Electrolyte additive composition, electrolyte and lithium ion battery

Abstract

The application discloses an electrolyte additive composition, an electrolyte and a lithium ion battery, and the electrolyte additive composition is composed of an additive A and an additive B, wherein the molecular structure of the additive A is shown as formula (I), and the molecular structure of the additive B is shown as formula (II); wherein in formula (II), R1, R2 and R3 are independently selected from one of a hydrogen atom, a halogen atom, an amino group, a C1-C4 alkyl group, a methoxy group, a methylsulfonyl group, an ethylsulfonyl group, a fluorosulfonyl group, a trifluoromethyl group, a phenyl group, an isocyanide group and a -COORa, wherein Ra in the -COORa is a C1-C3 alkyl group; and n is an arbitrary integer between 0 and 3. Through the mutual cooperation of the two specific additives, the high-voltage cycle life, the high-temperature storage performance and the impedance growth in the cycle process of the lithium ion battery are remarkably improved.

Description

Technical Field

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

[0002] With the increasing energy density requirements of electric vehicles and energy storage systems, higher operating voltages (≥4.45V) are becoming increasingly important. vs. Li / Li + The cathode material has become crucial for the development of lithium-ion batteries. However, under high-voltage conditions, carbonate solvents in the electrolyte are prone to irreversible oxidative decomposition, generating highly reactive alkyl oxygen radicals (such as RO·). These radicals trigger chain side reactions, not only continuously consuming the electrolyte and generating gas, but also attacking the cathode material, leading to the dissolution of transition metal ions, destruction of the crystal structure, and the formation of an unstable organic enriched cathode-electrolyte interface (CEI film), ultimately causing rapid capacity decay and reduced cycle life.

[0003] To address the aforementioned issues, existing technologies primarily focus on material modification and electrolyte additives. Electrolyte engineering, due to its good process compatibility, has been extensively studied; however, traditional additives (such as vinylene carbonate and fluoroethylene carbonate) or their improved versions still have significant limitations. For example, some existing technologies (such as CN107910586A and CN107394268A) mainly rely on specific functional groups (such as piperidinyl and amino groups) to complex acidic substances (such as HF) in the electrolyte, or on silicon-oxygen bonds and sulfonyl groups to improve film formation and high-temperature performance. Their mechanisms of action emphasize proton capture or physical barriers, generally lacking efficient and targeted electron transfer capabilities to scavenge highly reactive alkyl oxygen radicals. Other solutions (such as CN114069049A), while featuring multi-functional group designs, still cannot effectively quench free radicals generated at high voltages of 4.45V and above, failing to fundamentally solve the core problem of free radicals attacking the positive electrode lattice oxygen and triggering chain reactions.

[0004] In summary, existing electrolyte additive strategies, especially for high-voltage systems, generally fail to efficiently and effectively capture and quench alkyl oxygen radicals generated under high voltage, leading to instability at the cathode-electrolyte interface (CEI), continuous side reactions, and deterioration of battery high-voltage cycle performance. Summary of the Invention

[0005] In view of this, the primary objective of this application is to provide an electrolyte additive composition comprising additive A and additive B, wherein additive A contains nitrile radicals and -NH-SO3. -The lithium salt additive with anionic groups, and additive B is a silicon-based isocyanate compound, work together to significantly improve the high-voltage cycle life, high-temperature storage performance and impedance growth during cycling of lithium-ion batteries.

[0006] To achieve the above objectives, this application adopts the following technical solution: One aspect of this application discloses an electrolyte additive composition comprising additive A and additive B, wherein the molecular structure of additive A is shown in formula (I), and the molecular structure of additive B is shown in formula (II): ; In formula (II), R1, R2, and R3 are each independently selected from one of hydrogen, halogen, amino, C1-C4 alkyl, methoxy, methanesulfonyl, ethanesulfonyl, fluorosulfonyl, trifluoromethyl, phenyl, isocyano, or -COORa, where Ra is a C1-C3 alkyl group and n is any integer between 0 and 3.

[0007] Another aspect of this application discloses an electrolyte comprising an electrolyte lithium salt, an organic solvent, and the electrolyte additive composition described in this application.

[0008] Another aspect of this application discloses a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte described in this application.

[0009] The beneficial effects of this application are: The electrolyte additive composition in this application consists of additive A and additive B. Additive A contains nitrogen oxide radicals and -NH-SO3. - The lithium salt additive with anionic groups, and additive B being a silicon-based isocyanate compound, work synergistically to significantly improve the high-voltage cycle life, high-temperature storage performance, and impedance growth during cycling of lithium-ion batteries. Specifically: Additive A contains nitrile radicals and -NH-SO3 in its structure. - Anionic groups possess both free radical capture and electric field-driven directional migration functions. Among them, nitroxide radicals have highly efficient electron transfer capabilities, rapidly capturing and neutralizing alkyl oxygen radicals, thus blocking chain reactions at the source and significantly reducing the continuous decomposition of the electrolyte and battery gas accumulation problems under high-voltage conditions (≥4.45V); secondly, -NH-SO3 -Anionic groups are highly polar. During charging, anions migrate to and accumulate on the high-voltage positive electrode surface. Sulfur (S) and nitrogen (N) elements work synergistically to form a uniform, dense, and S- and N-rich cathode electrolyte interphase (CEI) film on the positive electrode surface, significantly improving the ionic conductivity of the CEI and reducing the interfacial impedance of the battery. Simultaneously, N atoms interact with transition metal ions (such as Co) on the positive electrode surface. 3+ Ni 4+ (etc.) form strong coordination bonds, which inhibits the dissolution of transition metal ions under high voltage, and improves the density and corrosion resistance of the interfacial film, effectively preventing direct contact between the electrolyte and the positive electrode.

[0010] Additive B contains a silicon-based isocyanate group in its structure. The electrophilic center of Si-NCO has a higher positive charge, and the highly active -NCO group can preferentially and efficiently capture and consume trace amounts of water in the electrolyte, fundamentally cutting off the main pathway for HF generation. At the same time, additive A, as a highly efficient free radical scavenger, directly inhibits the free radical-mediated lithium salt decomposition chain reaction.

[0011] The two additives work together to form a protective mechanism of "water removal at the source, free radical scavenging during the process, and stable interface at the end", which blocks the mutual catalytic relationship between "oxidation" and "acid etching" and significantly improves the battery's high-voltage cycle life, high-temperature storage performance, and impedance growth during the cycle.

[0012] Furthermore, the additives in this application exhibit good compatibility with existing carbonate electrolytes and conductive lithium salts, requiring no changes to existing battery manufacturing processes. Simultaneously, they demonstrate significant performance enhancement effects on various high-voltage cathode materials, exhibiting strong versatility and suitability for large-scale application in power batteries, energy storage batteries, and other fields. Detailed Implementation

[0013] The embodiments of this application will be clearly and completely described below. The technical solutions in the embodiments described below are exemplary and only possible technical implementations of this application, not all possible implementations. Those skilled in the art can combine the embodiments of this application to obtain other embodiments without creative effort, and these embodiments are also within the protection scope of this application.

[0014] The first aspect of this application discloses an electrolyte additive composition, which consists of additive A and additive B, wherein the molecular structure of additive A is shown in formula (I), and the molecular structure of additive B is shown in formula (II): ; In formula (II), R1, R2, and R3 are each independently selected from one of hydrogen, halogen, amino, C1-C4 alkyl, methoxy, methanesulfonyl, ethanesulfonyl, fluorosulfonyl, trifluoromethyl, phenyl, isocyano, or -COORa, where Ra is a C1-C3 alkyl; and n is any integer between 0 and 3 (e.g., 0, 1, 2, or 3).

[0015] Additive A contains nitric oxide radicals and -NH-SO3 in its structure. - Lithium salt additives with anionic groups, obtained by introducing -NH-SO3 onto a nitrogen-containing heterocycle. - Anionic groups are used to construct structures that possess both free radical capture and electric field-driven directional migration functions. -NH-SO3 - Anionic groups are directionally enriched at the positive electrode interface under the action of a high-voltage electric field. Nitrogen oxide radicals, with their efficient electron transfer capabilities, can rapidly capture and neutralize alkyl oxide radicals, thereby using the -NO· group to target and quench free radicals, blocking the chain reaction at its source and reducing the continuous decomposition of the electrolyte and battery gas accumulation under high-voltage conditions. Simultaneously, the reaction products can further participate in the construction of a CEI layer enriched with sulfur, nitrogen, and other inorganic components, synergistically inhibiting transition metal dissolution and continuous electrolyte decomposition. Additive B utilizes the electrophilic center of the more positively charged Si-NCO group, enabling the highly active -NCO group to preferentially and efficiently capture and consume trace amounts of water in the electrolyte, fundamentally cutting off the main pathway for HF generation. The synergistic effect of both significantly improves the battery's high-voltage cycle life, high-temperature storage performance, and impedance growth during cycling.

[0016] In this application, the method for synthesizing additive A specifically includes the following steps: Step (1) Sulfonation reaction: Under an inert atmosphere, the 4-amino-2,2,6,6-tetramethylpiperidine-1-oxo radical is dissolved in an anhydrous organic solvent and cooled to... At 10-10°C, slowly add the sulfonating agent, controlling the reaction temperature to not exceed 20°C, and stir the reaction for 2 minutes. The reaction lasted 12 hours. After the reaction was complete, the reaction solution was quenched in ice water, and then extracted, dried, and concentrated to obtain the intermediate sulfonic acid compound. The sulfonating agent used was selected from chlorosulfonic acid and sulfur trioxide. Triethylamine complex, sulfur trioxide One of the dioxane complexes, used in an amount of 1.0% of the compound of formula (I). 1.5 equivalents. The organic solvent used is selected from dichloromethane, tetrahydrofuran, N,N One or more mixed solvents of dimethylformamide.

[0017] Step (2) Salt formation reaction: Dissolve the intermediate obtained in step (1) in an alcohol solvent or an alcohol / water mixed solvent, add a lithium base compound, and react at 10... Stirred reaction at 60°C 1 The reaction was carried out for 6 hours. After the reaction was completed, the solvent was removed under reduced pressure, and the resulting solid was purified by recrystallization or column chromatography to obtain the target product, lithium sulfonyl salt. The lithium base compound was selected from lithium hydroxide, lithium carbonate, and lithium methoxide, and its amount was 1.0% of the intermediate compound. 1.2 Equivalent. The alcohol solvent is selected from methanol, ethanol, and isopropanol.

[0018] In some specific examples of this application, the preparation method of additive A is as follows: (1) Under argon protection, 4-amino TEMPO (1.72 g, 10.0 mmol) was dissolved in 30 mL of anhydrous dichloromethane and cooled to 0°C in an ice bath. Chlorosulfonic acid (1.07 g, 9.2 mmol) was slowly added dropwise, keeping the reaction temperature below 5°C. After the addition was complete, the mixture was brought to room temperature and stirred for 6 hours. The reaction solution was poured into 50 g of ice water and extracted with dichloromethane (3 × 30 mL). The combined organic phases were dried over anhydrous sodium sulfate and concentrated under reduced pressure to give an orange-red solid intermediate. .

[0019] (2) The above intermediate was dissolved in 20 mL of methanol, and lithium hydroxide monohydrate (0.50 g, 11.9 mmol) was added. The mixture was stirred at room temperature for 3 hours. The solvent was removed by vacuum distillation, and the residual solid was recrystallized from ethanol / water (9:1) to obtain 2.05 g of the target product in orange-red crystals, with a yield of about 78%. .

[0020] In some specific examples of this application, the additive B is selected from any one or a mixture of two or more compounds SiNO1 to SiNO6, but is not limited thereto: .

[0021] It is understandable that additive B can be obtained through commercially available products or by referring to existing technologies, which will not be elaborated here.

[0022] In this application, the appropriate dosage of additive A and additive B can be determined experimentally. As a preferred example, the mass ratio of additive A to additive B is 1:5 to 5:1, more preferably 1:2 to 2:1. For example, it can be any ratio or a range between any of the following: 1:2, 1:1.8, 1:1.6, 1:1.5, 1:1.2, 1:1, 2:1. When the ratio of A to B is within the above preferred range, additive A is enriched on the positive electrode surface due to the electric field, and its sulfonamide structure participates in film formation and provides sulfur and nitrogen elements. Additive B, by removing moisture and HF, reduces the corrosion of the positive electrode active material by acid and the damage to the initial CEI layer, providing a good chemical environment for additive A to construct a dense and stable interface layer. The synergistic effect of both gives the CEI layer good ionic conductivity, density, and chemical stability, thereby more effectively suppressing transition metal dissolution and interfacial impedance growth during high-voltage long-cycle operation. If additive A is excessive, although its free radical scavenging ability is strong, the effects of moisture and residual acid may become more prominent; if additive B is excessive, although the system acidity is low, its free radical quenching ability is insufficient, and oxidation side reactions will still be aggravated. Within this preferred ratio range, the two can be ensured to achieve optimal complementarity in molecular function, achieving systematic blocking of the "oxidation-acid etching" cycle, thereby achieving optimal optimization in electrolyte stability, interface engineering, and electrochemical performance, and achieving the best balance in high-voltage cycle life, high-temperature storage stability, and safety performance of the battery.

[0023] The second aspect of this application discloses an electrolyte comprising an electrolyte lithium salt, an organic solvent, and the electrolyte additive composition described in the first aspect of this application.

[0024] By adding the electrolyte additive composition of this application to conventional electrolytes in the art, the performance of the electrolyte and the corresponding lithium-ion battery can be significantly improved, especially the cycle performance and high-temperature storage performance.

[0025] In this electrolyte, the content of additive A is 0.01wt%-5wt%, and the content of additive B is 0.01wt%-5wt%. For example, additive A can be any value or a range between two of the following: 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%. Similarly, additive B can be any value or a range between two of the following: 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%. Preferably, the content of additive A is 0.05wt%-2wt%, and the content of additive B is 0.05wt%-2wt%.

[0026] It is understood that the electrolyte lithium salt and organic solvent used in this application can be of types well known in the art or independently developed, without any particular limitation.

[0027] In some specific examples, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), lithium difluorophosphate (LiPO2F2), and lithium perchlorate (LiClO4), but is not limited thereto. Selecting a suitable lithium salt based on the electrolyte system can yield better ionic conductivity and a more stable interfacial film, thereby further improving the performance of lithium-ion batteries; those skilled in the art possess the ability to do so. As a preferred example, the electrolyte lithium salt is LiFSI.

[0028] There is no particular limitation on the mass content of lithium salt in the electrolyte. Those skilled in the art can determine the appropriate amount of lithium salt to add based on experience or through experimental methods. A suitable lithium salt content allows the electrolyte to achieve an optimal balance between ionic conductivity and suitable viscosity, further enhancing the excellent electrochemical performance of lithium-ion batteries. As a specific example, the total content of the electrolyte lithium salt in the electrolyte is 5 wt% to 20 wt%, for example, it can be any value or a range between 5 wt%, 6 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, and 20 wt%; preferably, the lithium salt content is 10 wt% to 15 wt%.

[0029] In some specific examples, the organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), 1,4-butyrolactone (GBL), methyl propionate (MP), ethyl propionate (EP), and ethyl butyrate (EB), but is not limited thereto. Preferably, the organic solvent is a mixed solvent composed of cyclic carbonates and chain carbonates, utilizing the good dissociation ability of cyclic carbonates (high dielectric constant) for lithium salts and the dilution effect of chain carbonates (low viscosity) on the electrolyte system, thereby obtaining an electrolyte matrix with high ion mobility. More preferably, in the mixed solvent, the volume ratio of cyclic carbonates (such as EC, FEC) to chain carbonates (such as DMC, DEC, EMC) is 1:9 to 4:6. More preferably, the cyclic carbonate may also contain 1%-20% FEC by mass, which can participate in the formation of a LiF-rich stable solid electrolyte interface (SEI) film on the negative electrode surface, thereby further improving the first efficiency and cycle life.

[0030] Furthermore, it is understood that the electrolyte of this application can also be supplemented with a certain amount of functional additives based on performance requirements. These functional additives can synergize with the electrolyte additive composition in this application to further optimize the performance of the lithium-ion battery. For example, film-forming additives, including but not limited to vinylene carbonate (VC) and / or vinyl sulfate (DTD), are preferably present in a content of 0.5wt%-3wt%. They can preferentially undergo reduction or oxidation reactions on the surface of the positive and negative electrode active materials before the solvent, forming an initial protective film and reducing the continuous decomposition of the main solvent. Another example is flame-retardant additives, including but not limited to trimethyl phosphate (TMP) or fluorophosphates, preferably present in a content of 1wt%-5wt%. These can increase the flash point of the electrolyte system and enhance the thermal safety of the battery. Other additives, such as overcharge protection additives, can also be added. Those skilled in the art can make appropriate selections and additions based on actual application needs, without specific limitations.

[0031] The third aspect of this application discloses a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the electrolyte described in the second aspect of this application. Benefiting from the advantages of the electrolyte in this application, it naturally brings corresponding technical benefits to the lithium-ion battery, which will not be elaborated here.

[0032] The positive electrode, negative electrode, and separator in lithium-ion batteries are all conventional materials used in battery construction. There are no particular restrictions on their specific types; any type well-known in the field or independently developed can be used.

[0033] In some specific examples, the positive electrode includes a positive electrode current collector and a positive electrode active material layer coated on its surface. The positive electrode active material layer contains positive electrode active substances and also includes functional aids such as a conductive agent and a binder.

[0034] For the positive electrode active substances, specific examples include lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNixCoyMnzO2, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1), lithium nickel cobalt aluminate (NCA), lithium-rich manganese-based materials or their doped / coated modified bodies, but are not limited thereto. As a preferred example, the positive electrode active substance is lithium cobalt oxide or a high-nickel ternary material (such as LiNi vs. Li / Li + ) with a charging cut-off voltage not lower than 4.45V ( 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 O2, among others). Preferably, its mass proportion in the positive electrode active material layer is preferably 90wt% - 98wt%, and this high proportion ensures that the electrode has a high volumetric energy density.

[0035] For the conductive agent, specific examples include at least one of carbon black (such as Super P), conductive graphite, carbon nanotubes, and graphene, but are not limited thereto. As a preferred example, its mass proportion is 0.5wt% - 5wt%. Introducing a sufficient amount of the conductive agent can build an efficient electron conduction network and reduce electrode polarization.

[0036] For the binder, specific examples include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a mixture of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), but are not limited thereto. Its mass proportion is preferably 1wt% - 5wt%, and an appropriate amount of the binder ensures a firm bond between the active substances and the current collector and the structural integrity of the electrode.

[0037] In some specific examples, the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the current collector. Similar to the positive electrode active material layer, the negative electrode active material layer contains negative electrode active substances and functional aids such as a conductive agent and a binder.

[0038] Specific examples of negative electrode active materials include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon-based materials (such as silicon-oxygen SiOx, silicon-carbon composite materials), and metallic lithium, but are not limited to these. As a preferred example, the negative electrode active material is artificial graphite. Its specific proportion in the negative electrode active material layer is preferably 92wt%-98wt%.

[0039] For conductive agents, specific examples include, but are not limited to, at least one of carbon black, carbon nanotubes, and graphene. As a preferred example, its proportion in the negative electrode active material layer is 0.5wt%-3wt%.

[0040] For the binder, specific examples include, but are not limited to, at least one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and sodium alginate, with a preferred mass percentage of 1wt%-5wt%. Choosing a suitable binder can buffer the huge volume expansion during the charging and discharging process.

[0041] It is understandable that both positive and negative electrodes can be obtained by mixing the above components with a solvent to form a slurry, uniformly coating it onto the corresponding current collector, and then drying, rolling, and slitting it.

[0042] Furthermore, in some specific examples, the diaphragm is a polyolefin microporous membrane, a nonwoven membrane, or a composite diaphragm, but is not limited thereto. As a preferred example, the diaphragm is a single-layer polyethylene (PE) membrane, a single-layer polypropylene (PP) membrane, or a PP / PE / PP three-layer composite microporous membrane. There is no specific limitation on the thickness of the base membrane, which can be selected according to performance requirements. A preferred base membrane thickness is 9 μm to 25 μm, and the preferred porosity is 35%-55%, thereby providing excellent ion permeability and mechanical strength while ensuring electronic insulation.

[0043] As a preferred example, at least one surface of the separator is coated with an inorganic ceramic coating (such as alumina, silicon oxide, etc.) or an organic aramid coating. The coating thickness is preferably 1 μm to 5 μm. By introducing an inorganic ceramic coating, the heat resistance and wettability of the separator with electrolyte are further improved, and excessive shrinkage of the separator at high temperatures is prevented, greatly enhancing the safety performance of the battery.

[0044] For the assembly of lithium-ion batteries, refer to the known techniques in this field. Usually, the battery assembly is carried out under conditions that isolate water and oxygen, such as in a glove box, which will not be elaborated here.

[0045] The present application will be further illustrated below with reference to specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present application in any way.

[0046] 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.

[0047] In addition, unless otherwise specified, methods without detailed conditions or steps are conventional methods, and the reagents and materials used are commercially available.

[0048] Table 1. Composition of non-aqueous electrolytes in Examples 1-16 and Comparative Examples 1-5

[0049] Electrolytes were prepared according to the compositions and ratios in Table 1. The specific preparation steps are as follows: In an argon-protected glove box, LiFSI was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 to form a basic electrolyte. Additives were added to the basic electrolyte and dissolved completely to form the electrolyte. The specific ratios and compositions are shown in Table 1.

[0050] Performance testing The electrolytes from the examples and comparative examples were assembled into coin cells for corresponding performance tests.

[0051] (1) Battery assembly: Cathode preparation: using LiNi 0.8 Co 0.1 Mn 0.1 O2 is the active material, SP is the conductive agent, PVDF is the binder, and N-methyl-2-pyrrolidone (NMP) is the dispersant, according to LiNi 0.8 Co 0.1 Mn 0.1 The slurry was prepared with a mass ratio of O2:SP:PVDF of 96:2:2. The positive electrode slurry was then uniformly coated onto the current collector aluminum foil with a coating amount of 10.2 g / cm³. 2 After drying at 85°C, the positive electrode sheet is obtained through coating, rolling, and die cutting.

[0052] Negative electrode preparation: Taking artificial graphite negative electrode material as an example: artificial graphite is used as the negative electrode active material, SP as the conductive agent, and CMC and SBR as binders. A slurry is prepared according to the mass ratio of Gr:SP:CMC:SBR:CNT=94.44:2:2:1.5:0.06. The negative electrode slurry is then uniformly coated onto the current collector copper foil with a coating amount of 7.1 g / cm³. 2 After drying at 85°C, the negative electrode sheet is obtained through coating, rolling, and die cutting.

[0053] The above-mentioned positive electrode, negative electrode, and separator (Celgard 2400 membrane) were used to assemble CR2025 coin cells with the electrolytes from the examples and comparative examples. The assembly sequence from negative electrode to positive electrode was as follows: negative electrode shell, spring contact, gasket, negative electrode sheet, electrolyte, separator, positive electrode sheet, and positive electrode shell, followed by sealing with a sealing machine. All operations were performed in a pure argon glove box. After standing for 10 hours, the cells were removed for electrochemical performance testing.

[0054] (2) Electrochemical performance testing (i) Electrolyte stability test: The lithium-ion battery electrolytes prepared in Examples 1-16 and Comparative Examples 1-5 were respectively placed in sealed aluminum bottles, which were vacuum-sealed with aluminum-plastic film. The electrolyte samples were stored in a constant temperature chamber set at 45°C. Samples were taken in a glove box before storage and 30 days later to test the acidity and color values ​​of the electrolyte. The acidity was tested using a potentiometric titrator, and the acidity value was converted to HF in ppm. The color was measured using platinum titrator. Cobalt colorimetry was performed, with the chromaticity unit being Hazen. The test results are shown in Table 2.

[0055] Table 2 Effects of additives on electrolyte acid value and color

[0056] Table 2 shows that after storage at 30℃, the acidity value of Comparative Example 1 (base group) increased rapidly. Building on this, Comparative Example 2, with the addition of additive A, showed a decrease in acidity value under the same storage conditions. While the strong electron-withdrawing groups in its molecule have some electrophilicity, they are not highly efficient moisture scavengers, thus limiting its ability to inhibit HF formation. In Comparative Example 3, with the addition of additive B (silicone isocyanate compound), the acidity value decreased significantly. This is because silicon-based isocyanates have highly reactive isocyanate groups that can efficiently remove trace amounts of moisture from the electrolyte through irreversible nucleophilic addition reactions, fundamentally blocking the LiPF6 hydrolysis acid production pathway and thus significantly reducing HF formation. Comparative Example 4 shows that lithium difluorophosphate, as a conventional lithium salt, does not possess the free radical capture and directional migration function of additive A, and may decompose at high temperatures, introducing additional acidic substances or oxidation products. Comparative Example 5 demonstrates that conventional isocyanate additives lack the special structure of silicon-based isocyanates, resulting in a significantly reduced synergistic effect and an inability to effectively inhibit side reactions. In this application, the simultaneous addition of additives A and B resulted in a significant reduction in the color and acidity values ​​of Examples 1-16. This indicates that additive B preferentially and rapidly removes moisture, while additive A helps stabilize the system. The nitrogen heterocycles or strong electron-withdrawing groups in additive A's molecular structure can react with residual trace amounts of moisture or HF, further reducing the HF content.

[0057] (ii) High-voltage cycle performance test and high-temperature storage performance test of lithium-ion batteries High-voltage cycle performance test: At a set temperature, the lithium-ion battery is charged to 4.45V at a constant current of 1C, then charged to 0.05C at a constant voltage of 4.45V, and then discharged to 3.0V at a constant current of 1C. This constitutes one charge-discharge cycle. Taking the capacity of the first discharge as 100%, calculate the capacity retention rate of the lithium-ion battery after 200 cycles.

[0058] Capacity retention rate (%) after 200 cycles = Discharge capacity after 200 cycles / Capacity of the first discharge × 100%.

[0059] High-temperature storage internal resistance change rate test: Example 1 The batteries obtained in Examples 16 and 1-7 were subjected to 5 charge-discharge cycles at a charge-discharge rate of 1C at room temperature, and finally fully charged at a 1C rate. The battery internal resistance T was recorded. The fully charged batteries were stored at 60°C for 14 days, and the battery internal resistance T0 was recorded. The rate of change of battery internal resistance was calculated.

[0060] Rate of change of internal resistance = (T) T0) / T×100% High-temperature storage capacity performance test: After storing the battery at 60℃ for 14 days, it was removed and allowed to stand at room temperature for 60 minutes. After cooling to room temperature, the battery was first discharged to 3.0V at a constant current of 1C at 25℃, then charged to 4.45V at a constant current of 1C, and further charged to 0.05C at a constant voltage of 4.45V. The first discharge capacity after storage was recorded, and the battery capacity recovery rate was calculated. The results are recorded in Table 3.

[0061] Capacity recovery rate = (discharge capacity before storage / discharge capacity after storage) × 100%.

[0062] Table 3. Effects of additives on high-pressure cycling and high-temperature storage performance

[0063] As can be seen from the test results in Table 3, the high-voltage cycle performance and high-temperature storage performance of lithium-ion batteries are significantly improved after the introduction of the additive composition in this application.

[0064] Furthermore, according to Example 8 12. When additive A is fixed, silicon-based isocyanate compounds (SiNO1-SiNO6) with different structures can all produce excellent and similar synergistic effects. This proves that the key to additive B in this application lies in its common core structure of silicon-based isocyanate (Si-NCO), rather than a specific substituent. This core structure endows it with efficient water removal, good compatibility with electrolyte, and synergistic effects with additive A, thus verifying the rationality and feasibility of the general structural formula definition of additive B in the claims.

[0065] According to Example 13 16. When the mass ratio of additives A to B is within a wide range of 1:5 to 5:1, they can effectively exert a synergistic effect and significantly improve battery performance, indicating that the composition of this application has good process tolerance.

[0066] As shown in Table 3, after cycling, especially after high-temperature cycling, the capacity retention rate of the group using additives A and B (Examples 1-16) was significantly higher than that of other control groups. This demonstrates that the synergistic system can construct a stable inorganic-enriched CEI interface layer, synergistically suppress transition metal dissolution, and greatly improve the degradation of the cathode interface during cycling. Furthermore, the combined group also exhibited a higher capacity recovery rate after storage, indicating that it maintained excellent electrode reaction kinetics during recharge and discharge, and that interfacial side reactions were fundamentally suppressed. Secondly, the interfacial impedance growth rate of the combined group remained at the lowest level, directly verifying its synergistic mechanism. The use of nitroxide radical sulfonamide compounds can efficiently quench free radicals generated by solvent molecules through free radical capture and electric field-driven directional migration. Simultaneously, the use of silicon-based isocyanate greatly improved the HF removal capacity, helping to reduce the impedance growth of high-voltage cathode materials during cycling.

[0067] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrolyte additive composition for lithium-ion batteries, characterized in that, It consists of additive A and additive B, wherein the molecular structure of additive A is shown in formula (I), and the molecular structure of additive B is shown in formula (II): ； In formula (II), R1, R2, and R3 are each independently selected from one of hydrogen, halogen, amino, C1-C4 alkyl, methoxy, methanesulfonyl, ethanesulfonyl, fluorosulfonyl, trifluoromethyl, phenyl, isocyano, or -COORa, where Ra is a C1-C3 alkyl group and n is any integer between 0 and 3.

2. The electrolyte additive composition according to claim 1, characterized in that, The additive B is selected from any one or a mixture of two or more compounds SiNO1 to SiNO6: 。 3. The electrolyte additive composition according to claim 1, characterized in that, The mass ratio of additive A to additive B is 1:5 to 5:

1.

4. An electrolyte, characterized in that, The electrolyte comprises an electrolyte lithium salt, an organic solvent, and an electrolyte additive composition according to any one of claims 1-3.

5. The electrolyte as described in claim 4, characterized in that, The content of additive A is 0.01wt%-5wt% based on the total mass of the electrolyte, and the content of additive B is 0.01wt%-5wt%.

6. The electrolyte as described in claim 4, characterized in that, The electrolyte lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, lithium difluorophosphate, and lithium perchlorate.

7. The electrolyte as described in claim 4, characterized in that, The content of the lithium salt electrolyte in the electrolyte is 5%. 20wt%.

8. The electrolyte as described in claim 4, characterized in that, The organic solvent is ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl propyne carbonate, 1,4-methyl propyne carbonate, 1,4-methyl propyne carbonate, etc. At least one of butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, or ethyl butyrate.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the electrolyte as described in any one of claims 4-8.

10. The lithium-ion battery as described in claim 9, characterized in that, The positive electrode includes a positive electrode active material, which is lithium nickel cobalt manganese oxide, and the general chemical formula of lithium nickel cobalt manganese oxide is LiNixCoyMnzO2,0. <x<1,0<y<1,0<z<1,x+y+z=1。 11. The lithium-ion battery as described in claim 10, characterized in that, The positive electrode active material is LiNi. 1 / 3 Co 1 / 3Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2.

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