Positive electrode sheet and battery

Abstract

A positive electrode sheet comprises a positive current collector (1), a first paste (2) located on the surface(s) of one side or two sides of the positive current collector (1), and a second paste (3) located on the surface of the first paste (2). The first paste (2) comprises a lithium-rich manganese-based material, and the second paste (3) comprises a ternary material. The chemical formula of the ternary material is Li aNi xCo yMn dA kO 2, wherein 0.9≤a≤1.1, 0.5≤x≤0.8, 0.2≤y<0.5, 0≤k≤0.05, 0.2≤d<0.5, A is a doping element, and the ratio of the content of Mn element in the first paste (2) to the content of Mn element in the second paste(3) is (0.68-45): 1. The battery comprising the positive electrode sheet has the characteristics of high energy density and long cycle life.

Description

Positive electrode sheet and battery Technical Field

[0001] The present disclosure relates to the technical field of batteries, and in particular to a positive electrode sheet and a battery including the positive electrode sheet.

[0002] Background of the Invention

[0003] New energy vehicles have become a key industry being vigorously promoted by the Chinese government. To address the range anxiety associated with new energy vehicles, the industry is increasingly demanding higher energy density and fast-charging performance for power batteries, a core component of these vehicles. Among all power battery components, the positive electrode plays a significant role in determining the battery's cycle life and energy density. However, existing commercially available positive electrodes struggle to meet the industry's demanding requirements for higher performance in future power batteries.

[0004] Therefore, it is very important to invent a battery with both high energy density and long cycle life.

[0005] Summary of the Invention

[0006] Traditional pole pieces are generally single-layer structures, that is, active materials, conductive agents, binders and other components are evenly dispersed in the pole piece paste, and the proportion of the components is the same from the bottom layer to the surface layer of the pole piece. This single-layer structure has the advantages of simple coating process and good consistency, but due to the uneven distribution of electrolyte concentration and current density from the bottom layer of the pole piece close to the current collector to the surface layer far away from the current collector, there is polarization inside the pole piece, and the polarization conditions of the surface and bottom layers are also different. This uneven polarization will be more obvious when the thickness of the pole piece increases, resulting in the surface active material in the pole piece preferentially deintercalating lithium, and the bottom active material deintercalating lithium more lagging, the overall gram capacity is lower, and the capacity decay will occur faster during the cycle.

[0007] Among the active materials of lithium-ion battery cathodes, lithium-rich manganese-based materials have higher theoretical gram capacity (>250mAh / g) and charging voltage (≥4.5V). Therefore, lithium-rich manganese-based materials have become candidate materials for the preparation of high energy density batteries. However, lithium-rich manganese-based materials still have some disadvantages that hinder their practical application. For example, under high voltage conditions, lithium-rich manganese-based materials will undergo Li + and O 2- The common escape of O 2-It will be further oxidized to produce oxygen, causing irreversible structural defects in the positive electrode. At the same time, due to the poor ionic conductivity and electronic conductivity of lithium-rich manganese materials, the rate performance of the battery prepared therefrom is also relatively limited. In addition, under high voltage, due to the large polarization, the contact between the lithium-rich manganese-based material and the electrolyte will also intensify the oxygen evolution reaction, thereby aggravating the structural aging and decomposition of the electrolyte and generating irreversible by-products. Therefore, due to the poor structural stability of the lithium-rich manganese-based material, by-products will be generated and accumulated on the surface of the positive electrode. In addition, the lithium ion diffusion coefficient and electronic conductivity of the lithium-rich manganese-based material itself are low, which will affect the cycle life and rate performance of the battery.

[0008] Based on the above shortcomings of lithium-rich manganese-based materials themselves, when lithium-rich manganese-based materials are applied to pole pieces with a single-layer structure, the polarization phenomenon of the surface and bottom layers caused by the structure of the pole pieces will further aggravate the side reactions and irreversible phase changes of the lithium-rich manganese-based materials, causing the performance of the pole pieces to deteriorate rapidly and unable to meet the requirements of power batteries for pole pieces.

[0009] The present invention aims to overcome the aforementioned problems of the prior art by providing a positive electrode sheet and a battery including the same. The positive electrode sheet disclosed herein has high specific capacity and high cycling stability; batteries including the positive electrode sheet have both high energy density and long cycle life.

[0010] The inventors of the present disclosure have discovered that by improving the gram capacity and cycle stability of the positive electrode sheet, the energy density and cycle stability of the battery can be improved, thereby achieving the effect of both increasing the energy density and extending the cycle life of the battery. In order to improve the gram capacity and cycle stability of the positive electrode sheet, the gram capacity and cycle stability of the positive electrode sheet can be improved by changing the structure of the positive electrode sheet and using different positive electrode materials to work synergistically. The inventors of the present disclosure have discovered a specific structure that can improve the gram capacity and cycle stability of the positive electrode sheet.

[0011] In order to achieve the above-mentioned object, the first aspect of the present disclosure provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a first paste located on one side or both sides of the positive electrode current collector, and a second paste located on the surface of the first paste, wherein the first paste comprises a lithium-rich manganese-based material, and the second paste comprises a ternary material, the chemical formula of the ternary material is Li a Ni x Co y Mn d A k O2, wherein 0.9≤a≤1.1, 0.5≤x≤0.8, 0.2≤y<0.5, 0≤k≤0.05, 0.2≤d<0.5; A is a doping element, and the ratio of the content of Mn element in the first paste to the content of Mn element in the second paste is (0.68-45):1.

[0012] A second aspect of the present disclosure provides a battery, comprising the positive electrode sheet described in the first aspect of the present disclosure.

[0013] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0014] The positive electrode sheet disclosed in the present invention has a specific double-layer structure. By regulating the two layers of paste, the present invention can reduce the impact of positive electrode polarization on the lithium-rich manganese-based material in the first paste, thereby improving the specific capacity of the positive electrode sheet. At the same time, through the coordinated cooperation of the lithium-rich manganese-based material and the ternary material, the paste located on the surface of the positive electrode sheet (the second paste) has a higher lithium ion concentration and electrolyte potential, so that the lithium ion deintercalation reaction will occur preferentially, thereby giving full play to the advantages of the ternary material's better rate performance and promoting faster diffusion of lithium ions. In addition, the medium nickel (corresponding to the value of x) ternary material is more stable under high voltage. Using it as the surface paste can ensure that it is not prone to irreversible phase change when polarization occurs, thereby improving the cycle life of the positive electrode.

[0015] Given the poor conductivity of lithium-rich manganese-based materials, placing them in the bottom layer (the first paste) can compensate for this lack of conductivity, increase the depth of lithium insertion and removal, and fully utilize their high operating voltage and high specific capacity to increase the overall energy density of the battery. Furthermore, because the bottom layer paste has relatively less contact with the electrolyte, this design can also reduce side reactions between the lithium-rich manganese-based material and the electrolyte.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description.

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a schematic structural diagram of the positive electrode sheet disclosed in the present invention.

[0019] FIG2 is a SEM image of the positive electrode sheet in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0020] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

[0021] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0022] The present disclosure provides a positive electrode sheet in a first aspect, comprising a positive electrode current collector, a first paste located on one or both sides of the positive electrode current collector, and a second paste located on the surface of the first paste, wherein the first paste comprises a lithium-rich manganese-based material, and the second paste comprises a ternary material, wherein the chemical formula of the ternary material is Li a Ni x Co y Mn d A k O2, wherein 0.9≤a≤1.1, 0.5≤x≤0.8, 0.2≤y<0.5, 0≤k≤0.05, 0.2≤d<0.5; A is a doping element, and the ratio of the content of Mn element in the first paste to the content of Mn element in the second paste is (0.68-45):1.

[0023] The positive electrode sheet includes a positive electrode current collector 1, a first paste 2 located on one or both sides of the positive electrode current collector 1, and a second paste 3 located on the surface of the first paste. As shown in Figures 1 and 2, the first paste 2 is located at the bottom layer close to the positive electrode current collector 1, and the second paste 3 is located at the surface layer away from the positive electrode current collector 2.

[0024] The first paste may include a lithium-rich manganese-based material, and the second paste may include a ternary material. The ternary material should meet the above-mentioned chemical formula definition and the ratio of the content of the Mn element in the first paste to the content of the Mn element in the second paste meets a specific ratio. Under the coordinated cooperation of the lithium-rich manganese-based material located at the bottom layer of the positive electrode sheet (the first paste) and the ternary material located at the surface coating of the positive electrode sheet (the second paste), the dissolution of Mn can be reduced during the deintercalation of lithium ions, and the crystal phase transformation of the lithium-rich manganese-based material can be avoided, thereby making the structure of the positive electrode material more stable and improving the cycle stability of the positive electrode sheet.

[0025] The positive electrode sheet disclosed in the present invention has a specific double-layer structure. Since the lithium ion concentration and electrolyte potential of the surface layer are higher (relative to the bottom layer), lithium ion deintercalation reaction will occur preferentially. The second paste comprising the ternary material is arranged on the surface layer away from the positive electrode current collector, which can give full play to the advantages of the good rate performance of the ternary material and promote the faster deintercalation of lithium ions. Moreover, since the ternary material has high cycle stability under high voltage, it can also ensure that its structural stability is not easily destroyed when polarization occurs, thereby improving the cycle stability of the positive electrode sheet. Since the structural stability and conductivity of the lithium-rich manganese-based material are relatively poor, the first paste comprising the lithium-rich manganese-based material is arranged on the bottom layer close to the positive electrode current collector, which can compensate for the poor conductivity of the lithium-rich manganese-based material and increase the depth of lithium deintercalation of the lithium-rich manganese-based material. Since the bottom layer has less contact with the electrolyte (relative to the surface layer), the side reaction between the lithium-rich manganese-based material and the electrolyte can be suppressed. In addition, the characteristics of the high operating voltage and high specific capacity of the lithium-rich manganese-based material can be utilized to improve the specific capacity of the positive electrode sheet.

[0026] In the present disclosure, through the coordinated cooperation of the above-mentioned specific structures of the positive electrode sheet, the specific capacity of the positive electrode sheet can be improved and the cycle stability can be improved, so that the battery can achieve the effects of high energy density and long cycle life.

[0027] By designing the positive electrode sheet with the above-mentioned specific structure, the positive electrode sheet can achieve higher specific capacity and higher cycle stability than the existing technology. To further improve the effect, one or more of the technical features can be further optimized.

[0028] The chemical formula of the ternary material is Li a Ni x Co y Mn d A k O2. In the chemical formula Li a Ni x Co y Mn d A k The elements in O2 conform to the principle that the algebraic sum of the positive and negative valences of various elements in a compound is zero.

[0029] Wherein, 0.9≤a≤1.1, a can be a decimal, for example, 0.9, 0.92, 0.95, 0.97, 1, 1.02, 1.05, 1.07, 1.1. In order to ensure sufficient lithium source during the lithium insertion and extraction process, a can be adjusted within the above range.

[0030] Wherein, 0.5≤x≤0.8, x can be a decimal, for example, 0.5, 0.51, 0.55, 0.6, 0.65, 0.7, 0.75, 0.79.

[0031] Wherein, 0.2≤y<0.5, y can be a decimal, for example, 0.21, 0.25, 0.3, 0.35, 0.4, 0.45, 0.49.

[0032] Wherein, 0.2≤d<0.5, x can be a decimal, for example, 0.21, 0.25, 0.3, 0.35, 0.4, 0.45, 0.49.

[0033] Wherein, 0≤k≤0.05, k can be a decimal, for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05. When k is 0, it indicates that the doping element A is not present in the ternary material.

[0034] Preferably, x+y+d=1.

[0035] A may be a doping element, and A is selected from one or more of Al, Mg, Ti, Zr and F.

[0036] In one embodiment, the ternary material is a single crystal material. This means that each particle of the ternary material contains only a single crystal grain, and there are no grain boundaries within the particles. Compared to polycrystalline materials, single crystal particles are more structurally stable during cycling, which is beneficial to the cycling stability of the positive electrode sheet.

[0037] According to a specific embodiment, the median particle size Dv50 of the ternary material is 3 μm-10 μm (e.g., 3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.3 μm, 5 μm, 7 μm, 10 μm). When the median particle size of the ternary material is controlled within the above range, the ternary material has the characteristic of high stability.

[0038] In one example, the median particle size Dv50 of the ternary material is 3.5 μm-6 μm.

[0039] According to a specific embodiment, the specific surface area of ​​the ternary material is 0.3m 2 / g-1m 2 / g (for example, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 When the specific surface area of ​​the ternary material is controlled within the above range, the ternary material has the characteristic of high stability.

[0040] In one embodiment, the specific surface area of ​​the ternary material is 0.5 m 2 / g-0.8m 2 / g.

[0041] In one embodiment, the ternary material is a single crystal material, the median particle size Dv50 of the ternary material is 3.5 μm-6 μm, and the specific surface area of ​​the ternary material is 0.5 m 2 / g-0.8m 2 When the crystal structure, median particle size Dv50 and specific surface area of ​​the ternary material are controlled within the above ranges, the ternary material has higher cycle stability.

[0042] The ratio of the content of the Mn element in the first paste to the content of the Mn element in the second paste is (0.68-45):1 (for example, 0.68:1, 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1).

[0043] In one example, the ratio of the weight of the Mn element in the first paste to the content of the Mn element in the second paste is (1.5-20):1.

[0044] According to a specific embodiment, the weight ratio of the first coating paste to the second coating paste is (1-9):1 (e.g., 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1). When the weight ratio of the first coating paste to the second coating paste is controlled within the above range, the positive electrode sheet can have both high specific capacity and high cycle stability.

[0045] In one example, the weight ratio of the first active substance to the weight of the second paste is (2.2-4):1.

[0046] In one embodiment, the ratio of the weight of the first active material to the weight of the second paste is (2.2-4):1, and the ratio of the weight of the Mn element in the first paste to the content of the Mn element in the second paste is (1.5-20):1. Through the above definition, the disadvantage of the poor conductivity of the lithium-rich manganese-based material can be further compensated, the depth of lithium deintercalation of the lithium-rich manganese-based material can be increased, and the side reaction between the lithium-rich manganese-based material and the electrolyte can be further suppressed. At the same time, the advantage of the good rate performance of the ternary material can be further utilized, and the lithium ions can be promoted to be deintercalated faster, so that the positive electrode sheet can have the characteristics of high specific capacity and high cycle stability.

[0047] In one embodiment, the ratio of the median particle size Dv50 of the lithium-rich manganese-based material to the median particle size Dv50 of the ternary material is (0.8-7):1 (for example, 0.8:1, 1:1, 1.5:1, 1.85:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.7:1, 4:1, 4.05:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.7:1, 7:1). When the ratio of the median particle size Dv50 of the lithium-rich manganese-based material to the median particle size Dv50 of the ternary material is controlled within the above range, the lithium-rich manganese-based material and the ternary material can have good lithium ion diffusion performance while maintaining good dispersion, thereby improving the rate performance of the positive electrode sheet.

[0048] In one example, the ratio of the median particle size Dv50 of the lithium-rich manganese-based material to the median particle size Dv50 of the ternary material is (1.4-3.5):1.

[0049] According to a specific embodiment, the ratio of the specific surface area of ​​the lithium-rich manganese-based material to the specific surface area of ​​the ternary material is (1.2-11):1 (for example, 1.2:1, 1.5:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 10.7:1, 11:1). When the ratio of the specific surface area of ​​the lithium-rich manganese-based material to the specific surface area of ​​the ternary material is controlled within the above range, the lithium-rich manganese-based material and the ternary material can reduce the side reaction between the electrode and the electrolyte while maintaining good dispersion, thereby improving the cycle life of the battery.

[0050] In one example, the ratio of the specific surface area of ​​the lithium-rich manganese-based material to the specific surface area of ​​the ternary material is (1.8-6):1.

[0051] In one embodiment, the chemical formula of the lithium-rich manganese-based material is zLi2MnO3·(1-z)LiM c N b O2. In the chemical formula zLi2MnO3·(1-z)LiM c N b The elements in O2 conform to the principle that the algebraic sum of the positive and negative valences of various elements in a compound is zero.

[0052] Wherein, 0<z<1. z can be a decimal, for example, z is 0.1, 0.2, 0.25, 0.3, 0.33, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0053] Wherein, 0≤b<1. b can be a decimal, for example, b is 0.1, 0.122, 0.2, 0.243, 0.3, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0054] Wherein, 0<c<1. c can be a decimal, for example, c is 0.1, 0.122, 0.2, 0.243, 0.3, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0055] M can be selected from one or more of Ni, Co, and Mn. When M is a plurality of elements, the sum of the atomic numbers of the plurality of elements is c. For example, when M is Ni and Mn, the sum of the atomic number of Ni and the atomic number of Mn is c.

[0056] N may include a transition metal element, preferably one or more of Al, Cr, Nb, Mg, Mo, Ta, and V. When N is a plurality of elements, the sum of the atomic numbers of the plurality of elements is b. For example, when N is Al and Nb, the sum of the atomic numbers of Al and Nb is b.

[0057] In one example, the lithium-rich manganese-based material is a polycrystalline particle.

[0058] In one embodiment, the chemical formula of the lithium-rich manganese-based material is zLi2MnO3·(1-z)LiM c N b O2, wherein 0<z<1, 0≤b<1, 0<c<1, and M is selected from one or more of Ni, Co and Mn, and N includes one or more of Al, Cr, Nb, Mg, Mo, Ta and V, and the lithium-rich manganese-based material is a polycrystalline particle.

[0059] According to a specific embodiment, the median particle size Dv50 of the lithium-rich manganese-based material is 8μm-20μm (for example, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 15μm, 17μm, 20μm). When the median particle size of the lithium-rich manganese-based material is controlled within the above range, the cycle stability of the lithium-rich manganese-based material can be improved, thereby further improving the cycle stability of the positive electrode sheet. In the present disclosure, the median particle size Dv50 can be obtained by testing using a laser particle size analyzer.

[0060] In one example, the median particle size Dv50 of the lithium-rich manganese-based material is 8.4 μm-12 μm.

[0061] In one embodiment, the specific surface area of ​​the lithium-rich manganese-based material is 1.3 m 2 / g-3.2m 2 / g (for example, 1.5m2 / g, 1.8m 2 / g, 2m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.7m 2 / g、3m 2 By limiting the specific surface area of ​​the lithium-rich manganese-based material to the above-mentioned specific range, the contact between the lithium-rich manganese-based material and the electrolyte can be reduced, the oxygen evolution reaction can be reduced, and the cycle stability of the positive electrode sheet can be improved.

[0062] In one embodiment, the specific surface area of ​​the lithium-rich manganese-based material is 1.5 m 2 / g-3m 2 / g.

[0063] In one embodiment, the median particle size Dv50 of the lithium-rich manganese-based material is 8.4 μm-12 μm, and the specific surface area of ​​the lithium-rich manganese-based material is 1.5 m 2 / g-3m 2 / g, and the ternary material is a single crystal material, the median particle size Dv50 of the ternary material is 3.5μm-6μm, and the specific surface area of ​​the ternary material is 0.5m 2 / g-0.8m 2 When the above characteristics of the lithium-rich manganese-based material and the ternary material are simultaneously limited to the above specific ranges, the gram capacity and cycle stability of the positive electrode sheet can be further improved.

[0064] According to a specific embodiment, based on the total weight of the first paste, the weight content of the lithium-rich manganese-based material is 90wt%-99.8wt% (for example, 90wt%, 91wt%, 92wt%, 92.5wt%, 93wt%, 93.5wt%, 94wt%, 94.5wt%, 95wt%, 95.5wt%, 96wt%, 96.5wt%, 97wt%, 97.5wt%, 98wt%, 98.5wt%, 99wt%, 99.8wt%).

[0065] In one example, based on the total weight of the first paste, the weight content of the lithium-rich manganese-based material is 92 wt %-98 wt %.

[0066] In one example, the first paste includes a first conductive agent and a first adhesive.

[0067] In one example, the first conductive agent includes one or more of conductive carbon black (SP), Ketjen black, acetylene black, graphite conductive agent (KS-6, KS-15, SO, SEG-6), carbon fiber (VGCG), carbon nanotube (CNT) and graphene.

[0068] In one example, the first binder includes one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyhexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, and polytetrafluoroethylene.

[0069] In one example, based on the total weight of the first paste, the weight content of the first conductive agent is 0.1wt-5wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%), and the weight content of the first adhesive is 0.1wt-5wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%).

[0070] In one example, based on the total weight of the first paste, the weight content of the first conductive agent is 1 wt%-4 wt%, and the weight content of the first binder is 1 wt%-4 wt%.

[0071] According to a specific embodiment, based on the total weight of the second paste, the weight content of the ternary material is 90wt%-99.8wt% (for example, 90wt%, 91wt%, 92wt%, 92.5wt%, 93wt%, 93.5wt%, 94wt%, 94.5wt%, 95wt%, 95.5wt%, 96wt%, 96.5wt%, 97wt%, 97.5wt%, 98wt%, 98.5wt%, 99wt%, 99.8wt%).

[0072] In one example, based on the total weight of the second paste, the weight content of the ternary material is 92 wt %-98 wt %.

[0073] In one example, the second paste includes a second conductive agent and a second adhesive.

[0074] In one example, the second conductive agent includes one or more of conductive carbon black (SP), Ketjen black, acetylene black, graphite conductive agent (KS-6, KS-15, SO, SEG-6), carbon fiber (VGCG), carbon nanotube (CNT) and graphene.

[0075] In one example, the second binder includes one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyhexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, and polytetrafluoroethylene.

[0076] In one example, based on the total weight of the second paste, the weight content of the second conductive agent is 0.1wt-5wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%), and the weight content of the second binder is 0.1wt-5wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%).

[0077] In one example, based on the total weight of the second paste, the weight content of the second conductive agent is 1 wt%-4 wt%, and the weight content of the second binder is 1 wt%-4 wt%.

[0078] The positive electrode sheet can be prepared by conventional preparation methods, or by the following method:

[0079] (1) Mixing the first binder, the first conductive agent, and the solvent, placing the mixture in a stirring tank and stirring for at least 60 minutes to make the prepared first adhesive solution uniform;

[0080] (2) Mixing the lithium-rich manganese-based material and the first glue solution, stirring for 60-80 minutes until the first slurry is evenly dispersed;

[0081] (3) Mixing the second binder, the second conductive agent, and the solvent, and stirring them in a stirring tank for at least 60 minutes to make the prepared second adhesive uniform;

[0082] (4) Mix the ternary material and the second glue, and stir for 60-80 minutes until the second slurry is evenly dispersed;

[0083] (5) The first slurry is evenly coated on one side or both sides of the surface of the positive electrode current collector to form a first paste, and the second slurry is evenly coated on the surface of the first paste to form a second paste.

[0084] In one example, the solvent includes one or more of N-methylpyrrolidone (NMP), N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0085] In one example, the solid content of the first slurry is 67 wt % to 71.5 wt %.

[0086] In one example, the solid content of the second slurry is 67 wt % to 71.5 wt %.

[0087] A second aspect of the present disclosure provides a battery, comprising the positive electrode sheet described in the first aspect of the present disclosure.

[0088] The materials of the battery except the positive electrode sheet can be prepared according to the methods in the art, and can achieve the effects of high energy density and long cycle life.

[0089] The battery may be a lithium-ion battery.

[0090] The battery cell may have a laminated structure or a wound structure.

[0091] Since the battery disclosed herein includes the positive electrode sheet disclosed herein, the energy density of the battery is improved and the cycle life is prolonged.

[0092] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0093] The following examples are used to illustrate the positive electrode sheet of the present disclosure.

[0094] Example 1

[0095] (1) Preparation of ingredients

[0096] Positive electrode current collector: aluminum foil;

[0097] First paste: 97 parts by weight of lithium-rich manganese-based material, 1.5 parts by weight of first binder (PVDF), and 1.5 parts by weight of first conductive agent (Super-P);

[0098] Second paste: ternary material (LiNi 0.7 Co 0.1 Mn 0.2 O2) 97 parts by weight, a second binder (PVDF) 1.5 parts by weight, and a second conductive agent (PVDF) 1.5 parts by weight.

[0099] (2) Preparation of positive electrode

[0100] (1) mixing a first binder, a first conductive agent, and a solvent, placing the mixture in a stirring tank and stirring for 60 minutes to obtain a uniform first adhesive solution;

[0101] (2) mixing the lithium-rich manganese-based material and the first glue, and stirring for 60 minutes to obtain a uniformly dispersed first slurry;

[0102] (3) mixing the second binder, the second conductive agent, and the solvent, placing the mixture in a stirring tank and stirring for 60 minutes to obtain a uniform second adhesive solution;

[0103] (4) Mixing the ternary material and the second glue, stirring for 60 minutes to obtain a uniformly dispersed second slurry;

[0104] (5) The first slurry is evenly coated on the surface of both sides of the positive electrode current collector to form a first paste, and the second slurry is evenly coated on the surface of the first paste to form a second paste, wherein the weight ratio of the first paste to the weight of the second paste is 2.33:1, and the weight ratio of the Mn element in the first paste to the weight of the Mn element in the second paste is 5.83:1; and then the positive electrode sheet is obtained by rolling and slitting.

[0105] The positive electrode sheet prepared in Example 1 was subjected to SEM testing, and an SEM image as shown in FIG2 was obtained. As can be seen from FIG2 , the lithium-rich manganese-based material is located in the first paste on the surface of the positive electrode current collector, and the ternary material is located in the second paste on the surface of the first paste.

[0106] Example 2 group

[0107] This embodiment group was carried out with reference to embodiment 1, except that the specific selection of the ternary material was changed. For details, see Table 1.

[0108] Example 3 group

[0109] This embodiment group was carried out with reference to embodiment 1, except that the median particle size Dv50 and specific surface area of ​​the lithium-rich manganese-based material and the median particle size Dv50 and specific surface area of ​​the ternary material were changed. See Table 1 for details.

[0110] Example 4 Group

[0111] This embodiment group was carried out with reference to the embodiment 1, except that the weight ratio of the first coating paste to the second coating paste was changed. See Table 1 for details.

[0112] Example 5

[0113] The process was carried out in accordance with Example 1, except that the crystal structure of the lithium-rich manganese-based material was changed. For details, see Table 1.

[0114] Comparative Example 1

[0115] The process is carried out in accordance with Example 1, except that the ternary material is replaced with the lithium-rich manganese-based material in the same weight portion. For details, see Table 1.

[0116] Comparative Example 2

[0117] Refer to Example 1, except that the ternary material is adjusted to LiNi 0.9 Co 0.05 Mn 0.05 O2, see Table 1 for details.

[0118] Comparative Example 3

[0119] The process is carried out in accordance with Example 1, except that the ratio B of the weight of the Mn element in the first paste to the weight of the Mn element in the second paste is adjusted to 0.28. For details, see Table 1.

[0120] Comparative Example 4

[0121] The same procedure was followed as in Example 1, except that the ratio B of the weight of the Mn element in the first paste to the weight of the Mn element in the second paste was adjusted to 47.5. See Table 1 for details.

[0122] Table 1

[0123] A represents the ratio of the weight of the first paste to the weight of the second paste;

[0124] B represents the ratio of the weight of the Mn element in the first paste to the content of the Mn element in the second paste;

[0125] *Same as Example 1.

[0126] - means it does not exist.

[0127] Preparation Example

[0128] Batteries were prepared using the positive electrode sheets obtained in the examples and comparative examples in the following manners.

[0129] (1) Positive electrode

[0130] The positive electrode sheets obtained in the above embodiments and comparative examples were used respectively.

[0131] (2) Negative electrode

[0132] A negative electrode active material (artificial graphite, 95 parts by weight), a binder (SBR, 2 parts by weight), a thickener (sodium carboxymethyl cellulose, 1.5 parts by weight), and a conductive agent (conductive carbon black, 1.5 parts by weight) were mixed and stirred at high speed to obtain a uniformly dispersed mixture containing the negative electrode active material. A solvent (deionized water) was added to prepare a negative electrode slurry, wherein the solid content of the negative electrode slurry was 50 wt%. The negative electrode slurry was evenly coated on both sides of the negative electrode current collector (copper foil), dried, and compacted using a roller press to obtain a negative electrode sheet.

[0133] (3) Electrolyte

[0134] 1 mol / L lithium hexafluorophosphate was mixed with a solvent (volume ratio: ethylene carbonate: dimethyl carbonate: 1,2-propylene glycol carbonate = 1:1:1) to prepare an electrolyte.

[0135] (4) Preparation of batteries

[0136] After punching the negative electrode sheet from step (2) and the positive electrode sheet from step (1), Z-type lamination is used to form a bare cell, and aluminum tabs and copper-nickel-plated tabs are respectively turned out. The bare cell is clamped with a glass clamp with a force of 100 MPa / m 2 The cells were then vacuum-baked at 85°C for 24 hours and then encapsulated with aluminum-plastic film. After encapsulation, the cells were formed and aged to produce a 60mm x 40mm x 5mm square soft-package battery. The cell's design capacity was 4000mAh.

[0137] Test Case

[0138] The batteries obtained in the examples and comparative examples were tested as follows:

[0139] (1) Test of gram capacity

[0140] The ratio of the battery capacity (mAh) at the first 0.33C discharge to the mass of the positive electrode active material (g), where the mass of the positive electrode active material is the sum of the masses of the lithium-rich manganese-based material and the ternary material. See Table 2 for details.

[0141] (2) Initial effectiveness test

[0142] For the ratio of the battery's initial discharge capacity to its initial charge capacity, see Table 2.

[0143] (3) Cyclic performance test

[0144] 1) 1C / 1C cycle performance at room temperature

[0145] At 25°C, charge at a constant current of 1C to 4.4V, then charge at a constant voltage with a cutoff current of 0.05C. Finally, discharge at a constant current of 1C to 2.5V, and repeat this cycle. When the ratio of discharge capacity to initial discharge capacity (capacity retention) decays to 80%, record the number of cycles at this point. See Table 2 for details.

[0146] 2) 2C / 1C cycle performance at room temperature

[0147] At 25°C, the battery was charged at a constant current of 2C to 4.4V, then charged at a constant voltage with a cutoff current of 0.05C. Finally, the battery was discharged at a constant current of 1C to 2.5V. The number of cycles was recorded when the ratio of discharge capacity to initial discharge capacity (capacity retention) decreased to 80%. See Table 2 for details.

[0148] (4) Energy density test

[0149] The ratio of the energy (Wh) of the battery during the first 0.33C discharge to the battery mass (kg), where the battery mass is the sum of the masses of the positive electrode, negative electrode, separator, electrolyte, positive and negative electrode tabs, and aluminum-plastic film casing.

[0150] Table 2

[0151] As can be seen from Table 2, the comparative examples and the examples show that the gram capacity of the positive electrode sheet of the examples is improved, and the 1C / 1C cycle performance of the battery made from the positive electrode sheet of the examples is improved at room temperature and the 2C / 1C cycle performance at room temperature is improved, indicating that the positive electrode sheet of the present invention and the battery including the positive electrode sheet, by setting the positive electrode sheet to have a specific double-layer structure and limiting the two layers of paste, improve the gram capacity of the positive electrode sheet, improve the energy density of the battery, and extend the cycle life of the battery.

[0152] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode current collector, a first paste located on one side or both sides of the positive electrode current collector, and a second paste located on the surface of the first paste, wherein the first paste includes a lithium-rich manganese-based material, and the second paste includes a ternary material, wherein the chemical formula of the ternary material is Li a Ni x Co y Mn d A k O2, wherein 0.9≤a≤1.1, 0.5≤x≤0.8, 0.2≤y<0.5, 0≤k≤0.05, 0.2≤d<0.5; A is a doping element, and the ratio of the content of Mn element in the first paste to the content of Mn element in the second paste is (0.68-45):

1.

2. The positive electrode sheet according to claim 1, wherein: The chemical formula of the lithium-rich manganese-based material is zLi2MnO3·(1-z)LiM c N b O2, where 0<z<1, 0≤b<1, 0<c<1; and / or, M is selected from one or more of Ni, Co and Mn; and / or, N comprises a transition metal element, preferably N comprises one or more of Al, Cr, Nb, Mg, Mo, Ta and V; and / or, the lithium-rich manganese-based material comprises polycrystalline particles; And / or, the median particle size Dv50 of the lithium-rich manganese-based material is 8 μm-20 μm; And / or, the specific surface area of ​​the lithium-rich manganese-based material is 1.3m 2 / -3.2m 2 / g.

3. The positive electrode sheet according to claim 1 or 2, wherein: The median particle size Dv50 of the lithium-rich manganese-based material is 8.4 μm-12 μm; And / or, the specific surface area of ​​the lithium-rich manganese-based material is 1.5m 2 / g-3m 2 / g.

4. The positive electrode sheet according to any one of claims 1 to 3, wherein: The lithium-rich manganese-based material includes polycrystalline particles and the ternary material includes single crystalline particles.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein: The ternary material includes single crystal particles; and / or, A is selected from one or more of Al, Mg, Ti, Zr and F; And / or, the median particle size Dv50 of the ternary material is 3 μm-10 μm; And / or, the specific surface area of ​​the ternary material is 0.3m 2 / g-1m 2 / g.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein: The median particle size Dv50 of the ternary material is 3.5 μm-6 μm; And / or, the specific surface area of ​​the ternary material is 0.5m 2 / g-0.8m 2 / g.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein: The weight ratio of the first coating paste to the second coating paste is (1-9):1, preferably (2.2-4):

1.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein: The ratio of the median particle size Dv50 of the lithium-rich manganese-based material to the median particle size Dv50 of the ternary material is (0.8-7):1, preferably (1.4-3.5):

1.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein: The ratio of the specific surface area of ​​the lithium-rich manganese-based material to the specific surface area of ​​the ternary material is (1.2-11):1, preferably (1.8-6):

1.

10. The positive electrode sheet according to any one of claims 1 to 9, wherein: The ratio of the weight of the Mn element in the first paste to the content of the Mn element in the second paste is (1.5-20):

1.

11. The positive electrode sheet according to any one of claims 1 to 10, wherein: Based on the total weight of the first paste, the weight content of the lithium-rich manganese-based material is 90wt%-99.8wt%, preferably 92wt%-98wt%; And / or, based on the total weight of the second paste, the weight content of the ternary material is 90wt%-99.8wt%, preferably 92wt%-98wt%.

12. The positive electrode sheet according to any one of claims 1 to 11, wherein: The first paste includes a first conductive agent and a first adhesive; And / or, the second paste includes a second conductive agent and a second adhesive.

13. The positive electrode sheet according to claim 12, wherein, based on the total weight of the first paste, the weight content of the first conductive agent is 0.1wt-5wt%, and the weight content of the first binder is 0.1wt-5wt%; And / or, based on the total weight of the second paste, the weight content of the second conductive agent is 0.1wt-5wt%, and the weight content of the second binder is 0.1wt-5wt%.

14. A battery, characterized in that: The battery comprises the positive electrode sheet according to any one of claims 1 to 13.

15. The battery according to claim 14, wherein The battery is a lithium-ion battery; And / or, the battery cell is a laminated structure or a wound structure.

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