Electrolyte, secondary battery and electric equipment
By adding melamine-based additives with specific structures to the secondary battery electrolyte, the hydrolysis and pyrolysis reaction of lithium salts are suppressed, and the problems of increased impedance and deterioration of performance during the cycle are solved, thereby achieving higher stability and performance improvement.
Patent Information
- Application Number
- CN202510144411.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-10
- Publication Date
- 2025-06-13
AI Technical Summary
During the charging and discharging cycle of secondary batteries, the hydrolysis and pyrolysis reaction of lithium salt lead to an increase in lithium ion consumption, an increase in impedance, and deterioration of circulation and storage performance, making it difficult to meet the electrochemical performance requirements of pure electric vehicles and hybrid electric vehicles for secondary batteries.
Using an electrolyte containing lithium salts, organic solvents and melamine-based additives, melamine-based additives include compounds with specific structures, such as perfluoroalkylacyl melamine and melamine, which can form stable hydrogen bonds with the HF and trace amounts of water generated by the hydrolysis and pyrolysis of lithium salts, inhibiting the progress of these reactions.
By inhibiting the hydrolysis and pyrolysis reaction of lithium salt, the lithium ion consumption and HF damage to the SEI film are reduced, the stability of the electrolyte is improved, the impedance of the secondary battery is reduced, the capacity retention rate, circulation performance and storage performance are improved, and the service life of the secondary battery is extended.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of secondary batteries, and in particular to an electrolyte, a secondary battery and an electrical device using the same. Background Art
[0002] In secondary batteries, electrolytes play an important role in promoting charge transfer and ion conduction between the positive electrode plate and the negative electrode plate and suppressing the occurrence of side reactions.
[0003] Currently, the additives in electrolytes 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 secondary batteries. However, during the charge and discharge cycles of secondary batteries, the hydrolysis reaction and pyrolysis reaction of lithium salts in the electrolyte will consume a large amount of lithium ions in the secondary batteries, resulting in a decrease in the capacity of the secondary batteries. 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 batteries and deterioration of the cycle performance and storage performance, making it difficult to meet the requirements for the electrochemical performance of secondary batteries in current pure electric vehicles and hybrid electric vehicles. 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 problems of increased impedance, deterioration of capacity retention rate, cycle performance and storage performance in secondary batteries prepared based on electrolytes in related technologies.
[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 a melamine additive; the melamine additive includes a compound having formula (I), and / or a compound having formula (II):
[0007]
[0008] Wherein, R in formula (I) f represents a perfluoroalkyl group with f carbon atoms, f is any integer from 1 to 6; x, y and z each independently take a value of 0 or 1, and the sum of x and a is 2, the sum of y and b is 2, and the sum of z and c is 2.
[0009] Further, in the electrolyte, the mass ratio of the first additive is 0.2 wt% to 3 wt%.
[0010] 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, fluorinated ethylene carbonate, lithium bis(oxalate)borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.
[0011] Further, in the electrolyte, the mass percentage of the second additive is 5 wt% to 10 wt%.
[0012] Further, in the electrolyte, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, and lithium difluorophosphate.
[0013] Further, in the electrolyte, the mass percentage of the lithium salt is 8 wt% to 16 wt%.
[0014] Further, in the electrolyte, the organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
[0015] Further, in the electrolyte, the mass percentage of the organic solvent is 74 wt% to 85 wt%.
[0016] 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.
[0017] The present invention also provides an electrical device, wherein the electrical device includes the above secondary battery, and the secondary battery serves as a power supply for the electrical device.
[0018] Compared with the prior art, the embodiments of the present invention have the following advantages:
[0019] The electrolyte provided by an embodiment of the present invention includes a lithium salt, an organic solvent, and a first additive; the first additive includes a melamine-based additive, and the melamine-based additive includes a compound having formula (I) and / or a compound having formula (II); wherein, both the compound having formula (I) and the compound having formula (II) include amino groups and cyano groups, and the nitrogen atoms in the amino groups and cyano groups not only have relatively high electronegativity but also contain lone pairs of electrons, such that the amino groups and cyano groups in the first additive are extremely likely to react with HF generated by the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte and trace amounts of water in the electrolyte to form stable hydrogen bonds, inhibiting the progress of the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte, being conducive to reducing the consumption of lithium ions in the secondary battery by the hydrolysis reaction and pyrolysis reaction of the lithium salt, reducing the degree of damage of HF to the SEI film, and further reducing the steric hindrance of the electrolyte, improving the stability of the electrolyte. When the stability of the electrolyte is improved, the impedance of the secondary battery can be reduced, and the capacity retention rate, cycle performance, and storage performance of the secondary battery can be improved.
[0020] 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 Embodiments
[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. 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.
[0022] 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 embodiments.
[0023] In the related art, during the charge and discharge cycle of a secondary battery, the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte will consume a large amount of lithium ions (Li + ) in the secondary battery, resulting in a reduction in the capacity of the secondary battery. Further, HF generated by the hydrolysis reaction and pyrolysis reaction of the lithium salt 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 requirements of the current pure electric vehicles and hybrid electric vehicles for the electrochemical performance of secondary batteries.
[0024] An embodiment of the present invention provides an electrolyte to solve the above problems. The electrolyte includes a lithium salt, an organic solvent, and a first additive.
[0025] Among them, the first additive includes a melamine-based additive; the melamine-based additive includes a compound having formula (I), and / or a compound having formula (II):
[0026]
[0027] It should be noted that R in formula (I) f represents a perfluoroalkyl group having f carbon atoms, where f is any integer from 1 to 6; x, y, and z each independently take a value of 0 or 1, and the sum of x and a is 2, the sum of y and b is 2, and the sum of z and c is 2.
[0028] Specifically, the compound having formula (I) is a perfluoroalkyl acyl melamine; in formula (I), each perfluoroalkyl group R f connected to a carbon atom independently selects any integer from 1 to 6 for the number of carbon atoms.
[0029] The perfluoroalkyl group R f can be represented by the structural formula -(CF 2 ) n CF 3 , where n takes a value of f - 1.
[0030] In formula (I), in the perfluoroalkyl acyl NH x (R f ) a connected to a carbon atom, x takes a value of 0 or 1, and x + a = 2; in the perfluoroalkyl acyl NH y (R f ) b connected to a carbon atom, y takes a value of 0 or 1, and y + b = 2; in the perfluoroalkyl acyl NH z (R f ) c connected to a carbon atom, z takes a value of 0 or 1, and z + c = 2.
[0031] In the implementation of the present invention, x, y, and z each independently take a value of 0 or 1, that is, the values of x, y, and z can be the same or different, and the embodiments of the present invention do not limit this.
[0032] The compound having formula (II) is melamine.
[0033] It can be understood that the hydrolysis reaction of the lithium salt in the electrolyte usually involves the cation or anion in the lithium salt and a small amount of water molecules (H 2The chemical reaction between (O), and the pyrolysis reaction of the lithium salt refers to the process of the lithium salt decomposing 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 reduction 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, leading to an increase in the impedance of the secondary battery and deterioration of the cycling performance and storage performance, making it difficult to meet the requirements for the electrochemical performance of secondary batteries in current pure electric vehicles and hybrid electric vehicles. Among them, the high-temperature condition refers to the high-temperature condition during the operation of the secondary battery. In the embodiments of the present invention, the temperature range corresponding to the high-temperature condition can be 40°C to 60°C.
[0034] In the embodiments of the present invention, when the melamine-based additive includes a compound having the formula (I), the compound having the formula (I) includes an amino group (-NH x -), and a cyano group (-CN). The nitrogen (N) atoms in the amino group (-NH x -) and the cyano group (-CN) not only have a relatively high electronegativity but also contain lone pairs of electrons, making the amino group (-NH x -) and the cyano group (-CN) in the melamine-based additive extremely likely to react with HF generated by the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte and trace amounts of water in the electrolyte to form stable hydrogen bonds; when the melamine-based additive includes a compound having the formula (II), the compound having the formula (II) includes an amino group (-NH 2 ), and a cyano group (-CN). The nitrogen atoms in the amino group (-NH 2 ) and the cyano group (-CN) not only have a relatively high electronegativity but also contain lone pairs of electrons, making the amino group (-NH 2 ) and the cyano group (-CN) in the melamine-based additive extremely likely to react with HF in the electrolyte and trace amounts of water in the electrolyte to form stable hydrogen bonds.
[0035] Furthermore, in the amino group (-NH x - and / or -NH 2) When the cyano group (-CN) reacts with HF and trace amounts of water in the electrolyte to form hydrogen bonds, based on the interaction between the nitrogen atom and the hydrogen atom in the hydrogen bond, the stability of the electrolyte system can be improved, significantly increasing the energy required for the hydrolysis reaction and pyrolysis reaction of the lithium salt, thereby inhibiting the progress of the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte, reducing the consumption of lithium ions in the secondary battery by the hydrolysis reaction and pyrolysis reaction of the lithium salt, and the degree of damage to the SEI film by the reaction product HF; further, the process of the amino group and the cyano group reacting with HF and trace amounts of water in the electrolyte to form hydrogen bonds will also break the hydrogen bond network between water molecules in the electrolyte, reducing the steric hindrance of the electrolyte; it should be noted that when the electrolyte operates under high-rate conditions, the interaction between lithium ions and organic solvent molecules in the electrolyte is strong, and it is difficult for lithium ions to desolvate at the interface of the negative electrode plate of the secondary battery, thus easily forming a highly polarized interface on the surface of the negative electrode plate, resulting in a decrease in the capacity of the secondary battery and the formation of lithium dendrites on the surface of the negative electrode plate. In the embodiment of the present invention, by reducing the steric hindrance of the electrolyte, the steric hindrance effect of the electrolyte can be reduced, the solvation structure and the desolvation behavior of lithium ions can be regulated, thereby improving the stability of the electrolyte. When the stability of the electrolyte is improved, the side reaction between the electrolyte and the electrode plate can be reduced, unnecessary interfacial films or precipitates can be avoided, the stability of the solvation structure can be improved, making the transmission of lithium ions in the electrolyte smoother, reducing the resistance of ion transmission in the electrolyte, which is beneficial to reducing the impedance of the secondary battery; in addition, when the stability of the electrolyte is improved, the volume change during the charge and discharge cycle of the secondary battery can also be reduced, improving the capacity retention rate, cycle performance and storage performance of the secondary battery, and extending the service life of the secondary battery.
[0036] In addition, the fluorine (F) atom in the perfluoroalkyl group R in the compound having the formula (I) f can also react with HF in the electrolyte and trace amounts of water in the electrolyte to form a hydrogen bond F-H-F(O), thereby providing more hydrogen bond reaction sites for the formation of hydrogen bonds.
[0037] When the melamine-based additive includes both the compound having the formula (I) and the compound having the formula (II) at the same time, the amino group (-NH x -) and the cyano group (-CN) in the compound having the formula (I), and the amino group (-NH 2 ) and the cyano group (-CN) in the compound having the formula (II) can react with HF in the electrolyte and trace amounts of water in the electrolyte to form hydrogen bonds at the same time, providing more hydrogen bond reaction sites for the formation of hydrogen bonds, which is beneficial to improving the inhibitory effect on the hydrolysis reaction and pyrolysis reaction processes of the lithium salt in the electrolyte, and further improving the stability of the electrolyte.
[0038] In addition, the first additive in the electrolyte provided by the embodiments of the present invention is a melamine-based additive, which also has the characteristics of low toxicity, low cost, stability, flame retardancy and low surface tension. While improving the stability of the electrolyte, it is also beneficial to improve the environmental protection performance and safety performance of the electrolyte, reduce the preparation cost of the electrolyte, and improve the filling effect of the electrolyte.
[0039] Optionally, in some embodiments, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the first additive is 0.2 wt% to 3 wt%; specifically, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the first additive can be one of 0.2 wt%, 0.5 wt%, 1 wt%, 1.8 wt%, 2.2 wt%, 2.5 wt% and 3 wt% or the range value of any two of them. Within this range value, the effect of the melamine-based additive in improving the stability of the electrolyte can be further exerted.
[0040] It should be noted that when the melamine-based additive only includes the compound with formula (I), the mass ratio of the compound with formula (I) in the electrolyte is 0.2 wt% to 3 wt%; when the melamine-based additive only includes the compound with formula (II), the mass ratio of the compound with formula (II) in the electrolyte is 0.2 wt% to 3 wt%; when the melamine-based additive includes both the compound with formula (I) and the compound with formula (II) at the same time, in the electrolyte, the sum of the mass ratio of the compound with formula (I) and the mass ratio of the compound with formula (II) is 0.2 wt% to 3 wt%.
[0041] Optionally, in some embodiments, the electrolyte provided by the embodiments of the present invention 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), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (4-Fluoro-1,3-dioxolan-2-one, FEC), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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 the occurrence of side reactions; 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.
[0047] 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.
[0048] Lithium bis(trifluoromethanesulfonyl)imide has high conductivity and chemical stability and can enhance the overall performance of the electrolyte.
[0049] It can be understood that the above-mentioned second additives can cooperate with the first additive to inhibit the hydrolysis reaction and pyrolysis reaction processes of the lithium salt in the electrolyte, improve the stability of the electrolyte, and further reduce the impedance of the secondary battery, improve the capacity retention rate, cycle performance and storage performance of the secondary battery, and extend the service life of the secondary battery.
[0050] Optionally, in some embodiments, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the second additive is 5 wt% to 10 wt%; specifically, in the electrolyte provided by the embodiments of the present invention, 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. Within this range value, the effect of the second additive in improving the performance of the electrolyte can be further exerted.
[0051] Optionally, in some embodiments, in the electrolyte provided by the embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate (LiPF 6 )、lithium tetrafluoroborate (LiBF 4 ), lithium difluorooxalate borate (LiODFB), lithium difluorophosphate (LiPO 2 F 2 ) or at least one of them.
[0052] 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 temperature 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 difluorooxalate borate has excellent high and low temperature performance and can maintain stable electrochemical performance in a wide temperature range; in addition, lithium difluorooxalate 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.
[0053] Optionally, in some embodiments, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the lithium salt is 8 wt% to 16 wt%; specifically, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the lithium salt can be one of 8 wt%, 10 wt%, 12 wt%, 13 wt%, 15 wt% and 16 wt% or the range value of any two of them. Within this range value, while improving the conductivity of the electrolyte, the viscosity of the electrolyte can be made moderate, which can effectively balance the conductivity and viscosity of the electrolyte and further exert the effect of the lithium salt in improving the performance of the electrolyte.
[0054] Optionally, in some embodiments, in the electrolyte provided by the embodiments of the present invention, the organic solvent includes at least two of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).
[0055] Among them, ethylene carbonate has a high film-forming potential on the negative electrode sheet and participates in the formation of the SEI film on the surface of the graphite negative electrode sheet, reducing side reactions on the surface of the electrode sheet. Moreover, ethylene carbonate has a relatively high dielectric constant, which can improve the ionic conductivity of the electrolyte.
[0056] Propylene carbonate can enhance the stability of the secondary battery, protect the negative electrode sheet, reduce the polarity of the electrolyte, and reduce the possibility of secondary battery failure; propylene carbonate can inhibit the expansion of the mercury alloy negative electrode and extend the cycle life of the secondary battery; propylene carbonate can improve the discharge capacity and cycle life of the secondary battery and improve the structural stability and electrochemical performance of the positive electrode material; in addition, propylene carbonate can also reduce the operating temperature of the secondary battery and improve the stability of the secondary battery.
[0057] Dimethyl carbonate can mix with electrolyte components with low polarity, such as ethylene carbonate and diethyl carbonate, to form a balanced dissolution, enabling the secondary battery to reach a stable state faster and improving the cycle life and capacity retention rate of the secondary battery; dimethyl carbonate can increase the electrochemical window of the secondary battery, reduce the film formation rate on the surface of the electrode sheet, reduce the interfacial resistance, and improve the capacity and cycle life of the secondary battery.
[0058] Diethyl carbonate can be used in combination with other solvents, such as ethylene carbonate and dimethyl carbonate, to improve the solubility of the electrolyte.
[0059] Ethyl methyl carbonate mainly plays a role in providing an ion conduction channel in the electrolyte, enabling the ions in the electrolyte to be transferred 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.
[0060] Optionally, in some embodiments, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the organic solvent is 74wt% to 85wt%; specifically, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the organic solvent can be one of 74wt%, 76wt%, 78wt%, 80wt%, 82wt% and 85wt% or the range value of any two of them. Within this range value, it is beneficial to fully dissolve the lithium salt, provide a necessary migration medium for lithium ions, improve the conductivity of the electrolyte, and further improve the safety performance of the secondary battery and extend the service life of the secondary battery.
[0061] 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 100wt%.
[0062] The present invention also provides a preparation method of an electrolyte. The preparation method includes: under the protection of an inert gas, mixing a lithium salt and an organic solvent to obtain a colorless and transparent liquid; mixing the above-mentioned first additive, second additive and the above-mentioned colorless and transparent liquid to obtain an electrolyte.
[0063] Among them, during the process of mixing the lithium salt and the organic solvent, since the addition of 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 during the addition of the lithium salt, it is necessary to control the temperature of the electrolyte; specifically, when the temperature of the electrolyte rises by more than 2°C, stop adding the lithium salt, and when the temperature of the electrolyte rises below 2°C, continue to add the lithium salt.
[0064] Among them, the temperature control of the above-mentioned electrolyte can adopt ice bath, dry ice circulation cooling, liquid nitrogen cooling, etc.
[0065] Optionally, in some embodiments, the above-mentioned organic solvent includes a variety of solvents. Before mixing the lithium salt and the organic solvent, it is necessary to pre-mix and dehydrate the various solvents, 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 and transparent liquid; then mix the above-mentioned first additive, second additive with the above-mentioned colorless and transparent liquid to obtain an electrolyte. Among them, the organic solvent can be dehydrated by means of molecular sieve adsorption.
[0066] The present invention also proposes a secondary battery, wherein the secondary battery includes a positive electrode plate, a negative electrode plate and the above-mentioned electrolyte.
[0067] Among them, the lithium salt in the electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate.
[0068] 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 lithium-ion transition metal oxide includes at least one of lithium cobaltate, lithium manganate, and lithium iron phosphate, and the ternary positive electrode material may specifically be a high-nickel layered ternary positive electrode material.
[0069] Optionally, in some embodiments, the positive electrode sheet further includes a conductive agent and a binder. The conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fiber, and carbon microspheres. The binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.
[0070] In some embodiments, the positive electrode sheet is prepared as follows: Dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the binder, and any other components, in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; Coating the positive electrode slurry on both sides of a positive electrode current collector such as aluminum foil; After processes such as baking, rolling, and cutting, the positive electrode sheet can be obtained.
[0071] 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 negative electrode active material layer may adopt 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.
[0072] In the secondary battery provided by the embodiments of the present invention, the negative electrode sheet further includes a conductive agent and a binder; Optionally, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes a carboxymethyl cellulose-based binder and a resin-based binder.
[0073] 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.
[0074] In some embodiments, the negative electrode sheet is prepared as follows: Dispersing the components for preparing the negative electrode sheet, such as the negative electrode active material, the binder, and the conductive agent, in a solvent such as deionized water to form a negative electrode slurry; Coating the negative electrode slurry on both sides of a negative electrode current collector such as copper foil; After processes such as baking, rolling, and cutting, the negative electrode sheet can be obtained.
[0075] Understandably, the secondary battery provided by the embodiments of the present invention further includes a separator.
[0076] In practical applications, the negative electrode sheet, the separator and the 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. After baking the bare battery cell, it is filled with electrolyte, formed, secondarily sealed and sorted to obtain the above-mentioned secondary battery.
[0077] The present invention also proposes an electrical device. Among them, the electrical device includes the above-mentioned secondary battery, and this secondary battery serves as the power supply of the electrical device.
[0078] 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. For related parts, refer to the partial description of the electrolyte embodiments.
[0079] 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.
[0080] The present invention will be described in detail below through embodiments.
[0081] Embodiment 1
[0082] (1) Preparation of electrolyte:
[0083] At room temperature, in a glove box filled with argon (H 2 O < 1 ppm, O 2 < 1 ppm), ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate are mixed evenly to obtain an organic solvent; lithium hexafluorophosphate is added to the organic solvent successively, and continuous stirring and dry ice cooling are used to ensure that when the temperature of the electrolyte rises by no more than 2 °C, lithium hexafluorophosphate can be added continuously to obtain a colorless transparent liquid; perfluoroalkyl acyl melamine of the compound having the formula (I) and melamine of the compound having the formula (II), as well as a second additive vinylene carbonate, propylene sulfite and fluoroethylene carbonate are added to the colorless transparent liquid, and stirred evenly to obtain an electrolyte; wherein, in the electrolyte, the mass ratio of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, perfluoroalkyl acyl melamine and melamine is 29.4:27.5:19.5:15.7:2.9:2:1:1:1.
[0084] (2) Preparation of positive electrode sheet:
[0085] The positive electrode active material Li(Ni 0.8 Mn 0.1 Co0.1 )O 2 、 The conductive agent acetylene black (Super P) and the binder polyvinylidene fluoride are mixed evenly in a mass ratio of 95:3:2, and uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to make a positive electrode slurry. The positive electrode slurry is coated on both sides of the aluminum foil, baked, rolled, and cut into pieces to obtain a positive electrode sheet.
[0086] (3) Preparation of the negative electrode sheet
[0087] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed evenly in a mass ratio of 95:2:1.5:1.5, and uniformly dispersed in deionized water to make a negative electrode slurry. The negative electrode slurry is coated on both sides of the copper foil, baked, rolled, and cut into pieces to obtain a negative electrode sheet.
[0088] (4) Preparation of the secondary battery
[0089] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and tab welding, a bare battery core is obtained. The bare battery core is placed in an outer packaging aluminum-plastic film and baked in an oven at 85 ± 10 °C for 24 h. The electrolyte prepared in step (1) is injected into the dried battery, and after standing, forming, and grading, the preparation of a 10AH lithium manganate ternary system secondary battery is completed to obtain a secondary battery.
[0090] Examples 2 to 4
[0091] The differences between Examples 2 to 4 and Example 1 are 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, perfluoroalkyl acyl melamine, and melamine are 29.4:27.5:19.5:15.7:3.8:2.6:1.3:0.1:0.1, 29.4:27.5:19.4:15.7:2.45:1.7:0.85:1.5:1.5, and 29.4:27.5:19.5:15.7:2.9:2:1:1.5:0.5, respectively.
[0092] Example 5
[0093] Example 5 is different from Example 1 in that in step (1), a perfluoroalkyl acyl melamine compound of formula (I) and second additives vinylene carbonate, propylene sulfite, and fluoroethylene carbonate are added to the colorless transparent liquid, and the mixture is stirred evenly to obtain an electrolyte; wherein, in the electrolyte, the mass ratio of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and perfluoroalkyl acyl melamine is 29.4:27.5:19.5:15.7:2.9:2:1:2.
[0094] Examples 6 - 7
[0095] Examples 6 - 7 are different from Example 5 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 perfluoroalkyl acyl melamine are 29.4:27.5:19.5:15.7:3.8:2.6:1.3:0.2 and 29.4:27.5:19.4:15.7:2.45:1.7:0.85:3, respectively.
[0096] Example 8
[0097] Example 8 is different from Example 1 in that in step (1), melamine of formula (II) and second additives vinylene carbonate, propylene sulfite, and fluoroethylene carbonate are added to the colorless transparent liquid, and the mixture is stirred evenly to obtain an electrolyte; wherein, in the electrolyte, the mass ratio of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and melamine is 29.4:27.5:19.5:15.7:2.9:2:1:2.
[0098] Examples 9 - 10
[0099] Examples 9 - 10 are different from Example 8 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 melamine are 29.4:27.5:19.5:15.7:3.8:2.6:1.3:0.2 and 29.4:27.5:19.4:15.7:2.45:1.7:0.85:3, respectively.
[0100] Comparative Example 1
[0101] The difference between Comparative Example 1 and Example 1 is that in step (1), the electrolyte does not include the first additive, and in the electrolyte, the mass ratio of ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, vinylene carbonate, propylene sulfite, and fluoroethylene carbonate is 30:28:20:16:3:2:1.
[0102] The components and parameters of the electrolytes in Example 1, Example 5, Example 8, and Comparative Example 1 are shown in Table 1.
[0103] Table 1
[0104]
[0105] Test methods:
[0106] (1) Cycling performance test: The temperature of the constant temperature box is set at 45 ± 2 °C, charged and discharged at 1C, and cycled within the voltage range of (2.8V - 4.2V).
[0107] (2) Storage performance test: Charge the battery at a constant current and constant voltage of 1C until it is fully charged. After leaving it at 55 ± 2 °C for 30 days, perform charge and discharge cycling at room temperature for 4 weeks, and calculate the capacity retention rate and capacity recovery rate of the secondary battery.
[0108] (3) Direct Current Resistance (DCR) test: Discharge the secondary battery at a rate of 30C for 30s when the battery is at 50% State of Charge (SOC).
[0109] (4) Volume change rate test: First, hang the porous box on the load-bearing member and completely immerse the porous box under the liquid level of deionized water, and read the first value M0 of the electronic scale; then, place the secondary battery into the porous box, hang the porous box on the load-bearing member and completely immerse the porous box under the liquid level of deionized water, and read the second value M1 of the electronic scale; then, determine the volume of the secondary battery based on the first value M0 and the second value M1; specifically, according to the buoyancy calculation formula F 浮 =(M1 - M0)g = ρ 水 gV, the calculation formula for the volume of the secondary battery is: V = (M1 - M0) / ρ 水 , where F 浮 represents the buoyancy force received by the secondary battery, ρ 水 represents the density of deionized water, g represents the acceleration due to gravity, and V represents the volume of the secondary battery.
[0110] Perform storage performance test, DCR test, and volume change rate test on the secondary batteries prepared in Example 1, Example 5, Example 8, and Comparative Example 1, and the test data are shown in Table 2.
[0111] Table 2
[0112] Example Volume change rate DCR growth rate Capacity retention rate Capacity recovery rate Example 1 3.06％ 6.52％ 96.72％ 99.20％ Example 5 3.89％ 5.81％ 96.63％ 99.47％ Example 8 3.53％ 6.72％ 97.21％ 98.96％ Comparative Example 1 11.02％ 18.39％ 94.72％ 97.23％
[0113] The cycle performance of the secondary batteries prepared in Example 1, Example 5, Example 8 and Comparative Example 1 was tested, and the test data are shown in Table 3.
[0114] Table 3
[0115]
[0116] According to the test data in Table 2, it can be seen that the volume change rate of the secondary batteries prepared by Example 1, 5 and 8 is maintained below 4%, which is more than 7% lower than the volume change rate of 11.02% of the secondary batteries prepared by Comparative Example 1; further, the DCR growth rate of the secondary batteries prepared by Example 1, 5 and 8 is maintained below 7%, which is more than 11% lower than the DCR growth rate of 18.39% of the secondary batteries prepared by Comparative Example 1. In addition, after the storage performance test, the capacity retention rate of the secondary batteries prepared by Example 1, 5 and 8 is above 96.5%, and the capacity recovery rate is above 98.9%, while the capacity retention rate of the secondary batteries prepared by Comparative Example 1 is only 94.72% and the capacity recovery rate is only 97.23%. Thus, it can be seen that the volume change rate and internal impedance of the secondary batteries prepared based on the electrolyte provided in the embodiments of the present invention are significantly reduced, and the storage performance is significantly improved.
[0117] According to the test data in Table 3, it can be seen that with the increase of the cycle number, compared with Comparative Example 1, the capacity retention rates of the secondary batteries prepared by Example 1, 5 and 8 all increase significantly, and when the cycle number reaches 577, the capacity retention rates of the secondary batteries prepared by Example 1, 5 and 8 can still be maintained above 97%, while the capacity retention rate of the secondary batteries prepared by Comparative Example 1 is only 93.09%. Thus, it can be seen that the cycle performance of the secondary batteries prepared based on the electrolyte provided in the embodiments of the present invention is significantly improved.
[0118] In summary, the electrolyte provided by the embodiments of the present invention includes a lithium salt, an organic solvent, and a first additive; the first additive includes a melamine-based additive, and the melamine-based additive includes a compound having the formula (I) and / or a compound having the formula (II); wherein, both the compound having the formula (I) and the compound having the formula (II) include amino groups and cyano groups, and the nitrogen atoms in the amino groups and cyano groups not only have relatively high electronegativity but also contain lone pairs of electrons, so that the amino groups and cyano groups in the first additive are extremely easy to react with HF generated by the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte and trace amounts of water in the electrolyte to form stable hydrogen bonds, inhibiting the progress of the hydrolysis reaction and pyrolysis reaction of the lithium salt in the electrolyte, which is beneficial to reducing the consumption of lithium ions in the secondary battery by the hydrolysis reaction and pyrolysis reaction of the lithium salt, reducing the damage degree of HF to the SEI film, and further reducing the steric hindrance of the electrolyte, improving the stability of the electrolyte. When the stability of the electrolyte is improved, the impedance of the secondary battery can be reduced, and the capacity retention rate, cycle performance, and storage performance of the secondary battery can be improved.
[0119] The above has introduced in detail an electrolyte, a secondary battery, and an electrical device using the same 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 a melamine additive; the melamine additive includes a compound having formula (I) and / or a compound having formula (II): Wherein, R in formula (I) f It represents a perfluoroalkyl group having f carbon atoms, where f is any integer from 1 to 6; x, y and z are each independently 0 or 1, and the sum of x and a is 2, the sum of y and b is 2, and the sum of z and c is 2.
2. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass percentage of the first additive is 0.2 wt % to 3 wt %.
3. 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).
4. The electrolyte according to claim 3, characterized in that In the electrolyte, the mass percentage of the second additive is 5wt% to 10wt%.
5. The electrolyte according to claim 1, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate.
6. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass percentage of the lithium salt is 8wt% to 16wt%.
7. The electrolyte according to claim 1, characterized in that The organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
8. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass proportion of the organic solvent is 74wt% to 85wt%.
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.