Lithium ion battery electrolyte, preparation method and application

Abstract

The invention discloses a lithium ion battery electrolyte, a preparation method and application. The lithium ion battery electrolyte comprises a lithium salt and an organic solvent, wherein the lithium salt comprises a combination of at least two of lithium hexafluorophosphate, lithium difluoro bis (oxalato) phosphate, lithium bis (fluorosulfonyl) imide and lithium bis (oxalato) borate, and the organic solvent comprises 30 wt%-50 wt% of hydrofluoroether, 10 wt%-30 wt% of acetate and 20 wt%-60 wt% of carbonate. The lithium ion battery electrolyte provided by the invention can keep the diaphragm structure complete, realizes filling of pores with lithium salt, and reduces the permeability of the diaphragm, thereby controlling possible shrinkage of the diaphragm in a temperature change process under a low-temperature or high-temperature condition; the crosstalk problem caused by gas penetration between the positive electrode and the negative electrode is inhibited, and the battery prepared by utilizing the lithium ion battery electrolyte provided by the invention has good cycle performance and rate capability under a low-temperature condition and has relatively high safety under a high-temperature condition.

Description

Technical Field

[0001] The present application belongs to the field of battery technology and relates to a lithium-ion battery electrolyte, a preparation method and an application. Background Art

[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. They suffer from the following drawbacks: At low temperatures, they can easily cause lithium deposition in the lithium anode and damage the graphite structure; at high temperatures, lithium salts cannot be effectively retained, and there is a risk of thermal runaway.

[0003] Conventional electrolytes cannot balance low-temperature cycling performance with high-temperature safety. 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] Based on this, it is necessary to provide a lithium-ion battery electrolyte, a preparation method and application that can have both cycle performance in low temperature environments and safety in high temperature environments.

[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 difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide salt and lithium dioxalatoborate.

[0007] The organic solvent includes 30 wt % to 50 wt % of hydrofluoroether, 10 wt % to 30 wt % of acetate, and 20 wt % to 60 wt % of carbonate.

[0008] In some embodiments, the lithium salt includes at least a first lithium salt and a second lithium salt, the first lithium salt includes a bisfluorosulfonyl imide lithium salt, and the second lithium salt includes at least one of lithium difluorobisoxalatophosphate and lithium dioxalatoborate;

[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-1.5 mol / L.

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

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

[0013] (1) The hydrofluoroether includes 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 ester includes at least one of ethyl methyl 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 includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

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

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

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

[0021] The lithium salt comprises lithium bis(fluorosulfonyl)imide salt and lithium difluorobis(oxaloyl)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 solvent includes 30 wt % to 50 wt % of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 10 wt % to 30 wt % of ethyl acetate and 20 wt % to 60 wt % of carbonate.

[0023] In some embodiments, a method for preparing a lithium ion battery electrolyte is provided, comprising the steps of: 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 difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide salt and lithium dioxalatoborate.

[0025] The organic solvent includes 30 wt % to 50 wt % of hydrofluoroether, 10 wt % to 30 wt % of acetate, and 20 wt % to 60 wt % of carbonate.

[0026] In some embodiments, there is provided use of the lithium-ion battery electrolyte or the lithium-ion battery electrolyte prepared by the preparation method in preparing a lithium-ion battery.

[0027] In some embodiments, a lithium-ion battery is provided, comprising 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 lithium-ion battery electrolyte provided above can maintain the integrity of the diaphragm structure, enable lithium salt to fill the pores, and reduce the permeability of the diaphragm, thereby controlling the shrinkage of the diaphragm that may occur during temperature changes under low or high temperature conditions; suppressing the crosstalk problem between the positive and negative electrodes caused by gas penetration, and achieving that the battery prepared using the provided lithium-ion battery electrolyte has good cycle performance and rate performance under low temperature conditions, and has high safety under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments and examples of this application and to provide a more complete understanding of the application and its beneficial effects, the following briefly introduces the drawings required for use in the description of the embodiments or examples. Obviously, the drawings described below are only some embodiments of this application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0030] Figure 1 The cycle performance diagram of the battery prepared with the lithium ion battery electrolyte in Example 1 and Comparative Example 1;

[0031] Figure 2 The figure is a rate performance diagram of 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 negative electrode graphite morphology of the batteries prepared with the lithium ion battery electrolytes in Example 1 and Comparative Example 1, wherein (a) is a TEM image of the negative electrode graphite morphology of the battery prepared with the lithium ion battery electrolyte in Comparative Example 1, and (b) is a TEM image of the negative electrode graphite morphology of the battery prepared with the lithium ion battery electrolyte in Example 1;

[0033] Figure 4 The following are scanning electron microscope (SEM) images of the diaphragm morphology of the lithium-ion battery prepared with the electrolytes in Example 1 and Comparative Example 1 at high temperature. (a) is an SEM image of the diaphragm morphology of the battery prepared with the electrolyte in Comparative Example 1 at high temperature. It can be seen from the image that the diaphragm has shrunk and closed pores. (b) is an SEM image of the diaphragm morphology of the battery prepared with the electrolyte in Example 1 at high temperature.

[0034] Figure 5 Hot box test temperature diagram of batteries prepared with the lithium ion battery electrolytes in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

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

[0036] It should be noted that when an element is referred to as being “fixed to” another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or there may be an intermediate element.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present 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 specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0039] The terms "and / or", "or / and", and "and / or" used in this application include any one of two or more related listed items, and also include any and all combinations of the related listed items, and the said any 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 by 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 technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all 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, "plurality", "multiple", "multiple times", "multiples", 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 "combination thereof", "any combination thereof", "any combination thereof" and the like used in this application include all suitable combinations of any two or more of the listed items.

[0042] In this application, the "suitable" mentioned in "suitable combination", "suitable method", "any suitable method", etc. is based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0043] In this application, "preferred", "better", "more preferred" and "suitable" are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute a limitation on the scope of protection of this application.

[0044] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0045] In this application, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no contradictions or constraints.

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

[0047] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0048] In this application, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval and includes the two numerical endpoints of the numerical range (i.e., the minimum and maximum values), as well as each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two endpoint integers of the numerical range, as well as each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, 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 included therein.

[0049] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

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

[0051] The "room temperature" in this application generally refers to 5°C to 30°C, preferably 25±5°C.

[0052] In traditional lithium-ion battery electrolytes, under low-temperature conditions, the electrolyte fluidity is reduced, ion transport is hindered, and the interface stability is poor, which can easily cause lithium deposition at the lithium negative electrode and damage the graphite structure. Under high-temperature conditions, the electrolyte is prone to decomposition or volatilization, and the diaphragm shrinks due to heat, resulting in the inability to effectively retain lithium salts. At the same time, it may cause gas crosstalk and increase the risk of thermal runaway of the battery.

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

[0054] The lithium salt includes a combination of at least two of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium bisfluorosulfonyl imide salt and lithium dioxalatoborate.

[0055] The organic solvent includes 30 wt % to 50 wt % of hydrofluoroether, 10 wt % to 30 wt % of acetate, and 20 wt % to 60 wt % of carbonate.

[0056] Without limitation, hydrofluoroether is used to enhance the interfacial bonding between the electrolyte and the polyethylene separator, thereby improving high-temperature safety and low-temperature fluidity.

[0057] Without limitation, acetate is used to improve low temperature conductivity and low temperature fluidity.

[0058] Without limitation, carbonates are used to increase low temperature conductivity.

[0059] Without limitation, lithium salts are used to improve low temperature conductivity and provide a high temperature gas barrier.

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

[0061] The lithium-ion battery electrolyte provided by the company achieves a significantly enhanced interfacial bonding strength between the electrolyte and the separator through component design, with this interfacial bonding strength exceeding the surface tension of the electrolyte itself. This property ensures that the lithium salt remains within the pores of the separator after the solvent evaporates, thereby controlling the separator's shrinkage that may occur 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. The resulting soft-pack battery has a hot box temperature tolerance exceeding 200°C. By enhancing the interfacial bonding between the electrolyte and the separator, the volatilization or displacement of lithium salts due to high temperatures is prevented, effectively alleviating the safety risks 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, the first lithium salt includes a bisfluorosulfonyl imide lithium salt, and the second lithium salt includes at least one of lithium difluorobisoxalatophosphate and lithium bisoxalatoborate.

[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, etc., or a range selected from any two of the foregoing ratios.

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

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

[0067] In some embodiments, in the lithium-ion battery electrolyte, the hydrofluoroether 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 the hydrofluoroether may further include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

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

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

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

[0071] The lithium salt includes lithium bis(fluorosulfonyl)imide salt and lithium difluorobis(oxaloyl)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;

[0072] The organic solvent includes 30 wt % to 50 wt % of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 10 wt % to 30 wt % of ethyl acetate and 20 wt % to 60 wt % of carbonate.

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

[0074] The lithium salt includes a combination of at least two of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium bisfluorosulfonyl imide salt and lithium dioxalatoborate.

[0075] The organic solvent includes 30 wt % to 50 wt % of hydrofluoroether, 10 wt % to 30 wt % of acetate, and 20 wt % to 60 wt % of carbonate.

[0076] In some embodiments, a lithium-ion battery electrolyte or a lithium-ion battery electrolyte prepared by the preparation method is provided for use in preparing a lithium-ion battery.

[0077] In some embodiments, a lithium-ion battery is provided, comprising 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, comprising the aforementioned lithium-ion battery.

[0079] The lithium-ion battery electrolyte provided 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 is further described in conjunction with specific examples and comparative examples. Unless otherwise specified, the raw materials involved in the following specific examples can all be sourced from commercial sources, and the instruments used can all be sourced from commercial sources unless otherwise specified.

[0081] 1. Preparation of lithium-ion battery electrolyte

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

[0083] The formula compositions of the lithium ion battery electrolytes of 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(oxalatophosphate), LiFSI is lithium bis(fluorosulfonyl)imide salt, LiBOB is lithium dioxalatoborate, 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] 2. Electrochemical performance test

[0089] (1) Preparation of batteries:

[0090] The QH02-Ni90 / SiC-15 battery cells purchased from Dongguan Kelude New Energy Technology Co., Ltd. were injected with the lithium-ion battery electrolytes of Examples 1-5 and Comparative Examples 1-5 in a dry room with a dew point of -40°C. The cells were left to stand for 2 days and then subjected to battery formation with a formation current of 0.1 A to obtain soft-pack batteries for testing.

[0091] (2) Cycle performance and rate performance test of batteries under low temperature environment

[0092] The batteries prepared from 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 cyclically charged and discharged at a current of 0.2A at -20°C, and the charging capacity was recorded. The first discharge was then performed at a current of 0.2A, and the discharge capacity was recorded. The discharge capacity of the battery after multiple cycles was recorded, and the capacity retention rate at different cycle numbers, i.e., the battery durability, was calculated. The battery discharge capacity at -20°C, 0.3A, 1A, 2A, and 3A was recorded, and the capacity retention rate at different rates, i.e., the rate performance, was calculated. The results are shown in FIG. Figure 1 、 Figure 2 and as shown in Table 2. Figure 1 and Figure 2 In the figure, TTE is Example 1 and BASE is Comparative Example 1. Figure 1 The cycle performance results of the batteries prepared with the lithium ion battery electrolytes in Example 1 and Comparative Example 1 are as follows: Figure 2 The rate performance results of the batteries prepared with the electrolytes in Example 1 and Comparative Example 1 are as follows:

[0093] Capacity retention rate at different cycle numbers = discharge capacity after cycle / initial discharge capacity;

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

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

[0096] Table 2

[0097]

[0098] As shown in Table 2 and Figure 1 As shown in the graph, under 0.2C conditions, the NCM811 / graphite soft pack battery prepared with the electrolyte of Example 1 was cycled 100 times, and the capacity retention rate reached 99.5%, which is higher than the NCM811 / graphite soft pack battery prepared with the electrolyte of the comparative example. Figure 2 As shown, when the charge and discharge tests were carried out at different rates from 1 / 3C to 3C, Example 1 ( Figure 2 TTE) showed better performance than Comparative Example 1 ( Figure 2The capacity retention performance of the BASE in the embodiment is shown. Among them, at a 3C rate, the discharge capacity of Example 1 is 4.20 Ah, which is significantly higher than the 4.16 Ah of Comparative Example 1; at a 2C rate, the discharge capacity of Example 1 is 4.24 Ah, and the discharge capacity of Comparative Example 1 is 4.21 Ah; at a 1C rate, the discharge capacity of Example 1 is 4.34 Ah, and the discharge capacity of Comparative Example 1 is 4.32 Ah; even at a low rate of 1 / 3C, Example 1 is slightly better, with the discharge capacities of Example 1 and Comparative Example 1 being 4.47 Ah and 4.46 Ah, respectively. The electrolyte provided in the embodiment has high rate performance. This result fully demonstrates 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 batteries prepared with the electrolytes 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. As can be seen from the figures, the graphite layered structure of the soft-pack battery prepared with the lithium-ion battery electrolyte in Comparative Example 1 is destroyed, while the graphite layered structure of the soft-pack battery prepared with the lithium-ion battery electrolyte in Example 1 is intact. This indicates that the lithium-ion battery electrolyte provided in Example 1 can prevent the destruction of the graphite layered structure and improve the interface stability.

[0100] (3) Battery safety testing in high temperature environments

[0101] The prepared soft pack battery was placed in a 130℃ environment for 1 hour, and the battery was disassembled to obtain a polyethylene membrane sample. The cross section of the membrane was observed under a high-performance field emission scanning electron microscope Zeiss Merlin electron microscope, and the air permeability of the polyethylene membrane to air was tested using a BYT-B3P air permeability tester using the pressure difference method. The membrane morphology at high temperature is as follows: Figure 4 The results of the membrane's air permeability are shown in Table 3.

[0102] Figure 4 The figures are scanning electron microscope (SEM) images of the diaphragm morphology of the batteries prepared with the lithium-ion battery electrolytes in Example 1 and Comparative Example 1 at high temperature, wherein (a) is an SEM image of the diaphragm morphology of the battery prepared with the electrolyte in Comparative Example 1 at high temperature, from which it can be seen that the diaphragm shrinks and closes the pores, and (b) is an SEM image of the diaphragm morphology of the battery prepared with the electrolyte in Example 1 at high temperature, from which it can be seen that the lithium salt fills the pores of the diaphragm and can keep the diaphragm structure intact.

[0103] Table 3

[0104]

[0105] As can be seen from Table 3 above, the air permeability test of the polyethylene separator of the soft-pack battery placed in a 130°C environment for 1 hour shows that the time it takes for 100cc of air to pass through the polyethylene separator of the soft-pack battery prepared with the lithium-ion battery electrolyte of Example 1 at a pressure differential of 1.21 kPa is 1156639 seconds per square inch. The time it takes for 100cc of air to pass through the polyethylene separator of the soft-pack battery prepared with the lithium-ion battery electrolyte of Comparative Example 1 at a pressure differential of 1.21 kPa is 37118 seconds per square inch. This indicates that the lithium-ion battery electrolyte of Example 1 can effectively reduce the air permeability of the separator, thereby reducing the attack of organic gases on the battery positive electrode.

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

[0107] The prepared soft pack battery was tested in accordance with the national standard GB 38031-2020 using the battery thermal abuse test chamber BE-8103. The results are shown in Table 4 and Figure 5 shown.

[0108] Table 4

[0109]

[0110] From Table 4 and Figure 5 It can be seen that the battery of Example 1 and the battery of Comparative Example 1 were placed in a battery thermal abuse test chamber BE-8103, the ambient temperature was uniformly increased at a rate of 5°C per minute, and the fire and smoking 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-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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 above-described embodiments merely represent several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims, and the description and drawings shall 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 comprises a combination of at least two of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide salt and lithium dioxalatoborate. The organic solvent includes 30 wt % to 50 wt % of hydrofluoroether, 10 wt % to 30 wt % of acetate, and 20 wt % to 60 wt % of carbonate.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium salt includes at least a first lithium salt and a second lithium salt, the first lithium salt includes a bisfluorosulfonyl imide lithium salt, and the second lithium salt includes at least one of lithium difluorobisoxalatophosphate and lithium dioxalatoborate; Optionally, 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-1.5 mol / L.

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

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

7. The lithium-ion battery electrolyte according to any one of claims 1 to 3, characterized in that including lithium salts and organic solvents; The lithium salt comprises lithium bis(fluorosulfonyl)imide salt and lithium difluorobis(oxaloyl)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 includes 30 wt % to 50 wt % of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 10 wt % to 30 wt % of ethyl acetate and 20 wt % to 60 wt % of carbonate.

8. A method for preparing a lithium ion battery electrolyte, characterized in that: The method comprises the following steps: dissolving a lithium salt in an organic solvent to obtain the lithium ion battery electrolyte; The lithium salt comprises a combination of at least two of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide salt and lithium dioxalatoborate. The organic solvent includes 30 wt % to 50 wt % of hydrofluoroether, 10 wt % to 30 wt % of acetate, and 20 wt % to 60 wt % of carbonate.

9. Use of the lithium ion battery electrolyte according to any one of claims 1 to 7 or the lithium ion battery electrolyte prepared by the preparation method according to claim 8 in the preparation of a lithium ion battery.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and the lithium ion battery electrolyte according to any one of claims 1 to 7 or the lithium ion battery electrolyte prepared by the preparation method according to claim 8.

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