Electrolyte for improving dynamics of strong-coordination solvent passivation low-temperature lithium metal battery

Abstract

The invention discloses an electrolyte for improving dynamics of a strong-coordination solvent passivated low-temperature lithium metal battery, and belongs to the technical field of electrolytes. The electrolyte comprises the following components: lithium salt, an organic solvent and an additive, wherein the additive comprises at least two of fluoroethylene carbonate, fluoropropylene carbonate, diethylene glycol dimethyl ether, 1, 1, 2, 2-tetrafluoroethyl 2, 2, 3, 3-tetrafluoropropyl ether, ethylene glycol dimethyl ether, 2, 2, 2-trifluoroethyl ether, methyl trifluoroethyl carbonate and triethylene glycol dimethyl ether. The electrolyte prepared by the invention can keep good conductivity and battery reaction power in a low-temperature environment, has relatively high power and capacity, can ensure rapid and efficient transmission of lithium ions in an electrode solution, accelerates the charging and discharging speed of the battery, shortens the charging time, has good compatibility with positive and negative electrode materials, reduces interface side reactions, and improves the service life of the battery. And the battery has higher energy output under the same volume or weight, and the cruising ability of the battery is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of electrolytes, and in particular to an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent. Background Art

[0002] Lithium metal batteries use lithium metal as the negative electrode. They have an ultra-high theoretical specific capacity (3860mAh / g) and the lowest electrochemical potential (-3.04V vs. standard hydrogen electrode), which makes lithium metal batteries considered to be high-energy density battery systems with great development potential. During the battery charging and discharging process, lithium ions shuttle between the positive and negative electrodes. Under low temperature conditions, the kinetic performance of lithium metal batteries will be seriously affected. On the one hand, the ionic conductivity of the electrolyte will decrease significantly with decreasing temperature. For example, the migration speed of ions in traditional liquid electrolytes slows down at low temperatures, resulting in an increase in the ohmic polarization of the battery; on the other hand, the charge transfer process of lithium ions at the electrode / electrolyte interface will also become slow.

[0003] Strongly coordinated solvents generally refer to solvents that can interact strongly with lithium ions. In the electrolyte, these solvent molecules will tightly wrap around the lithium ions to form a solvation sheath. This solvation sheath is beneficial to the dissolution and transmission of lithium ions to a certain extent. It can help lithium ions to stably exist in the electrolyte and achieve migration. However, in a low-temperature environment, since the strongly coordinated solvents tightly wrap the lithium ions, this tight solvation structure is more difficult to destroy, which will hinder the desolvation process of lithium ions and make the transmission of lithium ions more difficult, resulting in a decrease in the battery's charge and discharge rate performance, an increase in the polarization of the battery, and ultimately a deterioration of the kinetic performance of low-temperature lithium metal batteries. How to improve the strongly coordinated solvents to prepare lithium metal battery electrolytes that still have excellent kinetic performance in low-temperature environments is one of the key issues that need to be urgently addressed in the current research on lithium metal battery electrolytes. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide an electrolyte that improves the kinetics of low-temperature lithium metal batteries passivated by strong coordinating solvents, so as to solve the problem that when a strong coordinating solvent is used to prepare a lithium metal battery electrolyte, the battery charge and discharge rate performance decreases, the battery polarization increases, and the kinetic performance deteriorates under low temperature conditions.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] An electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordination solvent, the electrolyte comprising the following components:

[0007] Lithium salts, organic solvents and additives;

[0008] The additive includes at least two of fluoroethylene carbonate, fluoropropylene carbonate, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, ethylene glycol dimethyl ether, 2,2,2-trifluoroethyl ether, methyl trifluoroethyl carbonate and triethylene glycol dimethyl ether.

[0009] The beneficial effects of the present invention are: by increasing the salt / solvent ratio, the interaction between lithium ions and anions is enhanced, thereby reducing the amount of free solvent, which is one of the solutions to reduce the influence of strong coordination solvents on lithium ions. However, high-concentration electrolytes will increase their viscosity, hindering the diffusion of lithium ions in the dielectric, especially under low temperature conditions, the viscosity increase is more obvious, which will lead to a decrease in the rate performance of the battery. The present invention achieves the passivation of the strong coordination solvent by binding the lithium salt to the strong coordination solvent and adding specific additives, which not only retains the advantages of the anion-dominated solvation structure in the high-concentration electrolyte, but also reduces the overall viscosity, improves the mobility of lithium ions, and reduces the binding ability of the strong coordination solvent to lithium ions, thereby effectively reducing the possibility of strong coordination solvent reduction on the lithium metal surface, reducing the occurrence of side reactions, and improving the cycle life of the lithium metal battery and the charge and discharge rate performance in a low temperature environment.

[0010] Furthermore, the additive is any two of fluoroethylene carbonate, fluoropropylene carbonate, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, ethylene glycol dimethyl ether, 2,2,2-trifluoroethyl ether, methyl trifluoroethyl carbonate and triethylene glycol dimethyl ether.

[0011] Furthermore, the volume ratio between any two additives is 3-7:3-7.

[0012] Further, the lithium salt includes at least two of lithium difluorooxalatoborate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium trifluoromethylsulfonyl imide, lithium difluoroborate, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0013] Furthermore, the total concentration of the lithium salt is 0.1-6 mol / L.

[0014] Preferably, the total concentration of lithium salt is 2-6 mol / L.

[0015] Further, the organic solvent includes at least three of diethyl sulfate, ethyl methyl carbonate, triethyl phosphate, methyl propyl carbonate, triethyl phosphite, ethylene carbonate, dimethyl carbonate, tributyl phosphate, tripropyl phosphate and dimethyl sulfite.

[0016] Preferably, the organic solvent is any three of diethyl sulfate, ethyl methyl carbonate, triethyl phosphate, methyl propyl carbonate, triethyl phosphite, ethylene carbonate, dimethyl carbonate, tributyl phosphate, tripropyl phosphate and dimethyl sulfite.

[0017] Furthermore, the volume ratio of any three organic solvents is 2-4:3-5:2-4.

[0018] Furthermore, the volume ratio of the organic solvent to the additive is 80-95:5-20.

[0019] The above electrolyte for improving the kinetics of low-temperature lithium metal battery passivated by strong coordinating solvents is used in lithium batteries.

[0020] The present invention has the following beneficial effects:

[0021] (1) The electrolyte prepared by the present invention can maintain good ionic conductivity and battery reaction dynamics under low temperature environment, effectively reduce the internal resistance of the battery, enable the battery to still output higher power and capacity under low temperature conditions, reduce the battery performance degradation caused by low temperature, and expand the battery's operating temperature range.

[0022] (2) The electrolyte prepared by the present invention can ensure that lithium ions can be transmitted quickly and efficiently in the electrolyte, accelerate the charging and discharging speed of the battery, shorten the charging time, and improve the power performance of the battery, so that the battery can meet the needs of high-power application scenarios, such as the fast charging needs of electric vehicles.

[0023] (3) The electrolyte prepared by the present invention has good compatibility with the lithium metal negative electrode and the positive and negative electrode materials of the battery, and can form a stable interface layer on the electrode surface, reduce the occurrence of interfacial side reactions, and maintain the structural integrity and electrochemical activity of the electrode material.

[0024] (4) The present invention optimizes the performance of the electrolyte, enhances the charge transfer efficiency and reaction kinetics within the battery, helps to fully utilize the capacity of the electrode material, enables the battery to store more electricity, improves the energy density of the battery, achieves higher energy output at the same volume or weight, and improves the battery's endurance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The charge and discharge curves of the electrolytes prepared in the examples and comparative examples at -20°C. DETAILED DESCRIPTION

[0026] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0027] Embodiment 1:

[0028] A method for preparing an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent comprises the following steps:

[0029] In a glove box (H2O<0.1ppm, O2<0.1ppm), equimolar amounts of lithium oxalate borate and lithium nitrate were weighed in an argon atmosphere and dissolved in a mixed non-aqueous organic solvent consisting of diethyl sulfate, ethyl methyl carbonate and triethyl phosphate (volume ratio of 3:4:3), and a mixed additive consisting of fluoroethylene carbonate and fluoropropylene carbonate (volume ratio of 1:1) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 10:90, the total concentration of the lithium salt was 1.2 mol / L, and the mixture was shaken and stirred for 20 minutes to prepare an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordination solvent.

[0030] Embodiment 2:

[0031] A method for preparing an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent comprises the following steps:

[0032] In a glove box (H2O<0.1ppm, O2<0.1ppm), equimolar lithium nitrate and lithium bis(fluorosulfonyl)imide were weighed in an argon atmosphere and dissolved in a mixed non-aqueous organic solvent consisting of ethyl methyl carbonate, propyl methyl carbonate and triethyl phosphite (volume ratio of 3:4:3), and a mixed additive consisting of fluoroethylene carbonate and diethylene glycol dimethyl ether (volume ratio of 1:1) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 20:80, the total concentration of lithium salt was 2 mol / L, and the mixture was shaken and stirred for 20 minutes to prepare an electrolyte for improving the kinetics of a strong coordination solvent passivated low-temperature lithium metal battery.

[0033] Embodiment 3:

[0034] A method for preparing an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent comprises the following steps:

[0035] In a glove box (H2O<0.1ppm, O2<0.1ppm), equimolar amounts of lithium tetrafluoroborate and lithium trifluoromethylsulfonyl imide were weighed in an argon atmosphere and dissolved in a mixed non-aqueous organic solvent consisting of ethylene carbonate, dimethyl carbonate and tributyl phosphate (volume ratio of 3:4:3), and a mixed additive consisting of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and ethylene glycol dimethyl ether (volume ratio of 3:7) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 8:92, the total concentration of the lithium salt was 3 mol / L, and the mixture was shaken and stirred for 20 minutes to prepare an electrolyte for improving the kinetics of a strong coordination solvent passivated low-temperature lithium metal battery.

[0036] Embodiment 4:

[0037] A method for preparing an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent comprises the following steps:

[0038] In a glove box (H2O<0.1ppm, O2<0.1ppm), equimolar amounts of lithium difluoroborate, lithium trifluoromethylsulfonyl imide and lithium hexafluorophosphate were weighed in an argon atmosphere and dissolved in a mixed non-aqueous organic solvent consisting of ethyl methyl carbonate, propyl methyl carbonate and tripropyl phosphate (volume ratio of 3:4:3), and a mixed additive consisting of 2,2,2-trifluoroethyl ether and fluoropropylene carbonate (volume ratio of 3:7) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 5:95, the total concentration of the lithium salt was 6 mol / L, and the mixture was shaken and stirred for 20 minutes to prepare an electrolyte for improving the kinetics of a strong coordination solvent passivated low-temperature lithium metal battery.

[0039] Embodiment 5:

[0040] A method for preparing an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent comprises the following steps:

[0041] In a glove box (H2O<0.1ppm, O2<0.1ppm), equimolar amounts of lithium difluorooxalatoborate and lithium nitrate were weighed in an argon atmosphere and dissolved in a mixed non-aqueous organic solvent consisting of ethylene carbonate, dimethyl sulfite and triethyl phosphate (volume ratio of 3:4:3), and a mixed additive consisting of fluoroethylene carbonate and diethylene glycol dimethyl ether (volume ratio of 3:7) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 15:85, the total concentration of the lithium salt was 2 mol / L, and the mixture was shaken and stirred for 20 minutes to prepare an electrolyte for improving the kinetics of a strong coordination solvent passivated low-temperature lithium metal battery.

[0042] Embodiment 6:

[0043] A method for preparing an electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent comprises the following steps:

[0044] In a glove box (H2O<0.1ppm, O2<0.1ppm), equimolar amounts of lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate were weighed in an argon atmosphere and dissolved in a mixed non-aqueous organic solvent consisting of dimethyl carbonate, dimethyl sulfite and tripropyl phosphate (volume ratio of 3:4:3), and a mixed additive consisting of methyl trifluoroethyl carbonate and triethylene glycol dimethyl ether (volume ratio of 1:1) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 20:80, the total concentration of the lithium salt was 4 mol / L, and the mixture was shaken and stirred for 20 minutes to prepare an electrolyte for improving the kinetics of a strong coordination solvent passivated low-temperature lithium metal battery.

[0045] Comparative Example 1:

[0046] A method for preparing an electrolyte for a lithium metal battery comprises the following steps:

[0047] In a glove box (H2O < 0.1ppm, O2 < 0.1ppm), an appropriate amount of lithium difluorooxalatoborate was weighed in an argon atmosphere and dissolved in a non-aqueous organic solvent consisting of ethyl methyl carbonate and triethyl phosphate (volume ratio of 8:2), and a mixed additive consisting of fluoroethylene carbonate and methyl trifluoroethyl carbonate (volume ratio of 3:7) was added, the volume ratio of the mixed additive to the mixed non-aqueous organic solvent was 10:90, the total concentration of the lithium salt was 1 mol / L, and the mixture was shaken and stirred for 20 minutes to obtain an electrolyte for improving the kinetics of a strong coordination solvent passivated low-temperature lithium metal battery.

[0048] Test example:

[0049] In an inert atmosphere, the seven electrolytes prepared in Examples 1-6 and Comparative Example 1 were measured in sequence to prepare lithium batteries. The preparation process of the lithium battery is as follows: in a glove box (H2O < 0.1ppm, O2 < 0.1ppm), the positive electrode shell, NCM622 pole piece, electrolyte, diaphragm, electrolyte, lithium sheet, stainless steel gasket, spring sheet and negative electrode were assembled from bottom to top, and then transferred to a tablet press for stamping and packaging to prepare a full battery.

[0050] Then the electrochemical performance of the assembled full battery was tested using the Xinwei testing equipment. The test parameters are as follows:

[0051] (1) 25°C Cycling: The prepared full battery was subjected to 0.1C / 0.4C cycling tests at 25°C to analyze the effects of different solvent types on the battery cycling performance.

[0052] (2) -20℃ Cycling: The prepared full battery was subjected to 0.1C / 0.4C cycling tests at -20℃ to analyze the effects of different solvent types on the battery cycling performance.

[0053] (4) 4.3 V cycle: The prepared full battery was subjected to 0.1C / 0.4C cycle test at -20°C to analyze the effect of different solvent types on the battery cycle performance.

[0054] (5) 4.4 V cycle: The prepared full battery was subjected to 0.1C / 0.4C cycle test at -20°C to analyze the effect of different solvent types on the battery cycle performance.

[0055] (6) 4.5 V cycle: The prepared full battery was subjected to 0.1C / 0.4C cycle test at -20°C to analyze the effect of different solvent types on the battery cycle performance.

[0056] The experimental results are shown in Tables 1-2 and Figure 1 shown.

[0057] Table 1 Electrochemical performance test results at different temperatures

[0058]

[0059] Table 2 Cycle test results at different cut-off voltages (not less than 85%)

[0060] sample 4.3V(circle) 4.4V(circle) 4.5V(circle) Example 1 185 180 170 Example 2 175 160 150 Example 3 185 170 160 Example 4 190 185 175 Example 5 180 175 170 Example 6 185 170 160 Comparative Example 1 80 65 50

[0061] According to the test results in Table 1, the electrolyte prepared in the embodiment of the present invention maintains excellent cycle stability both at low temperature and at room temperature, while the basic electrolyte prepared in Comparative Example 1 has poor stability both at low temperature and at room temperature, especially at low temperature, and its performance is extremely unstable.

[0062] Depend on Figure 1 As shown in the experimental results in Table 2, at the cut-off voltages of 4.3 V, 4.4 V and 4.5 V, the electrolyte prepared in Example 4 of the present invention has a higher battery specific capacity than the electrolyte prepared in Comparative Example 1, and the battery specific capacity can reach 3.5 mAh·cm -2 、3.8 mAh cm -2 and 4 mAh cm -2 , it still has a large number of charge and discharge times under high voltage and low temperature conditions, and the capacity retention rate is high.

[0063] It can be seen that the electrolyte prepared by the present invention for improving the kinetics of low-temperature lithium metal batteries passivated by strong coordinating solvents can effectively solve the problem of poor cycle stability of existing lithium batteries under low temperature and high pressure, and can still maintain a large number of charge and discharge times with a high capacity retention rate at an ultra-high positive electrode active material loading.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent, characterized in that: The electrolyte includes the following components: Lithium salts, organic solvents and additives; The additive includes at least two of fluoroethylene carbonate, fluoropropylene carbonate, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, ethylene glycol dimethyl ether, 2,2,2-trifluoroethyl ether, methyl trifluoroethyl carbonate and triethylene glycol dimethyl ether.

2. The electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent according to claim 1, characterized in that: The lithium salt includes at least two of lithium difluorooxalatoborate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium trifluoromethylsulfonyl imide, lithium difluoroborate, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

3. The electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent according to claim 1 or 2, characterized in that: The total concentration of the lithium salt is 0.1-6 mol / L.

4. The electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent according to claim 1, characterized in that: The organic solvent includes at least three of diethyl sulfate, ethyl methyl carbonate, triethyl phosphate, methyl propyl carbonate, triethyl phosphite, ethylene carbonate, dimethyl carbonate, tributyl phosphate, tripropyl phosphate and dimethyl sulfite.

5. The electrolyte for improving the kinetics of a low-temperature lithium metal battery passivated by a strong coordinating solvent according to claim 1, characterized in that: The volume ratio of the organic solvent to the additive is 80-95:5-20.

6. Use of the electrolyte for improving the kinetics of low-temperature lithium metal batteries passivated by strong coordinating solvents as described in any one of claims 1 to 5 in lithium batteries.

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