Positive electrode sheet, battery comprising the same, and electric device

Abstract

The application relates to a positive electrode sheet, a battery containing the positive electrode sheet and a power utilization device, and belongs to the technical field of batteries. The application is characterized in that lithium nickel manganese oxide is distributed in layers according to a specific particle size Dn50, and the thickness ratio between the layers is controlled within a suitable range. While ensuring that the lithium nickel manganese oxide has high kinetic performance, the application reduces the side reaction between the lithium nickel manganese oxide and electrolyte, improves the compaction density and the uniformity of the pore size of the positive electrode sheet, and effectively improves the kinetic performance and cycle performance of the positive electrode sheet.

Description

This application is a divisional application of application number CN202510431270.6, filed on April 28, 2025, entitled "Positive Electrode Sheet, Battery and Electrical Device Including the Positive Electrode Sheet". Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a positive electrode, a battery comprising the positive electrode, and an electrical device. Background Technology

[0002] The demand for high energy density and high output power in lithium-ion power batteries has drawn significant attention to the development of high-voltage cathode materials. Spinel-type lithium nickel manganese oxide (LNMO) materials, with their crystal structure providing three-dimensional lithium-ion transport channels, exhibit good ionic conductivity, a high voltage plateau of 4.7V (vs Li / Li+), and a theoretical specific capacity of 147mAh / g, demonstrating great potential. However, LNMO (0.5601eV) has a large band gap, resulting in relatively poor conductivity. Under high-voltage operating conditions, side reactions at the cathode interface and electrolyte intensify, leading to an increase in interfacial byproducts. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a positive electrode, a battery containing the positive electrode, and an electrical device, so that the positive electrode using LNMO has both good kinetic performance and cycle performance.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a positive electrode sheet comprising: Positive current collector; A first positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. The first positive electrode active material layer comprises lithium nickel manganese oxide particles, wherein the particle size Dn50 of the lithium nickel manganese oxide particles is a μm, and a ranges from 1 to a ≤ 4. The second positive electrode active material layer is disposed on the surface of the first positive electrode active material layer away from the positive electrode current collector. The second positive electrode active material layer contains lithium nickel manganese oxide particles, wherein the particle size Dn50 of the lithium nickel manganese oxide particles is b μm, and the range of b is 5≤b≤8. Wherein, based on the total thickness of the first positive electrode active material layer and the second positive electrode active material layer, the thickness ratio of the second positive electrode active material layer is M. b M b The range is 0.5 to 0.8.

[0005] Secondly, the present invention provides a battery comprising the positive electrode plate.

[0006] Thirdly, the present invention provides an electrical device comprising the battery.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: By distributing LNMO in layers according to a specific particle size Dn50 and controlling the thickness ratio between each layer within a suitable range, the present invention ensures that LNMO has high kinetic performance while reducing side reactions between it and the electrolyte (even at high voltage, side reactions are relatively few), improving the compaction density and pore size uniformity of the positive electrode, and effectively enhancing the kinetic and cycle performance of the positive electrode. Detailed Implementation

[0008] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0009] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0010] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0011] In this invention, there are no particular limitations on the specific dispersion and stirring methods.

[0012] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0013] In this invention, expressions such as "first time" and "second time" are not used to limit the number of times.

[0014] Positive electrode film This invention provides a positive electrode sheet, comprising: Positive current collector; A first positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. The first positive electrode active material layer comprises lithium nickel manganese oxide particles (hereinafter referred to as "first lithium nickel manganese oxide particles"), wherein the particle size Dn50 of the lithium nickel manganese oxide particles is a μm, and the range of a is 1≤a≤4; and The second positive electrode active material layer is disposed on the surface of the first positive electrode active material layer away from the positive electrode current collector. The second positive electrode active material layer contains lithium nickel manganese oxide particles (hereinafter referred to as "second lithium nickel manganese oxide particles"), wherein the particle size Dn50 of the lithium nickel manganese oxide particles is b μm, and the range of b is 5≤b≤8. Wherein, based on the total thickness of the first positive electrode active material layer and the second positive electrode active material layer, the thickness ratio of the second positive electrode active material layer is M. b M b The range is 0.5 to 0.8.

[0015] The first lithium nickel manganese oxide particles have a relatively small particle size (Dn50) and good kinetic performance. Placing them in the first positive electrode active material layer near the positive electrode current collector reduces their contact with the electrolyte, thus weakening the reaction between them. The second lithium nickel manganese oxide particles have a relatively large particle size (Dn50), small specific surface area, high strength, and good structural stability. Placing them in the second active material layer away from the positive electrode current collector reduces side reactions between the positive electrode interface and the electrolyte, even under high voltage. Furthermore, placing the smaller-sized first lithium nickel manganese oxide particles and the larger-sized second lithium nickel manganese oxide particles in the first and second positive electrode active material layers respectively allows pressure to be transferred from the second active material layer to the first active material layer during compaction. This reduces damage to the first lithium nickel manganese oxide particles with the support of the second particles, increases compaction density, makes the pore size in the positive electrode sheet more uniform, facilitates smoother ion and electron transport, reduces resistance, lowers polarization, and improves kinetic and cycle performance.

[0016] Simultaneously, the particle size Dn50(a) of the first lithium nickel manganese oxide particles, the particle size Dn50(b) of the second lithium nickel manganese oxide particles, and the thickness ratio (M) of the second positive electrode active material layer are controlled. b Within the aforementioned suitable range, not only can the first and second lithium nickel manganese oxide particles function better, but it also helps to further improve the uniformity of the compaction density and pore size of the positive electrode sheet, resulting in better kinetic and cycle performance of the positive electrode sheet.

[0017] This invention distributes LNMO in layers according to a specific particle size Dn50 and controls the thickness ratio between each layer within a suitable range. This ensures that LNMO has high kinetic performance while reducing side reactions between it and the electrolyte (even at high voltage, side reactions are relatively few), thereby improving the compaction density and pore size uniformity of the positive electrode and effectively enhancing the kinetic and cycle performance of the positive electrode.

[0018] For example, 'a' can be an interval range formed by any two values ​​of 1.00, 1.30, 1.55, 1.80, 2.05, 2.20, 2.55, 2.72, 3.00, 3.25, 3.50, 3.75, 4.00, or more.

[0019] For example, b is an interval range formed by any two values ​​of 5.00, 5.25, 5.40, 5.65, 5.80, 6.00, 6.25, 6.40, 6.65, 6.80, 7.00, 7.25, 7.40, 7.65, 7.80, 8.00 or above.

[0020] For example, the M b The range of values ​​is formed by any two values ​​of 0.50, 0.52, 0.54, 0.56, 0.58, 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, 0.74, 0.76, 0.78, 0.80 or above.

[0021] The particle size Dn50(a) of the first lithium nickel manganese oxide particle and the particle size Dn50(b) of the second lithium nickel manganese oxide particle can be controlled by adjusting the following process conditions: calcination conditions (such as calcination temperature, calcination time, etc.), grinding conditions (such as grinding time, rotation speed, etc. If sand milling is used, it can also be controlled by adjusting the sand-to-material ratio (i.e., the mass ratio of sand particles to material, the same below). If ball milling is used, it can also be controlled by adjusting the ball-to-material ratio.

[0022] This invention does not limit the detection method for the particle size Dn50(a) of the first lithium nickel manganese oxide particle and the particle size Dn50(b) of the second lithium nickel manganese oxide particle. Those skilled in the art can detect the particle size Dn50(a) and particle size Dn50(b) of the first lithium nickel manganese oxide particle using conventional techniques. For example, the particle size Dn50(a) of the first lithium nickel manganese oxide particle and the particle size Dn50(b) of the second lithium nickel manganese oxide particle can be detected using the following method: Take an empty battery, disassemble it to obtain the positive electrode sheet, perform CP (Cross-Section Polishing) on ​​the positive electrode sheet, and observe and measure it using SEM (Scanning Electron Microscope). The magnification is adjusted to 5Kx. Take pictures of the upper, middle and lower regions of each active material layer, measure the particle length of all particles in the three regions in the pictures, and obtain the average particle size Dn50 of the 50% distribution in these three regions. Then calculate the average value of Dn50 in these three regions to obtain the average particle size Dn50 of each active material layer, that is, the particle size Dn50 of the first lithium nickel manganese oxide particle (a) and the particle size Dn50 of the second lithium nickel manganese oxide particle (b).

[0023] The thickness percentage of the second positive electrode active material layer (M) b The coating gap width, coating speed, and solid content of the slurry can be controlled by adjusting factors such as the coating machine's coating gap width, coating speed, and slurry solid content.

[0024] The present invention relates to the thickness ratio (M) of the second positive electrode active material layer. b The detection method for the second positive electrode active material layer is not limited. Those skilled in the art can use conventional techniques to determine the thickness ratio (M) of the second positive electrode active material layer. b The detection is performed. For example, the thickness percentage (M) of the second positive electrode active material layer... b The following methods can be used for detection: Take an empty battery, disassemble it to obtain the positive electrode sheet, perform CP cross-section processing on the positive electrode sheet, and use SEM (scanning electron microscope) to determine the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer at the cross-section. Then calculate the thickness ratio (M) of the second positive electrode active material layer. b ).

[0025] In some implementations, a and b satisfy the relationship: 0.125 ≤ a / b ≤ 0.5. For example, a / b is 0.125, 0.150, 0.200, 0.250, 0.300, 0.355, 0.405, 0.455, 0.500, or any range formed by any two of the above values.

[0026] In one preferred embodiment, a and b satisfy the relationship: 0.3 ≤ a / b ≤ 0.4. For example, a / b is 0.300, 0.315, 0.320, 0.345, 0.350, 0.365, 0.370, 0.385, 0.390, 0.400, or any range formed by any two of the above values.

[0027] When a / b is in the range of 0.125 to 0.5, especially in the range of 0.3 to 0.4, the effect of the first and second lithium nickel manganese oxide particles can be better utilized, while the volume change difference between the first and second lithium nickel manganese oxide particles during the lithium insertion / extraction process is smaller. This avoids large stress at the interface between the first and second positive electrode active material layers, which could lead to cracks or detachment, thereby improving the kinetics and cycle performance of the positive electrode sheet.

[0028] In some embodiments, the range of 'a' is 2 μm to 3 μm to improve the kinetics and cycle performance of the positive electrode. For example, 'a' can be 2.00 μm, 2.15 μm, 2.20 μm, 2.35 μm, 2.40 μm, 2.55 μm, 2.60 μm, 2.75 μm, 2.80 μm, 2.95 μm, 3.00 μm, or any range formed by two of the above values.

[0029] In some embodiments, the range of b is 6 μm to 7 μm to improve the kinetics and cycle performance of the positive electrode. For example, b is 6.00 μm, 6.15 μm, 6.20 μm, 6.35 μm, 6.40 μm, 6.55 μm, 6.60 μm, 6.75 μm, 6.80 μm, 6.95 μm, 7.00 μm, or any range formed by two of the above values.

[0030] In some implementations, the M b The range is 0.6 to 0.7 to improve the kinetics and cycle performance of the positive electrode. For example, the M... b The range is defined by 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, or any two of the above values.

[0031] In some embodiments, after 200 cycles at 25°C, the amount of transition metal ions dissolved is k%; the positive electrode sheet satisfies: 0.06 ≤ k / M b ≤0.3. For example, k / M b The range is defined as 0.06, 0.07, 0.08, 0.09, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.29, 0.30, or any two of the above values.

[0032] In one preferred embodiment, the positive electrode sheet satisfies: 0.1 ≤ k / M b ≤0.2.

[0033] k% = the transition metal ion content in the negative electrode after 200 cycles at 25℃ / the transition metal ion content in the positive electrode before cycling, multiplied by 100%. During their research, the inventors discovered that the amount of transition metal ions dissolved (k) after 200 cycles at 25℃ effectively reflects the ease of battery capacity decay, and that controlling k / M... b At 0.06 <k / M b In the range <0.3, especially in the range 0.1 ≤ k / M b Within the range of ≤0.2, the LNMO structure in the cathode sheet has better stability, and the cathode sheet has higher compaction density and better uniformity of pore size, which is more conducive to improving the kinetics and cycle performance of the cathode sheet.

[0034] In some implementations, k ranges from 0.05 to 0.2. For example, k is 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.16, 0.18, 0.20, or any interval formed by two of the above values.

[0035] By controlling the value of k within the above-mentioned suitable range, not only is the surface stability of the positive electrode better, but the SEI film (i.e., the solid electrolyte interface film formed on the surface of the negative electrode active material) is less affected by transition metal ions, has better stability, and lower impedance, which is conducive to lithium ion transport. As a result, the cycle performance and kinetic performance of the battery using this positive electrode are better. At the same time, the surface of the positive electrode is not easily passivated, the ion and electron transport is good, and the kinetic performance of the positive electrode is good.

[0036] The amount of transition metal ion dissolution (k) after 200 cycles at 25℃ can be adjusted by modifying the thickness of the coating layer (if any), the particle size Dn50 of the first lithium nickel manganese oxide particle (a), the particle size Dn50 of the second lithium nickel manganese oxide particle (b), and the thickness ratio of the second positive electrode active material layer (M). b (etc.) to control.

[0037] This invention does not limit the method for detecting the amount of transition metal ions (k) dissolved after 200 cycles at 25°C. Those skilled in the art can detect the amount of transition metal ions (k) dissolved after 200 cycles at 25°C using conventional techniques. For example, the amount of transition metal ions (k) dissolved after 200 cycles at 25°C can be detected using the following method: Take an empty battery, disassemble it to obtain the positive electrode sheet, and soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (e.g., 25℃, the same below) for 1 hour to remove the electrolyte. Take it out, let it dry, scrape off the positive electrode material from the current collector surface, digest the positive electrode material, and use an ICP (inductively coupled plasma) instrument to measure the total mass of Ni and Mn. The sum of the two is M1. A total of 5 parallel samples were measured (i.e., 5 batteries were used for testing), and the average value of M1 was calculated and recorded as . ; Take an empty battery and disassemble it to obtain the positive and negative electrode sheets. Mix the disassembled positive and negative electrode sheets with an electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent; then dissolve thoroughly dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L). Assemble the battery, first at 25°C for 2 cycles, then at 25°C and 1C for 200 cycles. Then disassemble to obtain the negative electrode sheet. Immerse the negative electrode sheet in DMC (dimethyl carbonate) at room temperature (e.g., 25°C, the same below) for 1 hour to remove the electrolyte. Remove, dry, scrape off the negative electrode material from the current collector surface, digest the negative electrode material, and use ICP to measure the total mass M2 of Ni and Mn. Measure 5 parallel samples (i.e., use 5 batteries for testing), calculate the average value of M2, and record it as _____. ; Calculate k, k%= / 100%; The digestion methods are as follows: disperse the positive or negative electrode material in 20 mL of water, add 10 mL of nitric acid (HNO3 mass percentage is 66%), disperse and heat until the positive or negative electrode material is completely dissolved, dilute with water to 100 mL to obtain the test solution, and perform ICP test on the test solution. The operating conditions of the ICP instrument are set as follows: gas flow rate 0.5 L / min, power 1150 W; The constant-capacity method is as follows: charge at 0.33C constant current and constant voltage to 4.75V, cut off current in the constant voltage section ≤0.05C, then discharge at 0.33C constant current to 3.5V, repeat the charge and discharge process twice; The cyclic method is as follows: charge at a constant current and constant voltage of 1C to the upper limit voltage of 4.75V, and then charge at a constant voltage until the current is less than or equal to 0.05C; then discharge at 1C to the lower limit voltage of 3.5V, and repeat the above charge and discharge process 200 times.

[0038] In some embodiments, the first lithium nickel manganese oxide particle has a disordered Fd-3m structure, and the second lithium nickel manganese oxide particle has an ordered P4332 structure. The disordered structure (Fd3m space group) of lithium nickel manganese oxide is a face-centered cubic lattice. Unlike the ordered structure (P4332 space group), Mn and Ni ions in the disordered structure are randomly distributed at the 16d sites, rather than being ordered to specific sites. Disordered lithium nickel manganese oxide exhibits higher conductivity and ion diffusion coefficient, typically 2.5 orders of magnitude higher than the ordered structure. This is mainly due to the presence of a small amount of Mn in the disordered structure. 3+ Its radius is greater than Mn 4+ This increases the lattice parameter, which to some extent benefits Li + The diffusion and electron conduction are improved; the ordered Fd-3m structure of LNMO exhibits good stability. By setting the first lithium nickel manganese oxide particle to a disordered Fd-3m structure and the second lithium nickel manganese oxide particle to an ordered P4332 structure, the kinetics and cycle performance of the positive electrode can be improved.

[0039] This invention does not limit the method for detecting the lithium nickel manganese oxide crystal structure in each active material layer of the positive electrode. Those skilled in the art can detect the lithium nickel manganese oxide crystal structure in each active material layer of the positive electrode using conventional techniques. For example, the lithium nickel manganese oxide crystal structure in each active material layer of the positive electrode can be detected using Raman spectroscopy after scraping off materials from each active material layer. If the Raman spectrum reaches 594 cm⁻¹... -1 F within the range 2g(1) The peaks exhibit a distinct splitting phenomenon, indicating an increased degree of disorder in Ni / Mn, leading to the transformation of the ordered structure into a disordered Fd-3m structure. The Raman spectroscopy testing conditions can be selected as follows: laser wavelength of 514 nm, Raman shift range of 100–2000 cm⁻¹. -1 For Raman spectrometers, the Renishaw RM2000 confocal micro Raman spectrometer from the UK is a good choice.

[0040] In some embodiments, the total thickness of the first positive electrode active material layer and the second positive electrode active material layer is 100μm to 160μm, such as 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm or any range formed by any two of the above values.

[0041] The first and second lithium nickel manganese oxide particles are spinel-type with the chemical formula LiNi. x Mn 2-xO4, where x > 0, such as 0.1, 0.2, 0.3, 0.4, 0.5, or any range formed by two of the above values. Their surfaces may be uncoated, or at least part or all of the surface of the first lithium nickel manganese oxide particle and the second lithium nickel manganese oxide particle may be coated with a coating layer formed by a coating material. The coating material may be selected from at least one of the following materials: alumina, titanium oxide, lithium phosphate, zirconium oxide, tantalum oxide, magnesium oxide, iron oxide, etc. In some embodiments, the coating layer thickness on the surface of the first lithium nickel manganese oxide particle is 5~50 nm, such as 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any range formed by two of the above values. In some embodiments, the thickness of the coating layer on the surface of the second lithium nickel manganese oxide particle is 5~50 nm, such as 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any range formed by two of the above values. When both the first lithium nickel manganese oxide particle and the second lithium nickel manganese oxide particle are provided with a coating layer, the material and thickness of the coating layer are independent of each other.

[0042] The first and second lithium nickel manganese oxide particles may or may not contain doped elements. This invention does not limit the type of doped element in the first and second lithium nickel manganese oxide particles; for example, it may be at least one of Si, Mg, P, Co, Al, Cr, Nb, etc. Whether the first and second lithium nickel manganese oxide particles contain doped elements, as well as the type and content of the doped elements, are independent of each other and do not affect each other.

[0043] This invention does not limit the preparation method of the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles. Those skilled in the art can prepare the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles using conventional techniques. For example, the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles can be prepared by a method including the following steps: The lithium source, nickel source, and manganese source are mixed and dispersed in a solvent to obtain a mixture; The mixture was calcined at a temperature range of 650~900℃ and then cooled to obtain raw lithium nickel manganese oxide. The raw lithium nickel manganese oxide material is ground and dried to obtain lithium nickel manganese oxide particles.

[0044] In the process of preparing the mixture using lithium, nickel, and manganese sources, the solvent can be at least one selected from solvents such as ethanol, NMP, acetonitrile, and DMC. In some embodiments, the mixing and dispersion method can be a solid-state method, such as ball milling or sand milling.

[0045] In the process of preparing the first nickel manganese oxide bare material using the mixture, the calcination process conditions can be set as follows: calcination temperature range 650-900℃, calcination time 12-24h, heating rate 1~5℃ / h; Calcination can be carried out in calcination equipment such as muffle furnaces and tube furnaces.

[0046] In the process of preparing lithium nickel manganese oxide particles using bare lithium nickel manganese oxide material, the grinding method can be sand milling, and the sand milling conditions can be selected as follows: sand-to-material ratio (mass ratio, the same below) 8-20:1, rotation speed 1000-3000 rpm, sand milling time 4-24h, and the sand particles can be selected from at least one of alumina, zirconium oxide, silicon carbide, and boron carbide.

[0047] The lithium source includes, but is not limited to, at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, or lithium acetate; and / or Nickel sources include, but are not limited to, at least one of nickel carbonate, nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate; and / or The manganese source includes, but is not limited to, at least one of manganese dioxide, manganese hydroxide, manganese oxide, and manganese sulfate.

[0048] When the first or second lithium nickel manganese oxide particles have a disordered Fd-3m structure, the corresponding calcination temperature is 750-900℃ and the calcination time is 16-20h. When the first or second lithium nickel manganese oxide particles have an ordered P4332 structure, the corresponding calcination temperature is 650~700℃ and the calcination time is 12~18h.

[0049] In addition, the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles can be coated. For example, atomic layer deposition (ALD) technology can be used to coat the surface of the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles with a coating material. The coating material can be selected from at least one of alumina, titanium oxide, zinc oxide, and magnesium oxide. The number of ALD deposition layers can be selected from 50 to 500, and the thickness of one ALD deposition layer can be selected from 0.1 to 0.3 nm.

[0050] In addition, when preparing the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles, a certain amount of dopant element source (if any) can be mixed and dispersed together with the lithium source, nickel source and manganese source to prepare the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles. The dopant element source is at least one of Si source, Mg source, P source, Co source, Al source, Cr source, Nb source, etc., to obtain the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles containing a certain amount of dopant element.

[0051] In some embodiments, the mass percentage of the first lithium nickel manganese oxide particles in the first positive electrode active material layer is 94% to 98%, such as 94%, 95%, 96%, 97%, 98%, or any two of the above values.

[0052] The first positive electrode active material layer further comprises a conductive agent and a binder. The conductive agent in the first positive electrode active material layer is used to provide conductivity; any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent in the positive electrode active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP (Super P), acetylene black, Ketjen black, etc.

[0053] In some embodiments, the mass percentage of the conductive agent in the first positive electrode active material layer is 0.05% to 3.5%, such as 0.05%, 0.08%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or any range formed by any two of the above values.

[0054] The binder of the first positive electrode active material layer is used to improve the adhesion between the first LNMO particles and the adhesion between the first LNMO particles and the positive electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binder of the first positive electrode active material layer includes, but is not limited to, fluorinated polyolefin binders, including but not limited to polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acids, acrylic acid, acrylonitrile, etc.).

[0055] In some embodiments, the mass percentage of the binder in the first positive electrode active material layer is 0.5% to 2.5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, or any range formed by any two of the above values.

[0056] In some embodiments, the mass percentage of the second lithium nickel manganese oxide particles in the second positive electrode active material layer is 94% to 98%, such as 94%, 95%, 96%, 97%, 98%, or any range formed by any two of the above values.

[0057] The second positive electrode active material layer further comprises a conductive agent and a binder. The conductive agent in the second positive electrode active material layer is used to provide conductivity; any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent in the positive electrode active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP (Super P), acetylene black, Ketjen black, etc.

[0058] In some embodiments, the mass percentage of the conductive agent in the second positive electrode active material layer is 0.05% to 3.5%, such as 0.05%, 0.08%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or any range formed by any two of the above values.

[0059] The binder for the second positive electrode active material layer is used to improve the adhesion between the second LNMO particles and the adhesion between the second LNMO particles and the first positive electrode active material layer. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binder for the second positive electrode active material layer includes, but is not limited to, fluorinated polyolefin binders, including but not limited to polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acids, acrylic acid, acrylonitrile, etc.).

[0060] In some embodiments, the mass percentage of the binder in the second positive electrode active material layer is 0.5% to 2.5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, or any range formed by any two of the above values.

[0061] The present invention does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: aluminum, nickel, titanium, stainless steel, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0062] The positive electrode sheet of this invention can be prepared according to conventional methods in the art. For example: The first positive electrode active material, conductive agent and binder are dispersed in a solvent to obtain the first positive electrode slurry; The second positive electrode active material, conductive agent and binder are dispersed in a solvent to obtain the second positive electrode slurry; The first and second positive electrode slurries are then coated onto at least one side of the positive electrode current collector, and after cold pressing, slitting, and other processes, a positive electrode sheet is obtained. The solvent includes, but is not limited to, at least one of N-methylpyrrolidone (NMP) and deionized water. When coating the first and second positive electrode slurries onto at least one side of the positive electrode current collector, the first positive electrode slurry is coated first, followed by the second positive electrode slurry.

[0063] Battery The present invention also provides a battery, including the positive electrode, the negative electrode and the electrolyte.

[0064] In some embodiments, the transition metal elements in the negative electrode include Ni and Mn; the Ni content in the negative electrode ranges from 50 to 200 ppm, and the Mn content ranges from 500 to 1500 ppm. For example, the Ni content in the negative electrode is 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 170 ppm, 200 ppm, or any two of the above values; the Mn content is 500 ppm, 700 ppm, 1000 ppm, 1200 ppm, 1500 ppm, or any two of the above values. By controlling the Ni and Mn content in the negative electrode, the damage of transition metal ions to the SEI film of the negative electrode is reduced, improving battery cycle performance; at the same time, excessive passivation of the positive electrode is avoided.

[0065] This invention does not limit the method for detecting the Ni and Mn content in the negative electrode sheet. Those skilled in the art can detect the Ni and Mn content in the negative electrode sheet using conventional techniques. For example, the Ni and Mn content in the negative electrode sheet can be detected using the following method: Take an empty battery and disassemble it to obtain the positive and negative electrode sheets. Mix the disassembled positive and negative electrode sheets with the electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent, then dissolve fully dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L) and assemble it into a battery. First, circulate it at 25°C for 2 cycles, then circulate it at 25°C for 1C for 200 cycles. Then, disassemble it to obtain the negative electrode sheet. Soak the negative electrode sheet in DMC (dimethyl carbonate) at room temperature (e.g., 25°C, the same below) for 1 hour to remove the electrolyte. Take it out, dry it, scrape off the negative electrode material from the surface of the current collector, digest the negative electrode material (digestion method as above), and use ICP to measure the mass ratio of Ni and Mn to obtain the Ni and Mn element content in the negative electrode sheet.

[0066] The negative electrode sheet of the present invention includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material.

[0067] The present invention places no particular limitation on the negative electrode active material. Exemplarily, the negative electrode active material includes, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, SiO f (0 < f < 2, such as f = 1), silicon carbide, Li4Ti5O 12 and at least one of them.

[0068] In some of these embodiments, the mass percentage content of the negative electrode active material in the negative electrode active material layer is 92% - 98%. For example, the content of the positive electrode active substance in the negative electrode active material layer is 92%, 93%, 94%, 95%, 96%, 96.4%, 97%, 98% or the range formed by any two of the above values.

[0069] The negative electrode active material layer may further contain a conductive agent, and / or a binder, and / or a thickening agent.

[0070] The conductive agent in the negative electrode active material layer is used to provide conductivity. Any conductive agent can be used without particular limitation as long as it has appropriate electron conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the negative electrode active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fiber, activated carbon, mesoporous carbon, fullerenes, etc. Among them, the carbon fiber is, for example, carbon nanofiber, etc.; the carbon black is, for example, SP, acetylene black, Ketjen black, etc.

[0071] In some of these embodiments, the mass percentage content of the conductive agent in the negative electrode active material layer is 0.5% - 2.5%, such as 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2%, 2.5% or the range formed by any two of the above values.

[0072] The binder in the negative electrode active material layer is used to improve the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Any binder can be used without particular limitation as long as it has appropriate binding property and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder in the negative electrode active material layer includes, but is not limited to, at least one of carboxymethyl cellulose (CMC), styrene - butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, aqueous acrylic resin.

[0073] In some embodiments, the mass percentage of the binder in the negative electrode active material layer is 1% to 3%, such as 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any range formed by any two of the above values.

[0074] The thickener in the negative electrode active material layer is used to improve the stability of the negative electrode slurry. Any thickener can be used without particular limitation, as long as it has suitable thickening properties and does not significantly cause adverse chemical changes in the battery. For example, the thickener in the negative electrode active material layer includes, but is not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and hydrogenated styrene-butadiene rubber (H-SBR).

[0075] In some embodiments, the mass percentage of the thickener in the negative electrode active material layer is 0.5% to 2.5%, such as 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2%, 2.5%, or any range formed by any two of the above values.

[0076] The present invention does not impose any particular restrictions on the negative electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0077] The electrolyte of this invention can be any of the various electrolytes suitable for batteries in the art. The electrolyte comprises an electrolyte and a solvent, and the electrolyte typically includes a lithium salt.

[0078] For example, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be selected as 0.5~5 mol / L.

[0079] For example, the solvent includes, but is not limited to, at least one selected from ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The mass percentage of the solvent in the electrolyte can be selected from 70% to 98%.

[0080] In addition, the electrolyte may also contain additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery high-temperature performance, additives that improve battery overcharge performance, additives that improve battery low-temperature performance, etc.

[0081] The battery may further include a separator located between the positive and negative electrode plates to separate them and prevent short circuits. The separator can be any suitable battery separator material in the art. Exemplary examples include, but are not limited to, polypropylene, etc. At least one of polyethylene.

[0082] Electrical appliances The present invention also provides an electrical device comprising the battery. The battery serves as the power supply for the electrical device.

[0083] The term "electrical device" refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0084] The present invention is further illustrated below with specific embodiments. It should be noted that, unless otherwise specified, the calcination is carried out in an air atmosphere: Example 1 This embodiment provides a lithium-ion battery, and the specific preparation method is as follows: (1) Preparation of the first lithium nickel manganese oxide particles Li2CO3, NiCO3, and MnO2 were processed according to the chemical formula LiNi 0.5 Mn 1.5 The stoichiometric ratio of Li, Ni, and Mn in O4 is added to a ball mill for mixing and dispersion to obtain a mixture. The mixture is then added to a muffle furnace and heated to T1℃ for t1h. After cooling to room temperature, the material is transferred to a sand mill and sand-milled using zirconia sand particles at a sand-to-material ratio of S1:1 for t1'h. After sand milling, the material is dried, and then an alumina coating layer is deposited on the surface of the material using an ALD instrument with a deposition thickness of 0.1nm per ring to obtain alumina-coated lithium nickel manganese oxide, which is the first lithium nickel manganese oxide particle. The coating layer thickness is C1nm. The values ​​of T1, t1, S1, t1', and C1 are shown in Table 1.

[0085] (2) Preparation of the second lithium nickel manganese oxide particles Li2CO3, NiCO3, and MnO2 were processed according to the chemical formula LiNi 0.5 Mn 1.5 The stoichiometric ratio of Li, Ni, and Mn in O4 is added to a ball mill for mixing and dispersion to obtain a mixture. The mixture is then added to a muffle furnace and heated to T2℃ for t2h. After cooling to room temperature, the material is transferred to a sand mill and sand-milled using zirconia sand particles at a sand-to-material ratio of S2:1 for t2'h. After sand milling, the material is dried, and then an alumina coating layer is deposited on the surface of the material using an ALD instrument with a deposition thickness of 0.1nm per ring to obtain alumina-coated lithium nickel manganese oxide, which is the second lithium nickel manganese oxide particle. The coating layer thickness is C2nm. The values ​​of T2, t2, S2, t2', and C2 are shown in Table 1.

[0086] (3) Preparation of positive electrode sheet The first lithium nickel manganese oxide particles were used as the positive electrode active material. The positive electrode active material was mixed with conductive agent CNTs and binder PVDF at a mass ratio of 97:1:2. The solvent NMP was added and the mixture was stirred in a vacuum mixer to obtain the first positive electrode slurry (used to form the first positive electrode active material layer). The second lithium nickel manganese oxide particles were used as the positive electrode active material. The positive electrode active material was mixed with conductive agent CNTs and binder PVDF at a mass ratio of 97:1:2. The solvent NMP was added and the mixture was stirred in a vacuum mixer to obtain the second positive electrode slurry (used to form the second positive electrode active material layer). A first positive electrode slurry and a second positive electrode slurry are coated on both sides of the positive electrode current collector aluminum foil. During coating, the first positive electrode slurry is first coated on both sides of the positive electrode current collector. After the first positive electrode slurry dries, the second positive electrode slurry is coated on the surface of the first slurry. Then, after drying, cold pressing and slitting, a positive electrode sheet is obtained. The thickness of the second positive electrode active material layer is calculated based on the total thickness of the first and second positive electrode active material layers, with the thickness percentage of the second positive electrode active material layer being M. b M b The values ​​are shown in Table 1.

[0087] (4) Preparation of negative electrode sheet The negative electrode active material artificial graphite, conductive agent acetylene black, thickener CMC and binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water is added as solvent. The mixture is stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector copper foil, and then cold-pressed and slit to obtain the negative electrode sheet.

[0088] (5) Preparation of electrolyte Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1 to obtain an organic solvent. Then, dried lithium salt LiPF6 was dissolved in the obtained organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0089] (6) Preparation of lithium-ion batteries The positive electrode, separator (PE), and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing and standing for 24 hours, it undergoes formation to obtain a lithium-ion battery. The formation process is as follows: the battery is charged to 4.8V with a constant current of 0.33C using a LAND system, and then discharged to 3.5V with a constant current of 0.33C. This cycle is repeated twice, and then the battery is removed from the charging device.

[0090] Examples 2-27 and Comparative Examples 1-6 These examples and comparative examples all provide a lithium-ion battery, and the preparation method is similar to that of Example 1, except that: (a) In step (1), the values ​​of T1, t1, S1, t1' and C1 are shown in Table 1; (b) In step (2), the values ​​of T2, t2, S2, t2' and C2 are shown in Table 1; (c) In step (3), the total thickness of the first positive electrode active material layer and the second positive electrode active material layer remains unchanged, M b The values ​​are shown in Table 1.

[0091] Table 1 The following method was used to detect the particle size Dn50 (denoted as a μm) of the first lithium nickel manganese oxide particles, the particle size Dn50 (denoted as b μm) of the second lithium nickel manganese oxide particles, and the proportion of the thickness of the second positive electrode active material layer in the total thickness of the first and second positive electrode active material layers (denoted as M). b The amount of transition metal ions dissolved (denoted as k%) after 200 cycles at 25°C on the positive electrode and the crystal structures of the first and second lithium nickel manganese oxide particles are shown in Table 1 or Table 2: Particle size of the first and second lithium nickel manganese oxide particles: Take an empty battery, disassemble it to obtain the positive electrode sheet, perform CP cross-section processing on the positive electrode sheet, and observe and measure it using SEM. The rate is adjusted to 5Kx. Take pictures of the upper, middle and lower regions of each active material layer. Measure the particle length of all particles in these three regions and obtain the average particle size Dn50 of the 50% distribution in these three regions. Then calculate the average value of Dn50 in these three regions to obtain the average particle size Dn50 of each active material layer, which is the particle size Dn50 of the first lithium nickel manganese oxide particle (a) and the particle size Dn50 of the second lithium nickel manganese oxide particle (b).

[0092] The thickness percentage of the second positive electrode active material layer: An empty battery was disassembled to obtain the positive electrode sheet. The positive electrode sheet was subjected to CP cross-section processing. SEM (Scanning Electron Microscopy) was used to determine the thickness of the first and second positive electrode active material layers at the cross-section. The thickness percentage (M) of the second positive electrode active material layer was then calculated. b ).

[0093] Transition metal ion dissolution after 200 cycles at 25℃: An empty battery was disassembled to obtain the positive electrode. The positive electrode was immersed in DMC (dimethyl carbonate) at 25℃ for 1 hour to remove the electrolyte. It was then removed, dried, and the positive electrode material on the current collector surface was scraped off. After digestion, the total mass of Ni and Mn was measured using an ICP (inductively coupled plasma) instrument. The sum of the two was M1. Five parallel samples were measured (i.e., five batteries were used for testing), and the average value of M1 was calculated and denoted as M1. ; Take an empty battery and disassemble it to obtain the positive and negative electrode sheets. Mix the disassembled positive and negative electrode sheets with an electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent; then dissolve thoroughly dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L). Assemble the battery, first at 25°C for 2 cycles, then at 25°C and 1C for 200 cycles. Then disassemble to obtain the negative electrode sheet, immerse it in DMC (dimethyl carbonate) at 25°C for 1 hour to remove the electrolyte, remove it, dry it, scrape off the negative electrode material from the current collector surface, digest the negative electrode material, and use ICP to measure the total mass M2 of Ni and Mn. Measure 5 parallel samples (i.e., test with 5 batteries), calculate the average value of M2, and record it as _____. ; Calculate k, k%= / 100%; The digestion methods are as follows: disperse the positive or negative electrode material in 20 mL of water, add 10 mL of nitric acid (HNO3 mass percentage is 66%), disperse and heat until the positive or negative electrode material is completely dissolved, dilute with water to 100 mL to obtain the test solution, and perform ICP test on the test solution. The operating conditions of the ICP instrument are set as follows: gas flow rate 0.5 L / min, power 1150 W; The constant-capacity method is as follows: charge at 0.33C constant current and constant voltage to 4.75V, cut off current in the constant voltage section ≤0.05C, then discharge at 0.33C constant current to 3.5V, repeat the charge and discharge process twice; The cyclic method is as follows: charge at a constant current and constant voltage of 1C to the upper limit voltage of 4.75V, and then charge at a constant voltage until the current is less than or equal to 0.05C; then discharge at 1C to the lower limit voltage of 3.5V, and repeat the above charge and discharge process 200 times.

[0094] Determination of the crystal structures of the first and second lithium nickel manganese oxides: The configuration of the prepared materials was analyzed using a confocal Raman micro-specimen analyzer (RM2000, Renishaw, UK). Test conditions: laser wavelength 514 nm, Raman shift range 100–2000 cm⁻¹. -1 The Raman spectrum at 638.8 cm⁻¹ –1 A at location 1g The peaks are at 594.7 and 611.3 cm. –1 F 2g(1) The peak corresponds to the symmetric stretching vibration of the Mn-O bond, and simultaneously, at 408.4 cm⁻¹... –1 The Eg peak at 498.4 cm⁻¹–1 The F2g(2) peak at [location] corresponds to the stretching vibration of the Ni-O bond. Compared to the ordered structure sample, the disordered structure sample shows [significant differences] at 638.8, 498.4, and 408.4 cm⁻¹. –1 The intensity of the peak at this point is significantly reduced. Furthermore, the peak intensity at 594.7 cm⁻¹ is significantly reduced in disordered samples. –1 F at the location 2g(1) The peaks exhibit more pronounced splitting, a phenomenon mainly due to the increased degree of disorder in Ni / Mn, which causes its structure to transform from an ordered P4332 structure to a disordered Fd-3m structure.

[0095] Using the lithium-ion batteries obtained in the above embodiments and comparative examples as the test objects, the following tests were conducted: Battery capacity retention and DCR growth rate after 100 cycles at 45℃: After resting, the battery was charged to 4.8V at a constant current of 0.33C using a LAND system, then discharged to 3.5V at a constant current of 0.33C, for two cycles. The battery was then removed from the charging device for activation. After activation, the battery was charged at 45℃ at a constant current rate of 1C to 4.8V, then charged at a constant voltage rate until the current was less than 0.05C; then discharged at a 1C rate until the voltage reached 3.5V. One complete charge-discharge cycle was counted as 100 cycles. The capacity retention was calculated using the following formula: Capacity retention = Discharge capacity in the 100th cycle / Discharge capacity in the first cycle * 100%. The DCR value after 100 cycles at 45℃ is recorded as R1, and the initial DCR value before the cycle is recorded as R0; then the DCR growth rate after 100 cycles = (R1-R0) / R0*100%.

[0096] The DCR test condition is when the battery is at 50% SOC. Specific DCR test methods are as follows: A1. Let the battery stand at room temperature (25℃) for 10 minutes first; A2. First, charge the battery with constant current and constant voltage. The constant current rate is 0.33C and the voltage is 4.80V. Continue the constant voltage process until the current is ≤0.05C. Then, discharge the battery with constant current until it reaches 3.5V and the current rate is 0.33C. A3. Repeat steps A1-A2 three times, and record the discharge capacity of the last step A2 process as C1; A4. Continue repeating steps A1-A2 until the battery is fully charged; A5. Constant current discharge to a capacity of 0.5C1, discharge rate of 0.33C, at which point the battery is at 50% SOC. A6. Let the battery stand for 120 minutes and record the voltage at the end of the stand period as V0. A7. Constant current discharge for 18s, current multiplier 1C, record the voltage V1 at the end of discharge.

[0097] Table 2 For the batteries prepared in the various embodiments of the present invention, the capacity retention rate after 100 cycles at 45°C and 1C is ≥85%, and the DCR growth rate after 100 cycles at 45°C and 1C is ≤4.6%. It can be seen that the batteries containing the positive electrode of the present invention have excellent kinetic performance and high-temperature cycling performance.

[0098] Comparing Examples 1-7 with Examples 11-12, Example 13 with Example 15, and Example 14 with Example 16, it can be seen that when the particle size Dn50 of the first lithium nickel manganese oxide particle and the second lithium nickel manganese oxide particle meets the preferred range described in this invention, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0099] As can be seen from the comparison of Examples 1-7 with Examples 8-10, when the positive electrode sheet satisfies 0.3≤a / b≤0.4, the battery's dynamic performance and high-temperature cycle performance are relatively better.

[0100] Comparing Examples 1 and 6-7 with Examples 18-19, and Example 20 with Examples 21-22, it can be seen that when the thickness ratio M of the second positive electrode active material layer... b When the value of satisfies the preferred range described in this invention, the battery's dynamic performance and high-temperature cycle performance are relatively better.

[0101] By comparing Example 15 with Example 16, Examples 1-7 with Example 20, and Examples 18-19 with Examples 21-22, it can be seen that when the positive electrode plate satisfies 0.1 ≤ k / M b When the value is ≤0.2, the battery's dynamic performance and high-temperature cycling performance are relatively better.

[0102] As can be seen from the comparison between Example 1 and Examples 25-27, when the first lithium nickel manganese oxide particle has a disordered Fd-3m structure and the second lithium nickel manganese oxide particle has an ordered P4332 structure, the battery's kinetic performance and high-temperature cycle performance are relatively better.

[0103] According to Comparative Examples 1-6, when the particle size Dn50 of the first lithium nickel manganese oxide particle, the particle size Dn50 of the second lithium nickel manganese oxide particle, or the thickness ratio M of the second positive electrode active material layer... b If the value is too large or too small, the battery's dynamic performance and high-temperature cycle performance will be relatively poor.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

1. A positive electrode plate, characterized in that, Include: Positive current collector; A first positive electrode active material layer is disposed on at least one surface of the positive electrode current collector, the first positive electrode active material layer comprising lithium nickel manganese oxide particles, wherein the particle size Dn50 of the lithium nickel manganese oxide particles is a μm; and The second positive electrode active material layer is disposed on the surface of the first positive electrode active material layer away from the positive electrode current collector. The second positive electrode active material layer contains lithium nickel manganese oxide particles, wherein the particle size Dn50 of the lithium nickel manganese oxide particles is b μm. Wherein, based on the total thickness of the first positive electrode active material layer and the second positive electrode active material layer, the thickness ratio of the second positive electrode active material layer is M. b ; After 200 cycles at 25℃, the amount of transition metal ions dissolved was k% The positive electrode plate satisfies: 0.06 ≤ k / M b ≤0.3, 0.125≤a / b≤0.

5.

2. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode plate satisfies: 0.1 ≤ k / M b ≤0.

2.

3. The positive electrode sheet as described in claim 1, characterized in that, The relationship between a and b is: 0.3 ≤ a / b ≤ 0.

4.

4. The positive electrode sheet as described in claim 1, characterized in that, The range of a is 1 ≤ a ≤ 4; and / or The range of b is 5 ≤ ​​b ≤ 8; and / or The M b The range is 0.5 to 0.

8.

5. The positive electrode sheet as described in claim 4, characterized in that, The range of a is 2 ≤ a ≤ 3; and / or The range of b is 6 ≤ b ≤ 7; and / or The M b The range is 0.6 to 0.

7.

6. The positive electrode sheet as described in claim 1, characterized in that, The range of k is 0.05≤k≤0.

2.

7. The positive electrode sheet as described in claim 1, characterized in that, The lithium nickel manganese oxide particles in the first and second positive electrode active material layers each have the independent chemical formula LiNi. x Mn 2-x O4, where x > 0.

8. The positive electrode sheet as described in claim 1, characterized in that, In the first positive electrode active material layer and the second positive electrode active material layer, at least one of the lithium nickel manganese oxide particles contains a coating material on its surface, and the coating material includes at least one of the following materials: alumina, titanium oxide, lithium phosphate, zirconium oxide, tantalum oxide, magnesium oxide, and iron oxide.

9. The positive electrode sheet as described in claim 1, characterized in that, In the first positive electrode active material layer and the second positive electrode active material layer, at least one of the lithium nickel manganese oxide particles contains a doping element, which is at least one of Si, Mg, P, Co, Al, Cr and Nb.

10. The positive electrode sheet as described in claim 1, characterized in that, The lithium nickel manganese oxide particles in the first positive electrode active material layer have a disordered Fd-3m structure, while the lithium nickel manganese oxide particles in the second positive electrode active material layer have an ordered P4332 structure.

11. A battery, characterized in that, It includes the positive electrode sheet as described in any one of claims 1 to 10.

12. The battery as claimed in claim 11, characterized in that, It also includes a negative electrode, wherein the transition metal elements in the negative electrode include Ni and Mn; wherein the Ni content in the negative electrode ranges from 50 to 200 ppm and the Mn content ranges from 500 to 1500 ppm.

13. An electrical appliance, characterized in that, It includes the battery as described in claim 11 or 12.

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