Electrolyte additive, electrolyte, secondary battery, and terminal device

Abstract

The present application provides an electrolyte additive, an electrolyte, a secondary battery, and a terminal device. The electrolyte additive provided by the present application is a polydentate cyclic polynitrile additive having an ether-based backbone, which is obtained by special molecular design. The additive can enable an electrolyte to have the advantages of high-voltage resistance and a wide temperature range, so that a battery has excellent cycle performance and excellent high-temperature / low-temperature performance under a high voltage.

Description

Electrolyte additive, electrolyte, secondary battery and terminal device

[0001] The present application claims priority to the Chinese patent application No. 202411303105.4, filed on September 18, 2024, entitled "Electrolyte additive, electrolyte, secondary battery and terminal device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of battery, in particular to an electrolyte additive, an electrolyte, a secondary battery and a terminal device. BACKGROUND

[0003] With the rapid expansion of the electronic device, power and energy storage markets, consumers' demand for the endurance of secondary batteries is growing, and improving the energy density and operating voltage of the battery is the key direction of current research. In secondary batteries, the composition of the electrolyte plays a key role in the performance of the cycle performance, fast charging performance and wide temperature range performance of the battery. However, when the secondary battery uses a high-voltage positive electrode material (such as lithium cobaltate) or a high-capacity negative electrode material (such as silicon-based material or lithium metal), the electrolyte is often consumed rapidly and the transition metal is dissolved seriously, which not only reduces the cycle stability and high-temperature performance of the battery, but also increases the safety hazard, thereby severely limiting the use of the battery at high voltage.

[0004] Therefore, it is a technical problem to be solved in the art to develop an electrolyte system resistant to high voltage to meet the use scenarios of the battery at high voltage. SUMMARY

[0005] The present application provides an electrolyte additive, an electrolyte, a secondary battery and a terminal device. The electrolyte additive of the present application is a multi-dentate cyclic polynitrile additive with an ether group backbone obtained by special molecular design. The additive can make the electrolyte have the advantages of high voltage resistance and wide temperature range, so that the battery has excellent cycle performance and high and low temperature performance at high voltage.

[0006] In a first aspect, the present application provides an electrolyte additive, the electrolyte additive has the structure shown in formula I:

[0007] In formula I, R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of alkyloxy nitrile, substituted alkyloxy nitrile, alkenyloxy nitrile, substituted alkenyloxy nitrile, aryloxy nitrile, substituted aryloxy nitrile, hydrogen atom, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy, and at least three of R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of alkyloxy nitrile, substituted alkyloxy nitrile, alkenyloxy nitrile, substituted alkenyloxy nitrile, aryloxy nitrile, substituted aryloxy nitrile;

[0008] X is selected from any one of oxygen atom, sulfur atom, alkylene, substituted alkylene, imine group, substituted imine group, alkenylene, substituted alkenylene;

[0009] j is selected from an integer between 1 and 3, and k is selected from an integer between 0 and 3.

[0010] The compound having the structure shown in formula I is a multi-dentate cyclic polynitrile additive with ether group main chain, wherein the multi-dentation is that there are not less than 3 cyano groups in R1 to R8, and the design of multi-dentation effectively improves the number and density of cyano functional groups in the molecule, and the cyano group can be preferentially complexed with transition metal ions in the positive active material, inhibit the dissolution of transition metal ions, reduce the side reaction of electrolyte and positive active material, inhibit the further oxidative decomposition of electrolyte, and improve the stability of electrolyte at high voltage; the ether group main chain means that the cyano group is connected to the parent ring through substituted or unsubstituted alkyloxy nitrile, alkenyloxy nitrile, aryloxy nitrile, so that the compound contains at least three ether bonds, which can make the electrolyte have high conductivity and low viscosity, and improve the wide temperature range performance of the battery; in addition, the main body of the additive is a cyclic structure, which can improve the rigidity of the molecule, limit the stretching and movement of the molecular chain, inhibit the intramolecular movement, thereby improving the coordination ability of cyano group at the positive electrode interface, further improving the high voltage performance of the battery, and compared with linear structure, the cyclic structure is more easily to slide between molecules, thereby reducing the freezing point of the molecule, further improving the wide temperature range performance of the battery. In summary, the electrolyte additive shown in formula I obtained by special design of the molecular structure can make the electrolyte have the advantages of high voltage resistance and wide temperature range, so that the battery has excellent cycle performance and high and low temperature performance at high voltage.

[0011] The electrolyte additive as described above, wherein the number of carbon atoms in the substituted alkylene nitrile, the substituted alkenylene nitrile, and the substituted arylene nitrile is 2-10; and / or the number of carbon atoms in the substituted alkylene, the substituted imine, and the substituted alkenylene is 3-10; and / or the number of carbon atoms in the substituted arylene is 4-20. If the carbon number is too long, the molecular size is too large, which is not conducive to the dissolution of the electrolyte additive in the solvent, and is also not conducive to the conductivity of the electrolyte. By controlling the number of carbon atoms in the substituted or unsubstituted alkylene nitrile, the substituted or unsubstituted alkenylene nitrile, and the substituted or unsubstituted arylene nitrile within the above range, it is beneficial to keep the electrolyte additive with good solubility and keep the electrolyte with good conductivity.

[0012] The electrolyte additive as described above, wherein the number of carbon atoms in the substituted alkylene nitrile, the substituted alkenylene nitrile, and the substituted arylene nitrile is 2-6; and / or the number of carbon atoms in the substituted alkylene, the substituted imine, and the substituted alkenylene is 3-6; and / or the number of carbon atoms in the substituted arylene is 4-10. Within the above carbon number range, it will further be beneficial to improve the solubility and conductivity of the electrolyte additive.

[0013] The electrolyte additive as described above, wherein the substituents in the substituted alkylene nitrile, the substituted alkenylene nitrile, the substituted arylene nitrile, the substituted alkylene, the substituted imine, and the substituted alkenylene are each independently selected from one or more of halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, and haloaryloxy. Through the above selection of substituents, the film-forming reactivity of the electrolyte additive can be controlled, which is beneficial to optimize the interface film formation, and the absence of active hydrogen in the above substituents will not cause side reactions with other substances in the electrolyte.

[0014] The electrolyte additive as described above, wherein the number of carbon atoms in the alkyl, the haloalkyl, the alkoxy, and the haloalkoxy is 1-20; and / or the number of carbon atoms in the alkenyl, the haloalkenyl, the alkynyl, the haloalkynyl, the alkenyloxy, and the haloalkenyloxy is 2-20; and / or the number of carbon atoms in the aryl, the haloaryl, the aryloxy, and the haloaryloxy is 3-20. Within the above carbon number range, it is not only conducive to the synthesis and preparation of the corresponding groups, but also enables the groups represented by Formula I to have a suitable carbon chain length, and enables the compounds represented by the structure of Formula I to have a suitable viscosity, flexibility, and rigidity.

[0015] The electrolyte additive as described above, wherein at least three of R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from any one of ethyleneoxy nitrile, ethylenyloxy nitrile, and ethyleneoxy benzonitrile. The above groups are not only easy to be prepared by using existing synthesis process, but also have suitable carbon chain length and suitable content of oxygen atom, which can further improve the conductivity of the electrolyte and reduce the viscosity thereof.

[0016] The electrolyte additive as described above, wherein X is selected from any one of oxygen atom, sulfur atom, imine group, methylene group, alkyl-substituted methylene group, and halogen-substituted alkyl-substituted methylene group. When X is selected from the above groups, the solubility of the electrolyte additive can be further optimized, and the molecule has better flexibility, further enhancing the chelating ability of the cyano group to the dissolved transition metal ions in the positive active material.

[0017] The electrolyte additive as described above, wherein the electrolyte additive comprises one or more of the following compounds:

[0018] It is found through experimental research that when the electrolyte additive comprises one or more of the above compounds, the battery has more excellent cycle performance and high-low temperature performance at high voltage.

[0019] The second aspect of the present application provides an electrolyte comprising an organic solvent, an electrolyte salt, and an additive, wherein the additive comprises the electrolyte additive having the structure shown in Formula I provided in the first aspect of the present application. Since the electrolyte comprises the electrolyte additive having the structure shown in Formula I, the electrolyte of the present application has the advantages of high voltage resistance and wide temperature range, and is suitable for use in a high-voltage battery system.

[0020] The electrolyte as described above, wherein the mass percentage content of the electrolyte additive having the structure shown in Formula I in the electrolyte is 0.05% to 10%.

[0021] The electrolyte as described above, wherein the mass percentage content of the electrolyte additive having the structure shown in Formula I in the electrolyte is 0.5% to 5%. When the content of the additive shown in Formula I is too low, it is difficult to effectively improve the high-voltage resistance of the electrolyte, and when the content of the additive shown in Formula I is too high, the viscosity of the electrolyte is too high, the conductivity is too low, lithium dendrites are easily generated, thereby inducing interface side reactions and internal short circuit phenomenon, and the cycle performance and storage performance are reduced. When the mass content of the electrolyte additive having the structure shown in Formula I in the electrolyte is in the range of 0.05% to 10%, especially in the range of 0.5% to 5%, the high-voltage resistance, cycle performance, and storage performance of the electrolyte are more excellent.

[0022] The electrolyte as described above, wherein the additive further comprises one or more of biphenyl, fluorobenzene, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, bis-fluoroethylene carbonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, methanediyl methane disulfonate, dimethyl sulfate, dimethyl sulfite, diethyl sulfite, diethyl sulfate, 4-methyl ethylene sulfite, butanedinitrile, pentanedinitrile, hexanedinitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetristitnitrile. The above additives are all conventional additives used in the electrolyte for positive electrode film formation or negative electrode film formation, which can further protect the positive and negative electrode interface and improve the stability of the electrolyte at high voltage.

[0023] The electrolyte as described above, wherein the organic solvent comprises one or more of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, ether solvents. Among them, the cyclic carbonate solvents have high dielectric constant but large viscosity, the linear carbonate solvents have lower dielectric constant but smaller viscosity, and both have good electrochemical stability and high oxidation potential, and good compatibility with carbon negative electrode materials; compared with carbonate solvents, carboxylic acid ester solvents have lower freezing point and viscosity, which is beneficial to improve the low temperature performance of the electrolyte; ether solvents generally have lower viscosity and higher conductivity, which can improve the conductivity performance of the electrolyte. However, the dielectric constant of ether solvents is relatively low, and the solubility of lithium salt is weak, so it is usually used in combination with other solvents. In summary, the organic solvent in the electrolyte needs to have high dielectric constant and low viscosity, which can effectively dissolve lithium salt and promote the transmission of lithium ions, and in practical application, the above kinds of solvents can be selected according to this principle to meet the corresponding requirements.

[0024] The electrolyte as described above, wherein the electrolyte salt comprises one or more of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt. The electrolyte of the present application has good solubility for electrolyte salts such as lithium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt, and is accordingly suitable for application in lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, magnesium secondary batteries, zinc secondary batteries, and aluminum secondary batteries.

[0025] The electrolyte as described above, wherein the electrolyte salt comprises MClO4, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C2O4)2, MBF2C2O4, M[(CF3SO2)2N], M[(C m F 2m+1 SO2)(C n F 2n+1One or more of [(FSO2)2N] and [(FSO2)2N], wherein M is Li, Na, or K, and m and n are natural numbers. The above electrolyte salts are all conventionally used electrolyte salts in this field, possessing advantages such as easy solubility in organic solvents, easy dissociation, good electrochemical and chemical stability, and low cost and easy availability.

[0026] In the electrolyte described above, the molar concentration of the electrolyte salt in the electrolyte is from 0.01 mol / L to 5.0 mol / L. The higher the concentration of the electrolyte in the electrolyte, the more conductive ions there are, and the higher the conductivity. However, as the electrolyte concentration continues to increase, the probability of recombination between anions and cations also increases, causing the conductivity to reach its upper limit or even show a downward trend. Within the above concentration range, the electrolyte salt can be fully dissolved while maintaining a high conductivity in the electrolyte.

[0027] A third aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte provided in the third aspect of this application. Because the electrolyte provided in the second aspect of this application has the characteristics of high voltage resistance and a wide temperature range, the secondary battery including this electrolyte exhibits excellent cycle performance and high / low temperature performance under high voltage.

[0028] This application provides a terminal device in a fourth aspect, including a housing and electronic components and a secondary battery housed within the housing, wherein the secondary battery includes the secondary battery provided in this application. The terminal device of this application can be a consumer electronic product, such as a mobile phone, tablet computer, power bank, laptop computer, portable computer, smart wearable device, etc., or it can be a vehicle, energy storage device, base station, etc. Terminal products with the above-mentioned secondary battery have higher product safety and reliability.

[0029] The electrolyte additive provided by the application has the structure shown in Formula I, is a multi-dentate cyclic polynitrile additive with an ether group main chain, the multi-dentate design effectively increases the number and density of intramolecular cyano functional groups, can effectively complex transition metal ions in the positive active material, inhibit the dissolution of the transition metal ions, reduce the side reaction of the electrolyte with the positive active material, and thus make the electrolyte have excellent high-pressure stability; the ether group main chain is beneficial to improving the conductivity of the electrolyte and reducing the viscosity of the electrolyte, improving the wide-temperature-range performance of the battery, and making the battery have excellent high-temperature and low-temperature performance; the cyclic molecular main structure can on the one hand improve the rigidity of the molecule, limit the stretching movement of the molecular chain, and be beneficial to improving the coordination ability of the cyano group at the positive electrode interface, so as to synergistically act with the multi-dentate feature to further improve the high-pressure resistance of the battery, and on the other hand be helpful to the sliding between molecules, so as to reduce the freezing point of the molecule, and synergistically with the ether group main chain to further improve the wide-temperature-range performance of the battery. In summary, the electrolyte additive shown in Formula I obtained by the special design of the molecular structure of the application can make the electrolyte have the advantages of high-pressure resistance and wide-temperature-range, so that the battery has excellent cycle performance and high-temperature and low-temperature performance at high voltage. BRIEF DESCRIPTION OF DRAWINGS

[0030] Fig. 1 is a schematic diagram of the structure of a secondary battery according to an embodiment of the application;

[0031] Fig. 2 is a comparison diagram of the capacity retention rate of 300 cycles of Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 6.

[0032] Explanation of reference signs: 10-positive electrode; 101-positive electrode current collector; 102-positive active material; 20-negative electrode; 201-negative electrode current collector; 202-negative active material; 30-separator; 40-electrolyte. DETAILED DESCRIPTION

[0033] To make the purpose, technical scheme and advantages of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below in combination with the embodiments of the application. Obviously, the described embodiments are some embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0034] FIG. 1 is a schematic diagram of a secondary battery structure according to an embodiment of the present application. As shown in FIG. 1, the secondary battery mainly comprises a positive electrode 10, a negative electrode 20, a separator 30 and an electrolyte 40. The positive electrode 10 comprises a positive electrode current collector 101 and a positive electrode active material 102 on the surface of the positive electrode current collector 101. The negative electrode 20 comprises a negative electrode current collector 201 and a negative electrode active material 202 on the surface of the negative electrode current collector 201. Taking a lithium ion battery as an example, when the battery is charged, lithium ions are released from the crystal lattice of the positive electrode active material 102, transported through the electrolyte 40 and deposited into the negative electrode 20 through the separator 30. When the battery is discharged, lithium ions are released from the negative electrode 20, transported through the electrolyte 40 and inserted into the crystal lattice of the positive electrode active material 102 through the separator.

[0035] When charging and discharging at high voltage, transition metals in the positive electrode active material of the battery are easily dissolved into the electrolyte to produce side reactions, and lattice oxygen is oxidized and precipitated to join in, resulting in unstable structure of the positive electrode active material and easy occurrence of adverse phase change. Meanwhile, the electrolyte is more prone to decomposition under the action of high voltage, which aggravates the occurrence of interface side reactions with the positive electrode active material, further accelerating the dissolution of transition metals and the destruction of the structure of the positive electrode active material. The combined effect of the above factors limits the application of the battery at high voltage, especially the traditional electrolyte system, which is difficult to meet the use requirements of the battery at ≥4.60V high voltage.

[0036] Based on this, the first aspect of the present application provides an electrolyte additive having the structure shown in formula I:

[0037] In formula I, R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of alkyloxy nitrile, substituted alkyloxy nitrile, alkenyloxy nitrile, substituted alkenyloxy nitrile, aryloxy nitrile, substituted aryloxy nitrile, hydrogen atom, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy, and at least three of R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of alkyloxy nitrile, substituted alkyloxy nitrile, alkenyloxy nitrile, substituted alkenyloxy nitrile, aryloxy nitrile, substituted aryloxy nitrile;

[0038] X is selected from any one of oxygen atom, sulfur atom, alkylene, substituted alkylene, imine group, substituted imine group, alkenylene, substituted alkenylene, alkynylene;

[0039] j is selected from an integer between 1 and 3, and k is selected from an integer between 0 and 3.

[0040] In the present application, the alkylene nitrile, alkenylene nitrile and arylenic nitrile refer to the group obtained by connecting one end of the alkylene, alkenylene or arylenic group to a cyano group.

[0041] Halogen includes fluorine, chlorine, bromine or iodine.

[0042] Halogenated refers to one or more hydrogen atoms in the group being replaced by halogen, which can be fully halogenated or partially halogenated.

[0043] The alkylene nitrile, substituted alkylene nitrile, alkenylene nitrile, substituted alkenylene nitrile, arylenic nitrile, substituted arylenic nitrile, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkynyl, halogenated alkynyl, alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy, halogenated aryloxy, alkylene, substituted alkylene, alkenylene, substituted alkenylene and alkynylene can be linear or branched.

[0044] The compound having the structure shown in formula I is a multi-dentate cyclic polynitrile additive with an ether group main chain, wherein the multi-dentation is that there are not less than three cyano groups in R1 to R8, and the design of multi-dentation effectively increases the number and density of cyano functional groups in the molecule. The cyano group can be preferentially complexed with transition metal ions in the positive active material, inhibit the dissolution of transition metal ions, reduce the side reaction of electrolyte and positive active material, inhibit the further oxidative decomposition of electrolyte, and improve the stability of electrolyte at high voltage. The ether group main chain means that the cyano group is connected to the parent ring through a substituted or unsubstituted alkylene nitrile, alkenylene nitrile or arylenic nitrile, so that the compound contains at least three ether bonds, which can make the electrolyte have high conductivity and low viscosity, and improve the wide temperature range performance of the battery. In addition, the main body of the additive is a cyclic structure, which can improve the rigidity of the molecule, limit the stretching and movement of the molecular chain, inhibit the intramolecular movement, thereby improving the coordination ability of cyano group at the positive electrode interface, further improving the high voltage performance of the battery, and compared with linear structure, the cyclic structure is more easily to slide between molecules, thereby reducing the freezing point of the molecule, further improving the wide temperature range performance of the battery. In summary, the electrolyte additive shown in formula I obtained by special design of the molecular structure in the present application can make the electrolyte have the advantages of high voltage resistance and wide temperature range, so that the battery has excellent cycle performance and high and low temperature performance at high voltage.

[0045] In a specific embodiment, the number of carbon atoms in the alkylene nitrile and substituted alkylene nitrile is 2-10, specifically can be 2, 3, 4, 5, 6, 7, 8, 9, 10, preferably 2-6; and / or, the number of carbon atoms in the alkenylene nitrile and substituted alkenylene nitrile is 3-10, specifically can be 3, 4, 5, 6, 7, 8, 9, 10, preferably 3-6; and / or, the number of carbon atoms in the aryloxy nitrile and substituted aryloxy nitrile is 4-20, specifically can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, preferably 4-10.

[0046] If the number of carbon atoms is too long, the molecular size is too large, which is not conducive to the dissolution of the electrolyte additive in the solvent, and is also not conducive to the conductivity of the electrolyte. By controlling the number of carbon atoms in the substituted or unsubstituted alkylene nitrile, the substituted or unsubstituted alkenylene nitrile, and the substituted or unsubstituted aryloxy nitrile within the above range, it is beneficial to maintain good solubility of the electrolyte additive and good conductivity of the electrolyte.

[0047] For example, the alkylene nitrile can be ethylene nitrile, propylene nitrile, butylene nitrile, etc.; the alkenylene nitrile can be ethylene nitrile, propylene nitrile, butylene nitrile, etc.

[0048] In this application, the aromatic ring contained in the aryloxy nitrile, substituted aryloxy nitrile, aryl, halogenated aryl, aryloxy, and substituted aryloxy can be an aromatic ring without heteroatoms, such as a benzene ring, a naphthalene ring, an anthracene ring, or a heteroaromatic ring containing O, S, N, etc. heteroatoms, such as a furan ring, a thiophene ring, a pyrrole ring, an imidazole ring, a pyridine ring, an indole ring, etc.

[0049] Further, the substituents in the substituted alkylene nitrile, the substituted alkenylene nitrile, the substituted aryloxy nitrile, the substituted alkyl, the substituted imine group, and the substituted alkenyl group are each independently selected from one or more of halogen, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkynyl, halogenated alkynyl, alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy, and halogenated aryloxy.

[0050] Through the selection of the above substituents, the film-forming reactivity of the electrolyte additive can be controlled, which is beneficial to optimize the interface film formation, and the absence of active hydrogen in the above substituents will not cause side reactions with other substances in the electrolyte.

[0051] Further, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy in the present application is 1-20, and specifically can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and exemplarily can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, monofluoromethyl, difluoromethyl, trifluoromethyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, monofluoromethoxy, difluoromethoxy, trifluoromethoxy, and the like.

[0052] Further, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy in the present application is 1-20, and specifically can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and exemplarily can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, monofluoromethyl, difluoromethyl, trifluoromethyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, monofluoromethoxy, difluoromethoxy, trifluoromethoxy, and the like.

[0053] Further, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy in the present application is 1-20, and specifically can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and exemplarily can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, monofluoromethyl, difluoromethyl, trifluoromethyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, monofluoromethoxy, difluoromethoxy, trifluoromethoxy, and the like.

[0054] Within the above carbon number range, both the synthesis and preparation of the corresponding groups are facilitated, and the groups shown in formula I have a suitable carbon chain length, and the compounds shown in formula I have a suitable viscosity, flexibility and rigidity.

[0055] In a preferred embodiment, at least three of R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of ethyleneoxy nitrile, ethenyleneoxy nitrile, ethyleneoxy benzene nitrile. The above groups not only facilitate the preparation by using existing synthesis process, but also have a suitable carbon chain length and a suitable content of oxygen atoms, which can further improve the conductivity of the electrolyte and reduce the viscosity thereof.

[0056] wherein the structure of ethyleneoxy nitrile is shown in formula a, the structure of ethenyleneoxy nitrile is shown in formula b, and the structure of ethyleneoxy benzene nitrile is shown in formula c, wherein “*” in formula a, formula b and formula c represents the bonding position.

[0057] In a preferred embodiment, X is selected from any one of an oxygen atom, a sulfur atom, an imine group, a methylene group, an alkyl-substituted methylene group, and a haloalkyl-substituted methylene group. When X is selected from the above groups, the solubility of the electrolyte additive can be further optimized, and the molecule has better flexibility, further enhancing the chelating ability of the cyano group to the dissolved transition metal ions in the positive active material.

[0058] It has been found through research that when the electrolyte additive comprises one or more of the following compounds, the battery has more excellent cycle performance and high-low temperature performance at high voltage.

[0059] The preparation method of the electrolyte additive of formula I is not particularly limited in the present application, which can be obtained by reasonably designing according to the conventional preparation process of cyclopolyketone compounds combined with the properties of different substituents.

[0060] For example, additives A to M can be prepared by a Michael addition reaction. For example, additive B can be prepared by a method comprising the following steps (reaction formula is shown below):

[0061] 1) Dissolve 3.0 eq of inositol and 20.0 eq of acrylonitrile in deionized water to obtain a raw material system; 2) Dissolve 20.0 eq of sodium hydroxide in deionized water to form a saturated sodium hydroxide solution, and slowly drop the saturated sodium hydroxide solution into the raw material system; 3) After the saturated sodium hydroxide solution is added, the reaction system is heated to 60 degC and reacted for at least 5 hours; 4) After the reaction is completed, the reaction solution is cooled to room temperature, then pure water is added to quench, neutralized to neutral with 0.1M dilute hydrochloric acid, then extracted with ethyl acetate, washed with sodium carbonate aqueous solution and saturated brine, dried over anhydrous sodium sulfate for at least 30 minutes, filtered, and evaporated to dryness. The ethyl acetate in the filtrate is evaporated to dryness in a 40 degC vacuum oven overnight, and then dried over molecular sieves to obtain additive B.

[0062] The second aspect of the present application provides an electrolyte comprising an organic solvent, an electrolyte salt and an additive, wherein the additive comprises the electrolyte additive of formula I provided in the first aspect of the present application.

[0063] Due to the inclusion of the electrolyte additive having the structure of formula I, the electrolyte of the present application has the advantages of high voltage resistance and wide temperature range, and is suitable for use in high voltage battery systems.

[0064] In a preferred embodiment, the electrolyte additive having the structure of Formula I has a mass percentage content of 0.05% to 10% in the electrolyte, more preferably 0.5% to 5%. When the content of the additive of Formula I is too low, it is difficult to effectively improve the high-voltage resistance of the electrolyte, and when the content of the additive of Formula I is too high, the viscosity of the electrolyte is too high, the conductivity is too low, lithium dendrites are easily generated, thereby inducing interface side reactions and internal short circuit phenomena, and the cycle performance and storage performance are reduced.

[0065] For example, the mass percentage content of the electrolyte additive having the structure of Formula I in the electrolyte can be 0.05%, 0.1%, 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0066] It can be understood that the above-mentioned content values will have certain effects on material testing due to the formation of interface films after battery formation, capacity distribution or cycling, and certain measurement test errors can be allowed, and values within the error range can be understood as the range defined in the present application, or the material testing value range after actual battery formation, capacity distribution or cycling is still within the above-mentioned range, which can be understood as the range defined in the present application.

[0067] In a specific embodiment, in addition to the electrolyte additive having the structure of Formula I, other additives can also be added to the electrolyte according to different battery performance requirements, and the other additives specifically include but are not limited to one or more of biphenyl (BP), fluorobenzene (FB), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), 1,4-butane sultone (BS), vinyl sulfate (DTD), vinyl sulfite, methane disulfonate (MMDS), dimethyl sulfate, dimethyl sulfite, diethyl sulfite, diethyl sulfate, 4-methyl ethylene sulfite, succinonitrile (SN), glutaronitrile, adiponitrile (ADN), 1,2-bis(2-cyanoethoxy)ethane (DENE), and 1,3,6-hexane trinitrile (HTCN). The above additives are all conventional additives used for positive electrode film formation or negative electrode film formation in electrolytes, which can further protect the positive and negative electrode interface and improve the stability of the electrolyte at high voltage. The specific selection can be made according to different battery performance requirements.

[0068] In a specific embodiment, the organic solvent in the electrolyte includes one or more of a cyclic carbonate solvent, a linear carbonate solvent, a carboxylic acid ester solvent, and an ether solvent. Among them, the cyclic carbonate solvent has a high dielectric constant but a large viscosity, the linear carbonate solvent has a lower dielectric constant but a smaller viscosity, and both have good electrochemical stability and high oxidation potential, and have good compatibility with carbon negative electrode materials; compared with the carbonate solvent, the carboxylic acid ester solvent has a lower freezing point and viscosity, which is conducive to improving the low-temperature performance of the electrolyte; the ether solvent generally has a lower viscosity and a higher conductivity, which can improve the conductivity performance of the electrolyte. However, the dielectric constant of the ether solvent is relatively low, and the solubility of lithium salt is weak, so it is usually used in combination with other solvents. In summary, the organic solvent in the electrolyte needs to have a high dielectric constant and a low viscosity, which can effectively dissolve lithium salt and promote the transmission of lithium ions, and in practical application, the above types of solvents can be selected according to this principle to meet the corresponding requirements.

[0069] Specifically, the cyclic carbonate solvent includes but is not limited to one or more of ethylene carbonate (EC), propylene carbonate (PC), and trifluoromethyl ethylene carbonate.

[0070] The linear carboxylic acid ester solvent includes but is not limited to one or more of diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), bis(2,2,2-trifluoroethyl) carbonate, and (2,2,2-trifluoroethyl) methyl carbonate.

[0071] The carboxylic acid ester solvent includes but is not limited to one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate (PP), methyl difluoroacetate, and methyl trifluoroacetate.

[0072] The ether solvent includes but is not limited to one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0073] In a specific embodiment, the electrolyte salt includes one or more of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt. The electrolyte of the present application has good solubility for electrolyte salts such as lithium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt, and is accordingly suitable for application in lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, magnesium secondary batteries, zinc secondary batteries, and aluminum secondary batteries.

[0074] Specifically, the electrolyte salt includes one or more of MCI04, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C204)2, MBF2C204, M[(CF3SO2)2N], M[(FSO2)2N], M[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein M is Li, Na or K, and m and n are natural numbers. The above electrolyte salts are all electrolyte salts commonly used in the art, and have the advantages of being easily soluble in organic solvents, easily dissociated, good electrochemical stability and chemical stability, and inexpensive and easy to obtain.

[0075] Further, the molar concentration of the electrolyte salt in the electrolyte is 0.01 mol / L-5.0 mol / L, and more preferably 0.8 mol / L-1.5 mol / L. Exemplarily, the molar concentration of the electrolyte salt can be 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, 5.0 mol / L, etc. The greater the concentration of the electrolyte in the electrolyte, the greater the number of conductive ions, and the conductivity also increases accordingly. However, as the concentration of the electrolyte continues to increase, the probability of anion and cation complexing also increases, resulting in an upper limit to the increase in conductivity and even a downward trend. The electrolyte salt in the above concentration range can enable the electrolyte salt to be fully dissolved while maintaining a high conductivity of the electrolyte.

[0076] In a specific embodiment, the electrolyte of the present application can be prepared by the following method:

[0077] In an inert or closed environment, the fully dried electrolyte salt is dissolved in an organic solvent, mixed uniformly to obtain a solution, and then the additive is added to the solution, and the electrolyte is obtained after uniform mixing.

[0078] The third aspect of the present application provides a secondary battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the electrolyte provided in the second aspect of the present application.

[0079] Since the electrolyte provided in the second aspect of the present application has the characteristics of high pressure resistance and wide temperature range, the secondary battery including the electrolyte has excellent cycle performance and high and low temperature performance under high voltage.

[0080] The secondary battery of the present application can be a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, an aluminum secondary battery, etc.

[0081] The positive electrode of the present application comprises a positive electrode current collector and a positive electrode material layer coated on one side surface or both side surfaces of the positive electrode current collector, and the positive electrode material layer comprises a positive electrode active material. In addition to the positive electrode active material, the positive electrode material layer can further comprise a certain amount of binder, conductive agent and other components.

[0082] The positive electrode current collector can be a metal foil, such as an aluminum foil, a gold foil, a platinum foil, etc.

[0083] The positive electrode active material can be one or more of transition metal oxides of lithium, sodium, potassium, magnesium, zinc and aluminum, Prussian blue (white) compounds, and polyanionic compounds of lithium, sodium, potassium, magnesium, zinc and aluminum. Specifically, when the secondary battery is a lithium secondary battery, the positive electrode active material can include, but is not limited to, one or more of lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium manganese acid, and lithium nickel manganese acid.

[0084] The binder in the positive electrode material layer can be polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), etc., and the conductive agent can be super carbon black (Super-P), amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The above binder and conductive agent are only exemplary and are not specifically limited.

[0085] The negative electrode of the present application comprises a negative electrode current collector and a negative electrode material layer coated on one side surface or both side surfaces of the negative electrode current collector, and the negative electrode material layer comprises a negative electrode active material. In addition to the negative electrode active material, the negative electrode material layer can further comprise a certain amount of binder, conductive agent and other components.

[0086] The negative electrode current collector can be a metal foil, such as a copper foil, a gold foil, a platinum foil, etc.

[0087] The negative electrode active material can include one or more of carbon-based materials, tin-based materials, silicon-based materials, phosphorus-based materials, lithium titanate, metal lithium and its alloys, metal sodium and its alloys, metal potassium and its alloys, metal magnesium and its alloys, metal zinc and its alloys, and metal aluminum and its alloys.

[0088] Specifically, the carbon-based material can include one or more of graphite, hard carbon, soft carbon, graphene, and porous carbon; the silicon-based material can include one or more of silicon, silicon carbon, silicon oxygen, and silicon metal compounds; the tin-based material can include one or more of tin, tin carbon, tin oxygen, and tin metal compounds; the phosphorus-based material can include one or more of red phosphorus, black phosphorus, and phosphorus compounds; and the lithium alloy can include one or more of lithium silicon alloy, lithium sodium alloy, lithium potassium alloy, lithium aluminum alloy, lithium tin alloy, and lithium indium alloy.

[0089] The binder in the negative material layer can be sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), polyvinylidene fluoride (PVDF), etc., and the conductive agent can be Super-P, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The above binders and conductive agents are only exemplary and are not specific limitations.

[0090] The function of the separator is to separate the positive electrode and the negative electrode and to block the passage of electrons and allow the passage of ions. The separator of the present application includes, but is not limited to, a single-layer polypropylene, a single-layer polyethylene, a double-layer polypropylene / polyethylene composite separator, a double-layer polypropylene / polypropylene composite separator, a three-layer polypropylene / polyethylene / polypropylene composite separator, and a ceramic-coated polyethylene separator, etc.

[0091] The fourth aspect of the present application provides a terminal device comprising the secondary battery provided in the third aspect of the present application. Specifically, the terminal device of the present application comprises a shell, electronic components accommodated in the shell, and the secondary battery as described above, wherein the secondary battery is used to supply power to the electronic components. The terminal device of the present application can be a consumer electronic product, such as a mobile phone, a tablet computer, a mobile power supply, a notebook computer, a portable computer, a smart wearable device, etc., or a vehicle, an energy storage device, a base station, etc. The terminal product with the above secondary battery has higher product safety and reliability.

[0092] Hereinafter, the technical solutions of the present application will be further described through specific examples.

[0093] Unless otherwise specified, the materials or reagents used in the present application can be purchased or prepared by methods known in the art.

[0094] Example 1

[0095] The present example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0096] 1. Preparation of electrolyte

[0097] 1) Preparation of additive A: referring to the preparation method of additive B listed in the above specific embodiments, the difference is that the raw material inositol is replaced by quercitol (CAS No.: 62076-18-0).

[0098] The hydrogen spectrum data of additive A is 1H NMR (400 MHz, DMSO-d6): δ 3.63-3.65 (m, 3H), 3.73-3.75 (t, J = 7.6 Hz, 10H), 3.44 (m, 2H), 1.83 (m, 1H), 1.56 (m, 1H), 2.56-2.58 (t, J = 7.2 Hz, 10H).

[0099] 2) In the glove box filled with argon, EC, DEC, PC and PP were mixed to form an organic solvent, and then fully dried LiPF6 and LiDFOB were dissolved in the above solvent, stirred and mixed to form a uniform solution, and then additives A, FEC and PS were added into the above solution respectively, and mixed uniformly to obtain an electrolyte;

[0100] In the electrolyte, the mass percentage of EC, DEC, PC and PP is 10%, 22.5%, 15% and 30% respectively, the mass percentage of additives A, FEC and PS is 2%, 5% and 3% respectively, the concentration of LiPF6 is 1.0 mol / L, and the concentration of lithium difluoro(oxalato)borate (LiDFOB) is 0.05 mol / L.

[0101] 2. Preparation of a lithium secondary battery

[0102] 1) PVDF with a mass percentage of 2%, conductive agent Super-P with a mass percentage of 2% and LiCoO2 with a mass percentage of 96% were weighed and sequentially added into NMP, and then stirred and mixed uniformly to obtain a positive electrode slurry, which was coated on an aluminum foil current collector, dried, cold-pressed, and cut to obtain a positive electrode sheet;

[0103] 2) CMC-Na with a mass percentage of 1.5%, SBR with a mass percentage of 2.5%, carbon nanotubes with a mass percentage of 1% and silicon-carbon material (the content of silicon is 15 wt%) with a mass percentage of 95% were weighed and sequentially added into deionized water, and then stirred and mixed uniformly to obtain a slurry, which was coated on a copper foil current collector, dried, cold-pressed, and cut to obtain a negative electrode sheet;

[0104] 3) After the positive electrode sheet, the negative electrode sheet and the polyethylene separator prepared above were made into an electric core, the electric core was packaged with an outer packaging foil, and then the electrolyte prepared above was injected into the electric core, and after a formation process, a 4 Ah soft-pack lithium secondary battery was prepared.

[0105] Example 2

[0106] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0107] 1. Preparation of an electrolyte

[0108] 1) Preparation of Additive B: a. Take 3.0 eq of inositol and 20.0 eq of acrylonitrile dissolved in deionized water to obtain a raw material system; b. Take 20.0 eq of sodium hydroxide dissolved in deionized water to form a saturated sodium hydroxide solution, and slowly drop the saturated sodium hydroxide solution into the raw material system; c. After the saturated sodium hydroxide solution is added, the reaction system is heated to 60 degC for at least 5 hours; d. After the reaction is completed, after cooling to room temperature, pure water is added to the reaction solution for quenching, neutralized to neutral with 0.1M dilute hydrochloric acid, then extracted with ethyl acetate, washed with sodium carbonate aqueous solution and saturated brine, dried over anhydrous sodium sulfate for at least 30 minutes, filtered, and the ethyl acetate in the filtrate is evaporated, dried in a 40 degC vacuum oven overnight, and dried over molecular sieves to obtain Additive B.

[0109] The hydrogen spectrum data of Additive B is 1 H NMR (400 MHz, DMSO-d6): δ 3.63 (s, 6H), 3.73-3.75 (t, J = 7.8 Hz, 12H), 2.56-2.58 (t, J = 7.0 Hz, 12H).

[0110] 2) Basically the same as step 2) of Example 1, except that Additive A is replaced by Additive B.

[0111] 2, Preparation of lithium secondary battery

[0112] Basically the same as the preparation steps of Example 1, except that the electrolyte in step 3) is replaced by the electrolyte prepared in this example.

[0113] Example 3

[0114] This example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0115] 1, Preparation of electrolyte

[0116] 1) Preparation of Additive D: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced by (CAS No.: 2748710-62-3).

[0117] The hydrogen spectrum data of Additive D is 1 H NMR (400 MHz, DMSO-d6): δ 1.41 (m, 1H), 1.62 (m, 1H), 3.75-3.77 (t, J = 8.1 Hz, 8H), 3.33 (m, 2H), 3.71 (m, 1H), 3.66 (m, 2H), 2.58-2.59 (t, J = 7.5 Hz, 8H).

[0118] 2) The same as step 2) of Example 1, except that additive A is replaced with additive D.

[0119] 2. Preparation of a lithium secondary battery

[0120] The same as the preparation steps of Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0121] Example 4

[0122] This example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0123] 1. Preparation of an electrolyte

[0124] 1) Preparation of additive E: Refer to the preparation method of additive B listed above, except that the raw material inositol is replaced with (CAS No.: 2808357-47-1).

[0125] The hydrogen spectrum data of additive E is 1 H NMR (400 MHz, DMSO-d6): δ 3.89 (m, 3H), 4.55 (d, J = 3.6 Hz, 2H), 3.74-3.77 (t, J = 8.2 Hz, 10H), 2.57-2.58 (t, J = 7.3 Hz, 10H).

[0126] 2) The same as step 2) of Example 1, except that additive A is replaced with additive E.

[0127] 2. Preparation of a lithium secondary battery

[0128] The same as the preparation steps of Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0129] Example 5

[0130] This example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0131] 1. Preparation of an electrolyte

[0132] 1) Preparation of additive F: Refer to the preparation method of additive B listed above, except that the raw material inositol is replaced with (CAS No.: 656813-78-4).

[0133] The hydrogen spectrum data of additive F is1 H NMR (400 MHz, DMSO-d6): δ 5.68 (dd, J = 4.2 Hz, 2H), 4.02 (dd, J = 4.5 Hz, 2H), 3.76-3.77 (t, J = 7.4 Hz, 8H), 2.57-2.59 (t, J = 7.2 Hz, 8H).

[0134] 2) The same as step 2) of Example 1, except that the additive A is replaced by the additive F.

[0135] 2. Preparation of a lithium secondary battery

[0136] The same as the preparation steps of Example 1, except that the electrolyte in step 3) is replaced by the electrolyte prepared in this example.

[0137] Example 6

[0138] This example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0139] 1. Preparation of an electrolyte

[0140] The same as Example 1, except that the additive A is replaced by a mixture of the additive B and the additive D, and the mass percentage of the additive B and the additive D in the electrolyte is 1%.

[0141] 2. Preparation of a lithium secondary battery

[0142] The same as Example 1, except that the electrolyte in step 3) is replaced by the electrolyte prepared in this example.

[0143] Example 7

[0144] This example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0145] 1. Preparation of an electrolyte

[0146] The same as Example 1, except that the additive A is replaced by a mixture of the additive B and the additive F, and the mass percentage of the additive B and the additive F in the electrolyte is 1%.

[0147] 2. Preparation of a lithium secondary battery

[0148] The same as Example 1, except that the electrolyte in step 3) is replaced by the electrolyte prepared in this example.

[0149] Example 8

[0150] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0151] 1. Preparation of electrolyte

[0152] The present embodiment is basically identical with example 5, except that the mass percentage of additive F is replaced by 0.2%, and the mass percentage of EC, DEC, PC and PP is adjusted to 10.2%, 22.7%, 15.2% and 30.2% respectively.

[0153] 2. Preparation of lithium secondary battery

[0154] The present embodiment is basically identical with example 5, except that the electrolyte in step 3) is replaced by the electrolyte prepared in the present embodiment.

[0155] Example 9

[0156] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0157] 1. Preparation of electrolyte

[0158] The present embodiment is basically identical with example 5, except that the mass percentage of additive F is replaced by 10%, and the mass percentage of EC, DEC, PC and PP is adjusted to 8%, 20.5%, 13% and 28% respectively.

[0159] 2. Preparation of lithium secondary battery

[0160] The present embodiment is basically identical with example 5, except that the electrolyte in step 3) is replaced by the electrolyte prepared in the present embodiment.

[0161] Example 10

[0162] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0163] 1. Preparation of electrolyte

[0164] The present embodiment is basically identical with example 5, except that the mass percentage of additive F is replaced by 0.5%, and the mass percentage of EC, DEC, PC and PP is adjusted to 10.1%, 22.7%, 15.1% and 30.1% respectively.

[0165] 2. Preparation of lithium secondary battery

[0166] The present embodiment is basically identical with example 5, except that the electrolyte in step 3) is replaced by the electrolyte prepared in the present embodiment.

[0167] Example 11

[0168] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0169] 1. Preparation of electrolyte

[0170] The preparation steps of the present embodiment are basically the same as those of Example 5, except that the mass percentage of additive F is replaced by 5%, and the mass percentages of EC, DEC, PC and PP are adjusted to 9%, 22.5%, 14% and 29% respectively.

[0171] 2. Preparation of lithium secondary battery

[0172] The preparation steps of the present embodiment are basically the same as those of Example 5, except that the electrolyte in step 3) is replaced by the electrolyte prepared in the present embodiment.

[0173] Example 12

[0174] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0175] 1. Preparation of electrolyte

[0176] 1) Preparation of additive C: referring to the preparation method of additive B listed above, except that the raw material inositol is replaced by (CAS No. 1112963-22-0).

[0177] The hydrogen spectrum data of additive C is 1 H NMR (400 MHz, DMSO-d6): δ 0.89 (d, J = 6.4 Hz, 3H), 3.74-3.75 (t, J = 7.6 Hz, 8H), 3.43 (m, 2H), 2.00 (m, 1H), 3.72 (m, 2H), 2.58-2.59 (t, J = 7.3 Hz, 8H).

[0178] 2) The preparation steps of the present embodiment are basically the same as those of Example 1, except that additive A is replaced by additive C.

[0179] 2. Preparation of lithium secondary battery

[0180] The preparation steps of the present embodiment are basically the same as those of Example 1, except that the electrolyte in step 3) is replaced by the electrolyte prepared in the present embodiment.

[0181] Example 13

[0182] The present embodiment provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0183] 1. Preparation of electrolyte

[0184] 1) Preparation of Additive G: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced by (CAS No.: 4096-52-0).

[0185] The hydrogen spectrum data of Additive G is 1 H NMR (400 MHz, DMSO-d6): δ 2.96 (dd, J = 4.6 Hz, 1H), 2.80 (dd, J = 4.7 Hz, 1H), 3.75-3.76 (t, J = 7.8 Hz, 8H), 3.35 (m, 2H), 4.71 (m, 1H), 3.76 (m, 2H), 2.57-2.59 (t, J = 7.1 Hz, 8H).

[0186] 2) Basically the same as Step 2) of Example 1, except that Additive A is replaced by Additive G.

[0187] 2, Preparation of lithium secondary battery

[0188] Basically the same as the preparation steps of Example 1, except that the electrolyte in Step 3) is replaced by the electrolyte prepared in this example.

[0189] Example 14

[0190] This example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0191] 1, Preparation of electrolyte

[0192] 1) Preparation of Additive H: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced by (CAS No.: 29782-84-1).

[0193] The hydrogen spectrum data of Additive H is 1 H NMR (400 MHz, DMSO-d6): δ 4.23 (dd, J = 5.2 Hz, 1H), 4.41 (dd, J = 5.0 Hz, 2H), 3.72-3.76 (t, J = 7.4 Hz, 6H), 5.91-5.92 (dd, J = 5.1 Hz, 2H), 2.57-2.61 (t, J = 7.2 Hz, 6H).

[0194] 2) Basically the same as Step 2) of Example 1, except that Additive A is replaced by Additive H.

[0195] 2, Preparation of lithium secondary battery

[0196] The preparation procedure of Example 1 was basically followed except that the electrolyte in step 3) was replaced with the electrolyte prepared in this example.

[0197] Example 15

[0198] This example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0199] 1. Preparation of electrolyte

[0200] 1) Preparation of additive K: the preparation method of additive B listed above was followed except that the raw material acrylonitrile was replaced with methacrylonitrile.

[0201] The hydrogen spectrum data of additive K is 1 H NMR (400 MHz, DMSO-d6): δ 1.33-1.34 (d, J = 8.2 Hz, 18H), 3.75-3.79 (m, 6H), 3.51-3.62 (d, J = 6.6 Hz, 12H), 2.84-2.87 (dd, J = 7.9 Hz, 6H).

[0202] 2) The procedure of step 2) of Example 1 was basically followed except that additive A was replaced with additive K.

[0203] 2. Preparation of lithium secondary battery

[0204] The preparation procedure of Example 1 was basically followed except that the electrolyte in step 3) was replaced with the electrolyte prepared in this example.

[0205] Example 16

[0206] This example provides an electrolyte and a lithium secondary battery, and the preparation method is as follows:

[0207] 1. Preparation of electrolyte

[0208] 1) Preparation of additive M: the preparation method of additive B was followed except that the raw material acrylonitrile was replaced with propynyl cyanide.

[0209] The hydrogen spectrum data of additive M is 1 H NMR (400 MHz, DMSO-d6): δ 7.10-7.14 (d, J = 7.0 Hz, 6H), 4.33-4.38 (d, J = 6.8 Hz, 6H), 4.00-4.05 (dd, J = 5.7 Hz, 6H).

[0210] 2) The procedure of step 2) of Example 1 was basically followed except that additive A was replaced with additive M.

[0211] 2. Preparation of a lithium secondary battery

[0212] The preparation steps are substantially identical to those of Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0213] Example 17

[0214] This example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0215] 1. Preparation of an electrolyte

[0216] 1) Preparation of additive N: referring to the preparation method of additive B listed above, except that the raw material acrylonitrile is replaced with 4-vinylbenzonitrile.

[0217] The hydrogen spectrum data of additive N is 1 H NMR (400 MHz, DMSO-d6): δ 3.67-3.69 (dd, J = 6.3 Hz, 6H), 3.52-3.59 (t, J = 7.2 Hz, 12H), 2.58-2.62 (t, J = 8.5 Hz, 12H), 7.81-7.85 (d, J = 9.5 Hz, 12H), 7.41-7.50 (d, J = 9.8 Hz, 12H).

[0218] 2) Substantially identical to step 2) of Example 1, except that additive A is replaced with additive N.

[0219] 2. Preparation of a lithium secondary battery

[0220] The preparation steps are substantially identical to those of Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0221] Comparative Example 1

[0222] This example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0223] 1. Preparation of an electrolyte

[0224] Substantially identical to Example 1, except that additive A is replaced with butanedinitrile.

[0225] The structure of butanedinitrile is as follows:

[0226] 2. Preparation of a lithium secondary battery

[0227] The electrolyte in step 3) was replaced with the electrolyte prepared in this comparative example.

[0228] Comparative Example 2

[0229] This comparative example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0230] 1. Preparation of electrolyte

[0231] The additive A was replaced with 1,3,6-hexanetricarbonitrile, except that the other conditions were the same as in Example 1.

[0232] The structure of 1,3,6-hexanetricarbonitrile is as follows:

[0233] 2. Preparation of lithium ion battery

[0234] The electrolyte in step 3) was replaced with the electrolyte prepared in this comparative example, except that the other conditions were the same as in Example 1.

[0235] Comparative Example 3

[0236] This comparative example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0237] 1. Preparation of electrolyte

[0238] The additive A was replaced with 1,2-bis(2-cyanoethoxy)ethane, except that the other conditions were the same as in Example 1.

[0239] The structure of 1,2-bis(2-cyanoethoxy)ethane is as follows:

[0240] 2. Preparation of lithium ion battery

[0241] The electrolyte in step 3) was replaced with the electrolyte prepared in this comparative example, except that the other conditions were the same as in Example 1.

[0242] Comparative Example 4

[0243] This comparative example provides an electrolyte and a lithium secondary battery, which are prepared as follows:

[0244] 1. Preparation of electrolyte

[0245] The additive A was replaced with additive L, except that the other conditions were the same as in Example 1.

[0246] The structure of additive L is as follows:

[0247] 2. Preparation of lithium ion battery

[0248] The preparation method of the lithium secondary battery of the present example is as follows:

[0249] Comparative Example 5

[0250] The preparation method of the lithium secondary battery of the present example is as follows:

[0251] 1. Preparation of electrolyte

[0252] The preparation method of the lithium secondary battery of the present example is as follows:

[0253] The structure of the additive J is as follows:

[0254] 2. Preparation of lithium ion battery

[0255] The preparation method of the lithium secondary battery of the present example is as follows:

[0256] Comparative Example 6

[0257] The preparation method of the lithium secondary battery of the present example is as follows:

[0258] 1. Preparation of electrolyte

[0259] The preparation method of the lithium secondary battery of the present example is as follows:

[0260] 2. Preparation of lithium ion battery

[0261] The preparation method of the lithium secondary battery of the present example is as follows:

[0262] Test Example

[0263] The lithium secondary batteries prepared in the above examples and comparative examples were tested for the following performances:

[0264] 1. 25°C cycle performance

[0265] Test method: at 25±3°C, the lithium secondary battery was charged at a current of 1.0C to 4.6V, then charged at a constant voltage until the current decreased to 0.025C, and then rested for 5 min, then discharged at a current of 1.0C to 3.0V, and this cycle was repeated for 300 times, the discharge capacity of the 1st cycle and the 300th cycle was recorded, and the capacity retention rate of the battery after 300 cycles at room temperature was calculated according to the following formula, and the results were recorded in Table 1.

[0266] Capacity retention rate (%) = discharge capacity of the 300th cycle / discharge capacity of the 1st cycle x 100%.

[0267] The capacity retention rate curves of the cycle capacity of Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 6 were plotted according to the data recorded in the above test process, and Figure 2 is a comparison of the capacity retention rate of Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 6 after 300 cycles, as shown in Figure 2, the group without any nitrile additive (Comparative Example 6) has the worst cycle performance; the group with traditional commercial nitrile additives (Comparative Examples 1-3) has a greater improvement in cycle performance; and the group with the newly designed additive (Example 2) has a further improvement in cycle performance, which is significantly different from the comparative examples.

[0268] 2, 60°C storage performance

[0269] Test method: at 25±3°C, the lithium secondary battery was charged to 4.6V at a current of 0.2C, then charged to a current of 0.025C, then placed for 5min, then discharged to 3.0V at a current of 0.5C, and the capacity was recorded as the initial capacity. The battery was then fully charged in the same way, and then the fully charged battery was placed in a constant temperature oven at 60°C for 7 days, then placed at room temperature for 2 hours, then discharged to a cut-off voltage of 3.0V at a constant current of 0.5C, and the capacity was recorded as the remaining capacity. The capacity retention rate of the battery after 7 days of storage at 60°C was calculated according to the following formula, and the results are recorded in Table 1.

[0270] Capacity retention rate (%) = remaining capacity / initial capacity x 100%.

[0271] 3, low temperature cycle performance

[0272] Test method: at 12±3°C, the lithium secondary battery was charged to 4.6V at a current of 1.0C, then charged to a current of 0.025C, then placed for 5min, then discharged to 3.0V at a current of 1.0C, and this cycle was repeated 300 times, and the discharge capacity of the 1st and 300th cycles was recorded. The capacity retention rate of the battery after 300 cycles at room temperature was calculated according to the following formula, and the results are recorded in Table 1.

[0273] Capacity retention rate (%) = discharge capacity of the 300th cycle / discharge capacity of the 1st cycle x 100%.

[0274] For convenience of comparison, the types and contents of the multi-nitrile additives used in the above examples and comparative examples are also listed in Table 1.

[0275] Table 1

[0276] From Table 1, the following conclusions can be drawn:

[0277] 1. The lithium ion batteries in Examples 1-5 and 12-14 have higher 25°C cycle capacity retention (83.9%-86.1%), 60°C storage capacity retention (87.9%-91.3%), and low-temperature cycle capacity retention (83.2%-86.1%) than Comparative Examples 1-2, which indicates the necessity of the ether group main chain and cyclic structure in the electrolyte additive structure of the present application. The additive molecules in Examples 1-5 and 12-14 all contain ether bonds, which are conducive to maintaining the high electrical conductivity and low viscosity of the electrolyte and improving the wide-temperature-range cycle performance of the battery. The additive molecules in Comparative Examples 1-2 have multiple chelating cyan groups, but do not contain ether group main chains and cyclic structures, so the electrolyte prepared therefrom has lower electrical conductivity, higher viscosity, and poorer wide-temperature-range cycle performance and high-temperature storage performance.

[0278] 2. The lithium ion batteries in Examples 1-5 and 12-14 have higher 25°C cycle capacity retention (83.9%-86.1%), 60°C storage capacity retention (87.9%-91.3%), and low-temperature cycle capacity retention (83.2%-86.1%) than Comparative Example 4, which indicates the necessity of the multiple chelating cyan groups in the electrolyte additive structure of the present application. The additive molecules in Examples 1-5 and 12-14 all have three or more cyan ligands, which increases the number and density of effective functional groups in the molecules. Cyan groups can preferentially complex with transition metal ions at the positive electrode interface, inhibit the dissolution of transition metal ions, reduce the side reactions between the electrolyte and the positive electrode material, inhibit the further oxidative decomposition of the electrolyte, and improve the high-voltage stability of the electrolyte. The additive molecules in Comparative Example 4 have the common structural feature of "cyclic structure + ether group main chain", but do not meet the "multiple chelating cyan groups" characteristic, so there are fewer coordination sites at the positive electrode interface, and the positive electrode interface protection film cannot be effectively formed, which results in poorer wide-temperature-range cycle performance and high-temperature storage performance under high-voltage conditions.

[0279] 3. The lithium ion batteries in Examples 1-5, 12-14 of the present application have higher 25℃ cycle capacity retention rate (83.9%-86.1%), 60℃ storage capacity retention rate (87.9%-91.3%) and low-temperature cycle capacity retention rate (83.2%-86.1%) than Comparative Example 5, which indicates the necessity of the cyclic structure in the electrolyte additive structure of the present application. The additive molecules in Examples 1-5, 12-14 all have cyclic structures, which on the one hand can increase intermolecular motion (cyclic structures can more easily slide between molecules than linear structures), thereby reducing the freezing point and viscosity of such additives and improving the low-temperature cycle performance of the battery; on the other hand can inhibit intramolecular motion (cyclic structures increase the rigidity of the molecule and limit the stretching and motion of the molecular chain), thereby improving the coordination ability of the cyano group at the positive electrode interface and improving the high-voltage performance of the battery. The additive molecule of Comparative Example 5 has the common structural feature of “polydentate cyano group + ether group backbone” compared with Examples 1-5, 12-14, but does not meet the “cyclic structure” feature, so the coordination ability at the positive electrode interface is weaker and cannot effectively form a positive electrode interface protection film, and its wide-temperature-range cycle performance and high-temperature storage performance under high-voltage conditions are poorer.

[0280] 4. The lithium ion batteries in Examples 5, 8, 9, 10, 11 of the present application have higher 25℃ cycle capacity retention rate (67.1%-83.9%), 60℃ storage capacity retention rate (74.2%-91.3%) and low-temperature cycle capacity retention rate (63.7%-83.4%) than Comparative Example 6, which indicates that the addition of the electrolyte additive of the present application can effectively improve the wide-temperature-range cycle performance and high-temperature storage performance of the battery under high voltage, and the wide-temperature-range cycle performance and 60℃ storage capacity retention rate of the lithium ion batteries of Examples 5, 10, 11 are superior to Examples 8 and 9, which indicates that the concentration of the electrolyte additive of the present application is more preferably 0.5%-5%. If the amount of addition is too small, the effective functional group concentration is too small and cannot effectively complex transition metals to form a positive electrode interface protection film (CEI); if the amount of addition is too large, the electrolyte conductivity decreases, the battery impedance increases, and the interface film thickens, thereby leading to a decrease in battery performance.

[0281] 5. The lithium ion batteries in Examples 6-7 of the present application have higher 25℃ cycle capacity retention rate (84.9%-85.8%), 60℃ storage capacity retention rate (88.4%-89.2%) and low-temperature cycle capacity retention rate (82.6%-83.8%) than Comparative Examples 1-5, and are on par with Examples 1-5, which indicates that the electrolyte additives of the present application have high compatibility between types, and the cycle performance and high-temperature storage performance of the battery can still be significantly improved after mixed use of multiple components. Each single component contains the structural features of “polydentate cyano group + ether group backbone + cyclic structure”.

[0282] 6. The lithium ion batteries in Examples 15-17 have higher 25℃ cycle capacity retention (85.4%-86.7%), 60℃ storage capacity retention (87.1%-89.6%) and low temperature cycle capacity retention (84.5%-85.6%) than Comparative Example 6, and comparable performance to Examples 1-5, which indicates that the ether-based main chain structure has higher compatibility, and can be changed to different lengths of carbon chains, or to an alkenylene oxygen group, an aryloxy group, and still exhibit good wide temperature range cycle performance and high temperature storage performance.

[0283] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the embodiments of the present application, but not to limit them; although the embodiments of the present application have been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An electrolyte additive characterized in that, The electrolyte additive has a structure shown in Formula I: In formula I, R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of alkylenoxynitrile, substituted alkylenoxynitrile, alkenylenoxynitrile, substituted alkenylenoxynitrile, arylenoxynitrile, substituted arylenoxynitrile, hydrogen atom, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy, and at least three of R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of alkylenoxynitrile, substituted alkylenoxynitrile, alkenylenoxynitrile, substituted alkenylenoxynitrile, arylenoxynitrile, substituted arylenoxynitrile; X is selected from any one of oxygen atom, sulfur atom, alkylene, substituted alkylene, imino, substituted imino, alkenylene, substituted alkenylene; j is selected from an integer between 1 and 3, and k is selected from an integer between 0 and 3.

2. The electrolyte additive according to claim 1, characterized in that, The number of carbon atoms in the alkylenoxynitrile and the substituted alkylenoxynitrile is 2-10; and / or, the number of carbon atoms in the alkenylenoxynitrile and the substituted alkenylenoxynitrile is 3-10; and / or, the number of carbon atoms in the arylenoxynitrile and the substituted arylenoxynitrile is 4-20.

3. The electrolyte additive according to claim 2, characterized in that, The number of carbon atoms in the alkylenoxynitrile and the substituted alkylenoxynitrile is 2-6; and / or, the number of carbon atoms in the alkenylenoxynitrile and the substituted alkenylenoxynitrile is 3-6; and / or, the number of carbon atoms in the arylenoxynitrile and the substituted arylenoxynitrile is 4-10.

4. The electrolyte additive according to any one of claims 1 to 3, characterized in that The substituents in the substituted alkylenoxynitrile, the substituted alkenylenoxynitrile, the substituted arylenoxynitrile, the substituted alkylene, the substituted imino and the substituted alkenylene are each independently selected from one or more of halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy.

5. The electrolyte additive according to any one of claims 1 to 4, characterized in that, The number of carbon atoms in the alkyl, the haloalkyl, the alkoxy, the haloalkoxy is 1-20; and / or, the number of carbon atoms in the alkenyl, the haloalkenyl, the alkynyl, the haloalkynyl, the alkenyloxy, the haloalkenyloxy is 2-20; and / or, the number of carbon atoms in the aryl, the haloaryl, the aryloxy, the haloaryloxy is 3-20.

6. The electrolyte additive according to any one of claims 1 to 5, characterized in that At least three of R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from any one of ethylenoxynitrile, ethenylenoxynitrile, ethylenoxynitrile.

7. The electrolyte additive according to claim 6, characterized in that X is selected from any one of oxygen atom, sulfur atom, imino, methylene, alkyl-substituted methylene, haloalkyl-substituted methylene.

8. The electrolyte additive according to any one of claims 1 to 7, characterized in that, The electrolyte additive includes one or more of the following compounds:

9. An electrolyte comprising an organic solvent, an electrolyte salt and an additive, characterized in that, The additive comprises an electrolyte additive having a structure shown in formula I according to any one of claims 1-8.

10. The electrolyte of claim 9, wherein, The mass percentage of the electrolyte additive having a structure shown in formula I in the electrolyte is 0.05%-10%.

11. The electrolyte of claim 10, wherein, The mass percentage of the electrolyte additive having a structure shown in formula I in the electrolyte is 0.5%-5%.

12. The electrolyte according to any one of claims 9 to 11, characterized in that, The additive further includes one or more of biphenyl, fluorobenzene, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, bis-fluoroethylene carbonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, methylene methane disulfonate, dimethyl sulfate, dimethyl sulfite, diethyl sulfite, diethyl sulfate, 4-methyl ethylene sulfite, butanedinitrile, pentanedinitrile, hexanedinitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetricarbonitrile.

13. The electrolyte according to any one of claims 9 to 12, characterized in that, The organic solvent includes one or more of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and ether solvents.

14. The electrolyte according to any one of claims 9 to 13, characterized in that, The electrolyte salt includes one or more of lithium salts, sodium salts, potassium salts, magnesium salts, zinc salts, and aluminum salts.

15. The electrolyte of claim 14, wherein, The electrolyte salt includes one or more of MCI04, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C204)2, MBF2C204, M[(CF3SO2)2N], M[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], M[(FSO2)2N], wherein M is Li, Na or K, and m and n are natural numbers.

16. The electrolyte according to any one of claims 9 to 15, characterized in that, The molar concentration of the electrolyte salt in the electrolyte is 0.01 mol / L to 5.0 mol / L.

17. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized by The electrolyte is the electrolyte of any one of claims 9-16.

18. A terminal device comprising a housing and electronic components and a secondary battery housed in the housing, characterized by The secondary battery includes the secondary battery of claim 17.

Images