium ion transport rate in the lithium-rich positive electrode.

[0067] Adding lithium replenishing agents to the electrodes allows them to act as "sacrificial agents" during the first charge cycle, releasing as many lithium ions as possible at once to replenish the irreversible lithium ions consumed in the formation of the SEI film on the negative electrode. This maintains an abundance of lithium ions in the battery system, improving the battery's initial efficiency and overall electrochemical performance.

[0068] When the particle size of the lithium replenisher is below the above range, its dispersibility is poor, easily causing particle agglomeration, which is not conducive to mixing the lithium replenisher with the positive electrode active material. When the particle size of the lithium replenisher is above the above range, the particles are too large, increasing the transport path of lithium ions in the lithium replenisher and leading to a decrease in the lithium ion transport rate.

[0069] In one implementation method, please refer to Figure 3 and Figure 4 The functional layer 20 can be a multi-layer structure. The functional layer 20 includes a lithium-rich cathode material layer 21 and a composite material layer 22; the lithium-rich cathode material layer 21 includes lithium-rich cathode material A, and the composite material layer 22 includes composite material B.

[0070] For example, functional layer 20 may include at least one lithium-rich cathode material layer 21 and at least one composite material layer 22. Lithium-rich cathode material layer 21 includes lithium-rich cathode material A and may not include composite material B. Composite material layer 22 includes composite material B and may not include lithium-rich cathode material A.

[0071] In one implementation method, please refer to Figure 3 The lithium-rich cathode material layer 21 and the composite material layer 22 can both be a single layer, and the lithium-rich cathode material layer 21 is disposed between the current collector 10 and the composite material layer 22.

[0072] Specifically, during the preparation of functional layer 20, a slurry of lithium-rich cathode material A can be pre-placed on current collector 10. After the slurry dries, a lithium-rich cathode material layer 21 is formed. Then, a slurry of composite material B is placed on the lithium-rich cathode material layer 21. Therefore, the lithium-rich cathode material layer 21 and the composite material layer 22 are connected by the polymer material in composite material B.

[0073] By placing the lithium-rich cathode material layer 21 between the current collector 10 and the composite material layer 22, the composite material B can cover the exposed side of the lithium-rich cathode material layer 21, thereby protecting the opposite sides of the lithium-rich cathode material layer 21 from the current collector 10 and the composite material layer 22, thus reducing pulverization and shedding.

[0074] In one implementation method, please refer to Figure 4 Both the lithium-rich cathode material layer 21 and the composite material layer 22 can be a single layer, with the composite material layer 22 disposed between the current collector 10 and the lithium-rich cathode material layer 21.

[0075] Specifically, during the preparation of functional layer 20, a slurry of composite material B can be pre-placed on current collector 10. After the slurry dries, composite material layer 22 is formed, and then a slurry of lithium-rich cathode material A is placed on composite material layer 22. Therefore, lithium-rich cathode material layer 21 and composite material layer 22 are connected by the polymer material in composite material B.

[0076] By placing the composite material layer 22 between the current collector 10 and the lithium-rich cathode material layer 21, the strong adhesion of the composite material layer 22 can be used to fix the lithium-rich cathode material layer 21 onto the current collector 10, and the lithium-rich cathode material layer 21 can also improve the lithium-ion transport efficiency by exposing one side.

[0077] In other embodiments, the lithium-rich cathode material layer 21 and / or composite material layer 22 may be multilayered (not shown in the figure).

[0078] For example, the composite material layer 22 can be two layers, and the lithium-rich cathode material layer 21 is one layer. Specifically, the composite material layer 22 is directly disposed on the current collector 10, and the lithium-rich cathode material layer 21 is directly disposed on the composite material layer 22. Furthermore, another composite material layer 22 is disposed on the side of the lithium-rich cathode material layer 21 facing away from the current collector 10 (i.e., the lithium-rich cathode material layer 21 is disposed between the two composite material layers 22).

[0079] Alternatively, the composite material layer 22 can be a single layer, and the lithium-rich cathode material layer 21 can be two layers, that is, the composite material layer 22 is disposed between the two lithium-rich cathode material layers 21.

[0080] Optionally, both the composite material layer 22 and the positive electrode active layer can be multi-layered (two or more layers), and the composite material layer 22 and the lithium-rich positive electrode material layer 21 can be staggered.

[0081] In one embodiment, the thickness of the lithium-rich cathode material layer is 0.1 μm to 200 μm, and the thickness of the composite material layer is 0.1 μm to 100 μm. Specifically, the thickness of the lithium-rich cathode material layer can be, but is not limited to, 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 150 μm, or 200 μm. The thickness of the composite material layer can be, but is not limited to, 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or 100 μm. Controlling the thickness of the lithium-rich cathode material layer and the composite material layer within the above ranges not only helps control the overall thickness of the lithium-rich cathode sheet but also helps control the overall mass ratio of the composite material in the lithium-rich cathode sheet.

[0082] When the thickness of the lithium-rich cathode material layer is less than the above range, the overall mass ratio of the lithium-rich cathode material decreases, resulting in insufficient performance of the lithium-rich cathode sheet. When the thickness of the lithium-rich cathode material layer is greater than the above range, the lithium-rich cathode sheet becomes too thick. When the thickness of the composite material layer is less than the above range, the mass ratio of the composite material is too low, failing to effectively bond and fix the lithium-rich cathode material. When the thickness of the composite material layer is greater than the above range, the mass ratio of the composite material is too high, and since the composite material does not contribute lithium ions, the performance of the lithium-rich cathode sheet deteriorates.

[0083] In one embodiment, the lithium-rich cathode material and the composite material are uniformly mixed in the functional layer, that is, the mass ratio of the lithium-rich cathode material and the composite material in any unit volume of the functional layer is a constant value.

[0084] Specifically, the functional layer can be a single layer with various materials uniformly distributed within it. To clarify, the uniform distribution of various materials within the functional layer means that during the material preparation process, various materials (including lithium-rich cathode materials and composite materials) are mixed together to form a uniform slurry, which is then applied to the current collector via coating. The functional layer is a single-layer structure.

[0085] By coating the lithium-rich cathode material and the composite material together, the bonding strength between them can be improved. This is because, compared to the methods described above, all the lithium-rich cathode material can come into contact with the composite material, allowing for a tight bond between the lithium-rich cathode material and the polymer material. This prevents the lithium-rich cathode material from pulverizing and detaching during the electrode coating drying and high-temperature battery formation processes.

[0086] In one embodiment, the mass ratio of lithium-rich cathode material to composite material is (99.1–90):(0.9–10). Specifically, the mass ratio of lithium-rich cathode material to composite material can be, but is not limited to, 90:10, 92:8, 94:6, 96:4, 98:2, 99:1, or 99.1:0.9. Controlling the mass ratio of lithium-rich cathode material to composite material within the above range is beneficial for ensuring battery energy density while suppressing the pulverization and shedding of lithium-rich cathode material.

[0087] When the mass ratio of lithium-rich cathode material to composite material is lower than the above range, it indicates that the proportion of composite material is too high. Since composite material does not contribute lithium ions, this will lead to a lower energy density of the battery. When the mass ratio of lithium-rich cathode material to composite material is higher than the above range, it indicates that the proportion of composite material is too low, resulting in a weaker effect of using composite material to suppress the pulverization and shedding of lithium-rich cathode material.

[0088] In one embodiment, the thickness of the lithium-rich positive electrode sheet is 0.2 μm to 300 μm. Specifically, the thickness of the lithium-rich positive electrode sheet can be, but is not limited to, 0.2 μm, 1 μm, 5 μm, 7 μm, 8 μm, 10 μm, 20 μm, 40 μm, 50 μm, 100 μm, 150 μm, 200 μm, and 300 μm. Controlling the thickness of the lithium-rich positive electrode sheet within the above range is beneficial for ensuring the energy density of the battery.

[0089] When the thickness of the lithium-rich cathode sheet is less than the above range, the content of lithium-rich cathode material in the lithium-rich cathode sheet is relatively low, resulting in a lower energy density of the battery. When the thickness of the lithium-rich cathode sheet is greater than the above range, it will affect the lithium-ion transport rate in the battery.

[0090] Secondly, this application also provides a method for preparing a lithium-rich positive electrode sheet, please refer to [reference needed]. Figure 5 Specifically, it is used in the preparation of the lithium-rich positive electrode sheet in the first aspect. Its preparation method includes the following steps:

[0091] Step S10: Mix the inorganic material and the polymer material in a certain proportion to obtain the composite material.

[0092] Step S20: The composite material and lithium-rich cathode material are fabricated on the current collector in proportion, and after drying and rolling, a lithium-rich cathode sheet is obtained.

[0093] Specifically, in step S10, inorganic and polymer materials can be mixed according to a mass ratio, then placed in a vacuum chamber and heated in a vacuum environment. This allows the polymer material to be bonded and fixed with the inorganic material, thereby obtaining a composite material.

[0094] Optionally, inorganic and polymeric materials can be used in accordance with the above embodiments, and will not be described in detail here. Preferably, the inorganic material is a hydrophobic material and has a porous structure.

[0095] Optionally, the heating temperature is 10℃~155℃, and the heating time is 1h~20h.

[0096] In step S20, the provided lithium-rich cathode material can be pre-mixed with a binder and a conductive agent. Specifically, the lithium-rich cathode material, binder, conductive agent, and solvent are ball-milled and mixed in a specific mass ratio to obtain a cathode slurry.

[0097] Optionally, the lithium-rich cathode material, binder, and conductive agent can be used in accordance with the above embodiments, and will not be described in detail here.

[0098] Optionally, the solvent includes one or more of methylpyrrolidone, ethanol, ethylene carbonate, dimethyl sulfoxide, or dimethylformamide.

[0099] In one embodiment, the composite material and the lithium-rich cathode material in step S20 can be fabricated separately on the current collector, and the lithium-rich cathode material layer and the composite material layer together constitute the functional layer. Please refer to [reference needed]. Figure 6 The specific steps are as follows:

[0100] Step S10: Mix the inorganic material and the polymer material in a certain proportion to obtain the composite material.

[0101] Step S21: Mix lithium-rich cathode material, binder, conductive carbon and solvent in a mass ratio to obtain cathode slurry, coat the cathode slurry onto the current collector, and obtain lithium-rich cathode material layer after drying and rolling.

[0102] Step S22: The composite material, binder, conductive carbon and solvent are mixed in a mass ratio to obtain a composite material slurry. The composite material slurry is coated on the lithium-rich cathode material layer, and after drying and cold pressing, the composite material slurry forms a composite material layer, thereby obtaining a lithium-rich cathode sheet.

[0103] Optionally, in step S21, the drying temperature of the positive electrode slurry is 110℃~130℃.

[0104] In other embodiments, the composite material and lithium-rich cathode material in step S20 can be fabricated separately on the current collector, and the lithium-rich cathode material layer and the composite material layer together constitute the functional layer. Please refer to [reference needed]. Figure 7 The specific steps are as follows:

[0105] Step S10: Mix the inorganic material and the polymer material in a certain proportion to obtain the composite material.

[0106] Step S21': The composite material, binder, conductive carbon and solvent are mixed in a mass ratio to obtain a composite material slurry. The composite material slurry is coated on the current collector and then dried and rolled to obtain a lithium-rich cathode material layer.

[0107] In step S22', lithium-rich cathode material, binder, conductive carbon and solvent are mixed in a mass ratio to obtain cathode slurry. The cathode slurry is coated on the composite material slurry and then dried and cold-pressed to form a lithium-rich cathode material layer, thereby obtaining a lithium-rich cathode sheet.

[0108] Optionally, in step S21', the drying temperature of the composite slurry is 110℃~130℃.

[0109] In other embodiments, the composite material and lithium-rich cathode material in step S20 can be mixed and then fabricated together on the current collector. Please refer to [reference needed]. Figure 8 The specific steps are as follows:

[0110] Step S10: Mix the inorganic material and the polymer material in a certain proportion to obtain the composite material.

[0111] In step S20', lithium-rich cathode material, composite material, binder, conductive carbon, and solvent are mixed in a mass ratio to obtain a mixed slurry. The mixed slurry is coated on the current collector and then dried and rolled to obtain a functional layer.

[0112] Optionally, in step S20', the drying temperature of the mixed slurry is 110℃~130℃.

[0113] Based on the above embodiments, the viscosity of the cathode slurry, composite material slurry, and mixed slurry can be between 1500 cps and 9500 cps. If the viscosity is too low, the adhesion is weak, and the lithium-rich cathode material is easy to fall off; if the viscosity is too high, the dispersibility of the lithium-rich cathode material is poor.

[0114] The lithium-rich cathode electrode prepared by the preparation method provided in this application can prevent the lithium-rich cathode material from pulverizing and falling off during the coating, drying and high-temperature formation of the battery, thereby ensuring the electrical performance of the lithium-rich cathode electrode; at the same time, it can also prevent external moisture from corroding the lithium-rich cathode material.

[0115] Thirdly, this application also provides a secondary battery, which includes a negative electrode, a separator, and the aforementioned lithium-rich positive electrode.

[0116] The technical solution of the present invention will be described in detail below through specific embodiments.

[0117] Example 1

[0118] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a uniformly mixed lithium-rich positive electrode material Li2NiO2 and a composite material. The composite material includes a hydrophobic material silicon dioxide and a polymer material guar gum.

[0119] The silica has a porous structure, and guar gum is located within the pores of the silica. The glass transition temperature of guar gum is 100℃. The mass ratio of guar gum to silica is 10:90. The porosity of the silica is 60%, and the particle size is 1.4 μm.

[0120] 1) Preparation of composite material: The porous silica and guar gum polymer were mixed at a mass ratio of 99:1 and placed in a vacuum drying oven. The mixture was then evacuated, heated to 120°C, and treated for 5 hours to introduce guar gum into the porous structure of the hydrophobic material, thus preparing the composite material.

[0121] 2) Preparation of lithium-rich positive electrode sheet: Li2NiO2, a lithium-rich positive electrode material, and a composite material are mixed at a mass ratio of 99:1 to obtain a mixture. The mixture, polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent are then ball-milled and stirred at a mass ratio of 93:3:2:100 to obtain a mixed slurry. The mixed slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and then rolled to obtain a lithium-rich positive electrode sheet.

[0122] Example 2

[0123] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a uniformly mixed lithium-rich positive electrode material Li2NiO2 and a composite material. The composite material includes a hydrophobic material zinc dioxide and a polymer material acrylate.

[0124] The zinc dioxide has a porous structure, and the acrylate is located within the porous structure of the zinc dioxide. The glass transition temperature of the acrylate is 120℃. The mass ratio of acrylate to zinc dioxide is 15:85, the porosity of the zinc dioxide is 75%, and the particle size is 1.5 μm.

[0125] 1) Preparation of composite material: The porous zinc dioxide and acrylate polymer were mixed at a mass ratio of 85:15, placed in a vacuum drying oven, vacuumed, heated to 140℃, and treated for 8 hours to introduce acrylate into the porous structure of the hydrophobic material and prepare the composite material.

[0126] 2) Preparation of lithium-rich positive electrode sheet: Li2NiO2, a lithium-rich positive electrode material, and a composite material are mixed at a mass ratio of 96:4 to obtain a mixture. The mixture, polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent are then ball-milled and stirred at a mass ratio of 93:3:2:100 to obtain a mixed slurry. The mixed slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and then rolled to obtain a lithium-rich positive electrode sheet.

[0127] Example 3

[0128] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a uniformly mixed lithium-rich positive electrode material Li2NiO2 and a composite material. The composite material includes a hydrophobic material fluorinated hard carbon and a polymer material polystyrene.

[0129] The fluorinated hard carbon has a porous structure, and polystyrene is located within the pores of the fluorinated hard carbon. The glass transition temperature of polystyrene is 100℃. The mass ratio of polystyrene to fluorinated hard carbon is 20:80. The porosity of the fluorinated hard carbon is 90%, and the particle size is 1.4 μm.

[0130] 1) Preparation of composite material: Fluorinated hard carbon with porous structure and polystyrene polymer are mixed at a mass ratio of 80:20, placed in a vacuum drying oven, vacuumed, heated to 140℃, and treated for 8 hours to introduce acrylate into the porous structure of the hydrophobic material to prepare composite material.

[0131] 2) Preparation of lithium-rich positive electrode sheet: Li2NiO2, a lithium-rich positive electrode material, and a composite material are mixed at a mass ratio of 80:20 to obtain a mixture. The mixture, polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent are ball-milled and stirred at a mass ratio of 93:3:2:100 to obtain a mixed slurry. The mixed slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and rolled to obtain a lithium-rich positive electrode sheet.

[0132] Example 4

[0133] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a uniformly mixed lithium-rich positive electrode material Li2NiO2 and a composite material. The composite material includes a hydrophobic material silicon dioxide and a polymer material guar gum.

[0134] In this material, silica lacks a porous structure, and guar gum is dispersed within the silica. Guar gum has a glass transition temperature of 100°C. The mass ratio of guar gum to silica is 1:99, and the silica particle size is 1.4 μm.

[0135] 1) Preparation of composite material: Silica without porous structure and guar gum polymer are treated at 120℃ for 5 hours in a mass ratio of 99:10 to obtain composite material.

[0136] 2) Preparation of lithium-rich positive electrode sheet: Li2NiO2, a lithium-rich positive electrode material, and a composite material are mixed at a mass ratio of 99:1 to obtain a mixture. The mixture, polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent are then ball-milled and stirred at a mass ratio of 93:3:2:100 to obtain a mixed slurry. The mixed slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and then rolled to obtain a lithium-rich positive electrode sheet.

[0137] Example 5

[0138] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a lithium-rich positive electrode material Li2NiO2 layer and a composite material layer. The lithium-rich positive electrode material layer is disposed between the current collector and the composite material layer. The composite material includes a hydrophobic material zinc dioxide and a polymer material acrylate.

[0139] The zinc dioxide has a porous structure, and the acrylate is located within the porous structure of the zinc dioxide. The glass transition temperature of the acrylate is 120℃. The mass ratio of acrylate to zinc dioxide is 15:85, the porosity of the zinc dioxide is 75%, and the particle size is 1.5 μm.

[0140] 1) Preparation of composite material: The porous zinc dioxide and acrylate polymer were mixed at a mass ratio of 20:80, placed in a vacuum drying oven, vacuumed, heated to 140℃, and treated for 8 hours to introduce acrylate into the porous structure of the hydrophobic material and prepare the composite material.

[0141] 2) Preparation of lithium-rich positive electrode sheet: Li₂NiO₂, a lithium-rich positive electrode material, is ball-milled and mixed with polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent at a mass ratio of 93:3:2:100 to obtain a slurry. The slurry is coated onto the surface of aluminum foil, vacuum-dried overnight at 110°C, and then rolled to obtain a lithium-rich positive electrode sheet. Alternatively, a composite material slurry is ball-milled and mixed with polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent at a mass ratio of 93:3:2:100 to obtain a composite material slurry. 4% of the composite material slurry relative to the mass fraction of the lithium-rich positive electrode material is coated onto the surface of the lithium-rich positive electrode sheet, vacuum-dried overnight at 110°C, and then rolled to obtain the lithium-rich positive electrode sheet.

[0142] Example 6

[0143] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a lithium-rich positive electrode material Li2NiO2 layer and a composite material layer. The composite material layer is disposed between the current collector and the lithium-rich positive electrode material layer. The composite material includes a hydrophobic material zinc dioxide and a polymer material acrylate.

[0144] The zinc dioxide has a porous structure, and the acrylate is located within the porous structure of the zinc dioxide. The glass transition temperature of the acrylate is 120℃. The mass ratio of acrylate to zinc dioxide is 15:85, the porosity of the zinc dioxide is 75%, and the particle size is 1.5 μm.

[0145] 1) Preparation of composite material: The porous zinc dioxide and acrylate polymer were mixed at a mass ratio of 20:80, placed in a vacuum drying oven, vacuumed, heated to 140℃, and treated for 8 hours to introduce acrylate into the porous structure of the hydrophobic material and prepare the composite material.

[0146] 2) Preparation of lithium-rich positive electrode sheet: The composite material is ball-milled and mixed with polyvinylidene chloride binder, SP conductive carbon and N-methylpyrrolidone solvent at a mass ratio of 93:3:2:100 to obtain a composite material slurry. The composite material containing 4% of the lithium-rich positive electrode material in the composite material slurry is coated on the surface of aluminum foil, vacuum dried overnight at 110°C, and rolled to obtain a composite material electrode sheet. The lithium-rich positive electrode material Li2NiO2 is ball-milled and mixed with polyvinylidene chloride binder, SP conductive carbon and N-methylpyrrolidone solvent at a mass ratio of 93:3:2:100 to obtain a mixed slurry. The mixed slurry is coated on the surface of the composite material electrode sheet, vacuum dried overnight at 110°C, and rolled to obtain a lithium-rich positive electrode sheet.

[0147] Example 7

[0148] This embodiment provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a uniformly mixed lithium-rich positive electrode material and a composite material. The lithium-rich positive electrode material includes the positive electrode active material lithium manganese iron phosphate and the lithium supplementing agent lithium ferrite. The composite material includes the hydrophobic material silica and the polymer material guar gum.

[0149] Among them, there are lithium manganese iron phosphate active material, Li5FeO4 lithium supplementer, and silica composite porous hydrophobic material containing guar gum with a glass transition temperature of 100℃ in the pore structure. In the composite porous hydrophobic material, the mass ratio of guar gum to silica is 10:90, the silica porosity is 90%, and the particle size is 1.4um.

[0150] 1) Preparation of composite material: The hydrophobic porous material of silica and the guar polymer are mixed at a mass ratio of 10:90. The mixture is then evacuated and heated to 120°C in a vacuum drying oven for 5 hours to introduce the guar gum into the pore structure of the hydrophobic porous material, thus preparing the composite material.

[0151] 2) Preparation of lithium-rich positive electrode sheet: Lithium manganese iron phosphate and Li5FeO4 are mixed at a mass ratio of 95:5 to obtain lithium-rich positive electrode active material. The lithium-rich positive electrode active material and the composite material are mixed at a mass ratio of 96:4 to obtain a mixture. The mixture is ball-milled and stirred with polyvinylidene chloride binder and SP conductive carbon and N-methylpyrrolidone solvent at a mass ratio of 93:3:2:100 to obtain lithium-rich positive electrode slurry. The lithium-rich positive electrode slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and rolled to obtain lithium-rich positive electrode sheet.

[0152] Comparative Example 1

[0153] This comparative example provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a uniformly mixed lithium-rich positive electrode material Li2NiO2 and a hydrophobic material, wherein the hydrophobic material is porous silicon dioxide.

[0154] Preparation of lithium-rich positive electrode sheet: Li2NiO2, a lithium-rich positive electrode material, and a hydrophobic material are mixed at a mass ratio of 99:1 to obtain a mixture. The mixture, polyvinylidene chloride binder, SP conductive carbon, and N-methylpyrrolidone solvent are then ball-milled and stirred at a mass ratio of 93:3:2:100 to obtain a mixed slurry. The mixed slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and then rolled to obtain a lithium-rich positive electrode sheet.

[0155] Comparative Example 2

[0156] This comparative example provides a lithium-rich positive electrode sheet and its preparation method. The lithium-rich positive electrode sheet includes a current collector and a functional layer disposed on the current collector. The functional layer includes a lithium-rich positive electrode material layer.

[0157] Preparation of lithium-rich positive electrode sheet: Lithium manganese iron phosphate and Li5FeO4 are mixed at a mass ratio of 95:5. The resulting lithium-rich positive electrode active material is ball-milled and mixed with polyvinylidene chloride binder and SP conductive carbon and N-methylpyrrolidone solvent at a mass ratio of 93:3:2:100 to obtain lithium-rich positive electrode slurry. The lithium-rich positive electrode slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and rolled to obtain lithium-rich positive electrode sheet.

[0158] The lithium-rich cathode sheets provided in Examples 1 to 7 above, and the lithium-rich cathode sheets provided in Comparative Examples 1-2, are respectively assembled into cathodes and lithium-ion batteries according to the following methods:

[0159] Negative electrode: Graphite negative electrode sheet;

[0160] Electrolyte: Ethyl carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7, and LiPF6 is added to form an electrolyte with a concentration of 1 mol / L.

[0161] Diaphragm: Polypropylene microporous diaphragm;

[0162] Lithium-ion battery assembly: Assemble button-type lithium-ion full cells in an inert atmosphere glove box according to the assembly sequence of graphite negative electrode sheet - separator - electrolyte - lithium-rich positive electrode sheet.

[0163] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery examples was tested under the following conditions:

[0164] Constant current and constant voltage charging: initial charge / discharge voltage 2.5–4.3V, current 0.1C, cutoff current 0.01C. Then, cycle at 1C for 500 cycles. The cycle capacity retention rate is calculated as: (Capacity after 500 cycles / Initial discharge capacity) * 100%.

[0165] The test results of the above lithium-ion batteries are shown in Table 1 below.

[0166] Table 1 Performance Test Results

[0167]

[0168] As can be seen from the electrochemical performance data of the above embodiments and comparative examples provided in Table 1, the first charge-discharge capacity and cycle capacity retention rate of Examples 1-6 are better than those of Comparative Example 1, and the first charge-discharge capacity and cycle capacity retention rate of Example 7 are better than those of Comparative Example 2. This indicates that the lithium-rich cathode sheet containing this application has good adhesion and stability. The high molecular polymer with a glass transition temperature of -20℃ to 150℃ contained in the composite material can improve the bonding force between the lithium-rich cathode material itself and the current collector and composite material, and prevent the lithium-rich cathode material in the lithium-rich cathode sheet from pulverizing and falling off during the electrode coating drying and high-temperature formation and long-term cycling of the battery, thereby reducing the electrochemical performance of the entire battery.

[0169] Specifically, the electrochemical performance data from Examples 1-3 show that as the content of the composite material increases, the initial charge-discharge capacity of the battery initially increases and then gradually decreases. Although the capacity retention rate of Example 3 remains as high as 95%, the discharge capacity of the battery is only 136.4 mAh / g, indicating a low overall energy density. Therefore, while achieving anti-powdering through the composite material, it is also necessary to control the content of the composite material in the lithium-rich cathode to avoid affecting the electrochemical performance of the lithium-rich cathode.

[0170] The electrochemical performance data from Examples 1 and 4 show that the specific structure of the provided inorganic material has a significant impact on the performance of the lithium-rich cathode sheet. Compared with Example 1, the lithium-rich cathode sheet provided in Example 4 exhibits a significant decrease in initial charge capacity, initial discharge capacity, and cycle capacity retention, but still shows a performance advantage compared to Comparative Example 1. The main reason for this is that the inorganic material fails to provide sufficient space for the polymer material, resulting in a reduced connection area and thus an increased pulverization rate. Furthermore, since most of the polymer is located on the outer surface of both the inorganic material and the lithium-rich cathode material, the lithium-ion transport efficiency in the lithium-rich cathode sheet is reduced.

[0171] The electrochemical performance data from Examples 4 and 5 show that the distribution of the composite material in the lithium-rich cathode does not affect the electrochemical performance of the battery, demonstrating the diversity of composite material placement methods. This further illustrates that the lithium-rich cathode provided in this application has universality and can be mass-produced.

[0172] As can be seen from Example 7 and Comparative Example 2, Example 7 contains the composite material of this application, so its electrochemical performance is better than that of Comparative Example 2, indicating that the lithium-rich positive electrode sheet of this application has a longer service life and higher stability.

[0173] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0174] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A lithium-rich cathode electrode sheet, characterized by, include: current collector; A functional layer is disposed on the current collector. The functional layer includes a lithium-rich cathode material and a composite material. The composite material includes an inorganic material and a polymer material. The lithium-rich cathode material and the inorganic material are connected by the polymer material. The inorganic material is a hydrophobic material. The functional layer also includes a binder and a conductive agent. The inorganic material has a porous structure, and the polymer material is embedded in the pores of the inorganic material; the glass transition temperature of the polymer material is -20℃ to 150℃. The method for preparing the composite material includes: mixing the inorganic material and the polymer material, and then heating the mixture to fix the polymer material to the inorganic material, thereby obtaining the composite material; The polymer material exhibits a fluid dynamic at high temperatures, which is used to capture the lithium-rich cathode material. After cooling, the polymer material solidifies and can connect the lithium-rich cathode material and the inorganic material.

2. The lithium-rich cathode sheet of claim 1, wherein, In the composite material, the mass ratio of the inorganic material to the polymer material is (80-90):(10-20); and / or, the porosity of the hydrophobic material is 60%-90%; and / or, the particle size D50 of the hydrophobic material is 50nm-10μm.

3. The lithium-rich cathode sheet of claim 1, wherein, The lithium-rich cathode material includes a lithium-rich compound Li 1+x M y O z wherein M is one or more elements selected from Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, and 0 < x ≤ 1, 0 < y, and 0 < z < 10.

4. The lithium-rich cathode sheet of claim 1, wherein, The functional layer includes a lithium-rich cathode material layer and a composite material layer; the lithium-rich cathode material layer includes the lithium-rich cathode material, the composite material layer includes the composite material, and the lithium-rich cathode material layer is disposed between the current collector and the composite material layer; or, the composite material layer is disposed between the current collector and the lithium-rich cathode material layer.

5. The lithium-rich cathode sheet of claim 4, wherein, The thickness of the lithium-rich cathode material layer is 0.1 μm to 200 μm, and the thickness of the composite material layer is 0.1 μm to 100 μm.

6. The lithium-rich cathode sheet of claim 1, wherein, The lithium-rich cathode material and the composite material are uniformly mixed in the functional layer.

7. The lithium-rich cathode sheet of claim 1, wherein, The mass ratio of the lithium-rich cathode material to the composite material is (99.1–80):(0.9–20).

8. A method of making a lithium-rich cathode electrode sheet, characterized by, The preparation method is used to fabricate the lithium-rich positive electrode sheet as described in any one of claims 1-7, and the preparation method includes: Inorganic materials and polymer materials are mixed in a certain proportion to obtain composite materials; The composite material, lithium-rich cathode material, binder and conductive agent are prepared on the current collector in proportion, and then dried and rolled to obtain the lithium-rich cathode sheet.

9. A secondary battery characterized by comprising: The secondary battery includes a negative electrode, a separator, and a lithium-rich positive electrode as described in any one of claims 1-7.

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