Lithium ion battery electrolyte, lithium ion battery, preparation method and application

Abstract

The invention discloses a lithium ion battery electrolyte, a lithium ion battery, a preparation method and application. The lithium ion battery electrolyte provided by the invention comprises lithium salt and a solvent, wherein the lithium salt comprises imidodisulfuryl fluoride lithium salt, lithium hexafluorophosphate and lithium salt A; the lithium salt A comprises one or more of lithium difluoro bis (oxalato) phosphate, lithium bis (oxalato) borate and lithium difluoro phosphate; the solvent comprises high steric hindrance branched-chain cyclic carbonate and straight-chain carbonate; the branched chain type cyclic carbonate with high steric hindrance comprises one or two of butylene carbonate and 1, 2-butylene carbonate; the straight-chain carbonic ester comprises one or two of dimethyl carbonate and diethyl carbonate. A battery prepared from the lithium ion battery electrolyte provided by the invention has relatively high thermal stability, cyclicity and rate capability.

Description

Technical Field

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

[0002] To meet the long driving range requirements of electric vehicles, high-nickel layered cathode materials (such as LiNi 0.8 Mn 0.1 Co 0.1 O2, abbreviated as NCM811) are often used. However, the currently widely used electrolyte based on ethylene carbonate (EC) shows poor thermal stability and a high risk of oxygen release under high-nickel cathodes, which easily leads to battery thermal runaway. Although some EC-free electrolyte formulations are used to improve the safety of high-nickel cathode lithium-ion batteries, they usually perform poorly in terms of cycling performance and rate performance. Therefore, the current electrolytes cannot balance thermal stability, cycling performance and rate performance in high-nickel cathode lithium-ion batteries. Summary of the Invention

[0003] Based on this, it is necessary to provide a lithium-ion battery electrolyte, a lithium-ion battery, a preparation method and an application that can balance thermal stability, cycling performance and rate performance.

[0004] In some embodiments, a lithium-ion battery electrolyte is provided, including a lithium salt and a solvent,

[0005] The lithium salt includes lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate and lithium salt A;

[0006] The lithium salt A includes one or more of lithium difluoro(oxalato)phosphate, lithium bis(oxalato)borate and lithium difluorophosphate;

[0007] The solvent includes a high steric hindrance branched cyclic carbonate and a linear carbonate;

[0008] The high steric hindrance branched cyclic carbonate includes one or both of butenyl carbonate and 1,2-butene carbonate;

[0009] The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate.

[0010] In some embodiments, in the provided lithium-ion battery electrolyte, the concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L to 2.7 mol / L.

[0011] In some embodiments, in the provided lithium-ion battery electrolyte, among the lithium salts, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate and lithium salt A is (0.5 to 1):(0.3 to 1):(0.1 to 0.2).

[0012] In some embodiments, in the provided lithium-ion battery electrolyte, the volume ratio of the high steric hindrance branched cyclic carbonate in the solvent is 10% - 40%.

[0013] In some embodiments, in the provided lithium-ion battery electrolyte, the volume ratio of the linear carbonate in the solvent is 60% - 90%.

[0014] In some embodiments, the lithium-ion battery electrolyte further contains an additive;

[0015] Optionally, the additive includes one or both of fluoroethylene carbonate and vinylene carbonate.

[0016] In some embodiments, in the provided lithium-ion battery electrolyte, the volume percentage of the additive in the total volume of the solvent and the additive is 0% - 10%.

[0017] In some embodiments, a method for preparing a lithium-ion battery electrolyte is provided, in which a lithium salt and a solvent are mixed to prepare the lithium-ion battery electrolyte;

[0018] Wherein, the lithium salt includes lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium salt A;

[0019] The lithium salt A includes one or more of lithium difluorobis(oxalato)phosphate, lithium bis(oxalato)borate, and lithium difluorophosphate;

[0020] The solvent includes a high steric hindrance branched cyclic carbonate and a linear carbonate;

[0021] The high steric hindrance branched cyclic carbonate includes one or both of butylene carbonate and 1,2-butylene carbonate;

[0022] The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate;

[0023] Optionally, the method for preparing the lithium-ion battery electrolyte further includes adding an additive.

[0024] In some embodiments, the provided lithium-ion battery electrolyte or the lithium-ion battery electrolyte prepared by the provided preparation method is used in the preparation of a lithium-ion battery.

[0025] In some embodiments, a lithium-ion battery is provided, which includes a positive electrode, a negative electrode, and the provided lithium-ion battery electrolyte or the lithium-ion battery electrolyte prepared by the provided preparation method.

[0026] The lithium-ion battery electrolyte provided above contains lithium salts such as lithium hexafluorophosphate, lithium difluorobis(oxalato)phosphate, and lithium salt A, as well as high steric hindrance branched cyclic carbonates and linear carbonates. By using these lithium salts in combination, the desolvation energy of the high steric hindrance branched cyclic carbonate solvent can be reduced, co-insertion on the surface of the graphite negative electrode can be prevented, and the formation of a complex solid electrolyte interface (SEI) rich in multiple components can be promoted. At the same time, the high steric hindrance of the high steric hindrance branched cyclic carbonate prevents the adsorption of the solvent on the surface of the positive electrode, improving the safety performance. The high steric hindrance branched cyclic carbonate can improve the safety and conductivity of the electrolyte, and the linear carbonate can reduce the viscosity of the electrolyte. By using the high steric hindrance branched cyclic carbonate and the linear carbonate in combination, the safety performance can be improved without sacrificing the battery durability and rate performance, taking into account the thermal stability, cycle performance, and rate performance. The battery prepared with the provided lithium-ion battery electrolyte has high thermal stability, cycle performance, and rate performance. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments and examples of the present application and to more fully understand the present application and its beneficial effects, the drawings required for use in the description of the embodiments or examples will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative efforts.

[0028] Figure 1 Element distribution maps and carbon element distribution maps of the lithium-ion battery electrolytes of Example 1, Example 8, and Comparative Example 3 obtained by scanning electron microscopy combined with energy spectroscopy, where (a) is the element distribution map of the lithium-ion battery electrolyte of Example 1 obtained by scanning electron microscopy combined with energy spectroscopy, (b) is the element distribution map of the lithium-ion battery electrolyte of Example 8 obtained by scanning electron microscopy combined with energy spectroscopy, (c) is the element distribution map of the lithium-ion battery electrolyte of Comparative Example 3 obtained by scanning electron microscopy combined with energy spectroscopy, (d) is the carbon element distribution map of the lithium-ion battery electrolyte of Example 1, (e) is the carbon element distribution map of the lithium-ion battery electrolyte of Example 8, and (f) is the carbon element distribution map of the lithium-ion battery electrolyte of Comparative Example 3;

[0029] Figure 2 Differential scanning calorimetry test result graphs of the lithium-ion battery electrolytes of Example 1, Example 7, and Example 8;

[0030] Figure 3 Battery thermal box temperature tolerance result graphs of the batteries prepared with the lithium-ion battery electrolytes of Example 1, Example 7, and Example 8. Detailed Embodiments

[0031] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0032] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may also be a middle element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a middle element at the same time.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention in this article are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0034] The term

[0035] Unless otherwise stated or there is a contradiction, the terms or phrases used herein have the following meanings:

[0036] The selection scope of the terms "and / or", "or / and", and "and / or" used in this application includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The said any and all combinations include combinations of any two related listed items, any more related listed items, or all related listed items. It should be noted that when at least two conjunctions selected from "and / or", "or / and", and "and / or" are used to connect at least three items, it should be understood that in this application, this technical solution undoubtedly includes the technical solution connected by "logical AND", and also undoubtedly includes the technical solution connected by "logical OR". For example, "A and / or B" includes three parallel solutions: A, B, and "the combination of A and B".

[0037] In this application, when it comes to "multiple", "multiple types", "multiple times", "multiple elements", etc., unless otherwise specified, it means greater than 2 or equal to 2 in quantity. For example, "one or more types" means one type or greater than or equal to two types.

[0038] In this application, "its combination", "any combination thereof", "any combination mode thereof", etc. include all suitable combination modes of any two or any two or more of the listed items.

[0039] In this application, the "suitable combination method", "suitable method", "any suitable method", etc., the "suitable" mentioned therein shall be subject to being able to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0040] In this application, "preferred", "better", "more preferable", "it is advisable" are only used to describe the implementation manners or embodiments with better effects. It should be understood that they do not constitute a limitation on the protection scope of this application.

[0041] In this application, "further", "even further", "especially", etc. are used for descriptive purposes, indicating differences in content, but should not be understood as a limitation on the protection scope of this application.

[0042] In this application, "optionally", "optional", "option", mean that it can be either present or absent, that is, it refers to any one of the two parallel options of "present" or "absent". If "optional" appears multiple times in a technical solution, without special instructions and without contradictions or mutual restrictions, each "optional" is independent of each other.

[0043] In this invention, in relation to "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive listing and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0044] In this application, for the technical features described in an open-ended manner, it includes the closed technical solutions composed of the listed features, as well as the open technical solutions containing the listed features.

[0045] In this application, regarding the numerical interval (that is, the numerical range), without special instructions, the optional numerical values are considered continuous within the above numerical interval, and include the two numerical endpoints (that is, the minimum value and the maximum value) of this numerical range, as well as each numerical value between these two numerical endpoints. Without special instructions, when the numerical interval only refers to the integers within this numerical interval, it includes the two endpoint integers of this numerical range, as well as each integer between the two endpoints. In this article, it is equivalent to directly listing each integer. For example, t is an integer selected from 1 to 10, indicating that t is any integer selected from the integer group composed of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. In addition, when providing multiple ranges to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed in this article should be understood to include any and all sub-ranges subsumed therein.

[0046] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0047] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0048] The "room temperature" in this application generally refers to 5°C to 30°C, preferably 25±5°C.

[0049] In some embodiments, a lithium-ion battery electrolyte formula is provided, which achieves the technical effect of taking into account stability, cyclability and rate performance by optimizing the type of lithium salt and solvent.

[0050] In some embodiments, a lithium ion battery electrolyte is provided, comprising a lithium salt and a solvent.

[0051] The lithium salt includes lithium bis(fluorosulfonyl)imide salt, lithium hexafluorophosphate and lithium salt A;

[0052] The lithium salt A includes one or more of lithium difluorobisoxalate phosphate, lithium dioxalate borate and lithium difluorophosphate;

[0053] The solvent includes a highly hindered branched-chain cyclic carbonate and a linear carbonate;

[0054] The high sterically hindered branched cyclic carbonate includes one or both of butylene carbonate and 1,2-butylene carbonate;

[0055] The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate.

[0056] The solvent of the lithium-ion battery electrolyte provided contains both high-steric branched cyclic carbonates and linear carbonates, which can significantly improve the safety and electrochemical performance of high-nickel lithium batteries. Among them, the oxidation reaction activation energy of high-steric branched cyclic carbonates mainly composed of one or two of butylene carbonate and 1,2-butylene carbonate is relatively high, which reduces the thermal reaction rate on the electrode surface, thereby reducing the risk of thermal runaway. The linear carbonates composed of one or two of dimethyl carbonate and diethyl carbonate can reduce the viscosity of the electrolyte. The composite use of high-steric branched cyclic carbonates and linear carbonates can improve safety performance without sacrificing battery durability and rate performance, taking into account thermal stability, cyclability and rate performance.

[0057] By using the above lithium salts in combination, the desolvation energy of the high steric hindrance branched-chain cyclic carbonate solvent can be reduced, preventing co-insertion on the surface of the graphite negative electrode, while promoting the formation of a complex solid electrolyte interface (SEI) rich in multiple components, which is thin and uniform, inhibiting side reactions and reducing the interfacial resistance.

[0058] Adding multiple lithium salts and high steric hindrance branched-chain cyclic carbonate solvents significantly improves the conductivity of the electrolyte, enabling good ionic conduction performance even in the absence of EC.

[0059] In some embodiments, in the provided lithium-ion battery electrolyte, the concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L to 2.7 mol / L. For example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 2.7 mol / L, etc., or a range composed of any two of the foregoing values.

[0060] In some embodiments, in the provided lithium-ion battery electrolyte, among the lithium salts, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium salt A is (0.5 to 1):(0.3 to 1):(0.1 to 0.2). For example, 0.5:0.3:0.1, 0.8:1:0.1, 0.5:0.3:0.2, 0.8:0.5:0.1, 1:0.3:0.1, 1:0.5:0.1, 1:1:0.2, etc., or a range composed of any two of the foregoing ratios.

[0061] In some embodiments, in the provided lithium-ion battery electrolyte, the volume ratio of the high steric hindrance branched-chain cyclic carbonate in the solvent is 10% to 40%. For example, 10%, 20%, 30%, 40%, etc., or a range composed of any two of the foregoing ratios.

[0062] In some embodiments, in the provided lithium-ion battery electrolyte, the volume ratio of the linear carbonate in the solvent is 60% to 90%. For example, 60%, 70%, 80%, 90%, etc., or a range composed of any two of the foregoing ratios.

[0063] In some embodiments, the lithium-ion battery electrolyte further contains an additive.

[0064] In some embodiments, the additive includes one or both of fluoroethylene carbonate and vinylene carbonate.

[0065] In some embodiments, in the provided lithium-ion battery electrolyte, the volume percentage of the additive in the total volume of the solvent and the additive is 0% to 10%. For example, 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., or a range composed of any two of the foregoing ratios.

[0066] In some embodiments, a method for preparing a lithium-ion battery electrolyte is provided, in which a lithium salt and a solvent are mixed to prepare a lithium-ion battery electrolyte;

[0067] Among them, the lithium salt includes lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium salt A;

[0068] Lithium salt A includes one or more of lithium difluorobis(oxalato)phosphate, lithium bis(oxalato)borate, and lithium difluorophosphate;

[0069] The solvent includes a high steric hindrance branched cyclic carbonate and a linear carbonate;

[0070] The high steric hindrance branched cyclic carbonate includes one or both of butylene carbonate and 1,2-butylene carbonate;

[0071] The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate.

[0072] In some embodiments, adding an additive is further included in the provided method for preparing a lithium-ion battery electrolyte.

[0073] In some embodiments, the provided lithium-ion battery electrolyte or the lithium-ion battery electrolyte prepared by the method for preparing the lithium-ion battery electrolyte is used in the preparation of a lithium-ion battery.

[0074] 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 method for preparing the lithium-ion battery electrolyte.

[0075] The following are specific examples. The purpose is to further elaborate on the present application to help those skilled in the art and researchers further understand the present application. The relevant technical conditions do not constitute any limitation to the present application. Any form of modification within the scope of the claims of the present application is within the protection scope of the claims of the present application.

[0076] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by known methods. The experimental methods without specific conditions noted in the examples are carried out under conventional conditions, such as the conditions described in the literature, books, or the methods recommended by the manufacturers.

[0077] I. Preparation of Lithium-Ion Battery Electrolyte

[0078] Examples 1-5 and Comparative Examples 1-5

[0079] The formulation compositions of the lithium-ion battery electrolytes of Examples 1-5 and Comparative Examples 1-5 are shown in Table 1.

[0080] Table 1

[0081]

[0082] In Table 1, LiPF6 is lithium hexafluorophosphate, LiDFOB is lithium difluoro(oxalato)phosphate, LiFSI is lithium bis(fluorosulfonyl)imide, LiBOB is lithium oxalate borate, LiPO2F2 is lithium difluorophosphate, LiTFSI is lithium bis(trifluoromethanesulfonyl)imide, EC is ethylene carbonate, and EMC is ethyl methyl carbonate.

[0083] The preparation method of the lithium-ion battery electrolyte is as follows: Mix a lithium salt, a high steric hindrance branched cyclic carbonate, a linear carbonate, and an additive to obtain the lithium-ion battery electrolyte.

[0084] II. Electrochemical Performance Test

[0085] (1) Preparation of the battery:

[0086] The QH02-Ni90 / SiC-15 battery cells purchased from Dongguan Kelude New Energy Technology Co., Ltd. were filled with the lithium-ion battery electrolytes of the examples and comparative examples in a drying room with a dew point of -40°C, left standing for 2 days, and then battery formation was carried out with a current of 0.1 A to obtain the soft-pack batteries for testing.

[0087] (2) Cycle performance and rate performance tests of the battery

[0088] The batteries prepared with the lithium-ion battery electrolytes in the examples and comparative examples were tested as follows using a Neware BTS4000 instrument. The prepared batteries were cycled for charge and discharge at a current of 0.33 A, and the charging capacity was recorded. Then, the first discharge was carried out at a current of 0.33 A, 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 was calculated, which is the battery durability performance. The discharge capacity of the battery at 25°C, 0.33 A, 1 A, 2 A, and 3 A was recorded, and the capacity retention rate at different rates was calculated, which is the rate performance. The test results of some examples and comparative examples are shown in Table 2-1 and Table 2-2. The calculation formulas for the capacity retention rate and cycle performance are as follows:

[0089] Capacity retention rate at different cycle numbers = Discharge capacity after cycling / Initial discharge capacity;

[0090] Capacity retention rate at different rates = Discharge capacity at different rates / Initial discharge capacity.

[0091] Table 2-1 Capacity retention rate at different cycle numbers

[0092]

[0093] As can be seen from the data in Table 2-1, Example 1 exhibited excellent capacity retention performance throughout the cycling process. At 200 cycles, its capacity retention rate was 98.24%, and it remained at 89.99% even at 1200 cycles, with a relatively slow capacity decay, indicating good cycling stability. In contrast, Comparative Example 3 had a slightly lower capacity retention rate than Example 1 at the initial stage of cycling (200 cycles), which was 96.45%. However, as the number of cycles increased, its capacity decayed rapidly, dropping to 88.39% only at 600 cycles, falling below 80% after 800 cycles, and remaining only 54.75% at 1200 cycles. This shows that there are obvious capacity decay problems in the electrolyte system of Comparative Example 3 during long-term cycling.

[0094] Table 2-2 Capacity Retention Rates at Different Rates

[0095]

[0096] From the rate performance data listed in Table 2-2, it can be seen that Example 1 showed good capacity retention ability at different rates. At a rate of 0.33C, the capacity retention rate of Example 1 was 100.14%, close to the theoretical capacity; at rates of 1C, 2C, and 3C, the capacities were 92.53%, 84.84%, and 72.97% respectively, demonstrating strong rate adaptability and electrochemical stability. In contrast, Comparative Example 3 also had relatively high capacity retention rates at low rates (0.33C and 1C), which were 100.84% and 93.61% respectively. However, under high-rate (2C and 3C) conditions, its capacity rapidly dropped to 83.13% and 68.90%, with a higher degree of decay than Example 1. The above results indicate that Example 1 can still maintain a high capacity output under high-rate discharge conditions, suggesting that its electrolyte system or electrode structure design helps to improve the transport efficiency of lithium ions at the electrode / electrolyte interface, slow down the polarization phenomenon, and thus enhance the rate performance and fast discharge ability of the battery.

[0097] (3)Conductivity Test

[0098] The ionic conductivity of the electrolyte was measured using a precisely calibrated Orion Star A212 conductivity meter. Before each test, the conductivity electrode probe was rinsed with distilled organic solvents and dried to remove any possible impurities remaining from the previous measurement. Subsequently, the cleaned conductivity probe was inserted into the electrolyte solution to be measured, and its conductivity value was recorded in millisiemens per centimeter (mS / cm). To ensure the accuracy of the test results, each electrolyte was tested at least 2 times, and the average value was taken to eliminate the influence of test errors.

[0099] The results are shown in Table 3.

[0100] Table 3

[0101]

[0102] As can be seen from the results in Table 3, the lithium-ion battery prepared with the provided lithium-ion battery electrolyte has a relatively high conductivity.

[0103] III. Safety Performance Test

[0104] (1)Test on the Adsorption Capacity of the Electrolyte to the Positive Electrode

[0105] To study the adsorption behavior of the electrolyte on the surface of the positive electrode material under high-temperature conditions, the prepared electrolyte was respectively mixed evenly with the positive electrode material NMC811 at a mass ratio of 2:5, placed in an aluminum crucible, and heated to 400 °C under an inert gas atmosphere, and kept warm for a period of time to simulate the possible reactions between the electrode / electrolyte during thermal runaway. After heating, the crucible was naturally cooled to room temperature, and the residual solid products therein were taken out for surface morphology and composition analysis. The positive electrode particles of the products after heating were characterized by using Zeiss Merlin scanning electron microscope (SEM) combined with energy-dispersive spectroscopy (EDS) technology. The results of some examples are as Figure 1 shown, where (a) is the element distribution map of the lithium-ion battery electrolyte of Example 1 by scanning electron microscope combined with energy-dispersive spectroscopy, (b) is the element distribution map of the lithium-ion battery electrolyte of Example 8 by scanning electron microscope combined with energy-dispersive spectroscopy, (c) is the element distribution map of the lithium-ion battery electrolyte of Comparative Example 3 by scanning electron microscope combined with energy-dispersive spectroscopy, (d) is the carbon element distribution map of the lithium-ion battery electrolyte of Example 1, (e) is the carbon element distribution map of the lithium-ion battery electrolyte of Example 8, and (f) is the carbon element distribution map of the lithium-ion battery electrolyte of Comparative Example 3. Figure 1 Among them, the scales of (a), (b), (d), and (e) are 25 μm, and the scales of (c) and (f) are 50 μm.

[0106] Analysis Figure 1 The results show that the carbon content of Example 1 is 12.63%wt, the carbon content of Example 8 is 14.23%wt, and the carbon content of Comparative Example 3 is 27.80%wt. The adsorption carbon layers formed by the residues of the electrolytes in Example 1 and Example 8 on the positive electrode surface after heating are significantly thinner, and the carbon element content is also significantly lower than that of Comparative Example 3, indicating that this type of compound is not easily adsorbed on the positive electrode surface and reacts with it under high-temperature conditions.

[0107] (2)Differential Scanning Calorimetry Test

[0108] The differential scanning calorimetry (DSC) test was performed on the prepared electrolyte and the positive electrode using a DSC2500 differential scanning calorimeter and a TA SDT650 synchronous thermal analyzer. The method is as follows: Place about 5-10 mg of the dry and homogeneous positive electrode sample in an aluminum crucible and mix it with the electrolyte at a mass ratio of 5:2. Use an empty crucible as a reference and place them together on the sample holder. Subsequently, set the heating rate, temperature range, and gas flow rate in the software. After starting the test, the instrument records the heat flow (DSC curve). After the test is completed, perform baseline correction, peak analysis, and calculation of thermal parameters through the supporting software to obtain the thermal characteristics and decomposition behavior of the sample. The results of some embodiments are as Figure 2 shown.

[0109] Figure 2 The results show that there is a violent reaction between Comparative Example 3 and the positive electrode powder at 200 °C, and the peak exothermic power is 8.2 mW / mg. In contrast, the peak exothermic power of Example 1 is 0.77 mW / mg, and the peak exothermic power of Example 8 is 1.62 mW / mg. This shows that the heat release amount of the reaction between the electrolyte and the positive electrode is greatly reduced, and the reaction is basically inhibited.

[0110] (3)Battery thermal box temperature tolerance test

[0111] The prepared soft-pack battery was tested using a battery thermal abuse test chamber BE-8103 instrument in accordance with the national standard GB 38031-2020. The results of some embodiments are shown in Table 4 and Figure 3 shown.

[0112] Table 4

[0113]

[0114] As can be seen from the above Table 4 and Figure 3 it can be seen that when the prepared battery is placed in the battery thermal abuse test chamber BE-8103 and the environmental temperature is increased at a uniform speed of 5 °C per minute, observe the fire and smoke situation of the battery. The soft-pack battery prepared with the lithium-ion battery electrolyte in Comparative Example 3 catches fire and explodes at 130 °C. The soft-pack batteries prepared with the lithium-ion battery electrolyte in Comparative Example 4 and Comparative Example 5 catch fire and explode at 145 °C and 140 °C respectively. However, the thermal box temperature tolerance of the soft-pack batteries prepared with the lithium-ion battery electrolyte in Example 1, Example 7, and Example 8 reaches 270 °C, 222 °C, and 244 °C respectively, with good thermal stability and high safety.

[0115] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, 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, it should be considered as the scope recorded in this specification.

[0116] The embodiments described above merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A lithium ion battery electrolyte, characterized in that: including lithium salt and solvent, The lithium salt includes bis(fluorosulfonyl)imide lithium salt, lithium hexafluorophosphate and lithium salt A; The lithium salt A includes one or more of lithium difluorobisoxalate phosphate, lithium dioxalate borate and lithium difluorophosphate; The solvent includes a highly sterically hindered branched-chain cyclic carbonate and a linear carbonate; The highly sterically hindered branched cyclic carbonate comprises one or both of butylene carbonate and 1,2-butylene carbonate; The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: The concentration of the lithium salt in the lithium ion battery electrolyte is 1 mol / L to 2.7 mol / L.

3. The lithium ion battery electrolyte according to claim 1, characterized in that In the lithium salt, the molar ratio of bis(fluorosulfonyl)imide lithium salt, lithium hexafluorophosphate and lithium salt A is (0.5-1): (0.3-1): (0.1-0.2).

4. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The volume ratio of the high steric hindrance branched cyclic carbonate in the solvent is 10% to 40%.

5. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The volume ratio of the linear carbonate in the solvent is 60% to 90%.

6. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that: The lithium ion battery electrolyte further comprises an additive; Optionally, the additive includes one or both of fluoroethylene carbonate and vinylene carbonate.

7. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The volume proportion of the additive in the total volume of the solvent and the additive is 0% to 10%.

8. A method for preparing a lithium ion battery electrolyte, characterized in that: Mixing a lithium salt and a solvent to prepare the lithium ion battery electrolyte; Wherein, the lithium salt includes bis(fluorosulfonyl)imide lithium salt, lithium hexafluorophosphate and lithium salt A; The lithium salt A includes one or more of lithium difluorobisoxalate phosphate, lithium dioxalate borate and lithium difluorophosphate; The solvent includes a highly sterically hindered branched-chain cyclic carbonate and a linear carbonate; The highly sterically hindered branched cyclic carbonate comprises one or both of butylene carbonate and 1,2-butylene carbonate; The linear carbonate comprises one or both of dimethyl carbonate and diethyl carbonate; Optionally, the preparation method of the lithium-ion battery electrolyte further comprises adding additives.

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 lithium ion batteries.

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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