A positive electrode material, a secondary battery

Abstract

The application discloses a positive electrode material and a secondary battery, and belongs to the technical field of batteries. The material is provided with a coating layer on the surface of a positive electrode active material. Meanwhile, the roundness of the coated positive electrode material and the ratio of the content of free transition metal ions after acid corrosion are regulated, the balance between stability and conductivity in the positive electrode material is coordinated, the secondary battery prepared from the positive electrode material has ideal electrochemical performance, and especially has relatively optimal cycle stability and storage capacity retention rate in a high-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode material and a secondary battery. BACKGROUND

[0002] In existing secondary batteries, especially lithium ion secondary batteries, the mainstream positive electrode active material includes ternary lithium nickel cobalt manganese oxide material, lithium iron phosphate and spinel structure lithium nickel manganese oxide, etc. These materials have ideal electrochemical activity, but all have the problem of transition metal ion elution (for ternary materials, it is the elution of nickel, cobalt and manganese, while for lithium iron phosphate, it is iron, and for lithium nickel manganese oxide, it is nickel and manganese). After the transition metal ions elute, the probability of the side reaction of the transition metal ions with the electrolyte increases, the gas production increases, and the performance of the secondary battery deteriorates. Especially in a high temperature environment, the degree of side reaction increases, and even safety problems may be caused.

[0003] Therefore, people try to modify the positive electrode active material by coating, so that the elution of transition metal ions is reduced by the inert protection of the coating layer. However, the coating layer material used in this method is mostly an insulating or semi-insulating material with low conductivity, which affects the ion / electron transport efficiency of the positive electrode active material. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a positive electrode material. The positive electrode material has a coating layer on the surface of the positive electrode active material, and the roundness of the coated positive electrode material and the ratio of the content of free transition metal ions after acid corrosion are adjusted. The balance between stability and conductivity in the positive electrode material is coordinated, so that the secondary battery prepared from the positive electrode material has ideal electrochemical performance, especially good cycle stability and storage capacity retention rate in a high temperature environment.

[0005] To achieve the above purpose, in the first aspect of the present application, the present application provides a positive electrode material, comprising positive electrode active material particles, the positive electrode active material particles being provided with a coating layer, the coating layer comprising a metal oxide;

[0006] The positive electrode material satisfies 0.2≤K / Rn≤1.2.

[0007] The K% is the content ratio of the free transition metal elements of the positive electrode active material particles to the content of transition metal elements in the positive electrode active material particles after the positive electrode active material particles are soaked in a 20wt% concentration hydrofluoric acid solution at a solid-liquid ratio of 1g:5mL at 70℃ for 72h.

[0008] The Rn is the roundness of the positive electrode active material particles.

[0009] The present application has the following beneficial effects:

[0010] The application provides a positive electrode material, which is provided with a coating layer on the surface of a positive electrode active material, and the roundness of the coated positive electrode material and the ratio of the content of free transition metal ions after acid corrosion are regulated, the balance between stability and conductivity in the positive electrode material is coordinated, so that the secondary battery prepared from the positive electrode material has ideal electrochemical performance, especially better cycle stability and storage capacity retention rate in a high temperature environment. DETAILED DESCRIPTION

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are some but not all of the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0012] In the application, the technical features described in an open form include a closed technical solution composed of listed features, and also include an open technical solution containing listed features.

[0013] In the application, if no special description is given, 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.

[0014] The application will be further described below with specific embodiments:

[0015] A positive electrode material includes positive electrode active material particles, the positive electrode active material particles are provided with a coating layer, and the coating layer includes a metal oxide.

[0016] The positive electrode material satisfies 0.2≤K / Rn≤1.2.

[0017] The K% is the content ratio of the free transition metal element in the positive electrode active material particles after the positive electrode active material particles are soaked in a 20wt% concentration hydrofluoric acid solution at a solid-liquid ratio of 1g:5mL at 70°C for 72h.

[0018] The Rn is the roundness of the positive electrode active material particles.

[0019] Before being used as a positive electrode material, the positive electrode active material is generally provided with an inert metal oxide coating layer on the surface of the particle to inhibit the occurrence of the dissolution of transition metal elements in the particle during the cyclic charging and discharging process and the increase in the probability of side reactions after the particle is in contact with the electrolyte. The coating layer inhibits such phenomena through the isolation and protection of the coating layer. However, the introduction of the coating layer hinders the ion / electron transport kinetics of the positive electrode active material particle and reduces the conductivity of the overall positive electrode active material particle, and ultimately the electrochemical performance is low. To overcome this technical difficulty, the technical solution of the present application provides a metal oxide coating layer on the surface of the positive electrode active material particle, and adjusts the coating effect of the coating layer by regulating the roundness of the coated positive electrode active material particle and the ratio of the content of free transition metal ions after acid etching, so as to balance the stability of the overall material and the ion / electron transport kinetics after coating. The roundness of the positive electrode active material particle is related to the irregularity of the particle form and the surface flatness, thereby affecting the contact effect when the particle is in contact with the electrolyte and the overall path length of ion / electron transport. On the other hand, after the coating layer is provided, the degree of freedom of the transition metal elements changes, and by regulating the free content of the transition metal elements after acid etching of the positive electrode active material particle, the structural stability and ion / electron conductivity of the material can be simultaneously regulated. When the ratio K / Rn of the two key factors is controlled to be in the range of 0.2 to 1.2, the positive electrode material can balance the conductivity and structural stability when applied to a secondary battery, the probability of side reactions after the material is in contact with the electrolyte is reduced, and at the same time, the ion / electron transport kinetics of the material itself is not weakened, and the secondary battery can exhibit excellent electrochemical performance. If the ratio K / Rn is not properly set, the probability of side reactions between the positive electrode active material particle and the electrolyte may be too large, affecting the service life of the secondary battery and even causing safety problems, or the charging and discharging efficiency of the secondary battery is low, and the energy density is reduced.

[0020] In some embodiments, the K / Rn is one of or a range value of any two of 0.2, 0.25, 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, 1.05, 1.1, 1.15, 1.2.

[0021] In some embodiments, the 0.4≤Rn≤0.8.

[0022] Further preferably, the Rn is one of or a range value of any two of 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8.

[0023] Further preferably, the 0.6≤Rn≤0.7.

[0024] When the roundness of the positive electrode active material particle after the coating layer is set is low, it indicates that the flatness of the particle surface after coating is low, and the irregularity of the particle is high. When the roundness is high, it indicates that the coating completeness of the particle is good, and the regularity of the particle is also high. The contact area of the positive electrode active material particles with different roundness when contacting with the electrolyte is also different. At the same time, the regularity of the particle also makes the compaction tightness and structural stability when used for preparing the electrode sheet different. When the roundness is preferably within the above range, the positive electrode active material particle can achieve moderate contact area when contacting with the electrolyte, and the balance of the transition metal ion dissolution probability and the ion / electron transmission difficulty of the material can be adjusted by the coating degree. At the same time, the ideal electrode sheet stability and compactness can be achieved when preparing the positive electrode sheet, so that the overall electrochemical performance of the material is better.

[0025] It should be noted that the test method of the roundness Rn of the positive electrode material active material particle described in the present application is as follows: the positive electrode material is dispersed in ethanol, and then the FC200s+HR type particle morphology analyzer of OCCHIO company is used as the test instrument (the camera resolution is 10 million pixels, the telephoto lens is Callisto 2012 version analysis processing software), the positive electrode material ethanol dispersion is pumped into the instrument sample pool through a 5 mm sample tube, and after image acquisition and analysis, the average value of Ai and A of the positive electrode material is confirmed, wherein Ai is the maximum inscribed circle area of the positive electrode active material particle, and A is the projection area of the positive electrode active material particle. Finally, the software automatically calculates the roundness of the positive electrode active material particle in the positive electrode material through Rn=Ai / A.

[0026] In some embodiments, the roundness of the positive electrode active material particle can be adjusted by the calcination temperature and calcination time in the preparation process, but it is not limited thereto. According to the actual needs, the person skilled in the art can also adjust it through common positive electrode active material particle preparation or processing means such as ball milling process, spray treatment process, etc.

[0027] In some embodiments, the 0.1%≤K≤0.5%.

[0028] Further preferably, the K is one of 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% or a range value of any two thereof.

[0029] Further preferably, the 0.2%≤K≤0.3%.

[0030] The content of free transition metal elements in the positive electrode active material particles after acid etching is related to the type of positive electrode active material and the coating effect of the coating layer, so the size of K also affects the ion / electron transport capacity 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.

[0031] It should be noted that the test method of the K value of the positive electrode active material particles described in the present application is as follows: the positive electrode material is placed in a 40wt% sodium hydroxide solution for digestion treatment, and then tested by ICP. The ICP test conditions are as follows: select the element detection spectrum wavelength, set appropriate ICP instrument working conditions according to the characteristics of the sample and the elements to be detected, including gas flow 0.5L / min, power 1150W; the content of transition elements is tested by ICP to confirm the total content of transition metal elements M1 in the positive electrode active material particles (for example, if the positive electrode active material is lithium nickel manganese oxide, the total content of transition metal elements is the total content of nickel and manganese elements; if it is lithium iron phosphate, it is the total content of iron elements; if it is lithium nickel cobalt manganese oxide, it is the total content of nickel, cobalt and manganese elements); then, the parallel sample is placed in a 20wt% hydrofluoric acid solution at a solid-liquid ratio of 1g:5mL at 70°C and soaked for 72h, and the supernatant of the hydrofluoric acid solution is taken for ICP test. The ICP test conditions are as follows: select the element detection spectrum wavelength, set appropriate ICP instrument working conditions according to the characteristics of the sample and the elements to be detected, including gas flow 0.5L / min, power 1150W; the content of transition elements is tested by ICP to confirm the total content of free transition metal elements M2 after acid etching, and the final result is calculated according to K=M2 / M1*100%.

[0032] In some embodiments, the K can be controlled by the number of deposition circles of the coating layer during ALD atomic layer deposition, but it is not limited thereto. Those skilled in the art can also adjust other conditions during deposition and other process conditions such as temperature and time during sintering of the positive electrode active material particles according to actual needs.

[0033] In some embodiments, the metal oxide includes at least one of aluminum oxide, tungsten oxide, and zirconium oxide.

[0034] The metal oxide as the coating layer of the positive electrode active material particles can protect it from being corroded by acidic substances such as hydrofluoric acid in the electrolyte when it is in contact with the electrolyte, thereby generating by-products and affecting its electrochemical activity and service life; but the metal oxide is not limited to the above three, and other metal oxides with similar inert protection effect can be used instead of the above three.

[0035] In some embodiments, the average particle size Dv50 of the positive electrode active material particles is 4-8 pm;

[0036] In the present application, the average particle size of the positive electrode active material particles is directly tested by a laser particle size analyzer.

[0037] In some embodiments, the concentration of the metal oxide in the positive electrode material is 100-4000 ppm.

[0038] In some embodiments, the positive electrode active material particles include at least one of lithium nickel cobalt manganese oxide particles, lithium iron phosphate particles, and lithium nickel manganese oxide particles.

[0039] The positive electrode active material particles in the positive electrode material described in the present application can be lithium nickel manganese oxide particles, which are high-voltage positive electrode materials, or ternary lithium nickel cobalt manganese oxide particles with a layered structure, whose chemical formula is LiNi x Co y Mn (1-x-y) O2, wherein 0 x Mn 1-x PO4, wherein 0

[0040] In some embodiments, the positive electrode active material particles further include at least one of doped lithium nickel cobalt manganese oxide particles, doped lithium iron phosphate particles, and doped lithium nickel manganese oxide particles.

[0041] For the above three active material particles that are modified by doping, the modification means in the present application and the positive electrode material obtained after the modification can also achieve ideal improvement of electrochemical performance, and therefore the positive electrode active material particles in the present application are not limited to the three systems of undoped positive electrode materials.

[0042] In some embodiments, the positive electrode active material particles include lithium nickel manganese oxide particles, and the 0.3

[0043] In some embodiments, the positive electrode active material particles are LiNi x Mn y O4, wherein 0

[0044] Compared with ternary materials or lithium iron phosphate materials, the working voltage of the lithium nickel manganese oxide particles is relatively high, and the stability is relatively poor. The structure of the lithium nickel manganese oxide particles has many edges and corners, and the surface flatness is low. Therefore, the coating effect of the coating layer needs to be specially controlled to avoid the edges and corners of the surface being broken during the rolling of the electrode sheet, which causes the coating layer on the surface to be partially invalid, and the probability of the side reaction with the electrolyte increases. When the K / Rn is controlled to be in the range of 0.3-0.5, the coating effect of the positive electrode active material particles is good, the edges and corners are fully coated, the surface flatness is high, the transition metal element dissolution rate is lower, the conductivity effect is higher, and the comprehensive use effect is more optimal.

[0045] In embodiments, the application further provides a positive electrode sheet comprising the positive electrode material.

[0046] In some embodiments, the positive electrode sheet comprises a current collector and a positive electrode material layer, and the positive electrode material layer comprises the positive electrode material.

[0047] In some embodiments, the positive electrode material layer further comprises a conductive agent and a binder.

[0048] Further preferably, the conductive agent comprises at least one of acetylene black and carbon nanotubes, and the binder comprises polyvinylidene fluoride.

[0049] In embodiments, the application further provides a secondary battery comprising the positive electrode sheet.

[0050] In some embodiments, the secondary battery further comprises a negative electrode sheet and an electrolyte.

[0051] In some embodiments, the negative electrode sheet comprises a negative electrode active material.

[0052] In some embodiments, the negative electrode active material comprises at least one of a carbon-based material, a silicon-based material, and a silicon-carbon composite material.

[0053] Further preferably, the negative electrode material layer comprises a negative electrode material, a binder, a thickening agent, and a conductive agent.

[0054] In some embodiments, the electrolyte comprises a solvent and a lithium salt.

[0055] In some embodiments, the solvent comprises at least one of a carbonate-based solvent, a carboxylic acid ester-based solvent, an ether-based solvent, a sulfone-based solvent, a nitrile-based solvent, and a phosphate-based solvent.

[0056] Exemplarily, the carbonate-based solvent includes, but is not limited to, 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-based solvent includes, but is not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether-based solvent includes at least one of dimethyl tetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone-based solvent includes at least one of methyl sulfone and dimethyl sulfoxide; the nitrile-based solvent includes at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetricarbonitrile; and the phosphate-based solvent includes at least one of trimethyl phosphate and triethyl phosphate.

[0057] Further preferably, the solvent can further include, but is not limited to, at least one of a carbonate-based solvent fluorinated derivative, a carboxylic acid ester-based solvent fluorinated derivative, an ether-based solvent fluorinated derivative, a sulfone-based solvent fluorinated derivative, a nitrile-based solvent fluorinated derivative, and a phosphate-based solvent fluorinated derivative.

[0058] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorobisoxalate borate, lithium triflate, lithium bisfluoromethanesulfonimide, lithium bis-trifluoromethanesulfonimide, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, and the like.

[0059] Further preferably, the concentration of the lithium salt in the electrolyte is 0.8-2.5 mol / L.

[0060] Further preferably, the concentration of the lithium salt in the electrolyte is one of 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, 2.5 mol / L or a range value of any two thereof.

[0061] In some embodiments, the secondary battery is prepared by the following method:

[0062] Preparation of the positive active material:

[0063] The lithium source, the nickel source, and the manganese source are mixed in a target molar ratio, and zirconium oxide balls with a diameter of 0.6-1.0 mm are mixed in a ball-to-material ratio of 5:1-8:1, and the mixture is ball-milled at a rotation speed of 1700-2300 rpm for 5-12 h, and then the ball-milled mixture is calcined at a temperature of 600-1200 ℃ for 6-20 h and cooled to room temperature to obtain spinel lithium nickel manganese oxide.

[0064] The lithium source is selected from: lithium carbonate, lithium hydroxide;

[0065] Nickel source selection: nickel hydroxide, nickel carbonate, nickel oxide;

[0066] Manganese source selection: manganese hydroxide, manganese carbonate, manganese oxide;

[0067] Or:

[0068] Mix the lithium source, nickel source, cobalt source and manganese source according to the target molar ratio, and mix with zirconium oxide balls with a diameter of 0.6-1.0 mm at a ball-to-material ratio of 5:1-8:1, under the condition of a rotation speed of 1700-2300 rpm, ball mill mixing for 5-12 h, and then calcine the ball-milled mixture at a temperature of 600-1200 ℃ for 6-20 h and cool to room temperature to obtain lithium nickel cobalt manganese oxide.

[0069] The lithium source is selected from: lithium carbonate, lithium hydroxide;

[0070] The nickel source is selected from: nickel hydroxide, nickel carbonate, nickel oxide;

[0071] The cobalt source is selected from: cobalt hydroxide, cobalt carbonate, cobalt oxide;

[0072] The manganese source is selected from: manganese hydroxide, manganese carbonate, manganese oxide;

[0073] Or:

[0074] Mix the lithium source, iron source and phosphorus source according to the target molar ratio, and mix with zirconium oxide balls with a diameter of 0.6-1.0 mm at a ball-to-material ratio of 5:1-8:1, under the condition of a rotation speed of 1700-2300 rpm, ball mill mixing for 5-12 h, and then calcine the ball-milled mixture at a temperature of 500-800 ℃ for 6-20 h and cool to room temperature to obtain lithium iron phosphate.

[0075] The lithium source is selected from: lithium carbonate, lithium hydroxide;

[0076] The iron source is selected from: ferrous oxalate, ferrous acetate;

[0077] The phosphorus source is selected from: ammonium phosphate, ammonium dihydrogen phosphate;

[0078] The positive electrode active material, the conductive agent, and the binder are dispersed in N-methyl pyrrolidone (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 an aluminum foil to obtain an aluminum foil coated with a positive electrode slurry. After drying, rolling, and cutting, a positive electrode sheet is obtained.

[0079] The binder is selected from polytetrafluoroethylene or polyvinylidene fluoride.

[0080] The conductive agent is selected from one or more of conductive carbon black, acetylene black, and carbon nanotubes.

[0081] The preparation method of the negative electrode sheet of the secondary battery is:

[0082] The negative electrode material, the binder and the conductive agent are dispersed in deionized water according to a mass ratio of (93.0-99.8):(0.1-2.0):(0.1-5.0) to obtain a negative electrode slurry, and the negative electrode slurry is coated on a copper foil; after drying, cold pressing and slitting, the negative electrode sheet is obtained.

[0083] The negative electrode main material is selected from one or more of natural graphite, artificial graphite, soft carbon and hard carbon;

[0084] The binder is selected from one or more of polyacrylic acid (PAA), styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC);

[0085] The conductive agent is selected from conductive carbon black and / or carbon nanotubes.

[0086] The preparation method of the electrolyte of the secondary battery is:

[0087] The solvent and the lithium salt are mixed according to a mass ratio of (98-99.99):(0.01:2) to obtain the electrolyte.

[0088] The solvent is at least one of a carbonate solvent, a carboxylate solvent, an ether solvent, a sulfone solvent, a nitrile solvent and a phosphate solvent.

[0089] The carbonate solvent is at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC); the carboxylate solvent is at least one of ethyl acetate, methyl formate and 1,4-butyrolactone; the ether solvent is at least one of dimethyl tetrahydrofuran, tetrahydrofuran and 1,2-dimethoxyethane; the sulfone solvent is at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvent is at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole and 1,3,6-hexanetricarbonitrile; and the phosphate solvent is at least one of trimethyl phosphate and triethyl phosphate.

[0090] The lithium salt is 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 difluorophosphate borate (LiDFOB), lithium difluorophosphate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorophosphate (LiDFOP) and lithium tetrafluorophosphate (LiTFOP).

[0091] After obtaining the components, the positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked and wound to assemble a battery cell, which is packaged, injected with electrolyte, packaged, formed, and fixed volume to obtain the secondary battery.

[0092] The electrolyte of the secondary battery is compounded by various suitable solvents and lithium salts according to actual needs, and the concentration of the lithium salt is adjusted, as long as the normal use effect can be achieved, and is not limited by the scheme.

[0093] The application is further described below with specific examples, which cannot be understood as limiting the scope of the application:

[0094] Example 1

[0095] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0096] (1) Preparation of the positive electrode material: Li2CO3, NiCO3 and MnO2 are mixed at a metering ratio under A rate ball milling for Bh, and then sintered at T ℃ for H h in an air atmosphere, and then sintered at 850 ℃ for 12 h, to obtain positive electrode active material particles LiNi 0.5 Mn 1.5 O4, and then using an ALD atomic deposition instrument with aluminum oxide powder as raw material, setting the deposition pressure to h, and setting the deposition number of circles to C circles, to deposit aluminum oxide on the surface of the positive electrode active material particles to obtain the positive electrode material;

[0097] The preparation and characteristic parameters of the positive electrode material are shown in Table 1;

[0098] (2) Preparation of the positive electrode sheet: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, and the slurry is prepared by vacuum stirring, and then coated on both sides of the current collector aluminum foil, and then dried, cold-pressed, and cut to obtain the positive electrode sheet;

[0099] The resistance value of the obtained positive electrode sheet is directly tested by using a resistance meter;

[0100] (3) Preparation of the negative electrode sheet: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and the slurry is prepared by vacuum stirring, and then coated on both sides of the current collector copper foil, and then dried, cold-pressed, and cut to obtain the negative electrode sheet, and the negative electrode material is graphite;

[0101] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm is selected;

[0102] (5) Preparation of electrolyte: ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0103] (6) The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked and wound to assemble a battery cell. The battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing for 24 h, formation, and constant volume, the secondary battery is obtained.

[0104] Examples 2-14

[0105] A positive electrode material and a secondary battery, which 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.

[0106] Examples 15-18

[0107] A positive electrode material and a secondary battery, which 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.

[0108] Examples 19-22

[0109] A positive electrode material and a secondary battery, which 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.

[0110] Examples 23-28

[0111] A positive electrode material and a secondary battery, which 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.

[0112] Example 29

[0113] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0114] (1) Preparation of positive electrode material: Li2CO3, NiCO3, and MnO2 are mixed at a metering ratio under A rate for Bh, then sintered at T ℃ for H h in an air atmosphere, and then sintered at 850 ℃ for 12 h. The obtained positive active material particles LiNi 0.5 Mn 1.5 O4, then an ALD atomic deposition instrument is used to deposit aluminum oxide powder as a raw material, the deposition pressure is set to h, the deposition number of circles is set to C, and aluminum oxide is deposited on the surface of the positive active material particles to obtain a positive electrode material LiNi0.2 Mn 1.8 O4;

[0115] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0116] (2) Preparation of the positive electrode tab: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut, and the positive electrode tab is obtained.

[0117] The resistance value of the obtained positive electrode tab is directly tested by using a resistance meter.

[0118] (3) Preparation of the negative electrode tab: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut, and the negative electrode tab is obtained, and the negative electrode material is graphite.

[0119] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm is selected.

[0120] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0121] (6) The positive electrode tab, the separator, and the negative electrode tab are sequentially stacked and wound to assemble a battery cell, the battery cell is placed in an outer packaging shell, dried, and then injected with the electrolyte, vacuum packaged, and placed for 24 h, and then formed, constant volume, and the secondary battery is obtained.

[0122] Example 30

[0123] A positive electrode material and a secondary battery, and the preparation method comprises the following steps:

[0124] (1) Preparation of the positive electrode material: Li2CO3, NiCO3, Co(OH)2, and MnO2 are mixed at a metering ratio by ball milling at a rate of A for Bh, then sintered at T ℃ for H h in an air atmosphere, and then sintered at 900 ℃ for 12 h, and the obtained positive electrode active material particles LiNi 0.4 Co 0.2 Mn 0.4 O2, and then aluminum oxide is deposited on the surface of the positive electrode active material particles by using an ALD atomic deposition instrument with aluminum oxide powder as the raw material, the deposition pressure is set to h, and the number of deposition circles is set to C, and the positive electrode material LiNi 0.4 Co0.2 Mn 0.4 O2;

[0125] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0126] (2) Preparation of the positive electrode tab: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut, to obtain the positive electrode tab;

[0127] The resistance value of the obtained positive electrode tab is directly tested by using a resistance meter;

[0128] (3) Preparation of the negative electrode tab: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut, to obtain the negative electrode tab, and the negative electrode material is graphite;

[0129] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm is selected;

[0130] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0131] (6) The positive electrode tab, the separator, and the negative electrode tab are sequentially stacked and wound to assemble a cell, the cell is placed in an outer packaging shell, the electrolyte is injected after drying, vacuum packaging, standing for 24 h, formation, and constant volume, to obtain the secondary battery.

[0132] Example 31

[0133] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0134] (1) Preparation of the positive electrode material: Li2CO3, FeC2O4·2H2O, and NH4H2PO4 are mixed at a metering ratio by ball milling at a rate of A for Bh, then sintered at T ℃ for H h under an argon atmosphere, and then sintered at 750 ℃ for 12 h, to obtain positive electrode active material particles LiFePO4, then an ALD atomic deposition instrument is used to deposit aluminum oxide on the surface of the positive electrode active material particles by using aluminum oxide powder as a raw material, setting the deposition pressure at h, and setting the number of deposition circles at C, to obtain the positive electrode material LiFePO4;

[0135] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0136] (2) Preparation of the positive electrode sheet: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, the slurry was prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut to obtain the positive electrode sheet;

[0137] The resistance value of the obtained positive electrode sheet was directly tested by using a resistance meter;

[0138] (3) Preparation of the negative electrode sheet: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber were dispersed in water at a mass ratio of 96.4:1:1.2:1.4, the slurry was prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut to obtain the negative electrode sheet, and the negative electrode material was graphite;

[0139] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm was selected;

[0140] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 was added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0141] (6) The positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked and wound to assemble a battery cell, the battery cell was placed in an outer packaging shell, the electrolyte was injected after drying, vacuum packaging, standing for 24 h, formation, and constant volume, to obtain the secondary battery.

[0142] Comparative Examples 1-4

[0143] A kind of positive electrode material, secondary battery, and the difference with Example 1 only lies 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.

[0144] Comparative Examples 5-6

[0145] A kind of positive electrode material, secondary battery, and the difference with Example 1 only lies 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 of the ALD deposition is replaced with zirconium oxide powder, as shown in Table 1.

[0146] Comparative Example 7

[0147] A kind of positive electrode material, secondary battery, (1) preparation of the positive electrode material: Li2CO3, NiCO3 and MnO2 were mixed at a metering ratio under A rate ball milling Bh, then sintered at T ℃ under air atmosphere H h, and then heated to 850 ℃ and sintered for 12 h, to obtain the positive electrode active material particles LiNi 0.5 Mn1.5 O4, and then using an ALD atomic deposition instrument with aluminum oxide powder as a raw material, setting a deposition pressure h, and setting a deposition number of C circles, depositing aluminum oxide on the surface of the positive electrode active material particles to obtain a positive electrode material LiNi 0.2 Mn 1.8 O4.

[0148] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0149] (2) Preparation of the positive electrode sheet: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone according to a mass ratio of 97:1:2, and a slurry was prepared by vacuum stirring, and then coated on both sides of the current collector aluminum foil, and then dried, cold-pressed, and cut to obtain the positive electrode sheet.

[0150] The resistance value of the obtained positive electrode sheet was directly tested by using a resistance meter.

[0151] (3) Preparation of the negative electrode sheet: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber were dispersed in water according to a mass ratio of 96.4:1:1.2:1.4, and a slurry was prepared by vacuum stirring, and then coated on both sides of the current collector copper foil, and then dried, cold-pressed, and cut to obtain the negative electrode sheet, and the negative electrode material was graphite.

[0152] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm was selected.

[0153] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate were mixed according to a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0154] (6) The positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked and wound to assemble a battery cell, the battery cell was placed in an outer packaging shell, and after drying, the electrolyte was injected, vacuum packaged, and statically placed for 24 h, and then formed, constant volume, to obtain the secondary battery.

[0155] Comparative Example 8

[0156] A positive electrode material and a secondary battery, (1) Preparation of the positive electrode material: Li2CO3, NiCO3, and MnO2 were ball-milled at an A rate for Bh, and then sintered at T ℃ for H h in an air atmosphere, and then heated to 850 ℃ for 12 h, to obtain positive electrode active material particles LiNi 0.5 Mn 1.5 O4, and then using an ALD atomic deposition instrument with aluminum oxide powder as a raw material, setting a deposition pressure h, and setting a deposition number of C circles, depositing aluminum oxide on the surface of the positive electrode active material particles to obtain a positive electrode material LiNi0.2 Mn 1.8 O4;

[0157] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0158] (2) Preparation of the positive electrode tab: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut, to obtain the positive electrode tab;

[0159] The resistance value of the obtained positive electrode tab is directly tested by using a resistance meter;

[0160] (3) Preparation of the negative electrode tab: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut, to obtain the negative electrode tab, and the negative electrode material is graphite;

[0161] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm is selected;

[0162] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0163] (6) The positive electrode tab, the separator, and the negative electrode tab are sequentially stacked and wound to assemble a battery cell, the battery cell is placed in an outer packaging shell, the electrolyte is injected after drying, vacuum packaging, standing for 24 h, formation, and constant volume, to obtain the secondary battery.

[0164] Comparative Example 9

[0165] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0166] (1) Preparation of the positive electrode material: Li2CO3, NiCO3, Co(OH)2, and MnO2 are mixed at a metering ratio by ball milling at a rate of A for Bh, then sintered at T ℃ for H h in an air atmosphere, and then sintered at 900 ℃ for 12 h, to obtain positive electrode active material particles LiNi 0.4 Co 0.2 Mn 0.4 O2, then aluminum oxide powder is used as a raw material by using an ALD atomic deposition instrument, the deposition pressure is set to h, the number of deposition circles is set to C, and aluminum oxide is deposited on the surface of the positive electrode active material particles, to obtain the positive electrode material LiNi 0.4 Co0.2 Mn 0.4 O2;

[0167] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0168] (2) Preparation of the positive electrode tab: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut, and the positive electrode tab is obtained.

[0169] The resistance value of the obtained positive electrode tab is directly tested by using a resistance meter.

[0170] (3) Preparation of the negative electrode tab: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, a slurry is prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut, and the negative electrode tab is obtained, and the negative electrode material is graphite.

[0171] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm is selected.

[0172] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0173] (6) The positive electrode tab, the separator, and the negative electrode tab are sequentially stacked and wound to assemble a cell, the cell is placed in an outer packaging shell, dried, and then injected with the electrolyte, vacuum packaged, left to stand for 24 h, formed, and constant volume, and the secondary battery is obtained.

[0174] Comparative Example 10

[0175] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0176] (1) Preparation of the positive electrode material: Li2CO3, NiCO3, Co(OH)2, and MnO2 are mixed at a metering ratio by ball milling at a rate of A for Bh, then sintered at T ℃ for H h in an air atmosphere, and then sintered at 900 ℃ for 12 h, and the obtained positive electrode active material particles LiNi 0.4 Co 0.2 Mn 0.4 O2, and then aluminum oxide is deposited on the surface of the positive electrode active material particles by using an ALD atomic deposition instrument with aluminum oxide powder as the raw material, the deposition pressure is set to h, and the number of deposition cycles is set to C cycles, and the positive electrode material LiNi 0.4 Co0.2 Mn 0.4 O2;

[0177] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0178] (2) Preparation of the positive electrode tab: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, the slurry was prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut, to obtain the positive electrode tab;

[0179] The resistance value of the obtained positive electrode tab was directly tested by using a resistance meter;

[0180] (3) Preparation of the negative electrode tab: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber were dispersed in water at a mass ratio of 96.4:1:1.2:1.4, the slurry was prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut, to obtain the negative electrode tab, and the negative electrode material was graphite;

[0181] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm was selected;

[0182] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 was added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0183] (6) The positive electrode tab, the separator, and the negative electrode tab were sequentially stacked and wound to assemble a battery cell, the battery cell was placed in an outer packaging shell, the electrolyte was injected after drying, vacuum packaging, standing for 24 h, formation, and constant volume, to obtain the secondary battery.

[0184] Comparative Example 11

[0185] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0186] (1) Preparation of the positive electrode material: Li2CO3, FeC2O4·2H2O, and NH4H2PO4 were mixed at a metering ratio by ball milling at a rate of A for Bh, then sintered at T ℃ for H h under an argon atmosphere, and then sintered at 750 ℃ for 12 h, to obtain positive electrode active material particles LiFePO4, then an ALD atomic deposition instrument was used to deposit aluminum oxide on the surface of the positive electrode active material particles, with aluminum oxide powder as the raw material, the deposition pressure was set to h, and the number of deposition cycles was set to C cycles, to obtain the positive electrode material LiFePO4;

[0187] The preparation and characteristic parameters of the positive electrode material are shown in Table 1.

[0188] (2) Preparation of the positive electrode sheet: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, the slurry is prepared by vacuum stirring, then coated on both sides of the current collector aluminum foil, dried, cold-pressed, and cut to obtain the positive electrode sheet;

[0189] The resistance value of the obtained positive electrode sheet is directly tested by using a resistance meter;

[0190] (3) Preparation of the negative electrode sheet: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, the slurry is prepared by vacuum stirring, then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut to obtain the negative electrode sheet, and the negative electrode material is graphite;

[0191] (4) Selection of the separator: a polyethylene separator with a thickness of 15 μm is selected;

[0192] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 is added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0193] (6) The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked and wound to assemble a battery cell, the battery cell is placed in an outer packaging shell, dried, and then injected with the electrolyte, vacuum packaged, and placed for 24 h, then formed, and the volume is determined to obtain the secondary battery.

[0194] Comparative Example 12

[0195] A positive electrode material and a secondary battery, the preparation method comprising the following steps:

[0196] (1) Preparation of the positive electrode material: Li2CO3, FeC2O4·2H2O, and NH4H2PO4 are mixed at a metering ratio by ball milling at a rate of A for Bh, then sintered at T ℃ for H h under an argon atmosphere, and then sintered at 750 ℃ for 12 h, to obtain positive electrode active material particles LiFePO4, then an ALD atomic deposition instrument is used to deposit aluminum oxide on the surface of the positive electrode active material particles by using aluminum oxide powder as a raw material, setting the deposition pressure at h, and setting the number of deposition cycles at C cycles, to obtain the positive electrode material LiFePO4;

[0197] The preparation of the positive electrode material and the characteristic parameters are shown in Table 1;

[0198] (2) Preparation of the positive electrode sheet: the positive electrode active material, the conductive agent carbon nanotube, and the binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 97:1:2, and the slurry was prepared by vacuum stirring, followed by coating on both sides of the current collector aluminum foil, drying, cold pressing, and slitting, to obtain the positive electrode sheet;

[0199] The resistance value of the obtained positive electrode sheet was directly tested by using a resistance meter;

[0200] (3) Preparation of the negative electrode sheet: the negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber were dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and the slurry was prepared by vacuum stirring, followed by coating on both sides of the current collector copper foil, drying, cold pressing, and slitting, to obtain the negative electrode sheet, and the negative electrode material was graphite;

[0201] (4) Selection of the separator: a commercially available polyethylene separator with a thickness of 15 μm was selected;

[0202] (5) Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1:1 to obtain an organic solvent, and lithium salt LiPF6 was added and dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0203] (6) The positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked and wound to assemble a battery cell, the battery cell was placed in an outer packaging shell, and after drying, the electrolyte was injected, followed by vacuum packaging, standing for 24 h, formation, constant volume, to obtain the secondary battery.

[0204] Table 1

[0205]

[0206]

[0207] Effect example

[0208] The positive electrode material and the secondary battery obtained in each example and comparative example were tested as follows:

[0209] (1) Positive electrode sheet resistance value test: direct testing as described above, which is not repeated here;

[0210] (2) High temperature cycle performance test: the secondary battery obtained in each example and the comparative example was pre-charged to the voltage upper limit at room temperature by using a LAND charge-discharge system with a rate of 0.33 C; then discharged to the voltage lower limit at a rate of 0.33 C, and cycled for 2 times; then placed in a 45°C environment and cycled for 100 times at the same working voltage by using the same system with a rate of 1 C / 1 C; the discharge capacity at each cycle was counted, and the high temperature cycle capacity retention rate (%) was finally calculated as the discharge capacity of the secondary battery after 100 times of 1 C / 1 C rate cycle / the discharge capacity of the secondary battery after the first 1 C / 1 C rate cycle;

[0211] The voltage lower limit of the secondary battery obtained in Examples 1-29 and Comparative Examples 1-8 was 2.5 V, and the voltage upper limit was 4.25 V.

[0212] The voltage lower limit of the secondary battery obtained in Example 30 and Comparative Examples 9-10 was 3.7 V, and the voltage upper limit was 4.2 V.

[0213] The voltage lower limit of the secondary battery obtained in Example 31 and Comparative Examples 11-12 was 2.2 V, and the voltage upper limit was 3.7 V.

[0214] (3) High temperature storage performance test: the secondary battery obtained in each example and the comparative example was pre-charged to the voltage upper limit at room temperature by using a LAND charge-discharge system with a rate of 0.33 C; then discharged to the voltage lower limit at a rate of 0.33 C, and cycled for 2 times; then placed in a 45°C environment and stored for 15 days; after the storage was completed, the sample was taken out and cycled for 1 time at room temperature by using the same system at the same working voltage and at the same rate; the high temperature storage capacity retention rate (%) was finally calculated as the discharge capacity of the secondary battery after the 0.33 C rate cycle at room temperature / the discharge capacity of the secondary battery after the 0.33 C rate cycle at the storage temperature.

[0215] The voltage lower limit of the secondary battery obtained in Examples 1-29 and Comparative Examples 1-8 was 2.5 V, and the voltage upper limit was 4.25 V.

[0216] The voltage lower limit of the secondary battery obtained in Example 30 and Comparative Examples 9-10 was 3.7 V, and the voltage upper limit was 4.2 V.

[0217] The voltage lower limit of the secondary battery obtained in Example 31 and Comparative Examples 11-12 was 2.2 V, and the voltage upper limit was 3.7 V.

[0218] The test results are shown in Table 3.

[0219] Table 2

[0220]

[0221]

[0222]

[0223] According to Table 2, it can be seen that:

[0224] (1) The positive electrode material described in the present application is prepared by setting a coating layer on the surface of the positive electrode active material, and simultaneously adjusting the roundness of the coated positive electrode material and the ratio of the content of free transition metal ions after acid corrosion, to coordinate the balance between stability and conductivity in the positive electrode material, so that the secondary battery prepared from the positive electrode material has ideal electrochemical performance. It can be seen that the resistance value of the positive electrode tab obtained in each embodiment is low, and the highest is only 300 mΩ. The cycle capacity retention rate of the secondary battery prepared from the positive electrode tab in a high temperature environment can reach at least 80%, and after high temperature storage for 15 days, the capacity retention rate of the battery can reach at least 79%, and the comprehensive performance is excellent. In contrast, although the positive electrode materials obtained in Comparative Examples 1-10 also construct a coating layer, the balance between roundness and stability of transition metal elements is not well controlled. The resistance value of the positive electrode tab prepared from the positive electrode material cannot be guaranteed at a low level, and the high temperature performance is poor. The secondary battery prepared therefrom cannot exhibit ideal high temperature stability.

[0225] (2) According to Examples 1-15 and Examples 16-29, it can be seen that in the present application, the types of positive electrode active material and coating layer are not limited when setting. Especially when the positive electrode active material is lithium nickel manganese oxide, when K / Rn is controlled in the range of 0.3-0.5, the positive electrode active material particle coating effect is good, the corners are fully coated and the surface flatness is high, the transition metal element dissolution rate is lower, and the conductivity effect is higher, and the comprehensive use effect is better. The resistance value of the positive electrode tab prepared from the positive electrode material can be maintained within 270 mΩ, and the capacity retention rate after high temperature cycling and high temperature storage can both reach more than 85%.

[0226] (3) When the positive electrode material is regulated, the roundness of the positive electrode active material particle after setting the coating layer will affect the coating integrity and regularity of the overall particle, and then cause the contact area of the material particle with the electrolyte to be different, and the compaction tightness and structural stability when preparing the pole piece are different, when the roundness of the material is preferably in the range of 0.6-0.7, the positive electrode active material particle can realize moderate contact area when contacting with the electrolyte, and the balance of transition metal ion dissolution probability and ion / electron transmission difficulty of the material can be realized by regulating the coating degree, and at the same time, the ideal pole piece stability and compactness can be realized when preparing the positive electrode pole piece; on the other hand, after acid etching, the content ratio of free transition metal elements in the positive electrode active material particle is related to the type of positive electrode active material and the coating effect of the coating layer, so the size of K also affects the ion / electron transmission ability and structural stability of the positive electrode active material particle, when the K value of the positive electrode active material particle is preferably in the range of 0.2-0.3%, the obtained positive electrode material has better structural stability and conductivity, when the obtained positive electrode material satisfies both of the above and the proportional relationship is also in the preferred range, the positive electrode pole piece prepared by the obtained positive electrode material not only can maintain the resistance value within 230 mΩ, when applied to prepare a secondary battery, the capacity retention rate after high-temperature cycle and high-temperature storage can reach more than 90%, the high-temperature cycle capacity retention rate can reach up to 95%, and the capacity retention rate after high-temperature storage can reach 94%.

Claims

1. A positive electrode material, characterized in that, The positive electrode active material particle includes at least one of a lithium nickel cobalt manganese oxide particle, a lithium iron phosphate particle, and a lithium nickel manganese oxide particle. The positive electrode material satisfies 0.2≤(100×K) / Rn≤1.

2. The K is a content ratio of a transition metal element in the positive electrode active material particle, which is released from the positive electrode active material particle after the positive electrode active material particle is soaked in a 20wt% concentration hydrofluoric acid solution at a solid-liquid ratio of 1g:5mL at 70℃ for 72h; and the 0.1%≤K≤0.5%. The Rn is a roundness of the positive electrode active material particle, and Rn=Ai / A, where Ai is a maximum inscribed circle area of the positive electrode active material particle, and A is a projection area of the positive electrode active material particle; and the 0.4≤Rn≤0.

8.

2. The cathode material of claim 1, wherein, The 0.6≤Rn≤0.

7.

3. The cathode material of claim 1, wherein, The 0.2%≤K≤0.3%.

4. The cathode material of claim 1, wherein, The positive electrode active material particle includes a lithium nickel manganese oxide particle, and the 0.3≤(100×K) / Rn≤0.

5.

5. The cathode material of claim 1, wherein, The metal oxide in the coating layer includes at least one of aluminum oxide, tungsten oxide, and zirconium oxide.

6. A secondary battery characterized by comprising: The positive electrode material includes the positive electrode material according to any one of claims 1-5.

7. An electrical device, characterized by The secondary battery according to claim 6 is used as a power supply for the electric device.

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