Electrolyte, battery and energy storage device

Abstract

The invention relates to the technical field of batteries, in particular to an electrolyte, a battery and an energy storage device. The electrolyte comprises a first additive, the first additive comprises a compound shown in the formula (I), R1, R2 and R3 are independently selected from substituted or unsubstituted functional groups used for polymerization reaction, the mass percent of the first additive in the electrolyte is a, and a is larger than or equal to 0.01% and smaller than or equal to 3%.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrolyte, a battery, and an energy storage device. Background Technology

[0002] Although secondary batteries have been widely used in energy storage devices, how to further optimize their performance remains a technical challenge that needs to be overcome, especially how to further improve the high-temperature cycle performance and safety performance of secondary batteries. Summary of the Invention

[0003] To address the aforementioned technical problems, embodiments of this application provide a graphite and its preparation method, a negative electrode sheet, a secondary battery, and an energy storage device.

[0004] In a first aspect, this application provides an electrolyte comprising a first additive, the first additive comprising a compound of formula (I):

[0005]

[0006] R1, R2, and R3 are each independently selected from substituted or unsubstituted functional groups for polymerization, and the mass percentage of the first additive in the electrolyte is a, where 0.01% ≤ a ≤ 3%.

[0007] Preferably, 0.05% ≤ a ≤ 2%.

[0008] Optionally, the functional group used for the polymerization reaction includes at least one of unsubstituted alkenyl, alkynyl, epoxy, aldehyde, amino, or cyano groups.

[0009] Optionally, the functional group for the polymerization reaction includes at least one of alkyl, alkenyl, alkynyl, epoxy, aldehyde or amino groups having substituents, and the substituents include at least one of C1 to C6 alkyl, alkenyl, alkynyl, carbonyl, epoxy, ether, aryl, acyl, amino, cyano, fluorine or chlorine atoms.

[0010] Preferably, the first additive comprises at least one of the following compounds:

[0011]

[0012] Furthermore, the electrolyte also includes a lithium salt, which includes lithium fluorosulfonylimide, and the mass percentage of the lithium fluorosulfonylimide in the electrolyte is t, where 0.05% ≤ t ≤ 15%.

[0013] Furthermore, 1 ≤ t / a ≤ 100.

[0014] Preferably, 1 ≤ t / a ≤ 10.

[0015] Optionally, the fluorinated sulfonyl imide lithium includes at least one of lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium tri(trifluoromethylsulfonyl)methyl, or lithium bis(pentafluoroethylsulfonyl)imide.

[0016] Furthermore, the electrolyte also includes a second additive, which includes at least one of vinyl sulfate or methylene disulfonate, and the mass percentage of the second additive in the electrolyte is b, where 0.01% ≤ b ≤ 3%.

[0017] Furthermore, the electrolyte also includes an organic solvent, which includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, or propyl propionate.

[0018] Furthermore, the lithium salt also includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxaborate, or lithium difluorooxaborate.

[0019] Secondly, embodiments of this application provide a battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte as described in the first aspect, 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.

[0020] Thirdly, embodiments of this application provide an energy storage device, which includes a battery as described in the second aspect.

[0021] Compared with the prior art, the beneficial effects of this application are as follows:

[0022] The electrolyte provided in this application, by using a specific amount of the first additive shown in formula (I), can significantly improve the thermal stability and structural stability of the electrolyte interface film in the battery, reduce interfacial side reactions and overcharge heat accumulation, and suppress the battery heat accumulation caused by the vicious cycle between side reactions and battery temperature rise, thereby improving the high-temperature cycle performance and safety performance of the battery. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a residential energy storage system according to an embodiment of this application;

[0025] Figure 2 This is a schematic diagram of the structure of an energy storage system according to an embodiment of this application.

[0026] Reference numerals: 100, energy storage system; 10, energy storage device; 20, power conversion device; 30, first user load; 40, second user load; 50, high-voltage cable; 60, first power conversion device; 70, second power conversion device. Detailed Implementation

[0027] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.

[0028] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0029] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0030] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0031] The technical solution of the present invention will be further described below with reference to the embodiments.

[0032] In secondary batteries such as lithium-ion or sodium-ion batteries, the electrolyte formulation has a significant impact on the electrolyte interface film (i.e., the interface film formed by the reaction between the electrode and the electrolyte) on the positive and / or negative electrode sides. For example, an unstable electrolyte interface film on the negative electrode side is prone to decomposition and damage, leading to side reactions between the solvent and lithium salt, which in turn deteriorates the battery's cycle performance. Especially under high-temperature conditions (e.g., above 45°C) or abuse conditions, the stability of the electrolyte interface film is even worse, making it more susceptible to damage. This results in continuous interfacial side reactions between the electrolyte and the electrode, not only worsening the battery's cycle performance but also, due to the heat and gas-generating characteristics of these side reactions, creating a vicious cycle where side reactions lead to increased battery temperature, which in turn exacerbates the side reactions. Furthermore, it increases the risk of battery fires and even explosions. Therefore, it is essential to further improve electrolyte performance to enhance interfacial stability, especially under high-temperature conditions and abuse conditions, to improve the high-temperature cycle stability and safety performance of batteries and promote the development of batteries with wide temperature ranges and long lifespans.

[0033] Based on the above analysis, this application provides an electrolyte, a battery, and an energy storage device that have superior high-temperature interface stability properties, which can improve the battery's high-temperature cycle stability while also enhancing its safety performance.

[0034] In a first aspect, embodiments of this application provide an electrolyte comprising a first additive, the first additive being a compound of formula (I):

[0035]

[0036] R1, R2, and R3 are each independently selected from substituted or unsubstituted functional groups for polymerization, and the mass percentage of the first additive in the electrolyte is a, where 0.01% ≤ a ≤ 3%.

[0037] The inventors of this application have discovered that by using the first additive of the above formula (I) with a special group structure and controlling its mass percentage in the electrolyte, the thermal stability and mechanical properties of the electrolyte interface film can be significantly improved, the interfacial side reactions and overcharge heat accumulation can be reduced, thereby suppressing the battery heat accumulation caused by the vicious cycle between side reactions and battery temperature rise, thereby improving the high-temperature cycle performance and safety performance of the battery.

[0038] In the electrolyte of this application embodiment, the first additive of formula (I) simultaneously possesses a six-membered ring with alternating carbon and nitrogen distribution, a carbonyl group attached to the nitrogen in the six-membered ring, and a functional group attached to the carbon of the carbonyl group that can undergo polymerization. Through the interaction between these three special groups, the performance of the electrolyte interface membrane is improved. The interaction between the nitrogen in the six-membered ring and the carbonyl group is manifested in the following aspects: First, the nitrogen in the six-membered ring and the carbonyl group are conjugated, approximating an amide structure. This conjugation effect makes it easier for the carbonyl group and the six-membered ring to form a planar molecular structure, making it easier for them to be adsorbed onto the electrode interface. Second, this amide-like structure also affects the charge distribution of the six-membered ring, causing its carbon-nitrogen bonds to tend to break rather than maintain the six-membered ring structure. This property makes the first additive easier to reduce. Therefore, through the interaction between the above-mentioned groups, the first additive is more likely to preferentially act on the electrode interface and more likely to undergo reduction or oxidation reactions at the electrode interface.

[0039] There is also an interaction between the six-membered ring and the functional groups attached to the carbonyl group that are used for polymerization. Specifically, after the carbon-nitrogen bonds in the six-membered ring break, they will undergo polymerization with these functional groups to form a cross-linked network thin-layer polymer, a composite of organic and inorganic components. On the one hand, this cross-linked network thin-layer polymer helps improve the uniformity of the interfacial film at the electrode interface and provides good mechanical strength and thermal stability, thereby improving the battery's cycle thermal stability under high-temperature conditions and reducing the degree of heat accumulation under abuse conditions such as overcharging. On the other hand, this cross-linked network thin-layer polymer can effectively block the contact between the electrolyte and the electrode, inhibit the reaction of other substances in the electrolyte, reduce side reactions at the electrode interface during high-temperature cycling, and lower battery impedance.

[0040] Controlling the mass percentage 'a' of the first additive in the electrolyte within the range of 0.01% ≤ a ≤ 3% is beneficial for maximizing the aforementioned effects of the first additive and fully optimizing the thermal stability and mechanical strength of the electrolyte interface film. When 'a' is less than 0.01%, the first additive is difficult to effectively optimize the performance of the electrolyte interface film; when 'a' is greater than 3%, the addition of the first additive can easily deteriorate other battery performance characteristics. Understandably, 0.01% ≤ a ≤ 3% includes any value within this range, for example, 'a' being 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, or 3%.

[0041] Preferably, 0.05% ≤ a ≤ 2%. When the mass percentage of the first additive in the electrolyte is further controlled within the above range, it is beneficial to further improve the high-temperature cycle performance and safety performance of the battery.

[0042] In the electrolyte of this application embodiment, when the functional group used for the polymerization reaction includes an unsubstituted functional group, the unsubstituted functional group includes at least one selected from alkenyl, alkynyl, epoxy, aldehyde, amino, or cyano. When the functional group used for the polymerization reaction includes a substituted functional group, the functional group having a substituted group includes at least one selected from alkyl, alkenyl, alkynyl, epoxy, aldehyde, or amino, and the substituted group includes at least one selected from C1 to C6 alkyl, alkenyl, alkynyl, carbonyl, epoxy, ether, aryl, acyl, amino, cyano, fluorine, or chlorine atoms. Wherein, C1 to C6 refers to the number of carbon atoms in the substituted group being 1 to 6; for example, when the substituted group is alkyl, it can be an alkyl group with 1 to 6 carbon atoms. The double or triple equivalent bond characteristics of the aforementioned functional groups facilitate the polymerization reaction between the carbon-nitrogen bonds and the aforementioned functional groups after the carbonyl group breaks, forming an organic-inorganic composite cross-linked network thin-layer structure, thereby further optimizing the mechanical strength and thermal stability of the electrolyte interface membrane.

[0043] Optionally, the first additive includes at least one of the following compounds:

[0044]

[0045] Using the aforementioned additives can significantly improve the high-temperature cycle performance and safety performance of batteries.

[0046] In this embodiment, the electrolyte further includes a lithium salt, which includes lithium fluorosulfonylimide. The mass percentage of lithium fluorosulfonylimide in the electrolyte is t, where 0.05% ≤ t ≤ 15%. After adding the above-mentioned lithium fluorosulfonylimide to the electrolyte, the lithium fluorosulfonylimide and the first additive of formula (I) can work synergistically to improve battery safety performance, ensure the initial energy efficiency of the battery, and further improve the high-temperature cycle performance of the battery, resulting in better overall battery performance.

[0047] Controlling the mass percentage (t) of lithium fluorosulfonylimide in the electrolyte within the range of 0.05% ≤ t ≤ 15% is beneficial for leveraging the synergistic effect between lithium fluorosulfonylimide and the first additive. When t < 0.05%, the effect of optimizing the solvation structure is weak, and its contribution to initial battery efficiency and improved high-temperature cycle performance is not significant. When t > 15%, lithium fluorosulfonylimide is more likely to reach the temperature window for thermal decomposition prematurely, increasing the accumulation of heat generated by the battery and increasing the risk of failure under abuse conditions. Understandably, 0.05% ≤ t ≤ 15% includes any point value within this range, such as t being 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 5%, 8%, 10%, or 15%.

[0048] Furthermore, 1 ≤ t / a ≤ 100. Understandably, t / a includes any value within the above range, for example, t / a being 1, 2, 3, 4, 5, 8, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100. Controlling the ratio of lithium fluorosulfonyl imide to the first additive within the above range is beneficial for better leveraging their synergistic effect.

[0049] While the addition of the first additive can improve the high-temperature cycle performance and safety of the battery, it can affect the initial energy efficiency. Although lithium fluorosulfonylimide can optimize the solvation structure, improve the electrolyte conductivity, and has a certain degree of thermal stability, once the battery temperature exceeds the thermal stability window of lithium fluorosulfonylimide, this substance will decompose, generating a large amount of heat and causing battery failure. Therefore, synergistically combining the first additive and lithium fluorosulfonylimide in the aforementioned dosage ratio allows the first additive to improve the properties of the electrolyte interface film, reducing the degree of heat accumulation in the battery under abuse conditions such as overcharging, thus lowering the probability of lithium fluorosulfonylimide reaching the thermal decomposition window or delaying the time it reaches the thermal decomposition window. Simultaneously, the lithium fluorosulfonylimide effectively optimizes the solvation structure, which on the one hand improves the electrolyte conductivity and the initial energy efficiency of the battery, and on the other hand further promotes the preferential reaction of the first additive over other components, forming an electrolyte interface film with good mechanical structure and thermal stability. Thus, through the synergistic effect of the two, the high-temperature cycle performance and safety performance of the battery can be effectively improved while ensuring the initial energy efficiency.

[0050] Preferably, 1 ≤ t / a ≤ 10. Controlling the ratio of lithium fluorosulfonyl imide to the first additive within the above range can significantly improve the high-temperature cycle performance and safety performance of the battery while ensuring its initial energy efficiency, especially by significantly reducing the battery surface temperature during overcharging to improve safety performance.

[0051] In addition to the above materials, the electrolyte of this application embodiment also includes a second additive, which includes at least one of vinyl sulfate or methanedisulfonate. The mass percentage of the second additive in the electrolyte is b, where 0.01% ≤ b ≤ 3%. The addition of the second additive can exert a further synergistic effect with the first additive. The second additive can decompose to generate organic sulfides, optimizing the composition of the electrolyte interface film on the negative electrode side and benefiting Li + The desolvation of metal ions improves battery efficiency, thereby compensating for the adverse effects of the first additive on the initial battery efficiency. As for the adverse effects of the second additive, which can easily increase the color and acidity of the electrolyte, these adverse effects are suppressed by the nitrogen atom in the carbon-nitrogen heterocycle of the first additive. Thus, through the synergistic effect of the second and first additives, the initial battery efficiency can be further improved.

[0052] Controlling the mass percentage b of the second additive in the electrolyte within the range of 0.01% ≤ a ≤ 3% is beneficial for maximizing the synergistic effect between the second and first additives. When b is less than 0.01%, the second additive has limited ability to compensate for the initial energy efficiency of the first additive; when b is greater than 3%, the increase in electrolyte color and acidity caused by the second additive becomes significant, and the first additive's inhibitory effect is poor. Understandably, 0.01% ≤ b ≤ 3% includes any value within this range, for example, a can be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, or 3%.

[0053] In the embodiments of this application, the electrolyte further includes an organic solvent, which includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, or propyl propionate.

[0054] In the embodiments of this application, the lithium salt further includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, or lithium difluorooxalate borate.

[0055] It should be noted that, in addition to the first and second additives mentioned above, other additives may be added in the embodiments of this application, including but not limited to at least one of vinylene carbonate and fluoroethylene carbonate, and this application does not impose any particular restrictions on this.

[0056] Secondly, embodiments of this application also provide a battery, which includes: a positive electrode, a negative electrode, a separator, and an electrolyte as described in the first aspect. The separator is disposed between the positive electrode and the negative electrode to form a cell, and the electrolyte is injected into the cell.

[0057] 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.

[0058] 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.

[0059] In this embodiment, there are no particular limitations on the arrangement of the negative electrode sheet, as long as the purpose of this embodiment can be achieved. The negative electrode sheet typically includes a negative current collector and a layer of negative active material 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 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 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.

[0060] 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.

[0061] 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.

[0062] Thirdly, embodiments of this application also provide an energy storage device 10, which includes the secondary battery described in the fourth aspect.

[0063] Taking electrochemical energy storage as an example, this application provides an energy storage device 10. The energy storage device 10 is equipped with a set of chemical batteries. It mainly uses the chemical elements in the batteries as energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. 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.

[0064] 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 10 include:

[0065] (1) Large-scale energy storage power stations applied to wind power and photovoltaic power stations can assist renewable energy power generation in meeting 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, energy storage power stations can achieve load matching of power in time and space, enhance the absorption capacity of renewable energy, reduce instantaneous power changes, reduce the impact on the power grid, improve the absorption of new energy power generation, and are of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation.

[0066] (2) Energy storage containers applied on the grid side mainly function as peak shaving, frequency regulation and grid congestion relief. In terms of peak shaving, they 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.

[0067] (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 10, 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 100 when the electricity price is low and discharging the energy storage system 100 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 the energy storage system 100 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 electricity 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.

[0068] Please see Figure 1 , Figure 1 This is a schematic diagram of a residential energy storage system 100 according to an embodiment of this application. The residential energy storage system 100 includes a power conversion device 20 (photovoltaic panel), a first user load 30 (streetlight), a second user load 40 (e.g., household appliances such as air conditioners), and an energy storage device 10. The energy storage device 10 is a small energy storage box that can be wall-mounted to an outdoor wall. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 10 stores this electrical energy and supplies it to streetlights and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0069] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 100 according to an 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 10 of this application is not limited to the energy storage scenario on the generation / distribution side.

[0070] This application provides an energy storage system 100, which includes a high-voltage cable 50, a first power conversion device 60, a second power conversion device 70, and the energy storage device 10 provided in this application. During power generation, the first power conversion device 60 and the second power conversion device 70 convert other forms of energy into electrical energy, which is then connected to the high-voltage cable and supplied to the power consumption side of the distribution network. When the power load is low and the first power conversion device 60 and the second power conversion device 70 generate excess power, the excess electricity is stored in the energy storage device 10, reducing wind and solar curtailment rates and improving the absorption of new energy power generation. When the power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 10, along with the high-voltage cable 50, in a grid-connected mode to supply power to the power consumption side. This provides various services for power grid operation, such as peak shaving, frequency regulation, and backup, fully leveraging the peak shaving function of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure on the power grid.

[0071] Optionally, the first power conversion device 60 and the second power conversion device 70 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0072] The number of energy storage devices 10 can be multiple, and the multiple energy storage devices 10 can be connected in series or in parallel. The multiple energy storage devices 10 are supported and electrically connected by an isolation plate (not shown). In this embodiment, "multiple" means two or more. An energy storage box can also be provided on the outside of the energy storage device 10 to house the energy storage device 10.

[0073] Optionally, the energy storage device 10 may include, but is not limited to, battery modules, battery packs, battery systems, etc. The actual application form of the energy storage device 10 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 10. This application embodiment only uses a multi-cell battery as an example for illustration. When the energy storage device 10 is a single battery, the energy storage device 10 may be at least one of cylindrical batteries, prismatic batteries, etc.

[0074] The solution of this application will be further described below with reference to specific embodiments and experimental data.

[0075] Example 1

[0076] This embodiment provides an electrolyte, which is prepared through the following steps:

[0077] In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 1:2:1; dried lithium hexafluorophosphate electrolyte is dissolved in the above mixed solvent and stirred until the lithium salt is dissolved; vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are added to the above mixed solvent; and a first additive is added to the above mixed solvent to obtain an electrolyte.

[0078] 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; the mass percentages of vinylene carbonate and fluoroethylene carbonate in the electrolyte are 1%.

[0079] Examples 2 to 15

[0080] The difference from Example 1 is that the types and mass percentages of lithium fluorosulfonylimide, the first additive, and the second additive are adjusted, as detailed in Table 1.

[0081] Comparative Examples 1 to 5

[0082] The difference from Example 1 is that the types and mass percentages of lithium fluorosulfonylimide, the first additive, and the second additive are adjusted, as detailed in Table 1.

[0083] Table 1: Types and content parameters of Examples 1 to 15 and Comparative Examples 1 to 5

[0084]

[0085]

[0086] Note: 1. In Table 1, " / " indicates that there are no relevant preparation parameters.

[0087] 2. In Table 1, LiFSI is lithium difluorosulfonyl imide, DTD is vinyl sulfate, and MMDS is methylene disulfonate.

[0088] 3. The first additive 1 in Table 1 is... The first additive 2 is The first additive 3 is The first additive 4 is The first additive 5 is Additives*

[0089] 4. When the first additive includes more than one, the content 'a' in Table 1 shall be filled in according to the order of the first additives. For example, in Example 12, the first additive includes first additive 2 and first additive 4, and the corresponding content 'a' is "0.10+0.10", which means that the content 'a' of first additive 2 is 0.10% and the content 'a' of first additive 4 is 0.10%.

[0090] <Battery Manufacturing>

[0091] Preparation of the positive electrode sheet: The positive electrode active material lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and binder polyvinylidene fluoride (PVDF) are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94:3:3, and mixed to form a positive electrode slurry with a solid content of 60wt%. The positive electrode slurry is uniformly coated on one surface of a 10μm thick aluminum foil for the positive electrode current collector. After drying, cold pressing, slitting, and cutting, the positive electrode sheet is obtained. The single-sided thickness of the positive electrode active material layer is 100μm.

[0092] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (CMC) (thickener), Super-P (conductive carbon black), and styrene-butadiene rubber emulsion (SBR) (binder) were mixed in a mass ratio of 96:2:1:1. 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 single-sided thickness of the negative electrode active material layer was 70 μm.

[0093] Separator: A 16μm polyethylene film (PE) is used as the separator.

[0094] Electrolyte: The electrolyte prepared in the above examples and comparative examples.

[0095] 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.

[0096] Performance Testing

[0097] Initial discharge: Allow the lithium-ion battery to stand for 5 hours at 25°C. Perform the initial discharge operation under the following conditions: ① Charge to 3.65V at a 0.5P rate; ② Let stand for 10 minutes; ③ Discharge to 2.5V at a 0.5P rate; ④ Let stand for 10 minutes. The initial discharge is complete.

[0098] (1) Initial energy efficiency change test

[0099] Initial energy efficiency test: The lithium-ion battery that has completed initial discharge was left to stand for 5 hours at 25℃. The initial energy efficiency test was conducted under the following conditions: ① Charged to 3.65V at a 0.5P rate; ② Left to stand for 10 minutes; ③ Discharged to 2.5V at a 0.5P rate; ④ Left to stand for 10 minutes.

[0100] Initial energy efficiency (initial charge / discharge energy efficiency) = (③ discharge energy) / (① charge energy); where "③ discharge energy" and "① charge energy" refer to the stage ③ discharge energy and stage ① charge energy in the initial energy efficiency test process, respectively.

[0101] The change in the initial energy efficiency of a certain battery = (the initial energy efficiency of the battery) / (the initial energy efficiency of the battery in Comparative Example 1).

[0102] (2) Cyclic performance test

[0103] The lithium-ion battery, after initial discharge, was left to stand for 5 hours at 45℃. Cycle performance testing was then conducted under the following conditions: ① Charged to 3.65V at a 0.5P rate; ② Left to stand for 10 minutes; ③ Discharged to 2.5V at a 0.5P rate; ④ Left to stand for 10 minutes.

[0104] Perform cycle performance testing according to the above charge-discharge process (①→②→③→④), record the discharge capacity of the 1000th charge-discharge cycle and the discharge capacity of the first charge-discharge cycle. The capacity retention rate after 1000 cycles at 45℃ = discharge capacity of 1000 charge-discharge cycles / discharge capacity of the first charge-discharge cycle.

[0105] <Security Testing>

[0106] Initial charging: Allow the lithium-ion battery to stand for 5 hours at 25℃. Perform the initial charging operation under the following conditions: ① Discharge to 2.5V at a 0.5P rate; ② Let stand for 10 minutes; ③ Charge to 3.65V at a 0.5P rate; ④ Let stand for 10 minutes. Initial charging is complete.

[0107] (3) Overcharge test

[0108] At 25℃, the lithium-ion battery that has completed initial charging is left to stand for 5 hours. An overcharge test is then performed under the following conditions: charge at a 0.5C rate until the battery voltage reaches 5.475V or the charging time reaches 1 hour, then stop charging and observe for 1 hour.

[0109] During the overcharge test, the current, time, voltage, and temperature are recorded during the charging and observation process; the temperature refers to the temperature at the center of the plane with the largest surface area of ​​the battery cell.

[0110] Before the test begins, place a temperature sensing wire at the center of a flat surface with a large surface area of ​​the battery and wrap and fix it with Teflon tape, and record the surface temperature of the battery during the overcharge test.

[0111] The test results are shown in Table 2.

[0112] Table 2: Test Results of Examples and Comparative Examples

[0113]

[0114] Based on the above performance tests, it can be seen from Examples 1, 2 and Comparative Example 1 that adding the first additive to the electrolyte can significantly reduce the battery heat generation under overcharge and other operating conditions, greatly improve the battery's safety performance, and also improve the battery's high-temperature cycle performance as the content of the first additive increases.

[0115] Comparative Examples 1 to 3 show that while adding only lithium fluorosulfonylimide to the electrolyte without the first additive improves the initial energy efficiency and high-temperature cycle performance, it easily leads to significant battery overheating under abuse conditions such as overcharging. Furthermore, comparing Examples 1, 3, and 2, as well as Examples 2, 6, and 3, it can be seen that adding both the first additive and lithium fluorosulfonylimide to the electrolyte has a good synergistic effect. The use of the first additive can suppress the significant overheating problem caused by lithium fluorosulfonylimide under overcharge conditions. This further improves the high-temperature cycle performance and safety performance of the battery without deteriorating its initial energy efficiency.

[0116] As can be seen from Examples 1, 3 to 5, with the addition of the first additive to the electrolyte, the initial energy efficiency and high-temperature cycle performance of the battery can be improved to a certain extent with the increase of the lithium fluorosulfonylimide content, but the battery temperature under overcharge conditions also shows an upward trend. A comparison between Example 4 and Comparative Example 3 shows that Example 4, due to the addition of the first additive, still effectively reduces battery heat generation. That is, although the addition of lithium fluorosulfonylimide may increase battery heat generation, the presence of the first additive still helps to reduce battery heat generation and improve battery heating problems under overcharge conditions.

[0117] As can be seen from Comparative Examples 3, 4, 6, and 7, considering the overall performance of the battery in terms of heat resistance, high-temperature cycle performance, and initial energy efficiency, the battery exhibits better overall performance when the mass percentage of the first additive in the electrolyte is 0.05% to 2%. Examples 3 to 7 also show that the ratio of lithium fluorosulfonylimide to the first additive significantly affects their synergistic effect. Considering all performance aspects, the battery exhibits better overall performance when the t / a range is 1 to 10.

[0118] As can be seen from Examples 6 and 8-11, among the several optional first additives, first additives 3 and 4 have a better impact on the overall battery performance, and can further improve the high-temperature cycle performance and safety performance of the battery without significant changes in the initial energy efficiency. A comparison of Examples 8, 10, and 12 shows that using a compounded first additive is beneficial for better improving the overall battery performance, a conclusion also confirmed by Example 13. Furthermore, Examples 13 and 14 show that adding a second additive to the electrolyte further optimizes the overall battery performance. In addition, Examples 14 and 15 show that the battery performance of lithium fluorosulfonylimide using LiFSI is superior to that of the battery using LiTFSI.

[0119] Furthermore, as can be seen from Comparative Example 5 and Examples 13 and 14, when no first additive is added to the electrolyte, but only lithium fluorosulfonylimide and the second additive are added, although the initial energy efficiency of the battery is significantly improved, the improvement in high-temperature cycle performance is weak, and the battery is prone to overheating under abuse conditions such as overcharging.

[0120] The technical solutions disclosed in the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a first additive, which includes a compound of formula (I): R1, R2, and R3 are each independently selected from substituted or unsubstituted functional groups for polymerization, and the mass percentage of the first additive in the electrolyte is a, where 0.01% ≤ a ≤ 3%.

2. The electrolyte according to claim 1, characterized in that, 0.05％≤a≤2％。 3. The electrolyte according to claim 1, characterized in that, The functional group used for the polymerization reaction includes at least one of unsubstituted alkenyl, alkynyl, epoxy, aldehyde, amino, or cyano groups; and / or, The functional group used for the polymerization reaction includes at least one of alkyl, alkenyl, alkynyl, epoxy, aldehyde or amino groups having a substituent group, and the substituent group includes at least one of C1 to C6 alkyl, alkenyl, alkynyl, carbonyl, epoxy, ether, aryl, acyl, amino, cyano, fluorine or chlorine atom.

4. The electrolyte according to claim 3, characterized in that, The first additive includes at least one of the following compounds:

5. The electrolyte according to claim 1, characterized in that, The electrolyte also includes a lithium salt, which includes lithium fluorosulfonylimide, and the mass percentage of the lithium fluorosulfonylimide in the electrolyte is t, where 0.05% ≤ t ≤ 15%.

6. The electrolyte according to claim 5, characterized in that, 1≤t / a≤100; and / or, The fluorinated sulfonyl imide lithium includes at least one of lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium tri(trifluoromethylsulfonyl)methyl, or lithium bis(pentafluoroethylsulfonyl)imide.

7. The electrolyte according to claim 6, characterized in that, 1≤t / a≤10.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, The electrolyte further includes a second additive, which includes at least one of vinyl sulfate or methylene disulfonate, and the mass percentage of the second additive in the electrolyte is b, where 0.01% ≤ b ≤ 3%.

9. The electrolyte according to any one of claims 1 to 7, characterized in that, The electrolyte further includes an organic solvent, which includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, or propyl propionate; and / or, The electrolyte also includes lithium salts, which further include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxaborate, or lithium difluorooxaborate.

10. 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 9, 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.

11. An energy storage device, characterized in that, The energy storage device includes the battery as described in claim 10.

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