Lithium-ion battery electrolyte, preparation method and application

Abstract

This application discloses a lithium-ion battery electrolyte, its preparation method, and its application. The provided lithium-ion battery electrolyte comprises a lithium salt and an organic solvent; wherein the lithium salt comprises a combination of at least two selected from lithium hexafluorophosphate, lithium difluorobis(oxalato)phosphate, lithium difluorosulfonylimide, and lithium di(oxalato)borate; and the organic solvent comprises 30wt%-50wt% hydrofluoroether, 10wt%-30wt% acetate, and 20wt%-60wt% carbonate. The provided lithium-ion battery electrolyte maintains the integrity of the separator structure, enables lithium salt to fill pores, and reduces separator permeability, thereby controlling possible separator shrinkage during temperature changes at low or high temperatures; it also suppresses crosstalk between the positive and negative electrodes caused by gas penetration, enabling batteries prepared using the provided lithium-ion battery electrolyte to exhibit good cycle performance and rate performance at low temperatures, and high safety at high temperatures.

Description

Technical Field

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

[0002] Lithium-ion batteries, as electrochemical energy storage devices, are widely used in new energy vehicles, portable electronic devices, and energy storage systems. However, their performance is significantly affected by ambient temperature, especially under extreme temperature conditions, where they suffer from the following drawbacks: at low temperatures, lithium plating on the lithium anode and damage to the graphite structure are easily triggered; at high temperatures, lithium salts cannot be effectively retained, and there is a risk of battery thermal runaway.

[0003] Traditional electrolytes cannot simultaneously address both low-temperature cycling performance and high-temperature safety issues. Therefore, there is an urgent need to develop an electrolyte that can operate stably over a wide temperature range, maintaining excellent cycling performance at low temperatures while effectively suppressing the risk of thermal runaway at high temperatures. Summary of the Invention

[0004] Therefore, it is necessary to provide a lithium-ion battery electrolyte, its preparation method, and its application that can combine the cycling performance at low temperatures with the safety at high temperatures.

[0005] In some embodiments, a lithium-ion battery electrolyte is provided, comprising a lithium salt and an organic solvent;

[0006] The lithium salt comprises a combination of at least two of lithium hexafluorophosphate, lithium difluorobis(oxalato) phosphate, lithium difluorosulfonylimide, and lithium di(oxalato) borate.

[0007] The organic solvents include 30wt%-50wt% hydrofluoroether, 10wt%-30wt% acetate and 20wt%-60wt% carbonate.

[0008] In some embodiments, the lithium salt comprises at least a first lithium salt and a second lithium salt, wherein the first lithium salt comprises lithium bis(fluorosulfonyl)imide and the second lithium salt comprises at least one of lithium difluorobis(oxalato)phosphate and lithium di(oxalato)borate.

[0009] Optionally, the molar ratio of the first lithium salt to the second lithium salt is 1:(0.2-0.5).

[0010] In some embodiments, the concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5 mol / L to 1.5 mol / L.

[0011] In some embodiments, the organic solvent comprises 30wt%-40wt% hydrofluoroether, 20wt%-30wt% acetate, and 30wt%-50wt% carbonate.

[0012] In some embodiments, the lithium-ion battery electrolyte satisfies one or more of the following conditions:

[0013] (1) The hydrofluoroether comprises at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1,1,2,2-tetrafluoroethyl ether;

[0014] (2) The acetate ester includes at least one of ethyl acetate, methyl formate, ethyl formate and methyl acetate;

[0015] (3) The carbonate includes at least one of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate.

[0016] In some embodiments, the lithium-ion battery electrolyte satisfies one or more of the following conditions:

[0017] (1) The hydrofluoroether comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0018] (2) The acetate includes ethyl acetate;

[0019] (3) The carbonate includes at least one of methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate.

[0020] In some embodiments, the lithium-ion battery electrolyte includes a lithium salt and an organic solvent;

[0021] The lithium salt comprises lithium bis(fluorosulfonyl)imide and lithium difluorobis(oxalato)phosphate in a molar ratio of 1:(0.2-0.5), and the concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L-1.2 mol / L.

[0022] The organic solvents include 30wt%-50wt% 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 10wt%-30wt% ethyl acetate, and 20wt%-60wt% carbonate.

[0023] In some embodiments, a method for preparing a lithium-ion battery electrolyte is provided, comprising the following steps: dissolving a lithium salt in an organic solvent to obtain the lithium-ion battery electrolyte;

[0024] The lithium salt comprises a combination of at least two of lithium hexafluorophosphate, lithium difluorobis(oxalato) phosphate, lithium difluorosulfonylimide, and lithium di(oxalato) borate.

[0025] The organic solvents include 30wt%-50wt% hydrofluoroether, 10wt%-30wt% acetate and 20wt%-60wt% carbonate.

[0026] In some embodiments, the lithium-ion battery electrolyte described herein or the lithium-ion battery electrolyte prepared by the aforementioned preparation method is provided for use in the preparation of lithium-ion batteries.

[0027] In some embodiments, a lithium-ion battery is provided, including a positive electrode, a negative electrode, and the lithium-ion battery electrolyte or the lithium-ion battery electrolyte prepared by the preparation method.

[0028] The aforementioned lithium-ion battery electrolyte can maintain the integrity of the separator structure, enable lithium salt to fill the pores, and reduce the gas permeability of the separator, thereby controlling the possible shrinkage of the separator during temperature changes under low or high temperature conditions; it also suppresses the crosstalk problem caused by gas penetration between the positive and negative electrodes, and enables the battery prepared using the provided lithium-ion battery electrolyte to have good cycle performance and rate performance under low temperature conditions, as well as high safety under high temperature conditions. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments and examples of this application, and to more completely understand this application and its beneficial effects, the accompanying drawings used in the description of the embodiments or examples will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0030] Figure 1 Cycle performance graphs of batteries prepared with the lithium-ion battery electrolytes in Example 1 and Comparative Example 1;

[0031] Figure 2 The rate performance diagrams are for the batteries prepared with the lithium-ion battery electrolytes in Example 1 and Comparative Example 1.

[0032] Figure 3 Transmission electron microscopy (TEM) images of the graphite morphology of the negative electrode of the battery prepared with the lithium-ion battery electrolyte in Example 1 and Comparative Example 1, wherein (a) is a TEM image of the graphite morphology of the negative electrode of the battery prepared with the lithium-ion battery electrolyte in Comparative Example 1, and (b) is a TEM image of the graphite morphology of the negative electrode of the battery prepared with the lithium-ion battery electrolyte in Example 1.

[0033] Figure 4 The images show scanning electron microscope (SEM) images of the separator morphology of the batteries prepared with the lithium-ion battery electrolyte in Example 1 and Comparative Example 1 at high temperature. (a) is a SEM image of the separator morphology of the battery prepared with the electrolyte in Comparative Example 1 at high temperature. It can be seen from the image that the separator shrinks and closes the pores. (b) is a SEM image of the separator morphology of the battery prepared with the electrolyte in Example 1 at high temperature.

[0034] Figure 5 The thermal test temperature diagram shows the batteries prepared with the lithium-ion battery electrolyte in Example 1 and Comparative Example 1. Detailed Implementation

[0035] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0036] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0039] The terms "and / or," "or / and," and "and / or" as used in this application encompass any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR." For example, "A and / or B" includes three parallel solutions: A, B, and "a combination of A and B."

[0040] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0041] The terms “combinations thereof,” “any combination thereof,” and “any combination thereof” as used in this application include all suitable combinations of any two or more of the listed items.

[0042] In this application, the term "suitable" as used in "suitable combination", "suitable method", "any suitable method", etc., refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0043] In this application, terms such as "preferred," "better," "more suitable," and "ideal" are merely used to describe implementation methods or embodiments that achieve better results, and should be understood not to limit the scope of protection of this application.

[0044] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0045] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0046] In this invention, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0047] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0048] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0049] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0050] In this application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass-volume percentage.

[0051] In this application, "room temperature" generally refers to 5℃~30℃, and more preferably 25±5℃.

[0052] Traditional lithium-ion battery electrolytes suffer from reduced fluidity, hindered ion transport, and poor interface stability at low temperatures, which can easily lead to lithium plating on the lithium anode and damage to the graphite structure. At high temperatures, the electrolyte is prone to decomposition or volatilization, and the separator shrinks due to heat, resulting in the inability to effectively retain lithium salts. This may also cause gas crosstalk and exacerbate the risk of battery thermal runaway.

[0053] In some embodiments, a lithium-ion battery electrolyte is provided, comprising a lithium salt and an organic solvent;

[0054] The lithium salts include combinations of at least two of lithium hexafluorophosphate, lithium difluorobis(oxalato) phosphate, lithium difluorosulfonylimide, and lithium di(oxalato) borate.

[0055] The organic solvents include 30wt%-50wt% hydrofluoroethers, 10wt%-30wt% acetates and 20wt%-60wt% carbonates.

[0056] In a non-limiting sense, hydrofluoroethers are used to enhance the interfacial bonding between the electrolyte and the polyethylene membrane, thereby improving high-temperature safety and low-temperature fluidity.

[0057] In addition, acetates are used to improve low-temperature electrical conductivity and low-temperature fluidity.

[0058] In a non-limiting sense, carbonates are used to improve electrical conductivity at low temperatures.

[0059] Lithium salts are used to improve low-temperature conductivity and provide high-temperature gas barrier properties.

[0060] The provided lithium-ion battery electrolyte, while ensuring low-temperature cycling performance, achieves a transition from liquid to solid thermal response by regulating the interfacial bonding force between the electrolyte and the separator, thereby suppressing battery thermal runaway under high-temperature conditions.

[0061] The provided lithium-ion battery electrolyte, through its composition design, significantly enhances the interfacial bonding between the electrolyte and the separator, exceeding the surface tension of the electrolyte itself. This characteristic ensures that after solvent evaporation, the lithium salt remains within the pores of the separator, thereby controlling potential membrane shrinkage during temperature changes (low or high temperatures) and suppressing crosstalk between the positive and negative electrodes caused by gas penetration.

[0062] The provided lithium-ion battery electrolyte not only improves ion transport and cycle stability at low temperatures but also significantly reduces the risk of thermal runaway at high temperatures, allowing the fabricated pouch battery to withstand temperatures exceeding 200°C. By enhancing the interfacial bonding between the electrolyte and the separator, lithium salts are prevented from volatilizing or migrating due to high temperatures, effectively mitigating safety hazards caused by separator shrinkage and gas crosstalk at high temperatures.

[0063] In some embodiments, the lithium salt includes at least a first lithium salt and a second lithium salt, wherein the first lithium salt includes lithium bis(fluorosulfonyl)imide and the second lithium salt includes at least one of lithium difluorobis(oxalato)phosphate and lithium di(oxalato)borate.

[0064] In some embodiments, the molar ratio of the first lithium salt to the second lithium salt is 1:(0.2-0.5), for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, or a range selected from any two of the aforementioned ratios.

[0065] In some embodiments, the concentration of lithium salt in the lithium-ion battery electrolyte is 0.5 mol / L to 1.5 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, or a range selected from any two of the aforementioned values.

[0066] In some embodiments, the organic solvent includes 30wt%-40wt% hydrofluoroether, 20wt%-30wt% acetate, and 30wt%-50wt% carbonate.

[0067] In some embodiments, the hydrofluoroether in the lithium-ion battery electrolyte includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1,1,2,2-tetrafluoroethyl ethyl ether, and may also include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0068] In some embodiments, the acetate ester in the lithium-ion battery electrolyte includes at least one of ethyl acetate, methyl formate, ethyl formate, and methyl acetate, and the acetate ester may also include ethyl acetate.

[0069] In some embodiments, the carbonate in the lithium-ion battery electrolyte includes at least one of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate. The carbonate may also include at least one of methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0070] In some embodiments, the lithium-ion battery electrolyte includes a lithium salt and an organic solvent;

[0071] The lithium salts include lithium bis(fluorosulfonyl)imide and lithium difluorobis(oxalato)phosphate in a molar ratio of 1:(0.2-0.5), and the concentration of the lithium salts in the lithium-ion battery electrolyte is 1 mol / L-1.2 mol / L.

[0072] The organic solvents include 30wt%-50wt% 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 10wt%-30wt% ethyl acetate, and 20wt%-60wt% carbonates.

[0073] In some embodiments, a method for preparing a lithium-ion battery electrolyte is provided, comprising the following steps: dissolving a lithium salt in an organic solvent to obtain a lithium-ion battery electrolyte;

[0074] The lithium salts include combinations of at least two of lithium hexafluorophosphate, lithium difluorobis(oxalato) phosphate, lithium difluorosulfonylimide, and lithium di(oxalato) borate.

[0075] The organic solvents include 30wt%-50wt% hydrofluoroethers, 10wt%-30wt% acetates and 20wt%-60wt% carbonates.

[0076] In some embodiments, the application of a lithium-ion battery electrolyte or a lithium-ion battery electrolyte prepared by a preparation method in the preparation of lithium-ion batteries is provided.

[0077] In some embodiments, a lithium-ion battery is provided, including a positive electrode, a negative electrode, and a lithium-ion battery electrolyte or a lithium-ion battery electrolyte prepared by the aforementioned preparation method.

[0078] In some embodiments, an electric vehicle and / or energy storage system is provided, which includes the aforementioned lithium-ion battery.

[0079] The provided lithium-ion battery electrolyte is suitable for high-energy-density lithium-ion batteries, especially in electric vehicles, energy storage systems, and other scenarios requiring high safety and long cycle life.

[0080] The following detailed description is provided in conjunction with specific embodiments and comparative examples. Unless otherwise specified, all raw materials and instruments used in the following specific embodiments are commercially available.

[0081] I. Preparation of Lithium-ion Battery Electrolyte

[0082] Examples 1-5 and Comparative Examples 1-5

[0083] The formulations of the lithium-ion battery electrolytes in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1.

[0084] Table 1

[0085]

[0086] In Table 1, LiPF6 is lithium hexafluorophosphate, LiDFOB is lithium difluorobis(oxalato)phosphate, LiFSI is lithium difluorosulfonylimide, LiBOB is lithium di(oxalato)borate, and TTE is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0087] The preparation method of lithium-ion battery electrolyte is as follows: lithium salt is dissolved in an organic solvent to obtain lithium-ion battery electrolyte.

[0088] II. Electrochemical Performance Testing

[0089] (1) Battery fabrication:

[0090] The QH02-Ni90 / SiC-15 battery cell purchased from Dongguan Kelude New Energy Technology Co., Ltd. was used to inject the lithium-ion battery electrolytes of Examples 1-5 and Comparative Examples 1-5 into a dry room with a dew point of -40°C. After standing for 2 days, the battery was formed with a formation current of 0.1A to obtain a test soft-pack battery.

[0091] (2) Cycle performance and rate performance testing of batteries under low temperature conditions

[0092] The batteries prepared with the lithium-ion battery electrolytes in Example 1 and Comparative Example 1 were tested using a Neware BTS4000 instrument as follows. The prepared batteries were cycled at -20°C and a current of 0.2A, and the charging capacity was recorded. Then, an initial discharge was performed at 0.2A, and the discharge capacity was recorded. The discharge capacity of the batteries after multiple cycles was recorded, and the capacity retention rate at different cycle numbers, i.e., battery durability, was calculated. The battery discharge capacity at -20°C and at 0.3A, 1A, 2A, and 3A was recorded, and the capacity retention rate at different rates, i.e., rate performance, was calculated. The results are as follows: Figure 1 , Figure 2 As shown in Table 2. Figure 1 and Figure 2 In this context, TTE represents Example 1, and BASE represents Comparative Example 1. Figure 1 The cycling performance results are for the batteries prepared with the lithium-ion battery electrolytes used in Example 1 and Comparative Example 1. Figure 2 The rate performance results of the batteries prepared using the electrolytes in Example 1 and Comparative Example 1 are shown below. The formulas for calculating capacity retention and cycle performance are as follows:

[0093] Capacity retention rate for different number of cycles = discharge capacity after cycle / initial discharge capacity;

[0094] Capacity retention rate at different rates = discharge capacity at different rates / initial discharge capacity.

[0095] The negative electrode sample of the battery after 100 cycles was observed using a Krios G3i TEM D3786 microscope. The results are as follows: Figure 3 As shown.

[0096] Table 2

[0097]

[0098] As shown in Table 2 and Figure 1 As shown, under 0.2C conditions, the NCM811 / graphite pouch cell prepared using the electrolyte of Example 1 retained 99.5% of its capacity after 100 cycles, demonstrating higher durability than the NCM811 / graphite pouch cell prepared using the electrolyte in the comparative example. Figure 2 As shown, during charge-discharge tests at different rates from 1 / 3C to 3C, Example 1 ( Figure 2 The medium TTE (Transcription Trace) showed superior performance compared to the control group 1 at all magnification rates. Figure 2The capacity retention performance of the electrolyte (based on the base) was compared. At 3C rate, Example 1 exhibited a discharge capacity of 4.20 Ah, significantly higher than Comparative Example 1's 4.16 Ah; at 2C rate, Example 1 had a discharge capacity of 4.24 Ah, compared to Comparative Example 1's 4.21 Ah; at 1C rate, Example 1 had a discharge capacity of 4.34 Ah, compared to Comparative Example 1's 4.32 Ah; even at low rates of 1 / 3C, Example 1 showed slight superiority, with discharge capacities of 4.47 Ah and 4.46 Ah for Example 1 and Comparative Example 1, respectively. The electrolyte provided in these examples demonstrates high rate performance. These results clearly indicate that the provided electrolyte can effectively improve the rate performance and durability of lithium-ion batteries in low-temperature environments.

[0099] Figure 3 Transmission electron microscopy (TEM) images of the negative electrode surfaces of the batteries prepared with the electrolytes in Example 1 and Comparative Example 1 are shown. (a) is a TEM image of the graphite morphology of the negative electrode in the battery prepared with the lithium-ion battery electrolyte of Comparative Example 1, and (b) is a TEM image of the graphite morphology of the negative electrode in the battery prepared with the lithium-ion battery electrolyte of Example 1. As can be seen from the images, the graphite layered structure of the pouch battery prepared with the lithium-ion battery electrolyte of Comparative Example 1 is disrupted, while the graphite layered structure of the pouch battery prepared with the lithium-ion battery electrolyte of Example 1 remains intact. This demonstrates that the lithium-ion battery electrolyte provided in Example 1 can prevent the disruption of the graphite layered structure and improve interface stability.

[0100] (3) Battery safety testing under high temperature environment

[0101] The prepared soft-pack battery was placed in an environment of 130℃ for 1 hour. The battery was then disassembled to obtain a polyethylene separator sample. The cross-section of the separator was observed under a high-performance field emission scanning electron microscope (SEM) by Zeiss Merlin. The air permeability of the polyethylene separator to air was measured using a BYT-B3P air permeability analyzer via the differential pressure method. The morphology of the separator at high temperature is as follows: Figure 4 As shown in Table 3, the results of the diaphragm's air permeability are shown in the table.

[0102] Figure 4 The images show scanning electron microscope (SEM) images of the separator morphology of the batteries prepared with the lithium-ion battery electrolyte in Example 1 and Comparative Example 1 at high temperature. (a) is a SEM image of the separator morphology of the battery prepared with the electrolyte in Comparative Example 1 at high temperature. It can be seen from the image that the separator shrinks and closes the pores. (b) is a SEM image of the separator morphology of the battery prepared with the electrolyte in Example 1 at high temperature. It can be seen from the image that lithium salt fills the pores of the separator and can maintain the integrity of the separator structure.

[0103] Table 3

[0104]

[0105] As shown in Table 3 above, the permeability test of the polyethylene separator of the pouch battery placed in a 130℃ environment for 1 hour showed that the polyethylene separator in the pouch battery prepared with the lithium-ion battery electrolyte of Example 1 took 1,156,639 s per square inch to allow 100 cc of air to pass through at a pressure difference of 1.21 kPa, while the polyethylene separator in the pouch battery prepared with the lithium-ion battery electrolyte of Comparative Example 1 took 37,118 s per square inch to allow 100 cc of air to pass through at a pressure difference of 1.21 kPa. This indicates that the lithium-ion battery electrolyte in Example 1 can effectively reduce the permeability of the separator, thereby reducing the attack of organic gases on the positive electrode of the battery.

[0106] (4) Battery thermal box temperature tolerance test

[0107] The prepared soft-pack batteries were tested using a BE-8103 battery thermal abuse test chamber according to the national standard GB 38031-2020. The results are shown in Table 4. Figure 5 As shown.

[0108] Table 4

[0109]

[0110] From Table 4 above and Figure 5 As can be seen, when the batteries of Example 1 and Comparative Example 1 were placed in the battery thermal abuse test chamber BE-8103 and the ambient temperature was increased at a constant rate of 5°C per minute, the fire and smoke of the batteries were observed. The soft-pack battery prepared with the lithium-ion battery electrolyte in Comparative Example 1 caught fire and exploded at 164.6°C, while the soft-pack battery prepared with the lithium-ion battery electrolyte in Example 1 did not catch fire or explode at 200°C.

[0111] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A lithium-ion battery electrolyte, characterized in that, Including lithium salts and organic solvents; The lithium salt is composed of a first lithium salt and a second lithium salt, wherein the first lithium salt is lithium bis(fluorosulfonyl)imide, and the second lithium salt is at least one of lithium difluorobis(oxalato)phosphate and lithium di(oxalato)borate. The organic solvent consists of 30wt%-50wt% hydrofluoroether, 10wt%-30wt% acetate and 20wt%-60wt% carbonate.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The molar ratio of the first lithium salt to the second lithium salt is 1:(0.2-0.5).

3. The lithium-ion battery electrolyte according to claim 2, characterized in that, The concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5 mol / L to 1.5 mol / L.

4. The lithium-ion battery electrolyte according to any one of claims 1-3, characterized in that, The organic solvent consists of 30wt%-40wt% hydrofluoroether, 20wt%-30wt% acetate and 30wt%-50wt% carbonate.

5. The lithium-ion battery electrolyte according to any one of claims 1-3, characterized in that, One or more of the following conditions must be met: (1) The hydrofluoroether is at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1,1,2,2-tetrafluoroethyl ether; (2) The acetate is at least one of ethyl acetate, methyl formate, ethyl formate and methyl acetate; (3) The carbonate is at least one of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that, One or more of the following conditions must be met: (1) The hydrofluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; (2) The acetate is ethyl acetate; (3) The carbonate is at least one of methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate.

7. The lithium-ion battery electrolyte according to any one of claims 1-3, characterized in that, Including lithium salts and organic solvents; The lithium salt is composed of lithium bis(fluorosulfonyl)imide and lithium difluorobis(oxalato)phosphate in a molar ratio of 1:(0.2-0.5), and the concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L-1.2 mol / L. The organic solvent consists of 30wt%-50wt% 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 10wt%-30wt% ethyl acetate and 20wt%-60wt% carbonate.

8. A method for preparing a lithium-ion battery electrolyte, characterized in that, The process includes the following steps: dissolving lithium salt in an organic solvent to obtain the lithium-ion battery electrolyte; The lithium salt is composed of a first lithium salt and a second lithium salt, wherein the first lithium salt is lithium bis(fluorosulfonyl)imide, and the second lithium salt is at least one of lithium difluorobis(oxalato)phosphate and lithium di(oxalato)borate. The organic solvent consists of 30wt%-50wt% hydrofluoroether, 10wt%-30wt% acetate and 20wt%-60wt% carbonate.

9. The application of the lithium-ion battery electrolyte according to any one of claims 1-7 or the lithium-ion battery electrolyte prepared by the preparation method according to claim 8 in the preparation of a lithium-ion battery, wherein the lithium-ion battery includes a separator.

10. A lithium-ion battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and a lithium-ion battery electrolyte as described in any one of claims 1-7 or a lithium-ion battery electrolyte prepared by the preparation method described in claim 8. The diaphragm includes a polyethylene diaphragm.

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