Preparation method and application of magnesium aluminate-coated lithium-rich manganese-based positive electrode material

Abstract

The present invention provides a lithium-rich manganese-based positive electrode material coated with magnesium aluminate, and its preparation method and application, characterized in that the interior of the material is a lithium-rich manganese-based positive electrode, and the outer coating layer is magnesium aluminate. The chemical formula of the lithium-rich manganese-based layered positive electrode material is x Li2MnO3·(1‑x)LiMO2, wherein 0<x<1, and M is at least one of Mn, Co, and Ni. The molar fraction of MgAl2O4 is 0.5% to 2% of the lithium-rich manganese-based positive electrode. Compared with the existing technology, the present invention can effectively inhibit the side reaction between the lithium-rich manganese-based positive electrode and the electrolyte, inhibit the precipitation of oxygen and the transformation of the crystal structure, and alleviate the problem of capacity and voltage attenuation during the cycle. The preparation process of the present invention is simple and easy to promote.

Description

Technical Field

[0001] The present invention belongs to the field of high energy density lithium ion battery positive electrode materials, and specifically relates to a preparation method and application of a magnesium aluminate-coated lithium-rich manganese-based positive electrode material. Background Art

[0002] Given the increasing global depletion of fossil fuels and the environmental problems caused by their combustion, the development of new green energy sources has become a global focus. Compared to other secondary batteries, lithium-ion batteries offer advantages such as high energy density, excellent cycle performance, high operating voltage, and low self-discharge, earning them the nickname "green power." They are now widely used in a variety of fields, including portable electronic tools, transportation, aerospace, and defense. Since 2015, the global lithium-ion battery industry has rapidly expanded, with electric vehicle power batteries accounting for nearly 50% of the total. Global electric vehicle sales forecasts predict that electric vehicle market share will reach approximately 85% by 2060. Given that China is a major electric vehicle sales country, the development of high-performance lithium-ion batteries is crucial. High-energy-density cathodes, as key components of lithium-ion batteries, have garnered significant attention from researchers.

[0003] Lithium-rich manganese-based cathode materials have a high theoretical specific capacity (~250 mAh g) due to the simultaneous redox reaction of transition metal cations and oxygen anions during the charge and discharge process. -1 ), and because it reduces the amount of cobalt and nickel, its cost is relatively low and more environmentally friendly, making it one of the most promising high-energy-density cathodes for the next generation of lithium-ion batteries. However, there is an irreversible oxygen evolution reaction (O 2- →O2), resulting in a low initial Coulombic efficiency and can cause irreversible transformation from layered phase to spinel phase, resulting in voltage and capacity decay. In addition, due to Ni 4+ It has high activity at high voltage, which will cause side reactions at the interface between the electrode and the electrolyte, generating inert substances, thereby affecting the electron ion migration of the lithium-rich manganese-based positive electrode, resulting in poor rate performance.

[0004] In order to solve the above problems, scientific researchers have conducted a large number of modification studies. Common modification methods include surface coating, bulk doping, morphology control, surface pretreatment, etc. Surface coating is an effective modification strategy that can avoid direct contact between the positive electrode material and the electrolyte, thereby reducing side reactions. On the other hand, some special coating layers can inhibit oxygen precipitation on the positive electrode surface, thereby inhibiting its voltage and capacity attenuation. Li Hua et al. used a double-layer coating method with an inner coating layer of Li3PO4 and an outer coating layer of PEDOT:PSS [Li Hua, A double-coated lithium-rich manganese-based material and its preparation, modification method and application, patent application number: CN202011209551.0] to modify the lithium-rich manganese-based positive electrode material. This method improved the material's cycle stability at 0.1C and improved its rate performance, but its modification method has many steps, which is not conducive to large-scale preparation. Hu Yanjie et al. [Hu Yanjie, A lithium-rich manganese-based / graphene composite positive electrode material, preparation method and application thereof, patent application number: CN201910454623.9] used graphene as a conductive coating layer to prepare a lithium-rich manganese-based / graphene composite material, which has improved capacity retention and rate performance, but the high cost of graphene is not conducive to large-scale commercialization. Summary of the Invention

[0005] In response to the above-mentioned problems existing in the lithium-rich manganese-based positive electrode, one of the objectives of the present invention is to provide a positive electrode material of a lithium-rich manganese-based material coated with magnesium aluminate, which utilizes the higher bonding strength between aluminum and magnesium elements and oxygen to stabilize the stability of the surface oxygen of the lithium-rich manganese-based material, and at the same time can inhibit the side reaction between the electrolyte and the lithium-rich manganese-based positive electrode, thereby improving the serious attenuation problem of capacity and voltage of the existing lithium-rich manganese-based positive electrode during the cycle process.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A magnesium aluminate-coated lithium-rich manganese-based positive electrode material, characterized by an interior portion of the material comprising a lithium-rich manganese-based positive electrode material and an exterior portion of a magnesium aluminate coating (MgAl2O4). The chemical formula of the lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiMO2, where 0<x<1, and M is at least one of Mn, Co, and Ni. The mole fraction of MgAl2O4 is 0.5% to 2% of the lithium-rich manganese-based positive electrode.

[0008] A second object of the present invention is to provide a method for preparing a magnesium aluminate-coated lithium-rich manganese-based material, which has low raw material costs, simple operating steps, and is easy to prepare on a large scale. The specific steps are as follows:

[0009] (1) Using a magnetic stirrer, the lithium-rich manganese-based cathode material is dispersed in ultrapure water and stirred for 0.5 h to form a uniform suspension A;

[0010] (2) dissolving magnesium salt and aluminum salt in ultrapure water at a molar ratio of 1:2 and stirring for 0.5 h to obtain a transparent solution B;

[0011] (3) Add solution B to suspension A under stirring at room temperature and stir until the mixture is uniform to obtain suspension C;

[0012] (4) Under stirring, add a certain concentration of ammonia water dropwise to the C suspension to adjust to a specific pH. 2+ 、Al 3+ It precipitates on the surface of the lithium-rich manganese-based positive electrode and then continues to stir until it reacts completely;

[0013] (5) The completely reacted suspension was centrifuged and washed several times, and then placed in a drying oven to dry;

[0014] (6) The dried and collected powder is calcined at high temperature in air to obtain a magnesium aluminate-coated lithium-rich manganese-based positive electrode material.

[0015] As a preferred solution, the aluminum salt in step (2) includes but is not limited to aluminum nitrate and aluminum acetate, the magnesium salt includes but is not limited to magnesium chloride, magnesium nitrate, and magnesium acetate, and the concentration of solution B is 0.01 to 0.05 mol / L.

[0016] As a preferred solution, the concentration of ammonia water in step (4) is 0.15-0.60 mol / L, and the pH of the solution is adjusted to 7.5-9.

[0017] As a preferred solution, the drying temperature in step (5) is 50-100° C. and the drying time is 12-24 hours.

[0018] As a preferred solution, the sintering temperature in step (6) is 600-800° C. and the sintering time is 1-5 hours.

[0019] The third object of the present invention is to provide an application of a magnesium aluminate-coated lithium-rich manganese positive electrode material, and to use the coated material as a battery positive electrode material in a lithium-ion battery.

[0020] Compared with the existing technology, the advantages of the present invention are as follows:

[0021] (1) The magnesium aluminate surface coating modified lithium-rich manganese positive electrode technology provided by the present invention, magnesium aluminate is coated on the surface of the lithium-rich manganese-based positive electrode. On the one hand, the coating layer can play a physical shielding role to hinder the direct interaction between the internal lithium-rich manganese-based material and the electrolyte, thereby suppressing the side reactions at the electrode / electrolyte interface. On the other hand, compared with the bonding ability of Ni / Co / Mn and O, the bond energy of the Al-O bond is greater, and Mg-O also has a higher bond energy than Li-O. Therefore, after magnesium aluminate coating, the oxygen anions on the surface of the lithium-rich manganese positive electrode are more stable, thereby suppressing the irreversible precipitation of oxygen and the transformation of the layered phase to the spinel phase during the cycle, thereby achieving the purpose of suppressing the capacity attenuation and voltage drop during the cycle of the lithium-rich manganese positive electrode.

[0022] (2) The magnesium aluminate-coated lithium-rich manganese-based positive electrode provided by the present invention has a dual modification advantage. The magnesium aluminate-coated lithium-rich manganese-based positive electrode was subjected to a lithium-ion battery electrochemical test. The results showed that at a current density of 2 to 4.8 V and 1C (1C = 250 mA g -1 ) After 200 cycles, its discharge capacity is 129.6 mAh g -1 , while the uncoated lithium-rich manganese-based cathode has only 106.9 mAh g -1 , the capacity retention rate increased by 13.9%. Correspondingly, after 200 cycles at a current density of 1C, the voltage of the magnesium aluminate-coated sample dropped by 0.51V, while the voltage of the unmodified sample dropped by 0.66V. This shows that the present invention can improve the capacity decay and voltage decay of lithium-rich manganese-based positive electrodes during cycling.

[0023] (3) The magnesium aluminate-coated lithium-rich manganese positive electrode material provided by the present invention has a simple preparation process and is easy to promote. It is a method that can effectively improve the capacity decay and voltage decay during the cycle of the lithium-rich manganese-based positive electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a transmission electron microscope image of the sample synthesized in Example 1.

[0025] Figure 2 The X-ray diffraction patterns of the synthesized sample and the unmodified sample in Example 2 are shown.

[0026] Figure 3 The mass specific capacity curves of the synthesized sample in Example 3 and the unmodified sample after 200 cycles at a current density of 1C.

[0027] Figure 4 The average discharge voltage curves of the synthesized sample and the unmodified sample in Example 3 after 200 cycles at a current density of 1C. DETAILED DESCRIPTION

[0028] The present invention is further described below with reference to examples, but the embodiments of the present invention are not limited thereto. Other examples obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0029] Unless otherwise specified, the reagents, raw materials, instruments and equipment used in this experiment can be purchased on the market.

[0030] Example 1:

[0031] The lithium-rich manganese-based positive electrode used in this example has the chemical formula Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The preparation steps of the lithium-rich manganese-based positive electrode coated with magnesium aluminate are as follows:

[0032] (1) Disperse 1 g of lithium-rich manganese-based cathode powder in 15 mL of ultrapure water under the action of a magnetic stirrer and stir for 0.5 h to form a uniform suspension A;

[0033] (2) Dissolve 0.0126 g of magnesium acetate and 0.0239 g of aluminum acetate in 15 mL of ultrapure water and stir for 0.5 h to obtain a clear solution B;

[0034] (3) Slowly pour solution B into suspension A while stirring at room temperature and stirring for 0.5 h until the mixture is uniform to obtain suspension C;

[0035] (4) While stirring, add 0.60 mol / L ammonia water dropwise to suspension C, adjust the pH to 8, and then stir for 1 h to allow the reaction to complete.

[0036] (5) The reaction-completed suspension was washed three times with ultrapure water by centrifugation and then dried at 60°C for 12 h;

[0037] (6) The dried and collected powder was sintered at 800 °C for 3 h in an air atmosphere with a heating rate of 3 °C / min. After natural cooling, a 0.5% magnesium aluminate-coated lithium-rich manganese-based positive electrode material was obtained, which was recorded as LR@0.5%MAO-800.

[0038] Example 2:

[0039] The lithium-rich manganese-based positive electrode used in this example has the chemical formula Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The preparation steps of the lithium-rich manganese-based positive electrode coated with magnesium aluminate are as follows:

[0040] (1) Disperse 1 g of lithium-rich manganese-based cathode powder in 15 mL of ultrapure water under the action of a magnetic stirrer and stir for 0.5 h to form a uniform suspension A;

[0041] (2) Dissolve 0.0251 g of magnesium acetate and 0.0479 g of aluminum acetate in 15 mL of ultrapure water and stir for 0.5 h to obtain a clear solution B;

[0042] (3) Slowly pour solution B into suspension A while stirring at room temperature and stirring for 0.5 h until the mixture is uniform to obtain suspension C;

[0043] (4) While stirring, add 0.60 mol / L ammonia water dropwise to suspension C, adjust the pH to 8, and then stir for 1 h to allow the reaction to complete.

[0044] (5) The reaction-completed suspension was washed three times with ultrapure water by centrifugation and then dried at 60°C for 12 h;

[0045] (6) The dried and collected powder was sintered at 800 °C for 3 h in an air atmosphere with a heating rate of 3 °C / min. After natural cooling, a 1% magnesium aluminate-coated lithium-rich manganese-based positive electrode material was obtained, which was recorded as LR@1%MAO-800.

[0046] Example 3:

[0047] The lithium-rich manganese-based positive electrode used in this example has the chemical formula Li 1.2 Mn 0.5 4Co 0.13 Ni 0.13 The preparation steps of the lithium-rich manganese-based positive electrode coated with magnesium aluminate are as follows:

[0048] (1) Disperse 1 g of lithium-rich manganese-based cathode powder in 15 mL of ultrapure water under the action of a magnetic stirrer and stir for 0.5 h to form a uniform suspension A;

[0049] (2) Dissolve 0.0377 g of magnesium acetate and 0.0719 g of aluminum acetate in 15 mL of ultrapure water and stir for 0.5 h to obtain a clear solution B;

[0050] (3) Slowly pour solution B into suspension A while stirring at room temperature and stirring for 0.5 h until the mixture is uniform to obtain suspension C;

[0051] (4) While stirring, add 0.60 mol / L ammonia water dropwise to suspension C, adjust the pH to 8, and then stir for 1 h to allow the reaction to complete.

[0052] (5) The reaction-completed suspension was washed three times with ultrapure water by centrifugation and then dried at 60°C for 12 h;

[0053] (6) The dried and collected powder was sintered at 800 °C for 3 h in an air atmosphere with a heating rate of 3 °C / min. After natural cooling, a 1.5% magnesium aluminate-coated lithium-rich manganese-based positive electrode material was obtained, which was recorded as LR@1.5%MAO-800.

[0054] Example 4:

[0055] The lithium-rich manganese-based positive electrode used in this example has the chemical formula Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The preparation steps of the lithium-rich manganese-based positive electrode coated with magnesium aluminate are as follows:

[0056] (1) Disperse 1 g of lithium-rich manganese-based cathode powder in 15 mL of ultrapure water under the action of a magnetic stirrer and stir for 0.5 h to form a uniform suspension A;

[0057] (2) Dissolve 0.0503 g of magnesium acetate and 0.0957 g of aluminum acetate in 15 mL of ultrapure water and stir for 0.5 h to obtain a clear solution B;

[0058] (3) Slowly pour solution B into suspension A while stirring at room temperature and stirring for 0.5 h until the mixture is uniform to obtain suspension C;

[0059] (4) While stirring, add 0.60 mol / L ammonia water dropwise to suspension C, adjust the pH to 8, and then stir for 1 h to allow the reaction to complete.

[0060] (5) The reaction-completed suspension was washed three times with ultrapure water by centrifugation and then dried at 60°C for 12 h;

[0061] (6) The dried and collected powder was sintered at 800 °C for 3 h in an air atmosphere with a heating rate of 3 °C / min. After natural cooling, a 2% magnesium aluminate-coated lithium-rich manganese-based positive electrode material was obtained, which was recorded as LR@2%MAO-800.

[0062] Example 5:

[0063] The lithium-rich manganese-based positive electrode used in this example has the chemical formula Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The preparation steps of the lithium-rich manganese-based positive electrode coated with magnesium aluminate are as follows:

[0064] (1) Disperse 1 g of lithium-rich manganese-based cathode powder in 15 mL of ultrapure water under the action of a magnetic stirrer and stir for 0.5 h to form a uniform suspension A;

[0065] (2) Dissolve 0.0377 g of magnesium acetate and 0.0719 g of aluminum acetate in 15 mL of ultrapure water and stir for 0.5 h to obtain a clear solution B;

[0066] (3) Slowly pour solution B into suspension A while stirring at room temperature and stirring for 0.5 h until the mixture is uniform to obtain suspension C;

[0067] (4) While stirring, add 0.60 mol / L ammonia water dropwise to suspension C, adjust the pH to 8, and then stir for 1 h to allow the reaction to complete.

[0068] (5) The reaction-completed suspension was washed three times with ultrapure water by centrifugation and then dried at 60°C for 12 h;

[0069] (6) The dried and collected powder was sintered at 700 °C for 3 h in an air atmosphere with a heating rate of 3 °C / min. After natural cooling, a 1% magnesium aluminate-coated lithium-rich manganese-based positive electrode material was obtained, which was recorded as LR@1.5%MAO-700.

[0070] Example 6:

[0071] The lithium-rich manganese-based positive electrode used in this example has the chemical formula Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The preparation steps of the lithium-rich manganese-based positive electrode coated with magnesium aluminate are as follows:

[0072] (1) Disperse 1 g of lithium-rich manganese-based cathode powder in 15 mL of ultrapure water under the action of a magnetic stirrer and stir for 0.5 h to form a uniform suspension A;

[0073] (2) Dissolve 0.0377 g of magnesium acetate and 0.0719 g of aluminum acetate in 15 mL of ultrapure water and stir for 0.5 h to obtain a clear solution B;

[0074] (3) Slowly pour solution B into suspension A while stirring at room temperature and stirring for 0.5 h until the mixture is uniform to obtain suspension C;

[0075] (4) While stirring, add 0.60 mol / L ammonia water dropwise to suspension C, adjust the pH to 8, and then stir for 1 h to allow the reaction to complete.

[0076] (5) The reaction-completed suspension was washed three times with ultrapure water by centrifugation and then dried at 60°C for 12 h;

[0077] (6) The dried and collected powder was sintered at 600 °C for 3 h in an air atmosphere with a heating rate of 3 °C / min. After natural cooling, a 1% magnesium aluminate-coated lithium-rich manganese-based positive electrode material was obtained, which was recorded as LR@1.5%MAO-600.

[0078] The material obtained in the above example is used as the positive electrode of lithium-ion battery. The specific method is as follows: take the active material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, use N-methylpyrrolidone (NMP) as a solvent, stir for 4 hours to form a slurry, then evenly coat the slurry on aluminum foil, vacuum dry at 110℃ for 12 hours and slice it, use lithium sheet as the counter electrode, 1.0M LiPF6 / EC:DMC:DEC=1:1:1 as the electrolyte, assemble it into a CR2032 button battery in an argon-filled glove box, and use the LAND test system for charge and discharge tests. All test voltages range from 2 to 4.8V, and the cycle performance adopts a current density of 1C for 200 charge and discharge cycles, where 1C = 250mAh g -1 .

[0079] Figure 1 This is a transmission electron microscope image of the sample synthesized in Example 1. It can be observed that MgAl2O4 is successfully coated on the surface of the lithium-rich manganese-based positive electrode.

[0080] Figure 2 This is the X-ray diffraction pattern of the sample synthesized in Example 2. By comparing the magnesium aluminate-coated lithium-rich manganese positive electrode and the uncoated lithium-rich manganese positive electrode, it can be found that after high-temperature sintering, the magnesium aluminate-coated lithium-rich manganese positive electrode shows an obvious characteristic peak of MgAl2O4, which indicates that magnesium aluminate has been coated on the surface of the lithium-rich manganese-based positive electrode.

[0081] Figure 3 The mass specific capacity curve of the synthesized sample and the unmodified sample in Example 3 was cycled 200 times at a current density of 1C. After testing at a current density of 2-4.8V and 1C (1C = 250mAh g -1 After 200 cycles, the discharge capacity of the magnesium aluminate-coated modified lithium-rich manganese-based cathode was 129.6 mAh g -1 , while the uncoated lithium-rich manganese-based cathode has only 106.9 mAh g -1 , after magnesium aluminate modification, its capacity retention rate increased by 13.9%. Figure 4The average discharge voltage curves of the synthesized sample and the unmodified sample in Example 3 after 200 cycles at a current density of 1C are shown. After 200 cycles at a current density of 1C, the average discharge voltage of the magnesium aluminate-coated sample decreased by 0.51V, while the voltage of the unmodified sample decreased by 0.66V. This shows that the magnesium aluminate coating strategy can significantly suppress the capacity and voltage decay problems of the lithium-rich manganese cathode during cycling, effectively improving the cycling performance of the material.

[0082] The examples described above are merely a few specific embodiments of the present invention and are not intended to be limiting. It should be noted that those skilled in the art may make various improvements and modifications to the present invention without departing from the technical principles and concepts of the present invention, and such modifications and variations fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A magnesium aluminate-coated lithium-rich manganese-based positive electrode material, characterized in that The internal material is a lithium-rich manganese-based cathode, and the outer coating layer is magnesium aluminate. The chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where 0 < x < 1, and M is at least one of Mn, Co, and Ni. The molar fraction of MgAl2O4 is 0.5% - 2% of the lithium-rich manganese-based cathode material.

2. The method for preparing a lithium-rich manganese-based positive electrode material coated with magnesium aluminate according to claim 1, characterized in that: It includes the following steps: (1) Use a magnetic stirrer to disperse the lithium-rich manganese-based cathode material in ultrapure water to form a uniform suspension A; (2) Dissolve magnesium salt and aluminum salt in ultrapure water according to a molar ratio of 1:2 to obtain a transparent solution B; (3) Add solution B to suspension A under stirring at room temperature and stir until evenly mixed to obtain suspension C; (4) Add a certain concentration of ammonia water dropwise to the C solution under stirring and adjust it to a specific pH to make Mg 2+ 、Al 3+ It is precipitated on the surface of the lithium-rich manganese-based cathode material and then stirred until the reaction is complete; (5) Centrifuge and wash the completely reacted suspension several times, and then place it in a drying oven for drying; (6) High-temperature calcine the dried and collected powder to obtain the lithium-rich manganese-based cathode material coated with magnesium aluminate.

3. The method for preparing the magnesium aluminate-coated lithium-rich manganese-based positive electrode material according to claim 2, characterized in that: The aluminum salt in step (2) includes aluminum nitrate and aluminum acetate, the magnesium salt includes magnesium chloride, magnesium nitrate, and magnesium acetate, and the concentration of solution B is 0.01 - 0.05 mol / L.

4. The method for preparing a lithium-rich manganese-based positive electrode material coated with magnesium aluminate according to claim 2, characterized in that: In step (4), the concentration of ammonia water is 0.15 - 0.60 mol / L, and the pH of the solution is adjusted to 7.5 - 9.

5. The method for preparing a lithium-rich manganese-based positive electrode material coated with magnesium aluminate according to claim 2, characterized in that: In step (5), the drying temperature is 50 - 100 °C, and the time is 12 - 24 h.

6. The method for preparing a lithium-rich manganese-based positive electrode material coated with magnesium aluminate according to claim 2, characterized in that: In step (6), the sintering temperature is 600 - 800 °C, and the sintering time is 1 - 5 h.

7. The use of the magnesium aluminate-coated lithium-rich manganese-based positive electrode material according to claim 1, characterized in that Apply the lithium-rich manganese-based cathode coated with magnesium aluminate as an electrode material in a lithium-ion battery.

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