Ethyl acetate-based electrolyte additive compositions, electrolytes and lithium ion batteries

Abstract

The application discloses an ethyl acetate-based electrolyte additive composition, an electrolyte and a lithium ion battery, and belongs to the technical field of lithium ion batteries, and comprises ethyl acetate and a functional additive; a single ethyl acetate additive has a side reaction with graphite, destroys the negative electrode interface in the later stage of high-temperature cycling, causes capacity to drop, and the negative electrode side reaction is significant in the high-temperature storage process, and the DCR grows too fast; after the functional additive is added, the functional additive will first decompose with ethyl acetate at the negative electrode, form a stable SEI, reduce the damage of ethyl acetate to the negative electrode, and improve the cycle stability. The electrolyte additive composition can compensate for the damage of a single carboxylic acid ester solvent to the negative electrode, can form stable CEI films and SEI films at the positive electrode and the negative electrode of the lithium ion battery respectively, has good stability, thereby the side reactions of the positive electrode and the negative electrode of the lithium ion battery in the high-temperature working state can be effectively reduced, and the application performance of the lithium ion battery at high temperature is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte preparation technology, specifically relating to ethyl acetate-based electrolyte additive compositions, electrolytes, and lithium-ion batteries. Background Technology

[0002] With the development of new energy vehicles, wearable devices, and portable mobile devices, the requirements for the high-temperature performance of lithium-ion batteries are constantly increasing. There is a growing expectation to develop lithium-ion batteries with superior high-temperature performance to meet people's daily needs. Under high-temperature environments, the electrolyte itself needs to have high stability to ensure the continuous stability of the lithium-ion battery at high temperatures. Currently, methods to improve the high-temperature performance of lithium-ion batteries include optimizing lithium salts, optimizing electrolyte solvents, and optimizing key electrolyte additives.

[0003] However, commercial lithium-ion battery electrolytes are generally composed of carbonate organic solvents and lithium hexafluorophosphate (LiPF6). The carbonate solvents are mainly composed of chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC), as well as cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC). Although EC in the electrolyte will undergo redox decomposition reactions on the surfaces of the ternary cathode and graphite anode, respectively, to form an effective positive / negative electrode electrolyte interface film (CEI / SEI), this film has poor stability at high temperatures. Furthermore, EC is more easily oxidized than ordinary linear carbonates. At approximately 3.8–4.0 V, hydrogen atoms on EC combine with oxygen atoms on the layered oxide cathode, leading to the dehydrogenation of EC, reduction of transition metal ions, and formation of ethylene carbonate. The active hydroxide groups on the oxide cathode surface can further react with PF6. – Anionic reaction, releasing PF5 gas. Secondly, above 4.2 V (approximately 80% SOC), Ni... 4+ Induced singlet oxygen 1 O2 and triplet oxygen 3 The generation of O2 gas. 1O2 immediately performs a nucleophilic attack on the EC (electrode electrode), forming ketone groups on the EC, which eventually decompose into CO2, CO, and H2O. H2O can also trigger the hydrolysis of the EC through nucleophilic attack, thereby releasing CO2. The FEC decomposes at high temperatures to produce HF, which corrodes the positive electrode interface, leading to increased interfacial impedance and dissolution of transition metal ions. These side reactions promote each other, forming a vicious cycle that causes problems such as battery gas production, increased internal resistance, and decreased cycle life.

[0004] The following methods are commonly used to improve the high-temperature performance of commercial lithium-ion batteries: 1) Optimizing lithium salts; adding LiFSI, which has good thermal stability at high temperatures, improves high-temperature storage performance and cycle performance. 2) Optimizing electrolyte solvents; EC-free electrolyte design concept, by inhibiting lattice oxygen release, reduces gas generation during high-temperature storage, significantly increasing the battery's thermal runaway trigger temperature, thereby improving battery safety characteristics; EC-free electrolytes reduce interfacial side reactions, significantly improving the cycle stability of high-nickel materials. 3) Key additives; adding dehydrating and deacidifying additives such as SN, AND, and TMSP to traditional electrolytes can effectively remove HF generated by FEC decomposition in the electrolyte, protecting the cathode from HF corrosion and improving high-temperature storage performance.

[0005] While the above methods can improve the high-temperature performance of electrolytes under certain conditions, they all have limitations. Introducing LiFSI into the electrolyte increases costs; EC-free electrolytes have excessively low conductivity, increasing internal resistance; EC-free electrolytes also exhibit poor interfacial repair, leading to deterioration in room-temperature cycling; nitrile additives significantly improve the high-voltage stability of the electrolyte through complexation of transition metal ions, self-oxidation film formation, and removal of water molecules, but their reduction stability is poor. Nitrile additives are incompatible with graphite anodes, worsening the anode interface during cycling and causing excessively rapid DCR growth, resulting in cycle failure. Therefore, there is an urgent need to develop novel additives to improve the overall performance of electrolytes at high temperatures. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide an ethyl acetate-based electrolyte additive composition, an electrolyte, and a lithium-ion battery to solve the technical problems of low capacity retention during high-temperature storage and capacity decay during high-temperature cycling.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] This invention discloses an ethyl acetate-based electrolyte additive composition, comprising: ethyl acetate and a functional additive; the functional additive has the following general structural formula:

[0009] ;

[0010] R1 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms;

[0011] R2 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms;

[0012] R3 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms;

[0013] R4 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms;

[0014] R5 is independently selected from either hydrogen or methyl.

[0015] Preferably, the mass ratio of ethyl acetate to functional additives is (10%-15%):(0.5%-1%).

[0016] Preferably, the ethyl acetate-based electrolyte additive composition further includes: fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, 1,3-propanesulfonate lactone, and lithium difluorophosphate.

[0017] Preferably, the functional additive is selected from at least one of the following compounds:

[0018]

[0019] The present invention also discloses an electrolyte comprising an organic solvent, a lithium salt, and the above-described ethyl acetate-based electrolyte additive composition.

[0020] Preferably, the organic solvent includes at least one of methyl ethyl carbonate, ethylene carbonate, and diethyl carbonate.

[0021] Preferably, the volume ratio of methyl ethyl carbonate, ethylene carbonate, diethyl carbonate and ethyl acetate is (55%-70%):(15%-20%):(15%-20%):(10%-15%).

[0022] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the concentration of the lithium salt in the electrolyte is 1.0-1.3 mol / L.

[0023] Preferably, the mass percentage of the composition of organic solvent, lithium salt and ethyl acetate-based electrolyte additive is (75%~82%): (15%~16%): (2%~10%).

[0024] The present invention also discloses a lithium-ion battery, which is assembled with the above-mentioned electrolyte, positive electrode, negative electrode and separator to form a lithium-ion battery; the lithium-ion battery retains a capacity of 90.2%~91.4% after 300 cycles at 10°C; a capacity retention of 94.3%~95.3% after 45 days of storage at 60°C; and a capacity retention of 87.3%~89.3% after 400 cycles at 45°C.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention discloses an ethyl acetate-based electrolyte additive composition. Regarding the synergistic improvement of interfacial stability, on the positive electrode side, EA preferentially oxidizes to form the CEI film framework, and the phenyl groups of the functional additives are embedded in the film layer to enhance hydrophobicity, jointly inhibiting TM dissolution and lattice oxygen evolution. On the negative electrode side, EA promotes Li… + Desolvation and optimization of SEI components with functional additives (such as the generation of Li3P, Li x PO y To enhance membrane toughness and accommodate the volume expansion of the silicon-carbon anode, ethyl acetate (EA) and functional additive A are used in combination to suppress impedance growth and improve the capacity retention of high-nickel ternary batteries. Ethyl acetate alone readily reacts with the graphite anode, leading to SEI film rupture and continuous electrolyte permeation and consumption. The functional additive, containing polar functional groups, preferentially decomposes on the anode surface before EA, forming a stable SEI film with an organic-inorganic composite layer, preventing EA from directly contacting graphite and reducing interfacial side reactions. Introducing fluorine (F) atoms can adjust the polarity, reduction potential, and film-forming components of the additive. F atoms lower the LUMO energy level of the additive molecules through a strong electron-withdrawing effect, making it easier to reduce and form a film on the anode surface; the conjugated structure of phenyl groups enhances the mechanical strength of the SEI film, suppressing rupture during cycling. A stable SEI film reduces impedance growth at high-temperature storage (slowing DCR growth), reducing active lithium consumption and thus improving capacity retention. This electrolyte additive composition can compensate for the damage to the negative electrode caused by a single carboxylic acid ester solvent, and can form stable CEI film and SEI film on the positive and negative electrodes of lithium-ion batteries, respectively, with good stability. This can effectively reduce the side reactions at the positive and negative electrode interfaces of lithium-ion batteries under high-temperature operating conditions and improve the application performance of lithium-ion batteries at high temperatures.

[0027] Furthermore, the functional additives neutralize acidic substances in the electrolyte through the strong nucleophilicity of the phosphine group, blocking the chain reaction of lithium salt decomposition. The phenyl substituents form a continuous protective layer on the positive electrode surface through π-π stacking, inhibiting the dissolution of transition metal ions. The alkyl substituents decompose on the negative electrode surface to generate an SEI film containing organic components; its flexible structure can adapt to changes in electrode volume. When R1-R4 are fluorophenyl groups, the strong electron-withdrawing effect of fluorine atoms promotes the reduction of the additives at low potentials, forming a LiF-rich inorganic layer and enhancing interfacial ion conductivity. The synergistic effect of ethyl acetate and the functional additives allows for both electrolyte stability maintenance and the formation of a composite interfacial film with a gradient structure at high temperatures. The functional additives decompose preferentially on the electrode surface compared to ethyl acetate, forming a composite film with a gradient structure, effectively blocking continuous electrolyte permeation. The phenyl substituents enhance the mechanical strength of the interfacial film, inhibiting the regeneration of side reactions caused by film rupture during cycling. The alkyl substituents optimize film density, reducing the irreversible consumption of active lithium during high-temperature storage. This synergistic effect enables the electrolyte to maintain ion transport efficiency and effectively suppress side reactions at the positive and negative electrode interfaces under high-temperature conditions, thereby improving the high-temperature cycling and storage performance of lithium-ion batteries.

[0028] Furthermore, under high-temperature operating conditions, ethyl acetate at a mass ratio of 10%-15% serves as the matrix solvent, providing a lithium-ion transport channel. Its upper limit reduces the probability of direct contact between free ethyl acetate molecules in the solvated structure and the graphite anode by suppressing the proportion of free ethyl acetate molecules. Functional additives at 0.5%-1% preferentially reduce to form a composite SEI film on the anode surface through the synergistic effect of phosphine and phenyl groups in the molecule. This film blocks the penetration of ethyl acetate molecules into the graphite interlayer through a dual mechanism of physical barrier and chemical passivation. When the ethyl acetate content is below 10%, the electrolyte viscosity increases, leading to a decrease in ion migration rate; when the functional additive content exceeds 1%, excessive accumulation of its decomposition products at the interface increases charge transfer resistance. By limiting the mass ratio range, a dynamic balance between interface protection and ion transport is achieved while maintaining the basic performance of the electrolyte.

[0029] Furthermore, fluoroethylene carbonate preferentially oxidizes on the positive electrode surface to form a fluoride-rich CEI film, inhibiting the dissolution of transition metal ions and the evolution of lattice oxygen at high temperatures; vinylene carbonate undergoes electropolymerization at the negative electrode interface to generate an elastic organic layer with a three-dimensional cross-linked structure, buffering the volume change of the silicon-carbon negative electrode; lithium borate produced by the decomposition of lithium bis(oxalate-borate) is embedded in the inorganic phase of the SEI film, reducing the lithium-ion diffusion barrier; 1,3-propanesulfonate lactone neutralizes free HF in the electrolyte through its sulfonic acid groups, reducing corrosion of the positive electrode material; and F2+ is released during the decomposition of lithium difluorophosphate. - With Li +The components combine to form LiF crystals, enhancing the mechanical strength and thermal stability of the interface layer. Through synergistic effects, they form a complementary organic-inorganic composite protective layer at the positive and negative electrode interfaces. This effectively suppresses the dissolution of transition metals from the positive electrode and the oxidative decomposition of the electrolyte at high temperatures, reduces the rate of side reactions at the negative electrode interface, minimizes HF corrosion of the electrode materials, and improves the interface layer's tolerance to volume expansion, thereby enhancing the battery's capacity retention and cycle stability in high-temperature environments.

[0030] This invention also discloses an electrolyte in which an additive composition forms a stable SEI film at the negative electrode, while the synergistic effect of the organic solvent and lithium salt forms a stable CEI film at the positive electrode, inhibiting the dissolution of transition metals at the positive electrode and electrolyte oxidation, thereby reducing the dual side reactions at the positive and negative electrode interfaces at high temperatures. The organic solvent provides an ion transport medium, the lithium salt provides a conductive lithium source, and the additive improves the interfacial impedance. The three work together to reduce the overall internal resistance of the electrolyte and improve the capacity retention rate during high-temperature cycling. Traditional electrolytes rely on ethylene carbonate as a film-forming component, but it is easily oxidized and decomposed at high temperatures, leading to interfacial degradation. This solution uses an EC-free solvent system to avoid lattice oxygen release, while functional additives compensate for the destructive effect of carboxylic acid esters on the negative electrode. Although nitrile additives in the prior art can improve voltage stability, they have poor compatibility with graphite negative electrodes. The functional additives in this solution, through the synergistic effect of phosphine and phenyl groups, form a stable organic-inorganic composite layer at the negative electrode, blocking direct contact of EA with graphite. Existing high-temperature electrolytes often sacrifice low-temperature performance, but this solution maintains adequate ionic conductivity of the SEI film at low temperatures by adjusting the solvent ratio and the reduction potential of the additives. This achieves dual interfacial stability of the electrolyte at high temperatures: on the positive electrode side, it inhibits transition metal dissolution and lattice oxygen evolution; on the negative electrode side, it mitigates SEI cracking caused by the volume expansion of silicon-carbon materials. The reduction in electrolyte internal resistance is achieved by optimizing solvent conductivity and the film-forming properties of the additives, significantly slowing capacity decay during high-temperature cycling. The neutralization of acidic byproducts and the inhibition of HF corrosion are achieved through the phosphine-based activity of the functional additives, thereby improving storage stability. The balance of low-temperature performance is achieved by avoiding the influence of EC freezing point and adjusting the SEI film composition, maintaining a balanced performance of the electrolyte over a wide temperature range.

[0031] Furthermore, by synergistically combining linear and cyclic carbonates, the stability of the solvent system is optimized while maintaining the electrolyte's film-forming ability. Ethylene carbonate preferentially oxidizes to form an initial interfacial film on the cathode surface, inhibiting the dissolution of transition metal ions; ethyl methyl carbonate increases the lithium-ion migration rate by reducing system viscosity, alleviating polarization at low temperatures; and diethyl carbonate reduces direct contact between the solvent and the highly active cathode material through the steric hindrance effect of its molecular chains. The ratio of these three components balances the requirements for conductivity and interfacial stability. By controlling the proportion of cyclic carbonates, their high-temperature decomposition and gas generation are avoided, while the inertness of linear carbonates inhibits dehydrogenation reactions, ultimately achieving a comprehensive performance improvement of the electrolyte over a wide temperature range.

[0032] Furthermore, the combined use of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide can create a complementary effect. Lithium hexafluorophosphate preferentially decomposes at the electrode interface to generate fluorine-containing compounds, which participate in the construction of the interfacial film's framework structure. Lithium bis(fluorosulfonyl)imide, through its stable chemical properties, inhibits the chain decomposition reaction of lithium salts at high temperatures, reducing the generation of acidic substances. When the lithium salt concentration is controlled at 1.0-1.3 mol / L, the number of free lithium ions is sufficient to maintain the high conductivity of the electrolyte, while avoiding excessive participation of solvent molecules in the lithium-ion solvation layer due to excessive concentration, thereby reducing electrolyte viscosity and inhibiting lithium salt crystallization. This concentration range can also optimize the lithium-ion solvation structure, promoting the formation of a uniform and dense solid electrolyte interfacial layer on the electrode surface.

[0033] Furthermore, the proportion of organic solvent is controlled within the range of 75% to 82%, which provides sufficient solvent molecules to maintain the solvation layer structure of lithium ions while avoiding excessive solvent dilution of the effective components, thus preventing a decrease in interfacial protection. The proportion of lithium salt is set at 15% to 16%, ensuring sufficient ionic conductivity of the electrolyte while preventing excessive salt concentration from causing viscosity increases or hindering lithium ion migration. The proportion of additive composition is limited to 2% to 10%, which meets the amount required to form a continuous and dense interfacial film on the positive and negative electrode surfaces while avoiding excessive additives from disrupting the chemical balance of the electrolyte system. The synergistic ratio of these three components allows the electrolyte to maintain a stable solvation environment at high temperatures through organic solvents, ensure efficient ion transport capabilities through lithium salts, and form a protective layer with mechanical strength and ion permeability at the electrode interface.

[0034] This invention also discloses a lithium-ion battery prepared with the above-mentioned electrolyte. The capacity retention rate after 400 cycles at 45°C is 87.3%~89.3%, attributed to the stable SEI film suppressing continuous EA consumption and reducing active lithium loss. After 45 days of storage at 60°C, the capacity retention rate is 94.3%~95.3%, indicating that interfacial side reactions are effectively suppressed. After 300 cycles at 10°C, the capacity retention rate is 90.2%~91.4%, indicating that the additives do not significantly increase low-temperature impedance, balancing high-temperature stability and low-temperature performance, thus broadening the application temperature range of the electrolyte. High-temperature performance optimization is achieved through the synergistic effect of electrolyte components and electrode materials. The ethyl acetate-based additive composition in the electrolyte preferentially oxidizes on the positive electrode side to form an interfacial film rich in inorganic components, inhibiting transition metal dissolution and lattice oxygen release; on the negative electrode side, the reduction and decomposition of functional additives forms an organic-inorganic composite layer, blocking direct contact between solvent molecules and graphite. The synergistic effect of the high-nickel active material and stable interfacial film in the positive electrode reduces oxidation side reactions at high temperatures, while the silicon-carbon material in the negative electrode, protected by the composite SEI film, mitigates film rupture caused by volume expansion. The ceramic coating of the separator enhances dimensional stability at high temperatures, and its synergistic wetting effect with the electrolyte ensures the integrity of the ion transport channels. This effectively suppresses interfacial side reactions between the electrode and electrolyte at high temperatures, significantly reduces the loss of active material due to transition metal dissolution, and alleviates the SEI film rupture problem caused by the volume expansion of the silicon-carbon negative electrode. The synergistic effect of the electrolyte composition and electrode structure enables the battery to maintain stable ion transport channels over a wide temperature range, reduces the rate of interfacial impedance growth during high-temperature storage, and decreases active lithium loss during cycling, thereby achieving a significant improvement in capacity retention under high-temperature conditions. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the dissolution of transition metal ions in a lithium-ion battery after 45 days of storage, as disclosed in Examples 1-6 and Comparative Example 1 of the present invention.

[0036] Figure 2 This is a schematic diagram of the DCR growth rate of the lithium-ion battery disclosed in Examples 1-6 and Comparative Example 1 of the present invention during cycling at 45°C. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0039] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0040] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0041] In this invention, unless otherwise specified, the components involved or their preferred components can be combined to form new technical solutions.

[0042] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0043] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0044] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0045] In this invention, unless otherwise stated, the various reaction or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0046] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0047] In a first aspect, the present invention provides an ethyl acetate-based electrolyte additive composition, comprising: a solvent and a functional additive, fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, 1,3-propanesulfonate lactone, and lithium difluorophosphate, wherein the solvent comprises ethyl acetate (EA), and the functional additive has the following general structural formula:

[0048] ;

[0049] R1, R2, R3, and R4 are each independently selected from hydrogen, substituted or unsubstituted phenyl groups, and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms, while R5 is independently selected from hydrogen and methyl groups.

[0050] The mass ratio of ethyl acetate to functional additives is (10%-15%): (0.5%-1%).

[0051] In a second aspect, the present invention provides an electrolyte comprising an organic solvent, a lithium salt, and an electrolyte additive, wherein the electrolyte additive comprises an ethyl acetate-based electrolyte additive composition as described in the first aspect.

[0052] The organic solvent includes at least one of methyl ethyl carbonate, ethylene carbonate, and diethyl carbonate. The volume percentage of the organic solvent is (55%-70%):(15%-20%):(15%-20%):(10%-15%).

[0053] The lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The concentration of the lithium salt in the electrolyte is 1.0-1.3 mol / L. The mass percentage of the organic solvent, lithium salt and ethyl acetate-based electrolyte additive composition is (75%~82%):(15%~16%):(2%~10%).

[0054] This invention provides a method for preparing the above-mentioned electrolyte, comprising: adding functional additives, fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, 1,3-propanesulfonate lactone, and lithium difluorophosphate to an organic solvent under an inert gas atmosphere, and stirring and mixing at low temperature to obtain the electrolyte. The inert gas is argon; the stirring and mixing conditions include: stirring and mixing at 5-15°C for 2-3 hours. The inert atmosphere prevents moisture and oxygen in the air from contaminating the electrolyte. Moisture reacts with LiPF6 to generate HF, which corrodes the SEI film and induces the dissolution of transition metals; oxygen may react with EA to generate byproducts such as carboxylic acids, exacerbating interface degradation. If the functional additive contains easily hydrolyzable groups (such as ester groups or haloalkyl groups), it can maintain structural stability in a dry, inert atmosphere, avoiding premature decomposition and failure, and ensuring controllable film formation.

[0055] Thirdly, the present invention provides a lithium-ion battery prepared with the above-mentioned electrolyte, using graphite as the negative electrode active material. A negative electrode slurry is prepared by mixing graphite, conductive agent acetylene black, binder CMC, and SBR in a mass percentage ratio of 94.8:1.5:2.4:1.3. The negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain a negative electrode sheet. NCM523 is used as the positive electrode active material. A positive electrode slurry is prepared by mixing the positive electrode active material, conductive agent acetylene black, and binder PVDF in a mass ratio of 95.5:2.2:2.3. The positive electrode slurry is coated onto an aluminum foil current collector and vacuum dried to obtain a positive electrode sheet. The electrolytes prepared in the examples and comparative examples are then assembled with the above-mentioned positive electrode sheet, negative electrode sheet, and separator to form a pouch battery.

[0056] Existing batteries suffer from low capacity retention and rapid capacity decay during high-temperature storage. This application provides an electrolyte additive composition comprising ethyl acetate (EA) and functional additive A. EA alone undergoes side reactions with graphite, damaging the negative electrode interface in the later stages of high-temperature cycling, leading to a significant capacity drop. Furthermore, the negative electrode side reactions are substantial during high-temperature storage, resulting in excessively rapid capacity reduction (DCR). Adding functional additive A allows it to decompose with EA at the negative electrode, forming a stable SEI, reducing the damaging effect of EA on the negative electrode and improving cycle stability.

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment provides an ethyl acetate-based electrolyte additive combination, comprising: a carboxylic acid ester additive EA and a functional additive; it also includes fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, 1,3-propanesulfonate lactone, and lithium difluorophosphate. The functional additive is formula I-1,1,2-bis(bis(pentafluorophenyl)phosphine)ethane.

[0060] This embodiment also provides an electrolyte composed of an organic solvent, lithium hexafluorophosphate, and the above-described ethyl acetate-based electrolyte additive composition. By volume percentage, the organic solvent comprises: 55% methyl ethyl carbonate, 20% ethylene carbonate, and 15% diethyl carbonate, and 10% ethyl acetate. Based on the total mass of the electrolyte (100%), the functional additives comprise 0.5% by mass, fluoroethylene carbonate 5% by mass, vinylene carbonate 0.5% by mass, lithium bis(oxalato)borate 0.5% by mass, lithium difluorophosphate 0.8% by mass, and 1,3-propanesulfonate lactone 0.5% by mass; ethyl acetate comprises 7% by mass, the organic solvent comprises 72% by mass, and the lithium salt comprises 13.2% by mass.

[0061] The concentration of lithium hexafluorophosphate in the electrolyte is 1.1 mol / L.

[0062] The electrolyte was prepared by the following method: Under an argon atmosphere, functional additives, fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, 1,3-propanesulfonate lactone, and lithium difluorophosphate were added to an organic solvent (volume percentage 55%:20%:15%:10%) formed by mixing methyl ethyl carbonate, ethylene carbonate, diethyl carbonate, and ethyl acetate. The mixture was stirred and mixed at 10°C for 2 hours to obtain the electrolyte.

[0063] Example 2

[0064] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 1 only in that the functional additive is formula I-2,1,2-bis(diphenylphosphine)ethane, and the addition amount is 0.5%, while the rest is the same as in Example 1.

[0065] Example 3

[0066] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 1 only in that the functional additive is formula I-3,1,2-bis(diphenylphosphine)propane, and the addition amount is 0.5%, while the rest is the same as in Example 1.

[0067] Example 4

[0068] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 1 only in that the functional additive is formula I-4,1,2-bis(di-tert-butylphosphine)ethane, and the addition amount is 0.5%, while the rest is the same as in Example 1.

[0069] Example 5

[0070] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 1 only in that the functional additive is formula I-5,1,2-bis(phosphono)ethane, and the addition amount is 0.5%, while the rest is the same as in Example 1.

[0071] Example 6

[0072] This embodiment provides an electrolyte additive and an electrolyte, which differ from Example 1 only in that the functional additive is of the structural formula I-6, 1,2-bis(methylphenylphosphine)ethane, and the addition amount is 0.5%, while the rest is the same as in Example 1.

[0073] Table 1. Names and structural formulas of functional additives corresponding to Examples 1-6.

[0074]

[0075] Table 1 shows the names and structural formulas of the functional additives corresponding to Examples 1-6; the table clearly shows the structure and name of the functional additives selected for each experimental example.

[0076] Comparative Example 1

[0077] This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain functional additives; otherwise, it is the same as Example 1.

[0078] Table 2 Comparison of capacity retention rates of lithium-ion batteries prepared in Examples 1-6 and Comparative Example 1

[0079]

[0080] Table 2 compares the capacity retention rates of lithium-ion batteries prepared in Examples 1-6 and Comparative Example 1. The table shows that the capacity retention rate of the lithium-ion batteries after 300 cycles at 10°C is 90.2%-91.4%; after 45 days of storage at 60°C, the capacity retention rate is 94.3%-95.3%; and after 400 cycles at 45°C, the capacity retention rate is 87.3%-89.3%. In Example 1, R1, R2, R3, and R4 were replaced by fluorophenyl groups, containing a large number of F atoms. F atoms have a strong electron-withdrawing effect, and the pentafluorophenyl groups significantly reduce the electron density of phosphorus atoms, promoting preferential oxidation of the additives at the positive electrode interface, forming a LiF-rich inorganic interface layer (CEI). LiF has high ionic conductivity and mechanical strength, which can inhibit the dissolution of transition metals. In Examples 2, 3 and 6, R1, R2, R3 and R4 are replaced by phenyl or benzyl groups, which contain phenyl groups. Phenyl groups enhance the passivation ability of the positive electrode and improve high-temperature cycling performance. In Example 4, R1, R2, R3 and R4 are replaced by tert-butyl groups. Tert-butyl groups have a large volume and form a dense SEI layer, which blocks the side reaction between the electrolyte and the negative electrode. Alkylphosphine is not easily decomposed at the low potential of the negative electrode, thus maintaining the integrity of the SEI.

[0081] Figure 1 This diagram illustrates the dissolution of transition metal ions in lithium-ion batteries after 45 days of storage, as disclosed in Examples 1-6 and Comparative Example 1 of this invention. As can be seen from the diagram, the dissolution amount of transition metal ions in Comparative Example 1 is significantly higher than that in Examples 1-6. The dissolution amounts of the three ions in Examples 1-6 are relatively low, and the differences between them are not significant. In all examples and comparative examples, the dissolution amount of Mn ions is generally higher than that of Ni and Co ions. The dissolution amount of the three transition metal ions in Comparative Example 1 is significantly higher than that in all examples. In Examples 1-6, the dissolution amounts of the three transition metal ions are relatively close, indicating that the dissolution of transition metal ions in these examples is relatively stable after 45 days of storage, without significant abnormal fluctuations.

[0082] Figure 2This diagram illustrates the DCR (Direct Current Resistance) growth rate of the lithium-ion batteries disclosed in Examples 1-6 and Comparative Example 1 during cycling at 45°C. As can be seen from the diagram, the DCR growth rate of all examples and the comparative example shows an upward trend. This indicates that during cycling at 45°C, the resistance of the lithium-ion battery gradually increases, and the battery performance gradually decreases. The DCR growth rate of Comparative Example 1 is significantly higher than that of all other examples. This indicates that the resistance increase of the battery in Comparative Example 1 is more pronounced during cycling, and its performance declines more rapidly. The DCR growth rates of Examples 1-6 are relatively low and close, still significantly lower than that of Comparative Example 1. During cycling, the upward trend of the DCR growth rate in Examples 1-6 is relatively gradual, indicating that the batteries in these examples have good stability under 45°C cycling conditions, with a slower increase in resistance and better performance retention.

[0083] Example 7

[0084] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 1 only in that the electrolyte is composed of an organic solvent, lithium difluorosulfonylimide, and the above-mentioned ethyl acetate-based electrolyte additive composition. By volume percentage, the organic solvent comprises: 65% methyl methyl carbonate, 20% diethyl carbonate, and 15% ethyl acetate. Based on the total mass of the electrolyte (100%), the functional additive comprises 0.5% by mass, fluoroethylene carbonate 5% by mass, vinylene carbonate 0.5% by mass, lithium bis(oxalato)borate 0.5% by mass, lithium difluorophosphate 0.8% by mass, and 1,3-propanesulfonyl lactone 0.5% by mass; ethyl acetate 10% by mass, the organic solvent 69.7% by mass, and the lithium salt 12.5% ​​by mass. The concentration of the lithium salt in the electrolyte is 1.0 mol / L.

[0085] The mixing temperature was 5℃ and the mixing time was 3 hours.

[0086] Everything else is the same as in Example 1.

[0087] Example 8

[0088] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 2 only in that the electrolyte is composed of an organic solvent, lithium hexafluorophosphate, lithium difluorosulfonylimide, and the above-mentioned ethyl acetate-based electrolyte additive composition. By volume percentage, the organic solvent includes: 70% methyl ethyl carbonate, 18% ethylene carbonate, and 12% ethyl acetate. Based on the total mass of the electrolyte (100%), the functional additive has a mass percentage of 0.5%, fluoroethylene carbonate 5%, vinylene carbonate 0.5%, lithium bis(oxalato)borate 0.5%, lithium difluorophosphate 0.8%, and 1,3-propanesulfonyl lactone 0.5%; ethyl acetate 7.5%, the organic solvent 69.7%, and the lithium salt 15%. The concentration of the lithium salt in the electrolyte is 1.2 mol / L.

[0089] The mixing temperature was 8℃ and the mixing time was 2.5 h.

[0090] Everything else is the same as in Example 1.

[0091] Example 9

[0092] This embodiment provides an electrolyte additive and an electrolyte, which differs from Example 3 only in that: by volume percentage, the organic solvent includes: 55% methyl ethyl carbonate, 15% ethylene carbonate, 18% diethyl carbonate, and 12% ethyl acetate. Based on the total mass of the electrolyte (100%), the functional additive has a mass percentage of 0.5%, fluoroethylene carbonate 5%, vinylene carbonate 0.5%, lithium bis(oxalato)borate 0.5%, lithium difluorophosphate 0.8%, and 1,3-propanesulfonyl lactone 0.5%; ethyl acetate 7.5%, organic solvent 68.7%, and lithium salt 16%. The concentration of lithium salt in the electrolyte is 1.3 mol / L.

[0093] The mixing temperature was 15℃ and the mixing time was 2 hours.

[0094] Everything else is the same as in Example 1.

[0095] In summary, the ethyl acetate-based electrolyte additive composition, electrolyte, method, and applications disclosed in this invention effectively address the severe capacity decay issues during high-temperature storage and cycling by improving the physicochemical properties of the electrolyte-negative electrode interface. This is achieved through protecting the battery interface, reducing side reactions, lowering internal resistance, and enhancing electrolyte stability. Through multi-dimensional synergy of molecular structure design, component ratio optimization, and process control, the interfacial stability problem of carboxylic acid ester solvents at high temperatures is systematically solved. The core advantage lies in the "sacrificial film-forming" characteristic of the functional additive, which transforms the originally harmful EA into an auxiliary component for stabilizing the SEI film, while simultaneously maintaining the electrolyte's ion conductivity and interfacial protection capabilities. This provides crucial technical support for the application of high-energy-density lithium-ion batteries in high-temperature scenarios (such as power batteries and energy storage systems).

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, 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 or all of the technical features; and 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 the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises an organic solvent, a lithium salt, and an ethyl acetate-based electrolyte additive composition; the lithium salt comprises at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the concentration of the lithium salt in the electrolyte is 1.0-1.3 mol / L. The ethyl acetate-based electrolyte additive composition comprises: ethyl acetate and a functional additive; the functional additive has the following general structural formula: ； R1 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms; R2 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms; R3 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms; R4 is independently selected from any one of hydrogen, substituted or unsubstituted phenyl groups and substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms; R5 is independently selected from either hydrogen or methyl; Based on the total mass of the electrolyte (100%), the functional additives comprise 0.5%-1% by mass. The organic solvent includes methyl ethyl carbonate, ethylene carbonate, and diethyl carbonate; based on a total volume of 100%, the volume percentage of methyl ethyl carbonate is 55%-70%, the volume percentage of ethylene carbonate is 15%-20%, the volume percentage of diethyl carbonate is 15%-20%, and the volume percentage of ethyl acetate is 10%-15%. The ethyl acetate-based electrolyte additive composition further includes: fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, 1,3-propanesulfonate lactone, and lithium difluorophosphate.

2. The electrolyte according to claim 1, characterized in that, The functional additive is selected from at least one of the following compounds: 。 3. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte (100%), the organic solvent accounts for 75% to 82% of the mass, the lithium salt accounts for 15% to 16% of the mass, and the ethyl acetate-based electrolyte additive composition accounts for 2% to 10% of the mass.

4. A lithium-ion battery, characterized in that, A lithium-ion battery is assembled using the electrolyte described in any one of claims 1 to 3, along with a positive electrode, a negative electrode, and a separator; the lithium-ion battery retains a capacity of 90.2% to 91.4% after 300 cycles at 10°C; a capacity retention of 94.3% to 95.3% after 45 days of storage at 60°C; and a capacity retention of 87.3% to 89.3% after 400 cycles at 45°C.

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