A modified ternary cathode material and its preparation method and application

Abstract

The present invention provides a modified ternary cathode material and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing an ultra-high nickel ternary precursor, a first additive and a lithium source, and subjecting the mixture to a one-step sintering treatment to obtain a one-sintered material; (2) mixing boric acid with water, and adding a polyhydroxy compound to obtain a mixed solution; (3) mixing the one-sintered material and a second additive to obtain a mixed material, atomizing the mixed solution and then mixing it with the mixed material, and subjecting the modified ternary cathode material to a two-step sintering treatment. In the present invention, the boric acid modified by the polyhydroxy compound coated by a spray method reacts with the residual alkali on the surface of the ultra-high nickel cathode material to generate an acid-base neutralization reaction, thereby avoiding problems such as capacity loss and battery flatulence. At the same time, the formed Li3BO3 acts as a good lithium ion conductor, which can not only promote the diffusion of lithium ions, but also effectively avoid the erosion of the electrolyte on the interior of the particles, reduce impedance, and improve the cycle stability of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a modified ternary positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, nickel-rich layered oxides have attracted significant attention as cathode materials for lithium-ion batteries due to their high energy density and low cost. With the large-scale adoption of lithium-ion batteries in new energy vehicles, the advantages of high energy density and low cost have become increasingly prominent and have become key performance indicators. Consequently, high-nickel and ultra-high-nickel materials are considered the most promising cathode materials. However, as the nickel content increases, problems such as high residual base content on the surface and mixed cation distribution, resulting in poor crystal structure stability and thermal stability, become more pronounced.

[0003] As we all know, the high sensitivity of cathode materials with high surface residual alkali to air and moisture hinders their practical application, which will lead to manufacturing difficulties and the formation of slurry during the slurry mixing process; high nickel material Ni 2+ With Li + The high cation mixing in the arrangement may also cause the crystal structure to collapse during the cycle and the cycle stability to deteriorate; at the same time, due to the Ni 4+ Due to the strong oxidizing properties of the battery, serious side reactions occur between the electrode material and the electrolyte, which slowly decomposes the electrolyte in the electrolyte. This is one of the main causes of battery flatulence and poses a safety hazard to actual use.

[0004] CN111200120A discloses a ternary cathode material, its preparation method, and a lithium-ion battery. The ternary cathode material primarily consists of a high-nickel ternary material core and a cobalt borate coating. The preparation method comprises: 1) mixing a boron source and a cobalt source, followed by sintering in a protective atmosphere to produce cobalt borate; and 2) mixing the cobalt borate with the high-nickel ternary material and heating in an oxidizing atmosphere to produce the ternary cathode material.

[0005] CN111370684A discloses a method for reducing the residual alkali content on the surface of a high-nickel positive electrode material for a lithium-ion battery. The method comprises: adding a certain amount of acid or an acid derivative to a certain amount of a non-aqueous, inactive hydrogen-free organic solvent at room temperature, stirring until completely dissolved, to obtain a washing liquid for reducing the residual alkali content on the surface of the high-nickel positive electrode material for a lithium-ion battery; the molar concentration of the acid or the acid derivative in the washing liquid is 0.5-1.5 times the molar amount of the residual alkali on the surface of the high-nickel positive electrode material to be treated; adding the high-nickel positive electrode material to be treated to the washing liquid while stirring at a linear speed of 1 m / s-10 m / s; and removing the solvent by centrifugation, vacuumizing, heating, and drying to obtain the treated high-nickel positive electrode material.

[0006] The positive electrode materials and the method for reducing residual alkali described in the above scheme have the problem of reduced electrochemical performance or obvious flatulence in the manufactured battery, which greatly limits their application in practice. Summary of the Invention

[0007] The purpose of the present invention is to provide a modified ternary cathode material, a preparation method, and an application thereof. The present invention coats boric acid modified with a polyhydroxy compound by a spray method, and removes residual alkali such as LiOH and Li2CO3 on the surface of the ultra-high nickel cathode material through an acid-base neutralization reaction, thereby avoiding problems such as irreversible capacity loss and battery flatulence. At the same time, the formed Li3BO3 acts as a good lithium ion conductor, which can not only promote the diffusion of lithium ions, but also effectively prevent the electrolyte from corroding the interior of the particles, reducing impedance and improving the cycle stability of the material.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a modified ternary cathode material, characterized in that the preparation method comprises the following steps:

[0010] (1) mixing an ultra-high nickel ternary precursor, a first additive, and a lithium source, and performing a one-step sintering treatment to obtain a single-fired material;

[0011] (2) mixing boric acid with water and adding a polyol to obtain a mixed solution;

[0012] (3) The sintered material obtained in step (1) is mixed with the second additive to obtain a mixed material, the mixed solution obtained in step (2) is atomized and then mixed with the mixed material, and the modified ternary positive electrode material is obtained by a two-step sintering process.

[0013] Boric acid is a typical Lewis acid. It dissolves in water to form a weak electrolyte hydrated boric acid, which ionizes to produce a small amount of B(OH)4 - and H + ions, the solution is very weakly acidic, so simply coating with boric acid cannot reduce the residual alkali. The acidity of the boric acid aqueous solution does not come from the proton itself. Since boron is an electron-deficient atom, its empty orbital adds OH from the water molecule. - , and release H + , the reaction is weak and thus exhibits extremely weak acidity. Taking advantage of this electron-deficient property, by adding polyhydroxy compounds (such as glycerol and mannitol, etc.) to form a stable complex, the ionization balance of the weak electrolyte hydrated boric acid is destroyed, moving in the direction of ionization, generating more H + Compared with acid washing, this method reduces the degree of corrosion on the surface of the positive electrode material, reduces the dissolution of transition metals and the loss of capacity, and effectively improves the processing performance and cycle life of the material.

[0014] Preferably, in step (1), the first additive comprises any one of aluminum oxide, magnesium hydroxide, zirconium oxide or tungsten oxide, or a combination of at least two thereof.

[0015] Preferably, the lithium source comprises lithium hydroxide and / or lithium carbonate.

[0016] Preferably, the molar ratio of the lithium element in the lithium source to the metal element in the ultra-high nickel ternary precursor is (1.01-1.1):1, for example: 1.01:1, 1.03:1, 1.05:1, 1.08:1 or 1.1:1, etc., preferably (1.01-1.06):1.

[0017] Preferably, the temperature of the one-step sintering treatment in step (1) is 600-900°C, for example, 600°C, 650°C, 700°C, 800°C or 900°C, etc., preferably 650-750°C.

[0018] Preferably, the one-step sintering treatment lasts for 8 to 24 hours, for example, 8 hours, 10 hours, 15 hours, 20 hours or 24 hours, and is preferably 10 to 20 hours.

[0019] Preferably, a carbon source may be added during the one-step sintering process.

[0020] Preferably, the chemical formula of the sintered material is Li 1+y (Ni a Co b Mn 1-a-b-c B c ) 1-y O2, where 0≤y≤0.1, 0.95≤a<1, 0.01≤b≤0.1, 0≤c≤0.05, B includes Mg 2+ , Al 3+ , W 6+ or Zr 4+ Any one or a combination of at least two of .

[0021] Preferably, the mass ratio of boric acid to water in step (2) is (0.1-5):100, for example: 0.1:100, 1:100, 2:100, 3:100, 4:100 or 5:100, etc.

[0022] Preferably, the polyol comprises any one or a combination of at least two of ethylene glycol, glycerol, erythritol, fructose, mannitol or sorbitol.

[0023] Not all polyols can increase the apparent ionization constant of H3BO3. For example, sucrose and glycogen, although also polyols, cannot enhance the ionization of H3BO3. Only glycerol, tetrahydroxy alcohols, fructose, sorbitol and mannitol can enhance the acidity of H3BO3. This is due to the influence of steric hindrance, which makes it difficult for some polyols and hydroxyl-containing compounds to form complexes with H3BO3.

[0024] Preferably, the second additive in step (3) includes any one of aluminum oxide, zirconium oxide or titanium oxide, or a combination of at least two of them.

[0025] Preferably, the mass ratio of the second additive to the calcined material is (0.05-0.2):100, for example: 0.05:100, 0.08:100, 0.1:100, 0.15:100 or 0.2:100, etc.

[0026] Preferably, the mass ratio of the mixed solution to the calcined material in step (3) is (0.1-5):100, for example: 0.1:100, 1:100, 2:100, 3:100, 4:100 or 5:100, etc., preferably (0.5-3):100.

[0027] Preferably, the temperature of the two-step sintering treatment in step (3) is 200-600°C, for example, 200°C, 300°C, 400°C, 500°C or 600°C, and preferably 250-500°C.

[0028] Preferably, the time for the two-step sintering treatment is 6 to 24 hours, for example, 6 hours, 8 hours, 10 hours, 15 hours or 24 hours, etc., preferably 6 to 15 hours.

[0029] In a second aspect, the present invention provides a modified ternary positive electrode material, which is prepared by the method described in the first aspect.

[0030] In a third aspect, the present invention provides a positive electrode plate, which comprises the modified ternary positive electrode material as described in the second aspect.

[0031] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet as described in the third aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention dissolves a polyhydroxy compound and boric acid in water to prepare a mixed solution, sprays the mixed solution into the positive electrode material through an atomizing device and mixes it evenly, and the atomized solution reacts with the residual lithium (LiOH, Li2CO3) on the surface of the positive electrode material to undergo an acid-base neutralization reaction, thereby greatly reducing the residual alkali content of the ultra-high nickel positive electrode material. The mixed solution is atomized and mixed with a sintered material instead of being used as a pickling solvent for pickling the material. Compared with pickling, this method reduces the degree of erosion on the surface of the positive electrode material, reduces the loss of capacity caused by the dissolution of transition metals, and effectively improves the processing performance and cycle life of the material.

[0034] (2) The Li3BO3 generated during the reaction of the method of the present invention forms a protective coating on the surface of the material, which can effectively avoid the erosion of the electrolyte and maintain the structural stability during the charge and discharge process. At the same time, Li3BO3 is a good lithium ion conductor and can promote the diffusion of lithium ions between the electrolyte interfaces. In addition, B 3+ Due to the small ionic radius, it is easy to embed into the crystal lattice, which can reduce the degree of cation mixing.

[0035] (3) The surface residual alkali content of the modified ternary positive electrode material of the present invention can reach below 8530 ppm, the first-week charging capacity of the prepared battery can reach above 241.6 mAh / g, the first-week discharge capacity can reach above 214.4 mAh / g, the first coulombic efficiency can reach above 87.6%, and the capacity retention rate after 50 cycles can reach above 89.7%. By adjusting the type of alcohol used and the reaction conditions, the surface residual alkali content of the modified ternary positive electrode material can reach 6580 ppm, the first-week charging capacity of the prepared battery can reach 244.4 mAh / g, the first-week discharge capacity can reach 215.5 mAh / g, the first coulombic efficiency can reach 88.2%, and the capacity retention rate after 50 cycles can reach 94%. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the SEM image of the modified ternary positive electrode material described in Example 5.

[0037] Figure 2 This is the SEM image of the modified ternary positive electrode material described in Comparative Example 1. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0039] Example 1

[0040] This embodiment provides a modified ternary cathode material, and the preparation method of the modified ternary cathode material is as follows:

[0041] (1) Ni0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0042] (2) dissolving boric acid in deionized water, adding ethylene glycol and stirring for 10 min to form a boric acid-ethylene glycol mixed solution;

[0043] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconia added to the primary sintered material, and a 2 wt% boric acid-ethylene glycol mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then heated at 350 ° C for 6 h at a heating rate of 2 ° C / min under an oxygen atmosphere, and naturally cooled with the furnace. After that, the mixture was crushed, sieved, and demagnetized to obtain boric acid-ethylene glycol modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0044] Example 2

[0045] This embodiment provides a modified ternary cathode material, and the preparation method of the modified ternary cathode material is as follows:

[0046] (1) Ni 0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0047] (2) Boric acid was dissolved in deionized water, and glycerol was added and stirred for 10 min to form a boric acid-glycerol mixed solution;

[0048] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconia added to the primary sintered material, and a 2 wt% boric acid-glycerol mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then heated at 350 ° C for 6 h at a heating rate of 2 ° C / min under an oxygen atmosphere, and naturally cooled with the furnace. After that, the mixture was crushed, sieved, and demagnetized to obtain boric acid-glycerol modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0049] Example 3

[0050] This embodiment provides a modified ternary cathode material, and the preparation method of the modified ternary cathode material is as follows:

[0051] (1) Ni 0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0052] (2) dissolving boric acid in deionized water, adding erythritol and stirring for 10 minutes to form a boric acid-erythritol mixed solution;

[0053] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconium oxide added in an amount of the primary sintered material, and a 2 wt% boric acid-erythritol mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then kept at 350 ° C at a heating rate of 2 ° C / min for 6 h in an oxygen atmosphere, and naturally cooled with the furnace. After that, the mixture was crushed, sieved, and demagnetized to obtain boric acid-erythritol modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0054] Example 4

[0055] This embodiment provides a modified ternary cathode material, and the preparation method of the modified ternary cathode material is as follows:

[0056] (1) Ni 0.96 Co 0.02Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0057] (2) Boric acid was dissolved in deionized water, and fructose was added and stirred for 10 min to form a boric acid-fructose mixed solution;

[0058] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconia added to the primary sintered material, and a 2 wt% boric acid-fructose mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then heated at 350 ° C for 6 h at a heating rate of 2 ° C / min in an oxygen atmosphere, and naturally cooled with the furnace. After that, the mixture was crushed, sieved, and demagnetized to obtain boric acid-fructose modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0059] Example 5

[0060] This embodiment provides a modified ternary cathode material, and the preparation method of the modified ternary cathode material is as follows:

[0061] (1) Ni 0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0062] (2) Boric acid was dissolved in deionized water, and mannitol was added and stirred for 10 min to form a boric acid-mannitol mixed solution;

[0063] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconia added to the primary sintered material, and a 2 wt% boric acid-mannitol mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then heated at 350 ° C. at a heating rate of 2 ° C. / min for 6 h in an oxygen atmosphere, cooled naturally with the furnace, and then crushed, sieved, and demagnetized to obtain boric acid-mannitol modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0064] The SEM image of the modified ternary cathode material is as follows: Figure 1 shown.

[0065] Example 6

[0066] This embodiment provides a modified ternary cathode material, and the preparation method of the modified ternary cathode material is as follows:

[0067] (1) Ni 0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0068] (2) dissolving boric acid in deionized water, adding sorbitol, and stirring for 10 min to form a boric acid-sorbitol mixed solution;

[0069] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconia added in an amount of the primary sintered material, and a 2 wt% boric acid-sorbitol mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then kept at 350 ° C at a heating rate of 2 ° C / min for 6 h in an oxygen atmosphere, cooled naturally with the furnace, and then crushed, sieved, and demagnetized to obtain boric acid-sorbitol modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0070] Example 7:

[0071] The only difference between this embodiment and embodiment 5 is that the heat treatment temperature in step (3) is 250° C., and the other conditions and parameters are exactly the same as those in embodiment 5.

[0072] Example 8:

[0073] The only difference between this embodiment and embodiment 5 is that the heat treatment temperature in step (3) is 600° C., and the other conditions and parameters are exactly the same as those in embodiment 5.

[0074] Example 9:

[0075] The only difference between this embodiment and embodiment 5 is that the mass of the boric acid-mannitol mixed solution is 0.1 wt % of the mass of the primary sintering material. Other conditions and parameters are exactly the same as those in embodiment 5.

[0076] Example 10:

[0077] The only difference between this embodiment and embodiment 5 is that the mass of the boric acid-mannitol mixed solution is 5 wt % of the mass of the primary sintering material. Other conditions and parameters are exactly the same as those in embodiment 5.

[0078] Comparative Example 1

[0079] This comparative example provides a modified ternary positive electrode material, and the preparation method of the modified ternary positive electrode material is as follows:

[0080] (1) Ni 0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-speed mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 690°C in an oxygen atmosphere at a heating rate of 2°C / min for 10 hours, and then naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material.

[0081] (2) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconium oxide, and then heated at 450 ° C for 6 h at a heating rate of 2 ° C / min in an oxygen atmosphere, and then naturally cooled with the furnace. After that, it was crushed, sieved, and demagnetized to obtain Mg-doped Li 1.01 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0082] The SEM image of the modified ternary cathode material is as follows: Figure 2 shown.

[0083] Comparative Example 2

[0084] (1) Ni0.96 Co 0.02 Mn 0.02 (OH)2 and battery-grade lithium hydroxide monohydrate are mixed in a high-pressure mixer at a lithium to metal molar ratio of 1.02:1, and magnesium hydroxide (0.1 wt% of the mass of the ternary precursor) is added. The mixture is heated at 700°C for 10 hours at a heating rate of 2°C / min in an oxygen atmosphere, and naturally cooled in the furnace. After that, the mixture is crushed and sieved to obtain a primary sintered material for the ultra-high nickel positive electrode material.

[0085] (2) Boric acid was dissolved in deionized water, and ethanol was added and stirred for 10 min to form a boric acid-ethanol mixed solution;

[0086] (3) The primary sintered material was mixed evenly with 0.1 wt% of alumina and 0.1 wt% of zirconia added to the primary sintered material, and a 2 wt% boric acid-ethanol mixed solution was atomized by a spray device and sprayed into a stirring chamber to fully mix the solution and the material. The mixture was then heated at 350 ° C for 6 h at a heating rate of 2 ° C / min in an oxygen atmosphere, and naturally cooled with the furnace. After that, the mixture was crushed, sieved, and demagnetized to obtain boric acid-ethanol modified Li 1.02 Ni 0.96 Co 0.02 Mn 0.02 O2 ultra-high nickel positive electrode material.

[0087] Performance testing:

[0088] The modified ternary cathode materials obtained in Examples 1-10 and Comparative Examples 1-2 were tested for alkali content, and button batteries were made to test capacity and cycle performance. The results are shown in Table 1:

[0089] Table 1

[0090]

[0091]

[0092] As can be seen from Table 1, it can be obtained from Examples 1-6 that the surface residual alkali amount of the modified ternary positive electrode material of the present invention can reach less than 8530 ppm, the first-week charging capacity of the prepared battery can reach more than 241.6 mAh / g, the first-week discharge capacity can reach more than 214.4 mAh / g, the first coulombic efficiency can reach more than 87.6%, and the capacity retention rate after 50 cycles can reach more than 89.7%. By adjusting the type of alcohol used and the reaction conditions, the surface residual alkali amount of the modified ternary positive electrode material can reach 6580 ppm, the first-week charging capacity of the prepared battery can reach 244.4 mAh / g, the first-week discharge capacity can reach 215.5 mAh / g, the first coulombic efficiency can reach 88.2%, and the capacity retention rate after 50 cycles can reach 94%.

[0093] By comparing Example 5 with Examples 7-8, it can be seen that the temperature of the sintering treatment in step (3) affects the performance of the obtained positive electrode material. When the temperature of the second-step sintering treatment is controlled at 250-600°C, the performance of the obtained positive electrode material is better. If the temperature of the second-step sintering treatment is too high, it is not conducive to the formation of Li3BO3. At the same time, if the temperature is too high, the primary particles will grow further, hindering the transmission of lithium ions. In addition, energy consumption will increase, increasing processing costs. If the temperature of the second-step sintering treatment is too low, other additives such as aluminum oxide and zirconium oxide cannot be melted well, forming an uneven coating on the surface of the particles, which is not conducive to reducing the residual alkali on the surface and affecting the cycle performance of the material. At the same time, some polyhydroxy compounds will remain, affecting the performance of the capacity.

[0094] By comparing the examples with examples 9-10, it can be seen that the mass ratio of the mixed solution of boric acid and polyhydroxy compound to the calcined material affects the performance of the prepared positive electrode material. When the mass ratio of the mixed solution to the calcined material is controlled at 0.5 to 3:100, the performance of the prepared positive electrode material is better. If the amount of the mixed solution added is too large, although the residual alkali on the surface of the material can be significantly reduced, the material will stick to the wall due to the high humidity and poor fluidity during the early mixing process, making it difficult to clean the high-pressure mixer and the mixing uniformity worse. At the same time, the degree of reaction with the residual alkali on the surface of the material is large, the surface area of ​​the material is increased, and the surface activity of the ultra-high nickel material is high, resulting in a decrease in cycle performance. If the amount of the mixed solution added is too small, the residual alkali such as LiOH and Li2CO3 on the surface of the ultra-high nickel positive electrode material undergoes acid-base neutralization reaction to remove less residual alkali, and the effect of reducing the residual alkali on the surface of the material is not obvious, which increases the risk of side reactions with the electrolyte and flatulence in the lithium-ion battery.

[0095] By comparing Example 1 and Comparative Example 1, it can be seen that the present invention coats the boric acid modified with a polyhydroxy compound by a spray method, and removes the residual alkali such as LiOH and Li2CO3 on the surface of the ultra-high nickel positive electrode material by an acid-base neutralization reaction, thereby avoiding problems such as irreversible capacity loss and battery flatulence. At the same time, the formed Li3BO3 acts as a good lithium ion conductor, which can not only promote the diffusion of lithium ions, but also effectively prevent the electrolyte from corroding the interior of the particles, reducing impedance, and improving the cycle stability of the material.

[0096] By comparison of Example 1 and Comparative Example 2, it can be seen that the present invention dissolves a polyhydroxy compound and boric acid in water to form a mixed solution, sprays the mixed solution into the positive electrode material through an atomizing device and mixes it evenly, and the atomized solution undergoes an acid-base neutralization reaction with the residual lithium (LiOH, Li2CO3) on the surface of the positive electrode material, thereby greatly reducing the residual alkali content of the ultra-high nickel positive electrode material. After atomization, the mixed solution is mixed with a sintered material instead of being used as a pickling solvent for pickling the material. Compared with pickling, this method reduces the degree of erosion on the surface of the positive electrode material, reduces the loss of capacity caused by the dissolution of transition metals, and effectively improves the processing performance and cycle life of the material.

[0097] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a modified ternary cathode material, characterized in that: The preparation method comprises the following steps: (1) mixing an ultra-high nickel ternary precursor, a first additive, and a lithium source, and performing a one-step sintering treatment to obtain a single-fired material; (2) mixing boric acid with water and adding a polyol to obtain a mixed solution; (3) mixing the sintered material obtained in step (1) with the second additive to obtain a mixed material, atomizing the mixed solution obtained in step (2) and mixing it with the mixed material, and performing a two-step sintering process to obtain the modified ternary cathode material; The polyhydroxy compound includes any one of ethylene glycol, glycerol, erythritol, fructose, mannitol or sorbitol, or a combination of at least two thereof.

2. The preparation method according to claim 1, wherein In step (1), the first additive includes any one of aluminum oxide, magnesium hydroxide, zirconium oxide or tungsten oxide, or a combination of at least two of them.

3. The preparation method according to claim 1, wherein The lithium source includes lithium hydroxide and / or lithium carbonate.

4. The preparation method according to claim 1, wherein The molar ratio of the lithium element in the lithium source to the metal element in the ultra-high nickel ternary precursor is (1.01-1.1):

1.

5. The preparation method according to claim 4, wherein The molar ratio of the lithium element in the lithium source to the metal element in the ultra-high nickel ternary precursor is (1.01-1.06):

1.

6. The preparation method according to claim 1, wherein The temperature of the one-step sintering treatment in step (1) is 600-900°C.

7. The preparation method according to claim 6, wherein The temperature of the one-step sintering treatment in step (1) is 650-750°C.

8. The preparation method according to claim 1, wherein The one-step sintering treatment takes 8 to 24 hours.

9. The preparation method according to claim 8, wherein The one-step sintering treatment takes 10 to 20 hours.

10. The preparation method according to claim 1, wherein The one-step sintering process may also include the addition of a carbon source.

11. The preparation method according to claim 1, wherein The chemical formula of the sintered material is Li 1+y (Ni a Co b Mn 1-a-b-c B c ) 1-y O2, where 0≤y≤0.1, 0.95≤a<1, 0.01≤b≤0.1, 0≤c≤0.05, B includes Mg 2+ , Al 3+ , W 6+ or Zr 4+ Any one or a combination of at least two of .

12. The preparation method according to claim 1, wherein The mass ratio of boric acid to water in step (2) is (0.1-5):

100.

13. The preparation method according to claim 1, wherein In step (3), the second additive includes any one of aluminum oxide, zirconium oxide or titanium oxide, or a combination of at least two of them.

14. The preparation method according to claim 1, wherein The mass ratio of the second additive to the calcined material is (0.05-0.2):

100.

15. The preparation method according to claim 1, wherein The mass ratio of the mixed solution in step (3) to the calcined material is (0.1-5):

100.

16. The preparation method according to claim 15, characterized in that The mass ratio of the mixed solution in step (3) to the calcined material is (0.5-3):

100.

17. The preparation method according to claim 1, wherein The temperature of the second-step sintering treatment in step (3) is 200-600°C.

18. The preparation method according to claim 17, wherein The temperature of the second-step sintering treatment in step (3) is 250-500°C.

19. The preparation method according to claim 1, wherein The time of the two-step sintering treatment is 6 to 24 hours.

20. The preparation method according to claim 19, wherein The time of the two-step sintering treatment is 6 to 15 hours.

21. A modified ternary cathode material, characterized in that: The modified ternary positive electrode material is prepared by the preparation method according to any one of claims 1 to 20.

22. A positive electrode plate, characterized in that: The positive electrode plate comprises the modified ternary positive electrode material as claimed in claim 21.

23. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet as claimed in claim 22.

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