Composite lithium manganate positive electrode material, preparation method and lithium manganate battery thereof

Abstract

The invention discloses a composite lithium manganate positive electrode material, a preparation method and a lithium manganate battery, the composite lithium manganate positive electrode material comprises lithium manganate and lithium-containing phosphate, the surface of the lithium manganate is coated with the lithium-containing phosphate, the chemical formula of the lithium-containing phosphate is LiMPO4, and M is one or more of Fe, Co, Ni, V, Ti and Mo, and the preparation method comprises the following steps: firstly, mixing and sintering a manganese source, a lithium source and a metal oxide in a solvent to obtain a mixture; crushing and sieving to obtain lithium manganate powder; the lithium manganate positive electrode material is obtained by dispersing lithium manganate powder into a suspension A, preparing a solution B from a lithium source, an M source and phosphate, carrying out a co-precipitation reaction, filtering, washing and drying to obtain a precursor, and finally carrying out heat treatment in an inert atmosphere, the lithium manganate positive electrode material is used as a positive electrode and lithium titanate is used as a negative electrode of the lithium manganate battery, and the problem of dissolution of a manganese element is solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and particularly relates to a composite lithium manganese oxide cathode material, its preparation method, and a lithium manganese oxide battery thereof. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, stable operating voltage, low self-discharge rate, and environmental friendliness, have been widely used in portable electronic products, electric vehicles, and energy storage power stations. Among the core components of lithium-ion batteries, the performance of the cathode material directly determines the battery's energy density, cycle life, and safety performance, and is one of the key factors restricting the development of battery technology.

[0003] Spinel-type lithium manganese oxide (LiMn2O4), as one of the mainstream cathode materials, has outstanding advantages such as abundant raw materials (manganese resources), low preparation cost, suitable working voltage platform (3.8~4.3V) and excellent safety performance, and has broad application prospects in the fields of power batteries and energy storage batteries. However, spinel-type lithium manganese oxide still has the following core problems in the actual charge and discharge cycle process, which seriously restricts its commercial promotion: (1) Manganese element dissolution problem: trace amounts of water or acidic substances in the electrolyte will react with lithium manganese oxide, causing the Mn in the lattice to dissolve. 3+ Disproportionation to Mn 2+ And it dissolves in the electrolyte; dissolved Mn 2+ Not only will it destroy the spinel crystal structure of lithium manganese oxide, but it will also deposit on the surface of the negative electrode, destroying the solid electrolyte interphase (SEI) film at the negative electrode interface, leading to increased battery impedance and capacity decay; (2) Jahn-Teller effect: During charging and discharging, Mn in the lithium manganese oxide lattice 3+ The electronic configuration of the battery is prone to Jahn-Teller distortion, which leads to irreversible expansion and contraction of the lattice. After long-term cycling, the crystal structure collapses, further aggravating the capacity decay. (3) Electrolyte decomposition problem: Under high temperature or high voltage conditions, the electrolyte is prone to oxidation decomposition reaction on the surface of lithium manganese oxide, generating byproducts with high impedance (such as organic carbonate decomposition products), which leads to a significant decrease in the rate performance and cycle stability of the battery.

[0004] To address these issues, existing technologies often employ modification methods such as ion doping and surface coating. However, conventional ion doping techniques can only partially alleviate the Jahn-Teller effect and cannot fundamentally solve the manganese dissolution problem. While conventional surface coating techniques (such as those using alumina or lithium fluoride) can, to some extent, prevent direct contact between the electrolyte and lithium manganese oxide, the coating layers are often made of insulating or low lithium-ion conductivity materials, which can easily increase the battery's interfacial impedance and sacrifice rate performance. At the same time, some coating processes suffer from cumbersome steps, poor coating uniformity, or excessive coating amount leading to increased costs, making it difficult to balance performance improvement with industrial feasibility.

[0005] Therefore, there is an urgent need to design a composite lithium manganese oxide cathode material, a preparation method, and a lithium manganese oxide battery to solve the problems mentioned above. Summary of the Invention

[0006] The purpose of this invention is to provide a composite lithium manganese oxide cathode material, a preparation method thereof, and a lithium manganese oxide battery thereof, which solves the problem of manganese dissolution.

[0007] To achieve the above objectives, the present invention provides a composite lithium manganese oxide cathode material, a preparation method thereof, and a specific technical solution for a lithium manganese oxide battery, as follows: A composite lithium manganese oxide cathode material includes: lithium manganese oxide and a lithium-containing phosphate, wherein the lithium-containing phosphate is coated on the surface of the lithium manganese oxide, and the chemical formula of the lithium-containing phosphate is LiMPO4, wherein M is one or more of Fe, Co, Ni, V, Ti, and Mo.

[0008] Furthermore, the mass ratio of the lithium-containing phosphate to the lithium manganese oxide is 1:1000 to 1:20.

[0009] Furthermore, the lithium-containing phosphate is in the form of nano-sized particles with a particle size of 10~100nm.

[0010] A method for preparing a composite lithium manganese oxide cathode material includes the following steps: S1: Manganese source, lithium source and metal oxide are mixed in a solvent and sintered to obtain lithium manganese oxide sintered material; S2: The lithium manganese oxide sintered material is crushed and sieved to obtain lithium manganese oxide powder; S3: Disperse the lithium manganese oxide powder in a solvent to obtain suspension A; S4: Dissolve the lithium source, M source and phosphate in a solvent to obtain solution B; S5: Under stirring conditions, the solution B is slowly added dropwise to the suspension A to carry out a coprecipitation reaction. The product of the coprecipitation reaction is filtered, washed, and dried to obtain the precursor. S6: The precursor is heat-treated in an inert atmosphere to obtain a lithium manganese oxide composite material with a surface coated with lithium phosphate.

[0011] Furthermore, the metal oxide is one or more of Al2O3 and ZrO2, and the solvent is one or more of deionized water, ethanol, acetone, and N-methylpyrrolidone (NMP).

[0012] Furthermore, the lithium source is one or more of lithium hydroxide, lithium acetate, lithium nitrate, and lithium carbonate; the M source is one or more of the nitrate, acetate, and chloride of metallic M; and the phosphate is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0013] Furthermore, the stoichiometric ratio of the lithium source, the M source, and the phosphate is 1~1.2:1:1.

[0014] Furthermore, the reaction temperature of the coprecipitation reaction is 20~80℃, and the reaction time is 1~10h.

[0015] Furthermore, the heat treatment temperature is 400~700℃, and the heat treatment time is 2~10h.

[0016] A lithium manganese oxide battery includes: a positive electrode sheet prepared using a composite lithium manganese oxide positive electrode material; a negative electrode sheet prepared using a lithium titanate material; a separator; a current collector; and an electrolyte.

[0017] The composite lithium manganese oxide cathode material, its preparation method, and the lithium manganese oxide battery of the present invention have the following advantages: 1. Significantly improved battery cycle life: The LiMPO4 coating layer can simultaneously block the electrolyte and assist lithium-ion conduction. On the one hand, it isolates lithium manganese oxide from direct contact with the electrolyte, inhibiting Mn dissolution and electrolyte decomposition; on the other hand, the lithium-ion conductivity of olivine-type LiMPO4 (≥1×10⁻⁶ at 25℃) is significantly improved. -8 The S / cm ratio is much higher than that of conventional insulating coatings, thus avoiding an increase in interface impedance. Experiments show that after 3000 cycles at 1C rate and 45℃, the battery using the material of this invention retains ≥90% of its capacity, which is far superior to the uncoated lithium manganese oxide battery (which retains only 80% of its capacity after 3000 cycles under the same conditions).

[0018] 2. Simple process and low cost: The preparation process adopts a "two-step method" without the need for complex pretreatment or multi-step sintering. The process has fewer steps and strong controllability, and can be directly adapted to existing lithium-ion battery cathode material production lines. The lithium phosphate coating content is only 0.1%~5%, the raw material consumption is small, and the manganese source, lithium source, M source and other materials used are all conventional raw materials in the lithium battery field, with low procurement costs and great potential for industrial application.

[0019] 3. Excellent performance balance: While improving cycle life, the high lithium-ion conductivity of LiMPO4 ensures that the battery maintains good rate performance. The capacity retention rate of the material of this invention is ≥85% at 5C rate (when the 1C specific capacity is 120mAh / g, the 5C specific capacity reaches 102mAh / g), which solves the contradiction between the improvement of cycle performance and the reduction of rate performance of conventional coating technology. 4. Optimization of battery safety performance: The combination of the structural stability of the composite cathode and the zero-strain characteristics of the lithium titanate anode can reduce volume changes and side reactions during battery charging and discharging, thereby reducing the risk of thermal runaway. At the same time, the introduction of FEC additives in the electrolyte can further optimize interface stability and improve the high-temperature safety performance of the battery. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the method for preparing the composite lithium manganese oxide cathode material of the present invention; Figure 2 This is a comparison chart of the cycle performance of lithium manganese oxide batteries in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments can be used in any combination.

[0023] The following is a reference to the appendix. Figure 1 To be continued Figure 2 This invention describes a composite lithium manganese oxide cathode material, its preparation method, and a lithium manganese oxide battery thereof.

[0024] A composite lithium manganese oxide cathode material includes: lithium manganese oxide and a lithium-containing phosphate, wherein the lithium-containing phosphate is coated on the surface of the lithium manganese oxide, and the chemical formula of the lithium-containing phosphate is LiMPO4, wherein M is one or more of Fe, Co, Ni, V, Ti, and Mo.

[0025] Specifically, the composite lithium manganese oxide cathode material uses spinel-type lithium manganese oxide as the matrix and achieves dual optimization of structural stability and ion conduction by coating the surface with functional lithium-containing phosphate. The specific structure is as follows: the core components include spinel-type lithium manganese oxide (LiMn2O4) and lithium-containing phosphate; the lithium-containing phosphate is uniformly attached to the surface of the lithium manganese oxide particles to form a continuous and dense coating layer, avoiding direct contact between lithium manganese oxide and electrolyte; Characteristics of lithium-containing phosphates: The chemical formula of the lithium-containing phosphates is LiMPO4, where M is one or more of Fe, Co, Ni, V, Ti, and Mo; these lithium-containing phosphates have an olivine-type crystal structure, possessing both excellent chemical stability and lithium-ion conductivity. They can physically block the electrolyte from corroding lithium manganese oxide and assist the transport of lithium ions within the cathode material, avoiding the increase in interfacial impedance caused by the coating layer.

[0026] Furthermore, the mass ratio of the lithium-containing phosphate to the lithium manganese oxide is 1:1000 to 1:20.

[0027] Specifically, the mass ratio of lithium phosphate to lithium manganese oxide is 1:1000 to 1:20, that is, the coating amount of lithium phosphate is 0.1% to 5%. When the coating amount is less than 0.1%, a complete coating layer cannot be formed and the barrier effect is insufficient. When it is higher than 5%, the coating layer is prone to agglomeration, which will increase the interfacial impedance. This range can balance the barrier effect, ion conduction efficiency and cost.

[0028] Furthermore, the lithium-containing phosphate is in the form of nano-sized particles with a particle size of 10~100nm.

[0029] Specifically, the nanoscale particle size ensures that the coating layer uniformly covers the surface of lithium manganese oxide, avoiding discontinuous coating due to excessively large particle size or agglomeration due to excessively small particle size. At the same time, it forms a reasonable size match with the lithium manganese oxide matrix particles, which typically have a particle size of 2~5μm, thus optimizing the interfacial contact area.

[0030] At room temperature, the lithium-ion conductivity of the lithium-containing phosphate is ≥1×10⁻⁶. -8 S / cm.

[0031] like Figure 1 As shown, a method for preparing a composite lithium manganese oxide cathode material includes the following steps: S1: Manganese source, lithium source and metal oxide are mixed in a solvent and sintered to obtain lithium manganese oxide sintered material; S2: The lithium manganese oxide sintered material is crushed and sieved to obtain lithium manganese oxide powder; S3: Disperse the lithium manganese oxide powder in a solvent to obtain suspension A; S4: Dissolve the lithium source, M source and phosphate in a solvent to obtain solution B; S5: Under stirring conditions, the solution B is slowly added dropwise to the suspension A to carry out a coprecipitation reaction. The product of the coprecipitation reaction is filtered, washed, and dried to obtain the precursor. S6: The precursor is heat-treated in an inert atmosphere to obtain a lithium manganese oxide composite material with a surface coated with lithium phosphate.

[0032] Furthermore, the metal oxide is one or more of Al2O3 and ZrO2, and the solvent is one or more of deionized water, ethanol, acetone, and NMP.

[0033] Furthermore, the lithium source is one or more of lithium hydroxide, lithium acetate, lithium nitrate, and lithium carbonate; the M source is one or more of the nitrate, acetate, and chloride of metallic M; and the phosphate is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0034] Furthermore, the stoichiometric ratio of the lithium source, the M source, and the phosphate is 1~1.2:1:1.

[0035] Furthermore, the reaction temperature of the coprecipitation reaction is 20~80℃, and the reaction time is 1~10h.

[0036] Furthermore, the heat treatment temperature is 400~700℃, and the heat treatment time is 2~10h.

[0037] Specifically, a manganese source, a lithium source, and a metal oxide are added to a solvent and stirred until uniformly dispersed to obtain a mixture. The mixture is then placed in a sintering apparatus and sintered at a specific temperature to obtain a spinel-type lithium manganese oxide sinter. The manganese source is a manganese oxide, carbonate, or organic acid salt (such as manganese tetroxide, manganese dioxide, manganese carbonate, manganese acetate, etc.), preferably manganese tetroxide (Mn3O4), which has high purity and few impurities, facilitating the formation of highly crystalline lithium manganese oxide. The lithium source is one or more of lithium hydroxide, lithium acetate, lithium nitrate, and lithium carbonate, preferably lithium hydroxide monohydrate (LiOH·H2O), which has good solubility and stable lithium content. The lithium-manganese ratio can be precisely controlled; the metal oxide is one or more of Al2O3 and ZrO2, and the amount added is 0.05%~0.5% of the manganese source mass, which is only used to slightly stabilize the lithium manganese oxide lattice and avoid capacity loss due to excessive doping; the solvent is one or more of deionized water, ethanol, acetone, and NMP (N-methylpyrrolidone), preferably a mixed solvent of deionized water and ethanol (volume ratio 1:1~3:1), which takes into account both the solubility of raw materials and subsequent drying efficiency; the sintering temperature is preferably 600~800℃, and the sintering time is preferably 2~15h to ensure that the manganese source and lithium source react fully to form pure spinel phase lithium manganese oxide.

[0038] The above-mentioned lithium manganese oxide sintered material is crushed and sieved, preferably through an 800-1200 mesh sieve, to obtain lithium manganese oxide powder with a particle size D50 of 2-5 μm. This particle size range can balance the energy density and ion diffusion efficiency of the battery, avoiding poor processability caused by excessively fine powder or insufficient rate performance caused by excessively coarse powder.

[0039] Lithium manganese oxide powder is dispersed in a solvent, and 0.01% to 0.05% of a dispersant (such as citric acid) can be selectively added. The powder is then dispersed by ultrasonication (30 to 60 min) or by high-speed stirring (200 to 600 rpm) to obtain a uniform and stable suspension A. The addition of the dispersant can further prevent the agglomeration of lithium manganese oxide powder, laying the foundation for the uniformity of subsequent coating.

[0040] The lithium source, M source, and phosphate were dissolved in a solvent at a stoichiometric ratio of 1~1.2:1:1 and stirred until completely dissolved to obtain a clear and transparent solution B (i.e., the LiMPO4 precursor solution). The lithium source was added in excess by 0.05 times to compensate for the trace volatilization of lithium during the subsequent heat treatment, ensuring the final formation of pure phase LiMPO4. The M source was one or more of the nitrate, acetate, and chloride of metal M (such as ferrous nitrate, cobalt acetate, nickel chloride, etc.), preferably anhydrous metal nitrates, which have high purity, good solubility, and no excess impurity ions. The phosphate was one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate, preferably ammonium dihydrogen phosphate, which has excellent solubility and its decomposition products are non-polluting.

[0041] Under stirring conditions (200~600 rpm), solution B is slowly added dropwise to suspension A at a rate of 0.5~2 ml / min, and the reaction temperature is controlled at 20~80℃ for co-precipitation reaction for 1~10 h. After the reaction, the product is filtered and washed with deionized water until the pH of the filtrate is 6.5~7.5 (to remove residual soluble impurities), and then vacuum dried at 80~120℃ for 8~12 h (vacuum degree ≤-0.095 MPa) to obtain a composite precursor with LiMPO4 precursor attached to the surface. The combination of slow dropwise addition and stirring can ensure that the LiMPO4 precursor is "deposited in situ" on the surface of lithium manganese oxide, avoiding the aggregation of the coating layer. The control of reaction temperature and time can adjust the particle size and dispersibility of LiMPO4 precursor. The reaction is preferably carried out at 50~70℃ for 3~6 h, at which time the coating uniformity is the best.

[0042] The aforementioned precursor was placed in a heat treatment apparatus under an inert atmosphere (such as argon or nitrogen, with a purity ≥ 99.99%) and heated to 400-700°C at a rate of 1-5°C / min, and held at that temperature for 2-10 hours for heat treatment. After heat treatment, it was naturally cooled to room temperature to obtain a composite lithium manganese oxide cathode material with an olivine-type LiMPO4 coating on its surface. The inert atmosphere can prevent lithium manganese oxide from reacting with oxygen and moisture in the air, ensuring the purity of the material. The control of the heating rate and holding temperature can promote the complete conversion of the LiMPO4 precursor into the pure olivine phase, while avoiding distortion of the lithium manganese oxide lattice due to sudden temperature changes.

[0043] A lithium manganese oxide battery includes: a positive electrode sheet prepared using a composite lithium manganese oxide positive electrode material; a negative electrode prepared using a lithium titanate material; a separator; a current collector; and an electrolyte.

[0044] Positive electrode sheet: The above-mentioned composite lithium manganese oxide positive electrode material, conductive agent (such as carbon black, graphene), and binder (such as polyvinylidene fluoride PVDF) are mixed in a mass ratio of 90~95:3~5:2~5, and a solvent (such as NMP) is added to form a uniform slurry; the slurry is coated onto the positive electrode current collector (aluminum foil), dried (80~120℃), and cold-pressed (compacted density 2.8~3.2 g / cm³). 3 (This is then used to make a positive electrode sheet;) Negative electrode: Spinel-type lithium titanate (Li4Ti5O) 12 In the preparation of materials, lithium titanate exhibits zero-strain characteristics, with almost no lattice expansion or contraction during charging and discharging, and it is not easily reacted with dissolved Mn. 2+ The reaction can avoid the conventional carbon anode due to Mn 2+ The SEI film damage caused by deposition synergistically with the performance of the composite cathode; The diaphragm is made of polypropylene (PP), polyethylene (PE) or PP / PE composite membrane, with a preferred thickness of 12~16μm, which has both excellent ion conductivity and mechanical strength. Current collector: The positive and negative electrode current collectors are 10~15μm thick aluminum foil to ensure uniform current collection and reduce battery internal resistance; Electrolyte: A system of 1.0~1.2 mol / L LiPF6 dissolved in a carbonate mixed solvent (such as ethylene carbonate EC / ethyl methyl carbonate EMC / dimethyl carbonate DMC, volume ratio 3:5:2) is used. 0.5%~1% of fluoroethylene carbonate (FEC) can be selectively added as a film-forming additive to further optimize the stability of the negative electrode interface.

[0045] The present invention will be further illustrated by specific embodiments below, but these embodiments do not limit the scope of protection of the present invention.

[0046] Example 1 Lithium hydroxide monohydrate (LiOH·H2O, 2.37 g) and manganese tetroxide (Mn3O4, 20.0 g) were weighed, and 0.1% (by mass) of Al2O3 (0.02 g) was added. The above raw materials were added to 200 ml of a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol:1), and mixed at a stirring rate of 400 rpm for 3 h to obtain a homogeneous mixture. The mixture was transferred to a muffle furnace and heated to 680 °C at a rate of 5 °C / min, held at that temperature for 6 h, and allowed to cool naturally to obtain spinel-type lithium manganese oxide sinter. The lithium manganese oxide sinter was crushed using a jaw crusher and passed through a 1000-mesh sieve to obtain lithium manganese oxide powder with a particle size D50 = 3 μm. Take 100g of lithium manganese oxide powder, disperse it in 200ml of the above mixed solvent, add 0.03g of citric acid as a dispersant, and ultrasonically disperse for 45min to obtain a uniform suspension A; weigh lithium hydroxide monohydrate (0.74g), anhydrous ferrous nitrate (Fe(NO3)3, 1.80g), and ammonium dihydrogen phosphate (1.15g) according to a stoichiometric ratio of 1.05:1:1, dissolve them in 50ml of deionized water, and stir until completely dissolved to obtain a clear solution B.

[0047] Suspension A was placed in a 50℃ constant temperature water bath. Solution B was slowly added dropwise to suspension A at a rate of 1.0 ml / min while stirring at 400 rpm. After the addition was complete, the reaction continued for 4 hours. After the reaction was complete, the product was separated by filtration and washed with deionized water until the pH of the filtrate reached 7.0. The filtrate was then dried at 90℃ and a vacuum of -0.098 MPa for 10 hours to obtain a composite precursor (containing lithium phosphate and lithium manganese oxide in a mass ratio of 1:100, i.e., a coating amount of 1%). The composite precursor was placed in an argon atmosphere furnace and heated to 550℃ at a rate of 3℃ / min, and held at that temperature for 6 hours. After naturally cooling to room temperature, a composite lithium manganese oxide cathode material with LiMPO4 surface coating was obtained (LiMPO4 particle size 20~50 nm, coating coverage ≥95%).

[0048] Positive electrode preparation: Composite lithium manganese oxide material, carbon black, and PVDF were mixed in a mass ratio of 93:4:3. NMP was added to form a slurry, which was then coated onto a 12μm thick aluminum foil. After drying at 80℃, the slurry was cold-pressed (compacted density 3.0 g / cm³). 3 ), to produce an areal density of 20 mg / cm³ 2 The positive electrode plate; Negative electrode preparation: spinel-type lithium titanate (D50=2μm), carbon black and PVDF are mixed in a mass ratio of 94:2:4, NMP is added to make a slurry, which is coated on a 12μm thick aluminum foil, dried and then cold pressed. Battery assembly: Using a 14μm thick PP / PE composite separator and a 1.1mol / L LiPF6-EC / EMC / DMC (3:5:2) electrolyte (containing 0.8% FEC) as components, 2Ah soft-pack batteries were assembled in an inert glove box. Performance testing: Under 1C rate and 45℃ conditions, and charge-discharge cycles within a voltage range of 1.5~2.8V, the results showed that after 3000 cycles, the battery capacity retention rate was 92.5%, and the Mn content in the electrolyte was [not specified]. 2+ The concentration is only 0.4 ppm.

[0049] Example 2 In Example 1, source M was replaced with anhydrous cobalt nitrate (Co(NO3)2, 1.49g) to prepare a LiCoPO4 coating layer (coating amount 2%, LiCoPO4 particle size 30~60nm); other steps were the same as in Example 1.

[0050] Performance test results: After 3000 cycles at 1C rate and 45℃, the battery capacity retention rate is 91.2%; at 5C rate, the capacity retention rate is 86.5%.

[0051] Example 3 In Example 1, the M source was replaced with anhydrous nickel nitrate (Ni(NO3)2, 1.45g) to prepare a LiMPO4 coating layer (coating amount 0.5%, LiMPO4 particle size 15~30nm); other steps were the same as in Example 1.

[0052] Performance test results: After 3000 cycles at 1C rate and 45℃, the battery capacity retention rate is 90.8%; at 5C rate, the capacity retention rate is 85.2%.

[0053] Comparative Example 1 Lithium manganese oxide powder was prepared according to the steps in Example 1, without any subsequent coating steps. Batteries were assembled and tested using the same method: after 3000 cycles at 1C rate and 45°C, the battery capacity retention was 80%, and the Mn content in the electrolyte was [not specified]. 2+ The concentration was 2.1 ppm; the capacity retention rate at 5C was 72%.

[0054] Depend on Figure 2 It can be seen that the lithium manganese oxide battery of Example 1 retained 92.5% of its capacity after 3000 cycles, while the capacity retention of Comparative Example 1 was only 80%. This indicates that the material preparation method provided by the present invention can effectively reduce or avoid the dissolution of manganese in the electrolyte at high temperatures, thereby improving the high-temperature cycle performance of lithium manganese oxide batteries.

[0055] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A composite lithium manganese oxide cathode material, characterized in that, include: Lithium manganese oxide and lithium-containing phosphate, wherein the lithium-containing phosphate coats the surface of the lithium manganese oxide, and the chemical formula of the lithium-containing phosphate is LiMPO4, wherein M is one or more of Fe, Co, Ni, V, Ti, and Mo.

2. The composite lithium manganese oxide cathode material according to claim 1, characterized in that, The mass ratio of the lithium-containing phosphate to the lithium manganese oxide is 1:1000 to 1:

20.

3. The composite lithium manganese oxide cathode material according to claim 1, characterized in that, The lithium-containing phosphate is in the form of nano-sized particles with a particle size of 10~100nm.

4. A method for preparing the composite lithium manganese oxide cathode material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Manganese source, lithium source and metal oxide are mixed in a solvent and sintered to obtain lithium manganese oxide sintered material; S2: The lithium manganese oxide sintered material is crushed and sieved to obtain lithium manganese oxide powder; S3: Disperse the lithium manganese oxide powder in a solvent to obtain suspension A; S4: Dissolve the lithium source, M source and phosphate in a solvent to obtain solution B; S5: Under stirring conditions, the solution B is slowly added dropwise to the suspension A to carry out a coprecipitation reaction. The product of the coprecipitation reaction is filtered, washed, and dried to obtain the precursor. S6: The precursor is heat-treated in an inert atmosphere to obtain a lithium manganese oxide composite material with a surface coated with lithium phosphate.

5. The method for preparing the composite lithium manganese oxide cathode material according to claim 4, characterized in that, The metal oxide is one or more of Al2O3 and ZrO2, and the solvent is one or more of deionized water, ethanol, acetone, and N-methylpyrrolidone.

6. The method for preparing the composite lithium manganese oxide cathode material according to claim 4, characterized in that, The lithium source is one or more of lithium hydroxide, lithium acetate, lithium nitrate, and lithium carbonate; the M source is one or more of the nitrate, acetate, and chloride of metallic M; and the phosphate is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

7. The method for preparing the composite lithium manganese oxide cathode material according to claim 4, characterized in that, The stoichiometric ratio of the lithium source, the M source, and the phosphate is 1~1.2:1:

1.

8. The method for preparing the composite lithium manganese oxide cathode material according to claim 4, characterized in that, The coprecipitation reaction is carried out at a temperature of 20-80℃ for 1-10 hours.

9. The method for preparing the composite lithium manganese oxide cathode material according to claim 4, characterized in that, The heat treatment temperature is 400~700℃, and the heat treatment time is 2~10h.

10. A lithium manganese oxide battery, characterized in that, include: The positive electrode sheet is prepared using the composite lithium manganese oxide positive electrode material as described in any one of claims 1 to 3; The negative electrode is prepared using lithium titanate material; Diaphragm; current collector; as well as Electrolyte.

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