Lithium ion battery electrolyte and preparation method and application thereof

Abstract

The invention provides a lithium ion battery electrolyte and a preparation method and application thereof, the lithium ion battery electrolyte comprises a lithium salt, an organic solvent, a fluorinated diluent and an additive, and the addition amount of the additive is 1-5 wt% of the lithium ion battery electrolyte; the volume ratio of the organic solvent to the fluorinated diluent is (8-9): (1-2); and the concentration of the lithium salt in the electrolyte of the lithium ion battery is 0.5 mol / L to 1.5 mol / L. According to the invention, the fluorinated diluent is added into the electrolyte, and the fluorinated diluent is a high-flash-point, flame-retardant and even flame-retardant solvent, so that the electrolyte is fundamentally endowed with excellent safety, the thermal runaway risk of the battery is greatly reduced, and the core potential safety hazard that the electrolyte is flammable and combustible is solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium-ion battery electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in electric vehicles and other fields. However, the driving range of electric vehicles is currently generally short, requiring users to charge very frequently. Furthermore, charging an electric vehicle takes longer than refueling a gasoline car, leading to low consumer acceptance. Therefore, the charging time is crucial to the user experience.

[0003] However, when lithium-ion batteries are charged at high rates, ohmic polarization and concentration polarization occur. Increased battery polarization leads to lithium plating, capacity reduction, excessive heat generation, and other harmful effects, thus impacting battery charging time and safety. The electrolyte, as a crucial component throughout the entire battery, significantly affects battery performance. Traditional electrolyte systems primarily consist of lithium hexafluorophosphate (LiPF6) dissolved in a carbonate-based mixed solvent. This electrolyte cannot support fast charging without compromising performance and lifespan; its kinetic performance is insufficient, and fast charging exacerbates a series of side reactions in the electrolyte solvent and structural degradation of the lithium layered transition metal oxide cathode material.

[0004] Traditional strategies for improving the fast-charging performance of electrolytes mainly include introducing low-viscosity co-solvents or designing locally high-concentration electrolytes. Introducing low-viscosity co-solvents (such as carboxylic esters and nitriles) into the electrolyte can rapidly improve fast-charging performance by improving ionic conductivity, but this method usually cannot form a stable SEI film on the graphite surface and has the risk of co-intercalation, making it difficult to put into practical use (Nature 627(8002) (2024) 101-107, Advanced Materials 37(19) (2025)). Locally high-concentration electrolytes, through ultra-high salt concentration combined with inert diluents, can construct dense inorganic-rich SEIs to improve fast-charging stability, but they face problems such as high cost, insufficient safety, and poor electrode wettability (Advanced Energy Materials 13(35) (2023)). Summary of the Invention

[0005] The technical problem to be solved by this invention is how to improve the fast charging performance and safety of lithium-ion battery electrolyte.

[0006] The present invention solves the above-mentioned technical problems through the following technical means: The first aspect of the present invention provides a lithium-ion battery electrolyte, comprising a lithium salt, an organic solvent, a fluorinated diluent, and an additive, wherein the amount of the additive is 1 wt% to 5 wt% of the lithium-ion battery electrolyte; the volume ratio of the organic solvent to the fluorinated diluent is 8 to 9:1 to 2; and the concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5 mol / L to 1.5 mol / L.

[0007] Beneficial Effects: The fluorinated diluent added to the electrolyte in this invention is a high flash point, flame-retardant, or even fire-resistant solvent, fundamentally endowing the electrolyte with excellent safety, greatly reducing the risk of thermal runaway in the battery, and solving the core safety hazard of flammability and explosion of the electrolyte. The fluorinated diluent and organic solvent form a synergistic effect, weakening the binding strength between lithium ions and the solvent through weak coordination ability, promoting the formation of a weak solvation structure dominated by contact ion pair aggregates, which can significantly accelerate the desolvation kinetics of lithium ions. Excellent fast charging capability can be achieved without relying on high salt concentration or a large number of additives. At the same time, an ultra-thin (about 6 nm) and fluorine-rich solid electrolyte interface (SEI) is formed, improving the first-cycle efficiency and long-term cycle performance.

[0008] Preferably, the lithium salt is lithium bis(fluorosulfonyl)imide.

[0009] Preferably, the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate.

[0010] Preferably, the DN value of the fluorinated diluent is 5 kcal / mol to 8 kcal / mol.

[0011] Preferably, the diluent is one of 2-trifluoromethyl-3-methoxyperfluoropentane, fluorobenzene, or trifluorobenzene.

[0012] Preferably, the concentration of lithium salt in the electrolyte is 0.8 mol / L to 1.2 mol / L.

[0013] Preferably, the additives include one or more of vinylene carbonate, fluoroethylene carbonate, and lithium nitrate.

[0014] Preferably, the amount of additive added is 1 wt% to 5 wt% of the lithium-ion battery electrolyte.

[0015] The second aspect of the present invention provides a method for preparing the above-mentioned lithium-ion battery electrolyte, wherein a diluent, an additive and a lithium salt are added to an organic solvent and mixed under an inert atmosphere to obtain the lithium-ion battery electrolyte.

[0016] A third aspect of the present invention provides a lithium-ion battery comprising the above-described lithium-ion battery electrolyte, a positive electrode, a negative electrode, and a separator, which are assembled to form a lithium-ion battery.

[0017] Preferably, the positive electrode includes lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and LiCo. x Ni y Mn （1-x-y） O2 materials, LiCoxNiAl （1-x-y） One of the lithium-rich materials xLiMnO3(1-x)LiMO2, where x>0, y>0, x+y≤1; the negative electrode includes one of graphite materials, lithium titanate and alloy materials.

[0018] Beneficial effects: This invention uses lithium bis(fluorosulfonyl)imide instead of traditional lithium hexafluorophosphate, significantly improving the chemical and hydrolytic stability of the electrolyte. It is less prone to decomposition at high temperatures, making the charge-discharge process safer and more reliable. Combined with a fluorinated diluent and the resulting fluorine-rich SEI film, side reactions at high temperatures are suppressed, enabling the lithium-ion battery to exhibit good cycle stability over a wide temperature range (-20℃ to 50℃).

[0019] Fluorinated diluents have ultra-low viscosity, which effectively reduces the overall viscosity of the electrolyte system. While improving safety, they also ensure ionic conductivity at low temperatures and ion migration ability at high rates, solving the problem of balancing high safety and high power.

[0020] This invention optimizes the solvation structure and ion transport performance by adjusting the concentration of lithium salt and the ratio of organic solvent to fluorinated diluent. While ensuring a weak solvation environment to reduce the desolvation energy barrier, it maintains suitable ionic conductivity, effectively improving the cycle stability of the battery under high voltage, high rate and different temperatures, resulting in more balanced performance. Attached Figure Description

[0021] Figure 1 These are safety performance test diagrams of the lithium-ion battery electrolytes in Example 1 and Comparative Example 1 of the present invention. Figure 2 The first charge-discharge curves of the lithium-ion batteries prepared in Example 1 and Comparative Example 1 of this invention at a rate of 0.1C are shown. Figure 3 The diagram shows the cycle capacity of lithium-ion batteries prepared in Example 1 and Comparative Example 1 of this invention at a 4C rate in the voltage range of 2.8-4.3V. Figure 4 This is a comparison chart of the rate performance of lithium-ion batteries prepared in Example 1 and Comparative Example 1 of the present invention in the voltage range of 2.8-4.3V. Figure 5 This is a comparison chart of the rate performance of lithium-ion batteries prepared in Example 1 and Comparative Example 1 of the present invention in the voltage range of 2.8-4.5V. Figure 6The diagram shows the cycle capacity of lithium-ion batteries prepared in Example 1 and Comparative Example 1 of this invention at a 4C rate in the voltage range of 2.8-4.5V. Figure 7 The diagram shows the cycle capacity of the lithium-ion battery obtained in Example 1 of this invention at a rate of 0.1C in a low-temperature environment of -20℃. Figure 8 The following are the cycle capacity diagrams of the soft-pack lithium-ion batteries prepared in Example 1 and Comparative Example 1 of the present invention at a 1C rate; Figure 9 The diagram shows the cycle capacity of the lithium-ion batteries obtained in Example 2 and Comparative Example 1 of this invention at a 1C rate. Detailed Implementation

[0022] 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.

[0023] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0024] 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.

[0025] The DN values ​​of the fluorinated diluents used in the examples and comparative examples are shown in the table below:

[0026] Example 1 This embodiment provides a lithium-ion electrolyte, its preparation method, and its application, as detailed below: 1. Preparation of lithium-ion electrolyte In a glove box filled with argon gas, the water content and oxygen content are less than 0.1 ppm.

[0027] Ethylene carbonate, 2-trifluoromethyl-3-methoxyperfluoropentane, and diethyl carbonate were mixed in a volume ratio of 1:1:8. Fluorinated ethylene carbonate and lithium difluorosulfonyl imide were then added to the mixture, such that the amount of fluoroethylene carbonate added was 5 wt% of the lithium-ion battery electrolyte, and the concentration of lithium difluorosulfonyl imide in the electrolyte was 1 mol / L, thus obtaining the lithium-ion electrolyte.

[0028] 2. Application of lithium-ion battery electrolytes The negative electrode is graphite material, and the positive electrode is LiCo. 0.1 Ni 0.8 Mn 0.1 The battery uses O2 material, a multilayer polyolefin separator, and the lithium-ion battery electrolyte of this embodiment, and is then assembled into a coin cell lithium-ion battery. The assembly method uses existing technology.

[0029] Preparation of positive and negative electrodes: First, graphite, conductive agent, and binder are mixed evenly at a mass ratio of 8:1:1 and coated onto copper foil. Then, the mixture is dried and cut to obtain graphite material, which serves as the negative electrode. This graphite material is weighed and stored in an argon-filled glove box for later use. The preparation of the positive electrode is roughly the same as the negative electrode. LiCo... 0.1 Ni 0.8 Mn 0.1 O2, conductive agent, and binder are mixed evenly at a mass ratio of 8:1:1 and coated onto aluminum foil. Then, the electrode is dried and cut to obtain LiCo. 0.1 Ni 0.8 Mn 0.1 O2 material, the LiCo 0.1 Ni 0.8 Mn 0.1 The O2 material was used as the positive electrode, weighed, and stored in a glove box filled with argon gas for later use.

[0030] Example 2 This embodiment provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this embodiment and Example 1 is that 2-trifluoromethyl-3-methoxyperfluoropentane and diethyl carbonate are mixed at a volume ratio of 2:8, while all other aspects are the same as in Example 1.

[0031] Example 3 This embodiment provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this embodiment and Example 1 is that ethylene carbonate, fluorobenzene, and diethyl carbonate are mixed in a volume ratio of 1:1:8, while all other aspects are the same as in Example 1.

[0032] Example 4 This embodiment provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this embodiment and Example 1 is that ethylene carbonate, trifluorobenzene, and diethyl carbonate are mixed in a volume ratio of 1:1:8, while all other aspects are the same as in Example 1.

[0033] Comparative Example 1 This comparative example provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this comparative example and Example 1 is that ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 2:8, while all other aspects are the same as in Example 1.

[0034] Comparative Example 2 This comparative example provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this example and Example 1 is that ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1:9, while all other aspects are the same as in Example 1.

[0035] Comparative Example 3 This comparative example provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this comparative example and Example 1 is that fluoroethylene carbonate and lithium bis(fluorosulfonyl)imide are added to diethyl carbonate, such that the amount of fluoroethylene carbonate added is 5 wt% of the lithium-ion battery electrolyte, and the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 1 mol / L, thus obtaining the lithium-ion electrolyte. All other aspects are the same as in Example 1.

[0036] Comparative Example 4 This comparative example provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this comparative example and Example 1 is that ethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and diethyl carbonate are mixed in a volume ratio of 1:1:8. All other aspects are the same as in Example 1.

[0037] Comparative Example 5 This comparative example provides a lithium-ion electrolyte, its preparation method, and its application. The difference between this comparative example and Example 1 is that ethylene carbonate, bis(2,2,2-trifluoroethyl) ether, and diethyl carbonate are mixed in a volume ratio of 1:1:8, while all other aspects are the same as in Example 1.

[0038] Experimental Example The lithium-ion battery electrolytes of Example 1 and Comparative Example 1 were subjected to safety performance tests. The specific steps are as follows: 1 mL of lithium-ion battery electrolyte was taken out and placed in an aluminum-shell container. The lithium-ion battery electrolyte was ignited with an igniter for 3 seconds each time. Then the ignition source was removed and the combustion of the lithium-ion battery electrolyte was observed.

[0039] like Figure 1 As shown, the lithium-ion battery electrolyte in Comparative Example 1 burned rapidly and violently until it was completely burned out; the lithium-ion battery electrolyte in Example 1 only showed a brief flame, which immediately self-extinguished after the ignition source was removed, demonstrating excellent flame-retardant properties. This fully demonstrates the inherent safety improvement brought about by the fluorinated diluent. The safety performance test results of the lithium-ion battery electrolytes in Examples 2-4 were the same as those in Example 1.

[0040] Lithium-ion battery performance testing: Before testing, the coin lithium-ion batteries assembled in Example 1 and Comparative Example 1 were left to rest for 7 hours. Then, the coin lithium-ion batteries assembled in Example 1 and Comparative Example 1 were subjected to constant current charge and discharge tests on the Xinwei Battery testing equipment.

[0041] like Figure 2As shown, the charge-discharge curves at 0.1C and cutoff voltages from 2.8V to 4.3V demonstrate that the lithium-ion battery electrolyte of Example 1 is compatible with ternary cathodes, illustrating the feasibility of assembling ternary lithium-ion batteries using the lithium-ion battery electrolyte of Example 1. It can be seen that the initial coulombic efficiency of the lithium-ion battery electrolyte prepared in Example 1 is basically the same as that of the lithium-ion battery prepared in Comparative Example 1.

[0042] like Figure 3 As shown, cycle performance tests were conducted at a cutoff voltage of 2.8V to 4.3V and a charging current density of 4C. The lithium-ion battery electrolyte of Example 1 showed better cycle stability and higher capacity than that of Comparative Example 1.

[0043] like Figure 4 As shown, rate performance tests were conducted at different current densities with a cutoff voltage of 2.8V-4.3V. When the current density was increased from 0.1C to 5C, the capacity retention rate of the lithium-ion battery electrolyte in Example 1 was 67%, while the capacity retention rate of Comparative Example 1 was only 21%.

[0044] like Figure 5 As shown, rate performance tests were conducted at different current densities within a cutoff voltage range of 2.8V-4.5V. When the current density increased from 0.1C to 5C, the capacity retention rate of the lithium-ion battery electrolyte in Example 1 was 52%, while that of Comparative Example 1 was only 8%. The significant decrease in battery capacity retention under the same conditions indicates that selecting a fluorinated diluent is more beneficial for improving the fast-charging performance of the lithium-ion battery electrolyte.

[0045] like Figure 6 As shown, cycle performance tests were conducted at a cutoff voltage of 2.8V to 4.5V and a charging current density of 4C. After 500 cycles at a charging rate of 4C, Example 1 achieved a capacity retention rate of 80%, while Comparative Example 1 showed rapid capacity decay during the first 50 cycles.

[0046] like Figure 7 As shown, the low-temperature performance of the lithium-ion battery of Example 1 was tested. At -20°C and 0.1C rate, the lithium-ion battery of Example 1 achieved stable cycling of more than 100 cycles with an average coulombic efficiency of 99%.

[0047] like Figure 8 As shown, at the positive electrode LiCo 0.1 Ni 0.8 Mn 0.1In a 1Ah soft-pack lithium-ion battery assembled with O2 material, negative electrode graphite material, lithium-ion battery electrolyte of Example 1, and separator, the lithium-ion battery electrolyte of Example 1 exhibits superior capacity retention and cycle stability at 1C rate, far exceeding that of Comparative Example 1, further highlighting the feasibility of the lithium-ion battery electrolyte of Example 1.

[0048] like Figure 9 As shown, cycle performance tests were conducted at a cutoff voltage of 2.8V to 4.5V and a charging current density of 1C. The lithium-ion battery electrolyte of Example 2 showed relatively stable cycling at a charging rate of 1C, while the capacity of Comparative Example 1 rapidly decreased. The lithium-ion batteries of Examples 3-4 exhibited similar performance to those of Example 2.

[0049] Test Example 1 The ionic conductivity of the lithium-ion battery electrolytes of 4 and Comparative Examples 1-4 is shown in Table 1.

[0050] Table 1 shows the ionic conductivity of different embodiments and comparative examples at different temperatures.

[0051] As shown in Table 1, the lithium-ion battery electrolytes in the embodiments can all be used as fast-charging electrolytes for lithium-ion batteries. When assembled into graphite and nickel-cobalt-manganese ternary lithium-ion batteries, they have good rate performance and can be applied to ternary higher voltage systems with high capacity retention.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, It includes lithium salt, organic solvent, fluorinated diluent and additives. The amount of additive added is 1wt% to 5wt% of the lithium-ion battery electrolyte; the volume ratio of organic solvent to fluorinated diluent is 8 to 9: 1 to 2; the concentration of lithium salt in the lithium-ion battery electrolyte is 0.5 mol / L to 1.5 mol / L.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is lithium bis(fluorosulfonyl)imide.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, Organic solvents include at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The DN value of fluorinated diluents is 5 kcal / mol to 8 kcal / mol.

5. The lithium-ion battery electrolyte according to claim 4, characterized in that, The fluorinated diluent is one of 2-trifluoromethyl-3-methoxyperfluoropentane, fluorobenzene, or trifluorobenzene.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The concentration of lithium salt in lithium-ion battery electrolyte is 0.8 mol / L to 1.2 mol / L.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additives include one or more of vinylene carbonate, fluoroethylene carbonate, and lithium nitrate.

8. The method for preparing the lithium-ion battery electrolyte according to any one of claims 1-7, characterized in that, Under an inert atmosphere, diluents, additives, and lithium salts are added to an organic solvent and mixed to obtain a lithium-ion battery electrolyte.

9. A lithium-ion battery, characterized in that, A lithium-ion battery is assembled from the lithium-ion battery electrolyte, positive electrode, negative electrode, and separator as described in any one of claims 1-7.

10. The lithium-ion battery according to claim 9, characterized in that, The cathode materials include lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and LiCo. x Ni y Mn （1-x-y） O2 materials, LiCoxNiAl （1-x-y） One of the lithium-rich materials xLiMnO3(1-x)LiMO2, where x>0, y>0, x+y≤1; the negative electrode includes one of graphite materials, lithium titanate and alloy materials.

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