Electrolyte, lithium-ion battery and electrical equipment

Abstract

The embodiments of the present invention disclose an electrolyte, a lithium-ion battery, and an electrical device. The electrolyte includes a lithium salt, a solvent, and an additive. The additive includes a perfluoroorganic compound represented by formula (I): #imgabs0# wherein R1 and R2 are independently selected from fluorine atoms or perfluoroalkyl groups, R3 is selected from a perfluoroalkyl group, M is selected from Fe or Cs, and n is 2 or 3. This perfluoroorganic compound can be adsorbed onto the surface of the battery's negative electrode through its ionic properties, accelerating the insertion kinetics of lithium ions and thereby slowing down the delithiation phenomenon. It can also stabilize the voltage under overcharge conditions through the shuttling reaction of its cations between the positive and negative electrodes, acting as an overcharge protection additive. It can also form fluorine-containing free radicals to capture hydrogen atoms, acting as a flame retardant. Its application in lithium-ion batteries can effectively improve the battery's cycle life and safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte, a lithium ion battery and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage due to their high energy density, long cycle life and good safety performance. In lithium-ion battery systems, the electrolyte plays a vital role as an intermediate bridge connecting the positive and negative electrode material systems, and the addition of functional molecules can improve the overall performance of the battery. At present, the method commonly used to address the problem of lithium plating at the negative electrode of the battery is to add electrochemical reduction-type film-forming additives to the electrolyte. The reduction potential of such additives is higher than that of the organic solvent in the electrolyte. They can decompose before the electrolyte and form a solid electrolyte interface film (SEI) on the surface of the negative electrode, thereby slowing down the lithium plating at the negative electrode by enhancing the stability of the SEI film. However, such additives have some limitations: (1) they will be gradually consumed and fail during the long cycle of the battery; (2) they are not suitable for use under low temperature and high rate conditions. In addition, lithium-ion battery electrolytes generally use highly flammable organic carbonate solvents. Under extreme conditions such as overheating and overcharging, the battery may thermally run away and cause fire or explosion, thereby creating safety hazards and posing great risks. In order to further improve the safety performance of batteries, overcharge protection additives and flame retardant additives have received increasing attention. Therefore, it is necessary to provide a multifunctional electrolyte additive to comprehensively solve the above problems. Summary of the Invention

[0003] Based on this, embodiments of the present invention provide an electrolyte, a lithium-ion battery, and an electrical device. The electrolyte contains a perfluorinated organic compound. This perfluorinated organic compound can adsorb onto the surface of the battery's negative electrode through its ionic properties, accelerating the insertion kinetics of lithium ions and thereby slowing the delithiation phenomenon. Furthermore, under overcharge conditions, its cations shuttle between the positive and negative electrodes to stabilize the voltage, acting as an overcharge protection additive. Furthermore, it can form fluorinated free radicals that capture hydrogen atoms, providing a flame retardant effect. Application of this electrolyte in lithium-ion batteries can effectively improve the battery's cycle life and safety performance.

[0004] In a first aspect, an embodiment of the present invention provides an electrolyte, the electrolyte comprising a lithium salt, a solvent and an additive, the additive comprising a perfluorinated organic compound represented by formula (I),

[0005]

[0006] Wherein, R1 and R2 are independently selected from fluorine atoms or perfluoroalkyl groups, R3 is selected from perfluoroalkyl groups, M is selected from Fe or Cs, and n is 2 or 3.

[0007] In an embodiment of the present invention, the perfluoroorganic compound includes at least one of perfluoro(2-methyl-3-oxahexanoate)iron and perfluoro(2-methyl-3-oxahexanoate)cesium.

[0008] In an embodiment of the present invention, the mass ratio of the perfluorinated organic compound to the electrolyte excluding the lithium salt is 0.01%-5%.

[0009] In an embodiment of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium trifluoromethylsulfonate, lithium bis(fluorosulfonyl imide), lithium hexafluoroarsenide, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium perchlorate and lithium tetrafluoroaluminate.

[0010] In an embodiment of the present invention, the concentration of the lithium salt in the electrolyte is 0.1 mol / L-4 mol / L.

[0011] In an embodiment of the present invention, the solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, γ-butyrolactone, tetrahydrofuran and dipropylene glycol dimethyl ether.

[0012] In an embodiment of the present invention, the solvent is a mixture of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0013] In an embodiment of the present invention, the additive further includes a film-forming additive, and the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, glycerol tris(propionitrile) ether, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, vinyl sulfite and propylene sulfite.

[0014] In an embodiment of the present invention, the mass ratio of the film-forming additive to the electrolyte excluding the lithium salt is 0.1%-5%.

[0015] The electrolyte provided by the embodiments of the present invention contains a perfluorinated organic compound. This compound can adsorb onto the surface of the battery's negative electrode through its ionic properties, accelerating the insertion kinetics of lithium ions and thus slowing the delithiation phenomenon. Furthermore, under overcharge conditions, its cations shuttle between the positive and negative electrodes to stabilize the voltage, acting as an overcharge protection additive. Furthermore, it can form fluorinated free radicals that capture hydrogen atoms, acting as a flame retardant. Therefore, the application of this electrolyte in lithium-ion batteries can effectively improve the battery's cycle life and safety performance.

[0016] In a second aspect, an embodiment of the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte comprises the electrolyte described in the first aspect.

[0017] The lithium-ion battery provided by the embodiment of the present invention contains a perfluorinated organic compound, which can not only alleviate the problem of lithium plating at the negative electrode, but also has anti-overcharge and flame retardant properties, which helps to improve the cycle stability and safety of the battery.

[0018] In a third aspect, an embodiment of the present invention further provides an electrical device, wherein the electrical device includes the lithium-ion battery described in the second aspect.

[0019] The electric device provided in the embodiment of the present invention includes the lithium-ion battery described in the second aspect. The lithium-ion battery has a long cycle life and good safety performance, so that the electric device can be used stably for a long time, which is conducive to improving the performance of the electric device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments of the present invention will be described below.

[0021] Figure 1 FIG. 1 is a schematic structural diagram of a lithium-ion battery 100 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0023] Lithium-ion batteries are widely used in various applications, including consumer electronics, electric vehicles, medical electronics, and drones. Lithium-ion batteries primarily consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is a key component of lithium-ion batteries, transporting lithium ions between the positive and negative electrodes. To further enhance the functionality of lithium-ion batteries, various electrolyte additives have been added. These additives, while effective in small amounts, have become a hot topic of research in recent years.

[0024] At present, the phenomenon of lithium plating at the negative electrode is the most important problem affecting the cycle life and safety performance of lithium-ion batteries. Lithium plating at the negative electrode not only accelerates the capacity decay of the battery and causes more electrolyte consumption, but may also puncture the diaphragm and cause internal short circuit and thermal runaway of the battery. Therefore, it is urgent to solve the problem of lithium plating. Existing research on slowing down lithium plating by adding electrolyte additives mainly focuses on electrochemical reduction film-forming additives (such as vinylene carbonate (VC)). Electrochemical reduction film-forming additives refer to organic solvents with a higher reduction potential than the electrolyte. They can decompose before the electrolyte and form an SEI film on the negative electrode surface, thereby slowing down lithium plating at the negative electrode by changing the characteristics of the SEI film. However, this type of additive has some limitations: (1) Because its mechanism of action is to decompose before the electrolyte and thus protect the electrolyte, once its content is exhausted, the battery capacity will be greatly decayed, so this type of additive will fail under long cycles. (2) Under conditions such as low temperature and high-rate charge and discharge, the diffusion of lithium ions in the solid phase is slow, which will cause lithium ions to aggregate at the surface of the electrode / electrolyte, and then lithium precipitation will occur. Therefore, this type of additive is not suitable for use under low temperature and high-rate conditions. In addition, lithium-ion battery electrolytes generally use highly flammable organic carbonate solvents. Under extreme conditions such as overheating and overcharging, the battery may thermally run away and cause fire or explosion, thereby creating safety hazards and posing great risks. In order to further improve the safety performance of batteries, overcharge protection additives and flame retardant additives have received increasing attention. Therefore, it is necessary to provide a multifunctional electrolyte additive to comprehensively solve the above problems.

[0025] Based on this, an embodiment of the present invention provides an electrolyte comprising a lithium salt, a solvent and an additive, wherein the additive comprises a perfluorinated organic compound represented by formula (I),

[0026]

[0027] Wherein, R1 and R2 are independently selected from fluorine atoms or perfluoroalkyl groups, R3 is selected from perfluoroalkyl groups, M is selected from Fe or Cs, and n is 2 or 3.

[0028] The electrolyte provided by the embodiment of the present invention contains a perfluoroorganic compound, which can be characteristically adsorbed onto the surface of the negative electrode of the battery, increase the diffusion rate and embedding rate of lithium ions, alleviate the phenomenon of lithium precipitation at the negative electrode, and act as an overcharge protection additive and a flame retardant additive, thereby effectively improving the cycle stability and safety of the battery. On the one hand, when the anion of the perfluoroorganic compound is adsorbed onto the surface of the negative electrode of the battery, since the adsorbed particles themselves are negatively charged, a potential difference between a tight layer and a dispersed layer can be formed, thereby promoting the diffusion and embedding of lithium ions, and the introduction of perfluoroorganic compounds can also reduce the concentration of lithium ions accumulated on the surface of the negative electrode, thereby reducing the occurrence of lithium precipitation. And unlike film-forming additives, the perfluoroorganic compound is adsorbed into the inner Helmholtz layer through ionic characteristics, affecting the embedding kinetics of lithium ions and reducing the concentration of lithium ions on the surface of the negative electrode to alleviate the problem of lithium precipitation. It does not participate in the formation of the SEI film, so it will not be consumed as the number of cycles increases, and can continue to play a role during a long cycle. On the other hand, the perfluoro organic compound contains ferrous ions or trivalent cesium ions. Due to its redox potential in the battery voltage overcharge interval, when the battery is overcharged, ferrous ions or trivalent cesium ions undergo oxidation reaction and become ferric ions and tetravalent cesium ions, thereby preventing the oxidative decomposition of the electrolyte at high voltage, reducing the loss of active materials and improving the safety performance of the battery. In addition, the solubility of ferrous ions and trivalent cesium ions in the electrolyte is better, which is conducive to better playing a role. Therefore, ferrous ions or trivalent cesium ions can absorb excess charge and stabilize the voltage by the shuttle reaction between the positive and negative electrodes, which helps to improve the anti-overcharge performance of the battery. In addition, the fluorine atoms in the perfluoro organic compound can form fluorine-containing free radicals when gasified, and fluorine-containing free radicals can capture hydrogen atoms, thereby suppressing the chain reaction of hydrogen radicals and having a flame retardant effect. In summary, this perfluorinated organic compound is a multifunctional additive that has the properties of preventing negative electrode lithium plating, overcharging and flame retardancy. When applied to lithium-ion batteries, it can better improve the overall performance of the battery compared to single-functional additives. At the same time, it can reduce the amount of other additives used, thereby increasing the battery capacity and reducing the battery preparation cost.

[0029] In some embodiments of the present application, M is Fe and n is 2; in some embodiments, M is Cs and n is 3.

[0030] In the embodiment of the present invention, a perfluoroalkyl group refers to a substituted alkyl group in which all hydrogen atoms in the alkyl molecule are replaced by fluorine atoms, which can be C1-C 18 That is to say, the number of carbon atoms of the perfluoroalkyl group can be 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 15 or 18. Specifically, the perfluoroalkyl group can be, but is not limited to, trifluoromethyl, pentafluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl, perfluoroheptyl or perfluorooctyl.

[0031] In the embodiment of the present invention, when R1 and / or R2, and R3 are perfluoroalkyl groups, they may be the same perfluoroalkyl group or different perfluoroalkyl groups.

[0032] In an embodiment of the present invention, the perfluorinated organic compound includes at least one of perfluoro(2-methyl-3-oxahexanoate)iron (FPFA) and perfluoro(2-methyl-3-oxahexanoate)cesium (CPFA). FPFA and CPFA are easily available, have good solubility, and can effectively inhibit lithium deposition on the electrode.

[0033] In an embodiment of the present invention, the proportion of the perfluorinated organic compound relative to the mass of the electrolyte excluding the lithium salt is 0.01%-5%, which can effectively alleviate the lithium plating problem of the negative electrode of the battery, improve the battery's anti-overcharge performance and flame retardant properties, while taking into account the battery's capacity, and avoid the waste of perfluorinated organic compounds, which is beneficial to cost control. In some embodiments, the proportion of the perfluorinated organic compound relative to the mass of the electrolyte excluding the lithium salt can be, for example, 0.01%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.3%, 4.5% or 5%.

[0034] In an embodiment of the present invention, the perfluorinated organic compound can be prepared by the following method: perfluoro(2-methyl-3-oxahexanoic acid), ferrous acetate or cesium trichloride, and polyacrylonitrile (PAN) are dissolved in a dimethylformamide (DMF) solution, and stirred continuously at 60°C for 12 hours to obtain a uniform and stable solution; the obtained solution is electrospun under a high voltage of 20 kV, with the distance between the needle and the roller being 12 cm, to obtain a spinning membrane; the obtained spinning membrane is calcined at 500°C for 3 hours to obtain FPFA or CPFA.

[0035] In the present invention, the main function of the lithium salt is to provide lithium ions to ensure that the battery has sufficient lithium ions during the charge and discharge process. These lithium ions are transferred between the positive and negative electrodes and are embedded and deintercalated in the negative electrode material during the charge and discharge process. In some embodiments, the lithium salt can include at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium trifluoromethylsulfonate, lithium bis(fluorosulfonyl imide), lithium hexafluoroarsenide, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium perchlorate, and lithium tetrafluoroaluminate.

[0036] In an embodiment of the present invention, the concentration of the lithium salt in the electrolyte is 0.1 mol / L to 4 mol / L, which can ensure the conductivity and ion transfer rate of the battery while avoiding waste of lithium salt, thereby helping to control costs. In some embodiments, the concentration of the lithium salt in the electrolyte can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L.

[0037] In the present invention, the role of the solvent is to effectively dissolve the lithium salt so that the ions between the positive and negative electrodes can move freely, thereby realizing the flow of electric current. In some embodiments, the solvent can include at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, gamma-butyrolactone, tetrahydrofuran and dipropylene glycol dimethyl ether. The above-mentioned solvent has high chemical stability, low volatility, high dielectric constant and low viscosity, which is conducive to improving the stability and safety of the battery. In some embodiments, the solvent can be a mixture of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0038] In an embodiment of the present invention, the additive may further include a film-forming additive, which prevents the electrode material from reacting with the electrolyte and has a stable structure by promoting the formation of a stable and effective SEI film on the surface of the electrode material, thereby further reducing the generation of lithium precipitation. Specifically, the film-forming additive may include at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, glycerol tris(propionitrile) ether, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, vinyl sulfite and propylene sulfite. In some embodiments, the film-forming additive may be vinylene carbonate, and the use of perfluorinated organic compounds in combination with vinylene carbonate can more effectively improve the structural stability of the electrode surface and better inhibit the effect of lithium precipitation.

[0039] In an embodiment of the present invention, the proportion of the film-forming additive relative to the mass of the electrolyte excluding the lithium salt is 0.5%-5%, which can not only further improve the structural stability of the battery electrode and alleviate the problem of lithium desorption, but also take into account the capacity of the battery, and avoid the waste of film-forming additives, which is beneficial to cost control. In some embodiments, the proportion of the film-forming additive relative to the mass of the electrolyte excluding the lithium salt is 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.7% or 5%.

[0040] An embodiment of the present invention further provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator positioned between the positive and negative electrodes, and an electrolyte, wherein the electrolyte comprises the electrolyte of any of the aforementioned embodiments. The lithium-ion battery provided by the embodiment of the present invention contains a perfluorinated organic compound, which not only alleviates the problem of lithium plating at the negative electrode but also exhibits overcharge resistance and flame retardancy, thereby improving the battery's cycling stability and safety.

[0041] In a specific embodiment, Figure 1 As shown, the lithium-ion battery 100 includes a negative electrode 10, an electrolyte 20, a separator 30, a positive electrode 40 and a battery case 50. The electrolyte 20 and the separator 30 are located between the negative electrode 10 and the positive electrode 40. The battery case 50 is used to encapsulate the negative electrode 10, the electrolyte 20, the separator 30 and the positive electrode 40.

[0042] In an embodiment of the present invention, the positive electrode 40 may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the negative electrode 10 may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the positive electrode active material layer may include a positive electrode active material, a conductive agent, and a binder, and the negative electrode active material layer may include a negative electrode active material, a conductive agent, and a binder. This application does not specifically limit these materials, and appropriate materials can be selected according to actual application requirements.

[0043] In an embodiment of the present invention, the positive electrode current collector may be aluminum foil; and the negative electrode current collector may be copper foil.

[0044] In an embodiment of the present invention, the positive electrode active material may be a phosphate positive electrode active material or a ternary positive electrode active material. Specifically, the positive electrode active material may be one or more of lithium iron phosphate, lithium cobaltate, lithium manganese oxide, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; the negative electrode active material may be one or more of graphite material, hard carbon material, soft carbon material, Si-based material, and Sn-based material.

[0045] In an embodiment of the present invention, the conductive agent may be one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes.

[0046] In an embodiment of the present invention, the binder may be one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0047] In the embodiment of the present invention, the separator may be a polypropylene film (PP), a polyethylene film (PE) or a PP / PE composite film.

[0048] An embodiment of the present invention further provides an electrical device comprising the lithium-ion battery of any of the above embodiments. Specifically, the electrical device may be an electric car, an electric motorcycle, an electric bicycle, a power bank, an unmanned aerial vehicle, a mobile phone, a computer, a camera, a power tool, a smart home appliance, or a wearable device.

[0049] The electric device provided in the embodiment of the present invention includes a lithium-ion battery. The lithium-ion battery has a long cycle life and good safety performance, so that the electric device can be used stably for a long time, which is beneficial to improving the performance of the electric device.

[0050] The technical solution of the present invention is further illustrated below through specific examples and comparative examples.

[0051] Example 1

[0052] According to the mass parts, 28.97 parts of ethylene carbonate (EC), 22.43 parts of dimethyl carbonate (DMC), 12 parts of diethyl carbonate (DEC) and 34 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 2.6 parts of perfluoro(2-methyl-3-oxahexanoic acid) iron ((C6F 11 O3)2Fe), ultrasonically mix it for 2h to make it evenly mixed; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0053] Example 2

[0054] According to the mass parts, 29.64 parts of ethylene carbonate (EC), 22.73 parts of dimethyl carbonate (DMC), 12.16 parts of diethyl carbonate (DEC) and 35.46 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 0.01 parts of perfluoro(2-methyl-3-oxahexanoic acid) iron ((C6F 11 O3)2Fe), ultrasonically mix it for 2h to make it evenly mixed; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0055] Example 3

[0056] According to the mass parts, 26.42 parts of ethylene carbonate (EC), 18.25 parts of dimethyl carbonate (DMC), 8.64 parts of diethyl carbonate (DEC) and 41.69 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 5 parts of perfluoro(2-methyl-3-oxahexanoic acid) iron ((C6F 11O3)2Fe), ultrasonically mix it for 2h to make it evenly mixed; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0057] Example 4

[0058] According to the mass parts, 30.12 parts of ethylene carbonate (EC), 22.86 parts of dimethyl carbonate (DMC), 10.16 parts of diethyl carbonate (DEC) and 36.36 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 0.5 parts of perfluoro(2-methyl-3-oxahexanoic acid)cesium ((C6F 11 O3)3Cs), ultrasonically mix it for 2h to make it evenly mixed; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0059] Example 5

[0060] According to the mass parts, 31.42 parts of ethylene carbonate (EC), 21.42 parts of dimethyl carbonate (DMC), 13.16 parts of diethyl carbonate (DEC) and 31.6 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 2.4 parts of perfluoro(2-methyl-3-oxahexanoic acid)cesium ((C6F 11 O3)3Cs), ultrasonically mix it for 2h to make it evenly mixed; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0061] Example 6

[0062] According to the mass parts, 30.52 parts of ethylene carbonate (EC), 20.64 parts of dimethyl carbonate (DMC), 10.74 parts of diethyl carbonate (DEC) and 33.1 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 5 parts of perfluoro(2-methyl-3-oxahexanoic acid)cesium ((C6F 11 O3)3Cs), ultrasonically mix it for 2h to make it evenly mixed; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0063] Example 7

[0064] In terms of mass, 31.41 parts of ethylene carbonate (EC), 19.65 parts of dimethyl carbonate (DMC), 12.42 parts of diethyl carbonate (DEC) and 34.12 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to mix them evenly; then 1.2 parts of perfluoro(2-methyl-3-oxahexanoic acid) iron and 1.2 parts of perfluoro(2-methyl-3-oxahexanoic acid) cesium were added and ultrasonicated for 2 hours to mix them evenly; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonicated for 2 hours to completely dissolve it to obtain an electrolyte containing 1 mol / L LiPF6.

[0065] Example 8

[0066] According to the mass parts, 30.26 parts of ethylene carbonate (EC), 20.66 parts of dimethyl carbonate (DMC), 13.26 parts of diethyl carbonate (DEC) and 30.82 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 2.6 parts of perfluoro(2-methyl-3-oxahexanoic acid) iron ((C6F 11 O3)2Fe) and 2.4 parts of vinylene carbonate (VC), ultrasonically mixed for 2 hours to make them uniform; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2 hours to obtain an electrolyte containing 1 mol / L LiPF6.

[0067] Comparative Example 1

[0068] In terms of mass, 28.97 parts of ethylene carbonate (EC), 21.88 parts of dimethyl carbonate (DMC), 16.26 parts of diethyl carbonate (DEC) and 32.89 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to mix them evenly; then lithium hexafluorophosphate (LiPF6) was added and ultrasonicated for 2 hours to completely dissolve it to obtain an electrolyte containing 1 mol / L LiPF6.

[0069] Comparative Example 2

[0070] In terms of mass, 26.97 parts of ethylene carbonate (EC), 20.88 parts of dimethyl carbonate (DMC), 16.26 parts of diethyl carbonate (DEC) and 32.89 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to mix them evenly; then 3 parts of vinylene carbonate (VC) were added and ultrasonicated for 2 hours to mix them evenly; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonicated for 2 hours to completely dissolve it to obtain an electrolyte containing 1 mol / L LiPF6.

[0071] Comparative Example 3

[0072] In terms of mass, 26.97 parts of ethylene carbonate (EC), 20.88 parts of dimethyl carbonate (DMC), 16.26 parts of diethyl carbonate (DEC) and 32.89 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to mix them evenly; then 3 parts of fluoroethylene carbonate (FEC) were added and ultrasonicated for 2 hours to mix them evenly; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonicated for 2 hours to completely dissolve it to obtain an electrolyte containing 1 mol / L LiPF6.

[0073] Comparative Example 4

[0074] According to the mass parts, 28.97 parts of ethylene carbonate (EC), 22.43 parts of dimethyl carbonate (DMC), 12 parts of diethyl carbonate (DEC) and 34 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 2.6 parts of lithium perfluoro(2-methyl-3-oxahexanoate) (C6F 11 O3Li), ultrasonically mixed for 2h to make it uniform; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0075] Comparative Example 5

[0076] According to the mass parts, 28.97 parts of ethylene carbonate (EC), 22.43 parts of dimethyl carbonate (DMC), 12 parts of diethyl carbonate (DEC) and 34 parts of ethyl methyl carbonate (EMC) were mixed at room temperature and stirred for 4 hours to make them uniform; then 2.6 parts of perfluoro(2-methyl-3-oxahexanoic acid)ammonium (C6F 11 O3NH4), ultrasonically mixed for 2h to make it uniform; finally, lithium hexafluorophosphate (LiPF6) was added and ultrasonically dissolved for 2h to obtain an electrolyte containing 1mol / L LiPF6.

[0077] The electrolytes provided in Examples 1-8 and Comparative Examples 1-5 were assembled into lithium-ion batteries according to the following methods and performance tests were performed:

[0078] Preparation of positive electrode sheet: Lithium iron phosphate positive electrode material (LFP), polyvinylidene fluoride (PVDF) binder, acetylene black (SuperP) conductive agent are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone (NMP) is added to make a positive electrode slurry. After degassing and sieving, the slurry is evenly coated on the surface of aluminum foil, and then dried, rolled, and cut to obtain the positive electrode sheet.

[0079] Preparation of negative electrode sheet: Graphite negative electrode material, styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) composite binder and acetylene black (SuperP) conductive agent were mixed in a mass ratio of 8:1:1 and added to deionized water to prepare negative electrode slurry. The slurry was degassed and sieved, and then evenly coated on the surface of aluminum foil. The negative electrode sheet was obtained after drying, rolling and cutting.

[0080] Battery preparation: The negative electrode sheet, separator, and positive electrode sheet are stacked in order to form a battery cell, which is encapsulated in an aluminum-plastic shell. After the battery cell is baked to remove moisture, the electrolyte of Examples 1-8 and the electrolyte of Comparative Examples 1-5 are respectively injected into the square battery cell. After aging, formation, aging, and capacity separation, the lithium-ion batteries of Examples 1-8 and Comparative Examples 1-5 are obtained.

[0081] (1) Cyclic performance test at different temperatures

[0082] Cycling performance test method at room temperature (25°C): 1) Capacity calibration: At 25±3°C, charge to 3.65V at 0.5C constant current and constant voltage, cut off at 0.05C, and let it sit for 30 minutes; discharge to 2.5V at 0.5C current, and let it sit for 30 minutes; cycle twice; record the second discharge capacity as the nominal discharge capacity of the battery; 2) let it sit for 2 hours, ensuring that the ambient temperature (25°C) and the battery temperature are consistent; 3) charge to 3.65V at 1.0C constant current and constant voltage, cut off at 0.05C; 4) let it sit for 30 minutes; 5) discharge to 2.5V at 1.0C constant current;

[0083] 6) Let stand for 30 minutes. 7) Repeat steps 2) to 6) 4000 times and calculate the capacity retention rate.

[0084] Cycling performance test method at low temperature (0℃): 1) Capacity calibration: same as above; 2) Place for 2 hours to ensure that the ambient temperature (0℃) and the battery temperature are consistent; 3) Charge at 1.0C constant current and constant voltage to 3.65V, and cut off at 0.05C; 4) Place for 30 minutes; 5) Discharge at 1.0C constant current to 2.5V; 6) Place for 30 minutes; 7) Cycle steps 2)-6) 4000 times and calculate the capacity retention rate.

[0085] The capacity retention rates of the batteries of Examples 1-8 and Comparative Examples 1-5 after 4000 cycles at room temperature (25° C.) and low temperature (0° C.) were tested according to the above method. The test results are shown in Table 1.

[0086] Table 1 Comparison of the capacity retention of the batteries of Examples 1-8 and Comparative Examples 1-5 after 4000 cycles

[0087] Serial number Capacity retention rate at room temperature (25°C) (%) Capacity retention rate at low temperature (0℃) (%) Example 1 90.3 82.2 Example 2 76.3 63.2 Example 3 85.4 78.6 Example 4 80.2 69.4 Example 5 88.6 81.7 Example 6 84.4 77.4 Example 7 87.6 82.2 Example 8 91.6 84.3 Comparative Example 1 74.2 60.4 Comparative Example 2 80.2 66.4 Comparative Example 3 78.6 63.2 Comparative Example 4 86.3 79.4 Comparative Example 5 87.5 80.9

[0088] As can be seen from Table 1, whether at room temperature (25°C) or low temperature (0°C), compared with Comparative Example 1, Examples 1-8 have higher capacity retention rates after 4000 cycles and slower cycle performance decay rates, indicating that the lithium-ion batteries provided by the embodiments of the present invention have good cycle stability at different temperatures. As can be seen from Example 1, Example 5 and Comparative Examples 2-5, compared with the additives VC, FEC, and C6F 11 O3Li and C6F 11 O3NH4, (C6F 11 O3)2Fe and (C6F 11 O3)3Cs has a better effect in improving battery cycle performance. As can be seen from Examples 1 and 5, (C6F 11 O3)2Fe is more effective than (C6F 11 O3)3Cs. As can be seen from Examples 1-3, adding 2wt%-3wt% of (C6F 11 O3)2Fe, helps to better improve the cycle performance of the battery. As can be seen from Examples 1 and 8, (C6F 11 The combination of O3)2Fe and film-forming additive VC can further improve the cycle performance of the battery.

[0089] (2) Overcharge protection test

[0090] Overcharge protection test method: 1) Charge at 0.5C constant current and constant voltage to 3.65V; 2) Wait for 30 minutes; 3) Discharge at 0.5C constant current to 2.5V; 4) Wait for 30 minutes; 5) Repeat steps 1)-4) three times; 6) Charge at 0.5C constant current and constant voltage to 5V, and record the charging time.

[0091] The time taken for the batteries of Examples 1-8 and Comparative Examples 1-5 to be overcharged to 5V was tested respectively according to the above method. The test results are shown in Table 2.

[0092] Table 2 Comparison of the time taken for the batteries of Examples 1-8 and Comparative Examples 1-5 to be charged to a cut-off voltage of 5V

[0093] Serial number Time to charge to cut-off voltage 5V (h) Example 1 15.2 Example 2 2.4 Example 3 30.6 Example 4 4.6 Example 5 14.6 Example 6 28.7 Example 7 14.9 Example 8 15.2 Comparative Example 1 2.1 Comparative Example 2 2.4 Comparative Example 3 2.6 Comparative Example 4 2.1 Comparative Example 5 2.1

[0094] As can be seen from Table 2, the time required for the batteries of Examples 1-8 to charge to a cut-off voltage of 5V is greater than that of Comparative Example 1, indicating that the lithium-ion batteries provided by the embodiments of the present invention have the performance of preventing overcharging. The 5V cut-off voltage set in this application is much higher than the normal operating voltage of 3.65V of the lithium iron phosphate / graphite system battery. When the battery is overcharged, the electrolyte containing perfluoro(2-methyl-3-oxahexanoic acid) iron and perfluoro(2-methyl-3-oxahexanoic acid) cesium takes a longer time to reach the cut-off voltage of 5V because it contains a redox couple. The longer time required indicates that the voltage rise can be better suppressed, the battery can be prevented from being overcharged, and the overcharging effect is played. As can be seen from Examples 1, 5 and Comparative Examples 2-5, compared with the additives VC, FEC, and C6F 11 O3Li and C6F 11 O3NH4, (C6F 11 O3)2Fe and (C6F 11 O3)3Cs has a significantly better effect in improving the battery's overcharge protection performance. As can be seen from Examples 1 and 5, (C6F 11 O3)2Fe is better than (C6F 11 O3)3Cs. As can be seen from Examples 1-3, an appropriate increase in (C6F 11 The addition of O3)2Fe helps to better improve the battery's anti-overcharge performance.

[0095] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a lithium salt, a solvent and an additive, wherein the additive comprises a perfluoro organic compound represented by formula (I), Wherein, R1 and R2 are independently selected from fluorine atoms or perfluoroalkyl groups, R3 is selected from perfluoroalkyl groups, M is selected from Fe or Cs, and n is 2 or 3.

2. The electrolyte according to claim 1, wherein The perfluoroorganic compound includes at least one of perfluoro(2-methyl-3-oxahexanoate)iron and perfluoro(2-methyl-3-oxahexanoate)cesium.

3. The electrolyte according to claim 1, wherein The perfluorinated organic compound accounts for 0.01% to 5% of the mass of the electrolyte excluding the lithium salt.

4. The electrolyte according to claim 1, wherein The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium trifluoromethylsulfonate, lithium bis(fluorosulfonyl imide), lithium hexafluoroarsenide, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium perchlorate and lithium tetrafluoroaluminate.

5. The electrolyte according to claim 1, wherein The concentration of the lithium salt in the electrolyte is 0.1 mol / L-4 mol / L.

6. The electrolyte according to claim 1, wherein The solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, γ-butyrolactone, tetrahydrofuran and dipropylene glycol dimethyl ether.

7. The electrolyte according to claim 6, wherein The solvent is a mixture of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

8. The electrolyte according to claim 1, wherein The additives further include film-forming additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, glycerol tris(propionitrile) ether, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, vinyl sulfite, and propylene sulfite.

9. The electrolyte according to claim 8, wherein The film-forming additive accounts for 0.1% to 5% of the mass of the electrolyte excluding the lithium salt.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte comprises the electrolyte according to any one of claims 1 to 9.

11. An electrical device, characterized in that: The electrical device comprises the lithium-ion battery according to claim 10.

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