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

Abstract

The application discloses a lithium ion battery electrolyte, a lithium ion battery, a preparation method and application. The provided lithium ion battery electrolyte comprises a lithium salt and a solvent, the lithium salt comprises a lithium bisfluorosulfonylimide salt, lithium hexafluorophosphate and a lithium salt A; the lithium salt A comprises one or more of lithium difluorobisoxalate phosphate, lithium bisoxalate borate and lithium difluorophosphate; the solvent comprises a high steric hindrance branched cyclic carbonate and a linear carbonate; the high steric hindrance branched cyclic carbonate comprises one or both of butylene carbonate and 1,2-butylene carbonate; and the linear carbonate comprises one or both of dimethyl carbonate and diethyl carbonate. The battery prepared from the provided lithium ion battery electrolyte has high thermal stability, cycle performance and rate performance.

Description

Technical Field

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

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

[0003] Therefore, it is necessary to provide a lithium-ion battery electrolyte, lithium-ion battery, preparation method, and application that can take into account thermal stability, cycle life, and rate performance.

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

[0005] The lithium salts include lithium difluorosulfonylimide, lithium hexafluorophosphate, and lithium salt A;

[0006] The lithium salt A includes one or more of lithium difluorobis(oxalato) phosphate, lithium di(oxalato) borate, and lithium difluorophosphate.

[0007] The solvent includes highly sterically hindered branched cyclic carbonates and linear carbonates;

[0008] The high-sterile-barrier branched cyclic carbonate includes one or both of butenyl carbonate and 1,2-butenyl carbonate.

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

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

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

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

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

[0014] In some embodiments, the lithium-ion battery electrolyte also contains additives;

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

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

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

[0018] The lithium salts include 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 di(oxalato) borate, and lithium difluorophosphate.

[0020] The solvent includes highly sterically hindered branched cyclic carbonates and linear carbonates;

[0021] The high-sterile-barrier branched cyclic carbonate includes one or both of butenyl carbonate and 1,2-butenyl carbonate.

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

[0023] Optionally, the preparation method of the lithium-ion battery electrolyte may further include adding additives.

[0024] 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.

[0025] 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.

[0026] The aforementioned lithium-ion battery electrolyte 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. The combined use of these lithium salts reduces the desolvation energy of the high-steric hindrance branched cyclic carbonate solvent, preventing co-intercalation on the graphite anode surface and promoting the formation of a complex solid electrolyte interface (SEI) rich in various components. Simultaneously, the high steric hindrance of the high-steric hindrance branched cyclic carbonate prevents solvent adsorption on the cathode surface, improving safety performance. The high-steric hindrance branched cyclic carbonate improves electrolyte safety and conductivity, while the linear carbonate reduces electrolyte viscosity. The combined use of high-steric hindrance branched cyclic carbonates and linear carbonates improves safety without sacrificing battery durability and rate performance, balancing thermal stability, cycle life, and rate performance. Batteries prepared with the provided lithium-ion battery electrolyte exhibit high thermal stability, cycle life, and rate performance. Attached Figure Description

[0027] 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.

[0028] Figure 1 The following are the elemental distribution maps and carbon elemental distribution maps of the lithium-ion battery electrolytes of Examples 1, 8, and Comparative Example 3, obtained by scanning electron microscopy combined with energy dispersive spectroscopy (EDS). Specifically, (a) is the elemental distribution map of the lithium-ion battery electrolyte of Example 1, (b) is the elemental distribution map of the lithium-ion battery electrolyte of Example 8, (c) is the elemental distribution map of the lithium-ion battery electrolyte of Comparative Example 3, (d) is the carbon elemental distribution map of the lithium-ion battery electrolyte of Example 1, (e) is the carbon elemental distribution map of the lithium-ion battery electrolyte of Example 8, and (f) is the carbon elemental distribution map of the lithium-ion battery electrolyte of Comparative Example 3.

[0029] Figure 2 The graph shows the differential scanning calorimetry test results of the lithium-ion battery electrolyte in Examples 1, 7, and 8.

[0030] Figure 3 Figure 1 shows the battery thermal box temperature tolerance results for the lithium-ion battery electrolytes prepared in Examples 1, 7, and 8. Detailed Implementation

[0031] 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.

[0032] 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.

[0033] 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.

[0034] the term

[0035] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0036] 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."

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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℃.

[0047] 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.

[0048] In this application, "room temperature" generally refers to 5℃~30℃, and more preferably 25±5℃.

[0049] In some embodiments, a lithium-ion battery electrolyte formulation is provided, which achieves a balance between stability, cycle life, and rate performance by optimizing the type of lithium salt and the solvent.

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

[0051] Lithium salts include lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium salt A;

[0052] Lithium salt A includes one or more of lithium difluorobis(oxalato) phosphate, lithium di(oxalato) borate, and lithium difluorophosphate;

[0053] Solvents include sterically hindered branched cyclic carbonates and linear carbonates;

[0054] Highly sterically hindered branched cyclic carbonates include one or both of butenyl carbonate and 1,2-butenyl carbonate.

[0055] Linear carbonates include one or both of dimethyl carbonate and diethyl carbonate.

[0056] The provided lithium-ion battery electrolyte contains both sterically hindered branched cyclic carbonates and linear carbonates in its solvent, which significantly improves the safety and electrochemical performance of high-nickel lithium batteries. The sterically hindered branched cyclic carbonates, primarily composed of one or two of butenyl carbonate and 1,2-butenyl carbonate, have higher activation energies for oxidation reactions, reducing the thermal reaction rate at the electrode surface and thus lowering the risk of thermal runaway. The linear carbonates, primarily composed of one or two of dimethyl carbonate and diethyl carbonate, can reduce electrolyte viscosity. The combined use of sterically hindered branched cyclic carbonates and linear carbonates improves safety without sacrificing battery durability and rate performance, balancing thermal stability, cycle life, and rate performance.

[0057] By using the above lithium salt composites, the desolvation energy of high steric hindrance branched cyclic carbonate solvents can be reduced, preventing co-intercalation on the graphite anode surface. At the same time, it promotes the formation of a complex solid electrolyte interface (SEI) rich in various components. This interface is thin and uniform, suppressing side reactions and reducing interfacial resistance.

[0058] The addition of various lithium salts and high-steric-impedance branched cyclic carbonate solvents significantly improves the conductivity of the electrolyte, achieving good ion conduction performance even in the absence of EC.

[0059] In some embodiments, the concentration of lithium salt in the provided 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, or a range consisting of any two of the aforementioned values.

[0060] In some embodiments, in the provided lithium-ion battery electrolyte, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium salt A is (0.5~1):(0.3~1):(0.1~0.2), 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 consisting of any two of the aforementioned ratios.

[0061] In some embodiments, the volume ratio of high-steric-resistance branched cyclic carbonate in the provided lithium-ion battery electrolyte is 10% to 40%, for example, 10%, 20%, 30%, 40%, or any range of the aforementioned two ratios.

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

[0063] In some implementations, the lithium-ion battery electrolyte also contains additives.

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

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

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

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

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

[0069] Solvents include sterically hindered branched cyclic carbonates and linear carbonates;

[0070] Highly sterically hindered branched cyclic carbonates include one or both of butenyl carbonate and 1,2-butenyl carbonate.

[0071] Linear carbonates include one or both of dimethyl carbonate and diethyl carbonate.

[0072] In some embodiments, the preparation method of the provided lithium-ion battery electrolyte further includes the addition of additives.

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

[0074] 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 a preparation method.

[0075] The following are specific embodiments. They are intended to provide a more detailed description of this application to help those skilled in the art and researchers better understand it. The technical conditions described do not constitute any limitation on this application. Any modifications made within the scope of the claims of this application are protected by the claims.

[0076] Unless otherwise stated, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods. Experimental methods not specifying particular conditions in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

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

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

[0079] The formulations of the lithium-ion battery electrolytes in 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 difluorobis(oxalato)phosphate, LiFSI is lithium difluorosulfonylimide, LiBOB is lithium di(oxalato)borate, LiPO2F2 is lithium difluorophosphate, LiTFSI is lithium bis(trifluoromethane)sulfonylimide, EC is ethylene carbonate, and EMC is methyl ethyl carbonate.

[0083] The preparation method of lithium-ion battery electrolyte is as follows: lithium salt, high steric hindrance branched cyclic carbonate, linear carbonate and additives are mixed to obtain lithium-ion battery electrolyte.

[0084] II. Electrochemical Performance Testing

[0085] (1) Battery fabrication:

[0086] The QH02-Ni90 / SiC-15 battery cell purchased from Dongguan Kelude New Energy Technology Co., Ltd. was used to inject the lithium-ion battery electrolyte of the examples and comparative examples 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.

[0087] (2) Battery cycle performance and rate performance test

[0088] The batteries prepared with the lithium-ion battery electrolytes in the examples and comparative examples were tested using a Neware BTS4000 instrument as follows. The prepared batteries were cycled at a current of 0.33A, and the charging capacity was recorded. Then, an initial discharge was performed at 0.33A, and the discharge capacity was recorded. The discharge capacity of the batteries after multiple cycles was recorded, and the capacity retention rate (i.e., battery durability) was calculated for different cycle numbers. The battery discharge capacity was recorded at 25°C and at 0.33A, 1A, 2A, and 3A, and the capacity retention rate (i.e., rate performance) was calculated for different rate operations. The test results for some examples and comparative examples are shown in Tables 2-1 and 2-2. The formulas for calculating capacity retention rate and cycle performance are as follows:

[0089] Capacity retention rate for different number of cycles = discharge capacity after cycle / 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 counts

[0092]

[0093] As shown in Table 2-1, Example 1 exhibited excellent capacity retention throughout the cycling process. At 200 cycles, its capacity retention rate was 98.24%, and it remained at 89.99% after 1200 cycles, demonstrating slow capacity decay and good cycling stability. In contrast, Comparative Example 3 initially maintained a slightly lower capacity retention rate of 96.45% at the beginning of the cycle (200 cycles), but its capacity rapidly decreased with increasing cycle count, dropping to 88.39% at only 600 cycles, falling below 80% after 800 cycles, and reaching only 54.75% after 1200 cycles. This indicates that the electrolyte system of Comparative Example 3 exhibited significant capacity decay during long-term cycling.

[0094] Table 2-2 Capacity retention rate at different magnification ratios

[0095]

[0096] As can be seen from the rate performance data listed in Table 2-2, Example 1 exhibits good capacity retention at different rates. At 0.33C, the capacity retention rate of Example 1 is 100.14%, close to the theoretical capacity; at 1C, 2C, and 3C, the capacities are 92.53%, 84.84%, and 72.97%, respectively, demonstrating strong rate adaptability and electrochemical stability. In contrast, Comparative Example 3 also has relatively high capacity retention rates at low rates (0.33C and 1C), at 100.84% ​​and 93.61%, respectively, but at high rates (2C and 3C), its capacity rapidly decreases to 83.13% and 68.90%, respectively, with a higher degree of degradation than Example 1. These results indicate that Example 1 can 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, mitigate polarization, and thus enhance the battery's rate performance and fast discharge capability.

[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 solvent and dried to remove any impurities that might have remained from the previous measurement. The cleaned conductivity probe was then inserted into the electrolyte solution to be tested, and the conductivity value was recorded in millisiemens per centimeter (mS / cm). To ensure the accuracy of the test results, each electrolyte was tested at least twice, and the average value was taken to eliminate the influence of testing errors.

[0099] The results are shown in Table 3.

[0100] Table 3

[0101]

[0102] As shown in Table 3, the lithium-ion batteries prepared with the provided lithium-ion battery electrolyte have high conductivity.

[0103] III. Safety Performance Testing

[0104] (1) Electrolyte adsorption capacity test for positive electrode

[0105] To investigate the adsorption behavior of the electrolyte on the surface of the cathode material under high-temperature conditions, the prepared electrolyte was mixed uniformly with the cathode material NMC811 at a mass ratio of 2:5, placed in an aluminum crucible, and heated to 400°C under an inert gas atmosphere. The mixture was held at this temperature for a period of time to simulate possible reactions between the electrode and electrolyte during thermal runaway. After heating, the crucible was allowed to cool naturally to room temperature, and the residual solid product was removed for surface morphology and composition analysis. The cathode particles of the heated product were characterized using Zeiss Merlin scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). Results of some embodiments are shown below. Figure 1 As shown, (a) is the elemental distribution map of the lithium-ion battery electrolyte of Example 1 obtained by scanning electron microscopy combined with energy dispersive spectroscopy, (b) is the elemental distribution map of the lithium-ion battery electrolyte of Example 8 obtained by scanning electron microscopy combined with energy dispersive spectroscopy, (c) is the elemental distribution map of the lithium-ion battery electrolyte of Comparative Example 3 obtained by scanning electron microscopy combined with energy dispersive spectroscopy, (d) is the carbon elemental distribution map of the lithium-ion battery electrolyte of Example 1, (e) is the carbon elemental distribution map of the lithium-ion battery electrolyte of Example 8, and (f) is the carbon elemental distribution map of the lithium-ion battery electrolyte of Comparative Example 3. Figure 1 In the diagram, the scales of (a), (b), (d), and (e) are 25 μm, and the scales of (c) and (f) are 50 μm.

[0106] analyze Figure 1 The results showed that the carbon content of Example 1 was 12.63%wt, the carbon content of Example 8 was 14.23%wt, and the carbon content of Comparative Example 3 was 27.80%wt. The adsorbed carbon layer formed on the positive electrode surface by the residue of the electrolyte after heating in Examples 1 and 8 was significantly thinner, and the carbon content was also significantly lower than that in Comparative Example 3, indicating that these compounds are not easily adsorbed and reacted with on the positive electrode surface under high temperature conditions.

[0107] (2) Differential scanning calorimetry

[0108] The prepared electrolyte and positive electrode were tested using a DSC2500 differential scanning calorimeter and a TA SDT650 simultaneous thermal analyzer. The method was as follows: Approximately 5–10 mg of dried and uniformly prepared positive electrode sample was placed in an aluminum crucible and mixed with the electrolyte at a mass ratio of 5:2. An empty crucible was used as a reference, and both were placed in a sample holder. The heating rate, temperature range, and atmosphere flow rate were then set in the software. After starting the test, the instrument recorded the heat flow (DSC curve). After the test, baseline correction, peak analysis, and thermal parameter calculations were performed using the accompanying software to obtain the thermal characteristics and decomposition behavior of the sample. Results from some examples are shown below. Figure 2 As shown.

[0109] Figure 2 The results showed that Comparative Example 3 exhibited a vigorous reaction with the cathode powder at 200℃, with a peak exothermic power of 8.2 mW / mg. In contrast, the peak exothermic power of Example 1 was 0.77 mW / mg, and that of Example 8 was 1.62 mW / mg. This indicates that the exothermic reaction between the electrolyte and the cathode was significantly reduced, and the reaction was essentially suppressed.

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

[0111] The prepared soft-pack batteries were tested using a BE-8103 battery thermal abuse test chamber according to the national standard GB 38031-2020. Results from some examples are shown in Table 4. Figure 3 As shown.

[0112] Table 4

[0113]

[0114] From Table 4 above and Figure 3 As can be seen, when the prepared batteries were placed in the battery thermal abuse test chamber BE-8103 and the ambient temperature was increased uniformly at a 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 3 caught fire and exploded at 130°C. The soft-pack batteries prepared with the lithium-ion battery electrolytes in Comparative Examples 4 and 5 caught fire and exploded at 145°C and 140°C, respectively. However, the soft-pack batteries prepared with the lithium-ion battery electrolytes in Examples 1, 7, and 8 withstood the thermal chamber temperatures of 270°C, 222°C, and 244°C, respectively, showing good thermal stability and high safety.

[0115] 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.

[0116] 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 solvents, The lithium salts include lithium difluorosulfonylimide, lithium hexafluorophosphate, and lithium salt A; The lithium salt A includes one or more of lithium difluorobis(oxalato) phosphate, lithium di(oxalato) borate, and lithium difluorophosphate. The solvent includes highly sterically hindered branched cyclic carbonates and linear carbonates; The high-sterile-barrier branched cyclic carbonate includes one or both of butenyl carbonate and 1,2-butenyl carbonate. The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate; The concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L to 2.7 mol / L; In the lithium salt, the molar ratio of lithium difluorosulfonylimide, lithium hexafluorophosphate, and lithium salt A is (0.5~1):(0.3~1):(0.1~0.2). The high-resistance branched cyclic carbonate in the solvent is 10% to 40% by volume. The linear carbonate in the solvent is 60% to 90% by volume.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium-ion battery electrolyte also contains additives.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that, The additives include one or both of fluoroethylene carbonate and vinylene carbonate.

4. The lithium-ion battery electrolyte according to claim 2 or 3, characterized in that, The volume percentage of the additive in the total volume of the solvent and the additive is 0% to 10%.

5. A method for preparing a lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte is prepared by mixing lithium salt and solvent. The lithium salts include lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium salt A; The lithium salt A includes one or more of lithium difluorobis(oxalato) phosphate, lithium di(oxalato) borate, and lithium difluorophosphate. The solvent includes highly sterically hindered branched cyclic carbonates and linear carbonates; The high-sterile-barrier branched cyclic carbonate includes one or both of butenyl carbonate and 1,2-butenyl carbonate. The linear carbonate includes one or both of dimethyl carbonate and diethyl carbonate; The concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L to 2.7 mol / L; In the lithium salt, the molar ratio of lithium difluorosulfonylimide, lithium hexafluorophosphate, and lithium salt A is (0.5~1):(0.3~1):(0.1~0.2). The high-resistance branched cyclic carbonate in the solvent is 10% to 40% by volume. The linear carbonate in the solvent is 60% to 90% by volume.

6. The method for preparing the lithium-ion battery electrolyte according to claim 5, characterized in that, The preparation method of the lithium-ion battery electrolyte also includes the addition of additives.

7. The method for preparing the lithium-ion battery electrolyte according to claim 6, characterized in that, The additives include one or both of fluoroethylene carbonate and vinylene carbonate.

8. The method for preparing the lithium-ion battery electrolyte according to claim 6 or 7, characterized in that, The volume percentage of the additive in the total volume of the solvent and the additive is 0% to 10%.

9. The application of the lithium-ion battery electrolyte according to any one of claims 1 to 4 or the lithium-ion battery electrolyte prepared by the preparation method according to any one of claims 5 to 8 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a lithium-ion battery electrolyte as described in any one of claims 1 to 4 or a lithium-ion battery electrolyte prepared by the preparation method described in any one of claims 5 to 8.

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