Non-aqueous electrolyte and secondary battery

Abstract

A non-aqueous electrolyte and a secondary battery. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and an additive; the additive comprises a first additive and a second additive; the first additive comprises a compound represented by structural formula 1 and / or a compound represented by structural formula 2; the second additive comprises fluoroethylene carbonate; [structural formula 1]; [structural formula 2]; and the non-aqueous electrolyte satisfies the following conditions: [equation 1], 0.001≤a≤1, 0.1≤b≤7, and 6≤σ≤13.

Description

A non-aqueous electrolyte and a secondary battery

[0001] This application claims priority to Chinese Patent Application No. 202510120113.3, filed on January 25, 2025, entitled “A Non-Aqueous Electrolyte and a Secondary Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of battery materials technology, specifically relating to a non-aqueous electrolyte and a secondary battery. Background Technology

[0003] With the gradual maturation and large-scale production of lithium-ion rechargeable battery technology, its applications cover various industries such as digital products, energy storage, and electric vehicles. As its market share increases, the market demands batteries with requirements for long cycle life, high energy density, and high operating voltage. Electrolyte is a crucial component of the battery and has a significant impact on its performance. Various novel solvents and additives for electrolytes are constantly being developed. Fluorinated ethylene carbonate can be used as an additive, decomposing on the negative electrode surface during battery formation to form a high-performance SEI film (solid electrolyte interface film) to reduce impedance. It can also be used as a solvent to enhance electrolyte wettability and conductivity, improving low-temperature battery performance, thus its applications are very widespread.

[0004] However, during cycling, fluoroethylene carbonate will undergo a de-F reaction with Lewis acids such as PF5 to produce HF. HF will damage the cathode interface film, for example, it can easily lead to the dissolution of transition metal (TM) ions in high-nickel ternary cathode materials, surface oxygen evolution, and irreversible damage to the cathode electrolyte interface (CEI). Summary of the Invention

[0005] To address the problem that existing fluoroethylene carbonates generate HF that damages the positive electrode interface film during battery cycling, this application provides a non-aqueous electrolyte and a secondary battery.

[0006] The technical solution adopted in this application to solve the above-mentioned technical problems is as follows:

[0007] On one hand, this application provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, wherein the additive comprises a first additive and a second additive, the first additive comprising a compound represented by structural formula 1 and / or a compound represented by structural formula 2, and the second additive comprising fluoroethylene carbonate.

[0008] Wherein, n is 0 or 1; R1 and R2 are each independently selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C1-C12 acyl, substituted or unsubstituted C2-C12 alkoxyacyl, and substituted or unsubstituted C2-C12 ether. Both are hydrogen, and R1 and R2 can be linked together to form a ring or not; R3 is selected from substituted or unsubstituted C1-C12 alkylene groups, substituted or unsubstituted C2-C12 alkenyl groups, substituted or unsubstituted C2-C12 alkyne groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 ether groups; when R1, R2, and R3 are substituted, the substituents are alkoxy, hydroxyl, acyl, ester, cyano, or halogen.

[0009] R4 and R5 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl or substituted or unsubstituted C1-C6 alkyl hydroxyl groups. R4 and R5 may be linked together to form a ring or not. R6 is selected from hydrogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl or substituted or unsubstituted C2-C6 alkynyl, C1-C6 cyano, C2-C6 ester, substituted or unsubstituted C2-C6 amide or substituted or unsubstituted C1-C6 amidine.

[0010] The non-aqueous electrolyte meets the following conditions:

[0011] And 0.001≤a≤1, 0.1≤b≤7, 6≤σ≤13;

[0012] Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0013] b represents the mass percentage of the second additive in the non-aqueous electrolyte, in %;

[0014] σ is the conductivity of the non-aqueous electrolyte at 25°C, in mS / cm.

[0015] Optionally, the non-aqueous electrolyte meets the following conditions:

[0016] Optionally, the non-aqueous electrolyte satisfies at least one of the following conditions:

[0017] (1) 0.05 ≤ a ≤ 0.5;

[0018] (2) 0.5 ≤ b ≤ 3;

[0019] (3)7≤σ≤11.

[0020] Optionally, the compound represented by structural formula 1 satisfies at least one of the following conditions:

[0021] (1) R1 is selected from hydrogen, and R2 is selected from… Substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, wherein R 10 Selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl, and substituted or unsubstituted C6-C20 aryl;

[0022] (2) R1 and R2 are each independently selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, or substituted or unsubstituted C6-C20 aryl.

[0023] (3) R1 is selected from R2 is selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, or... Among them, R 11 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, substituted or unsubstituted C2-C11 alkynyl groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 etheryl groups.

[0024] (4) R1 is selected from Among them, R 12 R2 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, and substituted or unsubstituted C2-C11 alkynyl; R2 is selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, and substituted or unsubstituted C6-C20 aryl or... Among them, R 13 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, and substituted or unsubstituted C2-C11 alkynyl groups.

[0025] Optionally, the compound represented by structural formula 1 includes one or more of the following compounds:

[0026] Optionally, the compound represented by structural formula 2 satisfies at least one of the following conditions:

[0027] (1) When R4 and R5 are substituted, the substituents are carboxyl, hydroxyl, halogen or cyano; when R6 is substituted, the substituents are hydroxyl, halogen or alkoxy.

[0028] (2) R6 is selected from cyano groups;

[0029] (3) R4 and R5 are each independently selected from substituted or unsubstituted C1-C6 alkyl groups.

[0030] Optionally, the compound represented by structural formula 2 includes one or more of the following compounds:

[0031] Optionally, the additive further includes a third additive, which includes vinylene carbonate (VC), and the mass ratio of the third additive to the first additive is (2-50):1.

[0032] Optionally, the non-aqueous electrolyte does not include polymerizable monomers and / or prepolymers obtained by polymerizing polymerizable monomers.

[0033] On the other hand, this application provides a secondary battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte as described above. According to the non-aqueous electrolyte provided in this application, a compound shown in structural formula 1 and / or a compound shown in structural formula 2 is used as a first additive, and fluoroethylene carbonate is used as a second additive. The inventors have discovered that when the mass percentage a of the first additive, the mass percentage b of the second additive, and the conductivity σ of the non-aqueous electrolyte at 25°C satisfy the condition… When 0.001≤a≤1, 0.1≤b≤7, and 6≤σ≤13, the resulting non-aqueous electrolyte, when applied to secondary batteries, can effectively improve the cycle life of the battery at both room temperature and high temperature. This is presumably because the first additive undergoes homolytic cleavage during formation and cycling, generating highly reactive free radicals that promote the ring-opening polymerization of fluoroethylene carbonate on the negative electrode surface. This reduces the desulfurization reaction of fluoroethylene carbonate, resulting in the formation of a sulfur-rich (F) SEI film on the negative electrode surface during SEI film recombination, thus improving the stability of the SEI film and extending cycle life. It is important to note that the ring-opening polymerization of fluoroethylene carbonate requires the participation of active lithium to form SEI film components such as LiF. The progress of this reaction is related to the conductivity of the non-aqueous electrolyte. The conductivity affects the replenishment of active lithium at the negative electrode interface during formation, thereby influencing the long-chain polymerization process of fluoroethylene carbonate. Therefore, when the mass percentage of the first additive a, the mass percentage of the second additive b, and the conductivity σ of the non-aqueous electrolyte are controlled in a synergistic manner, it can promote the formation of a highly stable SEI film on the negative electrode surface, while inhibiting the damage to the positive electrode material and the positive electrode electrolyte interface caused by the de-F reaction of fluoroethylene carbonate. Detailed Implementation

[0034] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0035] One embodiment of this application provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive includes a first additive and a second additive. The first additive includes a compound represented by structural formula 1 and / or a compound represented by structural formula 2. The second additive includes fluoroethylene carbonate.

[0036] Wherein, n is 0 or 1; R1 and R2 are each independently selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C1-C12 acyl, substituted or unsubstituted C2-C12 alkoxyacyl, and substituted or unsubstituted C2-C12 ether. Both are hydrogen, and R1 and R2 can be linked together to form a ring or not; R3 is selected from substituted or unsubstituted C1-C12 alkylene groups, substituted or unsubstituted C2-C12 alkenyl groups, substituted or unsubstituted C2-C12 alkyne groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 ether groups; when R1, R2, and R3 are substituted, the substituents are alkoxy, hydroxyl, acyl, ester, cyano, or halogen.

[0037] R4 and R5 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl or substituted or unsubstituted C1-C6 alkyl hydroxyl groups. R4 and R5 may be linked together to form a ring or not. R6 is selected from hydrogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl or substituted or unsubstituted C2-C6 alkynyl, C1-C6 cyano, C2-C6 ester, substituted or unsubstituted C2-C6 amide or substituted or unsubstituted C1-C6 amidine.

[0038] The non-aqueous electrolyte meets the following conditions:

[0039] And 0.001≤a≤1, 0.1≤b≤7, 6≤σ≤13;

[0040] Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0041] b represents the mass percentage of the second additive in the non-aqueous electrolyte, in %;

[0042] σ is the conductivity of the non-aqueous electrolyte at 25°C, in mS / cm.

[0043] The inventors discovered that when the mass percentage of the first additive (a), the mass percentage of the second additive (b), and the conductivity σ of the non-aqueous electrolyte meet the condition... When 0.001≤a≤1, 0.1≤b≤7, and 6≤σ≤13, the resulting non-aqueous electrolyte, when applied to secondary batteries, can effectively improve the cycle life of the battery at both room temperature and high temperature. This is presumably because the first additive undergoes homolytic cleavage during formation and cycling, generating highly reactive free radicals that promote the ring-opening polymerization of fluoroethylene carbonate on the negative electrode surface. This reduces the desulfurization reaction of fluoroethylene carbonate, resulting in the formation of a sulfur-rich (F) SEI film on the negative electrode surface during SEI film recombination, thus improving the stability of the SEI film and extending cycle life. It is important to note that the ring-opening polymerization of fluoroethylene carbonate requires the participation of active lithium to form SEI film components such as LiF. The progress of this reaction is related to the conductivity of the non-aqueous electrolyte. The conductivity affects the replenishment of active lithium at the negative electrode interface during formation, thereby influencing the long-chain polymerization process of fluoroethylene carbonate. Therefore, when the mass percentages of the first additive (a), the second additive (b), and σ are controlled under synergistic conditions, it can promote the formation of a highly stable SEI film on the negative electrode surface, while inhibiting the damage to the positive electrode material and the positive electrode electrolyte interface caused by the de-F reaction of fluoroethylene carbonate.

[0044] In a preferred embodiment, the non-aqueous electrolyte satisfies the following conditions:

[0045] When the mass percentage of the first additive (a), the mass percentage of the second additive (b), and the conductivity σ of the non-aqueous electrolyte further meet the above conditions, it is beneficial to further improve the high-temperature stability of the SEI film on the negative electrode and the CEI film on the positive electrode, thereby improving the high-temperature cycle performance of the secondary battery.

[0046] In a specific embodiment, the mass percentage 'a' of the first additive in the non-aqueous electrolyte can be 0.001%, 0.005%, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.18%, 0.2%, 0.22%, 0.28%, 0.3%, 0.32%, 0.38%, 0.4%, 0.42%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range of any two of these values.

[0047] In a preferred embodiment, 0.05 ≤ a ≤ 0.5.

[0048] The first additive is used to regulate the film quality of fluoroethylene carbonate (the second additive) on the electrode surface. If the content of the first additive is too low, it will be difficult to effectively inhibit the de-F reaction of fluoroethylene carbonate, leading to the deterioration of the positive electrode interface. If the content of the first additive is too high, it will promote the generation of too many free radicals in the non-aqueous electrolyte, increase the probability of side reactions with impurities in the non-aqueous electrolyte, and lead to the instability of the properties of the non-aqueous electrolyte itself.

[0049] In a specific embodiment, the mass percentage b of the second additive in the non-aqueous electrolyte is 0.1%, 0.2%, 0.4%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, 2.2%, 2.8%, 3%, 3.2%, 3.8%, 4%, 4.2%, 4.8%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of these values.

[0050] In a preferred embodiment, 0.5 ≤ b ≤ 3.

[0051] The second additive is fluoroethylene carbonate, which is the main additive component involved in the formation of the negative electrode film. If the content of the second additive is too low, it will be difficult to form a complete SEI film on the surface of the negative electrode, causing the active lithium to be continuously consumed during battery cycling and affecting the battery cycle life. If the content of the second additive is too high, HF is easily generated, which will affect the positive electrode material.

[0052] In a specific embodiment, the conductivity σ of the non-aqueous electrolyte at 25°C is 6 mS / cm, 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, or any combination of these values.

[0053] In a preferred embodiment, 7 ≤ σ ≤ 11.

[0054] The conductivity of the non-aqueous electrolyte at 25°C was measured using a conductivity meter.

[0055] The conductivity of the non-aqueous electrolyte is mainly affected by the combined effects of ion concentration, solvent polarity, and electrolyte viscosity. The conductivity of the electrolyte can be controlled by adjusting the ratio of lithium salt to solvent in the electrolyte.

[0056] The first additive generates free radicals to promote the ring-opening polymerization of fluoroethylene carbonate. This reaction needs to be carried out under certain conductivity conditions, and the conductivity needs to be controlled within the above range. If the conductivity σ of the non-aqueous electrolyte is too low, the active lithium cannot be replenished in time at the negative electrode interface during charging and discharging, thus preventing the long-chain polymerization of fluoroethylene carbonate and affecting the compactness of the SEI film. If the conductivity σ of the non-aqueous electrolyte is too high, the ion content may be too high, causing accelerated corrosion of the interface or material.

[0057] In the description of this application, the term "C2-C12 alkoxyacyl" should be interpreted broadly, specifically, it can be understood as one or more carbon atoms in a C2-C12 alkyl group being... The substituted group is obtained, and the position of the substituted carbon atom is not particularly limited. In a preferred embodiment, the C2-C12 alkoxyacyl group is selected from... Among them, R 16 Selected from single-bonded or C1-C11 alkyl groups, R 17 Alkyl groups selected from C1-C11.

[0058] In the description of this application, the term "C2-C12 ether group" should be interpreted broadly. Specifically, it can be understood as a group formed by connecting -O- between two adjacent carbon atoms in a C2-C12 alkyl group, where the number of oxygen atoms can be single or multiple.

[0059] In some embodiments, in the compound represented by structural formula 1, R1 is selected from hydrogen, and R2 is selected from… Substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, wherein R 10 Selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl, and substituted or unsubstituted C6-C20 aryl.

[0060] At this point, the compound represented by structural formula 1 is a hydroperoxide or an organic peroxy acid. When the compound represented by structural formula 1 is a hydroperoxide or an organic peroxy acid, its high oxygen content can remove reducing impurities in the electrolyte in advance, reduce the amount of gas generated during formation, improve the initial coulombic efficiency, and increase the initial discharge capacity of the secondary battery.

[0061] As an example, the compound represented by structural formula 1 may be selected from the following compounds:

[0062] In some embodiments, in the compound represented by structural formula 1, R1 and R2 are each independently selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, and substituted or unsubstituted C6-C20 aryl.

[0063] At this point, the compound represented by structural formula 1 is a dialkyl peroxide. When the compound represented by structural formula 1 is a dialkyl peroxide, it is beneficial to suppress solvent molecule co-intercalation and improve the interfacial compatibility between the electrolyte and the negative electrode.

[0064] As an example, the compound represented by structural formula 1 may be selected from the following compounds:

[0065] In some embodiments, in the compound represented by structural formula 1, R1 is selected from... R2 is selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, or... Among them, R 11 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, substituted or unsubstituted C2-C11 alkynyl groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 etheryl groups.

[0066] In some embodiments, in the compound represented by structural formula 1, R1 is selected from... R2 is selected from Among them, R 11 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, substituted or unsubstituted C2-C11 alkynyl groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 etheryl groups.

[0067] At this point, the compound represented by structural formula 1 is a diacyl peroxide. When the compound represented by structural formula 1 is a diacyl peroxide, in addition to improving battery cycle life, it can also decompose to form inert carbon dioxide during battery thermal runaway to dilute the explosion limits of flammable gases, which is beneficial to improving battery safety performance.

[0068] As an example, the compound represented by structural formula 1 may be selected from the following compounds:

[0069] In some embodiments, in the compound represented by structural formula 1, R1 is selected from... R2 is selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, and substituted or unsubstituted C6-C20 aryl, wherein R 11 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, substituted or unsubstituted C2-C11 alkynyl groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 etheryl groups.

[0070] At this point, the compound represented by structural formula 1 is a peroxy ester. When the compound represented by structural formula 1 is a peroxy ester, it can improve the wettability of the electrolyte to the electrode, reduce the ohmic internal resistance of the battery, and improve the discharge performance of the battery.

[0071] As an example, the compound represented by structural formula 1 may be selected from the following compounds:

[0072] In some embodiments, in the compound represented by structural formula 1, R1 is selected from... Among them, R 12 R2 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, and substituted or unsubstituted C2-C11 alkynyl; R2 is selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, and substituted or unsubstituted C6-C20 aryl or... Among them, R 13 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, and substituted or unsubstituted C2-C11 alkynyl groups.

[0073] At this point, the compound represented by structural formula 1 is a peroxycarbonate or a peroxydicarbonate. When the compound represented by structural formula 1 is a peroxycarbonate or a peroxydicarbonate, it promotes lithium-ion solvation and improves lithium diffusion performance inside the battery.

[0074] As an example, the compound represented by structural formula 1 may be selected from the following compounds:

[0075] In some embodiments, the compound represented by structural formula 1 includes one or more of the following compounds:

[0076] It should be noted that the compound shown in Structural Formula 2 has a symmetrical structure, that is, the compound shown in Structural Formula 2 is based on left-right symmetry of -N=N-. Under the constraints of this application, this symmetrical structure is beneficial to the function of the compound shown in Structural Formula 2. At the same time, the C connected to N needs to be sp3 hybridized to ensure the stability of the -N=N- structure.

[0077] In some embodiments, in the compound shown in Formula 2, when R4 and R5 are substituted, the substituents are carboxyl, hydroxyl, halogen, or cyano; when R6 is substituted, the substituents are hydroxyl, halogen, or alkoxy.

[0078] In some embodiments, in the compound represented by structural formula 2, R6 is selected from cyano.

[0079] In some embodiments, in the compound shown in Formula 2, R4 and R5 are each independently selected from substituted or unsubstituted C1-C6 alkyl groups.

[0080] The C1-C6 alkyl groups include methyl, ethyl, n-propyl, isopropyl, isobutyl, tert-butyl, tert-amyl, etc.

[0081] In some embodiments, the compound represented by structural formula 2 includes one or more of the following compounds:

[0082] In some embodiments, the additive further includes a third additive, which includes vinylene carbonate (VC), and the mass ratio of the third additive to the first additive is (2-50):1.

[0083] The inventors discovered that simultaneously adding a third additive and a first additive to the non-aqueous electrolyte of this application can further improve the battery's room temperature and high temperature cycling performance. In particular, the improvement in battery performance is especially significant when the mass ratio of the third additive to the first additive is (2-50):1. It is speculated that in this system, the third additive has a higher reduction potential than the first additive due to its higher reactivity. When the mass ratio of the third additive to the first additive is (2-50):1, the third additive reacts first on the negative electrode surface, undergoing polymerization and initially forming a preliminary protective film. Subsequently, the second additive and the first additive undergo bond-breaking and ring-opening polymerization on the negative electrode surface. The SEI film formed through this process is dense and uniform, exhibiting stable cycling performance and extending cycle life.

[0084] In some embodiments, the additive further includes one or more of the following: ethylene carbonate, biphenyl, fluorobenzene, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, succinate, adiponitrile, triglyceride, 1,3,6-hexanetrionitrile, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0085] It should be noted that, unless otherwise specified, the content of any optional substance in the additive in the non-aqueous electrolyte is generally less than 10%, preferably 0.01-5%, and more preferably 0.1% to 2%. Specifically, the content of any optional substance in the additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%, or any combination of these values.

[0086] In some embodiments, the non-aqueous organic solvent has a mass content of 65% to 90% based on the total mass of the non-aqueous electrolyte being 100%.

[0087] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, 90%, or any combination of these values.

[0088] In some embodiments, the non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0089] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may specifically include, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may specifically include, but are not limited to, dimethoxymethane, diethoxymethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone or in any combination and ratio of two or more. There are no particular restrictions on the content of ether compounds, and it is arbitrary as long as it does not significantly impair the performance of the high-pressure lithium-ion battery of this application. In the case of a non-aqueous solvent volume ratio of 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less.

[0090] In some embodiments, the nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

[0091] In some embodiments, the carbonate solvent includes cyclic carbonates or chain carbonates. Cyclic carbonates may specifically include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); chain carbonates may specifically include, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of cyclic carbonates is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery described in this application. However, when using only one type, its content is typically 3% or more, preferably 5% or more, by volume relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, making it easier to achieve good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. Furthermore, the upper limit is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby contributing to enhanced stability during high-temperature storage. The content of the chain carbonate is not particularly limited, but relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% or more by volume, preferably 20% or more, and more preferably 25% or more. Furthermore, it is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By keeping the chain carbonate content within the above range, it is easier to achieve an appropriate viscosity for the non-aqueous electrolyte, suppressing the decrease in ionic conductivity, and thus contributing to achieving a favorable range of output characteristics for the non-aqueous electrolyte battery. When using two or more chain carbonates in combination, it is sufficient to ensure that the total amount of chain carbonate meets the above range.

[0092] In some embodiments, fluorine-containing chain carbonates (hereinafter referred to as "fluorinated chain carbonates") are also preferably used. There is no particular limitation on the number of fluorine atoms in a fluorinated chain carbonate as long as it is 1 or more, but it is generally 6 or less, preferably 4 or less. When a fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon atom or to different carbon atoms. Examples of fluorinated chain carbonates include dimethyl fluorinated carbonate derivatives, methyl ethyl fluorinated carbonate derivatives, and diethyl fluorinated carbonate derivatives.

[0093] Carboxylic acid ester solvents include cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), butyl acetate, propyl propionate (PP), and butyl propionate.

[0094] In some embodiments, the sulfone solvent includes cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, it is typically a compound with 3 to 6 carbon atoms, more preferably 3 to 5 carbon atoms; in the case of chain sulfones, it is typically a compound with 2 to 6 carbon atoms, more preferably 2 to 5 carbon atoms. The content of the sulfone solvent is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of this application. Relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume. Furthermore, it is typically 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume. When using two or more sulfone solvents in combination, the total amount of sulfone solvent should satisfy the above range. When the content of the sulfone solvent is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability is preferred.

[0095] In some embodiments, the electrolyte salt is selected from lithium salts, including LiPF6, LiODFP, LiODFB, LiBOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium trioxazophosphate, lithium lower aliphatic carboxylic acid having four or fewer carbon atoms, or lithium tetraphenylborate.

[0096] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, or any combination of these values.

[0097] It should be emphasized that the non-aqueous electrolyte provided in this application is not a precursor to a gel electrolyte or solid electrolyte, nor is it suitable as a precursor to a gel electrolyte or solid electrolyte. The reason is that the improvement of the electrochemical performance of the secondary battery in this application relies on the compound shown in Formula 1 participating in the formation of the solid electrolyte interphase (SEI) film on the negative electrode surface during the battery charge-discharge formation stage, and the compound shown in Formula 1 remaining in the electrolyte continuously repairing the damaged solid electrolyte interphase (SEI) film during long-term battery cycling. However, as a precursor to a gel electrolyte or solid electrolyte, there is a polymerization operation to form a gel electrolyte before the battery charge-discharge formation. In this polymerization operation, the organic peroxide shown in Formula 1 acts as an initiator and reacts with the polymerizable monomer, resulting in the consumption of the compound shown in Formula 1, thus preventing it from playing its corresponding role in the charge-discharge formation and battery charge-discharge cycling process.

[0098] In some embodiments, the non-aqueous electrolyte does not include polymerizable monomers and / or prepolymers obtained by polymerizing polymerizable monomers.

[0099] In some embodiments, the polymerizable monomers include one or more of the following: acrylate monomers (such as methyl acrylate, ethyl acrylate, butyl acrylate), acrylamide monomers (such as acrylamide, N,N'-methylenebisacrylamide), vinyl compound monomers (such as polyvinyl alcohol, vinylpyrrolidone, vinylimidazole), epoxy resin monomers (such as bisphenol A epoxy resin), polyethylene oxide monomers, polyacrylonitrile monomers, and siloxane monomers.

[0100] In some embodiments, the non-aqueous electrolyte does not undergo polymerization under light or heating conditions.

[0101] In some embodiments, the non-aqueous electrolyte is in a liquid state after formation.

[0102] Another embodiment of this application provides a secondary battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte as described above.

[0103] In some embodiments, the secondary battery is a lithium-ion battery.

[0104] In some embodiments, the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes one or more of the following: lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide (e.g., lithium nickel oxide), lithium manganese oxide (e.g., spinel-type lithium manganese oxide, layered lithium manganese oxide, etc.), lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and doped / coated modified compounds thereof. Preferably, the positive electrode active material includes LiFe... 1-x’ M' x’PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2, wherein M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

[0105] In a preferred embodiment, the positive electrode active material is selected from LiFe. 1-x’ M' x’ PO4, wherein M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V, or Ti, and 0 ≤ x' < 1. The lithium-ion battery described has a high specific capacity, thereby effectively improving the battery's energy density. Furthermore, the battery's charging cut-off voltage can reach 3.8V, exhibiting a high discharge plateau and good cycle stability within a conventional voltage window. Moreover, since iron is relatively abundant and inexpensive globally, compared to rare and expensive metals such as cobalt, nickel, and manganese, using the aforementioned positive electrode active material helps reduce costs and alleviate dependence on limited resources.

[0106] In a more preferred embodiment, the positive electrode active material is selected from LiFe. 1-x’ Mn x’ PO4, where 0 ≤ x' ≤ 0.5.

[0107] In some specific embodiments, the positive electrode active material may include LiCoO2, LiFePO4, LiFe 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 One or more of O2.

[0108] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0109] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0110] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0111] In some embodiments, the positive current collector comprises a metallic material capable of conducting electrons. Preferably, the positive current collector comprises at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0112] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, and lithium negative electrode. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based negative electrode may include tin, tin-carbon, tin oxide, and tin metal compounds; the lithium negative electrode may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy.

[0113] In a more preferred embodiment, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, graphene, and silicon-carbon composite materials.

[0114] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0115] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector includes a metallic material capable of conducting electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0116] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0117] The negative electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0118] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0119] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0120] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0121] The present application will be further illustrated by the following examples.

[0122] Table 1

[0123] In Table 1, FEC stands for fluoroethylene carbonate and VC stands for vinylene carbonate.

[0124] Example 1

[0125] This embodiment illustrates the lithium-ion battery and its preparation method disclosed in this application, and includes the following steps:

[0126] (1) Preparation of the positive electrode sheet: The positive electrode active material LiFePO4, conductive agent carbon black (SP), conductive agent carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96:1.5:0.5:2, and then dispersed in N-methylpyrrolidone (NMP) to obtain the positive electrode slurry. The slurry was uniformly coated on both sides of aluminum foil, and after drying, rolling and vacuum drying, the positive electrode sheet was cut with a mold to obtain the positive electrode sheet with a thickness of 120-150 μm.

[0127] (2) Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent carbon black (SP), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 95:1:1.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry is coated on both sides of a copper foil, dried, rolled, and vacuum dried, and then cut into negative electrode sheets with a thickness of 120-150 μm using a mold.

[0128] (3) Preparation of non-aqueous electrolyte: In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), fully dried lithium hexafluorophosphate was rapidly added to a mixed solvent (EC:EMC = 3:7). The mass fraction of lithium hexafluorophosphate in the electrolyte was 11.8wt%. The composition of additives and solvents in the non-aqueous electrolyte is shown in Table 1. The conductivity of the non-aqueous electrolyte was measured and recorded in Table 1.

[0129] (4) Battery separator: 8-10 μm polyethylene separator is selected.

[0130] (5) Preparation of lithium-ion batteries: The positive electrode, negative electrode and separator prepared according to the above process are stacked to form lithium-ion batteries. The batteries are vacuum baked at 75°C for 10 hours and then injected with the electrolyte prepared above. After standing at 45°C for 48 hours, the batteries are placed in an environment of 45°C and subjected to a pressure of 3 kg. They are charged at 0.05C for 2 hours, at 0.1C for 1 hour, and at 0.2C for 1 hour. After that, the batteries are stood at 45°C for 2 days (to fully activate the batteries) to obtain the batteries.

[0131] Examples 2-36

[0132] Examples 2-36 illustrate the lithium-ion battery and its preparation method disclosed in this application, including most of the operational steps in Example 1, with the following differences:

[0133] In the preparation steps of the non-aqueous electrolyte:

[0134] The composition of additives and solvents in the non-aqueous electrolyte is shown in Table 1. The conductivity of the non-aqueous electrolyte at 25°C was tested and recorded in Table 1.

[0135] Comparative Examples 1-19

[0136] Comparative Examples 1-19 are used to illustrate the lithium-ion battery and its preparation method disclosed in this application, including most of the operation steps in Example 1, the difference being:

[0137] In the preparation steps of the non-aqueous electrolyte:

[0138] The composition of additives and solvents in the non-aqueous electrolyte is shown in Table 1. The conductivity of the non-aqueous electrolyte at 25°C was tested and recorded in Table 1.

[0139] Performance testing

[0140] The lithium-ion batteries prepared above were subjected to the following performance tests:

[0141] 1. Room temperature cycling performance

[0142] At 25℃, test the impedance of the battery before 1C cycle. Use 1C to charge and discharge the battery. The cycle capacity retention rate (%) = (nth discharge capacity / first discharge capacity) × 100% until the capacity retention rate reaches 70%. Record the number of cycles n. The number of cycles n is the cycle life. Test the battery impedance after n cycles.

[0143] Battery impedance test method: At 25℃, using a battery with a SOC of 50%, the test was conducted using an electrochemical workstation instrument. The frequency range was set to 1MHz-1mHz, and the constant voltage perturbation amplitude was 5mV. The experimental data were recorded. The first data point with an imaginary part of 0 corresponds to the real part R1, and the second data point with a slope of 0 corresponds to the real part R2. Battery impedance = R2-R1.

[0144] Battery impedance growth rate at room temperature (%) = (battery impedance after cycling - battery impedance before cycling) / battery impedance before cycling × 100%.

[0145] 2. High-temperature cycling performance

[0146] At 45℃, the battery is charged and discharged at 1C. The cycle capacity retention rate (%) = (the capacity of the nth discharge / the capacity of the first discharge) × 100% until the capacity retention rate reaches 70%. The number of cycles n is recorded, and this number of cycles n is the cycle life.

[0147] (1) The test results obtained from Examples 1-14 and Comparative Examples 1-19 are filled in Table 2.

[0148] Table 2

[0149] The test results from Examples 1-18 and Comparative Examples 1-19 show that in a non-aqueous electrolyte using compounds of structural formula 1 and / or structural formula 2 as the first additive and fluoroethylene carbonate as the second additive, the conditions are met by controlling the mass percentage a of the first additive, the mass percentage b of the second additive, and the conductivity σ of the non-aqueous electrolyte at 25°C. Furthermore, when 0.001≤a≤1, 0.1≤b≤7, and 6≤σ≤13, the resulting lithium-ion battery exhibits longer cycle life at both room temperature and high temperature, and lower impedance growth. This is presumably due to the homolytic cracking of the first additive during formation and cycling, generating highly reactive free radicals. These free radicals promote the ring-opening polymerization of fluoroethylene carbonate on the negative electrode surface, reducing the defluorination reaction of fluoroethylene carbonate. This results in the formation of a fluorine-rich SEI film on the negative electrode surface during SEI film recombination, thereby improving the stability of the SEI film and extending the battery's cycle life. It is important to note that the ring-opening polymerization of fluoroethylene carbonate requires the participation of active lithium to generate SEI film components such as LiF. This reaction is closely related to the conductivity of the non-aqueous electrolyte; the conductivity affects the replenishment of active lithium at the negative electrode interface during formation, thus influencing the long-chain polymerization process of fluoroethylene carbonate. Therefore, when the mass percentage of the first additive a, the mass percentage of the second additive b, and the conductivity σ of the non-aqueous electrolyte are in a synergistic state, it can promote the formation of a more stable SEI film on the negative electrode surface, while inhibiting the damage to the positive electrode material and the positive electrode electrolyte interface caused by the defluorination reaction of fluoroethylene carbonate.

[0150] The test results from Examples 1-18 show that when the mass percentage of the first additive a, the mass percentage of the second additive b, and the conductivity σ of the non-aqueous electrolyte further meet the conditions... Furthermore, when 0.05≤a≤0.5, 0.5≤b≤3, and 7≤σ≤11, it is beneficial to further improve the stability of the SEI film on the negative electrode surface, reduce the decomposition of non-aqueous electrolyte during cycling, and extend the cycle life of lithium-ion batteries.

[0151] The test results of Comparative Examples 1 to 19 show that even if the mass percentage of the first additive (a), the mass percentage of the second additive (b), and the conductivity σ of the non-aqueous electrolyte meet the conditions... Even when the a, b, or σ values ​​do not meet the specified ranges, lithium-ion batteries still do not exhibit good high-temperature storage performance and cycle performance. This indicates a strong correlation between the a, b, and σ values ​​and their impact on improving the cycle performance of lithium-ion batteries. Similarly, even when the a, b, or σ values ​​meet the specified ranges, lithium-ion batteries still do not exhibit good high-temperature storage performance and cycle performance. The value does not meet the above preset conditions. At that time, the improvement in battery performance was not significant.

[0152] (2) The test results obtained in Examples 1, 19 to 29 are filled in Table 3.

[0153] Table 3

[0154] As can be seen from the test results of Examples 1 and 19-29, in the electrolyte system provided in this application, the relationship 0.1≤ Given that 0.001≤a≤1, 0.1≤b≤7, and 6≤σ≤13, different first additives can improve both the room temperature cycle life and the high temperature cycle life of lithium-ion batteries. This indicates that the electrolyte system provided in this application is suitable for different first additives, and the compounds shown in structural formula 1 and structural formula 2 play similar roles in the electrolyte system of this application.

[0155] (3) The test results obtained in Examples 1, 30 to 36 are filled in Table 4.

[0156] Table 4

[0157] The test results of Examples 1 and 30-36 show that adding vinylene carbonate as a third additive to a non-aqueous electrolyte containing the first and second additives can further improve the cycle life of the battery and reduce the battery impedance. In particular, the improvement in battery performance is especially significant when the mass ratio of the third additive to the first additive is (2-50):1. It is speculated that under this condition, during the battery formation stage, the third additive preferentially forms a protective film on the surface of the negative electrode. Subsequently, the second additive and the first additive undergo bond-breaking and ring-opening polymerization on the surface of the negative electrode. The SEI film formed through this process is dense and uniform, and has stable cycling performance, which is beneficial to extending the cycle life of the battery.

[0158] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes non-aqueous organic solvents, electrolyte salts, and additives, wherein the additives include a first additive and a second additive, the first additive including compounds shown in structural formula 1 and / or compounds shown in structural formula 2, and the second additive including fluoroethylene carbonate. Wherein, n is 0 or 1; R1 and R2 are each independently selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C1-C12 acyl, substituted or unsubstituted C2-C12 alkoxyacyl, and substituted or unsubstituted C2-C12 ether. Both are hydrogen, and R1 and R2 can be linked together to form a ring or not; R3 is selected from substituted or unsubstituted C1-C12 alkylene groups, substituted or unsubstituted C2-C12 alkenyl groups, substituted or unsubstituted C2-C12 alkyne groups, substituted or unsubstituted C6-C20 aryl groups, and substituted or unsubstituted C2-C12 ether groups; when R1, R2, and R3 are substituted, the substituents are alkoxy, hydroxyl, acyl, ester, cyano, or halogen. R4 and R5 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl or substituted or unsubstituted C1-C6 alkyl hydroxyl groups. R4 and R5 may be linked together to form a ring or not. R6 is selected from hydrogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl or substituted or unsubstituted C2-C6 alkynyl, C1-C6 cyano, C2-C6 ester, substituted or unsubstituted C2-C6 amide or substituted or unsubstituted C1-C6 amidine. The non-aqueous electrolyte meets the following conditions: And 0.001≤a≤1, 0.1≤b≤7, 6≤σ≤13; Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %; b represents the mass percentage of the second additive in the non-aqueous electrolyte, in %; σ is the conductivity of the non-aqueous electrolyte at 25°C, in mS / cm.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte meets the following conditions:

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The non-aqueous electrolyte satisfies at least one of the following conditions: (1)0.05≤a≤0.5； (2)0.5≤b≤3； (3)7≤σ≤11.

4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that, The compound represented by structural formula 1 satisfies at least one of the following conditions: (1) R1 is selected from hydrogen, and R2 is selected from… Substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, wherein R 10 Selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl, and substituted or unsubstituted C6-C20 aryl. (2) R1 and R2 are each independently selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, or substituted or unsubstituted C6-C20 aryl. (3) R1 is selected from R2 is selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C20 aryl, or... Among them, R 11 Selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl, substituted or unsubstituted C6-C20 aryl, and substituted or unsubstituted C2-C12 ether. (4) R1 is selected from Among them, R 12 R2 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, and substituted or unsubstituted C2-C11 alkynyl; R2 is selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, and substituted or unsubstituted C6-C20 aryl or... Among them, R 13 Selected from substituted or unsubstituted C1-C11 alkyl groups, substituted or unsubstituted C2-C11 alkenyl groups, and substituted or unsubstituted C2-C11 alkynyl groups.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that, The compound represented by structural formula 1 includes one or more of the following compounds:

6. The non-aqueous electrolyte according to any one of claims 1 to 5, characterized in that, The compound represented by structural formula 2 satisfies at least one of the following conditions: (1) When R4 and R5 are substituted, the substituents are carboxyl, hydroxyl, halogen or cyano; when R6 is substituted, the substituents are hydroxyl, halogen or alkoxy. (2) R6 is selected from cyano groups; (3) R4 and R5 are each independently selected from substituted or unsubstituted C1-C6 alkyl groups.

7. The non-aqueous electrolyte according to any one of claims 1 to 6, characterized in that, The compound represented by structural formula 2 includes one or more of the following compounds:

8. The non-aqueous electrolyte according to any one of claims 1 to 7, characterized in that, The additive also includes a third additive, which includes vinylene carbonate (VC), and the mass ratio of the third additive to the first additive is (2-50):

1.

9. The non-aqueous electrolyte according to any one of claims 1 to 8, characterized in that, The non-aqueous electrolyte does not contain polymerizable monomers and / or prepolymers obtained by polymerizing polymerizable monomers.

10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a non-aqueous electrolyte as described in any one of claims 1 to 9.

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