A non-aqueous electrolyte and a secondary battery

Abstract

To overcome the problems of insufficient cycle performance and low-temperature discharge capacity existing in existing lithium iron phosphate batteries, the present invention provides a non-aqueous electrolyte and a battery. The non-aqueous electrolyte includes a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive includes a compound represented by Structural Formula 1 and a compound represented by Structural Formula 2:,. The non-aqueous electrolyte is detected by a liquid chromatography-mass spectrometry (LC-MS) instrument and has a characteristic peak at a retention time of 1.55 ± 0.1 min. The non-aqueous electrolyte provided by the present invention can delay the increase in internal resistance during the long cycle of the battery and improve the capacity release of the battery in a low-temperature environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage electronic components, and particularly relates to a non-aqueous electrolyte and a secondary battery. Background Art

[0002] In recent years, with the gradual maturity of the application technology of secondary batteries, the market demands for electric vehicles and large-scale energy storage have boomed. The lithium iron phosphate cathode material belongs to the olivine-type stable structure, and has the advantages of stable performance, environmental friendliness, low cost, safety and reliability, etc., and is widely used in energy storage lithium-ion batteries. Therefore, how to maintain the energy density of lithium iron phosphate batteries while improving the cycle life has always been a key technical topic for researchers.

[0003] In terms of technical principle, the core of the long-cycle technology of lithium-ion batteries lies in adjusting and optimizing the electrochemical stability of the solid electrolyte interface film (SEI) through electrolyte design. The SEI formed by conventional chemical systems has defects, and continuously dissolves and reorganizes during charge and discharge, which not only makes the interface film thicker and the impedance increase, but also consumes active substances and causes capacity attenuation. In addition, the poor low-temperature discharge ability of lithium iron phosphate batteries applied to electric vehicles has always been criticized by consumers. Summary of the Invention

[0004] Aiming at the problems of insufficient cycle performance and low-temperature discharge ability of existing lithium iron phosphate batteries, the present invention provides a non-aqueous electrolyte and a secondary battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] On the one hand, the present invention provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt and an additive, and the additive comprises a compound shown in Structural Formula 1 and a compound shown in Structural Formula 2:

[0007] ;

[0008] Structural Formula 1

[0009] Among them, 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 alkoxycarbonyl, substituted or unsubstituted C2-C12 ether group. R1 and R2 can be connected to each other to form a ring or not, and R1 and R2 are not both hydrogen at the same time; R3 is selected from substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted C2-C12 alkenylene, substituted or unsubstituted C2-C12 alkynylene, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C2-C12 ether group; when R1, R2, and R3 are substituted, the substituents are alkoxy, hydroxyl, acyl, ester, cyano or halogen;

[0010] ;

[0011] Among them, R4 is selected from substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene. When R4 is substituted, the substituents are C1-C5 alkyl, C1-C5 haloalkyl, C2-C5 alkenyl, C2-C5 haloalkenyl or halogen;

[0012] The non-aqueous electrolyte is detected by a liquid chromatography-mass spectrometry (LC-MS) instrument and has a characteristic peak at a retention time of 1.55 ± 0.1 min.

[0013] Optionally, in the compound represented by the 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, where R 10 is 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.

[0014] Optionally, in the compound represented by the 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, substituted or unsubstituted C6-C20 aryl.

[0015] Optionally, in the compound represented by the structural formula 1, 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 , wherein, R 11 is 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, substituted or unsubstituted C2-C12 ether group.

[0016] Optionally, in the compound shown in Formula 1, R1 is selected from , wherein, R 12 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, 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, substituted or unsubstituted C6-C20 aryl or , wherein, R 13 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl.

[0017] Optionally, the compound shown in Formula 1 includes one or more of the following compounds:

[0018] ; and / or,

[0019] The compound shown in Formula 2 includes one or more of the following compounds:

[0020] .

[0021] Optionally, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the compound shown in Formula 1 is 0.001% - 0.5%; and / or

[0022] Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the compound represented by the structural formula 2 is 0.01% to 2%; and / or

[0023] The mass ratio of the compound represented by the structural formula 2 to the compound represented by the structural formula 1 is 1 to 15.

[0024] Optionally, the additive further includes at least one of a sultone compound, a cyclic carbonate compound, a phosphate compound, a nitrile compound, a lithium salt type additive, or an alkane compound; and / or

[0025] The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, or methylene methanedisulfonate; and / or

[0026] The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene vinylene carbonate, methylene vinylene carbonate, or the compound represented by the structural formula 3:

[0027] ;

[0028] In the structural formula 3, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group; and / or

[0029] The phosphate compound includes the compound represented by the structural formula 4:

[0030] ;

[0031] In the structural formula 4, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a C1-C5 halogenated hydrocarbon group, a C6-C12 aryl group, a C6-C12 halogenated aryl group, -Si(C m H 2m+1 )3, and m is a natural number from 1 to 3; and / or

[0032] The nitrile compound includes at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, or sebaconitrile; and / or

[0033] The lithium salt type additives include at least one of lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium monofluoromethanesulfonate, lithium trioxalatophosphate, lithium difluorodioxalatophosphate, lithium tetrafluorooxalatophosphate, lithium dicyanamide or lithium lower aliphatic carboxylate having less than 4 carbon atoms; and / or

[0034] The alkane compounds include at least one of cyclopentane, cyclohexane, cycloheptane, methylcyclopentane, ethylcyclopentane, 1,3-dimethylcyclopentane, 1,4-dimethylcyclopentane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, butylcyclohexane, pentylcyclohexane, cis-1-methyl-3-ethylcyclohexane, trans-1-methyl-3-ethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, 1,3,5-trimethylcyclohexane and perfluoro(ethylcyclohexane).

[0035] Optionally, the non-aqueous electrolyte does not include polymerizable monomers and / or prepolymers obtained by polymerization of polymerizable monomers.

[0036] On the other hand, the present invention provides a secondary battery, including a positive electrode, a negative electrode and the non-aqueous electrolyte as described above;

[0037] The positive electrode includes a positive electrode material layer, and the mass fraction of iron element in the positive electrode material layer is greater than or equal to 17.7%.

[0038] According to the non-aqueous electrolyte provided by the present invention, the compound shown in Structural Formula 1 and the compound shown in Structural Formula 2 are added as additives. Among them, the compound shown in Structural Formula 2 has a cyclic sulfate structure, and its decomposition product on the surface of the negative electrode will form a solid electrolyte interface film (SEI) containing Li2SO4 and ROSO3Li on the surface of the negative electrode. This SEI film can block the direct contact between the non-aqueous electrolyte and the negative electrode, avoid the continuous decomposition of the non-aqueous electrolyte at the negative electrode interface, is beneficial to reducing the battery impedance and improving the battery cycle life. However, the increase in the content of ROSO3Li will affect the stability of the SEI film, resulting in an increase in impedance during the battery cycle. In this regard, through a large number of studies, the inventors found that adding the compound shown in Structural Formula 1 to the non-aqueous electrolyte containing the compound shown in Structural Formula 2 will induce the compound shown in Structural Formula 2 to open the ring in advance during the battery formation stage to form a specific species (related to the characteristic peak with a retention time of 1.55 min ± 0.1 min in the LC-MS specific conditions detection). This specific species forms a film prior to other additives, forming an SEI film with a relatively high content of Li2SO4 and a relatively low content of ROSO3Li, thereby delaying the increase in internal resistance during the long cycle of the battery and improving the capacity release of the battery in a low-temperature environment. Description of the Drawings

[0039] Figure 1 It is the detection result in the liquid chromatography-mass spectrometer (LC-MS) of the non-aqueous electrolyte provided in Embodiment 1 of the present invention;

[0040] Figure 2 It is the detection result in the liquid chromatography-mass spectrometer (LC-MS) of the non-aqueous electrolyte provided in Comparative Example 15 of the present invention. Detailed Embodiments

[0041] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clear, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] An embodiment of the present invention provides a non-aqueous electrolyte, including a non-aqueous organic solvent, an electrolyte salt and an additive, and the additive includes a compound represented by Structural Formula 1 and a compound represented by Structural Formula 2:

[0043] ;

[0044] 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 alkoxycarbonyl, substituted or unsubstituted C2-C12 ether group, R1 and R2 may be connected to form a ring or not, and R1 and R2 are not both hydrogen at the same time; R3 is selected from substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted C2-C12 alkenylene, substituted or unsubstituted C2-C12 alkynylene, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C2-C12 ether group; when R1, R2, and R3 are substituted, the substituents are alkoxy, hydroxyl, acyl, ester, cyano or halogen;

[0045] ;

[0046] wherein, R4 is selected from substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene, and when R4 is substituted, the substituents are C1-C5 alkyl, C1-C5 haloalkyl, C2-C5 alkenyl, C2-C5 haloalkenyl or halogen;

[0047] The non-aqueous electrolyte is detected by a liquid chromatography-mass spectrometer (LC-MS) and has a characteristic peak at a retention time of 1.55 ± 0.1 min.

[0048] The non-aqueous electrolyte is added with the compound shown in Structural Formula 1 and the compound shown in Structural Formula 2 as additives. Among them, the compound shown in Structural Formula 2 has a cyclic sulfate structure, and its decomposition product on the negative electrode surface will form a solid electrolyte interface film (SEI) containing Li2SO4 and ROSO3Li on the negative electrode surface. This SEI film can block the direct contact between the non-aqueous electrolyte and the negative electrode, avoid the continuous decomposition of the non-aqueous electrolyte at the negative electrode interface, is beneficial to reducing the battery impedance and improving the battery cycle life. However, the increase in the content of ROSO3Li will affect the stability of the SEI film, resulting in an increase in impedance during the battery cycle. In this regard, through a large number of studies, the inventors found that further adding the compound shown in Structural Formula 1 to the non-aqueous electrolyte containing the compound shown in Structural Formula 2 will induce the compound shown in Structural Formula 2 to open the ring in advance during the battery formation stage to form a specific species (related to the characteristic peak with a retention time of 1.55 min ± 0.1 min in the LC-MS specific condition detection). This specific species forms a film prior to other additives, forming an SEI film with a relatively high content of Li2SO4 and a relatively low content of ROSO3Li, thereby delaying the increase in internal resistance during the long cycle of the battery and improving the capacity release of the battery in a low-temperature environment.

[0049] In some embodiments, the model of the LC-MS is Waters ACQUITY UPLC / Xevo G2-XS QtofMS, and the chromatographic conditions are as follows: Waters T3 chromatographic column is used, the column temperature is 35 - 40 °C, the mobile phase is a mixed solution of 40% water and 60% acetonitrile, and the flow rate of the mobile phase is 0.2 - 0.3 mL / min.

[0050] In the description of the present invention, the term "C1-C12 alkyl" includes straight-chain alkyl, branched-chain alkyl, and cycloalkyl. Similarly, the term "C2-C12 alkenyl" includes straight-chain alkenyl, branched-chain alkenyl, and cycloalkenyl, the term "C2-C12 alkynyl" includes straight-chain alkynyl, branched-chain alkynyl, and cycloalkynyl, the term "C1-C12 alkylene" includes straight-chain alkylene, branched-chain alkylene, and cycloalkylene, the term "C2-C12 alkenylene" includes straight-chain alkenylene, branched-chain alkenylene, and cycloalkenylene, and the term "C2-C12 alkynylene" includes straight-chain alkynylene, branched-chain alkynylene, and cycloalkynylene.

[0051] In the description of the present invention, the term "C1-C12 acyl group" should be understood in a broad sense. Specifically, it can be understood as a group obtained by substituting one or more carbon atoms in the C1-C12 alkyl with a carbonyl group, and the position of the substituted carbon atom is not particularly limited. In a preferred embodiment, the C1-C12 acyl group is selected from , where R 14 and R 15Each independently selected from a single bond or an alkyl group having 1 to 11 carbon atoms.

[0052] In the description of the present invention, the term "alkoxycarbonyl group having 2 to 12 carbon atoms" should be understood in a broad sense. Specifically, it can be understood as a group obtained by substituting one or more carbon atoms in an alkyl group having 2 to 12 carbon atoms with an ester group and the position of the substituted carbon atom is not particularly limited. In a preferred embodiment, the alkoxycarbonyl group having 2 to 12 carbon atoms is selected from , where R 16 is selected from a single bond or an alkyl group having 1 to 11 carbon atoms, and R 17 is selected from an alkyl group having 1 to 11 carbon atoms.

[0053] In the description of the present invention, the term "ether group having 2 to 12 carbon atoms" should be understood in a broad sense. Specifically, it can be understood as a group formed by connecting two adjacent carbon atoms in an alkyl group having 2 to 12 carbon atoms and the number of oxygen atoms can be single or multiple.

[0054] In some embodiments, in the compound represented by Structural Formula 1, R1 is selected from hydrogen, and R2 is selected from , a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 12 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, where R 10 is selected from a substituted or unsubstituted alkyl group having 1 to 11 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 11 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 11 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

[0055] At this time, the compound represented by Structural Formula 1 is a hydroperoxide or an organic peroxyacid. When the compound represented by Structural Formula 1 is a hydroperoxide or an organic peroxyacid, having a relatively high oxygen content can scavenge reducing impurities in the electrolyte in advance, reduce the gas generation during formation, improve the initial Coulombic efficiency, and increase the initial discharge capacity of the secondary battery.

[0056] As an example, the compound represented by Structural Formula 1 can be selected from the following compounds:

[0057] .

[0058] In some embodiments, in the compound represented by Structural Formula 1, R1 and R2 are each independently selected from a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 12 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

[0059] At this time, the compound shown in Structural Formula 1 is a dialkyl peroxide. When the compound shown in Structural Formula 1 is a dialkyl peroxide, it can inhibit the co-insertion of solvent molecules and improve the interfacial compatibility between the electrolyte and the negative electrode.

[0060] As an example, the compound shown in Structural Formula 1 may be selected from the following compounds:

[0061] 。

[0062] In some embodiments, in the compound shown in Structural Formula 1, R1 is selected from ; R2 is selected from hydrogen, a substituted or unsubstituted C1-C12 alkyl group, a substituted or unsubstituted C2-C12 alkenyl group, a substituted or unsubstituted C2-C12 alkynyl group, a substituted or unsubstituted C6-C20 aryl group, or , where R 11 is selected from a substituted or unsubstituted C1-C11 alkyl group, a substituted or unsubstituted C2-C11 alkenyl group, a substituted or unsubstituted C2-C11 alkynyl group, a substituted or unsubstituted C6-C20 aryl group, a substituted or unsubstituted C2-C12 ether group.

[0063] In some embodiments, in the compound shown in Structural Formula 1, R1 is selected from ; R2 is selected from , where R 11 is selected from a substituted or unsubstituted C1-C11 alkyl group, a substituted or unsubstituted C2-C11 alkenyl group, a substituted or unsubstituted C2-C11 alkynyl group, a substituted or unsubstituted C6-C20 aryl group, a substituted or unsubstituted C2-C12 ether group.

[0064] At this time, the compound shown in Structural Formula 1 is a diacyl peroxide. When the compound shown in Structural Formula 1 is a diacyl peroxide, in addition to having the characteristic of improving the battery cycle life, it can also decompose to form inert carbon dioxide during battery thermal runaway to dilute the explosion limit of combustible gases, which is beneficial to improving the battery safety performance.

[0065] As an example, the compound shown in Structural Formula 1 may be selected from the following compounds:

[0066] 。

[0067] In some embodiments, in the compound shown in Structural Formula 1, R1 is selected from ; R2 is selected from hydrogen, a substituted or unsubstituted C1-C12 alkyl group, a substituted or unsubstituted C2-C12 alkenyl group, a substituted or unsubstituted C2-C12 alkynyl group, a substituted or unsubstituted C6-C20 aryl group, where R 11Selected 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, substituted or unsubstituted C2-C12 ether group.

[0068] At this time, the compound shown in the structural formula 1 is a peroxyacid ester. When the compound shown in the structural formula 1 is a peroxyacid ester, the wettability of the electrolyte to the electrode can be improved, the ohmic internal resistance of the battery can be reduced, and the discharge performance of the battery can be improved.

[0069] As an example, the compound shown in the structural formula 1 may be selected from the following compounds:

[0070] .

[0071] In some embodiments, in the compound shown in the structural formula 1, R1 is selected from , where R 12 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, 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, substituted or unsubstituted C6-C20 aryl or , where R 13 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl.

[0072] At this time, the compound shown in the structural formula 1 is a peroxycarbonate or peroxy-bicarbonate. When the compound shown in the structural formula 1 is a peroxycarbonate or peroxy-bicarbonate, it has the effect of promoting the solvation of lithium ions and improving the lithium diffusion performance inside the battery.

[0073] As an example, the compound shown in the structural formula 1 may be selected from the following compounds:

[0074] .

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

[0076] .

[0077] In some embodiments, the compound shown in the structural formula 2 includes one or more of the following compounds:

[0078] 。

[0079] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the compound represented by Structural Formula 1 is 0.001% to 0.5%.

[0080] In specific embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the compound represented by Structural Formula 1 can be 0.001%, 0.002%, 0.005%, 0.008%, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.28%, 0.3%, 0.32%, 0.34%, 0.35%, 0.38%, 0.4%, 0.42%, 0.44%, 0.45%, 0.48%, 0.5% or the range composed of any two of these values.

[0081] In preferred embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the compound represented by Structural Formula 1 is 0.001% to 0.2%.

[0082] The compound represented by Structural Formula 1 is used to promote the ring-opening of the compound represented by Structural Formula 2 before battery formation, forming specific species to promote the increase in the content of Li2SO4 in the SEI film, thereby improving the stability of the SEI film. When the mass percentage of the compound represented by Structural Formula 1 is too low, it is difficult to substantially improve the film-forming quality of the SEI film; when the mass percentage of the compound represented by Structural Formula 1 is too high, the probability of side reactions in the electrolyte increases, which is not conducive to improving the cycling performance of the non-aqueous electrolyte.

[0083] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the compound represented by Structural Formula 2 is 0.01% to 2%.

[0084] In specific embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the compound represented by Structural Formula 2 can be 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.18%, 0.2% or the range composed of any two of these values.

[0085] In a preferred embodiment, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the compound shown in Structural Formula 2 is 0.01% to 1%.

[0086] The compound shown in Structural Formula 2 is used as the main film-forming additive for forming a film on the negative electrode surface, and its content affects the compactness of the SEI film on the negative electrode surface; if the content of the compound shown in Structural Formula 2 is too low, it is difficult to form an SEI film with high ionic conductivity at the negative electrode interface, which is not conducive to the release of low-temperature capacity; if the content of the compound shown in Structural Formula 2 is too high, it will lead to an excessive film-forming thickness on the negative electrode surface, increasing the impedance of the secondary battery.

[0087] In some embodiments, the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Structural Formula 1 is 1 to 15. Thereby, it helps to further improve the cycle life and low-temperature performance of the battery.

[0088] In a specific embodiment, the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Structural Formula 1 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range composed of any two of these values.

[0089] In a preferred embodiment, the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Structural Formula 1 is 1 to 10.

[0090] The inventors have found through a large amount of research that when the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Structural Formula 1 is within the range of 1 to 15, the compound shown in Structural Formula 2 and the compound shown in Structural Formula 1 have the best synergistic effect, which is beneficial to improving the cycle capacity retention rate and low-temperature discharge performance of the battery.

[0091] It should be emphasized that the non-aqueous electrolyte provided in this application is not a precursor of a gel electrolyte or a solid electrolyte, nor is it suitable as a precursor of a gel electrolyte or a solid electrolyte. The reason is that for the improvement of the electrochemical performance of the secondary battery in this application, it is necessary to rely on the compounds shown in Structural Formula 1 and the compounds shown in Structural Formula 2 to participate in the formation of the solid electrolyte interface film (SEI) on the negative electrode surface during the charge and discharge formation stage of the battery, and the compounds shown in Structural Formula 1 and the compounds shown in Structural Formula 2 remaining in the electrolyte continuously repair the damaged solid electrolyte interface film (SEI) during the long-term cycling process of the battery. However, as a precursor of a gel electrolyte or a solid electrolyte, there will be a polymerization operation before the charge and discharge formation of the battery to form a gel electrolyte. In this polymerization operation, the organic peroxide shown in Structural Formula 1 reacts with the polymerizable monomer as an initiator, resulting in the consumption of the compound shown in Structural Formula 1, so that it cannot play the corresponding role during the charge and discharge formation and the charge and discharge cycling process of the battery.

[0092] In some embodiments, the non-aqueous electrolyte does not include polymerizable monomers and / or prepolymers obtained by polymerization of polymerizable monomers.

[0093] In some embodiments, the polymerizable monomers include one or more of 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, vinyl pyrrolidone, vinyl imidazole), epoxy resin monomers (such as bisphenol A epoxy resin), polyethylene oxide monomers, polyacrylonitrile monomers, and siloxane monomers.

[0094] In some embodiments, the non-aqueous electrolyte does not undergo a polymerization reaction under light or heating conditions.

[0095] In some embodiments, the non-aqueous electrolyte is in a liquid state after formation.

[0096] In some embodiments, the additive further includes at least one of sultone compounds, cyclic carbonate compounds, phosphate compounds, nitrile compounds, lithium salt additives, or alkane compounds in some embodiments.

[0097] In some embodiments, the sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, and methylene methanedisulfonate.

[0098] In some embodiments, the cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinylene carbonate, methylene vinylene carbonate, or the compound shown in Structural Formula 3:

[0099] ;

[0100] In the structural formula 3, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.

[0101] In some embodiments, the phosphate compound includes a compound represented by structural formula 4:

[0102] ;

[0103] In the structural formula 4, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a C1-C5 halogenated hydrocarbon group, a C6-C12 aryl group, a C6-C12 halogenated aryl group, -Si(C m H 2m+1 )3, and m is a natural number from 1 to 3.

[0104] In a preferred embodiment, the phosphate compound represented by structural formula 4 can be at least one of triphenyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tripropargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate.

[0105] In some embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

[0106] In some embodiments, the lithium salt type additive includes at least one of lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium monofluoromethanesulfonate, lithium trioxalate phosphate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium dicyanamide, or a lithium salt of a lower aliphatic carboxylic acid having 4 or fewer carbon atoms.

[0107] In some embodiments, the alkane compound includes at least one of cyclopentane, cyclohexane, cycloheptane, methylcyclopentane, ethylcyclopentane, 1,3-dimethylcyclopentane, 1,4-dimethylcyclopentane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, butylcyclohexane, pentylcyclohexane, cis-1-methyl-3-ethylcyclohexane, trans-1-methyl-3-ethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, 1,3,5-trimethylcyclohexane, and perfluoro(ethylcyclohexane).

[0108] In other embodiments, the additive may further include other additives that can improve battery performance: for example, additives that enhance battery safety performance, specifically flame retardant additives such as fluorophosphate esters and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0109] It should be noted that, unless otherwise specified, generally, the content of any optional substance in the additive in the non-aqueous electrolyte is less than 10%, preferably, the content is 0.01 - 5%, and more preferably, the content is 0.1% - 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 a range composed of any two of these values.

[0110] In some embodiments, the additive includes fluoroethylene carbonate, and based on the total mass of the non-aqueous electrolyte being 100%, the content of fluoroethylene carbonate is 0.01% - 30%.

[0111] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass content of the non-aqueous organic solvent is 65% - 90%.

[0112] Specifically, based on the total mass of the non-aqueous electrolyte being 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 a range composed of any two of these values.

[0113] 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.

[0114] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers having 3 to 10 carbon atoms and cyclic ethers having 3 to 6 carbon atoms. The cyclic ethers may specifically be, but are not limited to, at least one of 1,3-dioxolane, 1,4-dioxane, crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran. The chain ethers may specifically be, 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. Since chain ethers have a 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. The ether compounds may be used alone or in combination of two or more in any combination and ratio. The content of the ether compounds is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the high-compaction lithium-ion battery of the present invention. In a non-aqueous solvent with a volume ratio of 100%, it is usually 1% or more, preferably 2% or more, more preferably 3% or more by volume, and usually 30% or less, preferably 25% or less, more preferably 20% or less by volume.

[0115] In some embodiments, the nitrile solvent may specifically be, but is not limited to, at least one of acetonitrile, glutarodinitrile, and malononitrile.

[0116] In some embodiments, the carbonate solvents include cyclic carbonates or chain carbonates. The cyclic carbonates may specifically be, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); the chain carbonates may specifically be, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). There is no particular limitation on the content of the cyclic carbonate, and it can be arbitrary within the range that does not significantly damage the effects of the lithium-ion battery of the present invention. However, when using only one kind, the lower limit of its content is generally 3% or more, preferably 5% or more, by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to bring the high-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery into a good range. In addition, the upper limit is generally 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, which helps to improve the stability during high-temperature storage. There is no particular limitation on the content of the chain carbonate. Relative to the total amount of the solvents of the non-aqueous electrolyte, it is generally 15% or more, preferably 20% or more, more preferably 25% or more, by volume. In addition, it is generally 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By making the content of the chain carbonate within the above range, it is easy to bring the viscosity of the non-aqueous electrolyte into an appropriate range, suppress a decrease in ionic conductivity, and further help to bring the output characteristics of the non-aqueous electrolyte battery into a good range. When using two or more chain carbonates in combination, it is only necessary to make the total amount of the chain carbonates satisfy the above range.

[0117] In some embodiments, it is also preferable to use chain carbonates having fluorine atoms (hereinafter simply referred to as "fluorinated chain carbonates"). There is no particular limitation on the number of fluorine atoms in the fluorinated chain carbonate as long as it is 1 or more, but it is generally 6 or less, preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms may be bonded to the same carbon or to different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc.

[0118] The carboxylic ester solvents include cyclic carboxylic esters and / or chain carbonates. Examples of the cyclic carboxylic esters may include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of the chain carbonates may include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

[0119] In some embodiments, the sulfone solvents include cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, they are usually compounds with 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of chain sulfones, they are usually compounds with 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no special limitation on the content of the sulfone solvents, and it can be arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. Relative to the total amount of the solvents in the non-aqueous electrolyte, the volume ratio is usually 0.3% or more, preferably 0.5% or more, more preferably 1% or more. Additionally, the volume ratio is usually 40% or less, preferably 35% or less, more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvents only needs to meet the above range. When the content of the sulfone solvents is within the above range, it tends to obtain a non-aqueous electrolyte with excellent high-temperature storage stability.

[0120] In a preferred embodiment, the non-aqueous organic solvent includes a mixture of cyclic carbonates and chain carbonates.

[0121] In some embodiments, the electrolyte salt is selected from lithium salts, and the lithium salts include at least one of LiPF6, LiODFP, LiODFB, LiBOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborate, lithium trioxalate phosphate, lithium lower aliphatic carboxylate having 4 or less carbon atoms, or lithium tetraphenylborate.

[0122] In some embodiments, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.1 mol / L to 4 mol / L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the lithium salt 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 a range composed of any two of these values.

[0123] Another embodiment of the present invention provides a secondary battery, including a positive electrode, a negative electrode, and the non-aqueous electrolyte as described above.

[0124] In some embodiments, the secondary battery is a lithium-ion battery.

[0125] 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 lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide (such as lithium nickelate), lithium manganese oxide (such as spinel-type lithium manganese oxide, layered lithium manganese oxide, etc.), lithium iron phosphate, lithium manganese phosphate, lithium cobaltate, and one or more of their doped / coated modified compounds. 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 O2, where 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, 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.

[0126] In a preferred embodiment, the mass fraction of iron element in the positive electrode material layer is greater than or equal to 17.7%. When the mass fraction of iron element in the positive electrode material layer meets the above range, the positive electrode material layer has a high specific capacity, thereby effectively improving the energy density of the battery, and the charging cut-off voltage of the battery can reach 3.8V, having a high discharge platform and showing good cycle stability under a conventional voltage window; also, since iron element has relatively rich reserves and low prices globally, compared with rare and high-priced metals such as cobalt, nickel, and manganese, using the aforementioned positive electrode active material helps to reduce costs and reduce the dependence on limited resources.

[0127] In a more preferred embodiment, the positive electrode active material includes LiFe 1-x’ M’ x’ PO4. The compounds shown in Structural Formula 1 and the compounds shown in Structural Formula 2 have good synergistic effects, significantly reducing the dissolution of iron ions in the battery, effectively reducing the rupture and recombination of the SEI film caused by the deposition of iron ions on the surface of the SEI film, and effectively improving the cycle performance of the battery.

[0128] In some specific embodiments, the positive electrode active material may include one or more of 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 Al 0.05 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 O2.

[0129] 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.

[0130] The positive electrode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0131] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0132] In some embodiments, the positive electrode current collector includes a metal material capable of conducting electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0133] In some embodiments, the negative electrode includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material. The negative electrode active material includes at least one of carbon - based negative electrodes, silicon - based negative electrodes, tin - based negative electrodes, and lithium negative electrodes. Among them, 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 - oxygen, tin metal compounds; the lithium negative electrode may include metallic lithium or lithium alloys. The lithium alloy may specifically be at least one of lithium - silicon alloy, lithium - sodium alloy, lithium - potassium alloy, lithium - aluminum alloy, lithium - tin alloy, and lithium - indium alloy.

[0134] 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.

[0135] In some embodiments, the silicon material is one or several of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0136] 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 metal 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 foils.

[0137] 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.

[0138] The negative electrode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0139] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0140] In some embodiments, the secondary battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0141] The separator can be a conventional existing separator, which can be a ceramic separator, a polymer separator, a non - woven fabric, an inorganic - organic composite separator, etc., 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 separators.

[0142] The present invention is further illustrated by the following examples.

[0143] Table 1

[0144]

[0145] Among them, VC is vinylene carbonate, FEC is fluoroethylene carbonate, MMDS is methylene methanedisulfonate, and LiDFP is lithium difluorophosphate.

[0146] Example 1

[0147] This example is used to illustrate the preparation method of the lithium - ion battery disclosed by the present invention, including the following operating steps:

[0148] (1) Preparation of non-aqueous electrolyte:

[0149] Mix ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of EC:PC:DMC:EMC = 5:6:8, and then add 1 mol / L lithium hexafluorophosphate (LiPF6) as the electrolyte salt. Based on the total weight of the non-aqueous electrolyte being 100%, additives with the mass percentages shown in Table 1 are added in sequence.

[0150] (2) Electrolyte injection and formation of the battery cell:

[0151] In a glove box with a water content < 10 ppm and an oxygen content < 50 ppm, inject the above-prepared electrolyte into a dry battery cell with lithium iron phosphate as the positive electrode and artificial graphite as the negative electrode. The mass fraction of iron element in the positive electrode material layer is 34%. Maintain at a vacuum degree of 20 kPa for 10 min, and after encapsulation, let it stand at room temperature for one day.

[0152] Then perform the conventional formation for the first charge according to the following steps: Constant current charge at 0.05C for 120 min, constant current charge at 0.1C for 60 min, and constant current charge at 0.2C for 60 min. After the formation is completed, evacuate and seal, and let it stand in an oven at 45°C for one day. Subsequently, further charge at a constant current of 0.2C to 3.65V and charge at a constant voltage until cutoff at 0.03C to obtain a lithium iron phosphate / graphite battery.

[0153] Examples 2 - 23

[0154] Examples 2 - 23 are used to illustrate the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows:

[0155] The mass contents of each component in the electrolyte are as shown in Table 1.

[0156] Comparative Examples 1 - 27

[0157] Comparative Examples 1 - 27 are used to illustrate the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows:

[0158] The mass contents of each component in the electrolyte are as shown in Table 1.

[0159] Performance test

[0160] 1. The electrolytes obtained in Example 1 and Comparative Example 15 were detected using a liquid chromatography - mass spectrometer (LC - MS). The model of the LC - MS is Waters ACQUITY UPLC / Xevo G2 - XS Qtof MS. The chromatographic conditions are as follows: A Waters T3 chromatographic column is used, the column temperature is 35 - 40 °C, the mobile phase is a mixed solution of 40% water and 60% acetonitrile, and the flow rate of the mobile phase is 0.2 - 0.3 mL / min. The test results obtained are as Figure 1 and Figure 2 shown.

[0161] From Figure 1 and Figure 2 the test results, it can be seen that a characteristic peak appears at a retention time of 1.55 min in the chromatogram obtained from Example 1, while this characteristic peak is not reflected in the chromatogram of Comparative Example 15, indicating that there are differences in the material components between Example 1 and Comparative Example 15.

[0162] 2. The following performance tests were carried out on the lithium - ion batteries prepared in the above - mentioned examples and comparative examples:

[0163] 2.1 Battery room - temperature cycle test:

[0164] The fresh batteries after formation were placed in a constant - temperature environment at 25 °C. After a short rest, they were charged at a constant current and constant voltage of 1C to 3.65 V, with a cut - off current of 0.05C. After a short rest, they were discharged at a constant current of 1.5C to 2.5 V. Such charge - discharge cycles were carried out 2000 times. Record the discharge capacity of each cycle. The capacity retention rate (%) = the discharge capacity of the 2000th cycle / the discharge capacity of the first cycle * 100%, and the cyclic internal resistance growth rate (%) = (the internal resistance after 2000 cycles - the internal resistance after formation) / the internal resistance after formation * 100%, and calculate the average value between parallel samples.

[0165] 2.2 Battery low - temperature discharge test:

[0166] The fresh batteries after formation were placed in a constant - temperature environment at 25 °C. After a short rest, they were charged at a constant current and constant voltage of 0.5C to 3.65 V, with a cut - off current of 0.05C. Subsequently, they were transferred to a constant - temperature environment at - 20 °C. After being left for 2 h, they were discharged at a constant current of 0.5C to 2.0 V. Calculate according to the following formula:

[0167] Low - temperature discharge efficiency (%) = low - temperature discharge capacity / room - temperature charge capacity * 100%;

[0168] (1) The test results obtained from Examples 1 - 21 and Comparative Examples 1 - 8, 15 - 21 were filled into Table 2.

[0169] Table 2

[0170]

[0171] From the test results of Examples 1 to 21 and Comparative Examples 1 to 8, 15 to 21, it can be seen that compared with the non-aqueous electrolytes in the comparative examples where the compound shown in Structural Formula 1 or the compound shown in Structural Formula 2 is added alone, Examples 1 to 14 where the compound shown in Structural Formula 1 and the compound shown in Structural Formula 2 are added simultaneously have significant improvements in enhancing the cycle capacity retention rate, low-temperature discharge efficiency of lithium-ion batteries, and reducing the growth rate of internal resistance. This shows that the compound shown in Structural Formula 1 and the compound shown in Structural Formula 2 can effectively improve the ion conduction efficiency of the SEI film during the negative electrode film formation stage of battery formation. Specifically, the compound shown in Structural Formula 1 induces the compound shown in Structural Formula 2 to open the ring in advance during the battery formation stage to form specific species, and this specific species forms a SEI film with a relatively high content of Li2SO4 and a relatively low content of ROSO3Li prior to other additives, thereby delaying the growth of internal resistance during the long cycle of the battery and improving the capacity release of the battery in a low-temperature environment and extending the cycle life under normal temperature cycling.

[0172] From the test results of Examples 1 to 21, it can be seen that when the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Structural Formula 1 is in the range of 1 to 15, it is beneficial to improve the cycle performance and low-temperature discharge performance of the battery. This shows that there is a cooperative effect of mutual influence between the compound shown in Structural Formula 1 and the compound shown in Structural Formula 2. Therefore, when the contents of the two are in a synergistic state, it is beneficial to improve the electrochemical performance of lithium-ion batteries.

[0173] (2)The test results obtained from Examples 3, 22 to 27 and Comparative Examples 9 to 14, 22 to 27 are filled in Table 3.

[0174] Table 3

[0175]

[0176] From the test results of Examples 3, 22 to 27 and Comparative Examples 9 to 14, 22 to 27, it can be seen that compared with the comparative examples, when different compounds shown in Structural Formula 1 and different compounds shown in Structural Formula 2 are used as additives in each example, there are obvious improvement effects on the cycle performance and low-temperature performance of lithium-ion batteries. This shows that different compounds shown in Structural Formula 1 and different compounds shown in Structural Formula 2 have a common structure, that is, the common structure of different compounds shown in Structural Formula 1 is the peroxy bond -O-O-, and the common structure of different compounds shown in Structural Formula 2 is the sulfate ester ring, and this structural commonality is associated with the synergistic effect between the two.

[0177] (3)The test results obtained from Examples 3, 28 to 30 are filled in Table 4.

[0178] Table 4

[0179]

[0180] From the test results of Examples 3 and 28 to 30, it can be seen that in the electrolyte system of the present invention, further adding other additives (VC vinylene carbonate, FEC fluoroethylene carbonate, MMDS methylene methanedisulfonate, LiDFP lithium difluorophosphate) is beneficial to further improve the cycle capacity retention rate of the lithium-ion battery and reduce the growth of its internal resistance at low temperature, indicating that the improvement mechanism of other types of additives on the battery performance is different from the cooperation mechanism between the compound shown in Structural Formula 1 and the compound shown in Structural Formula 2, and can improve the performance of the lithium-ion battery from different aspects.

[0181] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium iron phosphate battery, characterized in that, It includes a positive electrode, a negative electrode and a non-aqueous electrolyte. The non-aqueous electrolyte includes a non-aqueous organic solvent, an electrolyte salt and an additive. The additive includes a compound represented by Structural Formula 1 and a compound represented by Structural Formula 2: Structural Formula 1 Wherein, n is 0 or 1; R1 and R2 are each independently selected from hydrogen, a substituted or unsubstituted C1-C12 alkyl group, a substituted or unsubstituted C2-C12 alkenyl group, a substituted or unsubstituted C2-C12 alkynyl group, a substituted or unsubstituted C6-C20 aryl group, a substituted or unsubstituted C1-C12 acyl group, a substituted or unsubstituted C2-C12 alkoxycarbonyl group, a substituted or unsubstituted C2-C12 ether group. R1 and R2 can be connected to each other to form a ring or not, and R1 and R2 are not both hydrogen at the same time; R3 is selected from a substituted or unsubstituted C1-C12 alkylene group, a substituted or unsubstituted C2-C12 alkenylene group, a substituted or unsubstituted C2-C12 alkynylene group, a substituted or unsubstituted C6-C20 aryl group, a substituted or unsubstituted C2-C12 ether group; when R1, R2 and R3 are substituted, the substituents are alkoxy, hydroxyl, acyl, ester, cyano or halogen; Structural Formula 2 Wherein, R4 is selected from a substituted or unsubstituted C1-C6 alkylene group, a substituted or unsubstituted C2-C6 alkenylene group. When R4 is substituted, the substituents are a C1-C5 alkyl group, a C1-C5 haloalkyl group, a C2-C5 alkenyl group, a C2-C5 haloalkenyl group or halogen; The non-aqueous electrolyte is detected by a liquid chromatography-mass spectrometry (LC-MS) after formation, and has a characteristic peak at a retention time of 1.55±0.1 min; Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the compound represented by Structural Formula 1 is 0.001% to 0.5%; Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the compound represented by Structural Formula 2 is 0.01% to 2%; The mass ratio of the compound represented by Structural Formula 2 to the compound represented by Structural Formula 1 is 1 to 15.

2. The lithium iron phosphate battery according to claim 1, wherein In the compound shown in Structural Formula 1, R1 is selected from hydrogen, and R2 is selected from , a substituted or unsubstituted C1-C12 alkyl group, a substituted or unsubstituted C2-C12 alkenyl group, a substituted or unsubstituted C2-C12 alkynyl group, a substituted or unsubstituted C6-C20 aryl group, wherein R 10 is selected from a substituted or unsubstituted C1-C11 alkyl group, a substituted or unsubstituted C2-C11 alkenyl group, a substituted or unsubstituted C2-C11 alkynyl group, a substituted or unsubstituted C6-C20 aryl group.

3. The lithium iron phosphate battery according to claim 1, characterized in that, In the compound represented by Structural Formula 1, R1 and R2 are each independently selected from a substituted or unsubstituted C1-C12 alkyl group, a substituted or unsubstituted C2-C12 alkenyl group, a substituted or unsubstituted C2-C12 alkynyl group, a substituted or unsubstituted C6-C20 aryl group.

4. The lithium iron phosphate battery according to claim 1, wherein, In the compound shown by the structural formula 1, 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 , wherein, R 11 is 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, substituted or unsubstituted C2-C12 ether group.

5. The lithium iron phosphate battery according to claim 1, characterized in that, In the compound shown by the structural formula 1, R1 is selected from , wherein R 12 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, 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, substituted or unsubstituted C6-C20 aryl or , wherein R 13 is selected from substituted or unsubstituted C1-C11 alkyl, substituted or unsubstituted C2-C11 alkenyl, substituted or unsubstituted C2-C11 alkynyl.

6. The lithium iron phosphate battery according to claim 1, wherein, The compound represented by Structural Formula 1 includes one or more of the following compounds: ； And / or, The compound represented by Structural Formula 2 includes one or more of the following compounds: 。 7. The lithium iron phosphate battery according to claim 1, characterized in that, The additive further includes at least one of a sultone compound, a cyclic carbonate compound, a phosphate compound, a nitrile compound, a lithium salt type additive or an alkane compound; and / or The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, methylene methanedisulfonate; and / or The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene vinyl carbonate, methylene vinylene carbonate or the compound represented by Structural Formula 3: Structural Formula 3 In the said structural formula 3, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group; and / or The phosphate compound includes the compound shown in Structural Formula 4: Structural Formula 4 In the said structural formula 4, R 31 , R 32 , R 33 are each independently selected from a saturated hydrocarbon group having 1 to 5 carbon atoms, an unsaturated hydrocarbon group having 1 to 5 carbon atoms, a halogenated hydrocarbon group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, a halogenated aryl group having 6 to 12 carbon atoms, -Si(C m H 2m+1 )3, and m is a natural number from 1 to 3; and / or The nitrile compound includes at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile; and / or The lithium salt type additive includes at least one of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium monofluoromethanesulfonate, lithium trioxalatophosphate, lithium difluorodioxalatophosphate, lithium tetrafluoroxalatophosphate, lithium dicyanamide, or lithium lower aliphatic carboxylate having 4 or less carbon atoms; and / or The alkane compound includes at least one of cyclopentane, cyclohexane, cycloheptane, methylcyclopentane, ethylcyclopentane, 1,3-dimethylcyclopentane, 1,4-dimethylcyclopentane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, butylcyclohexane, pentylcyclohexane, cis-1-methyl-3-ethylcyclohexane, trans-1-methyl-3-ethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, 1,3,5-trimethylcyclohexane, and perfluoroethylcyclohexane.

8. The lithium iron phosphate battery according to claim 1, wherein The non-aqueous electrolyte does not include a polymerizable monomer and / or a prepolymer obtained by polymerizing the polymerizable monomer.

9. The lithium iron phosphate battery according to claim 1, wherein, The positive electrode includes a positive electrode material layer, and the mass fraction of iron element in the positive electrode material layer is greater than or equal to 17.7%.

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