High-power long-cycle lithium ion battery electrolyte as well as preparation method and application thereof

Abstract

The invention provides a high-power long-cycle lithium ion battery electrolyte as well as a preparation method and application thereof, and belongs to the technical field of liquid lithium ion batteries, and raw materials comprise electrolyte salt, a non-aqueous organic solvent and an additive. Wherein the mass ratio of methyl ethyl carbonate to dimethyl carbonate to ethylene carbonate in the non-aqueous organic solvent is (24-27): (29-31): (23-26); the electrolyte salt is lithium hexafluorophosphate; the additive is vinyl linate, ethylidene sulfate and lithium bis (fluorosulfonyl) imide in a mass ratio of (0.7-2): (0.7-2): (0.7-2). Compared with the prior art, the electrolyte of the long-cycle-life battery, which well supports high-power charging and discharging and allows low-temperature charging, is provided through component design, proportioning combination of the raw materials and a synergistic effect, and the lithium ion battery prepared by using the electrolyte has excellent power performance and low-temperature performance; and meanwhile, the cycle life can be greatly prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid lithium ion batteries, and particularly relates to a high-power long-cycle lithium ion battery electrolyte, a preparation method and application thereof. BACKGROUND

[0002] In order to reduce the dependence on oil and reduce CO2 emissions, the electric development direction of automobiles has been widely recognized in the world under the background of low-carbon transportation. This also leads to the rapid development of lithium ion batteries with high specific energy, no memory effect and other advantages. At the same time, with the gradual maturity of technology, consumers have higher and higher requirements for the performance of lithium ion batteries, such as fast charging, low temperature, long cycle life and the like; and the lithium ion battery electrolyte, as a bridge between the positive and negative electrodes, as a channel for carrying lithium ion transport, plays a crucial important role in performance.

[0003] Most of the lithium ion battery electrolytes on the market, whether for power or energy storage applications, cannot meet the characteristics of high power, long life and low temperature charging. With the gradual improvement of consumer performance requirements, it is difficult to meet the expected requirements.

[0004] A high-power and high-voltage-resistant lithium ion battery electrolyte and a preparation method thereof are disclosed in a patent with publication number CN111082142 A published on April 28, 2020. The disclosed electrolyte is composed of the following raw materials in mass percentage: 77%-84% of non-aqueous organic solvent, 14%-18% of lithium salt, and 2%-5% of film-forming functional additive; the non-aqueous organic solvent includes ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate; the lithium salt is lithium hexafluorophosphate; the molar concentration of the lithium hexafluorophosphate is 1.1-1.3M; and the film-forming functional additive includes vinylene carbonate and difluoroethylene carbonate. However, it is tested at 25℃ and cannot solve the problem of low temperature performance. SUMMARY

[0005] The purpose of the present application is to provide a high-power long-cycle lithium ion battery electrolyte and a preparation method thereof, which improves the performance of the electrolyte by designing the composition and amount of raw materials.

[0006] Another purpose of the present application is to provide an application of a high-power long-cycle lithium ion battery electrolyte, which is used in liquid lithium ion batteries. The lithium ion battery prepared using the above-mentioned electrolyte has excellent power performance and low temperature performance, and can greatly improve the cycle life.

[0007] The specific technical scheme of the present application is as follows:

[0008] A high-power long-cycle lithium ion battery electrolyte, the raw materials of which include electrolyte salt, non-aqueous organic solvent and additive.

[0009] The non-aqueous organic solvent is a mixed solvent of methyl ethyl carbonate, dimethyl carbonate and ethylene carbonate.

[0010] Preferably, the mass ratio of methyl ethyl carbonate, dimethyl carbonate and ethylene carbonate in the non-aqueous organic solvent is 24-27:29-31:23-26.

[0011] The electrolyte salt is lithium hexafluorophosphate.

[0012] The additive is a mixture of vinylene carbonate, ethylene sulfate and lithium bisfluorosulfonylimide.

[0013] Preferably, in the additive, the mass ratio of vinylene carbonate, ethylene sulfate and lithium bisfluorosulfonylimide is 0.7-2:0.7-2:0.7-2.

[0014] Preferably, the high-power long-cycle lithium ion battery electrolyte comprises the following raw materials in mass percentage:

[0015] The electrolyte salt is 14%-16%, the non-aqueous organic solvent is 76-84%, the additive is 2.1-6%, and the total of each raw material is 100%.

[0016] The application provides a preparation method of a high-power long-cycle lithium ion battery electrolyte, and specifically comprises the following steps: uniformly mixing formula amount of an electrolyte salt, a non-aqueous organic solvent and an additive, and obtaining the high-power long-cycle lithium ion battery electrolyte.

[0017] The application provides an application of the high-power long-cycle lithium ion battery electrolyte, which is used in a liquid lithium ion battery.

[0018] The prepared battery has a capacity retention rate of 68% or more under 5C charge-discharge cycles for 5000 cycles at 25 DEG C, and a capacity retention rate of 80% or more under 1C cycles for 1000 cycles at-10 DEG C.

[0019] The lithium salt component is single and commonly used, the negative effects caused by the composite lithium salt are avoided, and the cost is saved. For the problem factors of the single lithium salt, the additive is used to solve the problem, the addition amount is small and the effect is significant. The application improves the performance requirements of the lithium battery in different aspects through the synergistic effect of the composite additive. The effect is direct and the mechanism is clear. The application ensures the stability of the lithium ion battery system in a wide temperature window through the synergistic effect of the solvent component, and provides performance guarantees for high-power performance, low-temperature performance and long-cycle performance.

[0020] The application adopts lithium hexafluorophosphate with excellent comprehensive performance as the lithium salt. Since the anion PF6- The association ability of lithium hexafluorophosphate is relatively poor, resulting in high conductivity, making it suitable for high-power lithium-ion battery systems. Furthermore, lithium hexafluorophosphate exhibits strong electrochemical stability, with a stable cathode voltage of 5.1V, far exceeding the upper limit of 4.3V for lithium-ion batteries. It also does not corrode the current collector, making it suitable for long-cycle systems. However, lithium hexafluorophosphate is hygroscopic and unstable, easily decomposing in solution to produce trace amounts of lithium fluoride and phosphorus pentafluoride, and generating HF in the presence of water, which damages the dense solid electrolyte interphase (SEI) film on the negative electrode surface. These drawbacks can be mitigated by the following additive system.

[0021] This invention uses ethylene carbonate, which has high electrical conductivity, does not decompose on the surface of graphitized carbon materials, and has good film-forming properties, as the basic solvent component. It is combined with dimethyl carbonate solvent with low viscosity to improve the solubility of lithium hexafluorophosphate and the dielectric constant of the solution, thereby improving the power performance and low-temperature performance of the system. At the same time, it is combined with ethyl methyl carbonate, which has a wide temperature window, as a third solvent component to improve the operating temperature window of the electrolyte system, ensure the high and low temperature performance of the lithium-ion battery, and stabilize the performance of the lithium-ion battery system.

[0022] This invention uses vinylene carbonate and lithium bis(fluorosulfonyl)imide as a composite film-forming additive. Because lithium bis(fluorosulfonyl)imide contains fluorine atoms, the lithium fluoride content in the solid electrolyte interphase (SEI) film formed is significantly higher than that in an electrolyte system containing only vinylene carbonate. As lithium fluoride is an inorganic lithium salt, the fluorine atoms and lithium atoms are bonded by ionic bonds, resulting in high bond energy and good stability, which enhances the long cycle life of lithium-ion batteries. At the same time, it also greatly prevents the HF generated by the decomposition of lithium hexafluorophosphate due to trace moisture in the system from etching and dissolving the solid electrolyte interphase (SEI) film. In other words, it greatly reduces the side effects caused by the decomposition of lithium hexafluorophosphate in the system. At the same time, it is combined with a low film-forming impedance ethylene sulfate additive, which has low film-forming impedance on the graphite anode surface, ensuring the power performance and low-temperature performance of the lithium-ion battery.

[0023] Compared with existing technologies, this invention provides an electrolyte for batteries with long cycle life that can support high-power charging and discharging and allow low-temperature charging through component design, ratio combination of various raw materials and synergistic effect. Lithium-ion batteries prepared using this electrolyte have excellent power performance and low-temperature performance, while significantly improving cycle life. Attached Figure Description

[0024] Figure 1 The rate discharge curve (left) and the highest surface temperature of the 20C discharged battery (right) are shown for the battery prepared with the electrolyte of Example 1.

[0025] Figure 2These are performance test graphs of batteries prepared with electrolytes from Example 1 and Comparative Example 1 after 5000 cycles of 5C charge-discharge cycle.

[0026] Figure 3 Comparison of the low-temperature cycling performance of batteries prepared with electrolytes from Example 1 and Comparative Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0029] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0030] The manufacturing process of the liquid lithium-ion battery described in this invention is as follows: Positive electrode powder (lithium iron phosphate), binder PVDF, conductive agent acetylene black, and conductive agent carbon nanotubes are mixed in a mass ratio of 93:3:3:1. An organic solvent NMP (N-methylpyrrolidone) is added and the mixture is uniformly mixed to form a slurry with a solid content of 55%, at a concentration of 0.0240 g / cm³. 2 The coating density is uniformly coated on both sides of the aluminum foil. After baking to remove the organic solvent, it is rolled to a thickness of 125μm using a roller mill. Then, it is die-cut into positive electrode sheets of the required length and width using a die-cutting machine. The negative electrode powder (graphite), binder (styrene-butadiene rubber SBR), suspending agent (sodium carboxymethyl cellulose CMC), and conductive agent acetylene black are mixed in a mass ratio of 95:1.8:1.2:2. Water is added as a solvent, and the mixture is uniformly mixed to form a slurry with a solid content of 50%. The slurry is prepared at a density of 0.0130 g / cm³. 2 The coating density is uniformly coated on both sides of the negative electrode current collector copper foil. After baking to remove the solvent, it is rolled to a thickness of 90μm using a roller mill. Then, it is die-cut into negative electrode sheets of the required length and width using a die-cutting machine. The electrodes are then baked to remove moisture, stacked and assembled into a 9AH single cell, then injected with the electrolyte and sealed. Finally, the battery undergoes formation, capacity testing, and electrical performance testing.

[0031] Example 1

[0032] A high-power, long-cycle lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. Specifically, based on the total mass of the electrolyte salt, non-aqueous organic solvent, and additives as 100%, the electrolyte salt is lithium hexafluorophosphate at 15%, and the non-aqueous organic solvents are ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate at mass fractions of 26%, 31%, and 25%, respectively. The additives are ethylene carbonate, ethylene sulfate, and lithium difluorosulfonyl imide at mass fractions of 1%, 1%, and 1%, respectively.

[0033] A 9AH soft-pack battery cell was fabricated using the high-power, long-cycle lithium-ion battery electrolyte prepared in Example 1. The discharge capacity and temperature rise of this cell were tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, and 20C were 100.00%, 98.34%, 96.55%, and 96.12%, respectively. The rate discharge curves and temperature rises are shown below. Figure 1 As shown in the figure, the discharge plateau voltage does not differ significantly between different discharge rates, from 1C to 20C; the highest surface temperature of the battery at 20C discharge is 35.8℃; the rate cycle performance is shown below. Figure 2 It can achieve 5000 cycles at 5C charge / discharge with a capacity retention of 70.86%. Low-temperature cycling performance is shown below. Figure 3 It can achieve 1000 cycles at -10℃ and 1C with a capacity retention of 87.7%.

[0034] Example 2

[0035] A high-power, long-cycle lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. The specific electrolyte composition is as follows: Based on a total mass of 100% for the electrolyte salt, non-aqueous organic solvent, and additives, the electrolyte salt is lithium hexafluorophosphate at 16%; the non-aqueous organic solvents are ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate at mass fractions of 26%, 30%, and 25%, respectively; and the additives are ethylene carbonate, ethylene sulfate, and lithium difluorosulfonyl imide at mass fractions of 0.8%, 1.1%, and 1.1%, respectively.

[0036] A 9AH soft-pack battery cell was fabricated using the electrolyte from Example 2. The discharge capacity of the cell was tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, and 20C were 100.00%, 98.55%, 96.87%, and 95.53%, respectively. After 5000 charge-discharge cycles at 5C, the capacity retention rate was 70.2%. After 1000 cycles at 1C at -10°C, the capacity retention rate was 81.3%.

[0037] Example 3

[0038] A high-power, long-cycle lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. The specific electrolyte composition is as follows: Based on a total mass of 100% for the electrolyte salt, non-aqueous organic solvent, and additives, the electrolyte salt is lithium hexafluorophosphate at 14%; the non-aqueous organic solvents are ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate at mass fractions of 27%, 30.5%, and 26%, respectively; and the additives are ethylene carbonate, ethylene sulfate, and lithium difluorosulfonyl imide at mass fractions of 1%, 0.75%, and 0.75%, respectively.

[0039] A 9AH soft-pack battery cell was fabricated using the electrolyte from Example 3. The discharge capacity of the cell was tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, 11C, and 20C were 100.00%, 98.11%, 96.57%, and 95.13%, respectively. After 5000 charge-discharge cycles at 5C, the capacity retention rate was 68.2%. After 1000 cycles at 1C at -10°C, the capacity retention rate was 80.7%.

[0040] Comparative Example 1

[0041] A lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. The specific electrolyte composition is as follows: Based on the total mass of the electrolyte salt, non-aqueous organic solvent, and additives as 100%, the electrolyte salt is lithium hexafluorophosphate at 16%; the non-aqueous organic solvents are ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate at mass fractions of 25%, 30%, and 21.9%, respectively; and the additives are vinylene carbonate, ethylene sulfate, propylene carbonate, and fluoroethylene carbonate at mass fractions of 0.6%, 1%, 5%, and 0.5%, respectively.

[0042] A 9AH soft-pack battery cell was fabricated using the electrolyte prepared in Comparative Example 1. The discharge capacity of this cell was tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, and 20C were 100.00%, 95.03%, 92.37%, and 87.33%, respectively. After 946 charge-discharge cycles at 5C, the capacity retention rate was 69.74%. At -10℃, after 840 cycles at 1C, the capacity retention rate was 70.01%. (See [reference needed]). Figure 3 .

[0043] Comparative Example 2

[0044] A lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. The specific electrolyte composition is as follows: Based on the total mass of the electrolyte salt, non-aqueous solvent, and additives as 100%, the electrolyte salt is lithium hexafluorophosphate at 16%; the non-aqueous organic solvents are ethylene carbonate, diethyl carbonate, dimethyl carbonate, and propylene carbonate at mass fractions of 25%, 25%, 15%, and 15%, respectively; and the additives are ethylene carbonate, ethylene sulfate, and lithium difluorosulfonylimide at mass fractions of 1%, 1.5%, and 1.5%, respectively.

[0045] A 9AH soft-pack battery cell was fabricated using the electrolyte prepared in Comparative Example 2. The discharge capacity of the cell was tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, and 20C were 100.00%, 94.01%, 91.21%, and 83.27%, respectively. After 1000 cycles at 5C, the capacity retention rate was 71.33%. After 900 cycles at 1C at -10℃, the capacity retention rate was 71.52%.

[0046] Comparative Example 3

[0047] A lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. The specific electrolyte composition is as follows: Based on the total mass of the electrolyte salt, non-aqueous organic solvent, and additives being 100%, the electrolyte salt is lithium hexafluorophosphate at 16%; the non-aqueous organic solvents are ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate at mass fractions of 26%, 29%, and 25%, respectively; and the additives are ethylene carbonate, ethylene sulfate, and lithium difluorosulfonyl imide at mass fractions of 0.8%, 0.7%, and 2.5%, respectively.

[0048] A 9AH soft-pack battery cell was fabricated using the electrolyte prepared in Comparative Example 3. The discharge capacity of the cell was tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, and 20C were 100.00%, 96.52%, 90.37%, and 88.16%, respectively. After 1320 cycles at 5C, the capacity retention rate was 70.5%. At -10℃, after 790 cycles at 1C, the capacity retention rate was 69.78%.

[0049] Comparative Example 4

[0050] A lithium-ion battery electrolyte comprises an electrolyte salt, a non-aqueous organic solvent, and additives. The specific electrolyte composition is as follows: Based on the total mass of the electrolyte salt, non-aqueous organic solvent, and additives being 100%, the electrolyte salt consists of 8% lithium hexafluorophosphate and 8% lithium difluorosulfonyl imide; the non-aqueous organic solvents are 26% methyl ethyl carbonate, 30% dimethyl carbonate, and 25% ethylene carbonate by mass, respectively; and the additives are 0.8% ethylene carbonate, 1.1% ethylene sulfate, and 1.1% bisfluorosulfonyl imide by mass, respectively.

[0051] A 9AH soft-pack battery cell was fabricated using the electrolyte prepared in Comparative Example 4. The discharge capacity of the cell was tested at different rates (1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 20C). The discharge capacity retention rates at typical rates of 1C, 5C, 10C, and 20C were 100.00%, 97.10%, 92.66%, and 89.71%, respectively. After 1500 cycles at 5C, the capacity retention rate was 70.9%. After 1000 cycles at 1C at -10℃, the capacity retention rate was 69.98%.

[0052] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A high-power, long-cycle lithium-ion battery electrolyte, characterized in that, The electrolyte raw materials for the high-power, long-cycle lithium-ion battery include electrolyte salts, non-aqueous organic solvents, and additives. The non-aqueous organic solvent is a mixed solvent of ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate.

2. The high-power, long-cycle lithium-ion battery electrolyte according to claim 1, characterized in that, The mass ratio of ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate in the non-aqueous organic solvent is 24-27:29-31:23-26.

3. The high-power, long-cycle lithium-ion battery electrolyte according to claim 1, characterized in that, The electrolyte salt is lithium hexafluorophosphate.

4. The high-power, long-cycle lithium-ion battery electrolyte according to claim 1, characterized in that, The additive is a mixture of vinylene carbonate, ethylene sulfate, and lithium difluorosulfonylimide.

5. The high-power, long-cycle lithium-ion battery electrolyte according to claim 4, characterized in that, The mass ratio of vinylene carbonate, ethylene sulfate, and lithium bis(fluorosulfonyl)imide is 0.7-2:0.7-2:0.7-2.

6. The high-power, long-cycle lithium-ion battery electrolyte according to claim 1 or 2, characterized in that, The high-power, long-cycle lithium-ion battery electrolyte comprises the following raw materials by mass percentage: Electrolyte salt 14%-16%, non-aqueous organic solvent 76-84%, additives 2.1-6%, totaling 100%.

7. A method for preparing a high-power, long-cycle lithium-ion battery electrolyte according to any one of claims 1-6, characterized in that, The preparation method is as follows: mix the prescribed amounts of electrolyte salt, non-aqueous organic solvent and additives evenly to obtain the final product.

8. The application of the high-power, long-cycle lithium-ion battery electrolyte according to any one of claims 1-6, characterized in that, Used in liquid lithium-ion batteries.

9. The application according to claim 8, characterized in that, The liquid lithium-ion battery retains over 68% of its capacity after 5000 cycles at 25°C (5C charge-discharge); and over 80% of its capacity after 1000 cycles at -10°C (1C charge-discharge).

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