Positive electrode material and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of batteries, and specifically relates to a positive electrode material and a preparation method therefor and a use thereof. A positive electrode material, comprising a positive electrode matrix and a coating layer applied on at least part of the surface of the positive electrode matrix. The chemical formula of the positive electrode matrix is LiaNixCoyMnzMbO2, wherein 0.97≤a≤1.1, 0.50≤x＜1.0, 0＜y≤0.1, 0＜z ≤0.1, x+y+z+b＝1, and the ion M in the positive electrode matrix is selected from at least one of Sb5+, Ti4+, Zr4+, V5+, Nb5+, W6+ and Mo6+; and the coating layer contains Li2SO4. The positive electrode material has low surface residual alkali and good structural stability, and can improve the cycle performance and safety performance of a battery.

Description

Positive electrode material, preparation method and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 202410293528.6, filed with the State Intellectual Property Office of China on March 14, 2024, entitled “A positive electrode material, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the field of battery technology, and in particular to a positive electrode material and a preparation method and application thereof. Background Art

[0004] In order to address the endurance problem of electric vehicles, ternary batteries with high nickel content are generally used for installation.

[0005] Although high-nickel ternary materials have significant advantages over several other positive electrode materials in terms of energy density, some of their defects restrict the further development and application of the materials. For example, they cause gas production during long charge and discharge cycles, leading to battery swelling, deformation, shortened cycle life, and safety hazards.

[0006] In view of this, the present invention is proposed.

[0007] Summary of the Invention

[0008] One object of the present invention is to provide a positive electrode material to solve the technical problems of the prior art positive electrode materials having too high surface residual alkali and poor cycle performance; the positive electrode material of the present invention has low surface residual alkali and good structural stability, which can improve the cycle performance and safety performance of the battery.

[0009] Another object of the present invention is to provide a method for preparing the positive electrode material, which can reduce the surface residual alkali of the positive electrode material and improve the structural stability of the positive electrode material through the coordination of various steps.

[0010] Another object of the present invention is to provide a positive electrode sheet.

[0011] Another object of the present invention is to provide a battery.

[0012] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0013] A positive electrode material, comprising a positive electrode substrate and a coating layer coated on at least a portion of the surface of the positive electrode substrate; the chemical formula of the positive electrode substrate is Li a Ni x Co y Mnz M b O2, where 0.97 ≤ a ≤ 1.1, 0.50 ≤ x < 1.0, 0 < y ≤ 0.1, 0 < z ≤ 0.1, and x + y + z + b = 1. The ion M in the positive electrode matrix is selected from at least one of Sb 5+ 、Ti 4+ 、Zr 4+ 、V 5+ 、Nb 5+ 、W 6+ and Mo 6+ ; the coating layer includes Li2SO4.

[0014] In one embodiment, the residual lithium content of the positive electrode material is 950 - 1200 ppm.

[0015] A method for preparing a positive electrode material, comprising the following steps:

[0016] Performing a first heat treatment on a mixture of nickel-cobalt-manganese hydroxide, a lithium source, and a compound of element M, where element M is selected from at least one of Sb 5+ 、Ti 4+ 、Zr 4+ 、V 5+ 、Nb 5+ 、W 6+ and Mo 6+ to obtain a first material; mixing the first material and water for water washing, where the temperature of the water is 6 - 20 °C, to obtain a positive electrode matrix; and performing a second heat treatment on a mixed material of the positive electrode matrix and ammonium sulfate.

[0017] In one embodiment, the mass ratio of the first material to the water is 1:(0.25 - 1).

[0018] In one embodiment, during the water washing process, first stirring treatment and second stirring treatment are employed. The time of the first stirring treatment is 1 - 3 min; the time of the second stirring treatment is 10 - 20 min; and the rotation speed of the second stirring treatment is 2000 - 4000 rpm.

[0019] In one embodiment, after the water washing, drying is performed. The drying temperature is 100 - 130 °C, and the drying time is 150 - 250 min.

[0020] In one embodiment, the mass of ammonium sulfate is 0.5% - 2% of the mass of the positive electrode matrix.

[0021] In one embodiment, the chemical formula of the nickel-cobalt-manganese hydroxide is Ni x1 Co y1 Mn z1(OH)2, where 0.50≤x1<1, 0 <y1≤0.1,0<z1≤0.1,x1+y1+z1=1。

[0022] In one embodiment, the compound of M is selected from at least one of oxides, hydroxides, carbonates, nitrates, sulfates, phosphates and acetates corresponding to element M.

[0023] In one embodiment, the molar ratio of the nickel-cobalt-manganese hydroxide, the lithium source and the compound of the element M is 1:(0.97-1.1):b1 based on the total nickel-cobalt-manganese, elemental lithium and elemental M, respectively, wherein 0 <b1≤0.05。

[0024] In one embodiment, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium acetate, and lithium nitrate.

[0025] In one embodiment, the first heat treatment includes 1 to 3 sintering treatments; the sintering treatment temperature is 500 to 900° C., the holding time is 1 to 20 hours, and the heating rate is 1 to 4° C. / min.

[0026] In one embodiment, during the first heat treatment, the material is crushed after each sintering process.

[0027] In one embodiment, the temperature of the second heat treatment is 300-500° C., the time of the second heat treatment is 4-7 hours, and the heating rate of the second heat treatment is 1-5° C. / min.

[0028] A positive electrode sheet comprises the positive electrode material, or the positive electrode material prepared by the positive electrode material preparation method.

[0029] A battery comprises the positive electrode sheet.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) In the cathode material of the present invention, the doping element has a higher valence state, which can form a strong transition metal-oxygen bond, increase the thermal decomposition temperature of the material, and thus alleviate the irreversible oxygen release process of the high nickel layered material under high voltage; at the same time, the doping element with a larger ionic radius enters the transition metal site to increase the lattice parameter c, thereby increasing the Li + Migration rate; the Li2SO4 compound coating layer further reduces the residual lithium on the surface of the ternary material; at the same time, Li2SO4 also has good electrical conductivity, thereby improving the ion transfer rate of the material.

[0032] (2) For the method of the positive electrode material of the present invention, ammonium sulfate is selected for coating. Since sulfonyl compounds can react with lithium hydroxide remaining on the surface of the positive electrode to form a stable compound lithium sulfate, it can not only reduce the residual lithium on the surface, but also isolate the material and the electrolyte, avoiding their direct contact and inhibiting the occurrence of side reactions. At the same time, the generated lithium sulfate also has good conductivity, thereby improving the ion transport rate of the material and enhancing the cycling performance of the positive electrode material. Meanwhile, the present invention selects low-temperature water for washing. Compared with normal-temperature water, it can better remove the residual lithium on the surface, thereby improving the cycling retention rate of the material and enhancing the battery's endurance capacity.

[0033] (3) The battery obtained from the positive electrode material of the present invention has excellent cycling performance, rate performance and safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] FIG. 1 is a scanning electron microscope image of the positive electrode material in Example 1 of the present invention;

[0036] FIG. 2 is a scanning electron microscope image of the positive electrode material in Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following will describe the implementation solutions of the present invention in detail in combination with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial procurement.

[0038] According to one aspect of the present invention, the present invention relates to a positive electrode material, including a positive electrode matrix and a coating layer coated on at least part of the surface of the positive electrode matrix; the chemical formula of the positive electrode matrix is Li a Ni x Co y Mn z M b O2, where 0.97 ≤ a ≤ 1.1, 0.5 ≤ x < 1.0, 0 < y ≤ 0.1, 0 < z ≤ 0.1, x + y + z + b = 1, and the ion M in the positive electrode matrix is selected from Sb 5+ , Ti 4+ , Zr 4+ , V 5+、Nb 5+ 、W 6+ and Mo 6+ At least one of; the coating layer includes Li2SO4.

[0039] The doping elements of the present invention have a higher valence state, can form a strong transition metal-oxygen bond, increase the thermal decomposition temperature of the material, thereby alleviating the irreversible oxygen release process of the high nickel layered material under high voltage; at the same time, the doping elements with larger ionic radius entering the transition metal site can increase the lattice parameter c, thereby improving the Li + Migration rate; the Li2SO4 compound coating layer further reduces the residual lithium on the surface of the ternary material; at the same time, Li2SO4 also has good electrical conductivity, thereby improving the ion transfer rate of the material.

[0040] In one embodiment, the value of a includes, but is not limited to, 0.97, 0.98, 1, 1.03, 1.05, 1.1, etc.; the value of x includes, but is not limited to, 0.5, 0.6, 0.7, 0.8, or 0.9, etc. The value of y includes, but is not limited to, 0.01, 0.02, 0.3, 0.05, 0.06, 0.07, 0.09, or 0.1, etc. The value of z includes, but is not limited to, 0.01, 0.02, 0.05, 0.06, 0.08, or 0.1, etc.

[0041] In one embodiment, the residual lithium content of the positive electrode material is 950 to 1200 ppm, for example, 950 ppm, 1000 ppm, 1100 ppm, or 1200 ppm.

[0042] In one embodiment, the D50 particle size of the positive electrode substrate is 8 to 12 μm, such as 8 μm, 10 μm or 12 μm, etc. In one embodiment, the thickness of the coating layer is 10 to 50 nm, such as 10 nm, 15 nm, 20 nm, 30 nm, 40 nm or 50 nm, etc.

[0043] According to another aspect of the present invention, the present invention also relates to a method for preparing a positive electrode material, comprising the following steps:

[0044] The mixture of nickel-cobalt-manganese hydroxide, lithium source and compound of element M is subjected to a first heat treatment to obtain a first material; element M is selected from Sb 5+ 、Ti 4+ 、Zr 4+ 、V 5+ 、Nb 5+ 、W 6+ and Mo 6+at least one of the following: mixing the first material and water for washing, wherein the temperature of the water is 6 to 20° C., to obtain a positive electrode matrix; subjecting the mixture of the positive electrode matrix and the ammonium sulfate to a second heat treatment.

[0045] The method of the present invention selects ammonium sulfate for coating because the sulfonyl compound can react with the lithium hydroxide remaining on the surface of the positive electrode to form a stable compound lithium sulfate, which can not only reduce the residual lithium on the surface, but also isolate the material and the electrolyte, avoid direct contact between the two, and inhibit the occurrence of side reactions; the generated lithium sulfate also has good electrical conductivity, thereby improving the ion transmission rate of the material; through the coordination of various steps, the structural stability of the positive electrode material can be improved, the change of the material structure can be suppressed, the reversibility of the material can be enhanced, and the cycle performance of the positive electrode material can be improved. At the same time, the present invention selects low-temperature water for water washing, which can better remove the residual lithium on the surface than normal temperature water, thereby improving the material cycle retention rate and improving the battery life.

[0046] In one embodiment, the water temperature is 6-20° C., for example, 6° C., 10° C., 12° C., 15° C., 18° C., or 20° C. The present invention selects low-temperature water for water washing to better remove residual lithium on the surface, thereby improving the material cycle retention rate and enhancing the battery life.

[0047] In one embodiment, the mass ratio of the first material to the water is 1:(0.25-1), such as 1:0.25, 1:0.4, 1:0.5, 1:0.8, 1:1, etc. The first material and water of the present invention are selected in an appropriate mass ratio to better ensure the washing effect.

[0048] In one embodiment, a first stirring treatment and a second stirring treatment are used during the water washing process, and the time of the first stirring treatment is 1 to 3 minutes, such as 1 minute, 2 minutes or 3 minutes. The time of the second stirring treatment is 10 to 20 minutes, such as 10 minutes, 15 minutes, 20 minutes, etc., and the rotation speed of the second stirring treatment is 2000 to 4000 rpm, such as 2000 rpm, 2500 rpm, 3000 rpm or 4000 rpm. The present invention adopts the first stirring treatment and the second stirring treatment under appropriate conditions in the water washing process, thereby better ensuring the effect of water washing, which is beneficial to reducing the surface residual alkali of the positive electrode material, avoiding the gas generated by the contact between the residual lithium and the electrolyte causing the battery cell to swell, reducing the consumption of the electrolyte, and ensuring the stability of the internal lattice of the material, thereby improving the circulation and safety performance of the material.

[0049] In one embodiment, drying is performed after the water washing. The drying temperature is 100-130 °C, such as 100 °C, 110 °C, 120 °C or 130 °C, etc. The drying time is 150-250 min, such as 150 min, 180 min, 200 min, 220 min or 250 min, etc. Appropriate drying conditions are adopted to remove moisture.

[0050] In one embodiment, the mass of ammonium sulfate is 0.5%-2% of the mass of the positive electrode substrate, such as 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%, etc. In the present invention, an appropriate amount of ammonium sulfate is used for coating. Since ammonium sulfate can react with lithium hydroxide remaining on the surface of the positive electrode to form a stable compound lithium sulfate, it can not only reduce the residual lithium on the surface, but also isolate the material and the electrolyte to avoid their direct contact. Ammonium sulfate also has good conductivity, thereby improving the ion transport rate of the material.

[0051] In one embodiment, the chemical formula of the nickel-cobalt-manganese hydroxide is Ni x1 Co y1 Mn z1 (OH)2, where 0.50 ≤ x1 < 1, 0 < y1 ≤ 0.1, 0 < z1 ≤ 0.1, and x1 + y1 + z1 = 1. The value of x1 includes but is not limited to 0.5, 0.6, 0.7, 0.8 or 0.9, etc. The value of y1 includes but is not limited to 0.01, 0.02, 0.03, 0.05, 0.06, 0.07, 0.09 or 0.1, etc. The value of z1 includes but is not limited to 0.01, 0.02, 0.05, 0.06, 0.08 or 0.1, etc.

[0052] In one embodiment, the compound of M is selected from at least one of the oxide, hydroxide, carbonate, nitrate, sulfate, phosphate and acetate corresponding to element M. The compound of M can be selected from any one of the above, or a combination of at least two, such as a combination of Nb2O5 and Sb2O5, a combination of V2O5 and Mo2O6, etc.

[0053] In one embodiment, the molar ratio of the nickel-cobalt-manganese hydroxide, the lithium source and the compound of element M in terms of total nickel-cobalt-manganese, elemental lithium and element M is 1:(0.97-1.1):b1, where 0 < b1 ≤ 0.05, such as 1:0.97:0.01, 1:0.99:0.02, 1:1:0.03, 1:1.1:0.05, etc. Total nickel-cobalt-manganese refers to the sum of elements nickel, cobalt and manganese in the nickel-cobalt-manganese hydroxide.

[0054] In one embodiment, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium acetate, and lithium nitrate. The lithium source can be any one of the above, or a combination of at least two, such as a combination of lithium hydroxide and lithium carbonate, a combination of lithium oxalate, lithium acetate, and lithium nitrate, etc.

[0055] In one embodiment, the first heat treatment includes 1 to 3 sintering treatments; the sintering temperature is 500 to 900°C, such as 500°C, 600°C, 650°C, 700°C, 800°C, 900°C, etc.; the holding time is 1 to 20 hours, such as 1 hour, 2 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, or 20 hours, etc.; the heating rate is 1 to 4°C / min, such as 1°C / min, 2°C / min, 3°C / min, or 4°C / min, etc. The present invention adopts appropriate first heat treatment conditions to ensure the physical and chemical properties of the first material, which is beneficial to the subsequent coating.

[0056] In one embodiment, during the first heat treatment, after each sintering process, the material is crushed, and the crushing process includes mechanical crushing to obtain a suitable particle size.

[0057] In one embodiment, the temperature of the second heat treatment is 300-500°C, for example, 300°C, 350°C, 400°C, 450°C, or 500°C; the time of the second heat treatment is 4-7 hours, for example, 4 hours, 5 hours, 6 hours, or 7 hours; the heating rate of the second heat treatment is 1-5°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, or 5°C / min. The present invention adopts appropriate second heat treatment conditions to form a coating layer with high conductivity and ion transport rate; it can improve the structural stability of the positive electrode material, inhibit changes in the material structure, enhance the reversibility of the material, and improve its overall performance.

[0058] According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising the positive electrode material, or the positive electrode material prepared by the method for preparing the positive electrode material.

[0059] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector; the positive electrode coating layer includes the positive electrode material, a conductive agent, and a binder. The conductive agent includes conductive carbon black, and the binder includes polyvinylidene fluoride. The preparation method of the positive electrode sheet includes: mixing the positive electrode material, the conductive agent, the binder, and the solvent; the mass ratio of the positive electrode material, the conductive agent, and the binder is (95-97): (1-2): (2-3) to obtain a positive electrode slurry; applying the positive electrode slurry to the positive electrode current collector, drying at 100-140°C, and rolling to a thickness of 100-120μm to obtain a positive electrode sheet.

[0060] According to another aspect of the present invention, the present invention also relates to a battery, comprising the positive electrode sheet.

[0061] In one embodiment, the battery of the present invention includes the above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte.

[0062] The following is further explained with reference to specific embodiments and comparative examples.

[0063] Example 1

[0064] In this example, Nb 5+ 、Sb 5+ Doping modified high cycle life ternary cathode material, its chemical formula is Li 1.03 Ni 0.928 Co 0.05 Mn 0.02 Nb 0.001 Sb 0.001 O2; the selected precursor chemical formula is Ni 0.93 Co 0.05 Mn 0.02 (OH)2; The specific preparation method comprises the following steps:

[0065] (1) The above ternary precursor is mixed with lithium hydroxide, Nb2O5 and Sb2O5 in a molar ratio of n(Ni+Co+Mn):n (Li) :n (Nb) :n (Sb) =1:1.03:0.001:0.001, mixed uniformly in a high-speed mixer, and the uniform mixture was put into a box furnace for a first heat treatment, the first heat treatment including primary sintering and secondary sintering, the primary sintering heating rate was 3°C / min, the temperature was increased to 550°C, and the temperature was kept for 5 hours, the secondary sintering heating rate was 4°C / min, the temperature was increased to 780°C, and the temperature was kept for 10 hours; after each sintering, the material was taken out and cooled, and then mechanically crushed to finally obtain the first material.

[0066] (2) Prepare distilled water at 10°C in advance, mix the obtained first material with water in a mass ratio of 1:1, stir manually for 1 minute until the slurry is uniform, put it into a centrifuge for water washing, the speed is 3000 rpm, and after centrifugation for 15 minutes, take out the filter cake and place it in a vacuum drying oven for drying at a drying temperature of 120°C and a drying time of 200 minutes to obtain the positive electrode matrix.

[0067] (3) The obtained positive electrode matrix and 1% ammonium sulfate relative to the mass of the positive electrode matrix were put into a high-pressure mixer, mixed evenly, and then placed in a box furnace for low-temperature sintering at a heating rate of 3°C / min to 400°C and kept warm for 6 hours.

[0068] (4) After sintering, the product is taken out, cooled, and screened to obtain a ternary positive electrode material with a high cycle life.

[0069] A scanning electron microscope image of the positive electrode material of the present invention is shown in FIG1 .

[0070] Example 2

[0071] The preparation method of the ternary cathode material of this embodiment is the same as that of Example 1 except that the temperature of the distilled water in step (2) is 6°C.

[0072] Example 3

[0073] The preparation method of the ternary cathode material of this embodiment is the same as that of Example 1 except that the temperature of the distilled water in step (2) is 20°C.

[0074] Example 4

[0075] The preparation method of the ternary positive electrode material of this embodiment is the same as that of Example 1, except that the mass of ammonium sulfate is 0.5% of the mass of the positive electrode matrix.

[0076] Example 5

[0077] The preparation method of the ternary positive electrode material of this embodiment is the same as that of Example 1, except that the mass of ammonium sulfate is 2% of the mass of the positive electrode matrix.

[0078] Example 6

[0079] In this example, W 6+ 、Mo 6+ Doping modified high cycle life ternary cathode material, its chemical formula is Li 1.03 Ni 0.928 Co 0.05 Mn 0.02 W 0.001 Mo 0.001 O2; the selected precursor chemical formula is Ni 0.93 Co 0.05 Mn0.02 (OH)2; The specific preparation method comprises the following steps:

[0080] (1) The above ternary precursor is mixed with lithium hydroxide, W2O6 and Mo2O6 in a molar ratio of n(Ni+Co+Mn):n (Li) :n (W) :n (Mo) =1:1.03:0.001:0.001, mixed in a high-speed mixer, and uniformly mixed, and the uniform mixture was put into a box furnace for a first heat treatment, the first heat treatment including primary sintering and secondary sintering, the primary sintering heating rate was 3°C / min, the temperature was increased to 650°C, and the temperature was kept for 3 hours, the secondary sintering heating rate was 4°C / min, the temperature was increased to 900°C, and the temperature was kept for 2 hours; after each sintering, the material was taken out and cooled, and then mechanically crushed to finally obtain the first material.

[0081] (2) Prepare distilled water at 10°C in advance, mix the obtained first material with water in a mass ratio of 1:1, stir manually for 3 minutes until the slurry is uniform, put it into a centrifuge for water washing, the speed is 2000 rpm, and after centrifugation for 20 minutes, take out the filter cake and place it in a vacuum drying oven for drying at a drying temperature of 120°C and a drying time of 200 minutes to obtain the positive electrode matrix.

[0082] (3) The obtained positive electrode matrix and 1% ammonium sulfate relative to the mass of the positive electrode matrix were put into a high-pressure mixer, mixed evenly, and then placed in a box furnace for low-temperature sintering at a heating rate of 3°C / min to 500°C and kept warm for 4 hours.

[0083] (4) After sintering, the product is taken out, cooled, and screened to obtain a ternary positive electrode material with a high cycle life.

[0084] Example 7

[0085] The preparation method of the ternary positive electrode material of this embodiment is as follows, except that the heating rate of the primary sintering in step (1) is 1°C / min, the temperature is raised to 500°C, and the temperature is kept for 7 hours, and the heating rate of the secondary sintering is 2°C / min, the temperature is raised to 790°C, and the temperature is kept for 8 hours; the rotation speed in step (2) is 4000 rpm, and the centrifugation is carried out for 10 minutes; the heating rate in step (3) is 3°C / min, the temperature is raised to 300°C, and the temperature is kept for 7 hours; other conditions are the same as those in Example 6.

[0086] Comparative Example 1

[0087] The preparation method of the ternary positive electrode material of this comparative example is the same as that of Example 1 except that step (3) is not performed.

[0088] Comparative Example 2

[0089] The preparation method of the ternary positive electrode material of this comparative example, without doping and coating, includes:

[0090] (1) The ternary precursor Ni 0.93 Co 0.05 Mn 0.02 (OH)2 and lithium hydroxide are in the form of n(Ni+Co+Mn):n (Li) =1:1.03 ratio, mixed evenly in a high-speed mixer, and the uniform mixture was put into a box furnace for the first heat treatment. The first heat treatment included primary sintering and secondary sintering. The primary sintering heating rate was 3°C / min, the temperature was raised to 550°C, and the temperature was kept for 5 hours. The secondary sintering heating rate was 4°C / min, the temperature was raised to 780°C, and the temperature was kept for 10 hours.

[0091] (2) After sintering, the sintered products were taken out and cooled, and then mechanically crushed to obtain the crushed product Li 1.03 Ni 0.93 Co 0.05 Mn 0.02 O2.

[0092] The scanning electron microscope image of the positive electrode material of this comparative example is shown in FIG2 .

[0093] Experimental example

[0094] 1. Surface residual alkali test of materials

[0095] The surface residual alkali test results of the positive electrode materials of various embodiments of the present invention and comparative examples are shown in Table 1, using an acid-base titration method.

[0096] Table 1 Surface residual alkali test results

[0097] As shown in Table 1, the method of the present invention can effectively reduce the surface residual alkali of the positive electrode material, making the structure of the positive electrode material more stable. The surface residual alkali of the positive electrode material obtained in Comparative Example 2 without doping and coating is even higher.

[0098] 2. Battery electrochemical performance test

[0099] The positive electrode materials obtained in each embodiment and comparative example were respectively prepared into batteries, which specifically comprised the following steps:

[0100] (1) A positive electrode material, a conductive material carbon black, and a binder polyvinylidene fluoride were mixed in an N-methyl-2-pyrrolidone solvent at a weight ratio of 97.0:1.0:2.0 to prepare a positive electrode slurry; the positive electrode slurry was coated on the surface of an aluminum foil, dried at 130° C., and then rolled into a pole sheet with a thickness of 115 μm to prepare a positive electrode, thereby obtaining a positive electrode sheet.

[0101] (2) The negative electrode active material carbon black and the binder polyvinylidene fluoride were mixed in a weight ratio of 97:3, and then added to an N-methylpyrrolidone solvent to prepare a negative electrode active material slurry; the negative electrode active material slurry was coated on a copper foil with a thickness of 16 μm, dried at 120°C, and then rolled into a pole sheet with a thickness of 121 μm to prepare a negative electrode.

[0102] (3) A porous polyethylene separator is inserted between the positive electrode and the negative electrode prepared above to prepare an electrode assembly, and the electrode assembly is placed in a battery case. Thereafter, an electrolyte is injected into the case to prepare a lithium secondary battery. At this time, as an electrolyte, LiPF6 is dissolved in an organic solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) mixed in a mass ratio of 3:4:3 to prepare a 1 mol / L electrolyte to obtain a battery.

[0103] Each lithium secondary battery prepared as described above was charged to 4.30 V at a constant current of 0.1 C at 20° C., and discharged to 2.80 V at a constant current of 0.1 C to measure initial discharge capacity and coulombic efficiency.

[0104] Thereafter, each secondary battery after initial charge / discharge was charged to 4.25 V at a constant current of 0.50 C at 45° C. and discharged to 2.80 V at a constant current of 0.50 C, which was set as 1 cycle, and 50 cycles of charge / discharge were performed to measure the capacity retention rate. The results are shown in Table 2 below.

[0105] Table 2 Electrochemical performance test results of the battery

[0106] As shown in Table 2, the batteries prepared with the positive electrode materials of Examples 1 to 3 of the present invention have higher discharge capacity, coulombic efficiency, and capacity retention. Comparative Example 1 was not coated, and Comparative Example 2 was not doped or coated, resulting in relatively poor discharge capacity, coulombic efficiency, and capacity retention of the positive electrode materials.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that It includes a positive electrode substrate and a coating layer coated on at least a portion of the surface of the positive electrode substrate; The chemical formula of the positive electrode matrix is Li a Ni x Co y Mn z M b O2, where 0.97 ≤ a ≤ 1.1, 0.50 ≤ x < 1.0, 0 < y ≤ 0.1, 0 < z ≤ 0.1, x + y + z + b = 1, and the ion M in the positive electrode matrix is selected from Sb 5+ 、Ti 4+ 、Zr 4+ 、V 5+ 、Nb 5+ 、W 6+ and Mo 6+ and at least one of them; The coating layer includes Li2SO4.

2. The positive electrode material according to claim 1, characterized in that The residual lithium content of the positive electrode material is 950 to 1200 ppm.

3. A method for preparing a positive electrode material, characterized in that: The following steps are involved: The mixture of nickel-cobalt-manganese hydroxide, lithium source and compound of element M is subjected to a first heat treatment to obtain a first material; element M is selected from Sb 5+ 、Ti 4+ 、Zr 4+ 、V 5+ 、Nb 5+ 、W 6+ and Mo 6+ At least one of; Mixing the first material and water and washing with water, wherein the temperature of the water is 6 to 20° C., to obtain a positive electrode matrix; The mixture of the positive electrode substrate and ammonium sulfate is subjected to a second heat treatment.

4. The method for preparing the positive electrode material according to claim 3, wherein: Contains at least one of the following features (1) to (3): (1) The mass ratio of the first material to the water is 1:(0.25-1); (2) a first stirring treatment and a second stirring treatment are used during the water washing process, wherein the first stirring treatment lasts for 1 to 3 minutes; the second stirring treatment lasts for 10 to 20 minutes; and the speed of the second stirring treatment is 2000 to 4000 rpm; (3) After washing, the product is dried at a temperature of 100 to 130° C. and for a time of 150 to 250 minutes.

5. The method for preparing the positive electrode material according to claim 3, wherein: The mass of the ammonium sulfate is 0.5% to 2% of the mass of the positive electrode substrate.

6. The method for preparing the positive electrode material according to claim 3, wherein: Contains at least one of the following features (1) to (4): (1) The chemical formula of the nickel-cobalt-manganese hydroxide is Ni x1 Co y1 Mn z1 (OH)2, where 0.50≤x1<1, 0 <y1≤0.1,0<z1≤0.1,x1+y1+z1=1; (2) the compound of M is selected from at least one of the oxide, hydroxide, carbonate, nitrate, sulfate, phosphate and acetate corresponding to the element M; (3) The molar ratio of the nickel-cobalt-manganese hydroxide, the lithium source and the compound of the element M is 1:(0.97-1.1):b1 based on the total nickel-cobalt-manganese, element lithium and element M, respectively, wherein 0 <b1≤0.05; (4) The lithium source includes a lithium salt which is at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium acetate and lithium nitrate.

7. The method for preparing the positive electrode material according to claim 3, wherein: Contains at least one of the following features (1) to (2): (1) The first heat treatment includes 1 to 3 sintering treatments; the sintering treatment temperature is 500 to 900°C, the holding time is 1 to 20 hours, and the heating rate is 1 to 4°C / min; (2) During the first heat treatment, the material is crushed after each sintering process.

8. The method for preparing the positive electrode material according to claim 3, wherein: The temperature of the second heat treatment is 300-500° C., the time of the second heat treatment is 4-7 hours, and the heating rate of the second heat treatment is 1-5° C. / min.

9. A positive electrode sheet, characterized in that: The invention comprises the positive electrode material according to claim 1 or 2, or the positive electrode material prepared by the preparation method of the positive electrode material according to any one of claims 3 to 8.

10. A battery, characterized in that: Including the positive electrode sheet according to claim 9.

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