Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive, an electrolyte and a lithium ion battery. The electrolyte additive comprises a compound I, the compound I contains R1 and R2 groups, R1 and R2 are independently selected from any one of hydrogen and alkoxy substituted by a substituent group, and the substituent group is at least one of sulfate and sulfite; r1 and R2 are not hydrogen at the same time. Sulfate and / or sulfite in the compound I can optimize the chemical characteristics of an electrode interface, significantly improve the cycle life and the high-temperature storage performance of the battery, and reduce the impedance of the battery, so that a controllable oxidation-reduction reaction can be performed on the surfaces of the positive and negative electrodes to form a compact solid electrolyte interface film with excellent conductivity; according to the present invention, the continuous decomposition of the electrolyte, the dissolution of the metal ions and the gas production side reaction can be effectively inhibited, the corrosion of HF on the electrode material can be reduced, and the cycle life and the high temperature storage performance of the battery assembled by the positive electrode active material and the negative electrode active material can be improved.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are now widely used in power, energy storage, and electronic products, leading to increasingly higher demands on their energy density, cycle performance, high-temperature performance, and safety. Improving battery cycle life and high-temperature performance is a pressing issue that needs to be addressed.

[0003] Currently available commercial electrolytes are prone to decomposition under high temperatures or high voltages, leading to a chain reaction such as the dissolution of transition metals in the positive electrode and the rupture of the SEI film in the negative electrode, resulting in capacity decay and the risk of thermal runaway. Therefore, how to provide an electrolyte that can improve the high-temperature performance of lithium-ion batteries is a problem that needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte additive, an electrolyte, and a lithium-ion battery, aiming to solve the problem of unstable performance of the electrolyte in existing lithium-ion batteries at high temperatures.

[0005] The first embodiment of this application provides an electrolyte additive, comprising compound I, the structural formula of which is shown in Formula I:

[0006] Formula I; R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, wherein the substituent is at least one of sulfate esters and sulfites; R1 and R2 are not both hydrogen.

[0007] In some embodiments, R1 and R2 are each independently selected from hydrogen, , , , and Any one of them; R1 and R2 are not both hydrogen.

[0008] In some embodiments, compound I is selected from any one of the compounds shown in Formulas I-1 to I-10:

[0009]

[0010]

[0011]

[0012] Formula I-10.

[0013] The second embodiment of this application provides an electrolyte including the electrolyte additives in any of the above embodiments, wherein the mass percentage of the electrolyte additives in the electrolyte is 0.1~10%.

[0014] In some embodiments, the electrolyte further includes lithium salt and organic solvent; The concentration of the lithium salt in the electrolyte is 5-20%; The organic solvent accounts for 70-90% by mass in the electrolyte.

[0015] In some embodiments, the electrolyte further includes auxiliary additives; the auxiliary additives include at least one of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds.

[0016] In some embodiments, the electrolyte additive and the auxiliary additive satisfy the following: 0.1%≤w1+w2≤20%; and 0.1≤w1 / w2≤1; In the formula, w1 is the mass percentage of the electrolyte additive in the electrolyte, and w2 is the mass percentage of the auxiliary additive in the electrolyte.

[0017] In some embodiments, the mass ratio of the ester compound, the nitrile compound, the silicon-based compound, the sulfur-containing compound, and the lithium salt compound is 0~5%:0~2%:0~3%:0~5%:0~5%.

[0018] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, and lithium bistrifluoromethylsulfonylimide.

[0019] In some embodiments, the organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0020] In some embodiments, the ester compound includes at least one of vinylene carbonate, fluoroethylene carbonate, and methyl (2,2,2-trifluoroethyl) carbonate.

[0021] In some embodiments, the nitrile compound includes at least one selected from butadionitrile, glutaronitrile, octadionitrile, sebaconitrile, 1,3,6-hexanetrionitrile, 1,3,5-pentanetrionitrile, and methoxypropionitrile.

[0022] In some embodiments, the sulfur-containing compound includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate.

[0023] In some embodiments, the lithium salt compound is selected from at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

[0024] The third embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte as described in any of the above embodiments; the high-temperature storage capacity retention rate (60d, 60℃) of the lithium-ion battery is 50~90%, and the high-temperature storage volume expansion rate (60d, 60℃) is 5~50%.

[0025] This application provides an electrolyte additive comprising compound I, wherein compound I contains R1 and R2 groups, each independently selected from hydrogen and alkoxy groups substituted with substituents, and the substituents are at least one of sulfate esters and sulfites; R1 and R2 are not simultaneously hydrogen. By adding compound I, containing sulfate esters and / or sulfites in its structure, this application optimizes the chemical properties of the electrode interface, significantly improves the cycle life and high-temperature storage performance of the battery, and reduces battery impedance. Compound I can not only undergo a controllable redox reaction on the positive and negative electrode surfaces to form a dense and ionicly conductive solid electrolyte interphase (SEI / CEI) film, effectively inhibiting the continuous decomposition of the electrolyte, the dissolution of metal ions, and gas generation side reactions, but also bind to HF generated in the electrolyte, reducing the corrosion of electrode materials by HF. Therefore, it can improve cycle life and enhance high-temperature storage performance for batteries assembled from positive and negative electrode active materials. Detailed Implementation

[0026] The technical solutions of this application will be clearly and completely described below with reference to the embodiments therein. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0027] In the description of this application, it should be noted that "multiple" means two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features.

[0028] The compounds of this application can be synthesized via synthetic routes including methods similar to those known in the field of chemistry, particularly with reference to the description contained herein. Starting materials are generally available from commercial sources or can be readily prepared using methods known to those skilled in the art. For illustrative purposes, the reaction schemes described below illustrate possible routes for synthesizing the compounds of this application and key intermediates. For a more detailed description of each reaction step, see the Examples section below. Those skilled in the art will recognize that other suitable starting materials, reagents, and synthetic routes can be used to synthesize the compounds of this application and their various derivatives.

[0029] Unless otherwise stated, the term "alkyl" as used herein refers to a saturated aliphatic hydrocarbon group, which may be straight-chain or branched. For example, the term "C1-C6 alkyl" refers to an alkyl group containing 1, 2, 3, 4, 5, or 6 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, neopentyl, hexyl, 2-methylpentyl, etc.). Similarly, the alkyl portion (i.e., alkyl) of alkoxy, alkylacyl, alkylphosphate, alkylsulfonyl, and alkylaminosulfonyl groups has the same definition above. For example, the term "C1-C3 alkyl" refers to an alkyl group containing 1, 2, or 3 carbon atoms (e.g., methyl, ethyl, propyl, and isopropyl). Alkyl groups may be substituted or unsubstituted, and when substituted, the substituents may be substituted at any usable link.

[0030] Unless otherwise stated, the term "alkoxy" as used herein refers to -O-alkyl, where alkyl is as defined in this application.

[0031] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure of this application, the configuration and arrangement of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0032] The first embodiment of this application provides an electrolyte additive, including compound I, the structural formula of which is shown in Formula I:

[0033] Formula I; R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, wherein the substituent is at least one of sulfate esters and sulfites; R1 and R2 are not both hydrogen.

[0034] It is understandable that the S=O bonds in sulfates and sulfites have strong polarity, thus giving compound I a high reduction site. During battery charging and discharging, it preferentially undergoes reduction reactions over carbonate solvents (such as vinylene carbonate) in the electrolyte, generating an SEI film rich in Li₂SO₃, Li₂SO₄, and alkyl lithium sulfate. This inorganic-organic composite film can inhibit the continuous decomposition of the electrolyte and improve high-temperature stability, while the high ionic conductivity of Li₂SO₄ can also reduce interfacial impedance. Furthermore, the presence of S=O allows it to form a CEI film on the positive electrode surface through oxidation, inhibiting transition metal dissolution and mitigating electrolyte oxidation caused by lattice oxygen release at high temperatures. Simultaneously, the sulfur atoms in the S=O bond can also capture hydroxyl radicals (…). OH), inhibiting the oxidation and gas production of the electrolyte.

[0035] In some embodiments, R1 and R2 are each independently selected from hydrogen, , , , and Any one of them; R1 and R2 are not both hydrogen.

[0036] It is understood that, in addition to sulfates and sulfites, the above-mentioned preferred functional groups also include alkoxy groups. The lone pair of electrons on the oxygen atom in the alkoxy group can coordinate with lithium ions in the electrolyte and has a certain polarity, which can improve the solubility and wettability of the electrolyte and facilitate the formation of a stable interfacial film.

[0037] In some embodiments, compound I is selected from any one of compounds I-1 to I-10:

[0038]

[0039]

[0040]

[0041] Compound I-10.

[0042] The above compounds can be prepared using methods known in the art.

[0043] The second embodiment of this application provides an electrolyte including the electrolyte additives in any of the above embodiments, wherein the mass percentage of the electrolyte additives in the electrolyte is 0.1~10%.

[0044] It is understandable that the mass percentage of electrolyte additives in the electrolyte can be any value from 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any range between any two values. When the proportion of electrolyte additives in the electrolyte meets the above range, it can effectively inhibit the dissolution of transition metals and the oxidative decomposition of the electrolyte, while avoiding the decline in cycle performance and high-temperature performance due to excessive addition.

[0045] In some embodiments, the electrolyte further includes lithium salt and organic solvent; The concentration of lithium salt in the electrolyte is 5-20%; The organic solvent accounts for 70-90% of the mass percentage in the electrolyte.

[0046] It is understood that the concentration of lithium salt in the electrolyte can be any value from 5%, 10%, 15%, 20%, or any value within a range of any two values; the mass percentage of organic solvent in the electrolyte can be any value from 70%, 75%, 80%, 85%, 90%, or any value within a range of any two values. By controlling the mass percentages of lithium salt and organic solvent in the electrolyte to meet the above-mentioned ranges, it is possible to ensure that the electrolyte has ideal conductivity and uniformity.

[0047] In some embodiments, the electrolyte further includes auxiliary additives; the auxiliary additives include at least one of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds.

[0048] Understandably, ester compounds exhibit good chemical stability under typical electrochemical conditions, enabling them to form stable interfacial films on electrode surfaces, reducing side reactions between electrode materials and electrolytes, and improving battery cycle performance and lifespan. Nitrile compounds, due to their cyano group content, possess high dielectric constants and low viscosity, inhibiting direct contact between the electrolyte and the positive electrode, thus improving the stability of the positive electrode interface. Simultaneously, the cyano group exhibits strong electrophilic activity, reacting with water in the electrolyte and active hydrogen in the positive and negative electrode materials, reducing lithium salt decomposition caused by active hydrogen. Silicon-based compounds can participate in lithium-ion battery applications. The film-forming reaction on the electrode material surface decomposes to produce film-forming products containing inorganic siloxanes and phosphates, promoting the formation of a uniform, dense, and stable solid electrolyte interface film. Simultaneously, it captures harmful substances such as hydrofluoric acid in the electrolyte, reducing side reactions between the electrolyte and electrode materials. Sulfur-containing compounds can participate in the formation of an SEI film on the negative electrode surface, effectively preventing direct contact between the electrolyte and the negative electrode active material. Lithium salt compounds can synergistically interact with ester compounds in the electrolyte on the negative electrode surface, reducing and generating an organic-inorganic composite low-resistance interface film, thereby improving the stability of the negative electrode interface. Adding auxiliary additives to the electrolyte can synergistically protect the positive and negative electrodes of the battery, thereby improving the battery's cycle performance and high-temperature performance.

[0049] In some embodiments, the electrolyte additive and auxiliary additives satisfy the following: 0.1%≤w1+w2≤20%; and 0.1≤w1 / w2≤1; In the formula, w1 is the mass percentage of electrolyte additives in the electrolyte, and w2 is the mass percentage of auxiliary additives in the electrolyte.

[0050] It is understandable that the value of w1+w2 can be any value or a range between any two of the following: 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%; and the value of w1 / w2 can be any value or a range between any two of the following: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1. By controlling the total amount and proportion of electrolyte additives and auxiliary additives in the electrolyte to meet the above-mentioned value ranges, it is possible to further ensure that the protective film formed on both the positive and negative electrodes of the battery has a relatively uniform thickness, while avoiding excessive additives that could lead to high electrolyte impedance and reduced battery electrical performance.

[0051] In some embodiments, the mass ratio of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds is 0~5:0~2:0~3:0~5:0~5.

[0052] Preferably, the mass of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds is not simultaneously 0.

[0053] It is understandable that by controlling the mass ratio of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds in the auxiliary additives to meet the above-mentioned range, the role of the auxiliary additives in protecting the positive and negative electrodes of the battery and reducing impedance in the electrolyte can be further balanced.

[0054] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, and lithium bistrifluoromethylsulfonylimide.

[0055] In some embodiments, the organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0056] In some embodiments, the ester compound includes at least one of vinylene carbonate, fluoroethylene carbonate, and methyl (2,2,2-trifluoroethyl) carbonate.

[0057] In some embodiments, the nitrile compound includes at least one selected from succinic anionyl nitrile, glutaronitrile, octanoic anionyl nitrile, 1,3,6-hexanetrionitrile, 1,3,5-pentanetrionitrile, and methoxypropionitrile.

[0058] In some embodiments, the sulfur-containing compound includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate.

[0059] In some embodiments, the lithium salt compound is selected from at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

[0060] The third embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte as described in any of the above embodiments; the high-temperature storage capacity retention rate (60d, 60°C) of the lithium-ion battery is 50-90%, and the high-temperature storage volume expansion rate (60d, 60°C) is 5-50%.

[0061] Specifically, the positive electrode includes a positive electrode active material, which includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, and lithium nickel cobalt aluminum oxide; the negative electrode includes a negative electrode active material, which includes at least one of soft carbon, hard carbon, artificial graphite, natural graphite, graphene, silicon oxide, or silicon carbide; the separator is one of polyethylene (PE) separator, polypropylene (PP) separator, PP / PE / PP three-layer composite membrane, polyimide (PI), and polyacrylonitrile (PAN).

[0062] The electrolyte additive, electrolyte, and lithium-ion battery provided in this application are described below with reference to specific embodiments: Example 1 This embodiment provides an electrolyte, which, based on 100% of the total mass of the electrolyte, comprises the following components: Compound I-1: 2%; Vinylene carbonate: 0.5%; Lithium bis(oxalate)borate: 0.5%; Lithium difluorophosphate: 0.8%; Lithium hexafluorophosphate: 11%; Lithium difluorosulfonylimide: 2.7%; Ethyl methyl carbonate: 41.25%; Ethylene carbonate: 24.75%; Diethyl carbonate: 16.5%.

[0063] The electrolyte was prepared as follows: The electrolyte was prepared in a glove box with a nitrogen content of 99.999%, an actual oxygen content of 0.1 ppm, and a moisture content of 0.1 ppm. Based on 100% of the total mass of the non-aqueous electrolyte, 24.75% ethylene carbonate, 41.25% methyl ethyl carbonate, and 16.5% diethyl carbonate (battery-grade organic solvent) were mixed evenly. Then, 11% lithium hexafluorophosphate and 2.7% lithium difluorosulfonyl imide (fully dried) were added to the above non-aqueous solvent. Additives of 2% compound 1.1, 0.8% lithium difluorophosphate, 0.5% ethylene carbonate, and 0.5% lithium bis(oxalato)borate were added to prepare the non-aqueous electrolyte for lithium-ion batteries.

[0064] The lithium-ion battery is prepared using the above electrolyte, and the preparation method is as follows: The positive electrode active material NCM811, conductive agent conductive carbon black, binder PVDF, and carbon nanotubes were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96.5:1.5:1.5:0.5. The mixture was then coated onto aluminum foil, dried, and hot-pressed to obtain the positive electrode sheet with an areal density of 230 g / m³. 2 The compacted density is 3.45 g / cm³. 3 .

[0065] The negative electrode active material graphite, conductive agent conductive carbon black, binder CMC, and SBR were thoroughly mixed in a deionized water solvent system at a mass percentage of 95.1:1.5:1.4:2.0. The mixture was then coated onto Cu foil, dried, and cold-pressed to obtain the negative electrode sheet with an areal density of 150 g / m³. 2 The compacted density is 1.5 g / cm³. 3 .

[0066] A diaphragm was obtained by using a 9μm thick polyethylene (PE) base film and coating a 2μm ceramic coating on both sides of the base film.

[0067] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as an insulator. The stacked electrodes then form a bare cell.

[0068] After the bare battery cell is placed in an aluminum-plastic film and baked at 80°C to remove moisture, the corresponding electrolyte is injected and the cell is sealed. Then, after processes such as settling, hot and cold pressing, formation, high-temperature settling, and capacity testing, the finished soft-pack lithium-ion secondary battery is obtained.

[0069] Examples 2-15 Examples 2-15 are similar to the electrolyte in Example 1, the difference being the adjustment of the components and the proportions added, see Table 1.

[0070] Comparative Example 1 The difference between this comparative example and Example 1 is that, with the total mass of the non-aqueous electrolyte being 100%, compound I is not added, and the amount of non-aqueous solvent is adjusted to make the total electrolyte amount 100%. The other raw materials, proportions, and mass percentages of each component are the same as in Example 1.

[0071] Comparative Example 2 Comparative Example 2 is similar to the electrolyte in Example 1, except for the adjustment of the components and the proportions of addition, see Table 1.

[0072] Table 1

[0073] Performance testing of lithium-ion batteries: (1) Lithium-ion battery cycle performance test The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 1C to a voltage of 4.25V, followed by charging at a constant voltage of 4.25V to a current of 0.05C, and then discharging at a constant current of 1C to a voltage of 2.75V. This constitutes one charge-discharge cycle. This cycle was repeated three times, and the discharge capacity of the last cycle was taken as the initial capacity of the lithium-ion battery. Starting from the initial capacity of 100%, the charge-discharge cycles were repeated until the discharge capacity decreased to 80%. The test was then stopped, and the number of cycles was recorded as an indicator of the lithium-ion battery's cycle performance.

[0074] Meanwhile, the cycle performance of lithium-ion batteries at 45°C was tested, and the testing method was the same as the 25°C cycle performance test mentioned above, except for the temperature difference.

[0075] (2) High-temperature storage test of lithium-ion batteries (60 degrees Celsius, storage for 60 days) The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a constant current of 0.33C to 2.75V. This cycle was repeated three times, and the discharge capacity of the last cycle was taken as the initial capacity of the lithium-ion battery. The tested lithium-ion battery was then transferred to a 60°C constant temperature chamber for storage for 60 days. After 60 days of storage, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. It was then discharged at a constant current of 0.33C to 2.75V, and the discharge capacity was recorded as the remaining capacity of the lithium-ion battery. It was then charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a constant current of 0.33C to 2.8V, and the discharge capacity was recorded as the recoverable capacity of the lithium-ion battery. The above are used as the performance indicators for high-temperature storage of the battery. The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. First, it was charged at a constant current of 1C until the voltage reached 4.25V, then charged at a constant voltage until the current reached 0.05C. After charging, the cell volume was measured using the water displacement method (V1). The tested lithium-ion battery was then transferred to a 60°C constant temperature chamber for storage for 60 days. After 60 days of storage, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. After the battery returned to room temperature, the cell volume was measured again using the water displacement method (V2). The cell volume expansion rate was calculated using the following formula. This is used as a performance indicator of the battery's high-temperature gas production.

[0076] .

[0077] The test results are shown in Table 2.

[0078] Table 2

[0079] The experimental comparison data shows that, as can be seen from the comparison between the examples and the comparative examples: Example 1: Optimal performance in room temperature cycling and DC resistance: After 1000 cycles at 25°C, the capacity retention rate is still 86.4% (23.9% improvement compared to Comparative Example 1). The DC resistance is only 10.9 mΩ. After 1000 cycles at 45°C, the capacity retention rate is still 85.1% (24.9% improvement compared to Comparative Example 1). After 60 days of storage at 60°C, the capacity retention rate is still 83.8% (20.4% improvement compared to Comparative Example 1), the capacity recovery rate is as high as 87.9% (19.7% improvement compared to Comparative Example 1), and the volume expansion rate is only 14.4% (19.4% lower than Comparative Example 1).

[0080] Comparative Example 1 (without the additive): Cyclic performance and high-temperature performance deteriorated significantly, verifying the key role of the additive.

[0081] Comparative Example 2 (excess additive): Compared with the above examples, the cycle performance and high temperature performance are deteriorated but better than Comparative Example 1. Excessive addition will lead to performance degradation, but it is still better than not adding.

[0082] The electrolyte additives, electrolytes, and lithium-ion batteries provided in the embodiments of this application have been described in detail above. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrolyte additive, characterized in that, Including compound I, the structural formula of which is shown in Formula I: Formula I; R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, wherein the substituent is at least one of sulfate esters and sulfites; R1 and R2 are not both hydrogen.

2. The electrolyte additive according to claim 1, characterized in that, R1 and R2 are each independently selected from hydrogen, , , , and Any one of them; R1 and R2 are not both hydrogen.

3. The electrolyte additive according to claim 2, characterized in that, Compound I is selected from any one of the compounds shown in Formulas I-1 to I-10: Formula I-10.

4. An electrolyte, characterized in that, The electrolyte additive includes any one of claims 1 to 3, wherein the electrolyte additive is present in the electrolyte at a mass percentage of 0.1 to 10%.

5. The electrolyte according to claim 4, characterized in that, It also includes lithium salts and organic solvents; The concentration of the lithium salt in the electrolyte is 5-20%; The organic solvent accounts for 70-90% by mass in the electrolyte.

6. The electrolyte according to claim 5, characterized in that, It also includes auxiliary additives; the auxiliary additives include at least one of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds and lithium salt compounds.

7. The electrolyte according to claim 6, characterized in that, The electrolyte additive and the auxiliary additive satisfy the following: 0.1%≤w1+w2≤20%; and 0.1≤w1 / w2≤1; In the formula, w1 is the mass percentage of the electrolyte additive in the electrolyte, and w2 is the mass percentage of the auxiliary additive in the electrolyte.

8. The electrolyte according to claim 6, characterized in that, The mass ratio of the ester compound, the nitrile compound, the silicon-based compound, the sulfur-containing compound, and the lithium salt compound is 0~5%:0~2%:0~3%:0~5%:0~5%.

9. The electrolyte according to claim 6, characterized in that, The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium bis(trifluoromethylsulfonyl)imide; and / or, The organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and / or, The ester compounds include at least one of vinylene carbonate, fluorovinyl carbonate, and methyl (2,2,2-trifluoroethyl) carbonate; and / or, The nitrile compounds include at least one selected from butadionitrile, glutaronitrile, octadionitrile, sebaconitrile, 1,3,6-hexanetrionitrile, 1,3,5-pentanetrionitrile, and methoxypropionitrile; and / or, The sulfur-containing compound includes at least one selected from 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate; and / or, The lithium salt compound is selected from at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is any one of claims 4 to 9; the high-temperature storage capacity retention rate (60 days, 60°C) of the lithium-ion battery is 50 to 90%, and the high-temperature storage volume expansion rate (60 days, 60°C) is 5 to 50%.

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