Coated modified lithium manganate positive electrode material, preparation method thereof and lithium battery

Abstract

The invention discloses a coated modified lithium manganate positive electrode material, a preparation method thereof and a lithium battery. Belongs to the technical field of cathode materials. The coated modified lithium manganate positive electrode material comprises an inner core which is LiMn2O4, a first coating layer which is coated on at least part of the surface of the inner core and is made of FePO4, and a second coating layer which is coated on at least part of the surface of the first coating layer, the second coating layer is coated on at least part of the surface of the first coating layer, and the coating material is LiFePO4; and the third coating layer is coated on at least part of the surface of the second coating layer, and the coating material is carbon. According to the invention, lithium manganate (LMO) is used as an inner core and is sequentially coated with ferric phosphate (FePO4), lithium iron phosphate (LFP) and a carbon layer from inside to outside to form a composite structure, and the three components synergistically construct an inner-layer adaptive base building-middle-layer active buffer-outer-layer conductive stable effect system, so that the specific capacity, the rate capability, the cycle life and the high-temperature stability of the lithium manganate positive electrode material are remarkably improved.

Description

Technical Field

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

[0002] Spinel-type lithium manganese oxide (LiMn2O4) is favored due to its abundant raw materials, low cost, environmental friendliness, and high voltage platform (approximately 4.0V vs. Li). + With advantages such as manganese dissolution and the Jahn-Teller effect, these materials are considered one of the most promising cathode materials for lithium-ion batteries for industrialization. However, they generally suffer from problems such as manganese dissolution, the Jahn-Teller effect, and electrolyte decomposition during electrochemical cycling, resulting in rapid capacity decay and poor high-temperature performance, which seriously restricts their practical application.

[0003] Existing technologies generally employ surface coating strategies to mitigate these shortcomings. This involves constructing a physical isolation layer on the surface of lithium manganese oxide particles to suppress manganese ion dissolution and reduce electrolyte side reactions. However, current coating technologies still have significant limitations: most traditional coating materials (such as metal oxides like Al₂O₃, ZrO₂, and SiO₂) have poor intrinsic electronic conductivity, and their adhesion to the lithium manganese oxide substrate is mostly physical, resulting in insufficient interfacial contact and a significant increase in interfacial impedance. While such high-impedance coatings can improve structural stability to some extent, they hinder the cross-interfacial transport of lithium ions and electrons during charging and discharging, leading to increased material polarization, deterioration of rate performance, and an inability to balance cycle stability and electrochemical activity, thus failing to meet the application requirements of high-power lithium-ion batteries. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a coated and modified lithium manganese oxide cathode material, its preparation method, and a lithium battery.

[0005] In a first aspect, the present invention provides a coated and modified lithium manganese oxide cathode material, comprising: Kernel: The kernel is LiMn2O4; First coating layer: covering at least a portion of the surface of the core, the coating material being FePO4; Second coating layer: coated on at least a portion of the surface of the first coating layer, the coating material being LiFePO4; The third coating layer is coated on at least a portion of the surface of the second coating layer, and the coating material is carbon.

[0006] Secondly, the present invention provides a method for preparing a coated and modified lithium manganese oxide cathode material, comprising the following steps: S1: Disperse lithium manganese oxide in water to obtain a dispersion; then add an iron source and a water-soluble phosphate-containing raw material to the dispersion for reaction. After the reaction is complete, add a carbon source to the reaction solution, stir and mix well, and then evaporate to remove the solvent to obtain a modified lithium manganese oxide precursor. S2: After mixing the modified lithium manganese oxide precursor with a lithium source, lithiation sintering is carried out under an inert atmosphere to obtain the modified lithium manganese oxide cathode material.

[0007] Thirdly, the present invention provides a lithium battery comprising the aforementioned coated and modified lithium manganese oxide cathode material.

[0008] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: This invention relates to a modified lithium-rich manganese-based cathode material with lithium manganese oxide (LMO) as the core, and a composite structure consisting of iron phosphate (FePO4), lithium iron phosphate (LFP), and a carbon layer, sequentially coated from the inside out. Through the functional division and complementary performance of each layer, a comprehensive synergistic effect is achieved, effectively improving the core performance bottleneck of lithium manganese oxide. The inner FePO4 layer, with its good lattice compatibility, fills micro-defects in the particles, isolates corrosive substances, provides a stable substrate for the outer coating, and initially inhibits manganese dissolution and structural distortion. The middle LFP layer provides protection and buffers the volume expansion stress of the core, while also participating in lithium-ion intercalation / deintercalation as an active layer to improve specific capacity, build ion transport channels, and increase ion transport rate. The outer carbon layer constructs a continuous conductive network, overcoming the conductivity bottleneck of FePO4 and LFP, inducing the formation of a dense CEI film to suppress side reactions, and maintaining the stability of the valence state of the active components. These three layers synergistically construct an "inner layer adaptation and foundation building - middle layer active buffer - outer layer conductive and stable" system, significantly improving the specific capacity, rate performance, cycle life, and high-temperature stability of the lithium manganese oxide cathode material. Attached Figure Description

[0009] Figure 1 The image shows a cross-sectional SEM image of the modified lithium manganese oxide cathode material prepared in Example 1.

[0010] Figure 2 The diagram shows the cycle performance of the cathode materials in Examples 1-5 and Comparative Examples 1-12. Detailed Implementation

[0011] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0012] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0013] As mentioned above, in a first aspect, the present invention provides a coated and modified lithium manganese oxide cathode material, comprising: Kernel: The kernel is LiMn2O4; First coating layer: covering at least a portion of the surface of the core, the coating material being FePO4; Second coating layer: coated on at least a portion of the surface of the first coating layer, the coating material being LiFePO4; The third coating layer is coated on at least a portion of the surface of the second coating layer, and the coating material is carbon.

[0014] In this invention, a composite structure is formed with lithium manganese oxide (LMO) as the core and coated with iron phosphate, lithium iron phosphate (LFP) and carbon layers from the inside out. Each coating layer can simultaneously carry out the functions of structural protection, electrochemical performance optimization and interface stability improvement.

[0015] FePO4 serves as a transitional layer between the core and outer structure, simultaneously fulfilling functions such as interface adaptation, basic protection, and ion transport assistance, thus laying a solid foundation for the overall synergistic system. In terms of structural protection, its excellent compatibility with the lattice parameters of lithium manganese oxide allows it to adhere tightly to the core surface, filling micro-defects in particles, reducing direct contact between the electrolyte and the LMO core, and initially suppressing Mn. 3+ / Mn 4+ The structure collapse caused by dissolution and Jahn-Teller distortion is mitigated, while its excellent chemical stability isolates corrosive substances such as HF in the electrolyte, preventing core erosion. Regarding interfacial stability, FePO4 effectively alleviates lattice mismatch and interfacial tension between LMO and the outer LFP layer, reducing the risk of interfacial delamination during subsequent coating and cycling processes. This provides a flat and stable substrate for the middle LFP coating, ensuring the tight bonding of the multilayer structure. In terms of electrochemical performance, it possesses certain ion conduction properties, which can promote Li... + Rapid migration between the LMO core and the FePO4 layer reduces polarization loss caused by interfacial ion accumulation, thus establishing a preliminary channel for subsequent charge transport.

[0016] As an intermediate layer combining activity and protection, LFP inherits the protective effect of the inner FePO4 layer while enhancing structural buffering and electrochemical activity, achieving a synergistic upgrade in protection and performance. In terms of structural protection, on the one hand, it further thickens the physical barrier, strengthening the inhibition of manganese ion dissolution; on the other hand, its stable olivine structure reduces lattice volume changes during charge and discharge, effectively buffering the volume expansion stress of the LMO core, preventing the coating layer from cracking due to stress concentration, maintaining the overall structural integrity. Simultaneously, its structural stability reduces the surface oxidation of the inner layer material, minimizing electrolyte decomposition under high voltage. Regarding interface stability, LFP forms good bonds with both the inner FePO4 layer and the outer carbon layer. It synergistically optimizes interface compatibility with FePO4 and forms a strong connection with the carbon layer through high-temperature treatment, preventing carbon layer detachment during cycling and ensuring long-term stability of the conductive network. In terms of electrochemical performance, LFP, as an active component, can participate in lithium-ion intercalation / deintercalation reactions, directly improving the overall specific capacity of the material, while simultaneously building a Li-ion intercalation / deintercalation network. + The "intermediate channel" between the FePO4 layer and the outer carbon layer solves the problem of insufficient active sites in a single LMO core, enabling stable discharge in the low voltage range and expanding the voltage adaptability range of the material.

[0017] As the outermost structural layer, the carbon layer focuses on enhancing conductivity while simultaneously strengthening dense protection and interface regulation, providing ultimate protection for the inner structure and achieving a closed-loop synergy of the three functions. In terms of structural protection, it forms a dense physical barrier, preventing electrolyte penetration into the FePO4, LFP, and LMO inner layers. Simultaneously, its chemical inertness prevents side reactions between LFP and the electrolyte, reducing abnormal growth of the cathode electrolyte interphase (CEI). Its elasticity and toughness also buffer the mechanical stress generated during cycling, preventing CEI film rupture and microcracks within the particles, thus blocking structural degradation pathways at their source. Regarding interface stability, the carbon layer can induce the formation of a thin and dense CEI film, preventing continuous electrolyte decomposition and loss of active materials. At high temperatures, it also maintains the Fe content in LFP through reduction. 2+ Its stable valence state ensures its electrochemical activity and also consumes residual oxygen in the system, providing an inert environment for the inner structure and further inhibiting the oxidation and deterioration of LMO and manganese dissolution. In terms of electrochemical performance, the carbon layer constructs a continuous conductive network on the material surface, significantly improving the electronic conductivity of the composite system, overcoming the bottleneck of low electronic conductivity of FePO4 and LFP, ensuring rapid electron transport to various active sites, and avoiding electrochemical polarization; at the same time, it can work synergistically with the inner FePO4 and the middle LFP to achieve a virtuous cycle of "rapid ion migration - efficient electron conduction".

[0018] The three coating layers of this invention are not functionally independent, but rather form a progressive synergistic system of "inner layer adaptation and foundation building - middle layer active buffer - outer layer conductive and stable performance": the interfacial compatibility of FePO4 provides the prerequisite for the functional performance of LFP and the carbon layer; the stress buffering and activity enhancement effects of LFP connect the inner layer protection and the outer layer conductivity; and the dense protection and conductivity enhancement of the carbon layer maximizes the locking of the inner layer structural stability and electrochemical activity. Through cross-layer functional complementarity, the three layers synergistically solve the core problems of LMO manganese dissolution, poor conductivity, and insufficient cycle stability, integrating the compatibility of FePO4, the structural stability of LFP, and the high conductivity advantage of carbon materials, enabling the coated and modified lithium manganese oxide cathode material to achieve comprehensive improvement in specific capacity, rate performance, cycle life, and high-temperature stability.

[0019] Secondly, the present invention provides a method for preparing a coated and modified lithium manganese oxide cathode material, comprising the following steps: S1: Disperse lithium manganese oxide in water to obtain a dispersion; then add an iron source and a water-soluble phosphate-containing raw material to the dispersion for reaction. After the reaction is complete, add a carbon source to the reaction solution, stir and mix well, and then evaporate to remove the solvent to obtain a modified lithium manganese oxide precursor. S2: After mixing the modified lithium manganese oxide precursor with a lithium source, lithiation sintering is carried out under an inert atmosphere to obtain the modified lithium manganese oxide cathode material.

[0020] The preparation method of this invention employs an in-situ conversion strategy, using lithium manganese oxide as the nucleation center. A first coating layer of FePO4 is deposited on its surface via co-precipitation, followed by coating with a carbon source to form a FePO4-carbon bilayer coating structure. During sintering, the lithium source permeates and reacts in situ with the FePO4 to generate a lithium iron phosphate intermediate layer, while the carbon layer is densified. This method constructs a seamless heterogeneous interface through chemical bonding, significantly improving the bonding strength between the three layers and substantially reducing interfacial impedance. The three-layer composite coating structure effectively suppresses manganese dissolution and lattice distortion, thereby improving cycle stability.

[0021] In some embodiments, step S1, the method for preparing lithium manganese oxide includes the following steps: mixing manganese dioxide and a lithium source, and then sintering to obtain lithium manganese oxide.

[0022] In some embodiments, the number of moles of Li in the lithium source is 0.5 to 0.55 times the number of moles of Mn in manganese dioxide, including but not limited to: 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, etc.

[0023] In some embodiments, the sintering temperature is 800~1000℃, including but not limited to: 800℃, 850℃, 900℃, 950℃, 1000℃, etc.; the sintering time is 6~20h, including but not limited to: 6h, 8h, 10h, 12h, 15h, 18h, 20h, etc.

[0024] In some embodiments, in step S1, the iron source is one or more of ferric sulfate, ferric nitrate, ferric chloride, and ferric acetate; the water-soluble phosphate-containing raw material is one or two of diammonium hydrogen phosphate and diammonium dihydrogen phosphate; and the carbon source is one or more of fructose, glucose, and starch.

[0025] In some embodiments, in step S1, the molar concentration of lithium manganese oxide in water is 0.8~2 mol / L, including but not limited to: 1:15, 1:18, 1:20, 1:22, 1:25, 1:28, 1:30, etc.

[0026] In some embodiments, in step S1, the molar number of Fe in the iron source is 5-10% of the molar number of Mn in lithium manganese oxide, including but not limited to: 5%, 6%, 7%, 8%, 9%, 10%, etc.; the molar ratio of phosphate in the water-soluble phosphate-containing raw material to Fe in the iron source is (1-1.05):1; the molar ratio of C in the carbon source to Fe in the iron source is 1:(2-3), including but not limited to: 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, etc.

[0027] In some embodiments, in step S1, the reaction time is 0.5~6h, including but not limited to: 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, etc.; the stirring and mixing temperature is 60~100℃, including but not limited to: 60℃, 70℃, 80℃, 90℃, 100℃, etc.

[0028] In some embodiments, in step S2, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate; the molar ratio of Li in the lithium source to Fe in the iron source is (1~1.05):(2~3), including but not limited to: 1:2, 1:2.5, 1:3, 1.03:2, 1.03:2.5, 1.03:3, 1.05:1, 1.05:2.5, 1.05:3, etc.

[0029] In this invention, if the molar ratio of Li in the lithium source to Fe in the iron source is less than 1:3, the resulting lithium iron phosphate interlayer will be thin, leading to decreased lithium-ion transport and hindering the improvement of cathode material performance. If the molar ratio of Li in the lithium source to Fe in the iron source is greater than 1:2, the inner iron phosphate interlayer will be too thin, increasing interfacial impedance and also hindering the improvement of cathode material performance.

[0030] In some embodiments, in step S2, the lithium mixing sintering temperature is 650~800℃, including but not limited to: 650℃, 680℃, 700℃, 720℃, 750℃, 780℃, 800℃, etc.; the lithium mixing sintering time is 6~15h, including but not limited to: 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0031] Thirdly, the present invention provides a lithium battery comprising the aforementioned coated and modified lithium manganese oxide cathode material.

[0032] Preparation Example 1 Manganese dioxide and lithium carbonate were mixed evenly at a molar ratio of 1:0.255 and then sintered at 900℃ for 12 h to obtain LiMn2O4 material.

[0033] Example 1 In this embodiment, the chemical formula of the modified lithium manganese oxide cathode material is: LiMn2O4@FePO4@LiFePO4@C, which includes: a LiMn2O4 material core, a first FePO4 coating layer, a second LiFePO4 coating layer, and a third carbon coating layer.

[0034] The preparation method of the modified lithium manganese oxide cathode material in this embodiment includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.05 mol of ferric nitrate and 0.051 mol of diammonium hydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 2 h, 0.003 mol of glucose was added and stirred until well mixed. The mixture was then heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0035] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.021 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0036] The SEM image of the modified lithium manganese oxide cathode material prepared in this embodiment can be seen. Figure 1 As can be seen, it is clearly divided into four layers, from the inside out, including a lithium manganese oxide intermediate layer, a first coating layer of iron phosphate, a second coating layer of lithium iron phosphate, and a third coating layer of carbon.

[0037] Comparative Example 1 The lithium manganese oxide prepared in Example 1 was used as the positive electrode material.

[0038] Comparative Example 2 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is LiMn2O4@FePO4, which includes a LiMn2O4 core and a FePO4 coating layer.

[0039] The preparation method of this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.05 mol of ferric nitrate and 0.051 mol of diammonium hydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 2 h, the mixture was heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0040] S2: The modified lithium manganese oxide precursor was sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0041] Comparative Example 3 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is LiMn2O4@LiFePO4, which includes a LiMn2O4 core and a LiFePO4 coating layer.

[0042] The preparation method of this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion; then 0.05 mol of ferrous nitrate and 0.051 mol of diammonium hydrogen phosphate were added to the dispersion, and the mixture was stirred at room temperature for 2 h. Then, it was heated to 80 °C under an inert atmosphere and stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0043] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.051 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0044] Comparative Example 4 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is LiMn2O4@C, which includes a LiMn2O4 material core and a carbon coating layer.

[0045] The preparation method of this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion; then 0.003 mol of glucose was added to the dispersion, stirred and mixed, and then heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0046] S2: The modified lithium manganese oxide precursor was sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0047] Comparative Example 5 In this comparative example, the modified lithium manganese oxide cathode material has the chemical formula LiMn2O4@FePO4@LiFePO4, comprising: a LiMn2O4 core, a FePO4 first coating layer, and a LiFePO4 second coating layer.

[0048] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.03 mol of ferric nitrate and 0.031 mol of diammonium hydrogen phosphate were added to the dispersion and stirred at room temperature for 2 h. Then, 0.02 mol of ferrous nitrate and 0.02 mol of diammonium hydrogen phosphate were added and stirred at room temperature for 2 h. Finally, the mixture was heated to 80 °C under an inert atmosphere and stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0049] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.021 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0050] Comparative Example 6 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is LiMn2O4@FePO4@C, which includes: a LiMn2O4 material core, a FePO4 first coating layer, and a carbon second coating layer.

[0051] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.05 mol of ferric nitrate and 0.051 mol of diammonium hydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 2 h, 0.003 mol of glucose was added and stirred until well mixed. The mixture was then heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0052] S2: The modified lithium manganese oxide precursor was sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0053] Comparative Example 7 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is LiMn2O4@LiFePO4@C, which includes: a LiMn2O4 material core, a LiFePO4 first coating layer, and a carbon second coating layer.

[0054] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.05 mol of ferrous nitrate and 0.051 mol of diammonium hydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 2 h, 0.003 mol of glucose was added and stirred until well mixed. The mixture was then heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0055] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.051 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0056] Comparative Example 8 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is: LiMn2O4@FePO4&LiFePO4&C, which includes: a LiMn2O4 material core and a mixed coating layer composed of FePO4, LiFePO4 and carbon.

[0057] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.05 mol of ferric nitrate, 0.051 mol of diammonium hydrogen phosphate and 0.003 mol of glucose were added to the dispersion. After stirring and reacting at room temperature for 2 h, the mixture was heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0058] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.021 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0059] Comparative Example 9 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is: LiMn2O4@C@FePO4@LiFePO4, which includes: a LiMn2O4 material core, a first carbon coating layer, a second FePO4 coating layer, and a third LiFePO4 coating layer.

[0060] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion; then 0.003 mol of glucose was added to the dispersion and stirred, followed by the addition of 0.05 mol of ferric nitrate and 0.051 mol of diammonium hydrogen phosphate. The mixture was stirred and reacted at room temperature for 2 h, and then heated to 80 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0061] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.021 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0062] Comparative Example 10 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is: LiMn2O4@LiFePO4@FePO4@C, which includes: a LiMn2O4 core, a LiFePO4 first coating layer, a FePO4 second coating layer, and a carbon third coating layer.

[0063] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.02 mol of ferrous nitrate and 0.02 mol of diammonium hydrogen phosphate were added to the dispersion, and the mixture was stirred at room temperature for 2 h. Then, it was heated to 80 °C under stirring until the water was completely evaporated to obtain precursor 1. After the precursor 1 was thoroughly mixed with 0.021 mol of lithium hydroxide, it was sintered at 700 °C for 10 h under a nitrogen atmosphere to obtain LiMn2O4@LiFePO4.

[0064] S2: LiMn2O4@LiFePO4 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.03 mol of ferric nitrate and 0.031 mol of diammonium hydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 2 h, 0.003 mol of glucose was added and stirred until well mixed. The mixture was then heated to 80 °C under stirring until the water was completely evaporated to obtain precursor 2. Precursor 2 was sintered at 700 °C for 10 h under a nitrogen atmosphere to obtain modified lithium manganese oxide cathode material.

[0065] Comparative Example 11 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is: LiMn2O4@LiFePO4@C@FePO4, which includes: a LiMn2O4 core, a LiFePO4 first coating layer, a carbon second coating layer, and a FePO4 third coating layer.

[0066] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.02 mol of ferrous nitrate and 0.02 mol of diammonium hydrogen phosphate were added to the dispersion, and the mixture was stirred at room temperature for 2 h. Then, the mixture was heated to 80 °C under a nitrogen atmosphere and stirring until the water was completely evaporated to obtain precursor 1. After the precursor 1 was thoroughly mixed with 0.021 mol of lithium hydroxide, the mixture was sintered at 700 °C for 10 h under a nitrogen atmosphere to obtain LiMn2O4@LiFePO4.

[0067] S2: LiMn2O4@LiFePO4 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.003 mol of glucose was added to the dispersion and stirred until homogeneous. Then, 0.03 mol of ferric nitrate and 0.031 mol of diammonium hydrogen phosphate were added. After stirring and reacting at room temperature for 2 h, the mixture was heated to 80 °C under stirring until the water was completely evaporated to obtain precursor 2. Precursor 2 was sintered at 700 °C for 10 h under a nitrogen atmosphere to obtain modified lithium manganese oxide cathode material.

[0068] Comparative Example 12 The chemical formula of the modified lithium manganese oxide cathode material in this comparative example is: LiMn2O4@C@LiFePO4@FePO4, which includes: a LiMn2O4 material core, a first carbon coating layer, a second LiFePO4 coating layer, and a third FePO4 coating layer.

[0069] The preparation method of the modified lithium manganese oxide cathode material in this comparative example includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 400 mL of deionized water to obtain a dispersion. Then, 0.003 mol of glucose was added to the dispersion and stirred until homogeneous. 0.02 mol of ferric nitrate and 0.02 mol of diammonium hydrogen phosphate were added and stirred at room temperature for 2 h. Then, the mixture was heated to 80 °C under nitrogen atmosphere and stirring until the water was completely evaporated to obtain precursor 1. Precursor 1 was thoroughly mixed with 0.021 mol of lithium hydroxide and sintered at 700 °C for 10 h under nitrogen atmosphere to obtain LiMn2O4@C@LiFePO4.

[0070] S2: LiMn2O4@C@LiFePO4 was dispersed in 400 mL of deionized water to obtain a dispersion; then 0.03 mol of ferric nitrate and 0.03 mol of diammonium hydrogen phosphate were added to the dispersion, and the mixture was stirred at room temperature for 2 h. Then, it was heated to 80 °C under stirring until the water was completely evaporated to obtain precursor 2; precursor 2 was sintered at 700 °C for 10 h under a nitrogen atmosphere to obtain modified lithium manganese oxide cathode material.

[0071] Example 2 Compared with Example 1, the difference lies in the amount of lithium hydroxide added in step S2. The specific preparation method is as follows: S1: Same as Example 1.

[0072] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.026 mol of lithium hydroxide and sintered at 700 °C for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0073] Example 3 Compared with Example 1, the difference lies in the amount of lithium hydroxide added in step S2. The specific preparation method is as follows: S1: Same as Example 1.

[0074] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.0168 mol of lithium hydroxide and sintered at 700℃ for 10 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0075] Example 4 In this embodiment, the chemical formula of the modified lithium manganese oxide cathode material is: LiMn2O4@FePO4@LiFePO4@C, which includes: a LiMn2O4 material core, a first FePO4 coating layer, a second LiFePO4 coating layer, and a third carbon coating layer.

[0076] The preparation method of the modified lithium manganese oxide cathode material in this embodiment includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 300 mL of deionized water to obtain a dispersion. Then, 0.025 mol of ferric sulfate and 0.026 mol of ammonium dihydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 1 h, 0.0021 mol of fructose was added and stirred until well mixed. The mixture was then heated to 100 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0077] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.00627 mol of lithium carbonate and sintered at 650 °C for 15 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0078] Example 5 In this embodiment, the chemical formula of the modified lithium manganese oxide cathode material is: LiMn2O4@FePO4@LiFePO4@C, which includes: a LiMn2O4 material core, a first FePO4 coating layer, a second LiFePO4 coating layer, and a third carbon coating layer.

[0079] The preparation method of the modified lithium manganese oxide cathode material in this embodiment includes the following steps: S1: 0.5 mol of the LiMn2O4 material prepared in Preparation Example 1 was dispersed in 600 mL of deionized water to obtain a dispersion. Then, 0.04 mol of ferric sulfate and 0.042 mol of ammonium dihydrogen phosphate were added to the dispersion. After stirring and reacting at room temperature for 3 h, 0.0023 mol of fructose was added and stirred until well mixed. The mixture was then heated to 100 °C under stirring until the water was completely evaporated to obtain the modified lithium manganese oxide precursor.

[0080] S2: The modified lithium manganese oxide precursor was thoroughly mixed with 0.0154 mol of lithium hydroxide and sintered at 800℃ for 6 h under a nitrogen atmosphere to obtain the modified lithium manganese oxide cathode material.

[0081] Performance testing: The positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-12 were assembled into batteries. The positive electrode material, conductive graphite, and PVDF were weighed and ground according to a mass ratio of 8:1:1. Then, an appropriate amount of N-methylpyrrolidone (NMP) was added, and grinding and stirring were continued to form a uniform slurry. The slurry was uniformly coated onto aluminum foil using a mold to a thickness of 200 μm, and then placed in a drying oven at 90°C for 10 hours. The coated foil was then cut into 12 mm diameter discs. The discs were used as the positive electrode, and lithium foil as the negative electrode. The electrolyte consisted of a solvent and LiPF6, with a LiPF6 concentration of 1 mol / L. The solvent for the electrolyte was a mixture of EC, DEC, and DMC in a volume ratio of 1:1:1. The batteries were assembled in a glove box according to the coin cell assembly sequence. The assembled batteries were subjected to performance testing. The assembled batteries, which had been left to stand overnight, were placed in a LAND2001CT battery test chamber for charge-discharge testing. The tests were conducted at 45°C, 1C rate, and a cycle voltage of 2-4V, with 100 cycles. The test results are shown below. Figure 2 See Table 1.

[0082] Table 1 As can be seen from the data in Table 1, the battery assembled with the modified lithium manganese oxide cathode material in Example 1 exhibits higher initial specific capacity and cycle stability at high temperatures. The battery assembled with the unmodified lithium manganese oxide cathode material in Comparative Example 1 shows poorer initial specific capacity and cycle stability at high temperatures. Comparative Examples 2-4, which use a single coating layer for modification, show improved specific capacity and cycle stability at high temperatures compared to Comparative Example 1, but are significantly inferior to Example 1. Comparative Examples 5-7, which use two coating layers for modification, show improved specific capacity and cycle stability at high temperatures compared to Comparative Example 1, but are significantly inferior to Example 1. Comparative Example 8, which mixes three coating materials for modification, shows improved specific capacity and cycle stability at high temperatures compared to Comparative Example 1, but is significantly inferior to Example 1. In Examples 9-12, adjusting the order of the coating layers resulted in batteries with modified lithium manganese oxide cathode materials that exhibited significantly improved specific capacity and cycle stability at high temperatures compared to Comparative Example 1, but still not as good as Example 1. Based on a comparison of Example 1 and Comparative Examples 1-12, Example 1, by adjusting the materials and order of the coating layers, can construct an "inner layer adaptation foundation - middle layer active buffer - outer layer conductive stabilization" coating system, thereby significantly improving the specific capacity and cycle stability of the modified lithium manganese oxide cathode material at high temperatures.

[0083] In Examples 2 and 3, the content of lithium iron phosphate in the coating layer was adjusted. The specific capacity and cycle stability of the batteries assembled with the corresponding modified lithium manganese oxide cathode materials fluctuated somewhat at high temperatures, but overall, they exhibited good comprehensive performance. In Examples 4 and 5, the process parameters were adjusted. The specific capacity and cycle stability of the batteries assembled with the corresponding modified lithium manganese oxide cathode materials fluctuated somewhat at high temperatures, but overall, they exhibited good comprehensive performance.

[0084] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A coated and modified lithium manganese oxide cathode material, characterized in that, include: Kernel: The kernel is LiMn2O4; First coating layer: covering at least a portion of the surface of the core, the coating material being FePO4; Second coating layer: coated on at least a portion of the surface of the first coating layer, the coating material being LiFePO4; The third coating layer is coated on at least a portion of the surface of the second coating layer, and the coating material is carbon.

2. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 1, characterized in that, Includes the following steps: S1: Disperse lithium manganese oxide in water to obtain a dispersion; then add an iron source and a water-soluble phosphate-containing raw material to the dispersion for reaction. After the reaction is complete, add a carbon source to the reaction solution, stir and mix well, and then evaporate to remove the solvent to obtain a modified lithium manganese oxide precursor. S2: After mixing the modified lithium manganese oxide precursor with a lithium source, lithiation sintering is carried out under an inert atmosphere to obtain the modified lithium manganese oxide cathode material.

3. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step S1, the method for preparing lithium manganese oxide includes the following steps: mixing manganese dioxide and a lithium source, and then sintering to obtain lithium manganese oxide.

4. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 3, characterized in that, The number of moles of Li in the lithium source is 0.5 to 0.55 times the number of moles of Mn in manganese dioxide; And / or: the sintering temperature is 800~1000℃, and the sintering time is 6~20h.

5. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step S1, the iron source is one or more of ferric sulfate, ferric nitrate, ferric chloride, and ferric acetate; the water-soluble phosphate-containing raw material is one or two of diammonium hydrogen phosphate and diammonium dihydrogen phosphate; and the carbon source is one or more of fructose, glucose, and starch.

6. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step S1, the molar concentration of lithium manganese oxide in water is 0.8~2 mol / L; And / or: the number of moles of Fe in the iron source is 5 to 10% of the number of moles of Mn in lithium manganese oxide; the molar ratio of phosphate in the water-soluble phosphate-containing raw material to Fe in the iron source is (1 to 1.05):1; the molar ratio of C in the carbon source to Fe in the iron source is 1:(2 to 3).

7. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step S1, the reaction time is 0.5 to 6 hours; the stirring and mixing temperature is 60 to 100°C.

8. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step S2, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium nitrate; the molar ratio of Li in the lithium source to Fe in the iron source is (1~1.05):(2~3).

9. The method for preparing the coated and modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step S2, the lithium mixing sintering temperature is 650~800℃, and the lithium mixing sintering time is 6~15h.

10. A lithium battery, characterized in that, It includes the coated and modified lithium manganese oxide cathode material according to claim 1, or the coated and modified lithium manganese oxide cathode material prepared by any of the preparation methods according to claims 2 to 9.

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