Electrolyte suitable for high-rate charge-discharge and low-temperature cycle and lithium metal battery

Abstract

The invention discloses an electrolyte suitable for high-rate charge-discharge and low-temperature circulation and a lithium metal battery, and belongs to the technical field of lithium batteries. The electrolyte comprises the lithium salt, the additive and the cosolvent mixture, the cosolvent mixture is composed of the methyl acetate, the methyl difluoroacetate and the fluoroethylene carbonate, and due to the synergistic effect of a mixed solvent system, the electrolyte can have high high voltage resistance and oxidation resistance; meanwhile, a low-impedance electrode electrolyte phase interfacial film rich in inorganic matter LiF can be formed, rapid desolvation of Li < + > is promoted, the rate capability and the low-temperature performance of the battery are further remarkably improved, and the battery can also normally work at the high rate of-30 DEG C and 2C. The preparation raw materials of the electrolyte are cheap and easy to obtain, the preparation process is simple and convenient, and a thought is provided for industrial production of the low-temperature electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to an electrolyte and a lithium metal battery suitable for high-rate charging and discharging and low-temperature cycling. Background Art

[0002] The use of batteries in some extreme environments (high latitudes, defense and space) faces severe challenges. The energy density of lithium metal batteries is higher than that of traditional lithium-ion batteries, which means they can store more energy and provide longer use time. In addition, lithium metal has an advantage over graphite negative electrodes in terms of the tendency of lithium plating at the negative electrode at low temperatures. Therefore, low-temperature lithium metal batteries are a very promising development direction.

[0003] Compared with electrode modification and battery structure design, electrolyte modification is a simpler and more efficient method to improve the low-temperature performance of batteries. The solvent EC (ethylene carbonate) in traditional carbonate-based electrolytes has a high freezing point and is easy to react with lithium metal, so it is not suitable for low-temperature lithium metal systems. Because the charge transfer impedance during low-temperature charging is much greater than that during normal temperature charging, the battery will show the characteristics of difficulty in low-temperature charging, so the current research on low-temperature electrolytes is more focused on improving the low-temperature discharge capacity under normal temperature charging. For lithium metal, the reaction with solvents, salt anions and trace amounts of water, as well as the mutual reaction between the reaction products will lead to changes in the composition of the electrode electrolyte interface film, which in turn shows differences in the protection effect on the electrode. It is generally believed that the rich LiF in the interface film not only contributes to the stability of the interface and the integrity of the structure, but also reduces the energy barrier for lithium ion transmission.

[0004] Therefore, it is necessary to develop an electrolyte suitable for high-rate charge and discharge of lithium metal, low-temperature cycle and capable of generating inorganic LiF-rich electrolyte, so as to realize the normal operation of lithium metal batteries at low temperatures and provide technical support for the widespread application of low-temperature lithium metal batteries. Summary of the invention

[0005] The main purpose of the present invention is to provide an electrolyte and a lithium metal battery suitable for high-rate charge and discharge and low-temperature cycling, so as to increase the content of LiF in the interface film and reduce the desolvation energy barrier at low temperature, so that the lithium metal battery containing the electrolyte has good rate performance and low-temperature performance.

[0006] In order to achieve the above-mentioned object, the present invention provides an electrolyte suitable for high-rate charge and discharge and low-temperature cycle, wherein the electrolyte comprises a lithium salt, an additive and a co-solvent mixture, wherein the co-solvent mixture comprises methyl acetate, methyl difluoroacetate and fluoroethylene carbonate.

[0007] Furthermore, the volume of the methyl difluoroacetate accounts for 10-30% of the volume percentage of the electrolyte.

[0008] Furthermore, the volume percentages of the methyl acetate, the methyl difluoroacetate and the fluoroethylene carbonate are (40% to 60%):(10% to 30%):(20% to 40%).

[0009] Furthermore, the lithium salt is a mixture of lithium hexafluorophosphate and lithium tetrafluoroborate; the additive is selected from one or more of lithium bis(oxalatoborate), lithium bis(fluorooxalatoborate), lithium difluorobis(oxalatophosphate), and lithium difluorophosphate.

[0010] Furthermore, the molar ratio of the lithium hexafluorophosphate to the lithium tetrafluoroborate is 1 to 9:1.

[0011] Furthermore, the concentration of the lithium salt is 0.5-2 mol / L; the concentration of the additive is 0.01-0.5 mol / L.

[0012] Furthermore, the electrolyte preparation process includes: stirring and mixing the lithium salt, the additive and the co-solvent mixture, and the stirring and mixing temperature is 15-20°C.

[0013] Another aspect of the present invention provides a use of the aforementioned electrolyte suitable for high-rate charge and discharge and low-temperature cycle in a lithium-ion battery.

[0014] Another aspect of the present invention provides a lithium metal battery, comprising the aforementioned electrolyte suitable for high-rate charge and discharge and low-temperature cycling.

[0015] Furthermore, the lithium metal battery also includes a positive electrode material, a negative electrode material and a separator, wherein the positive electrode material is a high-nickel ternary positive electrode material, and the high-nickel ternary positive electrode material is LiNi 1-x-y Co x Mn y O 2 , 0.075≤x≤0.2, 0.075≤y≤0.2.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the electrolyte of the present invention comprises a lithium salt, an additive and a co-solvent mixture, wherein the co-solvent mixture is composed of methyl acetate, methyl difluoroacetate and fluoroethylene carbonate, and the synergistic effect of the mixed solvent system can make the electrolyte have higher high-voltage resistance and oxidation resistance, and can form a low-impedance electrode electrolyte interphase film rich in inorganic LiF, and promote Li + The rapid desolvation of the electrolyte significantly improves the rate performance and low-temperature performance of the battery. The raw materials for the preparation of the electrolyte are cheap and easy to obtain, and the preparation process is simple, which provides ideas for the industrial production of low-temperature electrolytes.

[0017] In addition, the present invention provides a lithium metal battery containing the high-rate and low-temperature electrolyte of the present invention, wherein a strong and stable interface film with high ionic conductivity is generated at the electrode of the battery, thereby exhibiting the characteristics of high-rate resistance, and the capacity changes little with the rate. At the same time, based on the interaction between the solvent molecules in the electrolyte of the present invention, the Li + The appropriate distance shows a smaller solvation energy, which significantly improves the low-temperature rate performance of the battery and enables the battery to work normally at -30℃ and a high rate of 2C. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The linear sweep voltammetric scanning spectra of the Al / Li metal pair batteries of Example 1 and Comparative Examples 1 to 4 of the present invention are shown;

[0019] Figure 2 A comparison chart of the -40°C discharge specific capacity of the NCM811 / Li batteries of Example 1 and Comparative Examples 2 to 4 in the voltage range of 2.8-4.4V is shown;

[0020] Figure 3 A comparison chart of the -50°C discharge specific capacity of the NCM811 / Li batteries of Examples 1 to 4 in the voltage range of 2.8-4.4V is shown;

[0021] Figure 4 The low temperature cycle diagram of the NCM811 / Li battery of Example 1 at -30°C and 0.2C rate is shown in the voltage range of 2.8-4.4V;

[0022] Figure 5 A comparison chart of -30°C low temperature rate performance of NCM811 / Li batteries of Example 1 and Comparative Examples 2 and 3 is shown in the voltage range of 2.8-4.4V;

[0023] Figure 6 A comparison chart of the room temperature rate performance of NCM811 / Li batteries of Example 1 and Comparative Examples 2 and 3 at 25°C within a voltage range of 2.8-4.4V is shown. DETAILED DESCRIPTION

[0024] It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or the intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope. The present invention will be described in detail below in conjunction with the embodiments.

[0025] A first aspect of an embodiment of the present invention provides an electrolyte suitable for high-rate charge and discharge and low-temperature cycling, the electrolyte comprising a lithium salt, an additive and a co-solvent mixture, the co-solvent mixture comprising methyl acetate (MA), methyl difluoroacetate (MDFA) and fluoroethylene carbonate (FEC).

[0026] The present invention adopts methyl acetate, methyl difluoroacetate and fluoroethylene carbonate to form a co-solvent system. The three solvent molecules cooperate with each other to effectively balance the solubility of lithium salt in the solvent, the desolvation energy of ions, the freezing point of the electrolyte and other characteristics, thereby making the electrolyte have higher high-voltage resistance and oxidation resistance, and at the same time can form a low-impedance electrode electrolyte interphase film rich in inorganic LiF, and promote Li + The rapid desolvation of the battery can significantly improve the battery rate performance and low temperature performance.

[0027] Among them, MA can ensure that the electrolyte has a lower freezing point and provides higher ionic conductivity after dissolving lithium salt; MDFA is fluorinated methyl acetate, and its fluorine atoms have strong electron-withdrawing ability, which can change the electron cloud density and reduce the desolvation energy. At the same time, it is also conducive to the formation of an interface film rich in LiF, inhibiting the growth of lithium dendrites, protecting the integrity of the positive electrode material, and improving the cycle performance. Compared with methyl trifluoroacetate, while it can improve the electrochemical stability and reduce the desolvation energy, it has a more moderate solubility for lithium salts and is more conducive to expansion to lower temperatures; FEC is generally used as a good film-forming additive. Compared with VC (vinyl carbonate), it can increase the content of inorganic component LiF, has a lower degree of crosslinking with the organic phase, and is easy to conduct electricity. However, the present invention uses FEC as a solvent based on its extremely high dielectric constant, can dissolve lithium salts well, and can be used in conjunction with a difficult film-forming solvent (MA). When FEC is used as a solvent, FEC and Li + The binding energy is very small, which can further accelerate the desolvation process and protect the stability of the interfacial film.

[0028] In a preferred embodiment of the present invention, the volume of the methyl difluoroacetate accounts for 10-30% of the volume percentage of the electrolyte.

[0029] If the volume of the methyl difluoroacetate of the present invention is too high, the solubility of the lithium salt will decrease, resulting in a decrease in the rate performance and the low-temperature performance. If the volume is too low, the desolvation energy cannot be effectively improved. When the volume of the methyl difluoroacetate is controlled within the above range, the lithium salt can be guaranteed to have a better solubility, which is more conducive to expansion to a lower temperature, and the desolvation energy, which is one of the limiting factors during charging, can be reduced, thereby improving the rate performance and low-temperature charging performance, and is conducive to forming an interface film rich in LiF, thereby improving the cycle performance.

[0030] In a preferred embodiment of the present invention, the volume percentages of the methyl acetate, the methyl difluoroacetate and the fluoroethylene carbonate are (40% to 60%): (10% to 30%): (20% to 40%).

[0031] In the electrolyte of the present invention, unfluorinated methyl acetate is selected as the main solvent. Compared with other solvents, it has low toxicity, good biodegradability, low cost and easy availability, has better lithium salt solubility, can reduce electrolyte viscosity, and ensure that the electrolyte has a lower freezing point. On the basis of methyl acetate as the main solvent, a certain proportion of fluorinated auxiliary solvents methyl difluoroacetate and auxiliary solvent fluoroethylene carbonate are added to adjust the solvation structure and reduce the desolvation energy. At the same time, it can form a low-impedance electrode electrolyte interphase interface film rich in inorganic LiF with lithium ions to inhibit the growth of lithium dendrites. However, if the fluorination is too high, the solubility of the lithium salt in the electrolyte will be reduced, and the lithium salt will easily precipitate at low temperatures.

[0032] Therefore, the present invention controls methyl acetate, methyl difluoroacetate and fluoroethylene carbonate within the above range. The synergistic effect of the three can effectively balance the relationship between ionic conductivity, lithium salt solubility and desolvation energy, thereby significantly improving the rate performance, cycle performance and low temperature performance of the battery.

[0033] More preferably, the volume percentage of the methyl acetate, the methyl difluoroacetate and the fluoroethylene carbonate is 50%:20%:30%.

[0034] In a preferred embodiment of the present invention, the lithium salt is lithium hexafluorophosphate (LiPF 6 ) and lithium tetrafluoroborate (LiBF 4 ); the additive is selected from one or more of lithium bis(oxalatoborate), lithium bis(fluorooxalatoborate), lithium difluorobis(oxalatophosphate) or lithium difluorophosphate; more preferably, the additive is lithium bis(fluorooxalatoborate) (LiDFOB).

[0035] The lithium salt of the present invention uses a mixture of lithium hexafluorophosphate and lithium tetrafluoroborate. The lithium hexafluorophosphate has good film-forming properties and is currently the most widely used lithium salt. The regulation of the co-solvent system makes it more suitable for low-temperature scenes, which is conducive to commercialization. It will not corrode aluminum foil like LiFSI (lithium bis(fluorosulfonyl)imide), and the addition of lithium tetrafluoroborate can reduce the charge transfer impedance of the electrolyte at low temperatures, while not losing the good film-forming properties of lithium hexafluorophosphate. It can also adjust the distance between several salt anions and lithium ions in the solvation structure, thereby improving the low-temperature performance of the electrolyte. In addition, the present invention adds additives on the basis of the above-mentioned lithium salt, which can further improve the film-forming stability of the electrolyte on the electrode surface and improve the rate performance by affecting the anion coordination in the lithium ion solvation structure.

[0036] In order to further improve the rate performance and low temperature performance of the electrolyte, in some preferred embodiments of the present invention, the molar ratio of the lithium hexafluorophosphate to the lithium tetrafluoroborate is 1 to 9:1. For example, it may include but is not limited to 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1. More preferably, the molar ratio of the lithium hexafluorophosphate to the lithium tetrafluoroborate is 9:1. The concentration of the lithium salt is 0.5 to 2 mol / L, more preferably 1 to 1.4 mol / L. The concentration of the additive is 0.01 to 0.5 mol / L, more preferably 0.05 to 0.1 mol / L.

[0037] In a preferred embodiment of the present invention, the electrolyte preparation process comprises: stirring and mixing the lithium salt, the additive and the co-solvent mixture, and the stirring and mixing temperature is 15-20° C. Preparing the electrolyte at a lower temperature can reduce the rate of side reactions and make the electrolyte properties more stable.

[0038] In a second aspect of the embodiments of the present invention, there is provided a use of the aforementioned electrolyte suitable for high-rate charge and discharge and low-temperature cycle in a lithium-ion battery.

[0039] Based on the above reasons, the electrolyte of the present invention can effectively improve the high voltage resistance, low temperature resistance, rate performance and the like of lithium ion batteries.

[0040] In a third aspect of an embodiment of the present invention, a lithium metal battery is provided, comprising the aforementioned electrolyte suitable for high-rate charge and discharge and low-temperature cycling.

[0041] In a specific embodiment of the present invention, the lithium metal battery further comprises a positive electrode material, a negative electrode material and a separator, wherein the positive electrode material is a high-nickel ternary positive electrode material, and the high-nickel ternary positive electrode material is LiNi 1-x-y Co x Mn y O 2 , 0.075≤x≤0.2, 0.075≤y≤0.2. Further preferably, the high nickel ternary positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). The use of high-nickel ternary positive electrode materials has a positive effect on improving battery energy density, rate performance and low-temperature performance. The diaphragm is an alumina-coated polyolefin porous diaphragm. The alumina coating can increase the absorption and retention of electrolytes. At the same time, because ions are more easily transmitted at the diaphragm interface, the rate performance can be improved.

[0042] The present application is further described in detail below in conjunction with specific examples, which should not be construed as limiting the scope of protection claimed in the present application. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0043] Example 1

[0044] An electrolyte suitable for high-rate charge-discharge and low-temperature cycling, the preparation process of which is as follows: in an inert atmosphere glove box (H 2 O<0.01ppm, O 2 <0.01ppm), LiPF 6 , LiBF 4 LiDFOB was dissolved in a mixed solution of MA / MDFA / FEC with a volume ratio of 5:2:3, the lithium ion concentration was maintained at 1.05 mol / L (lithium salt 1 mol / L, additive 0.05 mol / L), and stirred at 17° C. for 4 hours to obtain the electrolyte, referred to as 5A2F.

[0045] Example 2

[0046] An electrolyte suitable for high-rate charge and discharge and low-temperature cycling, the difference from Example 1 is only that the volume ratio of methyl acetate, methyl difluoroacetate and fluoroethylene carbonate is 6:1:3, referred to as 6A2F.

[0047] Example 3

[0048] An electrolyte suitable for high-rate charge and discharge and low-temperature cycling, the difference from Example 1 is only that the volume ratio of methyl acetate, methyl difluoroacetate and fluoroethylene carbonate is 4:3:3, referred to as 4A2F.

[0049] Example 4

[0050] A MA-based electrolyte with MDFA as a co-solvent is as follows: in an inert atmosphere glove box (H 2 O<0.01ppm, O 2 <0.01ppm), LiPF 6 , LiBF 4 LiDFOB was dissolved in a mixed solution of MA / MDFA / FEC with a volume ratio of 3:4:3, the lithium ion concentration was maintained at 1.05 mol / L (lithium salt 1 mol / L, additive 0.05 mol / L), and stirred at 17°C for 4 hours to obtain an electrolyte, referred to as 3A2F.

[0051] Comparative Example 1

[0052] A commonly used low-temperature electrolyte, a commercially available product, whose lithium salt is LiPF 6 (1 mol / L), the solvent is a mixture of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1, and the electrolyte is referred to as EC / DEC.

[0053] Comparative Example 2

[0054] A MA-based electrolyte without methyl fluoride acetate as a cosolvent, specifically as follows: in an inert atmosphere glove box (H 2 O<0.01ppm, O 2 <0.01ppm), LiPF 6 , LiBF 4 LiDFOB was dissolved in a MA / FEC mixed solution with a volume ratio of 7:3, the lithium ion concentration was maintained at 1.05 mol / L (lithium salt 1 mol / L, additive 0.05 mol / L), and stirred at 17°C for 4 hours to obtain an electrolyte, referred to as 7A.

[0055] Comparative Example 3

[0056] A MA-based electrolyte with methyl trifluoroacetate (MTFA) as a co-solvent is prepared as follows: 2 O<0.01ppm, O 2 <0.01ppm), LiPF 6 , LiBF 4 LiDFOB was dissolved in a mixed solution of MA / MTFA / FEC with a volume ratio of 5:2:3, the lithium ion concentration was maintained at 1.05 mol / L (lithium salt 1 mol / L, additive 0.05 mol / L), and stirred at 17°C for 4 hours to obtain an electrolyte, referred to as 5A3F.

[0057] Comparative Example 4

[0058] A MA-based electrolyte with methyl chlorodifluoroacetate (MCDFA) as a cosolvent is as follows: in an inert atmosphere glove box (H 2 O<0.01ppm, O 2 <0.01ppm), LiPF 6 , LiBF 4 LiDFOB was dissolved in a mixed solution of MA / MCDFA / FEC with a volume ratio of 5:2:3, and the ion salt concentration was maintained at 1.05 mol / L (lithium salt 1 mol / L, additive 0.05 mol / L). The electrolyte was stirred at 17°C for 4 hours to obtain an electrolyte, referred to as 5AC2F.

[0059] Figure 1 The electrochemical window diagrams of the electrolyte 5A2F of Example 1 and the electrolytes of Comparative Examples 1 to 4 obtained by linear voltammetry scanning test, from which it can be seen that Example 1 and Comparative Examples 2 to 4 are very stable before 5.5 V, while Comparative Example 1 produces a strong oxidation peak at around 4 V. At the same time, the intensity of the oxidation peak of Example 1 in which methyl fluoride acetate is added as a co-solvent is lower than that of Comparative Example 2 in which methyl fluoride acetate is not added as a co-solvent.

[0060] The electrolytes of Example 1 and Comparative Examples 1 to 4 were used to construct NCM811 / Li batteries, and the discharge performance of the batteries was tested at -40°C and 0.5C discharge rate. Figure 2 As shown in the figure, it can be seen that the use of the electrolyte in Example 1 greatly improves the low-temperature discharge performance of the battery. The discharge specific capacity of Example 1 is 140mAh / g, while the comparative 5A3F, 7A, and 5AC2F are only 123mAh / g, 117mAh / g, and 3mAh / g, respectively. The EC / DEC of the commonly used comparative example 1 does not have the discharge capacity at a low temperature of -40°C.

[0061] The electrolytes of Examples 1 to 4 were used to construct NCM811 / Li batteries, and the discharge performance was tested at a temperature of -50°C and a discharge rate of 0.5C. Figure 3 As shown, the discharge specific capacity in Example 1 is the best, which can reach 86 mAh / g. The discharge specific capacities of Examples 2 to 4 are greatly reduced compared with Example 1, which are about 10 mAh / g.

[0062] The NCM811 / Li battery constructed with the electrolyte of Example 1 was subjected to a cycle performance test (test conditions: -30°C, 0.2C). Figure 4 As shown, the battery with electrolyte 5A2F of Example 1 can be cycled at least 60 times at -30°C and 0.2C rate, and the specific capacity is close to 140 mAh / g.

[0063] The electrolytes in Example 1 and Comparative Examples 2 and 3 were used to construct NCM811 / Li batteries, and the rate performance of the batteries was tested at -30°C. Figure 5 As shown in the figure, it can be seen that the use of the electrolyte in Example 1 has a great improvement on the low-temperature rate performance of the battery. 5A2F still has a specific capacity of more than 60mAh / g at a charge and discharge rate of 2C, which is much higher than 2mAh / g and 8mAh / g of Comparative Examples 2 and 3 (7A, 5A3F).

[0064] The electrolytes in Example 1 and Comparative Examples 2 and 3 were used to construct NCM811 / Li batteries, and the rate performance of the batteries was tested at 25°C. Figure 6As shown in the figure, it can be seen that the use of the electrolyte in Example 1 has a great improvement on the room temperature rate performance of the battery. The capacity change is small at a large rate of 0.1C to 8C, and the specific capacity is higher at a large rate. The capacity retention rate of 5A2F at 8C relative to 0.1C is 76.81%. The capacity retention rates of Comparative Examples 2 and 3 at 8C relative to 0.1C are 55.71% and 73.73%, respectively.

[0065] In summary, the lithium metal battery constructed by the present invention (including the electrolyte suitable for high-rate charge and discharge and low-temperature cycling of the present invention, the high-nickel ternary positive electrode material NCM811, and the metal lithium negative electrode) can perform stable, rapid, and reversible charge and discharge cycles at room temperature or low temperature within the voltage range of 2.8 to 4.4 V.

[0066] The above-described embodiments only represent the embodiments of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be regarded as illustrative rather than restrictive in any respect. The scope of the present invention should be described by the attached claims, and any changes equivalent to the intention and scope of the claims should also be included in the scope of the present invention.

Claims

1. An electrolyte suitable for high-rate charge and discharge and low-temperature cycles, characterized in that: The electrolyte includes a lithium salt, an additive and a co-solvent mixture, wherein the co-solvent mixture includes methyl acetate, methyl difluoroacetate and fluoroethylene carbonate.

2. The electrolyte suitable for high-rate charge-discharge and low-temperature cycle according to claim 1, characterized in that: The volume of the methyl difluoroacetate accounts for 10-30% of the volume percentage of the electrolyte.

3. The electrolyte suitable for high-rate charge-discharge and low-temperature cycle according to claim 2, characterized in that: The volume percentages of the methyl acetate, the methyl difluoroacetate and the fluoroethylene carbonate are (40% to 60%): (10% to 30%): (20% to 40%).

4. The electrolyte suitable for high-rate charge-discharge and low-temperature cycle according to claim 1, characterized in that: The lithium salt is a mixture of lithium hexafluorophosphate and lithium tetrafluoroborate; the additive is selected from one or more of lithium bis(oxalatoborate), lithium bis(fluorooxalatoborate), lithium difluorobis(oxalatophosphate) or lithium difluorophosphate.

5. The electrolyte suitable for high-rate charge-discharge and low-temperature cycle according to claim 4, characterized in that: The molar ratio of the lithium hexafluorophosphate to the lithium tetrafluoroborate is 1 to 9:

1.

6. The electrolyte suitable for high-rate charge-discharge and low-temperature cycle according to claim 4, characterized in that: The concentration of the lithium salt is 0.5-2 mol / L; the concentration of the additive is 0.01-0.5 mol / L.

7. The electrolyte suitable for high-rate charge-discharge and low-temperature cycle according to any one of claims 1 to 6, characterized in that: The electrolyte preparation process comprises: stirring and mixing the lithium salt, the additive and the co-solvent mixture, and the stirring and mixing temperature is 15-20°C.

8. Use of the electrolyte suitable for high-rate charge and discharge and low-temperature cycle as claimed in any one of claims 1 to 7 in a lithium-ion battery.

9. A lithium metal battery, characterized in that: The invention comprises an electrolyte suitable for high-rate charge and discharge and low-temperature cycle as described in any one of claims 1 to 7.

10. The lithium metal battery according to claim 9, characterized in that The lithium metal battery also includes a positive electrode material, a negative electrode material and a separator. The positive electrode material is a high-nickel ternary positive electrode material. The high-nickel ternary positive electrode material is LiNi 1-x- y Co x Mn y O2, 0.075≤x≤0.2, 0.075≤y≤0.2.

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