A method for preparing a lithium-rich manganese-based positive electrode material based on composite lithium molten salt low-temperature sintering

Abstract

This invention discloses a method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt, belonging to the technical field of lithium-ion battery cathode materials. The method includes the following steps: S1, preparing a manganese-nickel precursor with a manganese to nickel molar ratio of 0.70–0.80:0.20–0.30 using a co-precipitation method; S2, mixing the manganese-nickel precursor obtained in step S1 with composite lithium molten salt; S3, subjecting the mixture to drying and grinding pretreatment; S4, subjecting the pretreated powder from step S3 to two-step low-temperature sintering: pre-sintering at 450–550 °C for 4–6 h, and main sintering at 700–800 °C for 10–14 h, followed by cooling to obtain the lithium-rich manganese-based cathode material. This invention significantly reduces the sintering temperature, inhibits lithium volatilization and lattice oxygen loss, improves particle dispersibility, and the resulting material has advantages such as high initial coulombic efficiency, high specific capacity, stable cycling, and good rate performance, making it suitable for large-scale green production and widely applicable in the field of high-energy-density lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material preparation technology, specifically to a method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage systems, and portable electronic devices, the market has placed higher demands on the energy density, cycle life, cost control, and environmental friendliness of lithium-ion batteries. As a core component of lithium-ion batteries, the structural stability, reversible specific capacity, rate performance, and manufacturing cost of cathode materials directly affect the overall battery performance.

[0003] Lithium-rich manganese-based cathode materials are considered one of the most promising cathode materials for next-generation high-energy-density lithium-ion batteries due to their advantages such as high reversible specific capacity, high operating voltage, abundant manganese resources, low cost, and environmental friendliness. Existing methods for preparing lithium-rich manganese-based cathode materials mainly include solid-state methods, co-precipitation methods, and sol-gel methods, but high-temperature sintering is usually required to achieve crystal phase formation and structural ordering. In existing processes, the sintering temperature is generally high, typically above 800℃, and even reaching 900–1000℃.

[0004] However, the existing high-temperature sintering process generally has the following problems: (1) Lithium is easy to volatilize under high temperature conditions, which leads to the final material stoichiometry deviating from the design value, resulting in low initial coulombic efficiency and increased capacity decay; (2) High temperature easily induces the loss of lattice oxygen in lithium-rich manganese-based materials, especially irreversible oxygen loss of Li2MnO3 related structural units, which easily causes lattice distortion, structural collapse and decreased cycle stability; (3) High-temperature sintering easily causes excessive agglomeration and abnormal growth of particles, resulting in uneven particle size distribution, reduced specific surface area and increased lithium ion diffusion path, thereby affecting rate performance and electrochemical kinetic performance; (4) High-temperature process has high energy consumption and high requirements for equipment temperature resistance and production cost, which is not conducive to green and low-carbon manufacturing and large-scale application; (5) Although some existing low-temperature synthesis schemes can reduce the reaction temperature to a certain extent, they often have problems such as insufficient phase formation, insufficient crystal phase purity and poor layered structure order, making it difficult to balance low-temperature synthesis and material performance improvement.

[0005] In the prior art, CN106654250B discloses a method for preparing bubble-type lithium-rich manganese-based layered oxides and low-temperature molten salts, which uses mixed lithium salts to achieve low-temperature molten salt-assisted sintering. However, it does not precisely limit the lithium salt ratio, the two-step sintering process, and the precursor element ratio, leaving room for improvement in particle dispersibility and electrochemical performance. CN119858943A discloses a low-melting-point composite lithium salt and its preparation method, which uses melting... The preparation of composite lithium salts by gas atomization is a complex and costly process, which is not suitable for simple large-scale production. CN119786590A discloses a method for preparing lithium-rich manganese-based cathode materials with preferred orientation, which focuses on crystal plane control and does not systematically optimize the low-temperature sintering of composite lithium molten salts.

[0006] Therefore, developing a method for preparing lithium-rich manganese-based cathode materials with low sintering temperature, low energy consumption, controllable particle morphology, low lithium volatilization and oxygen loss, and excellent electrochemical performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] This invention provides a method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt, which solves the problems of lithium volatilization, lattice oxygen loss, particle agglomeration, high energy consumption, and poor phase formation and performance of existing low-temperature processes in traditional high-temperature sintering, and realizes the low-temperature, high-efficiency and high-performance preparation of lithium-rich manganese-based cathode materials.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt, comprising the following steps: S1. Preparation of manganese-nickel precursor: A manganese-nickel precursor with a manganese to nickel molar ratio of 0.70–0.80:0.20–0.30 was prepared by co-precipitation method; S2, Mixing of composite lithium molten salt: The manganese-nickel precursor obtained in step S1 is mixed with composite lithium molten salt; S3. Drying and Pretreatment: The mixture undergoes drying and grinding pretreatment; S4. Low-temperature two-step sintering: The powder pretreated in step S3 is subjected to two-step low-temperature sintering, with pre-firing at 450~550℃ for 4~6 h and main firing at 700~800℃ for 10~14 h, and then cooled to obtain lithium-rich manganese-based cathode material.

[0009] In the preferred embodiment, the manganese source of the manganese-nickel precursor is a manganese salt, and the nickel source is a nickel salt.

[0010] In a preferred embodiment, the molar ratio of manganese to nickel in the manganese-nickel precursor is 0.73–0.76:0.24–0.27.

[0011] In a further preferred embodiment, the molar ratio of manganese to nickel in the manganese-nickel precursor is 0.7479:0.2521.

[0012] In the preferred embodiment, the co-precipitation method specifically includes the following steps: preparing a metal salt solution by mixing the manganese source of the manganese-nickel precursor and the nickel of the manganese-nickel precursor, adding a precipitant and a complexing agent under stirring conditions, and carrying out an aging reaction. After the aging reaction is completed, a uniform precipitate is obtained, and after washing, filtering and drying, the manganese-nickel precursor is obtained.

[0013] In the preferred embodiment, the mass ratio of manganese-nickel precursor to composite lithium molten salt is 2~2.5:1.5~1.8.

[0014] In a preferred embodiment, the composite lithium molten salt is composed of LiOH·H2O and LiNO3.

[0015] In a further preferred embodiment, the molar ratio of LiOH·H2O to LiNO3 is 1:4 to 4:1.

[0016] In a further preferred embodiment, the molar ratio of LiOH·H2O to LiNO3 is 1:2 to 3:2.

[0017] In a further preferred embodiment, the molar ratio of LiOH·H2O to LiNO3 is 2:3.

[0018] In a preferred embodiment, the mixing is carried out by ball milling, and the average particle size after ball milling is 500~800 nm, so as to improve the dispersion uniformity of the precursor and the composite lithium molten salt.

[0019] In the preferred embodiment, the drying process is carried out at a temperature of 60–120 °C for a duration of 4–24 h.

[0020] In a preferred embodiment, the grinding pretreatment time is 5 to 30 minutes.

[0021] In a further preferred embodiment, the particle size after grinding is 300~nm.

[0022] In a further preferred embodiment, the grinding pretreatment time is 10 to 20 minutes.

[0023] In a further preferred embodiment, the grinding pretreatment time is 15 minutes.

[0024] In the preferred embodiment, the two-step low-temperature sintering is carried out in an oxygen or oxygen-enriched atmosphere.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Lowering the sintering temperature results in outstanding energy saving and emission reduction: This invention adopts a low-temperature molten salt-assisted sintering process, which completes the crystal phase synthesis and crystal growth of lithium-rich manganese-based cathode materials at a temperature lower than that of traditional high-temperature sintering (800-1000℃), thereby reducing the energy consumption of the heat treatment process, reducing the investment and operating costs of high-temperature equipment, and meeting the needs of green and low-carbon large-scale production.

[0026] (2) Improve particle morphology and dispersibility, and optimize ion / electron transport kinetics: Molten salt, as a liquid reaction medium, can play a good role in dispersion and barrier, suppressing excessive agglomeration and abnormal growth of particles at high temperature, and preparing lithium-rich manganese-based materials with uniform particle size and excellent dispersibility, effectively shortening the lithium ion diffusion path and improving the rate performance and kinetic characteristics of the material.

[0027] (3) Significantly improved comprehensive electrochemical performance: Thanks to the stable structure, controllable morphology and pure crystal phase, the first coulombic efficiency, reversible discharge specific capacity, cycle stability and rate performance of the prepared lithium-rich manganese-based materials are significantly improved compared with conventional temperature sintering, effectively solving the industry pain points of low first efficiency, fast capacity decay and poor high current charge and discharge performance of traditional high temperature sintering materials. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a flowchart of the present invention.

[0029] Figure 2 This is a diagram showing the charge and discharge performance during the first cycle.

[0030] Figure 3 This represents the specific discharge capacity of the battery at different discharge rates.

[0031] Figure 4 This is the electrochemical impedance spectroscopy diagram of the battery.

[0032] Figure 5 The graph shows the changes in discharge capacity and coulombic efficiency of the battery over 200 charge-discharge cycles.

[0033] Figure 6 Figure 1 shows the lithium-ion diffusion efficiency of the battery under charging and discharging conditions. Figure 2 shows the lithium-ion diffusion efficiency under charging conditions, and Figure 3 shows the lithium-ion diffusion efficiency under discharging conditions.

[0034] Figure 7 Figure 1 shows the morphology of the cathode material under SEM (scanning transmission electron microscopy). Figure 2 shows the cathode material obtained in Comparative Example 2; Figure 3 shows the cathode material obtained in Comparative Example 1; and Figure 4 shows the cathode material obtained in Example 1. Detailed Implementation

[0035] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.

[0036] Example 1 A method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt, the process is as follows: Figure 1 As shown, it includes the following steps: S1. Preparation of manganese-nickel precursor: MnSO4 H2O and NiSO4 A metal salt solution was prepared by adding NaOH as a precipitant and NH3 as a complexing agent under stirring at 800 rpm. H2O was used to control the reaction pH at 10.5, the reaction temperature at 55 °C, and the aging time at 12 h to obtain a uniform precipitate. After washing, filtering, and drying, a manganese-nickel precursor was obtained. The molar ratio of manganese to nickel in the manganese-nickel precursor was 0.7479:0.2521. S2. Mixing of composite lithium molten salt: 2.17g of the manganese-nickel precursor obtained in step S1 and 1.636g of composite lithium salt (including 0.472g of LiOH·H2O and 1.164g of LiNO3) are mixed; the molar ratio of LiOH·H2O to LiNO3 in the composite lithium molten salt is 2:3; the mixture is uniformly dispersed by ball milling, and the ball milling conditions are as follows: the ball milling jar is a polytetrafluoroethylene ball milling jar, the grinding beads are zirconia beads, the grinding aid is anhydrous ethanol, the ball milling time is 8 h, and the ball milling speed is 400 rpm; S3. Drying and pretreatment: After ball milling, the mixture is placed in a drying oven for drying; after drying, it is ground in a grinding bowl for 15 minutes to obtain a uniform precursor powder. S4. Low-temperature two-step sintering: The pretreated precursor powder from step S3 is loaded into a crucible and placed in an oxygen-filled tube furnace for sintering. The sintering procedure is as follows: first, pre-sinter at 500℃ for 5 h, then raise the temperature to 750℃ and hold for 12 h; after sintering, cool to room temperature with the furnace to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.53 Ni 0.27 O2.

[0037] Comparative Example 1 A method for preparing lithium-rich manganese-based cathode materials by low-temperature sintering is basically the same as that in Example 1, except that a single Li2CO3 is used as the lithium salt in step S2.

[0038] Comparative Example 2 A method for preparing lithium-rich manganese-based cathode materials by low-temperature sintering is basically the same as that of Comparative Example 1, except that the sintering temperature in step S4 is 850 °C.

[0039] Performance testing The cathode materials prepared in Example 1 and Comparative Examples 1-2 were used to assemble coin cells, and their electrochemical performance was tested. Figure 2 As shown in the first charge-discharge capacity data, Example 1 has a higher charge-discharge capacity compared to Comparative Examples 1 and 2, indicating that it has a higher energy density. Figure 3The discharge specific capacity of the battery at different discharge rates: Example 1 shows a higher discharge specific capacity than Comparative Examples 1 and 2 at discharge rates of 0.1C and 0.2C, indicating that the battery has low polarization, low internal resistance, and excellent rate performance, balancing high energy storage capacity and high power discharge capacity. Its capacity is less prone to shrinkage under heavy loads, and its output is more stable. Figure 4 As shown in the battery electrochemical impedance spectroscopy, compared to Comparative Examples 1 and 2, Example 1 represents a smaller resistance to battery interface reactions, faster lithium-ion migration, lower polarization, and higher charge-discharge efficiency. Figure 5 The discharge capacity of the battery after 200 charge-discharge cycles is given. Compared with Comparative Examples 1 and 2, Example 1 has a higher discharge capacity during the cycle, indicating that the battery has strong electrochemical stability and electrode structure stability. During the cycle, there are fewer losses such as material pulverization, particle breakage, electrolyte side reactions, and excessive growth of SEI film. The reversibility of lithium ion insertion and extraction is better, the internal resistance increase is small, the capacity decay rate is slow, and the anti-aging and anti-degradation capabilities are outstanding. Figure 6 The lithium-ion diffusion coefficient is denoted as ...

[0040] SEM images of the cathode materials prepared in Example 1 and Comparative Examples 1-2 are shown below. Figure 7 As shown, the particle size of the material morphology in Example 1 is smaller than that in Comparative Examples 1 and 2. The smaller particle size can effectively shorten the diffusion and migration path of lithium ions, increase the effective contact area between the electrode and the electrolyte, and accelerate the charge transfer kinetics.

[0041] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a lithium-rich manganese-based cathode material based on low-temperature sintering of a composite lithium molten salt, characterized in that, Includes the following steps: S1. Preparation of manganese-nickel precursor: A manganese-nickel precursor with a manganese to nickel molar ratio of 0.70–0.80:0.20–0.30 was prepared by co-precipitation method; S2, Mixing of composite lithium molten salt: The manganese-nickel precursor obtained in step S1 is mixed with composite lithium molten salt; S3. Drying and Pretreatment: The mixture undergoes drying and grinding pretreatment; S4. Low-temperature two-step sintering: The powder pretreated in step S3 is subjected to two-step low-temperature sintering, with pre-firing at 450~550 ℃ for 4~6 h, main firing at 700~800 ℃ for 10~14 h, and cooling to obtain lithium-rich manganese-based cathode material. 2.The method for preparing a lithium-rich manganese-based cathode material by low-temperature sintering based on composite lithium molten salt according to claim 1, characterized in that, The manganese source of the manganese-nickel precursor is a manganese salt, and the nickel source is a nickel salt. 3.The method for preparing a lithium-rich manganese-based cathode material by low-temperature sintering based on composite lithium molten salt according to claim 1, characterized in that, The manganese to nickel molar ratio of the manganese-nickel precursor is 0.73–0.76:0.24–0.

27.

4. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 1, characterized in that, The mass ratio of manganese-nickel precursor to composite lithium molten salt is 2~2.5:1.5~1.

8.

5. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 1, characterized in that, The composite lithium molten salt is composed of LiOH·H2O and LiNO3.

6. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 5, characterized in that, The molar ratio of LiOH·H2O to LiNO3 is 1:4 to 4:

1.

7. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 1, characterized in that, The mixing was carried out by ball milling, and the average particle size after ball milling was 500~800 nm.

8. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 1, characterized in that, The grinding pretreatment lasts for 5 to 30 minutes; the particle size after grinding is 300 to 500 nm.

9. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 1, characterized in that, The drying process is carried out at a temperature of 60–120 °C for a duration of 4–24 h.

10. The method for preparing lithium-rich manganese-based cathode materials based on low-temperature sintering of composite lithium molten salt according to claim 1, characterized in that, The two-step low-temperature sintering is carried out in an oxygen or oxygen-enriched atmosphere.

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