Electrolyte and lithium ion battery containing the same

Abstract

This application specifically discloses an electrolyte and a lithium-ion battery containing the electrolyte. The electrolyte includes an organic solvent, an electrolyte lithium salt, and a first additive. The first additive has the following structural formula: The first additive introduces Si-O groups into the electrolyte, which can capture water, PF5, HF, etc. in the electrolyte, thereby suppressing the influence of HF on the positive and negative electrode interfaces and improving the stability of the positive and negative electrode interfaces; In addition, unsaturated siloxanes can preferentially decompose into a film on the negative electrode surface to form a silicon-containing and stable interface material, thereby suppressing the occurrence of side reactions and the expansion of the silicon-containing negative electrode, thereby improving the cycle performance and high-temperature storage performance of the lithium-ion battery.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to an electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] Lithium-ion batteries are one of the main energy storage technologies in the new energy market due to their high energy density, portability, high design flexibility, and high safety. Currently, with the development of new energy technologies, the demand for high-energy-density lithium-ion batteries is increasing, and how to improve the energy density of lithium-ion batteries has gradually become a research hotspot.

[0003] Currently, using silicon or silicon-carbon anode materials is the most common way to improve the energy density of lithium-ion batteries. Silicon (Si), as one of the high-capacity anode materials, has attracted widespread attention due to its high theoretical specific capacity of 3579 mAh / g, and is expected to improve the volumetric energy density of lithium-ion batteries. However, Si undergoes significant volume changes during lithium insertion / extraction, leading to particle cracking / pulverization, which affects the cycle life and high-temperature storage performance of lithium-ion batteries. On the other hand, silicon-carbon materials have slow electrochemical kinetics and undergo significant volume expansion during lithium-ion battery cycling. The expanded and pulverized silicon is in an inert state, making silicon-carbon anode materials difficult to apply. Summary of the Invention

[0004] In order to improve the cycle performance and high-temperature storage performance of lithium batteries using silicon-containing anode materials, this application provides an electrolyte and a lithium-ion battery containing the electrolyte.

[0005] In a first aspect, this application provides an electrolyte, which adopts the following technical solution:

[0006] An electrolyte comprises an organic solvent, an electrolyte lithium salt, and a first additive, wherein the structural formula of the first additive is as follows:

[0007]

[0008] First, the electrolyte of this application uses a first additive containing Si-O groups. The Si-O groups can capture water, PF5, HF, etc. in the electrolyte, thereby inhibiting the destructive effect of HF on the positive and negative electrode interface and improving the stability at the positive and negative electrode interface. In addition, unsaturated siloxanes can preferentially decompose into a film on the surface of silicon negative electrode, forming a silicon-containing substance with interface stabilizing effect, inhibiting the occurrence of side reactions at the negative electrode and the expansion effect of silicon-carbon negative electrode, thereby improving the cycle performance and high-temperature storage performance of silicon-containing negative electrode lithium-ion battery. Secondly, the first additive also contains a CN six-membered ring. Each of the three N atoms in the CN six-membered ring has a lone pair of electrons that work synergistically with the carbonyl group, which can enhance the Lewis basicity of the carbonyl group. This allows it to preferentially react with PF5, a byproduct of lithium salt decomposition in the electrolyte system, thereby inhibiting the reaction between PF5 and organic solvents and preventing the organic solvents in the electrolyte system from being consumed during lithium battery cycling. In addition, the synergistic effect of the two can effectively enhance the complexation ability of N with high-valence metal atoms in the positive electrode of the lithium battery, thereby effectively reducing the oxidative decomposition of the positive electrode material on the electrolyte. All of these factors contribute to improving the cycle performance and high-temperature storage performance of silicon-containing negative electrode lithium batteries.

[0009] Preferably, the first additive accounts for 0.5%-3% of the mass of the electrolyte.

[0010] The second additive, in this application, has an insufficient mass proportion in the electrolyte, failing to generate a substance with interfacial stabilizing effect on the silicon-containing anode surface. This affects the stability of the silicon-containing anode interface. Furthermore, the first additive cannot effectively mitigate the reaction between the positive electrode interface and the electrolyte due to its inability to synergize with other additives. Moreover, because of the mutual influence between the positive and negative electrodes, the severe interfacial reaction at the negative electrode also negatively impacts the interfacial stability at the positive electrode, leading to performance degradation of the lithium-ion battery. Conversely, an excessive mass proportion of the first additive in the electrolyte reduces electrolyte stability, hindering the improvement of stability at both the negative and positive electrode interfaces. It also inhibits the performance of other types of additives, negatively impacting electrolyte performance and further reducing the cycle performance of the lithium-ion battery.

[0011] Preferably, it further includes a second additive, which includes at least one of vinyl sulfite, propylene sulfite, fluoroethylene carbonate, and vinylene carbonate.

[0012] Preferably, the second additive includes fluoroethylene carbonate and vinylene carbonate.

[0013] Fluorinated ethylene carbonate and vinylene carbonate have a synergistic effect, generating a dense, uniform, and elastic SEI film rich in more inorganic components. This reduces the reaction at the negative electrode interface, increases the ion conductivity of the SEI film, and thus improves the volume expansion problem of silicon-containing negative electrodes. This helps to improve the cycle stability and high-temperature storage performance of silicon-carbon negative electrode lithium-ion batteries.

[0014] Preferably, the mass percentages of fluoroethylene carbonate and vinylene carbonate in the electrolyte are independently selected from 1.5% to 3.5%.

[0015] Preferably, the mass ratio of fluoroethylene carbonate to vinylene carbonate is 1-2:1-2.

[0016] By controlling the mass percentage of fluoroethylene carbonate and vinylene carbonate in the electrolyte and their mixing ratio, on the one hand, it helps to further improve the stability of the SEI film and reduce side reactions at the negative electrode interface; on the other hand, it helps to improve the stability of the electrolyte, providing a good environmental basis for the first additive to play its role in the electrolyte, thereby further improving the cycle performance of lithium-ion batteries.

[0017] Preferably, the electrolyte lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium difluorosulfonylimide; the electrolyte lithium salt accounts for 10%-15% of the mass of the electrolyte.

[0018] By doping the electrolyte with appropriate types and concentrations of electrolyte lithium salts, it is possible to suppress the dissolution of metal ions at the positive electrode, prevent the dissolved metal ions from damaging the SEI film, and compensate for the consumption of active lithium during the lithium-ion battery cycle. All of these factors contribute to improving the cycle performance of lithium-ion batteries.

[0019] Preferably, the organic solvent includes ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; the mass ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 15-20:10-20:60-65.

[0020] The organic solvents used in this application, by employing a combination of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and controlling the ratio of their amounts, help improve the stability of the electrolyte. This provides a stable environmental basis for the individual and synergistic effects of the first and second additives, thereby enhancing the stability of the electrolyte and also contributing to improving the cycle performance of lithium-ion batteries.

[0021] Secondly, this application provides a lithium-ion battery, which adopts the following technical solution:

[0022] A lithium-ion battery includes a positive electrode, a separator, a negative electrode, and an electrolyte as described above.

[0023] Preferably, the active material of the positive electrode includes at least one of lithium manganese iron phosphate, lithium iron phosphate, and ternary positive electrode materials; the active material of the negative electrode includes at least one of pure silicon material and silicon / carbon composite material.

[0024] Preferably, the diaphragm is a PE diaphragm. Detailed Implementation

[0025] To better understand and implement this application, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of this application, and not all of them.

[0026] 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 application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0027] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0028] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0029] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where there are other unmentioned elements in addition to the mentioned elements.

[0030] All percentages in this application are weight percentages unless otherwise stated.

[0031] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.

[0032] The first additive in the embodiments of this application The CAS number is 26947-14-8.

[0033] Example 1

[0034] 1. Electrolyte and its preparation

[0035] The electrolyte in this embodiment comprises an organic solvent, an electrolyte lithium salt, a second additive, and a first additive in a mass ratio of 81%:12.5%:4%:2.5%.

[0036] The organic solvent consists of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 20:20:60.

[0037] The electrolyte lithium salt is lithium hexafluorophosphate (LiPF6).

[0038] The second additive consists of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a mass ratio of 1:1.

[0039] The preparation steps of the electrolyte are as follows: In an argon atmosphere, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are first mixed to obtain an organic solvent. The prescribed amount of electrolyte lithium salt and the second additive are added to the organic solvent. Finally, the first additive is added and stirred to obtain the electrolyte.

[0040] 2. Preparation of lithium batteries

[0041] The lithium battery of this embodiment includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0042] Preparation of positive electrode sheet: Positive electrode active material (lithium manganese iron phosphate), conductive agent (acetylene black) and binder (PVDF) are prepared into positive electrode slurry in a mass ratio of 94:3:3; the positive electrode slurry is coated on aluminum foil current collector and vacuum dried to obtain positive electrode sheet.

[0043] Preparation of negative electrode sheet: A negative electrode active material (silicon-carbon material), conductive agent (acetylene black), binder (CMC), and binder (SBR) are prepared into a negative electrode slurry in a mass percentage ratio of 94:1:2:3; the negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet.

[0044] After assembling the above-mentioned positive electrode, negative electrode and PE separator to obtain the battery cell, the battery cell is transferred into the casing, and then the electrolyte prepared in this embodiment is injected, formed and volume-adjusted to obtain the lithium-ion battery of this embodiment.

[0045] Example 2

[0046] 1. Electrolyte and its preparation

[0047] The electrolyte in this embodiment comprises an organic solvent, an electrolyte lithium salt, a second additive, and a first additive in a mass ratio of 83%:12.5%:4%:0.5%.

[0048] The organic solvent consists of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 20:20:60.

[0049] The electrolyte lithium salt is lithium hexafluorophosphate (LiPF6).

[0050] The second additive consists of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a mass ratio of 1:1.

[0051] The preparation steps of the electrolyte are as follows: In an argon atmosphere, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are first mixed to obtain an organic solvent. The prescribed amount of electrolyte lithium salt and the second additive are added to the organic solvent. Finally, the first additive is added and stirred to obtain the electrolyte.

[0052] 2. Preparation of lithium batteries

[0053] The lithium battery of this embodiment includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0054] Preparation of positive electrode sheet: Positive electrode active material (lithium manganese iron phosphate), conductive agent (acetylene black) and binder (PVDF) are prepared into positive electrode slurry in a mass ratio of 94:3:3; the positive electrode slurry is coated on aluminum foil current collector and vacuum dried to obtain positive electrode sheet.

[0055] Preparation of negative electrode sheet: A negative electrode active material (silicon-carbon material), conductive agent (acetylene black), binder (CMC), and binder (SBR) are prepared into a negative electrode slurry in a mass percentage ratio of 94:1:2:3; the negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet.

[0056] After assembling the above-mentioned positive electrode, negative electrode and PE separator to obtain the battery cell, the battery cell is transferred into the casing, and then the electrolyte prepared in this embodiment is injected, formed and volume-adjusted to obtain the lithium-ion battery of this embodiment.

[0057] Example 3

[0058] 1. Electrolyte and its preparation

[0059] The electrolyte in this embodiment includes an organic solvent, an electrolyte lithium salt, a second additive, and a first additive in a mass ratio of 77%:15%:6%:2%.

[0060] The organic solvent consists of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 15:20:65.

[0061] The electrolyte lithium salt is lithium hexafluorophosphate (LiPF6).

[0062] The second additive consists of vinyl sulfite ES and propylene sulfite TMS in a mass ratio of 1:1.

[0063] The preparation steps of the electrolyte are as follows: In an argon atmosphere, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are first mixed to obtain an organic solvent. The prescribed amount of electrolyte lithium salt and the second additive are added to the organic solvent. Finally, the first additive is added and stirred to obtain the electrolyte.

[0064] 2. Preparation of lithium batteries

[0065] The lithium battery of this embodiment includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0066] Preparation of positive electrode sheet: Positive electrode active material (lithium manganese iron phosphate), conductive agent (acetylene black) and binder (PVDF) are prepared into positive electrode slurry in a mass ratio of 94:3:3; the positive electrode slurry is coated on aluminum foil current collector and vacuum dried to obtain positive electrode sheet.

[0067] Preparation of negative electrode sheet: A negative electrode active material (silicon-carbon material), conductive agent (acetylene black), binder (CMC), and binder (SBR) are prepared into a negative electrode slurry in a mass percentage ratio of 94:1:2:3; the negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet.

[0068] After assembling the above-mentioned positive electrode, negative electrode and PE separator to obtain the battery cell, the battery cell is transferred into the casing, and then the electrolyte prepared in this embodiment is injected, formed and volume-adjusted to obtain the lithium-ion battery of this embodiment.

[0069] Example 4

[0070] 1. Electrolyte and its preparation

[0071] The electrolyte in this embodiment includes an organic solvent, an electrolyte lithium salt, a second additive, and a first additive in a mass ratio of 86%:12%:1%:3%.

[0072] The organic solvent consists of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 18:22:60.

[0073] The electrolyte lithium salt is lithium hexafluorophosphate (LiPF6).

[0074] The second additive consists of vinyl sulfite ES and fluorovinyl carbonate FEC in a mass ratio of 1:1.

[0075] The preparation steps of the electrolyte are as follows: In an argon atmosphere, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are first mixed to obtain an organic solvent. The prescribed amount of electrolyte lithium salt and the second additive are added to the organic solvent. Finally, the first additive is added and stirred to obtain the electrolyte.

[0076] 2. Preparation of lithium batteries

[0077] The lithium battery of this embodiment includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0078] Preparation of positive electrode sheet: Positive electrode active material (lithium manganese iron phosphate), conductive agent (acetylene black) and binder (PVDF) are prepared into positive electrode slurry in a mass ratio of 94:3:3; the positive electrode slurry is coated on aluminum foil current collector and vacuum dried to obtain positive electrode sheet.

[0079] Preparation of negative electrode sheet: A negative electrode active material (silicon-carbon material), conductive agent (acetylene black), binder (CMC), and binder (SBR) are prepared into a negative electrode slurry in a mass percentage ratio of 94:1:2:3; the negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet.

[0080] After assembling the above-mentioned positive electrode, negative electrode and PE separator to obtain the battery cell, the battery cell is transferred into the casing, and then the electrolyte prepared in this embodiment is injected, formed and volume-adjusted to obtain the lithium-ion battery of this embodiment.

[0081] Example 5

[0082] 1. Electrolyte and its preparation

[0083] The electrolyte in this embodiment differs from that in Example 1 in that the mass fraction of the first additive in the electrolyte is adjusted to 0.1%, and the portion of the electrolyte less than 100% can be obtained by adaptively adjusting the amount of organic solvent (one or more organic solvents can be adjusted). All other steps and parameter settings remain consistent with Example 1.

[0084] 2. Preparation of lithium batteries

[0085] The preparation of the lithium battery is consistent with that in Example 1.

[0086] Example 6

[0087] 1. Electrolyte and its preparation

[0088] The electrolyte in this embodiment differs from that in Example 1 in that the mass fraction of the first additive in the electrolyte is adjusted to 4%, and the portion of the electrolyte less than 100% can be obtained by adaptively adjusting the amount of organic solvent (one or more organic solvents can be adjusted). All other steps and parameter settings remain consistent with Example 1.

[0089] 2. Preparation of lithium batteries

[0090] The preparation of the lithium battery is consistent with that in Example 1.

[0091] Example 7

[0092] 1. Electrolyte and its preparation

[0093] The electrolyte in this embodiment differs from that in Example 1 in that the second additive consists of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a mass ratio of 1:2. All other steps and parameter settings remain consistent with Example 1.

[0094] 2. Preparation of lithium batteries

[0095] The preparation of the lithium battery is consistent with that in Example 1.

[0096] Example 8

[0097] 1. Electrolyte and its preparation

[0098] The electrolyte in this embodiment differs from that in Example 1 in that the second additive consists of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a mass ratio of 2:1. All other steps and parameter settings remain consistent with Example 1.

[0099] 2. Preparation of lithium batteries

[0100] The preparation of the lithium battery is consistent with that in Example 1.

[0101] Example 9

[0102] 1. Electrolyte and its preparation

[0103] The electrolyte in this embodiment differs from that in Example 1 in that the second additive consists of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a mass ratio of 1:7. All other steps and parameter settings remain consistent with Example 1.

[0104] 2. Preparation of lithium batteries

[0105] The preparation of the lithium battery is consistent with that in Example 1.

[0106] Example 10

[0107] 1. Electrolyte and its preparation

[0108] The electrolyte in this embodiment differs from that in Example 1 in that the second additive consists of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a mass ratio of 7:1. All other steps and parameter settings remain consistent with Example 1.

[0109] 2. Preparation of lithium batteries

[0110] The preparation of the lithium battery is consistent with that in Example 1.

[0111] Example 11

[0112] 1. Electrolyte and its preparation

[0113] The electrolyte in this embodiment differs from that in Example 1 in that the second additive consists of vinylene carbonate (VC) and vinyl sulfate (DTD) in a 1:1 mass ratio. All other steps and parameter settings remain consistent with Example 1.

[0114] 2. Preparation of lithium batteries

[0115] The preparation of the lithium battery is consistent with that in Example 1.

[0116] Example 12

[0117] 1. Electrolyte and its preparation

[0118] The electrolyte in this embodiment differs from that in Example 1 in that the second additive consists of vinyl sulfate (DTD) and fluoroethylene carbonate (FEC) in a 1:1 mass ratio. All other steps and parameter settings remain consistent with Example 1.

[0119] 2. Preparation of lithium batteries

[0120] The preparation of the lithium battery is consistent with that in Example 1.

[0121] Example 13

[0122] 1. Electrolyte and its preparation

[0123] The electrolyte in this embodiment differs from that in Example 1 in that the second additive is composed of vinylene carbonate (VC). All other steps and parameter settings remain consistent with Example 1.

[0124] 2. Preparation of lithium batteries

[0125] The preparation of the lithium battery is consistent with that in Example 1.

[0126] Example 14

[0127] 1. Electrolyte and its preparation

[0128] The electrolyte in this embodiment differs from that in Example 1 in that the second additive is composed of fluoroethylene carbonate (FEC). All other steps and parameter settings remain consistent with Example 1.

[0129] 2. Preparation of lithium batteries

[0130] The preparation of the lithium battery is consistent with that in Example 1.

[0131] Comparative Example 1

[0132] 1. Electrolyte and its preparation

[0133] The electrolyte in this comparative example differs from that in Example 1 in that it does not contain the first additive, and the portion of the electrolyte that is less than 100% can be obtained by adaptively adjusting the amount of organic solvent (one or more organic solvents can be adjusted). All other steps and parameter settings remain consistent with Example 1.

[0134] 2. Preparation of lithium batteries

[0135] The preparation of the lithium battery is consistent with that in Example 1.

[0136] Comparative Example 2

[0137] 1. Electrolyte and its preparation

[0138] The electrolyte in this comparative example differs from that in Example 1 in that it does not contain a second additive, and the portion of the electrolyte that is less than 100% can be obtained by adaptively adjusting the amount of organic solvent (one or more organic solvents can be adjusted). All other steps and parameter settings remain consistent with Example 1.

[0139] 2. Preparation of lithium batteries

[0140] The preparation of the lithium battery is consistent with that in Example 1.

[0141] Test methods

[0142] I. Lithium-ion battery cycle performance test

[0143] Charge the lithium-ion battery at 25°C with a constant current of 1C until the voltage reaches 4.5V, then charge it at a constant voltage of 4.5V until the current is ≤0.05C. After resting for 10 minutes, discharge it at a constant current of 1C until the cutoff voltage reaches 2.5V. This constitutes one charge-discharge cycle. Perform 1000 charge-discharge cycles at 25°C under the above conditions, calculate the cycle capacity retention rate of the lithium-ion battery, and record it in Table 1.

[0144] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0145] II. High-Temperature Storage Performance Testing of Lithium-ion Batteries

[0146] The lithium-ion battery was charged to 4.5V at 25℃ using a constant current and constant voltage of 1C, left to stand for 5 minutes, and then discharged to 2.5V at 0.1C. The discharged capacity was recorded as the initial capacity. The battery was then charged to 4.5V again using a constant current and constant voltage of 1C. The initial thickness of the cell and the initial internal resistance of the lithium-ion battery were measured. The lithium-ion battery was then stored in an open circuit at 60℃±2℃ for 30 days. After that, the lithium-ion battery was removed, and the hot thickness was measured. After standing at room temperature for 2 hours, the internal resistance after storage was measured. The cell was then charged and discharged at 1C, and the remaining capacity and recovery capacity were measured. The hot thickness change rate, internal resistance change rate, capacity retention rate, and capacity recovery rate were calculated, and the data were recorded in Table 1.

[0147] Hot thickness change rate (%) = (hot thickness - initial thickness) / initial thickness × 100%;

[0148] Internal resistance change rate (%) = (internal resistance after storage - initial internal resistance) / initial internal resistance × 100%;

[0149] Capacity retention rate (%) = (remaining capacity / initial capacity) × 100%;

[0150] Capacity recovery rate (%) = (recovered capacity / initial capacity) × 100%.

[0151] Table 1

[0152]

[0153]

[0154] Based on Examples 1-4, Comparative Example 1, and Table 1, it can be seen that the addition of the first additive to the electrolyte significantly improves the high-temperature storage performance and cycle performance of the lithium-ion battery. This is because the Si-O groups can capture HF in the electrolyte, avoiding the negative impact of HF on the positive and negative electrode interfaces. Furthermore, the unsaturated siloxane can decompose at the negative electrode surface to generate substances that improve the stability of the SEI film, effectively suppressing silicon expansion. Additionally, the three N atoms in the CN six-membered ring of the first additive work synergistically with the carbonyl group to preferentially react with PF5, a lithium salt decomposition byproduct in the electrolyte system, thereby preventing the PF5 reaction from consuming the organic solvent in the electrolyte. Moreover, it can effectively enhance the complexation ability of N with high-valence metal atoms in the positive electrode of the lithium battery, preventing the positive electrode material from oxidizing and decomposing the electrolyte. All of these contribute to improving the cycle performance of the silicon-containing negative electrode lithium battery, thus significantly improving the high-temperature storage performance and cycle performance of the lithium-ion battery.

[0155] Based on Examples 1-6 and Table 1, it can be seen that when the mass percentage of the first additive in the electrolyte is too low (Example 5), the SEI film formed at the negative electrode is unstable and cannot effectively reduce side reactions, resulting in a decrease in the cycle performance and high-temperature storage performance of the lithium battery. When the mass percentage of the first additive in the electrolyte is too high (Example 6), the interface stability at the positive and negative electrodes deteriorates, which is not conducive to its synergistic effect with other additives, resulting in a decrease in the cycle performance and high-temperature storage performance of the lithium battery. Furthermore, when the mass percentage of the first additive in the electrolyte is 2.5%, the cycle performance and high-temperature storage performance of the lithium-ion battery are even better.

[0156] Based on Examples 1, 7-10 and Table 1, it can be seen that by adjusting the mass ratio of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in the second additive to meet the above ratio limit, it is beneficial to maximize the synergistic effect of the two, ensuring a high content of inorganic components in the SEI film while also having good ion conductivity, which helps to improve the cycle performance and high-temperature storage performance of lithium-ion batteries.

[0157] Combined with Examples 1, Examples 11-14 and Table 1, it can be seen that by using vinylene carbonate (VC) and fluoroethylene carbonate (FEC) as components of the second additive in this application, a dense, uniform and stable SEI film can be generated at the negative electrode interface, which helps to alleviate the expansion of the silicon negative electrode and improve the cycle performance and high-temperature storage performance of the lithium battery.

[0158] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application, but such modifications or substitutions are all within the scope of protection of this application.

Claims

1. An electrolyte, characterized in that: It includes an organic solvent, an electrolyte lithium salt, and a first additive, the structural formula of which is as follows:

2. The electrolyte according to claim 1, characterized in that: The first additive accounts for 0.5%-3% of the mass of the electrolyte.

3. The electrolyte according to any one of claims 1-2, characterized in that: It also includes a second additive, which includes at least one of vinyl sulfite, propylene sulfite, fluoroethylene carbonate, and vinylene carbonate.

4. The electrolyte according to claim 3, characterized in that: The second additive includes fluoroethylene carbonate and vinylene carbonate.

5. The electrolyte according to claim 4, characterized in that: The mass percentages of fluoroethylene carbonate and vinylene carbonate in the electrolyte are independently selected from 1.5% to 3.5%.

6. The electrolyte according to claim 4, characterized in that: The mass ratio of fluoroethylene carbonate to vinylene carbonate is 1-2:1-2.

7. The electrolyte according to claim 1, characterized in that: The electrolyte lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium difluorosulfonylimide. The lithium salt electrolyte accounts for 10%-15% of the total mass of the electrolyte.

8. The electrolyte according to claim 1, characterized in that: The organic solvents include ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; The mass ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 15-20:10-20:60-65.

9. A lithium-ion battery, characterized in that: It includes a positive electrode, a separator, a negative electrode, and an electrolyte as described in any one of claims 1-8.

10. The lithium-ion battery according to claim 9, characterized in that: The active material of the positive electrode includes at least one of lithium manganese iron phosphate, lithium iron phosphate, and ternary positive electrode materials; the active material of the negative electrode includes at least one of pure silicon material and silicon / carbon composite material.

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