A lithium ion battery positive electrode material, a preparation method thereof, and a lithium ion battery

Abstract

The application provides a preparation method of a lithium ion battery positive electrode material, comprising the following steps: S1, uniformly mixing a high-nickel ternary precursor, a lithium salt and a dopant, and performing first sintering to obtain a high-nickel ternary positive electrode material matrix; S2, uniformly mixing the high-nickel ternary positive electrode material matrix and a cobalt-containing compound, and performing second sintering; and S3, uniformly mixing the second sintering product and coating raw materials, and performing third sintering to obtain a positive electrode material coated with a solid-state electrolyte on the surface. The thermal stability and lithium ion transmission kinetics performance of the positive electrode material prepared by the method are obviously improved, so that the metal elution amount and the electrochemical performance of the positive electrode material are obviously improved when the positive electrode material is used in a lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a lithium-ion battery cathode material and its preparation method. Background Technology

[0002] With the vigorous promotion of electric vehicles in China, the rapid rise of the new energy vehicle industry has driven the development of the lithium-ion battery market. Consumers' demands for vehicle range and safety performance are also constantly increasing. However, longer vehicle range requires increasingly lighter on-board batteries with continuously improving energy density. Ternary lithium batteries, due to their light weight and high electrochemical capacity, have become the preferred battery for high-end models. According to the electrochemical formula E=C*V, the unit energy density of the cathode material is directly proportional to the nickel content in the material and the battery's operating voltage. However, high-nickel materials can cause electrolyte decomposition reactions during the reaction process at high cutoff voltages, leading to increased dissolution of transition metals and ineffective suppression of irreversible phase transformation during lithium insertion / extraction reactions. This further increases the gas production rate of the entire battery, causes excessively rapid DCR growth, and deteriorates cycle stability.

[0003] To improve the solid-gas / liquid interface stability of high-nickel cathode materials, many research teams have recently employed coating modification techniques to construct a protective film on the cathode material surface, which is an effective method to enhance surface stability. In lithium-ion batteries, the interface between the electrode and the electrolyte is a crucial region for charge and ion transport, significantly impacting battery performance. Constructing nanoscale coatings on the cathode surface can improve lithium-ion battery performance. Currently, various surface coating materials and their effects on electrochemical performance have been reported in the literature. Surface-coated films can effectively suppress surface phase transitions and reduce the loss of active materials on the cathode material surface. Reported coating materials can be categorized into inert oxide coatings, ion conductor / solid electrolyte coatings, etc.

[0004] The patent with publication number CN114656000A provides a design that incorporates trivalent and pentavalent antimony into lithium nickel cobalt manganese oxide materials. Lithium nickel cobalt manganese oxide materials containing trivalent and pentavalent antimony can effectively suppress side reactions between the material and the electrolyte, inhibit the dissolution of transition metals, improve the diffusion coefficient of the material, and enhance the safety performance and long-term cycle capacity retention of the material.

[0005] Patent CN114497494A discloses a nickel-rich ternary material that is simultaneously modified with boron lattice doping and surface Li4B2O5-LiF coating by using a special modifier NH4BF4 at a specific temperature. Due to the boron lattice doping, the structural stability of the modified nickel-rich ternary material is greatly improved. At the same time, the formation of the surface coating layer helps to protect the material interface, inhibit the dissolution of transition metals on the material surface, and reduce the catalytic decomposition of the electrolyte.

[0006] Patent CN109473657A discloses a doped and coated nickel-cobalt-aluminum-manganese quaternary lithium-ion battery cathode material. The preparation method mainly includes four sintering processes and one cleaning process. The doping element is Ti, Al, or Mg, and the coating element is Zr, Zn, or Al. The material prepared by this invention has a low surface residual alkali content and good stability, but the preparation process is relatively complex.

[0007] Patent CN111422919A discloses a multi-element cathode material co-doped with aluminum and zirconium and coated with boron. In this multi-element cathode material, the co-doping of aluminum and zirconium has a good synergistic effect, which can better improve the structural stability of the matrix, while the boron coating can effectively reduce the specific surface area of ​​the material and improve the electrochemical performance of the cathode material.

[0008] Existing coating methods suffer from several drawbacks, including insignificant modification effects, uneven coating, poor interface uniformity, and unsatisfactory improvement in electrochemical performance. At higher voltages or temperatures, side reactions can easily occur between the material interface or the coating layer and the electrolyte, exacerbating the dissolution of transition metals from the material. Summary of the Invention

[0009] To address the above problems, this invention provides a lithium-ion battery cathode material, its preparation method, and a lithium-ion battery.

[0010] To address the problems existing in the prior art, the present invention provides the following technical solution:

[0011] A method for preparing a lithium-ion battery cathode material, comprising:

[0012] S1. Mix the high-nickel ternary precursor, lithium salt and dopant evenly to obtain a primary mixture, perform the first sintering, crushing and sieving to obtain the high-nickel ternary cathode material matrix.

[0013] S2. Mix the high-nickel ternary cathode material matrix with the cobalt-containing compound evenly and perform a second sintering.

[0014] S3. Mix the second sintering product with the coating material evenly, and perform a third sintering to obtain a positive electrode material with a solid electrolyte coating on its surface.

[0015] Preferably, in step S2, the temperature of the second sintering is 700-800℃, and the sintering time is 6-10 hours. Preferably, the atmosphere for the second sintering is an oxidizing atmosphere, specifically an oxygen atmosphere or an air atmosphere. If the second sintering temperature is too low, the coating agent will have a low degree of coating, resulting in uneven coating and insufficient reaction with residual lithium on the surface to form an effective coating layer; if the temperature is too high, the first coating agent will react excessively with the residual lithium on the surface, failing to form an effective gradient and exacerbating the mixing of lithium and nickel on the subsurface of the material. After the second sintering, the coated cobalt element will be enriched on the surface, resulting in a higher proportion of cobalt on the surface compared to the interior.

[0016] Preferably, in step S3, the temperature of the third sintering is 300-500℃, and the sintering time is 3-10h, more preferably 5.5-8.5h. The preferred heating rate is 0.5-10℃ / min, more preferably 1-5℃ / min; the third sintering is preferably carried out in an oxygen atmosphere, more preferably with an oxygen concentration ≥89%. In this invention, the second and third sintering can reduce lithium-nickel mixing and increase crystallinity and arrangement order. If the third sintering temperature is too low, an effective solid electrolyte intercalation coating layer cannot be formed; if it is too high, the lithium-nickel mixing degree of the material may be aggravated. The role of the third sintering in this invention is to perform in-situ synthesis coating on the surface of the second sintering product, generating a thin solid electrolyte layer to achieve uniform coating. Simultaneously, a solid solution reaction is achieved at high temperature, allowing the solid electrolyte layer generated by the coating material to better coat the surface of the cathode material, improving ionic conductivity, enhancing the stability of the cathode material, reducing side reactions with the electrolyte, and improving the electrochemical performance of the cathode material.

[0017] Preferably, after the third sintering, the cooled product is subjected to a crushing, sieving, and demagnetizing process. The sieve mesh size is 200-350 mesh.

[0018] Preferably, the molar ratio of the high-nickel ternary precursor to the cobalt-containing compound is 1:0.001-0.05, more preferably 1:0.01-0.05;

[0019] Optionally, the cobalt-containing compound is selected from, but not limited to, one or more of cobalt hydroxyoxide, cobalt(II) hydroxide, cobalt(III) oxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt phosphate, cobalt acetylacetonate, and cobalt sulfate. By using a cobalt-containing compound as the first coating agent, sintering results in a high concentration of cobalt on the surface, naturally forming a cobalt concentration gradient. By forming a cobalt-containing coating layer, the rate performance and high-temperature cycling stability of the material can be increased, the lithium-nickel mixing phenomenon on the outer surface can be reduced, and cobalt, being a transition metal site, can improve the irreversible phase transition of the material and enhance structural stability.

[0020] Preferably, the molar ratio of the high-nickel ternary precursor to the solid electrolyte formed by sintering the coating raw material is 1:0.0001~0.01, more preferably 1:0.0005~0.005. If the molar ratio is too high, the specific capacity of the cathode material will decrease and the electrochemical performance will be lower; if the molar ratio is too low, the coating will not be sufficient, the thermal stability of the material will not be sufficiently improved, and the amount of transition metal ions dissolved will increase.

[0021] The coating material includes one or more of the oxides, hydroxides or non-organic acid salts of Li, Co, Sr, Al, W, Ti, Mg, Zr, Ta, Mo, F, B, Y, La, V, and P.

[0022] Optionally, the lithium (Li) oxide, hydroxide, or non-organic acid salt is lithium oxide, lithium hydroxide, lithium carbonate, lithium nitrate, lithium fluoride, etc.

[0023] The oxides, hydroxides, or non-organic acid salts of aluminum (Al) are aluminum oxide, aluminum hydroxide, lithium aluminate, aluminum carbonate, aluminum nitrate, aluminum sulfate, aluminum bicarbonate, etc.

[0024] The oxides or hydroxides or non-organic acid salts of titanium (Ti) are titanium dioxide, titanium hydroxide, titanium carbonate, titanium nitrate, titanium phosphate, etc.

[0025] The zirconium (Zr) oxides, hydroxides, or non-organic acid salts mentioned are zirconium oxide, zirconium hydroxide, zirconium carbonate, zirconium chloride, zirconium sulfate, zirconium nitrate, etc.

[0026] The oxides, hydroxides, or non-organic acid salts of strontium (Sr) are strontium oxide, strontium hydroxide, strontium carbonate, strontium nitrate, strontium sulfate, strontium chloride, and strontium hydrogen phosphate, etc.

[0027] The oxides, hydroxides, or non-organic acid salts of lanthanum (La) are lanthanum trioxide, lanthanum carbonate, lanthanum chloride, and lanthanum nitrate, etc.

[0028] The oxides or hydroxides or non-organic acid salts of tantalum (Ta) are tantalum oxide, tantalum hydroxide, tantalum carbonate, tantalum chloride, tantalum sulfate, tantalum nitrate, etc.; the oxides or hydroxides or non-organic acid salts of boron (B) are boric acid, boron trioxide, boron carbonate, boron nitride, boron chloride, and boron nitrate, etc.

[0029] The oxides or hydroxides or non-organic acid salts of phosphorus (P) are phosphoric acid, aluminum phosphate, lithium phosphate, titanium phosphate, etc.

[0030] Preferably, the solid electrolyte formed by sintering the coating material is titanium aluminum phosphate strontium lanthanum lithium and / or lithium lanthanum zirconium tantalum cobalt niobium oxide.

[0031] Preferably, the molar ratio of the high-nickel ternary precursor, lithium salt, and dopant is 1:1.0~1.08:0.0005~0.005. If the molar ratio of the dopant is too high, the specific capacity will decrease; if it is too low, the doping effect will decrease, affecting the structural stability or rate performance.

[0032] Preferably, the chemical formula of the high-nickel ternary precursor is Ni x Co y Mn z (OH)2, wherein 0.5≤x≤0.95, preferably 0.5≤x≤0.8, 0.01≤y≤0.2, preferably 0.1≤y≤0.2, 0.01≤z≤0.3, preferably 0.1≤z≤0.3, and 0.95≤x+y+z≤1.05, preferably x+y+z=1;

[0033] Preferably, the lithium salt includes one or more of lithium hydroxide monohydrate, lithium hydroxide, lithium chloride, lithium sulfate, lithium borate, lithium nitrate, lithium acetate, and lithium carbonate.

[0034] Preferably, the dopant is one or more of Al and / or Mg oxides, hydroxides, or carbonates. Doping with aluminum compounds allows aluminum to replace transition metals in the precursor, improving the material's high-temperature stability. Doping with magnesium compounds allows magnesium to replace lithium sites in the precursor, thereby improving the material's structural stability. The Al oxides, hydroxides, or carbonates include aluminum hydroxide, aluminum oxide, aluminum carbonate, aluminum bicarbonate, etc. The Mg oxides, hydroxides, or carbonates include magnesium hydroxide, magnesium oxide, magnesium carbonate, magnesium bicarbonate, etc.

[0035] Preferably, the temperature of the first sintering is 850-1000℃; the time of the first sintering is 8-20h, preferably 10-15h; and the atmosphere of the first sintering is an oxygen atmosphere. The preferred heating rate is 0.5-10℃ / min, more preferably 1-5℃ / min; and the preferred oxygen concentration of the oxygen atmosphere is ≥89%. If the first sintering temperature is too low, the primary crystal particles will be too small, resulting in low crystallinity and uneven doping; if it is too high, the primary crystal particles will be too large, leading to excessive lithium-nickel mixing, resulting in poor material structural stability and hindered lithium ion insertion / extraction.

[0036] As a general inventive concept, the present invention provides a lithium-ion battery cathode material, which is prepared by the aforementioned preparation method.

[0037] Preferably, the leaching amount of the transition metal element in the cathode material is 100-5000 ppm, more preferably 1000-2500 ppm, such as 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400 ppm, etc., and the particle size D50 of the cathode material is 2-20 μm, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 μm, etc., or the tap density is 2-4 g / cm³. 3 For example, 2.5, 3, 3.5 g / cm³ 3 Or, a specific surface area of ​​0.5-5.0 m². 3 / g, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, etc. 3 / g.

[0038] The test conditions for the dissolution of transition metal elements in the positive electrode material are as follows: after assembling the battery, charge it to 4.3V after one full charge-discharge cycle (2.8V-4.3V), remove the positive electrode sheet, clean it, immerse it in an appropriate amount of electrolyte and seal it in aluminum-plastic seal. After storing it at 60℃ for 7 days, compare the dissolution of the metals of Ni, Co and Mn.

[0039] The particle size of the cathode material depends on the particle size of the precursor and the subsequent pulverization steps. The particle size can be controlled by adjusting the specific parameters of the pulverization steps. The tap density of the product is affected by the intrinsic properties of the material, such as whether it is a monocrystalline or polycrystalline material, and whether it has a hollow structure. The cathode material of this invention is preferably a monocrystalline material. The specific surface area of ​​the product is directly proportional to the specific surface area of ​​the coating material; the larger the specific surface area of ​​the coating material, the larger the specific surface area of ​​the product. In the prior art, the leaching amount of transition metal elements in cathode materials is mostly above 3000 ppm.

[0040] As a general inventive concept, the present invention also provides a lithium-ion battery, including the aforementioned lithium-ion battery cathode material.

[0041] This invention also provides a method for detecting the dissolution of transition metal ions in a lithium-ion battery cathode material, wherein the lithium-ion battery cathode material is prepared by the aforementioned method and includes the following steps:

[0042] (1) Place the lithium-ion battery positive electrode material in a centrifuge tube, soak it in the electrolyte solvent, seal and store it in an inert atmosphere at 40-60°C in the dark, and collect the washing liquid;

[0043] (2) The washing solution is filtered, diluted to a fixed volume, and subjected to ICP testing to obtain the content of transition metal elements.

[0044] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0045] (1) In this invention, a doping and mixing step is first used to pre-dope modified elements during the lithiation reaction of the medium-high nickel ternary precursor to improve the electrochemical performance of the cathode material. Then, the doped and modified medium-high nickel cathode material matrix is ​​mixed and sintered with a cobalt-containing compound to form a cobalt-containing coating layer on the surface of the cathode material matrix. After rapid passivation, a dense passivation layer of cobalt tetroxide and cobalt oxide is formed on the surface of the cathode material, preventing further oxygen release and degradation behavior on the subsurface of the cathode material. The second sintering product with the cobalt-containing coating layer is then mixed and sintered with the coating material to further coat the cathode material with a solid electrolyte coating layer, suppressing interfacial side reactions. Through the specific solid electrolyte with high intrinsic lithium content of this invention, which can replenish lithium in situ on the surface of the layered cathode material at high temperature, the thermal stability of the cathode material under deep charging and delithiation state at high voltage can be improved through synergistic coating, the lithium ion transport kinetics at the electrode / electrolyte interface can be improved, and the ion conductivity at the electrode / electrolyte interface can be increased.

[0046] (2) In this invention, by doping Al and Mg in the lithiation reaction of high-nickel ternary precursors, the lithium-ion diffusion channels can be broadened, the generation of phase transition can be suppressed, the conductivity of electrons and ions can be improved, the internal resistance can be reduced, and thus the electrochemical performance of the cathode material can be improved.

[0047] (3) In this invention, a cobalt-containing coating layer is formed on the surface of the positive electrode material by mixing and sintering the positive electrode material with a cobalt-containing compound, and a cobalt concentration gradient is formed between the inner and outer layers of the material. The high cobalt concentration on the surface of the material is beneficial to improving the surface / interface charge transport, reducing the lithium-nickel mixing phenomenon on the outer surface, improving the stability of the structure, and improving the rate performance and high-temperature cycling stability of the material.

[0048] (4) This invention mixes the coating material with the cathode material and then performs a third sintering to coat the cathode material with a solid electrolyte coating layer containing multiple specific elements. The electrochemical performance is improved by the synergistic modification effect of cobalt and multiple elements. By using a second coating agent with a specific element combination and performing in-situ synthesis and coating of the solid electrolyte, the solid electrolyte can be fully reacted and uniformly coated, thereby achieving the effect of suppressing the dissolution of transition metals, reducing the amount of coating agent used, improving interface stability, suppressing interface side reactions, improving high voltage stability, suppressing side reactions between the material and the electrolyte, resisting the corrosion of the active material by HF, suppressing irreversible phase transitions, improving the lithium ion transport kinetics at the electrode / electrolyte interface, and improving the ion conductivity at the electrode / electrolyte interface.

[0049] (5) This invention employs a third sintering step, utilizing a high-temperature interfacial solid solution reaction to form a metal oxide solid solution phase between the cobalt-containing coating layer and the solid electrolyte coating layer. This allows the Li-Co-O metal compound in the cobalt-containing coating layer on the surface of the cathode material and various metal ions in the solid electrolyte coating agent, such as titanium aluminum phosphate, strontium lanthanum lithium, to undergo interfacial solid solution reactions. Furthermore, these ions react fully with residual lithium on the surface of the cathode material, such as LiOH and LiCO3, to generate a lithium active bond oxide coating layer with multiple metal ion oxygen bonds. This promotes the Li... + Diffusion enhances electrochemical performance and can consume residual lithium to reduce electrochemical polarization, ultimately synergistically improving the surface / subsurface conductivity and ion conductivity of the ternary cathode material. This results in effective improvement of the electrochemical performance of the synergistically coated cathode material, including discharge specific capacity, initial coulombic efficiency, and cycle performance.

[0050] (6) The preparation process of the cathode material of the present invention is relatively simple, and it has the advantages of low cost, simple operation and safety without pollution, and can be applied to large-scale production. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 Here is a SEM image of the cathode material from Example 1;

[0053] Figure 2 Here is a SEM image of the cathode material from Example 2;

[0054] Figure 3 Here is a SEM image of the cathode material in Example 3;

[0055] Figure 4 The images show the XRD patterns of the cathode materials prepared in Example 1, Comparative Examples 1 and 3. Detailed Implementation

[0056] The following describes the manufacturers of the raw materials and instruments used in the embodiments and comparative examples, as well as the instruments and analytical methods used in the product analysis. The raw materials or reagents used in the embodiments of this invention are all purchased from mainstream manufacturers and are of analytical purity or higher. There are no special restrictions as long as they achieve the expected effect. Where specific techniques or conditions are not specified in the embodiments of this invention, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Instruments or raw materials whose manufacturers are not specified are all conventionally available commercial products. Reagents whose manufacturers or concentrations are not specified are all conventionally obtainable analytical purity reagents. There are no special restrictions as long as they achieve the expected effect. The reaction vessels, scanning electron microscopes, particle size analyzers, drying equipment, and other instruments and equipment used in the embodiments of this invention are all purchased from major manufacturers in the market. There are no special limitations as long as they achieve the expected effect.

[0057] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0058] Example 1

[0059] (1) Using a high-speed mixer, 1.0 mol of medium-high nickel precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, 1.04 mol of LiOH and 0.002 mol of aluminum hydroxide were mixed evenly to obtain a mixture for primary sintering.

[0060] (2) The above-mentioned mixture for sintering is subjected to first sintering in an oxygen atmosphere with an oxygen concentration of 92%, the heating rate is 2℃ / min, the temperature is raised to 900℃, and the temperature is kept constant for 12h; after cooling to room temperature, it is crushed and sieved to obtain the first sintering product.

[0061] (3) The first calcined product is mixed with 0.03 mol cobalt hydroxide and coated evenly to obtain a first coating mixture. The first coating mixture is then sintered for the second time under an oxidizing atmosphere at a temperature of 750°C and a holding time of 8 h to form a cobalt-containing coating layer on the surface of the first calcined product, thus obtaining the second calcined product.

[0062] (4) Lithium nitrate, aluminum nitrate, tetrabutyl titanate, strontium hydroxide, lanthanum nitrate, and ammonium dihydrogen phosphate are thoroughly mixed in a molar ratio of 1.3:0.2:1.2:1.0:0.1:3.0 to obtain a mixed powder. The mixed powder is added to an equal mass of ethanol and stirred at 80°C for 30 min to fully mix and disperse, thereby obtaining a second coating agent composition for preparing lithium titanium aluminum strontium lanthanum lithium titanium phosphate (Taplas-A).

[0063] Then, the secondary sintering product is thoroughly stirred and mixed with a second coating agent composition that can prepare 0.002 mol of Taplas-A to obtain a secondary coating mixture for in-situ coating and in-situ sintering.

[0064] Then, the secondary coating mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 3℃ / min, heated to 400℃, and sintered at a constant temperature for 7h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0065] Example 2

[0066] (1) Using a high-speed mixer, 1.0 mol of medium-high nickel precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, 1.0 mol of LiOH and 0.0005 mol of aluminum hydroxide are mixed evenly to obtain a mixture for primary sintering.

[0067] (2) The above-mentioned mixture for sintering is subjected to first sintering in an oxygen atmosphere with an oxygen concentration of 92%, the heating rate is 1.0℃ / min, the temperature is raised to 850℃, and the temperature is kept constant for sintering for 15h; after cooling to room temperature, it is crushed and sieved to obtain the first sintering product.

[0068] (3) The first sintering product is mixed with 0.01 mol cobalt hydroxide and coated evenly to obtain a first coating mixture. The first coating mixture is then sintered for the second time under an oxidizing atmosphere at a temperature of 700°C and a holding time of 10 h to form a cobalt-containing coating layer on the surface, thus obtaining the second sintering product.

[0069] (4) Lithium nitrate, aluminum nitrate, tetrabutyl titanate, strontium hydroxide, lanthanum nitrate and ammonium dihydrogen phosphate are thoroughly mixed in a molar ratio of 1.3:0.2:1.2:1.0:0.1:3.0 to obtain a mixed powder. The mixed powder is added to an equal mass of ethanol and then stirred at 70°C for 45 min to fully mix and disperse, thereby obtaining the second coating agent composition for preparing Taplas-A.

[0070] Then, the secondary sintering product is thoroughly stirred and mixed with a second coating agent composition that can prepare 0.0005 mol of Taplas-A to obtain a secondary coating mixture for in-situ coating and in-situ sintering.

[0071] Finally, the secondary coated mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 1℃ / min, heated to 300℃, and sintered at a constant temperature for 8.5h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0072] Example 3

[0073] (1) Using a high-speed mixer, 1.0 mol of medium-high nickel precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, 1.08 mol of LiOH and 0.005 mol of aluminum hydroxide are mixed evenly to obtain a mixture for primary sintering;

[0074] (2) The above-mentioned mixture for sintering is subjected to first sintering in an oxygen atmosphere with an oxygen concentration of 92%, the heating rate is 5.0℃ / min, the temperature is raised to 1000℃, and the temperature is kept constant for sintering for 10h; after cooling to room temperature, it is crushed and sieved to obtain the first sintering product.

[0075] (3) The first sintering product is mixed with 0.05 mol cobalt hydroxide and coated evenly to obtain a first coating mixture. The first coating mixture is then sintered for the second time under an oxidizing atmosphere at a temperature of 800°C and a holding time of 6 h to form a cobalt-containing coating layer on the surface, thus obtaining the second sintering product.

[0076] (4) Lithium nitrate, aluminum nitrate, tetrabutyl titanate, strontium hydroxide, lanthanum nitrate and ammonium dihydrogen phosphate are thoroughly mixed in a molar ratio of 1.3:0.2:1.2:1.0:0.1:3.0 to obtain a mixed powder. The mixed powder is added to an equal mass of ethanol and stirred at 85°C for 30 min to fully mix and disperse, thereby obtaining the second coating agent composition for preparing Taplas-A.

[0077] Then, the secondary sintering product is thoroughly stirred and mixed with a second coating agent composition that can prepare 0.005 mol of Taplas-A to obtain a secondary coating mixture for in-situ coating and in-situ sintering.

[0078] Finally, the secondary coated mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 5℃ / min, heated to 500℃, and sintered at a constant temperature for 5.5h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0079] Example 4

[0080] The basic steps and processes of this embodiment are the same as those of Embodiment 1, except that in step (1), magnesium oxide is used instead of aluminum hydroxide; in step (3), cobalt tetroxide is used instead of cobalt hydroxide; and in step (4), lithium titanium aluminum phosphate strontium lanthanum lithium (Li) is used to prepare 0.002 mol of the product. 1.3 Al 0.1 Ti 1.4 Sr 0.6 La 0.2 The second coating agent composition of (PO4)3, step (4) is as follows:

[0081] Lithium nitrate, aluminum nitrate, tetrabutyl titanate, strontium hydroxide, lanthanum nitrate, and ammonium dihydrogen phosphate were thoroughly mixed in a molar ratio of 1.3:0.1:1.4:0.6:0.2:3.0 to obtain a mixed powder. The mixed powder was then added to an equal mass of ethanol and stirred at 80°C for 30 minutes to ensure thorough mixing and dispersion, thus obtaining the second coating agent composition for preparing Taplas-B.

[0082] The secondary sintering product is then thoroughly mixed with a second coating agent composition capable of preparing 0.002 mol of Taplas-B to obtain a secondary coating mixture for in-situ coating and in-situ sintering.

[0083] Then, the secondary coating mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 3℃ / min, heated to 400℃, and sintered at a constant temperature for 7h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0084] Example 5

[0085] The basic steps and processes of this embodiment are the same as those of Embodiment 1, except that in step (1), 1.0 mol of medium-high nickel precursor Ni is used. 0.5 Co 0.3 Mn 0.3 (OH)2 was used to replace 1.0 mol of the medium-high nickel precursor Ni. 0.7 Co 0.1 Mn 0.2 (OH)2, using 0.001 mol aluminum hydroxide and 0.001 mol magnesium oxide instead of 0.002 mol aluminum hydroxide; in step (3), using cobalt hydroxide instead of cobalt hydroxide; in step (4), using a second coating agent composition capable of preparing 0.002 mol lithium lanthanum zirconium tantalum cobalt niobium oxide (Tocnall-A), the specific steps of step (4) are as follows:

[0086] Lithium hydroxide, lanthanum trioxide, zirconium dioxide, tantalum pentoxide, cobalt hydroxide, and niobium pentoxide were thoroughly mixed in a molar ratio of 6.4:1.5:1.0:0.1:0.8:0.2 to obtain a mixed powder. The mixed powder was then added to an equal mass of ethanol and stirred at 80°C for 30 minutes to ensure thorough mixing and dispersion, thus obtaining the second coating agent composition for preparing Tocnall-A.

[0087] The secondary sintering product is then thoroughly mixed with a second coating agent composition capable of preparing 0.002 mol of Tocnall-A to obtain a secondary coating mixture for in-situ coating and in-situ sintering.

[0088] Then, the secondary coating mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 3℃ / min, heated to 400℃, and sintered at a constant temperature for 7h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0089] Example 6

[0090] The basic steps and processes of this embodiment are the same as those of Embodiment 1, except that in step (1), 1.0 mol of medium-high nickel precursor Ni is used. 0.8 Co 0.1 Mn 0.1 (OH)2 was used to replace 1.0 mol of the medium-high nickel precursor Ni. 0.7 Co 0.1 Mn 0.2 (OH)2, using 0.0015 mol aluminum hydroxide and 0.0005 mol magnesium oxide instead of 0.002 mol aluminum hydroxide; in step (3), using cobalt hydroxide instead of cobalt hydroxide; in step (4), using a second coating agent composition capable of preparing 0.002 mol lithium lanthanum zirconium tantalum cobalt niobium oxide (Tocnall-B), the specific steps of step (4) are as follows:

[0091] Lithium hydroxide, lanthanum trioxide, zirconium dioxide, tantalum pentoxide, cobalt hydroxide, and niobium pentoxide were thoroughly mixed in a molar ratio of 6.4:1.5:1.2:0.2:0.4:0.1 to obtain a mixed powder. The mixed powder was then added to an equal mass of ethanol and stirred at 80°C for 30 minutes to ensure thorough mixing and dispersion, thus obtaining the second coating agent composition for preparing Tocnall-B.

[0092] The secondary sintering product is then thoroughly mixed with a second coating agent composition capable of preparing 0.002 mol of Tocnall-B to obtain a secondary coating mixture for in-situ coating and in-situ sintering.

[0093] Then, the secondary coating mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 3℃ / min, heated to 400℃, and sintered at a constant temperature for 7h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0094] Example 7

[0095] The basic steps and processes of this embodiment are the same as those of Example 1. The difference is that in step (4), 0.001 mol of titanium dioxide and 0.001 mol of boron trioxide are used as the second coating agent to replace the second coating agent composition used in Example 1 for preparing titanium aluminum strontium lanthanum lithium (Taplas-A). Step (4) is as follows:

[0096] The secondary sintering product was thoroughly mixed with 0.001 mol of titanium dioxide and 0.001 mol of boron trioxide to obtain a secondary coating mixture.

[0097] Then, the secondary coating mixture was sintered for the third time in an oxygen atmosphere with an oxygen concentration of 92%, with a heating rate of 3℃ / min, heated to 400℃, and sintered at a constant temperature for 7h to obtain the 3-sintered product. After cooling to room temperature, it was thoroughly pulverized and sieved through a 300-mesh sieve to obtain the lithium-ion battery cathode material.

[0098] Comparative Example 1

[0099] The basic steps and processes are the same as in Example 1, except that the secondary sintering step (3) is omitted.

[0100] Comparative Example 2

[0101] The basic steps and processes are the same as in Example 1. The difference is that the amount of cobalt hydroxide used in step (3) is different. The amount of cobalt hydroxide used in this comparative example is 0.2 mol.

[0102] Comparative Example 3

[0103] The basic steps and processes are the same as in Example 1, except that step (4) is omitted.

[0104] Comparative Example 4

[0105] The basic steps and processes are the same as in Example 1. The difference is that in step (4), the amount of the second coating agent composition that can prepare titanium aluminum strontium lanthanum lithium phosphate is different. In this comparative example, the amount of the second coating agent composition is the amount that can prepare 0.05 mol of titanium aluminum strontium lanthanum lithium phosphate.

[0106] Comparative Example 5

[0107] The basic steps and processes are the same as in Example 1. The difference is that the sintering temperature is different in step (3). In this comparative example, the sintering temperature is 400℃.

[0108] XRD analysis was performed on the cathode materials prepared in Example 1, Comparative Examples 1 and 3, and the results are as follows: Figure 4 As shown, from Figure 4 As can be seen, compared to products coated only with a solid electrolyte and products coated only with a cobalt coating, the (003) main peak of the material coated with a cobalt coating first and then with a solid electrolyte shifts to a lower angle by approximately 0.02-0.03°, resulting in an increase in the c-axis lattice spacing of the modified material. It is speculated that this phenomenon is caused by a solid solution reaction between the Li-Co-O metal compound containing the cobalt coating and the solid electrolyte coating layer (titanium aluminum phosphate, strontium lanthanum lithium) during the third sintering process, forming a metal oxide solid solution phase. This phase then reacts fully with residual lithium on the surface of the cathode material, such as LiOH and LiCO3, to generate a lithium active bond oxide coating layer with multiple metal ion oxygen bonds. The increase in c-axis lattice spacing can expand the Li ion diffusion channels and promote Li... + Diffusion is beneficial to improving lithium-ion kinetics, which is consistent with electrochemical performance data.

[0109] [Preparation of button cells]

[0110] (1) Preparation of positive electrode

[0111] The positive electrode material prepared in the comparative examples above, the conductive agent SuperP, the binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) were mixed and stirred evenly at a mass ratio of 90:5:5 to form a positive electrode slurry (solid content approximately 40%). This slurry was coated onto a current collector aluminum foil, dried at 105°C, and then rolled at room temperature until the areal density reached 2.8-3.3 g / cm³. 3 Then, punch holes and cut them into φ14mm round sheets to make positive electrode sheets.

[0112] (2) Assembly of lithium-ion batteries

[0113] The button cell batteries are assembled inside the glove box. They are assembled in the following order: negative electrode shell - nickel foam - lithium sheet - 8 drops of electrolyte - separator - 8 drops of electrolyte - positive electrode sheet - positive electrode shell. The electrolyte is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC: EMC: DMC volume ratio = 1:1:1), and contains 1.0 M LiPF6.

[0114] The positive electrode has a diameter of 14mm, the lithium electrode has a diameter of 18mm, the separator has a diameter of 22mm, and the battery casing (positive and negative electrode casings) has a diameter of 24mm. The separator is a 16μm thick membrane. The assembled coin cells are placed in the mold cavity of a hydraulic sealing machine (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), locked, and pressure >450kg / cm² is applied. 2 Then unlock it and remove the sealed button battery.

[0115] [Performance Testing of Button Cell Batteries]

[0116] At 25℃, the charge-discharge cycle characteristics of the above-mentioned button batteries were tested using a Blue Electric test cabinet. The charge-discharge cycle was performed at a charge-discharge rate of 0.1C within a voltage range of 2.8V-4.3V. Specifically, the batteries were charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V to the cutoff current of 0.02C, and left to rest for 5 minutes. The batteries were then discharged at 0.1C to 2.8V and left to rest for 5 minutes. The charge-discharge capacity after the first cycle was recorded.

[0117] Next, the battery was charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V to the cutoff current of 0.02C, rested for 5 minutes, discharged at 0.1C to 2.8V, and rested for 5 minutes. This cycle was repeated 100 times. After the 100th cycle, the charge / discharge capacity was recorded, and the initial coulombic efficiency of the battery in the first cycle and the capacity retention rate after 100 cycles were determined.

[0118] [Detection of transition metal dissolution in cathode materials]

[0119] (1) After the battery is fully charged and discharged once at 0.1C, it is fully charged (4.3V). The positive electrode is removed, washed, and placed in a centrifuge tube. Dimethyl carbonate (DMC) as the electrolyte solvent is used to soak the battery. The battery is stored at 60°C under argon for 7 days. The washing solution is collected.

[0120] (2) The washing solution was filtered, and the volume was adjusted to 100 ml. ICP-MS test was performed to determine the content of various transition metal elements.

[0121] Table 1. Physical parameters and transition metal dissolution amounts of the cathode materials in the embodiments and comparative examples of this invention.

[0122] Particle size D50 (μm) Tap density (g / cm3) Specific surface area (m² / g) Ni leaching amount (ppm) Co leaching amount (ppm) Mn leaching amount (ppm) Example 1 2.26 2.38 0.92 990 54.5 97.1 Example 2 2.17 2.17 0.94 1179 131 320 Example 3 2.13 2.06 1.04 1673 88 156 Example 4 2.45 2.21 0.85 1833 169 329 Example 5 2.28 2.09 0.92 1623 112 350 Example 6 2.11 2.18 1.08 1179 131 320 Example 7 2.25 2.12 1.01 2175 281 902 Comparative Example 1 2.01 2.23 0.97 3103 425 1278 Comparative Example 2 2.04 2.16 0.83 2475 290 890 Comparative Example 3 2.35 2.06 0.95 3466 358.5 936 Comparative Example 4 2.44 2.18 0.88 2837 306 716 Comparative Example 5 2.51 2.09 0.99 2249 365 889

[0123] Table 2. Performance test data of the cathode materials in the embodiments and comparative examples of this invention for coin cells.

[0124] First charge capacity / mAh / g (2.5-4.3V@0.2C) Initial discharge specific capacity / mAh / g (2.5-4.3V@0.2C) First-time efficiency (%) 0.1C discharge median voltage (V) Capacity retention (%) after 100 cycles Example 1 228 210 92 3.84 91 Example 2 227 200 88 3.83 88.9 Example 3 228 201 88 3.83 88.5 Example 4 229 208 91 3.83 90 Example 5 213 190 89 3.84 91.5 Example 6 243 220 91 3.84 88.2 Example 7 218 185 85 3.84 88.1 Comparative Example 1 220 201 91 3.85 87.1 Comparative Example 2 218 191 87 3.85 87.5 Comparative Example 3 220 189 86 3.85 87.7 Comparative Example 4 228 204 89 3.83 87.2 Comparative Example 5 215 190 88 3.82 81.2

[0125] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium ion battery cathode material, characterized in that, The application relates to a lithium ion battery cathode material, which comprises the following steps: S1, uniformly mixing a high-nickel ternary precursor, a lithium salt and a dopant to obtain a primary mixture, performing first sintering, crushing and sieving to obtain a high-nickel ternary cathode material matrix; S2, uniformly mixing the high-nickel ternary cathode material matrix and a cobalt-containing compound, and performing second sintering; the molar ratio of the high-nickel ternary precursor to the cobalt-containing compound is 1:0.001-0.05; the second sintering temperature is 700-800 DEG C; S3, uniformly mixing the second sintering product and a coating raw material, and performing third sintering to obtain a cathode material coated with a solid electrolyte; the coating raw material comprises one or two or more of oxides or hydroxides or non-organic acid salts of Li, Co, Sr, Al, W, Ti, Mg, Zr, Ta, Mo, F, B, Y, La, V and P, and the solid electrolyte formed by sintering the coating raw material is phosphotitanium aluminum strontium lanthanum lithium and / or lithium lanthanum zirconium tantalum cobalt niobium oxide; the molar ratio of the high-nickel ternary precursor to the solid electrolyte formed by sintering the coating raw material is 1:0.0001-0.01; the third sintering temperature is 300-500 DEG C.

2. The method for preparing the lithium-ion battery cathode material as described in claim 1, characterized in that, In step S2, the sintering time is 6-10h.

3. The method for preparing the lithium-ion battery cathode material as described in claim 1, characterized in that, In step S3, the sintering time is 3-10h.

4. The method of producing a cathode material for lithium ion batteries according to any one of claims 1 to 3, characterized in that, The cobalt-containing compound is one or two or more of cobalt oxyhydroxide, cobalt hydroxide, tricobalt tetraoxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt phosphate, cobalt acetylacetonate and cobalt sulfate.

5. The method of producing a cathode material for lithium ion batteries according to any one of claims 1 to 3, characterized in that, In step S1, the molar ratio of the high-nickel ternary precursor, the lithium salt and the dopant is 1:1.0-1.08:0.0005-0.005; The high nickel ternary precursor has a chemical formula of Ni x Co y Mn z (OH)2, wherein 0.5≤x≤0.95, 0.01≤y≤0.2, 0.01≤z≤0.3, 0.95≤x+y+z≤1.05; The lithium salt comprises one or two or more of lithium hydroxide monohydrate, lithium hydroxide, lithium chloride, lithium sulfate, lithium borate, lithium nitrate, lithium acetate and lithium carbonate; The dopant is one or two or more of oxides, hydroxides or carbonates of Al and / or Mg.

6. The method for preparing the lithium-ion battery cathode material according to any one of claims 1-3, characterized in that, In step S1, the first sintering temperature is 850-1000 DEG C; the first sintering time is 8-20h; and the first sintering atmosphere is an oxygen atmosphere.

7. A lithium-ion battery cathode material, characterized in that, The positive electrode material is prepared by the preparation method in any one of claims 1-6, has a particle size D50 of 2-20 μm, a tap density of 2-4 g / cm 3 , a specific surface area of 0.5-5.0 m 3 / g, and a transition metal element elution amount of 100-5000 ppm.

8. A lithium-ion battery, characterized by, The application further relates to a lithium ion battery cathode material as claimed in claim 7.

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