Single-crystal high-entropy lithium-rich cathode material, preparation method and application thereof

Abstract

The application relates to a single-crystal high-entropy lithium-rich positive electrode material, a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. 1+x (M1 y M2 z ) 1‑x O 2‑w A w , wherein 0.1<=x<=0.25, 0 The particle size of the single-crystal high-entropy lithium-rich positive electrode material is 0.7 mu m<=d<=5 mu m. The lithium-rich positive electrode material obtained by adopting a sol-gel method is single-crystal and high-entropy, and the structure is designed, irreversible oxygen release is avoided, the initial efficiency is greatly improved, and the structural degradation and performance attenuation in the cycle process are relieved.

Description

Technical Field

[0001] This invention relates to a single-crystal high-entropy lithium-rich cathode material, its preparation method, and its application, belonging to the field of lithium-ion battery technology. Background Technology

[0002] With the depletion of fossil fuels and the rapid development of electronic products, people have placed higher demands on the performance indicators of lithium-ion batteries. Lithium-ion batteries have advantages such as high energy density and long cycle life, and their energy density and lifespan often depend on the electrochemical performance of the positive and negative electrode materials. Among existing positive electrode material systems, lithium-rich manganese-based positive electrode materials exhibit ultra-high specific capacity (250 mAh·g⁻¹). -1 It has attracted widespread attention due to its high operating voltage (4.8V), but its low compaction density is not conducive to achieving high energy density. Furthermore, it suffers from irreversible oxygen loss, voltage decay, and structural degradation during cycling, which restricts its commercial development.

[0003] The monocrystalline formation of cathode materials has become a research hotspot. Compared with traditional polycrystalline cathode materials, monocrystalline cathodes have higher mechanical strength and compaction density. Furthermore, due to the reduced surface area, they alleviate side reactions and structural degradation problems during cycling. However, their preparation process typically requires high temperatures of over 1000 degrees Celsius to promote grain growth, which poses significant challenges to both economic cost and safety. In recent years, high-entropy oxides (HEOs) have shown great potential in energy applications, such as electrocatalytic activity and electrochemical energy storage. Whether used directly as a negative electrode material in batteries or as high-entropy doping of cathode materials, they exhibit good performance. However, the synthesized materials are mostly layered or rock-salt structures, and the problem of structural fragility remains. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a single-crystal high-entropy lithium-rich cathode material, its preparation method, and its application. The lithium-rich cathode material obtained through single-crystalization and high-entropy structural design avoids irreversible oxygen release, significantly improves initial efficiency, and alleviates structural degradation and performance decline during cycling.

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

[0006] A single-crystal high-entropy lithium-rich cathode material, wherein the chemical formula of the material is Li. 1+x (M1 y M2 z ) 1-x O 2-w A wWhere 0.1≤x≤0.25, 0<y<1, 0<z<1, y+z=1, 0<w≤0.5, M1 is two or more of the low-valence metals Mn, Ni, Co, Fe and Cr with redox activity, M2 is two or more of the high-valence d0 elements Mo, V, Nb, Ti and W, and A is one or more of the anions F, S and Se; p1, p2, p3…pn represent the molar content of cations, where n is a natural number greater than or equal to 5; q1, q2, q3…qm represent the molar content of anions, where m is a natural number greater than or equal to 2; the molar entropy satisfies Furthermore, the valence state and proportion of the elements meet the requirements of molecular valence; the particle size of the single-crystal high-entropy lithium-rich cathode material is 0.7μm≤d≤5μm.

[0007] Preferably, the particle size of the single-crystal high-entropy lithium-rich cathode material is 1~2μm.

[0008] Preferably, the specific surface area of ​​the single-crystal high-entropy lithium-rich cathode material is 1~50m². 2 ·g -1 .

[0009] Preferably, the single-crystal high-entropy lithium-rich cathode material has a rock salt disordered structure, and the single-crystal high-entropy lithium-rich cathode material is Li. 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Mo 0.1 O 1.95 F 0.05 Li 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Fe 0.1 O 1.98 S 0.02 .

[0010] This invention provides a method for preparing a single-crystal high-entropy lithium-rich cathode material, the method comprising the following steps:

[0011] (1) Dissolution: According to the stoichiometric ratio and based on the solubility of lithium salt, M1 metal salt, M2 metal salt and substances containing A anion, the substances soluble in alcohol solvents are dissolved in alcohol solvents and stirred evenly to obtain solution A; the substances soluble under acidic conditions are dissolved together with the complexing agent in alcohol solvents and stirred evenly to obtain solution B.

[0012] (2) Synthesis: Add solution B dropwise to solution A, stir evenly, and evaporate at a constant temperature in a water bath to obtain gel; transfer the gel to a clean crucible, freeze dry under vacuum at -20~-50℃ for 12~24h, and grind the dried product to obtain uniform precursor powder;

[0013] (3) Calcination: 0.5~1g of precursor powder is pressed into a block under a pressure of 4~6MPa for 5~10min. In an oxygen atmosphere, it is calcined at 600~750℃ for 8~12h. After the heat preservation is completed, it is quenched and cooled by liquid nitrogen. The cooled material is then ball-milled to obtain a single crystal high-entropy lithium-rich cathode material.

[0014] Preferably, in step (1), the alcohol solvent is ethanol or methanol; the water bath temperature is determined according to the boiling point of the alcohol solvent. For example, if the boiling point of ethanol is around 75°C, then a water bath temperature of 70°C is suitable. More preferably, the alcohol solvent is ethanol.

[0015] Preferably, in step (1), the total concentration of metal salt in both solution A and solution B is 0.2~2 mol / L, more preferably 0.5~1 mol / L.

[0016] Preferably, in step (1), the metal salt is an acetate, nitrate, ammonium salt, or alkoxide. More preferably, the metal salt is an acetate.

[0017] Preferably, in step (1), the salt containing the A anion is ammonium fluoride, sulfur powder, or selenium powder. It is preferably an alcohol-soluble substance.

[0018] Preferably, in step (1), the molar ratio k of element A to Li satisfies 0 < k ≤ 0.45;

[0019] Preferably, in step (1), the complexing agent is citric acid, oxalic acid, tartaric acid or ammonium citrate, and the total molar ratio of the complexing agent to the metal ions is 1.1 to 1.5:1, with the most preferred ratio being 1.2:1.

[0020] Preferably, in step (2), the vacuum freeze-drying temperature is -30~-40℃ and the time is 16~20h.

[0021] Preferably, in step (3), the high-temperature calcination heating rate is 2~4℃ / min, the high-temperature calcination is carried out in a tube furnace, and the oxygen gas flow rate is controlled at 100~250mL / min.

[0022] Preferably, in step (3), the high-energy ball milling speed is 300~600 r / min and the ball milling time is 2~4 h.

[0023] An application of the single-crystal high-entropy lithium-rich cathode material described in this invention, wherein the material is used as a cathode material for lithium-ion batteries.

[0024] Beneficial effects

[0025] 1. This invention provides a single-crystal high-entropy lithium-rich cathode material. The single-crystal material has a small specific surface area and a large compaction density and mechanical strength, which enhances the material's cycle stability. The multi-element high-entropy process enhances the material's entropy stability and facilitates the formation of a rock salt disordered structure with 3D lithium transport orbitals. The introduction of 4d and 5d high-valence elements, due to the strong MO bonds, can also stabilize the lattice oxygen, thereby improving the material's first efficiency and cycle performance, which is beneficial for lithium-ion battery applications.

[0026] 2. This invention synthesizes single-crystal cathode materials using a one-step sol-gel method. The sol-gel method can synthesize uniform nanoscale particles. Compared to large-particle materials prepared by traditional co-precipitation methods, the growth of nanoscale particles into single-crystal particles requires lower temperatures, offering advantages in energy consumption and safety. Vacuum freeze-drying, compared to high-temperature drying, helps maintain the uniform dispersion between gel particles, avoiding particle agglomeration or uneven elemental distribution during high-temperature drying. Pressing into blocks and calcining increases the contact between nanoparticles and applies pressure, facilitating the growth of larger-diameter single-crystal materials at high temperatures. Without pressing, particles will grow at high temperatures, but all will be smaller than 500 nm, making it difficult to achieve the particle size required for single crystal growth. Single crystal growth requires high-quality grain growth conditions; this method uses pressing into sheets to promote growth. To avoid excessive material density hindering heat transfer / oxidation, the calcination temperature and holding time need to be carefully controlled during high-temperature calcination to provide sufficient conditions for crystal growth. Quenching after high-temperature calcination and rapid cooling help maintain the material's disorder at high temperatures, achieving disordered high entropy. If the material is cooled during furnace operation, the resulting material will have increased order but will still be a layered cathode material, making it difficult to obtain a disordered rock salt structure that is more favorable for ion transport. Furthermore, controlling the heating rate and oxygen flow rate during calcination can make the crystal structure more uniform. The preparation method described in this invention is environmentally friendly, requiring no ultra-high temperature, long-term calcination process, which helps reduce production costs and achieve industrialization. Attached Figure Description

[0027] Figure 1 The single-crystal high-entropy cathode material Li prepared in Example 1 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Fe 0.1 O 1.9 8S 0.02 The scanning electron microscope (SEM) test image.

[0028] Figure 2The single-crystal high-entropy lithium-rich cathode material Li prepared in Example 2 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Mo 0. 1O 1.95 F 0.05 Local SEM and EDS images.

[0029] Figure 3 The single-crystal high-entropy lithium-rich cathode material Li prepared in Example 3 1.2 Ti 0.1 Mn 0.5 Ni 0.275 V 0.1 Mo 0. 1O 1.95 F 0.05 X-ray diffraction (XRD) pattern.

[0030] Figure 4 The first-week charge-discharge curves of the single-crystal high-entropy lithium-rich cathode materials prepared in Examples 1-3 are shown in the comparison diagram.

[0031] Figure 5 The graph shows a comparison of the cycle performance of the single-crystal high-entropy lithium-rich cathode materials prepared in Examples 1-3. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments.

[0033] In the following embodiments:

[0034] Battery assembly: The active material is mixed with acetylene black and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1, NMP is added and the mixture is ground into a slurry. The slurry is coated onto aluminum foil with a scraper, dried, and cut into positive electrode sheets. Then, CR2025 coin cell half-cells are assembled in an argon glove box (water < 0.01 ppm, oxygen < 0.01 ppm). The positive electrode is the above-mentioned positive electrode sheet, the counter electrode is a lithium sheet, the separator is Celgard 2500, and the electrolyte is a solution prepared with dimethyl carbonate, diethyl carbonate, and ethyl carbonate in a volume ratio of 1:1:1 as solvents and 1 mol / L LiPF6 as solute.

[0035] Scanning electron microscope (SEM) test: FEI Quanta, Netherlands, EDS Accessories.

[0036] Powder X-ray diffraction (XRD) test: The X-ray diffractometer used was the IV-185 model diffractometer manufactured by Rigaku Corporation of Japan.

[0037] Battery cycle performance test: LAND CT 2001A tester purchased from Wuhan Landian Electronics Co., Ltd.

[0038] Example 1

[0039] (1) Dissolution: according to Li 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Fe 0.1 O 1.98 S 0.02 Lithium acetate, tetrabutyl titanate, manganese acetate, nickel acetate, niobium ethanol, and ferric nitrate were dissolved in an ethanol solution according to the stoichiometric ratio and stirred until homogeneous to obtain solution A; citric acid complexing agent and sulfur powder were dissolved in an ethanol solution at a molar ratio of 1.2:1 and stirred until homogeneous to obtain solution B.

[0040] (2) Synthesis: Add solution B dropwise to solution A, stir evenly, and heat in a water bath at 70°C to evaporate and obtain gel; transfer the gel to a clean crucible and dry it under vacuum freeze-drying at -40°C for 18 h; grind the dried product to obtain uniform precursor powder.

[0041] (3) Calcination: 0.7g of precursor powder was pressed into a block at 4.5MPa for 10min and calcined at high temperature. The temperature was increased to 650℃ at 2℃ / min and held for 8h with an oxygen flow rate of 200mL / min. After the holding period, the material was quenched and cooled with liquid nitrogen. The cooled material was then ball-milled at 300r / min for 4h to obtain the final cathode material.

[0042] like Figure 1 As shown, the material Li 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Fe 0.1 O 1.98 S 0.02 It has a polyhedral structure, with a particle size distribution of about 0.5-2μm and a relatively uniform distribution.

[0043] The sample was assembled into a half-cell for testing. The test cutoff voltage was 1.5-4.8V. Activation was performed at a 0.05 C rate during the first week, achieving a capacity of 264.4 mAh / g and a coulombic efficiency of 97.84%. Subsequent cycling tests at a 0.1 C rate showed a capacity retention of 66.18% after 20 cycles. This demonstrates the effectiveness of the single-crystal high-entropy Li₂. 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Fe0.1 O 1.98 S 0.02 The cathode material exhibits high first-cycle coulombic efficiency and cycle performance.

[0044] Example 2

[0045] (1) Dissolution: according to Li 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Mo 0.1 O 1.95 F 0.05 Lithium acetate, tetrabutyl titanate, manganese acetate, nickel acetate, niobium ethoxide, and ammonium fluoride were dissolved in ethanol in a stoichiometric ratio and stirred until homogeneous to obtain solution A; citric acid complexing agent and ammonium molybdate were dissolved in ethanol in a molar ratio of 1.2:1 and stirred until homogeneous to obtain solution B.

[0046] (2) Synthesis: Add solution B dropwise to solution A, stir evenly, and heat in a water bath at 70°C to evaporate and obtain gel; transfer the gel to a clean crucible and dry it under vacuum freeze-drying at -40°C for 18 hours; grind the dried product to obtain uniform precursor powder.

[0047] (3) Calcination: 1g of precursor powder was pressed into a block at 5MPa for 6min and calcined at high temperature. The temperature was increased to 750℃ at 5℃ / min and held for 6h with an oxygen flow rate of 100mL / min. After the holding period, the material was quenched and cooled with liquid nitrogen. The cooled material was then ball-milled at 300r / min for 5h to obtain the final cathode material.

[0048] like Figure 2 As shown, the material Li 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Mo 0.1 O 1.95 F 0.05 The particle size is approximately 1 μm, the elements contained are consistent with the design, and they are evenly distributed throughout the particle.

[0049] The sample was assembled into a half-cell for testing. The test cutoff voltage was 1.5-4.8V. Activation was performed at a rate of 0.05 C in the first week, achieving a capacity of 259.1 mAh / g and a coulombic efficiency of 95.65%. Subsequent cycling tests at a rate of 0.1 C showed a capacity retention of 52.77% after 20 cycles. This demonstrates the effectiveness of the single-crystal high-entropy Li₂. 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb0.1 Mo 0.1 O 1.95 F 0.05 The cathode material exhibits high first-cycle coulombic efficiency and cycling performance.

[0050] Example 3

[0051] (1) Dissolution: According to Li 1.2 Ti 0.1 Mn 0.5 Ni 0.275 V 0.1 Mo 0.1 O 1.95 F 0.05 Lithium acetate, tetrabutyl titanate, manganese acetate, nickel acetate, and ammonium fluoride were dissolved in ethanol in a stoichiometric ratio and stirred until homogeneous to obtain solution A; citric acid complexing agent, ammonium molybdate, and ammonium metavanadate were dissolved in ethanol in a molar ratio of 1.2:1 and stirred until homogeneous to obtain solution B.

[0052] (2) Synthesis: Add solution B dropwise to solution A, stir evenly, and heat in a water bath at 70°C to evaporate and obtain gel; transfer the gel to a clean crucible and dry it under vacuum freeze-drying at -40°C for 18 hours; grind the dried product to obtain uniform precursor powder.

[0053] (3) Calcination: 0.5g of precursor powder was pressed into a block at 5.5MPa for 4min and calcined at high temperature. The temperature was increased to 650℃ at 3℃ / min and held for 8h with an oxygen flow rate of 150mL / min. After the holding period, liquid nitrogen was used for quenching and cooling. The cooled material was then ball-milled at 300r / min for 4h to obtain the final cathode material.

[0054] like Figure 3 As shown, the material Li 1.2 Ti 0.1 Mn 0.5 Ni 0.275 V 0.1 Mo 0.1 O 1.95 F 0.05 It has high crystallinity, matches well with the characteristic peaks of lithium oxide compounds of the contained elements, and has few impurities.

[0055] The sample was assembled into a half-cell for testing. The test cutoff voltage was 1.5-4.8V. Activation was performed at a rate of 0.05 C in the first week, achieving a capacity of 249.9 mAh / g and a coulombic efficiency of 98.12%. Subsequent cycling tests at a rate of 0.1 C showed a capacity retention of 66.47% after 20 cycles. This demonstrates the effectiveness of the single-crystal high-entropy Li₂. 1.2 Ti 0.1 Mn 0.5 Ni0.275 V 0.1 Mo 0.1 O 1.95 F 0.05 The cathode material exhibits high first-cycle coulombic efficiency and cycle performance.

[0056] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A single-crystal high-entropy lithium-rich cathode material, characterized in that: The chemical formula of the material is Li 1+x (M1 y M2 z ) 1- x O 2-w A w Where 0.1≤x≤0.25, 0<y<1, 0<z<1, y+z=1, 0<w≤0.5, M1 is two or more of the low-valence metals Mn, Ni, Co, Fe and Cr with redox activity, M2 is two or more of the high-valence d0 elements Mo, V, Nb, Ti and W, and A is one or more of the anions F, S and Se; p1, p2, p3…pn represent the molar content of cations, where n is a natural number greater than or equal to 5; q1, q2, q3…qm represent the molar content of anions, where m is a natural number greater than or equal to 2; the molar entropy satisfies Furthermore, the valence state and proportion of the elements meet the requirements of molecular valence; the particle size of the single-crystal high-entropy lithium-rich cathode material is 0.7μm≤d≤5μm.

2. The single-crystal high-entropy lithium-rich cathode material as described in claim 1, characterized in that: The particle size of the single-crystal high-entropy lithium-rich cathode material is 1~2μm.

3. The single-crystal high-entropy lithium-rich cathode material as described in claim 1, characterized in that: The specific surface area of ​​the monocrystalline high-entropy lithium-rich cathode material is 1~50m². 2 ·g -1 .

4. The single-crystal high-entropy lithium-rich cathode material as described in claim 1, characterized in that: The single-crystal high-entropy lithium-rich cathode material has a rock salt disordered structure, and the single-crystal high-entropy lithium-rich cathode material is Li. 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Mo 0.1 O 1.95 F 0.05 Li 1.2 Ti 0.1 Mn 0.4 Ni 0.375 Nb 0.1 Fe 0.1 O 1.98 S 0.02 .

5. A method for preparing a single-crystal high-entropy lithium-rich cathode material as described in any one of claims 1 to 4, characterized in that: The method steps include: (1) According to the stoichiometric ratio and based on the solubility of lithium salt, M1 metal salt, M2 metal salt and substances containing A anion, dissolve substances soluble in alcohol solvents in alcohol solvents and stir evenly to obtain solution A; dissolve substances soluble under acidic conditions together with complexing agents in alcohol solvents and stir evenly to obtain solution B. (2) Add solution B dropwise to solution A, stir evenly, and heat in a water bath to evaporate at a constant temperature to obtain gel; transfer the gel to a clean crucible, freeze dry under vacuum at -20~-50℃ for 12~24h, and grind the dried product to obtain uniform precursor powder; (3) Press 0.5~1g of precursor powder into a block under a pressure of 4~6MPa for 5~10min, calcine it at 600~750℃ for 8~12h in an oxygen atmosphere, and then quench it with liquid nitrogen after the heat preservation is completed. The cooled material is then subjected to high-energy ball milling to obtain a single-crystal high-entropy lithium-rich cathode material.

6. The method for preparing a single-crystal high-entropy lithium-rich cathode material as described in claim 5, characterized in that: In step (1), the alcohol solvent is ethanol or methanol; The total concentration of metal salts in both solutions A and B is 0.2–2 mol / L; The metal salt is an acetate, nitrate, ammonium salt, or alkoxide; The salt containing the A anion is ammonium fluoride, sulfur powder, or selenium powder; The molar ratio k of element A to Li satisfies 0 < k ≤ 0.45; The complexing agent is citric acid, oxalic acid, tartaric acid or ammonium citrate, and the total molar ratio of the complexing agent to the metal ions is 1.1~1.5:

1.

7. The method for preparing a single-crystal high-entropy lithium-rich cathode material as described in claim 5, characterized in that: In step (2), the vacuum freeze-drying temperature is -30~-40℃ and the time is 16~20h.

8. The method for preparing a single-crystal high-entropy lithium-rich cathode material as described in claim 5, characterized in that: In step (3), the high-temperature calcination heating rate is 2~4℃ / min, the high-temperature calcination is carried out in a tube furnace, and the oxygen gas flow rate is controlled at 100~250mL / min.

9. The method for preparing a single-crystal high-entropy lithium-rich cathode material as described in claim 5, characterized in that: In step (3), the high-energy ball milling speed is 300~600 r / min and the ball milling time is 2~4 h.

10. An application of the single-crystal high-entropy lithium-rich cathode material as described in any one of claims 1 to 4, characterized in that: The material is used as a cathode material for lithium-ion batteries.

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