Deep eutectic electrolyte, preparation method and application thereof, and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a deep eutectic electrolyte, a preparation method and application thereof and a lithium ion battery. The deep eutectic electrolyte provided by the invention comprises a lithium salt and fluorine-containing amide, the mass ratio of the lithium salt to the fluorine-containing amide is 1: (1-12). According to the deep eutectic electrolyte provided by the invention, the lithium salt and the fluorine-containing amide are compounded, so that the obtained electrolyte can be kept in a liquid state within a relatively wide temperature range; the strong interaction between the fluorine-containing amide and the lithium salt can dissociate a large amount of lithium salt, promote rapid conduction of ions and increase the migration rate of lithium ions in the electrolyte, so that the electrochemical performance of the electrolyte is improved; the fluorine-containing amide molecules and the lithium ions form a solvation effect, and a layer of SEI film rich in LiF and Li3N is formed on the surface of the lithium metal in the circulation process, so that uniform deposition of the lithium ions is promoted, growth of lithium dendrites is inhibited, consumption of electrolyte is reduced, and the circulation stability of the lithium ion battery is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a deep - eutectic electrolyte and its preparation method and application, and a lithium - ion battery. Background Art

[0002] As one of the greatest inventions in the 20th century, lithium - ion batteries are widely used in various aspects of human society such as clothing, food, housing, and transportation due to their advantages of high specific energy, long cycle life, no memory effect, and low self - discharge rate. In the field of 3C electronic products (computers, communications, and consumer electronics), lithium - ion batteries almost occupy the entire market. A lithium - ion battery is a secondary battery, which mainly works by the movement of lithium ions between the positive electrode and the negative electrode. During the charge - discharge process, Li + intercalates and de - intercalates between the two electrodes: during charging, Li + de - intercalates from the positive electrode, passes through the electrolyte and intercalates into the negative electrode, and the negative electrode is in a lithium - rich state; during discharging, the situation is reversed.

[0003] Different from other types of batteries, lithium batteries have advantages such as high energy density, long cycle life, high coulomb efficiency, low self - discharge rate, low operation and maintenance costs, wide operating temperature range, and excellent reliability. Therefore, lithium batteries have good application prospects, especially in portable electronic products, electric vehicles, and aerospace fields. However, in order to make lithium batteries more efficiently applied in these fields, their characteristics such as energy density, power density, low - temperature resistance, safety, and cycle life need to be further improved. Research teams worldwide are also focusing on directions such as positive and negative electrode materials and electrolyte materials in order to develop lithium - ion batteries with excellent performance. Currently, the unsatisfactory capacity and cycle performance of commercial organic electrolytes hinder the practical application of lithium - metal batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a deep - eutectic electrolyte and its preparation method and application, and a lithium - ion battery. The deep - eutectic electrolyte provided by the present invention can exhibit high capacity and excellent cycle and rate performance when applied to lithium - ion batteries.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a deep - eutectic electrolyte, comprising a lithium salt and a fluoroamide;

[0007] The molar ratio of the lithium salt to the fluoroamide is 1:1 to 12.

[0008] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium nitrate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0009] Preferably, the fluoroamide is difluoroacetamide, N-methyltrifluoroacetamide, trifluoroacetamide or bistrifluoroacetamide.

[0010] The present invention also provides a method for preparing the deep eutectic electrolyte described in the above technical solution, including the following steps:

[0011] Mix a lithium salt and a fluoroamide to obtain the deep eutectic electrolyte.

[0012] Preferably, the mixing method is stirring; the temperature of the stirring is 30-70 °C, and the time is 10-36 h.

[0013] The present invention also provides the application of the deep eutectic electrolyte described in the above technical solution or the deep eutectic electrolyte prepared by the preparation method described in the above technical solution in a lithium-ion battery.

[0014] The present invention also provides a lithium-ion battery, including a positive electrode, an electrolyte, a separator and a negative electrode;

[0015] The electrolyte is the deep eutectic electrolyte described in the above technical solution or the deep eutectic electrolyte prepared by the preparation method described in the above technical solution.

[0016] Preferably, the positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector;

[0017] The positive current collector is aluminum foil;

[0018] Calculated by mass percentage, the positive active material includes 80-90% of a positive active material, 5-10% of a conductive agent and 5-10% of a binder.

[0019] Preferably, the positive active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate and lithium-rich manganese-based materials;

[0020] The conductive agent includes one or more of acetylene black, Ketjen black, conductive carbon black and graphene;

[0021] The binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, polypropylene resin and carboxymethyl cellulose.

[0022] Preferably, the negative electrode is a lithium sheet or a lithium-containing alloy;

[0023] The separator is a polyethylene film, a polypropylene film, a glass fiber film or a cellulose film.

[0024] The present invention provides a deep eutectic electrolyte, comprising a lithium salt and a fluoroamide; the molar ratio of the lithium salt to the fluoroamide is 1:1 to 12. The deep eutectic electrolyte provided by the present invention combines a lithium salt and a fluoroamide, and the resulting electrolyte can remain liquid within a relatively wide temperature range; the strong interaction between the fluoroamide and the lithium salt can dissociate a large amount of lithium salt, promote the rapid conduction of ions, increase the migration rate of lithium ions in the electrolyte, and improve the electrochemical performance of the electrolyte; the amide molecule forms a solvation effect with lithium ions, and a SEI film rich in LiF and Li3N will be formed on the surface of the lithium metal during the cycling process, thereby promoting the uniform deposition of lithium ions, inhibiting the growth of lithium dendrites, reducing the consumption of the electrolyte, and being beneficial to improving the cycle stability of the lithium-ion battery; among amide molecules, fluoroamide has higher specific capacity and more excellent cycle and rate performance when applied to lithium batteries compared with non-fluoroamide. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0026] Figure 1 It is a process diagram for preparing the deep eutectic electrolyte obtained in Example 1;

[0027] Figure 2 It is a differential scanning calorimetry test diagram of the deep eutectic electrolyte obtained in Example 1;

[0028] Figure 3 It is a cycle rate curve diagram of the lithium metal battery obtained in Example 1;

[0029] Figure 4 It is a charge-discharge curve diagram of the lithium metal battery obtained in Example 2 cycling 100 times at a rate of 1C;

[0030] Figure 5 It is a cycle rate curve diagram of the lithium metal battery obtained in Example 3;

[0031] Figure 6 It is a scanning electron microscope image of the lithium metal negative electrode obtained in Example 3;

[0032] Figure 7 It is a charge-discharge curve diagram of the lithium metal battery obtained in Example 4 cycling 50 times at a rate of 1C;

[0033] Figure 8 It is a charge-discharge curve diagram of the lithium metal battery obtained in Comparative Example 1 cycling 30 times at a rate of 1C;

[0034] Figure 9 The cyclic magnification curve graph of the lithium metal battery obtained in Comparative Example 2. Specific Embodiments

[0035] The present invention provides a deep eutectic electrolyte, comprising a lithium salt and a fluoroamide;

[0036] The molar ratio of the lithium salt to the fluoroamide is 1:1 to 12.

[0037] In the present invention, unless otherwise specified, the raw material components are all commercially available products well-known to those skilled in the art.

[0038] In the present invention, the lithium salt preferably includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium nitrate (LiNO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); more preferably one or more of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium nitrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide; most preferably one or more of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide; when two or more of the above specific selections are used as the lithium salt, the present invention has no special limitation on the ratio of the lithium salts.

[0039] In the present invention, the fluoroamide is preferably difluoroacetamide, N-methyltrifluoroacetamide, trifluoroacetamide, or bistrifluoroacetamide; more preferably difluoroacetamide, N-methyltrifluoroacetamide, or trifluoroacetamide.

[0040] In the present invention, the molar ratio of the lithium salt to the fluoroamide is 1:1 to 12, preferably 1:1 to 10, more preferably 1:1 to 9.

[0041] The deep eutectic electrolyte provided by the present invention uses a composite of a lithium salt and a fluoroamide. The eutectic temperature of the obtained electrolyte is -80 °C, and it can remain liquid within a relatively wide temperature range; the strong interaction between the fluoroamide and the lithium salt can dissociate a large amount of the lithium salt, promote the rapid conduction of ions, increase the migration rate of lithium ions in the electrolyte, and improve the electrochemical performance of the electrolyte; the amide molecule forms a solvation effect with lithium ions, and a SEI film rich in LiF and Li3N will be formed on the surface of the lithium metal during the cycling process, thereby promoting the uniform deposition of lithium ions, inhibiting the growth of lithium dendrites, reducing the consumption of the electrolyte, and being beneficial to improving the cycling stability of the lithium ion battery; among amide molecules, fluoroamides have higher specific capacity and more excellent cycling and magnification performance when applied to lithium batteries compared to non-fluoroamides.

[0042] The present invention also provides a preparation method of the deep eutectic electrolyte described in the above technical solution, comprising the following steps:

[0043] Mix the lithium salt and the fluoroamide to obtain the deep eutectic electrolyte.

[0044] In the present invention, the mixing method is preferably stirring; the temperature of the stirring is preferably 30 - 70 °C, more preferably 30 - 60 °C, and most preferably 30 - 50 °C; the time is preferably 10 - 36 h, more preferably 12 - 32 h, and most preferably 12 - 24 h; the present invention has no special limitation on the rotation speed of the stirring, as long as a uniform and transparent deep eutectic electrolyte can be obtained.

[0045] The preparation method provided by the present invention is simple to operate, and the obtained deep eutectic electrolyte has the characteristics of a wide liquid temperature range, relatively stable to the lithium metal negative electrode, and a wide voltage window.

[0046] The present invention also provides the application of the deep eutectic electrolyte described in the above technical solution or the deep eutectic electrolyte prepared by the preparation method described in the above technical solution in a lithium-ion battery.

[0047] The present invention has no special limitation on the application of the deep eutectic electrolyte in a lithium-ion battery, and the application of the lithium-ion electrolyte well-known to those skilled in the art can be adopted.

[0048] The present invention also provides a lithium-ion battery, including a positive electrode, an electrolyte, a separator, and a negative electrode;

[0049] The electrolyte is the deep eutectic electrolyte described in the above technical solution or the deep eutectic electrolyte prepared by the preparation method described in the above technical solution.

[0050] In the present invention, the positive electrode preferably includes a positive electrode current collector and a positive electrode active material attached to the surface of the positive electrode current collector; the positive electrode current collector is preferably aluminum foil.

[0051] In the present invention, calculated by mass percentage, the positive electrode active material preferably includes 80 - 90%, more preferably 80 - 85% of the positive electrode active material; the positive electrode active material preferably includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium-rich manganese-based materials, more preferably one or more of lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium-rich manganese-based materials, and most preferably lithium nickel cobalt manganese oxide and / or lithium iron phosphate; when there are two or more of the above specific selections for the positive electrode active material, the present invention has no special limitation on the ratio of the positive electrode active material.

[0052] In the present invention, by mass percentage, the positive electrode active material preferably includes 5-10% of a conductive agent, more preferably 7-10%; the conductive agent preferably includes one or more of acetylene black, Ketjen black, conductive carbon black, and graphene, more preferably one or more of acetylene black, Ketjen black, and conductive carbon black, and most preferably Ketjen black and / or conductive carbon black; when the conductive agent is two or more of the above specific selections, the present invention does not have any special limitation on the ratio of the conductive agent.

[0053] In the present invention, by mass percentage, the positive electrode active material preferably includes 5-10% of a binder, more preferably 7-10%; the binder preferably includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, polypropylene resin, and carboxymethyl cellulose, more preferably one or more of polyvinylidene fluoride, styrene-butadiene rubber, and polypropylene resin, and most preferably polyvinylidene fluoride and / or polypropylene resin; when the binder is two or more of the above specific selections, the present invention does not have any special limitation on the ratio of the binder.

[0054] In the present invention, the mass of the positive electrode is preferably 1.8-3.5 mg, more preferably 2-3.1 mg.

[0055] The present invention does not have any special limitation on the amount of the deep eutectic electrolyte, and the amount of the lithium ion battery electrolyte well-known to those skilled in the art can be used; specifically, when the lithium ion battery is a CR2025 type button cell, the amount of the electrolyte is preferably 20-70 μL, more preferably 25-60 μL.

[0056] In the present invention, the negative electrode is preferably a lithium sheet or a lithium-containing alloy, more preferably a lithium sheet.

[0057] In the present invention, the separator is preferably a polyethylene film, a polypropylene film, a glass fiber film, or a cellulose film, more preferably a polyethylene film or a polypropylene film.

[0058] The present invention does not have any special limitation on the preparation method of the lithium ion battery, and the assembly method of the lithium ion battery well-known to those skilled in the art can be used.

[0059] In order to further illustrate the present invention, the deep eutectic electrolyte provided by the present invention, its preparation method and application, and the lithium ion battery will be described in detail below with reference to the drawings and examples, but they cannot be understood as limiting the protection scope of the present invention.

[0060] Example 1

[0061] In this example, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the fluoroamide is N-methyltrifluoroacetamide. The two solids, LiTFSI and N-methyltrifluoroacetamide, are mixed in a molar ratio of 1:6 and stirred at 30 °C for 12 h to obtain a homogeneous transparent solution, i.e., the deep eutectic electrolyte. The preparation process is shown in Figure 1 .

[0062] The CR2025 coin cell is assembled by a conventional method. Among them, the positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector. The positive current collector is aluminum foil. The positive active material includes 80 wt% of a positive active material, 10 wt% of a conductive agent, and 10 wt% of a binder. The positive active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, the conductive agent is conductive carbon black, the binder is polyvinylidene fluoride, and the mass of the positive electrode is 2.12 mg; the negative electrode is a lithium sheet; the electrolyte is the above-mentioned deep eutectic electrolyte, and the dropwise addition amount of the electrolyte is 55 μL; the separator is a polypropylene film.

[0063] Example 2

[0064] In this example, the lithium salt is a mixed lithium salt composed of lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate (the molar ratio of LiTFSI:LiDFOB is 6:1), and the fluoroamide is trifluoroacetamide. The mixed lithium salt and trifluoroacetamide are mixed in a molar ratio of 1:7 and stirred at 40 °C for 18 h to obtain a homogeneous transparent solution, i.e., the deep eutectic electrolyte.

[0065] The CR2025 coin cell is assembled by a conventional method. Among them, the positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector. The positive current collector is aluminum foil. The positive active material includes 83 wt% of a positive active material, 9 wt% of a conductive agent, and 8 wt% of a binder. The positive active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, the conductive agent is conductive carbon black, the binder is polypropylene resin, and the mass of the positive electrode is 2.52 mg; the negative electrode is a lithium sheet; the electrolyte is the above-mentioned deep eutectic electrolyte, and the dropwise addition amount of the electrolyte is 50 μL; the separator is a polypropylene film.

[0066] Example 3

[0067] In this example, the lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), and the fluoroamide is difluoroacetamide. The lithium bis(fluorosulfonyl)imide and difluoroacetamide are mixed in a molar ratio of 1:3 and stirred at 35 °C for 20 h to obtain a homogeneous transparent solution, i.e., the deep eutectic electrolyte.

[0068] The CR2025 button cell was assembled by a conventional method. Among them, the positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector. The positive current collector is aluminum foil, and the positive active material includes 83 wt% of a positive active material material, 9 wt% of a conductive agent, and 8 wt% of a binder. The positive active material is LiFePO4, the conductive agent is Ketjen black, and the binder is polyvinylidene fluoride. The mass of the positive electrode is 3.04 mg; the negative electrode is a lithium sheet; the electrolyte is the above-mentioned deep eutectic electrolyte, and the dropping amount of the electrolyte is 50 μL; the separator is a polyethylene film.

[0069] Example 4

[0070] In this example, the lithium salt is a mixed lithium salt, which is composed of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate (the molar ratio of LiTFSI:LiBOB is 5:1), and the fluorinated amide is bis(trifluoroethyl)amide. The mixed lithium salt and bis(trifluoroethyl)amide were mixed in a molar ratio of 1:5 and stirred at 40 °C for 15 h to obtain a homogeneous transparent solution, which is the deep eutectic electrolyte.

[0071] The CR2025 button cell was assembled by a conventional method. Among them, the positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector. The positive current collector is aluminum foil, and the positive active material includes 85 wt% of a positive active material material, 8 wt% of a conductive agent, and 7 wt% of a binder. The positive active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, the conductive agent is conductive carbon black, the binder is polypropylene resin, the mass of the positive electrode is 2.24 mg; the negative electrode is a lithium sheet; the electrolyte is the above-mentioned deep eutectic electrolyte, and the dropping amount of the electrolyte is 60 μL; the separator is a polyethylene film.

[0072] Comparative Example 1

[0073] Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and acetamide were mixed in a molar ratio of 1:4 and stirred at 35 °C for 20 h to obtain a homogeneous transparent solution, which is the deep eutectic electrolyte.

[0074] The CR2025 button cell was assembled by a conventional method. Among them, the positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector. The positive current collector is aluminum foil, and the positive active material includes 80 wt% of a positive active material material, 10 wt% of a conductive agent, and 10 wt% of a binder. The positive active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, the conductive agent is conductive carbon black, the binder is polyvinylidene fluoride, the mass of the positive electrode is 2.01 mg; the negative electrode is a lithium sheet; the electrolyte is the above-mentioned deep eutectic electrolyte, and the dropping amount of the electrolyte is 50 μL; the separator is a polyethylene film.

[0075] Comparative Example 2

[0076] Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and N-methylacetamide were mixed in a molar ratio of 1:4.5 and stirred at 45 °C for 15 h to obtain a homogeneous transparent solution, i.e., a deep eutectic electrolyte.

[0077] A CR2025 coin cell was assembled by a conventional method. Among them, the positive electrode included a positive current collector and a positive active material attached to the surface of the positive current collector. The positive current collector was aluminum foil, and the positive active material included 85 wt% of a positive active material material, 8 wt% of a conductive agent, and 7 wt% of a binder. The positive active material was LiNi 0.6 Co 0.2 Mn 0.2 O2, the conductive agent was Ketjenblack, the binder was polyvinylidene fluoride, and the mass of the positive electrode was 2.09 mg; the negative electrode was a lithium sheet; the electrolyte was the above-mentioned deep eutectic electrolyte, and the dropwise addition amount of the electrolyte was 50 μL; the separator was a polyethylene film.

[0078] Test Example 1

[0079] The deep eutectic electrolyte prepared in Example 1 was tested by differential scanning calorimetry (DSC). The test temperature range was from -100 °C to 100 °C, and the test results are shown in Figure 2 .

[0080] It can be seen from Figure 2 that only one endothermic peak appears, corresponding to its glass transition temperature (Tg), which proves that the prepared electrolyte has typical eutectic characteristics. The eutectic point temperature is -80.48 °C, and the prepared deep eutectic electrolyte has a wide liquid temperature range.

[0081] Test Example 2

[0082] The coin cell obtained in Example 1 was tested for cyclic rate performance in the voltage range of 2.8 - 4.3 V, and the test results are shown in Figure 3 .

[0083] It can be seen from Figure 3 that at room temperature, the specific capacity at a rate of 0.2C is 165 mAh / g; the specific capacity at a rate of 0.5C is 154 mAh / g; the specific capacity at a rate of 1C is 143 mAh / g; the specific capacity at a rate of 2C is 130 mAh / g; the specific capacity at a rate of 5C is 106 mAh / g: when returning to a rate of 0.2C again, the specific capacity can reach 170 mAh / g. It can be seen that applying the deep eutectic electrolyte prepared in Example 1 to the coin cell, the obtained battery has excellent rate performance.

[0084] The coin-type battery obtained in Example 2 was tested for charge-discharge performance at a cycle of 100 circles at a 1C rate in the voltage range of 2.8 - 4.3V. The test results are shown in Figure 4 .

[0085] It can be seen from Figure 4 that the initial capacity of the coin-type battery obtained in Example 2 at a 1C rate is 153 mAh / g. After 30 cycles, the capacity remains 152 mAh / g. After 60 cycles, the capacity is 139 mAh / g. After 100 cycles, the discharge capacity still remains 133 mAh / g, indicating that the coin-type lithium-ion battery assembled with the deep eutectic electrolyte provided by the present invention has good high-rate long-cycle stability performance.

[0086] The coin-type battery obtained in Example 3 was tested for cycle rate performance in the voltage range of 2.5 - 3.8V. The test results are shown in Figure 5 . The lithium metal negative electrode after the rate performance test was tested by scanning electron microscopy (SEM). The test results are shown in Figure 6 .

[0087] It can be seen from Figure 5 that at room temperature, the specific capacity at a 0.2C rate is 166 mAh / g; the specific capacity at a 0.5C rate is 160 mAh / g; the specific capacity at a 1C rate is 153 mAh / g; the specific capacity at a 2C rate is 144 mAh / g; the specific capacity at a 5C rate is 113 mAh / g; when returning to a 0.2C rate again, the specific capacity can still reach 165 mAh / g. It can be seen from Figure 6 that the surface of the lithium negative electrode after cycling is flat and no lithium dendrites are generated. It can be seen that the coin-type battery obtained in Example 3 has excellent rate cycling performance and is relatively stable for the lithium metal negative electrode.

[0088] The coin-type battery obtained in Example 4 was tested for charge-discharge performance at a cycle of 50 circles at a 1C rate with a cut-off voltage of 2.8 - 4.5V. The test results are shown in Figure 7 .

[0089] It can be seen from Figure 7 that the initial capacity of the coin-type battery obtained in Example 4 at a 1C rate is 159 mAh / g, and the capacity remains at 154 mAh / g after 25 and 50 cycles, indicating that the coin-type battery obtained in Example 4 has excellent long-cycle performance.

[0090] The coin-type battery obtained in Comparative Example 1 was tested for charge-discharge performance at a cycle of 50 circles at a 1C rate in the voltage range of 2.8 - 4.3V. The test results are shown in Figure 8 .

[0091] It can be seen from Figure 8It can be seen that the button cell obtained in Comparative Example 1 has an initial capacity of 155 mAh / g at a rate of 1C. After 20 cycles, the capacity is 133 mAh / g, and after 30 cycles, the capacity is only 102 mAh / g. This shows that the button cell obtained in Comparative Example 1 has serious capacity decay during cycling and does not have long-cycle performance.

[0092] The cycling rate performance of the button cell obtained in Comparative Example 2 was tested in the voltage range of 2.5 - 3.8V. The test results are shown in Figure 9 .

[0093] As Figure 7 can be seen, at room temperature, the specific capacity at a rate of 0.2C is 172 mAh / g; the specific capacity at a rate of 0.5C is 168 mAh / g; the specific capacity at a rate of 1C is 155 mAh / g; at a rate of 2C, the specific capacity after 5 cycles is only 100 mAh / g; at a rate of 5C, the specific capacity after 5 cycles is only 16 mAh / g; when the rate returns to 0.2C again, the specific capacity is 96 mAh / g. This shows that the button cell obtained in Comparative Example 2 cannot be cycled at high rates.

[0094] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. Other embodiments can be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A deep eutectic electrolyte, characterized in that, It includes a lithium salt and a fluoroamide; The molar ratio of the lithium salt to the fluoroamide is 1:1 to 12.

2. The deep eutectic electrolyte according to claim 1, wherein The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium nitrate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

3. The deep eutectic electrolyte according to claim 1, characterized in that, The fluoroamide is difluoroacetamide, N-methyltrifluoroacetamide, trifluoroacetamide, or bis(trifluoroacetamide).

4. The preparation method of the deep eutectic electrolyte according to any one of claims 1 to 3, characterized in that, It includes the following steps: Mix the lithium salt and the fluoroamide to obtain the deep eutectic electrolyte.

5. The preparation method according to claim 4, wherein The mixing method is stirring; the stirring temperature is 30 to 70 °C, and the time is 10 to 36 h.

6. Application of the deep eutectic electrolyte according to any one of claims 1 to 3 or the deep eutectic electrolyte prepared by the preparation method according to claim 4 or 5 in a lithium-ion battery.

7. A lithium-ion battery, characterized in that, It includes a positive electrode, an electrolyte, a separator, and a negative electrode; The electrolyte is the deep eutectic electrolyte according to any one of claims 1 to 3 or the deep eutectic electrolyte prepared by the preparation method according to claim 4 or 5.

8. The lithium ion battery according to claim 7, characterized in that, The positive electrode includes a positive current collector and a positive active material attached to the surface of the positive current collector; The positive current collector is aluminum foil; Calculated by mass percentage, the positive active material includes 80 to 90% of a positive active material, 5 to 10% of a conductive agent, and 5 to 10% of a binder.

9. The lithium ion battery according to claim 8, characterized in that, The positive active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium-rich manganese-based materials; The conductive agent includes one or more of acetylene black, Ketjen black, conductive carbon black, and graphene; The binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, polypropylene resin, and carboxymethyl cellulose.

10. The lithium-ion battery according to claim 7, characterized in that, The negative electrode is a lithium sheet or a lithium-containing alloy; The separator is a polyethylene membrane, a polypropylene membrane, a glass fiber membrane, or a cellulose membrane.

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