Electrolyte, secondary battery and electric equipment

Abstract

The embodiment of the invention provides an electrolyte, a secondary battery and electric equipment, and relates to the technical field of secondary batteries, the electrolyte comprises a lithium salt, an organic solvent and a first additive; wherein the first additive comprises a fatty alcohol-polyoxyethylene ether additive, the fatty alcohol-polyoxyethylene ether additive comprises a compound with a formula (I), and the fatty alcohol-polyoxyethylene ether additive with the structure of the formula (I) is used as a nonionic surface active additive, so that the surface tension of the electrolyte can be reduced; the wettability and the permeation rate of the electrolyte to the diaphragm in the liquid injection process are improved, the liquid injection time is shortened, the wettability of the electrolyte to the high-specific-surface-area active material in the pole piece is improved, the contact resistance between the active materials is reduced, the internal resistance of the secondary battery prepared based on the electrolyte provided by the embodiment of the invention is reduced, and the service life of the secondary battery is prolonged. And the utilization rate of the active material in the charge-discharge cycle process is improved, so that the comprehensive performance of the secondary battery is improved.

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. Background Art

[0002] With the rapid development of pure electric vehicles and hybrid electric vehicles, the requirements for the energy density, cycle life and rate performance of secondary batteries are also increasing. The electrolyte in the secondary battery is not only used for ion conduction between the positive electrode and the negative electrode, but also forms a stable solid electrolyte interface (SEI) on the surface of the electrode to prevent the electrolyte from further decomposing and protect the electrode structure, thereby improving the energy density, cycle life, rate performance and safety performance of the secondary battery.

[0003] At present, the electrolyte is mainly composed of organic solvents, lithium salts and additives, among which the additives are generally carbonate additives. The electrolyte containing such additives has a large surface tension and poor wettability with the active materials in the diaphragm and the electrode, resulting in a long injection time for such electrolytes and a relatively high internal resistance of the secondary batteries prepared based on such electrolytes. 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 to solve the problem that the electrolyte in the related art has a long injection time and the internal resistance of the secondary battery prepared based on the electrolyte is high.

[0005] In order to solve the above problems, the present invention is achieved through 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 fatty alcohol polyoxyethylene ether additive, and the fatty alcohol polyoxyethylene ether additive includes a compound having formula (I):

[0007]

[0008] Among them, R 1 and R 2 Each is independently selected from a hydrocarbon group having 12 to 18 carbon atoms; m represents --CH 2 --CH 2 --O-- addition number, and m is an integer greater than 0.

[0009] Furthermore, in the electrolyte, the fatty alcohol polyoxyethylene ether additive is selected from one or more of polyethylene glycol maltamide alcohol, polysorbate, polyoxyethylene stearyl alcohol ether, and chlorinated fatty alcohol polyoxyethylene ether.

[0010] Furthermore, in the electrolyte, the content of the fatty alcohol polyoxyethylene ether additive in the electrolyte is 0.1wt% to 3wt%.

[0011] Furthermore, in the electrolyte, m is any integer from 1 to 5.

[0012] Furthermore, in the electrolyte, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate.

[0013] Furthermore, in the electrolyte, the added amount of the lithium salt in the electrolyte is 8wt% to 16wt%.

[0014] Furthermore, in the electrolyte, the organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0015] Furthermore, in the electrolyte, the amount of the organic solvent added in the electrolyte is 74wt% to 85wt%.

[0016] The present invention also provides a secondary battery, wherein the secondary battery comprises a positive electrode sheet, a negative electrode sheet and any one of the above-mentioned electrolytes.

[0017] The present invention further provides an electric device, wherein the electric device comprises the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electric device.

[0018] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0019] In an embodiment of the present invention, the provided electrolyte includes a lithium salt, an organic solvent and a first additive; wherein the first additive includes a fatty alcohol polyoxyethylene ether additive, the fatty alcohol polyoxyethylene ether additive includes a compound having formula (I), and the fatty alcohol polyoxyethylene ether additive having the structure of formula (I) as a non-ionic surfactant additive can reduce the surface tension of the electrolyte, improve the wettability and penetration rate of the electrolyte to the diaphragm during the injection process, shorten the injection time, and improve the wettability of the electrolyte to the high specific surface area active material in the electrode sheet, reduce the contact resistance between the active materials, reduce the internal resistance of the secondary battery prepared based on the electrolyte provided by the embodiment of the present invention, improve the utilization rate of the active material during the charge and discharge cycle, and thereby improve the comprehensive performance of the secondary battery.

[0020] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an electrochemical impedance spectroscopy test result diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] At present, the electrolyte in the related technology is mainly composed of organic solvents, lithium salts and additives, among which the additives are generally carbonate additives. The electrolyte containing such additives has a large surface tension and poor wettability with the active materials in the diaphragm and the electrode, resulting in a long injection time for such electrolytes and high internal resistance of the secondary batteries prepared based on such electrolytes.

[0024] In order to solve the above problems, an embodiment of the present invention provides an electrolyte, which includes a lithium salt, an organic solvent and a first additive; the first additive includes a fatty alcohol polyoxyethylene ether additive, and the fatty alcohol polyoxyethylene ether additive includes a compound having formula (I):

[0025]

[0026] Among them, R 1 and R 2 Each independently selected from a hydrocarbon group having 12 to 18 carbon atoms (C12 to C18); m represents an oxyethylene group (--CH 2 --CH 2 --O--), and m is an integer greater than 0.

[0027] In some embodiments, R 1 and R 2 Each is independently selected from a saturated hydrocarbon group having 12 to 18 carbon atoms.

[0028] In some embodiments, R 1 and R 2 Each is independently selected from an unsaturated hydrocarbon group having 12 to 18 carbon atoms.

[0029] In some embodiments, R 1 is selected from unsaturated hydrocarbon groups having 12 to 18 carbon atoms; 2 It is selected from saturated hydrocarbon groups having 12 to 18 carbon atoms.

[0030] In some embodiments, R 1 is selected from saturated hydrocarbon groups having 12 to 18 carbon atoms; R 2 It is selected from unsaturated hydrocarbon groups having 12 to 18 carbon atoms.

[0031] In some embodiments, R 1 and R 2 Each is independently selected from a straight-chain hydrocarbon group or a branched hydrocarbon group having 12 to 18 carbon atoms.

[0032] In some embodiments, R 1 and R 2 Each is independently selected from a hydrocarbon group having 12 to 18 carbon atoms, and the hydrogen atoms in the hydrocarbon group may be partially or completely substituted by one or more of a hydrocarbon group having 12 to 18 carbon atoms, a halogen, a phenyl group, a cyano group, and a carboxyl group.

[0033] Wherein, m in formula (I) represents vinyl (--CH 2 --CH 2 --O--) addition number; in the embodiment of the present invention, by adjusting the addition number of vinyl, the dissolution effect of the fatty alcohol polyoxyethylene ether additive in the electrolyte can be adjusted, so that the effect of the fatty alcohol polyoxyethylene ether additive in reducing the surface tension of the electrolyte can be fully exerted. It can be understood that in actual application scenarios, the specific value of m can be determined based on the dissolution effect of the fatty alcohol polyoxyethylene ether additive in the electrolyte, and the embodiment of the present invention does not specifically limit this.

[0034] In an embodiment of the present invention, a fatty alcohol polyoxyethylene ether additive having a structure of formula (I) as a non-ionic surfactant additive can significantly reduce the surface tension of the electrolyte, so that the electrolyte is easier to spread and penetrate when contacting the internal materials of the secondary battery (such as diaphragms, pole pieces, etc.), which helps to reduce the generation of bubbles during the injection process, shorten the injection time, and improve the injection efficiency; the surface tension of the electrolyte is reduced, so that the electrolyte can penetrate into every corner of the secondary battery more quickly, including the surface of active materials with high specific surface area, thereby ensuring that the active materials are fully wetted and penetrated, and improving the utilization rate of the active materials; further, optimizing the wettability and permeability of the electrolyte to the active materials helps to reduce the contact resistance between the active materials, thereby reducing the internal resistance of the secondary battery, which is beneficial to reducing the energy loss of the secondary battery during the charging and discharging process, and improving the charging and discharging cycle performance of the secondary battery.

[0035] It should be noted that, in the embodiment of the present invention, the electrode sheet may be at least one of a positive electrode sheet and a negative electrode sheet; when the electrode sheet is a positive electrode sheet, the active material is the positive electrode active material in the positive electrode active material layer of the positive electrode sheet; when the electrode sheet is a negative electrode sheet, the active material is the negative electrode active material in the negative electrode active material layer of the negative electrode sheet.

[0036] Optionally, in some embodiments, the electrolyte further includes a second additive, and the second additive includes one or more of vinylene carbonate (VC), propylene sulfite (PS), vinyl sulfate (1,3,2-dioxathiolane 2,2-dioxide (DTD), vinylene carbonate (VEC), fluoroethylene carbonate (4-Fluoro-1,3-dioxolan-2-one, FEC), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0037] In the electrolyte provided by the embodiment of the present invention, the amount of the second additive added is 5wt% to 10wt%. For example, in the electrolyte provided by the embodiment of the present invention, the amount of the second additive added can be one of 5wt%, 6wt%, 7wt%, 8wt%, 9wt% and 10wt%, or any two of the range values.

[0038] Among them, vinylene carbonate and / or vinylene carbonate have good electrochemical stability and thermal stability, can reduce the decomposition and volatilization of electrolyte, improve the stability of electrolyte, and thus extend the service life of secondary batteries; vinylene carbonate and / or vinylene carbonate can form a stable SEI film on the surface of the electrode of the secondary battery, reduce the side reactions on the surface of the electrode, and improve the charge and discharge cycle performance of the secondary battery; vinylene carbonate and / or vinylene carbonate can also increase the capacity and energy density of the secondary battery by increasing the electrical conductivity of the electrolyte; in addition, vinylene carbonate and / or vinylene carbonate can inhibit the decomposition and volatilization of the electrolyte, reduce the risk of leakage and combustion of the electrolyte, and thus improve the safety of the secondary battery.

[0039] As the second additive, propylene sulfite can improve the performance of the electrolyte at low temperatures and enhance the low-temperature cycle stability of the secondary battery. In addition, in a specific electrolyte system, propylene sulfite can also prevent polycarbonate (PC) molecules from embedding into the graphite pole piece, thereby protecting the pole piece structure and improving the performance of the secondary battery.

[0040] Vinyl sulfate as the second additive can inhibit the decrease in the initial capacity of the secondary battery and improve the initial discharge capacity of the secondary battery; vinyl sulfate can also improve the charge and discharge performance and cycle stability of the secondary battery by reducing the expansion of the secondary battery after being placed at high temperature.

[0041] Fluoroethylene carbonate can form an effective SEI film on the surface of the electrode of the secondary battery, increase the migration rate of lithium ions in the secondary battery, and improve the charge and discharge performance of the secondary battery at high rates; because the SEI film formed by fluoroethylene carbonate is thin, tough and self-healing, it can inhibit the structural breakage of the silicon-carbon negative electrode during the charge and discharge process and improve the service life.

[0042] Lithium bis(oxalatoborate) can form a dense boron-containing polymer as a solid electrolyte intermediate layer, isolating the electrode material from the electrolyte and preventing the occurrence of side reactions; lithium bis(oxalatoborate) can also avoid the dissolution of transition metal ions caused by hydrofluoric acid corrosion and maintain the structural integrity of the electrode.

[0043] Lithium bis(fluorosulfonyl)imide can effectively reduce the low-temperature resistance of the SEI layer formed on the surface of the electrode at low temperatures, thereby improving the low-temperature performance of the secondary battery. Lithium bis(fluorosulfonyl)imide helps to improve the capacity and electrochemical performance of the secondary battery by reducing the capacity loss of the secondary battery during storage.

[0044] Lithium bis(trifluoromethanesulfonyl imide) has high electrical conductivity and chemical stability, and can improve the overall performance of the electrolyte. In addition, because lithium bis(trifluoromethanesulfonyl imide) has a good electrochemical window, lithium bis(trifluoromethanesulfonyl imide) is particularly suitable as an additive for the electrolyte in a high-voltage lithium-ion battery system.

[0045] It can be understood that the above-mentioned second additive can cooperate with the fatty alcohol polyoxyethylene ether additive having the structure of formula (I) to improve the wettability and penetration rate of the electrolyte to the diaphragm during the injection process, shorten the injection time, and improve the wettability of the electrolyte to the high specific surface area active material in the electrode, reduce the internal resistance of the secondary battery prepared based on the electrolyte provided by the embodiment of the present invention, improve the utilization rate of the active material during the charge and discharge cycle, and thereby improve the comprehensive performance of the secondary battery.

[0046] Optionally, in some embodiments, the fatty alcohol polyoxyethylene ether additive is selected from one or more of polyethylene glycol maltamide alcohol, polysorbate, polyoxyethylene stearyl ether (Ceteareth), and chlorinated fatty alcohol polyoxyethylene ether.

[0047] Optionally, in some embodiments, in the electrolyte, the content of the fatty alcohol polyoxyethylene ether additive is 0.1 wt % to 3 wt %.

[0048] Exemplarily, the content of the fatty alcohol polyoxyethylene ether additive in the electrolyte can be one of or any two of 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt% and 3wt%; when the content of the fatty alcohol polyoxyethylene ether additive in the electrolyte is within this range, the fatty alcohol polyoxyethylene ether additive can further play a role in reducing the surface tension of the electrolyte and improving the wettability between the electrolyte and the diaphragm and the active material.

[0049] Alternatively, in some embodiments, in the compound having formula (I), the oxyethylene group (--CH 2 --CH 2 --O--) is any integer from 1 to 5. For example, m can be any value of 1, 2, 3, 4 and 5.

[0050] It should be noted that since oxygen atoms are elements with strong electronegativity, they can easily form hydrogen bonds with hydrogen atoms in water molecules. In the embodiments of the present invention, the larger the value of m, the more oxygen on the hydrophilic group in the fatty alcohol polyoxyethylene ether additive, the more oxygen atoms on the hydrophilic group, and the more hydrogen bonds formed with water molecules, which makes it easier for the fatty alcohol polyoxyethylene ether additive molecules to be surrounded and dissolved by water molecules, that is, the better the water solubility. The organic solvent in the electrolyte is generally an ester organic solvent. By controlling the value of m to 1 to 5, the compound having formula (I) in the fatty alcohol polyoxyethylene ether additive can be soluble in oil but not easily soluble in water, and can be used as a surfactant of ester anions.

[0051] In the embodiment of the present invention, when an ester solvent is used as the organic solvent of the electrolyte, the value of m can be controlled within a range of 1 to 5 to improve the dissolution effect of the fatty alcohol polyoxyethylene ether additive in the electrolyte.

[0052] Optionally, in some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF 4 ), lithium difluorooxalatoborate (LiODFB), lithium difluorophosphate (LiPO2F 2 )

[0053] Among them, lithium hexafluorophosphate has high ion conductivity and good electrochemical stability; lithium tetrafluoroborate has good thermal stability and can maintain its chemical properties stable at a certain high temperature; under high and low temperature conditions, the electrochemical properties of lithium tetrafluoroborate are relatively good, which can effectively prevent the corrosion of the electrode and improve the cycle life and safety of the secondary battery; lithium difluorooxalatoborate has excellent high and low temperature performance and can maintain stable electrochemical properties over a wide temperature range; in addition, lithium difluorooxalatoborate as a 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 resistance of the secondary battery, improve the overall efficiency of the secondary battery, and extend the service life of the secondary battery.

[0054] Optionally, in some embodiments, in the electrolyte, the amount of lithium salt added is 8wt% to 16wt%; illustratively, in the electrolyte, the amount of lithium salt added can be one of 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% and 16wt% or any two of the range values.

[0055] In the electrolyte provided by the embodiment of the present invention, the addition amount of lithium salt is controlled in the range of 8wt% to 16wt%, so that the conductivity of the electrolyte is excellent and the viscosity of the electrolyte is moderate, which can effectively take into account both the conductivity and viscosity of the electrolyte.

[0056] Optionally, in some embodiments, 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).

[0057] Among them, ethylene carbonate has a high film-forming potential on the negative electrode plate, participates in the formation of the SEI film on the surface of the graphite negative electrode plate, reduces the side reactions on the surface of the plate, and has a high dielectric constant, which can improve the ionic conductivity of the electrolyte.

[0058] Propylene carbonate can enhance the stability of secondary batteries, protect negative electrode materials, reduce the polarity of electrolytes, and reduce the possibility of secondary battery failure; propylene carbonate can inhibit the expansion of amalgam negative electrodes and extend the cycle life of secondary batteries; propylene carbonate can increase the discharge capacity and cycle life of secondary batteries and improve the structural stability and electrochemical properties of positive electrode materials; in addition, propylene carbonate can also reduce the operating temperature of the battery and improve the stability of the secondary battery.

[0059] Dimethyl carbonate can be mixed with electrolyte components with low polarity, such as ethylene carbonate and diethyl carbonate, to form a balanced solution, so that the secondary battery can reach a stable state faster, and the cycle life and capacity retention rate of the secondary battery can be improved; dimethyl carbonate can increase the electrochemical window of the secondary battery, reduce the film formation rate on the surface of the electrode, reduce the interface resistance, and improve the capacity and cycle life of the secondary battery; dimethyl carbonate can also increase the energy density of the secondary battery and reduce the loss inside the secondary battery by reducing the decomposition of the electrolyte.

[0060] Diethyl carbonate can be used together with other solvents, such as ethylene carbonate, dimethyl carbonate, etc., to improve the solubility of the electrolyte.

[0061] Ethyl methyl carbonate mainly plays the role of providing ion conduction channels in the electrolyte, enabling the ions in the electrolyte to be transferred between the positive and negative electrodes to undergo chemical reactions, which is beneficial to improving the efficiency and stability of the electrochemical reaction. In addition, compared with other traditional solvents, ethyl methyl carbonate has the advantages of higher conductivity, higher stability and lower explosion risk.

[0062] Optionally, in some embodiments, in the electrolyte, the amount of organic solvent added is 74wt% to 85wt%; exemplarily, in the electrolyte, the amount of organic solvent added can be one of or any two of 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt% and 85wt%.

[0063] In an embodiment of the present invention, the amount of organic solvent added to the electrolyte is controlled within the range of 74wt% to 85wt%, which is beneficial to fully dissolve the lithium salt, provide the necessary migration medium for lithium ions, improve the conductivity of the electrolyte, and thus improve the safety of the secondary battery and extend the service life of the secondary battery.

[0064] The present invention also provides a method for preparing an electrolyte, which comprises: mixing a lithium salt and an organic solvent under the protection of an inert gas to obtain a colorless transparent liquid; and mixing the additive and the colorless transparent liquid to obtain an electrolyte.

[0065] Among them, in the process of mixing lithium salt and organic solvent, since the addition of lithium salt will cause the electrolyte temperature to rise, causing the lithium salt to decompose to a certain extent due to heat, the electrolyte temperature is controlled when adding lithium salt. When the electrolyte temperature rises by more than 2°C, the addition of lithium salt is stopped. When the electrolyte temperature is lower than 2°C, the addition of lithium salt continues.

[0066] The electrolyte temperature can be controlled by ice bath, dry ice circulation cooling or liquid nitrogen cooling.

[0067] Optionally, in some embodiments, the organic solvent includes multiple solvents, the multiple solvents are mixed and dehydrated in advance, and then the lithium salt and the organic solvent are mixed under the protection of an inert gas to obtain the colorless transparent liquid; and then the additive is mixed with the colorless transparent liquid to obtain an electrolyte. The organic solvent can be dehydrated by molecular sieve adsorption.

[0068] The present invention also provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet and the above-mentioned electrolyte.

[0069] Among them, the electrolyte in the electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate.

[0070] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed 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 cobalt oxide, lithium manganese oxide, and lithium iron phosphate, and the ternary positive electrode material can specifically be a high-nickel layered ternary positive electrode material.

[0071] Optionally, in one embodiment, the positive electrode plate further includes an adhesive, and the adhesive 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.

[0072] In some embodiments, the positive electrode sheet is prepared as follows: the components for preparing the positive electrode sheet, such as the positive electrode active material, the binder and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of a positive electrode collector such as aluminum foil; after baking, rolling, cutting and other processes, the positive electrode sheet can be obtained.

[0073] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer can be a negative electrode active material used for batteries. The negative electrode active material can be a carbon silicon negative electrode material, graphite or hard carbon.

[0074] In some embodiments, the negative electrode material comprises hard carbon. Compared with other negative electrode materials, hard carbon has disordered crystal arrangement and larger interlayer spacing, which is more conducive to the first additive in the electrolyte to form a protective film on its surface, further optimizing the stability of the protective film. In some embodiments, the hard carbon is spherical or quasi-spherical particles, further improving the stability of the negative electrode material and the electrolyte film.

[0075] In the secondary battery provided by the embodiment of the present invention, the negative electrode plate also 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 binder.

[0076] Optionally, in one embodiment, 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.

[0077] In some embodiments, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode collector such as copper foil; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0078] It can be understood that the secondary battery provided in the embodiment of the present invention further includes a separator.

[0079] In practical applications, the negative electrode sheet, the separator and the positive electrode sheet are stacked in order and wound to obtain a core, the core is packaged to obtain a bare cell, and the bare cell is baked and then injected, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0080] The present invention further provides an electric device, wherein the electric device comprises the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electric device.

[0081] For the above-mentioned secondary battery embodiment and electrical equipment embodiment, they include the above-mentioned electrolyte and can achieve the same technical effect. In order to avoid repetition, they will not be described here. For relevant details, please refer to the partial description of the positive electrode material embodiment.

[0082] In order to make the invention purpose, technical scheme and beneficial effect of the present invention clearer, the present invention is further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0083] The present invention is described in detail below by way of examples.

[0084] Example 1

[0085] (1) Preparation of electrolyte:

[0086] At room temperature, in an argon-filled glove box (H 2 O<1ppm, O 2 <1ppm), ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate are mixed uniformly in a mass ratio of 37.81:19.9:19.9 to obtain an organic solvent, lithium hexafluorophosphate is added to the obtained organic solvent in succession, stirring is continued and cooling is performed with dry ice to ensure that the electrolyte temperature does not rise by more than 2°C, lithium hexafluorophosphate can be added continuously, and the mass ratio between lithium hexafluorophosphate and the organic solvent is controlled to be 13.93:77.61, finally a colorless transparent liquid is obtained, a first additive and a second additive are added, wherein the second additive comprises vinylene carbonate equivalent to 3.98% of the total mass of the electrolyte, 2.985% of propylene sulfite, and 0.995% of fluoroethylene carbonate, and the first additive comprises polyethylene glycol maltoamide alcohol equivalent to 0.5% of the total mass of the electrolyte, and stirring is uniform to obtain an electrolyte; the addition number of oxyethylene groups in the polyethylene glycol maltoamide alcohol is 3.

[0087] (2) Preparation of positive electrode sheet:

[0088] The positive electrode active material lithium iron phosphate (LiFePO 4 , LFP), conductive agent acetylene black (Super P) and binder polyvinylidene fluoride are mixed evenly in a mass ratio of 97:2:1, and evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry is coated on both sides of the aluminum foil, and then baked, rolled and cut into pieces to obtain the positive electrode sheet.

[0089] (3) Preparation of negative electrode sheet

[0090] The negative electrode active material graphite, the conductive agent acetylene black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene copolymer (SBR) were prepared into a slurry in a mass ratio of 96:2:1:1, and then coated on the surface of the negative electrode collector and rolled to form a negative electrode sheet.

[0091] (4) Preparation of secondary batteries

[0092] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets. The bare battery cell is obtained by winding, hot pressing, and welding the tabs. The bare battery cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24h. The prepared electrolyte is injected into the dried battery, allowed to stand, formed, and divided to complete the preparation of a soft-pack 20AH lithium iron phosphate system secondary battery.

[0093] Example 2

[0094] The difference between Example 2 and Example 1 is that in step (1), the mass ratio between lithium hexafluorophosphate and the organic solvent is 16:74; and in the organic solvent, the mass ratio between ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate is 37:18.5:18.5;

[0095] The second additive includes 4.95% of vinylene carbonate, 3.71% of propylene sulfite, and 1.24% of fluoroethylene carbonate, which is equivalent to 4.95% of the total mass of the electrolyte, and the first additive includes 0.1% of the total mass of the electrolyte.

[0096] Example 3

[0097] The difference between Example 3 and Example 1 is that in step (1), the mass ratio between lithium hexafluorophosphate and the organic solvent is 8:84; and in the organic solvent, the mass ratio between ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate is 42:21:21;

[0098] The second additive includes 2.5% of vinylene carbonate, 1.875% of propylene sulfite, and 0.625% of fluoroethylene carbonate, which is equivalent to 2.5% of the total mass of the electrolyte, and the first additive includes 3% of the total mass of the electrolyte.

[0099] Example 4

[0100] The difference between Example 4 and Example 1 is that in step (1), the mass ratio between lithium hexafluorophosphate and the organic solvent is 8:85; and in the organic solvent, the mass ratio between ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate is 42.5:21.25:21.25;

[0101] The second additive includes 3% of vinylene carbonate, 2.25% of propylene sulfite, and 0.75% of fluoroethylene carbonate, which is equivalent to 3% of the total mass of the electrolyte, and the first additive includes 1% of the total mass of the electrolyte.

[0102] Example 5

[0103] The difference between Example 5 and Example 1 is that in step (1), the number of addition of oxyethylene groups in polyethylene glycol maltoamide is 1.

[0104] Example 6

[0105] The difference between Example 6 and Example 1 is that in step (1), the number of oxyethylene groups added in polyethylene glycol maltamide alcohol is 5.

[0106] Example 7

[0107] The difference between Example 7 and Example 1 is that in step (1), the first additive includes polysorbate equivalent to 0.5% of the total mass of the electrolyte.

[0108] Example 8

[0109] The difference between Example 8 and Example 4 is that in step (1), the first additive also includes polyoxyethylene stearyl ether equivalent to 0.5% of the total mass of the electrolyte.

[0110] Example 9

[0111] The difference between Example 9 and Example 1 is that in step (1), propylene carbonate and diethyl carbonate are uniformly mixed in a mass ratio of 23.283:54.327 to obtain an organic solvent.

[0112] Example 10

[0113] The difference between Example 10 and Example 1 is that in step (1), the lithium salt is adjusted to lithium bis(fluorosulfonyl)imide.

[0114] Embodiment 11

[0115] The difference between Example 11 and Example 1 is that in step (1), the lithium salt is adjusted to lithium difluorooxalatoborate.

[0116] Comparative Example 1

[0117] The difference between Comparative Example 1 and Example 1 is that in step (1), the mass ratio between lithium hexafluorophosphate and the organic solvent is 14:78; and in the organic solvent, the mass ratio between ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate is 38:20:20;

[0118] The second additive includes 4% of vinylene carbonate, 3% of propylene sulfite, and 1% of fluoroethylene carbonate, which is equivalent to the total mass of the electrolyte;

[0119] No first additive was added.

[0120] The components and parameters of the electrolyte in Example 1 and Comparative Example 1 are shown in Table 1.

[0121] Table 1

[0122]

[0123] Test method:

[0124] (1) Electrolyte infiltration test: A soft-pack 20AH lithium iron phosphate secondary battery was used for verification in the same injection equipment. The electrolyte injection time was tested under the conditions of an ambient temperature of 25±5°C and a dew point of -45±3°C.

[0125] (2) DC internal resistance (DCR) test: The test was conducted in a constant temperature box at a temperature of 25±5°C. The secondary battery was at 50% SOC and discharged at a current of 60AH for 10s.

[0126] (3) Electrochemical impedance spectroscopy test: The test was conducted in a thermostat at a temperature of -20±5°C, and the secondary battery was tested at 50% SOC.

[0127] Example 1 and Comparative Example 1 were subjected to electrolyte infiltration tests, and the test data are shown in Table 2.

[0128] Table 2

[0129] Electrolyte Wetting Test Injection time / s Injection temperature / ℃ Injection volume / g Example 1 70 45±5 80 Comparative Example 1 90 45±5 80

[0130] According to the test data in Table 2, the injection time of the electrolyte containing the first additive prepared in Example 1 is 70s, while the injection time of the electrolyte not containing the first additive prepared in Comparative Example 1 is 90s. Compared with Comparative Example 1, the injection time of the electrolyte prepared in Example 1 is reduced by about 22%. It can be seen that the electrolyte provided in the embodiment of the present invention is beneficial to improving the wettability and penetration rate of the electrolyte to the diaphragm during the injection process, thereby shortening the injection time and improving the injection efficiency.

[0131] The DC internal resistance test was performed on Example 1 and Comparative Example 1, and the test data are shown in Table 3.

[0132] Table 3

[0133]

[0134] According to the test data in Table 3, the DC internal resistance of the secondary battery prepared by Example 1 is 1.004 mΩ, while the DC internal resistance of the secondary battery prepared by Comparative Example 1 is 1.213 mΩ, and the DC internal resistance of the secondary battery prepared by Example 1 is reduced by about 17.2% compared with Comparative Example 1; thus, it can be seen that the electrolyte provided by the embodiment of the present invention improves the wettability and penetration rate of the electrolyte to the diaphragm during the injection process, shortens the injection time, improves the injection efficiency, and also reduces the DC internal resistance of the secondary battery prepared based on the electrolyte provided by the embodiment of the present invention.

[0135] The electrochemical impedance spectroscopy test was performed on Example 1 and Comparative Example 1. The test data Figure 1 shown; reference Figure 1The diffusion impedance of the secondary battery prepared by Example 1 is significantly lower than that of the secondary battery prepared by Comparative Example 1. It can be seen that the electrolyte provided by the embodiment of the present invention improves the wettability and penetration rate of the electrolyte to the diaphragm during the injection process, shortens the injection time, improves the injection efficiency, and also reduces the impedance of the secondary battery prepared based on the electrolyte provided by the embodiment of the present invention.

[0136] In summary, the provided electrolyte includes a lithium salt, an organic solvent and a first additive; wherein the first additive includes a fatty alcohol polyoxyethylene ether additive, the fatty alcohol polyoxyethylene ether additive includes a compound having formula (I), and the fatty alcohol polyoxyethylene ether additive having the structure of formula (I) as a non-ionic surfactant additive can reduce the surface tension of the electrolyte, improve the wettability and penetration rate of the electrolyte to the diaphragm during the injection process, shorten the injection time, and improve the wettability of the electrolyte to the high specific surface area active material in the electrode, reduce the contact resistance between the active materials, reduce the internal resistance of the secondary battery prepared based on the electrolyte provided by the embodiment of the present invention, improve the utilization rate of the active material during the charge and discharge cycle, and thereby improve the comprehensive performance of the secondary battery.

[0137] The electrolyte, secondary battery and electrical equipment provided by the present invention are introduced in detail above. The principle and implementation mode of the present invention are explained by using specific examples in this article. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting 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 fatty alcohol polyoxyethylene ether additive, and the fatty alcohol polyoxyethylene ether additive includes a compound having formula (I): Wherein, R1 and R2 are each independently selected from a hydrocarbon group having 12 to 18 carbon atoms; m represents the addition number of -CH2CH2-O-, and m is an integer greater than 0.

2. The electrolyte according to claim 1, characterized in that The fatty alcohol polyoxyethylene ether additive is selected from one or more of polyethylene glycol maltamide alcohol, polysorbate, polyoxyethylene stearyl alcohol ether, and chlorinated fatty alcohol polyoxyethylene ether.

3. The electrolyte according to claim 1, characterized in that In the electrolyte, the content of the fatty alcohol polyoxyethylene ether additive is 0.1wt% to 3wt%.

4. The electrolyte according to claim 1, characterized in that m is any integer from 1 to 5.

5. The electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate.

6. The electrolyte according to claim 1, characterized in that In the electrolyte, the added amount 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 added amount 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 an electrolyte as claimed in any one of claims 1 to 8.

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

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