Electrolyte, secondary battery and electric equipment

Abstract

The embodiment of the invention provides an electrolyte, a secondary battery and electric equipment, the electrolyte provided by the embodiment of the invention comprises a lithium salt, an organic solvent and a first additive, and the first additive comprises at least one of an imine additive and a polyamine additive; the imine additive and the polyamine additive both comprise amino groups, and the amino groups can react with hydrofluoric acid generated by hydrolysis and pyrolysis of the lithium salt under a high-temperature condition and a trace amount of water in the electrolyte to generate stable hydrogen bonds, so that the hydrolysis reaction and pyrolysis reaction processes of the lithium salt in the electrolyte are inhibited; the consumption of lithium ions in the secondary battery by hydrolysis reaction and pyrolytic reaction of lithium salt is reduced, the damage degree of hydrofluoric acid to a solid electrolyte interface film is reduced, the capacity retention ratio of the secondary battery under a high-temperature condition is improved, the impedance of the secondary battery is reduced, and the service life of the secondary battery is prolonged. And the cycle performance and the storage performance of the secondary battery prepared based on the electrolyte provided by the embodiment of the invention under a high-temperature condition are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly to an electrolyte, a secondary battery, and an electrical device using the same. Background Art

[0002] In a secondary battery, as an ion carrier, the electrolyte can promote charge transfer and ion conduction between the positive electrode plate and the negative electrode plate.

[0003] Currently, the additives in the electrolyte are generally carbonate additives. Although carbonate additives can form a stable solid electrolyte interface (SEI) film on the surface of the electrode plate to improve the cycle stability of the secondary battery. However, with the rapid development of pure electric vehicles and hybrid electric vehicles, the requirements for the high-temperature cycle performance and storage performance of secondary batteries are constantly increasing. High-temperature conditions accelerate the hydrolysis reaction and pyrolysis reaction of lithium salts in the electrolyte, and the hydrolysis reaction and pyrolysis reaction of lithium salts will consume a large amount of lithium ions in the secondary battery, resulting in a decrease in the capacity of the secondary battery. Further, hydrofluoric acid (HF) generated by the hydrolysis reaction and pyrolysis reaction of lithium salts will also corrode and damage the SEI film, resulting in an increase in the impedance of the secondary battery and deterioration of the cycle performance and storage performance, making it difficult to meet the high-temperature performance requirements. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an electrolyte, a secondary battery, and an electrical device using the same, so as to solve the problem that the secondary battery prepared based on the electrolyte in the related art has deteriorated cycle performance and storage performance under high-temperature conditions.

[0005] To solve the above problems, the present invention is implemented by the following technical solutions:

[0006] The present invention provides an electrolyte, which includes a lithium salt, an organic solvent, and a first additive; the first additive includes at least one of an imine additive and a polyamine additive;

[0007] The imine additive includes a compound having the formula (I):

[0008]

[0009] The polyamine additive includes a compound having the formula (II):

[0010]

[0011] Wherein, R in the formula (I) 1 and R 2 are each independently selected from straight-chain alkanes having 1 to 5 carbon atoms.

[0012] Further, in the electrolyte, the imine additive is selected from aromatic aldehyde - tris(ethyleneamine) bis - Schiff base.

[0013] Further, in the electrolyte, the aromatic aldehyde - tris(ethyleneamine) bis - Schiff base is selected from at least one of benzaldehyde - tris(ethyleneamine) bis - Schiff base and o - vanillin - tris(ethyleneamine) bis - Schiff base.

[0014] Further, in the electrolyte, the polyamine additive is selected from at least one of triethylenetetramine, ethylenediamine, diethylenetriamine, and tetraethylenepentamine.

[0015] Further, in the electrolyte, the mass ratio of the first additive is 0.5 wt% - 1 wt%.

[0016] Further, in the electrolyte, the electrolyte further includes a second additive, and the second additive includes at least one of vinylene carbonate, propylene sulfite, ethylene sulfate, ethylene vinylene carbonate, fluoroethylene carbonate, lithium bis(oxalate)borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0017] Further, in the electrolyte, the mass ratio of the second additive is 5 wt% - 10 wt%.

[0018] Further, in the electrolyte, the mass ratio of the lithium salt is 8 wt% - 16 wt%.

[0019] The present invention also provides a secondary battery, wherein the secondary battery includes a positive electrode sheet, a negative electrode sheet, and the electrolyte as described in any one of the above.

[0020] The present invention also provides an electrical device, wherein the electrical device includes the above - mentioned secondary battery, and the secondary battery serves as the power supply of the electrical device.

[0021] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0022] The electrolyte provided by the embodiments of the present invention includes a lithium salt, an organic solvent, and a first additive. Among them, the first additive includes at least one of an imine additive and a polyamine additive; both the imine additive and the polyamine additive include an amino group (-NH 2And / or -NH-), the amino group can react with HF generated by the hydrolysis and pyrolysis of lithium salts at high temperature and trace water in the electrolyte to form stable hydrogen bonds, inhibit the hydrolysis and pyrolysis reactions of lithium salts in the electrolyte, reduce the consumption of lithium ions in the secondary battery by the hydrolysis and pyrolysis reactions of lithium salts, and reduce the damage degree of HF to the SEI film, improve the capacity retention rate of the secondary battery under high temperature conditions, reduce the impedance of the secondary battery, and further improve the cycling performance and storage performance of the secondary battery prepared with the electrolyte provided by the implementation of the present invention under high temperature conditions.

[0023] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present invention. Detailed implementation manners

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with specific implementation manners.

[0026] In the related art, the lithium salts in the electrolyte used in secondary batteries are prone to hydrolysis and pyrolysis at high temperature, which not only consume a large amount of lithium ions in the secondary battery, resulting in a reduction in the capacity of the secondary battery, but also the HF generated by the hydrolysis and pyrolysis reactions of lithium salts will corrode and damage the SEI film, resulting in an increase in the impedance of the secondary battery and deterioration of the cycling performance and storage performance, making it difficult to meet the high temperature performance requirements.

[0027] The embodiments of the present invention provide an electrolyte to solve the above problems. The electrolyte includes a lithium salt, an organic solvent, and a first additive.

[0028] Among them, the first additive includes at least one of an imine additive and a polyamine additive.

[0029] The imine additive includes a compound having the formula (I):

[0030]

[0031] The polyamine additive includes a compound having the formula (II):

[0032]

[0033] It should be noted that R in the formula (I)1 and R 2 are each independently selected from straight-chain alkanes having 1 to 5 carbon atoms.

[0034] Specifically, the hydrolysis reaction of the lithium salt in the electrolyte generally involves a chemical reaction between the cation or anion in the lithium salt and a small amount of water molecules (H 2 O) in the electrolyte, and the pyrolysis reaction of the lithium salt refers to the process of decomposition of the lithium salt under high-temperature conditions. The hydrolysis reaction and pyrolysis reaction of the lithium salt not only consume a large amount of lithium ions in the secondary battery, resulting in a decrease in the capacity of the secondary battery, but also the HF generated by the hydrolysis reaction and pyrolysis reaction of the lithium salt has strong corrosiveness, which will corrode and damage the SEI film, resulting in an increase in the impedance of the secondary battery and deterioration of the cycle performance and storage performance, and it is difficult to meet the high-temperature performance requirements. The first additive in the electrolyte provided by the embodiments of the present invention includes an imine additive having the structure of formula (I) and / or a polyamine additive having the structure of formula (II). The amino groups (-NH 2 and / or -NH-) in the imine additive and / or polyamine additive can react with HF generated by the hydrolysis and pyrolysis of the lithium salt under high-temperature conditions and trace water in the electrolyte to form stable hydrogen bonds. Through the interaction between the nitrogen atom and the hydrogen atom in the hydrogen bond, the stability of the electrolyte system is improved, so that the energy required for the hydrolysis reaction and pyrolysis reaction of the lithium salt is increased, thereby inhibiting the progress of the hydrolysis reaction and pyrolysis reaction of the lithium salt, reducing the consumption of lithium ions in the secondary battery by the hydrolysis reaction and pyrolysis reaction of the lithium salt and the damage degree of the product HF of the hydrolysis and pyrolysis of the lithium salt to the SEI film, which is beneficial to improving the capacity retention rate of the secondary battery under high-temperature conditions, reducing the impedance of the secondary battery, and further improving the cycle performance and storage performance of the secondary battery prepared based on the electrolyte provided by the present invention under high-temperature conditions.

[0035] Furthermore, the imine additive having the structure of formula (Ⅰ) also includes a C=N double bond. The lone pair electrons of the N atom connected to the C=N double bond in the SP2 hybrid orbital are affected by the electronegativity of the N atom and the delocalization of the electron cloud density of the adjacent C=N double bond, and have a strong coordination effect, and can coordinate with metal ions in the electrolyte to form a stable five-membered ring chelate structure; in addition, the N atoms in the amino groups of the imine additive having the structure of formula (Ⅰ) and the polyamine additive having the structure of formula (II) also participate in coordination, and coordinate with metal ions in the electrolyte to form a stable five-membered ring chelate structure, reducing the concentration of metal ions in the electrolyte, which helps to inhibit the formation of deposits (such as lithium dendrites) on the surface of the negative electrode plate, and reduce the damage of the deposits on the surface of the negative electrode plate to the structure of the negative electrode plate, and further improve the cycle performance and storage performance of the secondary battery.

[0036] It should be noted that the high-temperature conditions involved in the embodiments of the present invention refer to the high-temperature conditions during the operation of the secondary battery, and the temperature range corresponding to the high-temperature conditions can be 40°C to 60°C.

[0037] The metal ions that coordinate with N atoms in the electrolyte to form a five-membered ring chelate structure may include but are not limited to: metal ions dissolved from the positive electrode sheet of the secondary battery (e.g., Mn ions, Ni ions, and Co ions) and metal impurities introduced by each component in the electrolyte (e.g., Fe ions, Na ions, and Ca ions), etc.

[0038] In the embodiments of the present invention, the lithium salt may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluoro(oxalato)borate (LiODFB), lithium difluorophosphate (LiPO 2 F 2 ) or one or more of them.

[0039] Among them, lithium hexafluorophosphate has high ionic conductivity and good electrochemical stability; lithium tetrafluoroborate has good thermal stability and can maintain its chemical properties stable at a certain high temperature; in high and low temperature cases, the electrochemical performance of lithium tetrafluoroborate is relatively good, which can effectively prevent the corrosion of the electrode sheet and improve the cycle life and safety of the secondary battery; lithium difluoro(oxalato)borate has excellent high and low temperature performance and can maintain stable electrochemical performance in a wide temperature range; in addition, lithium difluoro(oxalato)borate as the lithium salt in the electrolyte can also provide high ionic conductivity, thereby improving the overall performance of the secondary battery; lithium difluorophosphate can significantly improve the cycle performance of the secondary battery, improve the high temperature storage performance of the secondary battery, reduce the internal impedance of the secondary battery, and improve the cycle performance and storage performance of the secondary battery.

[0040] The organic solvent may include at least two of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0041] Among them, ethylene carbonate has a high film-forming potential on the negative electrode sheet, participates in the formation of the SEI film on the surface of the graphite negative electrode sheet, reduces the side reactions on the electrode sheet surface, and the dielectric constant of ethylene carbonate is relatively high, which can improve the ionic conductivity of the electrolyte.

[0042] Propylene carbonate can enhance the stability of secondary batteries, protect the anode material, reduce the polarity of the electrolyte, and reduce the possibility of secondary battery failure; propylene carbonate can inhibit the swelling of the mercury alloy anode and extend the cycle life of secondary batteries; propylene carbonate can improve the discharge capacity and cycle life of secondary batteries and improve the structural stability and electrochemical performance of the cathode material; in addition, propylene carbonate can also reduce the operating temperature of secondary batteries and improve the stability of secondary batteries.

[0043] Dimethyl carbonate can mix with electrolyte components with low polarity, such as ethylene carbonate and diethyl carbonate, to form a balanced dissolution, enabling secondary batteries to reach a stable state faster and improving the cycle life and capacity retention rate of secondary batteries; dimethyl carbonate can increase the electrochemical window of secondary batteries, reduce the film formation rate on the surface of the electrode sheet, reduce the interfacial resistance, and improve the capacity and cycle life of secondary batteries.

[0044] Diethyl carbonate can be used together with other solvents, such as ethylene carbonate and dimethyl carbonate, to improve the solubility of the electrolyte.

[0045] Ethyl methyl carbonate mainly plays a role in providing an ion conduction channel in the electrolyte, enabling the ions in the electrolyte to be transmitted between the positive and negative electrode sheets for chemical reactions, which is beneficial to improving the efficiency and stability in the electrochemical reaction; in addition, compared with other traditional solvents, ethyl methyl carbonate has advantages such as higher conductivity, higher stability, and lower explosion risk.

[0046] Optionally, in the electrolyte, the mass percentage of the organic solvent is 74wt% - 85wt%; for example, in the electrolyte, the mass percentage of the organic solvent can be one of 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, and 85wt% or the range value of any two of them.

[0047] In the embodiment of the present invention, controlling the mass percentage of the organic solvent in the electrolyte within the range of 74wt% - 85wt% is beneficial to fully dissolve the lithium salt, provide a necessary migration medium for lithium ions, improve the conductivity of the electrolyte, thereby improving the safety of secondary batteries and extending the service life of secondary batteries.

[0048] Optionally, in some embodiments, the imine additive is selected from aromatic aldehyde tris(ethylenetetramine) bis-Schiff base. Aromatic aldehyde tris(ethylenetetramine) bis-Schiff base is an organic compound containing an imine (or methylimine) characteristic group (-RC=N-) formed by the condensation reaction of aromatic aldehydes with triethylenetetramine, wherein the imine (or methylimine) characteristic group (-RC=N-) includes a C=N double bond.

[0049] Specifically, the synthesis of aromatic aldehyde tris(ethylenetetramine) bis-Schiff base is obtained by carrying out a condensation reaction of aromatic aldehyde and triethylenetetramine under appropriate solvents and reaction conditions. In this reaction process, the aldehyde group of the aromatic aldehyde undergoes a nucleophilic addition reaction with the amino group of triethylenetetramine, and then dehydration forms an imine bond.

[0050] Aromatic aldehyde tris(ethylenetetramine) bis-Schiff base has good thermal stability and chemical stability. Using aromatic aldehyde tris(ethylenetetramine) bis-Schiff base as the first additive in the electrolyte, the amino group (-NH-) in aromatic aldehyde tris(ethylenetetramine) bis-Schiff base can react with HF generated by the hydrolysis and pyrolysis of lithium salt at high temperature and trace water in the electrolyte to form stable hydrogen bonds, inhibiting the hydrolysis reaction and pyrolysis reaction processes of lithium salt in the electrolyte, improving the capacity retention rate of the secondary battery under high temperature conditions, reducing the impedance of the secondary battery, and using the coordination effect of the N atom connected to the C=N double bond and the N atom in the amino group (-NH-) in aromatic aldehyde tris(ethylenetetramine) bis-Schiff base, so that the N atom connected to the C=N double bond and the N atom in the amino group (-NH-) can coordinate with metal ions in the electrolyte to form a stable five-membered ring chelate structure, reducing the concentration of metal ions in the electrolyte, inhibiting the formation of deposits on the surface of the negative electrode plate, and being beneficial to improving the cycle performance and storage performance of the secondary battery.

[0051] Optionally, in some embodiments, the aromatic aldehyde tris(ethylenetetramine) bis-Schiff base is selected from at least one of benzaldehyde tris(ethylenetetramine) bis-Schiff base and o-vanillin tris(ethylenetetramine) bis-Schiff base.

[0052] Among them, benzaldehyde tris(ethylenetetramine) bis-Schiff base and o-vanillin tris(ethylenetetramine) bis-Schiff base not only have high chemical stability, but also the triethylenetetramine part in benzaldehyde tris(ethylenetetramine) bis-Schiff base and o-vanillin tris(ethylenetetramine) bis-Schiff base can provide multiple amino groups (-NH-) with nitrogen atoms, so that more metal ions in the electrolyte can be coordinated to form a stable five-membered ring chelate structure, which is beneficial to further reducing the concentration of metal ions in the electrolyte and improving the cycle performance and storage performance of the secondary battery.

[0053] Optionally, in some embodiments, the polyamine additive is selected from at least one of triethylenetetramine (TETA), ethylenediamine (EDA), diethylenetriamine (DETA), and tetraethylenepentamine (TEPA).

[0054] Specifically, the polyamine additive is selected from triethylenetetramine, ethylenediamine, diethylenetriamine, and tetraethylenepentamine, which can provide multiple amino groups (-NH- and -NH 2 )), which is beneficial to further inhibiting the hydrolysis reaction and pyrolysis reaction processes of the lithium salt in the electrolyte, improving the capacity retention rate of the secondary battery under high-temperature conditions, reducing the impedance of the secondary battery, and using the N atoms in the amino group to coordinate with more metal ions in the electrolyte to form a stable five-membered ring chelate structure, thereby further reducing the concentration of metal ions in the electrolyte, inhibiting the formation of deposits on the surface of the negative electrode sheet, and improving the cycle performance and storage performance of the secondary battery.

[0055] Optionally, in some embodiments, in the electrolyte, the mass ratio of the first additive is 0.5 wt% to 1 wt%; specifically, the mass ratio of the first additive can be one of 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, and 1 wt% or the range value of any two of them. By controlling the mass ratio of the first additive in the electrolyte within the range of 0.5 wt% to 1 wt% in the embodiments of the present invention, the effect of the first additive in inhibiting the hydrolysis reaction and pyrolysis reaction processes of the lithium salt in the electrolyte, reducing the concentration of metal ions in the electrolyte, and improving the cycle performance and storage performance of the secondary battery can be improved.

[0056] Optionally, in some embodiments, the electrolyte further includes a second additive, and the second additive includes at least one of vinylene carbonate (VC), propylene sulfite (PS), ethylene sulfite (1,3,2-dioxathiolane 2,2-dioxide, DTD), vinylene ethylene carbonate (VEC), fluoroethylene carbonate (4-Fluoro-1,3-dioxolan-2-one, FEC), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0057] Among them, vinylene carbonate and / or ethylene vinylene carbonate have good electrochemical stability and thermal stability, can reduce the decomposition and volatilization of the electrolyte, improve the stability of the electrolyte, and extend the service life of the secondary battery; in addition, vinylene carbonate and / or ethylene vinylene carbonate can also form a stable SEI film on the surface of the electrode sheet of the secondary battery, reduce the side reactions on the surface of the electrode sheet, and improve the charge and discharge cycle performance of the secondary battery; further, vinylene carbonate and / or ethylene vinylene carbonate can also improve the capacity and energy density of the secondary battery by increasing the conductivity of the electrolyte; vinylene carbonate and / or ethylene vinylene carbonate can inhibit the decomposition and volatilization of the electrolyte, reduce the leakage and combustion risks of the electrolyte, thereby improving the safety of the secondary battery.

[0058] Propylene sulfite as the second additive can improve the performance of the electrolyte under low-temperature conditions and enhance the low-temperature cycle stability of the secondary battery.

[0059] Ethylene sulfate as the second additive can inhibit the decline of the initial capacity of the secondary battery and improve the initial discharge capacity of the secondary battery; ethylene sulfate can also improve the cycle stability and storage performance of the secondary battery by reducing the swelling of the secondary battery after being placed at high temperature.

[0060] Fluoroethylene carbonate can form an effective SEI film on the surface of the electrode sheet of the secondary battery, increase the lithium-ion migration rate in the secondary battery, and improve the charge and discharge performance of the secondary battery at high rates; due to the thin, tough and self-repairing SEI film formed by fluoroethylene carbonate, it can inhibit the structural fragmentation problem of the silicon-carbon negative electrode sheet during the charge and discharge process, which is beneficial to improving the service life of the secondary battery.

[0061] Lithium bis(oxalato)borate can form a dense boron-containing polymer as a solid electrolyte interlayer to isolate the electrode material from the electrolyte and prevent side reactions from occurring; lithium bis(oxalato)borate can also avoid the dissolution of transition metal ions caused by the erosion of hydrofluoric acid and maintain the structural integrity of the electrode sheet.

[0062] Lithium bis(fluorosulfonyl)imide can effectively reduce the low-temperature resistance of the SEI layer formed on the surface of the electrode sheet and improve the low-temperature performance of the secondary battery; lithium bis(fluorosulfonyl)imide can also improve the capacity retention rate and storage performance of the secondary battery by reducing the capacity loss of the secondary battery during storage.

[0063] Lithium bis(trifluoromethanesulfonyl)imide has high conductivity and chemical stability, can improve the overall performance of the electrolyte; in addition, due to its good electrochemical window, lithium bis(trifluoromethanesulfonyl)imide is particularly suitable as the second additive for the electrolyte in high-voltage lithium-ion battery systems.

[0064] It is understandable that the above-mentioned second additive can cooperate with the first additive to inhibit the hydrolysis reaction and pyrolysis reaction processes of the lithium salt in the electrolyte, reduce the concentration of metal ions in the electrolyte, and improve the cycling performance and storage performance of the secondary battery.

[0065] Optionally, in some embodiments, in the electrolyte, the mass ratio of the second additive is 5 wt% to 10 wt%; specifically, in the electrolyte, the mass ratio of the second additive can be one of 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% and 10 wt% or the range value of any two of them.

[0066] Optionally, in some embodiments, in the electrolyte, the mass ratio of the lithium salt is 8 wt% to 16 wt%; specifically, in the electrolyte, the mass ratio of the lithium salt can be one of 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt% and 16 wt% or the range value of any two of them. In the electrolyte provided by the embodiments of the present invention, controlling the mass ratio of the lithium salt within the range of 8 wt% to 16 wt% can improve the conductivity of the electrolyte while making the viscosity of the electrolyte moderate, and can effectively take into account both the conductivity and viscosity of the electrolyte.

[0067] It should be noted that in the electrolyte provided by the embodiments of the present invention, the sum of the mass ratios of the lithium salt, the organic solvent, the first additive and the second additive is 100 wt%.

[0068] The present invention also provides a preparation method of an electrolyte, which includes: under the protection of an inert gas, mixing a lithium salt and an organic solvent to obtain a colorless transparent liquid; mixing the above-mentioned first additive, second additive and the above-mentioned colorless transparent liquid to obtain an electrolyte.

[0069] Among them, in the process of mixing the lithium salt and the organic solvent, since adding the lithium salt will cause the temperature of the electrolyte to rise, resulting in a certain degree of thermal decomposition of the lithium salt, so in the process of adding the lithium salt, it is necessary to control the temperature of the electrolyte; specifically, when the temperature of the electrolyte rises more than 2°C, stop adding the lithium salt, and when the temperature of the electrolyte rises less than 2°C, continue to add the lithium salt.

[0070] Among them, the temperature control of the above-mentioned electrolyte can adopt ice bath, dry ice circulation cooling, liquid nitrogen cooling, etc.

[0071] Optionally, in some embodiments, the above-mentioned organic solvent includes multiple solvents. Before mixing the lithium salt and the organic solvent, it is necessary to pre-mix the multiple solvents and remove water, and then under the protection of an inert gas, mix the lithium salt and the above-mentioned organic solvent to obtain the above-mentioned colorless transparent liquid; then mix the above-mentioned first additive, second additive with the above-mentioned colorless transparent liquid to obtain the electrolyte. Among them, the molecular sieve adsorption method can be used to remove water from the organic solvent.

[0072] The present invention also provides a secondary battery, wherein the secondary battery includes a positive electrode sheet, a negative electrode sheet, and the above-mentioned electrolyte.

[0073] Among them, the lithium salt in the electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet.

[0074] The above-mentioned positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium ion transition metal oxide, a ternary positive electrode material, etc. The above-mentioned lithium ion transition metal oxide includes at least one of lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate, and the above-mentioned ternary positive electrode material can specifically be a high-nickel layered ternary positive electrode material.

[0075] Optionally, in some embodiments, the above-mentioned positive electrode sheet further includes a conductive agent and a binder. The above-mentioned conductive agent can include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fiber, and carbon microspheres. The above-mentioned binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0076] In some embodiments, the positive electrode sheet is prepared as follows: Disperse the components for preparing the positive electrode sheet, such as the above-mentioned positive electrode active material, binder, and any other components, in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; coat the positive electrode slurry on both sides of an aluminum foil or other positive electrode current collector; after processes such as baking, rolling, and cutting, the positive electrode sheet can be obtained.

[0077] Among them, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The above-mentioned negative electrode active material layer can use a negative electrode active material for a secondary battery, and the negative electrode active material includes any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon monoxide.

[0078] In the secondary battery provided by the embodiment of the present invention, the negative electrode sheet further includes a conductive agent and a binder; optionally, the above-mentioned conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the above-mentioned binder includes a carboxymethyl cellulose-based binder and a resin-based binder.

[0079] Optionally, in some embodiments, the carboxymethyl cellulose-based binder includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based binder includes one or more of styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.

[0080] In some embodiments, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the above-mentioned negative electrode active material, binder, and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as a copper foil; after processes such as baking, rolling, and cutting, the negative electrode sheet can be obtained.

[0081] It can be understood that the secondary battery provided by the embodiment of the present invention further includes a separator.

[0082] In practical applications, the negative electrode sheet, separator, and positive electrode sheet are stacked in sequence and wound to obtain a wound core, the wound core is encapsulated to obtain a bare battery cell, and the bare battery cell is baked and then filled with electrolyte, formed, secondarily sealed, and sorted to obtain the above-mentioned secondary battery.

[0083] The present invention also proposes an electrical device, wherein the electrical device includes the above-mentioned secondary battery, and this secondary battery serves as the power supply of the electrical device.

[0084] For the above-mentioned secondary battery embodiments and electrical device embodiments, they include the above-mentioned electrolyte and can achieve the same technical effects. To avoid repetition, they will not be elaborated here, and relevant parts can refer to the partial description of the electrolyte embodiments.

[0085] In order to make the invention purpose, technical solution, and beneficial effects of the present invention clearer, the present invention will be further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0086] The present invention will be described in detail below through embodiments.

[0087] Embodiment 1

[0088] (1) Preparation of electrolyte:

[0089] At room temperature, in a glove box filled with argon (H 2 O < 1 ppm, O 2(<1 ppm), mix ethylene methyl carbonate, dimethyl carbonate and ethylene carbonate uniformly to obtain an organic solvent; gradually add lithium hexafluorophosphate to the organic solvent, continuously stir and cool with dry ice. Ensure that when the temperature of the electrolyte solution rises by no more than 2 °C, lithium hexafluorophosphate can be continuously added to obtain a colorless and transparent liquid; add the first additives benzaldehyde tris(ethylene tetramine) bis-Schiff base and triethylenetetramine, as well as the second additives vinylene carbonate, propylene sulfite and fluoroethylene carbonate to the colorless and transparent liquid, and stir evenly to obtain an electrolyte solution; wherein, in the electrolyte solution, the mass ratio of ethylene methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, benzaldehyde tris(ethylene tetramine) bis-Schiff base and triethylenetetramine is 32.67:24.75:17.82:15.84:3.96:2.97:0.99:0.5:0.5.

[0090] (2) Preparation of the positive electrode sheet:

[0091] Mix the positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 , conductive agent acetylene black (Super P) and binder polyvinylidene fluoride in a mass ratio of 95:3:2 uniformly, and uniformly disperse them in 1-methyl-2-pyrrolidone (NMP) to make a positive electrode paste. Coat the positive electrode paste on both sides of the aluminum foil, and after baking, rolling, and cutting, obtain the positive electrode sheet.

[0092] (3) Preparation of the negative electrode sheet

[0093] Mix the negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a mass ratio of 95:2:1.5:1.5 uniformly, and uniformly disperse them in deionized water to make a negative electrode paste. Coat the negative electrode paste on both sides of the copper foil, and after baking, rolling, and cutting, obtain the negative electrode sheet.

[0094] (4) Preparation of the secondary battery

[0095] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and welding the electrode tabs, obtain a bare battery core. Place the bare battery core in an outer packaging aluminum-plastic film, and bake it in an oven at 85 ± 10 °C for 24 h. Inject the electrolyte solution prepared in step (1) into the dried battery, let it stand, form, and grade-capacity to complete the preparation of a 10 AH lithium manganate system secondary battery, and obtain the secondary battery.

[0096] Examples 2 - 3

[0097] Examples 2 to 3 are different from Example 1 in that in step (1), in the electrolyte, the mass ratios of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, benzaldehyde tris(ethylene tetramine) bis-Schiff base, and triethylenetetramine are 32.67:24.75:17.82:15.84:4.21:3.16:1.05:0.25:0.25 and 32.67:24.75:17.82:15.84:4.06:3.05:1.01:0.4:0.4, respectively.

[0098] Example 4

[0099] Example 4 is different from Example 1 in that in step (1), the first additive only includes benzaldehyde tris(ethylene tetramine) bis-Schiff base, and in the electrolyte, the mass ratios of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and benzaldehyde tris(ethylene tetramine) bis-Schiff base are 32.67:24.75:17.82:15.84:3.96:2.97:0.99:1.

[0100] Examples 5 to 6

[0101] Examples 5 to 6 are different from Example 4 in that in step (1), in the electrolyte, the mass ratios of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and benzaldehyde tris(ethylene tetramine) bis-Schiff base are 32.67:24.75:17.82:15.84:4.21:3.16:1.05:0.5 and 32.67:24.75:17.82:15.84:4.06:3.05:1.01:0.8, respectively.

[0102] Example 7

[0103] Example 7 is different from Example 1 in that in step (1), the first additive only includes triethylenetetramine, and in the electrolyte, the mass ratios of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and triethylenetetramine are 32.67:24.75:17.82:15.84:3.96:2.97:0.99:1.

[0104] Examples 8 to 9

[0105] Examples 8 - 9 are different from Example 7 in that in step (1), the first additive only includes triethylenetetramine, and in the electrolyte, the mass ratios of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and triethylenetetramine are 32.67:24.75:17.82:15.84:4.21:3.16:1.05:0.5 and 32.67:24.75:17.82:15.84:4.06:3.05:1.01:0.8, respectively.

[0106] Comparative Example 1

[0107] Comparative Example 1 is different from Example 1 in that in step (1), the electrolyte does not include the first additive, and in the electrolyte, the mass ratios of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, and fluoroethylene carbonate are 33:25:18:16:4:3:1.

[0108] The components and parameters of the electrolytes in Example 1, Example 4, Example 7, and Comparative Example 1 are shown in Table 1.

[0109] Table 1

[0110]

[0111] Testing method:

[0112] (1) High - temperature cycle performance test: Set the temperature of the constant - temperature oven at 45 ± 2°C, charge and discharge at 1C, and cycle within the voltage range (2.8V - 4.2V).

[0113] (2) High - temperature storage performance test: Charge the battery to full charge at a constant current and constant voltage of 1C, leave it standing at 55 ± 2°C for 7 days, and then perform charge - discharge cycling at room temperature for 4 weeks. The capacity retention rate is not less than 80%, and the capacity recovery rate is not less than 95%.

[0114] Perform high - temperature cycle performance tests on the secondary batteries prepared in Example 1, Example 4, Example 7, and Comparative Example 1. The test data are shown in Table 2.

[0115] Table 2

[0116]

[0117] Perform high - temperature storage performance tests on the secondary batteries prepared in Example 1, Example 4, Example 7, and Comparative Example 1. The test data are shown in Table 3.

[0118] Table 3

[0119]

[0120] According to the test data in Table 2, it can be seen that as the number of cycles increases, compared with Comparative Example 1, the capacity retention rates of the secondary batteries prepared by Examples 1, 4, and 7 all increase significantly. Moreover, when the number of cycles reaches 1000, the capacity retention rates of the secondary batteries prepared by Examples 1, 4, and 7 can still remain above 85%, while the capacity retention rate of the secondary battery prepared by Comparative Example 1 is only 79%. Thus, it can be seen that the high-temperature cycling performance of the secondary battery prepared based on the electrolyte provided by the embodiments of the present invention has been significantly improved.

[0121] According to the test data in Table 3, after the high-temperature storage performance test, the average internal resistance of the secondary batteries prepared by Examples 1, 4, and 7 remains at about 3.2 mΩ, while the internal resistance of the secondary battery prepared by Comparative Example 1 is about 3.6 mΩ after the high-temperature storage performance test; further, after the high-temperature storage performance test, the average capacity retention rate of the secondary batteries prepared by Examples 1, 4, and 7 is 94.42%, which is 3.7% higher than 90.68% of Comparative Example 1; after the high-temperature storage performance test, the average capacity recovery rate of the secondary batteries prepared by Examples 1, 4, and 7 is 97%, which is 1.95% higher than 95.05% of Comparative Example 1. Thus, it can be seen that the high-temperature storage performance of the secondary battery prepared based on the electrolyte provided by the embodiments of the present invention has also been significantly improved.

[0122] In summary, the electrolyte provided by the embodiments of the present invention includes a lithium salt, an organic solvent, and a first additive. Among them, the first additive includes at least one of an imine additive and a polyamine additive; both the imine additive and the polyamine additive include an amino group (-NH 2 and / or -NH-), and the amino group can react with HF generated by the hydrolysis and pyrolysis of the lithium salt under high-temperature conditions and trace water in the electrolyte to form stable hydrogen bonds, inhibit the progress of the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte, reduce the consumption of lithium ions in the secondary battery by the hydrolysis reaction and pyrolysis reaction of the lithium salt, and reduce the damage degree of HF to the SEI film, improve the capacity retention rate of the secondary battery under high-temperature conditions, reduce the impedance of the secondary battery, and further improve the cycling performance and storage performance of the secondary battery prepared based on the electrolyte provided by the present invention under high-temperature conditions.

[0123] The above has introduced in detail an electrolyte, a secondary battery, and an electrical device provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a lithium salt, an organic solvent and a first additive; the first additive includes at least one of an imine additive and a polyamine additive; The imine additives include compounds having formula (I): The polyamine additives include compounds having formula (II): Wherein, R1 and R2 in formula (I) are each independently selected from a straight-chain alkane having 1 to 5 carbon atoms.

2. The electrolyte according to claim 1, characterized in that The imine additive is selected from aromatic aldehyde triethylenetetramine bis-Schiff base.

3. The electrolyte according to claim 2, characterized in that The aromatic aldehyde triethylenetetramine bis-Schiff base is selected from at least one of benzaldehyde triethylenetetramine bis-Schiff base and o-vanillin triethylenetetramine bis-Schiff base.

4. The electrolyte according to claim 1, characterized in that The polyamine additive is selected from at least one of triethylenetetramine, ethylenediamine, diethylenetriamine and tetraethylenepentamine.

5. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass percentage of the first additive is 0.5wt% to 1wt%.

6. The electrolyte according to claim 1, characterized in that The electrolyte further includes a second additive, which includes at least one of vinylene carbonate, propylene sulfite, vinyl sulfate, vinylene carbonate, fluoroethylene carbonate, lithium bis(oxalatoborate), lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethanesulfonyl imide).

7. The electrolyte according to claim 6, characterized in that In the electrolyte, the mass percentage of the second additive is 5wt% to 10wt%.

8. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass percentage of the lithium salt is 8wt% to 16wt%.

9. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The electrical device comprises the secondary battery according to claim 9, and the secondary battery serves as a power supply for the electrical device.

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