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

[0001] The present application is a divisional application of application number CN202510431270.6, application date April 8, 2025, and invention creation name Positive electrode sheet, battery containing the positive electrode sheet, and electric device. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a battery containing the positive electrode sheet, and an electric device. BACKGROUND

[0003] The demand for high energy density and high output power of lithium ion power batteries has attracted attention to the research and development of high-voltage positive electrode materials. The crystal structure of spinel lithium nickel manganese oxide (LNMO) material can provide a three-dimensional lithium ion transmission channel, has good ion conductivity, has a high voltage platform of 4.7V (vs Li / Li+), and has a theoretical specific capacity of 147mAh / g, which has great potential. However, the large band gap of LNMO (0.5601eV) results in poor conductivity of the system; under high-voltage use conditions, the side reaction of the positive electrode interface with the electrolyte is intensified, and the interface by-products increase. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a positive electrode sheet, a battery containing the positive electrode sheet, and an electric device, so that the positive electrode sheet using LNMO has good kinetic performance and cycle performance.

[0005] To achieve the above-mentioned purpose, in a first aspect, the present application provides a positive electrode sheet, comprising:

[0006] a positive electrode current collector;

[0007] 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 a ranges from 1≤a≤4; and

[0008] 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 b ranges from 5≤b≤8;

[0009] 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 , and M b ranges from 0.5 to 0.8.

[0010] In a second aspect, the present application provides a battery comprising the positive electrode sheet.

[0011] In a third aspect, the present application provides an electric device comprising the battery.

[0012] Compared with the prior art, the present application has the beneficial effects that: by layering the LNMO according to a specific particle size Dn50 and controlling the thickness ratio between the layers within a suitable range, the present application ensures that the LNMO has high kinetic performance, reduces the side reaction between the LNMO and the electrolyte (even at high voltage, the side reaction is relatively small), 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. DETAILED DESCRIPTION

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below clearly and completely. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0014] In the present application, the technical features described in an open way include both the closed technical solutions consisting of the listed features and the open technical solutions containing the listed features.

[0015] In the present application, as long as there is no special description, the numerical range is regarded as continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all the ranges disclosed herein should be understood as including any and all sub-ranges falling within the range.

[0016] In the present application, the specific dispersion and stirring treatment methods are not particularly limited.

[0017] The reagents or instruments used in the present application are not specified by the manufacturer, and are all conventional products that can be obtained through commercial purchase.

[0018] In the present application, the expressions such as “first time” and “second time” are not used to limit the number of times.

[0019] Positive electrode sheet

[0020] The present application provides a positive electrode sheet comprising:

[0021] Positive electrode current collector

[0022] 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 (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"), wherein the particle size Dn50 of the lithium nickel manganese oxide particles is a μm, a ranges from 1≤a≤4; and

[0023] a second positive electrode active material layer disposed on a 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 (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"), wherein the particle size Dn50 of the lithium nickel manganese oxide particles is b μm, b ranges from 5≤b≤8;

[0024] 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 ranges from 0.5 to 0.8.

[0025] The particle size Dn50 of the first lithium nickel manganese oxide particles is relatively small, and the kinetic performance is good. Disposing the first positive electrode active material layer close to the positive electrode current collector can reduce the contact between the first lithium nickel manganese oxide particles and the electrolyte, and weaken the reaction between the first lithium nickel manganese oxide particles 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. Disposing the second positive electrode active material layer away from the positive electrode current collector can make the side reaction between the positive electrode interface and the electrolyte less even under high voltage. In addition, the first lithium nickel manganese oxide particles with a small particle size Dn50 and the second lithium nickel manganese oxide particles with a large particle size Dn50 are respectively disposed 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 positive electrode active material layer to the first positive electrode active material layer. In this way, under the support 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 improved, the pore size in the positive electrode sheet can be more uniform, the ion and electron transmission can be smoother, the resistance can be smaller, the polarization can be lower, and the kinetic and cycle performance can be better.

[0026] Meanwhile, 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 in the above suitable ranges can not only make the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles better play their roles, but also be beneficial to further improving the compaction density and the uniformity of the pore size of the positive electrode sheet, so that the kinetic and cycle performance of the positive electrode sheet can be better.

[0027] The present invention distributes LNMO in layers according to a specific particle size Dn50 and controls the thickness ratio between each layer within an appropriate range. While ensuring that LNMO has high kinetic performance, it reduces its side reactions with the electrolyte (even at high voltage, the side reactions are relatively small), improves the compaction density of the positive electrode sheet and the uniformity of the pore size, and effectively improves the kinetic performance and cycle performance of the positive electrode sheet.

[0028] Illustratively, a is 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 an interval range formed by any two of the above values.

[0029] Illustratively, b is 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 an interval range formed by any two of the above values.

[0030] For example, the M b 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 the interval formed by any two of the above values.

[0031] 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 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).

[0032] The present invention does not limit the method for detecting 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 using conventional technical means. For example, 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 using the following method:

[0033] The empty battery is taken apart to obtain the positive electrode sheet, the positive electrode sheet is subjected to CP (Cross-Section Polishing) section processing, and SEM (scanning electron microscope) is used for observation and measurement, wherein the magnification is adjusted to 5Kx, the upper region, the middle region and the lower region of each layer of active material layer are selected for photographing, the particle size length of all particles in the three regions in the photos is measured respectively, and the average particle size Dn50 of the number distribution of 50% in the three regions is obtained, then the average value of Dn50 of the three regions is calculated to obtain the average particle size Dn50 of each layer of active material layer, that is, the particle size Dn50 (a) of the first lithium nickel-manganese acid particle and the particle size Dn50 (b) of the second lithium nickel-manganese acid particle.

[0034] The thickness ratio (M b ) of the second positive electrode active material layer can be controlled by adjusting the coating gap width, coating speed, solid content of the slurry and other factors of the coating machine.

[0035] The detection method of the thickness ratio (M b ) of the second positive electrode active material layer is not limited in the present application, and the thickness ratio (M b ) of the second positive electrode active material layer can be detected by the skilled person in the art according to conventional technical means. For example, the thickness ratio (M b ) of the second positive electrode active material layer can be detected by the following method:

[0036] The empty battery is taken apart to obtain the positive electrode sheet, the positive electrode sheet is subjected to CP section processing, and SEM (scanning electron microscope) is used 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 the thickness ratio (M b ) of the second positive electrode active material layer is calculated.

[0037] In some embodiments, the a and the 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 an interval range formed by any two of the above values.

[0038] In a preferred embodiment, the a and the 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 an interval range formed by any two of the above values.

[0039] When a / b is in the range of 0.125-0.5, particularly in the range of 0.3-0.4, the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles can better play their roles while the volume change difference between the first lithium nickel manganese oxide particles and the second lithium nickel manganese oxide particles during the deintercalation of lithium is small, thus avoiding cracks or peeling of the interface between the first positive electrode active material layer and the second positive electrode active material layer due to large stress, and thus better kinetics and cycle performance of the positive electrode sheet.

[0040] In some embodiments, a is in the range of 2-3 μm, so as to better kinetics and cycle performance of the positive electrode sheet. 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 an interval range formed by any two of the above values.

[0041] In some embodiments, b is in the range of 6-7 μm, so as to better kinetics and cycle performance of the positive electrode sheet. 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 an interval range formed by any two of the above values.

[0042] In some embodiments, M b is in the range of 0.6-0.7, so as to better kinetics and cycle performance of the positive electrode sheet. 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 an interval range formed by any two of the above values.

[0043] In some embodiments, the amount of transition metal ion elution k% after 200 cycles at 25°C 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 an interval range formed by any two of the above values.

[0044] In a preferred embodiment, the positive electrode sheet satisfies 0.1≤k / M b ≤0.2.

[0045] k% = the content of transition metal ions detected in the negative electrode sheet after 200 cycles at 25°C / the content of transition metal ions in the positive electrode sheet before cycling x 100%. The inventors have found that the amount of transition metal ions dissolved (k) after 200 cycles at 25°C can well reflect the ease of capacity decay of the battery, and have found that when 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 LNMO structure in the positive electrode sheet is more stable, the compaction density of the positive electrode sheet is higher, the uniformity of the pore size is better, and it is more conducive to improving the kinetics and cycle performance of the positive electrode sheet.

[0046] In some 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 an interval range formed by any two of the above values.

[0047] Controlling the value of k in the above suitable range not only makes the positive electrode sheet surface more stable, but also makes the SEI film (i.e. the solid-state electrolyte interface film formed on the surface of the negative electrode active material) less affected by transition metal ions, more stable, and lower impedance, which is conducive to lithium ion transmission, thereby making the cycle performance and kinetics performance of the battery using the positive electrode sheet better, and the positive electrode sheet surface is less likely to be passivated, the ion and electron transmission is good, and the kinetics performance of the positive electrode sheet is good.

[0048] The amount of transition metal ions dissolved (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 (M b ) of the second positive electrode active material layer, etc.

[0049] The detection method of the amount of transition metal ions dissolved (k) after 200 cycles at 25°C is not limited in the present application, and those skilled in the art can detect the amount of transition metal ions dissolved (k) after 200 cycles at 25°C according to conventional technical means. For example, the amount of transition metal ions dissolved (k) after 200 cycles at 25°C can be detected by the following method:

[0050] Take an empty battery, disassemble it to get the positive electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (such as 25 ° C, the same below) for 1 hour to remove the electrolyte, take it out, dry it, scrape the positive electrode material on the surface of the current collector, and use ICP (inductively coupled plasma) instrument to measure the total mass of Ni and Mn after digestion. The sum of the two is M1. A total of 5 parallel samples are measured (that is, 5 batteries are used for testing), and the average value of M1 is calculated and recorded as

[0051] Take an empty battery and disassemble it to obtain the positive electrode and negative electrode respectively. The disassembled positive and negative electrode sheets are mixed 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, 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) to assemble into a battery. First, the volume is constant at 25°C for 2 cycles, and then 25°C 1C is cycled for 200 cycles. Then, the negative electrode sheet is disassembled to obtain the negative electrode sheet. The negative electrode sheet is soaked in DMC (dimethyl carbonate) at room temperature (such as 25°C, the same below) for 1 hour to remove the electrolyte. The battery is taken out, dried, and the negative electrode material on the surface of the current collector is scraped off. After the negative electrode material is digested, the total mass M2 of Ni and Mn is measured by ICP. A total of 5 parallel samples are measured (that is, 5 batteries are tested), and the average value of M2 is calculated and recorded as

[0052] Calculate k,

[0053] The digestion method is as follows: the positive electrode material or the negative electrode material is dispersed in 20 mL of water, 10 mL of nitric acid (HNO3 mass percentage of 66%) is added, and the dispersion is heated until the positive electrode material or the negative electrode material is completely dissolved, and the volume is adjusted to 100 mL with water to obtain a test solution, and the test solution is subjected to ICP testing;

[0054] The ICP instrument operating conditions were set as follows: gas flow rate 0.5 L / min, power 1150 W;

[0055] The constant capacity method is as follows: 0.33C constant current and constant voltage charging to 4.75V, the constant voltage cut-off current is ≤0.05C, then 0.33C constant current discharge to 3.5V, repeat the charge and discharge process twice;

[0056] The cycling method is as follows: charge at a constant current and constant voltage rate of 1C to an upper limit voltage of 4.75V, then charge at a constant voltage at this voltage until the current is less than or equal to 0.05C; then discharge at 1C to a lower limit voltage of 3.5V, and repeat the above charge and discharge process 200 times.

[0057] In some embodiments, the first lithium nickel manganese oxide particles are of a disordered Fd-3m structure, and the second lithium nickel manganese oxide particles are of an ordered P4332 structure. The disordered structure (Fd3m space group) of lithium nickel manganese oxide is a face-centered cubic lattice, and unlike the ordered structure (P4332 space group), the Mn ions and Ni ions in the disordered structure are randomly distributed at the 16d sites, rather than being orderly distributed at specific sites. The lithium nickel manganese oxide of the disordered structure has a higher electrical conductivity and ion diffusion coefficient, typically 2.5 orders of magnitude higher than that of the ordered structure, which is mainly because there is a small amount of Mn 3+ with a radius greater than that of Mn 4+ , so that the lattice parameter is larger, to some extent, facilitating the diffusion of Li + and electron conduction; the LNMO structure of the ordered Fd-3m structure has good structural stability. By setting the first lithium nickel manganese oxide particles to be of a disordered Fd-3m structure and the second lithium nickel manganese oxide particles to be of an ordered P4332 structure, the kinetics and cycle performance of the positive electrode sheet can be better.

[0058] The present application does not limit the detection method of the lithium nickel manganese oxide crystal structure in each active material layer of the positive electrode sheet, and those skilled in the art can detect the lithium nickel manganese oxide crystal structure in each active material layer of the positive electrode sheet according to conventional technical means. For example, the lithium nickel manganese oxide crystal structure in each active material layer of the positive electrode sheet can be detected by Raman spectroscopy after scraping the material of each active material layer, respectively. If there is a clear split peak phenomenon in the corresponding F -1 peak in the Raman spectrum 594cm 2g(1) , it indicates that the degree of disorder of Ni / Mn increases, resulting in the transformation of the ordered structure into the disordered Fd-3m structure. The test conditions of the Raman spectrum can be selected as follows: the wavelength of the laser is 514nm, the Raman shift interval is 100-2000cm -1 ; the Raman spectrometer can be a confocal microscopic Raman spectrum analyzer of RM2000 of the British Renishaw company.

[0059] In some embodiments, the total thickness of the first positive electrode active material layer and the second positive electrode active material layer is 100-160μm, such as 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, or an interval range formed by any two of the above values.

[0060] 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, wherein x > 0, such as 0.1, 0.2, 0.3, 0.4, 0.5, or an interval range formed by any two of the above values. The surface of each of the first and second lithium nickel manganese oxide particles can be free of a coating material, or can be coated with a coating layer formed by coating at least a portion of the surface of at least one of the first and second lithium nickel manganese oxide particles with a coating material. The coating material can be selected from at least one of alumina, titania, lithium phosphate, zirconia, tantalum oxide, magnesium oxide, iron oxide, etc. In some embodiments, the coating layer on the surface of the first lithium nickel manganese oxide particles has a thickness of 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 an interval range formed by any two of the above values. In some embodiments, the coating layer on the surface of the second lithium nickel manganese oxide particles has a thickness of 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 an interval range formed by any two of the above values. When the first and second lithium nickel manganese oxide particles are each provided with a coating layer, the material of the coating layer, the thickness of the coating layer, etc. are each independent.

[0061] The first and second lithium nickel manganese oxide particles can be free of a doping element, or can contain a doping element. The present application does not limit the type of doping element in the first and second lithium nickel manganese oxide particles, which can be selected from at least one of Si, Mg, P, Co, Al, Cr, Nb, etc. Whether the first and second lithium nickel manganese oxide particles contain a doping element, the type of doping element, and the content of the doping element are independent of each other and do not affect each other.

[0062] The present application does not limit the method for preparing the first and second lithium nickel manganese oxide particles, and those skilled in the art can prepare the first and second lithium nickel manganese oxide particles according to conventional techniques. For example, the first and second lithium nickel manganese oxide particles can be prepared by a method comprising the following steps:

[0063] Mixing and dispersing a lithium source, a nickel source, and a manganese source in a solvent to obtain a mixture;

[0064] Calcining the mixture at a temperature in the range of 650-900°C, and cooling to obtain a lithium nickel manganese oxide bare material;

[0065] Grinding and drying the lithium nickel manganese oxide bare material to obtain lithium nickel manganese oxide particles.

[0066] In the process of preparing the mixture by using the lithium source, the nickel source and the manganese source, the solvent can be at least one of ethanol, NMP, acetonitrile, DMC and the like. In some embodiments, the mixing and dispersing method can be a solid phase method, such as ball milling, sand milling and the like.

[0067] In the process of preparing the first lithium nickel manganese oxide bare material by using the mixture, the calcination process conditions can be set as follows: the calcination temperature is 650-900℃, the calcination time is 12-24h, and the heating rate is 1-5℃ / h.

[0068] The calcination can be performed in a muffle furnace, a tube furnace or the like.

[0069] In the process of preparing the lithium nickel manganese oxide particles by using the lithium nickel manganese oxide bare material, the grinding method can be sand milling, and the sand milling conditions can be selected as follows: the sand ratio (mass ratio, the same below) is 8-20:1, the rotation speed is 1000-3000rpm, the sand milling time is 4-24h, and the sand particles can be at least one of alumina, zirconia, silicon carbide and boron carbide.

[0070] 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

[0071] 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

[0072] The manganese source includes but is not limited to at least one of manganese dioxide, manganese hydroxide, manganese oxide and manganese sulfate.

[0073] When the first or second lithium nickel manganese oxide particles are disordered Fd-3m structure, the corresponding calcination temperature is 750-900℃, and the calcination time is 16-20h;

[0074] When the first or second lithium nickel manganese oxide particles are ordered P4332 structure, the corresponding calcination temperature is 650-700℃, and the calcination time is 12-18h.

[0075] In addition, the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles can be subjected to coating treatment, for example, the atomic layer deposition (ALD) technology is used to coat the coating material on the surface of the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles, wherein the coating material can be at least one of alumina, titanium oxide, zinc oxide and magnesium oxide, the ALD deposition circle number can be selected as 50-500 circles, and the thickness of one ALD deposition circle can be selected as 0.1-0.3nm.

[0076] In addition, in preparing the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles, a certain amount of a dopant source (if any) can be mixed and dispersed with the lithium source, the nickel source, and the manganese source as needed to prepare the first lithium nickel manganese oxide particles and / or the second lithium nickel manganese oxide particles, the dopant source being at least one of a Si source, a Mg source, a P source, a Co source, an Al source, a Cr source, a 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 the dopant.

[0077] In some embodiments, the mass percentage content 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 a range formed by any two of the above values.

[0078] 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 electrical 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. Illustratively, 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, fullerenes, etc., wherein the carbon fibers are, for example, carbon nanofibers, etc.; the carbon black is, for example, SP (Super P, same below), acetylene black, Ketjen black, etc.

[0079] In some embodiments, the mass percentage content 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 a range formed by any two of the above values.

[0080] 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, 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. Illustratively, the binder of the first positive electrode active material layer includes, but is not limited to, fluorine-containing polyolefin-based binders, which include, but are not limited to, polyvinylidene fluoride (PVDF), a polyvinylidene fluoride copolymer, or a modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivative thereof, etc.

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

[0082] In some embodiments, the second lithium nickel manganese oxide particles have a mass percentage content of 94% to 98% in the second positive electrode active material layer, such as 94%, 95%, 96%, 97%, 98%, or a range formed by any two of the above values.

[0083] 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 electrical 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. Illustratively, 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, fullerenes, and the like, wherein the carbon fibers are, for example, carbon nanofibers and the like; the carbon black is, for example, SP (Super P, same below), acetylene black, Ketjen black, and the like.

[0084] In some embodiments, the conductive agent has a mass percentage content of 0.05% to 3.5% in the second positive electrode active material layer, such as 0.05%, 0.08%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or a range formed by any two of the above values.

[0085] The binder in 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. Illustratively, the binder in the second positive electrode active material layer includes, but is not limited to, fluorine-containing polyolefin-based binders, which include, but are not limited to, polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, or modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives thereof, and the like.

[0086] In some embodiments, the binder has a mass percentage content of 0.5% to 2.5% in the second positive electrode active material layer, such as 0.5%, 1%, 1.5%, 2%, 2.5%, or a range formed by any two of the above values.

[0087] The positive electrode current collector of the present application is not particularly limited, as long as it has electrical conductivity without causing adverse chemical changes in the battery, and can be, for example, aluminum, nickel, titanium, stainless steel, baked carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like.

[0088] The positive electrode sheet of the present application can be prepared according to conventional methods in the art. For example:

[0089] The first positive electrode active material, the conductive agent, and the binder are dispersed in a solvent to obtain a first positive electrode slurry;

[0090] The second positive electrode active material, the conductive agent, and the binder are dispersed in a solvent to obtain a second positive electrode slurry;

[0091] The first positive electrode slurry and the second positive electrode slurry are further coated 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. The solvent includes but is not limited to at least one of N-methyl pyrrolidone (NMP) and deionized water. When the first positive electrode slurry and the second positive electrode slurry are coated on at least one side of the positive electrode current collector, the first positive electrode slurry is coated first, and then the second positive electrode slurry is coated.

[0092] Battery

[0093] The application also provides a battery comprising the positive electrode sheet, the negative electrode sheet, and an electrolyte.

[0094] In some embodiments, the transition metal elements in the negative electrode sheet include Ni elements and Mn elements; in the negative electrode sheet, the content of Ni elements ranges from 50 ppm to 200 ppm, and the content of Mn elements ranges from 500 ppm to 1500 ppm. For example, in the negative electrode sheet, the content of Ni elements is 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 170 ppm, 200 ppm, or an interval range formed by any two of the above values; the content of Mn elements is 500 ppm, 700 ppm, 1000 ppm, 1200 ppm, 1500 ppm, or an interval range formed by any two of the above values. By controlling the content of Ni elements and Mn elements in the negative electrode sheet, the damage of transition metal ions to the negative electrode SEI film is reduced, and the cycle performance of the battery is improved; at the same time, excessive passivation of the positive electrode is avoided.

[0095] The application does not limit the detection method of the content of Ni elements and Mn elements in the negative electrode sheet, and those skilled in the art can detect the content of Ni elements and Mn elements in the negative electrode sheet according to conventional technical means. For example, the content of Ni elements and Mn elements in the negative electrode sheet can be detected by the following method:

[0096] Take an empty battery and disassemble it to obtain the positive and negative electrodes respectively. The disassembled positive and negative electrodes are mixed 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, 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) to assemble into a battery. The battery is first fixed at 25°C for 2 cycles, then cycled at 25°C and 1C for 200 cycles. The negative electrode is then disassembled to obtain the negative electrode. The negative electrode is soaked in DMC (dimethyl carbonate) at room temperature (such as 25°C, the same below) for 1 hour to remove the electrolyte. The battery is taken out, dried, and the negative electrode material on the surface of the current collector is scraped off. The negative electrode material is digested (the digestion method is the same as above) and the mass ratio of Ni and Mn is measured by ICP to obtain the Ni and Mn element contents in the negative electrode.

[0097] The negative electrode sheet of the present invention comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material.

[0098] The present invention has no particular limitation on the negative electrode active material. Exemplary negative electrode active materials include but are not limited to natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, SiO f (0 <f<2,如f=1)、硅碳、Li4Ti5O 12 At least one of .

[0099] In some embodiments, the mass percentage of the negative electrode active material in the negative electrode active material layer is 92% to 98%. For example, the mass percentage of the positive electrode active material in the negative electrode active material layer is 92%, 93%, 94%, 95%, 96%, 96.4%, 97%, 98%, or an interval formed by any two of the above values.

[0100] The negative electrode active material layer may further include a conductive agent, and / or a binder, and / or a thickener.

[0101] The conductive agent in the negative electrode active material layer is used to provide electrical 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. Exemplary conductive agents in the negative electrode active material layer include, but are not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes. Examples of carbon fibers include carbon nanofibers; and examples of carbon black include SP, acetylene black, and Ketjen black.

[0102] In some embodiments, the negative active material layer includes the conductive agent in a mass percentage of 0.5% to 2.5%, such as 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2%, 2.5%, or a range defined by any two of the aforementioned values.

[0103] The binder in the negative active material layer is used to improve adhesion between the negative active material particles and between the negative active material and the negative current collector, 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. Exemplary binders in the negative active material layer include, but are not limited to, at least one of carboxymethyl cellulose (CMC), styrene butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and aqueous acrylic resin.

[0104] In some embodiments, the negative active material layer includes the binder in a mass percentage of 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 a range defined by any two of the aforementioned values.

[0105] The thickening agent in the negative active material layer is used to improve stability of the negative slurry, and any thickening agent 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. Exemplary thickening agents in the negative active material layer include, but are not limited to, at least one of carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and hydrogenated styrene butadiene rubber (H-SBR).

[0106] In some embodiments, the negative active material layer includes the thickening agent in a mass percentage of 0.5% to 2.5%, such as 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2%, 2.5%, or a range defined by any two of the aforementioned values.

[0107] The negative current collector is not particularly limited in the present application as long as it has electrical conductivity without causing adverse chemical changes in the battery, and examples include copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0108] The electrolyte solution can be selected from various electrolyte solutions suitable for use in batteries in the art. The electrolyte solution includes an electrolyte and a solvent, and the electrolyte can generally include a lithium salt.

[0109] 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 bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorophosphate bisoxalate (LiDFOP), lithium tetrafluorophosphate oxalate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be selected as 0.5-5 mol / L.

[0110] Exemplarily, the solvent includes, but is not limited to, at least one of 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), 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), methyl ethyl sulfone (EMS), diethyl sulfone (ESE). The mass percentage of the solvent in the electrolyte solution can be selected as 70%-98%.

[0111] In addition, the electrolyte solution can further include an additive. Exemplarily, the additive can include a negative electrode film-forming additive, can also include a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive capable of improving high-temperature performance of the battery, an additive capable of improving overcharge performance of the battery, an additive capable of improving low-temperature performance of the battery, etc.

[0112] The battery can further include a separator between the positive electrode sheet and the negative electrode sheet, for spacing the positive electrode sheet and the negative electrode sheet and preventing the positive electrode sheet and the negative electrode sheet from being in contact and short-circuiting. The separator can be any separator material suitable for use in a battery in the art. Exemplarily, the separator includes, but is not limited to, at least one of polypropylene and polyethylene.

[0113] Electric device

[0114] The present application further provides an electric device including the battery. The battery serves as a power supply for the electric device.

[0115] The power utilization device refers to any device that can utilize electric energy and convert it into mechanical energy, thermal energy, light energy, or other one or more forms of energy, such as an electric motor, an electric heating machine, an electric light source, etc. Specifically, it can be, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc. The mobile device can be a mobile phone, a notebook computer, a drone, a sweeping robot, an electronic cigarette, etc. The electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.

[0116] The present application is further illustrated by specific examples. It should be noted that the calcination below is performed in an air atmosphere unless otherwise specified:

[0117] Example 1

[0118] This example provides a lithium ion battery, and the specific preparation method is as follows:

[0119] (1) Preparation of first lithium nickel-manganese oxide particles

[0120] Li2CO3, NiCO3 and MnO2 are added to a ball mill according to the stoichiometric ratio of Li, Ni and Mn in LiNi 0.5 Mn 1.5 O4, mixed and dispersed, and the obtained mixture is added to a muffle furnace and heated to a temperature T1 ℃ for t1 h, cooled to room temperature, and then transferred to a sand milling device for sand milling with zirconia sand, with a sand ratio of S1:1 and a sand milling time of t1 ’h. After sand milling, the material is dried, and then an ALD instrument is used to coat an aluminum oxide coating layer on the surface of the material, with a deposition thickness of 0.1 nm per circle, to obtain aluminum oxide-coated lithium nickel-manganese oxide, i.e. the first lithium nickel-manganese oxide particles, wherein the thickness of the coating layer is C1 nm, and T1, t1, S1, t1 ’ and C1 are as shown in Table 1.

[0121] (2) Preparation of second lithium nickel-manganese oxide particles

[0122] Li2CO3, NiCO3 and MnO2 are added to a ball mill according to the stoichiometric ratio of Li, Ni and Mn in LiNi 0.5 Mn 1.5The stoichiometric ratio of Li, Ni and Mn in O4 is added to a ball mill for mixing and dispersion to obtain a mixture, the obtained mixture is added to a muffle furnace for calcination at a temperature T2℃ for t2h, and then cooled to room temperature, the material is transferred to a sand grinding device, zirconia sand is used for sand grinding, the sand ratio is S2:1, the sand grinding time is t2'h, after sand grinding, drying is performed, and then an ALD instrument is used to coat an aluminum oxide coating layer on the surface of the material, the deposition thickness of each circle is 0.1nm, to obtain aluminum oxide coated lithium nickel manganese acid, which is the second lithium nickel manganese acid particle, wherein the thickness of the coating layer is C2nm, and T2, t2, S2, t2' and C2 are as shown in Table 1.

[0123] (3) Preparation of the positive electrode sheet

[0124] The first lithium nickel manganese acid particle is used as a positive electrode active material, and the positive electrode active material, the conductive agent CNTs and the binder PVDF are mixed in a mass ratio of 97:1:2, the solvent NMP is added, and stirring is performed in a vacuum stirrer to obtain a first positive electrode slurry (for forming a first positive electrode active material layer);

[0125] The second lithium nickel manganese acid particle is used as a positive electrode active material, and the positive electrode active material, the conductive agent CNTs and the binder PVDF are mixed in a mass ratio of 97:1:2, the solvent NMP is added, and stirring is performed in a vacuum stirrer to obtain a second positive electrode slurry (for forming a second positive electrode active material layer);

[0126] The first positive electrode slurry and the second positive electrode slurry are coated on both sides of the positive electrode current collector aluminum foil, the first positive electrode slurry is coated on both sides of the positive electrode current collector first, the second positive electrode slurry is coated on the surface of the first slurry after the first positive electrode slurry is dried, and then drying, cold pressing and cutting are performed to obtain a positive electrode sheet;

[0127] The thickness of the second positive electrode active material layer accounts for M b , M b % of the total thickness of the first positive electrode active material layer and the second positive electrode active material layer, and the values are shown in Table 1.

[0128] (4) Preparation of the negative electrode sheet

[0129] The negative electrode active material artificial graphite, the conductive agent acetylene black, the thickening agent CMC and the binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4, the solvent deionized water is added, and stirring is performed in a vacuum stirrer 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 pressing and cutting are performed to obtain a negative electrode sheet.

[0130] (5) Preparation of the electrolyte

[0131] Ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed in a volume ratio of 1:1 to obtain an organic solvent, and then dry lithium salt LiPF6 is dissolved in the obtained organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0132] (6) Preparation of the lithium ion battery

[0133] The above positive electrode sheet, separator (PE), and negative electrode sheet are stacked in order with the separator between the positive and negative electrode sheets to play a separating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging and standing for 24 h, formation is performed, and thus a lithium ion battery is obtained, wherein the formation process is as follows: using a LAND system, constant current charging to 4.8 V at a current of 0.33 C, and then constant current discharging to 3.5 V at a current of 0.33 C, and cycling 2 times, and then the battery is removed from the charging device.

[0134] Examples 2-27 and Comparative Examples 1-6

[0135] These examples and comparative examples all provide a lithium ion battery, and the preparation method is similar to that of Example 1, and the difference lies in that:

[0136] (a) In step (1), T1, t1, S1, t1’, and C1 take the values in Table 1;

[0137] (b) In step (2), T2, t2, S2, t2’, and C2 take the values in Table 1;

[0138] (c) In step (3), the total thickness of the first positive electrode active material layer and the second positive electrode active material layer is unchanged, and M b takes the values in Table 1.

[0139] Table 1

[0140]

[001] T1 [T2] ​ [ t2 ] <![CDATA[S1]]> [S2] [t1'] [t2'] <![CDATA[C1]]> [C2] M b ]]> Example 1 850 650 16 14 15 10 12 12 25 25 0.65 Example 2 850 650 16 14 15 10 13.6 12.5 26 26 0.66 Example 3 800 650 16 14 15 10 14.2 11 24 24 0.65 Example 4 860 680 16 14 15 10 11 10 20 20 0.64 Example 5 850 650 16 14 15 10 12.8 10 28 28 0.63 Example 6 850 650 16 14 15 10 12 12 25 25 0.60 Example 7 850 650 16 14 15 10 12 12 25 25 0.70 Example 8 880 650 16 14 15 10 12 10.5 22 22 0.64 Example 9 850 650 16 14 15 10 13.8 10 21 21 0.65 Example 10 850 650 16 14 15 10 11.3 15 27 27 0.66 Example 11 850 650 16 14 15 10 14.8 18 35 35 0.65 Example 12 780 700 16 14 15 10 9.6 8 15 15 0.66 Example 13 850 650 16 14 15 10 19.7 12.8 27 27 0.64 Example 14 850 650 16 14 15 10 12.4 18 34 34 0.66 Example 15 850 650 16 14 20 8 9 8 18 18 0.65 Example 16 900 650 16 14 10 15 10 4 14 14 0.67 Example 17 900 650 16 14 15 10 5.5 10.4 18 18 0.66 Example 18 850 650 16 14 15 10 12 12 27 27 0.51 Example 19 850 650 16 14 15 10 12 12 23 23 0.78 Example 20 850 650 16 14 15 10 12 12 17 17 0.60 Example 21 850 650 16 14 15 10 12 12 45 45 0.78 Example 22 850 650 16 14 15 10 12 12 22 22 0.52 Example 23 850 650 16 14 15 10 12 12 19 19 0.53 Example 24 850 650 16 14 15 10 12 12 50 50 0.78 Example 25 850 750 16 16 15 10 12 12 25 25 0.66 Example 26 700 650 18 14 15 10 12 12 25 25 0.67 Example 27 700 750 18 16 15 10 12 12 25 25 0.65 Comparative Example 1 800 650 16 14 15 10 14.2 11 50 50 0.66 Comparative Example 2 850 750 16 14 15 10 12 3.5 10 10 0.65 Comparative Example 3 800 650 16 14 15 10 28 19 28 28 0.67 Comparative Example 4 950 650 16 14 15 10 3 3 22 22 0.66 Comparative Example 5 850 650 16 14 15 10 12 12 26 26 0.40 Comparative Example 6 850 650 16 14 15 10 12 12 21 21 0.90

[0141] The first nickel-lithium manganate particle size Dn50 (denoted as a μm), the second nickel-lithium manganate particle size Dn50 (denoted as b μm), the proportion of the thickness of the second positive electrode active material layer in the total thickness of the first positive electrode active material layer and the second positive electrode active material layer (denoted as M b ), the transition metal ion elution amount of the positive electrode sheet after 200 cycles at 25°C (denoted as k%), and the crystal structure of the first and second nickel-lithium manganate particles are detected by the following method and are shown in Table 1 or Table 2:

[0142] The first and second lithium nickel manganese oxide particle sizes: an empty battery is taken, the positive electrode sheet is disassembled, the positive electrode sheet is subjected to CP section treatment, and SEM is used for observation and measurement, wherein the magnification is adjusted to 5Kx, the upper region, the middle region and the lower region of each layer of active material layer are selected for photographing, the particle size of all particles in the three regions in the photos is measured respectively, and the average particle size Dn50 of the number distribution of 50% in the three regions is obtained, then the average value of Dn50 of the three regions is calculated, the average particle size Dn50 of each layer of active material layer is obtained, that is, 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.

[0143] The thickness ratio of the second positive electrode active material layer: an empty battery is taken, the positive electrode sheet is disassembled, the positive electrode sheet is subjected to CP section treatment, and SEM (scanning electron microscope) is used 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 the thickness ratio (M b ) of the second positive electrode active material layer is calculated.

[0144] 25℃ cycle 200 times transition metal ion dissolution amount: an empty battery is taken, the positive electrode sheet is disassembled, the positive electrode sheet is soaked in DMC (dimethyl carbonate) at 25℃ for 1h to remove the electrolyte, taken out, dried, and the positive electrode material on the surface of the current collector is scraped off, the positive electrode material is digested, and the total mass of Ni and Mn is measured by ICP (inductively coupled plasma) instrument, the sum of the two is M1, 5 parallel samples (i.e. 5 batteries are tested), the average value of M1 is calculated, and is recorded as

[0145] An empty battery is taken, and the positive electrode sheet and the negative electrode sheet are disassembled, respectively, the disassembled positive electrode sheet and the negative electrode sheet are assembled into a battery with an electrolyte (ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) are mixed according to a volume ratio of 1:1:1 to obtain an organic solvent, 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), first 25℃ constant volume 2 times, then 25℃ 1C cycle 200 times, then the negative electrode sheet is disassembled, the negative electrode sheet is soaked in DMC (dimethyl carbonate) at 25℃ for 1h to remove the electrolyte, taken out, dried, and the negative electrode material on the surface of the current collector is scraped off, the negative electrode material is digested, and the total mass M2 of Ni and Mn is measured by ICP, 5 parallel samples (i.e. 5 batteries are tested), the average value of M2 is calculated, and is recorded as

[0146] The k is calculated,

[0147] The digestion method is as follows: the positive electrode material or the negative electrode material is dispersed in 20 mL of water, 10 mL of nitric acid (66% by mass) is added, and the dispersion is heated until the positive electrode material or the negative electrode material is completely dissolved, and then the solution is diluted with water to 100 mL to obtain a test solution, and the test solution is subjected to ICP test.

[0148] The ICP instrument working condition settings are as follows: gas flow 0.5 L / min, power 1150 W.

[0149] The constant volume method is as follows: 0.33C constant current and constant voltage charging to 4.75V, constant voltage segment cutoff current ≤0.05C, then 0.33C constant current discharging to 3.5V, repeating the charging and discharging process 2 times.

[0150] The cycle method is as follows: 1C constant current and constant voltage charging to the upper limit voltage 4.75V, constant voltage charging at this voltage to a current less than or equal to 0.05C; then 1C discharging to the lower limit voltage 3.5V, repeating the above charging and discharging process 200 times.

[0151] First and second lithium nickel manganese oxide crystal structure determination: the prepared material was analyzed for configuration using a confocal micro-Raman spectrometer RM2000 produced by the British Renishaw company. Test conditions: wavelength of the laser is 514 nm, Raman shift range 100-2000 cm -1 -1. Raman test spectrum A -1 peak at 638.8 cm 1g , F -1 peak at 594.7 and 611.3 cm 2g(1) correspond to the symmetry stretching vibration of Mn-O bond, at the same time, Eg peak at 408.4 cm -1 and F2g(2) peak at 498.4 cm -1 correspond to the stretching vibration of Ni-O bond. Compared with the ordered structure sample, the intensity of the peaks at 638.8, 498.4 and 408.4 cm -1 significantly decreases in the disordered structure sample. In addition, the F -1 peak at 594.7 cm 2g(1) in the disordered structure sample is more obviously split, which is mainly due to the increase of the degree of Ni / Mn disorder, resulting in the structure changing from ordered P4332 structure to disordered Fd-3m structure.

[0152] The lithium ion battery obtained in the above examples and comparative examples is taken as the detection object, and the following tests are carried out:

[0153] Battery capacity retention rate after 100 cycles at 45℃ and DCR growth rate after 100 cycles at 45℃: after standing, 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, cycled 2 times, and the battery was removed from the charging device at the end for use (activation process). After the battery was activated, it was charged to 4.8V at a constant current of 1C at 45℃, then charged at a constant voltage until the current was less than 0.05C; then discharged at a rate of 1C to a voltage of 3.5V, and one complete charge-discharge process was considered a cycle, for a total of 100 cycles. The capacity retention rate was calculated according to the following formula: capacity retention rate = discharge capacity in the 100th cycle / discharge capacity in the first cycle * 100%;

[0154] The DCR value after 100 cycles at 45℃ 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, and the specific DCR test method is as follows:

[0156] A1, the battery was first placed at room temperature (25℃) for 10 minutes;

[0157] A2, the battery was first charged at a constant current and constant voltage, with a constant current rate of 0.33C and a voltage of 4.80V, and then discharged to 3.5V at a constant current rate of 0.33C;

[0158] A3, steps A1-A2 were repeated three times, and the discharge capacity of the last step A2 process was recorded 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 at a discharge rate of 0.33C, at which point the battery is at 50% SOC;

[0161] A6, the battery was placed for 120 minutes, and the voltage at the end of the standing period was recorded as V0;

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

[0163] Table 2

[0164]

[0165]

[0166]

[0167] The capacity retention rate of the battery prepared by each embodiment of the application after 1C cycle at 45 DEG C for 100 cycles is greater than or equal to 85%, and the DCR growth rate after 1C cycle at 45 DEG C for 100 cycles is less than or equal to 4.6%, which shows that the battery containing the positive plate of the application has excellent kinetic performance and high-temperature cycle performance.

[0168] As can be seen from the comparison of Examples 1-7 and Comparative Examples 11-12, the comparison of Examples 13 and 15, and the comparison of Examples 14 and 16, when the particle size Dn50 of the first lithium nickel-manganese oxide particles and the second lithium nickel-manganese oxide particles is within the preferred range described in the application, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0169] As can be seen from the comparison of Examples 1-7 and Comparative Examples 8-10, when the positive plate satisfies 0.3≤a / b≤0.4, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0170] As can be seen from the comparison of Examples 1, 6-7 and Comparative Examples 18-19, and the comparison of Examples 20 and 21-22, when the thickness ratio M b of the second positive active material layer is within the preferred range described in the application, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0171] As can be seen from the comparison of Examples 15 and 16, the comparison of Examples 1-7 and 20, and the comparison of Examples 18-19 and 21-22, when the positive plate satisfies 0.1≤k / M b ≤0.2, the kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0172] As can be seen from the comparison of Example 1 and Comparative Examples 25-27, when 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 kinetic performance and high-temperature cycle performance of the battery are relatively better.

[0173] As can be seen from Comparative Examples 1-6, when the particle size Dn50 of the first lithium nickel-manganese oxide particles, the particle size Dn50 of the second lithium nickel-manganese oxide particles, or the thickness ratio M b of the second positive active material layer 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 examples are only used to illustrate the technical solutions herein and do not limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions herein can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions herein.

Claims

1. A positive electrode sheet, characterized in that: Include: positive electrode current collector; a first positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein 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 is in the range of 2≤a≤3; and a second positive electrode active material layer disposed on a 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 b is in the range of 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 to 0.8; The a and the b satisfy the relationship: 0.125≤a / b≤0.

5.

2. The positive electrode sheet according to claim 1, wherein: The a and the b satisfy the relationship: 0.3≤a / b≤0.

4.

3. The positive electrode sheet according to claim 1, wherein: The range of b is 6 μm to 7 μm; and / or The M b The range is 0.6~0.

7.

4. The positive electrode sheet according to claim 1, wherein: 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.

5. The positive electrode sheet according to claim 4, wherein: The positive electrode sheet satisfies: 0.1≤k / M b ≤0.

2.

6. The positive electrode sheet according to claim 4, wherein: The range of k is 0.05≤k≤0.

2.

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

8. A battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 1 to 7.

9. The battery according to claim 8, wherein It also includes a negative electrode sheet, in which the transition metal elements include Ni and Mn. In the negative electrode sheet, the Ni content ranges from 50 to 200 ppm, and the Mn content ranges from 500 to 1500 ppm.

10. An electrical device, characterized in that: Comprising the battery according to claim 8 or 9.

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