Electrolyte and secondary battery

Abstract

This application discloses an electrolyte and a secondary battery. Additive A and additive B are added to the electrolyte. Additive A contains negatively charged sulfonate ions and positively charged nitrogen atoms, forming a zwitterionic compound. Additive A can generate passivation films on the surfaces of both the positive and negative electrodes, thereby stabilizing the electrolyte. Additive B includes any one of tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, and tris(trimethylsilane)phosphite, which helps reduce the electrolyte impedance. Additives A and B work synergistically to reduce gas production during cycling, improve the high-temperature storage performance of the secondary battery, and enhance its cycle performance.

Description

Technical Field

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

[0002] High energy density is the development direction of secondary batteries, among which nickel-rich layered transition metal oxide cathode active materials have attracted widespread attention due to their high capacity and high operating voltage. However, the structural stability and electrode / electrolyte interface stability of nickel-rich cathode active materials are limited, mainly due to the high valence of Ni. 4+ It is easily oxidized and reduced to Ni by the electrolyte. 3+ and Ni 2+ Ni 4+ Its catalytic activity leads to severe electrolyte decomposition, ultimately resulting in increased gas production, volume expansion, and reduced cycle performance during secondary battery cycling. Furthermore, the continuous exposure of fresh electrode surfaces during volume expansion in silicon-based secondary batteries causes repeated growth of the SEI on the silicon anode surface, constantly consuming lithium ions in the electrolyte, further contributing to battery volume expansion and reduced cycle performance.

[0003] Therefore, improving the interfacial stability of high-nickel cathode-electrolyte and silicon-based anode-electrolyte is particularly necessary to improve the performance of secondary batteries. Summary of the Invention

[0004] This application provides an electrolyte and a secondary battery, which can solve the problems of high gas production and poor cycle performance caused by poor interfacial stability between the high-nickel positive electrode and the electrolyte, and between the silicon-based negative electrode and the electrolyte in existing secondary batteries.

[0005] A first aspect of this application provides an electrolyte comprising additive A and additive B, a lithium salt, and an organic solvent;

[0006] The additive A comprises a compound with the structural formula shown in Formula I:

[0007]

[0008] In Formula I, n is 0 to 4, and R1 to R5 are each independently selected from hydrogen atoms, halogens, C1 to C5 amide groups, C1 to C5 aldehyde groups, C1 to C5 carbonyl groups, substituted or unsubstituted C1 to C5 hydrocarbon groups, and substituted or unsubstituted C1 to C5 ether groups; the substituted group is a halogen.

[0009] Additive B includes any one of tris(trimethylsilane)borate (B1), tris(trimethylsilane)phosphate (B2), and tris(trimethylsilane)phosphite (B3).

[0010] Optionally, additive A comprises at least one of compounds having the following structural formulas:

[0011]

[0012] Optionally, the electrolyte shall satisfy at least one of the following conditions:

[0013] (1) The mass of additive A accounts for 0.1% to 5.0% of the total mass of the electrolyte;

[0014] (2) The mass of additive B accounts for 0.1% to 1.0% of the total mass of the electrolyte;

[0015] (3) The ratio of additive A to B is 4 to 12.

[0016] Optionally, the lithium salt includes lithium hexafluorophosphate and a second lithium salt, the second lithium salt including at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0017] Optionally, in the electrolyte, the molar concentration of lithium hexafluorophosphate is 0.5 mol / L to 2.0 mol / L, and the molar concentration of the second lithium salt is 0.06 mol / L to 0.6 mol / L; the molar ratio of lithium hexafluorophosphate to the second lithium salt is (8 to 10):(1 to 3).

[0018] Optionally, the organic solvent includes linear esters and cyclic esters, wherein the linear esters account for 30% to 80% of the total mass of the electrolyte, the cyclic esters account for 15% to 50% of the total mass of the electrolyte, and the mass ratio of the linear esters to the cyclic esters is (4 to 9):(2 to 4).

[0019] Optionally, the chain ester includes one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate; the cyclic ester includes at least one of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, and γ-butyrolactone.

[0020] A second aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte as described above.

[0021] Optionally, the negative electrode sheet includes a negative electrode active material, which includes a silicon-based material, and the silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

[0022] Optionally, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes materials with the molecular formula Li. a Ni x Co y M z Compounds of O2, wherein 0.9≤a≤1.1, 0.6≤x≤0.88, 0≤y≤0.2, 0≤z≤0.2, x+y+z=1, and M is Mn or Al.

[0023] The beneficial effects of this application are that it provides an electrolyte and a secondary battery. By adding additive A and additive B to the electrolyte, additive A contains negatively charged sulfonate ions and positively charged nitrogen atoms to form a zwitterionic compound. Additive A can generate passivation films on the surfaces of the positive and negative electrodes, thereby stabilizing the electrolyte, while additive B helps to reduce the impedance of the electrolyte. Additives A and B work synergistically to reduce the gas production of the secondary battery during cycling, improve the high-temperature storage performance of the secondary battery, and enhance the cycle performance of the secondary battery. Detailed Implementation

[0024] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0025] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of".

[0026] In this specification, the range of values ​​indicated by “~” represents the range containing the minimum and maximum values ​​recorded before and after “~”, respectively.

[0027] In some embodiments of this application, an electrolyte is provided, which includes additive A and additive B, lithium salt and organic solvent;

[0028] Additive A includes compounds with the structure shown in Formula I:

[0029]

[0030] In Formula I, n is 0 to 4, and R1 to R5 are each independently selected from hydrogen atoms, halogens, C1 to C5 amide groups, C1 to C5 aldehyde groups, C1 to C5 carbonyl groups, substituted or unsubstituted C1 to C5 hydrocarbon groups, and substituted or unsubstituted C1 to C5 ether groups; the substituted group is a halogen.

[0031] Additive B includes any one of tris(trimethylsilane)borate (B1), tris(trimethylsilane)phosphate (B2), and tris(trimethylsilane)phosphite (B3).

[0032] The structure shown in Formula I contains a negatively charged sulfonate group and a positively charged nitrogen atom, forming a zwitterionic compound. The sulfonate group, due to its negative charge, reacts with lithium ions (Li) in the lithium hexafluorophosphate (LiPF6) (lithium salt) in the electrolyte. + They easily combine and separate, making them excellent exchange sites for lithium ions. Furthermore, the positively charged nitrogen atoms (N...) + It can act as a Lewis base by introducing PF6 into lithium hexafluorophosphate (LiPF6). - The phosphorus atom P in the compound provides a lone pair of electrons. Furthermore, due to the opposite charge polarities of the sulfonate ion and the nitrogen atom, the zwitterionic compound possesses a large molecular dipole moment. This allows additives containing compounds with the structure shown in Formula I to dissociate lithium salts, especially lithium hexafluorophosphate (LiPF6), from the electrolyte through the sulfonate ions and nitrogen atoms. + Combined, nitrogen atom N + With PF6 - The phosphorus atom (P) in the electrolyte provides a lone pair of electrons, forming a stable complex. This complex can form passivation films on both the positive and negative electrode surfaces, creating barriers between the positive electrode surface and the electrolyte, and between the negative electrode surface and the electrolyte. This prevents interfacial reactions between the electrolyte and the positive electrode, and between the electrolyte and the negative electrode, thus improving the interfacial stability between the electrolyte and the positive and negative electrodes. Specifically:

[0033] 1. The passivation film formed by the complex acts as a barrier, preventing the Ni content in the nickel-rich positive electrode active material of the positive electrode from being blocked. 4+ It will not undergo a redox reaction with the electrolyte to form Ni. 3+ and Ni 2+ This avoids Ni 2+ With Li+ The capacity loss of the secondary battery caused by the mixing of Li / Ni ions at the crystal sites is reduced, but the capacity retention rate of the secondary battery is improved.

[0034] II. The passivation film formed by the complex has a barrier effect, preventing the electrolyte from being affected by Ni. 4+ The catalytic activity of the electrolyte decomposes into oxidation byproducts, which leads to an increase in the internal resistance of the secondary battery. This method can effectively reduce the internal resistance of the secondary battery, while the electrolyte will not be oxidized and decomposed into oxidation byproducts. Therefore, it cannot reach the negative electrode surface through the cross-effect of the transition metal ions dissolved during the secondary battery cycle to destroy the SEI film on the negative electrode surface, thereby improving the cycle capacity retention rate of the secondary battery.

[0035] III. Due to the reaction of sulfonate ions with Li + They can easily combine and separate, which can improve the ionic conductivity in the electrolyte system, thereby forming a stable SEI film on the negative electrode surface and reducing the interfacial impedance.

[0036] Additive B in the electrolyte helps to form a more stable interfacial film between the positive and negative electrodes, reducing the electrolyte impedance.

[0037] In some embodiments of this application, at least one of R1 to R5 is not hydrogen.

[0038] In some embodiments of this application, additive A comprises at least one of compounds having the following structural formulas:

[0039]

[0040] In some embodiments of this application, the electrolyte satisfies at least one of the following conditions:

[0041] (1) The mass of additive A accounts for 0.1% to 5.0% of the total mass of the electrolyte;

[0042] (2) The mass of additive B accounts for 0.1% to 1.0% of the total mass of the electrolyte;

[0043] (3) The ratio of additive A to B is 4 to 12.

[0044] Additive A comprises 0.1% to 5.0% of the total electrolyte mass. Specifically, the percentage of additive A in the total electrolyte mass can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of two of these numbers. Additive B comprises 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1.0%, or any combination of two of these numbers. Too little additive may result in a passivation film that is too thin on the positive and negative electrode surfaces, making it prone to breakage and failing to effectively isolate the positive and negative electrodes from the electrolyte. Too much additive may result in a passivation film that is too thick on the positive and negative electrode surfaces, increasing the impedance and polarization of the secondary battery. When the mass content of additives A and B in the electrolyte is within the above-mentioned range, a stable passivation film can be formed on the surfaces of the positive and negative electrodes, improving the interfacial stability between the positive and negative electrodes and the electrolyte, enhancing the cycle stability of the secondary battery, reducing the internal resistance of the secondary battery, and mitigating the effects of expansion, increased impedance, and gas generation during battery cycling, thereby improving the cycle performance and high-temperature performance of the secondary battery. Preferably, the ratio of additive A to B is 5 to 10, and the mass ratio of additives A and B needs to be controlled within a reasonable range to promote the coordinated development of both in the electrolyte.

[0045] In some embodiments of this application, the lithium salt includes lithium hexafluorophosphate (LiPF6) and a second lithium salt, the second lithium salt including at least one of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium difluorodioxalato)phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0046] In some embodiments of this application, the molar concentration of lithium hexafluorophosphate in the electrolyte is 0.5 mol / L to 2.0 mol / L. Specifically, the molar concentration of lithium hexafluorophosphate in the electrolyte can be 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, or any two of these values.

[0047] In some embodiments of this application, the molar concentration of the second lithium salt in the electrolyte is 0.06 mol / L to 0.6 mol / L. Specifically, the molar concentration of the second lithium salt in the electrolyte can be 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, 0.24 mol / L, 0.28 mol / L, 0.3 mol / L, 0.34 mol / L, 0.38 mol / L, 0.4 mol / L, 0.44 mol / L, 0.48 mol / L, 0.5 mol / L, 0.54 mol / L, 0.58 mol / L, 0.6 mol / L, or any two of these values.

[0048] In some embodiments of this application, the molar ratio of lithium hexafluorophosphate to the second lithium salt includes (8-10):(1-3). Specifically, the molar ratio of lithium hexafluorophosphate to the second lithium salt can be 8:1, 8:2, 8:3, 9:1, 9:2, 9:3, 10:1, 10:2, 10:3 or any two of these ratios.

[0049] Too low a concentration of lithium salt in the electrolyte will affect the conductivity of the electrolyte, while too high a concentration will increase the viscosity of the electrolyte, which will also affect the conductivity. When the concentrations of lithium hexafluorophosphate and the second lithium salt in the electrolyte are within the above range, the conductivity of the electrolyte can be guaranteed and the internal resistance of the secondary battery can be reduced.

[0050] In some embodiments of this application, the organic solvent includes cyclic esters and chain esters.

[0051] In some embodiments of this application, the chain ester includes at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (EMC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (PA), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB).

[0052] In some embodiments of this application, the cyclic ester includes at least one of ethylene carbonate (EC), (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), and γ-butyrolactone (γ-GBL).

[0053] In some embodiments of this application, the mass of the chain ester accounts for 30% to 80% of the total mass of the electrolyte. Specifically, the mass of the chain ester as a percentage of the total mass of the electrolyte can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of these values.

[0054] In some embodiments of this application, the mass of the cyclic ester accounts for 15% to 50% of the total mass of the electrolyte. Specifically, the mass of the cyclic ester as a percentage of the total mass of the electrolyte can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any two of these values.

[0055] In some embodiments of this application, the mass ratio of the linear ester to the cyclic ester is (4–9):(2–4). Specifically, the mass ratio of the linear ester to the cyclic ester can be 4:2, 5:2, 6:2, 7:2, 8:2, 9:2, 4:3, 5:3, 6:3, 7:3, 8:3, 9:3, 4:4, 5:4, 6:4, 7:4, 8:4, 9:4, or any two of these ratios. Controlling the mass ratio of the linear and cyclic esters within the range specified in this application is beneficial for formulating solvents with suitable viscosity and high conductivity, thereby improving the performance of the secondary battery.

[0056] In some embodiments of this application, a secondary battery is also provided, including a positive electrode, a negative electrode, and the electrolyte described above.

[0057] In some embodiments of this application, the negative electrode sheet further includes a negative electrode active material, which includes a silicon-based material, and the silicon-based material includes at least one of elemental silicon, silicon-oxygen material, and silicon-carbon material.

[0058] In some embodiments of this application, the positive electrode sheet further includes a positive electrode active material, which includes materials with the molecular formula Li. a Ni x Co y M z The compound of O2, wherein 0.9≤a≤1.1, 0.6≤x≤0.88, 0≤y≤0.2, 0≤z≤0.2, x+y+z=1, and M is Mn or Al, indicates that the positive electrode active material is a nickel-rich material, which enables the secondary battery to have high cycle capacity retention and high operating voltage.

[0059] In some embodiments of this application, the positive electrode active material may also contain doped or coated elements.

[0060] The secondary battery provided in this application embodiment can be applied to electrical devices, which can be used in, but are not limited to, electric toys, power tools, electric vehicles, electric cars, energy storage devices, ships, spacecraft, etc.

[0061] The preparation method of the secondary battery provided in this application is described below with reference to specific embodiments:

[0062] The examples and comparative examples respectively provide an electrolyte and a secondary battery containing the electrolyte. The composition of the electrolyte is shown in Table 1.

[0063] 1. Preparation of electrolyte:

[0064] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), the solvents were mixed evenly according to the mass ratio shown in Table 1 to obtain a mixed solvent. Then, lithium salt and additives were added and stirred evenly to obtain an electrolyte.

[0065] Adding lithium salts releases heat, causing the electrolyte temperature to rise and resulting in some thermal decomposition of the lithium salts. Therefore, dry ice is used to cool the electrolyte when adding lithium salts. Lithium salts can be added only if the electrolyte temperature rises by no more than 2°C.

[0066] 2. Making a secondary battery:

[0067] The prepared electrolyte was injected into a 2Ah soft-pack lithium-ion battery with NCM811 as the positive electrode active material and SiO-C (SiO mass fraction of 5wt%) as the negative electrode active material. The injection amount was 10g. The battery was sealed once and placed at 25°C for 24 hours. It was then formed in a high-temperature fixture and sealed with a second aluminum-plastic film. After capacity testing, a secondary battery was produced.

[0068] 3. Battery performance test:

[0069] (1) Room temperature DCR test: At 25±2℃, the battery was charged to 4.5V at 1C, then discharged at 1C capacity for 30min. After adjusting to 50% SOC, it was pulsed discharged at 5C for 10s and then charged for 10s. 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%. The results are shown in Table 1.

[0070] (2) Room temperature cycle performance test: At 25±2℃, the battery was charged and discharged at a rate of 1C / 1C within the range of 3.0 to 4.5V. 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 of 500 cycles / discharge specific capacity in the first cycle × 100%. The recorded data are shown in Table 1.

[0071] (3) High-temperature storage performance: The battery was placed at 60±2℃ and charged and discharged at a rate of 1C / 1C within the range of 3.0 to 4.5V. The discharge specific capacity of the battery in the first week was recorded. Then, the battery was stored at 60±2℃ for 30 days, and the charge and discharge test was carried out again and the discharge specific capacity was recorded. High-temperature storage capacity retention rate = discharge specific capacity after 7 days / discharge specific capacity in the first week × 100%. The recorded data are shown in Table 1.

[0072] (4) High-temperature gas generation test: The battery was charged at 25±2℃ with a constant current of 1C to 4.5V, and then charged at 4.5V with a constant voltage until the current was below 0.05C, so that it was in a fully charged state of 4.5V. 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℃ for 2 days. After that, the battery was taken out and its volume after storage was measured immediately and recorded as V1. Volume expansion rate = (V1-V0) / V0×100%, and the recorded data are shown in Table 1.

[0073] The types and amounts of raw materials used in the electrolytes of the secondary batteries in the examples and comparative examples, as well as the performance of the secondary batteries prepared with these electrolyte ratios, are shown in Table 1.

[0074] Table 1 Electrolyte composition information and secondary battery performance

[0075]

[0076]

[0077] Note: The amount of lithium salt used refers to the molar concentration of lithium salt, the amount of organic solvent used refers to the mass ratio of the organic solvent used, and the amount of additive used refers to its content in the total mass of the electrolyte.

[0078] As shown in Table 1, comparing the experimental results of Examples 1-15 and Comparative Example 1, it can be seen that the addition of additives A and B to the electrolyte significantly improves the performance of the secondary battery. The combination of additives A and B can effectively reduce the internal resistance of the secondary battery and slow down the increasing trend of internal resistance during high-temperature storage, and improve the cycle retention rate at room temperature and the high-temperature storage retention rate of the secondary battery. At the same time, it also has a significant inhibitory effect on gas generation in the secondary battery.

[0079] By comparing Examples 1-4, it was found that as the mass content of additive A1 in the electrolyte increased, the internal resistance and storage capacity retention of the secondary battery showed a trend of first increasing and then decreasing, while the high-temperature storage volume expansion rate of the secondary battery showed a trend of first decreasing and then increasing. Specifically, when the mass content of additive A1 in the electrolyte reached 1%, the internal resistance and storage capacity retention of the secondary battery were optimal. More specifically, when additive A1 was 1% and additive B1 was 0.2% in the electrolyte, the performance of the secondary battery was superior.

[0080] The electrolyte and secondary battery provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises an additive A and an additive B, a lithium salt and an organic solvent; The additive A comprises a compound with a structural formula as shown in Formula I: Formula I In Formula I, n is 0-4, R1-R5 are each independently selected from a hydrogen atom, a halogen, a C1-C5 amide group, a C1-C5 aldehyde group, a C1-C5 carbonyl group, a substituted or unsubstituted C1-C5 hydrocarbon group, and a substituted or unsubstituted C1-C5 ether group; the substituted group is a halogen; The additive B comprises any one of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)phosphite; The mass of the additive A accounts for 0.1%-5.0% of the total mass of the electrolyte; The mass ratio of the additive A to the additive B is 4-12.

2. The electrolyte of claim 1, wherein The additive A comprises at least one of the following compounds: 、 、 、 、 、 、 。 3. The electrolyte of claim 1, wherein, The mass of the additive B accounts for 0.1%-1.0% of the total mass of the electrolyte.

4. The electrolyte of claim 1, wherein The lithium salt comprises lithium hexafluorophosphate and a second lithium salt, the second lithium salt comprising at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorodioxalate phosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

5. The electrolyte of claim 4, wherein In the electrolyte, the molar concentration of lithium hexafluorophosphate is 0.5 mol / L-2.0 mol / L, and the molar concentration of the second lithium salt is 0.06 mol / L-0.6 mol / L; the molar ratio of lithium hexafluorophosphate to the second lithium salt comprises (8-10):(1-3).

6. The electrolyte of claim 1, wherein The organic solvent comprises a chain ester and a cyclic ester, the mass of the chain ester accounting for 30%-80% of the total mass of the electrolyte, the mass of the cyclic ester accounting for 15%-50% of the total mass of the electrolyte, and the mass ratio of the chain ester to the cyclic ester being (4-9):(2-4).

7. The electrolyte of claim 6, wherein The chain ester comprises one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate and ethyl butyrate; the cyclic ester comprises at least one of vinyl carbonate, propylene carbonate, butylene carbonate, fluoro-vinyl carbonate and gamma-butyrolactone.

8. A secondary battery characterized by comprising: The electrolyte comprises an additive A and an additive B, a lithium salt and an organic solvent; 9. The secondary battery according to claim 8, wherein the negative electrode is a lithium metal electrode. The negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprising a silicon-based material, the silicon-based material comprising at least one of silicon single substance, silicon-oxygen material and silicon-carbon material.

10. The secondary battery according to claim 8, wherein the negative electrode is a lithium metal electrode. The positive electrode sheet includes a positive electrode active material including a compound of formula Li a Ni x Co y M z O2, wherein 0.9≤a≤1.1, 0.6≤x≤0.88, 0≤y≤0.2, 0≤z≤0.2, x+y+z=1, and M is Mn or Al.

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