Electrolyte for secondary battery and secondary battery

Abstract

This invention provides an electrolyte for a secondary battery, comprising an electrolyte salt, a solvent, a first additive, and a second additive. The first additive has the structure shown in Formula 1, and the second additive is a vinylsiloxane. During battery cycling, nitro-substituted bistyrene forms an inorganic SEI film component with high ionic conductivity, while the vinylsiloxane undergoes a crosslinking reaction to generate a polymer network structure elastic organic SEI film component. The combined use of the two additives forms an organic-inorganic composite film, avoiding the drawbacks of poor toughness of inorganic SEI films and poor ionic conductivity of organic films. This effectively regulates lithium-ion deposition while maintaining interfacial stability and effectively suppresses structural changes caused by negative electrode volume expansion, thereby effectively improving the cycle performance of the negative electrode. This invention also provides a secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to an electrolyte for secondary batteries and a secondary battery. Background Technology

[0002] Due to the high theoretical specific capacity of silicon-based anode materials, silicon-carbon composite materials can significantly improve the specific capacity of individual battery cells, increasing the driving range of electric vehicles. However, silicon anodes currently face the following problems: First, during lithium insertion / extraction, silicon particles undergo volume expansion and contraction, leading to particle pulverization and detachment, causing structural collapse and ultimately resulting in the separation of the electrode active material from the current collector. Second, due to the volume effect of silicon-based anode materials, silicon struggles to form a stable solid electrolyte interphase (SEI) film in the electrolyte, leading to irreversible consumption of the electrolyte and lithium source from the cathode through continuous SEI film growth. Current solutions involve modifying silicon anode materials to suppress pulverization and improving the stability of the SEI film through additives.

[0003] Currently, the commonly used additive for silicon anode electrolytes is FEC. FEC forms an inorganic film rich in LiF on the surface of the silicon anode, which regulates the uniform deposition of lithium ions to a certain extent. However, the SEI film formed by FEC additive has poor toughness and cannot resist the drastic volume changes of silicon, which leads to the cracking and repair thickening of the SEI film, ultimately affecting the migration and uniform deposition of lithium ions, forming a negative feedback mechanism.

[0004] Due to the abundant global reserves and low cost of sodium resources, sodium-ion battery technology, with its similar principles to lithium-ion batteries, has great potential in the energy storage field. However, the application of sodium-ion batteries also faces some challenges. Hard carbon, as a negative electrode material for sodium-ion batteries, exhibits poor rate performance and cycle stability. The stability of the SEI film and the electrode-electrolyte interface is crucial to the cycle life and rate performance of sodium-ion batteries. Therefore, researchers are searching for more effective electrolyte additives for the SEI film to improve the cycle life of sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide an electrolyte for secondary batteries and a secondary battery. The electrolyte of this invention can form a composite SEI film with high mechanical strength and toughness on the negative electrode surface, effectively suppressing the negative electrode volume effect, reducing side reactions or reaction area during charging and discharging, and exhibiting high ionic conductivity, which is beneficial for Li… + Na + This electrolyte promotes migration and uniform deposition. It can improve the stability of electrode materials, reduce the apparent rate of side reactions, and enhance battery cycle performance.

[0006] This invention provides an electrolyte for secondary batteries, comprising an electrolyte salt, a solvent, a first additive, and a second additive;

[0007] The first additive has the structure shown in Formula 1:

[0008]

[0009] In Formula 1, R1, R2, R4, R5, R1′, R2′, R4′, and R5′ are independently selected from hydrogen, halogen, C1-C5 alkyl, C1-C3 haloalkyl, or C1-C5 alkoxy.

[0010] R3 is selected from hydrogen, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, perfluorobutyl, nitro, cyano, isocyanate, amino, or mercapto.

[0011] The second additive is vinylsiloxane.

[0012] Preferably, the first additive has the structure shown in Formulas 1-1 to 1-6:

[0013]

[0014] Preferably, the first additive is prepared according to the following steps:

[0015] In the presence of an inert gas and a catalyst, a 4-nitrobenzyl bromide compound having the structure shown in Formula A is reacted with a benzaldehyde compound having the structure shown in Formula B to prepare a nitro-substituted bistyrene derivative having the structure shown in Formula 1 in one step.

[0016]

[0017] The catalyst comprises catalyst A and catalyst B. Catalyst A is one or more of triphenylphosphine, trimethylphosphine, triethylphosphine, N,N-dimethylcyclohexylamine, triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylantimony, chromium acetylacetone, and tetraethylammonium bromide. Catalyst B is one or more of potassium hydroxide, sodium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0018] The molar ratio of the 4-nitrobenzyl bromide compound A to the benzaldehyde compound B is preferably 1:(1-1.5), more preferably 1:(1.1-1.4).

[0019] The molar ratio of the 4-nitrobenzyl bromide compound to catalyst A is preferably (1-1.5):1, more preferably (1-1.3):1.

[0020] The molar ratio of the 4-nitrobenzyl bromide compound A to catalyst B is preferably (1.5–2.2):1, more preferably (1.6–2):1. The inert gas is selected from nitrogen or argon; the reaction temperature of the one-step reaction is 70–100°C.

[0021] Preferably, the second additive has the structure shown in Formula 2:

[0022]

[0023] In Formula 2, R6 is hydrogen or a C1-C3 alkyl group, and the hydrogen atoms on the alkyl group in the C1-C3 alkyl group may be completely or partially replaced by fluorine atoms;

[0024] R7 and R8 are independently selected from halogens, C1-C3 alkyl groups, C1-C3 haloalkyl groups, C2-C3 unsaturated hydrocarbon groups, C2-C3 halounsaturated hydrocarbon groups, C1-C3 cyano-substituted hydrocarbon groups, phenyl groups, trimethylsilyl groups, isocyanate groups, or trimethylsilyl groups.

[0025] Preferably, the mass fraction of the first additive in the electrolyte for secondary batteries is 0.1% to 5%;

[0026] The second additive has a mass fraction of 0.1% to 3% in the electrolyte for secondary batteries.

[0027] Preferably, the electrolyte salt includes lithium salt and sodium salt;

[0028] The lithium salt includes one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium bis(fluorosulfonyl)imide.

[0029] The sodium salts include sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalate borate, and sodium difluorosulfonamide.

[0030] The concentration of the electrolyte salt is 0.5–2.0 mol / L.

[0031] Preferably, the electrolyte for secondary batteries further includes a basic additive, which is selected from, but not limited to, one or more of sulfonates, sulfates, unsaturated cyclic carbonates, borates, and trimethylsilyl esters, and the mass fraction of the basic additive in the electrolyte for secondary batteries is 0.1% to 8%.

[0032] This invention provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the secondary battery electrolyte described above.

[0033] The negative electrode sheet includes silicon-based negative electrode active material and hard carbon negative electrode material.

[0034] This invention provides an electrolyte for secondary batteries, comprising an electrolyte salt, a solvent, a first additive, and a second additive; the first additive has the structure shown in Formula 1: in Formula 1, R1, R2, R4, R5, R1′, R2′, R4′, and R5′ are independently selected from hydrogen, halogen, C1-C5 alkyl, C1-C3 haloalkyl, or C1-C5 alkoxy; R3 is selected from hydrogen, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, perfluorobutyl, nitro, cyano, isocyanate, amino, or mercapto; the second additive is a vinylsiloxane. During battery cycling, nitro-substituted bistyrene forms an inorganic SEI film component with high ionic conductivity, while vinylsiloxane crosslinking reaction generates an elastic organic SEI film component with a polymer network structure. The combined use of these two additives forms an organic-inorganic composite film, which avoids the drawbacks of poor toughness of inorganic SEI films and poor ionic conductivity of organic films. It effectively regulates the deposition of lithium ions and sodium ions while maintaining the stability of the interface, and effectively suppresses the structural changes caused by the volume expansion of the negative electrode, thereby effectively improving the cycle performance of the negative electrode. Detailed Implementation

[0035] This invention provides an electrolyte for secondary batteries, comprising an electrolyte salt, a solvent, a first additive, and a second additive;

[0036] The first additive has the structure shown in Formula 1:

[0037]

[0038] In Formula 1, R1, R2, R4, R5, R1′, R2′, R4′, and R5′ are independently selected from hydrogen, halogen, C1-C5 alkyl, C1-C3 haloalkyl, or C1-C5 alkoxy.

[0039] R3 is selected from hydrogen, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, perfluorobutyl, nitro, cyano, isocyanate, amino, or mercapto.

[0040] The second additive is vinylsiloxane.

[0041] In this invention, the first additive has the structure shown in Formulas 1-1 to 1-6.

[0042]

[0043] The first additive used in this invention introduces a strongly electrophilic nitro group, which allows the nitro functional group to preferentially undergo an electrophilic substitution reaction with lithium ions to generate LiN. x O y / NaN x O yThe inorganic SEI film composition is uniformly distributed at the negative electrode interface, exhibiting high ionic conductivity to achieve efficient conduction and uniform deposition of lithium and sodium ions, reducing the generation of dead lithium and dead sodium. The introduction of nitro groups enhances the electrophilicity of the molecule, thereby enhancing the reactivity of vinyl groups with metallic lithium and metallic sodium, better eliminating dead lithium and dead sodium caused by battery performance degradation in the later stages of cycling, and making the reaction products more uniformly distributed. The hyperdelocalized conjugated structure of the double benzene rings on both sides of the C=C double bond enables uniform dispersion and rapid conduction of electrons in the hyperdelocalized structure, realizing the ultra-long-distance transmission of the nitro group-induced effect on the benzene ring. While the nitro group dissociates, the hyperdelocalized conjugated structure can maintain uniform charge dispersion and its own structural stability. This invention introduces functional substituents at the para-position of the nitro group in the bis(5-phenylene) structure, which can further improve battery performance. For example, the introduction of perfluoroalkyl groups enhances the induced polarity of the molecule, improves the electrolyte's ability to dissolve electrolyte salts, and simultaneously forms the inorganic component LiF on the electrode surface; the introduction of para-substituent cyano groups can reduce the dissolution of transition metal ions; and the introduction of para-substituent isocyanates can remove HF from the electrolyte, improving the high-temperature cycle performance of the negative electrode battery. The stability effect of this conjugated structure is particularly prominent when the para-substituent is a nitro or perfluoroalkyl group.

[0044] In addition, the styrene structure in the first additive undergoes electrochemical polymerization when the battery is overcharged, generating polystyrene derivatives, which form a conductive film on the surface of the positive electrode, increasing the battery's internal resistance and thus limiting the charging current to protect the battery.

[0045] In this invention, the first additive is prepared according to the following steps:

[0046] In the presence of an inert gas and a catalyst, 4-nitrobenzyl bromide compounds having the structure shown in Formula A are reacted with benzaldehyde compounds having the structure shown in Formula B to prepare bis(styrene) derivatives in one step.

[0047]

[0048] In this invention, the types of R1, R2, R4, R5, R1′, R2′, R4′, and R5′ are the same as those of R1, R2, R4, R5, R1′, R2′, R4′, and R5′ described above, and will not be repeated here.

[0049] In this invention, the molar ratio of the 4-nitrobenzyl bromide compound to the benzaldehyde compound is preferably 1:(1 to 1.5), more preferably 1:(1.1 to 1.4), such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, and preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0050] In this invention, the catalyst preferably comprises catalyst A and catalyst B. Catalyst A is one or more of triphenylphosphine, trimethylphosphine, triethylphosphine, N,N-dimethylcyclohexylamine, triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylantimony, chromium acetylacetone, and tetraethylammonium bromide. The molar ratio of the 4-nitrobenzyl bromide compound to catalyst A is preferably (1-1.5):1, more preferably (1-1.3):1, such as 1:1, 1.1:1, 1.2:1. The molar ratio of the 4-nitrobenzyl bromide compound to the catalyst B is preferably (1.5–2.2):1, more preferably (1.6–2):1, such as 1.5:1, 1.4:1, 1.5:1, or more preferably (1.6–2):1, such as 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or more preferably (1.5–2.2):1, or more preferably (1.6–2):1, or more preferably (1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or more preferably (1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or more preferably (1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or more preferably (1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 1.9:1, 1.5 ...

[0051] In this invention, the reaction temperature is preferably 70-100°C, more preferably 70-90°C, such as 70°C, 80°C, 90°C, 100°C, and preferably a range of values ​​with the above values ​​as the upper or lower limit; the reaction time is preferably 1-4 hours, more preferably 2-3 hours.

[0052] In this invention, the reaction of the 4-nitrobenzyl bromide compound with the benzaldehyde compound is preferably carried out in a solvent, preferably one or more of acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide and N,N-dimethylacetamide.

[0053] In the electrolyte of the present invention, the mass fraction of the first additive is preferably 0.1% to 5%, more preferably 0.2% to 0.4%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, and preferably a range of values ​​with the above values ​​as the upper or lower limit.

[0054] In this invention, the second additive is preferably a vinylsiloxane, and more preferably has the structure shown in Formula 2.

[0055]

[0056] In Formula 2, R6, R7 and R8 are independently selected from halogens, C1-C3 alkyl groups, C1-C3 haloalkyl groups, C2-C3 unsaturated hydrocarbon groups, C2-C3 halounsaturated hydrocarbon groups, C1-C3 cyanosubstituted hydrocarbon groups, phenyl groups, trimethylsilyl groups, isocyanate groups or trimethylsilyl groups.

[0057] In the electrolyte of the present invention, the mass fraction of the second additive is preferably 0.1% to 3%, more preferably 0.5% to 2.5%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0058] In this invention, the electrolyte salt preferably includes lithium salt and sodium salt;

[0059] The lithium salt is preferably one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate)borate, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(oxalate)borate, and sodium bis(fluorosulfonyl)imide. The concentration of the electrolyte salt is preferably 0.5 mol / L to 2.0 mol / L, more preferably 1 mol / L to 1.5 mol / L.

[0060] In this invention, the solvent in the electrolyte preferably includes two or more of the following: propylene carbonate, ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate, and γ-butyrolactone.

[0061] The electrolyte of the present invention preferably further includes a basic additive, which is preferably one or more of sulfonate compounds, sulfate compounds, unsaturated cyclic carbonate compounds, borate compounds and trimethylsilyl ester compounds. The mass fraction of the basic additive in the electrolyte for secondary batteries is preferably 0.1% to 8%, more preferably 1% to 6%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, preferably within the range of the above values ​​as the upper or lower limits.

[0062] The present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the secondary battery electrolyte described above.

[0063] The negative electrode includes a silicon-based negative electrode active material, such as silicon-carbon negative electrode active material or silicon suboxide negative electrode active material; the positive electrode includes a positive electrode active material, such as lithium cobalt oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0064] This invention provides an electrolyte for secondary batteries, comprising an electrolyte salt, a solvent, a first additive, and a second additive. The first additive has the structure shown in Formula 1: In Formula 1, R1, R2, R4, R5, R1′, R2′, R4′, and R5′ are independently selected from hydrogen, halogens, C1-C5 alkyl groups, C1-C3 haloalkyl groups, or C1-C5 alkoxy groups; R3 is selected from hydrogen, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, perfluorobutyl, nitro, cyano, isocyanate, amino, or mercapto groups; the second additive is a vinylsiloxane. In practical applications, these two additives form an organic-inorganic composite film during battery cycling, effectively regulating the deposition of lithium and sodium ions, significantly contributing to maintaining interface stability, and effectively suppressing structural changes caused by negative electrode volume expansion, thereby effectively improving the cycle performance of the secondary battery.

[0065] To further illustrate the present invention, the following detailed description of an electrolyte for a secondary battery and an electrolyte for a secondary battery provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0066] Preparation of the first additive

[0067] Example 1

[0068] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 1 mol of (4-nitro-2,5-difluoro)benzyl bromide and 1 mol of 4-(1,1,2,2,2-pentafluoroethyl)-benzaldehyde were added, along with 0.75 mol of triphenylphosphine and 0.5 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 80 °C. The mixture was stirred for 4 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compound with structural formula 1-1.

[0069] Example 2

[0070] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 1 mol of 4-nitrobenzyl bromide and 1.1 mol of 4-(1,1,2,2,2-pentafluoroethyl)-benzaldehyde were added, along with 1 mol of triphenylphosphine and 0.45 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 80 °C. The mixture was stirred for 3 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compounds with structural formulas 1-2.

[0071] Example 3

[0072] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 1 mol of 4-nitrobenzyl bromide and 1.5 mol of 4-(1,1,2,2,2-pentafluoroethyl)-benzaldehyde were added, along with 1 mol of triethylamine and 0.6 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 70 °C. The mixture was stirred for 4 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compounds with structural formulas 1-2.

[0073] Example 4

[0074] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 1 mol of (4-nitro-3,6-difluoro)benzyl bromide and 1.1 mol of 4-(1,1,2,2,2-pentafluoroethyl)-benzaldehyde were added, along with 0.75 mol of triphenylphosphine and 0.45 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 90 °C. The mixture was stirred for 2 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compounds with structural formulas 1-3.

[0075] Example 5

[0076] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 1 mol of (4-nitro-2,3,5,6-tetrafluoro)benzyl bromide and 1 mol of 4-(trifluoromethyl)-benzaldehyde were added, along with 0.75 mol of triethylamine and 0.5 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 70 °C. The mixture was stirred for 4 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compounds with structural formulas 1-4.

[0077] Example 6

[0078] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 0.5 mol of (4-nitro-2,5-difluoro)benzyl bromide and 1 mol of 4-(trifluoromethyl)-benzaldehyde were added, along with 0.75 mol of N,N-dimethylbenzylamine and 0.45 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 70 °C. The mixture was stirred for 4 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compounds with structural formulas 1-5.

[0079] Example 7

[0080] In a three-necked round-bottom flask containing 50 ml of dimethylformamide (DMF), 1 mol of (4-nitro-3,6-difluoro)benzyl bromide and 1.3 mol of 4-(trifluoromethyl)-benzaldehyde were added, along with 0.8 mol of N,N-dimethylbenzylamine and 0.6 mol of potassium hydroxide. Nitrogen gas was introduced into the flask, and the temperature was gradually raised to 70 °C. The mixture was stirred for 3 h. After the reaction was completed, the mixture was cooled to room temperature and eluted with a petroleum ether / ethyl acetate system to obtain compounds with structural formulas 1-6.

[0081] Preparation of electrolyte

[0082] Example 8

[0083] In an argon glove box, ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a mass ratio of 1:1:1 to prepare a non-aqueous solvent. Then, 12 parts by weight of LiPF6 were dissolved in the prepared non-aqueous solvent. 1 part by weight of fluoroethylene carbonate, 1 part by weight of 1,3-propanesulfonate lactone, and 0.5 parts by weight of lithium bis(oxalato)borate were added as the base electrolyte. Then, 0.5 parts by weight of compound of structural formula 1-1 and 0.5 parts by weight of vinylsiloxane (where R6 is vinyl, and R7 and R8 are the same, being trimethylsilyl) were added to obtain the non-aqueous electrolyte for lithium-ion batteries in this embodiment.

[0084] Example 9

[0085] The electrolyte formulation is the same as that in Example 8, except that 14 parts by weight of LiPF6 are replaced with 7 parts by weight of lithium difluorooxalate borate and 7 parts by weight of lithium difluorosulfonyl imide, 0.5 parts by weight of compound of formula 1-2 are added, and 0.5 parts by weight of vinylsiloxane (where R6, vinyl, R7, and R8 are trimethylsilyl) are added to obtain the non-aqueous electrolyte for lithium-ion batteries in this example.

[0086] Example 10

[0087] The electrolyte formulation is the same as that in Example 8, except that 0.5 parts by weight of compound 1-2 and 0.5 parts by weight of vinylsiloxane (where R6, R8, and R7 are all trimethylsilyl) are added to obtain the non-aqueous electrolyte for lithium-ion batteries in this example.

[0088] Example 11

[0089] The electrolyte formulation is the same as that in Example 8, except that 14 parts by weight of LiPF6 are replaced with 4 parts by weight of lithium perchlorate and 10 parts by weight of lithium tetrafluoroborate, 0.5 parts by weight of structural formulas 1-4 are added, and 0.5 parts by weight of vinylsiloxane (where R6, R7, and R8 are trimethylsilyl) are added to obtain the non-aqueous electrolyte for lithium-ion batteries in this example.

[0090] Example 12

[0091] The electrolyte formulation is the same as that in Example 8, except that 0.5 parts by weight of compounds of structural formulas 1-5 and 0.5 parts by weight of vinylsiloxane (where R6, R7, and R8 are trimethylsilyl) are added to obtain the non-aqueous electrolyte for lithium-ion batteries in this example.

[0092] Example 13

[0093] The electrolyte formulation is the same as that in Example 8, except that 0.5 parts by weight of structural formulas 1-6 and 0.5 parts by weight of vinylsiloxane (where R6, R7, and R8 are trimethylsilyl) are added to obtain the non-aqueous electrolyte for lithium-ion batteries in this example.

[0094] Example 14

[0095] In an argon glove box, ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate were mixed in a mass ratio of 3:2:5 to prepare a non-aqueous solvent. Then, 14 parts by weight of NaPF6 were dissolved in the prepared non-aqueous solvent. 3 parts by weight of fluoroethylene carbonate, 1 part by weight of ethylene sulfate, and 1 part by weight of sodium isopropoxide were added to form the basic sodium-ion battery electrolyte. Then, 0.5 parts by weight of compound of structural formula 1-1 and 0.5 parts by weight of vinylsiloxane (where R6, R7, and R8 are the same and are trimethylsilyl) were added to obtain the non-aqueous electrolyte for the sodium-ion battery of this embodiment.

[0096] Example 15

[0097] The electrolyte formulation is the same as that in Example 14, except that 14 parts by weight of NaPF6 are replaced with 7 parts by weight of sodium difluorooxalate borate and 7 parts by weight of sodium difluorosulfonyl imide, 0.5 parts by weight of structural formula 1-2 are added, and 0.5 parts by weight of vinylsiloxane (where R6, R7, and R8 are the same and are trimethylsilyl) are added to obtain the non-aqueous electrolyte for sodium-ion batteries in this example.

[0098] Example 16

[0099] The electrolyte formulation is the same as that in Example 14, except that 14 parts by weight of NaPF6 are replaced with 4 parts by weight of sodium perchlorate and 10 parts by weight of sodium tetrafluoroborate, 0.5 parts by weight of structural formula 1-2 are added, and 0.5 parts by weight of vinylsiloxane (where R6 is vinyl, and R7 and R8 are trimethylsilyl) are added to obtain the non-aqueous electrolyte for sodium-ion batteries in this example.

[0100] Comparative Example 1

[0101] The electrolyte formulation is the same as that in Example 8, except that 1 part by weight of 4,4'-dicyanostilbene additive is added instead of 0.5 parts by weight of compound of formula 1-1 and 0.5 parts by weight of vinylsiloxane in Example 8 to obtain the non-aqueous electrolyte for lithium-ion batteries in Comparative Example 1.

[0102] Comparative Example 2

[0103] The electrolyte formulation is the same as that in Example 8, except that 1 part by weight of stilbene bisbenzoxazole additive is added instead of 0.5 parts by weight of compound of formula 1-1 and 0.5 parts by weight of vinylsiloxane in Example 8 to obtain the non-aqueous electrolyte for lithium-ion batteries in Comparative Example 2.

[0104] Comparative Example 3

[0105] The electrolyte formulation is the same as that in Example 8, except that no additives (0.5 parts by weight of compound of structural formula 1-1 and 0.5 parts by weight of vinylsiloxane) are added to obtain the non-aqueous electrolyte for lithium-ion batteries in Comparative Example 3.

[0106] Comparative Example 4

[0107] The electrolyte formulation is the same as that in Example 8, except that 1 part by weight of compound 1-2 is added instead of 0.5 parts by weight of compound 1-1 and 0.5 parts by weight of vinylsiloxane in Example 8 to obtain the non-aqueous electrolyte for lithium-ion batteries in Comparative Example 4.

[0108] Comparative Example 5

[0109] The electrolyte formulation is the same as that in Example 8, except that 1 part by weight of vinylsiloxane (where R6, R8, and R7 are all trimethylsilyl) is added to replace 0.5 parts by weight of compound of formula 1-1 and 0.5 parts by weight of vinylsiloxane in Example 8, to obtain the non-aqueous electrolyte for lithium-ion batteries in Comparative Example 5.

[0110] Comparative Example 6

[0111] The electrolyte formulation is the same as that in Example 14, except that no additives (0.5 parts by weight of compound of structural formula 1-1 and 0.5 parts by weight of vinylsiloxane) are added to obtain the sodium-ion battery non-aqueous electrolyte of Comparative Example 6.

[0112] Electrode fabrication and battery assembly

[0113] Preparation of lithium-ion battery positive electrode: The positive electrode active material (LiNi) is prepared... 0.8 Co 0.1 Mn 0.1O2), polyvinylidene fluoride (PVDF), SP (super-P) and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5, dispersed in NMP organic solvent, and then coated onto aluminum foil to prepare the desired positive electrode sheet.

[0114] Preparation of negative electrode sheet for lithium-ion battery: The negative electrode active materials, artificial graphite, silicon suboxide, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP) and carbon nanotubes (CNT) are mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5, dispersed in deionized water, and coated onto copper foil to prepare the required negative electrode sheet.

[0115] Preparation of sodium-ion battery positive electrode sheet: The positive electrode material Na3V2(PO4)3, binder PVDF and conductive agent Super-P are mixed in a mass ratio of 90:4:6, dispersed in NMP organic solvent, and coated onto aluminum foil in a homogenous slurry to prepare the required positive electrode sheet.

[0116] Preparation of sodium-ion battery negative electrode sheet: Spherical hard carbon, binder PVDF, and conductive agent Super-P are mixed together in a mass ratio of 97:2:1, dispersed in NMP organic solvent, and coated onto aluminum foil in a homogenate to prepare the required negative electrode sheet.

[0117] Battery manufacturing process: The positive and negative electrode sheets are dried and die-cut, and stacked into cells. After being sealed with aluminum-plastic film, they are baked to ensure that the electrode moisture content meets the requirements. After baking, the cells are injected with electrolyte using the electrolytes in the above examples and comparative examples. After standing, formation, capacity testing and aging processes, the finished soft-pack cells are obtained.

[0118] Lithium-ion battery performance testing

[0119] ambient temperature cycling performance

[0120] Under normal temperature (25±2℃) conditions, the above batteries were charged to 4.2V at 1C constant current and constant voltage with a cutoff current of 0.05C; left to rest for 5 minutes, and then discharged to 3.0V at 1C constant current, left to rest for 5 minutes. This charging and discharging cycle was repeated to obtain the capacity retention rate of different formulations.

[0121] High temperature cycling performance

[0122] Under high temperature (45℃) conditions, the above batteries were charged to 4.2V at 1C constant current and constant voltage, with a cutoff current of 0.05C; rested for 5 minutes, and then discharged to 3.0V at 1C constant current, and rested for 5 minutes. This charging and discharging cycle was repeated to obtain the capacity retention rate of different formulations.

[0123] DCIR test method after formation: under 50% SOC state, the battery is discharged at 0.1C for 10s, discharged at 1C for 1s, DCIR = voltage difference / current difference;

[0124] The thickness of the negative electrode sheet after rolling and at 100% SOC were measured using a thickness gauge. The negative electrode sheet expansion rate was calculated as: (Negative electrode sheet thickness at 100% SOC - Negative electrode sheet thickness at compression) / Negative electrode sheet thickness at compression * 100%.

[0125] Overcharge protection test:

[0126] The batteries obtained in the examples and comparative examples were charged to 5V at a constant current rate of 3C and the battery status was recorded. If no leakage, fire or explosion occurred during the overcharge process, it means that the battery overcharge test was passed; otherwise, it is considered that the battery overcharge protection failed.

[0127] The test results are shown in Table 1.

[0128] Table 1 Performance tests of lithium-ion batteries assembled using the electrolytes of the embodiments and comparative examples of the present invention.

[0129]

[0130]

[0131] The results from the comparative examples and the embodiments show that the use of the two additives forms an effective SEI film, which maintains the stability of the interface during cycling and inhibits the continuous growth of the SEI film caused by silicon volume expansion, reduces the electrode expansion rate, and effectively improves the cycle performance of silicon-carbon anode lithium-ion batteries.

[0132] According to the results of Comparative Examples 3 and 4, the high ionic conductivity SEI film constructed by the first additive on the negative electrode is beneficial for lithium-ion conduction and reduces the battery DCIR. At the same time, the additive can polymerize when the battery is overcharged, increasing the battery internal resistance, thereby achieving the overcharge protection function.

[0133] According to the results of Comparative Examples 3 and 5, the organic film constructed by vinylsiloxane on the negative electrode can better withstand the volume strain of the silicon negative electrode and improve the high-temperature cycle performance of the battery.

[0134] The results of Comparative Examples 1, 2 and 4 show that the first additive is more likely to form an effective SEI film on the surface of the silicon anode than other stilbene-based additives, thus effectively improving battery performance.

[0135] Sodium-ion battery performance testing

[0136] DCIR test method after formation: under 50% SOC state, the battery is discharged at 0.1C for 10s, discharged at 1C for 1s, DCIR = voltage difference / current difference;

[0137] ambient temperature cycling performance test

[0138] Under normal temperature (25±2℃) conditions, the battery is charged to 3.9V with a constant current and constant voltage of 1C, cut off current of 0.05C, and left to rest for 5 minutes. Then it is discharged to 1.5V with a constant current of 1C and left to rest for 5 minutes. This charging and discharging cycle is repeated to obtain the capacity retention rate of different formulations.

[0139] High-temperature cycling performance test:

[0140] Under high temperature (45℃) conditions, the battery is charged to 3.9V with a constant current and constant voltage of 1C, cut off current of 0.05C, and left to rest for 5 minutes. Then it is discharged to 1.5V with a constant current of 1C and left to rest for 5 minutes. This charging and discharging cycle is repeated to obtain the high temperature capacity retention rate of different formulations.

[0141] Table 2 Performance tests of sodium-ion batteries assembled using the electrolytes of the embodiments and comparative examples of the present invention

[0142]

[0143] The results from the comparative examples and the embodiments show that the use of the two additives forms an effective SEI film that can inhibit the continuous repair of the hard carbon anode interface during cycling, effectively improving the cycle performance of the hard carbon anode sodium-ion battery.

[0144] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An electrolyte for a secondary battery, comprising an electrolyte salt, a solvent, a first additive, and a second additive; The first additive has the structure shown in Formula 1: Formula 1; In Formula 1, R1, R2, R4, R5, R1′, R2′, R4′, and R5′ are independently selected from hydrogen, halogen, C1-C5 alkyl, C1-C3 haloalkyl, or C1-C5 alkoxy. R3 is selected from trifluoromethyl, pentafluoroethyl, heptafluoropropyl, perfluorobutyl, cyano, isocyanate, amino, or mercapto. The second additive is vinylsiloxane; The second additive has the structure shown in Formula 2: Formula 2; In Formula 2, R6 is hydrogen or a C1~C3 alkyl group, and the hydrogen atoms on the alkyl group in the C1~C3 alkyl group may be completely or partially replaced by fluorine atoms; R7 and R8 are independently selected from halogens, C1-C3 alkyl groups, C1-C3 haloalkyl groups, C2-C3 unsaturated hydrocarbon groups, C2-C3 halounsaturated hydrocarbon groups, C1-C3 cyano-substituted hydrocarbon groups, phenyl groups, trimethylsilyl groups, isocyanate groups, or trimethylsilyl groups.

2. The electrolyte for a secondary battery according to claim 1, characterized by The first additive has the structure shown in formulas 1-1 to 1-6: 。 3. The electrolyte for a secondary battery according to claim 2, characterized by The preparation method of the first additive includes the following steps: In the presence of an inert gas and a catalyst, a 4-nitrobenzyl bromide compound having the structure shown in Formula A is reacted with a benzaldehyde compound having the structure shown in Formula B in a one-step reaction to prepare a nitro-substituted bistyrene derivative having the structure shown in Formula 1. Formula A, Formula B.

4. The electrolyte for a secondary battery according to claim 3, characterized by The catalyst comprises catalyst A and catalyst B, wherein catalyst A is one or more of triphenylphosphine, trimethylphosphine, triethylphosphine, N,N-dimethylcyclohexylamine, triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylantimony, chromium acetylacetone, and tetraethylammonium bromide; and catalyst B is one or more of potassium hydroxide, sodium hydroxide, rubidium hydroxide, and cesium hydroxide. The inert gas is selected from nitrogen or argon; The reaction temperature for the one-step reaction is 70~100℃.

5. The electrolyte for a secondary battery according to claim 4, characterized by The molar ratio of formula A to formula B is 1:(1~1.5); The molar ratio of formula A to catalyst A is (1~1.5):1; The molar ratio of formula A to catalyst B is (1.5~2.2):

1.

6. The electrolyte for a secondary battery according to claim 1, characterized by The mass fraction of the first additive is 0.1% to 5%; the mass fraction of the second additive is 0.1% to 3%.

7. The electrolyte for a secondary battery according to claim 1, characterized by The electrolyte salt includes lithium salt or sodium salt; The lithium salt includes one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium bis(fluorosulfonyl)imide. The sodium salts include sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalate borate, and sodium difluorosulfonamide. The concentration of the electrolyte salt is 0.5~2.0 mol / L.

8. The electrolyte for a secondary battery according to claim 1, characterized by The electrolyte for secondary batteries also includes basic additives, which are selected from one or more of sulfonate compounds, sulfate compounds, unsaturated cyclic carbonate compounds, borate compounds and trimethylsilyl ester compounds, and the mass fraction of the basic additives in the electrolyte for secondary batteries is 0.1% to 8%.

9. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the secondary battery electrolyte according to any one of claims 1 to 8; The negative electrode sheet includes silicon-based negative electrode active material or hard carbon negative electrode material.

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