Electrolyte, battery containing electrolyte, energy storage device and electric equipment

Abstract

The invention provides an electrolyte, a battery containing the electrolyte, an energy storage device and electric equipment, the electrolyte comprises a compound shown in a formula (I) and a compound shown in a formula (II), in the formula (I), R1 and R2 are independently selected from hydrogen or electron withdrawing groups, at least one of R1 and R2 is an electron withdrawing group, and the electron withdrawing group comprises fluorine atoms, nitryl or trifluoromethyl; in the formula (II), R3, R4, R5 and R6 are respectively and independently selected from hydrogen and substituted or unsubstituted C1-4 alkyl; based on the mass of the electrolyte, the mass percentage content of the compound shown in the formula (I) is a, the mass percentage content of the compound shown in the formula (II) is b, a is larger than or equal to 0.5% and smaller than or equal to 3%, and b is larger than or equal to 0.1% and smaller than or equal to 2%. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrolyte, a battery containing the electrolyte, an energy storage device, and an electrical equipment. Background Art

[0002] Secondary batteries (such as lithium-ion batteries) have the advantages of high energy density, low self-discharge, and light weight, and are therefore widely used in fields such as energy storage devices.

[0003] As people's requirements for the performance of secondary batteries increase, for example, the requirements for the performance of secondary batteries in energy storage scenarios increase, secondary batteries are not only required to have high energy density, but also required to have good short-term cycle performance and long-term cycle performance to ensure the service life of secondary batteries in energy storage application scenarios. Summary of the invention

[0004] In order to solve the above technical problems, the present application discloses an electrolyte, a battery containing the electrolyte, an energy storage device and an electrical equipment to improve the short-term cycle performance and long-term cycle performance of a secondary battery.

[0005] In a first aspect, the present application provides an electrolyte, comprising a compound represented by formula (I) and a compound represented by formula (II):

[0006]

[0007] In formula (I), R1 and R2 are each independently selected from hydrogen or an electron-withdrawing group, and at least one of R1 and R2 is the electron-withdrawing group, and the electron-withdrawing group includes a fluorine atom, a nitro group or a trifluoromethyl group;

[0008] In formula (II), R3, R4, R5, and R6 are each independently selected from hydrogen, substituted or unsubstituted C1-4 alkyl;

[0009] Based on the mass of the electrolyte, the mass percentage of the compound represented by formula (I) is a, the mass percentage of the compound represented by formula (II) is b, 0.5%≤a≤3%, and 0.1%≤b≤2%.

[0010] In some embodiments of the present application, 1%≤a≤2%.

[0011] In some embodiments of the present application, 0.5≤a / b≤5.

[0012] In some embodiments of the present application, the electrolyte further includes vinylene carbonate. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is c, satisfying: 0.5≤(a+b) / c≤3.

[0013] In some embodiments of the present application, the compound represented by formula (I) is selected from at least one of the following compounds:

[0014]

[0015] In some embodiments Q of the present application, the compound represented by formula (II) is selected from at least one of the following compounds:

[0016]

[0017] In some embodiments of the present application, the electrolyte also includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and ethylene glycol dimethyl ether.

[0018] In a second aspect, the present application provides a battery, comprising the electrolyte described in the first aspect.

[0019] In a third aspect, the present application provides an energy storage device, comprising a housing and at least one battery as described in the second aspect, wherein the battery is accommodated in the housing.

[0020] In a fourth aspect, the present application provides an electrical device, comprising the energy storage device described in the third aspect, wherein the energy storage device supplies power to the electrical device.

[0021] Compared with the prior art, this application has at least the following beneficial effects:

[0022] The present application provides an electrolyte, a battery containing the electrolyte, an energy storage device and an electrical device, wherein the electrolyte comprises a compound represented by formula (I) and a compound represented by formula (II), and based on the mass of the electrolyte, the mass percentage of the compound represented by formula (I) is a, and the mass percentage of the compound represented by formula (II) is b, 0.5%≤a≤3%, and 0.1%≤b≤2%. The electrolyte of the present application contains the above two compounds, and by regulating the content of the above two compounds, the short-term cycle performance and long-term cycle performance of the secondary battery are improved under the synergistic effect of the above two compounds. When the secondary battery of the present application is used in an energy storage device, the service life of the energy storage device is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 A schematic diagram of the structure of a household energy storage system according to an implementation scheme of the present application;

[0025] Figure 2 A schematic diagram of the structure of a commercial energy storage system according to an implementation scheme of the present application.

[0026] Explanation of the accompanying drawings: 1-energy storage device, 2-electric energy conversion device, 3-first user load, 4-second user load, 400-commercial energy storage system, 410-high voltage cable, 420-first electric energy conversion device, 430-second electric energy conversion device. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0029] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0030] In addition, the terms "installed", "set", "provided with", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0031] In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0032] It should be noted that, in the present application, a lithium-ion battery is used as an example of a secondary battery to explain the present application, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0033] The present application provides an electrolyte, comprising a compound represented by formula (I) and a compound represented by formula (II):

[0034]

[0035] In formula (I), R1 and R2 are each independently selected from hydrogen or an electron-withdrawing group, and at least one of R1 and R2 is an electron-withdrawing group, and the electron-withdrawing group includes a fluorine atom, a nitro group or a trifluoromethyl group; in formula (II), R3, R4, R5 and R6 are each independently selected from hydrogen, a substituted or unsubstituted C1-4 alkyl group; based on the mass of the electrolyte, the mass percentage of the compound represented by formula (I) is a, and the mass percentage of the compound represented by formula (II) is b, 0.5%≤a≤3%; in another optional embodiment, 1%≤a≤2%; 0.1%≤b≤2%. For example, a is 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5% or 3%; b is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5% or 2%.

[0036] The inventors have found that the compound represented by formula (II) has a high reactivity. In the formation stage, it will first undergo ring opening and then further decompose to form a SEI (Solid Electrolyte Interphase) film containing various inorganic components such as nitrogen (N) and sulfur (S) on the negative electrode interface (such as a graphite interface); and the compound represented by formula (I) contains electron-withdrawing groups, which makes the electron cloud density distribution of the compound represented by formula (I) uneven, and also has a high reactivity. In the formation stage, the bonds formed at the electron-withdrawing groups in the compound represented by formula (I) are easily broken, and the electrons on the ring structure of the compound represented by formula (I) are easily absorbed by the electron-withdrawing groups to generate carbon cations, which further promote the ring opening and decomposition of the compound represented by formula (II) into a film.

[0037] The inventors further discovered that when the content of the compound represented by formula (I) is too low (e.g., less than 0.5%), it is difficult to promote the ring-opening decomposition of the compound represented by formula (II), which is not conducive to improving the cycle performance of the lithium-ion battery; when the content of the compound represented by formula (I) is too high (e.g., greater than 3%), the initial energy efficiency of the lithium-ion battery is low; when the content of the compound represented by formula (II) is too low (e.g., less than 0.1%), it is difficult to form a sufficient SEI film containing inorganic components such as nitrogen (N) and sulfur (S) on the negative electrode interface; when the content of the compound represented by formula (II) is too high (e.g., greater than 2%), the compound will also decompose on the negative electrode surface to form a thicker SEI film, resulting in a larger lithium ion transmission resistance, affecting the cycle performance of the lithium-ion battery, and is not conducive to improving the initial energy efficiency of the lithium-ion battery. In the present application, when the contents of the above two compounds are controlled within the above range, under the joint action of the compound represented by formula (I) and the compound represented by formula (II), the SEI film formed has the characteristics of uniformity and density, which is beneficial to the improvement of the short-term cycle performance and long-term cycle performance of the lithium-ion battery, and the lithium-ion battery also has good initial energy efficiency.

[0038] In the present application, the initial energy efficiency refers to the energy efficiency corresponding to the third cycle during the charge and discharge cycle test of the lithium-ion battery.

[0039] In some embodiments of the present application, 0.5≤a / b≤5. For example, a / b=0.5, a / b=1, a / b=1.5, a / b=2, a / b=3, a / b=4 or a / b=5. By regulating a / b within the above range, it is beneficial to further enhance the synergistic effect of the compound represented by formula (I) and the compound represented by formula (II), so that the cycle performance of the lithium ion battery is further improved.

[0040] In some embodiments of the present application, the electrolyte further includes vinylene carbonate (VC), and the mass percentage of VC based on the mass of the electrolyte is c, satisfying: 0.5≤(a+b) / c≤3. For example, (a+b) / c=0.5, (a+b) / c=1, (a+b) / c=1.5, (a+b) / c=2, (a+b) / c=2.5 or (a+b) / c=3. When (a+b) / c is too high, it indicates that the sum of the contents of the compound represented by formula (I) and the compound represented by formula (II) is too high compared to the content of VC, and the interface impedance of the formed SEI film is large; when (a+b) / c is too low, it indicates that the sum of the contents of the compound represented by formula (I) and the compound represented by formula (II) is too low compared to the content of VC, and it is difficult to reduce the consumption of VC in the early stage of the cycle, which is not conducive to the improvement of the long-term cycle performance of the lithium-ion battery. By regulating (a+b) / c within the above range, the compound represented by formula (I), the compound represented by formula (II) and VC interact with each other, so that the compound represented by formula (I) and the compound represented by formula (II) decompose on the negative electrode interface in preference to VC to produce an SEI film containing inorganic components such as S, N and / or fluorine (F). This SEI film has the characteristics of being uniform, dense and having low impedance, which can reduce the consumption of VC in the early stage of the cycle and balance the influence on the interface impedance of the SEI film, which is beneficial to improving the long-term cycle performance of lithium-ion batteries.

[0041] In some embodiments of the present application, the compound represented by formula (I) is selected from at least one of the following compounds:

[0042]

[0043] The above compounds include electron-withdrawing groups such as fluorine atoms, trifluoromethyl and nitro groups, which are beneficial to promoting the ring-opening decomposition of the compound represented by formula (II) into film, thereby exerting a synergistic effect with the compound represented by formula (II).

[0044] In some embodiments of the present application, the compound represented by formula (II) is selected from at least one of the following compounds:

[0045]

[0046]

[0047] By selecting at least one of the compounds represented by the above formula (II-1) to (II-7), it is beneficial to exert a synergistic effect with the compound represented by formula (I), so that the lithium-ion battery exhibits excellent short-term cycle performance and long-term cycle performance.

[0048] The electrolyte of the present application may further include an organic solvent, illustratively, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and ethylene glycol dimethyl ether. The present application has no particular restrictions on the content of the organic solvent, for example, the mass percentage of the organic solvent in the electrolyte is 65% to 85%.

[0049] The present application has no particular restrictions on the preparation process of the electrolyte. For example, the above-mentioned solvents can be mixed in a certain mass ratio or volume ratio, and then lithium salt can be added to dissolve and mix evenly, and then electrolyte additives such as the compound represented by formula (I) and the compound represented by formula (II) can be added and dissolved.

[0050] The present application has no particular limitation on the lithium salt. For example, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorosulfonyl imide (LiFSI), lithium difluorooxalatoborate (LiODFB), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF4) and lithium bis(trifluoromethylsulfonyl imide) (LiTFSI).

[0051] The present application has no particular restrictions on the concentration of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. Taking LiPF6 as an example, the concentration of LiPF6 in the electrolyte is 10wt% to 15wt%, for example, the concentration of LiPF6 is 10wt%, 11wt%, 12wt%, 13wt% or 15wt%.

[0052] The present application also provides a battery, comprising the electrolyte described in any embodiment of the present application.

[0053] The lithium-ion battery of the present application also includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role.

[0054] The present application has no special restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet usually includes a positive current collector and a positive active material layer. The positive active material layer can be arranged on one surface in the thickness direction of the positive current collector, or on two surfaces in the thickness direction of the positive current collector. In the present application, the positive active material layer is arranged on the surface of the positive current collector, that is, the positive active material layer can be arranged in a partial area of ​​one surface of the positive current collector, or in the entire area of ​​one surface of the positive current collector. The present application has no special restrictions on the positive current collector, as long as the purpose of the present application can be achieved, for example, it can include but is not limited to aluminum foil, aluminum alloy foil or composite current collector. In the present application, there is no special restriction on the thickness of the positive current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 8μm to 13μm. The single-sided thickness of the positive active material layer of the present application can be 100μm to 200μm.

[0055] In the present application, the positive electrode active material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, it may include at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide and lithium iron manganese phosphate.

[0056] In the present application, the positive electrode active material layer may also include a positive electrode conductive agent. The present application has no particular restrictions on the positive electrode conductive agent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, acetylene black and graphene. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. In the present application, the positive electrode active material layer may also include a positive electrode binder. The present application has no particular restrictions on the positive electrode binder, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of fluorine-containing resins, polypropylene resins, fiber-type binders, rubber-type binders or polyimide-type binders.

[0057] The present application has no special restrictions on the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the negative electrode sheet usually includes a negative electrode collector and a negative electrode active material layer. The negative electrode active material layer can be arranged on one surface or two surfaces in the thickness direction of the negative electrode collector. In the present application, the negative electrode active material layer is arranged on the surface of the negative electrode collector, that is, the negative electrode active material layer can be arranged in a partial area of ​​one surface of the negative electrode collector, or in the entire area of ​​one surface of the negative electrode collector. The present application has no special restrictions on the negative electrode collector, as long as the purpose of the present application can be achieved. For example, it can include but is not limited to copper foil, copper alloy foil, nickel foil or composite current collector. In the present application, there is no special restriction on the thickness of the negative electrode collector, as long as the purpose of the present application can be achieved, for example, the thickness is 4μm to 12μm. The single-sided thickness of the negative electrode active material layer of the present application can be 70μm to 200μm.

[0058] In the present application, the negative electrode active material layer includes a negative electrode active material, wherein the negative electrode active material is not particularly limited as long as the purpose of the present application can be achieved, for example, it may include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, silicon, and silicon carbon.

[0059] In the present application, the negative electrode active material layer may further include a negative electrode binder. The present application has no particular restrictions on the negative electrode binder, as long as the purpose of the present application can be achieved, for example, it may include at least one of acrylate, polyamide, polyimide, polyamideimide, polyvinylidene fluoride (PVDF), styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0060] The present application has no particular restrictions on the diaphragm, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0061] The battery of the present application also includes a shell, and the present application has no particular limitation on the shell, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved. For example, the shell may include an aluminum-plastic film.

[0062] The present application does not particularly limit the preparation method of the battery, and a preparation method known in the art can be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the battery includes but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain a bare cell with a wound structure, placing the bare cell in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a battery.

[0063] The present application also provides an energy storage device, including a housing and at least one battery in any of the above embodiments, wherein the battery is contained in the housing. The energy storage device having the battery has excellent performance, which is beneficial to the use of the energy storage device. By containing the battery in the housing, the fixation and protection of the battery can be increased, thereby improving the service life of the energy storage device. It is understandable that the energy storage device may have one or more batteries, and when the energy storage device contains multiple batteries, the multiple batteries may be connected in at least one of parallel and series connection.

[0064] The present application also provides an electrical device, including the energy storage device in the above-mentioned implementation scheme, which is conducive to improving the product competitiveness and performance of the electrical device. In an optional implementation scheme, the electrical device includes an electrical device body, and the energy storage device is used to supply power to the electrical device body. In an optional implementation scheme, the electrical device body includes a positive electrode of the device and a negative electrode of the device, the positive electrode plate of the battery in the energy storage device is used to electrically connect to the positive electrode of the device body of the electrical device, and the negative electrode plate of the battery in the energy storage device is used to electrically connect to the negative electrode of the device body of the electrical device, so as to supply power to the electrical device.

[0065] The electrical equipment of the present application may include but is not limited to: containers, battery vehicles, electric vehicles, ships, spacecraft, electric toys and electric tools, etc., wherein spacecrafts include airplanes, rockets, space shuttles and spacecrafts, etc., electric toys include fixed or mobile electric toys, such as electric car toys, electric ship toys and electric airplane toys, etc., and electric tools include metal cutting power tools, grinding power tools, assembly power tools and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers.

[0066] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of a household energy storage system according to an implementation scheme of the present application, and the present application Figure 1 The implementation plan is described using a household energy storage scenario in user-side energy storage as an example, but the energy storage device of the present application is not limited to the household energy storage scenario.

[0067] The present application provides a household energy storage system, which includes an energy conversion device 2 (photovoltaic panel), a first user load 3 (street lamp), a second user load 4 (such as air conditioner and other household appliances), and an energy storage device 1. The energy storage device 1 is a small energy storage box that can be mounted on an outdoor wall by wall hanging. Specifically, the photovoltaic panel can convert solar energy into electrical energy during the period of low electricity prices. The energy storage device 1 is used to store the electrical energy and supply it to street lamps and household appliances for use during the peak electricity prices, or to supply power when the power grid is out of power / power outage.

[0068] See also Figure 2 , Figure 2 A schematic diagram of a commercial energy storage system 400 according to an embodiment of the present application. Figure 2 The implementation plan is described using the shared energy storage scenario on the generation / distribution side as an example, and the energy storage device 1 of the present application is not limited to the energy storage scenario on the generation / distribution side.

[0069] The present application provides a commercial energy storage system 400, which includes: a high-voltage cable 410, a first electric energy conversion device 420, a second electric energy conversion device 430 and an energy storage device 1 provided in the present application. In the case of power generation, the first electric energy conversion device 420 and the second electric energy conversion device 430 are used to convert other forms of energy into electric energy, which are connected to the high-voltage cable 410 and supplied to the power distribution network for use. When the power load is low and the first electric energy conversion device 420 and the second electric energy conversion device 430 generate excess power, the excess power is stored in the energy storage device 1, thereby reducing the wind and solar power abandonment rates and improving the problem of new energy power generation and consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 1 in conjunction with the high-voltage cable 410 in a grid-connected mode to the power consumption side, thereby providing peak load regulation, frequency regulation, standby and other services for the power grid operation, giving full play to the peak load regulation of the power grid, promoting peak load shaving and valley filling of the power grid, and alleviating the power supply pressure of the power grid.

[0070] Optionally, the first electric energy conversion device 420 and the second electric energy conversion device 430 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0071] The number of energy storage devices 1 can be multiple, and multiple energy storage devices 1 are connected in series or in parallel. Multiple energy storage devices 1 are supported and electrically connected by isolation plates (not shown). In this embodiment, "multiple" refers to two or more. An energy storage box can also be provided outside the energy storage device 1 to accommodate the energy storage device 1.

[0072] Optionally, the energy storage device 1 may include but is not limited to a battery module, a battery pack, a battery system, etc. Among them, the battery module may be a battery module formed by connecting multiple batteries of the present application in series / parallel, the battery pack may include multiple batteries of the present application, and the battery system may be a charging and discharging system including the battery or battery pack of the present application.

[0073] The actual application form of the energy storage device 1 provided in the embodiment of the present application may be, but is not limited to, the listed products, and may also be other application forms. The embodiment of the present application does not strictly limit the application form of the energy storage device 1. The embodiment of the present application only takes the energy storage device 1 as a multi-core battery as an example for explanation. When the energy storage device 1 includes a single cell, the single cell may be at least one of a cylindrical battery, a square battery, and the like.

[0074] Example

[0075] Hereinafter, the embodiments of the present application will be described in more detail with reference to preparation examples, examples and comparative examples. Various tests and evaluations were performed according to the following methods.

[0076] Example 1-1

[0077] <Preparation of positive electrode sheet>

[0078] The positive electrode active material lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and binder PVDF are mixed in a mass ratio of 97:0.7:2.3; then N-methylpyrrolidone (NMP) is added as a solvent to prepare a positive electrode slurry with a solid content of 60wt%, and stirred evenly, and then the positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 85℃; then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer. After cold pressing, striping, and cutting, a positive electrode sheet is obtained. The single-sided thickness of the positive electrode active material layer is 100μm.

[0079] <Preparation of negative electrode sheet>

[0080] The negative electrode active material artificial graphite (specific surface area 1.1m 2 / g), thickener sodium carboxymethyl cellulose (CMC-Na), conductive carbon black (Super-P), binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96:2:1:1, deionized water is added, and a negative electrode slurry with a solid content of 50wt% is prepared, and stirred evenly. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and dried at 85℃; then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. After cold pressing, stripping, and cutting, a negative electrode sheet is obtained. The single-sided thickness of the negative electrode active material layer is 70μm.

[0081] <Preparation of Electrolyte>

[0082] In an argon atmosphere glove box with a moisture content of ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 1:1:1, and then lithium salt LiPF6 is added and dissolved in the above solvent, and then the compound represented by formula (I) and the compound represented by formula (II) are added, and the electrolyte is obtained after mixing evenly. Among them, the types and contents of the compound represented by formula (I) and the compound represented by formula (II) are shown in Table 1, and the content of LiPF6 in the electrolyte is 12.5wt%.

[0083] <Preparation of Separator>

[0084] A polyethylene (PE) porous polymer film with a thickness of 16 μm was used as the separator.

[0085] <Preparation of lithium-ion batteries>

[0086] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode and the negative electrode to play an isolating role, and wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film packaging bag, vacuum dried, and then injected with electrolyte, and a lithium-ion battery is obtained through vacuum packaging, standing, and formation processes.

[0087] Example 1-2 to Example 1-18

[0088] Except that the types and contents of the compound represented by formula (I) and the compound represented by formula (II) are adjusted according to Table 1 in <Preparation of electrolyte>, the rest is the same as Example 1-1.

[0089] Example 2-1

[0090] Except that VC was further added to the electrolyte in <Preparation of Electrolyte>, the rest was the same as Example 1-4. The content of VC was as shown in Table 2.

[0091] Example 2-2 to Example 2-7

[0092] Except that the content of VC was adjusted according to Table 2 in <Preparation of Electrolyte>, the rest was the same as Example 2-1.

[0093] Comparative Example 1

[0094] Except that the compound represented by formula (I) and the compound represented by formula (II) are not added in <Preparation of electrolyte>, the rest is the same as Example 1-1.

[0095] Comparative Example 2 to Comparative Example 4

[0096] Except that the contents of the compound represented by formula (I) and the compound represented by formula (II) are adjusted according to Table 1 in <Preparation of electrolyte>, the rest is the same as Example 1-1.

[0097] Table 1: Preparation parameters of Example 1-1 to Example 1-18 and Comparative Example 1 to Comparative Example 4

[0098]

[0099]

[0100] Note: In Table 1, “ / ” indicates that there is no relevant preparation parameter.

[0101] Table 2: Preparation parameters of Examples 1-4, 2-1 to 2-7

[0102] a+b(wt%) c(wt%) (a+b) / c Examples 1-4 2.0 0 / Example 2-1 2.0 0.4 5 Example 2-2 2.0 0.66 3 Example 2-3 2.0 1.0 2 Embodiment 2-4 2.0 2.0 1 Embodiment 2-5 2.0 3.0 0.67 Embodiment 2-6 2.0 4.0 0.5 Embodiment 2-7 2.0 5.0 0.4

[0103] Note: In Table 2, “ / ” indicates that there is no relevant preparation parameter.

[0104] Test methods and equipment:

[0105] Energy efficiency and cycle performance testing:

[0106] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to charge and discharge cycle tests on a charge and discharge instrument (model: BAT-NEEFLCT-05300-V010), the test temperature was 25°C, the cycle rate was 1C (i.e., both the charge rate and the discharge rate were 1C), the charging voltage was 2.5V to 3.65V, and the energy efficiency and capacity retention rate after the cycle were calculated.

[0107] The energy efficiency calculation formula is: (discharge energy after the nth cycle / charge energy after the nth cycle) × 100%;

[0108] The capacity retention rate is calculated as follows: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0109] Table 3: Performance data of various embodiments and comparative examples

[0110]

[0111]

[0112] In combination with Table 1 and Table 3, it can be seen from Examples 1-1 to 1-11 and Comparative Examples 1 to 4 that when the electrolyte does not contain the compound represented by formula (I) and the compound represented by formula (II) (for example, Comparative Example 1), the 200 cycle capacity retention rate and 1000 cycle capacity retention rate of the lithium ion battery are both low; when only the compound represented by formula (I) is added to the electrolyte (for example, Comparative Example 2), the 200 cycle capacity retention rate and 1000 cycle capacity retention rate of the lithium ion battery are also low; when only the compound represented by formula (II) is added to the electrolyte (for example, Comparative Example 3), although the 200 cycle capacity retention rate of the lithium ion battery is improved to a certain extent, its 1000 cycle capacity retention rate is still low; when the addition amount of the compound represented by formula (I) and the compound represented by formula (II) in the electrolyte is too much, the capacity retention rate of the lithium ion battery is increased to a certain extent, and ... When the content of the compound represented by formula (I) and the compound represented by formula (II) is high (for example, comparative example 4), the 200-cycle capacity retention rate and 1000-cycle capacity retention rate of the lithium-ion battery are also low. This may be due to the excessive thickness of the SEI film formed in the initial film formation stage, which leads to a large resistance to lithium ion transmission, thereby affecting the cycle performance of the lithium-ion battery and causing a decrease in the initial energy efficiency. However, the electrolyte of the present application includes the compound represented by formula (I) and the compound represented by formula (II), and when the contents of the above two compounds are regulated within the scope of the present application, the 200-cycle capacity retention rate and 1000-cycle capacity retention rate of the lithium-ion battery are improved, and the initial energy efficiency is improved or is not much different from that of the comparative examples, indicating that the synergistic effect of the compound represented by formula (I) and the compound represented by formula (II) can improve the short-term cycle performance and long-term cycle performance of the lithium-ion battery.

[0113] It can also be seen from Examples 1-1 to 1-9 and 1-10 to 1-11 that, on the basis of the content of the compound represented by formula (I) and the compound represented by formula (II) in the electrolyte within the scope of this application, by regulating a / b within the scope of this application, it is beneficial for the lithium-ion battery to exhibit better short-term cycle performance and long-term cycle performance.

[0114] The types of the compound represented by formula (I) and the compound represented by formula (II) usually also have an impact on the performance of the lithium-ion battery. It can also be seen from Examples 1-1 and 1-12 to 1-18 that by regulating the types of the compound represented by formula (I) and the compound represented by formula (II) within the scope of this application, it is beneficial to obtain a lithium-ion battery with excellent short-term cycle performance and long-term cycle performance.

[0115] In combination with Table 2 and Table 3, it can also be seen from Examples 1-4 and 2-1 to 2-7 that after further adding VC to the electrolyte, by regulating (a+b) / c within the scope of this application, it is beneficial to obtain a lithium-ion battery with excellent short-term cycle performance and long-term cycle performance.

[0116] The above is a detailed introduction to an electrolyte, a battery containing the electrolyte, an energy storage device and an electrical equipment disclosed in the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core inventions of the embodiments of the present application. At the same time, for general technicians in this field, according to the ideas of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte, characterized in that: Including compounds represented by formula (I) and compounds represented by formula (II): In formula (I), R1 and R2 are each independently selected from hydrogen or an electron-withdrawing group, and at least one of R1 and R2 is the electron-withdrawing group, and the electron-withdrawing group includes a fluorine atom, a nitro group or a trifluoromethyl group; In formula (II), R3, R4, R5, and R6 are each independently selected from hydrogen, substituted or unsubstituted C1-4 alkyl; Based on the mass of the electrolyte, the mass percentage of the compound represented by formula (I) is a, the mass percentage of the compound represented by formula (II) is b, 0.5%≤a≤3%, and 0.1%≤b≤2%.

2. The electrolyte according to claim 1, characterized in that 1％≤a≤2％。 3. The electrolyte according to claim 1, characterized in that 0.5≤a / b≤5.

4. The electrolyte according to claim 1, characterized in that The electrolyte further includes vinylene carbonate. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is c, satisfying: 0.5≤(a+b) / c≤3.

5. The electrolyte according to claim 1, characterized in that The compound represented by formula (I) is selected from at least one of the following compounds:

6. The electrolyte according to claim 1, characterized in that The compound represented by formula (II) is selected from at least one of the following compounds:

7. The electrolyte according to any one of claims 1 to 6, characterized in that The electrolyte also includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and ethylene glycol dimethyl ether.

8. A battery, characterized in that: The electrolyte comprises the electrolyte according to any one of claims 1 to 7.

9. An energy storage device, characterized in that: The invention comprises a casing and at least one battery according to claim 8, wherein the battery is accommodated in the casing.

10. An electrical device, characterized in that: It includes the energy storage device as described in claim 9, and the energy storage device supplies power to the electrical equipment.

Images