Electrolyte additive, electrolyte, secondary battery, and terminal device

Abstract

The invention provides an electrolyte additive, an electrolyte, a secondary battery and terminal equipment. The electrolyte additive provided by the invention is a multi-tooth cyclic multi-nitrile additive with an ether main chain obtained through a special molecular design, and the additive can endow the electrolyte with the advantages of high voltage resistance and wide temperature range, and can endow the battery with excellent cycle performance and high and low temperature performance at high voltage.

Description

Technical Field

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

[0002] With the rapid expansion of the electronic devices, power, and energy storage markets, consumers' demands for the extended range of rechargeable batteries are increasing, making the improvement of battery energy density and operating voltage a key research focus. In rechargeable batteries, the composition of the electrolyte plays a crucial role in the battery's cycle performance, fast-charging performance, and wide-temperature range performance. However, when rechargeable batteries use high-voltage cathode materials (such as lithium cobalt oxide) or high-capacity anode materials (such as silicon-based materials or lithium metal), problems such as accelerated electrolyte consumption and severe transition metal dissolution often occur. This not only reduces the battery's cycle stability and high-temperature performance but also increases safety hazards, thus severely limiting the battery's use at high voltages.

[0003] Therefore, developing a high-voltage resistant electrolyte system to meet the needs of batteries in high-voltage applications is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application provides an electrolyte additive, an electrolyte, a secondary battery, and a terminal device. The electrolyte additive of this application is a multidentate cyclic polynitrile additive with an ether-based backbone obtained through special molecular design. This additive enables the electrolyte to have the advantages of high voltage resistance and wide temperature range, thereby enabling the battery to have excellent cycle performance and high and low temperature performance under high voltage.

[0005] The first aspect of this application is an electrolyte additive, said electrolyte additive having the structure shown in Formula I:

[0006]

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

[0008] X is selected from any one of oxygen atom, sulfur atom, alkylene group, substituted alkylene group, imino group, substituted imino group, alkenyl group, and substituted alkenyl group;

[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 multidentate cyclic polynitrile additive with an ether-based backbone. The multidentate structure is characterized by having at least three cyano groups in R1 to R8. This multidentate design effectively increases the number and density of cyano functional groups within the molecule. The cyano groups preferentially complex with transition metal ions in the positive electrode active material, inhibiting the dissolution of transition metal ions, reducing side reactions between the electrolyte and the positive electrode active material, suppressing further oxidative decomposition of the electrolyte, and improving the stability of the electrolyte at high voltages. The ether-based backbone refers to the cyano groups being substituted or unsubstituted with alkeneoxy groups. The compound contains at least three ether bonds, including nitrile, olefinic nitrile, and aryloxynitrile, linked to the parent ring. This enables the electrolyte to exhibit high conductivity and low viscosity, improving the battery's wide-temperature performance. Furthermore, the additive's main molecular structure is cyclic. Cyclic structures enhance molecular rigidity, restrict chain extension and movement, and inhibit intramolecular motion, thereby improving the coordination ability of the cyano group at the cathode interface and further enhancing the battery's high-voltage performance. Compared to linear structures, cyclic structures facilitate intermolecular sliding, lowering the freezing point and further improving the battery's wide-temperature performance. In summary, the electrolyte additive of Formula I obtained through special molecular structure design in this application enables the electrolyte to possess the advantages of high voltage resistance and a wide temperature range, thus allowing the battery to exhibit excellent cycle performance and high / low temperature performance at high voltages.

[0011] In the electrolyte additives described above, the number of carbon atoms in the alkoxide nitrile and the substituted alkoxide nitrile is 2 to 10; and / or, the number of carbon atoms in the olefin nitrile and the substituted olefin nitrile is 3 to 10; and / or, the number of carbon atoms in the aryloxynitrile and the substituted aryloxynitrile is 4 to 20. If the number of carbon atoms is too long, the molecular size will be too large, which is detrimental to the solubility of the electrolyte additive in the solvent and also negatively impacts the conductivity of the electrolyte. By controlling the number of carbon atoms in the substituted or unsubstituted alkoxide nitrile, the substituted or unsubstituted olefin nitrile, and the substituted or unsubstituted aryloxynitrile within the above range, it is beneficial to maintain good solubility of the electrolyte additive and good conductivity of the electrolyte.

[0012] In the electrolyte additive described above, the number of carbon atoms in the alkoxide nitrile and the substituted alkoxide nitrile is 2 to 6; and / or, the number of carbon atoms in the olefin nitrile and the substituted olefin nitrile is 3 to 6; and / or, the number of carbon atoms in the aryloxide nitrile and the substituted aryloxide nitrile is 4 to 10. Within these carbon number ranges, the solubility and conductivity of the electrolyte additive will be further improved.

[0013] In the electrolyte additive described above, the substituents in the substituted alkoxynitrile, substituted enyloxynitrile, substituted aryloxynitrile, substituted alkylene, substituted imine, and substituted alkenyl groups are each independently selected from one or more of halogens, alkyl groups, haloalkyl groups, alkoxy groups, haloalkoxy groups, alkenyl groups, haloalkenyl groups, alkynyl groups, haloalkynyl groups, alkenyloxy groups, haloalkenyloxy groups, aryl groups, haloaryl groups, aryloxy groups, and haloaryloxy groups. By selecting the above substituents, the film-forming reactivity of the electrolyte additive can be controlled, which is beneficial for optimizing interfacial film formation. Furthermore, none of the above substituents contain active hydrogen, so they will not undergo side reactions with other substances in the electrolyte.

[0014] In the electrolyte additive described above, the alkyl group, the haloalkyl group, the alkoxy group, and the haloalkoxy group have 1 to 20 carbon atoms; and / or, the alkenyl group, the haloalkenyl group, the alkynyl group, the haloalkynyl group, the alkenoxy group, and the haloalkenoxy group have 2 to 20 carbon atoms; and / or, the aryl group, the haloaryl group, the aryloxy group, and the haloaryloxy group have 3 to 20 carbon atoms. Within these carbon number ranges, it is beneficial for the synthesis and preparation of the corresponding groups, and it also allows the groups shown in Formula I to have suitable carbon chain lengths, giving the compounds with the structure shown in Formula I suitable viscosity, flexibility, and rigidity.

[0015] In the electrolyte additive described above, at least three of R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from any one of ethoxynitrile, vinyloxynitrile, and ethoxybenzonitrile. These groups are not only easy to prepare using existing synthetic processes, but also possess suitable carbon chain lengths and oxygen atom content, which can further improve the conductivity of the electrolyte and reduce its viscosity.

[0016] In the electrolyte additive described above, X is selected from any one of oxygen atoms, sulfur atoms, imine groups, methylene groups, alkyl-substituted methylene groups, and haloalkyl-substituted methylene groups. When X is selected from the above groups, the solubility of the electrolyte additive can be further optimized, the molecule can have better flexibility, and the chelating ability of the cyano group with the transition metal ions dissolved in the positive electrode active material can be further enhanced.

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

[0018]

[0019] Experimental studies have shown that when the electrolyte additive includes one or more of the above compounds, the battery can exhibit superior cycle performance and high and low temperature performance under high voltage.

[0020] A second aspect of this application provides an electrolyte comprising an organic solvent, an electrolyte salt, and an additive, wherein the additive includes the electrolyte additive having the structure shown in Formula I provided in the first aspect of this application. Because it includes the electrolyte additive having the structure shown in Formula I, the electrolyte of this application has the advantages of high voltage resistance and a wide temperature range, making it suitable for high-voltage battery systems.

[0021] In the electrolyte as described above, the electrolyte additive having the structure shown in Formula I has a mass percentage content of 0.05% to 10% in the electrolyte.

[0022] In the electrolyte described above, the electrolyte additive having the structure shown in Formula I has a mass percentage content of 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. When the content is too high, the electrolyte viscosity is too high, the conductivity is too low, and lithium dendrites are easily generated, thereby inducing interfacial side reactions and internal short circuits, resulting in a decrease in cycle performance and storage performance. When the mass content of the electrolyte additive with the structure shown in Formula I is in the range of 0.05% to 10%, especially in the range of 0.5% to 5%, the electrolyte exhibits superior high-voltage resistance, cycle performance, and storage performance.

[0023] The electrolyte described above, wherein the additives further include one or more of the following: biphenyl, fluorobenzene, vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methanedisulfonate, dimethyl sulfate, dimethyl sulfite, diethyl sulfite, diethyl sulfate, 4-methylethylene sulfate, succinic acid, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrionitrile. These additives are all conventionally used in electrolytes for positive or negative electrode film formation, and can further protect the positive and negative electrode interfaces, improving the stability of the electrolyte under high voltage.

[0024] The electrolyte described above, wherein the organic solvent includes one or more of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and ether solvents. Cyclic carbonate solvents have high dielectric constants but high viscosity, while linear carbonate solvents have low dielectric constants but low viscosity; both exhibit good electrochemical stability and high oxidation potential, and good compatibility with carbon anode materials. Compared to carbonate solvents, carboxylic acid ester solvents have lower freezing points and viscosity, which is beneficial for improving the low-temperature performance of the electrolyte. Ether solvents typically have lower viscosity and higher conductivity, which can improve the conductivity of the electrolyte. However, ether solvents have relatively low dielectric constants and weaker dissolving ability for lithium salts, and usually need to be mixed with other solvents during use. In summary, the organic solvent in the electrolyte needs to have both a high dielectric constant and low viscosity, effectively dissolving lithium salts and promoting lithium-ion transport. In practical applications, the above-mentioned solvents can be selected individually or in combination to meet specific requirements.

[0025] The electrolyte described above, wherein 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 invention exhibits good solubility properties for electrolyte salts such as lithium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt, and is accordingly suitable for applications in lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, magnesium secondary batteries, zinc secondary batteries, and aluminum secondary batteries.

[0026] The electrolyte as described above, wherein the electrolyte salts include 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+1 One 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] This application provides an electrolyte additive having the structure shown in Formula I. It is a multidentate cyclic polynitrile additive with an ether-based backbone. The multidentate design effectively increases the number and density of cyano functional groups within the molecule, enabling it to effectively complex transition metal ions in the positive electrode active material, inhibiting their dissolution, and reducing side reactions between the electrolyte and the positive electrode active material, thereby giving the electrolyte excellent high-voltage stability. Its ether-based backbone helps to improve the conductivity of the electrolyte and reduce its viscosity, improving the battery's wide-temperature performance and giving it excellent high and low temperature performance. Its cyclic molecular structure, on the one hand, can improve molecular rigidity and restrict the extension movement of molecular chains, which is beneficial to improving the coordination ability of cyano groups at the positive electrode interface. This, combined with the multidentate feature, further improves the battery's high-voltage performance. On the other hand, it facilitates intermolecular sliding, thereby lowering the molecular freezing point, and, together with the ether-based backbone, further improves the battery's wide-temperature characteristics. In summary, the electrolyte additive shown in Formula I obtained by special design of the molecular structure in this application enables the electrolyte to have the advantages of high voltage resistance and wide temperature range, thereby enabling the battery to have excellent cycle performance and high and low temperature performance under high voltage. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a secondary battery structure according to an embodiment of this application;

[0032] Figure 2 This is a comparison chart of the capacity retention rates of Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 6 after 300 cycles.

[0033] Explanation of reference numerals in the attached figures:

[0034] 10 - Positive electrode; 101 - Positive electrode current collector; 102 - Positive electrode active material;

[0035] 20 - Negative electrode; 201 - Negative electrode current collector; 202 - Negative electrode active material;

[0036] 30-Diaphragm;

[0037] 40 - Electrolyte. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] Figure 1 This is a schematic diagram of a secondary battery structure according to an embodiment of this application, as shown below. Figure 1 As shown, the secondary battery mainly includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40. The positive electrode 10 includes a positive current collector 101 and a positive active material 102 located on the surface of the positive current collector 101. The negative electrode 20 includes a negative current collector 201 and a negative active material 202 located on the surface of the negative current collector 201. Taking this battery as a lithium-ion battery as an example, when the battery is charging, lithium ions are extracted from the crystal lattice of the positive active material 102, transported through the electrolyte 40, and deposited into the negative electrode 20 through the separator 30. When the battery is discharging, lithium ions are extracted from the negative electrode 20, transported through the electrolyte 40, and inserted into the crystal lattice of the positive active material 102 through the separator.

[0040] During charging and discharging at high voltages, transition metals in the positive electrode active material of the battery easily dissolve into the electrolyte, causing side reactions. Simultaneously, the oxidation and precipitation of lattice oxygen introduces these substances, leading to structural instability in the positive electrode active material and making it prone to unfavorable phase transitions. Furthermore, the electrolyte is more prone to decomposition under high voltage, exacerbating interfacial side reactions with the positive electrode active material, further accelerating the dissolution of transition metals and structural damage to the positive electrode active material. The combined effect of these factors limits the application of batteries at high voltages, especially traditional electrolyte systems, which struggle to meet the requirements for battery use at ≥4.60V.

[0041] Based on this, the first aspect of this application provides an electrolyte additive having the structure shown in Formula I:

[0042]

[0043] In Formula I, R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from any one of alkoxide nitrile, substituted alkoxide nitrile, substituted enyloxy nitrile, substituted enyloxy nitrile, aryloxy nitrile, substituted aryloxy nitrile, hydrogen atom, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, and haloaryloxy, and at least three of R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from any one of alkoxide nitrile, substituted alkoxide nitrile, substituted enyloxy nitrile, substituted aryloxy nitrile, and substituted aryloxy nitrile;

[0044] X is selected from any one of oxygen atom, sulfur atom, alkylene group, substituted alkylene group, imino group, substituted imino group, alkenyl group, substituted alkenyl group, and alkyne group;

[0045] j is selected from an integer between 1 and 3, and k is selected from an integer between 0 and 3.

[0046] In this application, alkoxide nitrile, olefin nitrile, and aryloxy nitrile refer to the groups obtained by attaching one end of alkoxide, olefin, and aryloxy to a cyano group, respectively.

[0047] Halogens include fluorine, chlorine, bromine, or iodine.

[0048] Halogenation refers to the substitution of one or more hydrogen atoms in a group by a halogen. It can be either fully halogenated or partially halogenated.

[0049] Alkyloxynitrile, substituted alkyloxynitrile, alkenyloxynitrile, substituted alkenyloxynitrile, aryloxynitrile, substituted aryloxynitrile, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryl, alkylene, substituted alkylene, alkenyl, substituted alkenyl, and alkynyl can all have straight-chain or branched structures.

[0050] The compound having the structure shown in Formula I is a multidentate cyclic polynitrile additive with an ether-based backbone. The multidentate structure is characterized by having at least three cyano groups in R1 to R8. This multidentate design effectively increases the number and density of cyano functional groups within the molecule. The cyano groups preferentially complex with transition metal ions in the positive electrode active material, inhibiting the dissolution of transition metal ions, reducing side reactions between the electrolyte and the positive electrode active material, suppressing further oxidative decomposition of the electrolyte, and improving the stability of the electrolyte at high voltages. The ether-based backbone refers to the cyano groups being substituted or unsubstituted with alkeneoxy groups. The compound contains at least three ether bonds, including nitrile, olefinic nitrile, and aryloxynitrile, linked to the parent ring. This enables the electrolyte to exhibit high conductivity and low viscosity, improving the battery's wide-temperature performance. Furthermore, the additive's main molecular structure is cyclic. Cyclic structures enhance molecular rigidity, restrict chain extension and movement, and inhibit intramolecular motion, thereby improving the coordination ability of the cyano group at the cathode interface and further enhancing the battery's high-voltage performance. Compared to linear structures, cyclic structures facilitate intermolecular sliding, lowering the freezing point and further improving the battery's wide-temperature performance. In summary, the electrolyte additive of Formula I obtained through special molecular structure design in this application enables the electrolyte to possess the advantages of high voltage resistance and a wide temperature range, thus allowing the battery to exhibit excellent cycle performance and high / low temperature performance at high voltages.

[0051] In one specific embodiment, the number of carbon atoms in the alkoxide nitrile and the substituted alkoxide nitrile is 2 to 10, specifically 2, 3, 4, 5, 6, 7, 8, 9, 10, preferably 2 to 6; and / or, the number of carbon atoms in the alkoxide nitrile and the substituted alkoxide nitrile is 3 to 10, specifically 3, 4, 5, 6, 7, 8, 9, 10, preferably 3 to 6; and / or, the number of carbon atoms in the aryloxide nitrile and the substituted aryloxide nitrile is 4 to 20, specifically 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, preferably 4 to 10.

[0052] If the number of carbon atoms is too long and the molecular size is too large, it will hinder the solubility of electrolyte additives in the solvent and also negatively affect the conductivity of the electrolyte. By controlling the number of carbon atoms in substituted or unsubstituted alkoxynitriles, substituted or unsubstituted enoxynitriles, and substituted or unsubstituted aryloxynitriles within the above range, it is beneficial to maintain good solubility of electrolyte additives and good conductivity of the electrolyte.

[0053] For example, alkoxide nitrile can be ethoxide nitrile, propoxide nitrile, butoxide nitrile, etc.; olefin nitrile can be vinyloxide nitrile, propene oxynitrile, butene oxynitrile, etc.

[0054] In this application, the aromatic ring contained in aryloxynitrile, substituted aryloxynitrile, aryl, haloaryl, aryloxy, and substituted aryloxy can be an aromatic ring without heteroatoms, such as a benzene ring, naphthalene ring, or anthracene ring, or a heteroaromatic ring containing heteroatoms such as O, S, or N, such as a furan ring, thiophene ring, pyrrole ring, imidazole ring, pyridine ring, or indole ring.

[0055] Furthermore, the substituents in the substituted alkoxynitrile, substituted alkenoxynitrile, substituted aryloxynitrile, substituted alkylene, substituted imine, and substituted alkenyl groups are each independently selected from one or more of halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenoxy, haloalkenoxy, aryl, haloaryl, aryloxy, and haloaryloxy groups.

[0056] By selecting the above substituents, the film-forming reactivity of electrolyte additives can be controlled, which is beneficial to optimizing interfacial film formation. Furthermore, none of the above substituents contain active hydrogen, so they will not undergo side reactions with other substances in the electrolyte.

[0057] Furthermore, the alkyl, haloalkyl, alkoxy, and haloalkoxy groups in this application have 1 to 20 carbon atoms, specifically 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. For example, they 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, etc.

[0058] And / or, the number of carbon atoms of alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenyloxy, and haloalkenyloxy in this application is 2 to 20, specifically 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. For example, they can be vinyl, n-propenyl, isopropenyl, n-butenyl, isobutenyl, fluorovinyl, fluoropropenyl, fluorobutenyl, ethynyl, propynyl, fluoroethynyl, fluoropropynyl, ethyleneoxy, propenyloxy, fluoroethyleneoxy, fluoropropenyloxy, etc.

[0059] And / or, the number of carbon atoms of aryl, haloaryl, aryloxy, and haloaryloxy in this application is 3 to 20, specifically 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. For example, they can be imidazolyl, furanyl, thiophene, pyrrole, pyridyl, phenyl, anthracenel, naphthyl, phenoxy, furanoxy, fluorophenyl, etc.

[0060] Within the above carbon number range, it is not only beneficial to the synthesis and preparation of the corresponding groups, but also enables the groups shown in Formula I to have suitable carbon chain lengths, and enables the compounds with the structure shown in Formula I to have suitable viscosity, flexibility and rigidity.

[0061] In a preferred embodiment, at least three of R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from any one of ethoxynitrile, vinyloxynitrile, and ethoxybenzonitrile. These groups are not only easy to prepare using existing synthetic processes, but also have suitable carbon chain lengths and oxygen atom content, which can further improve the conductivity of the electrolyte and reduce its viscosity.

[0062] The structures of ethoxynitrile are shown in Formula a, ethoxynitrile in Formula b, and ethoxybenzonitrile in Formula c. In Formulas a, b, and c, "*" represents the bonding position.

[0063]

[0064] In a preferred embodiment, X is selected from any one of oxygen atoms, sulfur atoms, imine groups, methylene groups, alkyl-substituted methylene groups, and haloalkyl-substituted methylene groups. When X is selected from the above groups, the solubility of the electrolyte additive can be further optimized, the molecule can have better flexibility, and the chelating ability of the cyano group with the transition metal ions dissolved in the positive electrode active material can be further enhanced.

[0065] Research has shown that when electrolyte additives include one or more of the following compounds, the battery can exhibit superior cycle performance and high and low temperature performance at high voltages.

[0066]

[0067] This application does not impose any particular limitation on the preparation method of the electrolyte additive shown in Formula I. It can be obtained by reasonably designing based on the conventional preparation process of cyclic polynitrile compounds and the properties of different substituents.

[0068] For example, additives A through M can be prepared using the Michael addition reaction. Taking additive B as an example, it can be prepared by a method including the following steps (reaction formulas are shown below):

[0069]

[0070] 1) Dissolve 3.0 eq of inositol and 20.0 eq of acrylonitrile in deionized water to obtain the raw material system; 2) Dissolve 20.0 eq of sodium hydroxide in deionized water to form a saturated sodium hydroxide solution, and slowly add the saturated sodium hydroxide solution dropwise to the raw material system; 3) After the saturated sodium hydroxide is added, heat the reaction system to 60°C and react for at least 5 hours; 4) After the reaction is completed, cool to room temperature and add pure water to quench the reaction solution, neutralize to neutral with 0.1M dilute hydrochloric acid, and then add ethyl acetate for extraction. Wash the extract with sodium carbonate aqueous solution and saturated brine, dry in anhydrous sodium sulfate for at least 30 minutes, filter, evaporate the ethyl acetate in the filtrate, dry in a vacuum oven at 40°C overnight, and remove water by molecular sieve to obtain additive B.

[0071] A second aspect of this application provides an electrolyte comprising an organic solvent, an electrolyte salt, and an additive, wherein the additive comprises an electrolyte additive with the structure shown in Formula I provided in the first aspect of this application.

[0072] Because it includes electrolyte additives with the structure shown in Formula I, the electrolyte of this application has the advantages of high voltage resistance and wide temperature range, making it suitable for high-voltage battery systems.

[0073] In a preferred embodiment, the electrolyte additive having the structure shown in 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 shown in Formula I is too low, it is difficult to effectively improve the high voltage resistance of the electrolyte. When the content is too high, the electrolyte viscosity is too high, the conductivity is too low, and lithium dendrites are easily generated, thereby inducing interfacial side reactions and internal short circuits, which reduces cycle performance and storage performance.

[0074] For example, the mass percentage of the electrolyte additive having the structure shown in 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.

[0075] It is understood that the above-mentioned content values ​​may have a certain impact on material testing due to the formation of the interface film after battery formation, capacity testing, or cycling. A certain measurement and testing error is permissible. Values ​​within the error range can be understood as the range defined in this application. Alternatively, if the value range of material testing after actual battery formation, capacity testing, or cycling is still within the above-mentioned range, it can be understood as the range defined in this application.

[0076] In one specific embodiment, in addition to the electrolyte additive having the structure shown in Formula I, other additives may be added to the electrolyte according to different battery performance requirements. These other additives include, but are not limited to, one or more of the following: biphenyl (BP), fluorobenzene (FB), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), 1,4-butanesulfonate lactone (BS), vinyl sulfate (DTD), vinyl sulfite, methanedisulfonate (MMDS), dimethyl sulfate, dimethyl sulfite, diethyl sulfite, diethyl sulfate, 4-methyl ethylene sulfate, succinate (SN), glutaronitrile, adiponitrile (ADN), 1,2-bis(2-cyanoethoxy)ethane (DENE), and 1,3,6-hexanetrionitrile (HTCN). The above additives are all commonly used in electrolytes for positive or negative electrode film formation, which can further protect the positive and negative electrode interfaces and improve the stability of the electrolyte under high voltage. Specific selection can be made according to the different performance requirements of the battery.

[0077] In one specific embodiment, the organic solvent in the electrolyte includes one or more of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and ether solvents. Cyclic carbonate solvents have high dielectric constants but high viscosity, while linear carbonate solvents have low dielectric constants but low viscosity. Both exhibit good electrochemical stability and high oxidation potential, and are well-compatible with carbon anode materials. Compared to carbonate solvents, carboxylic acid ester solvents have lower freezing points and viscosity, which is beneficial for improving the low-temperature performance of the electrolyte. Ether solvents typically have lower viscosity and higher conductivity, which can improve the conductivity of the electrolyte. However, ether solvents have relatively low dielectric constants and weaker dissolving ability for lithium salts, so they usually need to be mixed with other solvents during use. In summary, the organic solvent in the electrolyte needs to have both a high dielectric constant and low viscosity to effectively dissolve lithium salts and promote lithium-ion transport. In practical applications, the above-mentioned solvents can be selected individually or in combination to meet specific requirements.

[0078] Specifically, cyclic carbonate solvents include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), and trifluoromethyl ethylene carbonate.

[0079] Linear carboxylic acid ester solvents include, but are not limited to, one or more of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), bis(2,2,2-trifluoroethyl) carbonate, and (2,2,2-trifluoroethyl)methyl carbonate.

[0080] Carboxylic acid ester solvents include, but are not limited to, one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate (PP), methyl difluoroacetate, and methyl trifluoroacetate.

[0081] Ether solvents include, but are 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.

[0082] In one 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 this invention exhibits good solubility for lithium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt, and is therefore suitable for applications in lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, magnesium secondary batteries, zinc secondary batteries, and aluminum secondary batteries.

[0083] Specifically, the electrolyte salts include MClO4, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C2O4)2, MBF2C2O4, M[(CF3SO2)2N], M[(FSO2)2N], M[(C m F 2m+1 SO2)(C n F 2n+1 One or more of [SO2)N], 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 availability.

[0084] Furthermore, the molar concentration of the electrolyte salt in the electrolyte solution is 0.01 mol / L to 5.0 mol / L, more preferably 0.8 mol / L to 1.5 mol / L. For example, 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 higher the concentration of the electrolyte in the electrolyte solution, 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 increase in conductivity to reach its upper limit or even show a decreasing trend. Within the above concentration range, the electrolyte salt can be fully dissolved while maintaining a high conductivity in the electrolyte solution.

[0085] In one specific embodiment, the electrolyte of this application can be prepared by the following method:

[0086] In an inert or closed environment, the fully dried electrolyte salt is dissolved in an organic solvent and mixed evenly to obtain a solution. Then, additives are added to the solution and mixed evenly to obtain the electrolyte.

[0087] A third aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte provided in the second aspect of this application.

[0088] Because the electrolyte provided in the second aspect of this application has the characteristics of high voltage resistance and wide temperature range, the secondary battery including the electrolyte has both excellent cycle performance and high and low temperature performance under high voltage.

[0089] The secondary battery in this 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.

[0090] The positive electrode of this application includes a positive current collector and a positive electrode material layer coated on one or both surfaces of the positive current collector. The positive electrode material layer includes a positive electrode active material. In addition to the positive electrode active material, the positive electrode material layer may also include a certain amount of binder, conductive agent and other components.

[0091] The positive current collector can be a metal foil, such as aluminum foil, gold foil, platinum foil, etc.

[0092] The positive electrode active material comprises one or more of the following: transition metal oxides such as lithium, sodium, potassium, magnesium, zinc, and aluminum; Prussian blue (white) compounds; and polyanionic compounds such as lithium, sodium, potassium, magnesium, zinc, and aluminum. Specifically, when the secondary battery is a lithium secondary battery, the positive electrode active material includes, but is not limited to, one or more of the following: lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium nickel manganese oxide.

[0093] 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 superconducting carbon black (Super-P), amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The above binders and conductive agents are for illustrative purposes only and are not specific limitations.

[0094] The negative electrode of this application includes a negative electrode current collector and a negative electrode material layer coated on one or both surfaces of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material. In addition to the negative electrode active material, the negative electrode material layer may also include a certain amount of binder, conductive agent and other components.

[0095] The negative electrode current collector can be a metal foil, such as copper foil, gold foil, platinum foil, etc.

[0096] The negative electrode active materials include one or more of the following: carbon-based materials, tin-based materials, silicon-based materials, phosphorus-based materials, lithium titanate, lithium metal and its alloys, sodium metal and its alloys, potassium metal and its alloys, magnesium metal and its alloys, zinc metal and its alloys, and aluminum metal and its alloys.

[0097] Specifically, carbon-based materials include one or more of graphite, hard carbon, soft carbon, graphene, and porous carbon; silicon-based materials include one or more of silicon, silicon-carbon, silicon-oxygen, and silicon metal compounds; tin-based materials include one or more of tin, tin-carbon, tin-oxygen, and tin metal compounds; phosphorus-based materials include one or more of red phosphorus, black phosphorus, and phosphorus compounds; and lithium alloys include one or more of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0098] The binder in the negative electrode 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 for illustrative purposes only and are not specific limitations.

[0099] The function of the separator is to isolate the positive and negative electrodes and block the passage of electrons while allowing ions to pass through. The separators in this application include, but are not limited to, single-layer polypropylene, single-layer polyethylene, double-layer polypropylene / polyethylene composite separators, double-layer polypropylene / polypropylene composite separators, triple-layer polypropylene / polyethylene / polypropylene composite separators, and polyethylene separators coated with ceramic coatings.

[0100] This application provides a fourth aspect of a terminal device, including the secondary battery provided in the third aspect of this application. Specifically, the terminal device includes a housing, electronic components housed within the housing, and the secondary battery as described above, wherein the secondary battery powers the electronic components. The terminal device 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.

[0101] The technical solution of this application will be further described below through specific embodiments.

[0102] Unless otherwise specified, the materials or reagents used in this article are commercially available or prepared using methods known in the art.

[0103] Example 1

[0104] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0105] 1. Preparation of electrolyte

[0106] 1) Preparation of Additive A: Refer to the preparation method of Additive B listed in the above specific embodiments, except that the raw material inositol is replaced with quercetin (CAS No.: 62076-18-0).

[0107]

[0108] The proton NMR data of additive A are as follows: 1 H NMR (400MHz, DMSO-d6): δ3.63-3.65(m,3H), 3.73-3.75(t,J=7.6Hz,10H), 3.44(m,2H), 1.83(m,1H), 1.56(m,1H), 2.56-2.58(t,J=7.2Hz,10H).

[0109] 2) In an argon-filled glove box, EC, DEC, PC and PP are mixed to form an organic solvent. Then, fully dried LiPF6 and LiDFOB are dissolved in the above solvent and stirred to form a homogeneous solution. Then, additives A, FEC and PS are added to the above solution respectively and mixed evenly to obtain the electrolyte.

[0110] The electrolyte contains 10%, 22.5%, 15%, and 30% by mass of EC, DEC, PC, and PP, respectively; 2%, 5%, and 3% by mass of additives A, FEC, and PS, respectively; 1.0 mol / L of LiPF6; and 0.05 mol / L of lithium difluorooxalate borate (LiDFOB).

[0111] 2. Preparation of lithium secondary batteries

[0112] 1) Weigh 2% PVDF, 2% Super-P conductive agent and 96% LiCoO2 by mass and add them to NMP in sequence. Stir and mix thoroughly to obtain a positive electrode slurry. Coat the positive electrode slurry onto an aluminum foil current collector, dry, cold press and cut to obtain a positive electrode sheet.

[0113] 2) Weigh out 1.5% CMC-Na, 2.5% SBR, 1% carbon nanotubes and 95% silicon-carbon material (silicon content is 15wt%), add them to deionized water in sequence, stir and mix thoroughly, coat the slurry on copper foil current collector, dry, cold press and cut to obtain negative electrode sheet.

[0114] 3) After the positive electrode, negative electrode and polyethylene separator prepared above are made into a battery cell, they are packaged with outer packaging foil, and then the electrolyte prepared above is injected into them. After formation and other processes, a 4Ah soft-pack lithium secondary battery is made.

[0115] Example 2

[0116] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0117] 1. Preparation of electrolyte

[0118] 1) Preparation of Additive B: a. Dissolve 3.0 eq of inositol and 20.0 eq of acrylonitrile in deionized water to obtain the raw material system; b. Dissolve 20.0 eq of sodium hydroxide in deionized water to form a saturated sodium hydroxide solution, and slowly add the saturated sodium hydroxide solution dropwise to the raw material system; c. After the saturated sodium hydroxide is added, heat the reaction system to 60°C and react for at least 5 hours; d. After the reaction is completed, cool to room temperature, add pure water to quench the reaction solution, neutralize to neutral with 0.1M dilute hydrochloric acid, and then add ethyl acetate for extraction. Wash the extract with sodium carbonate aqueous solution and saturated brine, dry in anhydrous sodium sulfate for at least 30 minutes, filter, evaporate the ethyl acetate in the filtrate, dry in a vacuum oven at 40°C overnight, and remove water by molecular sieve to obtain Additive B.

[0119]

[0120] The proton NMR data of additive B are as follows: 1 H NMR (400MHz, DMSO-d6): δ3.63 (s, 6H), 3.73-3.75 (t, J = 7.8 Hz, 12H), 2.56-2.58 (t, J = 7.0 Hz, 12H).

[0121] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive B.

[0122] 2. Preparation of lithium secondary batteries

[0123] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0124] Example 3

[0125] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0126] 1. Preparation of electrolyte

[0127] 1) Preparation of Additive D: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced with... (CAS No.: 2748710-62-3).

[0128]

[0129] The proton NMR data of additive D are as follows: 1 H NMR (400MHz, DMSO-d6): δ1.41 (m, 1H), 1.62 (m, 1H), 3.75-3.77 (t, J = 8.1Hz, 8H), 3.33 (m, 2H), 3.71 (m, 1H), 3.66 (m, 2H), 2.58-2.59 (t, J = 7.5Hz, 8H).

[0130] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive D.

[0131] 2. Preparation of lithium secondary batteries

[0132] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0133] Example 4

[0134] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0135] 1. Preparation of electrolyte

[0136] 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).

[0137]

[0138] The proton NMR data of additive E are as follows: 1 H NMR (400MHz, DMSO-d6): δ3.89 (m, 3H), 4.55 (d, J = 3.6Hz, 2H), 3.74-3.77 (t, J = 8.2Hz, 10H), 2.57-2.58 (t, J = 7.3Hz, 10H).

[0139] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive E.

[0140] 2. Preparation of lithium secondary batteries

[0141] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0142] Example 5

[0143] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0144] 1. Preparation of electrolyte

[0145] 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).

[0146]

[0147] The proton NMR data of additive F are as follows: 1 H NMR (400MHz, DMSO-d6): δ5.68 (dd,J=4.2Hz, 2H), 4.02 (dd,J=4.5Hz, 2H), 3.76-3.77 (t,J=7.4Hz, 8H), 2.57-2.59 (t,J=7.2Hz, 8H).

[0148] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive F.

[0149] 2. Preparation of lithium secondary batteries

[0150] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0151] Example 6

[0152] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0153] 1. Preparation of electrolyte

[0154] It is basically the same as Example 1, except that additive A is replaced with a mixture of additive B and additive D, wherein the mass percentage of additive B and additive D in the electrolyte is 1%.

[0155] 2. Preparation of lithium secondary batteries

[0156] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0157] Example 7

[0158] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0159] 1. Preparation of electrolyte

[0160] It is basically the same as Example 1, except that additive A is replaced with a mixture of additive B and additive F, wherein the mass percentage of additive B and additive F in the electrolyte is 1%.

[0161] 2. Preparation of lithium secondary batteries

[0162] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0163] Example 8

[0164] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0165] 1. Preparation of electrolyte

[0166] The method is basically the same as Example 5, except that the mass percentage of additive F is replaced with 0.2%, and the mass percentages of EC, DEC, PC and PP are adjusted to 10.2%, 22.7%, 15.2% and 30.2%, respectively.

[0167] 2. Preparation of lithium secondary batteries

[0168] It is basically the same as Example 5, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0169] Example 9

[0170] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0171] 1. Preparation of electrolyte

[0172] It is basically the same as Example 5, except that the mass percentage of additive F is replaced with 10%, and the mass percentages of EC, DEC, PC and PP are adjusted to 8%, 20.5%, 13% and 28%, respectively.

[0173] 2. Preparation of lithium secondary batteries

[0174] It is basically the same as Example 5, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0175] Example 10

[0176] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0177] 1. Preparation of electrolyte

[0178] The method is basically the same as Example 5, except that the mass percentage of additive F is replaced with 0.5%, and the mass percentages of EC, DEC, PC and PP are adjusted to 10.1%, 22.7%, 15.1% and 30.1%, respectively.

[0179] 2. Preparation of lithium secondary batteries

[0180] It is basically the same as Example 5, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0181] Example 11

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

[0183] 1. Preparation of electrolyte

[0184] It is basically the same as Example 5, except that the mass percentage of additive F is replaced with 5%, and the mass percentages of EC, DEC, PC and PP are adjusted to 9%, 22.5%, 14% and 29%, respectively.

[0185] 2. Preparation of lithium secondary batteries

[0186] It is basically the same as Example 5, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0187] Example 12

[0188] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0189] 1. Preparation of electrolyte

[0190] 1) Preparation of Additive C: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced with... (CAS No.: 1112963-22-0).

[0191]

[0192] The proton NMR data of additive C are as follows: 1H NMR (400MHz, DMSO-d6): δ0.89 (d,J=6.4Hz, 3H), 3.74-3.75 (t,J=7.6Hz, 8H), 3.43 (m, 2H), 2.00 (m, 1H), 3.72 (m, 2H), 2.58-2.59 (t,J=7.3Hz, 8H).

[0193] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive C.

[0194] 2. Preparation of lithium secondary batteries

[0195] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0196] Example 13

[0197] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0198] 1. Preparation of electrolyte

[0199] 1) Preparation of Additive G: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced with... (CAS No.: 4096-52-0).

[0200]

[0201] The proton NMR data of additive G are as follows: 1 H NMR (400MHz, DMSO-d6): δ2.96(dd,J=4.6Hz, 1H), 2.80(dd,J=4.7Hz, 1H), 3.75-3.76( t,J=7.8Hz, 8H), 3.35 (m, 2H), 4.71 (m, 1H), 3.76 (m, 2H), 2.57-2.59 (t,J=7.1Hz, 8H).

[0202] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive G.

[0203] 2. Preparation of lithium secondary batteries

[0204] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0205] Example 14

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

[0207] 1. Preparation of electrolyte

[0208] 1) Preparation of Additive H: Refer to the preparation method of Additive B listed above, except that the raw material inositol is replaced with... (CAS No.: 29782-84-1).

[0209]

[0210] The proton NMR data of additive H are as follows: 1 H NMR (400MHz, DMSO-d6): δ4.23 (dd,J=5.2Hz, 1H), 4.41 (dd,J=5.0Hz, 2H), 3.72-3 .76(t,J=7.4Hz, 6H), 5.91-5.92(dd,J=5.1Hz, 2H), 2.57-2.61(t,J=7.2Hz, 6H).

[0211] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive H.

[0212] 2. Preparation of lithium secondary batteries

[0213] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0214] Example 15

[0215] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0216] 1. Preparation of electrolyte

[0217] 1) Preparation of additive K: Refer to the preparation method of additive B listed above, except that the raw material acrylonitrile is replaced with methacrylonitrile.

[0218]

[0219] The proton NMR data of additive K are as follows: 1 H NMR (400MHz, DMSO-d6): δ1.33-1.34 (d,J=8.2Hz, 18H), 3.75-3.79 (m, 6H), 3.51-3.62 (d,J=6.6Hz, 12H), 2.84-2.87 (dd,J=7.9Hz, 6H).

[0220] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive K.

[0221] 2. Preparation of lithium secondary batteries

[0222] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0223] Example 16

[0224] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0225] 1. Preparation of electrolyte

[0226] 1) Preparation of additive M: Refer to the preparation method of additive B, except that the raw material acrylonitrile is replaced with propyne nitrile.

[0227]

[0228] The proton NMR data of additive M are 1 H NMR (400MHz, DMSO-d6): δ7.10-7.14 (d,J=7.0Hz, 6H), 4.33-4.38 (d,J=6.8Hz, 6H), 4.00-4.05 (dd,J=5.7Hz, 6H).

[0229] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive M.

[0230] 2. Preparation of lithium secondary batteries

[0231] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0232] Example 17

[0233] This embodiment provides an electrolyte and a lithium secondary battery, the preparation method of which is as follows:

[0234] 1. Preparation of electrolyte

[0235] 1) Preparation of additive N: Refer to the preparation method of additive B listed above, except that the raw material acrylonitrile is replaced with 4-vinylbenzonitrile.

[0236]

[0237] The proton N spectrum data of additive N are as follows 1H NMR (400MHz, DMSO-d6): δ3.67-3.69(dd,J=6.3Hz, 6H), 3.52-3.59(t,J=7.2Hz, 12H), 2. 58-2.62 (t, J=8.5Hz, 12H), 7.81-7.85 (d, J=9.5Hz, 12H), 7.41-7.50 (d, J=9.8Hz, 12H).

[0238] 2) is basically the same as step 2) of Example 1, except that additive A is replaced with additive N.

[0239] 2. Preparation of lithium secondary batteries

[0240] The preparation steps are basically the same as those in Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this example.

[0241] Comparative Example 1

[0242] This comparative example provides an electrolyte and a lithium secondary battery, the preparation methods of which are as follows:

[0243] 1. Preparation of electrolyte

[0244] It is basically the same as Example 1, except that additive A is replaced with succinic anhydride.

[0245] The structure of succinic anion is as follows:

[0246]

[0247] 2. Preparation of lithium-ion batteries

[0248] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this comparative example.

[0249] Comparative Example 2

[0250] This comparative example provides an electrolyte and a lithium secondary battery, the preparation methods of which are as follows:

[0251] 1. Preparation of electrolyte

[0252] It is basically the same as Example 1, except that additive A is replaced with 1,3,6-hexanetrionitrile.

[0253] The structure of 1,3,6-hexanetrionitrile is as follows:

[0254]

[0255] 2. Preparation of lithium-ion batteries

[0256] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this comparative example.

[0257] Comparative Example 3

[0258] This comparative example provides an electrolyte and a lithium secondary battery, the preparation methods of which are as follows:

[0259] 1. Preparation of electrolyte

[0260] It is basically the same as Example 1, except that additive A is replaced with 1,2-bis(2-cyanoethoxy)ethane.

[0261] The structure of 1,2-bis(2-cyanoethoxy)ethane is as follows:

[0262]

[0263] 2. Preparation of lithium-ion batteries

[0264] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this comparative example.

[0265] Comparative Example 4

[0266] This comparative example provides an electrolyte and a lithium secondary battery, the preparation methods of which are as follows:

[0267] 1. Preparation of electrolyte

[0268] It is basically the same as Example 1, except that additive A is replaced with additive L.

[0269] The structure of additive L is as follows:

[0270]

[0271] 2. Preparation of lithium-ion batteries

[0272] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this comparative example.

[0273] Comparative Example 5

[0274] This comparative example provides an electrolyte and a lithium secondary battery, the preparation methods of which are as follows:

[0275] 1. Preparation of electrolyte

[0276] It is basically the same as Example 1, except that additive A is replaced with additive J.

[0277] The structure of additive J is as follows:

[0278]

[0279] 2. Preparation of lithium-ion batteries

[0280] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this comparative example.

[0281] Comparative Example 6

[0282] This comparative example provides an electrolyte and a lithium secondary battery, the preparation methods of which are as follows:

[0283] 1. Preparation of electrolyte

[0284] It is basically the same as Example 1, except that additive A was not added and the mass percentages of FEC and PS in the electrolyte were adjusted to 6% and 4%, respectively.

[0285] 2. Preparation of lithium-ion batteries

[0286] It is basically the same as Example 1, except that the electrolyte in step 3) is replaced with the electrolyte prepared in this comparative example.

[0287] Test case

[0288] The following performance tests were performed on the lithium secondary batteries prepared in the above embodiments and comparative examples:

[0289] 1. Cyclic performance at 25℃

[0290] Test method: At 25±3℃, the lithium secondary battery was charged to 4.6V at a constant current of 1.0C, then charged at a constant voltage until the current dropped to 0.025C. After standing for 5 minutes, it was discharged to 3.0V at a constant current of 1.0C. This cycle was repeated 300 times. The discharge capacity of the first and 300th cycles was recorded. The capacity retention rate of the battery after 300 cycles at room temperature was calculated using the following formula. The results are recorded in Table 1.

[0291] Capacity retention (%) = Discharge capacity of the 300th cycle / Discharge capacity of the 1st cycle × 100%.

[0292] Based on the data recorded during the above tests, capacity retention curves of the cycle capacity batteries of Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 6 after 300 cycles were plotted. Figure 2 This is a comparison chart of capacity retention rates after 300 cycles for Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 6. Figure 2As shown, the group without any nitrile additives (Comparative Example 6) had the worst cycle performance; the groups with conventional commercial nitrile additives (Comparative Examples 1-3) showed a significant improvement in cycle performance; and the group with the newly designed additives (Example 2) showed an even further improvement in cycle performance, showing a clear difference from the comparative examples.

[0293] 2. Storage performance at 60℃

[0294] Test method: At 25±3℃, the lithium secondary battery was charged at a constant current of 0.2C to 4.6V, then charged at a constant voltage until the current dropped to 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V. The capacity at this point was recorded as the initial capacity. The battery was then fully charged using the same charging method. The fully charged battery was then placed in a constant temperature chamber at 60℃ for 7 days. After being placed at room temperature for 2 hours, it was discharged at a constant current of 0.5C to the cutoff voltage of 3.0V. The capacity at this point was recorded as the remaining capacity. The capacity retention rate of the battery after 7 days of storage at 60℃ was calculated using the following formula. The results are recorded in Table 1.

[0295] Capacity retention rate (%) = Remaining capacity / Initial capacity × 100%.

[0296] 3. Low-temperature cycling performance

[0297] Test method: At 12±3℃, the lithium secondary battery was charged at a constant current of 1.0C to 4.6V, then charged at a constant voltage until the current dropped to 0.025C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 3.0V. This cycle was repeated 300 times. The discharge capacity of the first 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. The results are recorded in Table 1.

[0298] Capacity retention (%) = Discharge capacity of the 300th cycle / Discharge capacity of the 1st cycle × 100%.

[0299] For ease of comparison, the types and contents of polynitrile additives used in the above examples and comparative examples are also listed in Table 1.

[0300] Table 1

[0301]

[0302]

[0303] The following conclusions can be drawn from Table 1:

[0304] 1. The lithium-ion batteries in Examples 1-5 and 12-14 of this application exhibit higher capacity retention rates at 25°C (83.9%-86.1%), 60°C (87.9%-91.3%), and low-temperature (83.2%-86.1%) than those in Comparative Examples 1-2. This demonstrates the necessity of the ether-based backbone and cyclic structure in the electrolyte additive structure of this application. The additive molecules in Examples 1-5 and 12-14 all contain ether bonds, which helps maintain the high conductivity and low viscosity of the electrolyte, improving the wide-temperature-range cycling performance of the battery. In contrast, the additive molecules in Comparative Examples 1-2, compared to Examples 1-5 and 12-14, have multidentate cyano groups but lack the ether-based backbone and cyclic structure. Therefore, the prepared electrolytes have lower conductivity and higher viscosity, resulting in poorer wide-temperature-range cycling performance and high-temperature storage performance.

[0305] 2. The lithium-ion batteries in Examples 1-5 and 12-14 of this application exhibit higher capacity retention rates at 25°C (83.9%-86.1%), 60°C (87.9%-91.3%), and low-temperature (83.2%-86.1%) than those in Comparative Example 4. This demonstrates the necessity of multidentate cyano ligands in the electrolyte additive structure of this application. The additive molecules in Examples 1-5 and 12-14 all contain three or more cyano ligands, increasing the number and density of effective functional groups within the molecule. The cyano group can preferentially complex with transition metal ions at the positive electrode interface, inhibiting the dissolution of transition metal ions, reducing side reactions between the electrolyte and the positive electrode material, suppressing further oxidative decomposition of the electrolyte, and improving the high-voltage stability of the electrolyte. Compared with Examples 1-5 and 12-14, the additive molecule of Comparative Example 4 has the common structural features of "cyclic structure + ether-based backbone", but does not meet the feature of "multidentate cyano group". Therefore, it has fewer coordination sites at the positive electrode interface and cannot effectively form a positive electrode interface protective film. Its wide temperature range cycling performance and high temperature storage performance under high voltage conditions are worse.

[0306] 3. The lithium-ion batteries in Examples 1-5 and 12-14 of this application exhibit higher capacity retention rates at 25°C (83.9%-86.1%), 60°C (87.9%-91.3%), and low-temperature (83.2%-86.1%) than those in Comparative Example 5. This demonstrates the necessity of the cyclic structure in the electrolyte additive structure of this application. The additive molecules in Examples 1-5 and 12-14 all possess cyclic structures. This structure, on the one hand, increases intermolecular motion (cyclic structures can slide more easily between molecules than linear structures), thereby lowering the freezing point and viscosity of such additives and improving the low-temperature cycling performance of the battery; on the other hand, it inhibits intramolecular motion (cyclic structures increase molecular rigidity and restrict the extension and movement of molecular chains), thereby enhancing the coordination ability of cyano groups at the positive electrode interface and improving the high-voltage performance of the battery. Compared with Examples 1-5 and 12-14, the additive molecule of Comparative Example 5 has the common structural feature of "multidentate cyano group + ether group backbone", but does not meet the feature of "cyclic structure". Therefore, its coordination ability at the positive electrode interface is weak and it cannot effectively form a positive electrode interface protective film. Its wide temperature range cycling performance and high temperature storage performance under high voltage conditions are even worse.

[0307] 4. The lithium-ion batteries in Examples 5, 8, 9, 10, and 11 of this application exhibit higher cycle capacity retention rates (67.1%-83.9%) at 25°C, (74.2%-91.3%) at 60°C, and (63.7%-83.4%) at low temperatures than Comparative Example 6. This indicates that the addition of the electrolyte additive of this application can effectively improve the wide-temperature-range cycle performance and high-temperature storage performance of the battery under high voltage. Furthermore, the wide-temperature-range cycle performance and 60°C storage capacity retention rate of the lithium-ion batteries in Examples 5, 10, and 11 are superior to those in Examples 8 and 9, suggesting that the electrolyte additive concentration of this application is more preferably 0.5%-5%. If the amount added is too small, the effective functional group concentration will be too low, failing to achieve the effect of complexing transition metals and forming a positive electrode interface protective film (CEI). If the amount added is too large, the electrolyte conductivity will decrease, the battery impedance will increase, and the interface film will thicken, thereby leading to a decrease in battery performance.

[0308] 5. The lithium-ion batteries in Examples 6-7 of this application exhibit higher cycle capacity retention rates (84.9%-85.8%) at 25°C, (88.4%-89.2%) at 60°C, and (82.6%-83.8%) at low temperatures than Comparative Examples 1-5, and are comparable to the performance of Examples 1-5. This indicates that the electrolyte additives in this application have high compatibility, and the multi-component mixture can still significantly improve the battery's cycle performance and high-temperature storage performance. Each individual component contains the structural features of "multidentate cyano group + ether group backbone + cyclic structure".

[0309] 6. The lithium-ion batteries in Examples 15-17 of this application exhibit higher cycle capacity retention rates (85.4%-86.7%) at 25°C, (87.1%-89.6%) at 60°C, and (84.5%-85.6%) at low temperatures than Comparative Example 6, and are comparable to the performance of Examples 1-5. This indicates that the structure of the ether-based backbone has high compatibility and can be changed to carbon chains of different lengths, or to olefinic or aryloxy groups, while still exhibiting good wide-temperature-range cycling performance and high-temperature storage performance.

[0310] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of this application, and are not intended to limit them. Although the embodiments of this application have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrolyte additive, characterized in that, The electrolyte additive has the structure shown in Formula I: In Formula I, R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from any one of alkoxide nitrile, substituted alkoxide nitrile, substituted enyloxy nitrile, substituted enyloxy nitrile, aryloxy nitrile, substituted aryloxy nitrile, hydrogen atom, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, and haloaryloxy, and at least three of R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from any one of alkoxide nitrile, substituted alkoxide nitrile, substituted enyloxy nitrile, substituted aryloxy nitrile, and substituted aryloxy nitrile; X is selected from any one of oxygen atom, sulfur atom, alkylene group, substituted alkylene group, imino group, substituted imino group, alkenyl group, and substituted alkenyl group; 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 alkeneoxynitrile and the substituted alkeneoxynitrile is 2 to 10; And / or, the number of carbon atoms in the substituted alkylene oxide nitrile and the substituted alkylene oxide nitrile is 3 to 10; And / or, the number of carbon atoms in the aryleneoxynitrile and the substituted aryleneoxynitrile is 4 to 20.

3. The electrolyte additive according to claim 2, characterized in that, The number of carbon atoms in the alkoxide nitrile and the substituted alkoxide nitrile is 2 to 6; And / or, the number of carbon atoms in the substituted alkylene oxide nitrile and the substituted alkylene oxide nitrile is 3 to 6; And / or, the number of carbon atoms in the aryleneoxynitrile and the substituted aryleneoxynitrile is 4 to 10.

4. The electrolyte additive according to any one of claims 1-3, characterized in that, The substituents in the substituted alkoxynitrile, substituted alkenoxynitrile, substituted aryloxynitrile, substituted alkylene, substituted imine, and substituted alkenyl groups are each independently selected from one or more of halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkenoxy, haloalkenoxy, aryl, haloaryl, aryloxy, and haloaryloxy groups.

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

6. The electrolyte additive according to any one of claims 1-5, characterized in that, R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from any one of ethoxynitrile, vinyloxynitrile, and ethoxybenzonitrile.

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

8. The electrolyte additive according to any one of claims 1-7, 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 additives, characterized in that, The additive includes the electrolyte additive having the structure shown in Formula I as described in any one of claims 1-8.

10. The electrolyte according to claim 9, characterized in that, The electrolyte additive having the structure shown in Formula I has a mass percentage content of 0.05% to 10% in the electrolyte.

11. The electrolyte according to claim 10, characterized in that, The electrolyte additive having the structure shown in Formula I has a mass percentage content of 0.5% to 5% in the electrolyte.

12. The electrolyte according to any one of claims 9-11, characterized in that, The additives also include one or more of the following: biphenyl, fluorobenzene, vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methanedisulfonate, dimethyl sulfate, dimethyl sulfite, diethyl sulfite, diethyl sulfate, 4-methyl ethylene sulfate, succinate, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrionitrile.

13. The electrolyte according to any one of claims 9-12, 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 9-13, characterized in that, The electrolyte salt includes one or more of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt.

15. The electrolyte according to claim 14, characterized in that, The electrolyte salts include 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+1 One or more of [(FSO2)N] and [(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 9-15, characterized in that, The molar concentration of the electrolyte salt in the electrolyte solution 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 in that, The electrolyte is the electrolyte according to any one of claims 9-16.

18. A terminal device, comprising a housing and electronic components and a secondary battery housed within the housing, characterized in that, The secondary battery includes the secondary battery as described in claim 17.

Images