A high-roundness single-crystal lithium-rich manganese-based positive electrode material and a preparation method thereof

Abstract

The application discloses a high-roundness single-crystal lithium-rich manganese-based positive electrode material and a preparation method thereof. A lithium-rich manganese-based precursor is pre-sintered, and then the treated precursor, a lithium source and a composite additive are mixed and subjected to high-temperature sintering treatment to obtain a single-crystal lithium-rich manganese-based positive electrode material; wherein the composite additive comprises at least two additives selected from borate, zirconium salt, strontium salt and titanium salt. The application utilizes the synergistic effect of multiple additives at high temperature, and through molten salt assistance and selective adsorption of crystal faces, the roundness growth and grain boundary fusion of the crystal grains are promoted together. The prepared single-crystal lithium-rich manganese-based material has a roundness index of the particles of greater than or equal to 0.85, a rest angle of less than or equal to 30 degrees, and a powder compaction density of greater than or equal to 3.30 g / cm 3 . Through the synergistic effect of multiple additives, the application realizes the precise regulation of the single-crystal particle morphology, and the obtained material has excellent processing performance and electrochemical stability, and has significant industrial application value.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular relates to a single-crystal lithium-rich manganese-based cathode material with high roundness, a preparation method therefor, and a lithium-ion battery comprising the cathode material. Background Art

[0002] Lithium-rich manganese-based cathode materials (aLi₂MnO₃·(1-a)LiMO₂, M = Ni, Co, Mn, etc., 0<a<1) are considered as ideal cathode materials for next-generation high-energy-density lithium-ion batteries due to their advantages of high specific capacity (≥250 mAh / g) and low cost. However, traditional polycrystalline lithium-rich manganese-based materials have problems such as low compaction density and tendency to generate microcracks during cycling. Single crystallization is an effective approach to solve the above problems, but the preparation of single-crystal lithium-rich manganese-based materials faces challenges such as high sintering temperature and difficulty in controlling grain morphology.

[0003] Existing studies show that additive-assisted sintering is an effective means to regulate the morphology of single-crystal particles. However, the prior art mostly uses single-component additives, which have a limited effect on improving particle roundness and can hardly meet the requirements of high compaction density. How to realize the rounded growth and precise morphology regulation of single-crystal particles through optimization of formula design and sintering process design is a technical problem urgently to be solved in the art. Summary of the Invention

[0004] Aiming at the problems of irregular particle morphology and to-be-improved compaction density of single-crystal lithium-rich manganese-based materials in the prior art, the present invention provides a single-crystal lithium-rich manganese-based cathode material with high roundness and a preparation method thereof.

[0005] To achieve the above purpose, the present invention provides the following technical solutions: (1) subjecting a lithium-rich manganese-based precursor to pre-sintering treatment in an air atmosphere with a certain oxygen content; (2) mixing the pre-sintered precursor, a lithium source and a composite additive to obtain a mixed material, wherein the composite additive comprises at least two additives selected from borates, zirconium salts, strontium salts and titanium salts; (3) subjecting the mixed material to sintering treatment to obtain the single-crystal lithium-rich manganese-based cathode material.

[0006] Preferably, the lithium-rich manganese-based precursor is Ni x Co y Mn 1-x-y CO₃ and Ni x Co y Mn 1-x-y (OH)₂, wherein x≥0, y≥0, and x+y<0.5.

[0007] Preferably, the lithium-rich manganese-based precursor is subjected to pre-sintering treatment at 400-650°C for 2-8 hours in an air atmosphere with an oxygen content of 2%-10% to obtain pre-sintered oxide with a particle size D50 of 2-5 μm.

[0008] Preferably, the atmosphere during the pre-sintering treatment in step (1) is an air atmosphere with an oxygen content of 5%.

[0009] Preferably, the lithium source is battery-grade Li2CO3 or LiOH·H2O.

[0010] Preferably, the composite additive is a borate, a zirconium salt, and a strontium salt.

[0011] Preferably, the amount of the composite additive is 0.05~5wt% of the total mass of the lithium-rich manganese-based precursor and the lithium source.

[0012] Preferably, the sintering process is a two-stage sintering process, including: a first sintering stage: heating to 800~1150℃ and holding for 6~20 hours; and a second sintering stage: cooling to 550~800℃ and holding for 2~8 hours.

[0013] The present invention also provides a high roundness single crystal lithium-rich manganese-based cathode material prepared according to the above method, wherein the material is a single crystal particle and meets the following characteristics: (1) the particle surface is round and smooth, and the roundness index is ≥0.85; (2) the powder repose angle is ≤30° and the flowability index is ≥80; (3) the powder compaction density is ≥3.30 g / cm³.

[0014] The present invention further provides a lithium-ion battery comprising the above-mentioned high-roundness single-crystal lithium-rich manganese-based cathode material.

[0015] The working principle of this invention is as follows: The multiple components in the composite additive form a multi-component eutectic molten salt system at high temperatures, which coats the grain surface, promoting mass transport and grain boundary migration, and inducing grain growth. Simultaneously, it synergistically inhibits the excessively rapid growth of high surface energy crystal planes, promoting isotropic grain growth and resulting in single-crystal particles with rounded surfaces and blunted edges. The synergistic effect of multiple additives makes the morphology control effect far superior to that of a single additive system.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Significantly improved particle roundness: Through the synergistic effect of various additives, the resulting single crystal particles have smooth surfaces and blunted edges, with a roundness index ≥0.85.

[0017] Excellent flowability: The improved particle roundness directly improves the flowability of the powder, with an angle of repose ≤30° and a flowability index ≥80, which is more than 20% higher than that of conventional single crystal materials.

[0018] Significantly improved compaction density: Optimized particle morphology and gradation enable powder compaction densities of 3.30~3.38 g / cm³. 3 The ratio is more than 10% higher than that of the control group without additives.

[0019] Excellent electrochemical performance: The regular particle morphology and the co-doping effect of multiple elements significantly improve the cycling stability of the material.

[0020] High process integration: This invention achieves rounded grain growth and morphology control in a single sintering process through the synergistic design of multiple additives, simplifying the process flow. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope (SEM) image of the high-roundness single-crystal lithium-rich manganese-based cathode material prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the conventional single-crystal lithium-rich manganese-based cathode material prepared in Comparative Example 1 of this invention. Detailed Implementation

[0022] To better illustrate the present invention and facilitate understanding of its technical solutions, specific embodiments are provided below for further detailed description. However, the present invention is not limited to the following embodiments, and any improvements or substitutions based on the concept of the present invention should fall within the protection scope of the present invention.

[0023] The lithium-rich manganese-based precursor Ni used in the embodiments of the present invention 0.33 Mn 0.67 (OH)2 is a commercially available product; the lithium source is battery-grade Li2CO3 or LiOH·H2O; all other reagents are of analytical grade.

[0024] Example 1: Ternary composite system of borate + zirconium salt + strontium salt (1) Precursor preparation: Weigh out lithium-rich manganese-based precursor Ni 0.33 Mn 0.67 (OH)2 is placed in a muffle furnace, and air with an oxygen content of 5% is passed through it. The temperature is increased to 600℃ at 5℃ / min and pre-fired for 5 hours to obtain a pre-sintered oxide with a D50 of 3.5μm.

[0025] (2) Mixing: Weigh Li2CO3 and pre-sintered oxide at a Li / Me molar ratio of 1.12:1 and mix them; add composite additives, which are a mixture of H3BO3, ZrO2 and SrCO3, with a mass ratio of 1:0.8:0.5; the total mass of the additives is 1.2wt% of the total mass of the precursor and the lithium source; mix in a high-speed mixer for 40 minutes.

[0026] (3) Sintering: The mixture is placed in a box furnace and heated to 950°C at 2°C / min and held for 12 hours (first sintering section); then cooled to 620°C at 1.5°C / min and held for 4 hours (second sintering section); then cooled with the furnace.

[0027] (4) Post-processing: The sintered product is crushed, passed through a 300-mesh sieve and iron is removed to obtain the target product, denoted as S1.

[0028] Example 2: Borate + Zirconium Salt Binary Composite System The process is essentially the same as in Example 1, except that the composite additive is a mixture of H3BO3 and ZrO2 in a mass ratio of 1:0.8. The resulting product is denoted as S2.

[0029] Example 3: Borate + Strontium Salt Binary Composite System The process is essentially the same as in Example 1, except that the composite additive is a mixture of H3BO3 and SrCO3 in a mass ratio of 1:0.5. The resulting product is denoted as S3.

[0030] Example 4: Binary composite system of zirconium salt and strontium salt The process is essentially the same as in Example 1, except that the composite additive is a mixture of ZrO2 and SrCO3 in a mass ratio of 1:0.625. The resulting product is designated as S4.

[0031] Example 5: Ternary composite system of borate + zirconium salt + titanium salt The process is essentially the same as in Example 1, except that the composite additive is a mixture of H3BO3, ZrO2, and TiO2 in a mass ratio of 1:0.8:0.8. The resulting product is designated as S5.

[0032] Example 6: Ternary composite system of borate + titanium salt + strontium salt The process is essentially the same as in Example 1, except that the composite additive is a mixture of H3BO3, TiO2, and SrCO3 in a mass ratio of 1:0.8:0.5. The resulting product is designated as S6.

[0033] Example 7: Ternary composite system of titanium salt + zirconium salt + strontium salt The process is essentially the same as in Example 1, except that the composite additive is a mixture of TiO2, ZrO2, and SrCO3 in a mass ratio of 1:1:0.625. The resulting product is designated as S7.

[0034] Example 8: Binary composite system of borate and titanium salt The process is essentially the same as in Example 1, except that the composite additive is a mixture of H3BO3 and TiO2 in a mass ratio of 1:0.8. The resulting product is designated as S8.

[0035] Example 9: Binary composite system of zirconium salt and titanium salt The process is essentially the same as in Example 1, except that the composite additive is a mixture of ZrO2 and TiO2 in a mass ratio of 1:1. The resulting product is designated as S9.

[0036] Example 10: Pre-sintering treatment with oxygen content controlled at 10% The process is essentially the same as in Example 1, except that air with an oxygen content of 10% is introduced during the pretreatment of the lithium-rich manganese-based precursor. The resulting product is designated as S10.

[0037] Example 11: Pre-sintering treatment with oxygen content controlled at 2% The process is essentially the same as in Example 1, except that air with an oxygen content of 2% is introduced during the pretreatment of the lithium-rich manganese-based precursor. The resulting product is designated as S11.

[0038] Comparative Example 1: No additives The process is essentially the same as in Example 1, except that no composite additives are added. The resulting product is denoted as D1.

[0039] Comparative Example 2: Adding only H3BO3 (single borate) The process is essentially the same as in Example 1, except that only H3BO3 is added. The resulting product is denoted as D2.

[0040] Comparative Example 3: SrCO3 (single strontium salt) added only The process is essentially the same as in Example 1, except that only SrCO3 is added. The resulting product is denoted as D3.

[0041] Comparative Example 4: No precursor pre-sintering treatment The process is essentially the same as in Example 1, except that the lithium-rich manganese-based precursor is not pre-sintered. The resulting product is designated as D4.

[0042] The performance of the products of the examples and comparative examples was tested. The performance test items and test methods are shown in Table 1, and the test results are shown in Table 2.

[0043] Table 1 Performance Test Items and Test Methods Table 2 Test Results Examples 1-3 (using two or three additives in combination) showed significantly better overall performance than all single-component systems and the additive-free system. S1 (ternary composite) achieved a compaction density of 3.38 g / cm³, a roundness index of 0.89, and an angle of repose of 26°, with all indicators being optimal. This indicates a significant synergistic effect among the multiple additives, far exceeding the simple summation of the effects of a single additive.

[0044] Comparative Examples 2-3 (single-component systems) showed some improvement compared to the system without additives, but were significantly lower than the composite system. This demonstrates that the ability of a single additive to regulate particle morphology is limited, and a significant improvement in roundness can only be achieved through the synergistic effect of multiple additives.

[0045] The ternary effect of Examples 5-7 is worse than that of borate + zirconium + strontium, thus indicating that the synergistic effect of borate + zirconium + strontium is the strongest.

[0046] The D4 system without pre-sintering has the worst performance in all aspects.

[0047] A comparison of Examples 1 and 10-11 demonstrates that atmosphere control during pre-sintering treatment can help optimize the surface properties of the precursor, reducing the surface energy and increasing the fluidity of the precursor after pre-sintering, which helps to uniformly disperse the additives and further enhance the synergistic effect.

[0048] In summary, this invention, through precursor pretreatment and the synergistic design of multiple additives, significantly improves the particle roundness of single-crystal lithium-rich manganese-based materials, thereby enhancing the material's flowability and compaction density, while also achieving excellent cycle stability. The various performance indicators have yielded unexpected technical results, demonstrating significant innovation and industrial application value.

[0049] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a high-roundness single-crystal lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: (1) The lithium-rich manganese-based precursor was pre-sintered in an air atmosphere with a certain oxygen content. (2) The pre-sintered precursor, lithium source and composite additive are mixed to obtain a mixture, wherein the composite additive contains at least two additives selected from borates, zirconium salts, strontium salts and titanium salts. (3) The mixture is sintered to obtain the single-crystal lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The lithium-rich manganese-based precursor is Ni x Co y Mn 1-x-y CO3 and Ni x Co y Mn 1-x-y One or two of (OH)2, wherein x≥0, y≥0, and x+y<0.

5.

3. The preparation method according to claim 1, characterized in that, The lithium-rich manganese-based precursor is pre-sintered at 400-650°C for 2-8 hours in an air atmosphere with an oxygen content of 2%-10% to obtain pre-sintered oxides with a particle size D50 of 2-5 μm.

4. The preparation method according to claim 3, characterized in that, The atmosphere during the pre-sintering process in step (1) is an air atmosphere with an oxygen content of 5%.

5. The preparation method according to claim 1, characterized in that, The lithium source is battery-grade Li2CO3 or LiOH·H2O.

6. The preparation method according to claim 1, characterized in that, The composite additive is a borate, a zirconium salt, and a strontium salt.

7. The preparation method according to claim 1, characterized in that, The amount of the composite additive is 0.05~5wt% of the total mass of the lithium-rich manganese-based precursor and the lithium source.

8. The preparation method according to claim 1, characterized in that, The sintering process is a two-stage sintering process, including: a first sintering stage: heating to 800~1150℃ and holding for 6~20 hours; and a second sintering stage: cooling to 550~800℃ and holding for 2~8 hours.

9. A high-roundness single-crystal lithium-rich manganese-based cathode material, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

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