Electrolyte, battery, energy storage device and electric equipment

Abstract

The invention relates to an electrolyte, a battery, an energy storage device and electric equipment. The electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a first additive, and the first additive comprises a compound shown in the formula (I); wherein R1 is selected from H, a substituted or unsubstituted alkyl group of C1 to C6, a substituted or unsubstituted alkenyl group of C2 to C6, a substituted or unsubstituted alkynyl group of C2 to C6, or an amide group; the mass percent of the first additive in the electrolyte is a, and a is more than or equal to 0.1% and less than or equal to 1%. The electrolyte can effectively improve the overcharge safety performance of the battery, does not sacrifice the cycle performance of the battery, and ensures that the battery has good safety performance and cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to an electrolyte, a battery, an energy storage device and an electric equipment. BACKGROUND

[0002] With the development of the energy storage industry, higher requirements are put forward for the overcharge safety performance of batteries, regardless of the wind and light power generation side, household energy storage side or other user scenarios. Especially in the wind and light power generation side, a large number of batteries are needed, and it is more necessary to further improve the overcharge safety performance. At the same time, in the wind and light power generation side, the cycle service life of the matching energy storage battery is often less than the service life of the power generation facility, so how to improve the cycle performance of the battery is also very important.

[0003] However, at present, while improving the overcharge safety performance of the battery, it is easy to adversely affect the cycle performance of the battery. Therefore, it is necessary to further improve and optimize the performance of the battery. SUMMARY

[0004] Based on this, the application provides an electrolyte, a battery, an energy storage device and an electric equipment, which can improve the overcharge safety performance of the battery while ensuring that the battery has good cycle performance and alleviating the self-discharge problem of the battery.

[0005] In order to achieve the above purpose, in a first aspect, the application provides an electrolyte, which comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a first additive, and the first additive comprises a compound represented by formula (I): Formula (I); wherein R1 is selected from H, a substituted or unsubstituted C1 to C6 alkyl group, a substituted or unsubstituted C2 to C6 alkenyl group, a substituted or unsubstituted C2 to C6 alkynyl group, or an amide group; The mass percentage of the first additive in the electrolyte is a, and 0.1%≤a≤1%.

[0006] Optionally, the first additive is selected from at least one of the following structural formulas: Formula (I-1), Formula (I-2), Formula (I-3), Formula (I-4), Formula (I-5), Formula (I-6), Formula (I-7), Formula (I-8).

[0007] Further, the additive further comprises a second additive, the second additive being an additive having Si-O bond; a mass percentage of the second additive in the electrolyte being b, 0.1%≤b≤1%.

[0008] Further, 0.2≤a / b≤10.

[0009] Preferably, 0.1%≤a≤0.5%.

[0010] Preferably, 0.1%≤b≤0.5%.

[0011] Optionally, the second additive comprises at least one of dimethyldimethoxysilane, tris(trimethylsilyl)phosphate, hexamethyldisiloxane or bis(trimethylsilyl) sulfate.

[0012] Further, the organic solvent comprises a main solvent and a fluorinated organic solvent, the fluorinated organic solvent comprising at least one of difluoroacetic acid, trifluoroacetic acid, methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, a mass percentage of the fluorinated organic solvent in the electrolyte being c, 1%≤c≤5%.

[0013] Further, 0.02≤a / c≤0.5.

[0014] In a second aspect, the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte as described in the first aspect, the separator being arranged between the positive electrode sheet and the negative electrode sheet to form an electrode core, and the electrolyte being injected into the electrode core.

[0015] In a third aspect, the present application provides an energy storage device, comprising a box body and at least one battery as described in the second aspect, the battery being accommodated in the box body.

[0016] In a fourth aspect, the present application provides an electrical equipment, comprising an energy storage device as described in the third aspect, the energy storage device being used to supply power to the electrical equipment.

[0017] Compared with the prior art, the present application has the following beneficial effects: By adding 0.1%~1% of the first additive with specific chemical structure into the electrolyte, the present application can effectively improve the overcharge safety performance of the battery while ensuring the cycle performance of the battery.

[0018] The first additive of the present application is a nitrogen-doped six-membered ring with two para nitrogen atoms, which can simultaneously weaken the reaction degree of electrolyte with negative active material and positive active material, and reduce the reaction heat, thereby effectively improving the overcharge safety performance of the battery. First, the nitrogen-doped six-membered ring can participate in interface film formation to form an interface film with good compactness and rich in organic polymers. The compact interface film can effectively prevent the reaction between the solvent in the electrolyte and the metalized negative active material (such as lithiated graphite), thereby reducing the reaction heat and avoiding a series of chain reactions caused by rapid temperature rise of the battery during overcharge, thereby achieving the purpose of improving the overcharge safety performance. Second, the two nitrogen atoms on the nitrogen-doped six-membered ring are arranged in para position. The lone pair electrons on the para-structured nitrogen atoms have good unsaturation and good complexing ability to the empty orbit of transition metal, so as to effectively inhibit the oxidation catalysis of transition metal in the positive active material to the electrolyte during overcharge, and also inhibit the dissolution of transition metal in the positive active material, thereby further reducing the reaction heat of the electrolyte with the positive active material. Finally, the nitrogen-doped six-membered ring with para nitrogen atoms is also connected with a carbonyl group. The carbonyl group has a certain binding capacity with lithium ions and other migrating ions, which can enhance the possibility of the first additive to bind with the negative electrode surface, and promote the film formation effect of the first additive on the negative electrode.

[0019] At the same time, since the reaction degree of electrolyte with active material of electrode can be effectively controlled, the above amount of first additive also helps to ensure the cycle performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 is a structural schematic diagram of an energy storage system (user side energy storage) of an embodiment of the present application; Figure 2 is a structural schematic diagram of an energy storage system (power generation / distribution side energy storage) of another embodiment of the present application; Figure 3 is a structural schematic diagram of an energy storage system (industrial / commercial side energy storage) of still another embodiment of the present application.

[0022] Main figure mark explanation: 400. Energy storage system; 410. First power conversion device; 420. First user load; 430. Second user load; 440. Energy storage device; 450. High-voltage cable; 460. Second power conversion device; 470. Automobile; 480. Photovoltaic-energy storage-charging station. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0025] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that terms such as “comprising / including” or “having” specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Furthermore, the term “and / or” as used in this specification is merely a description of the relationship between related objects, indicating that three relationships may exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. That is, the term “and / or” as used in this specification includes any and all combinations of the related listed items.

[0026] The technical solution of this application will be further described in detail below with reference to the accompanying drawings.

[0027] The energy storage sector is placing increasingly stringent requirements on the overcharge safety performance of energy storage devices, especially those used in wind and solar power generation. Due to their large scale and complex operating environments, these devices require even higher overcharge safety standards. The overcharge safety performance of energy storage devices is highly dependent on the performance of the battery materials, making battery overcharge safety particularly crucial. This is especially true for high-capacity energy storage batteries (such as lithium-ion batteries with capacities of 300 Ah and above), where overcharging can trigger thermal runaway, leading to more severe damage due to their higher capacity. Furthermore, for wind and solar power generation applications, the cycle life of the accompanying energy storage devices is typically shorter than the lifespan of the power generation facilities; therefore, improving the cycle performance of these energy storage devices is also essential.

[0028] However, the inventors of this application discovered during the process of optimizing battery overcharge safety that while improving the electrolyte formulation, such as developing more effective additives, can enhance battery overcharge safety, this can easily negatively impact battery cycle performance. It is evident that optimizing overcharge safety can easily sacrifice other aspects of battery performance, such as cycle performance. Therefore, it is necessary to develop an electrolyte with better overall performance, enabling it to effectively improve battery overcharge safety while maintaining good cycle performance.

[0029] Based on the above analysis, the embodiments of this application provide an electrolyte, a battery, an energy storage device, and an electrical device, which can not only improve the overcharge safety performance of the battery, but also ensure that the battery has good cycle performance.

[0030] This application provides an electrolyte comprising an electrolyte salt, an organic solvent, and an additive. The additive includes a first additive, which comprises a compound of formula (I): Formula (I); R1 is selected from H, substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C2 to C6 alkynyl, or amide group. The mass percentage of the first additive in the electrolyte is a, where 0.1% ≤ a ≤ 1%.

[0031] In this embodiment of the application, the first additive of formula (I) in the electrolyte at the above-mentioned amount can effectively improve the overcharge safety performance of the battery without sacrificing the cycle performance of the battery, thus ensuring that the battery has good safety performance and cycle performance.

[0032] In this embodiment, a first additive, comprising 0.1% to 1% by mass, is added to the electrolyte. This additive is a nitrogen-doped six-membered ring with two para-nitrogen atoms. It can simultaneously weaken the reaction between the electrolyte and both the negative and positive electrode active materials, reducing heat generation and thus effectively improving the overcharge safety performance of the battery. Firstly, this nitrogen-doped six-membered ring can participate in interfacial film formation, creating a dense interfacial film rich in organic polymers. This dense interfacial film effectively prevents the reaction between the solvent in the electrolyte and the metallized negative electrode active material (e.g., lithium graphite), thereby reducing heat generation and preventing a rapid rise in battery temperature during overcharge, which could lead to a series of chain reactions and ultimately improve overcharge safety performance. Secondly, the two nitrogen atoms on the nitrogen-doped six-membered ring are arranged in a para configuration. This para configuration provides excellent unsaturation of the lone pair electrons on the nitrogen atoms, resulting in a strong ability to complex with empty orbitals of transition metals. Therefore, it effectively suppresses the oxidative catalytic effect of transition metals on the electrolyte during overcharging in the positive electrode active material, and also inhibits the dissolution of transition metals from the positive electrode active material, thereby further reducing the heat generated by the reaction between the electrolyte and the positive electrode active material. Finally, a carbonyl group is also attached to the nitrogen-doped six-membered ring with the para nitrogen atom. The carbonyl group has a certain binding ability with migrating ions such as lithium ions, which can enhance the possibility of the first additive binding to the negative electrode surface groups, promoting the film formation effect of the first additive on the negative electrode.

[0033] Meanwhile, since the degree of reaction between the electrolyte and the electrode active material can be effectively controlled, the aforementioned amount of the first additive also helps to ensure the cycle performance of the battery. For example, the mass percentage 'a' of the first additive in the electrolyte is 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, or 1%. Preferably, 0.1% ≤ a ≤ 0.5%.

[0034] Optionally, the first additive is selected from at least one of the following structural formulas: Equation (Ⅰ-1) Equation (Ⅰ-2), Equation (Ⅰ-3), Equation (Ⅰ-4), Equation (Ⅰ-5), Equation (Ⅰ-6), Equation (Ⅰ-7), Equation (Ⅰ-8).

[0035] Using the first additives with the above-mentioned structural formulas can achieve better improvement in overcharge safety performance, suppression of battery self-discharge, and assurance of good cycle performance. Among these, the first additives of formulas (I-2), (I-5), and (I-3) are preferred. In these first additives, the R1 group has a relatively shorter chain length and smaller molecular weight, resulting in less steric hindrance and easier access to the electrode reaction interface to participate in film formation. Formulas (I-2) and (I-5) are more preferred, as they provide a better overall balance in overcharge safety performance, self-discharge suppression performance, and cycle performance. For example, in the first additive of formula (I-5), the R1 group has an unsaturated bond at its end, which helps to form a denser organic network in the interfacial film formation reaction, thus better improving overcharge safety performance.

[0036] Furthermore, the additive in this embodiment of the application also includes a second additive, which is an additive having Si-O bonds; the mass percentage of the second additive in the electrolyte is b, where 0.1%≤b≤1%.

[0037] In this embodiment of the application, the first additive of the above formula (I) and the second additive having Si-O bonds are used in the electrolyte to work synergistically. This can effectively improve the overcharge safety performance of the battery, without affecting the cycle performance of the battery, and can also control the self-discharge level of the battery. This ensures that the battery has good safety performance and cycle performance, while further improving the self-discharge phenomenon of the battery.

[0038] In further research, the inventors discovered that while using a nitrogen-doped six-membered ring with a para-nitrogen atom can complex the transition metal in the positive electrode active material to reduce heat generation during the reaction, it easily leads to self-discharge problems in the battery. This is because the electrolyte usually contains trace amounts of hydrofluoric acid, which can corrode the metal of the current collector. For example, the reaction of hydrofluoric acid with copper foil current collectors generates trace amounts of copper ions. When using a nitrogen-doped six-membered ring with a para-nitrogen atom, since it can also complex copper ions, it promotes the reaction between hydrofluoric acid and copper foil in a direction that continuously generates copper ions, leading to an increase in the Cu content in the electrolyte. This results in more Cu being deposited on the electrodes during battery cycling, exacerbating the self-discharge problem.

[0039] To overcome the self-discharge problem caused by improving overcharge safety performance, the first embodiment of this application involves attaching a carbonyl functional group to the aforementioned nitrogen-doped six-membered ring. The carbonyl functional group adjusts the electron cloud density of compound (I) to regulate the complexation ability of the nitrogen-doped six-membered ring for transition metals, thus balancing the promotion of overcharge performance and its impact on self-discharge. The second embodiment uses a second additive with Si-O bonds in synergistic action with the first additive. The Si-O bonds in the second additive can remove water and acid, reducing the hydrofluoric acid content in the electrolyte and decreasing the corrosion of the current collector. This reduces the degree to which the generated copper ions and other transition metal ions are complexed by the first additive, thereby reducing the copper ion content in the electrolyte and improving the battery self-discharge problem caused by the deposition of copper ions and other transition metal ions onto the electrode. Therefore, by attaching a carbonyl functional group to the nitrogen-doped six-membered ring and simultaneously using a second additive with Si-O bonds, the combined improvement of these two aspects allows the first and second additives to work together to improve overcharge safety performance and alleviate battery self-discharge problems.

[0040] By controlling the mass percentage b of the second additive in the electrolyte within the range of 0.1% to 1%, it can effectively remove water and acid without significantly increasing internal resistance, thus preventing the metal current collector from being affected by the first additive and ultimately leading to self-discharge. For example, the mass percentage b of the second additive in the electrolyte is 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, or 1%. Preferably, it is 0.1% ≤ b ≤ 0.5%.

[0041] Furthermore, 0.2 ≤ a / b ≤ 10. Controlling the ratio of the first additive to the second additive within this range achieves a more balanced improvement in overcharge safety, self-discharge suppression, and cycle performance. If the a / b ratio is too low, the amount of the first additive is relatively small, while the amount of the second additive is relatively large. A small amount of the first additive will affect its improvement in overcharge safety, while a large amount of the second additive, although resulting in more significant acid removal and a reduced risk of self-discharge, can easily increase the battery's internal resistance. Conversely, if the a / b ratio is too high, the amount of the first additive is relatively large, while the amount of the second additive is relatively small. While a large amount of the first additive ensures excellent overcharge safety, the overall weakening of water and acid removal capabilities also reduces the ability to suppress battery self-discharge. Therefore, controlling a / b within the above range achieves a better balance in overcharge safety, self-discharge suppression, and cycle performance.

[0042] Optionally, the second additive includes at least one of dimethyldimethoxysilane, tris(trimethylsilane)phosphate, hexamethyldisiloxane, or bis(trimethylsilyl)sulfate. These second additives, which have Si-O bonds, can synergistically work with the first additive to suppress the problem of more pronounced battery self-discharge due to the use of the first additive.

[0043] Furthermore, the organic solvent includes a host solvent and a fluorinated organic solvent. The fluorinated organic solvent includes at least one of difluoroethyl acetate, trifluoroethyl acetate, methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The mass percentage of the fluorinated organic solvent in the electrolyte is c, where 1% ≤ c ≤ 5%.

[0044] Understandably, the main solvent refers to the organic solvent with a relatively large mass percentage, serving as the primary medium for dissolving electrolyte salts and facilitating ion transport. Fluorinated organic solvents refer to the organic solvent with a relatively small mass percentage; they also perform the aforementioned dissolution and ion transport functions, but in addition, they can synergistically work with the first additive to modify and optimize the performance of the solid electrolyte interfacial membrane. For example, the mass percentage c of the fluorinated organic solvent in the electrolyte is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0045] The fluorinated organic solvent used in this embodiment is an organic solvent with fluorinated groups, comprising 1% to 5% by mass. On one hand, this fluorinated organic solvent has stronger oxidation resistance than conventional non-fluorinated carbonates and other organic solvents, reducing electrolyte oxidation at the positive electrode during overcharging. On the other hand, during the film-forming reaction at the negative electrode, the fluorinated organic solvent and the first additive can remove fluorine (F) to produce inorganic components such as LiF, giving the solid electrolyte interfacial film on the negative electrode surface a characteristic of alternating distribution of organic and inorganic components, thus improving the thermal stability of the solid electrolyte interfacial film. Therefore, under the synergistic effect of the first additive and the fluorinated organic solvent, the solid electrolyte interfacial film not only reduces excessive electrolyte participation in the reaction through higher density, achieving the goal of reducing heat generation, but also enhances the thermal stability of the solid electrolyte interfacial film by introducing alternating inorganic components, protecting the organic components from excessive dissolution and ensuring the heat reduction effect of the organic components. Consequently, due to the improved density and stability of the solid electrolyte interfacial film, the overcharge safety and cycle performance of the battery are further improved.

[0046] Furthermore, 0.02 ≤ a / c ≤ 0.5. Controlling a / c within this range helps to better balance the excellent density and thermal stability of the solid electrolyte interface film, thereby synergistically improving overcharge safety and cycle performance, while avoiding the risks of lithium plating and self-discharge caused by excessive first additive.

[0047] In the electrolyte of this application embodiment, the main organic solvent may include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, or propyl propionate. The electrolyte salt can be selected according to the properties of the battery. When the battery is a lithium-ion battery, the electrolyte salt is a lithium salt, which may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, or lithium difluorooxalate borate, etc., and this application does not limit this. When the battery is a sodium-ion battery, the electrolyte salt is a sodium salt, which may include at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, etc., and this application does not limit this.

[0048] This application embodiment also provides a battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte as described above. The separator is disposed between the positive electrode and the negative electrode to form a battery cell, and the electrolyte is injected into the battery cell.

[0049] In this embodiment, there are no particular limitations on the arrangement of the positive electrode sheet, as long as the purpose of this embodiment can be achieved. The positive electrode sheet typically includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. There are no particular limitations on the type and thickness of the positive current collector material, as long as the purpose of this embodiment can be achieved. For example, the positive current collector includes, but is not limited to, aluminum foil, stainless steel foil, titanium foil, or composite current collectors; the thickness of the positive current collector is 5 μm to 30 μm. Similarly, there are no particular limitations on the type and thickness of the positive active material layer, as long as the purpose of this embodiment can be achieved. For example, the positive active material includes, but is not limited to, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, or lithium-rich manganese-based materials; the thickness of the positive active material is 50 μm to 200 μm.

[0050] In addition to the positive electrode active material, the positive electrode active material layer may also include positive electrode conductive agents, positive electrode binders, and other additives. This application embodiment does not impose any particular restrictions on the type and amount of these materials, as long as they achieve the purpose of this application embodiment. For example, positive electrode conductive agents may include, but are not limited to, conductive carbon black, carbon nanotubes, graphene, or carbon fibers; positive electrode binders may include, but are not limited to, fluorinated resins, polypropylene resins, fiber-type binders, rubber-type binders, or polyimide-type binders, for example, polyvinylidene fluoride can be used as the positive electrode binder.

[0051] In this application embodiment, there are no particular limitations on the arrangement of the negative electrode sheet, as long as the purpose of this application embodiment can be achieved. The negative electrode sheet typically includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. There are no particular limitations on the type and thickness of the negative current collector material, as long as the purpose of this application embodiment can be achieved. For example, the negative current collector includes, but is not limited to, aluminum foil, stainless steel foil, titanium foil, or composite current collectors; the thickness of the negative current collector is 5 μm to 30 μm. Similarly, there are no particular limitations on the type and thickness of the negative active material layer, as long as the purpose of this application embodiment can be achieved. For example, the negative active material includes, but is not limited to, carbon-based materials (such as natural graphite, artificial graphite, or mesophase carbon microspheres), silicon-based materials (such as silicon or silicon-carbon), tin-based materials, or lithium titanate; the thickness of the negative active material is 50 μm to 200 μm.

[0052] In addition to the negative electrode active material, the negative electrode active material layer may also include auxiliary agents such as negative electrode conductive agents and negative electrode binders. This application embodiment does not impose any particular restrictions on the type and amount of these materials, as long as they achieve the purpose of this application embodiment. For example, negative electrode conductive agents may include, but are not limited to, conductive carbon black, carbon nanotubes, graphene, or carbon fibers; negative electrode binders may include, but are not limited to, fluorinated resins, polypropylene resins, fiber-type binders, rubber-type binders, or polyimide-type binders, for example, styrene-butadiene rubber may be used as the negative electrode binder.

[0053] In the embodiments of this application, there are no particular limitations on the arrangement of the diaphragm, as long as the purpose of the embodiments of this application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane 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, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0054] The battery in this application embodiment may also include a casing. This application does not impose any particular limitations on the casing, and those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the casing may include an aluminum-plastic film.

[0055] This application does not impose any particular limitation on the battery preparation method; any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the battery preparation method includes, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a bare cell with a wound structure; placing the bare cell in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the battery.

[0056] This application also provides an energy storage device, including a housing and at least one battery as described above, the battery being housed within the housing. The energy storage device with this battery exhibits excellent performance, which is beneficial for its use. Housing the battery within the housing increases its stability and protection, thereby extending the lifespan of the energy storage device. It is understood that the energy storage device may contain one or more batteries, and when the energy storage device contains multiple batteries, the multiple batteries can be connected in at least one manner, such as parallel or series connection.

[0057] This application also provides an electrical device including the energy storage device described in the above embodiments, which is beneficial for improving the product competitiveness and performance of the electrical device. In an optional embodiment, 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 embodiment, the electrical device body includes a positive electrode and a negative electrode, the positive electrode of the battery in the energy storage device is used to electrically connect to the positive electrode of the electrical device body, and the negative electrode of the battery in the energy storage device is used to electrically connect to the negative electrode of the electrical device body, so as to supply power to the electrical device.

[0058] The electrical equipment in this application embodiment may include, but is not limited to: containers, household energy storage systems, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. Among them, spacecraft include, for example, airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include, for example, stationary or mobile electric toys, specifically, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include, for example, metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, specifically, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0059] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form for future applications. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels. Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0060] Taking electrochemical energy storage as an example, this solution provides an energy storage device for use in energy storage systems. The energy storage device is equipped with a set of chemical batteries, which mainly use the chemical elements in the batteries as energy storage media. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage media. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical batteries. When the use of external electrical energy reaches its peak, the stored electricity is released for use, or transferred to places with a shortage of electricity for use.

[0061] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices include: (1) Large-scale energy storage power stations (composed of multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, the energy storage power station realizes the load matching of power in time and space, enhances the renewable energy absorption capacity, reduces instantaneous power changes, reduces the impact on the power grid, improves the problem of new energy power generation absorption, and is of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation. (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption. (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system when the electricity price is low and discharging the energy storage system when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use energy storage systems to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0062] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 1 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 440 of this application is not limited to the home energy storage scenario.

[0063] This application provides an energy storage system 400, which includes a first power conversion device 410 (photovoltaic panel), a first user load 420 (household lighting fixture), a second user load 430 (e.g., household appliances such as air conditioners), and an energy storage device 440. The energy storage device 440 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 440 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 440 stores this electrical energy and supplies it to lighting fixtures and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0064] In some embodiments, see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 400 according to another embodiment of this application, and this application Figure 2 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 440 of this application is not limited to the energy storage scenario on the generation / distribution side.

[0065] This application provides an energy storage system 400, which includes: a high-voltage cable 450, a first power conversion device 410, a second power conversion device 460, and an energy storage device 440 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 460 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 440 through grid connection. The energy storage device 440 is connected to the high-voltage cable and outputs smooth electricity to the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and stable grid operation; or, wind power... The conversion device is always connected to the high-voltage cable. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 440 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 440 together with the high-voltage cable 450 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0066] In some embodiments on the distribution network side, the first power conversion device 410 can be a photovoltaic panel, and the energy storage device 440 is connected to the high-voltage cable 450 and installed downstream of the high-voltage cable 450 and between the user load. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 440, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 450 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0067] In some embodiments, see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 400 according to another embodiment of this application, and this application Figure 3 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 440 of this application is not limited to industrial and commercial energy storage scenarios.

[0068] This application provides an energy storage system 400, which includes: an energy storage device 440, a high-voltage cable 450, a factory equipped with a first power conversion device 410, a photovoltaic-energy storage-charging station 480, and a vehicle 470. In some embodiments of industrial and commercial scenarios, the first power conversion device 410 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 440 in the factory. In the event of a power grid failure, the energy storage device 440 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 440 in conjunction with the high-voltage cable 450 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the first power conversion device 410 can also convert solar energy into electrical energy and store it in the energy storage device 440 of the photovoltaic-energy storage-charging station 480, which can then directly charge the vehicle 470, making it fast and convenient.

[0069] Optionally, the first power conversion device 410 may include, but is not limited to, a photovoltaic panel, and the second power conversion device 460 may include, but is not limited to, a wind power conversion device. The first power conversion device 410 and the second power conversion device 460 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0070] Optionally, the energy storage device 440 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0071] Optionally, the energy storage device 440 may include, but is not limited to, individual batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / prefabricated energy storage compartments, and other battery integrated systems composed of individual batteries. The actual application form of the energy storage device 440 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 440.

[0072] Optionally, the individual cell can be, but is not limited to, at least one of cylindrical, prismatic, prismatic, or other shaped cells.

[0073] Optionally, the single cell can be a rechargeable battery, which refers to a single cell that can be recharged after discharge to activate the active materials and continue to be used. The single cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0074] The present application will be further described below with reference to more specific embodiments.

[0075] Example 1 This embodiment provides an electrolyte, which is prepared through the following steps: In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a mass ratio of 1:1:1; dried lithium hexafluorophosphate electrolyte is dissolved in the above mixed solvent and stirred until the lithium salt is dissolved; the first additive and the second additive are added to the above mixed solvent to obtain the electrolyte.

[0076] The types and mass percentages of the first additive in the electrolyte are shown in Table 1. Additionally, the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L.

[0077] Examples 2 to 21 The difference from Example 1 lies in the types and / or mass percentages of the first and second additives. Additionally, some examples also include fluorinated organic solvents. See Table 1 for details.

[0078] Comparative Examples 1 to 3 The difference from Example 1 is that the types and mass percentages of the first additive, the second additive, and the fluorinated organic solvent are adjusted, as detailed in Table 1.

[0079] Table 1. Types and contents of each component in the electrolytes of each embodiment and comparative example.

[0080] Note: 1. In Table 1, " / " indicates that there are no relevant preparation parameters.

[0081] 2. The first additive formula (I-1) in Table 1 is: The first additive formula (I-2) is The first additive (I-5) is .

[0082] <Battery Manufacturing> Preparation of the positive electrode sheet: Lithium iron phosphate (LiFePO4), conductive carbon black, and polyvinylidene fluoride (PVDF) binder were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:0.7:2.3, and mixed to form a positive electrode slurry with a solid content of 60 wt%. This slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil current collector. After drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The unit area of ​​the positive electrode active material layer was 1540.25 mm². 2 The weight of a single-sided coating is 300 mg.

[0083] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), conductive carbon black, and styrene-butadiene rubber emulsion (binder) were mixed in a mass ratio of 96.5:0.5:1:2. Water was added to prepare a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained. The unit area of ​​the negative electrode active material layer was 1540.25 mm². 2 The weight of a single-sided coating is 144 mg.

[0084] Diaphragm: A 16 μm polyethylene film is used as the diaphragm.

[0085] Electrolyte: The electrolyte prepared in the above examples and comparative examples.

[0086] Assembly of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator placed between the positive and negative electrode to separate them. After winding, a bare cell is obtained. After welding the tabs, the cell is assembled into the outer packaging, dried, and injected with electrolyte. The cell is then encapsulated, left to stand, formed, and shaped to finally produce a lithium-ion battery.

[0087] Performance Testing (1) Overcharge safety test The lithium-ion battery to be tested was tested on a charge-discharge instrument (Nebula: BAT-NEEFLCT-05600-V012). It was left to stand for 5 hours at (25±2)℃, discharged to 2.5V at 0.5P, charged to 3.65V at 0.5P, and left to stand for 10 minutes.

[0088] The lithium-ion battery was then transferred to an overcharge tester for testing. It was charged with a constant current of 0.5C until the voltage of the lithium-ion battery reached 5.475V or the charging time reached 1 hour. The battery was observed for 1 hour, and any signs of expansion, leakage, smoke, fire, or explosion were recorded.

[0089] The rating criteria are as follows: Level 1 is considered compliant as the lithium-ion battery shows no leakage; Level 2 is compliant as the lithium-ion battery shows leakage but no thermal runaway; Level 3 is compliant as the lithium-ion battery shows leakage, smoke, and thermal runaway, but no fire or explosion; and Level 4 is non-compliant as the lithium-ion battery catches fire or explodes. The criteria for determining whether thermal runaway has occurred are: a temperature sensor is placed on the surface of the test sample, the temperature monitoring sampling frequency is 1 second, and if the temperature rise rate at the monitoring point is ≥3℃ / s for three consecutive times, or if fire or explosion occurs, it is considered thermal runaway.

[0090] (2) Cyclic performance test The lithium-ion battery under test was subjected to charge-discharge cycle testing on a charge-discharge meter at a test temperature of 25℃. The cycle rate was 1C (i.e., both the charge and discharge rates were 1C), and the charging voltage ranged from 2.5V to 3.65V. The capacity retention rate after each cycle was calculated. The formula for calculating the capacity retention rate at 25℃ is: Capacity retention rate after the nth cycle = (Discharge capacity after the nth cycle / Discharge capacity of the first cycle) × 100%. In this test, n is 2000 cycles.

[0091] (3) Self-discharge test The lithium-ion battery to be tested was tested on a charge / discharge meter at a test temperature of 25℃. It was discharged to 2.5V at 0.1C, then charged at 0.5C for 35 minutes. After being left to stand at 25℃ for 24 hours, its open-circuit voltage OCV1 was measured. After being left to stand at 25℃ for 48 hours, its open-circuit voltage OCV was measured again. B Self-discharge K value = (OCV1 - OCV) B ) / 48, the unit of K value is mV / h.

[0092] Table 2: Performance test results of lithium-ion batteries in each embodiment and comparative example

[0093] Comparing Example 1 and Comparative Examples 1 to 3, it can be seen that adding the first additive to the electrolyte can significantly improve overcharge performance and cycle performance. However, for the electrolytes of Comparative Examples 1 to 3, although the K value is acceptable without the introduction of the first additive, the overcharge performance is not up to standard and the cycle performance is also at a low level.

[0094] Further comparison of Examples 1 to 3 shows that, among the various optional first additives, the first additive of formula (I-2) has a more comprehensive effect on improving overcharge and cycle performance.

[0095] Further comparison of Examples 1 and 4-6 shows that optimizing the mass percentage of the first additive in the electrolyte helps to better improve the overall performance of the battery. Preferably, when the content 'a' of the first additive is 0.1% to 0.5%, the overcharge and cycle performance is better, and the self-discharge K value is also lower. More preferably, when the content 'a' of the first additive is 0.3% to 0.5%, the above-mentioned overall performance of the battery is even better.

[0096] Further comparison of Examples 1 and 7-10 shows that adding a second additive while adding the first additive improves overcharge performance and cycle performance. More importantly, it significantly reduces the K value, indicating that the addition of the second additive has a significant inhibitory effect on self-discharge. In a more preferred embodiment, when the second additive is bis(trimethylsilyl)sulfate, the battery shows even better comprehensive improvement in overcharge performance, cycle performance, and self-discharge suppression.

[0097] Further comparisons of Examples 10-15 show that when the ratio of the first additive to the second additive is controlled within 0.2-10, the battery exhibits good overcharge safety, cycle performance, and a low degree of self-discharge. Furthermore, controlling the ratio of a to b within the range of 0.3-1 results in even more significant improvements in overcharge performance, cycle performance, and self-discharge suppression. In particular, the improvement effect on the battery is optimal when the ratio of a to b is 1.

[0098] Further comparison of Examples 12 and 16-18 shows that the addition of fluorinated organic solvents can further improve overcharge performance and cycle performance. Among them, difluoroethyl acetate has the best overall effect when used as a fluorinated organic solvent, achieving Level 1 overcharge pass standard, good cycle performance, and a very low self-discharge K value.

[0099] Further comparison of Examples 18-21 shows that when the ratio of the first additive to the fluorinated organic solvent is controlled within a preferred range, the improvement effects on overcharge performance, cycle performance, and self-discharge level can be further enhanced. Controlling the ratio of a to c within a more preferred range of 0.06-0.3 has a better promoting effect on overcharge improvement, maintenance of cycle performance, and reduction of the K value. In particular, when the ratio of a to c is further controlled within the range of 0.06-0.10, the battery exhibits optimal overcharge performance, maintains a high level of cycle performance, and has a very low K value, resulting in superior overall battery performance.

[0100] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the content of this specification should not be construed as a limitation of this application, and the protection scope of this application should be determined by the appended claims.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises an electrolyte salt, an organic solvent, and an additive, wherein the additive comprises a first additive, which comprises a compound of formula (I): Equation (I); R1 is selected from H, substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C2 to C6 alkynyl, or amide group. The mass percentage of the first additive in the electrolyte is a, where 0.1% ≤ a ≤ 1%.

2. The electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of the following structural formulas: Equation (Ⅰ-1) Equation (Ⅰ-2), Equation (Ⅰ-3), Equation (Ⅰ-4), Equation (Ⅰ-5), Equation (Ⅰ-6), Equation (Ⅰ-7), Equation (Ⅰ-8).

3. The electrolyte according to claim 1, characterized in that, The additive also includes a second additive, which is an additive having Si-O bonds; the mass percentage of the second additive in the electrolyte is b, where 0.1% ≤ b ≤ 1%.

4. The electrolyte according to claim 3, characterized in that, 0.2 ≤ a / b ≤ 10; and / or, 0.1% ≤ a ≤ 0.5%; and / or, 0.1%≤b≤0.5%。 5. The electrolyte according to claim 3, characterized in that, The second additive includes at least one of dimethyldimethoxysilane, tris(trimethylsilane) phosphate, hexamethyldisiloxane or bis(trimethylsilyl)sulfate.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The organic solvent comprises a main solvent and a fluorinated organic solvent. The fluorinated organic solvent comprises at least one of difluoroethyl acetate, trifluoroethyl acetate, methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The mass percentage of the fluorinated organic solvent in the electrolyte is c, where 1% ≤ c ≤ 5%.

7. The electrolyte according to claim 6, characterized in that, 0.02≤a / c≤0.

5.

8. A battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1 to 7, wherein the separator is disposed between the positive electrode and the negative electrode to form a cell, and the electrolyte is injected into the cell.

9. An energy storage device, characterized in that, It includes a housing and at least one battery as described in claim 8, the battery being housed within the housing.

10. An electrical appliance, characterized in that, The device includes the energy storage device of claim 9, wherein the energy storage device supplies power to the electrical equipment.

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