Positive electrode sheet, secondary battery, and electric device

Abstract

The application discloses a positive electrode sheet, a secondary battery and an electric device, and relates to the technical field of batteries, the positive electrode sheet comprising a current collector, a first active coating and a second active coating, the first active coating being arranged on one side of the current collector, and the second active coating being arranged on the other side of 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 contains at least one of a boron element or a tungsten element; the content of the first element in the first lithium nickel oxide is greater than the content of the first element in the second lithium nickel oxide. By coating the first active coating and the second active coating of the lithium nickel oxide with different contents of the boron element and / or the tungsten element on both sides of the current collector, the overpotential between the two sides of the positive electrode sheet and the negative electrode sheet can be reduced, polarization can be reduced, the cycle capacity retention rate of the lithium nickel oxide can be improved, and the lithium precipitation interface of the negative electrode can be improved.

Description

Technical Field

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

[0002] Cathode materials, as key materials for rechargeable batteries, have always been a focus of research and development in the industry. Currently, the mainstream cathode materials are lithium phosphate and lithium nickel oxide. Among them, lithium nickel oxide has a higher specific capacity and plateau voltage than lithium phosphate, which makes rechargeable batteries based on lithium nickel oxide cathode materials have higher energy density and can bring longer driving time to electric vehicles. However, rechargeable batteries based on lithium nickel oxide cathode materials are prone to lithium plating and rapid capacity decay during cycling.

[0003] Therefore, it is necessary to improve the cycle performance of secondary batteries based on lithium nickel oxide. 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] The positive electrode sheet of a first aspect embodiment of the present invention includes a current collector, a first active coating and a second active coating, wherein the first active coating is disposed on one side of the current collector and the second active coating is disposed on the other side of 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 first lithium nickel oxide is greater than the content of the first element in the second 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 reduces the overpotential between the positive electrode and the negative electrode by coating the current collector with a first active coating and a second active coating of lithium nickel oxide with different boron and / or tungsten content on both sides, thereby reducing polarization, improving the cycle capacity retention rate of lithium nickel oxide and improving the negative electrode cycle lithium plating interface.

[0014] According to some embodiments of the present invention, the boron content in the first lithium nickel oxide is 700 to 1000 ppm, including any value therein and all ranges and any subranges. For example, it includes, but is not limited to, 700 to 900 ppm, 700 to 800 ppm, 800 to 1000 ppm, 800 to 900 ppm, and 900 to 1000 ppm.

[0015] According to some embodiments of the present invention, the boron content in the second lithium nickel oxide is 400-900 ppm, including any value therein and all ranges and any subranges thereof. Examples include, but are not limited to, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, and 400-800 ppm, 400-700 ppm, 400-600 ppm, 400-500 ppm, 500-900 ppm, 500-800 ppm, 500-700 ppm, 500-600 ppm, 600-900 ppm, 600-800 ppm, 600-700 ppm, 700-900 ppm, 700-800 ppm, and 800-900 ppm.

[0016] This invention controls the CB (cell balance) of the positive and negative electrodes by controlling the difference in boron content between the first and second lithium nickel oxides.

[0017] According to some embodiments of the present invention, the tungsten content in the first lithium nickel oxide is 1500–2500 ppm, including any value therein and all ranges and any subranges thereof. Examples include, but are not limited to, 1500 ppm, 1700 ppm, 1900 ppm, 2100 ppm, 2300 ppm, 2500 ppm, and 1500–2400 ppm, 1500–2300 ppm, 1500–2200 ppm, 1500–2100 ppm, 1500–2000 ppm, 1500–1900 ppm, 1500–1800 ppm, 1500–1700 ppm, 1500–1600 ppm, 1700–2500 ppm, 1700–2400 ppm, 1700–2300 ppm, 1700–2200 ppm, and 1700–2100 ppm. pm, 1700~2000ppm, 1700~1900ppm, 1700~1800ppm, 1900~2500ppm, 1900~2400ppm, 1900~2300ppm, 1900~2200ppm, 1900~2100ppm, 1900~2000pp m, 2100~2500ppm, 2100~2400ppm, 2100~2300ppm, 2100~2200ppm, 2200~2500ppm, 2200~2400ppm, 2200~2300ppm, 2300~2500ppm, 2300~2400ppm.

[0018] According to some embodiments of the present invention, the tungsten content in the second lithium nickel oxide is 1300–2200 ppm, including any value therein and all ranges and any subranges thereof. Examples include, but are not limited to, 1300 ppm, 1500 ppm, 1700 ppm, 1900 ppm, 2100 ppm, 2200 ppm, and 1300–2100 ppm, 1300–2000 ppm, 1300–1900 ppm, 1300–1800 ppm, 1300–1700 ppm, 1300–1600 ppm, 1300–1500 ppm, 1300–1400 ppm, 1500–2200 ppm, and 1500–2100 ppm. pm, 1500~2000ppm, 1500~1900ppm, 1500~1800ppm, 1500~1700ppm, 1500~1600ppm, 1700~2200ppm, 1700~2100pp m, 1700~2000ppm, 1700~1900ppm, 1700~1800ppm, 1900~2200ppm, 1900~2100ppm, 1900~2000ppm, 2100~2200ppm.

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

[0020] According to some embodiments of the present invention, the first element further includes strontium, and the content of strontium in the first lithium nickel oxide is 800 to 1000 ppm, including any value therein and all ranges and any subranges therein. For example, including but not limited to 800 ppm, 900 ppm, 1000 ppm and 800-900 ppm, 900-1000 ppm.

[0021] According to some embodiments of the present invention, the strontium content in the second lithium nickel oxide is 700 to 950 ppm, including any value therein and all ranges and any subranges thereof. For example, it includes, but is not limited to, 700 ppm, 800 ppm, 850 ppm, 900 ppm, 950 ppm and 700-800 ppm, 700-850 ppm, 700-900 ppm, 800-950 ppm, 800-900 ppm.

[0022] The addition of strontium in this invention further increases the interlayer spacing of lithium nickel oxide. In addition, it has a synergistic effect with tungsten and boron, which not only improves the specific capacity and structural stability of lithium nickel oxide, but also reduces polarization.

[0023] According to some embodiments of the present invention, the specific capacity of the first lithium nickel oxide is 192 to 195 mAh / g.

[0024] According to some embodiments of the present invention, the specific capacity of the second lithium nickel oxide is 191.5 to 194 mAh / g, including any value therein and all ranges and any subranges thereof. Examples include, but are not limited to, 191.5mAh / g, 192mAh / g, 192.5mAh / g, 193mAh / g, 193.5mAh / g, 194mAh / g, and 191.5~193.5mAh / g, 191.5~193mAh / g, 191.5~192.5mAh / g, 191.5~192mAh / g, 192~194mAh / g, 192~193.5mAh / g, 192~193mAh / g, 192~192.5mAh / g, 192.5~194mAh / g, 192.5~193.5mAh / g, 192.5~193mAh / g, 193~194mAh / g, 193~193.5mAh / g, and 193.5~194mAh / g.

[0025] This invention controls the cell balance (CB) of the positive and negative electrodes by controlling the difference in specific capacity between the first lithium nickel oxide and the second lithium nickel oxide.

[0026] According to some embodiments of the present invention, the mass percentages of the components of the first active coating are as follows:

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

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

[0029] First adhesive: 1.0%–2.5%.

[0030] According to some embodiments of the present invention, the mass percentages of the components of the second active coating are as follows:

[0031] Second lithium nickel oxide: 96%–98.5%;

[0032] Second conductive agent: 0.5%–1.5%;

[0033] Second adhesive: 1.0%–2.5%.

[0034] According to some embodiments of the present invention, the first conductive agent and the second conductive agent independently include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0035] According to some embodiments of the present invention, the first adhesive and the second adhesive 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.

[0036] According to some embodiments of the present invention, the length of the first active coating is L1 and the length of the second active coating is L2, satisfying: L1>L2.

[0037] According to some embodiments of the present invention, the first lithium nickel oxide and the second lithium nickel oxide independently comprise at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0038] 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.

[0039] 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.

[0040] According to some embodiments of the present invention, the second lithium nickel oxide comprises lithium nickel cobalt aluminum oxide, wherein the molar amount of nickel, cobalt and aluminum in the lithium nickel cobalt aluminum oxide is 1, and the molar amount of nickel is greater than or equal to 0.8.

[0041] 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.).

[0042] According to some embodiments of the present invention, the method for preparing the positive electrode sheet includes the following steps:

[0043] S1. Mix the first lithium nickel oxide, the first conductive agent and the first binder to obtain the first active coating slurry, and coat the first active coating slurry on one side of the positive electrode current collector to form the first active coating;

[0044] S2. Mix the second lithium nickel oxide, the second conductive agent, and the second binder to obtain a second active coating slurry. Coat the second active coating slurry onto the other side of the positive electrode current collector to form a second active coating; thus obtaining a positive electrode sheet.

[0045] 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 battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of 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.

[0046] 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.

[0047] 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.

[0048] 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.).

[0049] 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.

[0050] 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).

[0051] 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.

[0052] According to some embodiments of the present invention, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Some embodiments of the third aspect of the present invention provide an electrical device including the secondary battery described above.

[0059] 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.

[0060] 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

[0061] 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:

[0062] Figure 1 This is a schematic diagram of the positive electrode structure of Example 1. Detailed Implementation

[0063] 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.

[0064] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0065] It should be noted that, in the present invention, "the first active coating is disposed on the long paste surface of the positive electrode current collector, and the second active coating is disposed on the short paste surface of the positive electrode current collector" means that the length of the first active coating on the current collector is greater than the length of the second active coating.

[0066] Example 1

[0067] Example 1 provides a positive electrode sheet, the structural schematic diagram of which is shown below. Figure 1 As shown, it includes a current collector, a first active coating and a second active coating. The first active coating is disposed on the long paste surface of the positive electrode current collector, and the second active coating is disposed on the short paste surface of the positive electrode current collector. Both the first active coating and the second active coating include a ternary material containing boron, tungsten and strontium.

[0068] Its preparation method is as follows:

[0069] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0070] S2, using a ternary material (LiNi) with a specific capacity of 192.5 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, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0071] Example 2

[0072] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0073] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0074] S2, a ternary material (LiNi) with a specific capacity of 192 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 500 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0075] Example 3

[0076] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0077] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0078] S2, using a ternary material (LiNi) with a specific capacity of 191.5 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 400 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0079] Example 4

[0080] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0081] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0082] S2, a ternary material (LiNi) with a specific capacity of 193 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, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0083] Example 5

[0084] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0085] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0086] S2, using a ternary material (LiNi) with a specific capacity of 193.5 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 900 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0087] Example 6

[0088] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0089] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0090] S2, using a ternary material (LiNi) with a specific capacity of 193.5 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, 2000 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0091] Example 7

[0092] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0093] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0094] S2, a ternary material (LiNi) with a specific capacity of 193 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 700 ppm boron, 1800 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0095] Example 8

[0096] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0097] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0098] S2, a ternary material (LiNi) with a specific capacity of 192 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, 1300 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0099] Example 9

[0100] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0101] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0102] S2, using a ternary material (LiNi) with a specific capacity of 194 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, 2200 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0103] Example 10

[0104] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0105] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0106] S2, using 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 second active coating slurry. The ternary material contained 700 ppm boron, 1500 ppm tungsten, and 900 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0107] Example 11

[0108] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0109] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0110] S2, using a ternary material (LiNi) with a specific capacity of 192.5 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, 1500 ppm tungsten, and 950 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0111] Example 12

[0112] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0113] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0114] S2, using a ternary material (LiNi) with a specific capacity of 192.5 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, 1500 ppm tungsten, and 850 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0115] Example 13

[0116] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0117] S1, 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 first active coating slurry. The ternary material contained 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0118] S2, using 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 second active coating slurry. The ternary material contained 700 ppm boron, 1500 ppm tungsten, and 700 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0119] Example 14

[0120] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron and tungsten. The preparation method is as follows:

[0121] S1, a ternary material (LiNi) with a specific capacity of 195 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 1000 ppm boron and 2500 ppm tungsten. The first active coating slurry is coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0122] S2, using a ternary material (LiNi) with a specific capacity of 192.5 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 and 1500 ppm tungsten. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0123] Example 15

[0124] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0125] S1, 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 are mixed in a mass percentage ratio of 96%:1.5%:2.5% to obtain a first active coating slurry. The ternary material contains 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry is coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0126] S2, using a ternary material (LiNi) with a specific capacity of 192.5 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 700 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0127] Example 16

[0128] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0129] S1, 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 are mixed in a mass percentage ratio of 98.5%:0.5%:1.0% to obtain a first active coating slurry. The ternary material contains 1000 ppm boron, 2500 ppm tungsten, and 1000 ppm strontium. The first active coating slurry is coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0130] S2, using 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 98.5%:0.5%:1.0% to obtain a second active coating slurry. The ternary material contained 700 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0131] Example 17

[0132] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0133] S1, a ternary material (LiNi) with a specific capacity of 192.5 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 first active coating slurry. The ternary material contained 700 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry was coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0134] S2, using a ternary material (LiNi) with a specific capacity of 191.5 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 400 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0135] Example 18

[0136] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0137] 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 900 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0138] S2, using a ternary material (LiNi) with a specific capacity of 191.5 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 400 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0139] Example 19

[0140] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. The preparation method is as follows:

[0141] 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 paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0142] 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 400 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0143] Example 20

[0144] Example 20 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron. The preparation method is as follows:

[0145] S1, 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 are mixed in a mass percentage ratio of 97.8%:1.0%:1.2% to obtain a first active coating slurry. The ternary material contains 1000 ppm of boron. The first active coating slurry is coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0146] S2, a ternary material (LiNi) with a specific capacity of 190 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 boron with a content of 700 ppm. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm; thus, a positive electrode sheet was obtained.

[0147] Comparative Example 1

[0148] Comparative Example 1 provides a positive electrode sheet, the preparation method of which is as follows:

[0149] The ternary material (LiNi) with a specific capacity of 191.5 mAh / g (0.5C) was used. 0.83 Co 0.05 Mn 0.12A 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 400 ppm of element B, 1500 ppm of element W, and 800 ppm of element Sr. 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.

[0150] Comparative Example 2

[0151] 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 Comparative Example 2 uses a ternary material containing only the element strontium.

[0152] Comparative Example 3

[0153] 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 coated surface of the positive current collector, and the second active coating is disposed on the short coated surface of the positive current collector. Both the first and second active coatings comprise a ternary material containing boron, tungsten, and strontium. Its preparation method is as follows:

[0154] 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 400 ppm boron, 1500 ppm tungsten, and 800 ppm strontium. The first active coating slurry is coated on the long paste surface of the positive electrode current collector aluminum foil to form a first active coating with a thickness of 60 μm.

[0155] S2, using a ternary material (LiNi) with a specific capacity of 192.5 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, 1500 ppm tungsten, and 800 ppm strontium. The second active coating slurry was coated on the short paste surface of the positive electrode current collector aluminum foil to form a second active coating with a thickness of 60 μm, thus obtaining the positive electrode sheet.

[0156] Performance testing

[0157] Preparation of secondary batteries

[0158] (1) Preparation of negative electrode sheet

[0159] 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.

[0160] (2) Preparation of electrolyte

[0161] 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.

[0162] (3) Separator: 12μm polypropylene diaphragm.

[0163] The positive electrode sheet, negative electrode sheet, and separator prepared in Examples 1-20 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).

[0164] Cyclic performance test: number of cycles at 45℃ and capacity retention (1C / 1C) / %; parameters were set as follows: 2.5V~4.25V, 0.02C. Results are shown in Table 1.

[0165] Table 1. Data from Examples 1-20 and Comparative Examples 1-3

[0166]

[0167]

[0168] Comparative Examples 1-20 and Comparative Examples 1-3 show that when the active coatings on both sides of the current collector contain lithium nickel oxides with different boron and / or tungsten content, the cycle capacity retention rate can be improved. This is because when the boron and / or tungsten content in the lithium nickel oxides on both sides of the current collector is within an appropriate range, it can balance the influence of lithium nickel oxide structural stability and polarization on the cycle.

[0169] 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, a first active coating, and a second active coating, wherein the first active coating is disposed on one side of the current collector and the second active coating is disposed on the other side of 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, strontium, and tungsten; The content of the first element in the first lithium nickel oxide is greater than the content of the first element in the second lithium nickel oxide; the boron content in the first lithium nickel oxide is 700-1000 ppm; and the boron content in the second lithium nickel oxide is 400-900 ppm. The tungsten content in the first lithium nickel oxide is 1500–2500 ppm; the tungsten content in the second lithium nickel oxide is 1300–2200 ppm. The strontium content in the first lithium nickel oxide is 800–1000 ppm; the strontium content in the second lithium nickel oxide is 700–950 ppm.

2. The positive electrode sheet according to claim 1, characterized in that, The specific capacity of the first lithium nickel oxide is 192–195 mAh / g; And / or, the specific capacity of the second lithium nickel oxide is 191.5 to 194 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. Calculated by the total mass of the first active coating, the first active coating comprises the following components in the following mass percentages: first lithium nickel oxide 96%–98.5%; first conductive agent: 0.5%–1.5%; first binder: 1.0%–2.5%. And / or, the second active coating further includes a second conductive agent and a second binder, and the second active coating comprises the following components in mass percentage: 96% to 98.5% second lithium nickel oxide; 0.5% to 1.5% second conductive agent; and 1.0% to 2.5% second binder, based on the total mass of the first active coating.

4. The positive electrode sheet according to claim 1, characterized in that, The length of the first active coating is L1, and the length of the second active coating 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 independently include at least one of lithium nickel cobalt manganese oxide or 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 5.

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

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