Multilayer coated positive electrode sheet and preparation method, lithium-ion battery and electric device

Abstract

The present application belongs to the technical field of lithium-ion batteries. Disclosed are a multilayer coated positive electrode sheet and a preparation method, a lithium-ion battery and an electric device. The multilayer coated positive electrode sheet of the present application comprises a current collector and two or more active material layers from bottom to top, wherein a network structure layer is provided between any two active material layers, and each active material layer contains a positive active material.

Description

Multilayer coated positive electrode sheet and preparation method, lithium ion battery, and electrical device

[0001] This application claims priority to Chinese patent application No. 202410174197.4 filed on February 7, 2024, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of lithium-ion batteries, and in particular to a multi-layer coated positive electrode sheet and a preparation method thereof, a lithium-ion battery, and an electrical device. Background Art

[0003] In the technical field related to lithium-ion batteries, multi-layer coating is used to obtain multi-layer active materials on the positive electrode sheet, which can enable lithium-ion batteries to achieve higher energy density and excellent rate performance compared to single-layer active materials. However, there is poor compatibility between the layers of multi-layer coating, resulting in problems such as peeling and powdering of the active material slurry in the upper and lower layers.

[0004] In addition, in the process of replenishing lithium in the positive electrode, simply using lithium replenisher will face problems such as severe gas production and difficulty in exhausting. Technical issues

[0005] Based on the above-mentioned issues, the present application mainly provides a multi-layer coated positive electrode sheet and preparation method, a lithium-ion battery, and an electrical device. Technical Solutions

[0006] To achieve the above objectives, the present application provides, in a first aspect, a multi-layer coated positive electrode sheet, comprising, from bottom to top, a current collector and two or more active material layers, wherein a network structure layer is provided between any two active material layers, and each active material layer contains an active material;

[0007] The active material layer formed on the surface of the current collector is defined as the lower active material layer; the uppermost layer of the multi-layer coated positive electrode sheet is the active material layer, defined as the upper active material layer;

[0008] The active material layer formed between the lower active material layer and the upper active material layer is defined as a middle active material layer.

[0009] In some embodiments of the present application, the network structure layer includes a lithium supplement.

[0010] In some embodiments of the present application, the lithium supplement includes at least one of Li2NiO2, Li5FeO4, Li2O, Li2O2, Li3N, and Li2C2O4.

[0011] In some embodiments of the present application, the network structure layer is at least partially embedded in the active material layer formed on the upper surface and / or lower surface of the network structure layer.

[0012] In some embodiments of the present application, the mass of the network structure layer in the multi-layer coated positive electrode sheet accounts for 3% to 5% of the total mass of the active material.

[0013] In some embodiments of the present application, the porosity of the lower active material layer ranges from 20% to 30%;

[0014] and / or, the porosity of the middle active material layer ranges from 30% to 40%;

[0015] And / or, the porosity of the upper active material layer is in the range of 40% to 50%.

[0016] In some embodiments of the present application, the D50 of the active material in the lower active material layer ranges from 50 nm to 10 μm;

[0017] and / or, the D50 of the active material in the middle active material layer is in the range of 1 μm to 10 μm;

[0018] And / or, the active material in the upper active material layer has a D50 ranging from 2.5 μm to 20 μm.

[0019] In some embodiments of the present application, assuming that the D50 of the active material in the lower active material layer is X and the D50 of the active material in the upper active material layer is Y, then Y>X is satisfied.

[0020] In some embodiments of the present application, Y and X satisfy Y:X∈[2,1000].

[0021] In some embodiments of the present application, the active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium cobalt phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0022] A second aspect of the present application provides a method for preparing a multi-layer coated positive electrode sheet, comprising the following steps:

[0023] preparing an active material slurry, wherein the active material slurry contains an active material;

[0024] preparing a lithium supplementing slurry containing a lithium supplementing agent;

[0025] The active material slurry forms a lower active material layer on the surface of the current collector;

[0026] The lithium-supplementing slurry is used to form a network-shaped lithium-supplementing layer on the surface of the lower active material layer through an electrostatic spinning process;

[0027] The active material slurry forms an upper active material layer on the surface of the network-shaped lithium replenishing layer.

[0028] In some embodiments of the present application, the active material slurry and the lithium supplement slurry both include a conductive agent and a binder.

[0029] In some embodiments of the present application, the active material, the conductive agent, and the binder are dissolved in an organic solvent to form the active material slurry;

[0030] And / or, the lithium replenishing agent, the conductive agent and the binder are dissolved in an organic solvent to form the lithium replenishing slurry.

[0031] In some embodiments of the present application, the mass percentage of the conductive agent in the network lithium replenishing layer is 5% to 10%.

[0032] In some embodiments of the present application, the mass ratio of the active material, the conductive agent, and the binder is (90-98): (1-5): (1-5);

[0033] And / or, the mass ratio of the lithium supplement agent, the conductive agent and the binder is (80-90): (5-10): (5-10).

[0034] In some embodiments of the present application, the mass ratio of the active material, the conductive agent, and the binder is (95-98): (1-2.5): (1-2.5);

[0035] And / or, the mass ratio of the lithium supplement agent, the conductive agent and the binder is (80~85): (7.5~10): (7.5~10).

[0036] In some embodiments of the present application, the solid content of the active material slurry ranges from 65% to 70%;

[0037] And / or, the viscosity of the active material slurry is 5000 MPa·s to 7000 MPa·s.

[0038] In some embodiments of the present application, the receiving distance of the electrospinning is 5 cm to 10 cm;

[0039] And / or, the voltage of the electrospinning is 10 kV to 20 kV;

[0040] And / or, the electrospinning feed rate is 10 mL / h to 15 mL / h.

[0041] In some embodiments of the present application, the network lithium replenishing layer is dried at a temperature of 90° C. to 100° C.;

[0042] And / or, the upper active material layer is dried at a temperature of 90°C to 100°C.

[0043] A third aspect of the present application provides a lithium-ion battery, comprising the multi-layer coated positive electrode sheet as described above.

[0044] A fourth aspect of the present application provides an electrical device, which includes the lithium-ion battery described above. Beneficial effects

[0045] Beneficial effects that this application can achieve:

[0046] The present application adopts a multi-layer coating method to prepare multiple layers of active material layers on the positive electrode sheet, which is beneficial to improving the energy density and rate performance of the lithium-ion battery. Moreover, any two active material layers are connected together through a network structure layer. The network structure layer has a large specific surface area and a high porosity. The upper and lower active material layers can be firmly adhered together with the help of the network structure layer, thereby strengthening the bonding force between the active material layers and improving the overall peeling force of the positive electrode sheet. It can alleviate the problem of peeling and powdering of the active material slurry between the layers of the multi-layer coating, thereby improving the cycle performance of the lithium-ion battery cell. In addition, the rich pore structure of the network structure layer is also conducive to the infiltration of the electrolyte, which can improve the conductive performance of the lithium-ion battery.

[0047] In addition, the present application can also add a lithium supplement agent to the mesh structure layer to form a mesh lithium supplement layer. The lithium supplement layer with a mesh structure has rich pores, which is conducive to the exhaust of the lithium supplement agent after gas production, and can effectively alleviate the problem of severe gas production and difficulty in exhausting the lithium supplement agent.

[0048] The multi-layer coated positive electrode sheet of the present application not only retains the high energy density and excellent rate performance brought by the multi-layer coating, strengthens the bonding strength between the layers, and improves the peeling force of the positive electrode sheet, but can alleviate the problems of easy peeling and powder loss of the slurry, as well as poor electrolyte infiltration and poor conductivity. It can also alleviate the problems of serious gas production and difficulty in exhausting of the lithium supplement agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0050] FIG1 is a cross-sectional view of a multi-layer coated positive electrode sheet according to an embodiment of the present application;

[0051] FIG2 is a cross-sectional view of a network lithium replenishing layer after formation according to an embodiment of the present application;

[0052] FIG3 is a cross-sectional view of another embodiment of the present application after the network lithium replenishing layer is formed.

[0053] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. Modes for Carrying Out the Invention

[0054] It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0055] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0056] In this application, the descriptions of "first", "second", etc. are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features specified as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0057] In the technical field related to lithium-ion batteries, multi-layer coating is used to obtain multi-layer active materials on the positive electrode sheet, which can enable lithium-ion batteries to achieve higher energy density and excellent rate performance compared to single-layer active materials. However, there is poor compatibility between the layers of multi-layer coating, resulting in problems such as peeling and powdering of the active material slurry in the upper and lower layers.

[0058] In view of this, the first aspect of the present application proposes a multi-layer coated positive electrode sheet.

[0059] The multi-layer coated positive electrode sheet of the present application includes a current collector and two or more active material layers from bottom to top, a network structure layer is provided between any two active material layers, and each active material layer contains active material.

[0060] Among them, the active material layer formed on the surface of the current collector is defined as the lower active material layer; the top layer of the multi-layer coated positive electrode sheet is the active material layer, defined as the upper active material layer; the active material layer formed between the lower active material layer and the upper active material layer is defined as the middle active material layer.

[0061] The middle active material layer can be 0 layers, 1 layer or multiple layers, that is, the multi-layer coated positive electrode sheet of the present application contains at least an active material layer, a network structure layer and an active material layer in sequence from the current collector to the outside, and has a structure in which the active material layer and the network structure layer are arranged alternately in sequence, and the bottom layer and the top layer are both active material layers.

[0062] It can be seen that the multi-layer coated positive electrode sheet of the present application contains two or more active material layers, which is beneficial to improving the energy density and rate performance of lithium-ion batteries, and any two active material layers are connected together through a network structure layer. The network structure layer has a large specific surface area and a high porosity. The upper and lower active material layers can be firmly adhered together with the help of the network structure layer, thereby strengthening the bonding force between the active material layers and improving the overall peeling force of the positive electrode sheet. It can alleviate the problem of peeling and powdering of the active material slurry between the layers of the multi-layer coating, thereby improving the cycle performance of the lithium-ion battery cell. In addition, the rich pore structure of the network structure layer is also beneficial to the infiltration of the electrolyte, which can improve the conductivity of the lithium-ion battery.

[0063] The mesh structure layer in the multi-layer coated positive electrode sheet of the present application may include materials capable of forming a mesh structure in the technical field related to lithium-ion batteries, including at least one of a lithium supplement, a binder, and a conductive agent.

[0064] In some embodiments, the lithium supplement includes at least one of Li2NiO2, Li5FeO4, Li2O, Li2O2, Li3N, and Li2C2O4.

[0065] The active material layer can be prepared by using commonly used technical means in this technical field.

[0066] The mesh structure layer can be prepared by using methods that can form a mesh structure layer from materials that can form a mesh structure in the above-mentioned technical field related to lithium ion batteries, including electrospinning technology.

[0067] In one embodiment, a lithium supplement agent is dissolved in an organic solvent to form a slurry, and then a mesh structure layer is prepared on the surface of the active material layer by electrospinning technology. The mesh structure layer of this embodiment contains a lithium supplement agent to form a mesh lithium supplement layer. This not only utilizes the mesh structure to strengthen the bonding force between the upper and lower active material layers, improves the peeling force of the positive electrode sheet, and alleviates the problem of slurry between layers of multi-layer coating easily falling off and losing powder, which then affects the performance of the lithium-ion battery, but also because the lithium supplement agent is added, it can also improve the conductivity of the positive electrode sheet. In addition, the mesh lithium supplement layer has rich pores, which is conducive to the exhaust of gas generated by the lithium supplement agent, which can effectively alleviate the serious problem of gas generation by the lithium supplement agent. It is also conducive to the infiltration of the electrolyte, which can further improve the conductivity of the lithium-ion battery.

[0068] In one embodiment, the binder is dissolved in an organic solvent to form a slurry, and then the network structure layer is prepared on the surface of the active material layer by electrospinning technology.

[0069] In one embodiment, the conductive agent is dissolved in an organic solvent to form a slurry, and then a network structure layer is prepared on the surface of the active material layer by electrospinning technology.

[0070] In one embodiment, a lithium supplement agent, a conductive agent, and a binder are dissolved in an organic solvent to form a slurry, and then a mesh structure layer is prepared on the surface of the active material layer by electrospinning technology. The mesh structure layer of this embodiment contains a lithium supplement agent, which can form a mesh lithium supplement layer. It can not only use the mesh structure to strengthen the bonding force between the upper and lower active material layers, improve the peeling force of the positive electrode sheet, and alleviate the problem that the slurry between the layers of the multi-layer coating is prone to falling off and powdering, thereby affecting the performance of the lithium-ion battery, but also because the lithium supplement agent is added, the conductive properties of the positive electrode sheet can be improved. In addition, the mesh lithium supplement layer is rich in pores, which is conducive to the exhaust after the lithium supplement agent produces gas, which can effectively alleviate the serious problem of lithium supplement agent producing gas, and is also conducive to the infiltration of the electrolyte, improving the conductive properties of the lithium-ion battery. Optionally, the network structure layer of this embodiment contains a lithium supplement, a conductive agent and a binder, and the active material layer usually also contains a lithium-containing compound, a conductive agent and a binder. In this way, the types of materials used between the network structure layer and the active material layer tend to be the same, which is beneficial to further strengthen the bonding force between the network structure layer and the active material layer.

[0071] In some embodiments, the type of material used in the active material layer formed on the lower surface of the mesh structure layer is the same as the type of material used in the active material layer formed on the upper surface of the mesh structure layer, which can further enhance the bonding strength between the upper and lower active material layers of the mesh structure layer and improve the stratification phenomenon caused by different material types.

[0072] In the technical field related to lithium-ion batteries, the sole use of lithium supplement agents can lead to problems such as severe gas production and difficulty in exhausting. In view of this, in some embodiments, the mesh structure layer in the multi-layer coated positive electrode sheet of the present application includes a lithium supplement agent. By adding the lithium supplement agent to the mesh structure layer, a mesh lithium supplement layer is prepared. The mesh lithium supplement layer has abundant pores, which is conducive to exhausting after the lithium supplement agent produces gas, can effectively alleviate the problem of severe gas production by the lithium supplement agent, and is conducive to the infiltration of the electrolyte, thereby improving the conductivity of the lithium-ion battery.

[0073] Referring to Figure 1, Figure 1 is a cross-sectional view of a multilayer coated positive electrode sheet according to an embodiment of the present application, which includes, from bottom to top, a current collector 1, a lower active material layer 2, a mesh lithium replenishing layer 3, and an upper active material layer 4. The mesh lithium replenishing layer 3 can be understood as the mesh structure layer mentioned above in the present application. Because it contains a lithium replenishing agent, it can improve the conductivity of the positive electrode sheet, and it is rich in pores, which is conducive to the exhaust after the lithium replenishing agent produces gas, and can effectively alleviate the serious problem of lithium replenishing agent producing gas. It is also conducive to the infiltration of the electrolyte and can improve the conductivity of the lithium-ion battery. In addition, the mesh lithium replenishing layer 2 of this embodiment also retains the strong bonding force brought by the mesh structure, strengthens the bonding force between the lower active material layer 2 and the upper active material layer 3, improves the peeling force of the positive electrode sheet, and can alleviate the problem that the slurry between the layers of the multilayer coating is prone to falling off and powdering, thereby affecting the performance of the lithium-ion battery.

[0074] In some embodiments, the mesh structure layer is at least partially embedded in the active material layer formed on the upper surface and / or lower surface of the mesh structure layer, which can strengthen the bonding force between the mesh structure layer and the active material layer on its upper surface and / or lower surface, improve the peeling force of the electrode sheet, and alleviate the problem of peeling and falling off of the material in the active material layer or the material in the mesh structure layer.

[0075] In this embodiment, the mesh structure layer is at least partially embedded in the active material layer formed on its upper surface, and at the same time, is also at least partially embedded in the active material layer formed on its lower surface, which is conducive to strengthening the bonding force between the upper and lower active material layers of the mesh structure layer, and alleviating the problem of raw material peeling and falling off due to poor compatibility between the layers formed by multi-layer coating. In this embodiment, the mesh structure layer has a mesh structure. When at least a portion of the mesh structure is respectively embedded in the active material layers formed on the upper and lower surfaces of the mesh structure layer, the upper active material layer and the lower active material layer can contact each other through the mesh structure. When the slurry components between the upper active material layer and the lower active material layer tend to be the same and the compatibility is good, it is conducive to further strengthening the bonding force between the upper active material layer and the lower active material layer, greatly alleviating the problem of slurry peeling and falling off of the positive electrode sheet.

[0076] In some embodiments, the mass of the mesh structure layer in the multi-layer coated positive electrode sheet accounts for 3% to 5% of the total mass of the active material, and can be any value within the range of 3%, 3.5%, 4%, 4.5%, 5%, etc. The mesh structure layer is lightweight and does not easily affect the conductive properties of the multi-layer coated positive electrode sheet.

[0077] In some embodiments, the porosity of the lower active material layer formed on the surface of the current collector ranges from 20% to 30%, for example, it can be any value within the range of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc. The lower active material layer has a smaller porosity range, which is beneficial for increasing the compaction density of the electrode sheet and strengthening the bonding force between the current collector and the lower active material layer. Then, through the bonding force between the network structure layer and each active material layer, a multi-layer coated positive electrode sheet with various functional layers tightly bonded is obtained, which helps to alleviate the problem of slurry shedding and falling of each functional layer in the positive electrode sheet.

[0078] In some embodiments, the porosity of the middle active material layer ranges from 30% to 40%. For example, it can be any value in the range of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc. Within the above porosity range, the bonding strength between the layers can be strengthened, and it is also beneficial to exhaust.

[0079] In some embodiments, the porosity of the upper active material layer ranges from 40% to 50%. For example, it can be any value within the range of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, etc. In this embodiment, the relatively large porosity of the upper active material layer can enhance electrolyte infiltration and improve the conductivity of the lithium-ion battery. In addition, when the network structure layer contains a lithium replenisher to form a network lithium replenisher layer, it also facilitates the degassing of the lithium replenisher after gas production.

[0080] In the present application, different porosity ranges can be obtained by controlling the particle size of the active material in the active material layer.

[0081] In some embodiments, the D50 range of the active material in the lower active material layer formed on the surface of the current collector is 50 nm to 10 μm, and the particle size is small, which is conducive to obtaining a smaller porosity range, and then obtaining a higher compaction density, and strengthening the bonding force between the current collector and the lower active material layer. Then, through the bonding force between the network structure layer and each layer of active material layer, a multi-layer coated positive electrode sheet with various functional layers tightly combined is obtained, which is conducive to alleviating the problem of slurry shedding and falling in each functional layer of the positive electrode sheet.

[0082] In some embodiments, the active material in the upper active material layer has a D50 range of 1 μm to 10 μm. This larger particle size facilitates a wider porosity range, enhances electrolyte infiltration, and improves the conductivity of the lithium-ion battery. Furthermore, when the network structure layer contains a lithium replenisher, a network-like lithium replenisher layer is formed, which also facilitates the degassing of the lithium replenisher after it generates gas.

[0083] In some embodiments, the active material in the middle active material layer has a D50 ranging from 2.5 μm to 20 μm.

[0084] In some embodiments, the D50 of the active material in the lower active material layer formed on the current collector surface is X, and the D50 of the active material in the uppermost active material layer of the multilayer coated positive electrode sheet is Y, then Y>X. Optionally, Y and X satisfy Y:X∈[2,1000]. In this embodiment, the smaller particle size of the active material in the lower active material layer facilitates a smaller porosity range, thereby achieving a higher compaction density and strengthening the bonding between the current collector and the lower active material layer. The bonding between the network structure layer and each active material layer then creates a multilayer coated positive electrode sheet with tightly integrated functional layers, mitigating issues with slurry shedding and falling from each functional layer within the positive electrode sheet. The larger particle size of the active material in the upper active material layer facilitates a wider porosity range, enhancing electrolyte infiltration and improving the conductivity of the lithium-ion battery. Furthermore, when the network structure layer contains a lithium replenisher, a network-shaped lithium replenisher layer is formed, which also facilitates degassing of the lithium replenisher after gas production.

[0085] In some embodiments, the active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium cobalt phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0086] A second aspect of the present application provides a method for preparing a multi-layer coated positive electrode sheet, comprising at least the following steps:

[0087] preparing an active material slurry, wherein the active material slurry contains an active material;

[0088] preparing a lithium supplement slurry containing a lithium supplement agent;

[0089] The active material slurry forms a lower active material layer on the surface of the current collector;

[0090] The lithium-supplementing slurry is used to form a network-like lithium-supplementing layer on the surface of the lower active material layer through an electrostatic spinning process;

[0091] The active material slurry forms an upper active material layer on the surface of the network-shaped lithium replenishing layer.

[0092] In some embodiments, both the active material slurry and the lithium supplement slurry include a conductive agent and a binder.

[0093] In some embodiments, the conductive agent includes at least one of acetylene black, carbon black, carbon nanotubes, and graphene.

[0094] In some embodiments, the binder includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and styrene-butadiene rubber.

[0095] In some embodiments, the active material, the conductive agent, and the binder are dissolved in an organic solvent to form an active material slurry, wherein the organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and ethylene glycol dimethyl ether.

[0096] The active material slurry prepared above in this application does not refer to an active material slurry of a single formula. A variety of active material slurries with different formulas, such as active material slurry 1, active material slurry 2, and active material slurry 3, can be prepared, and then active material layers with different formulas can be prepared as needed.

[0097] In one embodiment, the present application prepares two active material slurries with different formulas, which are respectively marked as a lower active material slurry and an upper active material slurry, wherein the D50 of the active material in the lower active material slurry is greater than the D50 of the active material in the upper active material slurry, and the lower active material slurry forms a lower active material layer on the surface of the current collector, and the upper active material slurry forms an upper active material layer on the surface of the network lithium replenishing layer.

[0098] In some embodiments, the types of binder and conductive agent in the active material slurry used for the active material layer formed on the lower surface of the mesh lithium replenishing layer are the same as the types of binder and conductive agent in the active material slurry used for the active material layer formed on the upper surface of the mesh lithium replenishing layer. This can further enhance the bonding strength between the upper and lower active material layers of the mesh lithium replenishing layer, thereby improving the stratification phenomenon caused by different material types.

[0099] In some embodiments, the lithium replenishing agent, the conductive agent, and the binder are dissolved in an organic solvent to form a lithium replenishing slurry. The organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and ethylene glycol dimethyl ether.

[0100] In some embodiments, the mass percentage of the conductive agent in the network lithium supplement layer is 5% to 10%. For example, it can be any value in the range of 5% to 10%, such as 5%, 6%, 7%, 8%, 9%, 10%, etc. The high proportion of the conductive agent is beneficial to improving the conductive performance of the positive electrode sheet.

[0101] In some embodiments, the mass of the reticulated lithium-supplementing layer in the multi-layer coated positive electrode sheet accounts for 3% to 5% of the total mass of the active material, and can be any value within the range of 3%, 3.5%, 4%, 4.5%, 5%, etc. The reticulated lithium-supplementing layer is lightweight and does not easily affect the conductive properties of the multi-layer coated positive electrode sheet.

[0102] In some embodiments, the mass percentage of the conductive agent in the mesh lithium replenishing layer is 5% to 10%. At the same time, the mass of the mesh lithium replenishing layer in the multi-layer electrode-coated positive electrode sheet accounts for 3% to 5% of the total mass of the active material. The mesh lithium replenishing layer of this embodiment contains a relatively high proportion of the conductive agent, and the overall mass of the layer does not exceed 5% of the total mass of the active material. Therefore, it is not easy to have a negative impact on the overall conductivity of the positive electrode sheet. The lithium replenishing agent can also further improve the energy density of the battery cell.

[0103] In some embodiments, the mass ratio of the active material, the conductive agent, and the binder is (90-98): (1-5): (1-5); further (95-98): (1-2.5): (1-2.5), which is beneficial to improving the energy density of the battery.

[0104] In some embodiments, the mass ratio of the lithium supplement agent, the conductive agent, and the binder is (80-90): (5-10): (5-10), and further is (80-85): (7.5-10): (7.5-10), which is beneficial to improving the conductivity of the battery.

[0105] In some embodiments, the solids content of the active material slurry ranges from 65% to 70%, and can be any value within the range of 65%, 66%, 67%, 68%, 69%, 70%, or the like. In this embodiment, the active material slurry having a solids content within the above range facilitates at least partial embedding of the reticulated lithium replenisher into the active material layer it forms. This strengthens the bonding between the active material layer and the reticulated lithium replenisher, improves the peeling force of the electrode, and alleviates issues such as poor compatibility between layers or slurry peeling and shedding.

[0106] In some embodiments, the viscosity of the active material slurry is 5000 MPa·s to 7000 MPa·s, and can be 5000 MPa·s, 5100 MPa·s, 5200 MPa·s, 5500 MPa·s, 5800 MPa·s, 6000 MPa·s, 6200 MPa·s, 6500 MPa·s, 6700 MPa·s, 6800 MPa·s, 6900 MPa·s, 7000 MPa·s, or any value in the range of 5000 MPa·s to 7000 MPa·s. Within the above viscosity range, the active material slurry can form good adhesion between the current collector or the network lithium replenishment layer, strengthen the bonding between the layers, and alleviate the problem of delamination and slurry peeling between the layers.

[0107] In this application, electrospinning technology is used to prepare the lithium replenishment layer, so that the lithium replenishment layer forms a network structure with a rich pore structure, which is conducive to the exhaust of the lithium replenishment agent after gas production and enhances the infiltration of the electrolyte. Moreover, the network structure can strengthen the bonding force between the upper active material layer and the lower active material layer, improve the peeling force of the electrode, and alleviate the problem of easy stratification between layers and the shedding of slurry glass.

[0108] Referring to Figure 2, a cross-sectional view of an embodiment of the present invention illustrates the use of electrospinning technology to form a network-shaped lithium-replenishing layer 3 on the surface of a lower active material layer 2. In this embodiment, the network-shaped lithium-replenishing layer 3 is partially embedded in the lower active material layer 2, which helps strengthen the bonding between the network-shaped lithium-replenishing layer 3 and the lower active material layer 2.

[0109] Referring to Figure 3, it shows a cross-sectional view of an embodiment of the present invention, after the preparation of a network lithium-replenishing layer 3 using electrostatic technology, followed by the preparation of an upper active material layer 4 on the surface of the network lithium-replenishing layer 3. In this embodiment, the network lithium-replenishing layer 3 is partially embedded in the lower active material layer 2 and also partially embedded in the upper active material layer 4. The network structure strengthens the bonding between the lower active material layer 2 and the upper active material layer 4, which helps improve the peeling force of the electrode and alleviates the problem of delamination between the layers and the shedding of the paste glass.

[0110] In some embodiments, the electrospinning receiving distance is 5 cm to 10 cm, and can be any value within the range of 5 cm to 10 cm, such as 5 cm, 5.5 cm, 6 cm, 6.5 cm, 7 cm, 7.5 cm, 8 cm, 8.5 cm, 9 cm, 9.5 cm, or 10 cm. In this embodiment, controlling the electrospinning receiving distance facilitates partial embedding of the reticulated lithium-replenishing layer into the underlying active material layer, thereby strengthening the mutual bonding between the two layers.

[0111] In some embodiments, the electrospinning voltage is between 10 kV and 20 kV, and can be any value within the range of 10 kV to 20 kV, such as 10 kV, 11 kV, 12 kV, 13 kV, 14 kV, 15 kV, 16 kV, 17 kV, 18 kV, 19 kV, or 20 kV. In this embodiment, controlling the electrospinning voltage facilitates partial embedding of the reticulated lithium-replenishing layer into the underlying active material layer, thereby strengthening the mutual bonding between the two layers.

[0112] In some embodiments, the electrospinning feed rate is 10 mL / h to 15 mL / h, and can be any value within the range of 10 mL / h, 11 mL / h, 12 mL / h, 13 mL / h, 14 mL / h, 15 mL / h, etc. In this embodiment, controlling the electrospinning feed rate facilitates partial embedding of the reticulated lithium-replenishing layer into the underlying active material layer, thereby strengthening the mutual bonding between the two layers.

[0113] In some embodiments, after the network lithium replenishing layer is prepared and before the active material layer is prepared on the surface of the network lithium replenishing layer, the network lithium replenishing layer is further dried. After drying, the network structure of the network lithium replenishing layer is more solid, and its structure is not easily destroyed when the active material layer is formed on its surface. Moreover, it is easier to embed into the active material layer formed on its surface, thereby strengthening the bonding force between the upper and lower active material layers.

[0114] In some embodiments, the drying temperature is 90° C. to 100° C., and can be any value within the range of 90° C., 91° C., 92° C., 93° C., 94° C., 95° C., 96° C., 97° C., 98° C., 99° C., 100° C., etc. The above drying temperature conditions are conducive to promoting the network structure of the lithium-supplementing layer to be relatively strong.

[0115] In some embodiments, the upper active material layer is dried at a temperature of 90° C. to 100° C., and can be any value within the range of 90° C., 91° C., 92° C., 93° C., 94° C., 95° C., 96° C., 97° C., 98° C., 99° C., 100° C., etc. These drying temperatures facilitate a stronger structure for the upper active material layer.

[0116] In some embodiments, the lithium supplement agent slurry is sprayed onto the surface of the underlying active material layer through an electrospinning syringe.

[0117] The multi-layer coated positive electrode sheet prepared by the preparation method of the present application includes a current collector and at least two active material layers from bottom to top, and a network lithium replenishing layer is provided between any two of the active material layers.

[0118] The multilayer coated positive electrode sheet prepared by the above-mentioned preparation method of the present application contains, from bottom to top, a lower active material layer, a mesh lithium replenishing layer, and an upper active material layer. In some embodiments, one or more composite layers 1 may be prepared between the mesh lithium replenishing layer and the upper active material layer, and the composite layer 1 includes, from bottom to top, a middle active material layer formed by an active material slurry and a mesh lithium replenishing layer formed by a lithium replenishing slurry; and / or, one or more composite layers 2 may be prepared between the lower active material layer and the mesh lithium replenishing layer, and the composite layer 2 includes, from bottom to top, a mesh lithium replenishing layer formed by a lithium replenishing slurry and a middle active material layer formed by an active material slurry. That is, the multilayer coated positive electrode sheet of the present application includes, from bottom to top, a current collector and two or more active material layers, and a mesh lithium replenishing layer is prepared between any two active material layers. In this embodiment, each mesh lithium replenishing layer in the multilayer coated positive electrode sheet can be prepared from lithium replenishing slurries with different formulations.

[0119] The present application adopts a multi-layer coating method to prepare two or more active material layers on the positive electrode sheet, which is beneficial to improving the energy density and rate performance of the lithium-ion battery. Moreover, any two active material layers are connected together by a mesh lithium replenishing layer. The mesh structure of the mesh lithium replenishing layer can be used to strengthen the bonding force between the active material layers, thereby alleviating the problem that the active material slurry between the layers of the multi-layer coating is prone to peeling and powdering, which then affects the performance of the lithium-ion battery. In addition, the present application also replenishes lithium on the positive electrode sheet by preparing a mesh lithium replenishing layer. The mesh lithium replenishing layer has rich pores, which is beneficial to the exhaust of the lithium replenishing agent after gas production, can effectively alleviate the serious problem of lithium replenishing agent gas production, and is beneficial to the infiltration of the electrolyte, thereby improving the conductivity of the lithium-ion battery.

[0120] The multi-layer coated positive electrode sheet of the present application not only retains the high energy density and excellent rate performance brought by the multi-layer coating, but also alleviates the problems of serious gas production and poor exhaust of the lithium supplement agent, easy peeling and powder loss between the layers of the multi-layer coating, as well as poor electrolyte infiltration and poor conductivity.

[0121] The third aspect of the present application provides a lithium-ion battery, which includes the multi-layer coated positive electrode sheet as described above. The lithium-ion battery of the present application includes at least all the beneficial effects of the multi-layer coated positive electrode sheet as described above, which will not be repeated here.

[0122] In a fourth aspect, the present application provides an electrical device comprising the lithium-ion battery described above. The electrical device of the present application at least includes all the beneficial effects of the multi-layer coated positive electrode sheet described above, which will not be described in detail here.

[0123] The technical solution of the present application is further described in detail below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to explain the present application and are not used to limit the present application.

[0124] Example 1 to Example 10

[0125] The preparation methods of the multilayer coated positive electrode sheets of Examples 1 to 10 are as follows:

[0126] Step S10: weighing active materials, binders and conductive agents according to Table 1 and dissolving them in an organic solvent to form an internal active material slurry, and coating the internal active material slurry on the surface of the current collector to form a lower active material layer.

[0127] Step S20: According to Table 1, a lithium replenishing agent, a binder, and a conductive agent are weighed and dissolved in an organic solvent to form a lithium replenishing slurry. The lithium replenishing slurry is sprayed onto the surface of the lower active material layer according to the electrospinning parameters in Table 1 to form a network structure layer. This network structure layer is the network lithium replenishing layer, and then dried in an oven at 90°C to 100°C for 30 to 60 minutes.

[0128] Step S30: weigh active materials, binders and conductive agents according to Table 1 and dissolve them in an organic solvent to form an external active material slurry, and apply the external active material slurry to the surface of the network lithium replenishing layer that has been dried in step S20 to obtain an upper active material layer.

[0129] 3 , the multi-layer coated positive electrode sheets obtained in Examples 1 to 10 include, from bottom to top, a current collector 1 , a lower active material layer 2 , a network structure layer 3 and an upper active material layer 4 .

[0130] Comparative Examples 1 to 5

[0131] The preparation methods of the multilayer coated positive electrode sheets of Comparative Examples 1 to 5 are as follows:

[0132] Step S10: weighing active materials, binders and conductive agents according to Table 1 and dissolving them in an organic solvent to form an internal active material slurry, and coating the internal active material slurry on the surface of the current collector to form a lower active material layer.

[0133] Step S20: weigh active materials, binders and conductive agents according to Table 1 and dissolve them in an organic solvent to form an external active material slurry, and apply the external active material slurry to the surface of the lower active material layer in step S10 to obtain an upper active material layer.

[0134] The multi-layer coated positive electrode sheets prepared in Comparative Examples 1 to 5 contain two active material layers but no network structure layer.

[0135] Table 1 Composition of multilayer coated positive electrode sheets of Examples 1 to 5

[0136]

[0137] Table 2 Composition of multilayer coated positive electrode sheets of Examples 6 to 10

[0138]

[0139] Table 3 Composition of multilayer coated positive electrode sheets of Comparative Examples 1 to 5

[0140]

[0141] Performance Testing

[0142] 1. Pole piece peeling force test: According to the requirements of GB-T2790-1995 "Adhesive 180° peel strength test method - Flexible material to rigid material", the pole piece is fixed to the upper jaw of the tensile testing machine. One end of the tape is adhered to the pole piece, and the other end is folded 180° and fixed to the lower jaw of the tensile testing machine. It is pulled apart at the test rate specified in the above standard. The peeling force (N) is measured by the force required to continuously peel the tape from the pole piece. The test data is shown in Table 4.

[0143] 2. Diaphragm resistance test: Place the dried electrode on the insulating film according to the requirements of the "Four-Probe Method", cut the electrode to a size larger than the four-probe distance, and use the four-probe method to measure the electrode diaphragm resistance (mΩ). The test data is shown in Table 4.

[0144] Table 4 Performance comparison of the multilayer coated positive electrode sheets of the embodiment and the comparative example

[0145] Experimental group electrode peeling force: N electrode membrane resistance: mΩ Example 1 14.7256 Example 2 13.6308 Example 3 13.1205 Example 4 11.5256 Example 5 16.8248 Example 6 17.2306 Example 7 11.4189 Example 8 20.8196 Example 9 16.2268 Example 10 14.5312 Comparative Example 1 3.4993 Comparative Example 2 2.61261 Comparative Example 3 5.81158 Comparative Example 4 4.38934 Comparative Example 5 3.9913

[0146] From Tables 1 to 4, we can see that:

[0147] The multi-layer coated positive electrode sheets of Examples 1 to 10 are prepared with a mesh lithium replenishing layer between the two active material layers. The two active material layers are connected together by a mesh structure, which strengthens the bonding force between the layers and enables the electrode sheet to obtain a higher peeling force, thereby alleviating the problem of easy peeling and powdering of the slurry between the layers of the multi-layer coating. Moreover, the mesh structure of the lithium replenishing layer is not easy to affect the overall conductive properties of the electrode sheet. The lithium replenishing agent can also further improve the conductive properties of the electrode sheet, so that the electrode sheet can still obtain a lower resistance and have better conductive properties.

[0148] The positive electrode sheets in Comparative Examples 1 to 5 consisted of two active material layers obtained through multi-layer coating. Without a network structure layer between the two active material layers, the layers exhibited poor compatibility and adhesion. The maximum peel force achieved was only 5.8N, making the slurry susceptible to peeling and falling, thereby impacting the performance of the lithium-ion battery. Furthermore, the positive electrode sheets in Comparative Examples 1 to 5 lacked a lithium supplement, resulting in high resistance and relatively poor conductivity.

[0149] The above are only some embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A multi-layer coated positive electrode sheet, comprising from bottom to top: A current collector and two or more active material layers, wherein a network structure layer is provided between any two of the active material layers, and each of the active material layers contains an active material; The active material layer formed on the surface of the current collector is defined as the lower active material layer; the uppermost layer of the multi-layer coated positive electrode sheet is the active material layer, defined as the upper active material layer; The active material layer formed between the lower active material layer and the upper active material layer is defined as a middle active material layer.

2. The multi-layer coated positive electrode sheet according to claim 1, wherein: The network structure layer includes a lithium supplement.

3. The multi-layer coated positive electrode sheet according to claim 2, wherein: The lithium supplement includes at least one of Li2NiO2, Li5FeO4, Li2O, Li2O2, Li3N, and Li2C2O4.

4. The multi-layer coated positive electrode sheet according to claim 1, wherein: The middle active material layer includes 0 layer, 1 layer or multiple layers.

5. The multi-layer coated positive electrode sheet according to claim 1, wherein: The mesh structure layer includes a binder.

6. The multi-layer coated positive electrode sheet according to any one of claims 1 to 3, wherein: The network structure layer is at least partially embedded in the active material layer formed on the upper surface and / or lower surface of the network structure layer.

7. The multi-layer coated positive electrode sheet according to claim 1, wherein: The active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium cobalt phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; and / or, the mass of the network structure layer in the multi-layer coated positive electrode sheet accounts for 3% to 5% of the total mass of the active material; and / or, the porosity of the lower active material layer ranges from 20% to 30%; and / or, the porosity of the middle active material layer ranges from 30% to 40%; And / or, the porosity of the upper active material layer is in the range of 40% to 50%.

8. The multi-layer coated positive electrode sheet according to claim 1, wherein: The D50 of the active material in the lower active material layer is in the range of 50 nm to 10 μm; and / or, the D50 of the active material in the middle active material layer is in the range of 1 μm to 10 μm; And / or, the active material in the upper active material layer has a D50 ranging from 2.5 μm to 20 μm.

9. The multi-layer coated positive electrode sheet according to claim 1, wherein: Assuming that the D50 of the active material in the lower active material layer is X and the D50 of the active material in the upper active material layer is Y, then Y>X is satisfied.

10. The multi-layer coated positive electrode sheet according to claim 9, wherein: The Y and X satisfy Y:X∈[2,1000].

11. A method for preparing a multi-layer coated positive electrode sheet, comprising the following steps: preparing an active material slurry, wherein the active material slurry contains an active material; preparing a lithium supplementing slurry containing a lithium supplementing agent; The active material slurry forms a lower active material layer on the surface of the current collector; The lithium-supplementing slurry is used to form a network lithium-supplementing layer on the surface of the lower active material layer through an electrostatic spinning process; The active material slurry forms an upper active material layer on the surface of the network-shaped lithium replenishing layer.

12. The method for preparing a multi-layer coated positive electrode sheet according to claim 11, wherein: The active material slurry and the lithium replenishing slurry both include a conductive agent and a binder. The mass percentage of the conductive agent in the network-shaped lithium replenishing layer is 5% to 10%.

13. The method for preparing a multi-layer coated positive electrode sheet according to claim 12, wherein: The mass ratio of the active material, the conductive agent and the binder is (90-98): (1-5): (1-5); And / or, the mass ratio of the lithium supplement agent, the conductive agent and the binder is (80-90): (5-10): (5-10).

14. A lithium ion battery comprising the multi-layer coated positive electrode sheet according to any one of claims 1 to 10.

15. An electrical device comprising the lithium-ion battery according to claim 14.

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