A cation-doped lithium-rich manganese-based cathode material and its preparation method

Abstract

The present invention discloses a cation-doped lithium-rich manganese-based cathode material and a preparation method thereof. The chemical general formula of the cation-doped lithium-rich manganese-based cathode material is mLi2Mn 1‑x O3A x ·(1−m)LiTMO2, where A is W and / or Se, and the MnO2 doped with W 6+ and / or Se 6+ synthesized by the hydrothermal method is used as a precursor, and the nano-scale lithium-rich manganese-based cathode material is obtained through a high-temperature solid-state reaction with a nickel source, a cobalt source, and a lithium source. The doping amount of the cation is 0.5%−10%. By doping W 6+ and / or Se 6+ into the lithium-rich manganese-based cathode material, the rate performance of the cathode material is significantly improved, which is beneficial to improving the stability of the crystal lattice. The method of adding doping elements during the hydrothermal reaction for synthesizing MnO2 can more accurately incorporate the doping elements into the target positions and ensure that the doping elements are more evenly dispersed in the bulk phase of the material rather than aggregated on the surface of the material, thereby playing a more extensive regulatory role on the crystal lattice structure of the material.

Description

Technical Field

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

[0002] Lithium-ion batteries have attracted widespread attention as a new type of environmentally friendly energy storage device. Since their commercialization in the 1990s, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage. In the past decade, research on lithium-ion battery cathodes has mainly focused on spinel-structured LiCoO2 and LiMn2O4, olivine-structured LiFePO4, and their derivatives. Although LiCoO2 and LiFePO4 have successfully achieved large-scale commercial applications, they still have many problems that need to be solved. For example, the structure of LiCoO2 is unstable after delithiation, and it is also easy to have some side reactions with the electrolyte, resulting in irreversible capacity loss and safety issues. At the same time, their low available capacity (theoretical capacity <200mAh / g) can no longer meet the growing demand for electric vehicles with longer battery life. For this reason, the development of a lithium-ion battery cathode material with high specific capacity, high stability, high safety, and low cost has become the key to breaking through the bottleneck of energy development.

[0003] Among various material systems, layered materials have attracted much attention due to their higher theoretical capacity. Layered lithium-rich manganese-based cathode materials have a theoretical specific capacity of up to 250mAh / g and are considered to be the next generation of high-performance lithium-ion battery cathode materials with great research value. The chemical formula of lithium-rich manganese-based cathode materials can be expressed as xLi2MnO3·(1-x)LiMO2. It is generally believed that it is composed of layered Li2MnO3 and LiMO2, in which one-third of Li in the Li2MnO3 phase is Li + Mn 4+ Substitution, monoclinic crystal, space group C / 2m, LiMO2 is similar to the layered lithium cobalt oxide structure, space group R-3m. This special structure creates the characteristic of lithium-rich manganese-based positive electrode materials that both anions and cations participate in electrochemical reactions at the same time, which provides it with additional capacity. How to better stabilize the lattice oxygen and improve the cycle stability of the material is the current research focus. At this stage, surface treatment, surface coating and anion doping are mostly used to improve the stability of the material, but these methods are often accompanied by a loss of specific capacity. Therefore, seeking a modification method that synergistically optimizes the specific capacity and cycle stability of lithium-rich manganese-based positive electrode materials is a problem that needs to be solved urgently. Summary of the invention

[0004] To solve the above technical problems, the present invention provides a cation-doped lithium-rich manganese-based cathode material and a preparation method thereof. By doping W 6+ and / or Se 6+ into the lithium-rich manganese-based cathode material, the rate performance of the cathode material is significantly improved, which is beneficial to improving the stability of the crystal lattice.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A cation-doped lithium-rich manganese-based cathode material, the chemical general formula of the cation-doped lithium-rich manganese-based cathode material is mLi2Mn 1-x O3A x ·(1-m)LiTMO2, A is W and / or Se, 0.005 ≤ x ≤ 0.1. The cation-doped lithium-rich manganese-based cathode material is a nano-scale lithium-rich manganese-based cathode material obtained by high-temperature solid-phase reaction of cation-doped manganese dioxide synthesized by hydrothermal method with nickel source, cobalt source and lithium source. The molar doping amount of the cation is 0.5% - 10%.

[0007] By doping tungsten ions and / or selenium ions into the lithium-rich manganese-based cathode material, the ratio of LiMO2 and Li2MnO3 crystal domains in the material can be regulated, so as to regulate the average valence state of manganese in the material, realize the inhibition of the Jahn-Teller effect occurring during the cycling process of the material, and alleviate the dissolution of Mn 2+ during the cycling process of the material, so that the material has a longer cycling life. In addition, the strength of the W-O bond is stronger than that of the Mn-O bond. The introduction of tungsten element also improves the stability of lattice oxygen, which can reduce irreversible oxygen loss, and is beneficial to improving the first-cycle Coulomb efficiency and cycling stability of the material. Selenium particles replace Mn in the bulk phase, improve the near-neighbor atomic structure around Mn ions, adjust the bond length to improve stability, and optimize the cycling stability and rate performance of the cathode material. And when the molar ratio of the cation is in the range of 0.6% - 2.4%, the cycling stability and rate performance of the material can be synergistically optimized. When the doping amount is relatively small, the rate performance improvement of the material is not obvious enough. However, when the doping amount is too large, it will distort the crystal lattice structure of the material and rapidly decrease the cycling stability of the material.

[0008] Based on the same inventive concept, the present invention also provides a preparation method of a cation-doped lithium-rich manganese-based cathode material, including the following steps:

[0009] S1: Disperse manganese source, salt solution of doped cation, nitric acid and oxidant in aqueous solution, and synthesize cation-doped manganese dioxide by hydrothermal method;

[0010] S2: Mix the cation-doped manganese dioxide obtained in step S1 evenly with a cobalt source, a nickel source, and a lithium source through mechanical grinding, and then obtain the cation-doped lithium-rich manganese-based cathode material through high-temperature calcination;

[0011] wherein the doped cation is Se 6+ or W 6+ or Se 6+ and W 6+ are mixed.

[0012] Preferably, disperse the oxidant in a dilute nitric acid solution to obtain a mixed solution A; the hydrothermal method in step S1 is to disperse the manganese source and the salt of the doped cation in an aqueous solution according to the doping ratio to obtain a mixed solution B;

[0013] After mixing the mixed solution A and the mixed solution B according to a volume ratio of 1:1, carry out a hydrothermal reaction at a temperature of 80 - 250 °C. After the reaction is completed, filter, wash, and dry;

[0014] Among them, the dilute nitric acid solution is a mixed solution with a volume ratio of concentrated nitric acid to water of 1:40 - 1:100. Filtering, washing, and drying are to disperse the obtained product in deionized water, wash the product with 200 - 500 mL of deionized water, and then wash the material with 20 - 50 mL of ethanol to accelerate the drying speed, and dry at a temperature of 40 - 120 °C.

[0015] Preferably, the mixed solution B is added to the mixed solution A at a speed of 2 - 16 mL / min, and stirred for 1 - 10 h to mix evenly. By using this method of slowly adding the oxidant and nitric acid to the reaction system, the morphology of the obtained material can be regulated.

[0016] Preferably, the manganese source is selected from one or more of anhydrous Mn(CH3COO)2, Mn(CH3COO)2·4H2O, anhydrous Mn(NO3)2, Mn(NO3)2·4H2O, anhydrous MnC2O4, and MnC2O4·2H2O.

[0017] Preferably, the cobalt source is selected from one or more of anhydrous Co(CH3COO)2, Co(CH3COO)2·4H2O, anhydrous Co(NO3)2, Co(NO3)2·6H2O, and anhydrous CoC2O4.

[0018] Preferably, the nickel source is selected from one or more of anhydrous Ni(CH3COO)2, Ni(CH3COO)2·4H2O, anhydrous Ni(NO3)2, Ni(NO3)2·4H2O, and anhydrous NiC2O4.

[0019] Preferably, the doped W6+ The salt solution used is selected from one or more of Na2WO4·2H2O, anhydrous Na2WO4, and (NH4)2WO4;

[0020] The doped Se 6+ The salt solution used is selected from one or more of selenium powder, selenic acid, and potassium selenate.

[0021] Preferably, the oxidant is potassium permanganate.

[0022] Preferably, the mechanical grinding in step S2 is to perform two-step mechanical grinding of the cation-doped manganese dioxide obtained in step S1 with a cobalt source, a nickel source, and a lithium source by wet grinding and dry grinding. An appropriate amount of ethanol is added as a grinding aid during wet grinding.

[0023] Preferably, the high-temperature roasting in step S2 adopts a two-step sintering method. The first sintering reacts at a temperature of 300 - 600 °C in an oxygen or air atmosphere for 3 - 20 h, and the second sintering reacts at a temperature of 600 - 1000 °C in an oxygen or air atmosphere for 3 - 20 h.

[0024] Due to the adoption of the above technical solutions, the present invention has the following advantages and positive effects compared with the prior art:

[0025] In the present invention, by doping tungsten ions or selenium ions into the lithium-rich manganese-based cathode material, compared with the undoped material, the rate performance of the doped material has been significantly improved. Cation doping causes the lattice of the lithium-rich manganese-based cathode material to expand, increasing the layer spacing, which is beneficial to the migration of lithium ions in the bulk phase of the material. The strength of the W-O bond is higher than that of the Mn-O bond, which is beneficial to improving the lattice stability.

[0026] The present invention first uses the hydrothermal method to synthesize cation-doped manganese dioxide as a precursor, and then obtains the target product through a high-temperature solid-phase reaction with a nickel source, a cobalt source, and a lithium source. Compared with the co-precipitation method mostly used for doping modification and the solid-phase reaction of the compound of the doping element with the precursor of the lithium-rich material, this method of adding the doping element during the hydrothermal reaction to synthesize MnO2 can more accurately incorporate the doping element into the target position and can ensure that the doping element is more evenly dispersed in the bulk phase of the material rather than aggregating on the surface of the material, thereby playing a more extensive regulatory role on the lattice structure of the material. In addition, the raw materials used are inexpensive, the reaction conditions are mild, the method is simple to prepare, and there is the potential for mass production, which is conducive to commercialization. Description of the Drawings

[0027] Figure 1 It is the X-ray diffraction pattern of the w-doped lithium-rich manganese-based cathode material prepared in Example 1 of the present invention and the undoped lithium-rich manganese-based cathode material prepared in the comparative example;

[0028] Figure 2 Scanning electron microscope spectra of the W-doped lithium-rich manganese-based cathode material prepared in Example 1 of the present invention and the undoped lithium-rich manganese-based cathode material prepared in the comparative example

[0029] Figure 3 Transmission electron microscope spectra and high-resolution transmission electron microscope spectra of the W-doped lithium-rich manganese-based cathode material prepared in Example 1 of the present invention and the undoped lithium-rich manganese-based cathode material prepared in the comparative example;

[0030] Figure 4 Electrochemical test discharge data graph of the W-doped lithium-rich manganese-based cathode material prepared in Example 1 of the present invention as the cathode material and the undoped lithium-rich manganese-based cathode material prepared in the comparative example at a rate of 2.0C (1C = 250 mAh / g);

[0031] Figure 5 Rate performance graph of the W-doped lithium-rich manganese-based cathode material prepared in Example 1 of the present invention as the cathode material and the undoped lithium-rich manganese-based cathode material prepared in the comparative example;

[0032] Figure 6 Impedance graph of the W-doped lithium-rich manganese-based cathode material prepared in Example 1 of the present invention as the cathode material and the undoped lithium-rich manganese-based cathode material prepared in the comparative example.

[0033] Explanation of reference numerals: In the figure, LRM is the undoped lithium-rich manganese-based cathode material, and W-LRM is the lithium-rich manganese-based cathode material doped with W 6+ of the lithium-rich manganese-based cathode material. Detailed Description of the Invention

[0034] The following further describes in detail a cation-doped lithium-rich manganese-based cathode material and a preparation method thereof proposed by the present invention in conjunction with the accompanying drawings and specific examples. According to the following description, the advantages and features of the present invention will be clearer.

[0035] The present invention first synthesizes a cation-doped manganese dioxide as a precursor by a hydrothermal method, and then obtains a cation-doped lithium-rich manganese-based cathode material through a high-temperature solid-phase reaction with a nickel source, a cobalt source, and a lithium source. The chemical general formula of the cation-doped lithium-rich manganese-based cathode material is mLi2Mn 1-x O3A x ·(1 - m)LiTMO2, A is W and / or Se, 0.005 ≤ x ≤ 0.1, and the molar doping amount of the doping element is 0.5% - 10%.

[0036] Tungsten is a very abundant element in the earth's crust, with an exploitable reserve of about 2.9 million tons. At the same time, China is a major tungsten-producing country, ranking first in both production and exports in the world. In the field of catalysis, tungsten is a relatively commonly used doping element. Tungsten mainly exists in the form of 6-valent cations in nature. Due to its small radius, high valence, and strong polarization ability, tungsten mainly exists in the form of complex ions. By doping tungsten into the lithium-rich manganese-based cathode material, the ratio of LiMO2 and Li2MnO3 crystal domains in the material can be regulated, thereby regulating the average valence state of manganese in the material, achieving the inhibition of the Jahn-Teller effect occurring during the cycling process of the material, and alleviating the dissolution of Mn 2+ during the cycling process of the material, enabling the material to have a longer cycling life. In addition, the strength of the W-O bond is stronger than that of the Mn-O bond. The introduction of tungsten elements also improves the stability of lattice oxygen, which can reduce irreversible oxygen loss, and is beneficial to improving the first-cycle Coulomb efficiency and cycling stability of the material. Similar to the doping principle of W 6+ , Se 6+ can also bring the same effect. By replacing Mn in the bulk phase, improving the near-neighbor atomic structure around Mn ions, adjusting the bond length to improve stability, and adjusting covalency, etc., the dissolution of Mn 2+ during the cycling process of the material is alleviated.

[0037] The specific preparation method includes the following steps:

[0038] S1: Disperse the oxidant in a dilute nitric acid solution to form a mixed solution A. Disperse the manganese source and the salt of the doping element in an aqueous solution according to the doping ratio to form a mixed solution B. After mixing the mixed solution A and the mixed solution B evenly according to a volume ratio of 1:1, carry out a hydrothermal reaction at a temperature of 80 - 250 °C. After the reaction is completed, filter by suction and wash the precipitate with water and ethanol successively, and dry it at a temperature of 40 - 120 °C to obtain doped manganese dioxide;

[0039] S2: Mechanically grind and mix the doped manganese dioxide prepared in step S1 with the cobalt source, nickel source, and lithium source evenly, and then obtain the doped lithium-rich manganese-based cathode material by means of high-temperature roasting.

[0040] Among them, the dilute nitric acid solution is a mixed solution with a volume ratio of concentrated nitric acid to water of 1:40 - 1:100. Filtering by suction, washing, and drying means dispersing the obtained product in deionized water, washing the product with 200 - 500 mL of deionized water, and then washing the material with 20 - 50 mL of ethanol to accelerate the drying speed, and drying it at a temperature of 40 - 120 °C.

[0041] Preferably, the mixed solution B is added to the mixed solution A at a speed of 2 - 16 mL / min and stirred for 1 - 10 h to mix evenly.

[0042] Preferably, the manganese source is selected from one or more of anhydrous Mn(CH3COO)2, Mn(CH3COO)2·4H2O, anhydrous Mn(NO3)2, Mn(NO3)2·4H2O, anhydrous MnC2O4, and MnC2O4·2H2O.

[0043] Preferably, the cobalt source is selected from one or more of anhydrous Co(CH3COO)2, Co(CH3COO)2·4H2O, anhydrous Co(NO3)2, Co(NO3)2·6H2O, and anhydrous CoC2O4.

[0044] Preferably, the nickel source is selected from one or more of anhydrous Ni(CH3COO)2, Ni(CH3COO)2·4H2O, anhydrous Ni(NO3)2, Ni(NO3)2·4H2O, and anhydrous NiC2O4.

[0045] Preferably, the doped W 6+ The salt solution used is selected from one or more of Na2WO4·2H2O, anhydrous Na2WO4, and (NH4)2WO4;

[0046] The doped Se 6+ The salt solution used is selected from one or more of selenium powder, selenic acid, and potassium selenate.

[0047] Preferably, the oxidant is potassium permanganate.

[0048] Preferably, the mechanical grinding in step S2 is to perform two-step mechanical grinding of the cation-doped manganese dioxide obtained in step S1 with the cobalt source, nickel source, and lithium source by wet grinding and dry grinding, and an appropriate amount of ethanol is added as a grinding aid during wet grinding.

[0049] Preferably, the high-temperature roasting in step S2 adopts a two-step sintering method. The first sintering is carried out at a temperature of 300 - 600 °C in an oxygen or air atmosphere for 3 - 20 h, and the second sintering is carried out at a temperature of 600 - 1000 °C in an oxygen or air atmosphere for 3 - 20 h.

[0050] Example 1

[0051] A preparation method of a tungsten-doped lithium-rich manganese-based cathode material includes:

[0052] Step 1: Add 1.26 g of potassium permanganate to 40 mL of an aqueous solution containing 1 mL of nitric acid, and stir until the solution turns purplish red, named Solution A. Add 2.29 g of manganese acetate tetrahydrate and 0.129 g of sodium tungstate dihydrate to 40 mL of deionized water, and stir until the solution is clear and transparent, named Solution B. Use a peristaltic pump to add Solution B to Solution A at a rate of 16 mL / min and continuously stir for 30 min to obtain a brown suspension. Transfer the brown suspension to a 100 mL hydrothermal reactor, place it in an oven, react at 100 °C for 12 h, and after suction filtration, dry the sample in an oven at 80 °C for 12 h to obtain the precursor manganese dioxide doped with W.

[0053] Step 2: Weigh 0.549 g of manganese dioxide doped with W, mix it with 1.203 g of lithium nitrate, 0.88 g of nickel nitrate hexahydrate, and 0.89 g of cobalt nitrate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After thorough grinding, place the mortar in an oven at 80 °C and dry for 4 h, then perform dry grinding thoroughly. Then, calcine the uniformly ground powder in an air atmosphere at 450 °C for 6 h, slightly grind it, and then calcine it in an air atmosphere at 900 °C for 10 h to obtain the target product of the W-doped lithium-rich cathode material.

[0054] Example 2

[0055] A preparation method of a tungsten-doped lithium-rich manganese-based cathode material includes:

[0056] Step 1: Add 1.26 g of potassium permanganate to 40 mL of an aqueous solution containing 1 mL of nitric acid, and stir until the solution turns purplish red, named Solution A. Add 2.29 g of manganese acetate tetrahydrate and 0.139 g of ammonium tungstate to 40 mL of deionized water, and stir until the solution is clear and transparent, named Solution B. Add Solution B to Solution A at a rate of 16 mL / min and continuously stir for 30 min to obtain a brown suspension. Transfer the brown suspension to a 100 mL hydrothermal reactor, place it in an oven, react at 100 °C for 12 h, and after suction filtration, dry the sample in an oven at 80 °C for 12 h to obtain the precursor manganese dioxide doped with W.

[0057] Step 2: Weigh 0.549 g of manganese dioxide doped with W, mix it with 1.203 g of lithium acetate, 0.88 g of nickel acetate hexahydrate, and 0.89 g of cobalt acetate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After thorough grinding, place the mortar in an oven at 80 °C and dry for 4 h, then perform dry grinding thoroughly. Then, calcine the uniformly ground powder in an air atmosphere at 450 °C for 6 h, slightly grind it, and then calcine it in an air atmosphere at 900 °C for 10 h to obtain the target product of the W-doped lithium-rich cathode material.

[0058] Example 3

[0059] A method for preparing a tungsten-doped lithium-rich manganese-based positive electrode material comprises:

[0060] The first step is to add 1.26g potassium permanganate to 40mL of aqueous solution containing 1mL nitric acid, stir until the solution is purple-red, and name it solution A. Add 2.29g manganese acetate tetrahydrate and 0.129g sodium tungstate dihydrate to 40mL deionized water, stir until the solution is clear and transparent, and name it solution B. Add solution B to solution A at a rate of 16mL / min and continue stirring for 30min to obtain a brown suspension. Transfer the brown suspension to a 100mL hydrothermal reactor, place it in an oven, react at 100℃ for 12h, filter and place the sample in an oven at 80℃ for 12h to obtain precursor W-doped manganese dioxide.

[0061] The second step is to weigh 0.549g of W-doped manganese dioxide, mix it with 1.203g of lithium acetate, 0.88g of nickel acetate hexahydrate, and 0.89g of cobalt acetate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After sufficient grinding, place the mortar in an oven at 80°C to dry for 4h, and then fully dry grind. Then, the evenly ground powder is calcined at 450°C in an air atmosphere for 6h, and after a little grinding, it is calcined at 900°C in an air atmosphere for 10h to obtain the target product of W-doped lithium-rich positive electrode material.

[0062] Example 4

[0063] A method for preparing a selenium-doped lithium-rich manganese-based positive electrode material comprises:

[0064] The first step is to add 1.26g of potassium permanganate to 40mL of an aqueous solution containing 1mL of nitric acid, and stir until the solution is purple-red, named solution A. Add 2.29g of manganese acetate tetrahydrate and 0.139g of potassium selenate to 40mL of deionized water, stir until the solution is clear and transparent, and name it solution B. Add solution B to solution A at a rate of 16mL / min and continue stirring for 30min to obtain a brown suspension. Transfer the brown suspension to a 100mL hydrothermal reactor, place it in an oven, react at 100℃ for 12h, filter and place the sample in an oven at 80℃ for 12h to obtain precursor W-doped manganese dioxide.

[0065] The second step is to weigh 0.549g of Se-doped manganese dioxide, mix it with 1.203g of lithium acetate, 0.88g of nickel acetate hexahydrate, and 0.89g of cobalt acetate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After sufficient grinding, the mortar is placed in an oven at 80°C for 4 hours and then fully dry-ground. After that, the evenly ground powder is calcined at 450°C in an air atmosphere for 6 hours, and after a little grinding, it is calcined at 900°C in an air atmosphere for 10 hours to obtain the target product of Se-doped lithium-rich positive electrode material.

[0066] Example 5

[0067] A method for preparing a selenium-doped lithium-rich manganese-based positive electrode material comprises:

[0068] Step 1: Add 1.26g potassium permanganate to 40mL of aqueous solution containing 1mL nitric acid, stir until the solution is purple-red, named solution A. Add 2.29g manganese acetate tetrahydrate and 0.102g selenium powder to 40mL deionized water, stir until the solution is clear and transparent, named solution B. Add solution B to solution A at a rate of 16mL / min and continue stirring for 30min to obtain a brown suspension. Transfer the brown suspension to a 100mL hydrothermal reactor, place it in an oven, react at 100℃ for 12h, filter and place the sample in an oven at 80℃ for 12h to obtain the precursor Se-doped manganese dioxide.

[0069] The second step is to weigh 0.559g of Se-doped manganese dioxide, mix it with 1.203g of lithium acetate, 0.88g of nickel acetate hexahydrate, and 0.89g of cobalt acetate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After sufficient grinding, the mortar is placed in an oven at 80°C for 4 hours and then fully dry-ground. After that, the evenly ground powder is calcined at 450°C in an air atmosphere for 6 hours, and after a little grinding, it is calcined at 900°C in an air atmosphere for 10 hours to obtain the target product of W-doped lithium-rich positive electrode material.

[0070] Example 6

[0071] A method for preparing a tungsten-doped lithium-rich manganese-based positive electrode material comprises:

[0072] The first step is to add 1.26g potassium permanganate to 40mL of an aqueous solution containing 1mL of nitric acid, stir until the solution is purple-red, and name it solution A. Add 2.29g of manganese acetate tetrahydrate and 0.139g of ammonium tungstate to 40mL of deionized water, stir until the solution is clear and transparent, and name it solution B. Add solution B to solution A at a rate of 16mL / min and continue stirring for 30min to obtain a brown suspension. Transfer the brown suspension to a 100mL hydrothermal reactor, place it in an oven, react at 100℃ for 12h, filter and place the sample in an oven at 80℃ for 12h to obtain precursor W-doped manganese dioxide.

[0073] Step 2: Weigh 0.549 g of W-doped manganese dioxide, mix it with 1.213 g of lithium nitrate, 0.88 g of nickel nitrate tetrahydrate, and 0.89 g of cobalt nitrate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After thorough grinding, place the mortar in an oven at 80 °C and dry for 4 h, then perform dry grinding again. After that, calcine the uniformly ground powder in an air atmosphere at 450 °C for 6 h, slightly grind it, and then calcine it in an air atmosphere at 900 °C for 10 h to obtain the target product of the W-doped lithium-rich cathode material.

[0074] Example 7

[0075] A preparation method of a selenium-doped lithium-rich manganese-based cathode material includes:

[0076] Step 1: Add 1.26 g of potassium permanganate to 40 mL of an aqueous solution containing 1 mL of nitric acid, stir until the solution turns purple-red, and name it solution A. Add 2.29 g of manganese acetate tetrahydrate and 0.101 g of potassium selenate to 40 mL of deionized water, stir until the solution is clear and transparent, and name it solution B. Add solution B to solution A at a rate of 16 mL / min and continuously stir for 30 min to obtain a brown suspension. Transfer the brown suspension to a 100 mL hydrothermal reactor, place it in an oven, react at 100 °C for 12 h, filter it, and then place the sample in an oven at 80 °C and dry for 12 h to obtain the precursor W-doped manganese dioxide.

[0077] Step 2: Weigh 0.559 g of Se-doped manganese dioxide, mix it with 1.213 g of lithium nitrate, 0.88 g of nickel nitrate tetrahydrate, and 0.89 g of cobalt nitrate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After thorough grinding, place the mortar in an oven at 80 °C and dry for 4 h, then perform dry grinding again. After that, calcine the uniformly ground powder in an air atmosphere at 450 °C for 6 h, slightly grind it, and then calcine it in an air atmosphere at 900 °C for 10 h to obtain the target product of the W-doped lithium-rich cathode material.

[0078] Comparative example

[0079] A preparation method of a lithium-rich manganese-based cathode material includes:

[0080] Step 1: Add 1.26 g of potassium permanganate to 40 mL of an aqueous solution containing 1 mL of nitric acid, stir until the solution turns purple-red, and name it solution A. Add 2.29 g of manganese acetate tetrahydrate to 40 mL of deionized water, stir until the solution is clear and transparent, and name it solution B. Add solution B to solution A at a rate of 16 mL / min and continuously stir for 30 min to obtain a brown suspension. Transfer the brown suspension to a 100 mL hydrothermal reactor, place it in an oven, react at 100 °C for 12 h, filter it, and then place the sample in an oven at 80 °C and dry for 12 h to obtain the precursor W-doped manganese dioxide.

[0081] Step 2: Weigh 0.544 g of manganese dioxide, mix it with 1.213 g of lithium nitrate, 0.88 g of nickel nitrate tetrahydrate, and 0.89 g of cobalt nitrate hexahydrate in a mortar, and add an appropriate amount of ethanol as a grinding aid. After thorough grinding, place the mortar in an oven at 80 °C and dry for 4 h, then perform dry grinding again. After that, calcine the evenly ground powder in an air atmosphere at 450 °C for 6 h, slightly grind it, and then calcine it in an air atmosphere at 900 °C for 10 h to obtain the target product of the lithium-rich manganese-based cathode material.

[0082] Figures 1-3 They are the X-ray diffraction pattern, scanning electron microscope pattern, and transmission electron microscope pattern of the W-doped lithium-rich cathode material prepared in Example 1 and the undoped lithium-rich manganese-based material prepared in the comparative example. It can be seen from the X-ray pattern that the diffraction peaks of the prepared W-doped lithium-rich cathode material conform to the characteristics of the lithium-rich layered cathode material, and its diffraction peaks can well correspond to the R3m and C2m point groups. The (003) peak of the material is significantly higher than the (104) peak, indicating that the degree of Li / Ni ion mixing is relatively low, and its (018) peak and (110) peak can be clearly distinguished, which shows that the prepared material has a good layered structure. Figure 3 The high-resolution electron microscope pattern shows that the lattice spacing d = 0.439 nm of the W-doped lithium-rich material conforms to the (002) crystal plane of Li2MnO3 and is larger than that of the undoped material (d = 0.434 nm), which is beneficial to the transport of lithium ions in the bulk of the material and improves the rate performance of the material; Figure 2 Scanning electron microscope pattern, Figure 3 It can be seen from the transmission electron microscope pattern that the prepared W-doped lithium-rich cathode material has relatively uniform particle size, about 300 - 500 nm. Nanostructuring reduces the transport path of lithium ions and is beneficial to the improvement of rate performance.

[0083] Next, use the W-doped lithium-rich layered cathode material provided by the present invention to prepare a battery and then test the performance of the battery

[0084] Electrochemical performance test:

[0085] (1) Preparation of the battery

[0086] Before the electrochemical performance test, the sample needs to be made into a button-type lithium battery. The sample serves as the positive electrode material of the lithium battery, and a lithium sheet is used as the negative electrode. The manufacturing process includes four steps: pretreatment, slurry preparation, electrode fabrication, and battery assembly. The synthesized W-doped lithium-rich layered cathode material (80%) is mixed with a conductive agent Super-P (10%) and a binder polyvinylidene fluoride (10%) (by mass ratio), added with NMP, ground thoroughly, and then evenly coated on an aluminum foil. Then it is placed in a vacuum drying oven at 120 °C for 12 h. After drying, a coin cell positive electrode plate is made using a cutting machine, and the electrode plate is pressed at 4 - 6 atmospheres. Weigh the electrode plate coated with the active material, subtract the weight of the blank aluminum foil, and then calculate the weight of the active material in each electrode plate according to the proportion of the active material. Place the weighed electrode plate into an argon glove box.

[0087] A metallic lithium sheet is used as the negative electrode of the battery, and 1 M LiPF6-EC:DMC:EMC = 1:1:1 electrolyte is used. The coin cell assembly is carried out in an anhydrous and oxygen-free glove box filled with argon. The battery assembly process is as follows:

[0088] 1) Place the positive electrode plate in the center of the battery case, and use a pipette to drop 1 - 3 drops of electrolyte.

[0089] 2) Lay the PP separator flat on the electrode plate.

[0090] 3) Use a pipette to drop 1 - 3 drops of electrolyte in the center of the PP separator to completely wet the separator.

[0091] 4) Place the metallic lithium sheet in the center of the separator, making sure not to touch the battery case to avoid short-circuiting the battery.

[0092] 5) Place the stainless-steel gasket and spring plate on the lithium sheet in sequence and align them with the lithium sheet.

[0093] 6) Cover the negative electrode case, press it firmly, and use a sealer to seal the battery to complete the assembly. Let the battery stand for 5 - 12 h before performing the electrochemical test.

[0094] (2) Electrochemical performance test

[0095] The constant current charge-discharge cycle test of the sample is carried out on a LAND-201A battery test system, and the test voltage range is 2.0 - 4.8 V; the electrochemical impedance test is carried out on a CHIS600B electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.).

[0096] Figure 4 It is the discharge data graph of the electrochemical performance test for the W-doped lithium-rich manganese-based cathode material and the undoped lithium-rich manganese-based cathode material synthesized by the same method. Figure 5Rate performance graphs of the W-doped lithium-rich manganese-based cathode material and the undoped lithium-rich manganese-based cathode material synthesized by the same method. From Figure 4 It can be seen from the discharge data graph of the electrochemical performance test that after being formed for 3 cycles at a rate of 0.2C and then at a rate of 2C (1C = 250 mAh / g), the initial discharge specific capacity of the W-doped lithium-rich manganese-based cathode material is 180.2 mAh / g; while the discharge specific capacity of the undoped lithium-rich manganese-based cathode material is only 131.6 mAh / g, and the discharge capacity of the W-doped material is still as high as 151.4 mAh / g after 100 cycles, and the capacity retention rate is 84%. Such battery performance is very remarkable. From Figure 6 the rate performance graph, the rate performance of the W-doped lithium-rich manganese-based cathode material is significantly better than that of the undoped material. Combining Figure 6 with the impedance graph, it can be seen that the charge transfer impedance of the W-doped lithium-rich cathode material is smaller and the lithium ion transport rate is faster, which can well explain the significant improvement in the rate performance of the W-doped lithium-rich cathode material.

[0097] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, provided that these changes fall within the scope of the claims of the present invention and their equivalent technologies, they still fall within the protection scope of the present invention.

Claims

1. A cation-doped lithium-rich manganese-based cathode material, characterized in that, The cation-doped lithium-rich manganese-based cathode material is a nano-scale lithium-rich manganese-based cathode material obtained by a high-temperature solid-state reaction of manganese dioxide doped with W 6+ and / or Se 6+ as a precursor with a nickel source, a cobalt source, and a lithium source, and the molar doping amount of the cation is 0.5%-10%.

2. A preparation method of a cation-doped lithium-rich manganese-based cathode material, characterized in that, It includes the following steps: S1: Disperse a manganese source, a salt solution of a doped cation, nitric acid, and an oxidant in an aqueous solution, and synthesize cation-doped manganese dioxide by a hydrothermal method; S2: Mix the cation-doped manganese dioxide obtained in step S1 with a cobalt source, a nickel source, and a lithium source uniformly by mechanical grinding, and then obtain the cation-doped lithium-rich manganese-based cathode material by high-temperature calcination; wherein the doped cation is Se 6+ or W 6+ or Se 6+ and W 6+ are mixed.

3. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2, characterized in that, Disperse the oxidant in a dilute solution of nitric acid to obtain a mixed solution B; the hydrothermal method in step S1 is to disperse the manganese source and the salt of the doped cation in an aqueous solution according to the doping ratio to obtain a mixed solution A; After mixing the mixed solution A and the mixed solution B according to a volume ratio of 1:1, carry out a hydrothermal reaction at a temperature of 80 - 250 °C. After the reaction is completed, carry out suction filtration, washing, and drying; Among them, the dilute solution of nitric acid is a mixed solution with a volume ratio of concentrated nitric acid to water of 1:40 - 1:

100.

4. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 3, wherein The mixed solution B is added to the mixed solution A at a rate of 2 - 16 mL / min, and stirred for 1 - 24 h to be uniformly mixed.

5. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2 or 3, characterized in that, The manganese source is selected from one or more of anhydrous Mn(CH3COO)2, Mn(CH3COO)2·4H2O, anhydrous Mn(NO3)2, Mn(NO3)2·4H2O, anhydrous MnC2O4, and MnC2O4·2H2O.

6. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2 or 3, characterized in that, The cobalt source is selected from one or more of anhydrous Co(CH3COO)2, Co(CH3COO)2·4H2O, anhydrous Co(NO3)2, Co(NO3)2·6H2O, and anhydrous CoC2O4.

7. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2 or 3, characterized in that, The nickel source is selected from one or more of anhydrous Ni(CH3COO)2, Ni(CH3COO)2·4H2O, anhydrous Ni(NO3)2, Ni(NO3)2·4H2O, and anhydrous NiC2O4.

8. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2 or 3, characterized in that, The doped W 6+ The salt solution used is selected from one or more of Na2WO4·2H2O, anhydrous Na2WO4, and (NH4)2WO4; The doped Se 6+ The salt solution used is selected from one or more of selenium powder, selenic acid, and potassium selenate.

9. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2 or 3, characterized in that, The oxidant is potassium permanganate.

10. The preparation method of the cation-doped lithium-rich manganese-based cathode material according to claim 2, wherein The high-temperature calcination in step S2 adopts a two-step sintering method. The first-step sintering reacts at a temperature of 300 - 600 °C in an oxygen or air atmosphere for 3 - 20 h, and the second-step sintering reacts at a temperature of 600 - 1000 °C in an oxygen or air atmosphere for 3 - 20 h.

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