Fluoride solid electrolyte coated high-nickel single crystal material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium battery positive electrode materials, and particularly relates to a fluoride solid electrolyte coated high-nickel single crystal material and a preparation method and application thereof.The preparation method comprises the steps that a nickel-cobalt-manganese hydroxide precursor and lithium hydroxide are subjected to ball-milling mixing and segmented sintering, and the high-nickel positive electrode material is obtained; the method comprises the following steps: putting lithium carbonate and a high-nickel positive electrode material into ionic liquid BmimBF4, heating and stirring to obtain turbid liquid; and then adding nitrate, heating and stirring for reaction, washing and drying to obtain the fluoride solid electrolyte coated high-nickel single crystal material. According to the method, a fluoride solid electrolyte is adopted to coat a high-nickel single crystal material, so that the high-voltage stability, the conductivity and the air stability of the positive electrode material are synchronously improved; and the coating temperature is low, the structure of the high-nickel single crystal material is not damaged, the obtained coating layer is more uniform, and the cycle stability of the positive electrode material is more favorably improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery cathode material technology, specifically relating to a fluoride solid electrolyte-coated high-nickel single crystal material, its preparation method, and its application. Background Technology

[0002] The advantages of high-nickel single-crystal materials lie in their high energy density (nickel content increases capacity), excellent structural stability (single-crystal particles reduce grain boundary cracks), and long cycle life (strong resistance to mechanical breakage and electrolyte erosion); however, they also have problems such as complex synthesis process (high-temperature sintering easily leads to agglomeration), poor kinetic performance (slow lithium diffusion from single-crystal particles), and many surface side reactions (high nickel activity leads to interface instability). Further optimization of preparation technology and surface modification are needed.

[0003] Coating is a common technique for improving the overall performance of high-nickel single-crystal materials. Fluorides are a common type of coating material, such as CaF2, CeF3, LaF3, and NiF2. However, this generally requires high-temperature (≥500℃) sintering to achieve coating. During high-temperature processing, not only is the structure of the high-nickel single-crystal material itself damaged, but it is also difficult to obtain a uniform coating layer. Furthermore, general fluoride-coated materials have poor ionic conductivity. For example, in the article titled "Enhanced electrochemical performance and thermal properties of Ni-rich LiNi..." 0.8 Co 0.1 Mn 0.1 In their paper, "O2cathode material via CaF2 coating," Yuan et al. obtained CaF2-coated high-nickel LiNi through high-temperature treatment at 500℃. 0.8 Co 0.1 Mn 0.1 While the CaF2 coating effectively improves the electrochemical performance of O2 cathode materials, it is worth noting that the resulting coating is not uniform, and at room temperature, the ionic conductivity of CaF2 is extremely low, which hinders ion transport. These are problems faced by using traditional fluoride coatings to coat high-nickel single-crystal materials. Summary of the Invention

[0004] One objective of this invention is to provide a method for preparing a high-nickel single-crystal material coated with a fluoride solid electrolyte. This method uses a fluoride solid electrolyte to coat the high-nickel single-crystal material, thereby simultaneously improving the high-voltage stability, conductivity, and air stability of the cathode material. Compared with existing technologies, this method has a lower coating temperature, does not damage the structure of the high-nickel single-crystal material itself, and results in a more uniform coating layer.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a fluoride solid electrolyte coated with a high-nickel single crystal material includes the following steps: S1. A nickel-cobalt-manganese hydroxide precursor and lithium hydroxide are mixed, ball-milled, and sintered in stages to obtain a high-nickel cathode material; S2. Lithium carbonate and high-nickel cathode material are placed in ionic liquid BmimBF4, heated and stirred to obtain a homogeneous mixed solution; then nitrate is added, heated and stirred to react, washed and filtered with anhydrous ethanol, and dried to obtain high-nickel single crystal material.

[0006] Preferably, in step S1, the chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni x Co y Mn z (OH)₂, 0.9≤ x ≤0.95, 0≤ y ≤0.1, x + y =1; the molar ratio of the nickel cobalt manganese hydroxide precursor to lithium hydroxide is 1:1.03 to 1:1.05.

[0007] Preferably, in step S2, the molar ratio of lithium carbonate, high-nickel cathode material, and nitrate is 0.3~0.6:100:0.1~0.2; the nitrate is one of Ga(NO3)3·6H2O, Al(NO3)3·9H2O, or Y(NO3)3·6H2O; the heating and stirring temperature is 80℃~120℃, the stirring time is 10~16h; and the material is washed 3~5 times with anhydrous ethanol.

[0008] The second objective of this invention is to provide a fluoride solid electrolyte coated with a high-nickel single crystal material prepared by the above-mentioned preparation method.

[0009] The third objective of this invention is to provide an application of the above-mentioned fluoride solid electrolyte-coated high-nickel single crystal material in lithium-ion battery cathode materials.

[0010] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1) In the synthesis of high-nickel single-crystal materials coated with fluoride solid electrolytes, this invention utilizes the ionic liquid BmimBF4 as both a fluorine source and a reaction medium. Ionic liquids possess high polarity and strong coulombic interaction, effectively stabilizing the reaction transition state. In particular, the directional alignment of its cations and anions provides a local electric field, reducing the transition state energy and significantly lowering the energy barrier of the fluoride solid electrolyte reaction pathway. Therefore, compared to existing technologies, the coating of high-nickel single-crystal materials with fluoride solid electrolytes can be achieved within a temperature range of 80℃ to 120℃, significantly reducing the coating temperature and avoiding damage to the single-crystal structure caused by high temperatures. Furthermore, the lower coating temperature facilitates the formation of a uniform coating layer. A uniform fluoride solid electrolyte coating layer better isolates the single-crystal material from direct contact with the electrolyte, inhibiting electrolyte corrosion and transition metal dissolution, mitigating structural phase transitions and lattice oxygen loss in high-nickel materials, delaying capacity decay, and improving the material's cycle performance.

[0011] 2) The fluoride solid electrolyte coating layer on the surface of the high-nickel single crystal material prepared in this invention has good ionic conductivity, which can accelerate the charging and discharging process of Li + Diffusion at the cathode-electrolyte interface reduces impedance, ensuring that lithium ions can still efficiently insert into / extract from the cathode material under high voltage and high rate charge / discharge, maintaining the battery's high capacity output and fast response capability, and improving the material's charge / discharge performance.

[0012] 3) The fluoride solid electrolyte coating layer on the surface of the high-nickel single crystal material prepared by this invention exhibits excellent high-voltage stability, maintaining good stability even within a voltage window of approximately 5V. Therefore, at a high voltage of 4.5V, it can effectively mitigate the dissolution of transition metals (such as Ni, Co, Mn, etc.) in the cathode material during charging and discharging, thus mitigating the problem of reduced active material in the cathode material caused by the dissolution of transition metals into the electrolyte, thereby improving the cycle stability of the battery.

[0013] 4) The fluoride solid electrolyte coating layer on the surface of the high-nickel single crystal material prepared by the present invention can effectively reduce the reaction of the high-nickel single crystal material with CO2 and H2O in a humid environment, reduce the generation of residual lithium on the material surface (such as Li2CO3 / LiOH), avoid the problem of slurry gelation, and make the high-nickel single crystal material more suitable for high voltage and long life requirements. Attached Figure Description

[0014] Figure 1 XRD pattern of the fluoride solid electrolyte coated high-nickel single crystal material prepared in Example 1; Figure 2 SEM image of the fluoride solid electrolyte coated with high-nickel single crystal material prepared in Example 1; Figure 3 SEM image of the calcium fluoride-coated high-nickel single crystal material prepared in Comparative Example 4; Figure 4 Rate performance diagrams of the fluoride solid electrolyte coated high-nickel single crystal material prepared in Example 1 and the uncoated high-nickel single crystal material prepared in Comparative Example 1; Figure 5 The graphs show the cycling performance of the fluoride solid electrolyte-coated high-nickel single-crystal material prepared in Example 1 and the uncoated high-nickel single-crystal material prepared in Comparative Example 1. Detailed Implementation

[0015] The nickel-cobalt-manganese hydroxide precursor used in the embodiments and comparative examples listed in this invention is Ni. 0.9 Co 0.05 Mn 0.05 (OH)2 or Ni 0.95 Co 0.01 Mn 0.04 (OH)2, the method of the present invention is also applicable to materials conforming to the chemical formula Ni x Co y Mn 1-x-y (OH)2(0.9≤ x ≤0.95, 0≤y≤0.1, x Other nickel-cobalt-manganese hydroxide precursors (+y=1) are used to synthesize high-nickel cathode materials.

[0016] The present invention will be further described below with reference to embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto. The nickel-cobalt-manganese hydroxide precursor used in the present invention was purchased from Shenzhen Youyan Technology Co., Ltd. (product name: NCM9 series precursor); other pharmaceuticals and reagents were purchased from Aladdin.com or Sinopharm Reagents.com. Example 1

[0017] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0018] S2: 0.003 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 500 ml of ionic liquid BmimBF4, heated and stirred at 100 °C for 3 h, then 0.001 mol Ga(NO3)3·6H2O was added and the reaction was continued to be stirred for 13 h; the mixture was washed and filtered 4 times with anhydrous ethanol, and dried under vacuum at 80 °C for 20 h to obtain fluoride solid electrolyte coated high-nickel single crystal material.

[0019] Depend on Figure 1 The XRD pattern shows that the high-nickel cathode material exhibits high characteristic peak intensity and no other impurity peaks, indicating that fluoride coating does not damage the material's structure. Meanwhile, from... Figure 2 The SEM images showed no obvious particle aggregation on the material surface, indicating that the coating was relatively uniform. Example 2

[0020] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.03 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0021] S2: 0.006 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 600 ml of ionic liquid BmimBF4 and heated and stirred at 80 °C for 3 h; then, 0.002 mol Ga(NO3)3·6H2O was added and the reaction was continued to be stirred for 16 h. The mixture was washed and filtered three times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain fluoride solid electrolyte coated high-nickel single crystal material. Example 3

[0022] S1: Weigh 1 mol Ni 0.95 Co 0.01 Mn 0.04 The (OH)2 precursor and 1.05 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0023] S2: 0.0045 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 100 ml of ionic liquid BmimBF4 and heated and stirred at 100 °C for 3 h. Then, 0.0015 mol (NO3)3·6H2O was added and stirring was continued for 13 h. The mixture was washed and filtered 5 times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain fluoride solid electrolyte coated high-nickel single crystal material. Example 4

[0024] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0025] S2: 0.003 mol Li2CO3 and 1 mol g high-nickel single crystal material were placed in 500 ml of ionic liquid BmimBF4 and heated and stirred at 120 °C for 3 h; then, 0.001 mol Ga(NO3)3·6H2O was added and stirring was continued for 10 h. The mixture was washed and filtered 4 times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain fluoride solid electrolyte coated high-nickel single crystal material. Example 5

[0026] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0027] S2: 0.003 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 500 ml of ionic liquid BmimBF4 and heated and stirred at 100 °C for 3 h; then, 0.001 mol Al(NO3)3·9H2O was added and stirring was continued for 13 h. The mixture was washed and filtered 4 times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain fluoride solid electrolyte coated high-nickel single crystal material. Example 6

[0028] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0029] S2: 0.003 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 500 ml of ionic liquid BmimBF4 and heated and stirred at 100 °C for 3 h until a uniform suspension was obtained; then, 0.001 mol Y(NO3)3·6H2O was added and stirring was continued for 13 h. The mixture was washed and filtered 4 times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain fluoride solid electrolyte coated high-nickel single crystal material. Comparative Example 1

[0030] Compared to Example 1, Li2CO3 and Ga(NO3)3·6H2O were not added in step S2.

[0031] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0032] S2: 1 mol of high-nickel single crystal material was placed in 500 ml of ionic liquid BmimBF4, heated and stirred at 100 °C for 3 h; stirring was continued for 13 h, washed and filtered 4 times with anhydrous ethanol, and dried under vacuum at 80 °C for 20 h to obtain uncoated high-nickel single crystal material. Comparative Example 2

[0033] Compared to Example 1, in step S2, the heating and stirring reaction temperature is changed to 60°C.

[0034] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0035] S2: 0.003 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 500 ml of ionic liquid BmimBF4 and heated and stirred at 60 °C for 3 h; then, 0.001 mol Ga(NO3)3·6H2O was added and stirring was continued for 13 h. The mixture was washed and filtered 4 times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain the incompletely coated high-nickel single crystal material. Comparative Example 3

[0036] Compared to Example 1, in step S2, the ionic liquid BmimBF4 is replaced with anhydrous ethanol.

[0037] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0038] S2: 0.003 mol Li2CO3 and 1 mol high-nickel single crystal material were placed in 500 ml of anhydrous ethanol and heated and stirred at 100 °C for 3 h; then, 0.001 mol Ga(NO3)3·6H2O was added and stirring was continued for 13 h. The mixture was washed and filtered 4 times with anhydrous ethanol and dried under vacuum at 80 °C for 20 h to obtain uncoated high-nickel single crystal material. Comparative Example 4

[0039] Compared to Example 1, in step S2, the ionic liquid BmimBF4 is replaced with anhydrous ethanol, and Li2CO3 and Ga(NO3)3·6H2O are replaced with CaCl2 and NH4F.

[0040] S1: Weigh 1 mol Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and 1.04 mol LiOH were ball-milled and mixed. The uniformly mixed powder was placed in a high-temperature tube furnace and first heated to 500℃ for 4 hours, then heated to 750℃ for 5 hours, and finally cooled to 650℃ for 6 hours to obtain a high-nickel single crystal material.

[0041] S2: 0.001 mol CaCl2 and 1 mol high-nickel single crystal material were placed in 500 ml of anhydrous ethanol and heated and stirred at 100 °C. Then, 0.002 mol NH4F was added and stirring was continued for 13 h until the ethanol evaporated completely. Then, the mixture was dried under vacuum at 80 °C for 12 h and sintered in oxygen at 500 °C for 5 h to obtain the CaF2-coated high-nickel single crystal material.

[0042] from Figure 3 The SEM images revealed obvious particle aggregation on the material surface, indicating poor uniformity of the coating layer. Battery assembly and testing

[0043] The products prepared in Examples 1-6 and Comparative Examples 1-4 were tested for charge-discharge performance in CR2032 coin cells.

[0044] Battery assembly process: The products prepared according to the examples and comparative examples were mixed with conductive carbon and PVDF binder in a mass ratio of 90:5:5. The viscosity of the positive electrode slurry was adjusted with N-methylpyrrolidone (NMP) solvent. The slurry was uniformly coated onto aluminum foil and dried in a vacuum oven at 120°C for 12 hours. The dried electrode was then rolled, and the coated aluminum foil was cut into 12mm diameter discs using a slicing machine. These discs were then transferred to a glove box for battery assembly. The atmosphere inside the glove box was maintained with O2 < 0.1 ppm and H2O < 0.1 ppm. Lithium metal was used as the negative electrode, and the electrolyte was a 1M LiPF6 solution with EC / DMC / EMC (volume ratio 1:1:1) solvent. The assembled button batteries were allowed to stand for 4 hours to allow the electrolyte to fully impregnate them before electrochemical testing.

[0045] Electrochemical testing: Initial charge-discharge test, voltage range 2.7~4.5V; charge-discharge cycle test, voltage range 2.7~4.5V; rate capability 1.0C. Results are shown in Table 1 below:

[0046] As shown in the table above, the battery assembled using the fluoride solid electrolyte coated with high-nickel single-crystal material prepared in Example 1 exhibits a higher initial discharge capacity (218 mAh / g > 206 mAh / g) and better cycle performance (92.3% > 65.4%) compared to the lithium battery assembled using the uncoated high-nickel single-crystal material prepared in Comparative Example 1. This is because the fluoride solid electrolyte coating layer can isolate the single-crystal material from direct contact with the electrolyte, reduce the occurrence of side reactions with the electrolyte, alleviate the structural phase transition and lattice oxygen loss of the high-nickel material, delay capacity decay, and improve cycle performance; the good ionic conductivity of the fluoride solid electrolyte coating layer itself can accelerate the Li-C14 process. + Diffusion at the cathode-electrolyte interface ensures that lithium ions can still efficiently insert into / extract from the cathode material during high-voltage, high-rate charge-discharge, maintaining the battery's high capacity output and fast response capability, and improving the material's rate performance. The excellent high-voltage stability of the fluoride solid electrolyte coating layer itself can effectively mitigate the dissolution of transition metals (such as Ni, Co, Mn, etc.) in the cathode material during charge-discharge, reducing the reduction of active material in the cathode material caused by the dissolution of transition metals into the electrolyte, and improving the high-voltage charge-discharge performance of the high-nickel single crystal material. Similarly, the initial capacity and cycle performance of the fluoride solid electrolyte-coated single crystal materials prepared in Examples 2-6 are superior to those in Comparative Example 1.

[0047] The discharge capacity and cycle performance of Comparative Examples 2, 3, and 4 are all lower than those of Example 1. The poor material performance of Comparative Example 2 is due to the inability to form a fluoride solid electrolyte coating layer on the surface of the high-nickel single crystal material during low-temperature stirring. The poor material performance of Comparative Example 3 is due to the absence of ionic liquid BmimBF4, which results in the failure to form a fluoride solid electrolyte coating layer on the surface of the high-nickel single crystal material. Although the charge-discharge performance of Comparative Example 4 is better than that of Comparative Example 1, it is lower than that of Example 1. This is mainly because the high temperature causes uneven coating and the low ionic conductivity of CaF2 itself.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a fluoride solid electrolyte coated with a high-nickel single crystal material, characterized in that, Includes the following steps: S1. The nickel-cobalt-manganese hydroxide precursor and lithium hydroxide are ball-milled and mixed, and then sintered in stages to obtain a high-nickel cathode material; S2. Lithium carbonate and high-nickel cathode material are placed in ionic liquid BmimBF4, heated and stirred to obtain a homogeneous mixed solution; then nitrate is added, heated and stirred to react, washed and filtered with anhydrous ethanol, and dried to obtain fluoride solid electrolyte coated with high-nickel single crystal material.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of the nickel cobalt manganese hydroxide precursor to lithium hydroxide is 1:1.03 to 1:1.

05.

3. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of lithium carbonate, high-nickel cathode material, and nitrate is 0.3~0.6:100:0.1~0.2; the nitrate is one of Ga(NO3)3·6H2O, Al(NO3)3·9H2O, or Y(NO3)3·6H2O; the heating and stirring temperature is 80℃~120℃, and the stirring time is 10~16h; the material is washed 3~5 times with anhydrous ethanol.

4. A fluoride solid electrolyte coated high-nickel single crystal material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the fluoride solid electrolyte-coated high-nickel single crystal material as described in claim 4 in the cathode material of lithium-ion batteries.

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