Composite modified lithium manganate positive electrode material, preparation method and application thereof

Abstract

This invention discloses a composite modified lithium manganese oxide cathode material, its preparation method, and its applications, belonging to the field of cathode material technology. The structural formula of the composite modified lithium manganese oxide cathode material is: LiX a O b @LiYO2 / LiMn2O4, comprising: a core composed of LiYO2 and LiMn2O4, and LiX coating at least a portion of the surface of the core. a O b The coating layer; wherein: LiMn2O4 has a porous structure, and LiYO2 fills the channels of LiMn2O4. The cathode material in this invention uses lithium manganese oxide as a matrix, with LiYO2 filling the channels of the matrix, and LiX coated on the surface of the matrix. a O b Filling the pores with LiYO2 can reduce the Jahn-Teller effect of lithium manganese oxide without affecting the specific capacity of the cathode material. Moreover, LiYO2 can accelerate the lithium-ion diffusion rate, thereby improving the rate performance of the material.

Description

Technical Field

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

[0002] Lithium manganese oxides with a spinel structure are considered promising cathode materials for lithium-ion batteries due to their good safety, low cost, and non-toxicity. However, after LiMn2O4 cathode materials are assembled into batteries, the discharge specific capacity decreases significantly during electrochemical cycling. This is mainly because of the Mn content... 3+ The presence of [a specific substance] causes the spinel structure of lithium manganese oxide to transform from a cubic to a tetragonal phase due to the Jahn-Teller effect, resulting in volume changes and structural collapse of the spinel lattice. Secondly, the etching by the electrolyte causes the disproportionation reaction of trivalent manganese ions, generating Mn [a specific substance]. 2+ and Mn 4+ Mn 2+ It will dissolve in the electrolyte, damaging the LiMn2O4 structure and thus degrading battery performance. To address these issues, some researchers have used bulk ion doping methods, such as Al... 3+ Ti 4+ Cr 3+ Doping with single elements can enhance the material's structure and stability, but the effect of doping with single elements on improving the material's performance is limited; moreover, bulk ion doping can destroy the crystal structure of lithium manganese oxide, leading to a decrease in chemical activity and consequently a decrease in specific capacity. Summary of the Invention

[0003] Therefore, the purpose of this invention is to provide a composite modified lithium manganese oxide cathode material, its preparation method, and its application.

[0004] In a first aspect, the present invention provides a composite modified lithium manganese oxide cathode material, the structural formula of which is: LiX a O b @LiYO2 / LiMn2O4, comprising: a core composed of LiYO2 and LiMn2O4, and LiX coating at least a portion of the surface of the core. a O b The coating layer; wherein: LiMn2O4 has a porous structure, and LiYO2 fills the pores of LiMn2O4; X is one or more of Ti, Bi, and Sb, and Y is one or more of Al, Co, and Fe; 1≤a≤1.25, 2≤b≤3.

[0005] Secondly, the present invention provides a composite modified lithium manganese oxide cathode material, comprising the following steps:

[0006] (1) Prepare a mixed salt solution of manganese salt and zinc salt, add ammonia water and carry out hydrothermal reaction to obtain ZnO-Mn3O4 composite material; add ZnO-Mn3O4 composite material to alkaline solution and etch to obtain porous Mn3O4.

[0007] (2) Disperse porous Mn3O4 in a Y metal salt solution, and carry out a precipitation reaction by adjusting the pH of the reaction solution under pressure to obtain a reaction solution of Mn3O4 filled with Y hydroxide; under normal pressure, add X metal source to the reaction solution of Mn3O4 filled with Y hydroxide to carry out a hydrolysis reaction to obtain the precursor.

[0008] (3) After mixing the precursor with the lithium source, lithiation sintering is carried out to obtain composite modified lithium manganese oxide cathode material.

[0009] Preferably, in step (1), the manganese salt is one or more of manganese acetate, manganese nitrate, and manganese sulfate; the zinc salt is one or more of zinc acetate, zinc nitrate, and zinc sulfate; the molar ratio of manganese salt to zinc salt is (2.8~3.5):(0.1~0.3); the total concentration of metal ions in the mixed salt solution is 1.9~2.6 mol / L; the mass concentration of ammonia is 28~29%; and the molar volume ratio of manganese salt to ammonia is (2.8~3.5) mol:(0.4~0.6) L.

[0010] Preferably, in step (1), the hydrothermal reaction temperature is 160~220℃ and the hydrothermal reaction time is 10~24h.

[0011] Preferably, in step (1), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 2~4 mol / L.

[0012] Preferably, in step (1), the etching temperature is 30~50℃ and the etching time is 4~10h.

[0013] Preferably, in step (2), the metal salt of Y is one or two of nitrate and sulfate; the molar ratio of the metal salt of Y to the porous Mn3O4 material is (0.05~0.3):(2~4).

[0014] Preferably, in step (2), the pH of the reaction solution is adjusted to 5-9; the precipitation reaction time is 0.5-5h; and the pressure is 0.3-1MPa.

[0015] More preferably, when Y is Al, the pH of the reaction solution is adjusted to 5-6; when Y is one or both of Co and Fe, the pH of the reaction solution is adjusted to 7-8.

[0016] Preferably, in step (2), the X metal source is one or more of tetrabutyl titanate, bismuth chloride, and antimony chloride; the molar ratio of the X metal source to the porous Mn3O4 material is 1:(20~40).

[0017] Preferably, in step (2), the hydrolysis reaction time is 8~20h.

[0018] Preferably, in step (3), the lithium source is one or more of lithium hydroxide, lithium acetate, and lithium nitrate; the number of moles of Li in the lithium source is the sum of 0.5 to 0.55 times the number of moles of Mn, 0.8 to 1.05 times the number of moles of Y, and 1 to 1.03 times the number of moles of X in the precursor.

[0019] Preferably, in step (3), the lithiation sintering temperature is 880~1000℃ and the lithiation sintering time is 8~16h.

[0020] Thirdly, the present invention provides a lithium battery comprising the aforementioned composite modified lithium manganese oxide cathode material.

[0021] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0022] The cathode material in this invention uses lithium manganese oxide as a matrix, with LiYO2 filling the pores of the matrix and LiX coated on the matrix surface. a O b Filling the pores with LiYO2 can reduce the Jahn-Teller effect of lithium manganese oxide without affecting the specific capacity of the cathode material. Furthermore, LiYO2 can accelerate the lithium-ion diffusion rate, thereby improving the rate performance of the material; the outer layer of LiX... a O b Excellent structural stability can improve the structural stability of cathode materials, enhance the interfacial stability of electrode materials, and inhibit electrolyte corrosion, thereby further improving the cycle stability of the battery. In addition, the core-filled LiYO2 and the coating layer have a synergistic effect, which can significantly improve the overall electrochemical performance of the battery. Attached Figure Description

[0023] Figure 1 This is a SEM image of the porous Mn3O4 prepared in Example 1.

[0024] Figure 2 SEM image of Mn3O4 filled with Al(OH)3 prepared in Example 1.

[0025] Figure 3 The image shows a cross-sectional SEM image of the Al(OH)3-filled Mn3O4 particles prepared in Example 1.

[0026] Figure 4 The graphs show the cycle performance of batteries assembled with the cathode materials prepared in Examples 1-3 and Comparative Examples 1-4. Detailed Implementation

[0027] 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.

[0028] As mentioned above, in a first aspect, the present invention provides a composite modified lithium manganese oxide cathode material, the structural formula of which is: LiX a O b @LiYO2 / LiMn2O4, comprising: a core composed of LiYO2 and LiMn2O4, and LiX covering at least part of the surface of the core. a O b The coating layer; wherein: LiMn2O4 has a porous structure, and LiYO2 fills the pores of LiMn2O4; X is one or more of Ti, Bi, and Sb, and Y is one or more of Al, Co, and Fe; 1≤a≤1.25, 2≤b≤3.

[0029] In the cathode material of this invention, LiYO2 fills the channels of LiMn2O4 without affecting the LiMn2O4 lattice. Simultaneously, the presence of LiYO2 effectively reduces the Jahn-Teller effect of LiMn2O4, thereby improving the stability of the cathode material without reducing its specific capacity. The outer layer is coated with LiX... a O b outer LiX a O b Excellent structural stability can improve the structural stability of the cathode material, thereby further enhancing the cycle stability of the battery. Furthermore, this invention involves internally filling the cathode material with LiYO2 and externally coating it with LiX. a O b Dual modification can significantly improve the overall electrochemical performance of cathode materials.

[0030] Secondly, the present invention provides a composite modified lithium manganese oxide cathode material, comprising the following steps:

[0031] (1) Prepare a mixed salt solution of manganese salt and zinc salt, add ammonia water and carry out hydrothermal reaction to obtain ZnO-Mn3O4 composite material; add ZnO-Mn3O4 composite material to alkaline solution and etch to obtain porous Mn3O4.

[0032] (2) Disperse porous Mn3O4 in a Y metal salt solution, and carry out a precipitation reaction by adjusting the pH of the reaction solution under pressure to obtain a reaction solution of Mn3O4 filled with Y hydroxide; under normal pressure, add X metal source to the reaction solution of Mn3O4 filled with Y hydroxide to carry out a hydrolysis reaction to obtain the precursor.

[0033] (3) After mixing the precursor with the lithium source, lithiation sintering is carried out to obtain composite modified lithium manganese oxide cathode material.

[0034] In the method of this invention, zinc salt and manganese salt are prepared into ZnO-Mn3O4 composite material by hydrothermal method, and then zinc oxide is removed by alkaline etching to form porous Mn3O4. In this invention, zinc oxide is used as a pore-forming agent, which eliminates the need for sintering. Pore formation can be achieved by etching. Moreover, compared with other pore-forming agents, a small amount of zinc oxide residue will not affect the electrochemical performance of the cathode material.

[0035] In the method of this invention, the pressure co-precipitation method allows the generated Y hydroxide to primarily exist within the pores of Mn3O4, thereby reducing the Jahn-Teller effect of lithium manganese oxide. Simultaneously, the Y ions do not affect the crystal lattice of lithium manganese oxide, nor its specific capacity. Furthermore, the hydrolysis reaction used in this method allows for a tighter bond between the coating layer and the core, further enhancing the stability of the cathode material structure.

[0036] Preferably, in step (1), the manganese salt is one or more of manganese acetate, manganese nitrate, and manganese sulfate; the zinc salt is one or more of zinc acetate, zinc nitrate, and zinc sulfate; and the molar ratio of manganese salt to zinc salt is (2.8~3.5):(0.1~0.3), including but not limited to: 2.8:0.1, 2.8:0.2, 2.8:0.3, 3.0:0.1, 3.0:0.2, 3.0:0.3, 3.2:0.1, 3.2:0.2, 3.2:0.3, 3.5:0.1, 3.5 The ratios of manganese salt to ammonia are 0.2, 3.5, 0.3, etc.; the concentration of ammonia is 28-29%, including but not limited to: 28%, 28.5%, 29%, etc.; the total concentration of metal ions in the mixed salt solution is 1.9-2.6 mol / L, including but not limited to: 1.9 mol / L, 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, etc.; the molar volume ratio of manganese salt to ammonia is (2.8-3.5). mol:(0.4~0.6)L, including but not limited to: 2.8mol:0.4L, 2.8mol:0.5L, 2.8mol:0.6L, 3.0mol:0.4L, 3.0mol:0.5L, 3.0mol:0.6L, 3.2mol:0.4L, 3.2mol:0.5L, 3.2mol:0.6L, 3.5mol:0.4L, 3.5mol:0.5L, 3.5mol:0.6L, etc.

[0037] Preferably, in step (1), the hydrothermal reaction temperature is 160~220℃, including but not limited to: 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, etc.; the hydrothermal reaction time is 10~24h, including but not limited to: 10h, 12h, 15h, 18h, 20h, 22h, 24h, etc.

[0038] Preferably, in step (1), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 2~4 mol / L, including but not limited to: 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, etc.

[0039] Preferably, in step (1), the etching temperature is 30~50℃, including but not limited to: 30℃, 35℃, 40℃, 45℃, 50℃, etc., and the etching time is 4~10h, including but not limited to: 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0040] Preferably, in step (2), the metal salt of Y is one or two of nitrate and sulfate; the molar ratio of the metal salt of Y to the porous Mn3O4 material is (0.05~0.3):(2~4), including but not limited to: 0.05:2, 0.05:3, 0.05:4, 0.1:2, 0.1:3, 0.1:4, 0.2:2, 0.2:3, 0.2:1, 0.3:2, 0.3:4, etc.

[0041] Preferably, in step (2), the pH of the reaction solution is adjusted to 5~9, including but not limited to: 5, 6, 7, 8, 9, etc.; the precipitation reaction time is 0.5~5h, including but not limited to: 0.5h, 1h, 2h, 3h, 4h, 5h, etc.; the pressure is 0.3~1MPa, including but not limited to: 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1MPa, etc.

[0042] More preferably, when Y is Al, the pH of the reaction solution is adjusted to 5-6; when Y is one or both of Co and Fe, the pH of the reaction solution is adjusted to 7-8.

[0043] Preferably, in step (2), the X metal source is one or more of tetrabutyl titanate, bismuth chloride, and antimony chloride; the molar ratio of the X metal source to the porous Mn3O4 material is 1:(20~40), including but not limited to: 1:20, 1:25, 1:30, 1:35, 1:40, etc.

[0044] Preferably, in step (2), the hydrolysis reaction time is 8~20h, including but not limited to: 8h, 10h, 12h, 15h, 18h, 20h, etc.

[0045] Preferably, in step (3), the lithium source is one or more of lithium hydroxide, lithium acetate, and lithium nitrate; the number of moles of Li in the lithium source is the sum of 0.5 to 0.55 times the number of moles of Mn, 0.8 to 1.05 times the number of moles of Y, and 1 to 1.03 times the number of moles of X in the precursor.

[0046] Preferably, in step (3), the lithiation sintering temperature is 880~1000℃ and the lithiation sintering time is 8~16h.

[0047] Thirdly, the present invention provides a lithium battery comprising the aforementioned composite modified lithium manganese oxide cathode material.

[0048] Example 1

[0049] The chemical formula of the composite modified lithium manganese oxide cathode material in this embodiment is: Li4Ti5O 12@LiAlO2 / LiMn2O4; The specific preparation method is as follows:

[0050] (1) Dissolve 6 mol of manganese acetate and 0.4 mol of zinc acetate in 3 L of deionized water, add 500 mL of ammonia (28 wt%), mix well, and transfer to a polytetrafluoroethylene reactor. Perform a hydrothermal reaction at 180 °C for 18 h. After the reaction is complete, filter, wash, and dry to obtain the ZnO-Mn3O4 composite material. Disperse the ZnO-Mn3O4 composite material in a 3 mol / L sodium hydroxide solution, etch at 40 °C for 6 h, and then wash to obtain porous Mn3O4 material. Two mol of porous Mn3O4 material was dispersed in 100 ml of 1 mol / L aluminum nitrate solution. The pH of the solution was adjusted to 6 with ammonia at 0.5 MPa, and a co-precipitation reaction was carried out for 2 h to obtain a reaction solution containing Al(OH)3-filled Mn3O4. Then, 0.1 mol of tetrabutyl titanate was added to the reaction solution containing Al(OH)3-filled Mn3O4 under normal pressure, and a hydrolysis reaction was carried out for 20 h. After the reaction was completed, the mixture was filtered and washed to obtain the precursor (0.1 TiO2@0.1 Al(OH)3 / 2 Mn3O4).

[0051] (2) After mixing 47.38 g of precursor with 0.318 mol of lithium hydroxide evenly, the mixture was lithiated and sintered at 930 °C for 12 h to obtain the composite modified lithium manganese oxide cathode material Li4Ti5O 12 @LiAlO2 / LiMn2O4.

[0052] The SEM image of the porous Mn3O4 material prepared in this embodiment is shown below. Figure 1 As shown in the figure, the surface of the porous Mn3O4 material has a large number of pores. The surface SEM and cross-sectional SEM images of the Al(OH)3-filled Mn3O4 prepared in this embodiment are shown in the figure. Figure 2 and Figure 3 As shown, the surface of the particles has virtually no pores, and the internal channels of the particles are also very few, indicating that most of Al(OH)3 is deposited in the channels.

[0053] Comparative Example 1

[0054] The lithium manganese oxide cathode material in this comparative example is prepared using the following specific method:

[0055] After mixing 0.2 mol Mn3O4 and 0.3 mol lithium hydroxide evenly, the mixture was lithiated and sintered at 930 °C for 12 h to obtain lithium manganese oxide cathode material LiMn2O4.

[0056] Comparative Example 2

[0057] This is basically the same as Example 1, except that in step (2), Li4Ti5O is not included. 12 The coating layer is prepared using the following method:

[0058] (1) Dissolve 6 mol of manganese acetate and 0.4 mol of zinc acetate in deionized water, add 500 mL of ammonia (concentration of 28 wt%), mix well, and transfer to a polytetrafluoroethylene reactor. Perform hydrothermal reaction at 180 °C for 18 h. After the reaction is complete, filter, wash and dry to obtain ZnO-Mn3O4 composite material. Disperse ZnO-Mn3O4 composite material in 3 mol / L sodium hydroxide solution and etch at 40 °C for 6 h to obtain porous Mn3O4 material. Disperse 2 mol of porous Mn3O4 material in 100 mL of 1 mol / L aluminum nitrate solution. Under 0.5 MPa, add dilute sulfuric acid to the solution to adjust the pH value to 6 and perform coprecipitation reaction for 2 h. After the reaction is complete, filter and wash to obtain precursor of Mn3O4 filled with Al(OH)3 (0.1Al(OH)3 / 2Mn3O4).

[0059] (2) After mixing 46.5g of precursor with 0.31mol of lithium hydroxide evenly, the mixture was lithiated and sintered at 930℃ for 12h to obtain modified lithium manganese oxide cathode material.

[0060] Comparative Example 3

[0061] The preparation method is basically the same as in Example 1, except that the core does not contain LiAlO2. The specific preparation method is as follows:

[0062] (1) Disperse 2 mol of Mn3O4 material in water, add ammonia to adjust the pH to 6, then add 0.1 mol of tetrabutyl titanate and carry out hydrolysis reaction for 20 h. After the reaction is complete, filter and wash to obtain the precursor (0.1 TiO2@Mn3O4).

[0063] (2) After mixing 46.6g of precursor with 0.308mol of lithium hydroxide evenly, the mixture was lithiated and sintered at 930℃ for 12h to obtain modified lithium manganese oxide cathode material.

[0064] Comparative Example 4

[0065] The preparation method of the composite modified lithium manganese oxide cathode material in this embodiment is as follows:

[0066] (1) Dissolve 6 mol manganese acetate and 0.1 mol aluminum acetate in deionized water, add 500 mL ammonia (concentration 28 wt%), mix well, and transfer to a polytetrafluoroethylene reactor. Perform hydrothermal reaction at 180℃ for 18 h. After the reaction is complete, filter, wash and dry to obtain 0.05Al2O3-2Mn3O4 composite material. Disperse the prepared 0.05Al2O3-Mn3O4 composite material in water, add ammonia to adjust the pH to 6, and then add 0.1 mol tetrabutyl titanate to the reaction solution under normal pressure for hydrolysis reaction for 20 h. After the reaction is complete, filter and wash to obtain the precursor (0.1TiO2@0.05Al2O3 / 2Mn3O4).

[0067] (2) After mixing 47.1g of precursor with 0.318mol of lithium hydroxide evenly, the mixture was lithiated and sintered at 930℃ for 12h to obtain composite modified lithium manganese oxide cathode material.

[0068] Example 2

[0069] In this embodiment, the chemical formula of the composite modified lithium manganese oxide cathode material is: LiBiO2@LiCoO2 / LiMn2O4; the specific preparation method is as follows:

[0070] (1) Dissolve 7 mol of manganese acetate and 0.6 mol of zinc acetate in 3 L of deionized water, add 600 mL of ammonia (28 wt%), mix well, and transfer to a polytetrafluoroethylene reactor. Perform a hydrothermal reaction at 160 °C for 24 h. After the reaction is complete, filter, wash, and dry to obtain the ZnO-Mn3O4 composite material. Disperse the ZnO-Mn3O4 composite material in a 2 mol / L sodium hydroxide solution and etch it at 50 °C for 4 h to obtain porous Mn3O4 material. Two mol of porous Mn3O4 material was dispersed in 50 ml of 1 mol / L cobalt sulfate solution. Under a pressure of 0.3 MPa, ammonia was added to the solution to adjust the pH to 7, and a co-precipitation reaction was carried out for 5 h to obtain a reaction solution containing Co(OH)2-filled Mn3O4. Then, under normal pressure, 0.06 mol of bismuth chloride was added to the reaction solution containing Co(OH)2-filled Mn3O4, and a hydrolysis reaction was carried out for 20 h. After the reaction was completed, the solution was filtered and washed to obtain the precursor (0.06BiOCl@0.05Co(OH)2 / 2Mn3O4).

[0071] (2) After mixing 47.66g of precursor with 0.311mol of lithium hydroxide evenly, the mixture was lithiated and sintered at 880℃ in air atmosphere for 16h to obtain composite modified lithium manganese oxide cathode material.

[0072] Example 3

[0073] The chemical formula of the composite modified lithium manganese oxide cathode material in this embodiment is: LiSbO2@LiFeO2 / LiMn2O4; the specific preparation method is as follows:

[0074] (1) Dissolve 5.6 mol manganese acetate and 0.2 mol zinc acetate in deionized water, add 400 mL ammonia water (concentration of 29 wt%), mix well, and transfer to a polytetrafluoroethylene reactor. Perform hydrothermal reaction at 220℃ for 10 h. After the reaction is complete, filter, wash and dry to obtain ZnO-Mn3O4 composite material. Disperse the ZnO-Mn3O4 composite material in 4 mol / L sodium hydroxide solution, and etch it at 30℃ for 10 h to obtain porous Mn3O4 material. Two mol of porous Mn3O4 material was dispersed in 150 ml of 1 mol / L ferric nitrate solution. Under a pressure of 1.0 MPa, ammonia was added to the solution to adjust the pH to 8, and a co-precipitation reaction was carried out for 30 min to obtain a reaction solution containing Fe(OH)3-filled Mn3O4. Then, under normal pressure, 0.05 mol of antimony chloride was added to the reaction solution, and a hydrolysis reaction was carried out for 8 h. After the reaction was completed, the solution was filtered and washed to obtain the precursor (0.025Sb2O3@0.15Fe(OH)3 / 2Mn3O4).

[0075] (2) After mixing 48.13g of precursor with 0.32mol of lithium hydroxide, the mixture was lithiated and sintered at 1000℃ for 8h to obtain the composite modified lithium manganese oxide cathode material LiSbO2@LiFeO2 / LiMn2O4.

[0076] The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-4 were weighed and ground according to a mass ratio of positive electrode material: conductive graphite: PVDF 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 then uniformly coated onto aluminum foil using a mold to a thickness of 200 μm, and placed in a drying oven at 90°C for 10 hours. The coated foil was then cut into 12 mm diameter discs. Using the discs 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 electrolyte solvent 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. After being left to stand overnight, the assembled batteries were placed in the LAND2001CT battery test chamber for charge and discharge testing. The test was conducted at 25°C, 2C, and a cycle voltage of 2.7~4.2V, with 100 cycles.

[0077] Table 1

[0078]

[0079] From Table 1 and Figure 4 The data shows that the battery assembled with the unmodified lithium manganese oxide cathode material in Comparative Example 1 has poor specific capacity and cycle stability. The battery assembled with the modified lithium manganese oxide cathode material prepared by nested doping with lithium aluminate in Comparative Example 2 shows some improvement in specific capacity and cycle stability compared to Comparative Example 1, but the battery performance is still poor. The battery assembled with the lithium manganese oxide cathode material coated with lithium titanate in Comparative Example 3 shows some improvement in specific capacity and cycle stability compared to Comparative Example 1, but the battery performance is still poor. In Comparative Example 4, lithium aluminate exists in the form of doping in lithium manganese oxide, and the specific capacity and cycle stability of the battery assembled with the corresponding cathode material are improved compared to Comparative Examples 1-3, but the improvement is not significant. The battery assembled with the composite modified lithium manganese oxide cathode material prepared in Example 1 has significantly better specific capacity and cycle stability than Comparative Examples 1-4; this may be because the nested structure of lithium aluminate in this invention helps to improve the performance of the cathode material. Examples 2 and 3 adjusted the process parameters, and the specific capacity and cycle stability of the batteries assembled with the corresponding cathode materials fluctuated to some extent, but both had superior performance.

[0080] 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 composite modified lithium manganese oxide cathode material, characterized in that, LiX a O b @LiYO2 / LiMn2O4, comprising: a core composed of LiYO2 and LiMn2O4, and a LiX coating layer coated on at least part of the surface of the core a O b The coating layer; wherein: LiMn2O4 has a porous structure, LiYO2 is filled in the pore channels of LiMn2O4; X is one or more of Ti, Bi and Sb, Y is one or more of Al, Co and Fe; 1≤a≤1.25, 2≤b≤3.

2. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 1, characterized in that, Includes the following steps: (1) Prepare a mixed salt solution of manganese salt and zinc salt, add ammonia water and carry out hydrothermal reaction to obtain ZnO-Mn3O4 composite material; add ZnO-Mn3O4 composite material to alkaline solution and etch to obtain porous Mn3O4. (2) Disperse porous Mn3O4 in a Y metal salt solution, and carry out a precipitation reaction by adjusting the pH of the reaction solution under pressure to obtain a reaction solution of Mn3O4 filled with Y hydroxide; under normal pressure, add X metal source to the reaction solution of Mn3O4 filled with Y hydroxide to carry out a hydrolysis reaction to obtain the precursor. (3) After mixing the precursor with the lithium source, lithiation sintering is carried out to obtain composite modified lithium manganese oxide cathode material.

3. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step (1), the manganese salt is one or more of manganese acetate, manganese nitrate, and manganese sulfate; the zinc salt is one or more of zinc acetate, zinc nitrate, and zinc sulfate. And / or: the molar ratio of manganese salt to zinc salt is (2.8~3.5):(0.1~0.3); And / or: The total concentration of metal ions in the mixed salt solution is 1.9~2.6 mol / L; And / or: The mass concentration of ammonia water is 28~29%; And / or: the molar volume ratio of manganese salt to ammonia is (2.8~3.5) mol:(0.4~0.6) L; And / or: The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 2~4 mol / L.

4. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step (1), the hydrothermal reaction temperature is 160~220℃; the hydrothermal reaction time is 10~24h; And / or: In step (1), the etching temperature is 30~50℃ and the etching time is 4~10h.

5. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step (2), the metal salt of Y is one or two of nitrate and sulfate; the molar ratio of metal salt of Y to porous Mn3O4 material is (0.05~0.3):(2~4); And / or: Adjust the pH of the reaction solution to 5-9; the precipitation reaction temperature to 20-30℃; the precipitation reaction time to 0.5-5h; and the pressure applied to 0.3-1MPa.

6. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 5, characterized in that, When Y is Al, adjust the pH of the reaction solution to 5-6; when Y is one or both of Co and Fe, adjust the pH of the reaction solution to 7-8.

7. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step (2), the X metal source is one or more of tetrabutyl titanate, bismuth chloride, and antimony chloride; the molar ratio of the X metal source to the porous Mn3O4 material is 1:(20~40); And / or: The hydrolysis reaction time is 8~20h.

8. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step (3), the lithium source is one or more of lithium hydroxide, lithium acetate, and lithium nitrate; the number of moles of Li in the lithium source is the sum of 0.5 to 0.55 times the number of moles of Mn, 0.8 to 1.05 times the number of moles of Y, and 1 to 1.03 times the number of moles of X in the precursor.

9. The method for preparing the composite modified lithium manganese oxide cathode material according to claim 2, characterized in that, In step (3), the lithiation sintering temperature is 880~1000℃ and the lithiation sintering time is 8~16h.

10. A lithium battery, characterized in that: The composite modified lithium manganese oxide cathode material as described in claim 1, or the composite modified lithium manganese oxide cathode material prepared by any of the preparation methods described in claims 2 to 9.

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