Lithium manganese oxide cathode material and method for manufacturing the same

Abstract

Lithium manganese oxide cathode material, chemical formula: Li a Al b Mn 2-b-c B c O 4-d F d (In the formula, 0.96≦a≦1.15, 0

Description

[Technical Field]

[0001] This invention belongs to the field of lithium-ion battery materials, and more particularly to a spherical lithium manganese oxide cathode material and a method for producing the same. [Background technology]

[0002] Lithium-ion batteries are highly efficient, environmentally friendly, and renewable energy devices. Their advantages, including high energy density, light weight, and low self-discharge, have made them a primary energy source in fields such as conventional 3C products (computers, communication equipment, and consumer electronics), electric vehicles, and energy storage. The lithium-ion cathode material is a crucial component of lithium-ion batteries, and its performance directly impacts the battery's performance and lifespan.

[0003] Currently, the most widely used cathode materials for lithium-ion batteries on the market are primarily lithium cobalt oxide, ternary materials, and lithium iron phosphate cathode materials. The drawbacks of lithium cobalt oxide are its extremely limited cobalt reserves, high cost, and safety concerns due to its potential for thermal runaway reactions during use. Furthermore, the structural stability of lithium cobalt oxide materials is insufficient, making them prone to decomposition at high temperatures. Ternary materials, mainly lithium nickel-cobalt-manganate and lithium nickel-cobalt-aluminum oxide, are less expensive than lithium cobalt oxide cathode materials, but they suffer from problems such as temperature sensitivity and capacity degradation. On the other hand, lithium iron phosphate has low capacity and is therefore unsuitable for high-capacity battery applications. Consequently, recent research has focused on finding new cathode materials that combine high capacity, long lifespan, and low cost.

[0004] Lithium manganese oxide has advantages such as large capacity, high operating voltage, excellent safety performance, abundant resources, and low price, and has attracted attention as a new cathode material. However, lithium manganese oxide is prone to manganese elution during cycling, resulting in a decrease in cycle life, which greatly limits the development of lithium manganese oxide cathode materials. To solve the technical problem of manganese elution in lithium manganese oxide, the main technical means currently adopted are improvements by doping or coating, and modifying lithium manganese oxide with fluorine element is one of the effective technical means. However, in the prior art, the research on the penetration depth of fluorine element is insufficient, and it only stays at the surface coating of fluorine element, so the improvement effect of manganese elution has not reached the optimum.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and drawbacks in the above-mentioned background technology and provide a lithium manganese oxide cathode material and a manufacturing method thereof.

Means for Solving the Problems

[0006] The technical means of the present invention for solving the above-mentioned technical problems are as follows. A lithium manganese oxide cathode material, with the chemical formula: Li a [U+0000001]]Al b [U+0000002]]Mn 2-b-c [U+0000003]]B c [U+0000004]]O 4-d [U+0000005]]F d [U+0000006]](where 0.96 ≦ a ≦ 1.15, 0 < b ≦ 0.3, 0 < c ≦ 0.03, 0 < d ≦ 0.03), and the lithium manganese oxide cathode material has spherical secondary particles, the fluorine element penetrates into the spherical lithium manganese oxide cathode material, and the fluorine element content has a gradient distribution that gradually decreases from the surface of the spherical lithium manganese oxide cathode material particles towards the center of the particles. [[ID=]32]

[0007] The fluorine element has a gradient distribution that gradually decreases from the surface to the center of the spherical lithium manganese oxide cathode material particles. This strengthens the crystal structure of the lithium manganese oxide cathode material to some extent, reduces the effects of the Jahn-Teller effect, and suppresses manganese leaching caused by structural distortion. At the same time, the infiltration of the fluorine element can alter the electronic band structure of the lithium manganese oxide cathode material, improving its electronic conductivity and electrochemical reaction activity.

[0008] In the lithium manganese oxide cathode material described above, preferably, the fluorine content in the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 20% to 40% of the total fluorine content of the lithium manganese oxide cathode material, and the fluorine content in the region at a distance of L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 60% to 80% of the total fluorine content of the lithium manganese oxide cathode material, where R is the equivalent radius of the secondary particles of the lithium manganese oxide cathode material.

[0009] In the lithium manganese oxide cathode material described above, the sphericity of the lithium manganese oxide cathode material is preferably 0.8 to 1. Dissolution of lithium manganese oxide mainly occurs at the (111) crystal plane. This is because the structure of the lithium manganese oxide (111) crystal plane is more susceptible to erosion by ions in the electrolyte compared to other crystal planes, causing the dissolution of manganese ions. Therefore, by reducing the proportion of (111) crystal planes of lithium manganese oxide, the dissolution of manganese ions can be suppressed, improving the cycle life and stability of lithium-ion batteries. Studies have shown that the proportion of (111) planes in spherical lithium manganese oxide is smaller than that of octahedral lithium manganese oxide, and the amount of lithium manganese oxide dissolved in the electrolyte is about 40% lower compared to the octahedral crystal form. Therefore, by controlling the sphericity of the lithium manganese oxide cathode material to 0.8 to 1 and bringing it closer to a spherical shape, manganese dissolution can be effectively reduced.

[0010] In the above lithium manganese oxide cathode material, preferably, the manganese elution amount in the lithium manganese oxide cathode material is 0.01% to 0.1%.

[0011] In the above lithium manganese oxide cathode material, preferably, the D50 of the secondary particles of the lithium manganese oxide cathode material is 10 to 16 μm, and the particle size distribution coefficient Span is 0.5 to 0.9.

[0012] As the overall inventive concept, the present invention further provides a manufacturing method of the above lithium manganese oxide cathode material, (1) A step of weighing a lithium source, a manganese source, and a boron source in a stoichiometric ratio of lithium, manganese, and boron in a chemical formula, mixing them, and performing primary sintering to obtain a lithium manganese oxide cathode material precursor; (2) A step of mixing the lithium manganese oxide cathode material precursor with an aluminum source and a fluorine source in a stoichiometric ratio, performing secondary sintering, and sieving after the sintering is completed to obtain a lithium manganese oxide cathode material.

[0013] In the above manufacturing method, by introducing a boron source in step (1), on the one hand, the boron element acts as a flux to lower the temperature required for the reaction, suppress the volatilization of Li due to high temperature, and at the same time reduce energy consumption. On the other hand, the boron element modifies the surface of the polycrystalline lithium manganese oxide, uniformly grows the primary particles, and the boron element acts as a binder to tightly bond the polycrystalline primary particles, enhance the mechanical strength of the material, and further can well maintain the high sphericity of the precursor.

[0014] In the above-described manufacturing method, by simultaneously introducing an aluminum source and a fluorine source in step (2), the aluminum element can react with the fluorine element to form an aluminum fluoride compound. Since this compound has high ionic conductivity and low resistivity, it promotes the penetration and diffusion of the fluorine element into the lithium manganese oxide cathode material, and can form a gradient distribution of the fluorine element inside the material. The high gradient of fluorine on the surface combines with aluminum to form an aluminum fluoride compound as a physical coating layer, effectively reducing corrosion inside the material by the electrolyte, stabilizing the crystal structure of the lithium manganese oxide cathode material, reducing manganese elution, and improving the battery cycle life and energy density.

[0015] In the manufacturing method described above, the synergistic effect of uniform bulk doping of boron and aluminum allows the lithium manganese oxide cathode material to maintain the high sphericity of the precursor during the sintering process.

[0016] In the above-described manufacturing method, preferably, in step (1), the temperature of the primary sintering is 700 to 850°C, and the sintering time is 4 to 10 hours.

[0017] In the above-described manufacturing method, preferably, in step (2), the temperature of the secondary sintering is 300 to 600°C, and the sintering time is 2 to 8 hours.

[0018] In the above-described manufacturing method, preferably, in step (1), the manganese source includes at least one of aluminum-doped manganese carbonate, aluminum-doped trimanganese tetroxide, aluminum-doped dimanganese trioxide, aluminum-doped manganese hydroxide, and aluminum-doped manganese dioxide. By selecting an aluminum-doped manganese source, a precursor uniformly bulk-doped with aluminum can be obtained, thereby stabilizing the crystal structure of lithium manganese oxide, suppressing the generation of oxygen vacancies in lithium manganese oxide during the synthesis process, and improving cycle performance because the material undergoes a single-phase reaction across the entire high and low voltage range during the charging process.

[0019] In the above-described manufacturing method, preferably, in step (1), the lithium source comprises at least one of lithium carbonate and lithium hydroxide, and the boron source comprises at least one of H3BO3 or B2O3.

[0020] In the above-described manufacturing method, preferably in step (2), the fluorine source comprises at least one of lithium fluoride, ammonium fluoride, aluminum fluoride, polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, polyvinylidene fluoride-hexafluoropropylene polymer, and polytetrafluoroethylene, and the aluminum source comprises at least one of aluminum hydroxide, aluminum trioxide, and aluminum nitrate. [Effects of the Invention]

[0021] Compared to conventional technology, the advantages of the present invention are as follows: (1) The present invention enhances the stability of the internal crystal structure of the lithium manganese oxide cathode material by adjusting the gradient distribution of fluorine elements in the lithium manganese oxide cathode material, preventing the internal structure of the material from collapsing during the charge-discharge process. Furthermore, in the region at a distance L < 0.22R from the surface, high-concentration fluorine elements form an aluminum fluoride compound protective layer on the surface of the cathode material, preventing erosion of the material's interior by the electrolyte, reducing the amount of divalent manganese leached into the electrolyte, and improving the energy density of the battery. (2) The present invention improves the cycle life and stability of lithium-ion batteries by controlling the sphericity of the lithium manganese oxide cathode material to 0.8 to 1, thereby reducing the proportion of (111) crystal planes of lithium manganese oxide and suppressing the elution of divalent manganese ions. (3) In the manufacturing method of the present invention, by simultaneously introducing an aluminum source and a fluorine source, the aluminum element reacts with the fluorine element to form an aluminum fluoride compound having high ionic conductivity and low resistivity, thereby promoting the gradient distribution of the fluorine element in the lithium manganese oxide cathode material. (4) In the manufacturing method of the present invention, by employing a secondary low-temperature sintering process and adding a small amount of fluorine element, a spherical lithium manganese oxide cathode material having a gradient distribution in which the fluorine element gradually decreases from the surface of the material particles toward the center of the particles can be obtained, and the process cost is low and industrialization is easy. [Brief explanation of the drawing]

[0022] [Figure 1] This is a diagram showing the distribution of fluorine elements in the electron probe cross-section of the lithium manganese oxide cathode material fabricated in Example 1 of the present invention. [Figure 2] This is an SEM image of the lithium manganese oxide cathode material fabricated in Example 3 of the present invention. [Figure 3] This is an equivalent sphere diagram obtained by computer automatic recognition of the lithium manganese oxide cathode material fabricated in Example 3 of the present invention. [Figure 4]It is a charge-discharge curve diagram of the lithium manganese oxide positive electrode material fabricated in Example 3 of the present invention. [Figure 5] It is a 7C / 0.2C rate performance diagram of the lithium manganese oxide positive electrode materials fabricated in the examples and comparative examples of the present invention. [Figure 6] It is a capacity cycle retention rate diagram of the lithium manganese oxide positive electrode materials fabricated in the examples and comparative examples of the present invention.

Embodiments for Carrying out the Invention

[0023] To facilitate understanding of the present invention, the present invention will be described more comprehensively and in detail below by combining the attached drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The use of technical terms in this specification is for the purpose of explaining specific embodiments and is not intended to limit the protection scope of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, equipment and devices used in the present invention are commercially available or can be manufactured by known methods.

[0026] Example 1: The lithium manganese oxide positive electrode material of this example has the chemical formula: Li 1.05 Al 0.2 Mn 1.78 B 0.02 O 3.982 F 0.018The lithium manganese oxide cathode material is expressed as follows: the secondary particles are spherical, with a sphericity of 0.894, a secondary particle D50 of 14.5 μm, and a particle size distribution coefficient Span of 0.8. The fluorine element penetrates into the spherical lithium manganese oxide cathode material and has a gradient distribution that gradually decreases from the surface of the spherical lithium manganese oxide cathode material particles toward the center of the particles. The fluorine element content in the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 23% of the total fluorine element content of the lithium manganese oxide cathode material, and the fluorine element content in the region at a distance of L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 77% of the total fluorine element content of the lithium manganese oxide cathode material, where R is the equivalent radius of the secondary particles of the lithium manganese oxide cathode material.

[0027] The method for producing the lithium manganese oxide cathode material in this embodiment includes the following steps. (1) (Mn 0.95 Al 0.05 )3O4, lithium carbonate, and boric acid were weighed in a stoichiometric ratio of 1.78:1.05:0.02, put into a high-speed mixer and mixed until uniform, then put into a roller hearth kiln and heated to 760°C at a heating rate of 3°C / min under an air atmosphere, and sintered for 4 hours. After sintering was complete, it was cooled and pulverized with a jet mill, and the pulverized material was passed through a 300-mesh hand sieve to obtain a spherical lithium manganese oxide polycrystalline cathode material doped with aluminum and boron. (2) The spherical lithium manganese oxide polycrystalline cathode material obtained in step (1) was weighed with aluminum hydroxide and polyvinylidene fluoride in a stoichiometric ratio of 1:0.05:0.018, and the mixture was placed in a high-speed mixer and mixed uniformly. The mixture was then placed in a roller hearth kiln and heated to 300°C at a heating rate of 2°C / min under an air atmosphere and sintered for 5 hours. After sintering was complete, the material was cooled, and the cooled material was passed through a 300-mesh sieve to obtain the lithium manganese oxide cathode material.

[0028] The distribution of fluorine elements in the lithium manganese oxide cathode material fabricated in this embodiment was evaluated by electron probe cross-sectional analysis, and the results are shown in Figure 1. The fluorine element content in the region at a distance L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 77% of the total fluorine element content of the lithium manganese oxide cathode material, and the fluorine element content in the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 23% of the total fluorine element content of the lithium manganese oxide cathode material.

[0029] Through training, the computer was automatically trained to recognize particles, and the particle size of the lithium manganese oxide cathode material in tungsten filament electron microscope images was measured, and its sphericity was calculated. The calculated sphericity was 0.894.

[0030] Electrical Performance Test: A button-type battery was fabricated using the lithium manganese oxide cathode material sample prepared in this embodiment. A positive electrode sheet was prepared with active material:conductive agent:binder in a ratio of 92%:5%:3%, and a metallic lithium sheet was used as the negative electrode to create a 2032 type button-type battery. A charge / discharge test was performed at 1C / 1C with an operating voltage of 3.0~4.3V using the Wuhan Land electrochemical test apparatus. As a result, the capacity retention rate after 50 cycles at 60°C was 98.0%. The battery rate performance test was performed at room temperature with currents of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 7C, and the 7C / 0.2C rate retention rate was 89.9%.

[0031] Mn elution test: Button-type half-cells were fabricated using the lithium manganese oxide cathode material prepared in this example, following the same manufacturing method as described above. The half-cells were then placed in a 60°C constant temperature bath and charged at a constant voltage for 30 hours at 50% and 100% charge states, respectively, before being disassembled. The negative electrode sheet was removed, the residual electrolyte on the surface was washed with dimethyl carbonate, and after dissolving in hydrochloric acid solution, the Mn content was measured by ICP. The results showed that the amount of Mn eluted from the lithium manganese oxide cathode material at 50% and 100% charge states was 0.069 wt% and 0.085 wt%, respectively.

[0032] Example 2: The lithium manganese oxide cathode material in this example has the chemical formula: Li 1.05 Al 0.2 Mn 1.78 B 0.02 O 3.99 F 0.01 The lithium manganese oxide cathode material is expressed as follows, and the secondary particles are spherical, with a sphericity of 0.869, a secondary particle D50 of 15.2 μm, and a particle size distribution coefficient Span of 0.88. The fluorine element penetrates into the spherical lithium manganese oxide cathode material and has a gradient distribution that gradually decreases from the surface of the spherical lithium manganese oxide cathode material particles toward the center of the particles. The fluorine element content in the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 31% of the total fluorine element content of the lithium manganese oxide cathode material, and the fluorine element content in the region at a distance of L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 69% of the total fluorine element content of the lithium manganese oxide cathode material, where R is the equivalent radius of the lithium manganese oxide cathode material secondary particles.

[0033] The method for producing the lithium manganese oxide cathode material in this embodiment includes the following steps. (1) (Mn 0.95 Al 0.053O4, lithium carbonate, and boric acid were weighed in a stoichiometric ratio of 1.78:1.05:0.02, placed in a high-speed mixer and mixed until uniform, then placed in a roller hearth kiln and sintered in an air atmosphere at a heating rate of 3°C / min to 760°C for 4 hours. After sintering was complete, the material was cooled, pulverized in a jet mill, and the pulverized material was passed through a 300-mesh sieve to obtain a spherical lithium manganese oxide polycrystalline cathode material doped with aluminum and boron. (2) The spherical lithium manganese oxide polycrystalline cathode material obtained in step (1) was weighed with aluminum hydroxide and polyvinylidene fluoride in a stoichiometric ratio of 1:0.05:0.01, and the mixture was placed in a high-speed mixer and mixed uniformly. The mixture was then placed in a roller hearth kiln and heated to 450°C at a heating rate of 2°C / min under an air atmosphere, and sintered for 5 hours. After sintering was complete, the material was cooled, and the cooled material was passed through a 300-mesh sieve to obtain the lithium manganese oxide cathode material.

[0034] The distribution of fluorine elements in the lithium manganese oxide cathode material was evaluated by electron probe cross-sectional analysis. As a result, the fluorine element had a gradient distribution that gradually decreased from the surface to the center of the spherical lithium manganese oxide cathode material particles. The fluorine element content within the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particle accounted for 31% of the total fluorine element content of the lithium manganese oxide cathode material, and the fluorine element content within the region at a distance of L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particle accounted for 69% of the total fluorine element content of the lithium manganese oxide cathode material.

[0035] Through training, the computer was able to automatically recognize particles, and the particle size of the lithium manganese oxide cathode material in tungsten filament electron microscope images was measured, and its sphericity was calculated. The calculated sphericity was 0.869.

[0036] The performance of the lithium manganese oxide cathode material prepared in this example was evaluated according to the electrical performance test method and Mn elution test method of Example 1. As a result, the button cell made using the lithium manganese oxide cathode material of this example had a capacity retention rate of 98.2% after 50 cycles at 1C and 60°C, a 7C / 0.2C rate retention rate of 91.3% at room temperature, and the amount of Mn eluted from the lithium manganese oxide cathode material was 0.055 wt% and 0.071 wt% at 50% charge and 100% charge, respectively.

[0037] Example 3: The lithium manganese oxide cathode material in this example has the chemical formula: Li 1.05 Al 0.2 Mn 1.78 B 0.02 O 3.97 F 0.03 The lithium manganese oxide cathode material is expressed as follows: the secondary particles are spherical, with a sphericity of 0.906, a secondary particle D50 of 14.5 μm, and a particle size distribution coefficient Span of 0.84. The fluorine element penetrates into the spherical lithium manganese oxide cathode material and has a gradient distribution that gradually decreases from the surface of the spherical lithium manganese oxide cathode material particles toward the center of the particles. The fluorine element content within the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 38% of the total fluorine element content of the lithium manganese oxide cathode material, and the fluorine element content within the region at a distance of L ≤ 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 62% of the total fluorine element content of the lithium manganese oxide cathode material, where R is the equivalent radius of the secondary particles of the lithium manganese oxide cathode material.

[0038] The method for producing the lithium manganese oxide cathode material in this embodiment includes the following steps. (1) (Mn 0.95 Al 0.053O4, lithium carbonate, and boric acid were weighed in a stoichiometric ratio of 1.78:1.05:0.02, placed in a high-speed mixer and mixed until uniform, then placed in a roller hearth kiln and sintered in an air atmosphere at a heating rate of 3°C / min to 760°C for 4 hours. After sintering was complete, the material was cooled, pulverized in a jet mill, and the pulverized material was passed through a 300-mesh sieve to obtain a spherical lithium manganese oxide polycrystalline cathode material doped with aluminum and boron. (2) The spherical lithium manganese oxide polycrystalline cathode material obtained in step (1) was weighed with aluminum hydroxide and polyvinylidene fluoride in a stoichiometric ratio of 1:0.05:0.03, and the mixture was placed in a high-speed mixer and mixed uniformly. The mixture was then placed in a roller hearth kiln and heated to 600°C at a heating rate of 2°C / min under an air atmosphere, and sintered for 5 hours. After sintering was complete, the material was cooled, and the cooled material was passed through a 300-mesh sieve to obtain the lithium manganese oxide cathode material. An SEM image of the material is shown in Figure 2. From Figure 2, it can be confirmed that the secondary particles of the fabricated lithium manganese oxide cathode material are spherical.

[0039] The distribution of fluorine elements in lithium manganese oxide cathode material was evaluated by electron probe cross-sectional analysis. As a result, the fluorine element showed a gradient distribution from the surface to the center of the spherical lithium manganese oxide cathode material particles. The fluorine element content within the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounted for 38% of the total fluorine element content of the lithium manganese oxide cathode material, and the fluorine element content within the region at a distance of L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounted for 62% of the total fluorine element content of the lithium manganese oxide cathode material.

[0040] The computer was trained to automatically recognize particles, and the particle size of the lithium manganese oxide cathode material in tungsten filament electron microscope images was measured. The equivalent diameter diagram of the particles, as determined by the computer's automatic recognition, is shown in Figure 3, and its sphericity was calculated. The calculated sphericity was 0.906.

[0041] The performance of the lithium manganese oxide cathode material prepared in this example was measured according to the electrical performance test method and Mn elution test method of Example 1. As a result, the button cell battery prepared using the lithium manganese oxide cathode material of this example had a capacity retention rate of 98.7% after 50 cycles at 1C and 60°C, and a 7C / 0.2C rate retention rate of 94.2% at room temperature. The charge-discharge curve is shown in Figure 4, with an initial charge capacity of 114.9 mAh / g and an initial discharge capacity of 112.6 mAh / g at a current density of 0.1C, and an initial charge-discharge efficiency of 98.4%. At 50% charge and 100% charge states, the amount of Mn eluted from the lithium manganese oxide cathode material was 0.035 wt% and 0.043 wt%, respectively.

[0042] Comparative Example 1: The method for producing the lithium manganese oxide cathode material in this comparative example is substantially the same as in Example 1, and all other process parameters are the same as in Example 1, except that aluminum hydroxide is not added in step (2). The obtained lithium manganese oxide cathode material has the chemical formula: Li 1.05 Al 0.15 Mn 1.83 B 0.02 O 3.982 F 0.018 This is represented by the following. Electron probe cross-sectional analysis evaluated the fluorine element distribution in the lithium manganese oxide cathode material prepared in this comparative example. The results showed that the fluorine element content in the region at a distance L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounted for 100% of the total fluorine element content in the spherical region, where R is the equivalent radius of the lithium manganese oxide cathode material secondary particle.

[0043] The performance of the lithium manganese oxide cathode material prepared in this comparative example was measured according to the electrical performance test method and Mn elution test method of Example 1. As a result, the button cell made using the lithium manganese oxide cathode material of this comparative example had a capacity retention rate of 97.9% after 50 cycles at 1C and 60°C, a 7C / 0.2C rate retention rate of 87.0% at room temperature, and the amount of Mn eluted from the lithium manganese oxide cathode material was 0.086 wt% and 0.109 wt% at 50% charge and 100% charge, respectively.

[0044] Comparative Example 2: The lithium manganese oxide cathode material in this comparative example has the chemical formula: Li 1.05 Al 0.2 Mn 1.78 B 0.02 O 3.97 F 0.03 The lithium manganese oxide cathode material is expressed as follows: the secondary particles are spherical, with a sphericity of 0.874, a secondary particle D50 of 14.9 μm, a particle size distribution coefficient Span of 0.81, and the fluorine element is uniformly distributed within the lithium manganese oxide cathode material.

[0045] The method for producing the lithium manganese oxide cathode material in this comparative example includes the following steps. (Mn 0.95 Al 0.05 3O4, lithium carbonate, boric acid, and polyvinylidene fluoride were weighed in stoichiometric ratios of 1.78:1.05:0.02:0.03, placed in a high-speed mixer and mixed until uniform, then placed in a roller hearth kiln and sintered in an air atmosphere at a heating rate of 3°C / min to 760°C for 4 hours. After sintering was complete, the material was cooled and pulverized in a jet mill. The pulverized material was then passed through a 300-mesh sieve to obtain a spherical lithium manganese oxide polycrystalline cathode material uniformly doped with aluminum, boron, and fluorine.

[0046] Electron probe cross-sectional analysis evaluated the distribution of fluorine within lithium manganese oxide, revealing that fluorine is uniformly distributed within the oxide.

[0047] The performance of the lithium manganese oxide cathode material prepared in this comparative example was measured according to the electrical performance test method and Mn elution test method of Example 1. As a result, the button cell made using the lithium manganese oxide cathode material of this comparative example had a capacity retention rate of 97.4% after 50 cycles at 1C and 60°C, a 7C / 0.2C rate retention rate of 87.4% at room temperature, and the amount of Mn eluted from the lithium manganese oxide cathode material was 0.282 wt% and 0.396 wt% at 50% charge and 100% charge, respectively.

[0048] The fluorine distribution, Mn elution amount, and electrochemical performance of the lithium manganese oxide cathode materials prepared in the above-described examples and comparative examples are shown in Table 1, and in Figures 5 and 6.

[0049] Table 1: Fluorine distribution, Mn elution amount, and electrochemical performance of lithium manganese oxide cathode materials in examples and comparative examples. JPEG2026511844000002.jpg52159

[0050] Comparing Example 1 with Comparative Example 1, it can be seen that introducing Al during the secondary sintering process promotes the penetration of fluorine into the lithium manganese oxide, thereby forming a gradient distribution of fluorine. Furthermore, comparing Example 3 with Comparative Example 2, it can be seen that the lithium manganese oxide cathode material with a gradient distribution of fluorine exhibits superior Mn elution, cycle performance, and rate performance compared to the lithium manganese oxide cathode material with uniformly doped fluorine. This is because the fluorine with a gradient distribution forms more stable structural layers in different gradient regions within the material, stabilizing the internal structure and reducing the Jahn-Teller effect. Moreover, from the comparison of the above examples and comparative examples, it can be seen that the gradient distribution of fluorine is not only related to the promoting effect of Al, but that temperature increases also contribute to achieving gradient doping of fluorine. This is mainly because the diffusion rate of fluorine is accelerated by the increase in temperature, making it easier for it to pass through the lattice structure of lithium manganese oxide, and thus improving the penetration rate of fluorine into the lithium manganese oxide. Furthermore, the increase in temperature lowers the lattice energy of lithium manganese oxide, making it more susceptible to substitution by fluorine, which in turn promotes gradient doping of fluorine.

Claims

1. Lithium manganese oxide cathode material, wherein the lithium manganese oxide cathode material has the chemical formula: Li ａ Al ｂ Mn ２－ｂ－ｃ B ｃ O ４－ｄ F ｄ A lithium manganese oxide cathode material characterized in that the formula is expressed as 0.96 ≤ a ≤ 1.15, 0 < b ≤ 0.3, 0 < c ≤ 0.03, 0 < d ≤ 0.03, and the lithium manganese oxide cathode material is characterized in that the secondary particles are spherical, the fluorine element penetrates into the spherical lithium manganese oxide cathode material, and the fluorine element content has a gradient distribution that gradually decreases from the surface to the center of the spherical lithium manganese oxide cathode material particles.

2. The fluorine content within the spherical region at a distance of 0.22R ≤ L ≤ R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 20% to 40% of the total fluorine content of the lithium manganese oxide cathode material. The lithium manganese oxide cathode material according to claim 1, characterized in that the fluorine element content within a region at a distance L < 0.22R from the surface of the spherical lithium manganese oxide cathode material particles accounts for 60% to 80% of the total fluorine element content of the lithium manganese oxide cathode material, where R is the equivalent radius of the secondary particles of the lithium manganese oxide cathode material.

3. The lithium manganese oxide cathode material according to claim 1, characterized in that the sphericity of the lithium manganese oxide cathode material is 0.8 to 1.

4. The lithium manganese oxide cathode material according to claim 1, characterized in that the amount of unit manganese eluted in the lithium manganese oxide cathode material is 0.01% to 0.1%.

5. The lithium manganese oxide cathode material according to claim 1, characterized in that the secondary particles D50 of the lithium manganese oxide cathode material are 10 to 16 μm and the particle size distribution coefficient Span is 0.5 to 0.

9.

6. A method for producing a lithium manganese oxide cathode material according to any one of claims 1 to 5, (1) A step of mixing a lithium source, a manganese source, and a boron source and performing primary sintering to obtain a lithium manganese oxide cathode material precursor, (2) A manufacturing method characterized by comprising the steps of: (2) mixing the lithium manganese oxide cathode material precursor with an aluminum source and a fluorine source, performing secondary sintering, and sieving after the completion of sintering to obtain a lithium manganese oxide cathode material.

7. The manufacturing method according to claim 6, characterized in that, in step (1), the temperature of the primary sintering is 700 to 850°C and the sintering time is 4 to 10 hours.

8. The manufacturing method according to claim 6, characterized in that in step (2), the temperature of the secondary sintering is 300 to 600°C and the sintering time is 2 to 8 hours.

9. In step (1), the manganese source includes at least one of aluminum-doped manganese carbonate, aluminum-doped trimanganese tetroxide, aluminum-doped dimanganese trioxide, aluminum-doped manganese hydroxide, and aluminum-doped manganese dioxide. The lithium source comprises at least one of lithium carbonate and lithium hydroxide. The boron source is H ３ BO ３ and B ２ O ３ The production method according to claim 6, characterized by containing at least one of them.

10. In step (2), the fluorine source includes at least one of lithium fluoride, ammonium fluoride, aluminum fluoride, polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, polyvinylidene fluoride-hexafluoropropylene polymer, and polytetrafluoroethylene. The manufacturing method according to claim 6, characterized in that the aluminum source includes at least one of aluminum hydroxide, aluminum trioxide, and aluminum nitrate.

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