Low-temperature electrolyte for lithium ion battery, lithium ion battery and application of low-temperature electrolyte

Abstract

The invention relates to the technical field of lithium ion battery electrolytes, and discloses a low-temperature electrolyte for a lithium ion battery, the lithium ion battery and application of the lithium ion battery. The low-temperature electrolyte for the lithium ion battery is characterized by comprising a lithium salt, an organic solvent, a film-forming additive and a functional additive, according to the volume percentage, the organic solvent accounts for 85%-96%, the film-forming additive accounts for 3%-10%, and the functional additive accounts for 1%-5%. The organic solvent is linear carboxylic ester. In the low-temperature electrolyte for the lithium ion battery, both the linear carboxylic ester and the halogenated linear carboxylic ester contain C = O polar groups, have relatively high dielectric constants and can effectively dissolve lithium salt, so that the electrolyte keeps high ionic conductivity; halogenated linear carboxylic ester is decomposed prior to linear carboxylic ester, and an SEI film rich in lithium halide is formed on the surface of the negative electrode. Compared with an ethylene carbonate-based electrolyte, the lithium halide-rich SEI film formed by the electrolyte provided by the invention is low in impedance, rapid ion transmission is facilitated, and the low-temperature charge-discharge performance of the battery is remarkably improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion battery electrolytes, and particularly relates to a low-temperature electrolyte for lithium-ion batteries, a lithium-ion battery and its applications. Background Art

[0002] In recent years, with the wide application of personal electronic products and electric vehicles, the demand for rechargeable graphite-based lithium-ion batteries has been increasing. However, the operation of graphite-based lithium-ion batteries using conventional carbonate solvents is still a huge challenge under extreme conditions such as low temperature (≤ -20 °C), and they cannot cope with complex working conditions and scenarios such as space exploration, polar scientific research, and energy storage in cold regions.

[0003] Compared with the diffusion of Li + in the graphite bulk phase, the transport of Li + in the solid electrolyte interface (SEI) requires a higher activation energy and is considered the rate-determining step for low-temperature cycling. For commercial ethylene carbonate (EC)-based electrolytes, the strong interaction between Li + and the solvent makes it difficult to desolvate at low temperature, and a large energy barrier needs to be overcome, which leads to severe concentration polarization on the surface of the graphite negative electrode, resulting in a sharp increase in the charge transfer resistance at the graphite negative electrode / electrolyte interface. Therefore, the large voltage hysteresis during Li + insertion leads to the formation of a solvent-derived SEI rich in organic substances, accompanied by continuous interface degradation, including solvent co-intercalation, graphite exfoliation, and active lithium plating, thus causing the battery to experience rapid capacity decay at low temperature.

[0004] In previous studies, by using functional electrolytes such as weakly solvating electrolytes to weaken the bonding between Li + and the solvent, maintaining a low desolvation energy barrier, forming an anion-derived SEI rich in inorganic substances, and promoting interfacial ion transport. However, the weak solvation interaction hinders the complete dissociation of lithium salts, resulting in a decrease in ionic conductivity. How to achieve fast charge transport at the graphite / electrolyte interface while maintaining the advantages of strong bonding between Li + and the solvent is still a difficult scientific challenge in the design of current low-temperature electrolytes. Summary of the Invention

[0005] The present application provides a low-temperature electrolyte for lithium-ion batteries, a lithium-ion battery and its applications, aiming to solve the technical problem of poor low-temperature performance of lithium-ion batteries caused by low conductivity and high impedance of existing ethylene carbonate-based electrolytes at low temperature.

[0006] To achieve the above object, the present application adopts the following technical solutions.

[0007] In the first aspect of the present application, a low-temperature electrolyte for a lithium-ion battery is provided, which includes a lithium salt, an organic solvent, a film-forming additive, and a functional additive; in terms of volume percentage, the organic solvent is 85% - 96%, the film-forming additive is 3% - 10%, and the functional additive is 1% - 5%.

[0008] The organic solvent is a linear carboxylic acid ester.

[0009] Preferably, the lithium salt is any one or a mixture of two or more of sulfonimide lithium salts, phosphate lithium salts, and borate lithium salts.

[0010] Preferably, in the low-temperature electrolyte for a lithium-ion battery, the concentration of the lithium salt is 0.5 mol / L - 5 mol / L.

[0011] Preferably, the linear carboxylic acid ester includes at least one of ethyl acetate, methyl acetate, methyl butyrate, or methyl propionate.

[0012] Preferably, the film-forming additive includes at least one of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, lithium nitrate, lithium difluorophosphate, and lithium difluorooxalate borate.

[0013] Preferably, the functional additive is a halogenated linear carboxylic acid ester.

[0014] More preferably, the structural formula of the halogenated linear carboxylic acid ester is as follows:

[0015]

[0016] Among them, R1 is selected from fluorine, chlorine, or bromine; R2 is selected from methyl or ethyl.

[0017] In the second aspect of the present application, an application of the above low-temperature electrolyte for a lithium-ion battery in a lithium-ion battery is provided.

[0018] In the third aspect of the present application, a lithium-ion battery is provided, which includes a positive electrode, a negative electrode, a separator, and the above low-temperature electrolyte for a lithium-ion battery.

[0019] Preferably, the active material of the positive electrode includes at least one of LiCoO2, LiFePO4, LiMn2O4, or LiNi x Co y Mn z Al 1-x-y- z O2; where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1;

[0020] The active material of the negative electrode includes at least one of carbon, alloy-based negative electrodes, and transition metal oxide / sulfide / phosphide / selenide materials;

[0021] The separator is a PP film.

[0022] Compared with the prior art, the beneficial effects of the present application are as follows:

[0023] The low-temperature electrolyte for lithium-ion batteries of the present application uses linear carboxylic ester solvents as the main solvent and halogenated linear carboxylic esters as functional additives. On the one hand, both linear carboxylic esters and halogenated linear carboxylic esters contain C=O polar groups and have relatively high dielectric constants, which can effectively dissolve lithium salts and keep the electrolyte with high ionic conductivity. On the other hand, halogenated linear carboxylic esters decompose prior to linear carboxylic esters and form a SEI film rich in lithium halide on the surface of the negative electrode by reduction. This SEI film has a low impedance, can accelerate the lithium intercalation kinetics on the surface of graphite, is conducive to rapid ion transport, effectively inhibits the problem of lithium deposition on the negative electrode of lithium-ion batteries under low-temperature conditions, and significantly improves the low-temperature performance of the battery.

[0024] The lithium-ion battery containing the low-temperature electrolyte for lithium-ion batteries of the present application can maintain a high charge-discharge specific capacity in a low-temperature environment, and significantly improves the low-temperature performance of the lithium-ion battery. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is the test results of the conductivity of the electrolytes for Examples 1-4 and Comparative Examples 1-2;

[0027] Figure 2 It is the charge-discharge curves of the lithium-ion half-cells (graphite||Li) assembled with the electrolytes for Examples 1-4 and Comparative Examples 1-2 at different current densities (1C = 372 mAh / g) at room temperature;

[0028] Figure 3 It is the charge-discharge curves of the lithium-ion half-cell (graphite||Li) assembled with the electrolyte of Example 1 at a current density of 0.1C and different temperatures;

[0029] Figure 4 It is the charge-discharge curves of the lithium-ion half-cell (graphite||Li) assembled with the electrolyte of Example 2 at a current density of 0.1C and different temperatures;

[0030] Figure 5 It is the charge-discharge curves of the lithium-ion half-cell (graphite||Li) assembled with the electrolyte of Example 3 at a current density of 0.1C and different temperatures;

[0031] Figure 6 Charge-discharge curves of the lithium-ion half-cell (graphite||Li) assembled with the electrolyte of Example 4 at a current density of 0.1C and different temperatures;

[0032] Figure 7 Charge-discharge curves of the lithium-ion half-cell (graphite||Li) assembled with the electrolyte of Comparative Example 1 at a current density of 0.1C and different temperatures;

[0033] Figure 8 Charge-discharge curves of the lithium-ion half-cell (graphite||Li) assembled with the electrolyte of Comparative Example 2 at a current density of 0.1C and different temperatures.

[0034] Figure 9 Electrochemical impedance spectra of the electrolytes of Example 4, Comparative Example 1 and Comparative Example 2 at room temperature;

[0035] Figure 10 Electrochemical impedance spectra of the electrolytes of Example 4, Comparative Example 1 and Comparative Example 2 at -20°C;

[0036] Figure 11 Charge-discharge capacity diagrams of the lithium iron phosphate (LFP)||graphite soft-pack battery assembled with the electrolyte of Example 4 at different temperatures;

[0037] Figure 12 Charge-discharge capacity diagrams of the lithium iron phosphate (LFP)||graphite soft-pack battery assembled with the electrolyte of Comparative Example 1 at different temperatures;

[0038] Figure 13 Cycling performance diagram of the lithium iron phosphate (LFP)||graphite soft-pack battery assembled with the electrolyte of Example 4 at -20°C. Detailed implementation manners

[0039] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0040] In the following description of this embodiment, the terms "including", "comprising", "having" and "containing" are all open-ended terms, that is, meaning including but not limited to.

[0041] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: the case where A exists alone, the case where B exists alone, and the case where A and B exist simultaneously. Here, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0042] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or its similar expressions refer to any combination of these items, including any combination of single item(s) or plural item(s). For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or plural respectively.

[0043] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0044] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence numbers do not mean the sequence of execution. Some or all of the steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic and should not constitute any limitation to the implementation process of the embodiments of this application.

[0045] Those skilled in the art should understand that the numerical ranges in the embodiments of this application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each intermediate value within any stated value or stated range and each smaller range between any other stated value or intermediate value within the stated range are also included in this application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0046] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0047] In a first aspect, the present application provides a low-temperature electrolyte for a lithium-ion battery, which includes a lithium salt, an organic solvent, a film-forming additive, and a functional additive; in terms of volume percentage, the organic solvent is 85% - 96%, the film-forming additive is 3% - 10%, and the functional additive is 1% - 5%; wherein, the organic solvent is a linear carboxylic acid ester.

[0048] Exemplarily, for the low-temperature electrolyte for a lithium-ion battery of the present application, in terms of volume percentage, the organic solvent is 85%, the film-forming additive is 10%, and the functional additive is 5%, or the organic solvent is 87%, the film-forming additive is 10%, and the functional additive is 3%, or the organic solvent is 96%, the film-forming additive is 3%, and the functional additive is 1%.

[0049] The present application uses a linear carboxylic acid ester solvent to replace ethylene carbonate as the main solvent and a halogenated linear carboxylic acid ester as the functional additive. On the one hand, both the linear carboxylic acid ester and the halogenated linear carboxylic acid ester contain a C=O polar group and have a relatively high dielectric constant, which can effectively dissolve the lithium salt and keep the electrolyte with high ionic conductivity; on the other hand, the halogenated linear carboxylic acid ester is preferentially reduced on the surface of the negative electrode to form a SEI film with fast ion transport rich in inorganic lithium halide on the surface of the negative electrode. This SEI film has a low impedance, can accelerate the lithium intercalation kinetics on the surface of graphite, effectively inhibit the problem of lithium deposition on the negative electrode of the lithium-ion battery under low-temperature conditions, and significantly improve the low-temperature performance of the battery.

[0050] In the present application, the linear carboxylic acid ester includes at least one of ethyl acetate, methyl acetate, methyl butyrate, or methyl propionate, and preferably ethyl acetate.

[0051] In the present application, the lithium salt is any one or a mixture of two or more of sulfonimide lithium salts, phosphate lithium salts, and borate lithium salts, such as at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, or lithium tetrafluoroborate, and preferably lithium hexafluorophosphate. In the low-temperature electrolyte for a lithium-ion battery of the present application, the concentration of the lithium salt is 0.5 mol / L - 5 mol / L.

[0052] In the present application, the film-forming additive includes at least one of fluorinated ethylene carbonate, vinylene carbonate, ethylene sulfate, lithium nitrate, lithium difluorophosphate, or lithium difluorooxalate borate, and preferably fluorinated ethylene carbonate.

[0053] In the present application, the functional additive is a halogenated linear carboxylic acid ester, such as a linear carboxylic acid ester containing one, two, or three halogen substituents, for example, a linear carboxylic acid ester containing one, two, or three fluorine, chlorine, or bromine substituents.

[0054] As a preference, the structural formula of the halogenated linear carboxylic acid ester of the present application is shown as follows:

[0055]

[0056] Among them, R1 is selected from fluorine, chlorine or bromine, and R2 is selected from methyl or ethyl. The halogenated linear carboxylic acid ester is selected from at least one of ethyl fluoroacetate, ethyl chloroacetate or ethyl bromoacetate, and is preferably a mixture of ethyl fluoroacetate, ethyl chloroacetate and ethyl bromoacetate.

[0057] In this application, for the low-temperature electrolyte for lithium-ion batteries, in terms of volume percentage, the dosage of the halogenated linear carboxylic acid ester is more preferably 1-3%.

[0058] The low-temperature electrolyte for lithium-ion batteries of this application not only has a strong bonding effect between the solvent and Li + and can effectively dissolve the lithium salt, keeping the electrolyte with high ionic conductivity; but also enables rapid charge transfer at the graphite / electrolyte interface. The low-temperature electrolyte for lithium-ion batteries of this application can be used as an electrolyte for lithium-ion batteries and can significantly improve the low-temperature performance of lithium-ion batteries.

[0059] This application also provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator and the above-mentioned low-temperature electrolyte for lithium-ion batteries.

[0060] Among them, the active material of the positive electrode can be selected from at least one of LiCoO2, LiFePO4, LiMn2O4 or LiNi x Co y Mn z Al 1-x-y- z O2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x + y + z≤1.

[0061] The active material of the negative electrode can be selected from at least one of carbon materials, alloy negative electrodes, transition metal oxide / sulfide / phosphide / selenide materials. Among them, the carbon materials include at least one of artificial graphite, natural graphite, hard carbon or soft carbon; the alloy negative electrodes include at least one of Si, Sn, Sb, Bi or SnSb; among the transition metal oxide / sulfide / phosphide / selenide materials, the transition metal is at least one of Ni, Mn, Fe, Co, V, Cu or Ti.

[0062] The separator is selected as a PP film, such as Celgard 2500 separator.

[0063] The lithium-ion battery of this application has good low-temperature performance and can be used in low-temperature extreme environments, such as space exploration, polar scientific research, and energy storage in cold regions.

[0064] The following further illustrates this application through examples.

[0065] Example 1

[0066] In a glove box, ethyl acetate, fluoroethylene carbonate, and ethyl fluoroacetate were mixed at a volume ratio of 87:10:3, and then lithium hexafluorophosphate was added to make its concentration 1 mol / L. After stirring for 12 h and mixing evenly, the electrolyte solution was obtained.

[0067] Example 2

[0068] In a glove box, ethyl acetate, fluoroethylene carbonate, and ethyl chloroacetate were mixed at a volume ratio of 87:10:3, and then lithium hexafluorophosphate was added to make its concentration 1 mol / L. After stirring for 12 h and mixing evenly, the electrolyte solution was obtained.

[0069] Example 3

[0070] In a glove box, ethyl acetate, fluoroethylene carbonate, and ethyl bromoacetate were mixed at a volume ratio of 87:10:3, and then lithium hexafluorophosphate was added to make its concentration 1 mol / L. After stirring for 12 h and mixing evenly, the electrolyte solution was obtained.

[0071] Example 4

[0072] In a glove box, ethyl acetate, fluoroethylene carbonate, ethyl fluoroacetate, ethyl chloroacetate, and ethyl bromoacetate were mixed at a volume ratio of 87:10:1:1:1, and then lithium hexafluorophosphate was added to make its concentration 1 mol / L. After stirring for 12 h and mixing evenly, the electrolyte solution was obtained.

[0073] Comparative Example 1

[0074] In a glove box, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 1:1:1, and then lithium hexafluorophosphate was added to make its concentration 1 mol / L. After stirring for 12 h and mixing evenly, the electrolyte solution was obtained.

[0075] Comparative Example 2

[0076] In a glove box, ethyl acetate and fluoroethylene carbonate were mixed at a volume ratio of 90:10, and then lithium hexafluorophosphate was added to make its concentration 1 mol / L. After stirring for 12 h and mixing evenly, the electrolyte solution was obtained.

[0077] The conductivity data of the electrolyte solutions prepared in Examples 1-4 and Comparative Examples 1-2 were tested, and the results are as Figure 1 shown. It can be seen from Figure 1 that the electrolyte solutions with linear carboxylic esters as solvents in this application all have high ionic conductivity at -60 °C. The electrolyte solution with linear carboxylic esters as solvents in Comparative Example 2 also has high ionic conductivity at -60 °C, while the ionic conductivity of the electrolyte solution with ethylene carbonate-based solvent in Comparative Example 1 decreases sharply at low temperature, indicating that the electrolyte solutions in this application have significant advantages at low temperature.

[0078] An assembled lithium-ion half-cell was fabricated and its electrochemical performance was tested to evaluate the electrochemical performance of the electrolytes prepared in Examples 1-4 and Comparative Examples 1-2. Among them, the lithium-ion half-cell used a graphite electrode as the working electrode (the mass ratio of graphite powder, conductive agent and binder was 8:1:1), a lithium foil as the counter electrode, and 50 μL of the electrolytes of Examples 1-4 and Comparative Examples 1-2 were added to assemble a coin cell.

[0079] The assembled lithium-ion half-cell was charged and discharged at different current densities at room temperature to test its rate performance. The test results are shown in Table 1 and Figure 2 as follows.

[0080] Table 1 Test data of lithium-ion half-cell at room temperature and different current densities

[0081]

[0082] It can be seen from Figure 2 and Table 1 that for the lithium-ion half-cell using the electrolyte of the present application, its electrical performance is better than that of the lithium-ion half-cell using the conventional electrolyte in Comparative Example 1, and as the current density increases, the performance gap between the lithium-ion half-cell using the electrolyte of the present application and the lithium-ion half-cell using the conventional electrolyte in the comparative example becomes larger. For the lithium-ion half-cell assembled with the electrolyte of Comparative Example 2, its performance is slightly lower than that of the lithium-ion half-cell assembled with the electrolyte of the present application.

[0083] The assembled lithium-ion half-cell was cycled 5 times at a current density of 0.5C at room temperature, and then placed at different temperatures to test its low-temperature charge and discharge capacity at a current density of 0.1C. Among them, the test adopted constant current charge and discharge, and the voltage range was 0.01V to 2V. The test results are as Figures 3 - 8 follows. Among them, Figures 3 - 8 is the low-temperature charge and discharge test result diagram of the lithium-ion half-cells assembled with the electrolytes of Example 1, Example 2, Example 3, Example 4, Comparative Example 1 and Comparative Example 2. Among them, the low-temperature discharge capacity data of the lithium-ion half-cells assembled with the above electrolytes at -20°C and 0.1C are shown in Table 2.

[0084] Table 2 Discharge capacity of lithium-ion half-cell at -20°C and 0.1C

[0085]

[0086] It can be seen from Figures 3 - 8As can be seen from Table 2, the lithium-ion half-cells using the electrolyte in this application have excellent low-temperature charge and discharge performance, which are all higher than those of the lithium-ion half-cells using the electrolyte without halogenated linear carboxylic esters in Comparative Example 2, and significantly higher than those of the lithium-ion half-cells using the ethylene carbonate-based electrolyte in Comparative Example 1. Under the charge and discharge conditions of 0.1C at -20°C, the lithium-ion half-cells using the electrolyte of this application have a high reversible charge and discharge capacity, indicating that the low-temperature electrolyte of this application effectively improves the charge and discharge performance of lithium-ion batteries at low temperatures. In particular, the electrolyte in Example 4 containing 1% ethyl fluoroacetate + 1% ethyl chloroacetate + 1% ethyl bromoacetate has the optimal performance.

[0087] The electrochemical impedance spectra (EIS) of the electrolytes of Example 4, Comparative Example 1, and Comparative Example 2 were tested at room temperature and low temperature (-20°C) respectively. The EIS test results at room temperature are as Figure 9 shown, and the EIS test results at -20°C are as Figure 10 shown. From Figure 9 and Figure 10 it can be seen that the electrolytes of Example 4 all have the lowest impedance. This is because the halogenated additives preferentially decompose on the surface of the graphite negative electrode to form a SEI rich in inorganic halides, significantly reducing the battery interface impedance.

[0088] Lithium iron phosphate (LFP)||graphite soft-pack batteries were assembled using the electrolytes of Example 4 and Comparative Example 1 respectively. The positive electrode is a lithium iron phosphate electrode (the mass ratio of LFP, conductive agent, and binder is 95:2:3), the negative electrode is a graphite electrode (the mass ratio of graphite powder, conductive agent, and binder is 96:1:3), and the separator uses a Celgard 2500 separator. The charge and discharge capacities of the two batteries at different temperatures were tested, and the test results are as Figure 11 and Figure 12 shown.

[0089] Figure 11 is the charge and discharge capacity curve diagram of the battery assembled with the electrolyte of Example 4 at different temperatures. Its charge and discharge capacity at -10°C is 124.5 mAh / g, maintaining 93% of the room temperature capacity; its charge and discharge capacity at -20°C is 117 mAh / g, maintaining 87% of the room temperature capacity; its charge and discharge capacity at -30°C is 103.6 mAh / g, maintaining 77% of the room temperature capacity, and it has excellent low-temperature performance.

[0090] Figure 12 is the charge and discharge capacity curve diagram of the battery assembled with the electrolyte of Comparative Example 1 at different temperatures. Its charge and discharge capacity at -10°C is 113.9 mAh / g, maintaining 83% of the room temperature capacity; its charge and discharge capacity at -20°C is 79.3 mAh / g, maintaining 58% of the room temperature capacity; its charge and discharge capacity at -30°C is 53 mAh / g, maintaining 38% of the room temperature capacity.

[0091] The battery assembled with the electrolyte of Example 4 was tested for low-temperature cycle performance, and the test results are as follows Figure 13 shown. From Figure 13 it can be seen that the battery assembled with the electrolyte of Example 4 has excellent cycle stability at -20 °C. After 350 charge-discharge cycles at 0.1C, its capacity retention rate is as high as 95.6%, showing excellent low-temperature performance.

[0092] Although this application has been described in detail with general descriptions and specific embodiments in this specification, some modifications or improvements can be made based on this application, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of this application all fall within the scope claimed by this application.

Claims

1. A low-temperature electrolyte for a lithium-ion battery, characterized in that, It includes a lithium salt, an organic solvent, a film-forming additive and a functional additive; by volume percentage, the organic solvent is 85% - 96%, the film-forming additive is 3% - 10%, and the functional additive is 1% - 5%. The organic solvent is a linear carboxylic acid ester.

2. The low-temperature electrolyte for lithium-ion batteries according to claim 1, wherein, The lithium salt is any one or a mixture of two or more of sulfonimide lithium salts, phosphate lithium salts, and borate lithium salts.

3. The low-temperature electrolyte for lithium-ion batteries according to claim 2, characterized in that, In the low-temperature electrolyte for lithium-ion batteries, the concentration of the lithium salt is 0.5 mol / L - 5 mol / L.

4. The low-temperature electrolyte for lithium-ion batteries according to claim 1, wherein The linear carboxylic acid ester includes at least one of ethyl acetate, methyl acetate, methyl butyrate, or methyl propionate.

5. The low-temperature electrolyte for lithium-ion batteries according to claim 1, characterized in that, The film-forming additive includes at least one of fluorinated ethylene carbonate, vinylene carbonate, ethylene sulfate, lithium nitrate, lithium difluorophosphate, and lithium difluorooxalate borate.

6. The low-temperature electrolyte for lithium-ion batteries according to claim 1, wherein The functional additive is a halogenated linear carboxylic acid ester.

7. The low-temperature electrolyte for lithium-ion batteries according to claim 6, wherein The structural formula of the halogenated linear carboxylic acid ester is as follows: Among them, R1 is selected from fluorine, chlorine, or bromine; R2 is selected from methyl or ethyl.

9. Application of the low-temperature electrolyte for lithium-ion batteries according to any one of claims 1 - 7 in a lithium-ion battery.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the low-temperature electrolyte for lithium-ion batteries according to any one of claims 1 - 7.

10. The lithium-ion battery according to claim 9, wherein The active material of the positive electrode includes at least one of LiCoO2, LiFePO4, LiMn2O4 or LiNi x Co y Mn z Al 1-x-y-z O2; Among them, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1; The active material of the negative electrode includes at least one of carbon, alloy-based negative electrodes, and transition metal oxide / sulfide / phosphide / selenide materials; The separator is a PP film.

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