High-voltage low-temperature electrolyte, preparation method thereof and application of high-voltage low-temperature electrolyte in lithium metal battery

Abstract

The invention discloses a high-voltage low-temperature electrolyte, a preparation method thereof and application of the high-voltage low-temperature electrolyte in a lithium metal battery, and belongs to the technical field of lithium ion batteries. The high-voltage low-temperature electrolyte provided by the invention is a local high-concentration electrolyte and comprises ethylene glycol diethyl ether, 1, 2-difluorobenzene, a lithium salt and an additive, the lithium salt is lithium bis (fluorosulfonyl) imide and lithium bis (fluorooxalato) borate; the additive is one or more of a 3A molecular sieve, a 4A molecular sieve and a 5A molecular sieve. The high-voltage and low-temperature electrolyte provided by the invention can optimize low-temperature bulk phase transmission, interface chemistry and interface mass transfer kinetics in a lithium metal battery, so that the lithium metal battery has excellent electrochemical performance and high-voltage and low-temperature characteristics, the voltage window is about 4.6 V, good flowability can be kept at-40 DEG C to 40 DEG C, the ionic conductivity at-40 DEG C reaches up to 1.89 mS / cm, and the high-voltage and low-temperature electrolyte can be applied to the lithium metal battery. And in addition, the material has an excellent low-temperature capacity retention rate and has a wide application prospect in lithium metal batteries.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries, and in particular, relates to a high-voltage and low-temperature electrolyte and a preparation method thereof and application in lithium metal batteries. Background Art

[0002] With the rapid development of the lithium battery industry, people have put forward higher requirements on the energy density, power density and cycle stability of batteries, especially requiring lithium batteries to operate well under low temperature conditions. However, the operating temperature range of commercial lithium-ion batteries is relatively narrow. At sub-zero temperatures, their capacity retention rate is greatly reduced, and their rate performance is poor. Some batteries cannot be charged at temperatures of -30℃ or lower. The poor low-temperature performance has seriously limited the promotion and application of lithium-ion batteries in low-temperature environments.

[0003] Currently, local high-concentration electrolytes are usually used to solve the problems of high viscosity, poor wettability and unstable circulation at low temperatures of existing electrolytes. However, in low-temperature environments, the compatibility between existing local high-concentration electrolytes and the negative electrode and separator deteriorates, the viscosity of the local high-concentration electrolyte increases, and even partially solidifies, resulting in a decrease in the conductivity of the lithium-ion battery. In low-temperature environments, lithium precipitation from the negative electrode of the lithium-ion battery is serious, which has a great impact on the electrochemical performance. Therefore, how to improve the interface structure between the electrode and the local high-concentration electrolyte and thus improve the electrochemical performance of lithium-ion batteries has received widespread attention from all walks of life. Summary of the invention

[0004] The present application discloses a high-voltage, low-temperature electrolyte, a preparation method thereof, and application in lithium metal batteries, aiming to solve technical problems such as low ion conductivity, poor electrochemical cycle stability, narrow applicable voltage window, limited application at low temperatures, and high cost of existing local high-concentration electrolytes.

[0005] In order to achieve the above purpose, the technical solution of this application is:

[0006] The first aspect of the present application provides a high-voltage and low-temperature electrolyte, which is a local high-concentration electrolyte, including ethylene glycol diethyl ether, 1,2-difluorobenzene, lithium salt and additives;

[0007] The lithium salt is lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalate)borate;

[0008] The additive is one or more of 3A molecular sieve, 4A molecular sieve and 5A molecular sieve.

[0009] In combination with the first aspect, preferably, the volume ratio of ethylene glycol diethyl ether, 1,2-difluorobenzene and lithium salt is 1:1:10-200.

[0010] In combination with the first aspect, preferably, the concentration of the lithium salt is 2-6 mol / L.

[0011] In combination with the first aspect, preferably, the concentration of the lithium salt is 4 mol / L.

[0012] In combination with the first aspect, preferably, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium bis(fluorooxalatoborate) in the electrolyte is (6-8):(4-2).

[0013] In combination with the first aspect, preferably, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium bis(fluorooxalatoborate) in the electrolyte is 6:4.

[0014] In combination with the first aspect, preferably, the amount of the additive added is 10-20 times the sum of ethylene glycol diethyl ether, 1,2-difluorobenzene and the lithium salt.

[0015] The second aspect of the present application provides a method for preparing the high-voltage and low-temperature electrolyte according to the first aspect, the method comprising:

[0016] The additive is added to a mixed solution of ethylene glycol diethyl ether and 1,2-difluorobenzene for reaction, and then a lithium salt is added for mixed reaction to obtain the high-voltage and low-temperature electrolyte.

[0017] In combination with the second aspect, preferably, the additive is added to the mixed solution of ethylene glycol diethyl ether and 1,2-difluorobenzene for a reaction time of 40-50 hours;

[0018] And / or, the time for adding the lithium salt for mixed reaction is 6-12 hours.

[0019] The third aspect of the present application provides the use of the high-voltage and low-temperature electrolyte prepared by the preparation method described in the second aspect in a lithium metal battery.

[0020] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application include at least:

[0021] The high-voltage and low-temperature electrolyte provided in the present application includes ethylene glycol diethyl ether, 1,2-difluorobenzene, lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalatoborate), and additives. On the one hand, it can give the electrolyte an excellent anion-rich aggregate solvation structure, which is easier to participate in interface decomposition and construct a denser inorganic component-rich passivation layer, thereby effectively inhibiting the decomposition of free solvent molecules and promoting Li +The rapid transmission at the electrode / electrolyte interface further optimizes the interfacial chemistry and interfacial mass transfer kinetics of the electrode, showing excellent low-temperature stable cycle performance; on the other hand, it has high-voltage and low-temperature characteristics, with a voltage window of about 4.6V, and can maintain good fluidity at -40°C to 40°C, and the ionic conductivity at -40°C is as high as 1.89mS / cm, and has excellent low-temperature capacity retention (after 200 cycles at -20°C, the coulombic efficiency is still maintained at 97.1%); at the same time, the raw materials used are cheap and easy to obtain, which greatly reduces the cost of the electrolyte and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 Physical pictures of A1-high-pressure and low-temperature electrolyte (DS-4-6), A2-high-pressure and low-temperature electrolyte (DS-3-7), and A3-high-pressure and low-temperature electrolyte (DS-2-8) prepared in the examples of the present application;

[0024] Figure 2 Voltage-current density curves of A1-high-pressure and low-temperature electrolyte (DS-4-6), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) prepared in the examples of the present application at room temperature;

[0025] Figure 3 Variable temperature ionic conductivity test curves of A1-high pressure low temperature electrolyte (DS-4-6), A2-high pressure low temperature electrolyte (DS-3-7), A3-high pressure low temperature electrolyte (DS-2-8), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) prepared in the embodiments of the present application at -40°C to 40°C;

[0026] Figure 4 Long cycle data graph of lithium metal symmetric batteries at -20°C for A1-high-pressure and low-temperature electrolyte (DS-4-6), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) prepared in the examples of the present application;

[0027] Figure 5 The long cycle capacity diagram of the button cell assembled at -20°C with the A1-high-pressure and low-temperature electrolyte (DS-4-6) prepared in the embodiment of the present application and matched with lithium metal and nickel-cobalt-manganese ternary positive electrode. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0029] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0030] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0031] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0032] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0033] It should be noted that all raw materials and reagents in the examples of the present application are purchased on the market or prepared according to conventional methods well known to those skilled in the art, and the present application does not impose any particular limitation on this.

[0034] In a first aspect, an embodiment of the present application provides a high-voltage and low-temperature electrolyte, which is a local high-concentration electrolyte, including ethylene glycol diethyl ether, 1,2-difluorobenzene, a lithium salt, and an additive;

[0035] The lithium salt is lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalate)borate;

[0036] The additive is one or more of 3A molecular sieve, 4A molecular sieve and 5A molecular sieve.

[0037] On the one hand, it can give the electrolyte an excellent anion-rich aggregate solvation structure, which is easier to participate in interface decomposition and build a denser inorganic component-rich passivation layer, thereby effectively inhibiting the decomposition of free solvent molecules and promoting Li + The rapid transmission at the electrode / electrolyte interface further optimizes the interfacial chemistry and interfacial mass transfer kinetics of the electrode, showing excellent low-temperature stable cycle performance; on the other hand, it has high-voltage and low-temperature characteristics, with a voltage window of about 4.6V, and can maintain good fluidity at -40°C to 40°C, and the ionic conductivity at -40°C is as high as 1.89mS / cm, and has excellent low-temperature capacity retention (after 200 cycles at -20°C, the coulombic efficiency is still maintained at 97.1%); at the same time, the raw materials used are cheap and easy to obtain, which greatly reduces the cost of the electrolyte and has broad application prospects.

[0038] It should be noted that the additive of the present application is preferably one or more of 3A molecular sieve, 4A molecular sieve, and 5A molecular sieve, and more preferably 4A molecular sieve. The parameters are: radius 3-5mm, type Static water adsorption (25°C, saturated salt water, 24h), %: ≥22.5, static water adsorption (35°C, saturated salt water, 24h), %: ≥22; crushing resistance, N: ≥80, particle size (weight method), %: ≥98, shape: spherical. In addition, the amount of additive added is preferably 10-20 times the volume (ml) of the added liquid. By controlling the amount of additive added, the electrolyte of the lithium-ion battery can be dehydrated and deacidified, which can not only meet the dehydration requirements, but also greatly reduce the risk of Li + The introduction of impurity ions caused by ion exchange will not increase the content of other metal ions in the electrolyte, thereby reducing the adverse effects caused.

[0039] It should be noted that the operating conditions of low-temperature lithium metal batteries can be divided into the following main steps: First, the solvated Li + Migrate to the electrode surface through the bulk transport of the electrolyte; secondly, Li + Desolvation at the interfacial passivation film formed by the electrolyte / electrode; third, Li + Transmitted into the electrode through the interfacial passivation film; fourth, Li + Diffusion mass transfer in electrode materials.

[0040] In the embodiment of the present application, the volume ratio of ethylene glycol diethyl ether, 1,2-difluorobenzene and lithium salt is preferably 1:1:10-200. Among them, ethylene glycol diethyl ether (DGDE) is used as a solvent and 1,2-difluorobenzene (1,2-dFBn) is used as a co-solvent. The low freezing point and weak solvation of the high-purity DGDE solvent treated with molecular sieves and the 1,2-dFBn diluent ensure the good bulk fluidity and ionic conductivity of the high-voltage and low-temperature electrolyte under low temperature conditions. The DGDE solvent has a weak solvation property, which allows the lithium salt anions in the electrolyte to enter the Li + The first solvation shell promotes the formation of CIP or AGG solvation structure, which effectively broadens the electrochemical window of the electrolyte and also provides faster desolvation kinetics at low temperatures.

[0041] In the embodiment of the present application, the molar ratio of lithium bis(fluorosulfonyl)imide (LiFSi) and lithium bis(fluorooxalate)borate (LiDFOB) in the electrolyte is preferably (6-8): (4-2), for example, 8:2, 7:3, 6:4 or any ratio within the range, more preferably 6:4; the concentration of lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalate)borate in the electrolyte is preferably 2-6 mol / L, for example, 2 mol / L, 4 mol / L, 6 mol / L or any concentration within the range, more preferably 4 mol / L. Among them, by controlling the molar ratio and molar concentration of LiFSi and LiDFOB, the interaction between cations and anions and the solvent can be enhanced, the content of free solvent molecules is greatly reduced or even disappears, and a special salt-solvent coordination structure is formed, so that the electrolyte has a wide electrochemical window, thereby improving the cycle stability of the electrolyte in the battery and improving the cycle performance of the metal lithium battery.

[0042] It should be noted that the introduction of LiDFOB enhances the + -anion-(DFOB-, FSI-) bonding promotes the formation of more CIP and AGG solvation structures in the electrolyte, further broadens the electrochemical window of the electrolyte, and also provides faster desolvation kinetics and excellent interfacial film-forming ability. With the continuous increase of LiDFOB salt concentration, the ionic conductivity of the electrolyte has not changed significantly, which further confirms that the excellent properties of low freezing point and low viscosity of 1,2-dFBn diluent and DGDE solvent provide a favorable basis for the good flow of local high-concentration electrolyte under low temperature conditions. At the same time, the introduction of LiDFOB further reduces the desolvation barrier of the electrolyte, showing more excellent desolvation kinetics; it effectively promotes Li + The coordination with lithium salt anions results in the formation of more anion-dominated CIP and AGG solvation structures in the electrolyte, which effectively increases the Li +Desolvation kinetics. Due to its good desolvation kinetics, the Li||Li battery assembled with DS-4-6 can maintain low polarization and stable cycling at low temperature conditions of -20°C, showing extremely excellent low-temperature adaptability of lithium negative electrodes.

[0043] In a second aspect, the present application also provides a method for preparing the high-voltage and low-temperature electrolyte according to the first aspect, the method comprising:

[0044] The additive is added into a mixed solution of ethylene glycol diethyl ether and 1,2-difluorobenzene for reaction, and then lithium salt is added and mixed to obtain the high-voltage and low-temperature electrolyte.

[0045] In the embodiment of the present application, the time for adding the additive to the mixed solution of ethylene glycol diethyl ether and 1,2-difluorobenzene to react is preferably 40-50 hours; the time for adding lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalatoborate) to mix is ​​preferably 6-12 hours. Among them, by controlling each reaction time, it can be ensured that the prepared electrolyte has stable quality and performance, so that the electrolyte has high ionic conductivity and stable high-pressure and low-temperature performance.

[0046] It should be noted that the high-voltage and low-temperature electrolyte provided in the present application can synergistically optimize the low-temperature bulk phase transport, interface chemistry and interface mass transfer kinetics in lithium metal batteries, so that they have excellent electrochemical properties.

[0047] In the third aspect, the present application also provides the application of the high-voltage and low-temperature electrolyte prepared by the preparation method described in the second aspect in a lithium metal battery. Among them, based on the above-mentioned high-voltage and low-temperature electrolyte having excellent properties such as high transparency, high electrochemical stability, high ionic conductivity, low-temperature cycle stability, and low cost, it can enable lithium-ion batteries to operate stably at high capacity at -40°C to 40°C, and has broad application prospects.

[0048] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0049] Example 1

[0050] The preparation method of the A1-high-voltage and low-temperature electrolyte (DS-4-6) provided in this embodiment specifically includes:

[0051] 4A molecular sieve was added to 800 μL DGDE and 800 μL 1,2-dFBn solution and allowed to stand in a glove box for 48 h. 0.72 g LiFSi and 0.37 g LiDFOB were added to a container containing a magnetic stirrer for reaction to obtain A1- high-pressure and low-temperature electrolyte (DS-4-6).

[0052] Example 2

[0053] The preparation method of A2-high-pressure and low-temperature electrolyte (DS-3-7) provided in this embodiment specifically includes:

[0054] 4A molecular sieve was added to 800 μL DGDE and 800 μL 1,2-dFBn solution and allowed to stand in a glove box for 48 h. 0.84 g LiFSi and 0.28 g LiDFOB were added to a container containing a magnetic stirrer for reaction to obtain A2- high-pressure and low-temperature electrolyte (DS-3-7).

[0055] Example 3

[0056] The preparation method of A3-high-pressure and low-temperature electrolyte (DS-2-8) provided in this embodiment specifically includes:

[0057] 4A molecular sieve was added to 800 μL DGDE and 800 μL 1,2-dFBn solution and allowed to stand in a glove box for 48 h. 0.96 g LiFSi and 0.18 g LiDFOB were added to a container containing a magnetic stirrer for reaction to obtain A3- high-pressure and low-temperature electrolyte (DS-2-8).

[0058] At the same time, in order to verify the comprehensive performance of the high-voltage and low-temperature electrolyte prepared in the above embodiments, the present application provides the following comparative examples for detailed description.

[0059] Comparative Example 1

[0060] The preparation method of the B1-electrolyte (B1-DS) provided in this embodiment specifically includes:

[0061] 1.2 g of LiFSi was added to 800 μL of DGDE and 800 μL of 1,2-dFBn solution, and allowed to stand in a glove box for 48 h. The solution was then placed in a container containing a magnetic stirrer for reaction to obtain B1-electrolyte (B1-DS).

[0062] Comparative Example 2

[0063] The preparation method of the B2-electrolyte (B2-DS) provided in this comparative example specifically comprises:

[0064] 4A molecular sieve was added to 800 μL DGDE solution and allowed to stand in a glove box for 48 h, and 0.6 g LiFSi was added to a container containing a magnetic stirrer for reaction to obtain B2-electrolyte (B2-DS).

[0065] The difference between Comparative Example 1 of the present application and Example 1 is that LiDFOB is not added, and the difference between Comparative Example 2 and Example 1 is that LiDFOB and 1,2-dFBn are not added.

[0066] Comparative Example 3

[0067] The preparation method of the B3-electrolyte (DS-1-9) provided in this embodiment specifically includes:

[0068] 4A molecular sieve was added to 800 μL DGDE and 800 μL 1,2-dFBn solution and allowed to stand in a glove box for 48 h. 1.08 g LiFSi and 0.09 g LiDFOB were added to a container containing a magnetic stirrer for reaction to obtain B3-electrolyte (DS-1-9).

[0069] The present application observed the appearance of the electrolyte prepared in the example, and the result was Figure 1 As shown. Among them, Figure 1 These are the actual pictures of A1-high-pressure and low-temperature electrolyte (DS-4-6), A2-high-pressure and low-temperature electrolyte (DS-3-7), and A3-high-pressure and low-temperature electrolyte (DS-2-8).

[0070] according to Figure 1 As known, it can be seen that the electrolyte is transparent.

[0071] The present application conducted a comprehensive performance test on the electrolyte prepared in the example, and the results were Figure 2-4 As shown. Among them, Figure 2 The voltage-current density curves of A1-high-pressure and low-temperature electrolyte (DS-4-6), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) at room temperature; Figure 3 It is the temperature-variable ion conductivity test curve of A1-high-pressure low-temperature electrolyte (DS-4-6), A2-high-pressure low-temperature electrolyte (DS-3-7), A3-high-pressure low-temperature electrolyte (DS-2-8), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) at -40℃~40℃; Figure 4 Long cycle data of lithium metal symmetric batteries of A1-high-pressure and low-temperature electrolyte (DS-4-6), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) at -20°C; Figure 5 This is the long cycle capacity diagram of a button cell assembled with A1-high-voltage and low-temperature electrolyte (DS-4-6) at -20°C and matched with lithium metal and nickel-cobalt-manganese ternary positive electrode.

[0072] according to Figure 2It can be seen that the voltage-current density curve of the test A1-high-voltage and low-temperature electrolyte (DS-4-6) at room temperature has a voltage window of about 5.1V, the voltage-current density curve of the B1-electrolyte (B1-DS) at room temperature has a voltage window of about 4.6V, and the voltage-current density curve of the B2-electrolyte (B2-DS) at room temperature has a voltage window of about 4.8V. Due to the weak solvation ability of DGDE and the continuous increase in the local concentration of lithium salt in the electrolyte, the lithium salt anions in the local high-concentration electrolyte can smoothly enter the Li + The first solvation shell promotes the formation of CIP or AGG solvation structures. Thanks to the formation of more anion-dominated solvation structures, the number and reaction activity of free DGDE solvent molecules in the local high-concentration electrolyte are strongly suppressed, so that the electrochemical window of the electrolyte is effectively widened with the increase of local concentration.

[0073] according to Figure 3 It can be seen that the variable temperature ionic conductivity test curves of A1-high pressure and low temperature electrolyte (DS-4-6), A2-high pressure and low temperature electrolyte (DS-3-7), A3-high pressure and low temperature electrolyte (DS-2-8), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) at -40℃~40℃ can maintain good ionic conductivity at -40℃ to 40℃, and the ionic conductivity is as high as 1.89mS / cm at -40℃, and has excellent low temperature capacity retention rate.

[0074] according to Figure 4 It can be seen that the long cycle data of lithium metal symmetric batteries of A1-high-voltage and low-temperature electrolyte (DS-4-6), B1-electrolyte (B1-DS), and B2-electrolyte (B2-DS) at -20°C were tested. From the test results, it can be seen that the long cycle data of DS-4-6 is significantly better than that of B1-DS and B2-DS.

[0075] according to Figure 5 It can be seen that the long cycle capacity of the button cell assembled with A1-high-voltage and low-temperature electrolyte (DS-4-6) at -20°C and matched with lithium metal and nickel-cobalt-manganese ternary positive electrode was tested. After 200 cycles at -20°C, the battery still had excellent discharge capacity, with a discharge capacity of 120mAh / g and a coulombic efficiency of 97.1%. After the B1-DS battery was made and cycled 200 times at -20°C, the discharge capacity was 0mAh / g. The long cycle data of DS-4-6 was significantly better than that of B1-DS.

[0076] Table 1 Ionic conductivity test results of the embodiments and comparative examples

[0077]

[0078] Table 2 Polarization potential test results of lithium symmetric batteries of the embodiments and comparative examples

[0079] Serial number -20℃ Cyclic initial polarization -20℃ Cycle 500h Polarization Example 1 0.1V 0.13V Comparative Example 1 0.15V 0.23V Comparative Example 2 0.17V 0.31V Comparative Example 3 0.14V 0.24V

[0080] According to Table 2, the high-voltage and low-temperature electrolyte prepared in Example 1 circulates at -20°C for 500 hours, and its lithium symmetric battery polarization potential changes slightly, only 0.03V, while the electrolyte in the comparative example has a large change in polarization potential after circulating at -20°C for 500 hours.

[0081] Therefore, the high-voltage and low-temperature electrolyte provided in the present application includes ethylene glycol diethyl ether, 1,2-difluorobenzene, lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalatoborate) and additives, which can synergistically optimize the low-temperature bulk phase transport, interface chemistry and interface mass transfer kinetics in lithium metal batteries, so that it has excellent electrochemical properties; and has high-voltage and low-temperature characteristics, with a voltage window of approximately 4.6V, and can maintain good fluidity at -40°C to 40°C, and an ionic conductivity of up to 1.89mS / cm at -40°C, and has excellent low-temperature capacity retention.

[0082] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0083] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions recorded in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A high-pressure and low-temperature electrolyte, characterized in that A local high concentration electrolyte comprising ethylene glycol diethyl ether, 1,2-difluorobenzene, lithium salt and additives; The lithium salt is lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalate)borate; The additive is one or more of 3A molecular sieve, 4A molecular sieve and 5A molecular sieve.

2. The high-voltage and low-temperature electrolyte according to claim 1, characterized in that: The volume ratio of ethylene glycol diethyl ether, 1,2-difluorobenzene and lithium salt is 1:1:10-200.

3. The high-voltage and low-temperature electrolyte according to claim 1, characterized in that: The concentration of the lithium salt is 2-6 mol / L.

4. The high-voltage and low-temperature electrolyte according to claim 1, characterized in that: The concentration of the lithium salt is 4 mol / L.

5. The high-voltage and low-temperature electrolyte according to claim 1, characterized in that: The molar ratio of lithium bis(fluorosulfonyl)imide to lithium bis(fluorooxalatoborate) in the electrolyte is (6-8):(4-2).

6. The high-voltage and low-temperature electrolyte according to claim 1, characterized in that: The molar ratio of lithium bis(fluorosulfonyl)imide to lithium bis(fluorooxalatoborate) in the electrolyte is 6:

4.

7. The high-voltage and low-temperature electrolyte according to claim 1, characterized in that: The amount of the additive added is 10-20 times the sum of ethylene glycol diethyl ether, 1,2-difluorobenzene and lithium salt.

8. A method for preparing a high-voltage and low-temperature electrolyte according to any one of claims 1 to 7, characterized in that: The method comprises: The additive is added to a mixed solution of ethylene glycol diethyl ether and 1,2-difluorobenzene for reaction, and then a lithium salt is added for mixed reaction to obtain the high-voltage and low-temperature electrolyte.

9. The method for preparing a high-voltage and low-temperature electrolyte according to claim 8, characterized in that: The additive is added to the mixed solution of ethylene glycol diethyl ether and 1,2-difluorobenzene for a reaction time of 40-50 hours; And / or, the time for adding the lithium salt for mixed reaction is 6-12 hours.

10. Use of a high-voltage and low-temperature electrolyte prepared by the preparation method according to any one of claims 8 to 9 in a lithium metal battery.

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