Lithium ion battery electrolyte and application thereof

Abstract

The invention provides a lithium ion battery electrolyte and an application thereof. The electrolyte at least comprises the following components: a lithium salt; the solvent comprises a first solvent, and the first solvent comprises at least one of fluorocarboxylic acid esters; and an additive, the additive comprising a first additive, the first additive comprising 2-(thiophenyl) ethyl acrylate. The lithium ion battery electrolyte provided by the invention can promote rapid transmission of lithium ions, reduce side reactions and improve the high-temperature cyclic gas production performance of the battery in a high-voltage rapid charging scene.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a lithium-ion battery electrolyte and applications thereof. Background Art

[0002] As one of the key technologies to improve the fast charging performance of lithium-ion batteries, the fast charging electrolyte system includes high-concentration electrolytes, new solvents (such as fluorinated carbonates), functional additives (such as lithium salts and film-forming additives) and solid / semi-solid electrolytes. Although it can significantly improve the charging speed of the battery while taking into account the cycle life and safety of the battery, it will lead to limited lithium ion transfer and affect the low-temperature performance of the battery; it will also cause battery performance degradation due to the accumulation of side reactions; and the performance stability of the fast charging electrolyte system is insufficient in high and low temperature environments, which together limit the application of the fast charging electrolyte system under complex working conditions. Summary of the Invention

[0003] The present invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by the present invention can promote the rapid transfer of lithium ions, reduce the occurrence of side reactions, and improve the high-temperature cycle gas production performance of the battery under high-voltage fast charging scenarios.

[0004] To solve the above technical problems, the present invention provides a lithium-ion battery electrolyte comprising at least the following components:

[0005] lithium salts;

[0006] a solvent comprising a first solvent comprising at least one of a fluorocarboxylate; and

[0007] The additives include a first additive including 2-(phenylthio)ethyl acrylate.

[0008] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1 wt%-3 wt%.

[0009] In one embodiment of the present invention, the fluorocarboxylic acid ester includes at least one of methyl trifluoroacetate or ethyl difluoropropionate.

[0010] In one embodiment of the present invention, the content of the first solvent in the electrolyte is 10 wt %-20 wt %.

[0011] In one embodiment of the present invention, the mass ratio of the first solvent to the first additive is (10-20):1.

[0012] In one embodiment of the present invention, the additive further includes a second additive, and the second additive includes lithium tetrafluoroborate.

[0013] In one embodiment of the present invention, the content of the second additive in the electrolyte is 0.2 wt %-2 wt %.

[0014] In one embodiment of the present invention, the solvent further includes a second solvent, the second solvent includes at least one of ethylene carbonate, dimethyl carbonate or ethyl methyl carbonate, and the lithium salt includes at least one of lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide.

[0015] The present invention also provides a lithium ion battery, comprising at least:

[0016] The positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material includes a ternary positive electrode material, and the structural formula of the ternary positive electrode material is Li a Ni 1-x-y-z Co x Mn y Al z O 2-b , where 0.95≤a≤1.10, 0≤b≤0.2, 0≤x≤1, 0≤y≤1, 0≤z≤1 and 0 <x+y+z<1;

[0017] A negative electrode plate, comprising a negative electrode active material, wherein the negative electrode active material comprises a silicon-carbon material;

[0018] a separator, disposed between the positive electrode sheet and the negative electrode sheet; and

[0019] The electrolyte is selected from the above-mentioned lithium ion battery electrolyte.

[0020] In one embodiment of the present invention, the content of the silicon-carbon material in the negative electrode active material is 1 wt%-8 wt%.

[0021] In summary, the present invention proposes a lithium-ion battery electrolyte and its application. The first solvent can improve the antioxidant capacity of the electrolyte, so that the electrolyte remains stable under high voltage conditions, and reduce the occurrence of side reactions, thereby extending the service life of the battery. The first additive can prevent the dissolution of transition metal ions in the positive electrode material under high temperature and high pressure conditions, promote the rapid transfer of lithium ions, and reduce the impedance of the battery. The first solvent and the first additive act synergistically to jointly improve the fast charging performance and high-temperature cycle gas production performance of the battery. The first additive and the second additive act synergistically to reduce the battery impedance, inhibit battery lithium precipitation, improve the fast charging performance of the battery, and take into account the high-temperature cycle gas production performance of the battery. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0024] The technical solutions of the present invention are further described in detail below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] The present invention proposes a lithium-ion battery electrolyte, which at least includes a lithium salt, a solvent and an additive, wherein the solvent includes a first solvent, the first solvent includes at least one of fluorocarboxylic acid esters, and the additive includes a first additive, the first additive includes 2-(phenylthio)ethyl acrylate. In the lithium-ion battery electrolyte provided by the present invention, the first solvent can improve the antioxidant capacity of the electrolyte, so that the electrolyte remains stable under high voltage conditions, and reduces the occurrence of side reactions, thereby extending the service life of the battery. The first additive can prevent the dissolution of transition metal ions in the positive electrode material under high temperature and high pressure conditions, promote the rapid transfer of lithium ions, and reduce the impedance of the battery. The first solvent and the first additive act synergistically and can jointly improve the fast charging performance and high-temperature cycle gas production performance of the battery.

[0026] In one embodiment of the present invention, the fluorocarboxylate in the first solvent includes at least one of methyl trifluoroacetate or ethyl difluoropropionate. The high electronegativity of the fluorine atoms in the fluorocarboxylate can make the electrolyte have a stronger antioxidant capacity, so that the electrolyte can remain stable in a high voltage environment, reduce the occurrence of side reactions, and thus extend the service life of the battery. The content of the first solvent in the electrolyte is, for example, 10wt%-20wt%. By controlling the content of the first solvent, it is possible to take into account both the fast charging performance and the high-temperature cycle gas production performance of the battery.

[0027] In one embodiment of the present invention, the solvent further includes a second solvent, and the second solvent includes, for example, at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC). The present invention does not limit the mass ratio between the multiple second solvents, and can be selected according to actual needs.

[0028] In one embodiment of the present invention, the first additive 2-(phenylsulfanyl)ethyl acrylate (PTEA) can be used as a thiocarboxylate. Compared with carbonate solvents, PTEA has a higher highest occupied molecular orbital (HOMO) energy level and is better than carbonate solvents in electrochemical oxidation. Moreover, PTEA can form a uniform solid electrolyte interface (Cathode Electrolyte Interface, CEI) layer at the interface between the positive electrode and the electrolyte, effectively protecting the positive electrode material and preventing the dissolution of transition metal ions in the positive electrode material under high temperature and high pressure conditions. In addition, the phenyl and carboxylate groups in the PTEA molecular structure help to form a dense interface film, and the introduction of sulfur elements can change the polymer structure of the molecule and induce the formation of a network cross-linked structure, thereby promoting the rapid transfer of lithium ions and reducing battery impedance. However, when PTEA is used alone, its antioxidant capacity is limited and it is difficult to meet the needs of high-voltage systems. Therefore, the present application combines PTEA and the first solvent to synergize, which can not only significantly improve the ion conductivity of the electrolyte, but also enhance the antioxidant properties of the electrolyte system, thereby achieving better battery performance and jointly improving the battery's high-temperature cycle gas production performance and fast charging performance.

[0029] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.1wt%-3wt%, and further, for example, 0.5wt%-1wt%. Furthermore, the mass ratio of the first solvent to the first additive is, for example, (10-20):1. By controlling the content of the first additive and the mass ratio of the first solvent to the first additive, it is possible to balance the fast charging performance and high-temperature cycle gas production performance of the battery.

[0030] In one embodiment of the present invention, the additive further includes a second additive, and the second additive includes, for example, lithium tetrafluoroborate (LiBF4). The second additive and the first additive act synergistically to further improve the impedance, fast charging performance, and high-temperature cycle gas production performance of the battery. The content of the second additive in the electrolyte is, for example, 0.2wt%-2wt%. By controlling the content of the second additive, the fast charging performance and high-temperature cycle gas production performance of the battery can be taken into account.

[0031] In one embodiment of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide, and the content of the lithium salt in the electrolyte is, for example, 10 wt% to 18 wt%.

[0032] In one embodiment of the present invention, when preparing the electrolyte, a first solvent and a second solvent are mixed uniformly in a glove box with a stable gas atmosphere such as argon gas in a certain mass ratio to obtain a solvent. A lithium salt and an additive are then added to the solvent and mixed uniformly to prepare a lithium-ion battery electrolyte. The moisture content in the glove box is, for example, less than 10 ppm.

[0033] The present invention also provides a lithium-ion battery, which includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The separator is located between the positive electrode sheet and the negative electrode sheet to prevent short circuits between the positive and negative electrode sheets, allowing lithium ions to pass through. The electrolyte is filled between the positive electrode sheet, the separator, and the negative electrode sheet, and the electrolyte is the above-mentioned lithium-ion battery electrolyte, which acts as an ion conductor. The lithium-ion battery can be, for example, a primary battery or a secondary battery, and the secondary battery can be, for example, a soft-pack battery, a hard-shell battery, or a cylindrical battery. The present invention does not specifically limit the type and type of lithium-ion battery.

[0034] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer coated on at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a surface-treated foil of nickel, titanium, aluminum, silver, stainless steel, or carbon. In addition to foil, the positive electrode current collector may also be in the form of a film, mesh, porous material, foam, or non-woven fabric, among other forms, or any combination thereof.

[0035] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder. The ratio of the positive electrode active material, the conductive agent, and the binder can be selected according to actual needs. The positive electrode active material includes, for example, a ternary positive electrode material. The general structural formula of the ternary positive electrode material is Li a Ni 1-x-y-z Co x Mn y Al z O 2-b, where 0.95≤a≤1.10, 0≤b≤0.2, 0≤x≤1, 0≤y≤1, 0≤z≤1 and 0 <x+y+z<1。

[0036] In one embodiment of the present invention, the conductive agent is, for example, selected from at least one of conductive carbon black (SuperP), acetylene black, carbon nanotubes, or graphene, and the binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), or polyhexafluoropropylene.

[0037] In one embodiment of the present invention, the positive electrode current collector is, for example, aluminum foil, and the positive electrode active material has a general structural formula of, for example, LiNi 0.6 Mn 0.2 Co 0.2 O2, a conductive agent such as acetylene black, and a binder such as PVDF. The positive electrode active material, conductive agent, and binder are mixed in a mass ratio of, for example, 95:3:2, dissolved in an organic solvent, and stirred in a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, dried at room temperature, and then transferred to an oven for drying. The positive electrode sheet is obtained through processes such as roller pressing and cutting. The organic solvent is, for example, N-methylpyrrolidone (NMP).

[0038] In one embodiment of the present invention, the negative electrode plate includes, for example, a negative electrode current collector and a negative electrode active layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is, for example, selected from a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector.

[0039] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. The ratio of the negative electrode active material, the conductive agent, and the binder can be selected based on actual needs. In this embodiment, the negative electrode active material includes a silicon-carbon material and graphite, wherein the silicon-carbon material includes silicon carbide, for example. The content of the silicon-carbon material in the negative electrode active material is, for example, 1 wt% to 8 wt%, and the content of the graphite in the negative electrode active material is, for example, 92 wt% to 99 wt%.

[0040] In one embodiment of the present invention, the binder is selected from at least one of polypropylene, polyacrylate, polyvinyl ether, PMMA, polyhexafluoropropylene, or styrene butadiene rubber (SBR). The conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, or graphene. The thickener is selected from sodium carboxymethyl cellulose (CNC-Na).

[0041] In one embodiment of the present invention, the negative electrode current collector is, for example, copper foil, the negative electrode active material is, for example, a mixture of silicon carbide and graphite, the silicon carbide content in the mixture is, for example, 5wt%, the conductive agent is, for example, acetylene black, the thickener is, for example, CNC-Na, and the binder is, for example, SBR. Specifically, the negative electrode active material, conductive agent, thickener, and binder are mixed in a mass ratio of 96.5:1:1:1.5, and deionized water is added as a solvent. The mixture is then thoroughly stirred and mixed in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is then coated on copper foil, dried at room temperature, and then transferred to an oven for drying. After rolling and cutting, a negative electrode sheet is obtained.

[0042] In one embodiment of the present invention, the separator is, for example, a conventional separator, a ceramic separator, a polymer separator, a non-woven fabric, or an inorganic-organic composite separator. Specifically, the separator is, for example, a single-layer polypropylene (PP) film, a single-layer polyethylene (PE) film, a double-layer PP / PE film, a double-layer PP / PP film, or a triple-layer PP / PE / PP film. In this embodiment, a single-layer PP film is selected as the separator.

[0043] In one embodiment of the present invention, the above-mentioned positive electrode sheet, separator and negative electrode sheet are placed in sequence, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, and are enclosed in an aluminum-plastic film to obtain a dry battery cell. The dry battery cell is then baked at 80°C to remove water, and the electrolyte is injected into the dry battery cell and packaged to obtain a lithium-ion battery.

[0044] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0045] Example 1

[0046] Preparation of positive electrode: LiNi 0.6 Mn 0.2 Co 0.2O2, acetylene black and PVDF are mixed in a mass ratio of 95:3:2, dissolved in NMP organic solvent, and stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, and then dried at room temperature and transferred to an oven for drying. The positive electrode sheet is obtained through processes such as rolling and cutting.

[0047] Preparation of the negative electrode sheet: Silicon carbide and graphite are mixed to obtain a negative electrode active material, with the silicon carbide content in the negative electrode active material being 5wt%. The negative electrode active material, acetylene black, CNC-Na, and SBR are mixed in a mass ratio of 96.5:1:1:1.5, and deionized water is added. The mixture is then thoroughly stirred in a vacuum mixer to obtain a negative electrode slurry. The slurry is then coated onto copper foil, air-dried at room temperature, and then oven-dried. The negative electrode sheet is obtained through roll pressing and cutting.

[0048] Preparation of the electrolyte: In an argon atmosphere glove box with a moisture content of less than 1 ppm, EC, DMC, and EMC were mixed in a mass ratio of 3:5:2 to obtain a second solvent. Methyl trifluoroacetate, the first solvent, was then added and mixed to obtain a solvent. Following the electrolyte composition described in Table 1, the first additive, PTEA, and the lithium salt, LiPF6, were added to the solvent and mixed to prepare a lithium-ion battery electrolyte. The concentrations of methyl trifluoroacetate, PTEA, and LiPF6 in the electrolyte were 15 wt%, 0.1 wt%, and 12 wt%, respectively.

[0049] Selection of diaphragm: Choose single-layer PP film as the diaphragm.

[0050] Preparation of the battery: The positive electrode, separator and negative electrode are placed in sequence and enclosed in an aluminum-plastic film to obtain a dry cell. The dry cell is then baked at 80°C to remove water, and the electrolyte is injected into the dry cell and encapsulated to obtain a lithium-ion battery.

[0051] Example 2

[0052] The content of PTEA in the electrolyte was 0.5 wt %. Other steps were the same as those in Example 1.

[0053] Example 3

[0054] The content of PTEA in the electrolyte was 1 wt %. Other steps were the same as those in Example 1.

[0055] Example 4

[0056] The content of PTEA in the electrolyte was 3 wt %. Other steps were the same as those in Example 1.

[0057] Example 5

[0058] The content of PTEA in the electrolyte was 5 wt %. Other steps were the same as those in Example 1.

[0059] Example 6

[0060] The content of PTEA in the electrolyte was 0.05 wt %. Other steps were the same as those in Example 1.

[0061] Example 7

[0062] The content of methyl trifluoroacetate in the electrolyte was 10 wt %. Other steps were the same as those in Example 3.

[0063] Example 8

[0064] The content of methyl trifluoroacetate in the electrolyte was 20 wt %. Other steps were the same as those in Example 3.

[0065] Example 9

[0066] The content of methyl trifluoroacetate in the electrolyte was 30 wt %. Other steps were the same as those in Example 3.

[0067] Example 10

[0068] The content of methyl trifluoroacetate in the electrolyte was 5 wt %. Other steps were the same as those in Example 3.

[0069] Example 11

[0070] The first solvent is ethyl difluoropropionate, and the other steps are the same as in Example 3.

[0071] Example 12

[0072] The first solvent includes methyl trifluoroacetate and ethyl difluoropropionate, and the contents of methyl trifluoroacetate and ethyl difluoropropionate in the electrolyte are both 10 wt %. Other steps are the same as those in Example 3.

[0073] Example 13

[0074] The electrolyte further contains a second additive, LiBF 4 , and the content of LiBF 4 in the electrolyte is 0.2 wt %. The other steps are the same as those in Example 3.

[0075] Example 14

[0076] The content of LiBF4 in the electrolyte is 0.8 wt %, and the other steps are the same as those in Example 13.

[0077] Example 15

[0078] The content of LiBF4 in the electrolyte is 2 wt %, and the other steps are the same as those in Example 13.

[0079] Example 16

[0080] The content of LiBF4 in the electrolyte is 0.1 wt%, and the other steps are the same as those in Example 13.

[0081] Example 17

[0082] The content of LiBF4 in the electrolyte is 3 wt %, and the other steps are the same as those in Example 13.

[0083] Example 18

[0084] The electrolyte also contains a second additive LiBF4, and the content of LiBF4 in the electrolyte is 0.8 wt%. The other steps are the same as those in Example 12.

[0085] Comparative Example 1

[0086] The electrolyte does not contain the first additive PTEA, and the other steps are the same as those in Example 3.

[0087] Comparative Example 2

[0088] The electrolyte does not contain the first solvent methyl trifluoroacetate, and the other steps are the same as those in Example 3.

[0089] Comparative Example 3

[0090] The electrolyte does not contain the first additive PTEA, and the other steps are the same as those in Example 14.

[0091] Comparative Example 4

[0092] The electrolyte does not contain the first additive PTEA, but contains the additive tetravinylsilane (TVSi), and the content of TVSi in the electrolyte is 1 wt %. Other steps are the same as those in Example 1.

[0093] Comparative Example 5

[0094] The electrolyte does not contain the first additive PTEA, but contains the additive TVSi, and the content of TVSi in the electrolyte is 1 wt %. Other steps are the same as those in Example 2.

[0095] The raw material component contents and raw material mass ratios required for the electrolytes prepared in the examples and comparative examples are shown in Table 1. The content of each component is the mass percentage calculated based on the total mass of the electrolyte.

[0096] Table 1. Composition of the electrolyte in Examples 1-18 and Comparative Examples 1-5

[0097]

[0098]

[0099] In the present invention, performance tests were conducted on the lithium-ion batteries prepared using different electrolyte ratios in Examples 1-18 and Comparative Examples 1-5. The test results are shown in Table 2.

[0100] In one embodiment of the present invention, for example, a fast charge cycle lithium deposition test is performed on a lithium-ion battery. Specifically, the state of charge (SOC) of the battery is increased from 3% to 10% at 1C, and then the SOC is increased from 10% to 30% at 4C, the SOC is increased from 30% to 50% at 3C, the SOC is increased from 50% to 70% at 2.5C, the SOC is increased from 70% to 80% at 2C, and the SOC is increased from 80% to 97% at 1C. The battery is then discharged until the SOC drops to 3%. After 20 cycles of charge and discharge using the above system, the battery cell is disassembled to observe the lithium deposition condition of the negative electrode.

[0101] In one embodiment of the present invention, for example, a direct current resistance (DCR) test is performed on a lithium-ion battery. Specifically, the temperature of the thermostat is adjusted to 25°C, and the lithium-ion battery is allowed to stand in the thermostat for 10 minutes. The battery is then charged to 4.4V at a constant current of 0.33C, and then charged to 0.05C at a voltage of 4.4V. After standing for 30 minutes, the battery is then discharged to 2.8V at a constant current of 0.33C. The 0.33C charge and discharge cycle is repeated twice to obtain the last discharge capacity C0. After standing for 30 minutes, the battery is discharged to (50% C0) at 0.33C, the cell SOC is adjusted to 50%, and the cell is allowed to stand for 30 minutes. The static terminal voltage V1 is recorded. The battery is then discharged at a constant current of 4C0 for 30 seconds, and the terminal voltage V2 and current I are recorded. Calculate the 25°C DCR according to the following formula:

[0102] DCR=(V1-V2) / I.

[0103] In one embodiment of the present invention, for example, a high-temperature cyclic gas production performance test was conducted on a lithium-ion battery. Specifically, the lithium-ion battery was placed in a 45°C oven and cyclically charged and discharged at a current of 1C within the potential range of 2.8V-4.4V. The gas production growth rate was recorded after 500 cycles.

[0104] Table 2 Performance test results of lithium-ion batteries in Examples 1-18 and Comparative Examples 1-5

[0105]

[0106] Please refer to Table 1 and Table 2. From the comparison of Example 3 and Comparative Example 1, it can be seen that when the electrolyte contains the first additive PTEA, the gas production growth rate of the battery is significantly reduced, by about 64%, which shows that the first additive PTEA can optimize the stability of the CEI interface film and reduce the high-temperature cyclic gas production of the positive electrode interface; from the comparison of Example 3 and Comparative Example 2, it can be seen that when the electrolyte contains the first solvent, lithium deposition will not occur on the negative electrode sheet after 20 cycles, and the DCR of the battery is significantly reduced, which shows that the first solvent can reduce the viscosity of the electrolyte, improve the ion conductivity of the electrolyte, and improve the fast charging performance of the battery.

[0107] Please refer to Table 1 and Table 2. Comparison between Comparative Example 2 and Comparative Example 5 shows that when the electrolyte contains the first additive PTEA and the additive TVSi, the DCR, gas production growth rate and lithium deposition of the negative electrode are almost the same, indicating that the first additive PTEA and the additive TVSi have almost the same degree of improvement on battery performance. However, comparison between Comparative Examples 4-5 shows that when the electrolyte contains both the first solvent and the additive TVSi, although the impedance of the battery is slightly reduced, the gas production growth rate increases, and lithium deposition still occurs on the negative electrode; comparison between Example 3 and Comparative Examples 1-2 shows that when When the electrolyte contains both the first solvent and the first additive PTEA, no lithium deposition occurs on the negative electrode after 20 cycles, and the DCR and gas production growth rate of the battery are significantly reduced. That is, the DCR, lithium deposition and gas production growth rate of the battery can be well balanced. This indicates that only by using PTEA in combination with fluorocarboxylic acid esters can the ion conductivity be significantly improved, the oxidation resistance of the system be enhanced, and the synergistic effect of the two be fully utilized to achieve better battery performance. However, the use of TVSi in combination with fluorocarboxylic acid esters cannot achieve a balance between the DCR, lithium deposition and gas production growth rate of the battery.

[0108] As shown in Tables 1 and 2, it can be seen from the comparison of Examples 1-6 that as the content of the first additive PTEA increases from 0.05wt% to more than 3wt%, the DCR of the battery gradually increases, indicating that excessive use of the first additive will lead to an excessively thick positive electrode interface film, thereby affecting the fast charging performance of the battery; when the content of the first additive PTEA is reduced to less than 0.1wt%, the gas production growth rate of the battery increases significantly, indicating that too little use of the first additive will lead to an unstable positive electrode interface film and an increase in side reactions at the positive electrode interface. Therefore, by controlling the content of the first additive, the stability of the positive electrode interface film can be optimized and the gas production during high-temperature cycling at the positive electrode interface can be reduced.

[0109] Please refer to Table 1 and Table 2. By comparing Example 3 with Examples 7-10, it can be seen that when the mass ratio of the first solvent and the first additive is reduced to below 10:1, the DCR of the battery is significantly increased; when the mass ratio of the first solvent and the first additive is increased to above 20:1, the gas production growth rate of the battery is significantly increased, indicating that by controlling the mass ratio of the first solvent and the first additive, both the fast charging performance and the high-temperature cycle gas production performance of the battery can be taken into account.

[0110] Please refer to Table 1 and Table 2. Comparing Example 3 with Examples 7-10, it can be seen that as the content of the first solvent increases to more than 20wt%, although the DCR of the battery decreases significantly, the gas production growth rate increases significantly, indicating that when the content of the first solvent increases to more than 20wt%, although the battery exhibits good fast charging performance, the battery produces serious gas due to the high activity of the electrolyte, affecting the high-temperature cycle gas production performance of the battery. As the content of the first solvent decreases to less than 10wt%, although the gas production growth rate of the battery decreases significantly, the impedance of the battery increases significantly, indicating that when the content of the first solvent decreases to less than 10wt%, the high-temperature cycle gas production performance of the battery is improved, but the low content of the first solvent causes the viscosity of the electrolyte to increase and the ion conductivity to deteriorate, thereby affecting the fast charging performance of the battery. Therefore, by controlling the content of the first additive, it is possible to take into account both the fast charging performance and the high-temperature cycle gas production performance of the battery.

[0111] As shown in Tables 1 and 2, a comparison of Examples 3, 11, and 12 shows that, compared with the use of methyl trifluoroacetate or ethyl difluoropropionate alone, the combined use of methyl trifluoroacetate and ethyl difluoropropionate significantly reduces the DCR of the battery, but increases the gas production growth rate. This indicates that the combined use of methyl trifluoroacetate and ethyl difluoropropionate can improve the fast-charging performance of the battery, but affects the high-temperature cyclic gas production performance. Therefore, by controlling the type of the first solvent, the fast-charging performance and high-temperature cyclic gas production performance of the battery can be improved.

[0112] Please refer to Table 1 and Table 2. Comparing Comparative Example 1 and Comparative Example 3, it can be seen that when the electrolyte does not contain the second additive, although the gas production growth rate of the battery is reduced, the DCR is significantly increased, resulting in slower ion transfer kinetics at the interface, affecting the fast charging performance of the battery; comparing Example 3, Example 14, Comparative Example 1 and Comparative Example 3, it can be seen that when the electrolyte contains the first additive and the second additive at the same time, the gas production growth rate of the battery is reduced, and the DCR is also reduced, which shows that the first additive and the second additive work synergistically to take into account the fast charging performance and high-temperature cycle gas production performance of the battery.

[0113] Please refer to Table 1 and Table 2. Comparing Examples 13-17, it can be seen that as the content of the second additive increases to more than 2wt%, the DCR of the battery decreases slightly but the gas production growth rate increases significantly, indicating that: although the content of the second additive is too high, it can improve the fast charging performance of the battery, but due to the excessive inorganic components of the interface film, the CEI film and SEI film are easily broken during the cycle, thereby affecting the high-temperature cycle gas production performance of the battery; as the content of the second additive decreases to less than 0.2wt%, the DCR of the battery increases slightly, indicating that: too little content of the second additive will lead to insufficient ion conductivity of the interface film, affecting the fast charging performance of the battery. Therefore, by controlling the content of the second additive, it is possible to take into account both the fast charging performance and the high-temperature cycle gas production performance of the battery.

[0114] Please refer to Table 1 and Table 2. By comparing Example 3, Example 12, Example 14 and Example 18, it can be seen that when the content of the first additive, the type of the first additive and the content of the second additive are controlled at the same time, the DCR and gas production growth rate of the battery can be maintained at low values, indicating that by synergistically controlling the content of the first additive, the type of the first additive and the content of the second additive, the fast charging performance and high-temperature cycle gas production performance of the battery can be improved.

[0115] The present invention also provides an electronic device, which includes at least one of the above-mentioned lithium-ion batteries, and the lithium-ion battery is used to provide electrical energy. The electronic device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, which may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. The spacecraft includes airplanes, rockets, space shuttles, and spacecraft, etc. The electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. The electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the above-mentioned lithium-ion battery, and therefore includes the advantages of the above-mentioned lithium-ion battery, which will not be elaborated on here.

[0116] In summary, the present invention provides a lithium-ion battery electrolyte and its application. By introducing a first solvent and a first additive into the electrolyte, the first solvent and the first additive work synergistically to not only significantly improve the ion conductivity of the electrolyte, but also enhance the antioxidant properties of the electrolyte system, thereby jointly improving the battery's fast charging performance and high-temperature cyclic gas production performance. Moreover, the first additive and the second additive work synergistically to reduce battery impedance, inhibit lithium deposition in the battery, and improve the battery's fast charging performance, while also taking into account the battery's high-temperature cyclic gas production performance.

[0117] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by the mutual replacement of the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0118] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A lithium ion battery electrolyte, characterized in that At least the following components: lithium salts; a solvent comprising a first solvent comprising at least one of a fluorocarboxylate; and The additives include a first additive including 2-(phenylthio)ethyl acrylate.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first additive in the electrolyte is 0.1 wt%-3 wt%.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that The fluorocarboxylic acid ester includes at least one of methyl trifluoroacetate and ethyl difluoropropionate.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first solvent in the electrolyte is 10 wt%-20 wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that The mass ratio of the first solvent to the first additive is (10-20):

1.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that The additives further include a second additive including lithium tetrafluoroborate.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that The content of the second additive in the electrolyte is 0.2 wt%-2 wt%.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that The solvent further includes a second solvent, the second solvent includes at least one of ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate, and the lithium salt includes at least one of lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide.

9. A lithium-ion battery, characterized in that: include: The positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material includes a ternary positive electrode material, and the structural formula of the ternary positive electrode material is Li a Ni 1-x-y-z Co x Mn y Al z O 2-b , where 0.95≤a≤1.10, 0≤b≤0.2, 0≤x≤1, 0≤y≤1, 0≤z≤1 and 0 <x+y+z<1; A negative electrode plate, comprising a negative electrode active material, wherein the negative electrode active material comprises a silicon-carbon material; a separator, disposed between the positive electrode sheet and the negative electrode sheet; and The electrolyte is selected from the lithium ion battery electrolyte according to any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that The content of the silicon-carbon material in the negative electrode active material is 1 wt%-8 wt%.

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