Electrolyte, battery, energy storage device and energy storage system

Abstract

The invention provides an electrolyte, a battery, an energy storage device and an energy storage system. The electrolyte provided by the embodiment of the invention comprises an electrolyte salt, an organic solvent and a first additive, wherein the first additive comprises an N-nitro derivative.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to an electrolyte, a battery, an energy storage device and an energy storage system. Background Art

[0002] With the continuous development of lithium-ion battery technology, lithium-ion batteries have the advantages of large specific capacity, no memory effect, high operating voltage, fast charging speed, wide operating temperature range, long cycle life, small size and light weight compared with other types of batteries such as lead-acid and cadmium nickel. With the development of the energy storage industry, lithium-ion battery technology continues to develop and is widely used in electric vehicles, mobile devices and energy storage systems. Other user scenarios such as wind and solar power generation require lithium-ion energy storage batteries to have lower life attenuation and longer service life. However, the cycle performance of lithium-ion batteries in related technologies is poor at high temperatures, and the cycle capacity retention rate is not high. Summary of the invention

[0003] The embodiment of the present application provides an electrolyte, which, when applied to a battery, can enable the battery to have higher room temperature cycle performance and high temperature cycle performance.

[0004] In a first aspect, an embodiment of the present application provides an electrolyte solution, the electrolyte solution comprising an electrolyte salt, an organic solvent and a first additive, wherein the first additive comprises an N-nitro derivative.

[0005] In some embodiments, the structural formula of the N-nitro derivative is:

[0006]

[0007] Among them, R1 is one of imidazolidinyl, pyridyl, and pyrimidinyl, and R2 is one of hydrogen atom, alkyl group with 1 to 3 carbon atoms, and fluoroalkyl group with 1 to 3 carbon atoms.

[0008] In some embodiments, the N-nitro derivative comprises At least one of .

[0009] In some embodiments, in the electrolyte, the mass fraction a of the first additive is in the range of 0.01%≤a≤1%.

[0010] In some embodiments, the electrolyte further includes a second additive, and the second additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, propenyl-1,3-sultone, and methylene methanedisulfonate.

[0011] In some embodiments, the mass ratio a / b of the first additive to the second additive is in the range of 0.1≤a / b≤3.

[0012] In some embodiments, the mass fraction b of the second additive is in the range of 0.01%≤b≤5%.

[0013] In a second aspect, an embodiment of the present application further provides a battery, which includes: the electrolyte, positive electrode plate, separator and negative electrode plate described in the embodiment of the first aspect of the present application.

[0014] In a third aspect, an embodiment of the present application further provides an energy storage device, comprising:

[0015] The housing; and

[0016] A plurality of batteries according to the second aspect of the present application are contained in the box.

[0017] In a fourth aspect, an embodiment of the present application further provides an energy storage system, which includes:

[0018] The energy storage device described in the third aspect of the present application; and

[0019] An electric energy conversion device, wherein the electric energy conversion device is electrically connected to the energy storage device, the electric energy conversion device is used to convert other forms of energy into electric energy, and the energy storage device is used to store the electric energy.

[0020] The electrolyte of the embodiment of the present application includes an electrolyte salt, an organic solvent and a first additive, wherein the first additive includes an N-nitro derivative. Compared with a single nitro additive or an amino additive, the N-nitro derivative has the ability to form intermolecular hydrogen bonds, thereby forming a larger conjugated system, making the molecules of the N-nitro derivative easier to be reduced. During the battery charge and discharge cycle, the nitro group in the N-nitro derivative can be reduced in advance to produce an inorganic lithium salt to cover the surface of the negative electrode plate, reducing the consumption of other additives in the electrolyte during the battery formation process; in addition, the guanidine product produced by the reduction of the N-nitro derivative can also be combined with HF and PF5 to reduce the consumption of other additives during the battery charge and discharge cycle, thereby further improving the battery's cycle performance. Furthermore, the N-nitro derivative has a high film-forming reactivity, and its reduction products are lithium nitride and lithium oxide. Lithium nitride and lithium oxide have high high temperature stability and high voltage stability, thereby better improving the battery's room temperature cycle performance and high temperature cycle performance. In summary, the electrolyte of the present application includes an N-nitro additive, which can stabilize the SEI film interface of the negative electrode plate during the cycle of the battery, thereby reducing the loss of active lithium and improving the battery's room temperature (25°C) cycle capacity retention rate and high temperature (such as 45°C) cycle capacity retention rate. In addition, the higher the battery's cycle capacity retention rate, the fewer side reactions of the battery, the less active lithium loss, and the lower the battery's volume expansion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 It is a structural block diagram of an energy storage system according to an embodiment of the present application.

[0023] Figure 2 This is an application scenario diagram of an energy storage system according to an embodiment of the present application.

[0024] Figure 3 It is a schematic structural diagram of an energy storage device according to an embodiment of the present application.

[0025] Figure 4 It is a schematic diagram of the structure of a battery according to an embodiment of the present application.

[0026] Figure 5 The battery of one embodiment of the present application is Figure 4 Schematic diagram of the cross-sectional structure in the AA direction.

[0027] Figure 6 It is a schematic diagram of the structure of the positive electrode plate of one embodiment of the present application.

[0028] Figure 7 It is a schematic diagram of the structure of the negative electrode plate of one embodiment of the present application.

[0029] Description of reference numerals:

[0030] 100 -battery, 110 -positive electrode plate, 111 -positive current collector, 112 -positive electrode active layer, 120 -diaphragm, 130 -negative electrode plate, 131 -negative current collector, 132 -negative electrode active layer, 140 -housing, 150 -end cover assembly, 141 -receiving chamber, 200 -energy storage device, 210 -casing, 300 -energy storage system, 310 -electric energy conversion device. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0033] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0034] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same figure marks represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0035] At present, the generation of green electricity generally relies on photovoltaics, wind power, and hydropower, etc. However, wind and solar energy generally have problems of strong intermittency and large volatility, which will cause instability in the power grid, insufficient electricity during peak hours, and too much electricity during valley hours. Unstable voltage will also cause damage to electricity. Therefore, insufficient electricity demand or insufficient grid acceptance capacity may cause the problem of "abandoning wind and solar power". To solve these problems, we must rely on energy storage. That is, converting electrical energy into other forms of energy through physical or chemical means and storing it, and converting energy into electrical energy and releasing it when needed. In simple terms, energy storage is like a large "power bank". When photovoltaic and wind energy are sufficient, electrical energy is stored and the stored electricity is released when needed.

[0036] The current energy storage (i.e., energy storage) application scenarios are relatively broad, including power generation side energy storage, grid side energy storage, and power consumption side energy storage. The following uses power generation side energy storage as an example to describe the energy storage system of the embodiment of the present application in detail, which should not be understood as a limitation on the energy storage system of the embodiment of the present application.

[0037] See also Figure 1 and Figure 2 The embodiment of the present application also provides an energy storage system 300, which includes: an electric energy conversion device 310 and the energy storage device 200 described in the embodiment of the present application, the electric energy conversion device 310 is electrically connected to the energy storage device 200, the electric energy conversion device 310 is used to convert other forms of energy into electric energy, and the energy storage device 200 is used to store the electric energy.

[0038] Optionally, the electric energy conversion device 310 can convert at least one other form of energy such as solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0039] Optionally, the number of the electric energy conversion devices 310 may be one or more. When there are multiple electric energy conversion devices 310, the multiple electric energy conversion devices 310 may be connected in series, in parallel, or in mixed connection, which is not specifically limited in the present application.

[0040] Optionally, the electric energy conversion device 310 may be, but is not limited to, at least one of a photovoltaic panel, a wind power generation device, a hydropower generation device, and the like.

[0041] Optionally, the number of the energy storage devices 200 may be one or more. When the number of the energy storage devices 200 is multiple, the multiple energy storage devices 200 are connected in series, in parallel, or in mixed connection, which is not specifically limited in the present application.

[0042] When working, the power conversion device 310 is used to convert other forms of energy into electrical energy and store it in the energy storage device 200. The electrical energy stored in the energy storage device 200 can be supplied to electrical loads such as street lamps and household appliances for use when the electricity price is at a peak, or to supply power when the power grid is out of power. The electrical energy generated by the power conversion device 310 can also be supplied to the power grid through high-voltage cables to alleviate the power supply pressure of the power grid during peak hours.

[0043] See also Figure 3 The embodiment of the present application further provides an energy storage device 200 , which includes a box 210 and a plurality of batteries 100 , wherein the plurality of batteries 100 are stacked and accommodated in the box 210 .

[0044] The term "plurality" means greater than or equal to two.

[0045] It should be noted that the energy storage device 200 of the embodiment of the present application can be at least one of an energy storage cabinet, an energy storage box, a battery pack, etc. The energy storage device 200 illustrated in the drawings of the present application is only one of its many forms and should not be understood as limiting the energy storage device 200 of the present application.

[0046] In a specific embodiment, when the energy storage device 200 is an energy storage cabinet or an energy storage box, the energy storage cabinet or the energy storage box includes a box body 210 and a plurality of battery packs (not shown); the plurality of battery packs are stacked in the box body 210, and the plurality of battery packs can be electrically connected in series, in parallel, or in a mixed manner; the plurality of battery packs include a plurality of batteries 100, and the plurality of batteries 100 are electrically connected in series, in parallel, or in a mixed manner.

[0047] It should be noted that the term "stacked arrangement" in this application can mean that the multiple batteries 100 or battery packs are arranged in sequence, or the multiple batteries 100 or battery packs are arranged in sequence and spaced apart. In addition, the multiple batteries 100 or battery packs can be stacked in the transverse direction (such as the horizontal direction) or the longitudinal direction (such as the direction of gravity). The stacking method and stacking direction of the multiple batteries 100 or battery packs can be designed according to actual conditions.

[0048] It can be understood that the box body 210 has a receiving cavity (not shown), and multiple batteries 100 are received in the receiving cavity. In some embodiments, each receiving cavity receives one battery 100. In other embodiments, each receiving cavity receives multiple batteries 100.

[0049] With the continuous development of lithium-ion battery technology, lithium-ion batteries have the advantages of large specific capacity, no memory effect, high operating voltage, fast charging speed, wide operating temperature range, long cycle life, small size and light weight compared with other types of batteries such as lead-acid and cadmium nickel. With the development of the energy storage industry, lithium-ion battery technology continues to develop and is widely used in electric vehicles, mobile devices and energy storage systems. Other user scenarios such as wind and solar power generation require lithium-ion energy storage batteries to have lower life attenuation and longer service life. However, the cycle performance of lithium-ion batteries in related technologies is poor at high temperatures, and the cycle capacity retention rate is not high.

[0050] Battery degradation is mainly caused by the reaction of lithium ions on the surface of the negative electrode of the battery. First, during charging, ester solvents are easily reduced on the surface of the low-potential negative electrode and react with lithium, thereby consuming active lithium; secondly, the negative active layer of the negative electrode is constantly expanding and shrinking during the process of lithium extraction, causing the solid electrolyte interface membrane (SEI) on the surface of the negative active layer to be constantly pulled, exposing a new interface that continuously reacts with the electrolyte, resulting in the loss of active lithium. At high temperatures, the reaction between the surface of the negative electrode and the electrolyte is further intensified, and the interface stability of the negative electrode is further reduced, which greatly reduces the high-temperature cycle performance of the battery.

[0051] See also Figure 4 and Figure 5 The embodiment of the present application provides a battery 100 , which includes an electrolyte, a positive electrode plate 110 , a separator 120 and a negative electrode plate 130 , wherein the separator 120 is located between the positive electrode plate 110 and the negative electrode plate 130 .

[0052] It should be noted that the positive electrode sheet 110 and the negative electrode sheet 130 are at least partially immersed in the electrolyte.

[0053] It can be understood that the positive electrode sheet 110, the separator 120 and the negative electrode sheet 130 are stacked in sequence to form an electrode assembly. The electrode assembly can be, but is not limited to, a winding structure, a laminated structure, etc., which is not specifically limited in the present application.

[0054] It should be noted that the positive electrode sheet 110 and the negative electrode sheet 130 may be collectively referred to as electrode sheets. In other words, the electrode sheets include the positive electrode sheet 110 and the negative electrode sheet 130 .

[0055] See also Figure 6 Optionally, the positive electrode sheet 110 includes a positive current collector 111 and a positive active layer 112, and the positive active layer 112 is disposed on the surface of the positive current collector 111. It can be understood that the positive active layer 112 can cover one surface or two opposite surfaces of the positive current collector 111.

[0056] Optionally, the positive electrode current collector 111 may be, but is not limited to, an aluminum sheet, aluminum foil, or the like.

[0057] Optionally, the positive electrode active layer 112 includes a positive electrode active material, a positive electrode conductor, a positive electrode binder and a positive electrode thickener.

[0058] Optionally, the positive electrode active material may be, but is not limited to, lithium iron phosphate.

[0059] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of conductive carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0060] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0061] Optionally, in the positive electrode active layer 112, the mass fraction of the positive electrode binder ranges from 2wt% to 4wt%. Specifically, in the positive electrode active layer 112, the mass fraction of the positive electrode binder may be, but is not limited to, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc. If the mass fraction of the positive electrode binder is too small, the positive electrode active layer 112 is prone to pulverization or slag; if the mass fraction of the positive electrode binder is too large, the energy density of the positive electrode sheet 110 is reduced.

[0062] Optionally, the positive electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC for short), polyacrylamide (PAM) and polymethacrylate (PMA).

[0063] Optionally, the diaphragm 120 may be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic diaphragm 120 , and the like.

[0064] Optionally, the thickness of the diaphragm 120 is 14 μm to 18 μm. Specifically, the thickness of the diaphragm 120 may be, but is not limited to, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, etc.

[0065] See also Figure 7 Optionally, the negative electrode sheet 130 includes a negative electrode current collector 131 and a negative electrode active layer 132, and the negative electrode active layer 132 is disposed on the surface of the negative electrode current collector 131. It can be understood that the negative electrode active layer 132 can cover one surface or two opposite surfaces of the negative electrode current collector 131.

[0066] Optionally, the negative electrode current collector 131 may be, but is not limited to, a copper sheet, copper foil, or the like.

[0067] Optionally, the negative electrode active layer 132 includes a negative electrode active material, a negative electrode conductor, a negative electrode binder and a negative electrode thickener.

[0068] Optionally, the negative electrode active material may be, but is not limited to, graphite.

[0069] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0070] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0071] Optionally, in the negative electrode active layer 132, the mass fraction of the negative electrode binder ranges from 2wt% to 4wt%. Specifically, in the negative electrode active layer 132, the mass fraction of the negative electrode binder may be, but is not limited to, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc. If the mass fraction of the negative electrode binder is too small, the negative electrode active layer 132 is prone to pulverization or slag; if the mass fraction of the negative electrode binder is too large, the energy density of the negative electrode plate 130 is reduced.

[0072] Optionally, the negative electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC for short), polyacrylamide (PAM) and polymethacrylate (PMA).

[0073] Please see again Figure 4 and Figure 5 Optionally, the battery 100 further includes a shell 140 and an end cover assembly 150 , wherein the shell 140 and the end cover assembly 150 enclose a receiving cavity 141 , and the receiving cavity 141 is used to receive the electrolyte, the positive electrode plate 110 , the diaphragm 120 and the negative electrode plate 130 .

[0074] An embodiment of the present application further provides an electrolyte, which includes an electrolyte salt, an organic solvent and a first additive, wherein the first additive includes an N-nitro derivative.

[0075] The electrolyte of the embodiment of the present application can be applied to batteries 100 such as lithium-ion batteries 100 and sodium-ion batteries 100 to improve the room temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the battery 100.

[0076] The electrolyte of the embodiment of the present application includes an electrolyte salt, an organic solvent and a first additive, wherein the first additive includes an N-nitro derivative. Compared with a single nitro additive or an amino additive, the N-nitro derivative has the ability to form intermolecular hydrogen bonds, thereby forming a larger conjugated system, making the molecules of the N-nitro derivative easier to be reduced. During the charge and discharge cycle of the battery 100, the nitro group in the N-nitro derivative can be reduced in advance to produce an inorganic lithium salt to cover the surface of the negative electrode plate 130, reducing the consumption of other additives in the electrolyte during the formation process of the battery 100; in addition, the guanidine product produced by the reduction of the N-nitro derivative can also be combined with HF and PF5 to reduce the consumption of other additives during the charge and discharge cycle of the battery 100, thereby further improving the cycle performance of the battery 100. Furthermore, the N-nitro derivative has a high film-forming reactivity, and its reduction product is lithium nitride and lithium oxide. Lithium nitride and lithium oxide have high high temperature stability and high voltage stability, thereby better improving the room temperature cycle performance and high temperature cycle performance of the battery 100. In summary, the electrolyte of the present application includes an N-nitro additive, which can stabilize the SEI film interface of the negative electrode plate 130 during the cycle of the battery 100, thereby reducing the loss of active lithium and improving the room temperature (25°C) cycle capacity retention rate and high temperature (such as 45°C) cycle capacity retention rate of the battery 100. In addition, the higher the cycle capacity retention rate of the battery 100, the fewer side reactions of the battery 100, the less loss of active lithium, and the lower the volume expansion rate of the battery 100.

[0077] In some embodiments, the structural formula of the N-nitro derivative is:

[0078]

[0079] Among them, R1 is one of imidazolidinyl, pyridyl, and pyrimidinyl, and R2 is one of hydrogen atom, alkyl group with 1 to 3 carbon atoms, and fluoroalkyl group with 1 to 3 carbon atoms.

[0080] In this embodiment, the reduction products of N-nitro derivatives such as imidazolidinyl, pyridyl, and pyrimidyl have relatively low tautomeric energy (energy barrier required for the migration of protons and corresponding double bonds in the compound molecule), which can better reduce the damage of the decomposition products of the electrolyte salt in the electrolyte to the SEI film on the surface of the negative electrode plate 130. Taking N-nitroiminoimidazolidinyl as an example, its product aminoimidazolidinyl has relatively low tautomeric energy, so that guanidine-phosphorus pentafluoride (tautomeric product-lithium salt decomposition product) ligands can be generated in the electrolyte, thereby better reducing the damage of the lithium salt decomposition products to the interface. In addition, the smaller the tautomeric energy, the easier it is to produce such substances. The tautomeric energy of imidazolidinyl is less than the tautomeric energy of pyridyl and less than the tautomeric energy of pyrimidyl. Therefore, compared with N-nitroiminopyridine and N-nitroiminopyrimidine, N-nitroiminoimidazolidinyl has a better improvement effect on the room temperature capacity retention rate and high temperature cycle capacity retention rate of the battery 100. In summary, the use of these N-nitro additives can better stabilize the SEI film interface of the negative electrode plate 130 during the cycle of the battery 100, thereby reducing the loss of active lithium and improving the room temperature (25°C) cycle capacity retention rate and high temperature (such as 45°C) cycle capacity retention rate of the battery 100. In addition, the higher the cycle capacity retention rate of the battery 100, the fewer side reactions of the battery 100, the less loss of active lithium, and the lower the volume expansion rate of the battery 100.

[0081] In some embodiments, the N-nitro derivative comprises (2-N-nitroiminoimidazolidine), (2-N-nitroiminopyridine), (2-N-nitroiminopyrimidine).

[0082] In this embodiment, the reduction products of N-nitro derivatives such as imidazolidinyl, pyridyl, and pyrimidyl have relatively low tautomeric energy, which can better reduce the damage of the decomposition products of the electrolyte salt in the electrolyte to the SEI film on the surface of the negative electrode plate 130. Taking N-nitroiminoimidazolidinyl as an example, its product aminoimidazolidinyl has relatively low tautomeric energy, so that guanidine-phosphorus pentafluoride (tautomeric product-lithium salt decomposition product) ligands can be generated in the electrolyte, thereby better reducing the damage of the lithium salt decomposition products to the interface. In addition, the smaller the tautomeric energy, the easier it is to produce such substances. The tautomeric energy of imidazolidinyl is less than the tautomeric energy of pyridyl and less than the tautomeric energy of pyrimidyl. Therefore, compared with N-nitroiminopyridine and N-nitroiminopyrimidine, N-nitroiminoimidazolidinyl has a better improvement effect on the room temperature capacity retention rate and high temperature cycle capacity retention rate of the battery 100. In summary, the use of these N-nitro additives can better stabilize the SEI film interface of the negative electrode plate 130 during the cycle of the battery 100, thereby reducing the loss of active lithium and improving the room temperature (25°C) cycle capacity retention rate and high temperature (such as 45°C) cycle capacity retention rate of the battery 100. In addition, the higher the cycle capacity retention rate of the battery 100, the fewer side reactions of the battery 100 during the charge and discharge cycle, the less active lithium loss, and the lower the volume expansion rate of the battery 100.

[0083] In some embodiments, in the electrolyte, the mass fraction a of the first additive is in the range of 0.01%≤a≤1%.

[0084] Specifically, in the electrolyte, the mass fraction a of the first additive can be but is not limited to 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0085] In this embodiment, in the electrolyte, the mass fraction a of the first additive is too low, and the N-nitro additive has limited effect on improving the room temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the battery 100. In the electrolyte, if the mass fraction a of the first additive is too high, the consumption of active lithium in the early stage of the battery 100 will increase, resulting in a decrease in the initial capacity of the battery 100. In addition, if the mass fraction a of the first additive is too high, too much inorganic matter will be formed on the negative electrode plate 130. Too much inorganic matter covers the surface of the negative electrode plate 130, which will increase the impedance of the negative electrode plate 130 and reduce the kinetic performance of the battery 100. Furthermore, the reduction product of the N-nitro additive includes guanidines, which are alkaline substances. Too much guanidines in the electrolyte are not conducive to the preservation of the electrolyte. Guanidines will make the electrolyte prone to side reactions during the charge and discharge cycle of the battery 100 (for example, inducing the ring opening of ethylene carbonate (EC) in the electrolyte), reduce the ionic conductivity of the electrolyte, and thus reduce the kinetic performance of the battery 100.

[0086] In some embodiments, the electrolyte further includes a second additive, which includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), diethylene sulfate (DTD), propenyl-1,3-sultone (PST), methylene methane disulfonate (MMDS), etc.

[0087] In this embodiment, by adding a second additive to the electrolyte, the second additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), diethylene sulfate (DTD), propenyl-1,3-sultone (PST), methylene disulfonate (MMDS), etc. The second additive can continuously repair the SEI film on the surface of the negative electrode plate 130 during the charge and discharge cycle of the battery 100, thereby improving the normal temperature capacity retention rate and high temperature cycle capacity retention rate of the battery 100; in addition, these additives can form a better compounding effect with the N-nitro additive, better stabilize the SEI film interface on the surface of the negative electrode plate 130 of the battery 100, thereby better improving the normal temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the battery 100, and reducing the volume expansion rate of the battery 100 during the charge and discharge cycle.

[0088] In some embodiments, in the electrolyte, the mass ratio a / b of the first additive to the second additive is in the range of 0.1≤a / b≤3.

[0089] Specifically, in the electrolyte, the mass ratio a / b of the first additive to the second additive may be, but is not limited to, 0.1, 0.3, 0.5, 0.8, 1.0, 1.3, 1.5, 1.8, 2.0, 2.3, 2.5, 2.8, 3, etc.

[0090] In this embodiment, if the mass ratio a / b of the first additive to the second additive is too low, it may be that the content of the first additive is too little, or the content of the second additive is too much; when the content of the first additive is too little, the N-nitro additive has limited effect on the improvement of the normal temperature cycle capacity retention rate and the high temperature cycle capacity retention rate of the battery 100; when the content of the second additive is too much, it will increase the consumption of active lithium in the early stage of the battery 100 cycle, reduce the initial discharge capacity of the battery 100, and deteriorate the normal temperature cycle performance and high temperature cycle performance of the battery 100. If the mass ratio a / b of the first additive to the second additive is too high, it may be that the content of the first additive is too much, or the content of the second additive is too little; when the content of the first additive is too much, it will increase the consumption of active lithium in the early stage of the battery 100, resulting in a decrease in the initial capacity of the battery 100. In addition, if the mass fraction a of the first additive is too high, too much inorganic matter will be formed on the negative electrode sheet 130. Too much inorganic matter covers the surface of the negative electrode sheet 130, which will increase the impedance of the negative electrode sheet 130 and reduce the dynamic performance of the battery 100; furthermore, the N-nitro The reduction products of the additives include guanidines, which are alkaline substances. If the electrolyte contains too much guanidine, it will cause side reactions during the charge and discharge cycle of the battery 100 (for example, initiating the ring opening of ethylene carbonate (EC) in the electrolyte), reducing the ionic conductivity of the electrolyte, thereby reducing the kinetic performance of the battery 100; when the content of the second additive is too little, the SEI film on the surface of the negative electrode plate 130 cannot be continuously repaired during the charge and discharge cycle of the battery 100, thereby limiting the improvement of the room temperature capacity retention rate and high temperature cycle capacity retention rate of the battery 100.

[0091] In some embodiments, in the electrolyte, the mass fraction b of the second additive is in the range of 0.01%≤b≤5%.

[0092] Specifically, in the electrolyte, the mass fraction b of the second additive can be but is not limited to 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, 5%, etc.

[0093] In this embodiment, if the mass fraction b of the second additive in the electrolyte is too low, the SEI film on the surface of the negative electrode plate 130 cannot be continuously repaired during the charge and discharge cycle of the battery 100, thereby limiting the improvement in the room temperature capacity retention rate and high temperature cycle capacity retention rate of the battery 100; if the mass fraction b of the second additive in the electrolyte is too high, the consumption of active lithium in the early stage of the cycle of the battery 100 will be increased, the initial discharge capacity of the battery 100 will be reduced, and the room temperature cycle performance and high temperature cycle performance of the battery 100 will be deteriorated.

[0094] Optionally, the electrolyte salt includes a lithium salt or a sodium salt. In some embodiments, the electrolyte is applied to a lithium-ion battery 100, and the electrolyte salt is a lithium salt. In other embodiments, the electrolyte is applied to a sodium-ion battery 100, and the electrolyte salt is a sodium salt.

[0095] Optionally, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorobis(oxalatophosphate) (LiODFP), lithium difluorooxalatoborate (LiODFB), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (CF3SO3Li), etc.

[0096] Optionally, the sodium salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalatoborate), sodium difluorobis(oxalatophosphate), sodium difluorooxalatoborate, sodium difluorophosphate (NaPO2F2), sodium trifluoromethanesulfonate (CF3SO3Na), etc.

[0097] Optionally, in the electrolyte, the mass fraction of the electrolyte salt ranges from 10% to 15%. Specifically, the mass fraction of the electrolyte salt may be, but is not limited to, 10%, 10.5%, 11%, 11.5%, 11.8%, 12%, 12.5%, 13%, 13.5%, 14%, 14.2%, 14.5%, 15%, etc. If the mass fraction of the electrolyte salt in the electrolyte is too small, the concentration of free ions in the electrolyte is too small, which reduces the conductivity of the electrolyte and thus reduces the kinetic performance of the battery 100; if the mass fraction of the electrolyte salt in the electrolyte is too large, it is easy for a part of the electrolyte salt to be undissociated, and the viscosity of the electrolyte will increase, which in turn reduces the conductivity of the electrolyte and also reduces the kinetic performance of the battery 100. When the mass fraction of the electrolyte salt in the electrolyte is 10% to 15%, the electrolyte can have a higher conductivity, so that the battery 100 has better dynamic performance.

[0098] Optionally, the organic solvent includes at least one of a cyclic carbonate and a chain carbonate. Cyclic carbonate has a high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode plate 130, but its viscosity is relatively large. Chain carbonate has a lower viscosity than cyclic carbonate, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, when a mixed solvent of cyclic carbonate and chain carbonate is used, the electrolyte can have a more suitable viscosity and low-temperature stability, and the battery 100 using the electrolyte can form a better film.

[0099] Optionally, the cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC for short), propylene carbonate (PC for short), etc. The dielectric constant of ethylene carbonate is much greater than that of propylene carbonate, and ethylene carbonate can better promote the formation of SEI film.

[0100] Optionally, the linear carbonate may include but is not limited to at least one of dimethyl carbonate (DMC for short), diethyl carbonate (DEC for short), ethyl methyl carbonate (EMC for short), and the like.

[0101] Optionally, in the electrolyte, the mass fraction of the organic solvent is 60wt% to 85wt%, specifically, but not limited to, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, etc.

[0102] Optionally, the organic solvent further comprises at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0103] After testing, the cycle capacity retention rate of the battery 100 using the electrolyte of the embodiment of the present application after 500 cycles at 25°C is greater than or equal to 85%, specifically, it can be but not limited to 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, etc. The cycle capacity retention rate of the battery 100 using the electrolyte of the embodiment of the present application after 500 cycles at 45°C is greater than or equal to 81%, specifically, it can be but not limited to 81%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, etc.

[0104] After testing, the volume expansion rate of the battery 100 using the electrolyte of the embodiment of the present application stored at 60°C for 60 days is less than or equal to 11.8%. Specifically, the volume expansion rate of the battery 100 using the electrolyte of the embodiment of the present application stored at 60°C for 60 days can be, but is not limited to, 11.8%, 10%, 9%, 8%, 7%, 6%, 5%, etc.

[0105] The electrolyte and the battery 100 of the present application are further described below through specific embodiments.

[0106] Examples 1 to 20, Comparative Examples 1 to 3

[0107] The preparation method of the battery 100 of each embodiment and comparative example includes:

[0108] (1) Preparation of positive electrode sheet 110: The positive electrode active material lithium iron phosphate, conductive carbon black SP (positive electrode conductive agent), and adhesive PVDF (positive electrode binder) are dispersed in N-methylpyrrolidone (NMP) solvent according to a mass ratio of 97:0.7:2.3, and mixed evenly to obtain a positive electrode slurry with a solid content of 60 wt%; the positive electrode slurry is coated on the positive electrode current collector 111 aluminum foil, and after drying, cold pressing, slitting, and cutting, the positive electrode sheet 110 is obtained.

[0109] (2) Preparation of negative electrode sheet 130: artificial graphite, conductive carbon black SP (negative electrode conductive agent), thickener CMC (negative electrode thickener) and negative electrode binder SBR are dispersed in deionized water at a mass ratio of 96.5:0.5:1:2 and mixed evenly to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry is coated on the copper foil of the negative electrode collector 131. After drying, cold pressing, slitting and cutting, the negative electrode sheet 130 is obtained.

[0110] (3) Electrolyte preparation process: In an argon atmosphere glove box with a moisture content of ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 2:1:2 to obtain a mixed solvent, and then the dried electrolyte salt lithium hexafluorophosphate is dissolved in the mixed solvent, stirred until completely dissolved and uniformly dissolved, and the additives are added and mixed to obtain an electrolyte. The mass fraction of lithium hexafluorophosphate in the electrolyte of each embodiment and comparative example is 13wt%. The types and mass fractions of the first additive and the second additive in the electrolyte of each embodiment and comparative example are shown in Table 1 below.

[0111] (4) Separator 120 : A 16 μm polyethylene film is used as the separator 120 .

[0112] (5) Assembly of battery 100: The positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 are stacked in sequence to form an electrode assembly, and the electrode assembly is wound to obtain a bare cell. After the tabs are welded, the cell is assembled into an outer package, and after the prepared electrolyte is injected, the cell is packaged, allowed to stand, formed, shaped, and capacity tested, and finally the battery 100 is prepared.

[0113] The battery 100 of each embodiment and comparative example was subjected to a cycle performance test at room temperature (25°C) and high temperature (45°C), and a volume expansion rate test at high temperature (60°C). The cycle performance and volume expansion rate of the battery 100 of each embodiment and comparative example are shown in Table 2 below.

[0114] (1) 25°C cycle performance test: The battery 100 was subjected to a charge and discharge cycle test on a charge and discharge instrument (Nebula Charge and Discharge Test System - BAT-NEEFLCT-05300-V010). The test temperature was 25°C, the cycle rate was 1C (i.e., both the charge rate and the discharge rate were 1C), the charging voltage was 2.5V to 3.65V, and the capacity retention rate after 500 cycles was calculated. The cycle capacity retention rates of the batteries 100 of the embodiments and comparative examples after 500 cycles at 25°C and a charge and discharge rate of 1C are shown in Table 2 below.

[0115] The capacity retention rate of the 25°C cycle is calculated as follows: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0116] (2) 45°C cycle performance test: The battery 100 was subjected to a charge and discharge cycle test on a charge and discharge instrument (Nebula Charge and Discharge Test System - BAT-NEEFLCT-05300-V010). The test temperature was 45°C, the cycle rate was 1C (i.e., both the charge rate and the discharge rate were 1C), the charging voltage was 2.5V to 3.65V, and the capacity retention rate after 500 cycles was calculated. The cycle capacity retention rates of the batteries 100 of the embodiments and comparative examples after 500 cycles at 45°C and a charge and discharge rate of 1C are shown in Table 2 below.

[0117] The capacity retention rate of the 45°C cycle is calculated as follows: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0118] (3) Volume expansion rate test of battery 100 at 60°C: adjust the temperature of the thermostat to 25°C, let it stand for 10 minutes, charge at 0.5C constant current to 3.65V, then charge at 3.65V constant voltage until the charging current is cut off at 0.05C, let it stand for 1 hour, and test the volume V0 of the battery 100 in the initial fully charged state; adjust the temperature of the thermostat to 60°C, let it stand for 30 minutes, charge at 0.5C constant current to 3.65V, let it stand for 1 hour, and discharge at 0.5C constant current to 2.5V; then charge at 0.5C constant current to 3.65V again, let it stand for 1 hour, and discharge at 0.5C constant current to 2.5V; finally, charge at 0.5C constant current to 3.65V, store for 60 days, cool the battery 100, and test the volume V1 of the battery 100 in the fully charged state at this time; then the volume expansion rate of the battery 100 stored at 60°C for 60 days = [(V1 / V0)-1]×100%. The volume expansion ratios of the batteries 100 of the embodiments and comparative examples stored at 60° C. for 60 days are shown in Table 2 below.

[0119] Table 1 Composition and ratio of the electrolyte of each embodiment and comparative example

[0120]

[0121] Table 2 Performance parameters of the battery 100 of each embodiment and comparative example

[0122]

[0123]

[0124] It can be seen from the test results of Comparative Example 1 and Examples 1 to 3 that when the additive of the present application is not added to the electrolyte (Comparative Example 1), the room temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the battery 100 are both low, and the volume expansion rate of the battery 100 after being stored at 60°C for 60 days is high. When 2-N-nitroiminoimidazole, or 2-N-nitroiminopyridine, or 2-N-nitroiminopyrimidine of the present application is added to the electrolyte, the cycle capacity retention rate of the battery 100 at 25°C and the cycle capacity retention rate at 45°C are increased, and the volume expansion rate of the battery 100 after being stored at 60°C for 60 days is reduced. This is due to the high film-forming reactivity of N-nitro additives, and its reduction products are lithium nitride and lithium oxide. Lithium nitride and lithium oxide have high high temperature stability and high voltage stability, which can better improve the room temperature cycle performance and high temperature cycle performance.

[0125] It can be seen from the test results of Examples 1 to 3 that, compared with 2-N-nitroiminopyridine and 2-N-nitroiminopyrimidine, 2-N-nitroiminoimidazole can better improve the room temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the battery 100, and can better reduce the volume expansion rate of the battery 100 after storage at 60°C for 60 days.

[0126] It can be seen from the test data of Example 1, Comparative Example 2 and Comparative Example 3 that compared with the solution of adding nitroimidazole (such as Comparative Example 2) or aminoimidazole (such as Comparative Example 3) as an additive in the electrolyte, since N-nitro derivatives can better form intermolecular hydrogen bonds than monoamino / nitro, and their reduction products can isomerize to produce guanidine substances to combine with lithium salt decomposition products to further stabilize the electrolyte, adding 2-N-nitroiminoimidazole to the electrolyte can better improve the cycle capacity retention rate of battery 100 at 25°C and the cycle capacity retention rate at 45°C, and can better reduce the volume expansion rate of battery 100 after storage at 60°C for 60 days.

[0127] From the test results of Examples 4 to 8, it can be seen that when a small amount of 2-N-nitroimidazole is added, the room temperature cycle capacity retention rate, the high temperature cycle capacity retention rate and the volume expansion rate of the battery 100 after being stored at 60°C for 60 days can be improved. However, when the amount of 2-N-nitroimidazole added is small, the improvement of the room temperature cycle capacity retention rate, the high temperature cycle capacity retention rate and the volume expansion rate of the battery 100 after being stored at 60°C for 60 days is small. With the increase of the addition amount of 2-N-nitroiminoimidazolidine in the electrolyte, the cycle capacity retention rate of the battery 100 at 25°C and the cycle capacity retention rate at 45°C both increase gradually, and the volume expansion rate of the battery 100 after storage at 60°C for 60 days gradually decreases; when the content of 2-N-nitroiminoimidazolidine in the electrolyte continues to increase, the cycle capacity retention rate of the battery 100 at 25°C and the cycle capacity retention rate at 45°C both decrease, and the volume expansion rate of the battery 100 after storage at 60°C for 60 days gradually increases.

[0128] It can be seen from the test results of Example 1, Example 7 and Example 9 that compared with Example 1 and Example 7 in which only the first additive (2-N-nitroimidazole) is added, the battery 100 of the embodiment in which a considerable amount of the first additive and the second additive are added has a higher cycle capacity retention rate at 25°C and a cycle capacity retention rate at 45°C, and has a lower volume expansion rate. This is because when the two additives are used in a superimposed manner, the N-nitro derivative can be reduced in advance during the reduction process to produce an inorganic lithium salt that covers the surface of the negative electrode plate 130, reducing the consumption of the second additive during the formation process. At the same time, the guanidine products produced by the reduction of the N-nitro derivative can be combined with HF and PF5, reducing the consumption of the second additive by the battery 100 during the cycle process, and further improving the cycle of the battery 100.

[0129] It can be seen from the test results of Example 9 to Example 11 that when the addition amounts of the first additive and the second additive are the same, compared with the scheme of compounding 2-N-nitroimidazole and fluoroethylene carbonate, compounding 2-N-nitroimidazole and vinyl carbonate can make the battery 100 have a higher cycle capacity retention rate at 25°C and a higher cycle capacity retention rate at 45°C, and a lower volume expansion rate after storage at 60°C for 60 days. Similarly, compared with the scheme of compounding 2-N-nitroimidazole and vinyl sulfate, compounding 2-N-nitroimidazole and fluoroethylene carbonate can make the battery 100 have a higher cycle capacity retention rate at 25°C and a higher cycle capacity retention rate at 45°C, and a lower volume expansion rate after storage at 60°C for 60 days.

[0130] It can be seen from the test results of Example 9, Example 12 to Example 14 that when the addition amounts of 2-N-nitroimidazole and vinyl carbonate in the electrolyte are both low, the 25°C cycle capacity retention rate and the 45°C cycle capacity retention rate of the battery 100 are less improved, and the expansion rate of the battery 100 is less reduced; as the addition amounts of 2-N-nitroimidazole and vinyl carbonate in the electrolyte gradually increase, the 25°C cycle capacity retention rate and the 45°C cycle capacity retention rate of the battery 100 gradually increase, and the volume expansion rate of the battery 100 after storage at 60°C for 60 days gradually decreases; when the addition amounts of 2-N-nitroimidazole and vinyl carbonate in the electrolyte continue to increase, the 25°C cycle capacity retention rate and the 45°C cycle capacity retention rate of the battery 100 gradually decrease, and the volume expansion rate of the battery 100 after storage at 60°C for 60 days gradually increases. When the amount of the first additive and the second additive added reaches a certain level, the normal temperature cycle performance and high temperature cycle performance of the battery 100 will decrease if the amount of the first additive and the second additive is continued to be increased. This is because as the content of the first additive and the second additive increases, the film formation of the first additive and the second additive will consume a large amount of active lithium. A large amount of the first additive and the second additive will affect the overall active lithium content of the battery 100, resulting in a decrease in the discharge capacity of the battery 100, thereby deteriorating the normal and high temperature performance.

[0131] It can be seen from the test results of Examples 9 and 16 to 20 that as the mass ratio of 2-N-nitroimidazole to vinyl carbonate in the electrolyte increases, the cycle capacity retention rate at 25°C and the cycle capacity retention rate at 45°C of the battery 100 gradually increase, and the volume expansion rate of the battery 100 after storage at 60°C for 60 days gradually decreases; when the mass ratio of 2-N-nitroimidazole to vinyl carbonate in the electrolyte continues to increase, the cycle capacity retention rate of the battery 100 at 25°C and the cycle capacity retention rate at 45°C gradually decrease, and the volume expansion rate of the battery 100 after storage at 60°C for 60 days gradually increases.

[0132] Mentioning "embodiment" or "implementation method" in this application means that the specific features, structures, or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments. In addition, it should be understood that the features, structures, or characteristics described in the various embodiments of the present application, in the absence of contradictions between each other,

[0133] They can be combined arbitrarily to form another embodiment without departing from the spirit and scope of the technical solution of the present application.

[0134] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the above preferred implementation modes, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte includes an electrolyte salt, an organic solvent, and a first additive, wherein the first additive includes an N-nitro derivative.

2. The electrolyte according to claim 1, characterized in that The structural formula of the N-nitro derivative is: Among them, R1 is one of imidazolidinyl, pyridyl, and pyrimidinyl, and R2 is one of hydrogen atom, alkyl group with 1 to 3 carbon atoms, and fluoroalkyl group with 1 to 3 carbon atoms.

3. The electrolyte according to claim 1, characterized in that The N-nitro derivatives include At least one of .

4. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass fraction a of the first additive is in the range of 0.01%≤a≤1%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that the electrolyte further comprises a second additive, and the second additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, propenyl-1,3-sultone, and methylene methanedisulfonate. 6 . The electrolyte according to claim 5 , characterized in that, in the electrolyte, the mass ratio a / b of the first additive to the second additive is in the range of 0.1≤a / b≤3. 7 . The electrolyte according to claim 5 , characterized in that, in the electrolyte, the mass fraction b of the second additive is in the range of 0.01%≤b≤5%.

8. A battery, characterized in that: include: The electrolyte, positive electrode sheet, separator and negative electrode sheet as described in any one of claims 1 to 7.

9. An energy storage device, characterized in that: include: Box; as well as A plurality of batteries as claimed in claim 8, wherein the plurality of batteries are housed in the casing.

10. An energy storage system, characterized in that: include: The energy storage device according to claim 9; as well as An electric energy conversion device, wherein the electric energy conversion device is electrically connected to the energy storage device, the electric energy conversion device is used to convert other forms of energy into electric energy, and the energy storage device is used to store the electric energy.

Images