Modified lithium manganate positive electrode material and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery materials, and particularly relates to a modified lithium manganate positive electrode material and a preparation method and application thereof; the method takes spinel lithium manganate as a matrix, uniformly loads tellurium-doped lithium pyrovanadate and defect type niobium tungsten oxygen compound on the surface of lithium manganate particles through wet mixing, removes organic dispersants through stepwise heating and holding in an air atmosphere after drying, then switches to inert atmosphere to continue heating and sintering, and finally cools down under the protection of inert atmosphere to obtain a modified product. The tellurium-doped lithium pyrovanadate is prepared through a peroxovanadic acid complex sol-gel method, and the defect type niobium tungsten oxygen compound is prepared through an argon-hydrogen mixed gas reduction method and is completely isolated from air. The application forms a composite layer of coating and grain boundary modification on the surface of lithium manganate through the synergistic effect of the two modified compounds, effectively inhibits manganese dissolution and lattice distortion, and at the same time, the oxygen vacancy structure is preserved under the protection of inert atmosphere, so that the cycle stability and electrochemical performance of the material are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a modified lithium manganese oxide cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as the core power source for modern portable electronic devices and new energy vehicles, rely heavily on the performance of their cathode materials, which directly determine the overall battery performance. Lithium manganese oxide (LMO) cathode materials have been widely used in the lithium-ion battery field due to their abundant resources, low cost, high safety, and environmental friendliness. However, LMO materials suffer from several inherent defects in practical applications, limiting their full potential and large-scale commercial application. Spinel-type LMO materials are prone to manganese ion dissolution during charge-discharge cycles, leading to gradual crystal structure destruction and accelerated capacity decay. This dissolution problem is particularly severe at high temperatures, significantly shortening the battery's cycle life. Furthermore, LMO materials undergo Yang-Taylor distortion during deep charge-discharge cycles, causing changes in lattice parameters and further exacerbating structural instability. These problems severely restrict the application prospects of LMO cathode materials in high-energy-density, long-cycle-life lithium-ion batteries.

[0003] To improve the electrochemical performance of lithium manganese oxide cathode materials, researchers have developed various modification methods, mainly including surface coating, bulk doping, and composite modification strategies. Surface coating involves forming a protective film on the surface of lithium manganese oxide particles to inhibit direct contact between the electrolyte and the active material, thereby reducing the dissolution of manganese ions. Commonly used coating materials include metal oxides, phosphates, and conductive polymers. Bulk doping involves introducing foreign ions to replace some atoms in the crystal lattice, enhancing the stability of the crystal structure and suppressing structural distortion during charge and discharge. However, a single modification method often only addresses one aspect of the problem and cannot simultaneously improve multiple performance indicators of the material. Excessively thick surface coatings increase interfacial impedance, affecting lithium-ion transport kinetics; bulk doping may reduce the specific capacity of the material. Therefore, developing a composite modification technique that can synergistically leverage the advantages of multiple modification methods has become an important direction in current research on lithium manganese oxide cathode materials.

[0004] Existing composite modification technologies still suffer from problems such as complex processes, high costs, and unstable modification effects. Many modification methods require high-temperature, long-duration sintering, which consumes a lot of energy and can easily lead to excessive grain growth, affecting the electrochemical activity of the material. Some modification processes involve toxic and harmful solvents or precursors, causing environmental pollution and contradicting the development concept of green manufacturing. In addition, existing technologies still have shortcomings in terms of the bonding strength and distribution uniformity between the modified compound and the matrix material, resulting in a gradual decay of the modification effect during long-term cycling. In particular, for modified materials that need to retain specific defect structures, existing processes are unable to effectively protect these active sites during sintering, causing the performance of the final product to fail to meet the expected goals. Therefore, there is an urgent need to develop a simple, environmentally friendly method for preparing lithium manganese oxide cathode materials that can retain active defect structures, achieve stable modification effects, and meet the urgent demand of the lithium-ion battery industry for high-performance cathode materials. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a modified lithium manganese oxide cathode material, its preparation method and application.

[0006] In a first aspect, the present invention provides a method for preparing a modified lithium manganese oxide cathode material, comprising the steps of:

[0007] S1. By weight, 95-105 parts of spinel-type lithium manganese oxide powder are dispersed in 180-220 parts of anhydrous ethanol and ultrasonically dispersed to obtain a suspension; 0.5-5.0 parts of tellurium-doped lithium vanadate pyrovanadate and 0.2-3.0 parts of defective niobium-tungsten oxide composite are added to the suspension and stirred to mix; 0.1-1.0 parts of polyvinylpyrrolidone are added and stirring is continued to obtain a mixed slurry; the mixed slurry is distilled under reduced pressure to obtain a solid mixture;

[0008] S2. Place the solid mixture in a vacuum drying oven and dry it at 80-85℃ to obtain the dried precursor powder. Place the dried precursor powder in a corundum crucible and put it into a muffle furnace. First, in an air atmosphere, raise the temperature from room temperature to 450-500℃ and hold it thereafter, then continue to raise the temperature to 620-645℃ and hold it thereafter. Switch to an argon atmosphere and sinter at 650-680℃. After sintering, cool it to room temperature under the protection of an argon atmosphere to obtain the product. Crush and sieve the product.

[0009] In this invention, the preparation of modified lithium manganese oxide cathode material is based on the synergistic mechanism of wet composite loading and segmented atmosphere sintering. First, a spinel-type lithium manganese oxide matrix is ​​ultrasonically dispersed in anhydrous ethanol to form a uniform and stable suspension. The low surface tension of ethanol facilitates the uniform spreading of the modified compounds on the surface of the lithium manganese oxide particles. After the addition of tellurium-doped lithium vanadate and defective niobium-tungsten oxide composite, the two modified components are uniformly loaded onto the surface and grain boundaries of the lithium manganese oxide particles at the nanoscale through mechanical stirring and ultrasonic treatment. Polyvinylpyrrolidone (PVP) acts as a dispersant and binder; its polar groups form hydrogen bonds with the surface of the modified compound, preventing particle agglomeration. Simultaneously, it gradually volatilizes during vacuum distillation, avoiding residual impurities that could affect product purity. The dried precursor undergoes multiple physicochemical transformations during segmented atmosphere sintering. During the low-temperature holding stage in air atmosphere, organic components such as PPVP are completely oxidized and decomposed, preventing carbon residue from affecting material performance. During the intermediate-temperature holding stage, the modified compound diffuses across the interface with the lithium manganese oxide matrix, forming chemical bonds and enhancing the bonding strength between the coating layer and the matrix. Switching to an inert atmosphere and continuing sintering at elevated temperatures is crucial. The inert atmosphere effectively protects oxygen vacancies in the defective niobium-tungsten oxide composite from oxidation, while simultaneously suppressing manganese ion valence changes at high temperatures and reducing manganese dissolution tendency. The two modified components form a synergistic protective layer on the lithium manganese oxide surface: tellurium-doped lithium vanadate provides a dense surface barrier, preventing electrolyte erosion, while the defective niobium-tungsten oxide composite provides a rapid ion transport channel and buffers volume changes. Together, they construct a multi-layered protective system, significantly improving the cycle stability and electrochemical performance of the lithium manganese oxide cathode material.

[0010] According to a preferred embodiment of the present invention, in step S1, the temperature of vacuum distillation is 58-62°C.

[0011] According to a preferred embodiment of the present invention, in step S2, the sintering time at 650-680°C is 4-8 hours.

[0012] According to a preferred embodiment of the present invention, the method for preparing tellurium-doped lithium vanadate includes: A1. Adding 4.5-5.5 parts by weight of vanadium pentoxide to 45-55 parts of deionized water and stirring to obtain a suspension; adding 13.5-16.5 parts of hydrogen peroxide under stirring and reacting at 20-30°C to obtain a pervanadate cationic complex solution; dissolving 4.0-4.3 parts of lithium hydroxide monohydrate and 0.95-1.15 parts of lithium carbonate in 18-22 parts of deionized water to obtain an alkaline solution; adding the alkaline solution dropwise to the pervanadate cationic complex solution and adjusting the pH to 3. -4. After the addition is complete, continue stirring to obtain a mixture; dissolve 2.5-3.1 parts of telluric acid in 27-33 parts of deionized water to obtain an aqueous telluric acid solution; add the aqueous telluric acid solution to the mixture, heat to 78-82℃ and stir to react to obtain a sol; dry the sol at 115-125℃ to obtain a dry gel precursor; A2. Transfer the dry gel precursor to an alumina crucible, place it in a muffle furnace, and pre-decompose it at 395-405℃ in an air atmosphere; then calcine it at 650-700℃; after calcination, allow it to cool naturally to room temperature with the furnace to obtain the product; grind the product.

[0013] In this invention, the preparation of tellurium-doped lithium vanadate is based on the sol-gel chemistry principle of pervanadate complexes. First, vanadium pentoxide forms a suspension in deionized water. Upon addition of hydrogen peroxide, a redox reaction occurs, where pentavalent vanadium coordinates with peroxide ions to form a stable pervanadate cationic complex. This complex exhibits a characteristic orange-yellow color in aqueous solution and possesses good water solubility and reactivity. Subsequently, an alkaline solution containing lithium and sodium sources is slowly added dropwise to the complex solution. By precisely controlling the pH, the pervanadate cations gradually hydrolyze and condense, forming a vanadium-oxygen framework network structure. During this process, lithium and sodium ions intercalate between the vanadium-oxygen layers, playing a role in charge balance and structural stability. Next, an aqueous telluric acid solution is introduced. Tellurate ions partially replace the vanadium-oxygen units in the vanadium-oxygen framework through chemical bonding, achieving uniform tellurium doping. The introduction of tellurium not only modulates the electronic structure of the material but also generates appropriate lattice distortion in the crystal lattice, which is beneficial for lithium ion insertion and extraction. After drying, the organic components and water molecules gradually evaporate, yielding a dry gel precursor. During subsequent heat treatment, the dry gel undergoes a pre-decomposition stage, where residual organic ligands and peroxide groups completely decompose and volatilize, preventing gas generation during high-temperature sintering and ensuring a porous product. Finally, in the high-temperature calcination stage, the amorphous precursor undergoes a crystallization transformation, forming a tellurium-doped product with a pyrovanadate crystal structure. Tellurium is uniformly distributed within the crystal lattice in a solid solution form, rather than simply adhering to the surface, ensuring the stability and durability of the doping effect.

[0014] According to a preferred embodiment of the present invention, in step A1, the reaction time at 20-30°C is 30-40 min.

[0015] According to a preferred embodiment of the present invention, in step A2, the calcination time at 650-700°C is 8-10 hours.

[0016] According to a preferred embodiment of the present invention, the preparation method of the defective niobium-tungsten oxide composite includes: B1, placing 11.0-13.0 parts by weight of niobium pentoxide and 1.60-1.90 parts by weight of tungsten trioxide in a ball mill jar, adding 90-110 parts by weight of anhydrous ethanol, and ball milling to obtain a mixed slurry; drying the mixed slurry at 80-90°C to obtain a mixed precursor powder; B2, loading the mixed precursor powder into an alumina boat and pushing it into a tube furnace; purging the furnace chamber with argon gas; heating to 495-505°C and holding under an argon protective atmosphere; switching to an argon-hydrogen mixed gas and heating to 900-950°C and holding; after holding, switching the atmosphere to argon protection and cooling the furnace to room temperature to obtain the product; grinding and sieving the product in an argon glove box.

[0017] In this invention, the preparation of defective niobium-tungsten oxide composites is based on the oxygen vacancy formation mechanism under a high-temperature reducing atmosphere. First, niobium pentoxide and tungsten trioxide are ball-milled in anhydrous ethanol to achieve atomic-level homogeneous mixing. Ethanol, acting as a dispersion medium, effectively prevents particle agglomeration. After drying, a precursor powder with uniform composition is obtained. The precursor is then placed in a high-temperature resistant container, and an inert gas is introduced to purge the furnace chamber, removing oxygen from the air and preventing excessive oxidation of the raw materials at high temperatures. Under an inert atmosphere, the temperature is raised to a medium-temperature range and held. During this stage, pre-sintering of the precursor and initial bonding between particles mainly occur, laying the foundation for the subsequent high-temperature reduction reaction. Subsequently, a hydrogen-containing reducing mixed gas is switched. At high temperatures, hydrogen reacts with oxygen atoms on the surface of the metal oxide, generating water vapor which is carried away by the gas flow. This selectively removes some oxygen atoms at the crystal surface and grain boundaries, forming oxygen vacancy defects. These oxygen vacancies are not randomly distributed but preferentially form on specific crystal planes of the niobium-tungsten oxide lattice, forming an ordered defect structure. The presence of oxygen vacancies significantly alters the electronic structure of the material, increasing electronic conductivity and providing additional storage sites and rapid transport channels for lithium ions. After high-temperature holding, the process is switched back to inert atmosphere cooling to prevent oxygen in the air from refilling the formed oxygen vacancies at high temperatures, ensuring the integrity of the defect structure. The final product is ground and sieved in an inert atmosphere glove box, completely isolating it from air to prevent the oxygen vacancies from being oxidized and repaired, thus ensuring the stability and electrochemical activity of the defect structure.

[0018] According to a preferred embodiment of the present invention, in step B2, the time for holding the temperature at 495-505°C is 2-4 hours.

[0019] In a second aspect, the present invention provides a modified lithium manganese oxide cathode material prepared according to the method for preparing the modified lithium manganese oxide cathode material.

[0020] A third aspect of the present invention provides an application of the modified lithium manganese oxide cathode material in a lithium-ion battery.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The modified lithium manganese oxide cathode material provided by this invention exhibits a significant improvement in electrochemical performance. By introducing two functional components, tellurium-doped lithium vanadate pyrovanadate and defective niobium-tungsten oxide composite, the dissolution of manganese ions in the lithium manganese oxide matrix during charge-discharge cycles is effectively suppressed, significantly extending the cycle life of the battery. The modified material maintains excellent structural stability at high temperatures, overcoming the inherent defect of poor high-temperature performance of traditional lithium manganese oxide materials. At the same time, the modified layer has good ionic conductivity and does not significantly increase interfacial impedance, ensuring rapid transport of lithium ions in the electrode material and enabling the battery to have excellent rate performance. The modified cathode material shows a significant improvement in capacity retention, stable voltage plateau, and effective mitigation of polarization after long-term cycling, achieving an overall industry-leading level in electrochemical performance.

[0023] (2) The two modified compounds of this invention form a synergistic composite protective layer on the surface of lithium manganese oxide, achieving a comprehensive effect that cannot be achieved by a single modification method. Tellurium-doped lithium vanadate, as the main component of the coating layer, can form a dense protective film on the surface of lithium manganese oxide particles, blocking direct contact between the electrolyte and the active material, and reducing the dissolution of manganese ions from the source. The defective niobium-tungsten oxide composite, through its unique oxygen vacancy structure, forms a fast ion transport channel at the grain boundary, while also buffering volume changes and suppressing lattice distortion during charging and discharging. The two components work together, with the former focusing on surface protection and the latter on structural stability, to jointly construct a multi-layered protection system. In addition, the inert atmosphere sintering process effectively preserves the oxygen vacancy active sites in the defective niobium-tungsten oxide composite, allowing the modification effect to be maintained continuously during long-term cycling, avoiding the problem of defective structures being oxidized and failing due to traditional air sintering.

[0024] (3) This invention has significant advantages in preparation process and is suitable for large-scale industrial application. The entire preparation process adopts a wet mixing combined with segmented sintering technical route. The process steps are simple and clear, the operating conditions are mild, and no complex and expensive special equipment is required. All raw materials used are commercially available conventional chemicals, which are widely available and cost-controllable, which helps to reduce production costs. The vacuum distillation and vacuum drying processes effectively avoid solvent residue and ensure product purity. The segmented atmosphere sintering strategy ensures the complete removal of organic dispersants and protects the integrity of defective structures, achieving a perfect balance between process controllability and product performance. The entire preparation process does not use toxic and harmful solvents, and the waste gas emissions are low, which is in line with the concept of green manufacturing and sustainable development. The modified lithium manganese oxide cathode material can be directly applied to existing lithium-ion battery production lines without adjusting the subsequent electrode preparation process, and has good compatibility and industrialization prospects. Detailed Implementation

[0025] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0026] Example 1

[0027] This embodiment provides a method for preparing a modified lithium manganese oxide cathode material, the steps of which include:

[0028] Step S1: Weigh 100g of spinel-type lithium manganese oxide powder and disperse it in 200g of anhydrous ethanol. Sonicate the powder in an ultrasonic cleaner for 30min to obtain a suspension. Add 2.5g of the tellurium-doped lithium vanadate prepared above and 1.5g of the defective niobium-tungsten oxide composite prepared above to the suspension. Stir and mix at 500r / min for 1h. Add 0.5g of polyvinylpyrrolidone and continue stirring for 2h to obtain a mixed slurry. Distill the mixed slurry under reduced pressure at 60℃ in a rotary evaporator until no liquid flows out to obtain a solid mixture.

[0029] Step S2: The solid mixture is placed in a vacuum drying oven and dried at 82℃ for 12h to obtain the dried precursor powder. The dried precursor powder is placed in a corundum crucible and placed in a muffle furnace. First, the temperature is increased from room temperature to 475℃ at a rate of 5℃ / min under air atmosphere and held for 2h. Then, the temperature is increased to 632℃ at a rate of 3℃ / min and held for 3h. The temperature is then switched to an argon atmosphere with a flow rate of 100sccm and heated to 665℃ at a rate of 2℃ / min for sintering for 6h. After sintering, the temperature is reduced to room temperature under argon atmosphere protection to obtain the product. The product is crushed and passed through a 200-mesh sieve to obtain the modified lithium manganese oxide cathode material.

[0030] Preparation of tellurium-doped lithium vanadate:

[0031] Step A1: Weigh 5.0g of vanadium pentoxide powder and add it to 50g of deionized water. Stir the mixture on a magnetic stirrer at 300r / min for 30min to obtain a homogeneous suspension. Slowly add 15.0g of 30% hydrogen peroxide while continuously stirring. Control the reaction temperature at 25℃ and react for 35min. The solution turns orange-yellow to obtain a pervanadate cationic complex solution. Dissolve 4.15g of lithium hydroxide monohydrate and 1.0g of lithium carbonate in 20g of deionized water. A transparent alkaline solution was obtained. The alkaline solution was added dropwise to the pervanadate cationic complex solution at a rate of 2 mL / min. The pH value was adjusted to 3.5 using a pH meter. After the addition was completed, the mixture was stirred for 60 min to obtain a mixed solution. 2.8 g of telluric acid was dissolved in 30 g of deionized water to obtain a clear telluric acid aqueous solution. The telluric acid aqueous solution was added to the mixed solution, and the mixture was heated to 80 °C and stirred for 4 h to obtain a homogeneous sol. The sol was placed in an oven and dried at 120 °C for 12 h to obtain a dry gel precursor.

[0032] Step A2: Transfer the dry gel precursor to an alumina crucible, place it in a muffle furnace, and pre-decompose it at 400℃ for 2 hours at a heating rate of 5℃ / min in air atmosphere. Then, calcine it at 675℃ for 9 hours at a heating rate of 3℃ / min. After calcination, allow it to cool naturally to room temperature in the furnace to obtain a block product. Grind the product in a mortar and pass it through a 200-mesh sieve to obtain tellurium-doped lithium vanadate pyrovanadate powder.

[0033] Preparation of defective niobium-tungsten oxide composites:

[0034] Step B1: Weigh 12.0g of niobium pentoxide and 1.75g ​​of tungsten trioxide and place them in a zirconia ball mill jar. Add 100g of anhydrous ethanol and an appropriate amount of zirconia grinding balls. Mill the mixture in a planetary ball mill at 400r / min for 12h to obtain a mixed slurry. Dry the mixed slurry in an oven at 85℃ for 10h to obtain a mixed precursor powder.

[0035] Step B2: The mixed precursor powder is loaded into an alumina boat and pushed into a tube furnace. Argon gas with a flow rate of 100 sccm is purged into the furnace for 30 min. Under the argon protective atmosphere, the temperature is increased to 500℃ at a heating rate of 5℃ / min and held for 3 h. The temperature is then switched to an argon-hydrogen mixture with a volume ratio of 5% hydrogen and 95% argon at a flow rate of 100 sccm and increased to 925℃ at a heating rate of 3℃ / min and held for 4 h. After the holding period, the atmosphere is switched to argon gas with a flow rate of 100 sccm and cooled to room temperature with the furnace to obtain a black product. The product is then ground through a 300-mesh sieve in an argon glove box to obtain defective niobium-tungsten oxide composite powder.

[0036] Example 2

[0037] The difference between this embodiment and Example 1 lies in the preparation of tellurium-doped lithium vanadate:

[0038] Step A1: Weigh 4.5g of vanadium pentoxide powder and add it to 45g of deionized water. Stir the mixture at 300r / min for 30min on a magnetic stirrer to obtain a homogeneous suspension. Slowly add 13.5g of 30% hydrogen peroxide while continuously stirring. Control the reaction temperature at 20℃ and react for 30min. The solution turns orange-yellow to obtain a pervanadate cationic complex solution. Dissolve 4.0g of lithium hydroxide monohydrate and 1.15g of lithium carbonate in 18g of deionized water. A transparent alkaline solution was obtained in water. The alkaline solution was added dropwise to the pervanadate cationic complex solution at a rate of 2 mL / min. The pH value was adjusted to 3 using a pH meter. After the addition was completed, the mixture was stirred for 60 min to obtain a mixed solution. 2.5 g of telluric acid was dissolved in 27 g of deionized water to obtain a clear telluric acid aqueous solution. The telluric acid aqueous solution was added to the mixed solution, and the mixture was heated to 78 °C and stirred for 4 h to obtain a homogeneous sol. The sol was placed in an oven and dried at 115 °C for 12 h to obtain a dry gel precursor.

[0039] Step A2: Transfer the dry gel precursor to an alumina crucible, place it in a muffle furnace, and pre-decompose it at 395°C for 2 hours at a heating rate of 5°C / min in air atmosphere. Then, calcine it at 650°C for 8 hours at a heating rate of 3°C / min. After calcination, allow it to cool naturally to room temperature in the furnace to obtain a block product. Grind the product in a mortar and pass it through a 200-mesh sieve to obtain tellurium-doped lithium vanadate pyrovanadate powder.

[0040] Preparation of defective niobium-tungsten oxide composites:

[0041] Step B1: Weigh 11.0g of niobium pentoxide and 1.60g of tungsten trioxide and place them in a zirconia ball mill jar. Add 90g of anhydrous ethanol and an appropriate amount of zirconia grinding balls. Mill the mixture in a planetary ball mill at 400r / min for 12h to obtain a mixed slurry. Dry the mixed slurry in an oven at 80℃ for 10h to obtain a mixed precursor powder.

[0042] Step B2: The mixed precursor powder was loaded into an alumina boat and pushed into a tube furnace. Argon gas with a flow rate of 100 sccm was purged into the furnace for 30 min. Under the protection of argon gas, the temperature was increased to 495℃ at a heating rate of 5℃ / min and held for 2 h. The temperature was then switched to an argon-hydrogen mixture with a volume ratio of 5% hydrogen and 95% argon at a flow rate of 100 sccm and increased to 900℃ at a heating rate of 3℃ / min and held for 4 h. After the holding period, the atmosphere was switched to argon gas with a flow rate of 100 sccm and cooled to room temperature with the furnace to obtain a black product. The product was then ground through a 300-mesh sieve in an argon glove box to obtain defective niobium-tungsten oxide composite powder.

[0043] Preparation of modified lithium manganese oxide cathode material:

[0044] Step S1: Weigh 95g of spinel-type lithium manganese oxide powder and disperse it in 180g of anhydrous ethanol. Sonicate the powder in an ultrasonic cleaner for 30min to obtain a suspension. Add 0.5g of the tellurium-doped lithium vanadate prepared above and 0.2g of the defective niobium-tungsten oxide composite prepared above to the suspension. Stir and mix at 500r / min for 1h. Add 0.1g of polyvinylpyrrolidone and continue stirring for 2h to obtain a mixed slurry. Distill the mixed slurry under reduced pressure at 58℃ in a rotary evaporator until no liquid flows out to obtain a solid mixture.

[0045] Step S2: The solid mixture is placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain the dried precursor powder. The dried precursor powder is placed in an alumina crucible and placed in a muffle furnace. The temperature is first increased from room temperature to 450°C at a rate of 5°C / min under air atmosphere and held for 2 hours. Then, the temperature is increased to 620°C at a rate of 3°C / min and held for 3 hours. The temperature is then switched to an argon atmosphere with a flow rate of 100 sccm and heated to 650°C at a rate of 2°C / min for sintering for 4 hours. After sintering, the temperature is lowered to room temperature under argon atmosphere protection to obtain the product. The product is crushed and passed through a 200-mesh sieve to obtain the modified lithium manganese oxide cathode material.

[0046] Example 3

[0047] The difference between this embodiment and Example 1 lies in the preparation of tellurium-doped lithium vanadate:

[0048] Step A1: Weigh 5.5g of vanadium pentoxide powder and add it to 55g of deionized water. Stir the mixture at 300r / min for 30min on a magnetic stirrer to obtain a homogeneous suspension. Slowly add 16.5g of 30% hydrogen peroxide while continuously stirring. Control the reaction temperature at 30℃ and react for 40min. The solution turns orange-yellow to obtain a peroxyvanadate cationic complex solution. Dissolve 4.3g of lithium hydroxide monohydrate and 0.95g of lithium carbonate in 22g of deionized water. A transparent alkaline solution was obtained in water. The alkaline solution was added dropwise to the pervanadate cationic complex solution at a rate of 2 mL / min. The pH value was adjusted to 4 using a pH meter. After the addition was completed, the mixture was stirred for 60 min to obtain a mixed solution. 3.1 g of telluric acid was dissolved in 33 g of deionized water to obtain a clear telluric acid aqueous solution. The telluric acid aqueous solution was added to the mixed solution, and the mixture was heated to 82 °C and stirred for 4 h to obtain a homogeneous sol. The sol was placed in an oven and dried at 125 °C for 12 h to obtain a dry gel precursor.

[0049] Step A2: Transfer the dry gel precursor to an alumina crucible, place it in a muffle furnace, and pre-decompose it at 405℃ for 2 hours at a heating rate of 5℃ / min in air atmosphere. Then, calcine it at 700℃ for 10 hours at a heating rate of 3℃ / min. After calcination, allow it to cool naturally to room temperature in the furnace to obtain a block product. Grind the product in a mortar and pass it through a 200-mesh sieve to obtain tellurium-doped lithium vanadate pyrovanadate powder.

[0050] Preparation of defective niobium-tungsten oxide composites:

[0051] Step B1: Weigh 13.0g of niobium pentoxide and 1.90g of tungsten trioxide and place them in a zirconia ball mill jar. Add 110g of anhydrous ethanol and an appropriate amount of zirconia grinding balls. Mill the mixture in a planetary ball mill at 400r / min for 12h to obtain a mixed slurry. Dry the mixed slurry in an oven at 90℃ for 10h to obtain a mixed precursor powder.

[0052] Step B2: The mixed precursor powder was loaded into an alumina boat and pushed into a tube furnace. Argon gas with a flow rate of 100 sccm was purged into the furnace for 30 min. Under the argon protective atmosphere, the temperature was increased to 505℃ at a heating rate of 5℃ / min and held for 4 h. The temperature was then switched to an argon-hydrogen mixture with a volume ratio of 5% hydrogen and 95% argon at a flow rate of 100 sccm and increased to 950℃ at a heating rate of 3℃ / min and held for 4 h. After the holding period, the atmosphere was switched to argon gas with a flow rate of 100 sccm and cooled to room temperature with the furnace to obtain a black product. The product was then ground through a 300-mesh sieve in an argon glove box to obtain defective niobium-tungsten oxide composite powder.

[0053] Preparation of modified lithium manganese oxide cathode material:

[0054] Step S1: Weigh 105g of spinel-type lithium manganese oxide powder and disperse it in 220g of anhydrous ethanol. Sonicate the powder in an ultrasonic cleaner for 30min to obtain a suspension. Add 5.0g of the tellurium-doped lithium vanadate and 3.0g of the defective niobium-tungsten oxide composite prepared above to the suspension. Stir and mix at 500r / min for 1h. Add 1.0g of polyvinylpyrrolidone and continue stirring for 2h to obtain a mixed slurry. Distill the mixed slurry under reduced pressure at 62℃ in a rotary evaporator until no liquid flows out to obtain a solid mixture.

[0055] Step S2: The solid mixture is placed in a vacuum drying oven and dried at 85°C for 12 hours to obtain the dried precursor powder. The dried precursor powder is placed in an alumina crucible and placed in a muffle furnace. The temperature is first increased from room temperature to 500°C at a rate of 5°C / min under air atmosphere and held for 2 hours. Then, the temperature is increased to 645°C at a rate of 3°C / min and held for 3 hours. The temperature is then switched to an argon atmosphere with a flow rate of 100 sccm and heated to 680°C at a rate of 2°C / min for sintering for 8 hours. After sintering, the temperature is lowered to room temperature under argon atmosphere protection to obtain the product. The product is crushed and passed through a 200-mesh sieve to obtain the modified lithium manganese oxide cathode material.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that tellurium-doped lithium vanadate is not added in step S1, but only 1.5g of defective niobium-tungsten oxide composite is added. The remaining steps and parameters are the same as in Example 1.

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 1 is that no defective niobium-tungsten oxide composite is added in step S1; only 2.5g of tellurium-doped lithium vanadate is added. The remaining steps and parameters are the same as in Example 1.

[0060] Comparative Example 3

[0061] The difference between this comparative example and Example 1 is that in step S1, tellurium-doped lithium vanadate and defective niobium-tungsten oxide complex are not added, only 0.5g of polyvinylpyrrolidone is added, while the remaining steps and parameters are the same as in Example 1.

[0062] According to relevant national and industry standards, the performance of the modified lithium manganese oxide cathode materials provided in the above embodiments and comparative examples was tested, and the test methods are as follows:

[0063] First discharge specific capacity test: The modified lithium manganese oxide cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 8:1:1. N-methylpyrrolidone solvent was added, and the mixture was stirred in a planetary mixer at 500 r / min for 4 h to obtain a uniform slurry. The slurry was coated on a 20 μm thick aluminum foil current collector, dried in a vacuum drying oven at 80 °C for 12 h, and compacted by roller pressing to a compaction density of 2.8 g / cm³. The plates were then punched into circular electrode sheets with a diameter of 12 mm and an areal loading of 2. With a water oxygen content of less than 0.1 ppm in an argon glove box, a CR2032 coin cell was assembled using a lithium metal sheet as the counter electrode, a Celgard 2400 polypropylene membrane as the separator, and a 1 mol / L LiPF6 EC / DMC / EMC mixed solution in a volume ratio of 1:1:1 as the electrolyte. After standing for 12 hours, charge and discharge tests were performed on the Blue Battery Test System. The charge and discharge voltage range was 3.0-4.3V, the current density was 0.1C, and the first discharge specific capacity was recorded.

[0064] First Coulomb Efficiency Test: The first charge specific capacity is recorded simultaneously with the first discharge specific capacity test. The first Coulomb efficiency is equal to the first discharge specific capacity divided by the first charge specific capacity multiplied by 100%.

[0065] 100-cycle capacity retention test: Charge-discharge cycle tests were conducted on the Blue Battery testing system at a current density of 1C, with a charge-discharge voltage range of 3.0-4.3V and a temperature of 25℃. The specific capacity of the first and 100th cycles was recorded. The 100-cycle capacity retention rate is equal to the specific capacity of the 100th cycle divided by the specific capacity of the first cycle multiplied by 100%.

[0066] 1C discharge specific capacity test: Charge and discharge tests were conducted at a 1C current density on the Blue Battery testing system, with a charge and discharge voltage range of 3.0-4.3V and a temperature of 25℃. The discharge specific capacity after stabilization was recorded.

[0067] 5C discharge specific capacity test: Charge and discharge tests were conducted at a 5C current density on the Blue Battery test system, with a charge and discharge voltage range of 3.0-4.3V and a temperature of 25℃. The discharge specific capacity after stabilization was recorded.

[0068] Charge transfer impedance test: AC impedance test was performed on an electrochemical workstation with a frequency range of 0.01Hz-100kHz, an amplitude of 5mV, and a temperature of 25℃ to test the charge transfer impedance of the battery before cycling. The charge transfer impedance value was obtained by fitting the Nyquist spectrum.

[0069] The performance test data above are shown in Table 1.

[0070] Table 1 Performance Test Results

[0071]

[0072] As can be seen from the above, the modified lithium manganese oxide cathode materials prepared in Examples 1-3 are significantly better than those in Comparative Examples 1-3 in all electrochemical performance indicators. This fully demonstrates that the synergistic modification of tellurium-doped lithium vanadate pyrovanadate and defective niobium-tungsten oxide composite effectively solves the technical problems of poor cycle stability, insufficient rate performance and high charge transfer impedance of existing lithium manganese oxide cathode materials.

[0073] In terms of initial discharge specific capacity, the initial discharge specific capacity of Examples 1-3 was 128.3-130.5 mAh / g, while that of Comparative Examples 1-3 was only 118.4-123.6 mAh / g. Among them, Comparative Example 3 had the lowest initial discharge specific capacity of only 118.4 mAh / g because no modifying compound was added. This indicates that the synergistic effect of the two modifying compounds effectively improved the initial electrochemical activity of the material.

[0074] In terms of initial coulombic efficiency, Examples 1-3 achieved 96.8-97.5%, while Comparative Examples 1-3 only achieved 89.5-92.1%, indicating that synergistic modification reduced irreversible capacity loss during the first cycle and improved lithium-ion insertion / extraction efficiency. Regarding capacity retention after 100 cycles, Examples 1-3 achieved 90.8-92.5%, while Comparative Examples 1-3 only achieved 82.3-86.7%, with Comparative Example 3 showing the lowest capacity retention at only 82.3%. This indicates that the combined effect of tellurium-doped lithium vanadate and the defective niobium-tungsten oxide complex effectively suppressed manganese dissolution and structural collapse of lithium manganese oxide during cycling, significantly improving cycle stability.

[0075] In terms of rate performance, Examples 1-3 have a discharge specific capacity of 125.2-128.5 mAh / g at 1C current density and 108.3-112.5 mAh / g at 5C current density, while Comparative Examples 1-3 have a discharge specific capacity of 103.5-111.5 mAh / g at 1C and 81.5-92.4 mAh / g at 5C. In particular, Example 1 shows a significant improvement in discharge specific capacity compared to Comparative Example 3 at a high rate of 5C, demonstrating that synergistic modification significantly improves the lithium-ion diffusion kinetics of the material under high rate conditions.

[0076] From the perspective of charge transfer impedance, the charge transfer impedance of Examples 1-3 is 45.2-48.5Ω, while that of Comparative Examples 1-3 is 58.7-75.6Ω. Among them, the charge transfer impedance of Comparative Example 3 is the highest, reaching 75.6Ω. The charge transfer impedance of Example 1 is 40.2% lower than that of Comparative Example 3, indicating that the two modified compounds form an efficient ion-electron conduction network on the surface of lithium manganese oxide, reducing the charge transfer resistance at the electrode interface.

[0077] A comprehensive comparison of Comparative Examples 1 and 2 shows that adding defective niobium-tungsten oxide composites or tellurium-doped lithium vanadate alone can improve the electrochemical performance of lithium manganese oxide to some extent, but the improvement effect is limited. Only the synergistic addition of both can achieve the best modification effect. Among them, Example 1 has the best overall performance, which proves that tellurium-doped lithium vanadate mainly plays the role of stabilizing the crystal structure and inhibiting manganese dissolution, while defective niobium-tungsten oxide composites mainly play the role of improving electronic conductivity and reducing interfacial impedance. The synergistic effect of the two solves the technical problem that single modification cannot simultaneously take into account cycle stability and rate performance, and provides an effective technical solution for the preparation of high-performance lithium manganese oxide cathode materials.

Claims

1. A method for preparing a modified lithium manganese oxide cathode material, characterized in that the steps include... include: S1. By weight, 95-105 parts of spinel-type lithium manganese oxide powder are dispersed in 180-220 parts of anhydrous ethanol and ultrasonically dispersed to obtain a suspension; 0.5-5.0 parts of tellurium-doped lithium vanadate pyrovanadate and 0.2-3.0 parts of defective niobium-tungsten oxide composite are added to the suspension and stirred to mix; 0.1-1.0 parts of polyvinylpyrrolidone are added and stirring is continued to obtain a mixed slurry; the mixed slurry is distilled under reduced pressure to obtain a solid mixture; S2. Place the solid mixture in a vacuum drying oven and dry it at 80-85℃ to obtain the dried precursor powder. Place the dried precursor powder in a corundum crucible and put it into a muffle furnace. First, in an air atmosphere, raise the temperature from room temperature to 450-500℃ and hold it thereafter, then continue to raise the temperature to 620-645℃ and hold it thereafter. Switch to an argon atmosphere and sinter at 650-680℃. After sintering, cool it to room temperature under the protection of an argon atmosphere to obtain the product. Crush and sieve the product.

2. The method for preparing the modified lithium manganese oxide cathode material according to claim 1, characterized in that, In step S1, the temperature for vacuum distillation is 58-62℃.

3. The method for preparing the modified lithium manganese oxide cathode material according to claim 1, characterized in that, In step S2, the sintering time at 650-680℃ is 4-8 hours.

4. The method for preparing the modified lithium manganese oxide cathode material according to claim 1, characterized in that, The preparation method of the tellurium-doped lithium vanadate includes: A1. Adding 4.5-5.5 parts by weight of vanadium pentoxide to 45-55 parts of deionized water and stirring to obtain a suspension; adding 13.5-16.5 parts of hydrogen peroxide while stirring, and reacting at 20-30℃ to obtain a pervanadate cationic complex solution; dissolving 4.0-4.3 parts of lithium hydroxide monohydrate and 0.95-1.15 parts of lithium carbonate in 18-22 parts of deionized water to obtain an alkaline solution; adding the alkaline solution dropwise to the pervanadate cationic complex solution, adjusting the pH to 3-4, and continuing until the addition is complete. Afterwards, continue stirring to obtain a mixture; dissolve 2.5-3.1 parts of telluric acid in 27-33 parts of deionized water to obtain an aqueous telluric acid solution; add the aqueous telluric acid solution to the mixture, heat to 78-82℃ and stir to react, obtaining a sol; dry the sol at 115-125℃ to obtain a dry gel precursor; A2, transfer the dry gel precursor to an alumina crucible, place it in a muffle furnace, and pre-decompose it at 395-405℃ in an air atmosphere; then calcine it at 650-700℃; after calcination, allow it to cool naturally to room temperature in the furnace to obtain the product; grind the product.

5. The method for preparing the modified lithium manganese oxide cathode material according to claim 4, characterized in that, In step A1, the reaction time is 30-40 minutes at 20-30℃.

6. The method for preparing the modified lithium manganese oxide cathode material according to claim 4, characterized in that, In step A2, the calcination time at 650-700℃ is 8-10 hours.

7. The method for preparing the modified lithium manganese oxide cathode material according to claim 1, characterized in that, The preparation method of the defective niobium-tungsten oxide composite includes: B1, placing 11.0-13.0 parts by weight of niobium pentoxide and 1.60-1.90 parts by weight of tungsten trioxide in a ball mill jar, adding 90-110 parts by weight of anhydrous ethanol, and ball milling to obtain a mixed slurry; drying the mixed slurry at 80-90℃ to obtain a mixed precursor powder; B2, loading the mixed precursor powder into an alumina boat and pushing it into a tube furnace; purging the furnace chamber with argon gas; heating to 495-505℃ and holding under an argon protective atmosphere; switching to an argon-hydrogen mixed gas and heating to 900-950℃ and holding; after holding, switching the atmosphere to argon protection and cooling the furnace to room temperature to obtain the product; grinding and sieving the product in an argon glove box.

8. The method for preparing the modified lithium manganese oxide cathode material according to claim 7, characterized in that, In step B2, the temperature is raised to 495-505℃ and held for 2-4 hours.

9. A modified lithium manganese oxide cathode material, characterized in that, The modified lithium manganese oxide cathode material is prepared according to any one of claims 1-8.

10. An application of the modified lithium manganese oxide cathode material according to claim 9, characterized in that, Application of the modified lithium manganese oxide cathode material in lithium-ion batteries.

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