A lithium-rich manganese positive electrode material and a surface modification method and use thereof

Abstract

The application discloses a lithium-rich manganese positive electrode material and a surface modification method and application thereof, and belongs to the technical field of battery positive electrode material preparation. The specific process is as follows: (1) nickel salt, cobalt salt and manganese salt are stirred, dispersed and dissolved, then a precipitant and a complexing agent are added to prepare a lithium-rich manganese-based precursor; (2) the lithium-rich manganese-based precursor, a lithium source and fused salt are mixed and calcined to prepare a single-crystal lithium-rich manganese-based oxide material; (3) the single-crystal lithium-rich manganese-based oxide material and a surface modifier are stirred and reacted by a wet chemical method to prepare coated precursor powder; and (4) the coated precursor powder prepared in the step (3) is ground and calcined to prepare the surface-modified lithium-rich manganese positive electrode material. The preparation method provided by the application has low raw material cost, in-situ surface modification is combined with a wet chemical method and heat treatment, the operation is simple, the production environment requirement is low, the first coulomb efficiency and the cycle stability of the lithium-rich manganese-based positive electrode material are effectively improved, and the method is suitable for large-scale batch production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery cathode material preparation, and particularly relates to a lithium-rich manganese cathode material and a surface modification method and application thereof. BACKGROUND

[0002] Lithium-rich manganese-based layered oxide cathode materials have high specific capacity (more than 250 mAh / g) and energy density (more than 1000 Wh / kg), and are environmentally friendly and low-cost, and have been recognized as one of the most promising cathode materials for the next generation of lithium-ion batteries. Single-crystal lithium-rich manganese cathode materials have micron or sub-micron particles, and each particle is composed of only a small number of crystals, rather than many nanocrystals of traditional cathode particles. The single-crystal morphology limits the surface reactivity and particle cracking, and has greater compaction density and better cycle performance.

[0003] Despite these advantages, single-crystal lithium-rich manganese-based cathode materials still have inherent drawbacks, such as low initial coulombic efficiency and continuous capacity and voltage degradation during cycling. Especially during the initial charging process, Li2MnO3 will undergo an irreversible activation reaction, resulting in significant capacity loss. This capacity loss is irreversible and has a great impact on the overall performance of the battery. These weaknesses are mainly due to irreversible oxygen release, TM ion migration and cathode-electrolyte interface side reactions.

[0004] Doping and surface modification are two effective strategies to solve these problems and improve the performance of single-crystal lithium-rich manganese-based cathode materials. Surface modification technology has significant advantages over other modification methods, as it can form a protective layer on the surface of the cathode material, reducing direct contact with the electrolyte, thereby alleviating the generation of side reactions, improving the initial coulombic efficiency, and also effectively enhancing the structural stability of the material, preventing changes during charging and discharging, thereby improving the cycle life and stability of the battery.

[0005] However, most surface modification materials cannot significantly improve the initial coulombic efficiency and cycle life, and have problems such as complex and cumbersome preparation process, low mechanical strength, and uneven surface coating. In addition, there are few reports on in-situ modification by wet chemical method. SUMMARY

[0006] In view of the above deficiencies in the prior art, the present application provides a lithium-rich manganese cathode material and a surface modification method and application thereof, which can effectively improve the initial coulombic efficiency and cycle life of the lithium-rich manganese cathode material.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application to solve its technical problems is:

[0008] The purpose of the present application is to provide a surface modification method for a lithium-rich manganese cathode material, comprising the following steps:

[0009] (1) stirring and dispersing and dissolving nickel salt, cobalt salt and manganese salt in water to obtain a mixed metal salt solution, then adding a precipitant and a complexing agent to prepare a lithium-rich manganese-based precursor by a coprecipitation reaction;

[0010] (2) mixing the lithium-rich manganese-based precursor, a lithium source and a molten salt, calcining at 500-550℃ in an oxygen environment for 5-8h, then increasing the temperature to 900-950℃ and continuing to calcine for 10-15h to prepare a single-crystal lithium-rich manganese-based oxide material;

[0011] (3) stirring and reacting the single-crystal lithium-rich manganese-based oxide material and a surface modifier by a wet chemical method for 2-5h, then heating and stirring until the solvent is completely volatilized to prepare a coated precursor powder;

[0012] (4) grinding the coated precursor powder prepared in step (3) and calcining at 400-600℃ for 2-6h to complete the surface modification to prepare a surface-modified lithium-rich manganese positive electrode material.

[0013] Further, the mass ratio of manganese element contained in the lithium-rich manganese-based precursor is 50%-60%, the mass ratio of nickel element and cobalt element is 5%-15%, and the particle size is 4-8μm.

[0014] Further, the molar ratio of nickel salt, cobalt salt and manganese salt is 0.1-0.3:0.1-3:0.3-0.8.

[0015] Further, the molar ratio of nickel salt, cobalt salt and manganese salt is 0.25:0.15:0.6.

[0016] Further, the nickel salt is one or more of nickel sulfate, nickel nitrate, nickel acetate and nickel chloride;

[0017] the cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt acetate and cobalt chloride;

[0018] the manganese salt is one or more of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride.

[0019] Further, the precipitant is sodium carbonate or sodium bicarbonate; the complexing agent is ammonia water, ammonium carbonate or ammonium bicarbonate.

[0020] Further, the mass ratio of lithium-rich manganese-based precursor, lithium source and molten salt is 1.5-2:0.5-1:3-4.

[0021] Further, the mass ratio of lithium-rich manganese-based precursor, lithium source and molten salt is 2:0.5:4.

[0022] Further, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium nitride, lithium hydride, lithium oxide, lithium amide, methyl lithium and hexyl lithium;

[0023] The molten salt is one or more of potassium chloride, sodium chloride, lithium sulfate and lithium chloride.

[0024] Further, in step (2), first calcination is carried out at 500 DEG C for 5h, and then the temperature is raised to 900 DEG C, and the calcination is continued for 12h.

[0025] Further, the mass ratio of the single-crystal lithium-rich manganese-based oxide material and the surface modifier is 1:0.01-0.1.

[0026] Further, the surface modifier is ammonium dihydrogen phosphate, and the concentration after dissolution is 0.1-1mol / L.

[0027] Further, in step (3), when the wet chemical reaction is carried out, the rotating speed of mechanical stirring is 500-800rpm, and the mechanical stirring time is 2-5h.

[0028] Further, in step (3), the temperature of heating and stirring is 40 DEG C-80 DEG C, the rotating speed of mechanical stirring is 700-1000rpm, and the temperature for drying after the solvent is completely volatilized is 70 DEG C-80 DEG C.

[0029] Further, in step (3), the thickness of the coating layer formed by the surface modifier on the surface of the single-crystal lithium-rich manganese-based oxide material is 5-15nm, and the thickness of the coating layer after sintering in step (4) is 5-20nm.

[0030] Another object of the present application is to provide a lithium-rich manganese positive electrode material after surface modification, which is prepared by the above modification method.

[0031] Another object of the present application is to provide the use of the above lithium-rich manganese positive electrode material in preparing electrode material or lithium ion battery.

[0032] The present application has the following beneficial effects:

[0033] The present application provides a surface-modified single-crystal lithium-rich manganese positive electrode material and a preparation method thereof, in which a lithium-rich manganese-based precursor is prepared by co-precipitation reaction of metal salt solution in which nickel source, cobalt source and manganese source are dissolved in deionized water, and then the single-crystal lithium-rich manganese-based positive electrode material is obtained after sintering with lithium source and molten salt; the surface modification of the positive electrode material is carried out by wet chemical reaction of the positive electrode material and surface modifier using diammonium hydrogen phosphate solution as the surface modifier, and then drying and sintering, so that the surface-modified single-crystal lithium-rich manganese positive electrode material is successfully prepared, and the first coulomb efficiency and cycle stability of the lithium-rich manganese-based positive electrode material are effectively improved.

[0034] The preparation method has low raw material cost, in-situ surface modification is combined with wet chemical method and heat treatment, operation is simple, production environment requirement is low, and the first coulomb efficiency and cycle stability of the lithium-rich manganese-based positive electrode material are effectively improved, and the method is suitable for large-scale batch production. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 SEM image of the surface-modified single-crystal lithium-rich manganese-based oxide material prepared in Example 1;

[0036] Figure 2 SEM image of the unmodified lithium-rich positive electrode material prepared in Comparative Example 1;

[0037] Figure 3 Comparison diagram of the first charge-discharge curves of Example 1 and Comparative Example 1;

[0038] Figure 4 Comparison diagram of the cycle performance of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0039] The specific embodiments of the present application are described below to facilitate the understanding of the present application for those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

[0040] Example 1

[0041] A surface-modified lithium-rich manganese positive electrode material is prepared by the following method:

[0042] (1) A mixed salt solution (the molar ratio of Ni ions, Co ions and Mn ions is 0.25:0.15:0.60) with a total mass concentration of metal ions of 100 g / L, a 2 mol / L sodium carbonate solution and an ammonia water with a concentration of 0.5 mol / L are introduced into the reaction bottom liquid in parallel, and stirring is performed during the introduction, the temperature is controlled at 55°C, the pH is controlled between 7.5-8.5, and the stirring speed is 600 rpm, a co-precipitation reaction is performed, and the precipitate is a lithium-rich manganese-based precursor material;

[0043] (2) 10 g of the above lithium-rich manganese-based precursor, 5 g of lithium hydroxide and 20 g of potassium chloride are weighed and uniformly mixed by grinding, and then heated at 500°C for 5 h and at 900°C for 12 h in an oxygen atmosphere, and then naturally cooled, ground and dried to obtain a single-crystal lithium-rich manganese-based oxide material.

[0044] (3) 0.03 g of ammonium dihydrogen phosphate is dissolved in 30 mL of alcohol and stirred for 1 h at a stirring speed of 800 rpm to obtain a surface coating modifier; 1 g of the single-crystal lithium-rich manganese-based oxide is added, heated and stirred until the solvent is completely volatilized, a heating temperature is 60°C, and a stirring speed is 1000 rpm to obtain a coated precursor.

[0045] (4) The precursor powder is ground and sintered at a sintering temperature of 500°C for 5 h to finally obtain a surface-modified single-crystal lithium-rich positive electrode material.

[0046] Example 2

[0047] A lithium-rich manganese positive electrode material treated by surface modification, and a preparation method thereof is as follows:

[0048] (1) A mixed salt solution (a molar ratio of Ni ions, Co ions and Mn ions is 0.25:0.25:0.50) with a total mass concentration of metal ions of 100 g / L, a 2 mol / L sodium carbonate solution and ammonia water with a concentration of 0.5 mol / L are simultaneously introduced into a reaction bottom solution, a co-precipitation reaction is carried out in a process accompanied by stirring, a temperature is controlled to be 55°C, a pH is controlled to be between 7.5-8.5, and a stirring speed is 600 rpm to obtain a precipitate as a lithium-rich manganese-based precursor material;

[0049] (2) 16 g of the lithium-rich manganese-based precursor, 7 g of lithium hydroxide and 35 g of potassium chloride are weighed and uniformly ground and mixed, and are naturally cooled after being kept at 550°C for 56 h and kept at 950°C for 10 h in an oxygen atmosphere, and are ground and dried to obtain a single-crystal lithium-rich manganese-based oxide material.

[0050] (3) 0.03 g of ammonium dihydrogen phosphate is dissolved in 30 mL of alcohol and stirred for 1 h at a stirring speed of 800 rpm to obtain a surface coating modifier; 1 g of the single-crystal lithium-rich manganese-based oxide is added, heated and stirred until the solvent is completely volatilized, a heating temperature is 60°C, and a stirring speed is 1000 rpm to obtain a coated precursor.

[0051] (4) The precursor powder is ground and sintered at a sintering temperature of 400°C for 6 h to finally obtain a surface-modified single-crystal lithium-rich positive electrode material.

[0052] Example 3

[0053] A lithium-rich manganese positive electrode material treated by surface modification, and a preparation method thereof is as follows:

[0054] (1) The mixed salt solution (molar ratio of Ni ion, Co ion and Mn ion is 0.25:0.15:0.60) with total mass concentration of metal ions of 100 g / L, 2 mol / L sodium carbonate solution and 0.5 mol / L ammonia water are introduced into the reaction solution in parallel, accompanied by stirring during the process, the temperature is controlled at 55°C, the pH is between 7.5-8.5, the stirring speed is 600 rpm, and the coprecipitation reaction is carried out to obtain the precipitate as a lithium-rich manganese-based precursor material;

[0055] (2) 15 g of the above lithium-rich manganese-based precursor, 5 g of lithium hydroxide and 30 g of potassium chloride are weighed, mixed and ground uniformly, heated at 520°C for 8 h in an oxygen atmosphere, heated at 920°C for 15 h to natural cooling, ground and dried to obtain a single-crystal lithium-rich manganese-based oxide material.

[0056] (3) 0.03 g of ammonium dihydrogen phosphate is dissolved in 30 mL of alcohol, mixed and stirred for 1 h at a stirring speed of 800 rpm to obtain a surface coating modifier; then 1 g of the above single-crystal lithium-rich manganese-based oxide is added, heated and stirred until the solvent is completely volatilized, the heating temperature is 60°C, and the stirring speed is 1000 rpm to obtain a coated precursor.

[0057] (4) The above precursor powder is ground and sintered, the sintering temperature is 600°C, and the time is 5 h to finally obtain a surface-modified single-crystal lithium-rich positive electrode material.

[0058] Comparative Example 1

[0059] A lithium-rich manganese positive electrode material without surface modification treatment, according to the method of Example 1, the difference is that steps (3) and (4) are not surface modified, and the other steps are the same as Example 1.

[0060] Comparative Example 2

[0061] According to the method of Example 1, the difference is that in step (3), 10 g of lithium-rich manganese-based precursor, 2.5 g of lithium hydroxide and 20 g of potassium chloride are weighed, mixed and ground uniformly, heated at 500°C for 5 h in an oxygen atmosphere, heated at 900°C for 12 h to natural cooling, and ground and dried. The other steps are the same as Example 1.

[0062] Comparative Example 3

[0063] According to the method of Example 1, the difference is that in step (3), 10 g of lithium-rich manganese-based precursor, 7.5 g of lithium hydroxide and 20 g of potassium chloride are weighed, mixed and ground uniformly, heated at 500°C for 5 h in an oxygen atmosphere, heated at 900°C for 12 h to natural cooling, and ground and dried. The other steps are the same as Example 1.

[0064] Comparative Example 4

[0065] The method of example 1 is adopted, except that in step (2), the precursor 10 g, 5 g of lithium hydroxide and 10 g of potassium chloride are mixed uniformly by grinding, and after heating reaction, it is naturally cooled to room temperature, ground and dried, and the single crystal lithium-rich manganese-based material is collected. Other steps are the same as example 1.

[0066] Comparative example 5

[0067] The method of example 1 is adopted, except that in step (2), the precursor 10 g, 5 g of lithium hydroxide and 30 g of potassium chloride are mixed uniformly by grinding, and after heating reaction, it is naturally cooled to room temperature, ground and dried, and the single crystal lithium-rich manganese-based material is collected. Other steps are the same as example 1.

[0068] Comparative example 6

[0069] The method of example 1 is adopted, except that in step (2), the precursor 10 g, 5 g of lithium hydroxide and 30 g of potassium chloride are mixed uniformly by grinding, and after heating reaction, it is naturally cooled to room temperature, ground and dried, and the single crystal lithium-rich manganese-based material is collected. Other steps are the same as example 1.

[0070] Comparative example 7

[0071] The method of example 1 is adopted, except that in step (2), the precursor 10 g, 5 g of lithium hydroxide and 30 g of potassium chloride are mixed uniformly by grinding, and after heating reaction, it is naturally cooled to room temperature, ground and dried, and the single crystal lithium-rich manganese-based material is collected. Other steps are the same as example 1.

[0072] Comparative example 8

[0073] The method of example 1 is adopted, except that in step (3), 0.01 g of ammonium dihydrogen phosphate is dissolved in 30 mL of alcohol and stirred for 1 h at a stirring speed of 800 rpm to obtain a surface coating modifier; other steps are the same as example 1.

[0074] Comparative example 9

[0075] The method of example 1 is adopted, except that in step (4), the sintering temperature is 300 ℃, and the holding time is 5 h, and finally the surface modified single crystal lithium-rich positive electrode material is obtained; other steps are the same as example 1.

[0076] Comparative example 10

[0077] The method of example 1 is adopted, except that in step (4), the sintering temperature is 700 ℃, and the holding time is 5 h, and finally the surface modified single crystal lithium-rich positive electrode material is obtained; other steps are the same as example 1.

[0078] The scanning electron microscope is used to observe the surface modified single crystal lithium-rich manganese-based oxide material of example 1 and the surface unmodified single crystal lithium-rich positive electrode material of comparative example 1, respectively, as shown in Figure 1 andFigure 2

[0079] The positive electrode material prepared in Example 1 was mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 8:1:1, N-methylpyrrolidone was added as a dispersant, and the mixture was ground into a slurry; then the slurry was uniformly coated on one side of an aluminum foil, vacuum dried at 120°C for 10h, the dried electrode sheet was rolled using a roll machine, and the aluminum foil was cut into a circular electrode sheet with a diameter of 1.2cm using a slicing machine, and the loading of the active material was controlled at 5mg / cm 2 A liquid battery was assembled in an argon atmosphere glove box, in which a lithium sheet with a diameter of 1.6cm was used as the negative electrode, a 12μm PP / PE film was used as the separator, and 10μL of 1mol / L LiPF6 electrolyte was added at the interface between the positive electrode sheet, the lithium negative electrode and the electrolyte, and a CR2032 type button cell was assembled in an environment with a water partial pressure ≤0.1ppm and an oxygen partial pressure ≤0.1ppm. The button cells in Examples 2-3 and Comparative Examples 1-10 were prepared in the same way as in Example 1.

[0080] The button cells prepared in Example 1 and Comparative Example 1 were subjected to first charge-discharge efficiency test, first discharge capacity test and cycle performance test, respectively, and the test results are shown in Figure 3 and Figure 4 , and the specific process is as follows:

[0081] The cycle performance test method is as follows: under the condition of 25°C, the button cell is cycled at 1C charge and 1C discharge for 100 times, and the voltage range is 2.0V-4.8V.

[0082] The first charge-discharge efficiency test and the first discharge capacity test method are as follows: under the condition of 25°C, the button cell is cycled at 0.1C charge and 0.1C discharge for 1 week, and the voltage range is 2.0V-4.8V.

[0083] As shown in the test results of Figure 3 and Figure 4 , the first discharge, first efficiency and cycle performance of the lithium-rich positive electrode material prepared in Example 1 are significantly better than those of Comparative Example 1. Compared with Comparative Example 1, the first coulombic efficiency of Example 1 is increased from 69.5% to 78.7%, the first discharge specific capacity is increased from 251mAh / g to 263mAh / g, and the capacity retention rate after 100 cycles of charge and discharge is increased from 85.4% to 94.1%, which indicates that the surface coating modification has a good effect of improving capacity and inhibiting cycle decay.

[0084] The lithium-rich manganese-based positive electrode materials in Examples 1-3 and Comparative Examples 1-10 above were tested under the condition of 25°C, and the test results are shown in Table 1.

[0085] ​Table 1 Electrochemical performance of lithium-rich manganese-based lithium battery cathode materials synthesized by unmodified and different modification methods

[0086]

[0087] As can be seen from Table 1, the modification method provided by the present application effectively improves the first coulombic efficiency and high-voltage cycle performance of the lithium battery cathode material at room temperature, indicating that the modification method can effectively improve the interface stability of the battery.

[0088] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for surface modification of a lithium-rich manganese cathode material, characterized in that, It comprises the following steps: (1) stirring and dispersing and dissolving nickel salt, cobalt salt and manganese salt in water to obtain a mixed metal salt solution, then adding a precipitant and a complexing agent to prepare a lithium-rich manganese-based precursor by a co-precipitation reaction; (2) mixing the lithium-rich manganese-based precursor, a lithium source and a molten salt, calcining at 500-550℃ in an oxygen environment for 5-8h, then heating to 900-950℃ and continuing to calcine for 10-15h to prepare a single-crystal lithium-rich manganese-based oxide material; the mass ratio of the lithium-rich manganese-based precursor, the lithium source and the molten salt is 1.5-2:0.5-1:3-4; (3) stirring and reacting the single-crystal lithium-rich manganese-based oxide material and a surface modifier by a wet chemical method for 2-5h, then heating and stirring until the solvent is completely volatilized to prepare a coated precursor powder, wherein the thickness of the coating layer is 5-15nm; the mass ratio of the single-crystal lithium-rich manganese-based oxide material and the surface modifier is 1:0.01-0.1; the surface modifier is ammonium dihydrogen phosphate, and the concentration after dissolution is 0.1-1mol / L; (4) grinding the coated precursor powder prepared in step (3) and calcining at 400-600℃ for 2-6h to complete the surface modification to prepare a lithium-rich manganese positive electrode material with a coating layer thickness of 5-20nm and surface modification.

2. The surface modification method according to claim 1, wherein, The molar ratio of the nickel salt, the cobalt salt and the manganese salt is 0.1-0.3:0.1-3:0.3-0.

8.

3. The surface modification method according to claim 1 or 2, characterized in that, The nickel salt is one or more of nickel sulfate, nickel nitrate, nickel acetate and nickel chloride; The cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt acetate and cobalt chloride; The manganese salt is one or more of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride.

4. The surface modification method of claim 1, wherein The lithium source is one or more of lithium carbonate, lithium hydroxide, lithium nitride, lithium hydride, lithium oxide, lithium amide and methyl lithium; The molten salt is one or more of potassium chloride, sodium chloride, lithium sulfate and lithium chloride.

5. A surface-modification-treated lithium-rich manganese cathode material, characterized by, Prepared by the modification method of any one of claims 1-4.

6. Use of the lithium-rich manganese positive electrode material of claim 5 in the preparation of an electrode material or a lithium ion battery.

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