A lithium-rich manganese positive electrode material, a preparation method thereof and application thereof

Abstract

The application provides a lithium-rich manganese positive electrode material, and also provides a preparation method of the lithium-rich manganese positive electrode material, which comprises the following steps: preparing a lithium-rich manganese-based carbonate precursor according to a component proportion; mixing the lithium-rich manganese-based carbonate precursor with a lithium source according to a proportion, and then adding a tungsten source, and then pre-sintering and calcining under an air atmosphere to obtain the lithium-rich manganese positive electrode material. The application also provides a lithium ion battery. The lithium-rich manganese-based positive electrode material with excellent performance and low price is prepared by using the cheap tungsten element as an additive and by using a suitable sintering process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to lithium-rich manganese cathode materials, their preparation methods, and their applications. Background Technology

[0002] With the continuous improvement of lithium-ion battery materials, cell, and PACK manufacturing processes, lithium-ion batteries are finding increasing applications in the power battery field. The earliest commercially available layered cathode material, LiCoO2, is expensive, and its structure allows for the use of Li... + The energy density is relatively low, which conflicts with the high energy and low cost requirements of power batteries, and is currently mostly used in the 3C product field. Commercially available NCM ternary layered cathode materials have high energy density and good cycle performance, but their synthesis is difficult and their high-temperature safety is poor. Cobalt-free spinel nickel-manganese materials can achieve a discharge voltage of around 5V, and with high-voltage electrolytes, the energy density can reach 600Wh / kg, but they produce significant gas during cycling, and their high-temperature cycle performance needs further improvement. In addition, olivine-structured LiFePO4 cathode materials are inexpensive, have good cycle performance, and excellent safety, but their low energy density and poor rate performance make them suitable only for energy storage, mobile base stations, buses, ships, or commercial vehicles—fields where volumetric energy density requirements are not high.

[0003] Lithium-rich manganese-based cathode materials are considered to be xLi₂MnO₃·(1-x)LiMO₂ composite materials (where M represents Ni, Co, and Mn elements). They exhibit a high discharge specific capacity of 300 mAh / g at a low rate of 0.1C, significantly higher than the 210 mAh / g of high-nickel NCM811 ternary cathode materials at the same rate. This makes them the most promising cathode material for achieving a 400 Wh / kg cell energy density, and they hold broad application prospects as next-generation lithium-ion cathode materials. However, during the charging process of lithium-rich manganese-based cathode materials, the Ni phase in the LiMO₂ phase undergoes a change in the voltage range of 2.0–4.4V. 2+ and Co 3+ Oxidized into Ni 3+ and Co 4+ The process is the same as the charging mechanism of ternary NCM layered cathode materials, namely LiMO2→Li + +MO2+e - When the charging voltage exceeds 4.4V, a relatively flat voltage plateau appears around 4.5V. This stage occurs during the Li₂MnO₃ phase. + and O 2- The O2 is released, simultaneously generating electrochemically active MnO2. Researchers generally believe that during the charging process on this platform, O2... 2- The extraction of Li is accompanied by the precipitation of O2, which consumes free oxygen. The loss of free oxygen leads to the deintercalation of Li. +During subsequent discharge, it cannot be properly embedded back into the positive electrode material, causing Li + and O 2- It is extracted from xLi2MnO3·(1-x)LiMO2 in the form of Li2O, and the loss of oxygen vacancies also causes Mn 4+ From transition metal layer to Li + Layer migration generates a spinel phase, which is the "oxygen release" mechanism of lithium-rich manganese-based cathode materials. Furthermore, the released free oxygen, upon contact with the electrolyte, causes electrolyte oxidation, leading to severe gas generation in the battery. These factors contribute to the low initial efficiency and poor cycle performance of lithium-rich manganese-based cathode materials.

[0004] Therefore, in order to develop the next generation of high-capacity cathode materials, the drawbacks of low initial efficiency and poor cycle performance of lithium-rich manganese-based cathode materials urgently need to be addressed.

[0005] Chinese patent CN112599783A discloses a selenium-doped lithium-rich manganese-based cathode material, its preparation method, and its application. The preparation method includes: preparation of a mixture of materials, lithiation solution treatment, selenization doping, and selenization post-treatment. The prepared cathode material has a selenium content of 0-5%. The introduction of selenium can not only suppress the loss of lattice oxygen during cycling, but also suppress electrolyte decomposition, effectively alleviating the capacity decay and voltage drop problems of lithium-rich manganese-based cathode materials during cycling.

[0006] CN112875769A discloses a method for modifying the voltage decay and hysteresis of lithium-rich manganese-based cathode materials. This method involves adding osmium during the lithium formulation process. During calcination, osmium enters the crystal lattice of the lithium-rich material, anchoring lattice oxygen and modifying the material to suppress oxygen loss during cycling, thereby improving voltage retention and cycle stability. However, this method uses Os as a dopant, which is extremely expensive and unsuitable for large-scale production.

[0007] Chinese patent CN112599783A discloses a selenium-doped lithium-rich manganese-based cathode material, its preparation method, and its applications. Characterization revealed that the introduction of Se reduced the amount of oxygen vacancies, indicating that Se entered the oxygen vacancies. Se doping not only alleviates lattice oxygen loss but also eliminates oxygen free radicals generated during lattice oxygen oxidation, inhibiting electrolyte decomposition. However, this method is relatively cumbersome, requiring selenization doping followed by sintering after cathode sintering, adding an extra sintering process. Furthermore, the selenization post-treatment requires the use of organic solutions such as carbon disulfide and alcohol, further increasing the preparation cost.

[0008] The methods disclosed in the aforementioned patents for improving lithium-rich manganese-based cathode materials mostly involve selecting expensive transition metal elements as additives to enhance the MO bond energy between the transition metal elements and oxygen elements in the cathode material, thereby improving the cycle stability of the material. However, this method either requires expensive additives or additional sintering processes, making it unsuitable for production at the hundred-ton level. Summary of the Invention

[0009] The technical problem solved by this invention is to provide a method for preparing a lithium-rich manganese cathode material, which has good cycle stability.

[0010] In view of this, this application provides a lithium-rich manganese cathode material as shown in formula (I).

[0011] Li x W y Ni a Co b Mn c O2 (Ⅰ);

[0012] Wherein, 0.9≤x≤1.5, 0<y≤0.04, 0<a≤0.2, 0<b≤0.2, 0<c≤0.8.

[0013] Preferably, 1.0≤x≤1.2, 0.005≤y≤0.02, 0.1≤a≤0.18, 0.1≤b≤0.18, and 0.4≤c≤0.72.

[0014] Preferably, the lithium-rich manganese cathode material has an α-NaFeO2 crystal structure; the primary particles constituting the secondary particles have an average size of 200–500 nm and are randomly and tightly stacked; the secondary particles are spherical or near-spherical, with a particle size of 8–12 μm, a porosity greater than 1.5% and less than 3.5%, and a specific surface area of ​​3–6 m². 2 / g.

[0015] This application also provides a method for preparing the lithium-rich manganese cathode material, including the following steps:

[0016] Lithium-rich manganese-based carbonate precursors were prepared according to the component ratios.

[0017] The lithium-rich manganese-based carbonate precursor is mixed with a lithium source according to the specified ratio, and then a tungsten source is added. The mixture is pre-calcined and then calcined in an air atmosphere to obtain a lithium-rich manganese cathode material.

[0018] Preferably, the preparation method of the lithium-rich manganese-based carbonate precursor is as follows:

[0019] According to the specified ratio, nickel source, cobalt source, manganese source, precipitant, and complexing agent are subjected to a co-precipitation reaction to obtain a lithium-rich manganese-based carbonate precursor.

[0020] Preferably, the precipitant is a sodium carbonate solution, and the complexing agent is selected from one or more of citric acid, ammonia, ethylenediaminetetraacetic acid, sodium tripolyphosphate, sodium pyrophosphate, sodium hexametaphosphate, diethanolamine, and diethylenetriaminepentacarboxylate.

[0021] Preferably, the reaction temperature is 50–100°C, the time is 5–10 h, and the pH value is 7.0–10.0.

[0022] Preferably, the air flow rate in the air atmosphere is 0-15 L / min.

[0023] Preferably, the pre-firing temperature is 500-600℃ and the holding time is 5-15h; the calcination temperature is 800-900℃ and the holding time is 20-40h.

[0024] This application also provides a lithium-ion battery, including a positive electrode and a negative electrode, wherein the material of the positive electrode is selected from the lithium-rich manganese positive electrode material described above or the lithium-rich manganese positive electrode material prepared by the preparation method described above.

[0025] This application provides a method for preparing lithium-rich manganese cathode material. First, a lithium-rich manganese-based carbonate precursor is prepared, then mixed with a lithium salt, and finally a tungsten source is added. The mixture is pre-calcined and then calcined in air to obtain the lithium-rich manganese cathode material. This application introduces tungsten, which possesses 5d electrons, into the cathode material to anchor lattice oxygen and stabilize the material's crystal structure. Simultaneously, the addition of the tungsten source during the mixing stage of the precursor and lithium source allows the tungsten source to be doped during the sintering process of the cathode material, eliminating the need for additional additive sintering steps. Introducing an appropriate amount of air during sintering can improve the internal structure of the secondary spheres in the lithium-rich manganese cathode material, thereby enhancing the cycle stability of the cathode material. Attached Figure Description

[0026] Figure 1 Cross-sectional views of the cathode materials in Example 11 (left) and Comparative Example 3 (right);

[0027] Figure 2 Here is a SEM cross-sectional image of the lithium-rich cathode material in Example 5;

[0028] Figure 3 This is a schematic diagram of the process for preparing lithium-rich cathode materials according to the present invention. Detailed Implementation

[0029] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0030] In view of the problems in improving the cost of doped materials and preparation process in existing lithium-rich manganese-based cathode materials, this application provides a lithium-rich manganese cathode material that uses tungsten as an additive and employs a suitable sintering process to prepare a high-performance and low-cost lithium-rich manganese cathode material. Specifically, this invention discloses a lithium-rich manganese cathode material as shown in formula (I).

[0031] Li x W y Ni a Co b Mn c O2 (Ⅰ);

[0032] Wherein, 0.9≤x≤1.5, 0<y≤0.04, 0<a≤0.2, 0<b≤0.2, 0<c≤0.8.

[0033] More specifically, in the lithium-rich manganese cathode material, 1.0≤x≤1.2, 0.005≤y≤0.02, 0.1≤a≤0.18, 0.1≤b≤0.18, and 0.4≤c≤0.72.

[0034] In a specific embodiment, the lithium-rich manganese cathode material is specifically Li. 1.2 W y Ni (0.1625-y) Co 0.1625 Mn 0.675 O2, y is 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035 or 0.04, and the air flow rate during the sintering process is 0, 5, 10 and 15 L / min. The lithium-rich manganese cathode material of this application is mainly for carbonate precursors with Ni:Co:Mn = 1:1:4.

[0035] In this invention, the lithium-rich manganese cathode material has an α-NaFeO2 crystal structure; the primary particles constituting the secondary particles are uniform in size, with an average particle size of 200–500 nm, and are randomly and tightly stacked; the secondary particles are spherical or near-spherical, with a particle size of 8–12 μm, a compact profile without breaks, a porosity greater than 1.5% and less than 3.5%, and a specific surface area of ​​3–6 m². 2 / g. Testing revealed that the thermal decomposition initiation temperature of the lithium-rich manganese cathode material is greater than 260℃, with the thermal decomposition peak between 260 and 275℃; the compacted density of the lithium-rich manganese cathode material powder at 3.5T is 2.75–3.0 g / cm³. 3 The pressure resistance of the particles is 80-100 MPa.

[0036] This application also provides a method for preparing lithium-rich manganese cathode materials, the specific process of which is as follows: Figure 3 As shown, it includes the following steps:

[0037] Lithium-rich manganese-based carbonate precursors were prepared according to the component ratios.

[0038] The lithium-rich manganese-based carbonate precursor is mixed with a lithium source according to the specified ratio, and then a tungsten source is added. The mixture is pre-calcined and then calcined in an air atmosphere to obtain a lithium-rich manganese cathode material.

[0039] In the process of preparing lithium-rich manganese cathode material as described above, this application first prepares lithium-rich manganese-based carbonate precursor material. The preparation method is well known to those skilled in the art, and this application has no particular limitations on it. More specifically, the preparation method of the lithium-rich manganese-based carbonate precursor is as follows:

[0040] According to the specified ratio, nickel source, cobalt source, manganese source, precipitant, and complexing agent are subjected to a co-precipitation reaction to obtain a lithium-rich manganese-based carbonate precursor.

[0041] In the preparation process of the above-mentioned lithium-rich manganese-based carbonate precursor, the nickel source, cobalt source, and manganese source are all materials well known to those skilled in the art, and this application does not impose any particular restrictions on them; for example, in a specific embodiment, the nickel source is selected from nickel sulfate hexahydrate, the cobalt source is selected from cobalt sulfate heptahydrate, and the manganese source is selected from manganese sulfate. The precipitant is specifically selected from sodium carbonate solution, and the complexing agent is selected from one or more of citric acid, ammonia, ethylenediaminetetraacetic acid, sodium tripolyphosphate, sodium pyrophosphate, sodium hexametaphosphate, diethanolamine, and diethylenetriaminepentacarboxylate. The temperature of the coprecipitation reaction is 50-80℃, the time is 6-10h, and the pH value is 7-10.

[0042] According to this invention, after obtaining a lithium-rich manganese-based carbonate precursor, it is mixed with a lithium source and then a tungsten source is added. After thorough mixing, the mixture is pre-calcined and then calcined under different air flow rates to obtain a tungsten-doped lithium-rich manganese cathode material. In the above process, the tungsten source is tungsten metal or a tungsten metal oxide. The air flow rate is 0–15 L / min, more specifically, 5–10 L / min. Insufficient or excessive oxygen content degrades the electrical performance of the cathode material because, during high-temperature sintering, insufficient oxygen cannot remove the Co in the precursor. 2+ Oxidized to Co 3+ And provide enough oxygen vacancies, while excess oxygen will cause Ni to... 2+ Oxidation to Ni 3+This results in Li / Ni mixing; additionally, CO2 gas is generated during the sintering process of the carbonate precursor, and an appropriate air flow rate can carry away the waste gas; therefore, the air flow rate is related to the mass of the precursor. Experimental results show that the optimal positive electrode performance is obtained when the precursor mass is 1 kg and the air flow rate is 10 L / min. The addition of the tungsten source is used to anchor lattice oxygen and suppress its release; too little dopant will not achieve the desired effect. As mentioned above, the oxidation and release of some lattice oxygen during charging can provide additional capacity, while excessive dopant will excessively suppress the activity of lattice oxygen, causing capacity decay. The pre-calcination temperature is 500–600℃, and the holding time is 5–15 h; the calcination temperature is 800–900℃, and the holding time is 20–40 h.

[0043] This application also provides a lithium-ion battery, which includes a positive electrode and a negative electrode, wherein the material of the positive electrode is selected from the lithium-rich manganese positive electrode material described in the above-described scheme.

[0044] This application provides a lithium-rich manganese cathode material in which a tungsten source additive is added during the mixing of the precursor and lithium source. This eliminates the need for an additional additive sintering process, reducing the ternary sintering to a 2-stage process and saving costs. Introducing tungsten, an additive with 5d electrons, enhances the stability of lattice oxygen by strengthening the MO bonds in the crystal structure, thereby improving the cycle stability of the cathode material. Furthermore, providing appropriate airflow during sintering improves the internal structure of the material; suitable internal porosity increases electrolyte wetting and improves the Li-Li ratio. + The goal is to achieve a high mobility without causing side reactions in the electrolyte within the cathode material, which would worsen the material's cycle stability.

[0045] To further understand the present invention, the preparation method of the lithium-rich cathode material provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0046] Example 1

[0047] Prepare a 2.0 mol / L sulfate solution with a nickel-cobalt-manganese ratio of 1:1:4 using deionized water. Prepare a 2 mol / L Na₂CO₃ solution and a suitable concentration of complexing agent mixture in another reactor. Pour 1 L of water into a 2 L glass reactor, purge with nitrogen for 5 hours, and maintain the temperature at 60°C using a constant temperature water bath. Simultaneously pump the sulfate solution and the precipitant and complexing agent mixture into the reactor at a flow rate of 10 mL / min, maintaining the pH of the reactor solution at approximately 8.5. Stop the reaction after 8 hours. The raw material solution was introduced and allowed to stand for 12 hours. After filtration, washing, and drying, a lithium-rich manganese precursor was obtained. Battery-grade LiOH·H2O was mixed with the above precursor at a molar ratio of 1.4:1, and then 0.0200 mol of nano-sized tungsten oxide was added. The mixture was stirred at 1000 rpm / min for 8 minutes using a small high-speed mixer. The temperature was increased from room temperature to 500℃ at a heating rate of 2℃ / min under an air flow rate of 5 L / min and held for 10 hours. Then, the temperature was increased to 850℃ at the same heating rate and held for 24 hours. After natural cooling, the lithium-rich manganese cathode material Li was obtained. 1.2 W 0.02 Ni 0.1425 Co 0.1625 Mn 0.675 O2.

[0048] Example 2

[0049] Prepare a 2.0 mol / L sulfate solution with a nickel-cobalt-manganese ratio of 1:1:4 using deionized water. Prepare a 2 mol / L Na₂CO₃ solution and a suitable concentration of complexing agent mixture in another reactor. Pour 1 L of water into a 2 L glass reactor, purge with nitrogen for 5 hours, and maintain the temperature at 60°C using a constant temperature water bath. Simultaneously pump the sulfate solution and the precipitant and complexing agent mixture into the reactor at a flow rate of 10 mL / min, maintaining the pH of the reactor solution at approximately 8.5. Stop the reaction after 8 hours. The raw material solution was introduced and allowed to stand for 12 hours. After filtration, washing, and drying, a lithium-rich manganese precursor was obtained. Battery-grade LiOH·H2O was mixed with the above precursor at a molar ratio of 1.4:1, and then 0.0050 mol of nano-sized tungsten oxide was added. The mixture was stirred at 1000 rpm / min for 8 minutes using a small high-speed mixer. The temperature was increased from room temperature to 500℃ at a heating rate of 2℃ / min under an air flow rate of 10 L / min and held for 10 hours. Then, the temperature was increased to 850℃ at the same heating rate and held for 24 hours. After natural cooling, the lithium-rich manganese cathode material Li was obtained. 1.2 W 0.005 Ni 0.1575 Co 0.1625 Mn 0.675 O2.

[0050] Example 3

[0051] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0100 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.01 Ni 0.1525 Co 0.1625 Mn 0.675 O2.

[0052] Example 4

[0053] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0150 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.015 Ni 0.1475 Co 0.1625 Mn 0.675 O2.

[0054] Example 5

[0055] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0200 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.02 Ni 0.1425 Co 0.1625 Mn 0.675 O2.

[0056] Example 6

[0057] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0250 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.025 Ni 0.1375 Co 0.1625 Mn 0.675 O2.

[0058] Example 7

[0059] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0300 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.03 Ni 0.1325 Co 0.1625 Mn 0.675 O2.

[0060] Example 8

[0061] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0350 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li.1.2 W 0.035 Ni 0.1275 Co 0.1625 Mn 0.675 O2.

[0062] Example 9

[0063] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0400 mol, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.04 Ni 0.1225 Co 0.1625 Mn 0.675 O2.

[0064] Example 10

[0065] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0200 mol, the air flow rate during sintering is 15 L / min, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.02 Ni 0.1425 Co 0.1625 Mn 0.675 O2.

[0066] Example 11

[0067] The difference from Example 2 is that the amount of tungsten oxide nanoparticles used is 0.0200 mol, the air flow rate during sintering is 0 L / min, and the molecular formula of the resulting lithium-rich manganese cathode material is Li. 1.2 W 0.02 Ni 0.1425 Co 0.1625 Mn 0.67 5O2.

[0068] Comparative Example 1

[0069] Prepare a 2.0 mol / L sulfate solution with a nickel-cobalt-manganese ratio of 1:1:4 using deionized water. Prepare a 2 mol / L Na₂CO₃ solution and a complexing agent mixture of appropriate concentration in another mixing vessel. Pour 1 L of water into a 2 L glass reactor, purge with nitrogen for 5 hours, and maintain the temperature at 60°C using a constant temperature water bath. Simultaneously pump the sulfate solution and the precipitant and complexing agent mixture into the reactor at a flow rate of 10 mL / min, maintaining the pH of the reactor solution at 8. After reacting for approximately 8 hours, the feed solution was stopped, and the mixture was allowed to stand for 12 hours. After filtration, washing, and drying, a lithium-rich manganese precursor was obtained. Battery-grade LiOH·H₂O was mixed with the precursor at a molar ratio of 1.4:1. The mixture was stirred at 1000 rpm / min for 8 minutes using a small high-temperature mixer. The temperature was then increased from room temperature to 500°C at a rate of 2°C / min under an air flow rate of 10 L / min and held for 10 hours. The temperature was then increased to 850°C at the same rate and held for 24 hours. After natural cooling, the lithium-rich manganese cathode material Li₂ was obtained. 1.2 Ni 0.1625 Co 0.1625 Mn 0.675 O2.

[0070] Comparative Example 2

[0071] Prepare a 2.0 mol / L sulfate solution with a nickel-cobalt-manganese ratio of 1:1:4 using deionized water. Prepare a 2 mol / L Na₂CO₃ solution and a suitable concentration of complexing agent mixture in another reactor. Pour 1 L of water into a 2 L glass reactor, purge with nitrogen for 5 hours, and maintain the temperature at 60°C using a constant temperature water bath. Simultaneously pump the sulfate solution and the precipitant and complexing agent mixture into the reactor at a flow rate of 10 mL / min, maintaining the pH of the reactor solution at approximately 8.5. Stop the reaction after 8 hours. The raw material solution was introduced and allowed to stand for 12 hours. After filtration, washing, and drying, a lithium-rich manganese precursor was obtained. Battery-grade LiOH·H2O was mixed with the above precursor at a molar ratio of 1.4:1, and then 0.0500 mol of nano-sized tungsten oxide was added. The mixture was stirred at 1000 rpm / min for 8 minutes using a small high-speed mixer. The temperature was increased from room temperature to 500℃ at a heating rate of 2℃ / min under an air flow rate of 10 L / min and held for 10 hours. Then, the temperature was increased to 850℃ at the same heating rate and held for 24 hours. After natural cooling, the lithium-rich manganese cathode material Li was obtained. 1.2 W 0.05 Ni 0.1125 Co 0.1625 Mn 0.675 O2.

[0072] Comparative Example 3

[0073] Prepare a 2.0 mol / L sulfate solution with a nickel-cobalt-manganese ratio of 1:1:4 using deionized water. Prepare a 2 mol / L Na₂CO₃ solution and a suitable concentration of complexing agent mixture in another reactor. Pour 1 L of water into a 2 L glass reactor, purge with nitrogen for 5 hours, and maintain the temperature at 60°C using a constant temperature water bath. Simultaneously pump the sulfate solution and the precipitant and complexing agent mixture into the reactor at a flow rate of 10 mL / min, maintaining the pH of the reactor solution at approximately 8.5. Stop the reaction after 8 hours. The raw material solution was introduced and allowed to stand for 12 hours. After filtration, washing, and drying, a lithium-rich manganese precursor was obtained. Battery-grade LiOH·H2O was mixed with the above precursor at a molar ratio of 1.4:1, and then 0.0200 mol of nano-sized tungsten was added. The mixture was stirred at 1000 rpm / min for 8 minutes using a small high-speed mixer. The temperature was increased from room temperature to 500℃ at a heating rate of 2℃ / min under an air flow rate of 20 L / min and held for 10 hours. Then, the temperature was increased to 850℃ at the same heating rate and held for 24 hours. After natural cooling, the lithium-rich manganese cathode material Li was obtained. 1.2 W 0.02 Ni 0.1425 Co 0.1625 Mn 0.675 O2.

[0074] Electrochemical performance tests were conducted on the lithium-rich manganese cathode materials obtained in the comparative and example studies using coin cells. The test method was as follows: the cathode material, superconducting carbon black (SP), and binder (PVDF) were mixed in a mass ratio of 92:4:4, NMP was added as a solvent to form a slurry, which was then coated onto aluminum foil and vacuum dried at 120°C for 5 hours to obtain the cathode sheet. A lithium metal sheet was used as the anode. The cathode sheet, anode sheet, separator, and electrolyte were assembled into a coin cell for electrochemical performance testing. The test voltage range was 2.0–4.8V, and 1C = 250mA / g.

[0075] Table 1 presents the electrical performance data of the cathode materials prepared in each specific embodiment and comparative example.

[0076] Table 1. Statistical table of electrical performance data of cathode materials in the examples and comparative examples.

[0077]

[0078]

[0079]

[0080]

[0081] As shown in the table, the cathode materials of Examples 1, 5, 10, 11 and Comparative Example 3 were all doped with W element at a molar ratio of 0.02%. The difference was the air flow rate during sintering. Example 5 had the best electrical performance, with a first charge capacity of 310 mAh / g at 0.1C rate, a first discharge capacity of up to 298 mAh / g, an initial efficiency of 96.1%, and a capacity retention rate of 88.6% after 100 cycles at 1C rate.

[0082] Figure 1 (Left) is a cross-sectional view of the cathode material in Example 11. The scanning electron microscope image shows that the internal porosity of the cathode material without additional oxygen (air atmosphere) during sintering is higher than that of the cathode material with an air flux of 10 L / min. Furthermore, the former exhibits a more pronounced core-shell structure. This is mainly due to the presence of Co during sintering. 2+ and Mn 2+ It will be oxidized to Co 3+ and Mn 4+ When oxygen is deficient, the oxygen required for the above oxidation reaction comes partly from inside the cathode material, which causes the internal structure of the material to collapse. The high porosity inside the cathode material increases its contact area with the electrolyte, accelerating the side reactions between the cathode material and the electrolyte. The core-shell structure reflects the inconsistency of the internal composition of the cathode material. The above two phenomena will have a negative impact on the capacity and cycle performance of the material. Figure 1 (Right) is a cross-sectional view of the cathode material in Comparative Example 3. This cathode material exhibits a clear hollow structure, and some secondary spheres show cracks. This is because, under high-flux air conditions, excessive oxygen will cause the Ni in the co-precipitated precursor to be destroyed. 2+ Co 2+ and Mn 2+ The oxide is oxidized into a higher valence state independent phase oxide, separating from the xLi2MnO3·(1-x)LiMO2 composite phase, resulting in deteriorated electrical performance and reduced compaction density of the cathode material. In summary, the airflow rate during sintering has a significant impact on the electrical performance of the cathode material; insufficient oxygen content prevents the oxidation of Co in the precursor. 2+ Fully oxidized to Co 3+ This results in low electronic conductivity of the material, affecting its rate performance, while Ni... 2+ It will be oxidized into Ni again. 3+ This increases the degree of Li / Ni mixing in the cathode material, while also causing a noticeable hollow structure inside the secondary spheres, which reduces the material's cycle stability.

[0083] Examples 2-9 all use the same sintering process, with an air flow rate of 10 L / min during sintering. The electrical performance first increases and then decreases as the doping amount of W gradually increases. This is because the introduction of tungsten stabilizes the lattice oxygen in the crystal structure, alleviates the "oxygen release" phenomenon during cycling, and improves the cycling stability of the material. However, when there are too many doping elements, especially when the amount of tungsten oxide is greater than 0.04 mol, the electrical performance of the resulting lithium-rich manganese cathode material deteriorates sharply. This may be because excessive trace elements over-bind the lattice oxygen, leading to a decrease in the proportion of active oxygen and a decrease in capacity during the first charge process. Figure 2 This is a SEM cross-sectional image of the cathode material prepared in Example 5. With appropriate W doping and a suitable sintering air flow rate, the resulting cathode material has a dense structure without delamination. The suitable internal porosity can improve the wettability of the electrolyte and enhance the Li... + The mobility is such that it does not cause side reactions of the electrolyte within the positive electrode material. Simultaneously, due to... Figure 2 It is known that the lithium-rich manganese cathode material has an α-NaFeO2 crystal structure; the primary particles constituting the secondary particles are uniform in size, with an average particle size of 200-500 nm, and are randomly and tightly stacked; the secondary particles are spherical or near-spherical, with a particle size of 8-12 μm, a tight profile without breaks, a porosity greater than 1.5% and less than 3.5%, and a specific surface area of ​​3-6 m². 2 / g. Testing revealed that the thermal decomposition initiation temperature of the lithium-rich manganese cathode material is greater than 260℃, with the thermal decomposition peak between 260 and 275℃; the compacted density of the lithium-rich manganese cathode material powder at 3.5T is 2.75–3.0 g / cm³. 3 The pressure resistance of the particles is 80-100 MPa.

[0084] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0085] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lithium-rich manganese cathode material as shown in formula (Ⅰ), Li x W y Ni a Co b Mr c O2 (Ⅰ); in, 1 < x ≤ 1.5, 0 < y ≤ 0.04, 0 < a ≤ 0.2, 0 < b ≤ 0.2, 0 < c ≤ 0.8; The primary particles of the lithium-rich manganese cathode material have an average size of 200-500 nm and are randomly and tightly stacked; the secondary particles are spherical or near-spherical with a particle size of 8-12 μm. The lithium-rich manganese cathode material has an α-NaFeO2 crystal structure; a porosity greater than 1.5% and less than 3.5%; and a specific surface area of ​​3~6 m². 2 / g; The thermal decomposition initiation temperature of the lithium-rich manganese cathode material is greater than 260℃, and the thermal decomposition peak is between 260 and 275℃; at 3.5T, the compacted density of the lithium-rich manganese cathode material powder is 2.75~3.0 g / cm³. 3 The compressive strength of the particles is 80~100MPa; The lithium-rich manganese cathode material is obtained by mixing a lithium-rich manganese-based carbonate precursor with a lithium source and then adding a tungsten source, followed by pre-calcination and calcination in an air atmosphere, wherein the air flow rate is 5~15L / min.

2. The lithium-rich manganese cathode material according to claim 1, characterized in that, 1 < x ≤ 1.2, 0.005 ≤ y ≤ 0.02, 0.1 ≤ a ≤ 0.18, 0.1 ≤ b ≤ 0.18, 0.4 ≤ c ≤ 0.

72.

3. The method for preparing the lithium-rich manganese cathode material according to claim 1, comprising the following steps: Lithium-rich manganese-based carbonate precursors were prepared according to the component ratios. The lithium-rich manganese-based carbonate precursor was mixed with a lithium source according to the specified ratio, and then a tungsten source was added. The mixture was pre-calcined and then calcined in an air atmosphere to obtain a lithium-rich manganese cathode material. In the air atmosphere, the air flow rate is 5~15L / min.

4. The preparation method according to claim 3, characterized in that, The specific method for preparing the lithium-rich manganese-based carbonate precursor is as follows: According to the specified ratio, nickel source, cobalt source, manganese source, precipitant, and complexing agent are subjected to a co-precipitation reaction to obtain a lithium-rich manganese-based carbonate precursor.

5. The preparation method according to claim 4, characterized in that, The precipitant is a sodium carbonate solution, and the complexing agent is selected from one or more of citric acid, ammonia, ethylenediaminetetraacetic acid, sodium tripolyphosphate, sodium pyrophosphate, sodium hexametaphosphate, diethanolamine, and diethylenetriaminepentacarboxylate.

6. The preparation method according to claim 4, characterized in that, The reaction is carried out at a temperature of 50-100℃ for 5-10 hours, with a pH value of 7.0-10.

0.

7. The preparation method according to claim 3, characterized in that, The pre-firing temperature is 500~600℃, and the holding time is 5~15h; the calcination temperature is 800~900℃, and the holding time is 20~40h.

8. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, The cathode material is selected from the lithium-rich manganese cathode material according to any one of claims 1 to 2 or the lithium-rich manganese cathode material prepared by the preparation method according to any one of claims 3 to 7.

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