Electrolyte and secondary battery

Abstract

The application belongs to the technical field of electrolyte, and particularly relates to an electrolyte and a secondary battery. The electrolyte comprises a water removal and acid suppression additive, and the mass percentage of the water removal and acid suppression additive is 0.05% to 2.2% based on 100% of the total mass of the electrolyte. The water removal and acid suppression additive comprises a compound with a structure shown in Formula II and a compound with a structure shown in Formula III. The compound with the structure shown in Formula II is 3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine, and the compound with the structure shown in Formula III is 3-butyl-2-(1-ethylpentyl)-1,3-oxazolidine. The mass ratio of the compound with the structure shown in Formula II to the compound with the structure shown in Formula III is (1:2) to (1:4). The compound with the structure shown in Formula II and the compound with the structure shown in Formula III are compounded in a ratio of (1:2) to (1:4), so that the overall performance of the additive can be synergistically optimized. The compound with the structure shown in Formula II provides a rapid initial acid suppression response, and the compound with the structure shown in Formula III ensures long-term protection, so that a long-term cycle from formation to long-term cycle of the battery is covered.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically relating to an electrolyte and a secondary battery. Background Technology

[0002] Lithium-ion and sodium-ion batteries, as important energy storage devices, are widely used in consumer electronics, electric vehicles, and large-scale energy storage. In secondary batteries, the electrolyte is the key medium for ion transport, and its stability directly determines the battery's cycle life, safety performance, and storage performance.

[0003] Studies have found that trace amounts of water in the electrolyte can have extremely detrimental effects on battery performance. Water primarily reacts with electrolyte salts (such as LiPF6 and NaPF6) through hydrolysis, producing highly corrosive hydrofluoric acid (HF) and strong Lewis acids (such as PF5). HF and PF5 corrode the positive and negative electrode active materials, damaging the solid electrolyte interphase (SEI / CEI) film, leading to metal ion dissolution, increased interfacial impedance, and loss of active materials. This results in a series of problems, including rapid capacity decay, gas generation, and swelling of the battery.

[0004] To mitigate the harmful effects of moisture and acidic substances in electrolytes, existing technologies typically incorporate dehydrating and acid-suppressing additives. Among these, compounds containing oxazolidinyl structures, particularly oxazolidinones, have attracted attention due to their dehydrating capabilities and HF capture effects. Currently, existing technologies utilize oxazolidinone compounds containing silane groups as acid suppressants. These compounds react with HF through the silane groups to form fluorosilanes, and their function is achieved through the coordination of nitrogen atoms with Lewis acids.

[0005] However, the inventors of this application have discovered through in-depth research that such existing additives based on the oxazolidinone structure have the following limitations:

[0006] First, oxazolidinones are essentially cyclic carbamates. When they react with water (hydrolysis), the ring-opening decomposition products include carbon dioxide. In the closed system of a battery, the accumulation of CO2 can lead to increased internal pressure, causing the battery to bulge, posing a safety hazard, and deteriorating electrochemical performance.

[0007] Secondly, existing technologies generally rely on introducing silane groups such as trimethylsilyl to capture HF. However, silane groups are chemically reactive, and their reaction products (such as trimethylfluorosilane) may be volatile. Furthermore, silane substances can easily cause electrolyte discoloration and precipitation during reaction or storage, affecting the long-term stability of the electrolyte and posing risks to large-scale production and application.

[0008] Therefore, there is an urgent need in this field to develop a new type of electrolyte that can effectively solve the gas generation problem, has better chemical stability to achieve long-lasting effects, and does not introduce new side reaction risks, thereby significantly improving the cycle life and safety of secondary batteries.

[0009] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0010] This invention provides an electrolyte and a secondary battery, which at least solves the problems in the prior art where adding oxazolidinone additives to the electrolyte causes gas generation through hydrolysis, and the risk of side reactions introduced by silicon functional groups, thus failing to balance battery safety and long-term stability.

[0011] In existing technologies, fluorinated electrolytes are typically used in lithium-ion and sodium-ion secondary batteries to achieve high ionic conductivity. The most representative example is hexafluorophosphate (XPF6, where X can be Li, Na, K, etc.). However, these fluorinated electrolytes are extremely sensitive to moisture; in the presence of trace amounts of water, they undergo the following hydrolysis reaction chain:

[0012] XPF6→XF+PF5

[0013] H₂O + PF₅ → POF₃ + 2HF

[0014] As can be seen from the above reaction formula, hexafluorophosphate first decomposes to produce trace amounts of phosphorus pentafluoride (PF5). PF5 is a strong Lewis acid with extremely reactive chemical properties, and is a key intermediate that triggers the subsequent hydrolysis chain reaction. It reacts with water to ultimately produce highly corrosive hydrofluoric acid (HF). Therefore, the formation of HF in the electrolyte ultimately stems from the failure to effectively control the activity and content of PF5.

[0015] HF poses a significant threat to battery components. It corrodes the active materials of both the positive and negative electrodes, disrupts the stability of the solid electrolyte interphase (SEI / CEI) membrane, leading to metal ion dissolution, increased interfacial impedance, and accelerated capacity decay. Therefore, effectively suppressing the activity of PF5 in the electrolyte and reducing the content of generated HF has become a key challenge in improving the overall performance of rechargeable batteries, particularly cycle life and high-temperature stability.

[0016] Based on this, the present invention addresses the fundamental problem of controlling the activity of the acid source precursor PF5 and removing HF. By adding an additive with a specific structure to the electrolyte, it aims to simultaneously achieve the dual effects of inhibiting PF5 activity and neutralizing HF, thereby significantly improving the long-term reliability of the battery.

[0017] To achieve the above objectives, in a first aspect, the present invention provides an electrolyte comprising an electrolyte salt, an organic solvent, and a dehydrating and acid-suppressing additive; the dehydrating and acid-suppressing additive comprises a compound with the structure shown in Formula I:

[0018] Formula I;

[0019] Wherein, R1 is selected from straight-chain (C1~C5) alkyl, R2 is selected from branched (C3~C7) alkyl, and R3 is selected from straight-chain (C1~C3) alkyl or hydrogen;

[0020] Based on the total mass of the electrolyte as 100%, the mass percentage of the dehydration and acid-suppressing additive is 0.05%~2.2%.

[0021] The compound of Formula I of this invention has a 1,3-oxazolidine core structure. Specifically, on the oxazolidine ring, a substituent R1 is attached to the nitrogen atom (N) at position 3, and substituents R2 and R3 are attached to the carbon atom at position 2 (i.e., the carbon atom between the nitrogen and oxygen atoms).

[0022] Specifically, R1 is selected from straight-chain (C1~C5) alkyl groups, which may include methyl, ethyl, n-propyl, n-butyl, and n-pentyl.

[0023] R2 is selected from branched (C3~C7) alkyl groups, and may include, but is not limited to, isopropyl, isobutyl, sec-butyl, isopentyl, neopentyl, 1-ethylpropyl, 3-methylbutyl (isopentyl), and 1-ethylpentyl.

[0024] R3 is selected from a straight-chain (C1-C3) alkyl group or hydrogen. Straight-chain (C1-C3) alkyl groups can include methyl, ethyl, and n-propyl. It should be noted that when R3 is hydrogen, the oxazolidine ring has only one substituted alkyl group, R2, at the 2-carbon atom, resulting in a 2-monosubstituted oxazolidine. When R3 is selected from the aforementioned straight-chain (C1-C3) alkyl groups, it, together with R2, forms a 2,2-disubstituted oxazolidine structure.

[0025] In the compound shown in Formula I, R1 is selected from a straight-chain C1-C5 alkyl group, which is directly attached to the nitrogen atom at the 3-position of the oxazolidine ring. The straight-chain alkyl group has a moderate electron-donating effect, which can effectively enhance the electron cloud density of the lone pair electrons on the nitrogen atom, thereby significantly improving its strength as a Lewis base.

[0026] Furthermore, by limiting R1 to a straight-chain alkyl group and controlling the carbon number range, the present invention can optimize the balance between electronic effects and steric hindrance, ensuring its excellent complexing ability.

[0027] R2 is selected from branched C3-C7 alkyl groups, attached to the 2-carbon atom of the oxazolidine ring. Branched alkyl groups (such as 3-methylbutyl and 1-ethylpentyl) can provide suitable steric hindrance, effectively controlling the hydrolysis behavior of the oxazolidine ring. Appropriate steric hindrance slows down the reaction rate between this cyclic acetal-amine structure and water molecules, preventing the additive from being rapidly consumed in the early stages of battery formation. This ensures that it can continuously and slowly function throughout the battery's lifespan, achieving long-term water removal. This effectively overcomes the technical problem of traditional water removal additives (such as isocyanates) being consumed in large quantities during the formation stage, failing to provide continuous protection for long-term battery cycling.

[0028] More importantly, the branched structure of R2 directly determines the type and properties of its hydrolysis products. When the oxazolidinyl ring undergoes hydrolysis and ring opening, R2 will be converted into the corresponding ketone molecules (when R3 is alkyl) or branched aldehyde molecules (when R3 is hydrogen). These branched ketones or aldehydes have high molecular weight and chemical stability, low volatility, and are less likely to participate in side reactions on the electrode surface, thus avoiding the safety hazards or negative impacts on battery performance that small molecule aldehydes and ketones may bring. This characteristic effectively solves the technical problem in existing technologies where oxazolidinyl ketone additives, due to their urethane structure, decompose to produce carbon dioxide gas during hydrolysis, leading to increased battery internal pressure and safety hazards.

[0029] R3 is selected from a straight-chain C1-C3 alkyl group or hydrogen, and is also attached to the carbon atom at position 2. When R3 is a straight-chain C1-C3 alkyl group (such as methyl), it forms a 2,2-disubstituted oxazolidine structure together with R2. Under these conditions, the synergistic effect of R3 and R2 results in chemically inert ketones as hydrolysis products, further enhancing the stability of the system. Controlling the carbon number range of R3 within C1-C3 is to maintain the overall intricacy of the molecule while providing the necessary electrons and steric effects. When R3 is hydrogen, a 2-monosubstituted oxazolidine structure is formed, in which case the hydrolysis product is an aldehyde. This design provides flexibility for different application scenarios.

[0030] The electrolyte provided by this invention, due to the inclusion of specific dehydrating and acid-suppressing additives, effectively eliminates trace amounts of water in the electrolyte and inhibits the formation of acidic substances, thereby significantly improving the overall performance of the battery. Specifically, this additive, through its unique oxazolidine structure, undergoes a slow hydrolysis reaction with water to generate stable alkanolamines and ketones / aldehydes, avoiding the safety hazards of increased internal pressure and swelling of the battery caused by the generation of carbon dioxide gas during the hydrolysis of traditional oxazolidine-ketone additives. Simultaneously, the nitrogen atoms in the additive molecule possess strong Lewis basicity, enabling them to coordinate and complex with the Lewis acid PF5 generated in the electrolyte, inhibiting the chain reaction of HF formation at its source. Furthermore, its hydrolysis product, N-alkylethanolamine, can further neutralize the already generated HF, forming non-volatile ammonium salts and continuously reducing the acidity of the electrolyte. In addition, this additive is not rapidly consumed during the battery formation stage but is slowly released throughout its entire lifespan, achieving long-lasting dehydration and acid suppression, effectively protecting the stability of the electrode interface film (SEI / CEI), reducing metal ion dissolution and interfacial impedance growth, and thus significantly improving the battery's high-temperature storage performance, cycle life, and safety reliability.

[0031] Preferably, the mass percentage of the dehydration and acid-suppressing additive, based on 100% of the total electrolyte mass, is 0.05% to 2.2%, and can be 0.05%, 0.06%, 0.09%, 0.29%, 0.48%, 0.97%, 1.26%, 1.55%, 1.82%, 1.94%, 2.08%, 2.2%, or any value between them. This specific dosage range ensures that the additive can effectively dehydrate and suppress acid in the electrolyte. When the addition amount is not less than 0.05%, it is sufficient to establish an effective concentration gradient within the battery system, ensuring that it can continuously and fully react with trace amounts of water and acidic substances, thereby significantly inhibiting the hydrolysis of electrolyte salts and the formation of hydrofluoric acid (HF), achieving long-term protection of the electrode interface. When the addition amount is not higher than 2.2%, it avoids problems such as abnormally increased electrolyte viscosity, reduced lithium-ion migration rate, or increased battery internal resistance that may result from excessive additives, preventing negative impacts on the battery's rate performance and low-temperature performance. Therefore, this dosage range balances the water removal and acid suppression efficiency of the additive with the basic physicochemical properties of the electrolyte, achieving high cycle life, excellent high-temperature storage performance, and good safety of the secondary battery.

[0032] It can be seen that the present invention uses alkane-substituted oxazolidinyl cyclic compounds, which is substantially different from the oxazolidinone structures commonly used in the prior art. When facing the technical challenge of acid suppression in electrolytes, those skilled in the art have long held a technical bias: that highly reactive functional groups (such as trimethylsilyl groups) must be introduced into the additive molecule as sacrificial groups, achieving acid suppression through their irreversible reaction with HF. This bias directly led to the widespread use of oxazolidinones as the backbone structure in the prior art to facilitate the grafting of such sacrificial groups.

[0033] More specifically, in the existing oxazolidinone structure, the nitrogen atom is usually directly connected to the strong electron-withdrawing carbonyl group (-C=O) and trimethylsilyl group (TMS), which severely weakens the electron cloud density and Lewis basicity of the nitrogen atom; secondly, the trimethylsilyl group (TMS) introduced to compensate for the lack of acid suppression ability has huge steric hindrance, which physically prevents the nitrogen atom from approaching and complexing with the Lewis acid PF5.

[0034] The original design of the acid suppression process in existing technologies was to allow TMS to react with HF while simultaneously coordinating the nitrogen atom with PF5. However, the applicant of this application discovered that existing technologies essentially rely primarily on the consumable reaction of TMS to remove HF, while the auxiliary role of nitrogen atom coordinating with PF5 is actually very limited and unsustainable. Specifically, there are two scenarios: Less commonly, TMS remains connected to the nitrogen atom via a Si-N bond. In this case, the pairing ability of the nitrogen atom's lone pair electrons is significantly weakened by the strong electron-withdrawing effect of TMS, its large steric hindrance, and the strong electron-withdrawing effect of the adjacent carbonyl group. More commonly, TMS is released from the nitrogen atom. Because the existing molecular design itself is intended to promote TMS release, and given that the Si-N bond is relatively easy to break, the deliberately designed electron-withdrawing effect of the carbonyl group further promotes this process. In this case, the released TMS reacts with HF as follows:

[0035] (CH3)3Si-N+HF→(CH3)3Si-F+HN;

[0036] This reaction generates volatile trimethylfluorosilane ((CH3)3Si-F, boiling point approximately 16°C), leading to battery gas buildup. After TMS release, although the nitrogen atom is freed from steric hindrance, it is still suppressed by the electron-withdrawing effect of the carbonyl group, limiting its ability to complex PF5. It can be seen that existing technologies mainly consider acid suppression through silane groups, but do not consider the influence of carbonyl and silane groups on the coordination ability of the nitrogen atom.

[0037] The above conclusions indicate that current technologies primarily rely on the consumable reactions of silane groups to remove HF for acid suppression. However, the use of silane groups presents significant side effects, which are largely ignored in existing technologies. Specifically, trimethylsilane or alkane-silane groups exhibit poor stability and high reactivity, often reacting readily with electrolytes to cause discoloration and precipitation, hindering mass production. Furthermore, the silicon atoms in silane groups possess empty 3d orbitals, exhibiting strong Lewis acidity, and the Si-C and Si-N bonds have relatively low bond energies, resulting in high chemical reactivity. In the complex chemical environment of the electrolyte, especially under the catalytic effects of trace amounts of moisture, fluoride ions, or Lewis acids, silane groups readily undergo side reactions such as hydrolysis, fluorination, or self-condensation.

[0038] Furthermore, silane groups may first react with water or HF to generate unstable silanol intermediates. These silanol intermediates readily react with other components in the electrolyte (such as carbonate solvents, functional additives, or trace oxygen) or undergo oxidation themselves, generating byproducts containing chromophores (such as quinone structures, conjugated alkenes, etc.), causing the electrolyte to gradually change from colorless and transparent to yellow or even dark brown.

[0039] Furthermore, the generated silanol intermediates readily undergo condensation reactions to form siloxane oligomers or polymers. These siloxane polymers have limited solubility in nonpolar or weakly polar organic solvents. When they accumulate to a certain concentration in the electrolyte, they precipitate out as white flocculent or gel-like deposits, which not only affect the uniformity and stability of the electrolyte but may also clog the membrane pores and increase the battery's internal resistance.

[0040] It can be seen that additives containing silane groups actually pose significant technical risks in large-scale production and long-term use. However, existing technologies have established a path dependence for HF removal through silane groups, and few researchers have paid attention to this issue. This invention effectively solves the above-mentioned technical problems through molecular design, specifically:

[0041] First, this invention eliminates unstable silane groups and carbonyl groups that weaken basicity, replacing R1 with a stable straight-chain alkyl group that has a moderate electron-donating effect. On the one hand, the steric hindrance of a straight-chain alkyl group is much smaller than that of a silane group, effectively creating coordination space for the nitrogen atom; on the other hand, the continuous electron-donating effect of the alkyl group ensures that the nitrogen atom always maintains a high Lewis base strength. This allows the additive molecule of this invention to stably, efficiently, and continuously complex PF5, inhibiting the formation of HF at its source. Specifically, when trace amounts of PF5 are present in the electrolyte, the lone pair of electrons on the nitrogen atom attacks the empty d orbital of the phosphorus atom in the PF5 molecule, forming a stable Lewis acid-base adduct, the possible structure of which is shown below:

[0042] R1-N: +PF5 → R1-N → PF5

[0043] Where N represents the lone pair of electrons in a nitrogen atom, and → in the product represents a coordinate bond.

[0044] In this adduct, the PF5 molecule, which originally had a trigonal bipyramidal configuration and was highly reactive, had its phosphorus atom transformed into an sp... 3 d-hybridization transforms into sp 3 d 2 Hybridization results in a geometry closer to an octahedron. This transformation significantly reduces the Lewis acidity and electrophilicity of PF5, making it less susceptible to nucleophilic substitution reactions with water molecules. This interrupts the hydrolytic chain reaction initiated by PF5 and prevents the formation of HF.

[0045] Second, the compound shown in Formula I can be slowly hydrolyzed to open the ring and generate N-alkylethanolamines and the corresponding ketones or aldehydes. The N-alkylethanolamines obtained by hydrolysis (such as N-ethylethanolamine) are strong Lewis bases, and their strengthened amino group (-NH-) can efficiently neutralize the HF already generated, without relying on silane-containing groups. The specific reaction formula is as follows:

[0046] R-NH-CH2CH2OH + HF → R-NH2 + -CH2CH2OH·F - ;

[0047] The N-alkylethanolamine obtained by this invention has a stronger basicity than ordinary ethanolamine because an electron-donating alkyl group (R1) is attached to the amino group. It also has a better ability to neutralize HF. At the same time, the process generates a stable, non-volatile ammonium salt, which avoids the safety hazards caused by the generation of gas.

[0048] It is worth noting that the oxazolidinone structure in the prior art also generates ethanolamine through hydrolysis. However, when the silane groups of the oxazolidinone are not released, the ethanolamine obtained after hydrolysis still carries strongly electron-withdrawing silane groups, thereby weakening the Lewis basicity of the amino group. Ethanolamine with silane groups has extremely poor HF neutralization ability. Even if the silane groups of the oxazolidinone have been released, the ethanolamine obtained after hydrolysis only has ordinary amino groups, and its Lewis basicity is still limited, failing to provide sufficient HF neutralization ability.

[0049] In summary, this invention, by abandoning the oxazolidinone skeleton and silane groups that easily lead to gas production and side reactions in the prior art, adopts a specially designed alkyl-substituted oxazolidinone structure instead. This effectively uses sustainable coordination and slow-release neutralization as the acid-suppressing mechanism of the additive, balancing electronic effects, steric hindrance, hydrolysis kinetics and product stability. Ultimately, it obtains an excellent additive that can achieve water removal and acid suppression functions in a long-term and safe manner, while effectively avoiding side effects such as gas production and discoloration.

[0050] Preferably, the dehydrating and acid-suppressing additive comprises compounds with structures as shown in Formula II and Formula III:

[0051] Formula II;

[0052] Formula III.

[0053] It is understandable that when R1 is ethyl, R2 is 3-methylbutyl and R3 is methyl, a compound with the structure shown in Formula II (3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine) is obtained.

[0054] It is understandable that when R1 is butyl, R2 is 1-ethylpentyl, and R3 is hydrogen, a compound with the structure shown in Formula III (3-butyl-2-(1-ethylpentyl)-1,3-oxazolidine) is obtained.

[0055] The dehydration mechanism of the compound with the structure shown in Formula II is as follows:

[0056]

[0057] 3-Ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine hydrolyzes to give N-ethylethanolamine and isohepanone.

[0058] The dehydration mechanism of the compound with the structure shown in Formula III is as follows:

[0059]

[0060] 3-Butyl-2-(1-ethylpentyl)-1,3-oxazolidine hydrolyzes to give N-butylethanolamine and 2-ethylhexylaldehyde.

[0061] As can be seen from the above reaction formula, the oxazolidine additive of the present invention can react with trace water in the electrolyte to generate alkanolamines and ketones / aldehydes. According to relevant studies, these two products have little impact on the performance of the battery cell.

[0062] More specifically, existing technologies typically employ compounds with the structure shown in Formula IV (3-(trimethylsilyl)oxazolidine-2-one) as dehydrating and acid-suppressing additives:

[0063] Formula IV;

[0064] The dehydration mechanism of the compound with the structure shown in Formula IV is as follows:

[0065]

[0066] 3-(trimethylsilyl)oxazolidin-2-one is hydrolyzed to give N-(trimethylsilyl)ethanolamine and carbon dioxide.

[0067] As can be seen from the above reaction formula, existing oxazolidinone additives (such as Formula IV) produce gaseous byproduct carbon dioxide (CO2) during the dehydration process. In the sealed environment of a battery, the accumulation of CO2 can lead to increased internal pressure, causing swelling and even safety hazards. Simultaneously, in its hydrolysis product N-(trimethylsilyl)ethanolamine, the nitrogen atom remains bonded to the strongly electron-withdrawing trimethylsilyl group, severely weakening its Lewis basicity and limiting its ability to neutralize hydrofluoric acid (HF). This further demonstrates the significant advantages of the additive of this invention (which hydrolyzes to produce stable alkanolamines and ketones / aldehydes without gas generation) in terms of safety and long-lasting acid suppression.

[0068] Preferably, the dehydration and acid-suppressing additive includes compounds with structures shown in Formula II and Formula III, and the mass ratio of the compound with structure shown in Formula II to the compound with structure shown in Formula III is (1:2) to (1:4), which can be (1:2), (1:2.5), (1:3), (1:3.5), (1:4) and any value between them.

[0069] The principle behind this invention's use of this specific mass ratio range lies in the fact that, although the compounds shown in Formula II and Formula III both belong to the alkyl-substituted 1,3-oxazolidine additives, the difference in their alkyl substituents leads to complementary characteristics in dehydration and acid suppression kinetics and the persistence of their effects. In the compound of Formula II, R1 is an ethyl (straight-chain C2 alkyl), which has a moderate electron-donating effect and can effectively enhance the Lewis base strength of the nitrogen atom, making its complexation response to PF5 relatively rapid, suitable for quickly suppressing acid source precursors in the early stages of battery formation; at the same time, its 2,2-disubstituted structure, composed of R2 (3-methylbutyl, branched C5 alkyl) and R3 (methyl), provides moderate steric hindrance, allowing the hydrolysis rate to be controlled at a moderate level, thus playing a good dehydration and acid suppression role in the early stages of battery cycling. In compound III, R1 is butyl (straight-chain C4 alkyl), whose longer carbon chain brings a stronger electron-donating effect, making the Lewis basicity of the nitrogen atom more persistent, and enabling it to continuously complex PF5 and neutralize HF; its R2 is 1-ethylpentyl (branched C7 alkyl) and R3 is a 2-monosubstituted structure composed of hydrogen, which introduces greater steric hindrance, slowing down the hydrolysis rate of the oxazolidine ring, allowing it to slowly release its function during long-term battery cycling, thus achieving long-term protection. Therefore, by compounding compound II and compound III in a ratio of (1:2) to (1:4), the overall performance of the additive can be synergistically optimized, with compound II providing a rapid initial acid suppression response and compound III ensuring long-term protection, thereby covering the long-term cycle of the battery from formation to long-term cycling.

[0070] The ratio range of (1:2) to (1:4) used in this invention is preferred because it effectively balances the differences between the two compounds in electronic effects, steric hindrance, and hydrolysis kinetics, achieving a synergistic enhancement of the dehydration and acid suppression effects. When the ratio is lower than 1:2, the proportion of compound II is relatively high, which can improve the initial response speed, but may weaken the long-term acid suppression ability due to the insufficiency of compound III; when the ratio is higher than 1:4, the proportion of compound III is too high, which can enhance long-term stability, but may slow down the initial acidity control rate and affect the interface formation during the battery formation stage. In the range of (1:2) to (1:4), the rapid complexing ability of compound II and the persistent alkaline effect of compound III can be optimally matched, ensuring that the electrolyte can maintain a low moisture and low acidity state in all stages of storage, formation, and cycling, thereby significantly improving the overall electrochemical performance of the battery.

[0071] The combination of Formula II and Formula III compounds offers significant advantages over single compounds. While single additives can function effectively at specific stages, they struggle to balance rapid response with long-term durability. For example, using Formula II alone may lead to a decline in acid suppression capability during long-term cycling, while using Formula III alone may expose the battery to a higher acid risk in the initial stages. The combination achieves spatiotemporal complementarity of water removal and acid suppression functions through intermolecular synergistic effects: Formula II rapidly consumes trace amounts of water and complexes PF5 in the early stages of battery operation, inhibiting the initiation of the HF formation chain; Formula III, on the other hand, continuously and slowly hydrolyzes in subsequent cycles, continuously providing strongly alkaline N-alkylethanolamine to neutralize the generated HF and maintain the complexation capability with PF5. This synergistic effect not only extends the effective action time of the additives but also avoids performance fluctuations that may occur due to excessive consumption or reaction rate mismatches caused by single compounds. This more effectively protects the electrode interface film, reduces metal ion dissolution and impedance growth, and comprehensively improves the cycle life, high-temperature storage performance, and safety and reliability of the secondary battery.

[0072] Furthermore, the combination of compounds of formula II and formula III can produce dehydration and acid suppression performance exceeding that of single components, possibly because they form a complementary or even synergistic mechanism in the reaction system. Specifically, the possible principles are as follows: First, from the perspective of intermolecular forces, the molecules of formula II and formula III may form ordered aggregates in the system through non-covalent interactions such as hydrogen bonds, van der Waals forces, or π-π stacking. This ordered structure enhances their adsorption capacity and selectivity for water molecules or acidic substances. Second, the combined system may achieve kinetic optimization. Single components may cause reaction rate fluctuations due to excessively high or low local concentrations during the reaction process, while the difference in consumption rates of the two components at different stages after combination may make the overall reaction closer to the ideal steady state, thereby improving the utilization efficiency of unit mass of active material. Third, from the perspective of energy barriers, formula II and formula III may act on reaction steps with different energy barriers respectively. After the two are combined, the apparent activation energy of the overall reaction is reduced, making the dehydration and acid suppression process more thorough under the same conditions, breaking the thermodynamic or kinetic limitations of single compounds. Fourth, considering the reaction rates of both components with water, this rate difference likely avoids kinetic competitive inhibition. If the two components react at similar rates, they might compete for water molecules simultaneously in the early stages of the reaction, leading to a chaotic reaction pathway, or even mutual interference due to steric hindrance. A clear division of labor between fast and slow reactions constructs a clear and efficient cascade reaction pathway. This orderly reaction process ensures that each unit mass of active material is utilized efficiently, thus macroscopically manifesting as an improvement in overall dehydration and acid suppression capabilities.

[0073] Preferably, the electrolyte salt includes one or more of XPF6, XClO4, XBF4, XAsF6, XFSI, XTFSI, XBOB, XODFB, XCF3SO3, XPO2F2, or XOTFB; wherein X includes any one of Li, Na, or K. More preferably, the electrolyte salt is XPF6. The variety of electrolyte salts gives the electrolyte system high flexibility and wide applicability, making it suitable for various secondary battery systems such as lithium-ion, sodium-ion, or potassium-ion batteries. The electrolyte salts selected in this invention have high ionic conductivity and electrochemical stability, providing efficient ion transport channels and a wide electrochemical window for the battery, which is the foundation for building high-performance batteries. Although these electrolyte salts, especially hexafluorophosphate (XPF6), are susceptible to moisture, the dehydration and acid-suppressing additives of this invention can effectively avoid this side reaction, effectively complexing Lewis acids (such as PF5) produced by salt decomposition and neutralizing HF, thereby significantly inhibiting the hydrolysis side reaction of the electrolyte salt itself and ensuring the chemical stability of the electrolyte salt under long-term cycling and high-temperature environments.

[0074] Preferably, the concentration of the electrolyte salt in the electrolyte is 0.8 mol / L to 1.2 mol / L, and can be 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, or any value between them. More preferably, the concentration of the electrolyte salt in the electrolyte is 1.0 mol / L. This concentration range is set based on a comprehensive optimization of factors such as ionic conductivity, electrolyte viscosity, salt solubility, and cost. When the salt concentration is not lower than 0.8 mol / L, it can provide a sufficient number of charge carriers to ensure that the electrolyte has excellent ionic conductivity, thereby ensuring good rate performance and fast charge and discharge capability of the battery. When the salt concentration is not higher than 1.2 mol / L, it can effectively avoid problems such as a significant increase in electrolyte viscosity, a decrease in lithium ion transference number, low-temperature precipitation of salts, and poor wettability caused by excessive concentration, thus preventing an increase in battery internal resistance and deterioration of electrochemical performance.

[0075] Preferably, the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), trifluoropropyl ethylene carbonate (TFPC), ethyl acetate (EA), 2,2-difluoroethyl ester (DFEA), methyl acetate (MA), ethyl propionate (EP), methyl propionate (MP), propyl propionate (PP), ethyl butyrate (EB), methyl butyrate (MB), methyl valerate (MV), ethyl formate (EF), methyl formate (MF), 1,2-dimethoxyethane, ethylene glycol dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 2-methyltetrahydropyran, tetrahydropyran, 1,3-dioxolane (DOL), crown ether (18-crown -6) Any one or a combination of at least two of the following: diethylene glycol dimethyl ether (Diglyme), triethylene glycol dimethyl ether (Triglyme), tetraethylene glycol dimethyl ether (Tetraglyme), dipropylene glycol dimethyl ether (DPGDE), acetonitrile (AN), fluoroacetonitrile (FAN), adiponitrile (ADN), glutaronitrile (GLN), succinate (SN), 3-methoxypropionitrile (MPN), methoxyacetonitrile (MAN), fluoroether (HFE-7100), perfluoropolyether (PFPE), ethyl trifluoroacetate (ETFA), methyl trifluoropropionate (MTFP), γ-butyrolactone (GBL), N-methylpyrrolidone (NMP), vinylene carbonate (VC), vinyl sulfite (ES), propylene sulfite (PS), dimethyl sulfate (DMS), triethyl phosphate (TEP), trimethyl phosphate (TMP), nitromethane (NM), and dimethylformamide (DMF). The wide selection of organic solvents offers exceptional flexibility and broad compatibility, allowing electrolyte systems to optimize their overall performance through the properties and combinations of different solvents. For example, cyclic carbonates (such as EC) possess high dielectric constants, facilitating the dissociation of electrolyte salts; chain carbonates (such as EMC and DMC) and carboxylic esters (such as EA and EP) effectively reduce electrolyte viscosity and melting point, improving low-temperature performance; while fluorinated solvents (such as FEC) and sulfur / phosphorus-containing solvents (such as ES and TEP) participate in the formation of more stable electrode interface films. More importantly, the organic solvents selected in this invention exhibit excellent compatibility and synergy with the specific dehydration and acid-suppressing additives of this invention, collectively forming a stable and functionally integrated media environment.

[0076] Preferably, based on the total mass of the electrolyte (100%), the content of organic solvent is 58.5% to 92.7%, and can be 58.5%, 59%, 60%, 66%, 69%, 72%, 83%, 90%, 92.7%, or any value between them. This set content range ensures improved overall performance of the electrolyte system. When the organic solvent content is not less than 58.5%, it provides sufficient dissolution space for electrolyte salts and various functional additives, ensuring the formation of a homogeneous and stable solution system, thereby achieving excellent ionic conductivity and ensuring good wettability of the electrolyte to the electrodes and separator. This is the foundation for achieving low internal resistance and efficient ion transport in the battery. Simultaneously, this content range ensures that the electrolyte has suitable viscosity and fluidity, which is beneficial for electrolyte injection during battery manufacturing and interfacial transport kinetics during long-term cycling. When the organic solvent content is no higher than 92.7%, the problem of insufficient concentration of electrolyte salt and functional additives (especially the dehydration and acid-suppressing additive of this invention) caused by excessive solvent is effectively avoided. This ensures sufficient carrier concentration and effective functional concentration of additives, thereby guaranteeing the battery's capacity, interface stability, and long-term protection capability. Therefore, this solvent content, together with the specific concentration of electrolyte salt and additives, synergistically constructs an electrolyte environment with efficient ion transport, stable chemical properties, and long-lasting interface protection, effectively improving the energy density, cycle life, and safety performance of the secondary battery.

[0077] Preferably, the electrolyte further comprises functional additives, including one or more combinations of vinylene carbonate (VC), 1,3-propanesulfonyl lactone (1,3-PS), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), 1,3-propenyl-sulfonyl lactone, ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 2-methylmaleic anhydride, methyl disulfonate, fluorobenzene, vinyl sulfite, ethylene carbonate, adiponitrile, succinate, ethylene glycol dipropionitrile ether, difluoroethylene carbonate, 1,3,6-hexanetrionitrile, dicyclohexylcarbodiimide, and trifluoroethyl methyl carbonate. These functional additives can preferentially undergo electrochemical reduction or oxidation reactions on the positive and negative electrode surfaces during battery charging and discharging, forming a dense, stable, and ion-conducting solid electrolyte interphase (SEI) film and positive electrode electrolyte interphase (CEI) film. This effectively inhibits the continuous decomposition of the electrolyte on the electrode surface, reduces the loss of active materials, and decreases the increase in interfacial impedance.

[0078] Secondly, the present invention provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect. The secondary battery may be a lithium-ion battery, a sodium-ion battery, or a potassium-ion battery.

[0079] Preferably, the negative electrode sheet includes a negative electrode active material, which is selected from one or a combination of at least two of the following: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphdiene, lithium / sodium / potassium metal, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide, silicon-carbon composite, silicon / copper oxide composite, AG composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, or lithium titanate.

[0080] Preferably, the material of the diaphragm includes any one of polyethylene, polypropylene, or composite ceramic membrane.

[0081] The beneficial effects of this invention are as follows:

[0082] This invention effectively solves the safety risks and stability problems associated with traditional acid-suppressing additives in electrolytes. By eliminating the easily hydrolyzed and gas-producing oxazolidinone skeleton and unstable silane groups, and adopting a 1,3-oxazolidinyl structure with specific alkyl substitution, the additive reacts with trace amounts of water to generate only chemically stable, low-volatility alkanolamines and ketones / aldehydes, avoiding the generation of carbon dioxide gas and eliminating the safety hazard of battery swelling. Simultaneously, the strong Lewis base nitrogen atom in the additive molecule can efficiently and sustainably complex with the strong Lewis acid PF5, inhibiting the HF generation chain at its source. Furthermore, the N-alkylethanolamine produced by its hydrolysis can further neutralize the already generated HF, forming a non-volatile salt, achieving dual acid suppression at both the front and back ends. The entire process is free of side reaction risks, and the electrolyte exhibits excellent long-term storage stability. This invention combines Formula II and Formula III in a ratio of (1:2) to (1:4) to synergistically optimize the overall performance of the additives. Formula II provides a rapid initial acid suppression response, while Formula III ensures long-lasting protection in the later stages, thereby covering the long-term cycle of the battery from formation to long-term cycling. Detailed Implementation

[0083] In this invention, 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0084] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0085] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0086] The present invention will now be described in further detail with reference to specific embodiments, but these are exemplary and do not limit the scope of protection of the present invention in any way. Unless otherwise specified, all percentages in the following embodiments are mass percentages.

[0087] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field, and the reagents are all available commercially.

[0088] Experimental examples, implementation examples and comparative examples

[0089] The specific preparation methods of the sodium-ion batteries in the following experimental examples, embodiments, and comparative examples are as follows:

[0090] 1. Preparation of electrolyte

[0091] In an argon-filled glove box (water and oxygen content both <0.1ppm), organic solvents, electrolyte salts, dehydrating and acid-suppressing additives, and functional additives were mixed and stirred evenly according to the proportions shown in Table 1 to prepare the electrolytes for each experimental example, embodiment, and comparative example.

[0092] 2. Preparation of sodium-ion batteries

[0093] (1) Preparation of positive electrode: Sodium nickel iron manganese oxide, CNT and PVDF were homogenized in NMP solution at a mass ratio of 94:3:3. The positive electrode slurry was coated on the current collector. The double-sided areal density of the positive electrode active slurry was 70 g / m². 2The positive electrode sheet is rolled to achieve a compaction density of 1.31 g / cm³. 3 After drying, rolling, and slitting, positive electrode sheets that can be directly stacked are obtained.

[0094] (2) Preparation of negative electrode sheet: The negative electrode active material hard carbon, conductive agent SP and binder SBR are mixed in a mass ratio of 92:4:4 with deionized water as solvent and stirred to prepare a negative electrode active slurry. The negative electrode active slurry is uniformly coated on the negative electrode current collector. The double-sided surface density of the negative electrode active slurry coating is 30 g / m². 2 The negative electrode sheet is rolled to achieve a compaction density of 0.85 g / cm³. 3 After drying, rolling, and slitting, negative electrode sheets that can be directly stacked are obtained.

[0095] (3) Cell assembly: The slit positive and negative electrode sheets are stacked on a stacking machine, with a PP separator and a 9μm PP + 3μm alumina ceramic coating to form a soft-pack cell.

[0096] (4) Electrolyte Injection Formation: The above-mentioned soft-pack cells were uniformly injected with electrolyte for formation and aging. Specifically, after the cells were dried at high temperature, the electrolytes of the examples and comparative examples obtained in Table 1 were injected into the soft-pack cells. After the electrolyte was injected, the sodium-ion batteries underwent initial packaging, surface cleaning, and other preliminary work, and were placed at room temperature for one day. Formation was carried out using a step-by-step formation method. The first step formation current was 0.05C, and constant current charging was carried out for 2 hours. The second step formation current was 0.1C, and constant current charging was carried out until the voltage reached 4.1V. After formation, the cells were aged at 45°C for one day and then cooled to room temperature for secondary sealing.

[0097] The electrolyte composition of each experimental example, embodiment, and comparative example is shown in Table 1.

[0098] Table 1

[0099]

[0100] In Table 1, the electrolyte salt is sodium hexafluorophosphate (NaPF6), and the organic solvent is ethylene carbonate and methyl ethyl carbonate mixed at an EC:EMC ratio of 1:1. The dehydrating and acid-suppressing additives include the compound with the structure shown in Formula IV (3-(trimethylsilyl)oxazolidine-2-one) as follows:

[0101] Formula IV;

[0102] The dehydrating and acid-suppressing additive contains the compound (3-ethyl-oxazolidin-2-one) with the structure shown in formula V:

[0103] Formula V;

[0104] The dehydrating and acid-suppressing additive containing the compound with the structure shown in formula VI (2-ethyl-3-(trimethylsilyl)-1,3-oxazolidine) is as follows:

[0105] Formula VI.

[0106] All reagents listed in Table 1 of this invention are commercially available. The following are some exemplary methods for obtaining these reagents:

[0107] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and sodium hexafluorophosphate (NaPF6) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 99.99%.

[0108] Fluorinated ethylene carbonate (FEC), vinylene carbonate (VC), and vinyl sulfate (DTD) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. or Shanghai Mairui Biochemical Technology Co., Ltd., with a purity of 99.5%.

[0109] Compound II (3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine) and compound III (3-butyl-2-(1-ethylpentyl)-1,3-oxazolidine) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a purity of 99.5%.

[0110] Test case

[0111] The sodium-ion batteries obtained in the above experimental examples, embodiments, and comparative examples were subjected to cycling tests at 25°C and 45°C, and storage tests at 60°C and 70°C. The tests were conducted using the Xinwei charge-discharge testing system, and the test results are shown in Tables 2 and 3. The specific test methods are as follows:

[0112] 1. Room temperature cycling performance test

[0113] At 25°C, the sodium-ion batteries obtained in the experimental example, the example, and the comparative example were charged to 4.0V at a constant current and constant voltage of 0.5C, left to stand for 5 minutes, and then discharged to 2.0V at a constant current of 1C. This constitutes one charge / discharge cycle.

[0114] The capacity retention rate (%) of a sodium-ion battery after 2000 cycles = (discharge capacity of the 2000th cycle / initial discharge capacity) × 100%.

[0115] 2. High-temperature cycling performance test at 45℃

[0116] At 45°C, the sodium-ion batteries obtained in the experimental example, the example, and the comparative example were charged to 4.0V at a constant current and constant voltage of 0.5C, left to stand for 5 minutes, and then discharged to 2.0V at a constant current of 1C. This constitutes one charge / discharge cycle.

[0117] The capacity retention rate (%) of a sodium-ion battery after 1000 cycles = (discharge capacity of the 1000th cycle / initial discharge capacity) × 100%.

[0118] 3. 60℃ High Temperature Storage Test

[0119] At 25°C, the sodium-ion batteries obtained in the experimental example, the example, and the comparative example were charged to 4.0V at a constant current and constant voltage of 0.5C. After standing for 5 minutes, they were discharged to 2.0V at a constant current of 1C. After two cycles, they were fully charged, and the average discharge capacity over three weeks was taken as C0. The batteries were placed in a 60°C oven for 14 days, then removed and cooled to room temperature. They were then discharged to 2.0V at a constant current of 1C, and the discharge capacity at this time was recorded as C1. The batteries were then fully charged and discharged to 2.0V at a constant current of 1C, and the discharge capacity at this time was recorded as C2.

[0120] 60℃ high-temperature storage capacity retention rate = (C1 / C0) × 100%;

[0121] 60℃ high temperature storage capacity recovery rate = (C2 / C0) × 100%.

[0122] 4. 70℃ High Temperature Storage Test

[0123] At 25°C, the sodium-ion batteries obtained in the experimental example, the example, and the comparative example were charged to 4.0V at a constant current and constant voltage of 0.5C. After standing for 5 minutes, they were discharged to 2.0V at a constant current of 1C. After cycling for two weeks, they were fully charged. The volume at this time was measured by the water displacement method as V1. After the measurement, the batteries were placed in a 70°C oven for 10 days, then cooled to room temperature and the volume at this time was measured by the water displacement method as V2.

[0124] The volume expansion rate of a battery cell stored at 70℃ is calculated as (V2 - V1) / V1 × 100%.

[0125] 5. Moisture and acidity tests

[0126] Moisture and acidity tests before injection: Moisture content was tested directly using a Karl Fischer moisture analyzer; acidity was determined by titration using the triethylamine method.

[0127] Moisture and acidity tests of electrolyte after 10 days at room temperature: The remaining electrolyte after filling was placed in an aluminum bottle and sealed for storage. After 10 days, the moisture content was tested again using a Karl Fischer moisture analyzer. Acidity was determined by titration using the triethylamine method.

[0128] Moisture and acidity tests after cycling: First, cycle the battery cell for 500 cycles. Then, in a glove box filled with nitrogen, remove the aluminum-plastic film from the battery cell and immerse it in an aluminum-plastic bag containing 100 mL of dimethyl carbonate (DMC, which has been pre-treated to remove water and has a moisture content of less than 5 ppm). After standing for one day, test the leachate using a Karl Fischer moisture analyzer. The acidity is determined by titration using the triethylamine method.

[0129] 6. Electrolyte stability test

[0130] After sealing the electrolyte, place it in a 45℃ oven for 20 days and then remove it. Observe whether the electrolyte is a transparent, clear, and colorless liquid; otherwise, it is considered discolored.

[0131] Table 2

[0132]

[0133] Continued from Table 2

[0134]

[0135] Table 3

[0136]

[0137] Continued from Table 3

[0138]

[0139] Based on the experimental data in Table 3, the synergistic effect of the combination of compounds of formula II and formula III can be clearly observed. Specifically, in terms of the indicators reflecting the early reaction, namely "electrolyte moisture before injection" and "electrolyte acidity before injection," the initial values ​​of the experimental examples with added compound II were significantly lower than those of Comparative Example 1 without any dehydration and acid suppression agents. This confirms that compound II exerts a rapid and efficient dehydration and acid suppression function in the early stage of system construction. However, in key indicators characterizing later stability, such as "moisture content after 10 days at room temperature," "moisture content after cycling," "acidity after 10 days at room temperature," and "acidity after cycling," the experimental examples with added compound III showed excellent performance retention, with values ​​far lower than those of Comparative Example 1 without any dehydration and acid suppression agents.

[0140] Understandably, the data from Examples 1-3 show that a more balanced and stable water removal and acid suppression effect has been achieved throughout the battery life cycle.

[0141] Based on Examples 1-3, this invention further increases the total addition amount to more than 1.2% (preferably 1.5%) and further adjusts the ratio (as shown in Examples 4-8), which ultimately enables the electrolyte of this invention to improve the overall water removal and acid suppression capabilities while balancing the water removal and acid suppression effects in the early and late stages.

[0142] Specifically, through a direct comparison between Examples 4-8 and the experimental examples containing only a single component, the data shows that Examples 4-8 significantly outperformed Comparative Example 1 and the experimental examples containing only Formula II in terms of initial indicators "before liquid injection," achieving lower initial moisture and acidity. In terms of later indicators evaluating long-term stability, the performance degradation curves of Examples 4-8 were extremely smooth, and their moisture and acidity control capabilities "after 10 days of storage at room temperature" and "after cycling" were stronger than those of the experimental examples containing only Formula III.

[0143] In summary, Table 3 demonstrates that the combination of Formula II and Formula III is not a simple functional superposition. On the one hand, Formula II ensures the rapid establishment of a pure environment with low water and low acid in the early stage, and on the other hand, Formula III enables the system to be stored and recycled for a long time, achieving a more balanced, powerful and lasting water removal and acid suppression effect throughout the entire timeline of cell manufacturing.

[0144] More importantly, the superior dehydration and acid suppression effects resulting from this compounding process can be translated into improved cycle capacity retention in secondary batteries. According to the electrochemical performance data in Table 2, Examples 4-8 consistently maintained a capacity retention rate of over 95.9% after 2000 cycles at 25°C, superior to the examples using a single compound (maximum 95.5%), and significantly higher than the comparative examples without additives or using traditional additives. In the battery field, even a 1% improvement in capacity retention translates into a significant extension of battery life. For applications such as consumer electronics, electric vehicles, and large-scale energy storage, the economic benefits and performance gains from this improvement are extremely significant. This fully demonstrates that the synergistic effect of Formula II and Formula III is not only reflected in the microscopic control of moisture and acidity, but also ultimately in the macroscopic advantages of electrochemical performance. By constructing a cleaner and more stable electrolyte environment, it effectively suppresses side reactions at the electrode interface and the loss of active materials, thereby achieving a breakthrough in long-term battery cycle life.

[0145] As shown in Examples 1 to 8, the dehydration and acid suppression additives of the present invention (including compounds with structures shown in Formulas II and III) can effectively function within a specific addition range. Sodium-ion batteries using this additive exhibit excellent high capacity retention after 2000 cycles at 25°C and 1000 cycles at 45°C. They also show high capacity retention and recovery rates in high-temperature storage tests at 60°C. Furthermore, the related electrolytes show minimal increases in moisture and acidity after being placed at room temperature and undergoing long-term cycling. Moreover, the electrolytes in all examples did not show discoloration after accelerated aging at 45°C. This proves that the additives of the present invention can continuously remove moisture and inhibit HF generation through slow hydrolysis, thereby achieving long-lasting and stable dehydration and acid suppression functions. In addition, its hydrolysis products are stable and do not produce gas, avoiding the risk of battery swelling and ensuring excellent long-cycle performance and high safety of the electrolyte system and secondary battery.

[0146] Furthermore, electrolytes using a specific mass ratio of compounds of formulas II and III exhibited superior overall performance compared to single-compound additives in terms of battery cycle performance, high-temperature storage performance, and moisture and acidity control. The batteries demonstrated higher capacity retention and improved acidity and moisture suppression capabilities, validating the synergistic effect of the two compounds in their action kinetics and achieving a balance between rapid initial response and long-lasting protection.

[0147] According to the examples and comparative examples, Comparative Example 1, which did not add any dehydrating and acid-suppressing agents, performed the worst in terms of cycle performance, storage performance, and moisture and acidity control. Comparative Examples 2-4, which used traditional oxazolidinone or silane-containing additives, showed some improvement in the initial stage, but their overall performance was still inferior to the examples of the present invention. Furthermore, Comparative Examples 2 and 4 also exhibited electrolyte discoloration and instability. This comparative result strongly confirms that the specific alkyl-substituted 1,3-oxazolidinone additives provided by the present invention, through their unique molecular structure design, successfully solve the technical bottlenecks of traditional additives (such as oxazolidinones that produce gas and silane groups that are unstable and prone to discoloration). While achieving long-lasting and efficient dehydration and acid suppression, they also possess chemical stability and compatibility with the electrolyte system, thereby bringing significantly improved cycle life, high-temperature storage performance, and overall safety and reliability to secondary batteries.

[0148] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention. Those skilled in the art, based on existing embodiments and common technical knowledge in the field, can reasonably predict that other alkyl substituents within the scope of protection of the present invention can also achieve the effects of the present invention. Furthermore, any other suitable combination of technical features, these simple modifications and combinations, should also be considered as part of the content disclosed in the present invention and are all within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that, It includes electrolyte salts, organic solvents, and dehydrating and acid-suppressing additives; based on the total mass of the electrolyte (100%), the mass percentage of the dehydrating and acid-suppressing additives is 1.2% to 2.2%. The dehydrating and acid-suppressing additives include compounds with structures as shown in Formula II and Formula III: Formula II; Formula III; The mass ratio of the compound with the structure shown in Formula II to the compound with the structure shown in Formula III is (1:2) to (1:4).

2. The electrolyte according to claim 1, characterized in that, The electrolyte salt includes one or more of XPF6, XClO4, XBF4, XAsF6, XFSI, XTFSI, XBOB, XODFB, XCF3SO3, XPO2F2 or XOTFB; Wherein, X includes any one of Li, Na or K; The concentration of the electrolyte salt in the electrolyte is 0.8 mol / L to 1.2 mol / L.

3. The electrolyte according to claim 1, characterized in that, The organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, trifluoropropyl ethylene carbonate, ethyl acetate, 2,2-difluoroethyl ester, methyl acetate, ethyl propionate, methyl propionate, propyl propionate, ethyl butyrate, methyl butyrate, methyl valerate, ethyl formate, methyl formate, 1,2-dimethoxyethane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2-methyltetrahydropyran, tetra ... One or a combination of at least two of the following: hydropyran, 1,3-dioxolane, crown ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, acetonitrile, fluoroacetonitrile, adiponitrile, glutaronitrile, succinate, 3-methoxypropionitrile, methoxyacetonitrile, fluoroether, perfluoropolyether, ethyl trifluoroacetate, methyl trifluoropropionate, γ-butyrolactone, N-methylpyrrolidone, vinylene carbonate, vinyl sulfite, propylene sulfite, dimethyl sulfate, triethyl phosphate, trimethyl phosphate, nitromethane, and dimethylformamide.

4. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte as 100%, the content of the organic solvent is 58.5% to 92.7%.

5. The electrolyte according to claim 1, characterized in that, The electrolyte also contains functional additives, including one or more combinations of vinylene carbonate, 1,3-propanesulfonyl lactone, 1,3-propenyl-sulfonyl lactone, fluoroethylene carbonate, vinyl sulfate, ethoxy(pentafluoro)cyclotriphosphazene, 2-methylmaleic anhydride, methyl disulfonate, fluorobenzene, vinyl sulfite, ethylene ethylene carbonate, adiponitrile, succinic acid, ethylene glycol dipropionitrile ether, difluoroethylene carbonate, 1,3,6-hexanetrionitrile, dicyclohexylcarbodiimide, and trifluoroethyl methyl carbonate.

6. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1 to 5.

7. The secondary battery according to claim 6, characterized in that, The negative electrode sheet includes a negative electrode active material, which is selected from one or a combination of at least two of the following: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphdiene, lithium metal, sodium metal, potassium metal, nano-carbon, elemental silicon, silicon oxide, silicon-carbon composite, silicon / copper oxide composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, or lithium titanate.

8. The secondary battery according to claim 6, characterized in that, The membrane material includes any one of polyethylene, polypropylene, or composite ceramic membrane.

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