Application of lithium borate compounds in battery electrolytes

Abstract

The invention discloses an application of lithium borate compounds in battery electrolyte, belonging to the technical field of battery electrolyte. The lithium borate compounds and perfluoroalkyl lithium fluorosilicate are used as battery electrolyte additives in a mass ratio of (0.5-2):(7-25), and the amount of the battery electrolyte additive added is 5-8% of the mass of the battery electrolyte. The lithium borate compounds are used in battery electrolytes to improve the high-rate cycle performance and high-temperature storage performance of the battery and increase the service life of the battery.

Description

Technical Field

[0001] The invention belongs to the technical field of battery electrolytes, relates to an additive for battery electrolytes, and specifically relates to the application of lithium borate compounds in battery electrolytes. Background Art

[0002] In recent years, lithium secondary batteries have been widely used due to their advantages of high energy density, small size and light weight. With the continuous development of science and technology, people have continuously put forward higher and higher requirements on the energy density of lithium-ion batteries. Correspondingly, while obtaining high energy density batteries, the demand for high and low temperature cycle characteristics, high temperature storage and safety performance of lithium secondary batteries has also been increasing. Summary of the invention

[0003] In order to solve the above problems, the present invention proposes to use lithium borate compounds in battery electrolyte, thereby improving the high-rate charging and discharging characteristics, high-temperature storage and cycle performance of the battery, and increasing the service life of the battery.

[0004] The specific technical scheme adopted by the present invention is: the application of lithium borate compounds in battery electrolyte, the key is that lithium borate compounds, perfluoroalkyl lithium fluorosilicate, mono (hexafluoroisopropyl) bis (trimethylsilyl) phosphate are used as battery electrolyte additives according to a mass ratio of (0.5-2): (7-25): 1, and the amount of battery electrolyte additive added is 5-8% of the mass of the battery electrolyte;

[0005] The lithium borate compound is shown in formula (1):

[0006]

[0007] Furthermore, the perfluoroalkyl lithium fluorosilicate includes one or more of tris(undecafluoro-n-pentyl)lithium difluorosilicate, tris(pentafluoroethyl)lithium difluorosilicate, tris(undecafluoro-n-pentyl)lithium trifluorosilicate or di(nonafluoro-n-butyl)lithium tetrafluorosilicate.

[0008] Furthermore, the battery electrolyte comprises a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of (2-6):(13-17):1.

[0009] Furthermore, the lithium salt includes one or more of LiPF6, LiBF4, LiSO3CF3, LiClO4, LiN(CF3SO2)2, LiC(CF3SO2)3, LiODCB, LiBOB, LiODFB, and LiTDI.

[0010] Furthermore, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl trifluoroacetate, ethyl trifluoroacetate, and butyl trifluoroacetate.

[0011] The invention has the beneficial effect that the lithium borate compound is used in the battery electrolyte to improve the high-rate cycle performance and high-temperature storage performance of the battery and to increase the service life of the battery. The lithium borate compound and perfluoroalkyl lithium fluorosilicate are used as battery electrolyte additives in a mass ratio of (0.5-2): (7-25) to synergistically improve the high-rate charge and discharge characteristics of the battery. DETAILED DESCRIPTION

[0012] The present invention will be further described below in conjunction with specific embodiments.

[0013] Example 1

[0014] The battery electrolyte includes a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of 4:15:1. The lithium salt is LiPF6 and LiODFB in a mass ratio of 1:1, with a concentration of 1 mol / L, the organic solvent is ethylene carbonate and γ-valerolactone in a volume ratio of 20:80, and the battery electrolyte additive is and tris(undecafluoro-n-pentyl) lithium difluorosilicate, tris(pentafluoroethyl) lithium difluorosilicate, mono(hexafluoroisopropyl)bis(trimethylsilyl) phosphate, the addition amount being 5% of the mass of the battery electrolyte.

[0015] Example 2

[0016] The battery electrolyte includes a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of 2:17:1. The lithium salt is LiODCB with a concentration of 1 mol / L, the organic solvent is methyl propionate and methyl trifluoroacetate in a volume ratio of 33.1:66.9, and the battery electrolyte additive is Tris(undecafluoro-n-pentyl)dilithium trifluorosilicate, di(nonafluoro-n-butyl)dilithium tetrafluorosilicate, mono(hexafluoroisopropyl)bis(trimethylsilyl)phosphate, the added amount is 8% of the battery electrolyte mass.

[0017] Example 3

[0018] The battery electrolyte includes a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of 6:13:1. The lithium salt is LiBOB and LiTDI in a mass ratio of 1:1, and the concentration is 1 mol / L. The organic solvent is ethylene carbonate and methyl trifluoroacetate in a volume ratio of 83:17. The battery electrolyte additive is and lithium tris(undecafluoro-n-pentyl)difluorosilicate, lithium tris(undecafluoro-n-pentyl)trifluorosilicate, mono(hexafluoroisopropyl)bis(trimethylsilyl)phosphate, the addition amount being 6% of the mass of the battery electrolyte.

[0019] Example 4

[0020] The battery electrolyte includes a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of 5:14:1. The lithium salt is LiN(CF3SO2)2, LiC(CF3SO2)3, LiBF4, LiSO3CF3 in a mass ratio of 1:1:1:1, and the concentration is 1 mol / L. The organic solvent is propylene carbonate, γ-valerolactone, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1:1. The battery electrolyte additive is and tris(undecafluoro-n-pentyl)dilithium trifluorosilicate, mono(hexafluoroisopropyl)bis(trimethylsilyl)phosphate, the addition amount being 7% of the battery electrolyte mass.

[0021] Example 5

[0022] The battery electrolyte includes a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of 3:16:1. The lithium salt is LiClO4, LiN(CF3SO2)2, and LiODFB in a mass ratio of 1:1:1, with a concentration of 1 mol / L. The organic solvent is dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 15:75. The battery electrolyte additive is and tris(undecafluoro-n-pentyl)lithium difluorosilicate, tris(pentafluoroethyl)lithium difluorosilicate, tris(undecafluoro-n-pentyl)dilithium trifluorosilicate, di(nonafluoro-n-butyl)dilithium tetrafluorosilicate, mono(hexafluoroisopropyl)bis(trimethylsilyl) phosphate, the addition amount is 5% of the battery electrolyte mass.

[0023] Taking Example 1 as an example, the following comparison is made:

[0024] Comparative Example 1: The only difference is that tris(undecylfluoro-n-pentyl)lithium difluorosilicate is not included, and other components are the same as those in Example 1.

[0025] Comparative Example 2: The only difference is that tris(pentafluoroethyl)difluorolithium silicate is not included, and other components are the same as those in Example 1.

[0026] Comparative Example 3: The only difference is that tris(undecafluoro-n-pentyl)lithium difluorosilicate and tris(pentafluoroethyl)lithium difluorosilicate are not included, and other components are the same as those in Example 1.

[0027] Comparative Example 4: The only difference is that it does not include The other components are the same as in Example 1.

[0028] 2. Practical application test

[0029] Lithium cobalt oxide is used as the positive electrode material, mesophase carbon microspheres are used for the negative electrode, aluminum foil and copper foil are used for the positive and negative current collectors, and ceramic diaphragms are used to form soft-pack batteries. After injecting the electrolyte, the soft-pack batteries are assembled in the glove box and tested after standing for 8 hours. The electrolyte is prepared by dissolving LiODFB in a mixed solvent of ethylene carbonate, methyl trifluoroacetate and methyl propionate in a volume ratio of 1:1:1 to obtain a 1.0M solution, and the solution is used as the basic electrolyte, and the basic electrolyte is used as the blank group for battery performance comparison.

[0030] 1. The lithium secondary batteries using the battery electrolytes of the embodiment and the comparative example were charged to 4.25V / 55mA at 1.0C / 4.25V under constant current / constant voltage conditions at 60°C, and discharged to a voltage of 3.0V at 1.0C. This charge and discharge cycle was repeated, and the results are shown in Table 1 below: Capacity retention (%) = [discharge capacity after cycle (mAh)] / [initial discharge capacity (mAh)] × 100

[0031] Table 1

[0032] project Capacity retention rate after 400 cycles Capacity retention rate after 600 cycles Capacity retention rate after 800 cycles Blank Group 65.5 0 - Example 1 92.5 81.7 70.5 Example 2 92.3 81.5 70.3 Example 3 91.9 81.2 70.0 Example 4 92.0 81.0 70.1 Example 5 92.1 81.4 70.2 Comparative Example 1 83.8 65.3 43.1 Comparative Example 2 82.7 64.2 39.8 Comparative Example 3 79.2 60.2 35.7 Comparative Example 4 74.2 54.5 30.1

[0033] As can be seen from Table 1, adding The high temperature cycle performance of lithium-ion batteries can be improved. The synergy and dosage control of the added tris(undecafluoro-n-pentyl) lithium difluorosilicate and tris(pentafluoroethyl) lithium difluorosilicate have an impact on the improvement of the high temperature cycle performance of the battery. The synergy of mono(hexafluoroisopropyl)bis(trimethylsilyl) phosphate, tri(undecafluoro-n-pentyl) lithium difluorosilicate and tri(pentafluoroethyl) lithium difluorosilicate can further improve the high temperature cycle performance of the battery.

[0034] 2. The battery was initially charged and discharged at 0.1C / 4.25V to 4.25V / 55mA at constant current / constant voltage at room temperature, and discharged at 0.1C to a voltage of 2.0V. After that, the secondary battery was charged at 0.1C / 4.25V to 4.25V / 55mA at constant current / constant voltage at room temperature, and then stored at 80°C for 10 days. The capacity retention rate and capacity recovery rate of the battery were then measured. The results are shown in Table 2.

[0035] Table 2

[0036] project Capacity retention rate Capacity recovery rate Blank Group 63.1 60.3 Example 1 88.2 89.7 Example 2 88.1 89.6 Example 3 87.8 88.6 Example 4 87.9 88.9 Example 5 88.2 89.5 Comparative Example 1 72.6 74.6 Comparative Example 2 72.2 74.3 Comparative Example 3 70.1 73.0 Comparative Example 4 65.0 67.6

[0037] 3. The internal resistance of the battery was tested with a battery internal resistance tester. The internal resistance of the basic electrolyte was 1 and the conductivity was 1. The changes in the internal resistance and conductivity after adding the battery electrolytes of each embodiment and comparative example were examined. The results are shown in Table 3, where + indicates an increase and - indicates a decrease.

[0038] Table 3

[0039] project Conductivity Internal resistance Example 1 +19.8 -7.5 Example 2 +19.6 -7.4 Example 3 +18.7 -7.0 Example 4 +18.9 -7.2 Example 5 +19.5 -7.5 Comparative Example 1 +7.7 -3.1 Comparative Example 2 +7.5 -3.4 Comparative Example 3 +7.3 -3.0 Comparative Example 4 +7.2 -2.8

[0040] The specific embodiments of the present invention are described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions made to the present invention are also within the scope of the present invention. Therefore, the equalization changes and modifications made without departing from the spirit and scope of the present invention should be included in the scope of the present invention.

Claims

1. Application of lithium borate compounds in battery electrolyte, characterized in that: Lithium borate compounds, perfluoroalkyl lithium fluorosilicate, and mono(hexafluoroisopropyl)bis(trimethylsilyl) phosphate are used as battery electrolyte additives in a mass ratio of (0.5-2):(7-25):1, and the amount of the battery electrolyte additive added is 5-8% of the mass of the battery electrolyte; The lithium borate compound is shown in formula (1):

2. The use of the lithium borate compound in a battery electrolyte according to claim 1, characterized in that: The perfluoroalkyl lithium fluorosilicate includes one or more of tris(undecafluoro-n-pentyl) lithium difluorosilicate, tris(pentafluoroethyl) lithium difluorosilicate, tris(undecafluoro-n-pentyl) lithium trifluorosilicate or di(nonafluoro-n-butyl) lithium tetrafluorosilicate.

3. The use of the lithium borate compound in a battery electrolyte according to claim 1, characterized in that: The battery electrolyte comprises a lithium salt, an organic solvent and a battery electrolyte additive in a mass ratio of (2-6):(13-17):

1.

4. The use of the lithium borate compound in a battery electrolyte according to claim 3, characterized in that: The lithium salt includes one or more of LiPF6, LiBF4, LiSO3CF3, LiClO4, LiN(CF3SO2)2, LiC(CF3SO2)3, LiODCB, LiBOB, LiODFB, and LiTDI.

5. The use of the lithium borate compound in battery electrolyte according to claim 3, characterized in that: The organic solvent includes one or more of ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl trifluoroacetate, ethyl trifluoroacetate, and butyl trifluoroacetate.

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