Positive electrode material and secondary battery

Abstract

The invention discloses a positive pole piece and a secondary battery, and belongs to the technical field of batteries, according to the positive pole piece, a coating layer is arranged on the surface of a positive active substance of a positive material, and meanwhile, the roundness of the coated positive material in the positive pole piece and the ratio relation of the content ratio of free transition metal ions of the positive material after the acid corrosion effect are regulated and controlled; and the balance of the stability and the conductivity in the positive electrode material is coordinated, so that the secondary battery prepared from the positive electrode plate has ideal electrochemical performance, and particularly has relatively excellent cycling stability and storage capacity retention rate in a high-temperature environment.

Description

This application is a divisional application of CN119764416A (application date December 31, 2024, application number 202411990332.9, invention title: A positive electrode material, a secondary battery). Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode material and a secondary battery. Background Technology

[0002] In existing secondary batteries, especially lithium-ion secondary batteries, the mainstream positive electrode active materials include ternary lithium nickel cobalt manganese oxide, lithium iron phosphate, and spinel-structured lithium nickel manganese oxide. These materials have ideal electrochemical activity, but without exception, they all suffer from the problem of transition metal ion dissolution (for ternary materials, this means the dissolution of nickel, cobalt, and manganese; for lithium iron phosphate, it is iron; and for lithium nickel manganese oxide, it is nickel and manganese). This increases the probability of side reactions between the dissolution of transition metal ions and the electrolyte after the secondary battery has been in operation for a period of time, resulting in increased gas production and performance degradation of the battery. Especially under high temperature conditions, the degree of side reactions increases, and may even lead to safety issues.

[0003] To address this, researchers have attempted to modify the positive electrode active material by coating it. The inert protection of the coating layer reduces the dissolution of transition metal ions. However, the coating materials used in these methods are mostly insulating or semi-insulating materials with low conductivity, which affects the ion / electron transport efficiency of the positive electrode active material. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the existing technology and provide a positive electrode sheet. The positive electrode sheet has a coating layer on the surface of the positive active material of the positive electrode material. At the same time, the roundness of the coated positive electrode material and the ratio of its free transition metal ions after acid corrosion are controlled to coordinate the balance between stability and conductivity in the positive electrode material. This makes the secondary battery prepared by the positive electrode sheet have ideal electrochemical performance, especially with better cycle stability and storage capacity retention under high temperature environment.

[0005] To achieve the above objectives, in a first aspect of this application, this application provides a positive electrode sheet, comprising a positive electrode material and a conductive agent, wherein the positive electrode material comprises positive electrode active material particles, the positive electrode active material particles are provided with a coating layer, the positive electrode active material particles comprise lithium nickel manganese oxide, and the coating layer comprises a metal oxide. The positive electrode material satisfies: 0.3 ≤ K / Rn ≤ 1.0; The K% refers to the percentage of free transition metal elements in the positive electrode active material particles after soaking them in a 20wt% hydrofluoric acid solution at 70℃ with a solid-liquid ratio of 1g:5mL for 72 hours. Rn represents the roundness of the positive electrode active material particles; The conductive agent includes one or more of conductive carbon black, acetylene black, and carbon nanotubes.

[0006] The beneficial effects of this application are as follows: This application provides a positive electrode sheet, which has a coating layer on the surface of the positive active material of the positive electrode material. At the same time, the roundness of the coated positive electrode material and the ratio of its free transition metal ions after acid corrosion are controlled to coordinate the balance between stability and conductivity in the positive electrode material. This makes the secondary battery prepared by the positive electrode sheet have ideal electrochemical performance, especially with better cycle stability and storage capacity retention under high temperature environment. Detailed Implementation

[0007] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0008] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0009] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0010] The present application is further illustrated below with specific embodiments: A positive electrode sheet includes a positive electrode material and a conductive agent. The positive electrode material includes positive electrode active material particles, the positive electrode active material particles are provided with a coating layer, the positive electrode active material particles include lithium nickel manganese oxide, and the coating layer includes a metal oxide. The positive electrode material satisfies: 0.3 ≤ K / Rn ≤ 1.0; The K% refers to the percentage of free transition metal elements in the positive electrode active material particles after soaking them in a 20wt% hydrofluoric acid solution at 70℃ with a solid-liquid ratio of 1g:5mL for 72 hours. Rn represents the roundness of the positive electrode active material particles; The conductive agent includes one or more of conductive carbon black, acetylene black, and carbon nanotubes.

[0011] Before being used in cathode materials, in order to suppress the dissolution of transition metal elements in the particles during cyclic charging and discharging, which increases the probability of side reactions after contact with the electrolyte, an inert metal oxide coating layer is usually set on the particle surface. This coating layer isolates and protects against this phenomenon. However, the introduction of such coating layers will hinder the ion / electron transport kinetics of the cathode active material particles, reduce the overall conductivity of the cathode active material particles, and ultimately exhibit lower electrochemical performance. To overcome this technical predicament, the present application's technical solution involves setting a metal oxide coating layer on the surface of the positive electrode active material particles in the positive electrode material of the positive electrode sheet. Simultaneously, by controlling the roundness of the coated positive electrode active material particles and the ratio of their free transition metal ion content after acid etching, the coating effect is adjusted to coordinate the overall stability of the coated material and the balance of ion / electron transport kinetics. The roundness of the positive electrode active material particles is related to the irregularity of the particle shape and the surface smoothness, thus affecting the contact effect with the electrolyte and the overall path length of ion / electron transport. Furthermore, after setting the coating layer, the degree of free transition metal elements is altered. By controlling the free transition metal element content of the positive electrode active material particles after acid etching, the structural stability and ion / electron conduction performance of the material can be simultaneously controlled. When the ratio K / Rn of the two key factors mentioned above is controlled within the range of 0.3 to 1.0 in the present application scheme, the positive electrode sheet can balance conductivity and structural stability when applied to a secondary battery. The probability of side reactions after contact with the electrolyte is reduced, while the ion / electron transport kinetics of the material itself are not weakened, resulting in excellent electrochemical performance of the secondary battery. If the ratio K / Rn is not set properly, it may lead to an excessively high probability of side reactions between the positive electrode active material particles and the electrolyte, affecting the service life of the secondary battery or even causing safety issues, or reducing the charge / discharge efficiency and energy density of the secondary battery.

[0012] In some implementations, K / Rn = 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or any two of these values.

[0013] In some implementations, 0.4 ≤ Rn ≤ 0.8.

[0014] More preferably, Rn is a value within the range of one or any two of the following: 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, and 0.8.

[0015] More preferably, 0.6≤Rn≤0.7.

[0016] When the roundness of the positive electrode active material particles after coating is low, it indicates low surface flatness and high irregularity of the particles after coating. Conversely, high roundness indicates good coating integrity and high particle regularity. The contact area between the positive electrode active material particles with different roundness and the electrolyte also varies. At the same time, the regularity of the particles will also affect their compaction and structural stability when used to prepare the electrode sheet. When the roundness is preferably within the above range, the positive electrode active material particles can achieve a moderate contact area with the electrolyte. The degree of coating can control the balance between the dissolution probability of transition metal ions and the ease of ion / electron transport. At the same time, ideal electrode stability and compactness can be achieved when preparing the positive electrode sheet, resulting in better overall electrochemical performance of the material.

[0017] It should be noted that the test method for the roundness Rn of the positive electrode active material particles described in this application is as follows: The positive electrode material is dispersed in ethanol, and then an OCCHIO FC200s+HR particle morphology analyzer (camera resolution of 10 megapixels, telecentric zoom lens, Callisto 2012 analysis and processing software) is used as the testing instrument. The ethanol dispersion of the positive electrode material is pumped into the sample cell of the instrument through a 5mm sample tube. After image acquisition and analysis, the average values ​​of Ai and A of the positive electrode material are confirmed, where Ai is the maximum inscribed circle area of ​​the positive electrode active material particles, and A is the projected area of ​​the positive electrode active material particles. Finally, the software automatically calculates the roundness of the positive electrode active material particles in the positive electrode material using Rn=Ai / A.

[0018] In some embodiments, the roundness of the positive electrode active material particles can be adjusted by the calcination temperature and calcination time during the preparation process. However, it is not limited to this. Those skilled in the art can also adjust it by common positive electrode active material particle preparation or processing methods such as ball milling and spray treatment, according to actual needs.

[0019] In some implementations, 0.1% ≤ K ≤ 0.5%.

[0020] More preferably, K is a range of one or any two of the following: 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%.

[0021] More preferably, the percentage is 0.2% ≤ K ≤ 0.3%.

[0022] After acid etching, the proportion of free transition metal elements in the positive electrode active material particles is related to the type of positive electrode active material and the coating effect of the coating layer. Therefore, the value of K also affects the ion / electron transport capability and structural stability of the positive electrode active material particles. When the K value of the positive electrode active material particles is preferably within the above range, the obtained positive electrode material has better structural stability and conductivity.

[0023] It should be noted that the test method for the K value of the positive electrode active material particles described in this application is as follows: the positive electrode material is placed in a 40wt% sodium hydroxide solution for digestion treatment, followed by ICP testing. The ICP test conditions are as follows: the element detection spectral wavelength is selected, and appropriate ICP instrument operating conditions are set according to the characteristics of the sample and the element to be detected, including a gas flow rate of 0.5L / min and a power of 1150W. The content of transition elements is determined by ICP testing to confirm the total content M1 of transition metal elements in the positive electrode active material particles (taking lithium nickel manganese oxide as an example, the total content of transition metal elements is the total content of nickel and manganese; if lithium iron phosphate is an example, it is iron). The total element content (for example, lithium nickel cobalt manganese oxide, it is the total content of nickel, cobalt, and manganese). Subsequently, parallel samples were immersed in a 20wt% hydrofluoric acid solution at 70℃ with a solid-liquid ratio of 1g:5mL for 72h. The supernatant of the hydrofluoric acid solution was then used for ICP testing. The ICP testing conditions were as follows: the element detection spectral wavelength was selected, and appropriate ICP instrument operating conditions were set according to the characteristics of the sample and the element to be detected, including a gas flow rate of 0.5L / min and a power of 1150W. The content of transition elements was determined by ICP testing to confirm the total content M2 of free transition metal elements after acid etching. The final result was calculated according to K=M2 / M1*100%.

[0024] In some embodiments, K can be controlled by the number of deposition layers during the deposition of the coating layer in the ALD atomic layer. However, it is not limited to this. Those skilled in the art can also adjust other conditions during deposition, as well as other process conditions such as temperature and time during the preparation and sintering of the positive electrode active material particles, according to actual needs.

[0025] In some embodiments, the metal oxide includes at least one of aluminum oxide, tungsten oxide, and zirconium oxide.

[0026] The aforementioned metal oxides, as a coating layer for positive electrode active material particles, can protect them from corrosion by acidic substances in the electrolyte, such as hydrofluoric acid, when in contact with the electrolyte, thereby preventing the generation of byproducts that affect their electrochemical activity and service life. However, the metal oxides are not limited to the three types mentioned above; other metal oxides with similar inert protective effects can be used in place of the three types mentioned above.

[0027] In some embodiments, the average particle size Dv50 of the positive electrode active material particles is 4~8 μm; In this application, the average particle size of the positive electrode active material particles is directly measured using a laser particle size analyzer.

[0028] In some embodiments, the concentration of the metal oxide in the cathode material is 100 to 4000 ppm.

[0029] In some embodiments, the positive electrode active material particles further include at least one of lithium nickel cobalt manganese oxide particles and lithium iron phosphate particles.

[0030] The positive electrode active material particles in the positive electrode material described in this application include high-voltage positive electrode material lithium nickel manganese oxide particles, and may also include layered ternary lithium nickel cobalt manganese oxide particles with the chemical formula LiNi. x Co y Mn (1-x-y) O2, where 0 < x < 1, 0 < y < 1, or lithium iron phosphate particles with an olivine structure and the chemical formula LiFe x Mn 1-x PO4, where 0 < x < 1; as long as the ratio of K value to roundness in the material is effectively controlled after the surface coating layer is set, it can achieve improved structural stability compared with conventional cathode materials of the same system, while maintaining a high level of conductivity, so that the cathode sheet has ideal cycle performance and capacity performance when applied to secondary batteries, especially in high temperature environments.

[0031] In some embodiments, the positive electrode active material particles further include at least one of the following: lithium nickel cobalt manganese oxide particles, lithium iron phosphate particles, and lithium nickel manganese oxide particles.

[0032] For the three active material materials that have undergone doping modification, the modification methods and the resulting cathode materials obtained through regulation in this application can also achieve ideal electrochemical performance improvement. Therefore, the cathode active material particles in this application are not limited to the three undoped cathode materials.

[0033] In some embodiments, the positive electrode active material particles include lithium nickel manganese oxide particles, wherein 0.3 ≤ K / Rn ≤ 0.5.

[0034] In some embodiments, the positive electrode active material particles are LiNi. x Mn y O4, where 0 < x ≤ 0.5, y = 2 - x.

[0035] Compared to ternary materials or lithium iron phosphate materials, lithium nickel manganese oxide particles have a higher operating voltage, resulting in relatively poorer stability. Their structure has more sharp edges and lower surface flatness, thus requiring careful control of the coating effect to prevent the surface edges from breaking during electrode rolling, which could lead to partial failure of the coating layer and an increased probability of side reactions upon contact with the electrolyte. When K / Rn is controlled within the range of 0.3~0.5, the positive electrode active material particles exhibit good coating effect, with all edges fully covered and a high surface flatness, resulting in a lower dissolution rate of transition metal elements and higher conductivity, leading to superior overall performance.

[0036] In some embodiments, the positive electrode includes a current collector and a positive electrode material layer, wherein the positive electrode material layer contains the positive electrode material described in this application.

[0037] In some embodiments, the positive electrode material layer further includes a binder.

[0038] In an embodiment, the present application also provides a secondary battery, including the positive electrode sheet described in the present application.

[0039] In some embodiments, the secondary battery further includes a negative electrode and an electrolyte.

[0040] In some embodiments, the negative electrode sheet comprises a negative electrode active material.

[0041] In some embodiments, the negative electrode active material includes at least one of carbon-based materials, silicon-based materials, and silicon-carbon composite materials.

[0042] More preferably, the negative electrode material layer includes a negative electrode material, a binder, a thickener, and a conductive agent.

[0043] In some embodiments, the electrolyte comprises a solvent and a lithium salt.

[0044] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0045] Exemplary examples include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0046] More preferably, the solvent may also include, but is not limited to, at least one of carbonate solvent fluorinated derivatives, carboxylic acid ester solvent fluorinated derivatives, ether solvent fluorinated derivatives, sulfone solvent fluorinated derivatives, nitrile solvent fluorinated derivatives, and phosphate ester solvent fluorinated derivatives.

[0047] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0048] More preferably, the concentration of lithium salt in the electrolyte is 0.8~2.5 mol / L.

[0049] More preferably, the concentration of lithium salt in the electrolyte is one or any two of the following: 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, and 2.5 mol / L.

[0050] In some embodiments, the secondary battery is prepared by the following method: Preparation of positive electrode active material: Lithium, nickel, and manganese sources are mixed at a target molar ratio and then mixed with zirconia balls with a diameter of 0.6-1.0 mm at a ball-to-material ratio of 5:1-8:1. The mixture is ball-milled at a speed of 1700-2300 rpm for 5-12 hours. The ball-milled mixture is then calcined at a temperature of 600-1200℃ for 6-20 hours and cooled to room temperature to obtain spinel-type lithium nickel manganese oxide.

[0051] The lithium source options are: lithium carbonate and lithium hydroxide. Nickel source selection: nickel hydroxide, nickel carbonate, nickel oxide; Manganese source selection: manganese hydroxide, manganese carbonate, manganese oxide; or: Lithium, nickel, cobalt, and manganese sources are mixed at a target molar ratio and then mixed with zirconium oxide balls with a diameter of 0.6-1.0 mm at a ball-to-material ratio of 5:1-8:1. The mixture is ball-milled at a speed of 1700-2300 rpm for 5-12 hours. The ball-milled mixture is then calcined at a temperature of 600-1200℃ for 6-20 hours and cooled to room temperature to obtain lithium nickel cobalt manganese oxide.

[0052] The lithium source options are: lithium carbonate and lithium hydroxide. Nickel source selection: nickel hydroxide, nickel carbonate, nickel oxide; Cobalt source selection: cobalt hydroxide, cobalt carbonate, cobalt oxide; Manganese source selection: manganese hydroxide, manganese carbonate, manganese oxide; or: Lithium, iron, and phosphorus sources are mixed at a target molar ratio and then mixed with zirconium oxide balls with a diameter of 0.6-1.0 mm at a ball-to-material ratio of 5:1-8:1. The mixture is ball-milled at a speed of 1700-2300 rpm for 5-12 hours. The ball-milled mixture is then calcined at a temperature of 500-800℃ for 6-20 hours and cooled to room temperature to obtain lithium iron phosphate.

[0053] The lithium source options are: lithium carbonate and lithium hydroxide. Iron source selection: ferrous oxalate, ferrous acetate; Phosphorus source selection: ammonium phosphate, ammonium dihydrogen phosphate; The positive electrode active material, conductive agent, and binder are dispersed in N-methylpyrrolidone (NMP) at a mass ratio of (94.0~99.85):(0.05~1.0):(0.1~5.0) to obtain a positive electrode slurry. The positive electrode slurry is coated on aluminum foil to obtain an aluminum foil with the positive electrode slurry coated on its surface. After drying, it is rolled and cut to obtain a positive electrode sheet.

[0054] The adhesive is selected from polytetrafluoroethylene or polyvinylidene fluoride.

[0055] The conductive agent is selected from one or more of conductive carbon black, acetylene black, and carbon nanotubes. The method for preparing the negative electrode of the secondary battery is as follows: The negative electrode material, binder, and conductive agent are dispersed in deionized water at a mass ratio of (93.0~99.8): (0.1~2.0): (0.1~5.0) to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil. After drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0056] The negative electrode material is selected from one or more of natural graphite, artificial graphite, soft carbon, and hard carbon. The adhesive is selected from one or more of polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC); The conductive agent is selected from conductive carbon black and / or carbon nanotubes.

[0057] The preparation method of the electrolyte for secondary batteries is as follows: The solvent and lithium salt are mixed at a mass ratio of (98~99.99):(0.01:2) to obtain the electrolyte.

[0058] Solvent selection: at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents. The carbonate solvent is selected from at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC); the carboxylic acid ester solvent is selected from at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether solvent is selected from at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone solvent is selected from at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvent is selected from at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and the phosphate ester solvent is selected from at least one of trimethyl triphosphate and triethyl phosphate.

[0059] The lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0060] After obtaining the components, the positive electrode, separator, and negative electrode are stacked, wound, and assembled into a cell in sequence, packaged, injected with electrolyte, encapsulated, formed, and calibrated to obtain the secondary battery.

[0061] In this application, the electrolyte of the secondary battery is formulated with various suitable solvents and lithium salts according to actual needs, and the concentration of lithium salts is adjusted as long as normal use effect can be achieved, and is not limited to the above scheme.

[0062] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention: Example 1 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of cathode material: Li2CO3, NiCO3 and MnO2 were ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ in air for Hh, and then heated to 850℃ for 12h to obtain positive electrode active material particles LiNi 0.5 Mn 1.5 O4 was then used in an ALD atomic deposition instrument with alumina powder as raw material. The deposition pressure h was set and the number of deposition cycles was set to C cycles. Alumina was deposited on the surface of the positive electrode active material particles to obtain the positive electrode material. The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0063] Examples 2-14 A positive electrode material and a secondary battery differ from Example 1 only in that the preparation process parameters of the positive electrode material and the characteristic parameters of the obtained positive electrode material are different, as shown in Table 1.

[0064] Examples 15-18 A positive electrode material and a secondary battery differ from Example 1 only in that the preparation process parameters of the positive electrode material and the characteristic parameters of the obtained positive electrode material are different, and the raw material for ALD deposition is replaced with zirconium oxide powder, as shown in Table 1.

[0065] Examples 19-22 A positive electrode material and a secondary battery differ from Example 1 only in that the preparation process parameters of the positive electrode material and the characteristic parameters of the obtained positive electrode material are different, and the raw material for ALD deposition is replaced with tungsten oxide powder, as shown in Table 1.

[0066] Examples 23-28 A positive electrode material and a secondary battery differ from Example 1 only in that the preparation process parameters of the positive electrode material and the characteristic parameters of the obtained positive electrode material are different, as shown in Table 1.

[0067] Example 29 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of cathode material: Li2CO3, NiCO3 and MnO2 were ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ for Hh in air atmosphere, and then heated to 850℃ for 12h to obtain cathode active material particles LiNi 0.5 Mn 1.5 O4 was then used in an ALD atomic deposition system with alumina powder as the raw material. The deposition pressure was set to h, and the number of deposition cycles was set to C, to deposit alumina on the surface of the positive electrode active material particles, yielding the positive electrode material LiNi. 0.2 Mn 1.8 O4; The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0068] Example 30 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of cathode material: Li2CO3, NiCO3, Co(OH)2 and MnO2 were ball-milled at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ for Hh in an air atmosphere, and then sintered at 900℃ for 12h to obtain positive electrode active material particles LiNi 0.4 Co 0.2 Mn 0.4 O2 was then used, and alumina powder was deposited on the surface of the positive electrode active material particles using an ALD atomic deposition instrument. The deposition pressure was set to h, and the number of deposition cycles was set to C. The resulting positive electrode material was LiNi. 0.4 Co 0.2 Mn 0.4 O2; The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0069] Example 31 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of positive electrode material: Li2CO3, FeC2O4·2H2O and NH4H2PO4 were ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio. Then, they were sintered at T℃ for Hh under an argon atmosphere, and then heated to 750℃ for 12h to obtain positive electrode active material particles LiFePO4. Then, alumina powder was used as raw material in an ALD atomic deposition instrument, with the deposition pressure set to h and the number of deposition cycles set to C, to deposit alumina on the surface of the positive electrode active material particles to obtain positive electrode material LiFePO4. The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0070] Comparative Examples 1-4 A positive electrode material and a secondary battery differ from Example 1 only in that the preparation process parameters of the positive electrode material and the characteristic parameters of the obtained positive electrode material are different, as shown in Table 1.

[0071] Comparative Examples 5-6 A positive electrode material and a secondary battery differ from Example 1 only in that the preparation process parameters of the positive electrode material and the characteristic parameters of the obtained positive electrode material are different, and the raw material for ALD deposition is replaced with zirconium oxide powder, as shown in Table 1.

[0072] Comparative Example 7 A positive electrode material and a secondary battery, (1) Preparation of the positive electrode material: Li2CO3, NiCO3 and MnO2 are ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ for Hh in an air atmosphere, and then heated to 850℃ for 12h to obtain positive electrode active material particles LiNi 0.5 Mn 1.5 O4 was then used in an ALD atomic deposition system with alumina powder as the raw material. The deposition pressure was set to h, and the number of deposition cycles was set to C, to deposit alumina on the surface of the positive electrode active material particles, yielding the positive electrode material LiNi. 0.2 Mn 1.8 O4; The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0073] Comparative Example 8 A positive electrode material and a secondary battery, (1) Preparation of the positive electrode material: Li2CO3, NiCO3 and MnO2 are ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ for Hh in an air atmosphere, and then heated to 850℃ for 12h to obtain positive electrode active material particles LiNi 0.5 Mn 1.5O4 was then used in an ALD atomic deposition system with alumina powder as the raw material. The deposition pressure was set to h, and the number of deposition cycles was set to C, to deposit alumina on the surface of the positive electrode active material particles, yielding the positive electrode material LiNi. 0.2 Mn 1.8 O4; The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0074] Comparative Example 9 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of cathode material: Li2CO3, NiCO3, Co(OH)2 and MnO2 were ball-milled at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ for Hh in an air atmosphere, and then sintered at 900℃ for 12h to obtain positive electrode active material particles LiNi 0.4 Co 0.2 Mn 0.4 O2 was then used, and alumina powder was deposited on the surface of the positive electrode active material particles using an ALD atomic deposition instrument. The deposition pressure was set to h, and the number of deposition cycles was set to C. The resulting positive electrode material was LiNi. 0.4 Co 0.2 Mn 0.4 O2; The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0075] Comparative Example 10 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of cathode material: Li2CO3, NiCO3, Co(OH)2 and MnO2 were ball-milled at a rate of A for Bh according to the stoichiometric ratio, then sintered at T℃ for Hh in an air atmosphere, and then sintered at 900℃ for 12h to obtain positive electrode active material particles LiNi 0.4 Co 0.2 Mn 0.4 O2 was then used, and alumina powder was deposited on the surface of the positive electrode active material particles using an ALD atomic deposition instrument. The deposition pressure was set to h, and the number of deposition cycles was set to C. The resulting positive electrode material was LiNi. 0.4 Co 0.2 Mn 0.4 O2; The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0076] Comparative Example 11 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of positive electrode material: Li2CO3, FeC2O4·2H2O and NH4H2PO4 were ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio. Then, they were sintered at T℃ for Hh under an argon atmosphere, and then heated to 750℃ for 12h to obtain positive electrode active material particles LiFePO4. Then, alumina powder was used as raw material in an ALD atomic deposition instrument, with the deposition pressure set to h and the number of deposition cycles set to C, to deposit alumina on the surface of the positive electrode active material particles to obtain positive electrode material LiFePO4. The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0077] Comparative Example 12 A positive electrode material and a secondary battery, the preparation method of which includes the following steps: (1) Preparation of positive electrode material: Li2CO3, FeC2O4·2H2O and NH4H2PO4 were ball-milled and mixed at a rate of A for Bh according to the stoichiometric ratio. Then, they were sintered at T℃ for Hh under an argon atmosphere, and then heated to 750℃ for 12h to obtain positive electrode active material particles LiFePO4. Then, alumina powder was used as raw material in an ALD atomic deposition instrument, with the deposition pressure set to h and the number of deposition cycles set to C, to deposit alumina on the surface of the positive electrode active material particles to obtain positive electrode material LiFePO4. The preparation and characteristic parameters of the cathode material are shown in Table 1; (2) Preparation of positive electrode sheet: The positive active material, conductive carbon nanotubes and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2. The slurry is prepared by vacuum stirring and then coated on both sides of the current collector aluminum foil. After drying, cold pressing and cutting, the positive electrode sheet is obtained. The resistance value of the obtained positive electrode is directly measured using a resistance meter; (3) Preparation of negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material is graphite. (4) Selection of diaphragm: Select commercially available polyethylene diaphragm with a thickness of 15μm; (5) Preparation of electrolyte: Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (6) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing for 24 hours, formation and volume adjustment, the secondary battery is obtained.

[0078] Table 1 Example of effect The cathode materials and secondary batteries obtained in each embodiment and comparative example were tested as follows: (1) Test the resistance value of the positive electrode: As described above, the test is performed directly and will not be repeated here; (2) High-temperature cycling performance test: The secondary batteries obtained in each example and comparative example were pre-charged to the upper voltage limit and the rate of 0.33C using the LAND charge-discharge system at room temperature; then discharged to the lower voltage limit and the rate of 0.33C, and cycled twice. Then, they were placed in a 45°C environment and charged and discharged 100 times at the same operating voltage using the same system and the rate of 1C / 1C. The discharge capacity at each cycle was counted. Finally, the high-temperature cycling capacity retention rate (%) was calculated as: discharge capacity of secondary battery after 100 cycles of 1C / 1C / discharge capacity of secondary battery after the first 1C / 1C cycle. The secondary batteries obtained in Examples 1-29 and Comparative Examples 1-8 have a lower voltage limit of 2.5V and an upper voltage limit of 4.25V. The secondary batteries obtained in Example 30 and Comparative Examples 9-10 have a lower voltage limit of 3.7V and an upper voltage limit of 4.2V. The secondary batteries obtained in Example 31 and Comparative Examples 11-12 have a lower voltage limit of 2.2V and an upper voltage limit of 3.7V. (3) High-temperature storage performance test: The secondary batteries obtained in each example and comparative example were pre-charged to the upper voltage limit and the rate of 0.33C using the LAND charge-discharge system at room temperature; then discharged to the lower voltage limit and the rate of 0.33C, and cycled twice. After that, they were placed in a 45°C environment for static storage for 15 days. After storage, they were taken out and cycled once at the same system and the same working voltage and the same rate at room temperature. Finally, the high-temperature storage capacity retention rate (%) was calculated as: discharge capacity of the secondary battery after 0.33C cycle at room temperature / discharge capacity of the secondary battery after 0.33C cycle at room temperature. The secondary batteries obtained in Examples 1-29 and Comparative Examples 1-8 have a lower voltage limit of 2.5V and an upper voltage limit of 4.25V. The secondary batteries obtained in Example 30 and Comparative Examples 9-10 have a lower voltage limit of 3.7V and an upper voltage limit of 4.2V. The secondary batteries obtained in Example 31 and Comparative Examples 11-12 have a lower voltage limit of 2.2V and an upper voltage limit of 3.7V. The test results are shown in Table 2.

[0079] Table 2 As can be seen from Table 2: (1) The cathode material described in this application, by setting a coating layer on the surface of the cathode active material and simultaneously controlling the roundness of the coated cathode material and the ratio of the content of free transition metal ions after acid corrosion, coordinates the balance between stability and conductivity in the cathode material, so that the secondary battery prepared by the cathode material has ideal electrochemical performance. It can be seen that the resistance value of the cathode sheet obtained in each embodiment is low, with a maximum of only 300mΩ. The secondary battery prepared by the cathode sheet can achieve a cycle capacity retention rate of at least 80% under high temperature environment, and after 15 days of high temperature storage, the capacity retention rate of the battery can reach at least 79%, with excellent comprehensive performance. In contrast, although the cathode materials obtained in Comparative Examples 1 to 10 also have a coating layer constructed, the balance between roundness and stability of transition metal elements is not well controlled. The cathode material not only cannot guarantee a low resistance value after being prepared into a cathode sheet, but also has poor high temperature performance, and cannot achieve ideal high temperature stability after being prepared into a secondary battery.

[0080] (2) As can be seen from Examples 1-15 and Examples 16-29, the types of positive active materials and coating layers are not limited when setting the positive electrode material in this application. In particular, when the positive active material is lithium nickel manganese oxide, when K / Rn is controlled in the range of 0.3-0.5, the positive active material particles have a good coating effect, the edges are fully coated and the surface is smooth, the dissolution rate of transition metal elements is lower, and the conductivity is higher. The overall effect is better, and the resistance value of the positive electrode sheet prepared by the positive electrode material can be maintained within 270mΩ. Moreover, the capacity retention rate after high temperature cycling and high temperature storage can reach more than 85%.

[0081] (3) When regulating the positive electrode material, the roundness of the positive electrode active material particles after the coating layer is set will affect the overall coating integrity and regularity of the particles, which will lead to different contact areas when the material particles come into contact with the electrolyte. This will result in different compaction and structural stability when used to prepare the electrode sheet. When the roundness of the material is preferably in the range of 0.6 to 0.7, the positive electrode active material particles can achieve a moderate contact area when in contact with the electrolyte. The degree of coating can be used to control the balance between the dissolution probability of transition metal ions and the ease of ion / electron transport. At the same time, ideal electrode stability and compactness can be achieved when preparing the positive electrode sheet. On the other hand, after acid etching, the proportion of free transition metal elements in the positive electrode active material particles will be affected. The size of K is related to the type of positive electrode active material and the coating effect of the coating layer. Therefore, the size of K also affects the ion / electron transport capability and structural stability of the positive electrode active material particles. When the K value of the positive electrode active material particles is preferably in the range of 0.2~0.3%, the resulting positive electrode material has better structural stability and conductivity. When the obtained positive electrode material satisfies both of these preferences and the ratio of the components is also within the preferred range, the positive electrode sheet prepared from the obtained positive electrode material can not only maintain a resistance value of less than 230mΩ, but also, when applied to the preparation of secondary batteries, the capacity retention rate after high-temperature cycling and high-temperature storage can reach more than 90%, with the highest high-temperature cycling capacity retention rate reaching 95%, and the capacity retention rate after high-temperature storage reaching 94%.

Claims

1. A positive electrode plate, characterized in that, The device includes a positive electrode material and a conductive agent. The positive electrode material includes positive electrode active material particles, the positive electrode active material particles are provided with a coating layer, the positive electrode active material particles include lithium nickel manganese oxide, and the coating layer includes a metal oxide. The positive electrode material satisfies: 0.3 ≤ K / Rn ≤ 1.0; The K% refers to the percentage of free transition metal elements in the positive electrode active material particles after soaking them in a 20wt% hydrofluoric acid solution at 70℃ with a solid-liquid ratio of 1g:5mL for 72 hours. Rn represents the roundness of the positive electrode active material particles; The conductive agent includes one or more of conductive carbon black, acetylene black, and carbon nanotubes.

2. The positive electrode sheet as described in claim 1, characterized in that, The condition is 0.4≤Rn≤0.

8.

3. The positive electrode sheet as described in claim 2, characterized in that, The condition is 0.6≤Rn≤0.

7.

4. The positive electrode sheet as described in claim 1, characterized in that, The value is 0.1% ≤ K ≤ 0.5%.

5. The positive electrode sheet as described in claim 4, characterized in that, The value is 0.2%≤K≤0.3%.

6. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode active material particles also include at least one of lithium nickel cobalt manganese oxide particles and lithium iron phosphate particles.

7. The positive electrode sheet as described in claim 6, characterized in that, The positive electrode active material particles include lithium nickel manganese oxide particles, wherein 0.3≤K / Rn≤0.

5.

8. The positive electrode sheet as described in claim 1, characterized in that, The metal oxide in the coating layer includes at least one of aluminum oxide, tungsten oxide, and zirconium oxide.

9. A secondary battery, characterized in that, The secondary battery includes the positive electrode sheet as described in any one of claims 1 to 8; the secondary battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes at least one of carbon-based materials, silicon-based materials, and silicon-carbon composite materials.

10. The secondary battery as described in claim 9, wherein the negative electrode active material comprises at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.

11. The secondary battery as claimed in claim 9, further comprising an electrolyte, the electrolyte comprising a solvent and a lithium salt, wherein the solvent and the lithium salt are in a mass ratio of (98~99.99):(0.01:2).

12. The secondary battery of claim 11, wherein the solvent comprises at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

13. The secondary battery of claim 11, wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 9 to 13, wherein the secondary battery serves as the power supply for the electrical device.

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