Lithium Manganate Cathode Material Coated with Lithium Triborate and Preparation Method Thereof

Abstract

The present invention relates to the field of battery materials, and provides a lithium manganate cathode material coated with lithium triborate and a preparation method thereof. The cathode material is a porous lithium manganate / lithium triborate composite electrode material, which includes porous lithium manganate with a highly connected directional columnar pore structure and a lithium triborate coating covering the pore surface, with a mass ratio of (86.0~92.0):(8.0~14.0), a coating thickness of 600~800 nm, a pore diameter of 45~95 μm, and a porosity of 65~78%. The preparation method includes: preparing a precursor colloidal solution by the sol-gel method, obtaining porous lithium manganate through low-temperature freezing molding and freeze-drying, and forming a cathode substrate through pre-oxidation and high-temperature sintering; subsequently, using vacuum-assisted impregnation, ultrasound, and nitrogen pressure to promote the penetration of the lithium triborate precursor solution, and forming a uniform coating layer through gradient drying and annealing treatment. The present invention significantly improves the crystal structure stability of the cathode material, inhibits manganese dissolution, improves the cycle life and rate performance, and has wide application value.

Description

Technical Field

[0001] The present invention relates to the field of electrode materials, and in particular to a lithium triborate-coated lithium manganate positive electrode material and a preparation method thereof. Background Art

[0002] In the context of the rapid development of lithium-ion batteries, the performance of cathode materials directly determines the energy density, cycle life and safety of batteries. Lithium manganese oxide (LiMn2O4) has broad application prospects in portable electronic devices, electric vehicles and energy storage systems due to its low cost, environmental friendliness and high specific capacity. However, in practical applications, especially under high temperature, high rate charge and discharge or long cycle conditions, the structural stability of cathode materials and the problem of manganese dissolution have become key factors affecting battery performance. The stability of the crystal structure is directly related to whether the material can maintain a complete three-dimensional framework structure during the charge and discharge process to ensure the reversible insertion and extraction of lithium ions and long-term cycle stability. At the same time, the problem of manganese dissolution not only leads to the loss of active materials and reduces the capacity retention rate of the cathode material, but also may induce side reactions at the negative electrode interface, affecting the overall safety and reliability of the battery. Therefore, in order to further enhance the practical application value of lithium manganese oxide cathode materials, it is urgent to improve its crystal structure stability and inhibit manganese dissolution through material modification strategies to ensure that the battery can still achieve excellent cycle life and stable output performance under complex working conditions. This will not only help improve the overall performance of lithium-ion batteries, but will also promote the development of new high-performance lithium battery technology and broaden its application in new energy vehicles, large-scale energy storage systems and other fields.

[0003] At present, researchers have carried out a series of modification studies on the shortcomings of lithium manganese oxide positive electrode materials in high temperature cycle stability and manganese dissolution. For example, the Chinese patent with publication number CN118908285A discloses a lithium iron manganese phosphate coated lithium manganese oxide positive electrode material and its preparation method, but lithium manganese oxide does not adopt any special structural design, so there is a problem of poor crystal structure stability during actual use. Therefore, it is urgent to develop a more stable and efficient coating strategy to improve the structural integrity and anti-dissolution ability of the material. In this context, the use of lithium triborate as a coating layer has become a promising modification scheme. Lithium triborate can not only form a dense protective layer on the surface to reduce the erosion of lithium manganese oxide by the electrolyte, but also its good ionic conductivity can ensure the smooth transmission of lithium ions, thereby improving the stability of the material while taking into account the electrochemical performance. Therefore, how to achieve a uniform, stable and efficient protective layer structure by optimizing the lithium triborate coating process to effectively improve the cycle stability and high temperature resistance of lithium manganese oxide positive electrode materials is still the focus and challenge of current research. Summary of the invention

[0004] (1) Technical issues solved

[0005] The object of the present invention is to provide a lithium manganate cathode material coated with lithium triborate and a preparation method thereof, so as to solve the problems of poor crystal structure stability and manganese dissolution of the current cathode material.

[0006] (2) Technical solution

[0007] In order to achieve the above object, the present invention provides the following technical solution:

[0008] A lithium manganate cathode material coated with lithium triborate; the cathode material is a porous lithium manganate / lithium triborate composite electrode material;

[0009] The porous lithium manganate / lithium triborate composite electrode material includes porous lithium manganate and a lithium triborate coating covering the surface of the pores of the porous lithium manganate;

[0010] The mass ratio of the porous lithium manganate to lithium triborate is (86.0~92.0):(8.0~14.0);

[0011] The porous lithium manganate has a highly connected directional columnar pore structure;

[0012] The average diameter of the columnar pores of the porous lithium manganate is 45~95μm;

[0013] The porosity of the porous lithium manganate is 65~78%;

[0014] The thickness of the lithium triborate coating is 600~800nm.

[0015] The present invention adopts the design of a porous lithium manganate / lithium triborate composite electrode material, which is mainly used to enhance the crystal structure stability and manganese dissolution resistance of the cathode material of lithium-ion batteries. By constructing a highly connected directional columnar pore structure, while providing excellent electrochemical activity, the porous lithium manganate ensures the efficient transmission of lithium ions and optimizes the structural integrity of the electrode material. Its high porosity not only increases the specific surface area of the material, improves the wettability of the electrolyte, but also effectively alleviates the pulverization problem of the material caused by volume changes during charge and discharge, thereby enhancing the cycle stability. On this basis, the lithium triborate coating coated on the pore surface of the porous lithium manganate further plays a key role. Its dense and uniform covering layer can effectively block the direct erosion of the electrolyte on the lithium manganate, reduce the occurrence of interfacial side reactions, and thus inhibit manganese dissolution. In addition, the presence of the lithium triborate coating helps to regulate the interfacial electric field distribution and optimize the migration path of lithium ions in the electrode material, enabling the battery to maintain excellent stability under long cycle and high rate conditions. By reasonably controlling the mass ratio of the porous lithium manganate to the lithium triborate, it is ensured that while improving the stability, the lithium ion transmission efficiency will not be affected due to the too thick coating layer, thus achieving a good balance between the cycle life and the rate performance. Overall, the synergistic structure constructed by the present invention not only fully utilizes the efficient transmission characteristics of the porous lithium manganate, but also takes advantage of the protective effect of the lithium triborate, realizing the high stability and low solubility of the cathode material under complex working conditions, and providing reliable technical support for the long-life and high-safety applications of lithium-ion batteries.

[0016] The present invention also discloses a preparation method of a lithium triborate-coated lithium manganate cathode material, comprising the following steps:

[0017] S1. Dissolve lithium acetate and manganese acetate in absolute ethanol to form a metal salt solution, add an acetone solution of polymethyl methacrylate, and obtain a precursor colloidal solution through stirring; inject the colloidal solution into a pre-cooled mold for freezing and molding, and prepare porous lithium manganate through freeze-drying, pre-oxidation and high-temperature sintering;

[0018] S2. Penetrate the lithium triborate precursor solution into the pores of the porous substrate through vacuum-assisted impregnation, and form a lithium triborate-coated composite cathode material through gradient drying and annealing treatment.

[0019] Further, the preparation method of the precursor colloidal solution in the step S1 is as follows: by weight, 100 parts by weight of lithium acetate and 190 - 200 parts by weight of manganese acetate are dissolved in absolute ethanol, and the mass ratio of the volume of ethanol to the total metal salt is controlled to be 10 - 20 mL / g; under a nitrogen atmosphere, the oxygen content is controlled to be ≤50 ppm, and continuous mixing is carried out at a mechanical stirring rate of 300 - 500 rpm for 20 - 30 min to form a homogeneous and transparent metal salt ethanol solution; subsequently, 30 - 45 parts of an acetone solution of 3.0 - 5.0 wt.% polymethyl methacrylate are added dropwise to the above metal salt ethanol solution at a rate of 1.0 - 2.0 mL / min, and the temperature of the system is controlled to be maintained at 20 - 25 °C during the dropping process. After the dropping is completed, stirring is continued at a rate of 200 - 300 rpm for 40 - 60 min to obtain a stably dispersed precursor colloidal solution;

[0020] Further, the steps of freeze - forming and freeze - drying in the step S1 are as follows: the precursor colloidal solution is injected into a pre - cooled metal copper mold at - 50~ - 40 °C. The width of the micro - channels in the mold is 50 - 100 μm, the depth is 200 - 300 μm, the inner surface is pre - coated with a polytetrafluoroethylene emulsion with a solid content of 10 - 15 wt%, the coating thickness is 10 - 20 μm, and the micro - channel spacing is 1.0 - 2.0 mm; freezing is carried out at a cooling rate gradient of 2 - 3 °C / min to form a frozen green body with an oriented pore structure; subsequently, the frozen green body is transferred to a freeze - dryer, and solvent sublimation is carried out for 24 - 36 h under the conditions of a vacuum degree ≤5 Pa and a cold trap temperature ≤ - 85 °C, and the residual solvent content is ≤0.5 wt% to obtain a dried green body.

[0021] Further, the steps of pre - oxidation and high - temperature sintering in the step S1 are as follows: subsequently, the dried green body is placed in a muffle furnace, and under an air atmosphere, the flow rate is controlled to be 1 - 2 L / min, and it is heated to 350 - 380 °C at a heating rate of 3 - 5 °C / min and held for 2.0 - 2.5 h to complete the decomposition of the pore - forming agent and the oxidation of the precursor. Subsequently, the pre - oxidized green body is placed in an alumina crucible, and under a flowing air atmosphere, the flow rate is controlled to be 1.0 - 1.5 L / min, and it is heated to 700 - 720 °C at a heating rate of 5 - 6 °C / min and held for 2 - 4 h; after sintering is completed, it is slowly cooled to room temperature at a rate of 5 - 8 °C / min to obtain porous lithium manganese oxide.

[0022] Further, the preparation method of the lithium triborate precursor solution in the step S2 is as follows: Boric acid and lithium hydroxide are dissolved in deionized water at a molar ratio of 1:(0.33 - 0.35), the pH of the solution is adjusted to 6.5 - 7.5, and the total boron ion concentration is controlled to be 0.5 - 1.5 mol / L; stirring is carried out at 200 - 400 rpm at 25 - 40 °C for 30 - 60 min to form a transparent and homogeneous lithium triborate precursor solution.

[0023] Furthermore, the impregnation process in step S2 is as follows: Immerse the porous lithium manganate obtained in step S1 into the lithium triborate precursor solution, and maintain it at a vacuum degree of 10 - 30 kPa for 10 - 30 min to achieve sufficient penetration of the solution into the pores; Subsequently, apply ultrasonic treatment with a frequency of 20 - 40 kHz, a power of 50 - 150 W, and a time of 10 - 30 min. Then, perform nitrogen pressure impregnation with a pressure of 0.5 - 1.0 MPa and a pressurization time of 10 - 15 min to promote uniform distribution of the sol; After impregnation, purge the residual liquid droplets on the surface with nitrogen at a pressure of 0.5 - 1.0 MPa to ensure that there is no excessive solution accumulation in the pores.

[0024] Furthermore, the gradient drying process in step S2 includes: Place the impregnated material in a programmable temperature-controlled drying oven and perform gradient drying in three stages: The first stage is to dry at 25 - 40 °C and a humidity of 30 - 50% RH for 1 - 2 h; The second stage is to dry at 60 - 80 °C and a humidity of ≤10% RH for 2 - 4 h; The third stage is to dry at 100 - 120 °C and a vacuum degree of ≤1 kPa for 1 - 2 h to complete the dehydration and pre-crystallization of the precursor.

[0025] Furthermore, the annealing treatment in step S2 includes: Place the dried material in a tubular furnace and perform annealing in a nitrogen-oxygen mixed atmosphere, where the volume ratio of nitrogen to oxygen is (93 - 97):(3 - 7); The flow rate is 0.5 - 1.5 L / min. Heat it to 300 - 400 °C at a rate of 2 - 5 °C / min and hold for 1 - 2 h; Continue to heat it to 400 - 500 °C at a rate of 3 - 8 °C / min and hold for 3 - 5 h; Finally, cool it to room temperature at a rate of 2 - 10 °C / min to obtain the lithium triborate-coated lithium manganate cathode material.

[0026] The present invention adopts the design of lithium triborate coating on porous lithium manganate, which is mainly used to enhance the crystal structure stability and manganese dissolution resistance of the cathode material for lithium-ion batteries. Through a reasonable preparation method, a porous lithium manganate substrate with a highly connected directional pore structure is constructed, and a uniform lithium triborate coating layer is formed on its surface to optimize the overall performance of the material. First, in step S1, by dissolving lithium acetate and manganese acetate in absolute ethanol and combining with the acetone solution of polymethyl methacrylate, a stable precursor colloidal solution is formed to ensure the uniform dispersion of metal salts. Subsequently, the freeze-forming and freeze-drying technologies are used to make the material form a frozen green body with a directional columnar pore structure, thereby providing excellent ion transport channels. Through pre-oxidation and high-temperature sintering treatments, porous lithium manganate with high structural stability is obtained. Secondly, in step S2, the vacuum-assisted impregnation method is adopted to make the lithium triborate precursor solution uniformly penetrate into the pores of the material, and combined with ultrasonic treatment and nitrogen pressure impregnation technologies, the uniform distribution of the sol is further promoted to ensure the integrity and stability of the coating layer. The gradient drying process realizes the step-by-step dehydration and pre-crystallization of the lithium triborate precursor through a multi-stage temperature control strategy, avoiding structural defects caused by violent solvent volatilization. Then, annealing treatment is carried out in a nitrogen-oxygen mixed atmosphere to make the lithium triborate coating layer have good crystallinity and chemical stability, thereby effectively inhibiting the erosion of the electrolyte on the lithium manganate and reducing the occurrence of interfacial side reactions. Generally speaking, through the fine regulation of the material structure, this method enables the porous lithium manganate and the lithium triborate coating layer to act synergistically, while improving the cycle life of the material, optimizing the lithium-ion transport efficiency, achieving the balance of high-rate performance and long-cycle stability, and providing an effective solution for the optimized design of the cathode material for lithium-ion batteries.

[0027] (3) Beneficial technical effects

[0028] 1. Through the synergistic effect of the porous lithium manganate and the lithium triborate coating layer, the present invention significantly improves the crystal structure stability and manganese dissolution resistance of the cathode material. Compared with traditional materials, it has a longer cycle life and better rate performance. The highly connected directional pore structure optimizes the lithium-ion transport path and reduces the polarization effect, while the dense and uniform lithium triborate coating layer effectively inhibits the electrolyte erosion and reduces the interfacial side reactions. The reasonable component ratio, vacuum-assisted impregnation and gradient drying processes ensure the uniform and stable coating layer, optimizing the performance balance of the material under high-temperature and high-rate charge-discharge conditions. This technology breaks through the limitations of traditional modification methods, provides a reliable solution for high-safety and long-life lithium-ion batteries, and has broad industrialization prospects.

[0029] 2. Through the collaborative design of lithium triborate coating on porous lithium manganate, the present invention significantly improves the crystal structure stability and manganese dissolution resistance of the cathode material. Compared with traditional lithium manganate cathode materials, it has more excellent cycle life and rate performance. The highly connected directional pore structure optimizes the lithium-ion transport path and reduces the polarization effect, while the lithium triborate coating layer effectively inhibits electrolyte erosion and reduces interfacial side reactions. The synergistic effect of vacuum-assisted impregnation, ultrasonic waves and nitrogen pressure ensures a uniform and dense coating layer, and the gradient drying and annealing processes further enhance the chemical stability of the material. The reasonable component ratio and balanced structure design avoid the adverse effect of too thick coating layer on ion transport while improving the performance, enabling the material to still operate stably under high-temperature and high-rate charge-discharge conditions. This technical solution breaks through the limitations of traditional modification methods, provides a solution with high safety and long life for lithium-ion batteries, and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the morphology diagram of the porous lithium manganate prepared in Example 1 of the present invention.

[0031] Figure 2 It is the morphology diagram of the lithium triborate-coated lithium manganate cathode material prepared in Example 1 of the present invention.

[0032] Figure 3 It is the cross-sectional microstructure morphology diagram of the lithium triborate-coated lithium manganate cathode material prepared in Example 1 of the present invention.

[0033] Figure 4 It is the XRD phase analysis diagram of the porous lithium manganate and the lithium triborate-coated lithium manganate cathode material prepared in Example 1 of the present invention.

[0034] Figure 5 It is the cross-sectional microstructure morphology diagram of the lithium triborate-coated lithium manganate cathode material prepared in Example 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0036] Example 1

[0037] Lithium manganate cathode material coated with lithium triborate; the cathode material is a porous lithium manganate / lithium triborate composite electrode material; the porous lithium manganate / lithium triborate composite electrode material includes porous lithium manganate and a lithium triborate coating covering the pore surface of the porous lithium manganate; the mass ratio of porous lithium manganate to lithium triborate is 86.0:14.0; the porous lithium manganate has a highly connected directional columnar pore structure; the average diameter of the columnar pores of the porous lithium manganate is 45 μm; the porosity of the porous lithium manganate is 65%; the thickness of the lithium triborate coating is 600 nm.

[0038] A preparation method of a lithium manganate cathode material coated with lithium triborate according to this embodiment includes the following steps:

[0039] S1. Dissolve lithium acetate and manganese acetate in absolute ethanol to form a metal salt solution, add an acetone solution of polymethyl methacrylate, and obtain a precursor colloidal solution through stirring; inject the colloidal solution into a pre-cooled mold for freeze molding, and prepare porous lithium manganate through freeze drying, pre-oxidation, and high-temperature sintering; the preparation method of the precursor colloidal solution is as follows: by weight, dissolve 100 parts by weight of lithium acetate and 190 parts by weight of manganese acetate in absolute ethanol, and control the mass ratio of the volume of ethanol to the total metal salt to be 10 mL / g; under a nitrogen atmosphere, control the oxygen content ≤ 50 ppm, and continuously mix at a mechanical stirring rate of 300 rpm for 20 min to form a homogeneous and transparent metal salt ethanol solution; then add 30 parts of a 3.0 wt.% acetone solution of polymethyl methacrylate dropwise into the above metal salt ethanol solution at a rate of 1.0 mL / min, control the system temperature to be maintained at 20°C during the dropping process, and continue to stir at a rate of 200 rpm for 40 min after the dropping is completed to obtain a stably dispersed precursor colloidal solution; the steps of freeze molding and freeze drying are as follows: inject the precursor colloidal solution into a metal copper mold pre-cooled to -50°C, the width of the microchannels of the mold is 50 μm, the depth is 200 μm, the inner surface is pre-coated with a polytetrafluoroethylene emulsion with a solid content of 10 wt%, the coating thickness is 10 μm, and the microchannel spacing is 1.0 mm; freeze at a temperature reduction rate gradient of 2°C / min to form a frozen blank with a directional pore structure; then transfer the frozen blank to a freeze dryer, and perform solvent sublimation for 24 h under the conditions of a vacuum degree ≤ 5 Pa and a cold trap temperature ≤ -85°C, and the residual solvent content ≤ 0.5 wt% to obtain a dried blank. The steps of pre-oxidation and high-temperature sintering are as follows: then place the dried blank in a muffle furnace, control the flow rate to be 1 L / min under an air atmosphere, heat it to 350°C at a heating rate of 3°C / min, and keep it warm for 2.0 h to complete the decomposition of the pore-forming agent and the oxidation of the precursor. Then place the pre-oxidized blank in an alumina crucible, control the flow rate to be 1.0 L / min under a flowing air atmosphere, and heat it to 700°C at a heating rate of 5°C / min and keep it warm for 2 h; after sintering, cool it slowly to room temperature at a rate of 5°C / min to obtain porous lithium manganate.

[0040] S2. Impregnate the lithium triborate precursor solution into the pores of the porous substrate through vacuum-assisted impregnation, and perform gradient drying and annealing treatments to form a composite cathode material coated with lithium triborate. The preparation method of the lithium triborate precursor solution is as follows: Dissolve boric acid and lithium hydroxide in deionized water at a molar ratio of 1:0.33, adjust the pH of the solution to 6.5, and control the total boron ion concentration to be 0.5 mol / L; Stir at 200 rpm for 30 min at 25 °C to form a transparent and homogeneous lithium triborate precursor solution. The impregnation process is as follows: Immerse the porous lithium manganate obtained in step S1 into the lithium triborate precursor solution, keep it at a vacuum of 10 kPa for 10 min to achieve sufficient penetration of the solution into the pores; Subsequently, perform ultrasonic treatment, set the frequency to 20 kHz, the power to 50 W, and the time to 10 min, and then use nitrogen pressure impregnation, with a pressure of 0.5 MPa and a pressurization time of 10 min to promote the uniform distribution of the sol; After impregnation, purge the residual liquid droplets on the surface with nitrogen at 0.5 MPa to ensure that there is no excessive solution accumulation in the pores. The gradient drying process includes: Place the impregnated material in a programmable temperature drying oven and perform gradient drying in three stages: The first stage is to dry at 25 °C and a humidity of 30% RH for 1 h; The second stage is to dry at 60 °C and a humidity of ≤10% RH for 2 h; The third stage is to dry at 100 °C and a vacuum of ≤1 kPa for 1 h to complete the dehydration and pre-crystallization of the precursor. The annealing treatment includes: Place the dried material in a tube furnace and perform annealing in a nitrogen-oxygen mixed atmosphere, where the volume ratio of nitrogen to oxygen is 97:3; The flow rate is 0.5 L / min, heat up to 300 °C at a rate of 2 °C / min and hold for 1 h; Continue to heat up to 400 °C at a rate of 3 °C / min and hold for 3 h; Finally, cool to room temperature at a rate of 2 °C / min to obtain a lithium manganate cathode material coated with lithium triborate.

[0041] Figure 1 The morphological characteristics of the porous lithium manganate prepared in Example 1 of the present invention are shown, and a connected columnar pore structure can be clearly observed, which proves that the material has good pore connectivity and helps to improve the lithium ion transport rate. Figure 2 The morphology of the lithium manganate cathode material coated with lithium triborate prepared in Example 1 is shown. Compared with the uncoated material, the overall structure remains intact and no obvious collapse occurs, which proves that the coating process will not damage the original pore structure. Figure 3 The cross-sectional microstructure morphology of the material is further characterized, and it is observed that the lithium triborate layer is uniformly distributed on the surface of lithium manganate, and the coating layer is continuous and has no obvious cracks, indicating that the coating process is stable and reliable. Figure 4 This is the XRD phase analysis result of the porous lithium manganate and the lithium manganate cathode material coated with lithium triborate prepared in Example 1 of the present invention. The phase matching is good, and no impurity phase peaks are detected, which proves that the material maintains its original crystal structure during the coating process.

[0042] Example 2

[0043] Lithium manganate cathode material coated with lithium triborate; the cathode material is a porous lithium manganate / lithium triborate composite electrode material; the porous lithium manganate / lithium triborate composite electrode material includes porous lithium manganate and a lithium triborate coating covering the pore surface of the porous lithium manganate; the mass ratio of the porous lithium manganate to the lithium triborate is 88.0:12.0; the porous lithium manganate has a highly connected oriented columnar pore structure; the average diameter of the columnar pores of the porous lithium manganate is 60 μm; the porosity of the porous lithium manganate is 69%; the thickness of the lithium triborate coating is 660 nm.

[0044] A preparation method of a lithium manganate cathode material coated with lithium triborate according to this example includes the following steps:

[0045] S1. Dissolve lithium acetate and manganese acetate in absolute ethanol to form a metal salt solution, add an acetone solution of polymethyl methacrylate, and obtain a precursor colloidal solution through stirring; inject the colloidal solution into a pre-cooled mold for freezing and forming, and prepare porous lithium manganate through freeze-drying, pre-oxidation and high-temperature sintering; the preparation method of the precursor colloidal solution is as follows: by weight, dissolve 100 parts by weight of lithium acetate and 193 parts by weight of manganese acetate in absolute ethanol, and control the mass ratio of the volume of ethanol to the total mass of metal salts to be 13 mL / g; control the oxygen content ≤ 50 ppm under a nitrogen atmosphere, and continuously mix at a mechanical stirring rate of 360 rpm for 23 min to form a homogeneous and transparent metal salt ethanol solution; then add 35 parts of an acetone solution of 3.6 wt.% polymethyl methacrylate dropwise to the above metal salt ethanol solution at a rate of 1.3 mL / min, control the temperature of the system to be maintained at 22 °C during the dropping process, and continue to stir at a rate of 230 rpm for 46 min after the dropping is completed to obtain a stably dispersed precursor colloidal solution; the steps of freezing and forming and freeze-drying are as follows: inject the precursor colloidal solution into a pre-cooled metal copper mold at -47 °C, the width of the microchannels of the mold is 65 μm, the depth is 230 μm, the inner surface is pre-coated with a polytetrafluoroethylene emulsion with a solid content of 12 wt%, the coating thickness is 13 μm, and the microchannel spacing is 1.3 mm; freeze at a temperature reduction rate gradient of 2 °C / min to form a frozen blank with an oriented pore structure; then transfer the frozen blank to a freeze-dryer, and perform solvent sublimation for 28 h under the conditions of a vacuum degree ≤ 5 Pa and a cold trap temperature ≤ -85 °C, and the residual solvent content ≤ 0.5 wt% to obtain a dried blank. The steps of pre-oxidation and high-temperature sintering are as follows: then place the dried blank in a muffle furnace, control the flow rate to be 1 L / min under an air atmosphere, heat it to 359 °C at a heating rate of 4 °C / min, and keep it warm for 2.2 h to complete the decomposition of the pore-forming agent and the oxidation of the precursor. Then place the pre-oxidized blank in an alumina crucible, control the flow rate to be 1.2 L / min under a flowing air atmosphere, heat it to 706 °C at a heating rate of 5 °C / min, and keep it warm for 3 h; after sintering, cool it slowly to room temperature at a rate of 6 °C / min to obtain porous lithium manganate.

[0046] S2. The lithium triborate precursor solution is infiltrated into the pores of the porous substrate through vacuum-assisted impregnation, and after gradient drying and annealing treatment, a composite cathode material coated with lithium triborate is formed. The preparation method of the lithium triborate precursor solution is as follows: Boric acid and lithium hydroxide are dissolved in deionized water at a molar ratio of 1:0.34, the pH of the solution is adjusted to 6.8, and the total boron ion concentration is controlled at 0.8 mol / L; it is stirred at 260 rpm for 39 min at 30 °C to form a transparent and homogeneous lithium triborate precursor solution. The impregnation process is as follows: The porous lithium manganate obtained in step S1 is immersed in the lithium triborate precursor solution, and kept at a vacuum degree of 16 kPa for 16 min to achieve sufficient penetration of the solution into the pores; then ultrasonic treatment is applied, the frequency is set at 26 kHz, the power is 80 W, and the time is 16 min. Subsequently, nitrogen pressure impregnation is used, the pressure is 0.7 MPa, and the pressurization time is 12 min to promote the uniform distribution of the sol; after impregnation, the surface residual droplets are purged with nitrogen at 0.7 MPa to ensure that there is no excessive solution accumulation in the pores. The gradient drying process includes: placing the impregnated material in a programmable temperature drying oven and drying it in three stages: the first stage is dried at 30 °C and a humidity of 36% RH for 1 h; the second stage is dried at 66 °C and a humidity of ≤10% RH for 3 h; the third stage is dried at 106 °C and a vacuum degree of ≤1 kPa for 1 h to complete the dehydration and pre-crystallization of the precursor. The annealing treatment includes: placing the dried material in a tube furnace and annealing it in a nitrogen-oxygen mixed atmosphere, where the volume ratio of nitrogen to oxygen is 96:4; the flow rate is 0.8 L / min, heating up to 330 °C at 3 °C / min and holding for 1 h; continuing to heat up to 430 °C at 5 °C / min and holding for 4 h; finally cooling to room temperature at 5 °C / min to obtain a lithium triborate-coated lithium manganate cathode material.

[0047] Example 3

[0048] A lithium triborate-coated lithium manganate cathode material; the cathode material is a porous lithium manganate / lithium triborate composite electrode material; the porous lithium manganate / lithium triborate composite electrode material includes porous lithium manganate and a lithium triborate coating covering the pore surface of the porous lithium manganate; the mass ratio of porous lithium manganate to lithium triborate is 90.0:10.0; the porous lithium manganate has a highly connected oriented columnar pore structure; the average diameter of the columnar pores of the porous lithium manganate is 75 μm; the porosity of the porous lithium manganate is 73%; the thickness of the lithium triborate coating is 720 nm.

[0049] The preparation method of a lithium triborate-coated lithium manganate cathode material in this example includes the following steps:

[0050] S1. Dissolve lithium acetate and manganese acetate in absolute ethanol to form a metal salt solution, add an acetone solution of polymethyl methacrylate, and obtain a precursor colloidal solution through stirring; inject the colloidal solution into a pre-cooled mold for freezing and forming, and prepare porous lithium manganate through freeze-drying, pre-oxidation and high-temperature sintering; the preparation method of the precursor colloidal solution is as follows: by weight, dissolve 100 parts by weight of lithium acetate and 196 parts by weight of manganese acetate in absolute ethanol, and control the mass ratio of the volume of ethanol to the total mass of metal salts to be 16 mL / g; control the oxygen content ≤ 50 ppm under a nitrogen atmosphere, and continuously mix at a mechanical stirring rate of 420 rpm for 26 min to form a homogeneous and transparent metal salt ethanol solution; then add 39 parts of a 4.2 wt.% acetone solution of polymethyl methacrylate dropwise into the above metal salt ethanol solution at a rate of 1.6 mL / min, control the temperature of the system to be maintained at 23 °C during the dropping process, and continue to stir at a rate of 260 rpm for 52 min after the dropping is completed to obtain a stably dispersed precursor colloidal solution; the steps of freezing and forming and freeze-drying are as follows: inject the precursor colloidal solution into a metal copper mold pre-cooled to -44 °C, the width of the microchannels of the mold is 80 μm, the depth is 260 μm, the inner surface is pre-coated with a polytetrafluoroethylene emulsion with a solid content of 13 wt%, the coating thickness is 16 μm, and the microchannel spacing is 1.6 mm; freeze at a cooling rate gradient of 3 °C / min to form a frozen blank with a directional pore structure; then transfer the frozen blank to a freeze-dryer, and carry out solvent sublimation for 31 h under the conditions of a vacuum degree ≤ 5 Pa and a cold trap temperature ≤ -85 °C, and the residual solvent content ≤ 0.5 wt% to obtain a dried blank. The steps of pre-oxidation and high-temperature sintering are as follows: then place the dried blank in a muffle furnace, control the flow rate to be 2 L / min under an air atmosphere, heat it to 368 °C at a heating rate of 4 °C / min, and keep it warm for 2.3 h to complete the decomposition of the pore-forming agent and the oxidation of the precursor. Then place the pre-oxidized blank in an alumina crucible, control the flow rate to be 1.3 L / min under a flowing air atmosphere, heat it to 712 °C at a heating rate of 6 °C / min, and keep it warm for 3 h; after sintering, cool it slowly to room temperature at a rate of 7 °C / min to obtain porous lithium manganate.

[0051] S2. The lithium triborate precursor solution is infiltrated into the pores of the porous substrate by vacuum-assisted impregnation, and after gradient drying and annealing treatments, a composite cathode material coated with lithium triborate is formed. The preparation method of the lithium triborate precursor solution is as follows: Boric acid and lithium hydroxide are dissolved in deionized water at a molar ratio of 1:0.34, the pH of the solution is adjusted to 7.1, and the total boron ion concentration is controlled to be 1.1 mol / L; it is stirred at 320 rpm for 48 min at 34 °C to form a transparent and homogeneous lithium triborate precursor solution. The impregnation process is as follows: The porous lithium manganate obtained in step S1 is immersed in the lithium triborate precursor solution, and kept at a vacuum degree of 22 kPa for 22 min to achieve sufficient penetration of the solution into the pores; then ultrasonic treatment is applied, with the frequency set at 32 kHz, the power at 110 W, and the time at 22 min. Subsequently, nitrogen pressure impregnation is carried out, with the pressure at 0.8 MPa and the pressurization time at 13 min to promote the uniform distribution of the sol; after impregnation, the surface residual droplets are purged with nitrogen at 0.8 MPa to ensure that there is no excessive solution accumulation in the pores. The gradient drying process includes: placing the impregnated material in a programmable temperature drying oven and drying it in a three-stage gradient: the first stage is drying at 34 °C and a humidity of 42% RH for 2 h; the second stage is drying at 72 °C and a humidity of ≤10% RH for 3 h; the third stage is drying at 112 °C and a vacuum degree of ≤1 kPa for 2 h to complete the dehydration and pre-crystallization of the precursor. The annealing treatment includes: placing the dried material in a tubular furnace and annealing it in a nitrogen-oxygen mixed atmosphere, where the volume ratio of nitrogen to oxygen is 95:5; the flow rate is 1.1 L / min, heating it to 360 °C at 4 °C / min and holding for 2 h; continuing to heat it to 460 °C at 6 °C / min and holding for 4 h; finally cooling it to room temperature at 7 °C / min to obtain a lithium triborate-coated lithium manganate cathode material.

[0052] Example 4

[0053] Lithium triborate-coated lithium manganate cathode material; the cathode material is a porous lithium manganate / lithium triborate composite electrode material; the porous lithium manganate / lithium triborate composite electrode material includes porous lithium manganate and a lithium triborate coating covering the pore surfaces of the porous lithium manganate; the mass ratio of the porous lithium manganate to the lithium triborate is 92.0:8.0; the porous lithium manganate has a highly connected directional columnar pore structure; the average diameter of the columnar pores of the porous lithium manganate is 95 μm; the porosity of the porous lithium manganate is 78%; the thickness of the lithium triborate coating is 800 nm.

[0054] A preparation method of a lithium triborate-coated lithium manganate cathode material in this example includes the following steps:

[0055] S1. Dissolve lithium acetate and manganese acetate in absolute ethanol to form a metal salt solution, add an acetone solution of polymethyl methacrylate, and obtain a precursor colloidal solution through stirring; inject the colloidal solution into a pre-cooled mold for freeze molding, and prepare porous lithium manganate through freeze-drying, pre-oxidation and high-temperature sintering; the preparation method of the precursor colloidal solution is as follows: by weight, dissolve 100 parts by weight of lithium acetate and 200 parts by weight of manganese acetate in absolute ethanol, and control the mass ratio of ethanol volume to total metal salt to be 20 mL / g; under a nitrogen atmosphere, control the oxygen content ≤ 50 ppm, and continuously mix at a mechanical stirring rate of 500 rpm for 30 min to form a uniform and transparent metal salt ethanol solution; then add 45 parts of a 5.0 wt.% acetone solution of polymethyl methacrylate dropwise into the above metal salt ethanol solution at a rate of 2.0 mL / min, control the system temperature to be maintained at 25 °C during the dropping process, and continue to stir at a rate of 300 rpm for 60 min after the dropping is completed to obtain a stably dispersed precursor colloidal solution; the steps of freeze molding and freeze-drying are as follows: inject the precursor colloidal solution into a metal copper mold pre-cooled to -40 °C, the width of the microchannel of the mold is 100 μm, the depth is 300 μm, the inner surface is pre-coated with a polytetrafluoroethylene emulsion with a solid content of 15 wt%, the coating thickness is 20 μm, and the microchannel spacing is 2.0 mm; freeze at a cooling rate gradient of 3 °C / min to form a frozen blank with a directional pore structure; then transfer the frozen blank to a freeze-dryer, and perform solvent sublimation for 36 h under the conditions of a vacuum degree ≤ 5 Pa and a cold trap temperature ≤ -85 °C, and the residual solvent content ≤ 0.5 wt% to obtain a dried blank. The steps of pre-oxidation and high-temperature sintering are as follows: then place the dried blank in a muffle furnace, control the flow rate to be 2 L / min under an air atmosphere, heat it to 380 °C at a heating rate of 5 °C / min, and keep it warm for 2.5 h to complete the decomposition of the pore-forming agent and the oxidation of the precursor. Then place the pre-oxidized blank in an alumina crucible, control the flow rate to be 1.5 L / min under a flowing air atmosphere, heat it to 720 °C at a heating rate of 6 °C / min, and keep it warm for 4 h; after sintering, cool it slowly to room temperature at a rate of 8 °C / min to obtain porous lithium manganate.

[0056] S2. The lithium triborate precursor solution is infiltrated into the pores of the porous substrate through vacuum-assisted impregnation, and after gradient drying and annealing treatments, a composite cathode material coated with lithium triborate is formed. The preparation method of the lithium triborate precursor solution is as follows: Boric acid and lithium hydroxide are dissolved in deionized water at a molar ratio of 1:0.35, the pH of the solution is adjusted to 7.5, and the total boron ion concentration is controlled at 1.5 mol / L; it is stirred at 400 rpm for 60 min at 40 °C to form a transparent and homogeneous lithium triborate precursor solution. The impregnation process is as follows: The porous lithium manganate obtained in step S1 is immersed in the lithium triborate precursor solution, and kept at a vacuum degree of 30 kPa for 30 min to achieve sufficient penetration of the solution into the pores; subsequently, ultrasonic treatment is applied, with the frequency set at 40 kHz, the power at 150 W, and the time at 30 min, and then nitrogen pressure impregnation is carried out, with the pressure at 1.0 MPa and the pressurization time at 15 min to promote the uniform distribution of the sol; after impregnation, the surface residual droplets are purged with nitrogen at a pressure of 1.0 MPa to ensure that there is no excessive solution accumulation in the pores. The gradient drying process includes: placing the impregnated material in a programmable temperature drying oven and drying it in three stages: the first stage is drying at 40 °C and a humidity of 50% RH for 2 h; the second stage is drying at 80 °C and a humidity of ≤10% RH for 4 h; the third stage is drying at 120 °C and a vacuum degree of ≤1 kPa for 2 h to complete the dehydration and pre-crystallization of the precursor. The annealing treatment includes: placing the dried material in a tubular furnace and annealing it in a nitrogen-oxygen mixed atmosphere, where the volume ratio of nitrogen to oxygen is 93:7; the flow rate is 1.5 L / min, heating it to 400 °C at a rate of 5 °C / min and holding for 2 h; continuing to heat it to 500 °C at a rate of 8 °C / min and holding for 5 h; finally cooling it to room temperature at a rate of 10 °C / min to obtain a lithium triborate-coated lithium manganate cathode material.

[0057] Figure 5 Then, the cross-sectional microstructure of the lithium triborate-coated lithium manganate cathode material prepared in Example 4 of the present invention was further verified, and the results also showed that the lithium triborate layer was uniformly coated, further proving the feasibility and stability of the process of the present invention. In summary, these experimental results jointly confirmed the superiority of the lithium triborate-coated porous lithium manganate cathode material prepared by the present invention in terms of microstructure, phase retention, and coating uniformity.

[0058] Comparative Example 1

[0059] It is basically the same as Example 1, except that the mold was not pre-cooled during freeze forming, resulting in non-uniform pore structure and reduced pore connectivity.

[0060] Comparative Example 2

[0061] It is basically the same as Example 1, except that the volume ratio of ethanol to the total metal salt mass is set at 5 mL / g.

[0062] Comparative Example 3

[0063] It is basically the same as Example 1. In the freezing and forming process in step S1, gradient freezing is carried out at a cooling rate of 5°C / min.

[0064] Comparative Example 4

[0065] It is basically the same as Example 1, except that vacuum-assisted impregnation is not carried out, resulting in the inability of the lithium triborate precursor solution to fully penetrate into the pores.

[0066] Comparative Example 5

[0067] It is basically the same as Example 1, except that the pre-cooled mold is not used during freezing and forming, resulting in uneven pore structure and reduced pore connectivity.

[0068] Comparative Example 6

[0069] It is basically the same as Example 1, except that the ultrasonic treatment frequency is set to 10 kHz, which is lower than the standard range of the example, resulting in uneven distribution of the sol in the pores, too thin local coating layer, and affecting the long-cycle stability.

[0070] Comparative Example 7

[0071] It is basically the same as Example 1, except that the nitrogen pressure impregnation step is cancelled, resulting in uneven thickness distribution of the lithium triborate coating layer, and too thick layers are formed in some areas, affecting the diffusion rate of lithium ions.

[0072] Comparative Example 8

[0073] It is basically the same as Example 1, except that the heating rate of high-temperature sintering is set to 8°C / min instead of 5°C / min, resulting in too fast grain growth during sintering, collapse of the pore structure, and decrease in the specific capacity of the material.

[0074] Comparative Example 9

[0075] It is basically the same as Example 1, except that the thickness of the lithium triborate coating layer is set to 500 nm, which is lower than the standard range, resulting in insufficient protection ability of the coating layer and decrease in the manganese dissolution resistance of the material.

[0076] Comparative Example 10

[0077] It is basically the same as Example 3, except that the high-temperature sintering temperature is set to 750°C, which is higher than the standard range, resulting in lattice distortion of lithium manganate and shortening of the cycle life of the electrode material.

[0078] Performance Test:

[0079] Electrochemical cycling stability test: To evaluate the long-term cycling stability of lithium manganese oxide cathode material coated with lithium triborate, CR2032 coin cells (half-cells with metallic lithium as the counter electrode) and full cells (matched with graphite anode, strictly controlling the anode / cathode capacity ratio N / P = 1.1–1.2) were used for electrochemical tests respectively. The electrolyte was a conventional 1 M LiPF6 dissolved in a mixed solvent system of EC:DMC (1:1 volume ratio), and the test temperatures were set at 25°C and 55°C respectively. Constant current charge-discharge cycles were carried out at 0.1C and 1C rates, with the voltage range of 3.0–4.3 V (half-cell) and 2.8–4.2 V (full cell). Charge-discharge curves were recorded at the 1st, 10th, 25th, 50th, 75th, and 100th cycles respectively, and the capacity retention rate and Coulomb efficiency were calculated to analyze the variation trend of the polarization voltage, so as to comprehensively evaluate the cycling stability of the material under different temperature and rate conditions.

[0080] Rate performance and impedance analysis: To deeply study the influence of the lithium triborate coating layer on the rate performance and charge transfer kinetics of the cathode material, first, a CR2032 half-cell system was used to conduct constant current charge-discharge tests at 0.1C, 0.5C, 1C, 2C, and 5C rates successively at 25°C, and the rate-capacity relationship curve was plotted. After the rate test, the battery was cycled 5 times at 0.5C rate and left to stand for 2 hours after discharge to reach a stable state, and then electrochemical impedance spectroscopy (EIS) analysis was carried out. The frequency scanning range was set at 10 mHz–100 kHz, and the amplitude of the alternating current signal was 5 mV. ZView software was used to fit the impedance data to accurately extract kinetic parameters such as charge transfer resistance (R ct ) etc. In addition, the galvanostatic intermittent titration technique (GITT) was used to charge and discharge at C / 20 rate, and the change of the open-circuit voltage with time between each step was recorded in real time to calculate the lithium ion diffusion coefficient (D-Li⁺) to quantitatively analyze the correlation between the rate performance of the material and the internal ion diffusion kinetics.

[0081] Dynamic anti-manganese dissolution test: To systematically evaluate the inhibitory effect of lithium triborate coating on the manganese dissolution in lithium manganese oxide cathode materials, multiple parallel cells (CR2032 coin half-cells) were assembled respectively. After cycling at a rate of 1C for 10, 50, and 100 times at 60 °C, the cells were disassembled, the electrolytes were collected, and the concentration of dissolved Mn²⁺ in the electrolytes was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES) to analyze the dynamic evolution trend of manganese dissolution. Meanwhile, the corresponding cathode materials after cycling were taken out, and the chemical valence state distribution of Mn elements on the cathode surface was analyzed using X-ray photoelectron spectroscopy (XPS) to clarify the inhibition mechanism of the coating on manganese ion dissolution. In addition, synchrotron radiation X-ray diffraction technology (in-situ XRD) was used to track the changes in lattice parameters of the material during the charge-discharge cycle in real time, and to monitor the evolution of the LiMn2O4 crystal structure with the number of cycles, so as to explore the action mechanism of lithium triborate coating on Jahn-Teller distortion and manganese dissolution behavior.

[0082] The performance of the cathode materials of Examples 1-4 and Comparative Examples 1-10 is summarized in Table 1.

[0083] Table 1 Summary of the performance of the cathode materials of Examples 1-4 and Comparative Examples 1-10

[0084]

[0085] As can be seen from Table 1, too high a sintering temperature may lead to lattice distortion of lithium manganese oxide, affecting the cycling stability, but at the same time may improve the crystallinity of the material, reduce the interfacial impedance in the short term, and result in a relatively high initial capacity retention rate. Too fast a heating rate may lead to abnormal grain growth and pore structure collapse, thus reducing the rate performance and cycling stability. If the pre-cooling treatment of the mold is not adopted or the cooling rate is unreasonable during the freeze-forming process, it may lead to uneven pore structure and reduced pore connectivity, affecting the lithium ion diffusion rate, and further reducing the rate performance and cycle life. Improper ratio of ethanol volume to metal salt may affect the uniformity of the sol, resulting in uneven coating layer thickness distribution, and further affecting the rate performance and impedance characteristics. If vacuum-assisted impregnation or nitrogen pressure impregnation is not carried out, the lithium triborate precursor solution may not fully penetrate into the pores, resulting in local thinning or thickening of the coating layer, affecting the anti-manganese dissolution ability and charge transfer impedance. Too low an ultrasonic treatment frequency may lead to uneven distribution of the sol in the pores and local thinning of the coating layer, thus affecting the long-term cycling stability. Improper control of the heating rate or temperature during high-temperature sintering may lead to too fast grain growth, causing pore collapse, reducing the specific capacity of the material, and at the same time aggravating the Jahn-Teller distortion and increasing manganese dissolution. In addition, too thin a coating layer may not effectively inhibit manganese dissolution, while too thick a coating layer may hinder lithium ion diffusion and affect the rate performance.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention by using the content of the specification and drawings of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. Lithium manganate cathode material coated with lithium triborate, characterized in that, The positive electrode material described is a porous lithium manganate / lithium triborate composite electrode material; The porous lithium manganate / lithium triborate composite electrode material includes porous lithium manganate and a lithium triborate coating covering the pore surface of the porous lithium manganate; The mass ratio of the porous lithium manganate to lithium triborate is (86.0~92.0):(8.0~14.0); The porous lithium manganate has a highly connected oriented columnar pore structure; The average diameter of the columnar pores of the porous lithium manganate is 45~95μm; The porosity of the porous lithium manganate is 65~78%; The thickness of the lithium triborate coating is 600~800nm; The preparation method of the lithium triborate-coated lithium manganate positive electrode material includes the following steps: S1. Dissolve lithium acetate and manganese acetate in absolute ethanol to form a metal salt solution, add an acetone solution of polymethyl methacrylate, and obtain a precursor colloidal solution through stirring; Inject the colloidal solution into a pre-cooled mold for freeze molding, and prepare porous lithium manganate through freeze-drying, pre-oxidation and high-temperature sintering; S2. Vacuum-assisted impregnate and infiltrate the lithium triborate precursor solution into the pores of the porous substrate, and perform gradient drying and annealing treatment to form a composite positive electrode material coated with lithium triborate.

2. The lithium manganese oxide cathode material coated with lithium triborate as described in claim 1, wherein The preparation method of the precursor colloidal solution in step S1 is as follows: Calculated by weight, dissolve 100 parts by weight of lithium acetate and 190~200 parts by weight of manganese acetate in absolute ethanol, and control the mass ratio of the volume of ethanol to the total mass of metal salts to be 10~20mL / g; control the oxygen content ≤50ppm under a nitrogen atmosphere, and continuously mix at a mechanical stirring rate of 300~500rpm for 20~30min to form a homogeneous and transparent metal salt ethanol solution; then add 30~45 parts of an acetone solution of 3.0~5.0wt.% polymethyl methacrylate dropwise into the above metal salt ethanol solution at a rate of 1.0~2.0mL / min, control the system temperature to be maintained at 20~25°C during the dropping process, and continue to stir at a rate of 200~300rpm for 40~60min after the dropping is completed to obtain a stably dispersed precursor colloidal solution.

3. The lithium manganese oxide cathode material coated with lithium triborate according to claim 1, characterized in that The steps of freeze molding and freeze-drying in step S1 are as follows: Inject the precursor colloidal solution into a metal copper mold pre-cooled to -50~-40°C. The width of the microchannels of the mold is 50~100μm, the depth is 200~300μm, the inner surface is pre-coated with a polytetrafluoroethylene emulsion with a solid content of 10~15wt%, the coating thickness is 10~20μm, and the microchannel spacing is 1.0~2.0mm; perform gradient freezing at a cooling rate of 2~3°C / min to form a frozen blank with an oriented pore structure; then transfer the frozen blank to a freeze dryer, and perform solvent sublimation for 24~36h under the conditions of a vacuum degree ≤5Pa and a cold trap temperature ≤-85°C, and the residual solvent content ≤0.5wt% to obtain a dried blank.

4. The lithium manganese oxide cathode material coated with lithium triborate as claimed in claim 1, wherein, The steps of pre-oxidation and high-temperature sintering in step S1 are as follows: Subsequently, the dried green body is placed in a muffle furnace. Under an air atmosphere, the flow rate is controlled at 1 - 2 L / min, and it is heated at a heating rate of 3 - 5 °C / min to 350 - 380 °C, and held for 2.0 - 2.5 h to complete the decomposition of the pore-forming agent and the oxidation of the precursor. Subsequently, the pre-oxidized green body is placed in an alumina crucible. Under a flowing air atmosphere, the flow rate is controlled at 1.0 - 1.5 L / min, and it is heated to 700 - 720 °C at a heating rate of 5 - 6 °C / min, and held for 2 - 4 h; after sintering, it is slowly cooled to room temperature at a rate of 5 - 8 °C / min to obtain porous lithium manganate.

5. The lithium manganese oxide cathode material coated with lithium triborate according to claim 1, characterized in that, The preparation method of the lithium triborate precursor solution in step S2 is as follows: Boric acid and lithium hydroxide are dissolved in deionized water at a molar ratio of 1:(0.33 - 0.35), the pH of the solution is adjusted to 6.5 - 7.5, and the total boron ion concentration is controlled at 0.5 - 1.5 mol / L; it is stirred at 200 - 400 rpm for 30 - 60 min at 25 - 40 °C to form a transparent and homogeneous lithium triborate precursor solution.

6. The lithium manganese oxide cathode material coated with lithium triborate as described in claim 1, wherein The impregnation process in step S2 is as follows: The porous lithium manganate obtained in step S1 is immersed in the lithium triborate precursor solution, and kept at a vacuum degree of 10 - 30 kPa for 10 - 30 min to achieve full penetration of the solution into the pores; subsequently, ultrasonic treatment is applied, with the frequency set at 20 - 40 kHz, the power at 50 - 150 W, and the time at 10 - 30 min. Then, nitrogen pressure impregnation is used, with the pressure at 0.5 - 1.0 MPa and the pressurization time at 10 - 15 min to promote the uniform distribution of the sol; after impregnation, the surface residual droplets are purged with nitrogen at a pressure of 0.5 - 1.0 MPa to ensure that there is no excessive solution accumulation in the pores.

7. The lithium manganese oxide cathode material coated with lithium triborate according to claim 1, characterized in that, The gradient drying process in step S2 includes: The impregnated material is placed in a programmable temperature drying oven and dried in a three-stage gradient: The first stage is to dry at 25 - 40 °C and a humidity of 30 - 50%RH for 1 - 2 h; the second stage is to dry at 60 - 80 °C and a humidity of ≤10%RH for 2 - 4 h; the third stage is to dry at 100 - 120 °C and a vacuum degree of ≤1 kPa for 1 - 2 h to complete the dehydration and pre-crystallization of the precursor.

8. A lithium manganate cathode material coated with lithium triborate according to claim 1, characterized in that, The annealing treatment in step S2 includes: The dried material is placed in a tube furnace and annealed under a nitrogen-oxygen mixed atmosphere, where the volume ratio of nitrogen to oxygen is (93 - 97):(3 - 7); the flow rate is 0.5 - 1.5 L / min, and it is heated to 300 - 400 °C at a heating rate of 2 - 5 °C / min and held for 1 - 2 h; then it is continuously heated to 400 - 500 °C at a heating rate of 3 - 8 °C / min and held for 3 - 5 h; finally, it is cooled to room temperature at a rate of 2 - 10 °C / min to obtain the lithium triborate-coated lithium manganate cathode material.

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