High-Nickel Single-Crystal Cathode Material for Lithium-Ion Batteries, Preparation Method Thereof, and Low-Temperature Electrolyte

Abstract

The present invention provides a high-nickel single-crystal cathode material for lithium-ion batteries, a preparation method thereof, and a low-temperature electrolyte, including preparing a polycrystalline ternary cathode material of LiNi a Co b Mn c O2, then putting it into a sintering furnace for sintering, cooling after sintering, and using ball milling and crushing technology for crushing, and finally sintering again. After sintering, the single-crystal LiNi a Co b Mn c O2 cathode material is obtained in a total of five steps. The present invention as a whole prepares a high-nickel single-crystal cathode material by controlling the ball milling speed, calcination temperature and time, which is applicable to high-nickel ternary cathode material products with different performance requirements. By adopting a strategy of high-temperature calcination combined with ball milling, the process is simple and the energy consumption is low, realizing the large-scale preparation of high-performance lithium-ion battery cathode materials. Then, by adjusting the composition and dosage of the lithium salt, solvent and film-forming additive in the electrolyte, the electrochemical performance of the lithium-ion battery working at low temperature is improved, adapting to the low-temperature environment and ensuring the working efficiency of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials and electrolytes in lithium batteries, and particularly to a high-nickel single-crystal cathode material for lithium-ion batteries, a preparation method thereof, and a low-temperature electrolyte. Background Art

[0002] A lithium battery is a type of battery with a lithium metal or lithium alloy as the positive / negative electrode material and using a non-aqueous electrolyte solution. Due to the very active chemical properties of lithium metal, the processing, storage, and use of lithium metal have very high requirements for the environment. With the development of science and technology, lithium batteries have become the mainstream. Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium-ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. Their safety, specific capacity, self-discharge rate, and performance-price ratio are all superior to those of lithium metal batteries.

[0003] The cathode material with a high-nickel layered polycrystalline morphology has been commercialized and tends to be mature. Since the polycrystalline material particles are secondary particles aggregated from primary particles, there are anisotropic stresses during the cycling process. As the cycling process progresses, microcracks will occur in the secondary particles, and the electrolyte will infiltrate. Therefore, it is necessary to make the high-nickel polycrystalline cathode material into a high-nickel single-crystal cathode material. Since there are no grain boundaries inside the single crystal, microcracks are not easily generated, which can effectively inhibit the occurrence of interfacial side reactions and endow it with better cycling performance and thermal stability. However, in the prior art, the process for preparing the high-nickel single-crystal cathode material is relatively complex, resulting in an increase in the overall preparation time cost and energy consumption cost.

[0004] Furthermore, for a lithium-ion battery, it also includes an electrolyte. The electrolyte is a medium (with certain corrosiveness) used in chemical batteries, electrolytic capacitors, etc., provides ions for their normal operation, and ensures that the chemical reactions occurring during operation are reversible. However, in the prior art, in the face of a low-temperature environment, the performance of the electrolyte will be affected accordingly, resulting in a decline in the performance of the lithium-ion battery. Therefore, the present invention proposes a high-nickel single-crystal cathode material for lithium batteries, a preparation method thereof, and a low-temperature electrolyte to solve the problems existing in the prior art. Summary of the Invention

[0005] In view of the above problems, the object of the present invention is to provide a high-nickel single-crystal cathode material for lithium-ion batteries, a preparation method thereof, and a low-temperature electrolyte. The high-nickel single-crystal cathode material for lithium batteries, the preparation method thereof, and the low-temperature electrolyte have the advantages of simple process and low energy consumption, can adapt to a low-temperature environment, and thus can solve the problems existing in the prior art.

[0006] To achieve the object of the present invention, the present invention is realized through the following technical solutions: A preparation method of a high-nickel single-crystal cathode material for lithium-ion batteries, comprising the following steps:

[0007] Step 1: Prepare LiNi a Co b Mn c O2 polycrystalline ternary cathode material;

[0008] Step 2: Put the LiNi a Co b Mn c O2 polycrystalline ternary cathode material into a sintering furnace. After raising the sintering temperature to 750 - 950 °C, conduct sintering;

[0009] Step 3: Take it out and cool after sintering. After cooling to room temperature, put it into a ball mill for ball milling and crushing to obtain crushed material;

[0010] Step 4: Put the obtained crushed material into the sintering furnace again. After raising the sintering temperature to 700 - 850 °C, conduct sintering;

[0011] Step 5: Take it out and cool after sintering to obtain single crystal LiNi a Co b Mn c O2 cathode material.

[0012] Further improvement lies in: In the said Step 2, the sintering time is 10 - 18 h.

[0013] Further improvement lies in: In the said Step 3, the rotation speed of the ball mill is 250 - 350 rpm / min, and the ball milling time is 1 - 6 h.

[0014] Further improvement lies in: In the said Step 4, the sintering time is the same as that in Step 2.

[0015] High-nickel single crystal cathode material for lithium-ion batteries, and this high-nickel single crystal cathode material for lithium-ion batteries is the high-nickel single crystal cathode material prepared by the method described in Claims 1 - 4.

[0016] Low-temperature electrolyte for lithium-ion batteries, and this low-temperature electrolyte for lithium-ion batteries includes raw materials with the following molar mass ratios: 8% - 20% of lithium salt, 75% - 85% of organic solvent, and 1% - 7% of film-forming additive.

[0017] Further improvement lies in: The said lithium salt is any combination of four substances among LiPF6, LiDFOB, LiBF4, LiPO2F2, LiTFSi, LiFSI, and KNO3.

[0018] Further improvement lies in: The said organic solvent is any combination of three substances among EC, EMC, DMC, DOL, and DME.

[0019] A further improvement lies in that the film-forming additive is a combination of any three substances among VC, FEC, TMSP, EBC, and EC.

[0020] The beneficial effects of the present invention are as follows: This high-nickel single-crystal cathode material for lithium batteries, its preparation method, and the low-temperature electrolyte are obtained by calcining the polycrystalline ternary cathode material and performing ball milling and crushing, followed by calcination again. Overall, the high-nickel single-crystal cathode material is prepared by controlling the temperature and calcination time, which is applicable to high-nickel ternary cathode material products with different performance requirements. By adopting the strategy of high-temperature calcination combined with ball milling, the process is simple and the energy consumption is low, enabling the large-scale preparation of high-performance lithium-ion battery cathode materials. The obtained single-crystal cathode material has a better morphology. Further, by adjusting the composition and dosage of the lithium salt, solvent, and film-forming additive in the electrolyte, the electrochemical performance of the lithium-ion battery operating at low temperature is improved. Brief Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the preparation steps of the high-nickel single-crystal cathode material of the present invention.

[0022] Figure 2 It is a schematic diagram of the morphology of the high-nickel cathode material obtained in Example 2 of the present invention.

[0023] Figure 3 It is a HRTEM image of the high-nickel single-crystal cathode material obtained in Example 2 of the present invention and a schematic diagram of the Fourier transform of the selected area.

[0024] Figure 4 It is a graph of the cycle retention rate of the lithium-ion battery assembled with the high-nickel single-crystal cathode material and the low-temperature electrolyte of the present invention at low temperature. Detailed Embodiments

[0025] To deepen the understanding of the present invention, the following examples will be used to further elaborate on the present invention. These examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0026] In the following examples, in the LiNi a Co b Mn c O2 polycrystalline ternary cathode material, 0.6 ≤ a < 1, 0.01 ≤ b ≤ 0.2, 0.01 ≤ c ≤ 0.2, and a + b + c = 1. In the single-crystal LiNi a Co b Mn c O2 cathode material, 0.6 ≤ a < 1, 0.01 ≤ b ≤ 0.2, 0.01 ≤ c ≤ 0.2, and a + b + c = 1. Examples

[0027] According to Figure 1As shown in the figure, this embodiment presents a preparation method for a high-nickel single-crystal cathode material for lithium-ion batteries, including the following steps:

[0028] Step 1: Prepare LiNi 0.6 Co 0.2 Mn 0.2 O2 polycrystalline ternary cathode material;

[0029] Step 2: Put the LiNi 0.6 Co 0.2 Mn 0.2 O2 polycrystalline ternary cathode material into a sintering furnace. After raising the sintering temperature to 750 °C, carry out sintering, and the sintering time is 10 h;

[0030] Step 3: Take out and cool after sintering. After cooling to room temperature, put it into a ball mill for ball milling and crushing to obtain crushed material, where the rotational speed of the ball mill is 350 rpm / min and the ball milling time is 1 h;

[0031] Step 4: Put the obtained crushed material into the sintering furnace again. After raising the sintering temperature to 700 °C, carry out sintering, and the sintering time is the same as that in Step 2, which is 10 h;

[0032] Step 5: Take out and cool after sintering to obtain single-crystal LiNi 0.6 Co 0.2 Mn 0.2 O2 cathode material.

[0033] A high-nickel single-crystal cathode material for lithium-ion batteries. This high-nickel single-crystal cathode material for lithium batteries is the high-nickel single-crystal cathode material prepared by the above method.

[0034] A low-temperature electrolyte for lithium-ion batteries. This low-temperature electrolyte for lithium batteries includes the following raw materials in molar mass ratio: 8% lithium salt, 85% organic solvent, and 7% film-forming additive.

[0035] Among them, the lithium salt is any combination of four substances among LiPF6 (lithium hexafluorophosphate), LiDFOB (lithium difluorooxalate borate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), LiTFSi (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide salt), KNO3 (potassium nitrate). In this embodiment, the lithium salt is a composition of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiSFI (lithium bis(fluorosulfonyl)imide salt), and the ratio among LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiSFI (lithium bis(fluorosulfonyl)imide salt) is: 85:3:1:3.

[0036] The organic solvent is a combination of any three substances selected from EC (ethylene carbonate), EMC (ethyl methyl carbonate), DMC (dimethyl carbonate), DOL (1,3-dioxolane), and DME (dimethyl ether). In this embodiment, the organic solvent is a composition of EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate), and the ratio among the organic solvents EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate) is 1:1:1.

[0037] The film-forming additive is a combination of any three substances selected from VC (vinylene carbonate), FEC (fluoroethylene carbonate), TMSP (tris(trimethylsilyl) phosphate), EBC (ethyl benzyl chloride), and EC (ethylene carbonate). In this embodiment, the film-forming additive is a composition of VC (vinylene carbonate), FEC (fluoroethylene carbonate), and EBC (ethyl benzyl chloride), and the ratio among VC (vinylene carbonate), FEC (fluoroethylene carbonate), and EBC (ethyl benzyl chloride) is 3:15:6. Example

[0038] According to Figures 1 - 4 As shown, this embodiment provides a method for preparing a high-nickel single-crystal cathode material for a lithium-ion battery, including the following steps:

[0039] Step 1: Prepare a LiNi 0.8 Co 0.1 Mn 0.1 O2 polycrystalline ternary cathode material;

[0040] Step 2: Put the LiNi 0.8 Co 0.1 Mn 0.1 O2 polycrystalline ternary cathode material into a sintering furnace, raise the sintering temperature to 950 °C, and then carry out sintering for 13 h;

[0041] Step 3: Take it out and cool it after sintering. After cooling to room temperature, put it into a ball mill for ball milling and crushing to obtain crushed material, where the rotation speed of the ball mill is 250 rpm / min and the ball milling time is 6 h;

[0042] Step 4: Put the obtained crushed material into the sintering furnace again, raise the sintering temperature to 850 °C, and then carry out sintering. The sintering time is the same as that in Step 2, which is 13 h;

[0043] Step 5: Take it out and cool it after sintering to obtain a single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material.

[0044] High-nickel single-crystalline cathode material for lithium-ion batteries. The high-nickel single-crystalline cathode material for lithium batteries is the high-nickel single-crystalline cathode material prepared by the above method.

[0045] Low-temperature electrolyte for lithium-ion batteries. The low-temperature electrolyte for lithium batteries comprises the following raw materials in molar mass ratio: 20% lithium salt, 75% organic solvent, and 5% film-forming additive.

[0046] Among them, the lithium salt is any combination of four substances selected from LiPF6 (lithium hexafluorophosphate), LiDFOB (lithium difluorooxalate borate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), LiTFSi (lithium bis(trifluoromethanesulfonyl)imide), LiSFI (lithium bis(fluorosulfonyl)imide salt), and KNO3 (potassium nitrate). In this embodiment, the lithium salt is a composition of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiSFI (lithium bis(fluorosulfonyl)imide salt), and the ratio among LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiSFI (lithium bis(fluorosulfonyl)imide salt) is 85:3:1:3.

[0047] The organic solvent is any combination of three substances selected from EC (ethylene carbonate), EMC (ethyl methyl carbonate), DMC (dimethyl carbonate), DOL (1,3-dioxolane), and DME (dimethyl ether). In this embodiment, the organic solvent is a composition of DMC (dimethyl carbonate), DOL (1,3-dioxolane), and DME (dimethyl ether), and the ratio of DMC (dimethyl carbonate), DOL (1,3-dioxolane), and DME (dimethyl ether) is 1:1:1.

[0048] The film-forming additive is any combination of three substances selected from VC (vinylene carbonate), FEC (fluoroethylene carbonate), TMSP (tris(trimethylsilyl) phosphate), EBC (ethylbenzyl chloride), and EC (ethylene carbonate). In this embodiment, the film-forming additive is a composition of TMSP (tris(trimethylsilyl) phosphate), EBC (ethylbenzyl chloride), and EC (ethylene carbonate), and the ratio of TMSP (tris(trimethylsilyl) phosphate), EBC (ethylbenzyl chloride), and EC (ethylene carbonate) is 1:25:2.

[0049] As Figure 2 shown, it is the scanning electron microscope image of the sample prepared in this embodiment. It can be seen that the sample in this embodiment has a uniform single-crystalline structure and almost no aggregated secondary particles. Further, from Figure 3 it can be known that the sample in this embodiment is mainly a layered structure, and the phase is consistent with LiNiO2, indicating that the high-nickel single-crystalline cathode material has been successfully prepared. Example

[0050] According to Figures 1 - 4 as shown, this embodiment proposes a preparation method of a high-nickel single-crystal cathode material for lithium-ion batteries, including the following steps:

[0051] Step 1: Prepare LiNi 0.9 Co 0.05 Mn 0.05 O2 polycrystalline ternary cathode material;

[0052] Step 2: Put the LiNi 0.9 Co 0.05 Mn 0.05 O2 polycrystalline ternary cathode material into a sintering furnace. After raising the sintering temperature to 880 °C, perform sintering, and the sintering time is 18 h;

[0053] Step 3: Take out and cool after sintering. After cooling to room temperature, put it into a ball mill for ball milling and crushing to obtain crushed material, where the rotation speed of the ball mill is 300 rpm / min and the ball milling time is 3 h;

[0054] Step 4: Put the obtained crushed material into the sintering furnace again. After raising the sintering temperature to 800 °C, perform sintering, and the sintering time is the same as that in Step 2, which is 18 h;

[0055] Step 5: Take out and cool after sintering to obtain single-crystal LiNi 0.9 Co 0.05 Mn 0.05 O2 cathode material.

[0056] A high-nickel single-crystal cathode material for lithium-ion batteries, and this high-nickel single-crystal cathode material for lithium batteries is prepared by the above method.

[0057] A low-temperature electrolyte for lithium-ion batteries, and this low-temperature electrolyte for lithium batteries includes the following raw materials in molar mass ratio: 19% lithium salt, 80% organic solvent, and 1% film-forming additive.

[0058] Among them, the lithium salt is any combination of four substances among LiPF6 (lithium hexafluorophosphate), LiDFOB (lithium difluorooxalate borate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiTFSi (lithium bis(trifluoromethanesulfonyl)imide). In this embodiment, the lithium salt is a composition of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiSFI, and the ratio (molar ratio) among LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiPO2F2 (lithium difluorophosphate), and LiSFI is: 85:3:1:3.

[0059] The organic solvent is any combination of three substances among EC (ethylene carbonate), EMC (ethyl methyl carbonate), DMC (dimethyl carbonate), DOL (1,3-dioxolane), and DME (dimethyl ether). In this embodiment, the organic solvent is a composition of EMC (ethyl methyl carbonate), DME (dimethyl ether), and DOL (1,3-dioxolane), and the ratio among EMC (ethyl methyl carbonate), DOL (1,3-dioxolane), and DME (dimethyl ether) is 1:1:1.

[0060] The film-forming additive is any combination of three substances among VC (vinylene carbonate), FEC (fluoroethylene carbonate), TMSP (tris(trimethylsilyl) phosphate), EBC (ethyl benzyl chloride), and EC (ethylene carbonate). In this embodiment, the film-forming additive is a composition of VC (vinylene carbonate), EBC (ethyl benzyl chloride), and EC (ethylene carbonate). The ratio among VC (vinylene carbonate), EBC (ethyl benzyl chloride), and EC (ethylene carbonate) is 1:25:2.

[0061] Combining Example 1, Example 2, and Example 3, using the high-nickel single-crystal ternary cathode material prepared by the present invention as the cathode, using metallic lithium as the anode, and forming a lithium-ion battery with a low-temperature electrolyte, and then testing the long-cycle performance of the lithium-ion battery at -20°C, as Figure 4 shown. In the voltage range of 2.7 - 4.3 V, the capacity retention rates of the high-nickel single-crystal cathode materials prepared in Example 2 and Example 3 after 100 cycles at -20°C and a current density of 1C are both higher than that of Example 1. Among them, Example 2 is the best example, and there is a significant improvement in the capacity retention rate after 100 cycles compared with Example 1 and Example 3. Therefore, the high-nickel single-crystal cathode material prepared by the present invention, combined with the low-temperature electrolyte, can significantly improve the cycling performance stability of the lithium-ion battery at low temperatures.

[0062] The present invention prepares a high-nickel single-crystal cathode material by calcining a polycrystalline ternary cathode material, performing ball milling and crushing by ball milling, and then performing calcination again. Overall, by controlling the temperature and calcination time, it is applicable to high-nickel ternary cathode material products with different performance requirements. By adopting the strategy of high-temperature calcination combined with ball milling, the process is simple and the energy consumption is low, and it can realize the large-scale preparation of high-performance lithium-ion battery cathode materials. The obtained single-crystal cathode material has a better morphology. Further, by adjusting the composition and dosage of the lithium salt, solvent, and film-forming additive in the electrolyte, the electrochemical performance of the lithium-ion battery operating at low temperatures is improved, adapting to the low-temperature environment and ensuring the working efficiency of the lithium-ion battery.

[0063] The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the framework and scope of application of the present invention, the present invention will have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. Preparation method of high-nickel single-crystal cathode material for lithium-ion battery, characterized in that: It includes the following steps: Step 1: Prepare LiNi 0.8 Co 0.1 Mn 0.1 O2 polycrystalline ternary cathode material; Step 2: Put the LiNi 0.8 Co 0.1 Mn 0.1 O2 polycrystalline ternary cathode material into a sintering furnace. After raising the sintering temperature to 950 °C, perform sintering for 13 h; Step 3: Take out and cool after sintering. After cooling to room temperature, put it into a ball mill for ball milling and crushing to obtain crushed material, where the rotational speed of the ball mill is 250 rpm / min and the ball milling time is 6 h; Step 4: Put the obtained crushed material into the sintering furnace again. After raising the sintering temperature to 850 °C, carry out sintering, and the sintering time is the same as that in Step 2, which is 13 h; Step Five: Take out and cool after sintering to obtain single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material.

2. A lithium-ion battery, comprising a high-nickel single-crystal cathode material, characterized in that: The high-nickel single-crystal cathode material is the high-nickel single-crystal cathode material prepared by the method described in Claim 1.

3. A low-temperature electrolyte for the lithium-ion battery according to claim 2, characterized in that: The low-temperature electrolyte includes the following raw materials in molar mass ratio: 20% of lithium salt, 75% of organic solvent, and 5% of film-forming additive; The lithium salt is a composition of LiPF6, LiBF4, LiPO2F2, and LiSFI, and the ratio among LiPF6, LiBF4, LiPO2F2, and LiSFI is: 85:3:1:3; The organic solvent is a composition of DMC, DOL, and DME, and the ratio of DMC, DOL, and DME is 1:1:1; The film-forming additive is a composition of TMSP, EBC, and EC, and the ratio of TMSP, EBC, and EC is 1:25:2.

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