Electrolyte, secondary battery, and electric device

Abstract

The application relates to the technical field of batteries, in particular to an electrolyte, a secondary battery and an electric device. The electrolyte comprises an additive; the structural formula of the additive is shown in formula I: R1 is selected from substituted or unsubstituted C1-C5 alkyl; R2 is selected from at least one of substituted or unsubstituted allyl, substituted or unsubstituted aryl and substituted or unsubstituted heteroaryl; R3 is selected from at least one of substituted or unsubstituted allyl and ; wherein R4 is selected from C3-C6 alkylene, and R5 is selected from C1-C4 alkyleneoxy; X comprises at least one of substituted or unsubstituted sulfonate groups, acrylate groups and fluorinated carboxylate groups, and Y comprises at least one of amide groups, carboxylate groups and substituted or unsubstituted sulfonate groups. The additive of the application can inhibit impedance increase in the cycle process, improve the cycle stability performance, cycle and high-temperature storage gas production of the battery and the like.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] With the increasing number of lithium-ion batteries installed in electric vehicles, higher demands are being placed on their energy density. Silicon anode systems, with their advantages of high specific capacity and low potential, represent one specific direction for improving battery energy density. However, the practical application of silicon anode systems still faces many challenges, such as large volume changes during cycling. Unlike the intercalation / deintercalation mechanism of graphite and lithium, the interaction mechanism between silicon anodes and lithium is an alloying / dealloying reaction, accompanied by significant volume changes. This leads to the pulverization or destruction of the silicon particle structure, causing it to detach from the conductive agent and resulting in conductive network failure, hindering the commercial application of silicon anode systems.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One object of the present invention is to provide an electrolyte that can react with a silicon anode system to form a protective silyl ether network structure, forming a stable interface layer on the anode surface, thereby improving cycle stability and suppressing gas generation.

[0005] Another object of the present invention is to provide a secondary battery containing the above-mentioned electrolyte.

[0006] Another object of the present invention is to provide an electrical device comprising the above-mentioned secondary battery.

[0007] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted:

[0008] An electrolyte comprising an additive; the additive has the structural formula shown in Formula I:

[0009]

[0010] R1 is selected from substituted or unsubstituted C1-C5 alkyl groups;

[0011] R2 is selected from at least one of substituted or unsubstituted C2-C5 alkenyl, substituted or unsubstituted aryl, and substituted or unsubstituted heteroaryl.

[0012] R3 is selected from substituted or unsubstituted C2-C5 alkenyl groups. and At least one of them;

[0013] Wherein, R4 is selected from C3 to C6 alkylene groups, and R5 is selected from C1 to C4 alkene groups; X includes at least one of substituted or unsubstituted sulfonate groups, acrylate groups, and fluorocarboxylic acid ester groups, and Y includes at least one of amide groups, carboxylic acid ester groups, and substituted or unsubstituted sulfonate groups.

[0014] Furthermore, in R1, the substituted group includes a halogen atom;

[0015] In R2, the substituted group includes at least one of C1-C3 alkyl groups and halogen atoms;

[0016] In X or Y, the substituted group includes at least one of C1-C3 alkyl, phenyl, fluorophenyl and halogen atoms.

[0017] Furthermore, the additive comprises at least one of the following structural compounds:

[0018]

[0019] Furthermore, the amount of the additive is 0.2% to 6% of the total mass of the electrolyte.

[0020] Furthermore, at 25°C, the conductivity of the electrolyte is 7.5–9 mS / cm.

[0021] Furthermore, the electrolyte includes a solvent, which includes fluoroethylene carbonate and methyl ethyl carbonate.

[0022] Furthermore, in the electrolyte, based on the total mass of the solvent, the mass of fluoroethylene carbonate is 5% to 15%.

[0023] Furthermore, in the electrolyte, the mass ratio of fluoroethylene carbonate to methyl ethyl carbonate is 1:(4-9).

[0024] The present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of the above.

[0025] Furthermore, the negative electrode sheet includes a negative electrode active material, which includes a silicon-carbon composite material formed from silicon-based materials and carbon-based materials; the silicon-based materials include at least one of elemental silicon, silicon-oxygen compounds, and silicon-metal compounds; the carbon-based materials include graphite.

[0026] Furthermore, the positive electrode sheet includes a positive electrode active material, the chemical formula of which includes Li. a Ni x Co y Mn z M eO2, wherein 0.9≤a≤1.1, 0.6≤x≤0.9, 0<y≤0.2, 0≤z≤0.2, 0≤e≤0.1, and x+y+z+e=1, and M contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, Ce.

[0027] The present invention also provides an electrical device comprising any of the aforementioned secondary batteries.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The electrolyte of the present invention uses specific additives, which can react chemically with the surface of the silicon anode system to form a protective silicon ether network structure, form a stable interface layer on the surface of the anode, improve cycle stability and suppress gas production;

[0030] (2) The silyl ether structure in the additive used in the electrolyte of the present invention can remove HF in the electrolyte system, protect the interface layer and inhibit the dissolution of metal ions in the positive electrode material.

[0031] (3) The secondary battery using the electrolyte of the present invention can effectively improve the cycle stability and high-temperature storage gas generation performance of the battery. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0033] An electrolyte comprising an additive; the additive has the structural formula shown in Formula I:

[0034]

[0035] R1 is selected from substituted or unsubstituted C1-C5 alkyl groups;

[0036] R2 is selected from at least one of substituted or unsubstituted C2-C5 alkenyl, substituted or unsubstituted aryl, and substituted or unsubstituted heteroaryl.

[0037] R3 is selected from substituted or unsubstituted C2-C5 alkenyl groups. and At least one of them;

[0038] Wherein, R4 is selected from C3 to C6 alkylene groups, and R5 is selected from C1 to C4 alkene groups; X includes at least one of substituted or unsubstituted sulfonate groups, acrylate groups, and fluorocarboxylic acid ester groups, and Y includes at least one of amide groups, carboxylic acid ester groups, and substituted or unsubstituted sulfonate groups.

[0039] C1-C5 alkyl refers to alkyl groups with 1-5 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, etc.; C3-C6 alkylene refers to alkylene groups with 3-6 carbon atoms, such as propylene, butylene, etc.; C1-C4 alkoxide refers to alkoxide groups with 1-4 carbon atoms, such as methyleneoxy, ethoxy, propoxy, etc.

[0040] The additive used in the electrolyte of this invention has a polyalkoxysilane ether structure, wherein the Si-OR1 can react with the Si-OH on the surface of silicon particles to form a protective silane ether network structure, and remove HF acid in the system and inhibit the dissolution of transition metal ions; at the same time, it has suitable HOMO and LUMO orbitals, which can be reduced and decomposed on the negative electrode surface to form a stable SEI film.

[0041] When the additive contains C=C, a stable polymer interface layer can be constructed on the positive and negative electrode surfaces via redox polymerization, improving the mechanical strength of the interface layer. When the additive contains aryl or heteroaryl groups, the chemical stability of the interface layer can be improved. Fluorocarboxylic acid ester groups and sulfonate groups in the additive can be reduced on the negative electrode surface to form a stable SEI layer containing LiF or ROSO2Li, inhibiting the increase in cycling impedance and improving the lithium-ion conductivity within the interface layer. Amide groups in the additive can be redox decomposed on the positive and negative electrode surfaces to form an interface layer containing organic nitrides, lithium nitride, etc., improving the lithium-ion conductivity within the interface layer.

[0042] The additives described above can effectively suppress the continuous rupture and reconstruction of the SEI film caused by volume changes of silicon particles during charging and discharging, build a stable SEI layer, suppress the increase in impedance during cycling, and improve the cycle stability, cycling and high-temperature storage gas generation of the battery.

[0043] In some specific embodiments of the present invention, X possesses at least one of the following structural formulas:

[0044] (1) R6 is selected from substituted or unsubstituted C1-C5 alkyl groups and substituted or unsubstituted aryl groups;

[0045] (2) R7 is selected from H and methyl;

[0046] (3) R8 is selected from fluorinated C1 to C3 alkyl groups.

[0047] In some specific embodiments of the present invention, Y possesses at least one of the following structural formulas:

[0048] (1) R9 and R 10 Each is independently selected from C1-C3 alkyl and C2-C4 alkenyl groups;

[0049] (2) R 11 Selected from substituted or unsubstituted C1-C3 alkyl groups, with substituents including fluorine.

[0050] In some specific embodiments of the present invention, in R1, the substituted group includes a halogen atom;

[0051] In R2, the substituted group includes at least one of C1-C3 alkyl groups and halogen atoms;

[0052] In X or Y, the substituted group includes at least one of C1-C3 alkyl, phenyl, fluorophenyl and halogen atoms.

[0053] In some specific embodiments of the present invention, R3 has at least one of the following structural formulas:

[0054] (1)

[0055] (2) R6 is selected from substituted or unsubstituted C1-C5 alkyl groups and substituted or unsubstituted aryl groups;

[0056] (3) R7 is selected from H and methyl;

[0057] (4) R8 is selected from fluorinated C1-C3 alkyl groups;

[0058] (5) R9 and R 10 Each is independently selected from C1-C3 alkyl and C2-C4 alkenyl groups;

[0059] (6) R 11 Selected from substituted or unsubstituted C1-C3 alkyl groups, with substituents including fluorine;

[0060] Where n is an integer between 3 and 6, and m is an integer between 1 and 4.

[0061] In some specific embodiments of the present invention, R2 includes either allyl or phenyl.

[0062] In some specific embodiments of the present invention, the additive comprises at least one of the following structural compounds:

[0063]

[0064] In some specific embodiments of the present invention, the amount of the additive is 0.2% to 6% of the total mass of the electrolyte.

[0065] In different embodiments, the amount of the additive may be 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6% of the total mass of the electrolyte, or any combination thereof.

[0066] By using additives within the above dosage range, the effectiveness of the additives can be further guaranteed. When the amount of additive is too low, the passivation film formed on the positive and negative electrode surfaces is prone to rupture, which in turn reduces the inhibitory effect on the redox decomposition of the electrolyte; when the amount of additive is too high, the passivation film formed on the positive and negative electrode surfaces becomes too thick, which leads to an increase in battery impedance and polarization.

[0067] In some specific embodiments of the present invention, the conductivity of the electrolyte is 7.5 to 9 mS / cm at 25°C.

[0068] In different embodiments, at 25°C, the conductivity of the electrolyte can be a range of 7.5 mS / cm, 7.8 mS / cm, 8 mS / cm, 8.2 mS / cm, 8.5 mS / cm, 8.8 mS / cm, 9 mS / cm, or any combination thereof.

[0069] When the conductivity of the electrolyte is within the above range, the stability of the SEI interface layer and the rate performance of the battery can be further guaranteed.

[0070] In some specific embodiments of the present invention, the electrolyte includes a solvent comprising fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC). FEC participates in the construction of the SEI layer containing LiF, Li₂CO₃, and polycarbonate, continuously repairing the SEI layer damaged by large volume changes during the charge-discharge cycle of the silicon-containing anode. EMC, on the other hand, improves the solubility of lithium salts and adjusts the dielectric constant, viscosity, and conductivity of the electrolyte.

[0071] In some specific embodiments of the present invention, the electrolyte contains 5% to 15% fluoroethylene carbonate by mass, based on the total mass of the solvent.

[0072] In different embodiments, the mass of fluoroethylene carbonate in the electrolyte can be 5%, 8%, 10%, 12%, 15%, or any combination thereof, based on the total mass of the solvent.

[0073] In some specific embodiments of the present invention, the mass ratio of fluoroethylene carbonate (FEC) to methyl ethyl carbonate (EMC) in the electrolyte is 1:(4-9). In different embodiments, the mass ratio of FEC to EMC in the electrolyte can be within the range of 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or any combination thereof. A mass ratio of FEC to EMC within the above range is beneficial for improving the cycle performance of the battery.

[0074] In some specific embodiments of the present invention, the electrolyte may further include other solvents; the other solvents include at least one of: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl acetate (EA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0075] In some specific embodiments of the present invention, the solvent in the electrolyte may include fluoroethylene carbonate, methyl ethyl carbonate, ethylene carbonate, and diethyl carbonate.

[0076] In some specific embodiments of the present invention, the electrolyte further includes a lithium salt; the lithium salt includes lithium hexafluorophosphate and a second lithium salt; the second lithium salt includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodioxalatophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0077] In some specific embodiments of the present invention, the mass of the lithium hexafluorophosphate is 12% to 15% of the total mass of the electrolyte; and the mass of the second lithium salt is 0% to 5% of the total mass of the electrolyte.

[0078] In different embodiments, the mass of the lithium hexafluorophosphate may be 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15% of the total mass of the electrolyte, or any combination thereof; the mass of the second lithium salt may be 0%, 1%, 2%, 3%, 4%, 5% of the total mass of the electrolyte, or any combination thereof.

[0079] LiPF6 possesses suitable dissociation constants, appropriate lithium-ion transference numbers, good oxidation resistance, and excellent aluminum foil passivation capabilities in commonly used carbonate organic solvents. Furthermore, it is compatible with various positive and negative electrode materials, making it a primary lithium salt in lithium-ion batteries. Considering conductivity and system viscosity, LiPF6 accounts for 12%–15% of the total mass of the electrolyte in this invention. The second lithium salt, acting as an auxiliary lithium salt, can enhance the lithium-ion transference number and improve the stability of the SEI film.

[0080] The present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of the above.

[0081] In some specific embodiments of the present invention, the negative electrode sheet includes a negative electrode active material, which includes a silicon-carbon composite material formed by silicon-based materials and carbon-based materials; the silicon-based materials include at least one of elemental silicon, silicon-oxygen compounds, and silicon-metal compounds; the carbon-based materials include graphite.

[0082] In some specific embodiments of the present invention, the positive electrode sheet includes a positive electrode active material, and the chemical formula of the positive electrode active material includes Li. a Ni x Co y Mn z M e O2, wherein 0.9≤a≤1.1, 0.6≤x≤0.9, 0<y≤0.2, 0≤z≤0.2, 0≤e≤0.1, and x+y+z+e=1, and M contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, Ce.

[0083] The practical application of silicon anode systems faces numerous challenges, such as large volume changes during cycling, low diffusivity, low initial efficiency, and the formation of dynamic SEI films. Unlike the intercalation / deintercalation mechanism of graphite and lithium, the interaction mechanism between silicon anodes and lithium is an alloying / dealloying reaction, accompanied by significant volume changes. This leads to the pulverization or destruction of the silicon particle structure, causing it to detach from the conductive agent and resulting in the failure of the conductive network. The formation of dynamic SEI films originates from the large volume changes during charge and discharge, causing continuous destruction and reconstruction of the interface layer, continuous reduction and decomposition of the electrolyte, continuous thickening of the SEI film, severe loss of active lithium, and rapid capacity decay. Furthermore, the surface of silicon anodes is often covered with a SiO2 layer with Si-OH as the end-capping group, where the neutral SiO2 can be reduced to Li. x SiO y Or Si-C compounds, where the Si-OH group can be reduced and decomposed to form LiOH, Li₂O, H₂, and silicon free radicals, which in turn react with Li. +Reaction with solvents such as cyclic carbonates leads to the loss of active lithium on the silicon anode surface, affecting initial efficiency. The additive of this invention forms a protective silane network structure through a chemical reaction with the silicon anode surface. Simultaneously, it forms a thin SEI layer with high mechanical strength, low impedance, and high lithium-ion conductivity on the anode surface, inhibiting electrolyte reduction and decomposition. Furthermore, it forms a stable CEI layer on the cathode surface, inhibiting the dissolution of metal ions from the ternary cathode material and the oxidative decomposition of the electrolyte, improving battery cycle and storage gas generation performance.

[0084] The present invention also provides an electrical device comprising any of the aforementioned secondary batteries.

[0085] In some specific embodiments of the present invention, the additives used can be prepared according to the following reaction route:

[0086]

[0087] The reaction times involved in each of the above reaction routes can be adjusted according to the actual degree of reaction, and the specific degree of reaction can be monitored by conventional TLC.

[0088] Specifically, the preparation of A2 includes the following steps:

[0089] 1) Synthesis of phenyldimethoxysilane (PhSi(OMe)2H): Under nitrogen protection, PdCl2 (15.4 mg, 0.0876 mmol), benzene (210 mL), PhSiH3 (9.46 g, 87.6 mmol), and MeOH (7.1 mL, 175.2 mmol) were added sequentially to a pre-dried reaction flask. The mixture was stirred at room temperature for 9 h. The black solid was removed by filtration. The low-boiling solvent was removed from the filtrate by rotary evaporation. The residue was distilled under reduced pressure (bp 40℃, 1 mm Hg) to obtain 10.87 g of pure PhSi(OMe)2H (yield: 74%).

[0090] 2) Synthesis of Additive A2: Under nitrogen protection, pre-prepared allyl p-fluorobenzenesulfonate (14.58 g, 67.5 mmol), toluene (60 mL), and [Rh(OSiMe3)(cod)]2 (1.89 mg, 0.00315 mmol) were added dropwise to a pre-dried reaction flask with stirring at room temperature. PhSi(OMe)2H (10.59 g, 63 mmol) was added dropwise. After the addition was complete, the temperature was raised to 60 °C, and the reaction was carried out for 2 h. The low-boiling solvent was removed under reduced pressure. The residue was subjected to column chromatography and dried to obtain 20.57 g of the target compound A2 (yield: 85%), with a product purity of 99.3%. Target compound [M+H] + (C 17 H 22The high-resolution mass spectrometry measurement result of FO5SSi is 385.0931, and the theoretical calculation result is 385.0936.

[0091] The preparation of A3 includes the following steps:

[0092] 1) Synthesis of phenyldimethoxy(1-chloropropyl)silane: Under nitrogen protection, trimethoxy(1-chloropropyl)silane (39.76 g, 200 mmol) and anhydrous diethyl ether (200 mL) were added sequentially to a pre-dried reaction flask. 1.0 M PhMgBr (solvent: THF, 200 mL) was slowly added dropwise with stirring at room temperature. After the addition was complete, stirring was continued at room temperature for 16 h, followed by reflux for 4 h. The mixture was cooled to room temperature, filtered, and the filtrate was concentrated under reduced pressure. A certain amount of n-hexane was added to the residue and filtered. The filtrate was concentrated to dryness and distilled under reduced pressure to obtain 35.6 g of phenyldimethoxy(1-chloropropyl)silane (yield: 73%).

[0093] 2) Synthesis of Additive A3: Under nitrogen protection, phenyldimethoxy(1-chloropropyl)silane (23.2 g, 95 mmol), sodium acrylate (9.4 g, 100 mmol), polymerization inhibitor ZJ-705 (0.12 g), and tetrabutylammonium bromide (0.57 g) were added to a pre-dried reaction flask. The mixture was stirred at 145 °C for 6 h, cooled to room temperature, diluted with a certain amount of ethyl acetate, filtered, washed with ethyl acetate, concentrated, and subjected to column chromatography. After drying, 21.3 g of pure A3 was obtained (yield: 80%), with a product purity of 99%. Target compound [M+H] + (C 14 H 21 The high-resolution mass spectrometry measurement result of O4Si is 281.1207, and the theoretical calculation result is 281.1204.

[0094] The preparation of A6 includes the following steps:

[0095] 1) Synthesis of PhSi(OMe)2ONa: Under nitrogen protection, NaOH powder (6.0 g, 150 mmol) and THF (300 mL) were added to a pre-dried reaction flask and stirred for 15 min. Trimethoxyphenylsilane (32.7 g, 165 mmol) was slowly added dropwise. After the addition was complete, the mixture was stirred at room temperature for 12 h. The solvent was removed by rotary evaporator. A certain amount of n-hexane was added to the residue to precipitate a white solid. The solid was filtered, washed with n-hexane, and dried to obtain 21.1 g of pure PhSi(OMe)2ONa (yield: 70%).

[0096] 2) Synthesis of Additive A6: Under nitrogen protection, PhSi(OMe)₂ONa (20.6 g, 100 mmol) and DMF (150 mL) were added to a pre-dried reaction flask. N,N-diallyl-2-bromoacetamide (19.53 g, 90 mmol) was slowly added dropwise with stirring at room temperature. After the addition was complete, the mixture was stirred at room temperature for 2 h, then heated to 65 °C and stirred overnight. After cooling to room temperature, the mixture was diluted with ethyl acetate, washed with saturated brine, and the organic phase was concentrated. The residue was subjected to column chromatography and dried to obtain 23.1 g of pure A6 (yield: 80%), with a purity of 99.4%. Target compound [M+H] + (C 16 H 24 The high-resolution mass spectrometry measurement result of NO4Si is 322.1472, and the theoretical calculation result is 322.1469.

[0097] The present invention will now be described in detail with reference to specific embodiments.

[0098] The examples and comparative examples respectively provide an electrolyte and a lithium-ion battery containing the electrolyte. The composition of the electrolyte is shown in Table 1.

[0099] The preparation method of lithium-ion batteries may include the following steps:

[0100] (1) Preparation of the positive electrode: The positive electrode active material Li(Ni) is prepared. 0.8 Mn 0.1 Co 0.1 O2 (NMC811), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of N811:Super P:PVDF = 94:3:3, and then uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed slurry is coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet is obtained.

[0101] (2) Preparation of negative electrode sheet: The negative electrode active material graphite, SiOx, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in the mass ratio of graphite:SiOx:Super P:SBR = 84.6:9.4:3:3 and evenly dispersed in deionized water to prepare a uniform black slurry. The mixed black slurry is coated on both sides of copper foil, and then baked, rolled and cut into sheets to obtain the negative electrode sheet.

[0102] (3) Fabrication of lithium-ion batteries: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, the tabs are welded to obtain the bare battery. The bare battery is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte is injected into the dried battery, and the battery is allowed to stand, form and be divided to complete the preparation of lithium-ion batteries.

[0103] The preparation method of the electrolyte includes the following steps:

[0104] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), organic solvents are mixed in proportion and water is removed. Lithium salts are added to the organic solvents one by one while stirring and cooling continuously. When the electrolyte temperature rises by no more than 2°C, lithium salts can be added. Finally, a colorless and transparent liquid is obtained. Additives are added and the mixture is stirred evenly to obtain the electrolyte.

[0105] Electrochemical performance testing items include:

[0106] (1) Room temperature DCR test: At 25±2℃, the lithium-ion batteries obtained in the examples and comparative examples were charged to 4.3V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, they were subjected to 5C constant current pulse discharge for 10 seconds and then charged for 10 seconds. The DCR was calculated as (voltage before pulse discharge – voltage after pulse discharge) / discharge current × 100%. After storage at 60℃ for 30 days, the DCR was tested again when the battery was completely cooled to 25±2℃. The internal resistance change rate was calculated as (DCR after 30 days – DCR before 30 days) / DCR before 30 days × 100%.

[0107] (2) Room temperature cycle performance test: At 25±2℃, the lithium-ion batteries obtained in the examples and comparative examples were subjected to charge-discharge cycle tests at a charge-discharge rate of 1C / 1C within the range of 2.8 to 4.3V, and the discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle × 100%.

[0108] (3) High-temperature storage performance: The lithium-ion batteries obtained in the examples and comparative examples were placed at 60±2℃ and charged and discharged at a rate of 1C / 1C within the range of 2.8 to 4.3V. The discharge specific capacity of the batteries in the first week was recorded. After that, the batteries were stored at 60±2℃ for 30 days, and the charge and discharge tests were carried out again, and the discharge specific capacity was recorded. High-temperature storage capacity retention rate = discharge specific capacity after 30 days / discharge specific capacity in the first week × 100%.

[0109] (4) High-Temperature Gas Generation Test: The lithium-ion batteries obtained in the examples and comparative examples were charged at a constant current rate of 1C to 4.3V at 25±2℃, and then charged at a constant voltage of 4.3V until the current was below 0.05C, so that they were in a fully charged state at 4.3V. The volume of the fully charged battery before storage was measured and recorded as V0; then the fully charged battery was placed in an oven at 70±2℃, and after 2 days, the battery was taken out and its volume after storage was immediately measured and recorded as V1. Volume expansion rate = (V1 – V0) / V0 × 100%.

[0110] Table 1. Electrolyte composition information and its lithium-ion battery performance.

[0111]

[0112]

[0113] Note: The amounts of lithium salt and each additive refer to their respective percentages of the total mass of the electrolyte; the amounts of organic solvents refer to the mass ratio of each solvent; and the conductivity refers to the conductivity of the electrolyte.

[0114] The experimental results of Examples 1-15 and Comparative Example 1 show that when the electrolyte additive contains the additive with the structure shown in Formula I of the present invention, it can effectively reduce the internal resistance of the battery and slow down the increasing trend of the internal resistance of the battery during high-temperature storage, significantly improve the battery's capacity retention rate during room temperature cycling and high-temperature storage, and also have a significant inhibitory effect on battery gas production.

[0115] The experimental results of Examples 5 and 12-14 show that among the four additives, additive A6 has the best performance improvement effect. Its excellent performance may be due to the fact that, in addition to forming a protective silyl ether structure on the surface of silicon particles and forming a polymer-type stable interface layer on the positive and negative electrode surfaces through the redox decomposition and polymerization of olefins, A6 can also form an interface layer containing lithium siloxane, lithium nitride, organic nitride, etc. through the redox reaction of active siloxane and amide groups in the molecule, thereby improving the mechanical strength and stability of the interface layer and improving the lithium-ion conductivity within the interface layer.

[0116] The experimental results from Examples 5, 12-14, and Comparative Examples 2 and 3 show that the four silyl ether additives A1, A2, A3, and A6 have a better effect on improving battery performance than allyltriethoxysilane and alkenylmethyldiethoxysilane. Diallyl-substituted silyl ethers can form cross-linked polymers, constructing a flexible organic outer layer. The reduced polymers formed by monoallyl and alkenyl-substituted silyl ethers have poorer flexibility than those formed by dielyl-substituted silyl ethers. Furthermore, to achieve excellent battery performance in the silicon-containing anode system, the constructed SEI interface layer also needs to have good mechanical strength and include an interface inner layer mainly composed of inorganic salts. Therefore, it is necessary to introduce other functional groups into the additives. Consequently, the electrolyte battery containing additives A2, A3, and A6 has better performance than A1, allyltriethoxysilane, and alkenylmethyldiethoxysilane.

[0117] The experimental results of Examples 5 and 15 show that the addition of LiFSI and the adjustment of the solvent ratio can further improve the capacity retention rate during room temperature cycling and the capacity retention rate during high temperature storage, reduce the volume expansion rate during high temperature storage, and slightly increase the internal resistance of the battery, but the change in internal resistance after high temperature storage is small. The above performance changes may be due to the improvement of the SEI film by the reduction and decomposition of LiFSI on the surface of the negative electrode.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, Includes additives; the structural formula of the additives is shown in Formula I: ； R1 is selected from substituted or unsubstituted C1-C5 alkyl groups; R2 is selected from at least one of substituted or unsubstituted C2-C5 alkenyl, substituted or unsubstituted aryl, and substituted or unsubstituted heteroaryl. R3 is selected from at least one of the following structural formulas: （1） ； (2) R6 is selected from substituted or unsubstituted C1-C5 alkyl groups and substituted or unsubstituted aryl groups; (3) R7 is selected from H and methyl; (4) R9 and R 10 Each is independently selected from C2 to C4 alkenyl groups; Where n is an integer between 3 and 6, and m is an integer between 1 and 4.

2. The electrolyte according to claim 1, characterized in that, In R1, the substituted group includes a halogen atom; In R2, the substituted group includes at least one of C1-C3 alkyl groups and halogen atoms.

3. The electrolyte according to claim 1, characterized in that, The additive comprises at least one of the following structural compounds: 、 、 、 、 、 、 。 4. The electrolyte according to any one of claims 1 to 3, characterized in that, The amount of the additive is 0.2% to 6% of the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that, At 25°C, the conductivity of the electrolyte is 7.5–9 mS / cm.

6. The electrolyte according to claim 1, characterized in that, The electrolyte includes a solvent, and the solvent satisfies at least one of the following conditions: (1) The solvents include fluoroethylene carbonate and methyl ethyl carbonate; (2) Based on the total mass of the solvent, the mass of fluoroethylene carbonate is 5% to 15%; (3) The mass ratio of fluoroethylene carbonate to methyl ethyl carbonate is 1: (4-9).

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

8. The secondary battery according to claim 7, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes a silicon-carbon composite material formed from silicon-based materials and carbon-based materials; the silicon-based materials include at least one of elemental silicon, silicon-oxygen compounds, and silicon-metal compounds; the carbon-based materials include graphite.

9. The secondary battery according to claim 7, characterized in that, The positive electrode includes a positive electrode active material, the chemical formula of which includes Li. a Ni x Co y Mn z M e O2, wherein 0.9≤a≤1.1, 0.6≤x≤0.9, 0<y≤0.2, 0≤z≤0.2, 0≤e≤0.1, and x+y+z+e=1, and M contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, Ce.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 7 to 9.

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