Core-shell structure high-entropy nickel-rich cobalt-free positive electrode material and preparation method and application thereof

Abstract

The invention relates to a high-entropy nickel-rich cobalt-free positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a nickel salt and a manganese salt with a solvent to obtain a metal salt solution A; mixing nickel salt, manganese salt, aluminum salt, molybdenum salt and a titanium source with a solvent to obtain a metal salt solution B; mixing the metal salt solution A with the mixed alkali solution for first reaction to obtain a first reaction solution; adding a metal salt solution B into the first reaction solution, mixing with the mixed alkali solution, and carrying out a second reaction to obtain an intermediate; washing and drying the intermediate to obtain a precursor; and mixing and sintering the precursor and a lithium source to obtain the positive electrode material. The positive electrode material with the high-entropy oxide shell layer and the nickel-rich cobalt-free core layer is prepared, the internal core layer is the high-nickel nickel manganese oxide, and the problem that transmission dynamics of lithium ions in the high-entropy oxide is limited can be solved; the high-entropy doped shell layer effectively solves the problems of poor structural stability and the like of the low-cobalt positive electrode material, and prolongs the cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a core-shell structured high-entropy nickel-rich cobalt-free cathode material, its preparation method, and its applications. Background Technology

[0002] Nickel-cobalt-manganese (NCM) ternary cathode materials are considered candidates for next-generation lithium-ion battery cathode materials due to their high theoretical capacity and high discharge voltage. A higher proportion of nickel in NCM cathode materials generally results in higher energy density, while cobalt, although beneficial for reducing cation mixing and stabilizing the material structure, is a scarce and expensive resource. Therefore, high-nickel, low-cobalt, or even cobalt-free lithium-ion battery cathode materials are currently a research hotspot. However, existing high-nickel, low-cobalt, or high-nickel, cobalt-free cathode materials still face the problem of poor cycle stability in practical applications. Summary of the Invention

[0003] This invention provides a core-shell structured high-entropy nickel-rich cobalt-free cathode material, its preparation method, and its application, in order to solve the problem of poor cycle stability of high-nickel cobalt-free cathode materials in applications.

[0004] In a first aspect, the present invention provides a method for preparing a core-shell structured high-entropy nickel-rich cobalt-free cathode material, comprising: mixing nickel salt and manganese salt with a solvent to obtain a metal salt solution A; mixing nickel salt, manganese salt, aluminum salt, molybdenum salt, and titanium salt with a solvent to obtain a metal salt solution B; mixing metal salt solution A with a mixed alkaline solution to carry out a first reaction to obtain a first reaction solution; adding metal salt solution B to the first reaction solution and mixing it with the mixed alkaline solution to carry out a second reaction to obtain an intermediate; washing and drying the intermediate to obtain a precursor; and sintering the precursor with a lithium source to obtain the cathode material.

[0005] The "high entropy" mentioned in this invention refers to the doping of the shell layer of a core-shell structured cathode material with multiple elements. The high configurational entropy of the multi-element doped shell results in strong inter-atomic interactions, making its structure difficult to disrupt. This effectively solves the problems of poor structural stability and the dissolution of transition metal ions that catalyze electrolyte decomposition in low-cobalt cathode materials. Furthermore, the high-entropy material, due to the presence of multiple elements, initially forms a complex, mechanically strong, and dense inorganic CEI upon contact with the electrolyte, effectively preventing further reactions between the electrolyte and the cathode material.

[0006] In one optional embodiment, the concentration of total metal elements in the metal salt solution A is 0.8-1.2 mol / L; The molar ratio of nickel to manganese in the metal salt solution A is (7-8):1; The nickel salt includes nickel sulfate; The manganese salt includes manganese sulfate; The solvent includes deionized water.

[0007] In one optional embodiment, the concentration of total metal elements in the metal salt solution B is 0.8-1.2 mol / L; The molar ratio of nickel, manganese, aluminum, molybdenum, and titanium in the metal salt solution B is 1:(0.8-1.2):(0.8-1.2):(0.8-1.2):(0.8-1.2). The nickel salt includes nickel sulfate, the manganese salt includes manganese sulfate, the aluminum salt includes aluminum nitrate, the molybdenum salt includes ammonium molybdate, and the titanium salt includes titanium oxysulfate; The solvent includes deionized water.

[0008] In one optional embodiment, the mixed alkaline solution is prepared by mixing sodium hydroxide and ammonia. The concentration of the sodium hydroxide is 1-2 mol / L; The concentration of ammonia water is 0.8-1.5 mol / L.

[0009] In one optional embodiment, the first reaction includes: adding metal salt solution A to the mixed alkaline solution, adjusting the pH value to 10.5-11.5, and carrying out a heat-preserving reaction; The reaction temperature is 60-70℃; The reaction time is 1-1.5 hours; The reaction was carried out under stirring conditions.

[0010] In one optional embodiment, the second reaction includes: adding metal salt solution B to the first reaction solution, adding mixed alkaline solution to adjust the pH value to 10.5-11.5, and carrying out the reaction at a constant temperature; The amount of metal salt solution B added is 0.1-0.2 times the volume of metal salt solution A.

[0011] In one optional embodiment, the lithium source and the precursor are mixed at a molar ratio of lithium element to total metal element in the precursor of 1.05-1.10:1.

[0012] In one optional embodiment, the calcination includes: heating to 750-800°C at a heating rate of 2-3°C / min under an oxygen atmosphere and holding at that temperature for 10-12 hours.

[0013] Secondly, the present invention also provides a core-shell structured high-entropy nickel-rich cobalt-free cathode material, which is prepared by the above-described preparation method.

[0014] Thirdly, the present invention also provides an application of the aforementioned core-shell structured high-entropy nickel-rich cobalt-free cathode material in batteries.

[0015] The technical solution of this invention has the following advantages: This invention prepares a cathode material with a high-entropy oxide shell and a nickel-rich, cobalt-free core layer through a stepwise deposition reaction. The inner core layer is a high-nickel nickel-manganese oxide, which solves the problem of limited lithium-ion transport kinetics in high-entropy oxides. The high-entropy doped shell has a structure that is difficult to destroy due to the strong interaction forces between atoms with high configurational entropy, effectively solving the problems of poor structural stability and transition metal ion dissolution catalyzing electrolyte decomposition in low-cobalt cathode materials. In addition, the high-entropy material contains multiple elements, and initially forms a complex, mechanically strong, and dense inorganic CEI upon contact with the electrolyte, effectively preventing further reactions between the electrolyte and the cathode material and extending the cycle life of the battery. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0017] Figure 1 This is a SEM image of the positive electrode material prepared in Example 1 of the present invention; Figure 2 This is the XRD spectrum of the cathode material prepared in Example 1 of the present invention. Detailed Implementation The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0018] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0019] Example 1 This embodiment provides a method for preparing a core-shell structured high-entropy nickel-rich cobalt-free cathode material, including: Metal salt solution A: Metal salt solution A is prepared by mixing nickel sulfate, manganese sulfate and water, wherein the total content of metal elements is 1 mol / L, and the molar ratio of nickel in nickel sulfate to manganese in manganese sulfate is 8:1. The solution is stirred for 12 h under an argon atmosphere to obtain a homogeneous solution, and the obtained solution is stored in an argon atmosphere. Metal salt solution B: Metal salt solution B is prepared by mixing nickel sulfate, manganese sulfate, aluminum nitrate, titanium oxysulfate, and ammonium molybdate with water. The total content of metal elements is 1 mol / L. The molar ratio of nickel in nickel sulfate, manganese in manganese sulfate, aluminum in aluminum nitrate, titanium in titanium oxysulfate, and molybdenum in ammonium molybdate is 1:1:1:1:1. The solution is stirred for 12 hours under an argon atmosphere to obtain a homogeneous solution, which is then stored under an argon atmosphere. Precipitating agent solution: Sodium hydroxide solution with a concentration of 2 mol / L; Complexing agent solution: an ammonia solution with an ammonia content of 1.5 mol / L; S1. The precipitant solution and complexing agent solution are mixed at a volume ratio of 1:1 to obtain a mixed alkaline solution, which is then added to the reaction vessel. Under an argon atmosphere, metal salt solution A is added dropwise to the reaction vessel to initiate the first reaction. The pH value is controlled at 11 and the reaction temperature is 65℃. After the metal salt solution A is completely added, the reaction is stirred for 1 hour to obtain the first reaction solution. The volume ratio of metal salt solution A to mixed alkaline solution in the first reaction solution is not limited, as long as the pH value is 11. S2, add metal salt solution B to the first reaction solution. The amount of metal salt solution B added is 10% of the volume of metal salt solution A. Then, add mixed alkali solution to adjust the pH value to 11 before proceeding to the second reaction to obtain the intermediate. S3. The above intermediate is washed. The pH and transition metal content of the wastewater used for washing the intermediate need to be measured to ensure that there is no excessive transition metal on the surface of the obtained intermediate, which would affect the extent of the subsequent solid-state sintering reaction. The washed intermediate is then dried in a vacuum oven at 110°C for 24 hours to obtain the precursor. S4. The prepared precursor powder was mixed with LiOH at a ratio of Li element: metal element in the precursor = 1.07:1. After mixing, the mixture was heated to 750℃ for 12h under an oxygen atmosphere at a heating rate of 2℃ / min to obtain a high-entropy nickel-rich cobalt-free cathode material with a core-shell structure.

[0020] Example 2 This embodiment provides a method for preparing a core-shell structured high-entropy nickel-rich cobalt-free cathode material, including: Metal salt solution A: Metal salt solution A is prepared by mixing nickel sulfate, manganese sulfate and water, wherein the total content of metal elements is 0.8 mol / L, and the molar ratio of nickel in nickel sulfate to manganese in manganese sulfate is 7:1. The solution is stirred for 12 h under an argon atmosphere to obtain a homogeneous solution, and the obtained solution is stored in an argon atmosphere. Metal salt solution B: Metal salt solution B is prepared by mixing nickel sulfate, manganese sulfate, aluminum nitrate, titanium oxysulfate, and ammonium molybdate with water. The total content of metal elements is 1.2 mol / L. The molar ratio of nickel in nickel sulfate, manganese in manganese sulfate, aluminum in aluminum nitrate, titanium in titanium oxysulfate, and molybdenum in ammonium molybdate is 1:0.8:1.2:0.8:1.2. The solution is stirred for 12 hours under an argon atmosphere to obtain a homogeneous solution, which is then stored under an argon atmosphere. Precipitating agent solution: 1 mol / L sodium hydroxide solution; Complexing agent solution: an ammonia solution with an ammonia content of 0.8 mol / L; S1. The precipitant solution and complexing agent solution are mixed at a volume ratio of 1:1 to obtain a mixed alkaline solution, which is then added to the reaction vessel. Under an argon atmosphere, metal salt solution A is added dropwise to the reaction vessel to initiate the first reaction. The pH value is controlled at 11.5 and the reaction temperature is 60℃ during the reaction. After the metal salt solution A is completely added, the reaction is stirred for 1.5 hours to obtain the first reaction solution. The volume ratio of metal salt solution A to mixed alkaline solution in the first reaction solution is not limited, as long as the pH value is 11.5. S2, add metal salt solution B to the first reaction solution, the amount of metal salt solution B added is 15% of the volume of metal salt solution A, and add mixed alkali solution dropwise to adjust the pH value to 11.5 before proceeding to the second reaction to obtain the intermediate; S3. The above intermediate is washed. The pH and transition metal content of the wastewater used for washing the intermediate need to be measured to ensure that there is no excessive transition metal on the surface of the obtained intermediate, which would affect the extent of the subsequent solid-state sintering reaction. The washed intermediate is then dried in a vacuum oven at 110°C for 24 hours to obtain the precursor. S4. The prepared precursor powder was mixed with LiOH at a ratio of Li element: metal element in the precursor = 1.05:1. After mixing, the mixture was heated to 800℃ for 10h under an oxygen atmosphere at a heating rate of 3℃ / min to obtain a nickel-rich cobalt-free cathode material with a core-shell structure.

[0021] Example 3 This embodiment provides a method for preparing a core-shell structured high-entropy nickel-rich cobalt-free cathode material, including: Metal salt solution A: Metal salt solution A is prepared by mixing nickel sulfate, manganese sulfate and water, wherein the total content of metal elements is 1.2 mol / L, and the molar ratio of nickel in nickel sulfate to manganese in manganese sulfate is 8:1. The solution is stirred for 12 h under an argon atmosphere to obtain a homogeneous solution, and the obtained solution is stored in an argon atmosphere. Metal salt solution B: Metal salt solution B is prepared by mixing nickel sulfate, manganese sulfate, aluminum nitrate, titanium oxysulfate, and ammonium molybdate with water. The total content of metal elements is 0.8 mol / L. The molar ratio of nickel in nickel sulfate, manganese in manganese sulfate, aluminum in aluminum nitrate, titanium in titanium oxysulfate, and molybdenum in ammonium molybdate is 1:1.2:0.8:1.2:0.8. The solution is stirred for 12 hours under an argon atmosphere to obtain a homogeneous solution, which is then stored under an argon atmosphere. Precipitating agent solution: 1 mol / L sodium hydroxide solution; Complexing agent solution: an ammonia solution with an ammonia content of 1 mol / L; S1, the precipitant solution and complexing agent solution are mixed at a volume ratio of 1:1 to obtain a mixed alkaline solution, which is then added to the reaction vessel. Under an argon atmosphere, metal salt solution A is added dropwise to the reaction vessel to initiate the first reaction. The pH value is controlled at 11 and the reaction temperature is 70℃. After the metal salt solution A is completely added, the reaction is stirred for 1 hour to obtain the first reaction solution. The volume ratio of metal salt solution A to mixed alkaline solution in the first reaction solution is not limited, as long as the pH value is 11. S2, add metal salt solution B to the first reaction solution. The amount of metal salt solution B added is 20% of the volume of metal salt solution A. Then, add mixed alkali solution to adjust the pH value to 11 before proceeding to the second reaction to obtain the intermediate. S3. The above intermediate is washed. The pH and transition metal content of the wastewater used for washing the intermediate need to be measured to ensure that there is no excessive transition metal on the surface of the obtained intermediate, which would affect the extent of the subsequent solid-state sintering reaction. The washed intermediate is then dried in a vacuum oven at 110°C for 24 hours to obtain the precursor. S4. The prepared precursor powder was mixed with LiOH at a ratio of Li element: metal element in the precursor = 1.10:1. After mixing, the mixture was heated to 700℃ for 12h under an oxygen atmosphere at a heating rate of 2℃ / min to obtain a nickel-rich cobalt-free cathode material with a core-shell structure.

[0022] Comparative Example 1 This comparative example provides a method for preparing a high-entropy nickel-rich cobalt-free cathode material, including: Metal salt solution A: Metal salt solution A is prepared by mixing nickel sulfate, manganese sulfate and water, wherein the total content of metal elements is 1 mol / L, and the molar ratio of nickel in nickel sulfate to manganese in manganese sulfate is 8:1. The solution is stirred for 12 h under an argon atmosphere to obtain a homogeneous solution, and the obtained solution is stored in an argon atmosphere. Metal salt solution B: Metal salt solution B is prepared by mixing nickel sulfate, manganese sulfate, aluminum nitrate, titanium oxysulfate, and ammonium molybdate with water. The total content of metal elements is 1 mol / L. The molar ratio of nickel in nickel sulfate, manganese in manganese sulfate, aluminum in aluminum nitrate, titanium in titanium oxysulfate, and molybdenum in ammonium molybdate is 1:1:1:1:1. The solution is stirred for 12 hours under an argon atmosphere to obtain a homogeneous solution, which is then stored under an argon atmosphere. Precipitating agent solution: Sodium hydroxide solution with a concentration of 2 mol / L; Complexing agent solution: an ammonia solution with an ammonia content of 1.5 mol / L; S1, the precipitant solution and complexing agent solution are mixed at a volume ratio of 1:1 to obtain a mixed alkaline solution, which is then added to the reaction vessel. Subsequently, metal salt solution A and metal salt solution B are added dropwise to the reaction vessel simultaneously to carry out a co-precipitation reaction. The pH value is controlled at 11 and the reaction temperature is 65℃ during the reaction. After metal salt solution A and metal salt solution B are added dropwise, the reaction is stirred for 1 hour to obtain an intermediate. S3. The above intermediate is washed. The pH and transition metal content of the wastewater used for washing the intermediate need to be measured to ensure that there is no excessive transition metal on the surface of the obtained intermediate, which would affect the extent of the subsequent solid-state sintering reaction. The washed intermediate is then dried in a vacuum oven at 110°C for 24 hours to obtain the precursor. S4. The prepared precursor powder was mixed with LiOH at a ratio of Li element: metal element in the precursor = 1.07:1. After mixing, the mixture was calcined at 750℃ for 12h under an oxygen atmosphere at a heating rate of 2℃ / min to obtain a high-entropy nickel-rich cobalt-free cathode material.

[0023] Experimental Example 1. Electrochemical performance testing The positive electrode materials prepared in Examples 1-3 and Comparative Example 1 were used to fabricate coin cells, and their electrochemical performance was tested. The positive electrode of the coin cell was prepared by mixing the prepared materials with PVDF binder and Super P conductive carbon black in a mass ratio of 90:5:5, adding an appropriate amount of NMP as a solvent, and using a defoamer to form a homogeneous slurry. The slurry was coated onto aluminum foil, vacuum dried, and the resulting electrode sheet was cut into 12mm diameter circular positive electrodes. Lithium metal of the same size as the positive electrode was used as the negative electrode. The electrolyte was 1M LiPF6 dissolved in EC:DEC at a volume ratio of 3:7. The separator was a Celgard PP separator, and the battery module was CR2032. The testing instrument used was a Xinwei battery tester, with a charge / discharge voltage range of 2.5-4.4V and a current density of 1C = 180 mA / g. The test results are shown in the table below. Table 1 Electrochemical performance test results

[0024] A comparison of the data from Examples 1-3 with Comparative Example 1 shows that Comparative Example 1, by simultaneously depositing metal salt solutions A and B, failed to generate a cathode material with a high-entropy oxide shell and a nickel-rich, cobalt-free core. Examples 1-3, through a stepwise deposition reaction, prepared a cathode material with a high-entropy oxide shell and a nickel-rich, cobalt-free core. The internal core layer is a high-nickel nickel-manganese oxide, which solves the problem of limited lithium-ion transport kinetics in high-entropy oxides. The high-entropy doped shell, due to the strong inter-atomic interactions caused by high configurational entropy, is structurally difficult to destroy, effectively solving the problems of poor structural stability and transition metal ion dissolution catalyzing electrolyte decomposition in low-cobalt cathode materials. Furthermore, the high-entropy material, containing multiple elements, initially forms a complex, mechanically strong, and dense inorganic CEI upon contact with the electrolyte, effectively preventing further reactions between the electrolyte and the cathode material, significantly extending the battery's cycle life.

[0025] 2. Scanning electron microscopy test The morphology of the cathode material prepared in Example 1 was characterized by scanning electron microscopy, and the results are as follows: Figure 1 As shown.

[0026] 3. X-ray diffraction test X-ray diffraction tests were performed on the cathode material prepared in Example 1, such as... Figure 2 As shown. The material obtained in Example 1 has a distinct α-NaFeO2 structure. Figure 2 The peak values ​​of (003) and (104) are obvious, indicating that the material has good crystallinity. The peak positions are shifted to a lower angle relative to the cobalt-free high-nickel cathode material, which indicates that the cathode material prepared in Example 1 has a larger interlayer spacing than NCM811.

[0027] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a core-shell structured high-entropy nickel-rich cobalt-free cathode material, characterized in that, include: Nickel and manganese salts are mixed with a solvent to obtain metal salt solution A; nickel, manganese, aluminum, molybdenum, and titanium salts are mixed with a solvent to obtain metal salt solution B; metal salt solution A is mixed with a mixed alkaline solution to carry out a first reaction to obtain a first reaction solution; metal salt solution B is added to the first reaction solution and mixed with the mixed alkaline solution to carry out a second reaction to obtain an intermediate. The intermediate was washed and dried to obtain the precursor; The precursor and lithium source are mixed and sintered to obtain the cathode material.

2. The preparation method according to claim 1, characterized in that, The concentration of total metal elements in the metal salt solution A is 0.8-1.2 mol / L; And / or, the molar ratio of nickel to manganese in the metal salt solution A is (7-8):1; And / or, the nickel salt includes nickel sulfate; And / or, the manganese salt includes manganese sulfate; And / or, the solvent includes deionized water.

3. The preparation method according to claim 1, characterized in that, The concentration of total metal elements in the metal salt solution B is 0.8-1.2 mol / L; And / or, the molar ratio of nickel, manganese, aluminum, molybdenum and titanium in the metal salt solution B is 1:(0.8-1.2):(0.8-1.2):(0.8-1.2):(0.8-1.2). And / or, the nickel salt includes nickel sulfate, the manganese salt includes manganese sulfate, the aluminum salt includes aluminum nitrate, the molybdenum salt includes ammonium molybdate, and the titanium salt includes titanium oxysulfate; And / or, the solvent includes deionized water.

4. The preparation method according to claim 1, characterized in that, The mixed alkaline solution is prepared by mixing sodium hydroxide and ammonia water; And / or, the concentration of the sodium hydroxide is 1-2 mol / L; And / or, the concentration of ammonia water is 0.8-1.5 mol / L.

5. The preparation method according to claim 1, characterized in that, The first reaction includes: adding metal salt solution A to the mixed alkaline solution, adjusting the pH value to 10.5-11.5, and carrying out the reaction at a constant temperature; And / or, the reaction temperature is 60-70°C; And / or, the reaction time is 1-1.5 h; And / or, the reaction is carried out under stirring conditions.

6. The preparation method according to claim 1, characterized in that, The second reaction includes: adding metal salt solution B to the first reaction solution, adding mixed alkaline solution to adjust the pH value to 10.5-11.5, and carrying out the reaction at a constant temperature; And / or, the amount of metal salt solution B added is 0.1-0.2 of the volume of metal salt solution A.

7. The preparation method according to claim 1, characterized in that, The lithium source and the precursor are mixed according to a lithium element:precursor metal element molar ratio of 1.05-1.10:

1.

8. The preparation method according to claim 1, characterized in that, The calcination process includes heating to 750-800℃ at a heating rate of 2-3℃ / min under an oxygen atmosphere and holding at that temperature for 10-12 hours.

9. A core-shell structured high-entropy nickel-rich cobalt-free cathode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of a core-shell structured high-entropy nickel-rich cobalt-free cathode material as described in claim 9 in a battery.

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