Electrolyte and secondary battery

Abstract

The application relates to the technical field of secondary batteries, in particular to an electrolyte and a secondary battery. The electrolyte comprises an additive; the additive comprises a first additive and a second additive; the first additive comprises a pinacol borate compound; and the second additive comprises a fluoroborate compound. The pinacol borate compound and the fluoroborate compound are used in the electrolyte; the ring-opening polymerization of the pinacol borate compound and the branched structure of the fluoroborate compound can both promote the construction of a crosslinked network structure in the organic components of SEI and CEI, are beneficial to the improvement of the mechanical properties of the electrode / electrolyte interface, inhibit the interface damage caused by the volume expansion of the electrode or the side reaction, and improve the interface structure stability.

Description

Technical Field

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

[0002] Currently, the most promising materials for high-energy-density power batteries include high-nickel ternary cathode materials or silicon-carbon composite anode materials. However, the structural stability of high-nickel ternary cathodes is limited, and during charge and discharge processes, due to the Li... + / Ni 2+ Ion exchange leads to an irreversible phase transition on the cathode surface, accompanied by the dissolution of lattice oxygen and transition metal ions, resulting in capacity decay and catalyzing the oxidative decomposition of the electrolyte. For silicon-carbon composite anodes, the repeated volume expansion / contraction during cycling easily causes particle breakage, and the exposed fresh interfaces continuously consume Li and electrolyte, accelerating battery failure.

[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 promote the construction of a cross-linked network structure in the organic components of SEI and / or CEI, which is beneficial to improving the mechanical properties of the electrode / electrolyte interface, suppressing interface damage caused by electrode volume expansion or side reactions, improving interface structure stability, and improving battery cycle performance.

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

[0006] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted:

[0007] An electrolyte comprising additives; said additives include a first additive and a second additive, the first additive comprising a pinacol borate ester compound; the second additive comprising a fluoroboronic acid ester compound.

[0008] Further, the first additive comprises a compound of formula I; the second additive comprises at least one of a compound of formula II or formula III:

[0009]

[0010] R1 includes any one of C1-C10 hydrocarbon groups, C1-C10 alkoxy groups, C6-C10 aromatic groups, and borate pinacol ester groups;

[0011] R2, R3 and R4 each independently contain one of the following: a hydrogen atom, a substituted or unsubstituted C1-C6 hydrocarbon group, or a substituted or unsubstituted carbonyl-containing C1-C6 hydrocarbon group;

[0012] The substituted groups include halogens;

[0013] M includes any one of Li, Na, or K;

[0014] Among them, at least one of R2, R3 and R4 is halogenated.

[0015] Furthermore, the C1-C10 hydrocarbon group includes any one of C1-C10 alkyl, C2-C10 alkenyl, and C3-C10 cycloalkyl;

[0016] The substituted or unsubstituted C1-C6 hydrocarbon groups include substituted or unsubstituted C1-C6 alkyl groups;

[0017] The substituted or unsubstituted carbonyl-containing C1-C6 hydrocarbon group includes substituted or unsubstituted carbonyl-containing C1-C6 alkyl groups.

[0018] Furthermore, the first additive comprises at least one of the compounds with the following structural formulas:

[0019]

[0020]

[0021] Furthermore, the second additive comprises at least one of the compounds with the following structural formulas:

[0022] Furthermore, the electrolyte possesses at least one of the following characteristics (1) to (3):

[0023] (1) The mass of the first additive is 0.05% to 5% of the total mass of the electrolyte;

[0024] (2) The mass of the second additive is 0.05% to 6% of the total mass of the electrolyte;

[0025] (3) The mass ratio of the first additive to the second additive is (2-10):(1-50). Further, the additive also includes 1,3-propanesulfonate lactone and fluoroethylene carbonate.

[0026] 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.

[0027] Furthermore, 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 Mnz A e O₂, where 0.9 ≤ a ≤ 1.1, 0.6 ≤ x ≤ 0.96, 0 < y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 ≤ e ≤ 0.1, and x + y + z = 1, and A contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, Ce.

[0028] Furthermore, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material formed by a silicon-based material and a carbon-based material. The silicon-based material includes at least one of silicon单质, silicon oxide, and silicon metal compound; the carbon-based material includes graphite.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) In the electrolyte of the present invention, borate pinacol ester compounds and fluorinated borate ester compounds are used. The ring-opening polymerization reaction of borate pinacol ester compounds and the branched-chain structure of fluorinated borate ester compounds can both promote the construction of a cross-linked network structure in the organic components of SEI and / or CEI, which is beneficial to improving the mechanical properties of the electrode / electrolyte interface, inhibiting the interface damage caused by electrode volume expansion or side reactions, and enhancing the interface structure stability;

[0031] (2) Among the additives used in the electrolyte of the present invention, B can react with lattice oxygen due to its electron-deficient property, inhibiting the oxidative decomposition of the electrolyte at the positive electrode interface, and further enhancing the interface stability and safety performance of the battery;

[0032] (3) A secondary battery using the electrolyte of the present invention can effectively improve the cycling performance of the battery and enhance the battery safety. Specific Embodiments

[0033] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention. Those not specified in the embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0034] An electrolyte comprising additives; said additives include a first additive and a second additive, the first additive comprising a pinacol borate ester compound; the second additive comprising a fluoroboronic acid ester compound.

[0035] The borate pinacol ester compounds used in the electrolyte of this invention can form cross-linked network polymers through ring-opening during oxidation or reduction, exhibiting excellent film-forming properties and contributing to improved SEI and / or CEI mechanical strength. Fluoroboronic acid ester compounds have branched structures and can also form cross-linked network polymers, which can adapt to the stress generated by the volume expansion of the silicon-carbon composite anode during charging and discharging.

[0036] Furthermore, fluoroborate esters can provide an F source for the SEI and / or CEI film formation process, forming LiF, modulating the electrode / electrolyte interface structure, resulting in thin and dense films, and promoting Li... + Interface transmission.

[0037] In addition, the B atom is an electron-deficient site, which can absorb lattice oxygen deposited on the positive electrode surface through SN2 reaction, inhibiting the oxidative decomposition of the electrolyte at the positive electrode interface, thereby improving the battery's gas production performance and enhancing safety.

[0038] In some specific embodiments of the present invention, the first additive comprises a compound of formula I; the second additive comprises at least one of a compound of formula II or formula III:

[0039]

[0040] R1 includes any one of C1-C10 hydrocarbon groups, C1-C10 alkoxy groups, C6-C10 aromatic groups, and borate pinacol ester groups;

[0041] R2, R3 and R4 each independently contain one of the following: a hydrogen atom, a substituted or unsubstituted C1-C6 hydrocarbon group, or a substituted or unsubstituted carbonyl-containing C1-C6 hydrocarbon group;

[0042] The substituted groups include halogens;

[0043] M includes any one of Li, Na, or K;

[0044] Among them, at least one of R2, R3 and R4 is halogenated.

[0045] In some specific embodiments of the present invention, the C1-C10 hydrocarbon group includes any one of C1-C10 alkyl, C2-C10 alkenyl, and C3-C10 cycloalkyl;

[0046] The substituted or unsubstituted C1-C6 hydrocarbon groups include substituted or unsubstituted C1-C6 alkyl groups;

[0047] The substituted or unsubstituted carbonyl-containing C1-C6 hydrocarbon group includes substituted or unsubstituted carbonyl-containing C1-C6 alkyl groups.

[0048] In this context, alkyl refers to a fully saturated straight-chain or branched alkyl group; C1-C10 alkyl refers to an alkyl group with 1-10 carbon atoms. The structure of an alkoxy group can be represented as –O–R5, where R5 is selected from alkyl groups with 1-10 carbon atoms, i.e., C1-C10 alkyl groups; C1-C10 alkoxy refers to an alkoxy group with 1-10 carbon atoms. Alkenyl refers to a straight-chain or branched hydrocarbon containing an unsaturated double bond; C2-C10 alkenyl refers to an alkenyl group with 2-10 carbon atoms. Cyclic hydrocarbon groups refer to a single-ring alicyclic hydrocarbon group or a fused-ring alicyclic hydrocarbon group; C3-C10 cyclic hydrocarbon groups refer to cyclic hydrocarbon groups with 3-10 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc. A carbonyl-containing hydrocarbon group is –CO–R6, where –CO– is a carbonyl group, and R6 is selected from alkyl groups with 1-6 carbon atoms.

[0049] In some specific embodiments of the present invention, the pinacol borate ester compound has at least one of the following structural formulas:

[0050] (1) n1 is 1 or 0, and n2 is an integer between 0 and 9;

[0051] (2) m1 is 1 or 0, and m2 is an integer between 0 and 7;

[0052] (3) x1 is 1 or 0, and x2 is an integer between 0 and 6;

[0053] (4) R 11 Selected from C3-C10 cycloalkyl groups;

[0054] (5) y is an integer between 0 and 8;

[0055] (6) z is an integer between 0 and 2, R 12 Selected from aromatic groups of C6 to C10;

[0056] (7)

[0057] Both vinyl and cycloalkyl groups contain unsaturated bonds, which can further promote their preferential reduction on the negative electrode surface to form a passivation film.

[0058] In different implementations, n2 can be 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9; m2 can be 0, 1, 2, 3, 4, 5, 6 or 7; x2 can be 0, 1, 2, 3, 4, 5 or 6; y can be 0, 1, 2, 3, 4, 5, 6, 7 or 8; and z can be 0, 1 or 2.

[0059] In some specific embodiments of the present invention, at least one of R2, R3 and R4 comprises at least one of the following groups:

[0060] (1) a is 0 or 1, b is an integer between 0 and 4, and c is an integer between 0 and 2;

[0061] (2) d is 0 or 1, and e is an integer between 0 and 5.

[0062] In different implementations, b can be 0, 1, 2, 3 or 4; c can be 0, 1 or 2; and e can be 0, 1, 2, 3, 4 or 5.

[0063] In some specific embodiments of the present invention, the first additive comprises at least one of the compounds with the following structural formulas:

[0064]

[0065] In some specific embodiments of the present invention, the second additive comprises at least one of the compounds with the following structural formulas:

[0066]

[0067] In a specific embodiment of the present invention, the electrolyte has at least one of the following features (1) to (3):

[0068] (1) The mass of the first additive is 0.05% to 5% of the total mass of the electrolyte;

[0069] (2) The mass of the second additive is 0.05% to 6% of the total mass of the electrolyte;

[0070] (3) The mass ratio of the first additive and the second additive is (2-10): (1-50).

[0071] In different embodiments, the mass of the first additive may be a range of 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any combination thereof of the total mass of the electrolyte.

[0072] In different embodiments, the mass of the second additive may be a range of 0.05%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6% or any combination thereof of the total mass of the electrolyte.

[0073] In different embodiments, the mass ratio of the first additive to the second additive can be a range of 2:1, 1:5, 2:15, 1:10, 1:15, 1:20, 1:25, 5:1, 1:2, 1:4, 1:6, 1:8, 10:1, 1:1, 1:3, or any two of these.

[0074] The first additive, a pinacol borate ester, and the second additive, a fluoroboronic acid ester, possess cyclic and branched structures, respectively. Both facilitate the formation of a network-crosslinked polymer structure at the positive and negative electrodes during film formation. This component increases the elastic modulus of the SEI and CEI, allowing for greater volume expansion and improving the stability of the interfacial passivation layer. The F-containing group on the alkyl group of the second additive enhances the interfacial energy of the passivation layer and increases the LiF grain boundary content, which is beneficial for lithium-ion conduction at the interface. Furthermore, boron (B) can bind with singlet oxygen at the positive electrode interface, inhibiting its catalytic effect on side reactions in the electrolyte.

[0075] In some specific embodiments of the present invention, lithium salts and organic solvents are also included; the organic solvents include at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0076] In some specific embodiments of the present invention, the lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorodioxalatophosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Preferably, the lithium salt includes LiPF6.

[0077] In some specific embodiments of the present invention, the mass of the lithium hexafluorophosphate is 12% to 20% of the total mass of the electrolyte.

[0078] In different embodiments, the mass of the lithium hexafluorophosphate may be 12%, 12.5%, 15%, 18%, 20% of the total mass of the electrolyte or the range composed of any two of them.

[0079] Too low concentration of the lithium salt affects the conductivity of the electrolyte, and too high concentration will increase the viscosity of the electrolyte, which also affects the conductivity of the electrolyte. An appropriate concentration of the lithium salt is adopted to ensure the conductivity of the electrolyte. By cooperating with the second lithium salt, the stability of the electrolyte is improved, and an appropriate concentration is adopted to ensure an appropriate conductivity.

[0080] In a specific embodiment of the present invention, the additive further includes 1,3 - propane sultone (PS) and fluoroethylene carbonate (FEC). 1,3 - propane sultone (PS) can form a film at the electrode interface, play a role in protecting the interface, and is beneficial to improving the gas generation performance of the battery. Fluoroethylene carbonate can form a high - quality SEI in the silicon - based composite anode material, significantly improving the cycle stability of the battery.

[0081] In a specific embodiment of the present invention, the mass of the 1,3 - propane sultone is 0.05% - 3% of the total mass of the electrolyte.

[0082] In different embodiments, the mass of the 1,3 - propane sultone may be 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% of the total mass of the electrolyte or the range composed of any two of them.

[0083] In a specific embodiment of the present invention, the mass of the fluoroethylene carbonate (FEC) is 0.05% - 10% of the total mass of the electrolyte.

[0084] The present invention also provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, a separator and any one of the above - mentioned electrolytes.

[0085] In a specific embodiment of the present invention, the positive electrode sheet includes a positive electrode active material. The positive electrode active material has a chemical formula including Li a Ni x Co y Mn z A e O2, where 0.9 ≤ a ≤ 1.1, 0.6 ≤ x ≤ 0.96, 0 < y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 ≤ e ≤ 0.1, and x + y + z = 1, and A includes at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, Ce.

[0086] In a specific embodiment 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 oxide, and silicon metal compounds; the carbon-based materials include graphite.

[0087] Batteries using silicon-carbon composite materials as the negative electrode undergo significant volume expansion during charging and discharging, leading to particle breakage. This results in continuous side reactions at the exposed fresh interface, consuming lithium and electrolyte and passivating the interface. The expansion and contraction of the particles also cause the silicon-carbon composite material to detach from the current collector, hindering electron conduction and deteriorating kinetic performance. The aforementioned B-containing additive, through reduction and decomposition at the interface to form a cross-linked network polymer passivation layer, can improve the mechanical properties and elastic modulus of the SEI (Self-Intercalating Inductance), effectively mitigating the volume expansion of the silicon-carbon composite material and enhancing the structural stability of the negative electrode material.

[0088] In high-nickel ternary cathodes, the Li / Ni mixing leads to a charge compensation process, resulting in the formation of Ni in a high oxidation state. 4+ Singlet oxygen is released, and both the acidic byproducts and the active lithium have an oxidizing catalytic effect on the electrolyte, consuming the electrolyte and affecting the thermal stability of the material. Simultaneously, acidic byproducts in the electrolyte attack the cathode material interface, inducing the dissolution of transition metal ions from the electrolyte surface, resulting in an irreversible phase change, forming an insulating passivation layer, and increasing interfacial impedance. The dissolved transition metal ions may also migrate to the anode material surface and deposit on the SEI film. The aforementioned B-containing additive forms a CEI film passivation layer at the cathode interface, preventing direct contact between acidic byproducts and the cathode, and inhibiting cathode interface corrosion. Furthermore, B can combine with singlet oxygen, further suppressing interfacial electrolyte side reactions.

[0089] The present invention will now be described in detail with reference to specific embodiments.

[0090] 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.

[0091] The preparation method of lithium-ion batteries may include the following steps:

[0092] (1) Preparation of the positive electrode: The positive electrode active material Li(Ni) is prepared. 0.9 Mn 0.05 Co 0.05 O2 (N90), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of N90:Super P:PVDF = 90:6:4, and then evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform slurry. The mixed slurry is coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet is obtained.

[0093] (2) Preparation of negative electrode sheet: The negative electrode active material silicon-carbon composite material (silicon content is 10wt%, the rest is artificial graphite), conductive agent acetylene black (Super P) and binder SBR are mixed evenly in the mass ratio of silicon-carbon composite material:Super P:SBR = 92:4:4, and evenly dispersed in deionized water to form 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.

[0094] (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 cell. The bare cell 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 into capacities to complete the preparation of lithium-ion batteries.

[0095] The method for preparing the electrolyte includes the following steps:

[0096] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), after removing water from the organic solvent, lithium salt is added to the organic solvent one by one while continuously stirring and cooling. When the electrolyte temperature rises by no more than 2°C, lithium salt can be added to continue, and finally a colorless and transparent liquid is obtained. Additives are added and the mixture is stirred evenly to obtain the electrolyte.

[0097] Electrochemical performance testing items include:

[0098] (1) Room temperature DCR test: At 25±2℃, the lithium-ion batteries obtained in the examples and comparative examples were charged to 4.25V 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%.

[0099] (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 4.25V, 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%.

[0100] (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 4.25V. 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%.

[0101] (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 4.25V at 25±2℃, and then charged at a constant voltage of 4.25V until the current was below 0.05C, so that they were in a fully charged state of 4.25V. 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℃. After 7 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%.

[0102] Table 1. Electrolyte composition information and its lithium-ion battery performance.

[0103]

[0104]

[0105]

[0106] Note: The dosage of lithium salt and each additive refers to their respective percentage content in the total mass of the electrolyte.

[0107] Comparing Examples 3, 9-11 with Comparative Example 1, it is evident that the simultaneous addition of pinacol borate esters and fluoroboronate esters to the electrolyte further enhances the battery's DCR and its rate of change, high-temperature storage, room-temperature cycling, and high-temperature gas generation electrochemical performance. Furthermore, comparing Example 3 with Comparative Examples 2 and 3, it is clear that when the electrolyte additive contains only pinacol borate esters or only fluoroboronate esters, the improvement in gas generation and cycle performance is not as significant as the synergistic effect of the pinacol borate esters and fluoroboronate esters.

[0108] The comparisons of Examples 1-5 and Examples 6-8 show that changes in the content of pinacol borate esters or fluoroboronate esters in the electrolyte additives have a certain impact on the gas generation and cycle performance of the battery. It can also be concluded that when the mass ratio of pinacol borate esters to fluoroboronate esters is within the range of (2-10):(1-50) of this invention, the additive is more likely to exhibit higher performance in the battery.

[0109] The comparison between Examples 3 and 12 shows that when the electrolyte additive also contains FEC and PS, the battery exhibits superior gas generation and cycle performance. This is because PS protects the interface and improves the battery's gas generation performance. FEC can form a high-quality SEI in silicon-based composite anode materials, significantly enhancing the battery's cycle stability.

[0110] In summary, when borate pinacol esters and fluoroboronic acid esters are added to the electrolyte, they work synergistically, and with the promoting effects of FEC and PS, the battery's DCR and its rate of change, high-temperature storage, room-temperature cycling, and high-temperature gas generation electrochemical performance are all further improved.

[0111] 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 additives include a first additive and a second additive, wherein the first additive includes pinacol borate esters; and the second additive includes fluoroboronate esters. The mass of the first additive is 0.05% to 5% of the total mass of the electrolyte; The mass of the second additive is 0.05% to 6% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The first additive comprises a compound of formula I; the second additive comprises at least one compound of formula II or formula III. ； ； ； R1 includes any one of C1-C10 hydrocarbon groups, C1-C10 alkoxy groups, C6-C10 aromatic groups, and borate pinacol ester groups; R2, R3 and R4 each independently contain one of the following: a hydrogen atom, a substituted or unsubstituted C1-C6 hydrocarbon group, or a substituted or unsubstituted carbonyl-containing C1-C6 hydrocarbon group; The substituted groups include halogens; M includes any one of Li, Na, or K; Among them, at least one of R2, R3 and R4 is halogenated.

3. The electrolyte according to claim 2, characterized in that, The C1-C10 hydrocarbon groups include any one of C1-C10 alkyl groups, C2-C10 alkenyl groups, and C3-C10 cycloalkyl groups; The substituted or unsubstituted C1-C6 hydrocarbon groups include substituted or unsubstituted C1-C6 alkyl groups; The substituted or unsubstituted carbonyl-containing C1-C6 hydrocarbon group includes substituted or unsubstituted carbonyl-containing C1-C6 alkyl groups.

4. The electrolyte according to claim 1, characterized in that, The first additive includes at least one of the following compounds: (A1)、 (A2)、 (A3)、 (A4)、 (A5)、 (A6)、 (A7)、 (A8)、 (A9)、 (A10) (A11)ぁ (A12)、 (A13) (A14)、 (A15)ぁ (A16)、 (A17)、 (A18) 5. The electrolyte according to claim 1, characterized in that, The second additive includes at least one of the following compounds: (B1)、 (B2)、 (B3)、 (B4).

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The mass ratio of the first additive to the second additive is (2-10):(1-50).

7. The electrolyte according to claim 1, characterized in that, The additives also include 1,3-propanesulfonate lactone and fluoroethylene carbonate.

8. 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 7.

9. The secondary battery according to claim 8, 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 A e O2, wherein 0.9 ≤ a ≤ 1.1, 0.6 ≤ x ≤ 0.96, 0 < y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 ≤ e ≤ 0.1, and x + y + z = 1, and A contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd and Ce.

10. The secondary battery according to claim 9, 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.

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