Double-coated lithium nickel cobalt manganese oxide, method for manufacturing the same, cathode material, and lithium ion battery

Abstract

The application discloses a double-coated lithium nickel cobalt manganese oxide, a preparation method thereof, a positive electrode material and a lithium ion battery. The preparation method of the double-coated lithium nickel cobalt manganese oxide comprises the following steps: (1) uniformly mixing nickel acetate and anhydrous ethanol to obtain a solution; adding lithium nickel cobalt manganese oxide into the solution, uniformly dispersing, and then adding an ammonium fluoride aqueous solution to perform a reaction, and drying the obtained precipitate (NiF2) after washing; (2) mixing the dried sample in the step (1) with a carbon source and fully ball milling, and performing a heat treatment after the ball milling, so that the double-coated lithium nickel cobalt manganese oxide is prepared. The method provided by the application can improve the cycle performance of a layered ternary positive electrode material under high-voltage charging and discharging (such as 2.8-4.5 V), and can improve the initial coulomb efficiency, and has the advantages of simple and feasible preparation method and strong universality.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and particularly relates to a double-coated lithium nickel cobalt manganese oxide, its preparation method, cathode material, and lithium-ion battery. Background Technology

[0002] Layered nickel-cobalt-manganese oxide LiNi 1-x-y Co x Mn y O2 is one of the most widely used cathode materials for commercially available lithium-ion batteries. In recent years, high-nickel ternary cathode materials, such as LiN... 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) and LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and similar materials have attracted widespread attention due to their low cost and high specific capacity. The charge-discharge specific capacity of ternary cathode materials can be further improved by increasing the charge-discharge cutoff voltage. However, the capacity decay and poor initial coulombic efficiency of high-nickel-content layered cathode materials under high voltage are more pronounced during long-term cycling.

[0003] Currently, existing literature reports that coating with oxides can improve the cycle performance of high-nickel ternary layered cathode materials. For example, Zang M, Hu G, Wu L, et al. (Electrochimica Acta, 2017, 232:80–88) improved the cycle performance of LiN by surface coating with TiO2. 0.5 Co 0.2 Mn 0.3 Cyclic performance of O2; Shi Y, Zhang M, Qian D et al. (ElectrochimicaActa, 2016, 203:154-161) improved LiN by coating with Al2O3. 0.5 Co 0.2 Mn 0.3 The cycling performance of O2 is important. However, because the electrolytes currently used contain lithium salts (LiPF6), hydrogen fluoride (HF), a byproduct of partial electrolyte decomposition, corrodes the coating layer during long-term battery cycling, leading to a gradual deterioration in battery cycle performance. Therefore, it is necessary to find a more stable material in the electrolyte to coat the ternary cathode material. Due to the property that fluorides do not react with HF, there are already reports on coating LiN with AlF3. 0.5 Co 0.2 Mn 0.3O2 can be used to improve the cycle performance of high-nickel cathode materials. For example, Yang K, Fan LZ, Guo J, et al. (Electrochimica Acta, 2012, 63:363-368) improved the cycling performance of LiN by coating with AlF3. 0.5 Co 0.2 Mn 0.3 The initial coulombic efficiency and cycle performance of O2 were observed. However, due to the low ionic conductivity of AlF3, the coating layer impedance is relatively high, resulting in reduced charge transport efficiency at the three-phase interface and adversely affecting the discharge depth of the cathode material. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a dual-coated lithium nickel cobalt manganese oxide, its preparation method, a cathode material, and a lithium-ion battery. The present invention employs a dual-coating method of nickel fluoride and carbon (NiF2 and C) on lithium nickel cobalt manganese oxide, resulting in a cathode material with good cycle stability and initial coulombic efficiency. Specifically, to improve the conductivity and interfacial charge transport of the cathode material, the present invention uses a dual-coating method of NiF2 and carbon-based materials. NiF2 has higher conductivity than AlF3, but when used alone, it may still increase interfacial impedance. Therefore, introducing a carbon-based coating layer with better conductivity can effectively reduce interfacial impedance, thereby improving the electrochemical performance of the material.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing double-coated lithium nickel cobalt manganese oxide includes the following steps:

[0007] (1) Mix nickel acetate and anhydrous ethanol evenly to obtain a solution; add lithium nickel cobalt manganese oxide to the solution, disperse evenly, and then add ammonium fluoride aqueous solution to react. The precipitate (NiF2) obtained by the reaction is washed and dried.

[0008] (2) The dried sample from step (1) is mixed with a carbon source and ball-milled thoroughly. After ball milling, it is heat-treated to obtain double-coated lithium nickel cobalt manganese oxide.

[0009] Preferably, in step (1), nickel acetate is introduced in the form of Ni(CH3COO)2·4H2O.

[0010] Preferably, in step (1), the lithium nickel cobalt manganese oxide is LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0011] Preferably, the mass ratio of Ni(CH3COO)2·4H2O to anhydrous ethanol is 1:120~200.

[0012] Preferably, in step (1), the mass ratio of lithium nickel cobalt manganese oxide to theoretically generated NiF2 is 99.6:0.4 to 98.8:1.2.

[0013] Preferably, in step (1), the washing method is to wash repeatedly with anhydrous ethanol 3 to 4 times.

[0014] Preferably, in step (1), the method of uniform dispersion is to use ultrasound to fully disperse the sample.

[0015] Preferably, in step (1), the drying temperature is 70-80℃ and the drying time is 8-10h.

[0016] Preferably, in step (1), the mass ratio of lithium nickel cobalt manganese oxide to carbon in the carbon source in step (2) is 99.5:0.5 to 98.5:1.5.

[0017] Preferably, in step (2), the carbon source is at least one of sucrose, glucose and cellulose; more preferably, the cellulose is carboxymethyl cellulose.

[0018] Preferably, in step (2), the heat treatment conditions are: argon gas is introduced at a rate of 2 L / min, the temperature is raised to 450-550℃ at a rate of 2-4℃ / min and held for 2-4 hours.

[0019] The double-coated lithium nickel cobalt manganese oxide prepared by the above-mentioned method is a double-coated lithium nickel cobalt manganese oxide.

[0020] A cathode material comprising the above-mentioned double-coated lithium nickel cobalt manganese oxide.

[0021] A lithium-ion battery comprising the aforementioned positive electrode material.

[0022] Compared with the prior art, the beneficial effects of the present invention include:

[0023] This invention proposes a method to improve the electrochemical performance of high-nickel layered cathode materials through a double coating of nickel fluoride (NiF2) and carbon (C). NiF2 coating on the cathode material surface effectively prevents direct contact between the cathode material and the electrolyte, thereby improving the material's cycle performance. However, like traditional fluorides such as AlF3 and MgF2, NiF2 suffers from low electronic conductivity, and simple fluoride coating can negatively impact charge transport at the cathode material interface. Therefore, this application proposes a secondary coating using highly conductive carbon material while using nickel fluoride coating, thereby improving the conductivity of the coating layer and overcoming the shortcomings of pure fluoride coating. The method of this invention not only significantly improves the cycle performance of ternary cathode materials but also effectively increases the initial coulombic efficiency, and the preparation process exhibits good repeatability and wide applicability. Attached Figure Description

[0024] Figure 1 The LiNi described in Comparative Example 1 0.5 Co 0.2 Mn 0.3 A comparison of the first charge-discharge curves of the battery prepared by O2 and the double-coated lithium nickel cobalt manganese oxide as described in Example 5 in the voltage range of 2.8V to 4.5V, where a corresponds to Example 1 and b corresponds to Example 5.

[0025] Figure 2 The LiNi described in Comparative Example 1 0.5 Co 0.2 Mn 0.3 Comparison of cycling curves of batteries prepared by O2 and the double-coated lithium nickel cobalt manganese oxide as described in Example 5 in the voltage range of 2.8V to 4.5V, where a corresponds to Example 1 and b corresponds to Example 5. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Before performing electrochemical performance characterization, the following examples and comparative examples require the corresponding positive electrode materials to be assembled into CR2025 coin cells, wherein lithium metal is used as the negative electrode material and a 1 mol / L LiPF6 DMC:EC (1:1) solution is used as the electrolyte.

[0028] Comparative Example 1

[0029] With LiNi 0.5 Co 0.2 Mn 0.3 O2 was used as the positive electrode material, and its electrochemical performance was characterized. Within a voltage range of 2.8V to 4.5V, with a 15mAg... -1 The current density was tested, and the initial charge specific capacity was 220.7 mAh / g, the discharge specific capacity was 185.8 mAh / g, and the initial coulombic efficiency was 84.2%; within the same voltage range, at 150 mAg... -1 The current density was tested, and the initial discharge specific capacity was 174 mAh / g. After 50 cycles, the discharge specific capacity was 143 mAh / g, and the capacity retention rate was 82.2%.

[0030] Example 1

[0031] A method for preparing double-coated lithium nickel cobalt manganese oxide comprises the following steps:

[0032] (1) Weigh 0.3g Ni(CH3COO)2·4H2O and 60g anhydrous ethanol, mix and stir for 30min to dissolve Ni(CH3COO)2·4H2O to obtain a solution; weigh 29.022g LiNi 0.5 Co 0.2 Mn 0.3 O2 was added to the solution and ultrasonically dispersed for 30 min. 0.089 g of NH4F and 10 g of deionized water were weighed, mixed and stirred for 10 min to prepare an NH4F aqueous solution. The prepared NH4F aqueous solution was slowly added dropwise to the ultrasonically dispersed homogeneous solution. The resulting precipitate was washed 3-4 times with anhydrous ethanol and then dried at 70 °C for 8 h.

[0033] (2) The dried sample from step (1) was mixed with 1.106 g of glucose and ball-milled thoroughly. After ball milling, the sample was heated to 450 °C at a rate of 2 °C / min and heat-treated for 2 h under an argon flow rate of 2 L / min to obtain a ternary cathode material LiNi with nickel fluoride and carbon double coating. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), namely the double-coated lithium nickel cobalt manganese oxide.

[0034] Compared with Comparative Example 1, LiNi coated with 0.4 wt% NiF2 and 1.5 wt% carbon... 0.5 Co 0.2 Mn 0.3 O2, within a voltage range of 2.8V to 4.5V, at 15mAg -1 The current density was tested, and the initial charge specific capacity was 210.6 mAh / g, the discharge capacity was 181.5 mAh / g, and the initial coulombic efficiency was 86.2%; within the same voltage range, at 150 mAg... -1 The current density was tested, and the initial discharge specific capacity was 168.5 mAh / g. After 50 cycles, the discharge specific capacity was 147.3 mAh / g, with a capacity retention of 87.4%. These results indicate that the coating treatment significantly improves the capacitance of LiNi. 0.5 Co 0.2 Mn 0.3 The initial coulombic efficiency and cycle performance of O2.

[0035] Example 2

[0036] A method for preparing double-coated lithium nickel cobalt manganese oxide comprises the following steps:

[0037] (1) Weigh 0.3g Ni(CH3COO)2·4H2O and 48g anhydrous ethanol, mix and stir for 40min to dissolve Ni(CH3COO)2·4H2O to obtain a solution; weigh 14.453g LiNi 0.5 Co 0.2 Mn 0.3 O2 was added to the solution and ultrasonically dispersed for 35 min. 0.089 g of NH4F and 10 g of deionized water were weighed, mixed and stirred for 10 min to prepare an NH4F aqueous solution. The prepared NH4F aqueous solution was slowly added dropwise to the ultrasonically dispersed homogeneous solution. The resulting precipitate was washed 3-4 times with anhydrous ethanol and then dried at 75 °C for 9 h.

[0038] (2) The dried sample from step (1) was mixed with 0.182 g of glucose and ball-milled thoroughly. After ball milling, the sample was heated to 500 °C at a rate of 3 °C / min and heat-treated for 2 h under an argon flow rate of 2 L / min to obtain a ternary cathode material LiNi with nickel fluoride and carbon double coating. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), namely the double-coated lithium nickel cobalt manganese oxide.

[0039] Compared with Comparative Example 1, LiNi coated with 0.8 wt% NiF2 and 0.5 wt% carbon... 0.5 Co 0.2 Mn 0.3 O2, within a voltage range of 2.8V to 4.5V, at 15mAg -1 The current density was tested, and the initial charge specific capacity was 212.0 mAh / g, the discharge capacity was 186.8 mAh / g, and the initial coulombic efficiency was 88.1%. Within the voltage range of 2.8V to 4.5V, at a current density of 150 mAg... -1 The current density was tested, and the initial discharge specific capacity was 170.1 mAh / g. After 50 cycles, the discharge specific capacity was 153.2 mAh / g, with a capacity retention of 90.1%. These results indicate that the coating treatment significantly improves the specific capacity of LiNi. 0.5 Co 0.2 Mn 0.3 The initial coulombic efficiency and cycle performance of O2.

[0040] Example 3

[0041] A method for preparing double-coated lithium nickel cobalt manganese oxide comprises the following steps:

[0042] (1) Weigh 0.3g Ni(CH3COO)2·4H2O and 36g anhydrous ethanol, mix and stir for 50min to dissolve Ni(CH3COO)2·4H2O to obtain a solution; weigh 9.596g LiNi 0.5 Co 0.2 Mn 0.3 O2 was added to the solution and ultrasonically dispersed for 40 min. 0.089 g of NH4F and 10 g of deionized water were weighed, mixed and stirred for 10 min to prepare an NH4F aqueous solution. The prepared NH4F aqueous solution was slowly added dropwise to the ultrasonically dispersed homogeneous solution. The resulting precipitate was washed 3-4 times with anhydrous ethanol and then dried at 80 °C for 10 h.

[0043] (2) The dried sample from step (1) was mixed with 0.230 g of sucrose and ball-milled thoroughly. After ball milling, the sample was heated to 550 °C at a rate of 4 °C / min and heat-treated for 4 h under an argon flow rate of 2 L / min to obtain a ternary cathode material LiNi with nickel fluoride and carbon double coating. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), namely the double-coated lithium nickel cobalt manganese oxide.

[0044] Compared with Comparative Example 1, LiNi coated with 1.2 wt% NiF2 and 1.0 wt% carbon... 0.5 Co 0.2 Mn 0.3 O2, within a voltage range of 2.8V to 4.5V, at 15mAg -1 The current density was tested, and the initial charge specific capacity was 207.8 mAh / g, the discharge capacity was 178.7 mAh / g, and the initial coulombic efficiency was 86.0%; within the voltage range of 2.8V to 4.5V, at a current density of 150 mAg... -1 The current density was tested, and the initial discharge specific capacity was 165.2 mAh / g. After 50 cycles, the discharge specific capacity was 141.3 mAh / g, with a capacity retention of 85.5%. These results indicate that the coating treatment significantly improves the capacitance of LiNi. 0.5 Co 0.2 Mn 0.3 The initial coulombic efficiency and cycle performance of O2.

[0045] Example 4

[0046] A method for preparing double-coated lithium nickel cobalt manganese oxide comprises the following steps:

[0047] (1) Weigh 0.3g Ni(CH3COO)2·4H2O and 60g anhydrous ethanol, mix and stir for 30min to dissolve Ni(CH3COO)2·4H2O to obtain a solution; weigh 29.022g LiNi 0.5 Co 0.2 Mn 0.3 O2 was added to the solution and ultrasonically dispersed for 30 min. 0.089 g of NH4F and 10 g of deionized water were weighed, mixed and stirred for 10 min to prepare an NH4F aqueous solution. The prepared NH4F aqueous solution was slowly added dropwise to the ultrasonically dispersed homogeneous solution. The resulting precipitate was washed 3-4 times with anhydrous ethanol and then dried at 70 °C for 8 h.

[0048] (2) The dried sample from step (1) was mixed with 0.697 g of sucrose and ball-milled thoroughly. After ball milling, the sample was heated to 500 °C at a rate of 2 °C / min and heat-treated for 3 h under an argon flow rate of 2 L / min to obtain a ternary cathode material LiNi with nickel fluoride and carbon double coating. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), namely the double-coated lithium nickel cobalt manganese oxide.

[0049] Compared with Comparative Example 1, LiNi coated with 0.4 wt% NiF2 and 1.0 wt% carbon... 0.5 Co 0.2 Mn 0.3 O2, within a voltage range of 2.8V to 4.5V, at 15mAg -1 The current density was tested, and the initial charge specific capacity was 215.0 mAh / g, the discharge capacity was 191.4 mAh / g, and the initial coulombic efficiency was 89.0%; within the voltage range of 2.8V to 4.5V, at a current density of 150 mAg... -1 The current density was tested, and the initial discharge specific capacity was 168.4 mAh / g. After 50 cycles, the discharge specific capacity was 150.2 mAh / g, with a capacity retention of 89.2%. These results indicate that the coating treatment significantly improves the capacitance of LiNi. 0.5 Co 0.2 Mn 0.3 The initial coulombic efficiency and cycle performance of O2.

[0050] Example 5

[0051] A method for preparing double-coated lithium nickel cobalt manganese oxide comprises the following steps:

[0052] (1) Weigh 0.3g Ni(CH3COO)2·4H2O and 48g anhydrous ethanol, mix and stir for 40min to dissolve Ni(CH3COO)2·4H2O to obtain a solution; weigh 14.453g LiNi 0.5 Co 0.2 Mn 0.3 O2 was added to the solution and ultrasonically dispersed for 35 min. 0.089 g of NH4F and 10 g of deionized water were weighed, mixed and stirred for 10 min to prepare an NH4F aqueous solution. The prepared NH4F aqueous solution was slowly added dropwise to the ultrasonically dispersed homogeneous solution. The resulting precipitate was washed 3-4 times with anhydrous ethanol and then dried at 75 °C for 9 h.

[0053] (2) The dried sample from step (1) was mixed with 0.491 g of carboxymethyl cellulose and ball-milled thoroughly. After ball milling, the sample was heated to 550 °C at a rate of 3 °C / min and heat-treated for 4 h under an argon flow rate of 2 L / min to obtain a ternary cathode material LiNi with nickel fluoride and carbon double coating. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), namely the double-coated lithium nickel cobalt manganese oxide.

[0054] Compared with Comparative Example 1, LiNi coated with 0.8 wt% NiF2 and 1.0 wt% carbon... 0.5 Co 0.2 Mn 0.3 O2, within a voltage range of 2.8V to 4.5V, at 15mAg -1 The current density was tested, and the initial charge specific capacity was 212 mAh / g, the discharge capacity was 187.5 mAh / g, and the initial coulombic efficiency was 88.4%; within the voltage range of 2.8V to 4.5V, at a current density of 150 mAg... -1 The current density was tested, and the initial discharge specific capacity was 169.9 mAh / g. After 50 cycles, the discharge specific capacity was 154.8 mAh / g, with a capacity retention of 91.1%. These results indicate that the coating treatment significantly improves the capacitance of LiNi. 0.5 Co 0.2 Mn 0.3 The initial coulombic efficiency and cycle performance of O2.

[0055] Figure 1 The LiNi described in Comparative Example 1 0.5 Co 0.2 Mn 0.3 A comparison of the first charge-discharge curves of the battery prepared by O2 and the double-coated lithium nickel cobalt manganese oxide as described in Example 5 in the voltage range of 2.8V to 4.5V, where a corresponds to Example 1 and b corresponds to Example 5.

[0056] Figure 2 The LiNi described in Comparative Example 1 0.5 Co 0.2 Mn 0.3 Comparison of cycling curves of batteries prepared by O2 and the double-coated lithium nickel cobalt manganese oxide as described in Example 5 in the voltage range of 2.8V to 4.5V, where a corresponds to Example 1 and b corresponds to Example 5.

[0057] See Figures 1-2 We know that LiNi is double-coated with nickel fluoride (NiF2) and carbon (C). 0.5 Co 0.2 Mn 0.3 O2 can significantly improve its initial coulombic efficiency and cycle performance.

[0058] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A cathode material comprising double-coated lithium nickel cobalt manganese oxide, characterized in that, The preparation method of the double-coated lithium nickel cobalt manganese oxide includes the following steps: (1) Mix nickel acetate and anhydrous ethanol evenly to obtain a solution; add lithium nickel cobalt manganese oxide to the solution, disperse evenly, and then add ammonium fluoride aqueous solution to react. The precipitate obtained by the reaction is washed and dried. (2) The sample dried in step (1) is mixed with a carbon source and ball-milled thoroughly. After ball milling, it is heat-treated to obtain the double-coated lithium nickel cobalt manganese oxide.

2. The cathode material according to claim 1, characterized in that, In step (1), nickel acetate is introduced in the form of Ni(CH3COO)2·4H2O; The lithium nickel cobalt manganese oxide mentioned in step (1) is LiNi 0.5 Co 0.2 Mn 0.3 O2.

3. The cathode material according to claim 2, characterized in that, The mass ratio of Ni(CH3COO)2·4H2O to anhydrous ethanol is 1:120~200.

4. The cathode material according to claim 3, characterized in that, The mass ratio of the lithium nickel cobalt manganese oxide to the theoretically generated NiF2 in step (1) is 99.6:0.4 to 98.8:1.

2.

5. The positive electrode material according to claim 1, characterized in that, The washing method described in step (1) is as follows: wash repeatedly with anhydrous ethanol 3 to 4 times; The method for achieving uniform dispersion in step (1) is to use ultrasound to fully disperse the sample.

6. The cathode material according to claim 1, characterized in that, The drying temperature in step (1) is 70-80℃, and the drying time is 8-10h; The mass ratio of the lithium nickel cobalt manganese oxide in step (1) to the carbon in the carbon source in step (2) is 99.5:0.5 to 98.5:1.

5.

7. The cathode material according to claim 1, characterized in that, The carbon source in step (2) is at least one of sucrose, glucose, and cellulose; The heat treatment conditions in step (2) are as follows: argon gas is introduced at a rate of 2 L / min, the temperature is raised to 450-550℃ at a rate of 2-4℃ / min and held for 2-4 hours.

8. A lithium-ion battery, characterized in that, It includes the cathode material as described in claims 1-7.

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