A low temperature electrolyte for lithium ion battery

Abstract

The invention discloses a low-temperature electrolyte for a lithium ion battery. The electrolyte comprises a solvent, a solute and an additive. The mass ratio of the solvent, the solute and the additive is 90-100:17-28:1.7-2.3. The solvent comprises the following volume percentages: 18% of ethylene carbonate, 15% of ethyl methyl carbonate, 32% of propylene carbonate, 24% of dimethyl carbonate, 8% of methyl cyclohexyl carbonate and 3% of methyl trifluoroethyl carbonate. The solute is lithium tetrafluoroborate and lithium hexafluorophosphate. The invention overcomes the shortcomings of the prior art, optimizes the ratio of each component, and makes the performance of the electrolyte more excellent.

Description

Technical Field

[0001] The invention relates to the technical field of electrolytes, and in particular to a low-temperature electrolyte for lithium-ion batteries. Background Art

[0002] Lithium iron phosphate batteries are widely used in power supplies for mobile devices and electrical equipment due to their outstanding advantages such as high energy density, high operating voltage, long cycle life, no environmental pollution, and high-rate charging. However, lithium batteries need to adapt to high and low temperature environments when used, especially in low temperature environments. Lithium batteries are prone to insufficient power supply, resulting in the inability to properly use electronic and electrical equipment, which limits the use of lithium iron phosphate batteries. Therefore, it is necessary to develop electrolytes that are more suitable for use of lithium iron phosphate batteries at low temperatures.

[0003] The type of solute in the electrolyte, the composition of the solvent and the composition of the additives are all factors that affect the low-temperature performance of lithium batteries. In order to improve the low-temperature performance of lithium batteries, it is necessary to select suitable solvents, solutes and additives so that the lithium batteries can obtain excellent low-temperature performance. Summary of the invention

[0004] The purpose of the present invention is to provide a low-temperature electrolyte for lithium-ion batteries, which overcomes the problem of poor low-temperature performance of lithium iron phosphate batteries in the prior art.

[0005] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0006] A low-temperature electrolyte for lithium-ion batteries comprises a solvent, a solute and an additive, wherein the mass ratio of the solvent, the solute and the additive is 90-100:17-28:1.7-2.3, the solvent comprises the following volume percentages: 18% of ethylene carbonate, 15% of ethyl methyl carbonate, 32% of propylene carbonate, 24% of dimethyl carbonate, 8% of methyl cyclohexyl carbonate and 3% of methyl trifluoroethyl carbonate, and the solute is lithium tetrafluoroborate and lithium hexafluorophosphate.

[0007] Preferably, the additive is composed of 4,5-dimethyl-1,3-dioxol-2-one and 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester in a volume ratio of 1.2:2.3.

[0008] Preferably, the additive is composed of 4,5-dimethyl-1,3-dioxol-2-one and 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxol in a volume ratio of 0.8:1.7.

[0009] Preferably, the mass ratio of lithium tetrafluoroborate to lithium hexafluorophosphate is 0.6-1.2:2.1-2.7.

[0010] Preferably, the mass ratio of lithium tetrafluoroborate to lithium hexafluorophosphate is 1.2:2.7.

[0011] Preferably, the mass ratio of solvent, solute and additive is 92:17:1.9.

[0012] Preferably, a film-forming additive is also included, and the volume ratio of the film-forming additive to the solvent is 7-12:90-100.

[0013] Preferably, the film-forming additive is a mixture of fluoroethylene carbonate and monolayer graphene in a mass ratio of 80:1.3.

[0014] Compared with the prior art, the implementation effects of the present invention are as follows: the present invention adds additives 4,5-dimethyl-1,3-dioxol-2-one and 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester or 4,5-dimethyl-1,3-dioxol-2-one and 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxol to the electrolyte solvent, and the synergistic effect of the two ensures the low-temperature discharge capacity of the electrolyte; lithium tetrafluoroborate and lithium hexafluorophosphate are used as solutes to ensure the mobility of lithium ions in the electrolyte at low temperatures, and the additives improve the low-temperature cycle performance of the lithium ion battery. The present invention optimizes the ratio of each component to make the performance of the electrolyte more excellent. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] The 4,5-dimethyl-1,3-dioxol-2-one used in the present invention is a pharmaceutical intermediate, which is commonly used in the synthesis of antibiotics, antihypertensive drugs, and antiseptic drugs.

[0017] Example 1

[0018] A low-temperature electrolyte for a lithium-ion battery comprises a solvent, a solute and an additive in a mass ratio of 90:17:1.8, wherein the solvent comprises 18% by volume of ethylene carbonate, 15% by volume of ethyl methyl carbonate, 32% by volume of propylene carbonate, 24% by volume of dimethyl carbonate, 8% by volume of methyl cyclohexyl carbonate and 3% by volume of methyl trifluoroethyl carbonate, the solute comprises lithium tetrafluoroborate and lithium hexafluorophosphate in a mass ratio of 0.6:2.5, and the additive comprises 4,5-dimethyl-1,3-dioxol-2-one and 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester in a volume ratio of 1.2:2.3.

[0019] Example 2

[0020] A low-temperature electrolyte for a lithium-ion battery comprises a solvent, a solute and an additive in a mass ratio of 100:28:1.7, wherein the solvent comprises 18% by volume of ethylene carbonate, 15% by volume of ethyl methyl carbonate, 32% by volume of propylene carbonate, 24% by volume of dimethyl carbonate, 8% by volume of methyl cyclohexyl carbonate and 3% by volume of methyl trifluoroethyl carbonate, the solute comprises lithium tetrafluoroborate and lithium hexafluorophosphate in a mass ratio of 1.2:2.1, and the additive comprises 4,5-dimethyl-1,3-dioxole-2-one and 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole in a volume ratio of 0.8:1.7.

[0021] Example 3

[0022] A low-temperature electrolyte for a lithium-ion battery comprises a solvent, a solute and an additive in a mass ratio of 97:20:2.3, wherein the solvent comprises 18% by volume of ethylene carbonate, 15% by volume of ethyl methyl carbonate, 32% by volume of propylene carbonate, 24% by volume of dimethyl carbonate, 8% by volume of methyl cyclohexyl carbonate and 3% by volume of methyl trifluoroethyl carbonate, the solute comprises lithium tetrafluoroborate and lithium hexafluorophosphate in a mass ratio of 0.9:2.1, and the additive comprises 4,5-dimethyl-1,3-dioxol-2-one and 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester in a volume ratio of 1.2:2.3.

[0023] Example 4

[0024] A low-temperature electrolyte for a lithium-ion battery comprises a solvent, a solute and an additive in a mass ratio of 92:17:1.9, wherein the solvent comprises 18% by volume of ethylene carbonate, 15% by volume of ethyl methyl carbonate, 32% by volume of propylene carbonate, 24% by volume of dimethyl carbonate, 8% by volume of methyl cyclohexyl carbonate and 3% by volume of methyl trifluoroethyl carbonate, the solute comprises lithium tetrafluoroborate and lithium hexafluorophosphate in a mass ratio of 1.2:2.7, and the additive comprises 4,5-dimethyl-1,3-dioxole-2-one and 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole in a volume ratio of 0.8:1.7.

[0025] Example 5

[0026] A low-temperature electrolyte for a lithium-ion battery comprises a solvent, a solute, an additive and a film-forming additive in a mass ratio of 97:20:2.3:9, wherein the solvent comprises 18% by volume of ethylene carbonate, 15% by volume of ethyl methyl carbonate, 32% by volume of propylene carbonate, 24% by volume of dimethyl carbonate, 8% by volume of methyl cyclohexyl carbonate and 3% by volume of methyl trifluoroethyl carbonate, the solute comprises lithium tetrafluoroborate and lithium hexafluorophosphate in a mass ratio of 0.9:2.1, the additive comprises 4,5-dimethyl-1,3-dioxol-2-one and 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester in a volume ratio of 1.2:2.3, and the film-forming additive is a mixed solution of fluoroethylene carbonate and monolayer graphene in a mass ratio of 80:1.3.

[0027] Comparative Example 1

[0028] The difference from Example 3 is that the additive does not contain 4,5-dimethyl-1,3-dioxol-2-one.

[0029] Comparative Example 2

[0030] The difference from Example 3 is that the additive does not contain 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester.

[0031] Comparative Example 3

[0032] The difference from Example 3 is that the solvent does not contain methyl cyclohexyl carbonate.

[0033] Comparative Example 4

[0034] The difference from Example 3 is that the solvent does not contain methyl trifluoroethyl carbonate.

[0035] Comparative Example 5

[0036] The difference from Example 3 is that the solvent does not contain methyl trifluoroethyl carbonate and methyl cyclohexyl carbonate, no additives are added, and the solute is lithium hexafluorophosphate.

[0037] The electrolytes prepared in Examples 1-5 and Comparative Examples 1-5 were added to a 200Ah plastic-shell lithium-ion battery, and the capacity retention rates were tested respectively. The results are shown in the following table:

[0038] -20℃, capacity retention after 24h storage (%) -20℃ cycle 500 times capacity retention rate (%) Example 1 92.6 85.6 Example 2 92.1 84.7 Example 3 92.3 86.8 Example 4 92.5 85.1 Example 5 93.6 87.2 Comparative Example 1 72.3 53.2 Comparative Example 2 79.8 70.3 Comparative Example 3 82.6 73.8 Comparative Example 4 81.3 72.3 Comparative Example 5 71.2 48.7

[0039] The above data illustrate that the low-temperature performance of the electrolyte prepared by the present invention is improved, especially after adding a film-forming additive to the electrolyte, the capacity retention rate after 500 cycles at -20°C is as high as 87.2%, and the low-temperature performance of the lithium-ion battery is significantly improved.

[0040] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-temperature electrolyte for lithium-ion batteries, comprising a solvent, a solute and an additive, characterized in that: The mass ratio of the solvent, the solute and the additive is 90-100:17-28:1.7-2.3, the solvent comprises the following volume percentages of ethylene carbonate 18%, ethyl methyl carbonate 15%, propylene carbonate 32%, dimethyl carbonate 24%, methyl cyclohexyl carbonate 8% and methyl trifluoroethyl carbonate 3%, and the solute is lithium tetrafluoroborate and lithium hexafluorophosphate; The additive is composed of 4,5-dimethyl-1,3-dioxol-2-one and 2-fluoro-4-methyl-5-(methoxycarbonyl)phenylboronic acid pinacol ester in a volume ratio of 1.2:2.3; Or, the additive is composed of 4,5-dimethyl-1,3-dioxole-2-one and 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole in a volume ratio of 0.8:1.7; The mass ratio of lithium tetrafluoroborate to lithium hexafluorophosphate is 0.6-1.2:2.1-2.7; It also includes a film-forming additive, wherein the volume ratio of the film-forming additive to the solvent is 7-12:90-100; The film-forming additive is a mixed solution of fluoroethylene carbonate and single-layer graphene in a mass ratio of 80:1.3.