Positive electrode sheet, secondary battery, and electric device

Abstract

This invention discloses a positive electrode, a secondary battery, and an electrical device. The positive electrode includes a current collector and a positive electrode film disposed on at least one side of the current collector. The positive electrode film includes a first active coating and a second active coating disposed on the surface of the first active coating and away from the current collector. The first active coating includes a first lithium nickel oxide, and the second active coating includes a second lithium nickel oxide. The first and second lithium nickel oxides each independently contain a first element. The first element includes at least one of boron or tungsten. The content of the first element in the second lithium nickel oxide is greater than the content of the first element in the first lithium nickel oxide. By constructing a double-layer coating structure of a first active coating and a second active coating with lithium nickel oxides having different boron and / or tungsten content, this invention can reduce the overpotential between the surface layer of the positive electrode and the negative electrode, thereby improving the cycle capacity retention rate and improving the lithium plating interface of the negative electrode during cycling.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a positive electrode, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide range of applications, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, transportation vehicles, military equipment, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0003] Therefore, it is necessary to provide a positive electrode to prevent lithium plating and rapid capacity decay in secondary batteries during cycling. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a positive electrode sheet that can effectively prevent lithium plating and rapid capacity decay, and improve cycle performance.

[0005] A second aspect of the present invention also provides a secondary battery.

[0006] A third aspect of the present invention also provides an electrical appliance.

[0007] A positive electrode sheet according to a first aspect of the present invention includes a current collector and a positive electrode film disposed on at least one side of the current collector, the positive electrode film including a first active coating and a second active coating disposed on the surface of the first active coating and away from the current collector;

[0008] The first active coating comprises a first lithium nickel oxide, and the second active coating comprises a second lithium nickel oxide;

[0009] The first lithium nickel oxide and the second lithium nickel oxide each independently contain a first element;

[0010] The first element contains at least one of boron or tungsten;

[0011] The content of the first element in the second lithium nickel oxide is greater than the content of the first element in the first lithium nickel oxide.

[0012] The positive electrode sheet according to embodiments of the present invention has at least the following beneficial effects:

[0013] This invention constructs a double-layer coating structure consisting of a first active coating and a second active coating with different contents of the first element in lithium nickel oxide. This reduces the overpotential between the surface of the positive electrode and the negative electrode, thereby reducing polarization, improving cycle capacity retention, and improving the negative electrode lithium plating interface during cycling.

[0014] According to some embodiments of the present invention, the boron content in the second lithium nickel oxide is A, and the boron content in the first lithium nickel oxide is B, wherein 200ppm ≤ AB ≤ 500ppm. According to some embodiments of the present invention, the boron content in the second lithium nickel oxide is A, and the boron content in the first lithium nickel oxide is B, wherein AB is 200ppm, 300ppm, 400ppm, 500ppm, or within a range consisting of any two of the above values.

[0015] This invention controls the CB (cell balance) of the positive and negative electrodes by controlling the difference in boron content between the second lithium nickel oxide and the first lithium nickel oxide.

[0016] According to some embodiments of the present invention, the tungsten content in the second lithium nickel oxide is C, and the tungsten content in the first lithium nickel oxide is D, wherein 500ppm ≤ CD ≤ 1000ppm. According to some embodiments of the present invention, the tungsten content in the second lithium nickel oxide is C, and the tungsten content in the first lithium nickel oxide is C, wherein 700ppm ≤ CD ≤ 800ppm. According to some embodiments of the present invention, the tungsten content in the second lithium nickel oxide is C, and the tungsten content in the first lithium nickel oxide is D, wherein CD is 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, or within a range consisting of any two of the above values.

[0017] This invention controls the cell balance (CB) of the positive and negative electrodes by controlling the difference in tungsten content between the second lithium nickel oxide and the first lithium nickel oxide.

[0018] According to some embodiments of the present invention, the specific capacity of the second lithium nickel oxide in the second active coating is E, and the specific capacity of the first lithium nickel oxide in the first active coating is F, wherein 0.5 mAh / g ≤ EF ≤ 2.5 mAh / g. According to some embodiments of the present invention, the specific capacity of the second lithium nickel oxide in the second active coating is E, and the specific capacity of the first lithium nickel oxide in the first active coating is F, wherein EF is 0.5 mAh / g, 1 mAh / g, 1.5 mAh / g, 2 mAh / g, 2.5 mAh / g, or within a range consisting of any two of the above values.

[0019] This invention controls the cell balance (CB) of the positive and negative electrodes by controlling the difference in specific capacity between the second lithium nickel oxide and the first lithium nickel oxide.

[0020] According to some embodiments of the present invention, the first lithium nickel oxide and the second lithium nickel oxide further comprise strontium, wherein the strontium content in the second lithium nickel oxide is G, and the strontium content in the first lithium nickel oxide is H, wherein 100ppm ≤ GH ≤ 200ppm. According to some embodiments of the present invention, the first lithium nickel oxide and the second lithium nickel oxide further comprise strontium, wherein the strontium content in the second lithium nickel oxide is G, and the strontium content in the first lithium nickel oxide is H, wherein GH is 100ppm, 150ppm, 200ppm, or within a range consisting of any two of the above values.

[0021] The addition of strontium in this invention further increases the interlayer spacing of lithium nickel oxide. In addition, it has a synergistic effect with other elements such as tungsten and boron, which not only improves the specific capacity and structural stability of lithium nickel oxide, but also reduces polarization.

[0022] According to some embodiments of the present invention, the first active coating further includes a first conductive agent and a first binder, and the mass percentages of the components of the first active coating are as follows:

[0023] First lithium nickel oxide: 96%–98.5%;

[0024] First conductive agent: 0.5%–1.5%;

[0025] First adhesive: 1.0%–2.5%.

[0026] According to some embodiments of the present invention, the first active coating further includes a second conductive agent and a second binder, and the mass percentages of the components of the second active coating are as follows:

[0027] Second lithium nickel oxide: 96%–98.5%;

[0028] Second conductive agent: 0.5%–1.5%;

[0029] Second adhesive: 1.0%–2.5%.

[0030] According to some embodiments of the present invention, the first conductive agent and the second conductive agent each independently include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0031] According to some embodiments of the present invention, the first adhesive and the second adhesive each independently comprise at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0032] According to some embodiments of the present invention, the length of the positive electrode membrane disposed on one surface of the current collector is L1, and the length of the positive electrode membrane disposed on the other surface of the current collector is L2, satisfying: L1>L2.

[0033] It should be noted that the surface of the positive electrode membrane with length L1 is the long paste surface of the current collector, and the surface of the positive electrode membrane with length L2 is the short paste surface of the current collector.

[0034] According to some embodiments of the present invention, the first lithium nickel oxide and the second lithium nickel oxide independently include at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0035] According to some embodiments of the present invention, the first lithium nickel oxide comprises lithium nickel cobalt manganese oxide, wherein the molar amount of nickel, cobalt and manganese in the lithium nickel cobalt manganese oxide is 1, and the molar amount of nickel is greater than or equal to 0.8.

[0036] According to some embodiments of the present invention, the second lithium nickel oxide comprises lithium nickel cobalt manganese oxide, wherein the molar amount of nickel, cobalt and manganese in the lithium nickel cobalt manganese oxide is 1, and the molar amount of nickel is greater than or equal to 0.8.

[0037] According to some embodiments of the present invention, the first lithium nickel oxide and the second lithium nickel oxide each independently include a second element, the second element comprising at least one of Al, Mg, Ti, Zr, Zn, Ru or Y.

[0038] According to some embodiments of the present invention, the current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0039] According to some embodiments of the present invention, the method for preparing the positive electrode sheet includes the following steps:

[0040] S1. A first active coating slurry is obtained by mixing a first lithium nickel oxide, a first conductive agent and a first binder, and the first active coating slurry is coated on at least one side of the positive electrode current collector to form a first active coating.

[0041] S2. The second lithium nickel oxide, the second conductive agent and the second binder are mixed to obtain the second active coating slurry. The second active coating slurry is coated on the surface of the first active coating to form the second active coating. After drying, rolling and cutting, the positive electrode sheet is obtained.

[0042] A second aspect of the present invention provides a secondary battery, comprising a negative electrode, an electrolyte, a separator, and a positive electrode as described above. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte serves to conduct ions between the positive and negative electrode. The separator, disposed between the positive and negative electrode, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0043] According to some embodiments of the present invention, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0044] According to some embodiments of the present invention, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0045] According to some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0046] According to some embodiments of the present invention, the negative electrode active material may be any negative electrode active material known in the art for use in batteries. For example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0047] According to some embodiments of the present invention, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0048] According to some embodiments of the present invention, the negative electrode film layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0049] According to some embodiments of the present invention, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0050] According to some embodiments of the present invention, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0051] According to some embodiments of the present invention, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0052] According to some embodiments of the present invention, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0053] According to some embodiments of the present invention, the material of the diaphragm may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm may be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0054] According to some embodiments of the present invention, the positive electrode, the negative electrode, and the separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0055] Some embodiments of the third aspect of the present invention provide an electrical device including the secondary battery described above.

[0056] According to some embodiments of the present invention, the electrical devices of the present invention may include, for example, mobile phones, computers, wearable devices, power banks, electric vehicles, and energy storage devices.

[0057] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0058] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0059] Figure 1 This is a schematic diagram of the positive electrode structure of Example 1. Detailed Implementation

[0060] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0061] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0062] Example 1

[0063] Example 1 provides a positive electrode sheet, such as Figure 1 As shown, it includes a positive electrode current collector, a first active coating, and a second active coating. The first active coating is disposed on both the long and short coated surfaces of the positive electrode current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0064] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0065] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0066] Example 2

[0067] Example 2 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0068] S1, a ternary material (LiNi) with a specific capacity of 193 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 800 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0069] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0070] Example 3

[0071] Example 3 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0072] S1, a ternary material (LiNi) with a specific capacity of 193.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 900 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0073] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0074] Example 4

[0075] Example 4 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0076] S1, a ternary material (LiNi) with a specific capacity of 192 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 500 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0077] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0078] Example 5

[0079] Example 5 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0080] S1, a ternary material (LiNi) with a specific capacity of 191.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 400 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0081] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0082] Example 6

[0083] Example 6 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0084] S1, a ternary material (LiNi) with a specific capacity of 193.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 2000 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0085] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0086] Example 7

[0087] Example 7 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, strontium, and tungsten. The preparation method is as follows:

[0088] S1, a ternary material (LiNi) with a specific capacity of 193 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1800 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0089] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0090] Example 8

[0091] Example 8 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, strontium, and tungsten. The preparation method is as follows:

[0092] S1, a ternary material (LiNi) with a specific capacity of 192 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1300 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0093] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0094] Example 9

[0095] Example 9 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, strontium, and tungsten. The preparation method is as follows:

[0096] S1, a ternary material (LiNi) with a specific capacity of 194 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 2200 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0097] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0098] Example 10

[0099] Example 10 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, strontium, and tungsten. The preparation method is as follows:

[0100] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1500 ppm tungsten, and 900 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0101] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0102] Example 11

[0103] Example 11 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, strontium, and tungsten. Its preparation method is as follows:

[0104] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1500 ppm tungsten, and 850 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0105] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0106] Example 12

[0107] Example 12 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0108] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1500 ppm tungsten, and 950 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0109] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0110] Example 13

[0111] Example 13 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, strontium, and tungsten. Its preparation method is as follows:

[0112] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a first active coating slurry. The ternary material contained 700 ppm boron, 1500 ppm tungsten, and 700 ppm strontium. The first active coating slurry was coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0113] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0114] Example 14

[0115] Example 14 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron and tungsten. The preparation method is as follows:

[0116] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron and 1500 ppm tungsten. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0117] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron and 2500 ppm tungsten. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0118] Example 15

[0119] Example 15 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0120] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 96%:1.5%:2.5%. The ternary material contains 700 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0121] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 96%:1.5%:2.5% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0122] Example 16

[0123] Example 16 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0124] S1, a ternary material (LiNi) with a specific capacity of 192.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 98.5%:0.5%:1.0%. The ternary material contains 700 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0125] S2, a ternary material (LiNi) with a specific capacity of 195 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 98.5%:0.5%:1.0% to obtain a second active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0126] Example 17

[0127] Example 17 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. The first and second active layers comprise a ternary material containing boron. The preparation method is as follows:

[0128] S1, a ternary material (LiNi) with a specific capacity of 190 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a first active coating slurry. The ternary material contained boron with a content of 700 ppm. The first active coating slurry was coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0129] S2, using a ternary material (LiNi) with a specific capacity of 191 mAh / g (0.5C). 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 1000 ppm of boron. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0130] Example 18

[0131] Example 18 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. The first and second active layers comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0132] S1, a ternary material (LiNi) with a specific capacity of 191.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 500 ppm boron, 1300 ppm tungsten, and 650 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0133] S2, using a ternary material (LiNi) with a specific capacity of 193.5 mAh / g (0.5C). 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 800 ppm boron, 2000 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0134] Example 19

[0135] Example 19 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. The first and second active layers comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0136] S1, a ternary material (LiNi) with a specific capacity of 191.5 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 500 ppm boron, 1300 ppm tungsten, and 650 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0137] S2, a ternary material (LiNi) with a specific capacity of 193 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 700 ppm boron, 1800 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0138] Comparative Example 1

[0139] Comparative Example 1 provides a positive electrode sheet, the preparation method of which is as follows:

[0140] The ternary material (LiNi) with a specific capacity of 191.5 mAh / g (0.5C) was used. 0.83Co 0.05 Mn 0.12 A positive electrode slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 500 ppm boron, 1300 ppm tungsten, and 650 ppm strontium. During positive electrode coating, the above positive electrode slurry is coated onto the long paste surface of the positive electrode current collector aluminum foil to form a 60 μm thick active coating, and the above positive electrode slurry is coated onto the short paste surface of the positive electrode current collector aluminum foil to form a 60 μm thick active coating, thus obtaining the positive electrode.

[0141] Comparative Example 2

[0142] Comparative Example 2 provides a positive electrode sheet, which is prepared in the same way as Example 1 in terms of preparation method and component content. The difference is that the only element in Comparative Example 2 is strontium.

[0143] Comparative Example 3

[0144] Comparative Example 3 provides a positive electrode sheet, comprising a positive current collector, a first active coating, and a second active coating. The first active coating is disposed on the long and short coated surfaces of the positive current collector, and the second active coating is disposed on the surface of the first active coating. Both the first and second active layers comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0145] S1, a ternary material (LiNi) with a specific capacity of 193 mAh / g (0.5C) 0.83 Co 0.05 Mn 0.12 The first active coating slurry is prepared by mixing O2, conductive carbon black, and polyvinylidene fluoride in a mass percentage ratio of 97.8%:1.0%:1.2%. The ternary material contains 700 ppm boron, 1800 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long and short coating surfaces of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 30 μm.

[0146] S2, using a ternary material (LiNi) with a specific capacity of 191.5 mAh / g (0.5C). 0.83 Co 0.05 Mn 0.12O2), conductive carbon black, and polyvinylidene fluoride were mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a second active coating slurry. The ternary material contained 500 ppm boron, 1300 ppm tungsten, and 650 ppm strontium. The second active coating slurry was coated on the long and short coating surfaces of the first active coating, which were each 30 μm thick, to form a second active coating with a thickness of 30 μm. A positive electrode sheet was obtained.

[0147] Performance testing

[0148] Preparation of secondary batteries

[0149] (1) Preparation of negative electrode

[0150] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent conductive carbon black were mixed in a mass ratio of 97:1.2:1.3:0.5, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil with a thickness of 6 μm. The coated electrode was then transferred to a 120℃ oven for drying, and then cold-pressed and slit to obtain the negative electrode sheet.

[0151] (2) Preparation of electrolyte

[0152] The organic solvent was a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC:20:20:60. Thoroughly dried LiPF6 lithium salt was dissolved in the organic solvent and mixed thoroughly in an argon-atmosphere glove box with a water content of <10 ppm to obtain the electrolyte. The concentration of the lithium salt was 1 mol / L.

[0153] (3) Separator: 12μm polypropylene diaphragm.

[0154] The positive electrode sheet, negative electrode sheet, and separator prepared in Examples 1-19 and Comparative Examples 1-3 are wound to obtain a core. The core is then packaged to obtain a dry cell. After baking, the dry cell is injected with electrolyte, formed, resealed, and sorted to obtain a lithium-ion battery. Finally, the lithium-ion battery is tested (using the Blue Battery Testing System).

[0155] Cyclic performance test: number of cycles and capacity retention (1C / 1C) / % at 45℃; 2.5V~4.25V, 0.02C. The results are shown in Table 1.

[0156] Table 1. Data from Examples 1-19 and Comparative Examples 1-3

[0157]

[0158]

[0159] Data from Examples 1-5 show that the boron content in the second lithium nickel oxide is A, and the boron content in the first lithium nickel oxide is B. When 200ppm≤AB≤500ppm falls within this range, the cycle performance is good. This is because when the difference between the boron content in the second and first lithium nickel oxides is too large, the structural stability of the lithium nickel oxide in the inner layers of the long and short coated surfaces is slightly worse, leading to a decrease in cycle performance. Conversely, when the difference between the boron content in the second and first lithium nickel oxides is too small, the difference in specific capacity between the inner surfaces of the long and short coated surfaces becomes smaller, resulting in a larger overpotential and polarization with the long and short coated surfaces of the negative electrode, which also leads to a decrease in cycle performance.

[0160] Based on the data from Examples 1 and 6-9, the tungsten content in the second lithium nickel oxide is C, and the tungsten content in the first lithium nickel oxide is D. When 500ppm≤CD≤1000ppm is within this range, it exhibits good cycle performance. This is because: when the difference between the tungsten content in the second lithium nickel oxide and the first lithium nickel oxide is too large, the structural stability of the lithium nickel oxide in the inner layers of the long and short coated surfaces is slightly worse, leading to a decrease in cycle performance; conversely, when the difference between the tungsten content in the second and first lithium nickel oxides is too small, the difference in specific capacity between the inner surfaces of the long and short coated surfaces becomes smaller, resulting in a larger overpotential and polarization with the long and short coated surfaces of the negative electrode, which also leads to a decrease in cycle performance.

[0161] Data from Examples 1 and 10-13 show that the strontium content in the second lithium nickel oxide is G, and the strontium content in the first lithium nickel oxide is H. When 100ppm≤GH≤200ppm is within this range, the cycling performance is better. This is because when the difference between the strontium content in the second lithium nickel oxide and the first lithium nickel oxide is too large, the structural stability of the lithium nickel oxide in the inner layers of the long and short paste surfaces is slightly worse, resulting in a decrease in cycling performance. Conversely, when the difference between the strontium content in the second lithium nickel oxide and the first lithium nickel oxide is too small, the synergistic effect of strontium with boron or tungsten will worsen, and the polarization will increase, which will also lead to a decrease in cycling performance.

[0162] The data from Comparative Examples 1 to 3 show that when boron or tungsten is not present, and when the elemental content in the second lithium nickel oxide is less than or equal to the elemental content in the first lithium nickel oxide, its cycle performance is poor.

[0163] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode film disposed on at least one side of the current collector, the positive electrode film including a first active coating and a second active coating disposed on the surface of the first active coating and away from the current collector; The first active coating comprises a first lithium nickel oxide, and the second active coating comprises a second lithium nickel oxide; The first lithium nickel oxide and the second lithium nickel oxide each independently contain a first element; The first element includes boron, tungsten, and strontium; The content of the first element in the second lithium nickel oxide is greater than the content of the first element in the first lithium nickel oxide; The boron content in the second lithium nickel oxide is A, and the boron content in the first lithium nickel oxide is B, wherein 200ppm≤AB≤500ppm; The tungsten content in the second lithium nickel oxide is C, and the tungsten content in the first lithium nickel oxide is D, wherein 500ppm≤CD≤1000ppm; The strontium content in the second lithium nickel oxide is G, and the strontium content in the first lithium nickel oxide is H, wherein 100ppm≤GH≤200ppm.

2. The positive electrode sheet according to claim 1, characterized in that, The specific capacity of the second lithium nickel oxide in the second active coating is E, and the specific capacity of the first lithium nickel oxide in the first active coating is F, wherein 0.5 mAh / g ≤ EF ≤ 2.5 mAh / g.

3. The positive electrode sheet according to claim 1, characterized in that, The first active coating further includes a first conductive agent and a first binder, and the second active coating further includes a second conductive agent and a second binder; The first conductive agent and the second conductive agent each independently include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; The first adhesive and the second adhesive each independently comprise at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

4. The positive electrode sheet according to claim 1, characterized in that, The length of the positive electrode membrane disposed on one surface of the current collector is L1, and the length of the positive electrode membrane disposed on the other surface of the current collector is L2, satisfying: L1>L2.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The first lithium nickel oxide and the second lithium nickel oxide each independently include at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

6. A secondary battery, characterized in that, It includes a negative electrode, an electrolyte, a separator, and a positive electrode as described in any one of claims 1 to 4.

7. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 6.

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