Carbon-coated lithium-rich manganese-based positive electrode material, preparation method therefor and use thereof

Abstract

A carbon-coated lithium-rich manganese-based positive electrode material, a preparation method therefor and the use thereof. The carbon-coated lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based inner core and a carbon layer shell. The chemical formula of the lithium-rich manganese-based inner core is: xLi2MnO3·(1-x)LiNiaCobMncMdO2, wherein x+a+b+c+d=1, 0<x<1, 0<a<0.5, 0≤b≤0.2, 0.5≤c<0.8, 0<d<0.1, and M is a doping element comprising any one or a combination of at least two of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn, or W. By doping specific types of metal elements and using carbon coating, the positive electrode material alleviates the phenomenon of oxygen removal in a charging and discharging process thereof, thus improving the cycle performance of batteries, improving the battery capacity, and facilitating large-scale popularization and application.

Description

A carbon-coated lithium-rich manganese-based positive electrode material and its preparation method and application Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries and relates to a lithium-rich manganese-based positive electrode material, and in particular to a carbon-coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof. Background Art

[0002] Given the dual impacts of limited reserves of traditional energy sources like oil and coal, and carbon emissions on the global ecological environment, people are increasingly aware of the need to find clean energy. Currently, photovoltaic and wind power generation place significant pressure on the power grid due to weather and topography. Lithium-ion batteries, with their combined advantages of high operating voltage, compact size, long cycle life, high energy density, and low self-discharge, are widely used in various fields, including 3C mobile smart devices, power tools, electric vehicles, and energy storage. They play a vital role in peak-shaving and valley-filling for the power grid, making research on high-capacity lithium-ion batteries a hot topic.

[0003] Cathode materials are crucial factors in determining a range of key lithium-ion battery indicators, including energy density, cycle performance, and production cost. Precursors are the primary raw materials for preparing cathode materials. Currently, the discharge specific capacities of commercial ternary lithium batteries and lithium iron phosphate batteries are mostly below 200 mAh / g, and their operating voltages generally do not exceed 4.3V, failing to meet the high-range requirements of vehicles. Lithium-rich manganese-based cathode materials, however, operate in the 2.0-4.8V range and offer a discharge specific capacity exceeding 250 mAh / g, making them a promising option for achieving a high specific energy of 400 Wh / kg for lithium-ion batteries.

[0004] However, the traditional preparation method for lithium-rich manganese-based cathode materials is solid-phase synthesis, which has problems such as the introduction of magnetic foreign matter and uneven element distribution, which has a significant impact on battery performance. In addition, traditional lithium-rich manganese-based cathode materials have low electrical conductivity, resulting in poor rate performance, which seriously affects their commercial application. At the same time, during the charge and discharge process of lithium-rich manganese-based cathode materials, oxygen is released, causing the layered structure to transform into a spinel structure, resulting in a voltage drop, and the spinel structure gradually extends inward, which has an adverse effect on its cycle performance. The released oxygen also combines with free lithium ions to form Li2O. The layered structure transformation causes the transition metal valence to decrease, and the metallic manganese gradually dissolves, resulting in a decrease in battery capacity.

[0005] It can be seen that how to provide a lithium-rich manganese-based positive electrode material and its preparation method to alleviate the oxygen release phenomenon of the positive electrode material during the charge and discharge process, thereby improving the cycle performance of the battery and increasing the battery capacity has become an urgent problem that technical personnel in this field need to solve.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] In response to the shortcomings of the existing technology, the purpose of this application is to provide a carbon-coated lithium-rich manganese-based positive electrode material and its preparation method and application. The positive electrode material is doped with specific types of metal elements and carbon coated to alleviate the oxygen release phenomenon during the charge and discharge process, thereby improving the battery's cycle performance and increasing the battery capacity, which is conducive to large-scale promotion and application.

[0009] To achieve this goal, this application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a carbon-coated lithium-rich manganese-based positive electrode material, wherein the carbon-coated lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based core and a carbon layer shell.

[0011] The chemical formula of the lithium-rich manganese-based core is: xLi2MnO3·(1–x)LiNi a Co b Mn c M d O2.

[0012] Where: x+a+b+c+d=1, and 0<x<1, 0<a<0.5, 0≤b≤0.2, 0.5≤c<0.8, 0<d<0.1; for example, x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, a=0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, b=0, 0.02, 0.04 , 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, c = 0.5, 0.55, 0.6, 0.65, 0.7 or 0.75, d = 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008 or 0.009, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] The valence state of Mn in the lithium-rich manganese-based core of the present application will change during the charge and discharge process. For example, during the charge process, the manganese ions change from a low-valence state to a high-valence state. 3+ Transformed into high-valence Mn 4+ , while the opposite valence change occurs during the discharge process. This valence change is due to the change in the lattice structure of the lithium-rich manganese-based positive electrode material, in which manganese ions undergo redox reactions with oxygen ions during the charge and discharge process, thereby changing their own valence.

[0014] M is a doping element, including any one or a combination of at least two of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn or W. Typical but non-limiting combinations include the combination of Al and Ca, the combination of Ca and Cr, the combination of Cr and La, the combination of La and Ce, the combination of Ce and Mg, the combination of Mg and Na, the combination of Na and Nb, the combination of Nb and Ru, the combination of Ru and Ti, the combination of Ti and Zr, the combination of Zr and Fe, the combination of Fe and Cu, the combination of Cu and Zn, or the combination of Zn and W.

[0015] The present application dopes a specific type of metal element into the positive electrode material, reduces crystal defects, improves the crystallinity of the material, and at the same time, the strong bond energy effectively stabilizes the lattice oxygen and alleviates the oxygen escape phenomenon, thereby effectively inhibiting the migration of transition metal ions to the lithium layer of the lithium-rich manganese-based positive electrode material during the cycle, avoiding the formation of the spinel phase, and ultimately effectively inhibiting the capacity / voltage decay phenomenon during the cyclic charge and discharge process, improving the cycle performance of the battery, and increasing the battery capacity.

[0016] In addition, the present application coats the surface of the lithium-rich manganese-based core with a carbon shell, which effectively avoids side reactions between the material surface and the electrolyte, further improving battery performance. In addition, carbon coating is relatively simple, low-cost, and easy to achieve large-scale industrial application.

[0017] In one embodiment, the average particle size of the carbon-coated lithium-rich manganese-based positive electrode material is 2-20 μm, for example, it can be 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In a second aspect, the present application provides a method for preparing the carbon-coated lithium-rich manganese-based positive electrode material as described in the first aspect, the preparation method comprising the following steps:

[0019] (1) mixing nickel salt, cobalt salt, manganese salt and deionized water to obtain a first metal salt solution;

[0020] (2) mixing the doped metal salt and deionized water to obtain a second metal salt solution;

[0021] (3) independently preparing a reaction base solution, a precipitant solution, and a complexing agent solution;

[0022] (4) injecting the first metal salt solution, the second metal salt solution, the precipitant solution and the complexing agent solution into the reaction base liquid respectively to carry out a co-precipitation reaction, and obtaining a precursor after solid-liquid separation;

[0023] (5) mixing the precursor and the lithium source and performing a sintering process to obtain an intermediate material;

[0024] (6) The intermediate material and the carbon source are mixed and heat treated to obtain a carbon-coated lithium-rich manganese-based positive electrode material.

[0025] Wherein, steps (1) to (3) are performed in no particular order, and the metal element in the doping metal salt in step (2) includes any one or a combination of at least two of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn or W, and typical but non-limiting combinations include a combination of Al and Ca, a combination of Ca and Cr, a combination of Cr and La, a combination of La and Ce, a combination of Ce and Mg, a combination of Mg and Na, a combination of Na and Nb, a combination of Nb and Ru, a combination of Ru and Ti, a combination of Ti and Zr, a combination of Zr and Fe, a combination of Fe and Cu, a combination of Cu and Zn, or a combination of Zn and W.

[0026] The chemical formula of the precursor in step (4) is: Ni a Co b Mn c M d (OH)2, a+b+c+d=1.

[0027] In one embodiment, the nickel salt, cobalt salt and manganese salt in step (1) are independently any one of sulfate, nitrate, acetate or chloride of the corresponding metal element, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of sulfate and nitrate, a combination of nitrate and acetate, a combination of acetate and chloride, a combination of sulfate, nitrate and acetate, a combination of nitrate, acetate and chloride, or a combination of sulfate, nitrate, acetate and chloride.

[0028] In one embodiment, the total concentration of metal ions in the first metal salt solution in step (1) is 0.5-4 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0029] In one embodiment, the total concentration of metal ions in the second metal salt solution in step (2) is 0.01-0.3 mol / L, for example, it can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0030] In one embodiment, the preparation method of the reaction base liquid in step (3) comprises: mixing a precipitant, a complexing agent and deionized water in an atmosphere of protective gas, and stirring them uniformly to obtain the reaction base liquid.

[0031] In one embodiment, the protective gas includes nitrogen, helium or argon, more preferably nitrogen.

[0032] In one embodiment, the pH of the reaction base solution in step (3) is 9-12, for example, 9, 9.5, 10, 10.5, 11, 11.5 or 12, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] In one embodiment, the precipitant solution in step (3) comprises sodium hydroxide solution and / or potassium hydroxide solution.

[0034] In one embodiment, the complexing agent solution in step (3) comprises any one of ammonia water, acetic acid solution, sodium citrate solution, ethylenediamine solution, EDTA solution, oxalic acid solution or citric acid solution, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ammonia water and acetic acid solution, a combination of acetic acid solution and sodium citrate solution, a combination of sodium citrate solution and ethylenediamine solution, a combination of ethylenediamine solution and EDTA solution, a combination of EDTA solution and oxalic acid solution, or a combination of oxalic acid solution and citric acid solution.

[0035] In one embodiment, the injection method of step (4) includes: first heating the reaction base solution to a set temperature, then continuously injecting the first metal salt solution and the second metal salt solution and maintaining the solution pH at a set value to perform a co-precipitation reaction, while continuously injecting the precipitant solution and the complexing agent solution, accompanied by stirring.

[0036] In one embodiment, the set temperature is 30-100°C, for example, it can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In one embodiment, the set value of the solution pH is 7-13, for example, it can be 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or 13, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In one embodiment, the stirring speed is 100-1000 rpm, for example, it can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm or 1000 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] In one embodiment, after the solid-liquid separation in step (4), the precursor is sequentially washed, dried and treated to remove magnetic foreign matter.

[0040] In one embodiment, the lithium source in step (5) includes lithium carbonate and / or lithium hydroxide.

[0041] In one embodiment, the temperature of the sintering treatment in step (5) is 600-1200°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0042] In one embodiment, the sintering treatment time in step (5) is 6-24 hours, for example, it can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] In one embodiment, the carbon source in step (6) is a long carbon chain liquid organic solvent, including any one or a combination of at least two of oleylamine, octadecene or oleic acid. Typical but non-limiting combinations include a combination of oleylamine and octadecene, a combination of octadecene and oleic acid, a combination of oleylamine and oleic acid, or a combination of oleylamine, octadecene and oleic acid.

[0044] In one embodiment, the mixing mass ratio of the intermediate material and the carbon source in step (6) is (1-10):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] In one embodiment, the temperature of the heat treatment in step (6) is 400-600°C, for example, it can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 560°C, 580°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0046] In one embodiment, the heat treatment time in step (6) is 4-5 h, for example, 4 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] As an optional technical solution of the second aspect of the present application, the preparation method comprises the following steps:

[0048] (1) mixing a nickel salt, a cobalt salt, a manganese salt, and deionized water to obtain a first metal salt solution having a total metal ion concentration of 0.5-4 mol / L; wherein the nickel salt, cobalt salt, and manganese salt are independently any one of sulfate, nitrate, acetate, or chloride of the corresponding metal element, or a combination of at least two thereof;

[0049] (2) mixing a doped metal salt and deionized water to obtain a second metal salt solution having a total metal ion concentration of 0.01-0.3 mol / L; wherein the metal element in the doped metal salt comprises any one or a combination of at least two of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn, or W;

[0050] (3) preparing a reaction base liquid, a precipitant solution, and a complexing agent solution respectively and independently; the preparation method of the reaction base liquid comprises: mixing a precipitant, a complexing agent, and deionized water in a nitrogen atmosphere, and stirring to obtain a reaction base liquid with a pH of 9-12; the precipitant solution comprises a sodium hydroxide solution and / or a potassium hydroxide solution; the complexing agent solution comprises any one of ammonia water, acetic acid solution, sodium citrate solution, ethylenediamine solution, EDTA solution, oxalic acid solution, or citric acid solution, or a combination of at least two thereof;

[0051] (4) First, the reaction base liquid is heated to 30-100° C., and then the first metal salt solution and the second metal salt solution are continuously injected and the pH of the solution is maintained at 7-13 to perform a coprecipitation reaction. At the same time, the precipitant solution and the complexing agent solution are continuously injected, accompanied by stirring at a speed of 100-1000 rpm. After solid-liquid separation, a precursor is obtained, and the obtained precursor is washed, dried and treated to remove magnetic foreign matter in turn; the chemical formula of the precursor is: Ni a Co bMn c M d (OH)2, a+b+c+d=1;

[0052] (5) sintering the mixed precursor and lithium source at 600-1200° C. for 6-24 hours to obtain an intermediate material; the lithium source includes lithium carbonate and / or lithium hydroxide;

[0053] (6) The intermediate material and the carbon source are mixed in a mass ratio of (1-10):1 and heat-treated at 400-600°C for 4-5 hours to obtain a carbon-coated lithium-rich manganese-based positive electrode material; the carbon source is a long carbon chain liquid organic solvent, including any one of oleylamine, octadecene or oleic acid, or a combination of at least two thereof.

[0054] Among them, steps (1)-(3) are not in any particular order.

[0055] In a third aspect, the present application provides a lithium-ion battery, which comprises the carbon-coated lithium-rich manganese-based positive electrode material as described in the first aspect.

[0056] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0057] Compared with the prior art, the present invention has the following advantages:

[0058] (1) The present application doped a specific type of metal element into the positive electrode material, thereby reducing crystal defects and improving the crystallinity of the material. At the same time, the strong bond energy effectively stabilized the lattice oxygen and alleviated the oxygen escape phenomenon, thereby effectively inhibiting the migration of transition metal ions to the lithium layer of the lithium-rich manganese-based positive electrode material during the cycle process, avoiding the formation of the spinel phase, and ultimately effectively inhibiting the capacity / voltage decay phenomenon during the cyclic charge and discharge process, improving the cycle performance of the battery, and increasing the battery capacity;

[0059] (2) The present application coats the surface of the lithium-rich manganese-based core with a carbon shell, which effectively avoids side reactions between the material surface and the electrolyte, further improving battery performance. In addition, carbon coating is relatively simple, low-cost, and easy to achieve large-scale industrial application.

[0060] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0062] FIG1 is a TEM image of the precursor obtained by the preparation method provided in Example 1. DETAILED DESCRIPTION

[0063] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0064] Example 1

[0065] This embodiment provides a carbon-coated lithium-rich manganese-based positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0066] (1) mixing nickel sulfate, cobalt sulfate, manganese sulfate, and deionized water to obtain a first metal salt solution having a total metal ion concentration of 2 mol / L;

[0067] (2) mixing aluminum sulfate and deionized water to obtain a second metal salt solution having a total metal ion concentration of 0.2 mol / L;

[0068] (3) preparing a reaction base solution, a precipitant solution, and a complexing agent solution separately and independently; the preparation method of the reaction base solution comprises: mixing sodium hydroxide, ammonia water, and deionized water in a nitrogen atmosphere, and stirring uniformly to obtain a reaction base solution with a pH of 10; the precipitant solution is sodium hydroxide solution; and the complexing agent solution is ammonia water;

[0069] (4) The reaction base liquid is first heated to 60° C., and then the first metal salt solution and the second metal salt solution are continuously injected and the pH of the solution is maintained at 10 for coprecipitation reaction. At the same time, sodium hydroxide solution and ammonia water are continuously injected, accompanied by stirring at a speed of 300 rpm. After centrifugation, a precursor is obtained (see Figure 1), and the obtained precursor is washed, dried and demagnetized; the chemical formula of the precursor is: Ni 0.37 Co 0.02 Mn 0.6 Al 0.01 (OH)2;

[0070] (5) The mixed precursor and lithium carbonate are sintered at 800°C for 12 hours to obtain an intermediate material;

[0071] (6) 20 g of the intermediate material and 10 g of oleic acid were mixed and heat-treated at 500 °C for 4.5 h to obtain a carbon-coated lithium-rich manganese-based positive electrode material with an average particle size of 13 μm.

[0072] The carbon-coated lithium-rich manganese-based cathode material obtained in this embodiment includes a lithium-rich manganese-based core and a carbon layer shell, and the chemical formula of the lithium-rich manganese-based core is: Li 1.2 Ni 0.296 Co0.016 Mn 0.48 Al 0.008 O2.

[0073] Example 2

[0074] This embodiment provides a carbon-coated lithium-rich manganese-based positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0075] (1) mixing nickel sulfate, cobalt sulfate, manganese sulfate, and deionized water to obtain a first metal salt solution having a total metal ion concentration of 0.5 mol / L;

[0076] (2) mixing zirconium sulfate and deionized water to obtain a second metal salt solution having a total metal ion concentration of 0.01 mol / L;

[0077] (3) preparing a reaction base solution, a precipitant solution, and a complexing agent solution respectively and independently; the preparation method of the reaction base solution comprises: mixing potassium hydroxide, EDTA, and deionized water in a nitrogen atmosphere, and stirring uniformly to obtain a reaction base solution with a pH of 9; the precipitant solution is a potassium hydroxide solution; and the complexing agent solution is an EDTA solution;

[0078] (4) First, the reaction base liquid is heated to 50° C., and then the first metal salt solution and the second metal salt solution are continuously injected and the pH of the solution is maintained at 9 for coprecipitation reaction. At the same time, potassium hydroxide solution and EDTA solution are continuously injected, accompanied by stirring at a speed of 100 rpm. After centrifugation, a precursor is obtained, and the obtained precursor is washed, dried and demagnetized; the chemical formula of the precursor is: Ni 0.37 Co 0.02 Mn 0.6 Zr 0.01 (OH)2;

[0079] (5) The mixed precursor and lithium hydroxide are sintered at 600° C. for 24 h to obtain an intermediate material;

[0080] (6) 20 g of the intermediate material and 2 g of oleylamine were mixed and heat-treated at 400 °C for 5 h to obtain a carbon-coated lithium-rich manganese-based positive electrode material with an average particle size of 2 μm.

[0081] The carbon-coated lithium-rich manganese-based cathode material obtained in this embodiment includes a lithium-rich manganese-based core and a carbon layer shell, and the chemical formula of the lithium-rich manganese-based core is: Li 1.2 Ni 0.296 Co 0.016 Mn 0.48 Zr 0.008 O2.

[0082] Example 3

[0083] This embodiment provides a carbon-coated lithium-rich manganese-based positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0084] (1) mixing nickel sulfate, cobalt sulfate, manganese sulfate, and deionized water to obtain a first metal salt solution having a total metal ion concentration of 5 mol / L;

[0085] (2) mixing titanyl sulfate and deionized water to obtain a second metal salt solution having a total metal ion concentration of 1 mol / L;

[0086] (3) preparing a reaction base solution, a precipitant solution, and a complexing agent solution respectively and independently; the preparation method of the reaction base solution comprises: mixing sodium hydroxide, ethylenediamine, and deionized water in a nitrogen atmosphere, and stirring uniformly to obtain a reaction base solution with a pH of 12; the precipitant solution is a sodium hydroxide solution; and the complexing agent solution is an ethylenediamine solution;

[0087] (4) First, the reaction base liquid is heated to 30° C., and then the first metal salt solution and the second metal salt solution are continuously injected and the pH of the solution is maintained at 12 to perform a coprecipitation reaction. At the same time, sodium hydroxide solution and ethylenediamine solution are continuously injected, accompanied by stirring at a speed of 1000 rpm. After centrifugation, a precursor is obtained, and the obtained precursor is washed, dried and demagnetized; the chemical formula of the precursor is: Ni 0.37 Co 0.02 Mn 0.6 Ti 0.01 (OH)2;

[0088] (5) The mixed precursor and lithium carbonate are sintered at 1200° C. for 6 h to obtain an intermediate material;

[0089] (6) 20 g of the intermediate material and 16 g of octadecene were mixed and heat-treated at 600 °C for 4 h to obtain a carbon-coated lithium-rich manganese-based positive electrode material with an average particle size of 20 μm.

[0090] The carbon-coated lithium-rich manganese-based cathode material obtained in this embodiment includes a lithium-rich manganese-based core and a carbon layer shell, and the chemical formula of the lithium-rich manganese-based core is: Li 1.2 Ni 0.296 Co 0.016 Mn 0.48 Ti 0.008 O2.

[0091] Example 4

[0092] This embodiment provides a carbon-coated lithium-rich manganese-based positive electrode material and a preparation method thereof. Except that the aluminum sulfate in the second metal salt solution in step (2) is replaced with copper sulfate and zinc sulfate in an equal molar ratio, the remaining steps and conditions are the same as those in Example 1 and are therefore not described here.

[0093] The chemical formula of the lithium-rich manganese-based core in the carbon-coated lithium-rich manganese-based positive electrode material obtained in this embodiment is: Li 1.2 Ni 0.296 Co 0.016 Mn 0.48 Cu 0.004 Zn 0.004 O2.

[0094] Comparative Example 1

[0095] This comparative example provides a lithium-rich manganese-based positive electrode material and a preparation method thereof. Except that step (2) is not performed, that is, metal elements are not doped into the positive electrode material, the remaining steps and conditions are the same as those in Example 1, and therefore are not described here.

[0096] Comparative Example 2

[0097] This comparative example provides a lithium-rich manganese-based positive electrode material and a preparation method thereof. Except that step (6) is not performed, that is, the positive electrode material is not carbon-coated, the remaining steps and conditions are the same as those in Example 1, and therefore are not described in detail here.

[0098] Performance Testing

[0099] Button-type lithium-ion batteries were prepared using the positive electrode materials obtained in Examples 1-4 and Comparative Examples 1-2. The specific preparation method includes: adding the positive electrode material, acetylene black and polyvinylidene fluoride to N-methyl-2-pyridine alkanone in a mass ratio of 8:1:1 to prepare a solution, which was then evenly applied on aluminum foil, dried, and stamped into thin sheets; and assembling the battery pole piece, elemental lithium sheet, glass fiber diaphragm, electrolyte (LiClO4) gasket, shrapnel and battery shell in an argon glove box to form a button battery.

[0100] Table 1 below shows the electrochemical performance test data of button batteries prepared using the positive electrode materials obtained in Examples 1-4 and Comparative Examples 1-2, respectively.

[0101] Table 1

[0102] As shown in Table 1, the specific capacity of the modified lithium-rich manganese-based positive electrode materials obtained in Examples 1-4 at 4.5V can reach above 235.31 mAh / g, the first efficiency can reach above 81.7%, and the number of cycles with a capacity retention rate above 80% can reach above 1512 cycles.

[0103] It can be seen that the present application dopes a specific type of metal element into the positive electrode material, reduces crystal defects, improves the crystallinity of the material, and at the same time, the strong bond energy effectively stabilizes the lattice oxygen and alleviates the oxygen escape phenomenon, thereby effectively inhibiting the migration of transition metal ions to the lithium layer of the lithium-rich manganese-based positive electrode material during the cycle, avoiding the formation of the spinel phase, and ultimately effectively inhibiting the capacity / voltage decay phenomenon during the cyclic charge and discharge process, improving the cycle performance of the battery, and increasing the battery capacity.

[0104] In addition, the present application coats the surface of the lithium-rich manganese-based core with a carbon shell, which effectively avoids side reactions between the material surface and the electrolyte, further improving battery performance. In addition, carbon coating is relatively simple, low-cost, and easy to achieve large-scale industrial application.

[0105] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A carbon-coated lithium-rich manganese-based positive electrode material, comprising a lithium-rich manganese-based core and a carbon layer shell; The chemical formula of the lithium-rich manganese-based core is: xLi2MnO 3· (1–x)LiNi a Co b Mn c M d O2; in: x+a+b+c+d=1, and 0<x<1, 0<a<0.5, 0≤b≤0.2, 0.5≤c<0.8, 0<d<0.1; M is a doping element, including any one of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn or W, or a combination of at least two thereof.

2. The carbon-coated lithium-rich manganese-based positive electrode material according to claim 1, wherein: The average particle size of the carbon-coated lithium-rich manganese-based positive electrode material is 2-20 μm.

3. A method for preparing a carbon-coated lithium-rich manganese-based positive electrode material as claimed in claim 1 or 2, comprising the following steps: (1) mixing a nickel salt, a cobalt salt, a manganese salt and deionized water to obtain a first metal salt solution; (2) mixing a doped metal salt and deionized water to obtain a second metal salt solution; (3) independently preparing a reaction base solution, a precipitant solution and a complexing agent solution; (4) injecting the first metal salt solution, the second metal salt solution, the precipitant solution and the complexing agent solution into the reaction base liquid respectively to carry out a co-precipitation reaction, and obtaining a precursor after solid-liquid separation; (5) mixing the precursor and the lithium source and performing a sintering process to obtain an intermediate material; (6) mixing the intermediate material and the carbon source and performing heat treatment to obtain a carbon-coated lithium-rich manganese-based positive electrode material; Wherein, steps (1) to (3) are performed in no particular order, and the metal element in the doped metal salt in step (2) includes any one or a combination of at least two of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn or W, and the chemical formula of the precursor in step (4) is: Ni a Co b Mn c M d (OH)2, a+b+c+d=1.

4. The preparation method according to claim 3, wherein The nickel salt, cobalt salt and manganese salt in step (1) are independently any one of sulfate, nitrate, acetate or chloride of the corresponding metal element or a combination of at least two thereof; Optionally, in step (1), the total concentration of metal ions in the first metal salt solution is 0.5-4 mol / L; Optionally, in step (2), the total concentration of metal ions in the second metal salt solution is 0.01-0.3 mol / L.

5. The preparation method according to claim 3 or 4, wherein The preparation method of the reaction base liquid in step (3) comprises: mixing a precipitant, a complexing agent and deionized water in an atmosphere of protective gas, and stirring to obtain a reaction base liquid; Optionally, the protective gas includes nitrogen, helium or argon, and further may be nitrogen; Optionally, the pH of the reaction base solution in step (3) is 9-12; Optionally, the precipitant solution in step (3) comprises sodium hydroxide solution and / or potassium hydroxide solution; Optionally, the complexing agent solution in step (3) comprises any one of ammonia water, acetic acid solution, sodium citrate solution, ethylenediamine solution, EDTA solution, oxalic acid solution or citric acid solution, or a combination of at least two thereof.

6. The preparation method according to any one of claims 3 to 5, wherein: The injection method of step (4) includes: firstly heating the reaction base solution to a set temperature, then continuously injecting the first metal salt solution and the second metal salt solution and maintaining the solution pH at a set value to perform a co-precipitation reaction, and simultaneously continuously injecting the precipitant solution and the complexing agent solution, accompanied by stirring; Optionally, the set temperature is 30-100°C; Optionally, the set value of the solution pH is 7-13; Optionally, the stirring process has a rotation speed of 100-1000 rpm; Optionally, after the solid-liquid separation in step (4), the precursor is sequentially washed, dried and treated to remove magnetic foreign matter.

7. The preparation method according to any one of claims 3 to 6, wherein: The lithium source in step (5) includes lithium carbonate and / or lithium hydroxide; Optionally, the sintering temperature in step (5) is 600-1200° C. Optionally, the sintering time in step (5) is 6-24 hours.

8. The preparation method according to any one of claims 3 to 7, wherein: The carbon source in step (6) is a long carbon chain liquid phase organic solvent, including any one of oleylamine, octadecene or oleic acid, or a combination of at least two thereof; Optionally, in step (6), the mixing mass ratio of the intermediate material to the carbon source is (1-10):1; Optionally, the temperature of the heat treatment in step (6) is 400-600°C; Optionally, the heat treatment time in step (6) is 4-5 hours.

9. The preparation method according to any one of claims 3 to 8, wherein: The preparation method comprises the following steps: (1) mixing a nickel salt, a cobalt salt, a manganese salt and deionized water to obtain a first metal salt solution with a total metal ion concentration of 0.5-4 mol / L; the nickel salt, the cobalt salt and the manganese salt are independently any one of sulfates, nitrates, acetates or chlorides of the corresponding metal elements or a combination of at least two thereof; (2) mixing a doped metal salt and deionized water to obtain a second metal salt solution with a total metal ion concentration of 0.01-0.3 mol / L; the metal element in the doped metal salt comprises any one of Al, Ca, Cr, La, Ce, Mg, Na, Nb, Ru, Ti, Zr, Fe, Cu, Zn or W, or a combination of at least two thereof; (3) preparing a reaction base solution, a precipitant solution and a complexing agent solution respectively and independently; the preparation method of the reaction base solution comprises: mixing a precipitant, a complexing agent and deionized water in a nitrogen atmosphere, and stirring to obtain a reaction base solution with a pH of 9-12; the precipitant solution comprises a sodium hydroxide solution and / or a potassium hydroxide solution; the complexing agent solution comprises any one of ammonia water, acetic acid solution, sodium citrate solution, ethylenediamine solution, EDTA solution, oxalic acid solution or citric acid solution, or a combination of at least two thereof; (4) First, the reaction base solution is heated to 30-100°C, and then the first metal salt solution and the second metal salt solution are continuously injected and the pH of the solution is maintained at 7-13 to perform a coprecipitation reaction, and at the same time, the precipitant solution is continuously injected. The precursor is then washed, dried and demagnetized by the following steps: a Co b Mn c M d (OH)2, a+b+c+d=1; (5) sintering the mixed precursor and lithium source at 600-1200° C. for 6-24 hours to obtain an intermediate material; the lithium source includes lithium carbonate and / or lithium hydroxide; (6) mixing the intermediate material and the carbon source in a mass ratio of (1-10):1 and heat treating at 400-600°C for 4-5h to obtain a carbon-coated lithium-rich manganese-based positive electrode material; the carbon source is a long carbon chain liquid organic solvent, including any one of oleylamine, octadecene or oleic acid, or a combination of at least two thereof; Among them, steps (1)-(3) are performed in no particular order.

10. A lithium ion battery comprising the carbon-coated lithium-rich manganese-based positive electrode material as claimed in claim 1 or 2.

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