A lithium-rich manganese-based cathode material and a preparation method thereof

Abstract

The present invention relates to the field of lithium battery materials, in particular to a lithium-rich manganese-based positive electrode material and a preparation method thereof. The chemical structure of the lithium-rich manganese-based positive electrode material is as follows: Li[Li x M y Mn 0.62‑ z In z ]O2 wherein M is Co and / or Ni; x+y=0.38, and 0.1≤x≤0.2, 0.05≤z≤0.1, the surface of the lithium-rich manganese-based positive electrode material is coated with rare earth fluoride, and the lithium-rich manganese-based positive electrode material prepared by the present invention has a high first discharge capacity (≥293mAh / g) and a high coulombic efficiency (≥86.8%) under the test conditions of 2.75-4.30V and a discharge rate of 0.2C, and the rate performance is improved, and it has good cycle performance. The capacity retention rate is ≥92.2% after 200 charge and discharge cycles at a rate of 0.2C.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery materials, and in particular to a lithium-rich manganese-based positive electrode material and a preparation method thereof. Background Art

[0002] Energy and the environment are two paramount issues facing human survival and development today. With the advancement of global industrialization, the depletion of fossil fuels, and continued population growth, environmental pollution and ecological imbalances are becoming increasingly severe, leading to a growing energy shortage. Especially in the 21st century, with improved living standards and growing environmental awareness, environmental issues are gaining increasing attention, and governments around the world are formulating large-scale clean energy plans. The development and utilization of new energy and renewable clean energy are attracting increasing attention. The indirect and unstable nature of renewable energy sources such as wind and solar power requires the use of efficient energy storage systems. The booming new energy vehicle industry is also placing higher demands on energy storage systems. Traditional chemical power sources, due to their use in toxic metals such as lead and chromium, are causing significant environmental pollution, and their use is gradually being restricted.

[0003] Lithium-rich manganese-based positive electrode materials can achieve a specific capacity of more than 250mAh / g, and have a high discharge voltage platform and tap density, so they have a high energy density and can well meet the use requirements of lithium batteries in small electronic products and electric vehicles. As a manganese-based material, lithium-rich manganese-based positive electrode materials have abundant raw material sources, low prices, and stable electrochemical properties. Therefore, they have become ideal positive electrode materials for high-capacity lithium-ion batteries and have broad development prospects. The lithium-rich manganese-based positive electrode materials that are currently being studied more intensively are mainly layered LiMnO2 and spinel-type LiMn2O4. The layered LiMnO2 has low discharge capacity and poor cycle performance, making it difficult to be widely used. Therefore, it is crucial to find a lithium-rich manganese-based positive electrode material with high discharge specific capacity and more stable cycle performance. Summary of the Invention

[0004] Purpose of the invention: In response to the above technical problems, the present invention proposes a lithium-rich manganese-based positive electrode material and a preparation method thereof.

[0005] The technical solutions adopted are as follows:

[0006] A lithium-rich manganese-based positive electrode material, the chemical structure of the lithium-rich manganese-based positive electrode material is as follows:

[0007] Li[Li x M y Mn 0.62-z In z ]O2

[0008] Wherein, M is Co and / or Ni;

[0009] x+y=0.38, 0.1≤x≤0.2, 0.05≤z≤0.1, and the surface of the lithium-rich manganese-based positive electrode material is coated with rare earth fluoride.

[0010] Furthermore, M is Co and Ni.

[0011] Furthermore, the molar ratio of Co to Ni is 1:1.

[0012] Furthermore, x is 0.18.

[0013] Furthermore, y is 0.2.

[0014] Furthermore, z is 0.06.

[0015] Furthermore, the rare earth fluoride is any one or more combinations of lanthanum fluoride, cerium fluoride, and yttrium fluoride.

[0016] The present invention also provides a method for preparing a lithium-rich manganese-based positive electrode material:

[0017] Indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and / or nickel chloride are added to water and stirred evenly to form a solution. The temperature is raised to 75-85°C and citric acid is added. After the addition is completed, the pH of the solution is adjusted to 7-8 with ammonia water and stirred for 20-40 minutes. The stirring is continued until a wet gel is formed. The obtained wet gel is dried and then subjected to self-propagating combustion. The product obtained by the self-propagating combustion is calcined to obtain an intermediate. The intermediate is added to an ammonium fluoride solution, stirred evenly, and then a rare earth nitrate solution is added. The reaction is stirred at 80-85°C for 4-8 hours, filtered, and the obtained positive electrode material is washed, dried at 80-100°C under argon protection for 8-15 hours, and then calcined.

[0018] Furthermore, the self-propagating combustion product is calcined at a temperature of 800-850° C. and for a time of 5-10 hours.

[0019] Furthermore, the self-propagating combustion product needs to be pre-burned before calcination, with the pre-burning temperature being 400-450° C. and the pre-burning time being 2-3 hours.

[0020] Furthermore, the positive electrode material is calcined at a temperature of 500-550° C. and for a time of 4-6 hours.

[0021] Beneficial effects of the present invention:

[0022] The present invention provides a lithium-rich manganese-based positive electrode material. In order to improve the cycle performance of lithium manganate, the inventors reduce the Mn content by adding indium, cobalt and nickel elements into the layered structure of LiMnO2. 3+The content of rare earth fluoride makes the average oxidation state of manganese always remain greater than +3.5 during the charge and discharge process, thereby suppressing the occurrence of Jahn-Teller effect and achieving the purpose of stabilizing the structure. The rare earth fluoride is coated on the surface of the lithium-rich manganese-based positive electrode material, which can effectively reduce the reaction between the active substance and the electrolyte and suppress the disappearance of oxygen vacancies at the end of the first charge. At the same time, some rare earth metal ions will also enter the lattice of the parent material to stabilize the structure, thereby improving the stability of the material during the cycle, increasing the first discharge capacity, and improving the rate performance and cycle performance. The preparation of lithium-rich manganese-based positive electrode materials by self-propagating combustion helps to form a porous structure, which is beneficial to the full contact between the positive electrode material and the electrolyte, and increases Li + The deintercalation and intercalation ability of the lithium-rich manganese-based positive electrode material prepared by the present invention is improved, and the cycle stability is improved. Under the test conditions of 2.75-4.30V and a discharge rate of 0.2C, it has a high first discharge capacity (≥293mAh / g), a high coulombic efficiency (≥86.8%), and improved rate performance. It has good cycle performance. After 200 charge and discharge cycles at a rate of 0.2C, the capacity retention rate is ≥92.2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an SEM image of the lithium-rich manganese-based positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0025] Example 1:

[0026] A lithium-rich manganese-based positive electrode material, the chemical structure of the lithium-rich manganese-based positive electrode material is as follows:

[0027] Li[Li 0.18 Co 0.1 Ni 0.1 Mn 0.56 In 0.06 ]O2

[0028] The surface of the lithium-rich manganese-based positive electrode material is coated with lanthanum fluoride.

[0029] Preparation method of the above-mentioned lithium-rich manganese-based positive electrode material:

[0030] According to the stoichiometric ratio in the chemical formula, 169.2 g of indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and nickel chloride were weighed and added to 1500 mL of water, stirred evenly to form a solution, heated to 80 ° C, added 384 g of citric acid, stirred for 40 minutes after the addition, and then adjusted the pH of the solution to 8 with 25% ammonia water. Stirring was continued until a wet gel was formed. The obtained wet gel was dried and loaded into a vertical self-propagating combustion synthesis device (Hai Fu Da M368079), evacuated and then filled with 5 MPa high-purity nitrogen and high-purity oxygen. A mixed gas is prepared, in which the volume ratio of high-purity nitrogen and high-purity oxygen is 1:5, and a mixed powder composed of titanium powder and carbon powder in a mass ratio of 1:1 is used as an ignition agent. Electricity is applied to ignite and self-propagating combustion is carried out. The product obtained by self-propagating combustion is pre-calcined at 450°C for 2h, then heated to 850°C and calcined for 8h to obtain an intermediate. The intermediate is added to an ammonium fluoride solution, stirred evenly, and then added with a lanthanum nitrate solution. The reaction is stirred at 80°C for 6h, filtered, and the obtained positive electrode material is washed, dried at 80°C for 12h under argon protection, and then calcined at 550°C for 5h.

[0031] Example 2:

[0032] A lithium-rich manganese-based positive electrode material, the chemical structure of the lithium-rich manganese-based positive electrode material is as follows:

[0033] Li[Li 0.18 Co 0.1 Ni 0.1 Mn 0.56 In 0.06 ]O2

[0034] The surface of the lithium-rich manganese-based positive electrode material is coated with lanthanum fluoride.

[0035] Preparation method of the above-mentioned lithium-rich manganese-based positive electrode material:

[0036] According to the stoichiometric ratio in the chemical formula, 169.2 g of indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and nickel chloride were weighed and added to 1500 mL of water, stirred evenly to form a solution, heated to 85 ° C, added 384 g of citric acid, stirred for 40 minutes after the addition, and then adjusted the pH of the solution to 8 with 25% ammonia water. Stirring was continued until a wet gel was formed. The obtained wet gel was dried and loaded into a vertical self-propagating combustion synthesis device (Hai Fu Da M368079), evacuated and then filled with 5 MPa high-purity nitrogen and high-purity oxygen. A mixed gas, high-purity nitrogen and high-purity oxygen in a volume ratio of 1:5, a mixed powder consisting of titanium powder and carbon powder in a mass ratio of 1:1 is used as an ignition agent, and electricity is applied to ignite for self-propagating combustion. The product obtained by self-propagating combustion is pre-calcined at 450°C for 3 hours, then heated to 850°C and calcined for 10 hours to obtain an intermediate, which is added to an ammonium fluoride solution and stirred evenly. Lanthanum nitrate solution is added, stirred at 85°C for 8 hours, and filtered. The obtained positive electrode material is washed, dried at 100°C for 15 hours under argon protection, and then calcined at 550°C for 6 hours.

[0037] Example 3:

[0038] A lithium-rich manganese-based positive electrode material, the chemical structure of the lithium-rich manganese-based positive electrode material is as follows:

[0039] Li[Li 0.18 Co 0.1 Ni 0.1 Mn 0.56 In 0.06 ]O2

[0040] The surface of the lithium-rich manganese-based positive electrode material is coated with lanthanum fluoride.

[0041] Preparation method of the above-mentioned lithium-rich manganese-based positive electrode material:

[0042] According to the stoichiometric ratio in the chemical formula, 169.2 g of indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and nickel chloride were weighed and added to 1500 mL of water, stirred evenly to form a solution, heated to 75 ° C, added 384 g of citric acid, stirred for 20 minutes after the addition, and then adjusted the pH of the solution to 7 with 25% ammonia water. Stirring was continued until a wet gel was formed. The obtained wet gel was dried and loaded into a vertical self-propagating combustion synthesis device (Hai Fu Da M368079), evacuated and then filled with 5 MPa high-purity nitrogen and high-purity oxygen. A mixed gas is prepared, in which the volume ratio of high-purity nitrogen and high-purity oxygen is 1:5, and a mixed powder composed of titanium powder and carbon powder in a mass ratio of 1:1 is used as an ignition agent. Electricity is applied to ignite and self-propagating combustion is performed. The product obtained by self-propagating combustion is pre-calcined at 400°C for 2h, then heated to 800°C and calcined for 5h to obtain an intermediate. The intermediate is added to an ammonium fluoride solution, stirred evenly, and then added with a lanthanum nitrate solution. The reaction is stirred at 80°C for 4h, filtered, and the obtained positive electrode material is washed, dried at 80°C for 8h under argon protection, and then calcined at 500°C for 4h.

[0043] Example 4:

[0044] A lithium-rich manganese-based positive electrode material, the chemical structure of the lithium-rich manganese-based positive electrode material is as follows:

[0045] Li[Li 0.18 Co 0.1 Ni 0.1 Mn 0.56 In 0.06 ]O2

[0046] The surface of the lithium-rich manganese-based positive electrode material is coated with lanthanum fluoride.

[0047] Preparation method of the above-mentioned lithium-rich manganese-based positive electrode material:

[0048] According to the stoichiometric ratio in the chemical formula, 169.2 g of indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and nickel chloride were weighed and added to 1500 mL of water, stirred evenly to form a solution, heated to 85 ° C, added 384 g of citric acid, stirred for 20 minutes after the addition, and then adjusted the pH of the solution to 8 with 25% ammonia water. Stirring was continued until a wet gel was formed. The obtained wet gel was dried and loaded into a vertical self-propagating combustion synthesis device (Hai Fu Da M368079), evacuated and then filled with 5 MPa high-purity nitrogen and high-purity oxygen. A mixed gas, high-purity nitrogen and high-purity oxygen in a volume ratio of 1:5, a mixed powder consisting of titanium powder and carbon powder in a mass ratio of 1:1 is used as an ignition agent, and electricity is applied to ignite for self-propagating combustion. The product obtained by self-propagating combustion is pre-calcined at 400°C for 3 hours, then heated to 800°C and calcined for 10 hours to obtain an intermediate, which is added to an ammonium fluoride solution and stirred evenly. Lanthanum nitrate solution is added, and the reaction is stirred at 80°C for 8 hours, filtered, and the obtained positive electrode material is washed, dried at 80°C for 15 hours under argon protection, and then calcined at 500°C for 6 hours.

[0049] Example 5:

[0050] A lithium-rich manganese-based positive electrode material, the chemical structure of the lithium-rich manganese-based positive electrode material is as follows:

[0051] Li[Li 0.18 Co 0.1 Ni 0.1 Mn 0.56 In 0.06 ]O2

[0052] The surface of the lithium-rich manganese-based positive electrode material is coated with lanthanum fluoride.

[0053] Preparation method of the above-mentioned lithium-rich manganese-based positive electrode material:

[0054] According to the stoichiometric ratio in the chemical formula, 169.2 g of indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and nickel chloride were weighed and added to 1500 mL of water, stirred evenly to form a solution, heated to 75 ° C, added 384 g of citric acid, stirred for 40 minutes after the addition, and then adjusted the pH of the solution to 7 with 25% ammonia water. Stirring was continued until a wet gel was formed. The obtained wet gel was dried and loaded into a vertical self-propagating combustion synthesis device (Hai Fu Da M368079), evacuated and then filled with 5 MPa high-purity nitrogen and high-purity oxygen. A mixed gas is prepared, in which the volume ratio of high-purity nitrogen and high-purity oxygen is 1:5, and a mixed powder composed of titanium powder and carbon powder in a mass ratio of 1:1 is used as an ignition agent. Electricity is applied to ignite the mixture for self-propagating combustion. The product obtained by the self-propagating combustion is pre-calcined at 450°C for 2h, then heated to 850°C and calcined for 5h to obtain an intermediate. The intermediate is added to an ammonium fluoride solution, stirred evenly, and then added with a lanthanum nitrate solution. The mixture is stirred at 85°C for 4h and filtered. The obtained positive electrode material is washed, dried at 100°C for 8h under argon protection, and then calcined at 550°C for 4h.

[0055] Comparative Example 1

[0056] Comparative Example 1 is substantially the same as Example 1, except that the surface of the lithium-rich manganese-based positive electrode material is not coated.

[0057] Comparative Example 2

[0058] Comparative Example 2 is substantially the same as Example 1, except that self-propagating combustion is not performed when preparing the lithium-rich manganese-based positive electrode material.

[0059] Comparative Example 3

[0060] Comparative Example 3 is substantially the same as Example 1, except that indium nitrate is not added when preparing the lithium-rich manganese-based positive electrode material.

[0061] Comparative Example 4

[0062] Comparative Example 4 is substantially the same as Example 1, except that cobalt chloride is not added when preparing the lithium-rich manganese-based positive electrode material.

[0063] Comparative Example 5

[0064] Comparative Example 5 is substantially the same as Example 1, except that nickel chloride is not added when preparing the lithium-rich manganese-based positive electrode material.

[0065] Performance testing:

[0066] At room temperature, the lithium-rich manganese-based positive electrode materials prepared in Examples 1-5 of the present invention and Comparative Examples 1-5 were used as samples and conductive graphite, acetylene black, and PVDF were thoroughly stirred and mixed in an NMP solution at a mass ratio of 90:2:2:6. The samples were then coated on an aluminum foil current collector and dried at 110°C for 10 hours. The samples were then cut into circular electrodes with a diameter of 15 mm. Finally, the positive electrode electrodes, metal lithium negative electrodes, separators, and electrolytes were assembled into CR2016 button cells in a glove box filled with high-purity argon. The electrolyte was 1 mol / L LiPF6. The electrical performance was tested using a blue electric tester. The charge and discharge voltage was 2.75-4.30 V, and the discharge rate was 0.2C. The test results are shown in Table 1 below:

[0067] Table 1:

[0068]

[0069] As can be seen from Table 1 above, the lithium-rich manganese-based positive electrode material prepared by the present invention has a high first discharge capacity (≥293 mAh / g) and a high coulombic efficiency (≥86.8%) under the test conditions of 2.75-4.30 V and a discharge rate of 0.2C, and has improved rate performance and good cycle performance. The capacity retention rate is ≥92.2% after 200 charge and discharge cycles at a rate of 0.2C.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A lithium-rich manganese-based positive electrode material, characterized in that The chemical structure of the lithium-rich manganese-based positive electrode material is as follows: <h2 style=";text-align:left;direction:ltr">Li[Li<h2 style=";text-align:left;direction:ltr"> x <h2 style=";text-align:left;direction:ltr"> M<h2 style=";text-align:left;direction:ltr"> y <h2 style=";text-align:left;direction:ltr"> Mn<h2 style=";text-align:left;direction:ltr"> 0.62-z <h2 style=";text-align:left;direction:ltr"> In<h2 style=";text-align:left;direction:ltr"> z <h2 style=";text-align:left;direction:ltr"> ]O2 Wherein, M is Co and Ni, and the molar ratio of Co to Ni is 1:1; x is 0.18, y is 0.2, z is 0.06, and the surface of the lithium-rich manganese-based positive electrode material is coated with rare earth fluoride; Preparation method of the above-mentioned lithium-rich manganese-based positive electrode material: Indium nitrate, manganese acetate, lithium hydroxide, cobalt chloride and nickel chloride are added to water and stirred to form a solution. The temperature is raised to 75-85°C and citric acid is added. After the addition is completed, the pH of the solution is adjusted to 7-8 with ammonia water and stirred for 20-40 minutes. The stirring is continued until a wet gel is formed. The obtained wet gel is dried and then subjected to self-propagating combustion. The product obtained by the self-propagating combustion is calcined to obtain an intermediate. The intermediate is added to an ammonium fluoride solution, stirred to form a solution, and then a rare earth nitrate solution is added. The reaction is stirred at 80-85°C for 4-8 hours, filtered, and the obtained positive electrode material is washed, dried at 80-100°C under argon protection for 8-15 hours, and then calcined. The temperature for calcining the self-propagating combustion product is 800-850°C and the calcination time is 5-10h; The self-propagating combustion products need to be pre-burned before calcination. The pre-burning temperature is 400-450℃ and the pre-burning time is 2-3h. The positive electrode material is calcined at a temperature of 500-550°C and a calcination time of 4-6 hours; The rare earth fluoride is any one or more combinations of lanthanum fluoride, cerium fluoride and yttrium fluoride.

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