Positive pole piece, preparation method thereof and battery

Abstract

The invention provides a positive pole piece, a preparation method thereof and a battery, and aims to solve the technical problems that the capacity of LMFP is difficult to effectively exert and the cycle life of the battery is poor. The positive pole piece comprises a current collector and a first active material layer and a second active material layer which are arranged on the current collector, and the first active material layer and the second active material layer are sequentially distributed in the direction away from the current collector; the first active material layer and the second active material layer both contain lithium manganese iron phosphate; the first active material layer further comprises a first conductive agent and a first lithium supplement agent, and the second active material layer further comprises a second conductive agent and a second lithium supplement agent; wherein the gram volume K1 of the first lithium supplement agent is greater than the gram volume K2 of the second lithium supplement agent; the mass percentage D1 of the first conductive agent in the first active material layer is greater than the mass percentage D2 of the second conductive agent in the second active material layer.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode sheet, a method for preparing a positive electrode sheet, and a battery. Background Art

[0002] Lithium manganese iron phosphate (LMFP) is a positive electrode active material made by adding a certain proportion of manganese to lithium iron phosphate (LFP). LMFP and LFP both belong to the olivine structure, and their theoretical gram capacity is the same, but LMFP has a higher voltage platform, generally up to about 4.1V, higher than LFP's 3.3V~3.5V. Therefore, under equivalent conditions, the theoretical energy density of LMFP is 15%-20% higher than that of LFP. However, compared with LFP, LMFP has poor electronic conductivity and lithium ion diffusion rate, which makes it impossible to fully utilize the capacity of LMFP; and LMFP has a poor cycle life, especially at high temperatures, which is not as good as LFP.

[0003] In view of the defects of LMFP, positive electrode lithium supplementation is required. In the related art, the application of lithium supplement in LMFP system is relatively simple, which makes it difficult for the lithium supplement to play its role effectively, and thus makes it difficult to effectively exert the capacity of LMFP and improve the cycle life of the battery. Summary of the invention

[0004] The embodiments of the present application provide a positive electrode plate and a method for preparing the same, as well as a battery, to improve the technical problems that the capacity of LMFP is difficult to effectively exert and the battery cycle life is poor.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode sheet, comprising: a current collector and a first active material layer and a second active material layer arranged on the current collector, wherein the first active material layer and the second active material layer are distributed in sequence in a direction away from the current collector; the first active material layer and the second active material layer both contain lithium iron manganese phosphate; the first active material layer also contains a first conductive agent and a first lithium replenisher, and the second active material layer also contains a second conductive agent and a second lithium replenisher; wherein the gram capacity K1 of the first lithium replenisher is greater than the gram capacity K2 of the second lithium replenisher; the mass percentage D1 of the first conductive agent in the first active material layer is greater than the mass percentage D2 of the second conductive agent in the second active material layer.

[0006] In one embodiment, a ratio P1 of a mass percentage content D2 of the second conductive agent in the second active material layer to a mass percentage content D1 of the first conductive agent in the first active material layer is less than 0.78.

[0007] In one embodiment, the mass percentage content B2 of the second lithium supplement in the second active material layer is greater than the mass percentage content B1 of the first lithium supplement in the first active material layer.

[0008] In one embodiment, the ratio P2 of the mass percentage content B2 of the second lithium supplement in the second active material layer to the mass percentage content B1 of the first lithium supplement in the first active material layer is 1.25 - 6.

[0009] In one embodiment, the mass percentage content B1 of the first lithium supplement in the first active material layer is 2.0 wt% - 4.0 wt%.

[0010] In one embodiment, the mass percentage content B2 of the second lithium supplement in the second active material layer is 5.0 wt% - 15.0 wt%.

[0011] In one embodiment, the mass percentage content D1 of the first conductive agent in the first active material layer is 0.3 wt% - 1.4 wt%.

[0012] In one embodiment, the mass percentage content D2 of the second conductive agent in the second active material layer is 0.15 wt% - 0.7 wt%.

[0013] In one embodiment, the first lithium supplement includes at least one of LiNiO2 and Li5FeO4; and / or, the second lithium supplement includes a lithium-rich manganese-based material, and the chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M includes at least one transition metal.

[0014] In one embodiment, the initial charge calibration specific capacity of the first lithium supplement is greater than 300 mAh / g; and / or, the initial charge calibration specific capacity of the second lithium supplement is greater than 100 mAh / g.

[0015] In one embodiment, the mass percentage content H1 of lithium iron phosphate manganese in the first active material layer is 91.0 wt% - 95.3 wt%.

[0016] In one embodiment, the mass percentage content H2 of lithium iron phosphate manganese in the second active material layer is 80.0 wt% - 92.55.0 wt%.

[0017] In one embodiment, both the first active material layer and the second active material layer further include a binder. The content N1 of the binder in the first active material layer is 1.5 wt% - 2.0 wt%, and / or, the content N2 of the binder in the second active material layer is 1.5 wt% - 2.0 wt%.

[0018] In one embodiment, the first active material layer and the second active material layer both further comprise a dispersant, and a content F1 of the dispersant in the first active material layer is 0.1 wt% to 0.2 wt%, and / or a content F2 of the dispersant in the second active material layer is 0.1 wt% to 0.2 wt%.

[0019] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, wherein the method for preparing a positive electrode sheet is used to prepare the above-mentioned positive electrode sheet, comprising:

[0020] preparing a first slurry, wherein the first slurry comprises lithium manganese iron phosphate, a first conductive agent and a first lithium supplementing agent;

[0021] preparing a second slurry, wherein the second slurry comprises lithium manganese iron phosphate, a second conductive agent, and a second lithium supplementing agent;

[0022] Performing a film-forming process on the first slurry on a current collector to obtain a first active material layer;

[0023] The second slurry is subjected to a film-forming treatment on a side of the first active material layer away from the current collector to obtain a second active material layer.

[0024] In a third aspect, an embodiment of the present application provides a battery, comprising the above-mentioned positive electrode plate; or, the positive electrode plate prepared by the above-mentioned method.

[0025] Beneficial effects of the embodiments of the present application:

[0026] In an embodiment of the present application, the active material layers in the positive electrode plate are designed in layers, wherein the gram capacity of the first lithium replenisher in the first active material layer close to the current collector is relatively large, and the mass percentage of the first conductive agent is relatively high, while the gram capacity of the second lithium replenisher in the second active material layer far from the current collector is relatively small, and the mass percentage of the second conductive agent is relatively low. In this way, under the same mass, the first lithium replenisher can provide more lithium ions than the second conductive agent, and compared with the second active material layer, the first active material layer has a denser conductive network, so that in the battery formation process (i.e., the first charge and discharge process), when the first lithium replenisher can release a large amount of lithium ions to the negative electrode, it has lower lithium ion diffusion resistance, optimizes the transmission of lithium ions, and further promotes the use of the capacity of lithium iron manganese phosphate in the positive electrode plate, especially the use of the capacity of lithium iron manganese phosphate in the positive electrode plate close to the current collector, thereby improving the cycle life of the lithium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 It is a schematic diagram of the cross-sectional structure of the positive electrode plate provided in an embodiment of the present application.

[0029] Reference numerals:

[0030] 10. Positive electrode sheet; 11. Current collector; 12. First active material layer; 13. Second active material layer. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0032] In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0035] The terms "comprises," "includes," or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0036] In the description of the embodiments of the present application, words such as "example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "example" or "for example" in the embodiments of the present application is not to be interpreted as being more preferred or having more advantages than another embodiment or design. The use of words such as "example" or "for example" is intended to present relative concepts in a clear manner.

[0037] To facilitate understanding of the scheme of the present application, the spline curves and arrows used in the drawings are explained here: the components indicated by the spline curves without arrows are solid components, that is, components with solid structures; the components indicated by the spline curves with arrows are virtual components, that is, components without solid structures.

[0038] First, see Figure 1 An embodiment of the present application provides a positive electrode plate 10, which is used in a battery, such as a lithium-ion battery.

[0039] Specifically, the positive electrode sheet 10 includes a current collector 11, a first active material layer 12, and a second active material layer 13. The first active material layer 12 and the second active material layer 13 are arranged on the current collector 11, and the first active material layer 12 and the second active material layer 13 are distributed in sequence in the direction away from the current collector 11. The first active material layer 12 and the second active material layer 13 both contain a positive electrode active material lithium manganese iron phosphate (LMFP). The first active material layer 12 also contains a first conductive agent and a first lithium replenisher, and the second active material layer 13 also contains a second conductive agent and a second lithium replenisher. Among them, the gram capacity K1 of the first lithium replenisher is greater than the gram capacity K2 of the second lithium replenisher; the mass percentage content D1 of the first conductive agent in the first active material layer 12 is greater than the mass percentage content D2 of the second conductive agent in the second active material layer 13.

[0040] The chemical formula of lithium manganese iron phosphate is LiFe a Mn bPO4, where 0 < a < 1 and 0 < b < 1. As an example, a can be 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.999; b can be 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.999.

[0041] The lithium supplement can compensate for the irreversible lithium loss during the first charge and discharge process. The specific capacity of the lithium supplement refers to the capacity provided by each gram of the lithium supplement in the battery, usually expressed in mAh / g. The specific capacity of the lithium supplement varies depending on the specific composition.

[0042] As an example, lithium ferrite (LFO) is a lithium metal oxide with an antifluorite structure. The chemical formula of lithium ferrite is Li5FeO4, and its theoretical specific capacity can reach 700 mAh / g.

[0043] As an example, lithium nickelate (LNO) has a crystal structure belonging to layered lithium metal oxides. The chemical formula of lithium nickelate is LiNiO2, and its theoretical specific capacity can reach 400 mAh / g.

[0044] As an example, the chemical formula of the lithium-rich manganese-based material (LMR) is xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1 and M includes at least one transition metal. The theoretical specific capacity of the lithium-rich manganese-based material can reach 250 mAh / g.

[0045] The specific capacity K1 of the first lithium supplement is greater than the specific capacity K2 of the second lithium supplement. It can be understood that the first lithium supplement and the second lithium supplement are usually different substances.

[0046] The mass percentage content of the first conductive agent in the first active material layer 12 is different from the mass percentage content of the second conductive agent in the second active material layer 13, but the first conductive agent and the second conductive agent can be the same substance or different substances.

[0047] As an example, the first conductive agent and the second conductive agent can each independently include at least one of conductive carbon black, carbon nanotubes (CNT), mesoporous carbon materials, and vapor-grown carbon fibers (VGCF). As an example, the conductive carbon black includes at least one of acetylene black, Super P (SP), and Ketjen black. As an example, the carbon nanotubes include at least one of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). As an example, the mesoporous carbon material includes the ordered mesoporous carbon material CMK-3.

[0048] In the embodiment of the present application, the positive electrode plate 10 is provided by performing a hierarchical design on the active material layer. Among them, in the first active material layer 12 close to the current collector 11, the gram capacity of the first lithium supplement agent is relatively large, and the mass percentage content of the first conductive agent is relatively high. While in the second active material layer 13 far from the current collector 11, the gram capacity of the second lithium supplement agent is relatively small, and the mass percentage content of the second conductive agent is relatively low. In this way, under the same mass, the first lithium supplement agent can provide more lithium ions than the second conductive agent, and compared with the second active material layer 13, the first active material layer 12 has a denser conductive network. Therefore, during the battery formation process (i.e., the first charge-discharge process), when the first lithium supplement agent can release a large amount of lithium ions to the negative electrode, it has a lower lithium ion diffusion resistance, optimizes the transmission of lithium ions, and further promotes the capacity utilization of lithium iron phosphate manganese in the positive electrode plate 10, especially the capacity utilization of lithium iron phosphate manganese in the first active material layer 12, improving the capacity and cycle life of the battery.

[0049] In some embodiments, the first lithium supplement agent includes at least one of LiNiO2 and Li5FeO4. LiNiO2 and Li5FeO4 have a relatively high gram capacity. In a lithium iron phosphate manganese-based battery system, adding a small amount of LiNiO2 and / or Li5FeO4 can effectively improve the energy density of the battery. However, LiNiO2 and Li5FeO4 are unstable, not only having strong water absorption characteristics, but also being prone to decomposition when exposed to air for a long time. By adding LiNiO2 and / or Li5FeO4 to the first active material layer 12 and using the current collector 11 and the second active material layer 13 to shield the first active material layer 12, water vapor can be effectively isolated, reducing the risk of inactivation of LiNiO2 and / or Li5FeO4. Optionally, the first lithium supplement agent includes LNO. Compared with LFO, LNO has more stable properties and can more effectively promote the capacity utilization of lithium iron phosphate manganese.

[0050] In some embodiments, the second lithium supplement agent includes a lithium-rich manganese-based material. The chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M includes at least one transition metal. Although the gram capacity of the lithium-rich manganese-based material is not as high as that of LiNiO2 and Li5FeO4, the lithium-rich manganese-based material is relatively stable and has a relatively low price, which is beneficial to controlling the production cost of the battery. As an example, x is 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 0.999. M includes at least one of Ni, Co, and Mn.

[0051] In some embodiments, the ratio P1 of the mass percentage content D2 of the second conductive agent in the second active material layer 13 to the mass percentage content D1 of the first conductive agent in the first active material layer 12 is less than 0.78. In this way, the conductive system can be further optimized without changing the total amount of the conductive agent, and the lithium supplement agent can be effectively used. Optionally, P1 is less than 0.67. As an example, P1 is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.67.

[0052] In some embodiments, the mass percentage D1 of the first conductive agent in the first active material layer 12 is 0.3 wt% to 1.4 wt%. As an example, D1 is 0.3 wt%, 0.5 wt%, 0.6 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.3 wt% or 1.4 wt%.

[0053] In some embodiments, the mass percentage content D2 of the second conductive agent in the second active material layer 13 is 0.15 wt% to 0.7 wt%. As an example, D2 is 0.15 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt% or 0.7 wt%.

[0054] In some embodiments, the mass percentage content B2 of the second lithium replenisher in the second active material layer 13 is greater than the mass percentage content B1 of the first lithium replenisher in the first active material layer 12. Compared with the first active material layer 12, the second active material layer 13 is closer to the surface of the positive electrode plate 10, so that the transmission path of the lithium ions released by the second lithium replenisher is shorter and the diffusion resistance is smaller. By increasing the mass percentage content B2 of the second lithium replenisher in the second active material layer 13, the transmission of lithium ions in the positive electrode plate 10 can be further optimized as a whole.

[0055] In some embodiments, the ratio P2 of the mass percentage content B2 of the second lithium replenisher in the second active material layer 13 to the mass percentage content B1 of the first lithium replenisher in the first active material layer 12 is 1.25 to 6. Within this range, the capacity of the lithium iron manganese phosphate in the first active material layer 12 and the second active material layer 13 can be effectively utilized, thereby improving the capacity and cycle life of the battery. As an example, P2 is 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6.

[0056] In some embodiments, the mass percentage B1 of the first lithium supplement in the first active material layer 12 is 2.0 wt% to 4.0 wt%. As an example, B1 is 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3.0 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt% or 4.0 wt%.

[0057] In some embodiments, the mass percentage content B2 of the second lithium supplement agent in the second active material layer 13 is 5.0 wt% to 15.0 wt%. As an example, B2 is 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, 10.0 wt%, 10.5 wt%, 11.0 wt%, 11.5 wt%, 12.0 wt%, 12.5 wt%, 13.0 wt%, 13.5 wt%, 14.0 wt%, 14.5 wt% or 15.0 wt%.

[0058] In some embodiments, the first-charge rated gram capacity of the first lithium supplement is greater than 300mAh / g; the first-charge rated gram capacity of the second lithium supplement is greater than 100mAh / g. The first-charge rated gram capacity is also called the first-charge gram capacity, which refers to the ratio of the capacity that can be released by the lithium supplement to the mass of the lithium supplement during the first charging of the lithium-ion battery. The first-charge rated gram capacity of the lithium supplement is only related to the material type of the lithium supplement, that is, when the material type of the lithium supplement is determined, the first-charge rated gram capacity is a determined value, that is, the first-charge rated gram capacity is a property of the lithium supplement itself. As an example, the first lithium supplement includes at least one of LFO and LNO, the first-charge rated gram capacity of LFO is 590mAh / g, and the first-charge rated gram capacity of LNO is 350mAh / g. As an example, the second lithium supplement includes LMR, and the first-charge rated gram capacity of LMR is 140mAh / g.

[0059] In some embodiments, the mass percentage H1 of lithium manganese iron phosphate in the first active material layer 12 is 91.0wt% to 95.3wt%. Within this range, the energy density of the battery can be effectively guaranteed. As an example, H1 is 91.0wt%, 92.0wt%, 93.0wt%, 94.0wt% or 95.3wt%.

[0060] In some embodiments, the mass percentage H2 of lithium manganese iron phosphate in the second active material layer 13 is 80.0wt% to 92.55.0wt%. Within this range, the energy density of the battery can be effectively guaranteed. As an example, H2 is 80.0wt%, 82.0wt%, 84.0wt%, 86.0wt%, 88.0wt%, 90.0wt% or 92.55wt%.

[0061] In some embodiments, the first active material layer 12 and the second active material layer 13 further include a binder. Optionally, the binder includes at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA).

[0062] In some embodiments, the content N1 of the binder in the first active material layer 12 is 1.5 wt% to 2.0 wt%, and the content N2 of the binder in the second active material layer 13 is 1.5 wt% to 2.0 wt%. As an example, N1 is 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%, and N2 is 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%.

[0063] In some embodiments, the first active material layer 12 and the second active material layer 13 further include a dispersant. Optionally, the dispersant includes at least one of anhydride, polyvinyl pyrrolidone, sulfate ester salt, poly(N-vinyl acetamide), polyvinyl alcohol, sulfonate and polyethylene glycol.

[0064] In some embodiments, the content F1 of the dispersant in the first active material layer 12 is 0.1 wt% to 0.2 wt%, and the content F2 of the dispersant in the second active material layer 13 is 0.1 wt% to 0.2 wt%. As an example, F1 is 0.1 wt%, 0.12 wt%, 0.14 wt%, 0.16 wt%, 0.18 wt% or 0.2 wt%, and F2 is 0.1 wt%, 0.12 wt%, 0.14 wt%, 0.16 wt%, 0.18 wt% or 0.2 wt%.

[0065] In some embodiments, the current collector 11 may be aluminum foil, carbon-coated aluminum foil, safety-primed aluminum foil, etched aluminum foil or aluminum mesh. The thickness of the current collector 11 may be 5 μm to 20 μm, for example 5 μm, 10 μm, 15 μm or 20 μm.

[0066] In a second aspect, the present application also provides a method for preparing a positive electrode sheet, which is used to prepare the positive electrode sheet 10, comprising:

[0067] S1. Prepare a first slurry, wherein the first slurry comprises lithium manganese iron phosphate, a first conductive agent and a first lithium supplementing agent;

[0068] S2, preparing a second slurry, wherein the second slurry comprises lithium manganese iron phosphate, a second conductive agent, and a second lithium supplementing agent;

[0069] S3, performing film-forming treatment on the first slurry on the current collector to obtain a first active material layer;

[0070] S4, performing a film-forming treatment on the second slurry on a side of the first active material layer away from the current collector to obtain a second active material layer.

[0071] In some embodiments, the first slurry further includes a first solvent, and S3 includes:

[0072] S31, coating the first slurry on the current collector to obtain a first wet film layer;

[0073] S32, drying the first wet film layer to obtain a first active material layer.

[0074] In some embodiments, the second slurry further includes a second solvent, and S4 includes:

[0075] S41, coating the second slurry on the first wet film layer to obtain a second wet film layer;

[0076] S42, drying the second wet film layer to obtain a second active material layer.

[0077] Optionally, the coating process includes but is not limited to at least one of gravure coating, micro gravure coating, spray coating and electrostatic spinning techniques. The first solvent and the second solvent include N-methylpyrrolidone (NMP).

[0078] In a third aspect, an embodiment of the present application further provides a battery, comprising the above-mentioned positive electrode plate 10; or, the positive electrode plate prepared by the above-mentioned method.

[0079] In some embodiments, the battery is a lithium ion battery.

[0080] The following is a description with reference to specific embodiments.

[0081] Example 1

[0082] S1. Prepare the positive electrode: double-coat the positive electrode slurry onto the carbon-coated aluminum foil current collector, with the upper and lower layers having the same density. After drying, cold press the sheets.

[0083] The positive electrode slurry formula is:

[0084] 1. Upper slurry: LMFP (LiFe 0.5 Mn 0.5 PO4, 90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR: 0.6Li2MnO3·0.4LiNiO2, is added simultaneously with LMFP during the stirring process, and LMR is the lithium supplement agent for the upper layer.

[0085] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0086] S2. Prepare the negative electrode: apply a single layer of the negative electrode slurry onto the copper foil, and then cold press the cut pieces after drying.

[0087] The negative electrode slurry formula is: graphite: SP: CMC: SBR = 96.7: 0.6: 1.2: 1.5 (mass ratio).

[0088] S3. Prepare the battery: assemble the positive and negative pole pieces into a core pack by stacking them, and then perform vacuum baking after assembly. After baking, inject liquid (1M LiPF6 (EC:DEC:DMC=1:1:1, volume ratio)) after the moisture content is qualified. After injection, let it stand for 24 hours to evolve into capacity. After the capacity is evolved, vacuum seal it and the soft-pack battery cell is offline.

[0089] Example 2

[0090] The difference from Example 1 is that the positive electrode slurry formula is:

[0091] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer;

[0092] 2. Lower layer slurry: LMFP (94.7wt%), LNO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LNO is added simultaneously with LMFP during stirring, and LNO is the lithium supplement agent of the lower layer.

[0093] The rest is the same as Example 1.

[0094] Example 3

[0095] The difference from Example 1 is that the positive electrode slurry formula is:

[0096] 1. Upper slurry: LMFP (90.95wt%), LMR (7wt%), SP (0.1wt%), CNT (0.05wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0097] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0098] The rest is the same as Example 1.

[0099] Example 4

[0100] The difference from Example 1 is that the positive electrode slurry formula is:

[0101] 1. Upper slurry: LMFP (90.5wt%), LMR (7wt%), SP (0.4wt%), CNT (0.2wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0102] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0103] The rest is the same as Example 1.

[0104] Example 5

[0105] The difference from Example 1 is that the positive electrode slurry formula is:

[0106] 1. Upper slurry: LMFP (90.4wt%), LMR (7wt%), SP (0.45wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0107] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0108] The rest is the same as Example 1.

[0109] Example 6

[0110] The difference from Example 1 is that the positive electrode slurry formula is:

[0111] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0112] 2. Lower layer slurry: LMFP (94.89wt%), LFO (2.5wt%), SP (0.5wt%), CNT (0.21wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0113] The rest is the same as Example 1.

[0114] Example 7

[0115] The difference from Example 1 is that the positive electrode slurry formula is:

[0116] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0117] 2. Lower layer slurry: LMFP (94.5wt%), LFO (2.5wt%), SP (0.8wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent for the lower layer.

[0118] The rest is the same as Example 1.

[0119] Example 8

[0120] The difference from Example 1 is that the positive electrode slurry formula is:

[0121] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0122] 2. Lower layer slurry: LMFP (94.2wt%), LFO (2.5wt%), SP (0.9wt%), CNT (0.5wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0123] The rest is the same as Example 1.

[0124] Example 9

[0125] The difference from Example 1 is that the positive electrode slurry formula is:

[0126] 1. Upper slurry: LMFP (90.95wt%), LMR (7wt%), SP (0.1wt%), CNT (0.05wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0127] 2. Lower layer slurry: LMFP (95.3wt%), LFO (2.5wt%), SP (0.2wt%), CNT (0.1wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0128] The rest is the same as Example 1.

[0129] Example 10

[0130] The difference from Example 1 is that the positive electrode slurry formula is:

[0131] 1. Upper slurry: LMFP (90.4wt%), LMR (7wt%), SP (0.5wt%), CNT (0.2wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0132] 2. Lower layer slurry: LMFP (94.4wt%), LFO (2.5wt%), SP (0.9wt%), CNT (0.5wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0133] The rest is the same as Example 1.

[0134] Embodiment 11

[0135] The difference from Example 1 is that the positive electrode slurry formula is:

[0136] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0137] 2. Lower layer slurry: LMFP (93.2wt%), LFO (4.0wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0138] The rest is the same as Example 1.

[0139] Example 12

[0140] The difference from Example 1 is that the positive electrode slurry formula is:

[0141] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0142] 2. Lower layer slurry: LMFP (95.2wt%), LFO (2.0wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0143] The rest is the same as Example 1.

[0144] Embodiment 13

[0145] The difference from Example 1 is that the positive electrode slurry formula is:

[0146] 1. Upper slurry: LMFP (92.55wt%), LMR (5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0147] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0148] The rest is the same as Example 1.

[0149] Embodiment 14

[0150] The difference from Example 1 is that the positive electrode slurry formula is:

[0151] 1. Upper slurry: LMFP (85.05wt%), LMR (12.5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0152] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0153] The rest is the same as Example 1.

[0154] Embodiment 15

[0155] The difference from Example 1 is that the positive electrode slurry formula is:

[0156] 1. Upper slurry: LMFP (82.55wt%), LMR (15wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0157] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0158] The rest is the same as Example 1.

[0159] Example 16

[0160] The difference from Example 1 is that the positive electrode slurry formula is:

[0161] 1. Upper slurry: LMFP (92.55wt%), LMR (5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0162] 2. Lower layer slurry: LMFP (93.9wt%), LFO (3.3wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0163] The rest is the same as Example 1.

[0164] Embodiment 17

[0165] The difference from Example 1 is that the positive electrode slurry formula is:

[0166] 1. Upper slurry: LMFP (92.55wt%), LMR (5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0167] 2. Lower layer slurry: LMFP (93.2wt%), LFO (4wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0168] The rest is the same as Example 1.

[0169] Embodiment 18

[0170] The difference from Example 1 is that the positive electrode slurry formula is:

[0171] 1. Upper slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer;

[0172] 2. Lower layer slurry: LMFP (94.7wt%), LFO (1.25wt%), LNO (1.25wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LNO and LFO are added simultaneously with LMFP during stirring, and LNO and LFO are lithium supplements for the lower layer.

[0173] The rest is the same as Example 1.

[0174] Comparative Example 1

[0175] The difference from Example 6 is that step S1 (preparing the positive electrode):

[0176] The positive electrode slurry is coated on the carbon-coated aluminum foil current collector in a single layer, and then cold-pressed and cut into pieces after drying.

[0177] The positive electrode slurry formula is: LMFP (92.72wt%), LMR (4.75wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), and dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during the stirring process, and LMR is a lithium supplement.

[0178] The rest is the same as Example 1.

[0179] Comparative Example 2

[0180] The difference from Example 6 is that step S1 (preparing the positive electrode):

[0181] The positive electrode slurry is coated on the carbon-coated aluminum foil current collector in a single layer, and then cold-pressed and cut into pieces after drying.

[0182] The positive electrode slurry formula is: LMFP (92.72wt%), LFO (4.75wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), and dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during the stirring process, and LFO is a lithium supplement.

[0183] The rest is the same as Example 1.

[0184] Comparative Example 3

[0185] The difference from Example 6 is that the positive electrode slurry formula is:

[0186] 1. Upper slurry: LMFP (90.47wt%), LMR (7wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during the stirring process, and LMR is the lithium supplement agent of the upper layer;

[0187] 2. Lower layer slurry: LMFP (94.97wt%), LFO (2.5wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0188] The rest is the same as Example 1.

[0189] Comparative Example 4

[0190] The difference from Example 6 is that the positive electrode slurry formula is:

[0191] 1. Upper slurry: LMFP (90.39wt%), LMR (7wt%), SP (0.5wt%), CNT (0.21wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent of the upper layer.

[0192] 2. Lower layer slurry: LMFP (95.05wt%), LFO (2.5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the lower layer.

[0193] The rest is the same as Example 1.

[0194] Comparative Example 5

[0195] The difference from Example 6 is that the positive electrode slurry formula is:

[0196] 1. Upper slurry: LMFP (94.89wt%), LFO (2.5wt%), SP (0.5wt%), CNT (0.21wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during stirring, and LFO is the lithium supplement agent of the upper layer.

[0197] 2. Lower layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement agent for the lower layer.

[0198] The rest is the same as Example 1.

[0199] The parameters of each embodiment and comparative example are recorded in Table 1.

[0200] Table 1

[0201]

[0202]

[0203] The unit of the content of each material in Table 1 is wt%.

[0204] The batteries prepared in the examples and comparative examples were tested as follows:

[0205] 1. Gram capacity test: At 25°C, charge the battery at a rate of 0.33C, and then discharge it at 0.33C after being fully charged to obtain the discharge capacity. Perform capacity calibration to obtain the gram capacity. The results are recorded in Table 2.

[0206] 2. Capacity retention rate test: At 25°C, the battery was subjected to a 1C / 1C cycle test. The capacity retention rate was calculated by dividing the capacity after 500 cycles by the initial capacity to obtain the capacity retention rate after the cycle. The test results are recorded in Table 2.

[0207] 3. DC internal resistance (DCR) growth rate test: DCR test was performed at 1C@10s 70% SOC DCR; at 25°C, the battery was subjected to a 1C / 1C cycle test, and the DCR growth rate was calculated by dividing the difference between the DCR after 500 cycles and the initial DCR by the initial DCR to obtain the DCR growth rate after the cycle. The test results are recorded in Table 2.

[0208] Table 2

[0209]

[0210]

[0211] From the results in Table 2, we can see that:

[0212] The gram capacity of the batteries provided in Examples 1 to 18 was maintained above 139.6 mAh / g, and the capacity retention rate was above 95.3%, while the DCR growth rate was maintained below 8.9%.

[0213] Further comparing Example 6 and Comparative Examples 1 to Comparative Examples 5, when the total content of each material in the electrode is the same, compared with Comparative Examples 1 and 2 (the positive electrode is only provided with a single active material layer, and the lithium replenisher is simply mixed in the active material layer), Comparative Example 3 (the active material layer is arranged in layers, but the conductive agent content in the upper and lower active material layers is the same), Comparative Example 4 (the active material layer is arranged in layers, but the conductive agent content in the lower active material layer is less than that in the upper layer), and Comparative Example 5 (the active material layer is arranged in layers, but the conductive agent content in the lower active material layer is less than that in the upper layer, and the gram capacity of the upper lithium replenisher is greater than that in the lower layer), Example 6 is improved in both gram capacity and capacity retention rate, while the DCR growth rate is reduced. This shows that by arranging the active material layers in layers, and the gram capacity of the lithium replenisher in the inner layer is greater than the gram capacity of the lithium replenisher in the outer layer, and the content of the conductive agent in the inner layer is greater than the content of the conductive agent in the outer layer, the capacity of the LMFP in the active material layer can be effectively promoted, the cycle stability of the battery is improved, and the DC internal resistance growth rate of the battery is reduced, thereby improving the performance of the battery.

[0214] The embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A positive electrode sheet, characterized in that: Comprising: A current collector and a first active material layer and a second active material layer disposed on the current collector. Along the direction away from the current collector, the first active material layer and the second active material layer are sequentially distributed; both the first active material layer and the second active material layer contain lithium iron manganese phosphate; the first active material layer further contains a first conductive agent and a first lithium supplement agent, and the second active material layer further contains a second conductive agent and a second lithium supplement agent; wherein, the gram capacity K1 of the first lithium supplement agent is greater than the gram capacity K2 of the second lithium supplement agent; the mass percentage content D1 of the first conductive agent in the first active material layer is greater than the mass percentage content D2 of the second conductive agent in the second active material layer.

2. The positive electrode sheet according to claim 1, characterized in that: The ratio P1 of the mass percentage content D2 of the second conductive agent in the second active material layer to the mass percentage content D1 of the first conductive agent in the first active material layer is less than 0.

78.

3. The positive electrode sheet according to claim 1, characterized in that: The mass percentage content B2 of the second lithium supplement agent in the second active material layer is greater than the mass percentage content B1 of the first lithium supplement agent in the first active material layer.

4. The positive electrode sheet according to claim 3, characterized in that: The ratio P2 of the mass percentage content B2 of the second lithium supplement agent in the second active material layer to the mass percentage content B1 of the first lithium supplement agent in the first active material layer is 1.25 - 6.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The mass percentage content B1 of the first lithium supplement agent in the first active material layer is 2.0wt% - 4.0wt%; and / or, The mass percentage content B2 of the second lithium supplement agent in the second active material layer is 5.0wt% - 15.0wt%.

6. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The mass percentage content D1 of the first conductive agent in the first active material layer is 0.3wt% - 1.4wt%; and / or, The mass percentage content D2 of the second conductive agent in the second active material layer is 0.15wt% - 0.7wt%.

7. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The first lithium supplement agent includes at least one of LiNiO2 and Li5FeO4; and / or, the second lithium supplement agent includes a lithium-rich manganese-based material, and the chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M includes at least one transition metal.

8. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The first charge calibration gram capacity of the first lithium supplement agent is greater than 300mAh / g; and / or, the first charge calibration gram capacity of the second lithium supplement agent is greater than 100mAh / g.

9. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The mass percentage content H1 of the lithium iron manganese phosphate in the first active material layer is 91.0wt% - 95.3wt%; and / or, The mass percentage content H2 of the lithium iron manganese phosphate in the second active material layer is 80.0wt% - 92.55.0wt%.

10. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: Both the first active material layer and the second active material layer further contain a binder. The content N1 of the binder in the first active material layer is 1.5wt% - 2.0wt%, and / or, the content N2 of the binder in the second active material layer is 1.5wt% - 2.0wt%.

11. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The first active material layer and the second active material layer both further include a dispersant, wherein the content F1 of the dispersant in the first active material layer is 0.1 wt% to 0.2 wt%, and / or the content F2 of the dispersant in the second active material layer is 0.1 wt% to 0.2 wt%.

12. A method for preparing a positive electrode sheet, used for preparing the positive electrode sheet according to any one of claims 1 to 11, characterized in that: include: preparing a first slurry, wherein the first slurry comprises lithium manganese iron phosphate, a first conductive agent and a first lithium supplementing agent; preparing a second slurry, wherein the second slurry comprises lithium manganese iron phosphate, a second conductive agent, and a second lithium supplementing agent; Performing a film-forming process on the first slurry on a current collector to obtain a first active material layer; The second slurry is subjected to a film-forming treatment on a side of the first active material layer away from the current collector to obtain a second active material layer.

13. A battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet as claimed in any one of claims 1 to 11; or a positive electrode sheet prepared by the method according to claim 12.

Images