Positive plate, battery comprising positive plate and electric device

Abstract

The invention relates to a positive plate, a battery comprising the positive plate and an electric device, and belongs to the technical field of batteries. Layered distribution is carried out on the lithium nickel manganese oxide according to the specific particle size Dn50, and the thickness ratio of all layers is controlled in a suitable range, so that the lithium nickel manganese oxide has relatively high dynamic performance, side reaction between the lithium nickel manganese oxide and electrolyte is reduced, the compaction density of the positive plate and the uniformity of pore size are improved, and the service life of the positive plate is prolonged. And the dynamic performance and the cycle performance of the positive plate are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a positive electrode sheet, a battery including the positive electrode sheet, and an electrical device. Background Art

[0002] The demand for high energy density and high output power in lithium-ion power batteries has drawn people's attention to the research and development of high-voltage cathode materials. The crystal structure of spinel-type lithium nickel manganese oxide (LNMO) materials can provide a three-dimensional lithium-ion transport channel, with good ionic conductivity, a high-voltage platform of 4.7 V (vs Li / Li+), and a theoretical specific capacity of up to 147 mAh / g, showing great potential. However, LNMO (0.5601 eV) has a large band gap, resulting in poor conductivity of the system; under high-voltage operating conditions, the side reactions between the cathode interface and the electrolyte are aggravated, and the interface by-products increase. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a positive electrode sheet, a battery including the positive electrode sheet, and an electrical device, so that the positive electrode sheet using LNMO has both good kinetic performance and cycling performance.

[0004] To achieve the above purpose, in the first aspect, the present invention provides a positive electrode sheet, comprising:

[0005] A positive electrode current collector;

[0006] A first positive electrode active material layer 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 range of a is 1 ≤ a ≤ 4; and

[0007] A second positive electrode active material layer 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 comprising 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;

[0008] 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 of is 0.5 to 0.8.

[0009] In the second aspect, the present invention provides a battery including the positive electrode sheet.

[0010] In the third aspect, the present invention provides an electrical device including the battery.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: By stratifying and distributing LNMO according to a specific particle size Dn50 and controlling the thickness ratio between layers within an appropriate range, the present invention reduces the side reactions between LNMO and the electrolyte (even with fewer side reactions at high voltages) while ensuring high kinetic performance of LNMO, improves the compaction density of the positive electrode sheet and the uniformity of pore size, and effectively enhances the kinetic performance and cycling performance of the positive electrode sheet. Detailed Embodiments

[0012] 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. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] In the present invention, among the technically characterized descriptions in an open-ended manner, it includes a closed technical solution composed of the listed features, as well as an open technical solution containing the listed features.

[0014] In the present invention, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous, including the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0015] In the present invention, there are no particular limitations on the specific dispersion and stirring treatment methods.

[0016] The reagents or instruments used in the present invention that are not indicated by the manufacturer can all be obtained as conventional products through commercial purchases.

[0017] In the present invention, similar expressions such as "first time" and "second time" are not used to limit the number of times.

[0018] Positive electrode sheet

[0019] The present invention provides a positive electrode sheet, comprising:

[0020] A positive electrode current collector;

[0021] The 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 contains lithium nickel manganese oxide particles (hereinafter, the lithium nickel manganese oxide particles in the first positive electrode active material layer are referred to as "first lithium nickel manganese oxide particles"). The particle size Dn50 of the lithium nickel manganese oxide particles is a μm, and the range of a is 1 ≤ a ≤ 4; and

[0022] 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, the lithium nickel manganese oxide particles in the second positive electrode active material layer are referred to as "second lithium nickel manganese oxide particles"). The particle size Dn50 of the lithium nickel manganese oxide particles is b μm, and the range of b is 5 ≤ b ≤ 8;

[0023] 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 of is 0.5 to 0.8.

[0024] The particle size Dn50 of the first lithium nickel manganese oxide particles is relatively small, and the kinetic performance is good. Setting it in the first positive electrode active material layer close to the positive electrode current collector can reduce its contact with the electrolyte and weaken the reaction between it and the electrolyte; the particle size Dn50 of the second lithium nickel manganese oxide particles is relatively large, the specific surface area is small, the strength is high, and the structural stability is good. Setting it in the second active material layer away from the positive electrode current collector can reduce the side reactions between the positive electrode interface and the electrolyte even at high voltages. In addition, the first lithium nickel manganese oxide particles with a smaller particle size Dn50 and the second lithium nickel manganese oxide particles with a larger particle size Dn50 are respectively arranged in the first positive electrode active material layer and the second positive electrode active material layer. During the compaction process, the pressure is transmitted from the second active material layer to the first active material layer. In this way, under the supporting action of the second lithium nickel manganese oxide particles, the damage to the first lithium nickel manganese oxide particles can be reduced, the compaction density can be increased, the pore size in the positive electrode sheet can be made more uniform, the ion and electron transmission can be more smooth, the resistance can be smaller, the polarization can be lower, and the kinetic and cycling performance can be better.

[0025] At the same time, controlling 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 b ) of the second positive electrode active material layer within the above suitable ranges can not only make the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles play better roles, but also be beneficial to further improving the compaction density and the uniformity of the pore size of the positive electrode sheet, and making the kinetic and cycling performance of the positive electrode sheet better.

[0026] In the present invention, LNMO is distributed in layers according to a specific particle size Dn50, and the thickness ratio between layers is controlled within an appropriate range. While ensuring that LNMO has high kinetic performance, the side reactions between it and the electrolyte are reduced (even at high voltages, there are relatively few side reactions), the compaction density of the positive electrode sheet and the uniformity of pore size are improved, effectively enhancing the kinetic performance and cycling performance of the positive electrode sheet.

[0027] Exemplarily, a is in the range 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 any range formed by any two of the above values.

[0028] Exemplarily, b is in the range 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 any range formed by any two of the above values.

[0029] Exemplarily, the M b is in the range 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 any range formed by any two of the above values.

[0030] The values of the particle size Dn50(a) of the first lithium nickel manganese oxide particles and the particle size Dn50(b) of the second lithium nickel manganese oxide particles can both be adjusted by controlling the following process conditions: calcination conditions (such as calcination temperature, calcination time, etc.), grinding conditions (such as grinding time, rotation speed, etc. If sand grinding is used, it can also be adjusted by controlling the sand-to-material ratio (i.e., the mass ratio of sand particles to the material, the same below). If ball milling is used, it can also be adjusted by controlling the ball-to-material ratio).

[0031] The present invention does not limit the detection method for the particle size Dn50(a) of the first lithium nickel manganese oxide particles and the particle size Dn50(b) of the second lithium nickel manganese oxide particles. Those skilled in the art can detect the particle size Dn50(a) of the first lithium nickel manganese oxide particles and the particle size Dn50(b) of the second lithium nickel manganese oxide particles according to conventional technical means. Exemplarily, the particle size Dn50(a) of the first lithium nickel manganese oxide particles and the particle size Dn50(b) of the second lithium nickel manganese oxide particles can be detected by the following method:

[0032] Take an empty battery, disassemble it to obtain the positive electrode sheet, perform CP (Cross-Section Polishing) cross-section treatment on the positive electrode sheet, and use SEM (Scanning Electron Microscope) for observation and measurement. Adjust the magnification to 5Kx, select the upper region, middle region, and lower region of each active material layer for photographing, measure the particle size lengths of all particles in these three regions in the photos respectively, and obtain the average particle size Dn50 of the quantity distribution accounting for 50% 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, obtain the particle size Dn50(a) of the first lithium nickel manganate particles and the particle size Dn50(b) of the second lithium nickel manganate particles.

[0033] The thickness ratio (M b ) of the second positive electrode active material layer can be controlled by adjusting factors such as the coating gap width of the coater, coating speed, and solid content of the slurry.

[0034] The present invention does not limit the detection method for the thickness ratio (M b ) of the second positive electrode active material layer. Those skilled in the art can detect the thickness ratio (M b ) of the second positive electrode active material layer according to conventional technical means. Exemplarily, the thickness ratio (M b ) of the second positive electrode active material layer can be detected by the following method:

[0035] Take an empty battery, disassemble it to obtain the positive electrode sheet, perform CP cross-section treatment on the positive electrode sheet, use SEM (Scanning Electron Microscope) to obtain 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, and then calculate to obtain the thickness ratio (M b ) of the second positive electrode active material layer.

[0036] In some embodiments, 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 the range formed by any two of the above values.

[0037] 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 the range formed by any two of the above values.

[0038] When a / b is in the range of 0.125 to 0.5, especially in the range of 0.3 to 0.4, while better exerting the functions of the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles, the volume change difference between the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles during the lithium deintercalation and intercalation processes is relatively small, avoiding large stress at the interface between the first positive electrode active material layer and the second positive electrode active material layer, and preventing cracks or detachment, thereby making the kinetics and cycling performance of the positive electrode sheet better.

[0039] In some embodiments, the range of a is 2 μm to 3 μm to make the kinetics and cycling performance of the positive electrode sheet better. For example, a is 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 the range formed by any two of the above values.

[0040] In some embodiments, the range of b is 6 μm to 7 μm to make the kinetics and cycling performance of the positive electrode sheet better. 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 the range formed by any two of the above values.

[0041] In some embodiments, M b has a range of 0.6 to 0.7 to make the kinetics and cycling performance of the positive electrode sheet better. For example, M b is 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70 or the range formed by any two of the above values.

[0042] In some embodiments, after 200 cycles at 25 °C, the amount of transition metal ion dissolution is k%; the positive electrode sheet satisfies: 0.06 ≤ k / M b ≤ 0.3. For example, k / M b is 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 the range formed by any two of the above values.

[0043] In a preferred embodiment, the positive electrode sheet satisfies: 0.1 ≤ k / M b ≤ 0.2.

[0044] k% = (the content of transition metal ions in the negative electrode sheet detected after 200 cycles at 25°C) / (the content of transition metal ions in the positive electrode sheet before cycling) × 100%. During the research process, the inventors found that the dissolution amount of transition metal ions (k) after 200 cycles at 25°C can well reflect the ease of battery capacity attenuation, and also found that when controlling k / M b is in the range of 0.06 < k / M b < 0.3, especially in the range of 0.1 ≤ k / M b ≤ 0.2, the structural stability of LNMO in the positive electrode sheet is better, and at the same time, the tap density of the positive electrode sheet is higher, the uniformity of the pore size is better, which is more conducive to improving the kinetics and cycling performance of the positive electrode sheet.

[0045] In some of these embodiments, the range of k is 0.05 ≤ k ≤ 0.2. For example, the 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 the interval range formed by any two of the above values.

[0046] By controlling the value of k within the above suitable range, not only the surface stability of the positive electrode sheet is better, but also 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, lower impedance, is conducive to lithium ion transport, so that the cycling performance and kinetic performance of the battery using this positive electrode sheet are better. At the same time, the surface of the positive electrode sheet is not easily passivated, the ion and electron transportability is good, and the kinetic performance of the positive electrode sheet is good.

[0047] The dissolution amount of transition metal ions (k) after 200 cycles at 25°C can be controlled by adjusting the thickness of the coating layer (if there is a coating layer), 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, the thickness ratio of the second positive electrode active material layer (M b ), etc.

[0048] The present invention does not limit the detection method of the dissolution amount of transition metal ions (k) after 200 cycles at 25°C. Those skilled in the art can detect the dissolution amount of transition metal ions (k) after 200 cycles at 25°C according to conventional technical means. Exemplarily, the dissolution amount of transition metal ions (k) after 200 cycles at 25°C can be detected by the following method:

[0049] Take an empty battery, disassemble it to obtain the positive electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (e.g., 25 °C, the same below) for 1 h to remove the electrolyte, take it out, dry it, scrape off the positive electrode material on the surface of the current collector, digest the positive electrode material, and then 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 are measured (i.e., 5 batteries are used for testing), and the average value of M1 is calculated and denoted as

[0050] Take an empty battery, disassemble it to obtain the positive electrode sheet and the negative electrode sheet respectively. Assemble the disassembled positive electrode sheet and negative electrode sheet with the electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L) into a battery. First, constant volume is carried out at 25 °C for 2 cycles, then cycling is carried out at 25 °C at a rate of 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 h to remove the electrolyte, take it out, dry it, scrape off the negative electrode material on the surface of the current collector, digest the negative electrode material, and then use ICP to measure the total mass M2 of Ni and Mn. A total of 5 parallel samples are measured (i.e., 5 batteries are used for testing), and the average value of M2 is calculated and denoted as

[0051] Calculate k,

[0052] Among them, the digestion methods are as follows: Disperse the positive electrode material or the negative electrode material in 20 mL of water, then add 10 mL of nitric acid (the mass percentage content of HNO3 is 66%), perform dispersion and heating treatment until the positive electrode material or the negative electrode material is completely dissolved, and make up the volume to 100 mL with water to obtain the test solution, and perform ICP testing on the test solution;

[0053] The working conditions of the ICP instrument are set as follows: gas flow rate 0.5 L / min, power 1150 W;

[0054] The constant volume method is as follows: Constant current and constant voltage charge at 0.33C to 4.75 V, the cut-off current in the constant voltage section ≤ 0.05C, and then constant current discharge at 0.33C to 3.5 V, and repeat the charge and discharge process 2 times;

[0055] The cycling method is as follows: Constant current and constant voltage charge at a rate of 1C to the upper limit voltage of 4.75 V, and constant voltage charge at this voltage until the current is less than or equal to 0.05C; then discharge at 1C to the lower limit voltage of 3.5 V, and repeat the above charge and discharge process 200 times.

[0056] In some of these embodiments, the first lithium nickel manganese oxide particles have a disordered Fd-3m structure, and the second lithium nickel manganese oxide particles have an ordered P4332 structure. The disordered structure (Fd3m space group) of lithium nickel manganese oxide is a face-centered cubic lattice. Different from the ordered structure (P4332 space group), in the disordered structure, Mn ions and Ni ions are randomly distributed at the 16d sites instead of being orderly distributed at specific sites. The disordered lithium nickel manganese oxide has a higher electrical conductivity and ion diffusion coefficient, usually 2.5 orders of magnitude higher than that of the ordered structure. This is mainly because there is a small amount of Mn 3+ with a radius larger than that of Mn 4+ , which makes the lattice parameter larger and is conducive to the diffusion of Li + to a certain extent and electron conduction; the LNMO structure with an ordered Fd-3m structure has good structural stability. By setting the first lithium nickel manganese oxide particles to have a disordered Fd-3m structure and the second lithium nickel manganese oxide particles to have an ordered P4332 structure, the kinetics and cycling performance of the positive electrode sheet can be better.

[0057] The present invention does not limit the detection method of the crystal structure of lithium nickel manganese oxide in each active material layer of the positive electrode sheet. Those skilled in the art can detect the crystal structure of lithium nickel manganese oxide in each active material layer of the positive electrode sheet according to conventional technical means. Exemplarily, after scraping the materials of each active material layer respectively, the crystal structure of lithium nickel manganese oxide in each active material layer of the positive electrode sheet can be detected by Raman spectroscopy. If there is an obvious splitting peak phenomenon in the F -1 peak corresponding to the range of 594 cm 2g(1) , this indicates an increase in the degree of disorder of Ni / Mn, resulting in the transformation of the ordered structure into a disordered Fd-3m structure. The test conditions of the Raman spectroscopy can be selected as follows: the wavelength of the laser is 514 nm, and the Raman shift range is 100-2000 cm -1 ; the Raman spectrometer can be a confocal micro-Raman spectrometer RM2000 of Renishaw Company, UK.

[0058] In some of these embodiments, the total thickness of the first positive electrode active material layer and the second positive electrode active material layer is 100 μm to 160 μm, such as 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm or the range formed by any two of the above values.

[0059] The first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles are spinel-type, and the chemical formula is LiNi x Mn 2-xO4, where x > 0, such as 0.1, 0.2, 0.3, 0.4, 0.5, or the range formed by any two of the above values. Their surfaces may either not be provided with a coating material at all, or a coating layer formed by coating part or all of the surfaces of at least one of the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles with a coating material. The coating material can be selected to include at least one of the following materials: aluminum oxide, titanium oxide, lithium phosphate, zirconium oxide, tantalum oxide, magnesium oxide, iron oxide, etc. In some embodiments, the thickness of the coating layer on the surface of the first lithium nickel manganese oxide particles 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 the range formed by any two of the above values. In some embodiments, the thickness of the coating layer on the surface of the second lithium nickel manganese oxide particles 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 the range formed by any two of the above values. When coating layers are provided on the surfaces of both the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles, the material, thickness, etc. of the coating layers are each independent.

[0060] The first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles may either not contain doping elements or may contain doping elements. The present invention places no limitation on the types of doping elements in the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles. For example, they can be selected to be at least one of Si, Mg, P, Co, Al, Cr, Nb, etc. Whether the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles contain doping elements, the types of doping elements, and their contents are independent of each other and do not affect each other.

[0061] The present invention places no limitation on the preparation methods 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 according to conventional technical means. Exemplarily, 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:

[0062] Mix and disperse a lithium source, a nickel source, and a manganese source in a solvent to obtain a mixed material;

[0063] Calcine the mixed material in the temperature range of 650 - 900 °C, and then cool it to obtain a lithium nickel manganese oxide blank;

[0064] Grind and dry the lithium nickel manganese oxide blank to obtain lithium nickel manganese oxide particles.

[0065] During the process of preparing the mixture using a lithium source, a nickel source, and a manganese source, the solvent can be selected from at least one of solvents such as ethanol, NMP, acetonitrile, DMC, etc. In some embodiments, the method of mixing and dispersing can be selected as the solid-phase method, such as ball milling, sand milling, etc.

[0066] During the process of preparing the first lithium nickel manganese oxide bare material using the mixture, the process conditions of calcination can be set as follows: the calcination temperature range is 650 - 900 °C, the calcination time is 12 - 24 h, and the heating rate is 1 - 5 °C / h;

[0067] The calcination can be carried out in a calcination device such as a muffle furnace, a tube furnace, etc.

[0068] During the process of preparing lithium nickel manganese oxide particles using the lithium nickel manganese oxide bare material, the grinding method can be selected as sand milling, and the sand milling conditions can be selected as follows: the sand-to-material ratio (mass ratio, the same below) is 8 - 20:1, the rotation speed is 1000 - 3000 rpm, the sand milling time is 4 - 24 h, and the sand grains can be selected from at least one of aluminum oxide, zirconium oxide, silicon carbide, and boron carbide.

[0069] Among them, 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

[0070] The nickel source includes but is not limited to at least one of nickel carbonate, nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate; and / or

[0071] The manganese source includes but is not limited to at least one of manganese dioxide, manganese hydroxide, manganese oxide, and manganese sulfate.

[0072] When the first or second lithium nickel manganese oxide particle is in a disordered Fd-3m structure, the corresponding calcination temperature is 750 - 900 °C, and the calcination time is 16 - 20 h;

[0073] When the first or second lithium nickel manganese oxide particle is in an ordered P4332 structure, the corresponding calcination temperature is 650 - 700 °C, and the calcination time is 12 - 18 h.

[0074] In addition, the first lithium nickel manganese oxide particle and / or the second lithium nickel manganese oxide particle can also be subjected to a coating treatment. For example, an atomic layer deposition (ALD) technique is used to coat the coating material on the surface of the first lithium nickel manganese oxide particle and / or the second lithium nickel manganese oxide particle. Among them, the coating material can be selected from at least one of aluminum oxide, titanium oxide, zinc oxide, and magnesium oxide, the number of ALD deposition cycles can be selected as 50 - 500 cycles, and the thickness of one ALD deposition cycle can be selected as 0.1 - 0.3 nm.

[0075] In addition, when preparing the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles, a certain amount of doping element source (if any) can also be mixed and dispersed with the lithium source, nickel source, and manganese source as needed to prepare the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles. The doping element source is at least one of, for example, Si source, Mg source, P source, Co source, Al source, Cr source, Nb source, etc., so as to obtain the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles containing a certain amount of doping elements.

[0076] 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 the range formed by any two of the above values.

[0077] The first positive electrode active material layer further includes a conductive agent and a binder. The conductive agent in the first positive electrode active material layer is used to provide conductivity, and 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 positive 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 (Super P, the same below), acetylene black, Ketjen black, etc.

[0078] 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 the range formed by any two of the above values.

[0079] 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 appropriate binder properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder of the first positive electrode active material layer includes but is not limited to fluorinated polyolefin binders, and the fluorinated polyolefin binders include but are not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, or their modified (for example, modified with carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives, etc.

[0080] 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 the range formed by any two of the above values.

[0081] In some of these embodiments, the mass percentage content 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 the range formed by any two of the above values.

[0082] The second positive electrode active material layer further includes a conductive agent and a binder. The conductive agent in the second positive electrode active material layer is used to provide conductivity, and any conductive agent can be used without particular limitation as long as it has suitable electron conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, 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 fiber, activated carbon, mesoporous carbon, fullerenes, etc., where carbon fiber such as carbon nanofiber, etc.; carbon black such as SP (Super P, the same below), acetylene black, Ketjen black, etc.

[0083] In some of these embodiments, the mass percentage content 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 the range formed by any two of the above values.

[0084] The binder of 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, and any binder can be used without particular limitation as long as it has suitable binder properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder of the second positive electrode active material layer includes but is not limited to fluorinated polyolefin binders, and fluorinated polyolefin binders include but are not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, or their modified (such as carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives, etc.

[0085] In some of these embodiments, the mass percentage content 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 the range formed by any two of the above values.

[0086] The present invention has no particular limitation on the positive electrode current collector as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, aluminum, nickel, titanium, stainless steel, fired carbon can be used; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0087] The positive electrode sheet of the present invention can be prepared according to conventional methods in the art. For example:

[0088] Disperse the first positive electrode active material, conductive agent and binder in a solvent to obtain a first positive electrode paste;

[0089] Disperse the second positive electrode active material, conductive agent and binder in a solvent to obtain a second positive electrode paste;

[0090] Then coat the first positive electrode paste and the second positive electrode paste on at least one side of the positive electrode current collector, and after processes such as cold pressing and slitting, a positive electrode sheet is obtained. Among them, the solvent includes but is not limited to at least one of N-methylpyrrolidone (NMP) and deionized water. Among them, when coating the first positive electrode paste and the second positive electrode paste on at least one side of the positive electrode current collector, the first positive electrode paste is coated first, and then the second positive electrode paste is coated.

[0091] Battery

[0092] The present invention also provides a battery, including the positive electrode sheet, negative electrode sheet and electrolyte.

[0093] In some embodiments, the transition metal elements in the negative electrode sheet include Ni element and Mn element; in the negative electrode sheet, the content range of Ni element is 50 - 200 ppm, and the content range of Mn element is 500 - 1500 ppm. For example, in the negative electrode sheet, the content of Ni element is 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 170 ppm, 200 ppm or the interval range formed by any two of the above values; the content of Mn element is 500 ppm, 700 ppm, 1000 ppm, 1200 ppm, 1500 ppm or the interval range formed by any two of the above values. By controlling the contents of Ni element and Mn element in the negative electrode sheet, the damage of transition metal ions to the negative electrode SEI film is reduced, and the battery cycle performance is improved; at the same time, over-passivation of the positive electrode is avoided.

[0094] The present invention does not limit the detection method for the contents of Ni element and Mn element in the negative electrode sheet, and those skilled in the art can detect the contents of Ni element and Mn element in the negative electrode sheet according to conventional technical means. Exemplarily, the contents of Ni element and Mn element in the negative electrode sheet can be detected by the following method:

[0095] Take empty batteries and disassemble them to obtain the positive electrode sheet and the negative electrode sheet respectively. Assemble the obtained positive electrode sheet and negative electrode sheet with an electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to a volume ratio of 1:1:1 to obtain an organic solvent, and then dissolve the fully dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L) into a battery. First, perform 2 constant volume cycles at 25 °C, then perform 200 cycles at 25 °C at a current rate of 1C. Then disassemble the battery to obtain the negative electrode sheet. Immerse the negative electrode sheet in DMC (dimethyl carbonate) at room temperature (such as 25 °C, the same below) for 1 h to remove the electrolyte, take it out, dry it in the air, scrape off the negative electrode material on the surface of the current collector, and use ICP to measure the mass percentages of Ni and Mn after digesting the negative electrode material (the digestion method is the same as above), so as to obtain the contents of Ni element and Mn element in the negative electrode sheet.

[0096] 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.

[0097] 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 the above.

[0098] In some embodiments, the mass percentage 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.

[0099] The negative electrode active material layer may further contain a conductive agent, and / or a binder, and / or a thickening agent.

[0100] The conductive agent in the negative electrode active material layer is used to provide conductivity, and 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. 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.

[0101] In some of these embodiments, the mass percentage content of the conductive agent 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 the range formed by any two of the above values.

[0102] 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 suitable binding properties 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, and aqueous acrylic resin.

[0103] In some of these embodiments, the mass percentage content 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 the range formed by any two of the above values.

[0104] 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. Exemplarily, 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).

[0105] In some of these embodiments, the mass percentage content 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 the range formed by any two of the above values.

[0106] The present invention has no particular limitation on the negative electrode current collector as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy can be used.

[0107] The electrolyte of the present invention can select various electrolytes suitable for batteries in the art. The electrolyte includes an electrolyte and a solvent, and the electrolyte generally can include a lithium salt.

[0108] Exemplarily, 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 difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be selected to be 0.5 - 5 mol / L.

[0109] Exemplarily, the solvent includes but is not limited to at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE). The mass percentage content of the solvent in the electrolyte solution can be selected to be 70% - 98%.

[0110] In addition, the electrolyte solution may further contain additives. Exemplarily, the additives may include negative electrode film - forming additives, or may include positive electrode film - forming additives, or may also include additives that can improve certain battery performances, such as additives for improving the high - temperature performance of the battery, additives for improving the overcharge performance of the battery, additives for improving the low - temperature performance of the battery, etc.

[0111] The battery may further include a separator, which is located between the positive electrode sheet and the negative electrode sheet, for separating the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from contacting and short - circuiting. The separator can be various separator film materials applicable to batteries in the art. Exemplarily, the separator includes but is not limited to at least one of polypropylene and polyethylene.

[0112] Electric device

[0113] The present invention further provides an electric device including the battery. The battery serves as the power supply of the electric device.

[0114] The electric device refers to any device that can utilize electric energy and convert it into other forms of energy such as mechanical energy, thermal energy, and light energy, such as electric motors, electrothermal machines, electric light sources, etc. Specifically, it may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can be mobile phones, laptops, drones, floor cleaning robots, electronic cigarettes, etc.; electric vehicles can be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0115] The following uses specific embodiments to further elaborate the present invention. It should be noted that unless otherwise specified, the following calcination is carried out in an air atmosphere:

[0116] Example 1

[0117] This embodiment provides a lithium-ion battery, and the specific preparation method is as follows:

[0118] (1) Preparation of the first lithium nickel manganese oxide particles

[0119] Add Li2CO3, NiCO3, and MnO2 into a ball mill according to the stoichiometric ratio of Li, Ni, and Mn in the chemical formula LiNi 0.5 Mn 1.5 O4 for mixing and dispersion to obtain a mixture. Add the obtained mixture into a muffle furnace, heat it to a temperature of T1 °C and calcine for t1 h, cool it to room temperature, transfer the material to a sanding device, and use zirconia sand grains for sanding. The sanding ratio is S1:1, the sanding time is t1' h. After sanding, dry it, and then use an ALD instrument to coat an alumina coating on the surface of the material. The deposition thickness per cycle is 0.1 nm to obtain alumina-coated lithium nickel manganese oxide, that is, the first lithium nickel manganese oxide particles, where the coating thickness is C1 nm. The values of T1, t1, S1, t1', and C1 are shown in Table 1.

[0120] (2) Preparation of the second lithium nickel manganese oxide particles

[0121] Add Li2CO3, NiCO3, and MnO2 into a ball mill according to the stoichiometric ratio of Li, Ni, and Mn in the chemical formula LiNi 0.5 Mn 1.5The stoichiometric ratios of Li, Ni, and Mn in O4 are added to a ball mill for mixing and dispersion to obtain a mixed material. The obtained mixed material is added to a muffle furnace and heated to a temperature of T2 °C for calcination for t2 h, then cooled to room temperature. The material is transferred to a sand milling device and sand milled using zirconia sand grains with a sand-to-material ratio of S2:1 for a sand milling time of t2' h. After sand milling, it is dried, and then an alumina coating layer is coated on the surface of the material using an ALD instrument with a deposition thickness of 0.1 nm per cycle to obtain lithium nickel manganese oxide coated with alumina, i.e., the second lithium nickel manganese oxide particles, where the coating layer thickness is C2 nm. The values of T2, t2, S2, t2', and C2 are shown in Table 1.

[0122] (3) Preparation of the positive electrode sheet

[0123] Take the first lithium nickel manganese oxide particles as the positive electrode active material, and mix the positive electrode active material, the conductive agent CNTs, and the binder PVDF in a mass ratio of 97:1:2, add the solvent NMP, and stir in a vacuum mixer to obtain the first positive electrode slurry (for forming the first positive electrode active material layer);

[0124] Take the second lithium nickel manganese oxide particles as the positive electrode active material, and mix the positive electrode active material, the conductive agent CNTs, and the binder PVDF in a mass ratio of 97:1:2, add the solvent NMP, and stir in a vacuum mixer to obtain the second positive electrode slurry (for forming the second positive electrode active material layer);

[0125] Coat the first positive electrode slurry and the second positive electrode slurry on both sides of the positive electrode current collector aluminum foil. When coating, first coat the first positive electrode slurry on both sides of the positive electrode current collector. After the first positive electrode slurry is dried, coat the second positive electrode slurry on the surface of the first slurry, and then dry, cold press, and slit to obtain the positive electrode sheet;

[0126] Among them, 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 value is shown in Table 1.

[0127] (4) Preparation of the negative electrode sheet

[0128] Mix the negative electrode active material artificial graphite, the conductive agent acetylene black, the thickening agent CMC, and the binder SBR in a mass ratio of 96.4:1:1.2:1.4, add the solvent deionized water, and stir in a vacuum mixer to obtain the negative electrode slurry. Coat the negative electrode slurry on both sides of the negative electrode current collector copper foil, and then cold press and slit to obtain the negative electrode sheet.

[0129] (5) Preparation of the electrolyte

[0130] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1 to obtain an organic solvent, and then dry lithium salt LiPF6 was dissolved in the obtained organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0131] (6) Preparation of lithium-ion battery

[0132] The above positive electrode sheet, separator (PE), and negative electrode sheet were stacked in sequence, with the separator placed between the positive and negative electrode sheets to play an isolation role, and then wound to obtain a bare battery cell; the bare battery cell was placed in an outer packaging shell, dried, and injected with the electrolyte, and after vacuum packaging and standing for 24 h, formation was carried out to obtain the lithium-ion battery. The formation process is as follows: Use the LAND system to charge at a constant current to 4.8 V with a current of 0.33C, then discharge at a constant current to 3.5 V with a current of 0.33C, cycle 2 times, and finally remove the battery from the charging device.

[0133] Examples 2 to 27 and Comparative Examples 1 to 6

[0134] These examples and comparative examples all provided a lithium-ion battery, and the preparation method was similar to that of Example 1. The differences were as follows:

[0135] (a) In step (1), the values of T1, t1, S1, t1', and C1 are shown in Table 1;

[0136] (b) In step (2), the values of T2, t2, S2, t2', and C2 are shown in Table 1;

[0137] (c) In step (3), the total thickness of the first positive electrode active material layer and the second positive electrode active material layer remained unchanged, and the value of M b is shown in Table 1.

[0138] Table 1

[0139]

[0140]

[0141] The following method was used to detect the particle size Dn50 of the first lithium nickel manganate (denoted as a μm), the particle size Dn50 of the second lithium nickel manganate (denoted as b μm), 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 dissolution amount of transition metal ions after 200 cycles at 25 °C of the positive electrode sheet (denoted as k%), and the crystal structures of the first and second lithium nickel manganate particles are shown in Table 1 or Table 2:

[0142] Particle sizes of the first and second lithium nickel manganese oxides: Take an empty battery, disassemble it to obtain the positive electrode sheet, perform a CP cross-section treatment on the positive electrode sheet, and observe and measure it using SEM. Adjust the magnification to 5Kx, select the upper region, middle region, and lower region of each active material layer for photographing, measure the particle size lengths of all particles in these three regions in the photos respectively, and obtain the average particle size Dn50 accounting for 50% of the quantity 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, obtain the particle size Dn50(a) of the first lithium nickel manganese oxide particles and the particle size Dn50(b) of the second lithium nickel manganese oxide particles.

[0143] Thickness ratio of the second positive electrode active material layer: Take an empty battery, disassemble it to obtain the positive electrode sheet, perform a CP cross-section treatment on the positive electrode sheet, use SEM (scanning electron microscope) to obtain the thicknesses of the first positive electrode active material layer and the second positive electrode active material layer at the cross-section, and then calculate to obtain the thickness ratio (M b ) of the second positive electrode active material layer.

[0144] Dissolution amount of transition metal ions after 200 cycles at 25°C: Take an empty battery, disassemble it to obtain the positive electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at 25°C for 1 h to remove the electrolyte, take it out, dry it, scrape off the positive electrode material on the surface of the current collector, dissolve the positive electrode material, and use an ICP (inductively coupled plasma) instrument to measure the total masses of Ni and Mn. The sum of the two is M1. A total of 5 parallel samples are measured (i.e., 5 batteries are used for testing), calculate the average value of M1, and record it as

[0145] Take an empty battery, disassemble it to obtain the positive electrode sheet and the negative electrode sheet respectively. Assemble the disassembled positive electrode sheet and negative electrode sheet with the electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then dissolve the fully dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L) into a battery. First, hold the volume at 25°C for 2 cycles, then cycle at 25°C at 1C for 200 cycles, and then disassemble it to obtain the negative electrode sheet. Soak the negative electrode sheet in DMC (dimethyl carbonate) at 25°C for 1 h to remove the electrolyte, take it out, dry it, scrape off the negative electrode material on the surface of the current collector, dissolve the negative electrode material, and use ICP to measure the total masses of Ni and Mn as M2. A total of 5 parallel samples are measured (i.e., 5 batteries are used for testing), calculate the average value of M2, and record it as

[0146] Calculate k.

[0147] Among them, the digestion methods are as follows: Disperse the positive electrode material or negative electrode material in 20 mL of water, then add 10 mL of nitric acid (mass percentage content of HNO3 is 66%), disperse and heat-treat until the positive electrode material or negative electrode material is completely dissolved, make up the volume to 100 mL with water to obtain the test solution, and perform ICP test on the test solution;

[0148] The working conditions of the ICP instrument are set as follows: gas flow rate 0.5 L / min, power 1150 W;

[0149] The volume-making method is as follows: Constant current and constant voltage charge at 0.33C to 4.75V, the cut-off current in the constant voltage section ≤ 0.05C, then constant current discharge at 0.33C to 3.5V, and repeat the charge-discharge process 2 times;

[0150] The cycling method is as follows: Constant current and constant voltage charge at 1C rate to the upper limit voltage of 4.75V, and constant voltage charge at this 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-discharge process 200 times.

[0151] Determination of the crystal structures of the first and second lithium nickel manganate: Use the confocal micro-Raman spectrometer RM2000 produced by Renishaw Company in the UK to analyze the configuration of the prepared materials. Test conditions: The wavelength of the laser is 514 nm, and the Raman shift range is 100 - 2000 cm -1 . In the Raman test spectrum, the A -1 peak at 638.8 cm 1g and the F -1 peaks at 594.7 and 611.3 cm 2g(1) correspond to the symmetric stretching vibration of the Mn-O bond. At the same time, the Eg peak at 408.4 cm -1 and the F2g(2) peak at 498.4 cm -1 correspond to the stretching vibration of the Ni-O bond. Compared with the ordered structure sample, the intensities of the peaks at 638.8, 498.4, and 408.4 cm -1 of the disordered structure sample are significantly reduced. In addition, there is a more obvious splitting of the F -1 peak at 594.7 cm 2g(1) of the disordered structure sample. This phenomenon is mainly due to the increase in the degree of disorder of Ni / Mn, resulting in the transformation of its structure from the ordered P4332 structure to the disordered Fd-3m structure.

[0152] Taking the lithium-ion batteries obtained from the above examples and comparative examples as the detection objects, the following tests are carried out:

[0153] Battery capacity retention rate after 100 cycles at 45°C and DCR growth rate after 100 cycles at 45°C: After standing, use the LAND system to charge the battery at a constant current to 4.8V with a current of 0.33C, then discharge at a constant current to 3.5V with a current of 0.33C, and cycle 2 times. After that, remove the battery from the charging device for standby (activation process). After activating the battery, at 45°C, charge it at a constant current of 1C to 4.8V, and then charge it at a constant voltage until the current is less than 0.05C; then discharge it at a constant current of 1C until the voltage reaches 3.5V. One complete charge and discharge process is regarded as one cycle, and cycle 100 times. Calculate the capacity retention rate according to the following formula: Capacity retention rate = Discharge capacity of the 100th cycle / Discharge capacity of the first cycle * 100%;

[0154] The DCR value after 100 cycles at 45°C is denoted as R1, and the initial DCR value before cycling is denoted as R0; then the DCR growth rate after 100 cycles = (R1 - R0) / R0 * 100%.

[0155] The DCR test state is that the battery is at 50% SOC. The specific DCR test method:

[0156] A1. Let the battery stand at room temperature (25°C) for 10 minutes first;

[0157] A2. Charge the battery at a constant current and constant voltage first. The constant current rate is 0.33C, the voltage is 4.80V, and during the constant voltage process until the current ≤ 0.05C, then discharge at a constant current to 3.5V with a current rate of 0.33C;

[0158] A3. Repeat steps A1 - A2 three times. The discharge capacity during the last step A2 process is denoted as C1;

[0159] A4. Continue to repeat steps A1 - A2 until the battery is fully charged;

[0160] A5. Discharge at a constant current to a capacity of 0.5C1 with a discharge rate of 0.33C. At this time, the battery is in a 50% SOC state;

[0161] A6. Let the battery stand for 120 minutes, and record the voltage at the end of standing as V0;

[0162] A7. Discharge at a constant current for 18s with a current rate of 1C, and record the voltage at the end of discharge as V1.

[0163] Table 2

[0164]

[0165]

[0166]

[0167] For the batteries prepared in the 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 sheets of the present invention have excellent kinetic performance and high-temperature cycle performance.

[0168] From the comparison between Examples 1 to 7 and Comparative Examples 11 to 12, Example 13 and Comparative Example 15, and Example 14 and Comparative Example 16, it can be known that when the Dn50 values of the particle sizes of the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles satisfy the preferred ranges described in the present invention, the kinetic performance and high-temperature cycle performance of the batteries are relatively better.

[0169] From the comparison between Examples 1 to 7 and Comparative Examples 8 to 10, it can be known that when the positive electrode sheet satisfies 0.3 ≤ a / b ≤ 0.4, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0170] From the comparison between Examples 1, 6 to 7 and Comparative Examples 18 to 19, and Example 20 and Comparative Examples 21 to 22, it can be known that when the thickness ratio M of the second positive electrode active material layer b takes values that satisfy the preferred ranges described in the present invention, the kinetic performance and high-temperature cycle performance of the batteries are relatively better.

[0171] From the comparison between Example 15 and Comparative Example 16, Examples 1 to 7 and Comparative Example 20, and Examples 18 to 19 and Comparative Examples 21 to 22, it can be known that when the positive electrode sheet satisfies 0.1 ≤ k / M b ≤0.2, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0172] From the comparison between Example 1 and Comparative Examples 25 to 27, it can be known that when the first lithium nickel manganese oxide particles are in a disordered Fd-3m structure and the second lithium nickel manganese oxide particles are in an ordered P4332 structure, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0173] According to Comparative Examples 1 to 6, it can be known that when the Dn50 value of the particle size of the first lithium nickel manganese oxide particles, the Dn50 value of the particle size of the second lithium nickel manganese oxide particles, or the thickness ratio M of the second positive electrode active material layer b is too large or too small, the kinetic performance and high-temperature cycle performance of the battery are relatively poor.

[0174] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, but they do not depart from the essence and scope of the technical solutions of the present invention.

Claims

1. A positive electrode sheet, characterized in that, Comprising: A positive current collector; A first positive active material layer disposed on at least one surface of the positive current collector, the first positive active material layer comprising lithium nickel manganese oxide particles, wherein the Dn50 of the lithium nickel manganese oxide particles is a μm, and the range of a is 1 ≤ a ≤ 4; and A second positive active material layer disposed on the surface of the first positive active material layer remote from the positive current collector, the second positive active material layer comprising lithium nickel manganese oxide particles, wherein the 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 of the second positive electrode active material layer accounts for M b , M b The range is 0.5~0.

8.

2. The positive electrode sheet according to claim 1, wherein, The a and the b satisfy the relationship: 0.125 ≤ a / b ≤ 0.

5.

3. The positive electrode sheet according to claim 2, characterized in that, The a and the b satisfy the relationship: 0.3 ≤ a / b ≤ 0.

4.

4. The positive electrode sheet according to claim 1, wherein, The range of a is 2 μm to 3 μm; and / or The range of b is 6 μm to 7 μm; and / or The said M b ranges from 0.6 to 0.

7.

5. The positive electrode sheet according to claim 1, wherein, After 200 cycles at 25°C, the dissolution amount of transition metal ions is k%; the positive electrode sheet satisfies: 0.06 ≤ k / M b ≤ 0.

3.

6. The positive electrode sheet according to claim 5, characterized in that, The positive electrode sheet satisfies: 0.1 ≤ k / M b ≤ 0.

2.

7. The positive electrode sheet according to claim 5, characterized in that, The range of k is 0.05 ≤ k ≤ 0.

2.

8. The positive electrode sheet according to claim 1, characterized in that, The lithium nickel manganese oxide particles in the first positive active material layer are in a disordered Fd-3m structure, and the lithium nickel manganese oxide particles in the second positive active material layer are in an ordered P4332 structure.

9. A battery, characterized in that, Comprising the positive electrode sheet according to any one of claims 1 to 8.

10. The battery according to claim 9, characterized in that, It further includes a negative electrode sheet, wherein the transition metal elements in the negative electrode sheet include Ni element and Mn element; in the negative electrode sheet, the content range of Ni element is 50 - 200 ppm, and the content range of Mn element is 500 - 1500 ppm.

11. An electric device, characterized in that, Comprising the battery according to claim 9 or 10.

Images