Modified lithium-rich manganese-based layered oxide cathode material and its preparation method

Abstract

This invention discloses a modified lithium-rich manganese-based morphological oxide cathode material and its preparation method. The preparation method includes: (1) mixing and grinding ammonium fluoride particles, biomass carbon source, and lithium-rich manganese-based morphological oxide cathode material at a mass ratio of 0.001-0.1:0.01-0.30:1; (2) pressing the ground mixture into tablets and sintering them in a sealed environment at a sintering temperature of 180℃-400℃ for 1-3 hours, followed by natural cooling to room temperature to obtain a sintered product; (3) grinding, washing, and drying the sintered product, followed by further grinding and sieving to obtain the final product. The preparation method of this invention improves the capacity stability and voltage decay problems of lithium-rich manganese-based morphological oxide cathode materials during cycling. The process is simple, energy-efficient, and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material preparation technology, specifically to a modified lithium-rich manganese-based basal oxide cathode material and its preparation method. Background Technology

[0002] Lithium-ion rechargeable batteries hold a significant position in consumer electronics and power batteries due to their high energy density, portability, and high stability. However, limited by the development of positive and negative electrode materials, their actual energy density is generally between 150Wh / kg and 200Wh / kg. The relatively low capacity and energy density of positive electrode materials are more prominent than those of negative electrode materials and other components, and are a key factor restricting the development of lithium-ion batteries. Practical lithium-ion battery positive electrode material systems mainly include lithium cobalt oxide, lithium iron phosphate, and nickel-cobalt-manganese ternary layered oxides, but their capacity still falls short of application requirements. Lithium-rich manganese-based oxide positive electrode materials have attracted widespread attention due to their high specific capacity (250mAh / g to 300mAh / g) and high operating voltage, and hold the promise of breaking through existing bottlenecks in positive electrode materials and achieving ultra-high energy density. However, lithium-rich manganese-based oxide materials face problems such as oxygen loss, irreversible crystal phase transformation, dissolution of transition metal ions, electrolyte decomposition, and gas escape during charge-discharge reactions. The resulting poor cycle capacity and voltage stability are significant factors limiting their practical application. Furthermore, lithium-rich manganese-based oxide cathode materials also face challenges such as poor rate performance and low coulombic efficiency. To address these issues, extensive modification work has been conducted through doping and coating to improve their stability. Lun et al. discovered that fluorine doping can suppress Mn content in lithium-rich manganese-based oxide cathode materials. 3+ The Jahn-Teller distortion caused orbital rearrangement and introduced more manganese to participate in redox reactions, thereby improving the overall capacity of the material. Guo et al. achieved a capacity of 217 mAh g⁻¹ at 0.5C rate by introducing fluorine and aluminum co-doping. -1 The capacity retention rate after 150 cycles is 88.21%, and the material can still maintain 157 mAh g at 10C. -1 Specific capacity. In addition, heterostructure coating is also a common way to improve the performance of lithium-rich manganese-based oxide cathode materials. Ma et al. used Al... 3+ Chemical conversion in phosphate buffer resulted in the formation of a highly homogeneous AlPO4 coating layer on the surface of the lithium-rich manganese-based oxide cathode material. The material was subjected to [further action] at 30 mA g [g / L]. -1 It has a current density of 282.1 mAh g. -1 The discharge specific capacity. In 2018, Zhang et al. constructed a 14nm layer of Li4Mn5O on the surface of lithium-rich manganese-based oxide cathode material. 12Studies have shown that spinel coatings reduce activation and oxygen loss above 4.5V during the initial charging phase, increasing coulombic efficiency and significantly improving cycle stability and rate performance. The capacity retention rate of the material at 0.1C for 300 cycles is 83.1%. However, the effects of single doping or coating are limited and cannot take into account the differences in structural and performance degradation mechanisms driven by the different structural characteristics of the surface and bulk phases of lithium-rich manganese-based oxide cathode materials. This results in performance shortcomings under actual operating conditions, keeping the material somewhat distant from practical applications. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a modified lithium-rich manganese-based basal oxide cathode material with excellent electrochemical performance and cycle stability and its preparation method. The preparation method is simple, energy-efficient, and suitable for large-scale production, and is expected to promote the practical application of lithium-rich manganese-based basal oxide cathode materials.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A method for preparing a modified lithium-rich manganese-based layered oxide cathode material includes the following steps:

[0006] (1) Mix and grind ammonium fluoride particles, biomass carbon source and lithium-rich manganese-based layered oxide cathode material in a mass ratio of 0.001~0.1∶0.01~0.30∶1, and press them into discs with a diameter of 10mm~30mm under a pressure of 3MPa~20MPa;

[0007] (2) The disc is sintered in a closed environment at a temperature of 180℃~400℃ for 1h~3h. After sintering, it is naturally cooled to room temperature to obtain the sintered product.

[0008] (3) After grinding, washing and drying the sintered product, grind and sieve it again to obtain the final product.

[0009] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, in step (1), the biomass carbon source is one or more of sucrose, carrageenan, and cellulose acetate.

[0010] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, the biomass carbon source is sucrose.

[0011] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, in step (2), the sintering heating rate is 6℃ / min to 10℃ / min.

[0012] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, in step (1), the mass ratio of the ammonium fluoride particles, the biomass carbon source and the lithium-rich manganese-based basal oxide cathode material is 0.01-0.05:0.01-0.05:1.

[0013] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, in step (1), the mixing and grinding time is 5 min to 60 min.

[0014] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, in step (3), the drying temperature is 40℃~60℃ and the drying time is 1h~6h.

[0015] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, preferably, in step (3), the washing is performed using water.

[0016] In the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, it is further preferred that the mixing and grinding time in step (1) is 30 min.

[0017] In a more preferred embodiment of the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, step (2) involves a sintering temperature of 400°C and a sintering time of 3 hours.

[0018] In a more preferred embodiment of the above-mentioned method for preparing modified lithium-rich manganese-based basal oxide cathode material, the sintering heating rate in step (2) is 7°C / min.

[0019] As a general technical concept, the present invention also provides a modified lithium-rich manganese-based basal oxide cathode material prepared by the above-mentioned method.

[0020] Preferably, the modified lithium-rich manganese-based morphological oxide cathode material described above has a core structure of lithium-rich manganese-based morphological oxide cathode material and an outer layer of fluorine-doped spinel phase structure and nitrogen-doped carbon coating layer obtained in situ.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] The preparation method of this invention uses ammonium fluoride and biochar to synergistically modify lithium-rich manganese-based basal oxide cathode materials. High-temperature heat treatment decomposes ammonium fluoride into gaseous hydrogen fluoride and ammonia. A gas-solid reaction method is then used to further react the gaseous substances with the lithium-rich manganese-based basal oxide cathode material in a sealed crucible. This induced treatment yields fluoride-doped and spinel-phase-modified lithium-rich manganese-based basal oxide cathode materials. Simultaneously, the biochar source reacts in situ with the ammonia generated from the decomposition of ammonium fluoride under high-temperature treatment to form nitrogen-doped amorphous conductive carbon material, improving the electronic conductivity of the cathode material. Fluoride ion doping in the modified material improves the surface structural stability, inhibits oxygen loss under high voltage, suppresses transition metal ion dissolution and electrolyte decomposition, and significantly enhances its cycle stability. The interface matching degree between the spinel phase derived in situ under ammonia-induced oxidation and the lithium-rich manganese-based matrix oxide cathode material is relatively high. This provides a stable interface and facilitates the interfacial transfer and deintercalation of lithium ions during charging and discharging, thereby improving ionic conductivity. Meanwhile, nitrogen-doped biomass carbon has high electronic conductivity, which in turn improves its rate performance.

[0023] (2) The preparation method of the present invention is a one-step synthesis method. It only requires mixing and grinding ammonium fluoride particles, biomass carbon source and lithium-rich manganese-based morphological oxide cathode material in proportion, pressing into tablets and calcining in a closed environment of 180℃~400℃ for 1h~3h to synthesize the modified cathode material of the present invention. Compared with the prior art, the preparation method of the present invention is simple, energy-saving and low-cost. The synthesized cathode material has excellent electrical properties, which is conducive to industrial application and helps to promote the practical application of lithium-rich manganese-based morphological oxide cathode material.

[0024] (3) The modified lithium-rich manganese-based basal oxide cathode material of the present invention improves the reaction kinetics of the material under the synergistic effect of ammonium fluoride and biochar, and at the same time significantly suppresses voltage decay, indicating that the crystal phase transformation in the material is suppressed. The doping of fluorine ions also helps to improve the problem of transition metal ion dissolution in the cathode material. The cycle stability of the cathode material is significantly improved, and the electrochemical performance of the material is thus comprehensively improved. Attached Figure Description

[0025] Figure 1 The images show scanning electron microscope (SEM) images of the unmodified lithium-rich manganese-based morphological oxide cathode material. Figures a, b, and c are SEM images of the unmodified lithium-rich manganese-based morphological oxide cathode material at magnifications of 10 k, 50 k, and 100 k, respectively.

[0026] Figure 2 The images shown are scanning electron microscope (SEM) images of the modified lithium-rich manganese-based basal oxide cathode material prepared according to embodiments of the present invention. Figures a, b, and c are SEM images of the modified lithium-rich manganese-based basal oxide cathode material at magnifications of 10k, 50k, and 100k, respectively.

[0027] Figure 3 Figure 1 shows a transmission electron microscope (TEM) image of the modified lithium-rich manganese-based morphological oxide cathode material prepared according to an embodiment of the present invention. Figure 2a is a TEM image of the modified lithium-rich manganese-based morphological oxide cathode material, and Figure 3b is a high-resolution TEM image of the modified lithium-rich manganese-based morphological oxide cathode material.

[0028] Figure 4 The first charge-discharge curves of the lithium-rich manganese-based layered oxide cathode material half-cells of the embodiments and comparative examples 1 and 2 of the present invention at 1C are shown.

[0029] Figure 5 The figures show the capacity cycling curves of the lithium-rich manganese-based substrate oxide cathode materials in the embodiments and comparative examples 1 and 2 of this invention at 1C. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. In the following embodiments, unless otherwise specified, the raw materials and instruments used are commercially available, and the data obtained are the average values ​​of three or more repeated experiments. In the following embodiments, the room temperature conditions are all between 20°C and 30°C.

[0031] In this invention, the lithium-rich manganese-based layered oxide cathode material is prepared by the traditional carbonate co-precipitation method. The specific experimental steps are as follows: First, a mixed solution of manganese sulfate, cobalt sulfate, and nickel sulfate, each with a metal ion concentration of 1 mol / L, a sodium carbonate solution of 2 mol / L, and an ammonia solution of 0.6 mol / L are prepared according to the stoichiometric ratio. The three solutions are pumped into a reaction vessel under argon atmosphere protection using a peristaltic pump at a feed rate of 1 mL / min. The stirring speed inside the vessel is 650 rpm, and the vessel temperature is controlled at 60℃. The pH value of the reaction system is measured using a pH meter and controlled at 8.0 ± 0.1. After the reaction, the mixture is aged for 12 h, filtered, washed three times with deionized water, then washed three times with ethanol, and vacuum dried at 80℃ for 12 h to obtain Mn. 0.675 Co 0.1625 Ni 0.1625 A pink CO3 precursor was then produced. Subsequently, the precursor was ball-milled with a 5% excess of lithium carbonate for 30 min, followed by pre-sintering at 500℃ for 10 h and then secondary sintering at 900℃ for 15 h to obtain a lithium-rich layered oxide cathode material, Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0032] Example:

[0033] A method for preparing the modified lithium-rich manganese-based layered oxide cathode material of the present invention includes the following steps:

[0034] (1) Place 0.05g ammonium fluoride particles, 0.05g sucrose and 1.0g lithium-rich manganese base oxide cathode material in a ball mill jar and grind at 350rpm for 1h.

[0035] (2) Take out the ground mixture and press it into a disc with a diameter of 12 mm under a pressure of 10 MPa. Place it in a sealed crucible and then put the sealed crucible containing the mixture into a muffle furnace. The muffle furnace is heated to 400 °C at 7 °C / min and held for 3 h. Then it is naturally cooled to room temperature to obtain the sintered product.

[0036] (3) Grind the obtained sintered product, wash it three times with deionized water, dry it in a forced-air drying oven at 60°C for 4 hours, and then grind it again through a 200-mesh sieve to obtain the final product.

[0037] A modified lithium-rich manganese-based basal oxide cathode material was prepared by the preparation method of this embodiment.

[0038] Scanning electron microscopy revealed that the unmodified lithium-rich manganese-based layered oxide cathode material consisted of secondary spherical particles formed by the accumulation of tiny primary particles. The surfaces of these primary particles were smooth. Figure 1 As shown, in this embodiment, the surface of the modified lithium-rich manganese-based layered oxide cathode material becomes rough, and the loose porous structure becomes dense, as... Figure 2 As shown.

[0039] The core structure of this modified lithium-rich manganese-based layered oxide cathode material is a lithium-rich manganese-based layered oxide cathode material, with an outer layer consisting of an in-situ derived fluorine-doped spinel phase structure and a nitrogen-doped carbon coating layer, such as... Figure 3 As shown in (a)(b).

[0040] A 5% (w / w) PVDF (polyvinylidene fluoride) solution was prepared by dissolving PVDF in NMP (N-methylpyrrolidone) and stirring until homogeneous. The modified lithium-rich manganese-based layered oxide cathode material, conductive carbon black SP, and the PVDF solution were mixed at a mass ratio of 8:1:10 and ball-milled for 30 minutes to obtain a viscous cathode slurry. The cathode slurry was evenly coated onto aluminum foil using a 100-mesh scraper, vacuum dried at 110°C for 12 hours, and then rolled using a roller press to obtain the cathode sheet. The cathode sheet was punched into 12mm round sheets using a punching machine, weighed, and placed in a glove box for assembling 2032-type button batteries. A Celgard 2400 separator was used, the electrolyte lithium salt composition was 1.2M LiPF6, the solvent was EC (ethylene carbonate):EMC (ethyl methyl carbonate) = 3:7, and 2% VC (ethylene carbonate) additive was added. The assembled button cells were left to stand for 12 hours before electrochemical performance testing was conducted.

[0041] Electrochemical test results show that, after synergistic modification with ammonium fluoride and biomass carbon source, the modified lithium-rich manganese-based layered oxide cathode material prepared in this embodiment has an initial discharge capacity of 275.3 mAh / g at 0.2C, a cycle capacity of 175.0 mAh / g after 100 cycles at 1C, and a voltage decay of 1.82 mV per cycle.

[0042] Comparative Example 1:

[0043] Electrochemical performance tests were conducted on the unmodified lithium-rich manganese-based layered oxide cathode material according to the steps of the examples. The results showed that the unmodified lithium-rich manganese-based layered oxide cathode material had an initial discharge capacity of 259 mAh / g at 0.2C, a cycle capacity of 163.0 mAh / g after 100 cycles at 1C, and a voltage decay of 2.71 mV per cycle.

[0044] Comparative Example 2:

[0045] A method for preparing a modified lithium-rich manganese-based basal oxide cathode material is basically the same as the example, except that no biomass carbon source is added in step (1).

[0046] A modified lithium-rich manganese-based basal oxide cathode material was prepared by the method described in this comparative example.

[0047] Electrochemical tests were conducted following the steps outlined in the examples. The results showed that, compared to the unmodified cathode material in Comparative Example 1, the initial discharge capacity at 0.2C increased from 259.0 mAh / g to 259.3 mAh / g after ammonium fluoride-induced modification in Comparative Example 2, but the change was not significant. After 100 cycles at 1C, the specific capacity increased from 163.0 mAh / g to 164.7 mAh / g, and the voltage decay decreased from 2.71 mV per cycle to 2.38 mV per cycle. Although the voltage decay and cycle capacity of the material improved somewhat after simple ammonium fluoride-induced modification, the effect was not ideal.

[0048] Table 1. Comparison of electrochemical performance between Comparative Examples 1 and 2 and the Example (average of three measurements)

[0049]

[0050] Cyclic performance curves: At room temperature (25°C), the assembled coin cells were subjected to constant current charge-discharge and rate performance tests at a specific current density, with a cutoff voltage range of 2.0V to 4.8V (vs Li). + / Li), the result is as follows Figure 4 and Figure 5 As shown.

[0051] Combining the data in Table 1 and Figure 4 , Figure 5As can be seen, compared with Comparative Examples 1 and 2, especially compared with Comparative Example 1, the electrochemical performance of the Examples was significantly improved. The initial discharge capacity at 0.2C increased from 259.0 mAh / g to 275.3 mAh / g, the specific capacity after 100 cycles at 1C increased from 163.0 mAh / g to 175.0 mAh / g, and the voltage decay decreased from 2.71 mV per cycle to 1.82 mV per cycle, a reduction of 32.8%, demonstrating a significant effect in suppressing voltage decay.

[0052] In summary, after the synergistic modification treatment induced by biomass carbon source and ammonium fluoride, the discharge specific capacity and cycle capacity of the lithium-rich manganese-based basal oxide cathode material under high current are significantly improved. This is due to the high ionic conductivity of the spinel phase generated in situ. On the other hand, the biomass carbon source reacts with the ammonia gas generated by the decomposition of ammonium fluoride under high temperature treatment to form nitrogen-doped amorphous conductive carbon material in situ, which improves the electronic conductivity of the material. The combined effect improves the reaction kinetics of the material, and at the same time, the suppression effect on voltage decay is significant, indicating that the crystal phase transformation in the material is suppressed. The doping of fluoride ions also helps to improve the problem of transition metal ion dissolution in the cathode material. The cycle stability of the cathode material is significantly improved, and the electrochemical performance of the material is thus comprehensively improved.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a modified lithium-rich manganese-based layered oxide cathode material, characterized in that, Includes the following steps: (1) Mix and grind ammonium fluoride particles, biomass carbon source and lithium-rich manganese-based layered oxide cathode material in a mass ratio of 0.01~0.05∶0.01~0.05∶1, and press them into round sheets with a diameter of 10mm~30mm under a pressure of 3MPa~20MPa; (2) The disc is sintered in a closed environment at a temperature of 180℃~400℃ for 1h~3h and a heating rate of 6℃ / min~10℃ / min. After sintering, it is naturally cooled to room temperature to obtain the sintered product. (3) After grinding, washing and drying the sintered product, grind and sieve it again to obtain the final product; In step (1), the biomass carbon source is one or more of sucrose, carrageenan and cellulose acetate.

2. The method for preparing the modified lithium-rich manganese-based layered oxide cathode material according to claim 1, characterized in that, The biomass carbon source is sucrose.

3. The method for preparing the modified lithium-rich manganese-based basaltic oxide cathode material according to claim 1, characterized in that, In step (1), the mixing and grinding time is 5 min to 60 min.

4. The method for preparing the modified lithium-rich manganese-based basaltic oxide cathode material according to claim 1, characterized in that, In step (3), the drying temperature is 40℃~60℃ and the drying time is 1h~6h.

5. The method for preparing the modified lithium-rich manganese-based layered oxide cathode material according to claim 1, characterized in that, In step (2), the heating rate of the sintering is 7°C / min.

6. A modified lithium-rich manganese-based basal oxide cathode material prepared by a method according to any one of claims 1 to 5.

7. The modified lithium-rich manganese-based layered oxide cathode material according to claim 6, characterized in that, The core structure of the modified lithium-rich manganese-based morphological oxide cathode material is lithium-rich manganese-based morphological oxide cathode material, and the outer layer is a fluorine-doped spinel phase structure and a nitrogen-doped carbon coating layer obtained in situ.

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