Electrolyte, battery, energy storage device, and energy storage system

Abstract

An electrolyte, a battery, an energy storage device, and an energy storage system. The electrolyte of the present application comprises a lithium salt and an additive, wherein the structural formula of the additive is: formula I, wherein R1 is one of hydrogen, an alkyl group containing 1 to 5 carbon atoms, a trifluoromethyl group, an acyl group, and an alkylsilyl group; R2 is one of hydrogen, an alkyl group containing 1 to 5 carbon atoms, a trifluoromethyl group, an acyl group, and an alkylsilyl group; and R3 is one of hydrogen, an alkyl group containing 1 to 5 carbon atoms, a trifluoromethyl group, an acyl group, and an alkylsilyl group.

Description

Electrolyte, battery, energy storage device and energy storage system

[0001] The present application claims priority to the Chinese patent application No. 202410961278.9, filed on July 17, 2024, and entitled "Electrolyte, battery, energy storage device and energy storage system", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of energy storage, in particular to an electrolyte, a battery, an energy storage device and an energy storage system. BACKGROUND

[0003] With the continuous development of lithium ion battery technology, compared with other types of batteries such as lead-acid, cadmium-nickel, lithium ion batteries have the advantages of large specific capacity, no memory effect, high working voltage, fast charging speed, wide working temperature range, long cycle life, small volume, light weight, etc. At present, lithium ion batteries have been widely used in mobile phones, notebook computers, electric vehicles, energy storage cabinets and other fields, and their application range is becoming more and more extensive.

[0004] With the development of the energy storage industry, higher requirements are put forward for the life attenuation amplitude and service life of lithium ion batteries. However, the long cycle performance of existing lithium ion batteries still needs to be improved. SUMMARY

[0005] The electrolyte provided by the embodiments of the present application can make the battery have good high-temperature cycle performance and high-temperature storage performance when applied to the battery.

[0006] In a first aspect, the embodiments of the present application provide an electrolyte, which comprises a lithium salt and an additive, and the structural formula of the additive is:

[0007] wherein R1 is one of hydrogen, an alkyl group with 1-5 carbon atoms, a trifluoromethyl group, an acyl group, and an alkyl silicon group; R2 is one of hydrogen, an alkyl group with 1-5 carbon atoms, a trifluoromethyl group, an acyl group, and an alkyl silicon group; and R3 is one of hydrogen, an alkyl group with 1-5 carbon atoms, a trifluoromethyl group, an acyl group, and an alkyl silicon group.

[0008] In a second aspect, the embodiments of the present application also provide a battery, which comprises:

[0009] the electrolyte provided by the embodiments of the present application;

[0010] a positive electrode tab;

[0011] a separator located on one side of the positive electrode tab; and

[0012] The negative electrode sheet is arranged on the side of the separator away from the positive electrode sheet.

[0013] In a third aspect, the embodiments of the present application further provide a storage device, which comprises:

[0014] a box; and

[0015] a plurality of batteries as described in the embodiments of the present application are accommodated in the box.

[0016] In a fourth aspect, the embodiments of the present application further provide a storage system, which comprises: an electric energy conversion device and the storage device as described in the embodiments of the present application, the electric energy conversion device is electrically connected with the storage device, the electric energy conversion device is used for converting other forms of energy into electric energy, and the storage device is used for storing the electric energy.

[0017] The xanthine compound has a high reduction potential, and when the electrolyte is applied to a battery, the xanthine compound can preferentially undergo a reduction reaction on the surface of the negative electrode sheet, decompose and build a SEI film rich in nitrogen elements on the surface of the negative electrode sheet. The SEI film rich in nitrogen elements is relatively dense, has high high-temperature resistance and electrochemical stability, thereby improving the cycle life and cycle capacity retention rate of the battery. In addition, the lone pair of electrons on the N atom of the five-membered ring in the xanthine compound does not participate in film formation and has nucleophilicity, can form hydrogen bonds with water in the electrolyte, and can also complex with PF5 produced by the decomposition of LiPF6 in the electrolyte, preventing the further decomposition of PF5 to produce HF and POF3. Furthermore, when the xanthine compound contains a trifluoromethyl group, the trifluoromethyl group acts as an electron-withdrawing group, which can lower the lowest unoccupied molecular orbital energy level (LUMO energy level) of the xanthine compound, so that the xanthine compound preferentially reacts at the interface of the negative electrode sheet and participates in the construction of the SEI film, and at the same time, the content of LiF in the SEI film can be increased. Inorganic salts can further reduce the solubility of the SEI film in the electrolyte and improve the thermal stability of the SEI. Furthermore, when the xanthine compound contains an alkyl silicon group, the xanthine compound can also be used to remove acid and increase the content of trimethylsilicon compounds in the SEI film, thereby improving the stability of the SEI film, thereby better improving the cycle life and cycle capacity retention rate of the battery. When the lone pair of electrons on the N atom of the imidazole ring of the xanthine compound and Li + The solvent structure is more easily diffused to the surface of the negative electrode sheet and undergoes a reduction reaction after obtaining an electron on the surface of the negative electrode sheet. After the six-membered ring is opened, an SEI organic component containing an imidazole ring and an amide bond (-C(O)-N-) is constructed. Such organic components have good thermal stability, which prolongs the service life of the battery using the electrolyte. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 is a schematic diagram of the structure of a battery according to an embodiment of this application.

[0020] Figure 2 is a cross-sectional view of a battery according to an embodiment of this application along the AA direction in Figure 1.

[0021] Figure 3 is a cross-sectional view of the positive electrode sheet of an embodiment of this application along the AA direction in Figure 1.

[0022] Figure 4 is a cross-sectional view of the negative electrode sheet of an embodiment of this application along the AA direction in Figure 1.

[0023] Figure 5 is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0024] Figure 6 is a structural block diagram of an energy storage system according to an embodiment of this application.

[0025] Figure 7 is an application scenario diagram of an energy storage system according to an embodiment of this application.

[0026] Explanation of reference numerals in the attached drawings: 100-battery, 110-positive electrode, 111-positive current collector, 112-positive active layer, 120-separator, 130-negative electrode, 131-negative current collector, 132-negative active layer, 140-casing, 150-end cap assembly, 141-receiving cavity, 200-energy storage device, 210-box, 300-energy storage system, 310-power conversion device. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0028] The terms "first", "second", and the like in the description and claims of the application and the above drawings are used to distinguish different objects, and are not used to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product or device.

[0029] The technical solutions in the embodiments of the application will be described below with reference to the drawings.

[0030] It should be noted that, for the sake of brevity, the same reference numerals are used to denote the same components in the embodiments of the application, and detailed description of the same components is omitted in different embodiments.

[0031] With the continuous development of lithium ion battery technology, compared with lead-acid, cadmium-nickel and other types of batteries, lithium ion batteries have the advantages of large specific capacity, no memory effect, high working voltage, fast charging speed, wide working temperature range, long cycle life, small volume, light weight and the like. At present, lithium ion batteries have been widely used in mobile phones, notebook computers, electric vehicles, energy storage cabinets and other fields, and their application range is becoming more and more extensive.

[0032] With the development of the energy storage industry, higher requirements are put forward for the life attenuation amplitude and service life of lithium ion batteries. However, the long cycle performance of existing lithium ion batteries still needs to be improved.

[0033] At present, lithium iron phosphate is mostly used as the positive electrode material in the energy storage field, and graphite is used as the negative electrode material. During the cycle process, the battery life is mainly attenuated because the active lithium reacts with the electrolyte on the surface of the negative electrode, causing lithium to be deposited in the form of a salt on the surface of the negative electrode. On the one hand, ester solvents are easily reduced on the surface of the negative electrode at low potential and react with lithium, consuming active lithium; on the other hand, the deintercalation of lithium from the graphite negative electrode causes the graphite interlayer spacing to continuously expand and shrink, and the solid electrolyte interface film (SEI film) on the surface of the negative electrode is continuously pulled and exposed to the new graphite interface and the electrolyte, and the electrolyte continuously reacts, resulting in the loss of active lithium. Thus, the capacity retention rate of the battery gradually decreases during the continuous charge and discharge cycle process.

[0034] The embodiment of the application provides an electrolyte, which comprises a lithium salt and an additive, and the structural formula of the additive is:

[0035] (i.e. xanthine compounds),

[0036] wherein R1 is one of hydrogen, alkyl group with carbon number of 1-5, trifluoromethyl group, acyl group, alkyl silyl group; R2 is one of hydrogen, alkyl group with carbon number of 1-5, trifluoromethyl group, acyl group, alkyl silyl group; R3 is one of hydrogen, alkyl group with carbon number of 1-5, trifluoromethyl group, acyl group, alkyl silyl group.

[0037] The electrolyte of the embodiments of the present application can be applied to lithium ion batteries. The battery comprises a positive electrode sheet, a separator and a negative electrode sheet.

[0038] It can be understood that the xanthine compound comprises xanthine and xanthine derivatives.

[0039] The electrolyte of the present application adds xanthine compound as an additive. The xanthine compound has a high reduction potential. When the electrolyte is applied to a battery, the xanthine compound can preferentially undergo a reduction reaction on the surface of the negative electrode sheet, and decompose to build a nitrogen-rich SEI film on the surface of the negative electrode sheet. The nitrogen-rich SEI film is relatively dense, has high high-temperature resistance and electrochemical stability, thereby improving the cycle life and cycle capacity retention rate of the battery. In addition, the lone pair of electrons on the N atom of the five-membered ring in the xanthine compound does not participate in film formation and has nucleophilicity, which can form hydrogen bonds with water in the electrolyte, remove water in the electrolyte, and also complex with PF5 produced by the decomposition of LiPF6 in the electrolyte, preventing the further decomposition of PF5 to produce HF and POF3. Furthermore, when the xanthine compound contains a trifluoromethyl group, the trifluoromethyl group as an electron-withdrawing group can lower the lowest unoccupied molecular orbital energy level (LUMO energy level) of the xanthine compound, so that the xanthine compound preferentially reacts at the interface of the negative electrode sheet and participates in the construction of the SEI film, and at the same time, the content of LiF in the SEI film can be increased. Inorganic salts can further reduce the solubility of the SEI film in the electrolyte and improve the thermal stability of the SEI. Furthermore, when the xanthine compound contains an alkyl silyl group, the xanthine compound can also be used to remove acid and increase the content of trimethylsilyl compounds in the SEI film, thereby improving the stability of the SEI film, and thus the cycle life and cycle capacity retention rate of the battery can be better improved. When the lone pair of electrons on the N atom of the imidazole ring of the xanthine compound is coordinated with Li+, the xanthine compound can be reduced to form a stable SEI film on the surface of the negative electrode sheet, thereby improving the cycle life and cycle capacity retention rate of the battery. + The solvent structure is more easily diffused to the surface of the negative electrode sheet and undergoes a reduction reaction after obtaining an electron on the surface of the negative electrode sheet. After the six-membered ring is opened, an SEI organic component containing an imidazole ring and an amide bond (-C(O)-N-) is constructed. Such organic components have good thermal stability, which prolongs the service life of the battery using the electrolyte.

[0040] In some embodiments, the xanthine compound comprises at least one of the following structural formulas:

[0041] (xanthine), (1,3-dimethylxanthine or theophylline), (1,3-di(trifluoromethyl)xanthine), (1,3-di(trimethylsilyl)xanthine), (1,3,7,8-tetramethylxanthine), (1,3-dimethyl-7-acetylxanthine), (1,3-dimethyl-7-trifluoromethylxanthine), (1,3-dimethyl-7-trimethylsilylxanthine).

[0042] In the present embodiment, these xanthine compounds have a high reduction potential, and when the electrolyte is applied to a battery, a reduction reaction can occur preferentially on the surface of the negative electrode sheet, and a SEI film rich in nitrogen elements can be formed on the surface of the negative electrode sheet. The SEI film rich in nitrogen elements is relatively dense, has high high-temperature resistance and electrochemical stability, thereby improving the cycle life and cycle capacity retention rate of the battery. In addition, the lone pair of electrons on the N atom of the five-membered ring in these xanthine compounds does not participate in film formation and has nucleophilicity, can form hydrogen bonds with water in the electrolyte, and can also complex with PF5 generated by the decomposition of LiPF6 in the electrolyte, thereby preventing the further decomposition of PF5 to generate HF and POF3. Furthermore, when the xanthine compound contains a trifluoromethyl group, the trifluoromethyl group acts as an electron-withdrawing group, which can lower the lowest unoccupied molecular orbital energy level (LUMO energy level) of the xanthine compound, so that the xanthine compound preferentially reacts at the interface of the negative electrode sheet and participates in the formation of the SEI film, and at the same time, the content of LiF in the SEI film can be increased. Inorganic salts can further reduce the solubility of the SEI film in the electrolyte and improve the thermal stability of the SEI. Furthermore, when the xanthine compound contains an alkylsilyl group, the xanthine compound can also be used to remove acid and increase the content of trimethylsilyl compounds in the SEI film, thereby improving the stability of the SEI film and further improving the cycle life and cycle capacity retention rate of the battery. Furthermore, when the xanthine compound contains an acyl group, an amide bond structure (-C(O)-N-) can be formed in the SEI film. The amide bond structure can improve the thermal stability of the SEI film and prolong the service life of the battery using the electrolyte.

[0043] In some embodiments, the mass fraction of the xanthine compound in the electrolyte is 0.1% to 5%.

[0044] Specifically, the mass fraction of the xanthine compound in the electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0045] In the present embodiment, the mass fraction of the xanthine compound in the electrolyte is too low, and the improvement of the stability of the SEI film of the negative electrode plate is limited when the electrolyte is applied to a battery; the mass fraction of the xanthine compound in the electrolyte is too high, and the thickness of the SEI film formed by the negative electrode plate is too thick when the electrolyte is applied to a battery, which causes the impedance in the lithium intercalation process of the negative electrode plate, and thus the battery is prone to lithium precipitation during the charging and discharging process, thereby reducing the kinetic performance and cycle performance of the battery. When the mass fraction of the xanthine compound in the electrolyte is 0.1% to 5%, the electrolyte can be well applied to a battery to improve the high-temperature resistance of the SEI film of the negative electrode plate of the battery, thereby improving the cycle capacity retention rate of the battery and prolonging the service life of the battery, and the SEI film formed by the negative electrode plate has a suitable thickness, the battery has a low lithium intercalation impedance, and thus has a high kinetic performance.

[0046] Further, the mass fraction of the xanthine compound in the electrolyte is 0.1% to 3%. In this way, the electrolyte can be well applied to a battery to improve the high-temperature resistance of the SEI film of the negative electrode plate of the battery, thereby improving the cycle capacity retention rate of the battery and prolonging the service life of the battery, and the SEI film formed by the negative electrode plate has a suitable thickness, the battery has a low lithium intercalation impedance, and thus has a high kinetic performance.

[0047] Still further, the mass fraction of the xanthine compound in the electrolyte is 0.2% to 1%. In this way, the electrolyte can be well applied to a battery to improve the high-temperature resistance of the SEI film of the negative electrode plate of the battery, thereby improving the cycle capacity retention rate of the battery and prolonging the service life of the battery, and the SEI film formed by the negative electrode plate has a suitable thickness, the battery has a low lithium intercalation impedance, and thus has a high kinetic performance.

[0048] In some embodiments, the electrolyte further comprises fluoroethylene carbonate, and the mass fraction of the fluoroethylene carbonate in the electrolyte ranges from 0.1% to 4%.

[0049] Specifically, the mass fraction of the fluoroethylene carbonate in the electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0050] In this embodiment, the fluoroethylene carbonate is added to the electrolyte, when the electrolyte is applied to the battery, the content of LiF in the SEI film formed by the negative electrode sheet can be increased, the increase of LiF in the SEI film is beneficial to reduce the solubility of the SEI film in the electrolyte, improve the thermal stability of the SEI film, and thus improve the cycle performance of the battery; in addition, the increase of the content of inorganic salts such as LiF in the SEI film of the negative electrode sheet can reduce the impedance of the negative electrode sheet and improve the kinetic performance of the negative electrode sheet. Furthermore, compared with the electrolyte added with the xanthine compound alone or the electrolyte added with the fluoroethylene carbonate alone, the combination of the xanthine compound and the fluoroethylene carbonate can better improve the cycle capacity retention rate of the battery using the electrolyte.

[0051] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate dioxalate (LiODFP), lithium difluoro(oxalato)borate (LiODFB), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (CF3SO3Li), etc.

[0052] Optionally, the total molar concentration M of the lithium salt in the electrolyte is in the range of 0.7 mol / L≤M≤1.4 mol / L. The total molar concentration M of the lithium salt in the electrolyte can be, but is not limited to, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, etc. If the total molar concentration M of the lithium salt is too small, the free ion concentration in the electrolyte is too small, which reduces the conductivity of the electrolyte and thus reduces the kinetic performance of the battery; if the total molar concentration M of the lithium salt is too large, a part of the electrolyte salt may not be dissociated, and the viscosity of the electrolyte is increased, which reduces the conductivity of the electrolyte and also reduces the kinetic performance of the battery. When the total molar concentration M of the lithium salt in the electrolyte is in the range of 0.7 mol / L≤M≤1.4 mol / L, the electrolyte has a relatively high conductivity, and thus the battery has a good kinetic performance.

[0053] In some embodiments, the electrolyte further comprises a sulfur-containing additive, the sulfur-containing additive comprising at least one of methanedimethanesulfonic acid methylene ester, ethylene sulfate, tris(trimethylsilyl)phosphite, propene sulfonic acid lactone, butyl sulfonic acid lactone, propene sulfite. The sulfur-containing additive can form lithium sulfate or lithium alkyl sulfate salt on the positive electrode sheet, further stabilize the solid electrolyte interface film (SEI film) of the positive electrode sheet, and make the solid electrolyte interface film of the positive electrode sheet thinner, better reduce the impedance of the positive electrode sheet, thereby reducing the high-temperature heat generation of the positive electrode sheet and improving the safety performance of the battery. In addition, the sulfur-containing additive of the present embodiment is less likely to decompose to produce acid at high temperature, which can better reduce the consumption of electrolyte at high temperature, thereby keeping the battery at a higher cycle capacity retention rate.

[0054] Optionally, in the electrolyte, the mass fraction w1 of the sulfur-containing additive is in the range of 0.1wt%≤w1≤1wt%. Specifically, in the electrolyte, the mass fraction w1 of the sulfur-containing additive can be, but is not limited to, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, etc. If the mass fraction w1 of the sulfur-containing additive in the electrolyte is too low, the stability of the interface film of the positive electrode sheet is limited, and the safety performance of the battery cannot be improved well. If the mass fraction w1 of the sulfur-containing additive in the electrolyte is too high, the sulfur-containing additive is prone to decompose to produce acid at high temperature, which destroys the interface film of the positive electrode sheet, making the positive electrode active layer of the positive electrode sheet directly contact with the electrolyte, increasing the side reaction between the positive electrode active layer and the electrolyte, thereby increasing the consumption of the electrolyte and reducing the cycle capacity retention rate of the battery. When the mass fraction of the sulfur-containing additive in the electrolyte is 0.1wt%≤w1≤1wt%, the safety performance of the battery can be better improved, and at the same time, the battery can maintain a higher cycle capacity retention rate.

[0055] Optionally, the electrolyte further comprises a film-forming additive, which can be used to promote the formation of the interface film of at least one of the positive electrode sheet and the negative electrode sheet and maintain the stability of the interface film when the electrolyte is applied to a lithium ion battery.

[0056] Optionally, the film-forming additive comprises at least one of vinyl sulfide (DTD), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), sulfur tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, hexanedinitrile, butanedinitrile, 1,3,6-hexanetricarbonitrile.

[0057] Optionally, the mass fraction of the film-forming additive ranges from 1.5% to 3%. Specifically, the mass fraction of the film-forming additive can be, but is not limited to, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc.

[0058] Optionally, the electrolyte further comprises an organic solvent. The organic solvent comprises at least one of a cyclic carbonate and a chain carbonate. The cyclic carbonate has high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode sheet, but has relatively large viscosity. The chain carbonate has lower viscosity than the cyclic carbonate, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, when a mixed solvent of the cyclic carbonate and the chain carbonate is used, the electrolyte can have relatively suitable viscosity and low-temperature stability, and the battery using the electrolyte can form a better film.

[0059] Optionally, the cyclic carbonate can comprise, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). The dielectric constant of ethylene carbonate is much higher than that of propylene carbonate, and ethylene carbonate can better promote the formation of the SEI film.

[0060] Optionally, the chain carbonate can comprise, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0061] Optionally, in the electrolyte, the mass fraction of the organic solvent is 60wt% to 85wt%. Specifically, the mass fraction can be, but is not limited to, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, etc.

[0062] 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.

[0063] Referring to FIGS. 1 and 2, the battery 100 provided by the embodiments of the present application comprises the electrolyte, the positive electrode sheet 110, the separator 120, and the negative electrode sheet 130. The separator 120 is located on one side of the positive electrode sheet 110, and the negative electrode sheet 130 is arranged on the side of the separator 120 away from the positive electrode sheet 110.

[0064] It should be noted that the positive electrode sheet 110 and the negative electrode sheet 130 are at least partially soaked in the electrolyte.

[0065] It can be understood that the positive electrode sheet 110, the separator 120 and the negative electrode sheet 130 are sequentially stacked to form an electrode assembly. The electrode assembly can be, but is not limited to, a winding type structure, a stacking type structure, etc., and the present application does not make specific limitations thereto.

[0066] It should be noted that the positive electrode sheet 110 and the negative electrode sheet 130 can be collectively referred to as an electrode sheet, in other words, the electrode sheet includes the positive electrode sheet 110 and the negative electrode sheet 130.

[0067] Referring to FIG. 3, the positive electrode sheet 110 can include a positive current collector 111 and a positive active layer 112 disposed on a surface of the positive current collector 111. It can be understood that the positive active layer 112 can cover one surface or opposite two surfaces of the positive current collector 111.

[0068] Optionally, the positive current collector 111 can be, but is not limited to, an aluminum sheet.

[0069] Optionally, the positive active layer 112 can include a positive active material, a positive conductive agent, a positive binder and a positive thickening agent.

[0070] Optionally, the positive active material can be, but is not limited to, lithium iron phosphate.

[0071] Optionally, the positive conductive agent can be, but is not limited to, at least one of conductive carbon black, acetylene black, carbon nanotube, carbon fiber, graphene, etc.

[0072] Optionally, the positive binder can be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, polymerized styrene butadiene rubber (SBR), etc.

[0073] Optionally, the mass fraction of the cathode binder in the cathode active layer 112 ranges from 2wt% to 4wt%. Specifically, the mass fraction of the cathode binder in the cathode active layer 112 can be, but is not limited to, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, and the like. If the mass fraction of the cathode binder is too small, the cathode active layer 112 is prone to powdering or spalling; if the mass fraction of the cathode binder is too large, the energy density of the cathode sheet 110 is reduced.

[0074] Optionally, the cathode thickening agent can be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC for short), polyacrylamide (PAM), and polymethacrylate (PMA), and the like.

[0075] Optionally, the separator 120 can 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 separator 120, and the like.

[0076] Optionally, the thickness of the separator 120 is 14μm to 18μm, and specifically, the thickness of the separator 120 can be, but is not limited to, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, and the like.

[0077] Referring to FIG. 4, optionally, the anode sheet 130 includes an anode current collector 131 and an anode active layer 132, and the anode active layer 132 is arranged on the surface of the anode current collector 131. It can be understood that the anode active layer 132 can cover one surface or opposite two surfaces of the anode current collector 131.

[0078] Optionally, the anode current collector 131 can be, but is not limited to, a copper sheet.

[0079] Optionally, the anode active layer 132 includes anode active material, anode conductive agent, anode binder, and anode thickening agent.

[0080] Optionally, the anode active material can be, but is not limited to, graphite.

[0081] Optionally, the anode conductive agent can be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotube, carbon fiber, graphene, and the like.

[0082] Optionally, the anode binder can be, but is not limited to, at least one of polyvinylidene fluoride, polyamide, polyacrylonitrile, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, butadiene styrene rubber, and the like.

[0083] Optionally, in the negative active layer 132, the mass fraction of the negative binder ranges from 2wt% to 4wt%. Specifically, in the negative active layer 132, the mass fraction of the negative binder can be, but is not limited to, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc. If the mass fraction of the negative binder is too small, the negative active layer 132 is prone to powdering or dropping; if the mass fraction of the negative binder is too large, the energy density of the negative electrode sheet 130 is reduced.

[0084] Optionally, the negative thickening agent can be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC for short), polyacrylamide (PAM), and polymethacrylate (PMA), etc.

[0085] Please refer to FIG. 1 and FIG. 2 again. Optionally, the battery 100 further comprises a shell 140 and an end cover assembly 150, the shell 140 and the end cover assembly 150 enclose a receiving cavity 141, and the receiving cavity 141 is used to accommodate the electrolyte, the positive electrode sheet 110, the separator 120, and the negative electrode sheet 130.

[0086] The electrolyte and the battery 100 of the present application are further described below through specific examples.

[0087] Examples 1 to 28 and Comparative Examples 1 to 3

[0088] The preparation method of the battery 100 of each example and comparative example comprises:

[0089] (1) Preparation of the positive electrode sheet 110

[0090] The positive active material lithium iron phosphate, the conductive carbon black SP (positive conductive agent), and the adhesive PVDF (positive binder) are dispersed into the N-methyl pyrrolidone (NMP for short) solvent according to a preset mass ratio, mixed uniformly to obtain a positive slurry; the positive slurry is coated on the positive current collector 111 aluminum foil, and the coating weight of the positive slurry is 300mg / 1540.25mm 2 ; after drying, cold pressing, slitting, and cutting, the positive electrode sheet 110 is obtained.

[0091] (2) Preparation of the negative electrode sheet 130

[0092] The graphite (negative active material), the conductive carbon black SP (negative conductive agent), the thickening agent CMC (negative thickening agent), the negative binder SBR, and the asphalt are dispersed into deionized water according to a preset mass ratio, mixed uniformly to obtain a negative slurry, and the negative slurry is coated on the negative current collector 131 aluminum foil, and the coating weight of the negative slurry is 144mg / 1540.25mm 2 ; after drying, cold pressing, slitting, and cutting, the negative electrode sheet 130 is obtained.

[0093] (3) Electrolyte preparation process

[0094] In an argon atmosphere glove box with water content ≤1 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 1:1:1 to obtain a mixed solvent. Then, the dry electrolyte salt lithium hexafluorophosphate was dissolved in the mixed solvent, and stirring was performed until complete dissolution and uniformity. Additives were added to obtain an electrolyte. In the electrolyte, the molar concentration of lithium hexafluorophosphate was 1 mol / L. The types and amounts of xanthine compounds added in each example and the comparative example are shown in Table 1 below.

[0095] (4) Preparation of the separator 120

[0096] A 16-μm polyethylene film was used as the separator 120.

[0097] (5) Preparation of the lithium ion battery 100

[0098] The positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 were sequentially stacked to form an electrode assembly. After the electrode assembly was wound, a bare battery cell was obtained. After the tab was welded, the battery cell was assembled into an outer package. After the electrolyte prepared was injected, the battery cell was packaged, rested, formed, shaped, and tested for capacity, etc. Finally, the lithium ion battery 100 was prepared.

[0099] The battery 100 of each example and the comparative example was tested for high-temperature (45°C) cycle performance and high-temperature storage performance. The high-temperature cycle performance and high-temperature storage performance of the lithium ion battery 100 of each example and the comparative example are shown in Table 1 below.

[0100] (1) The battery 100 was tested for charge-discharge cycling on a charge-discharge instrument (Xingyun charge-discharge test system-BAT-NEEFLCT-05300-V010). The test temperature was 45°C. The lithium ion battery 100 was charged at a constant power of 0.5P to 3.65V, and then rested for 10 minutes. The battery was discharged at a constant power of 0.5P to 2.5V. The capacity obtained in this step was the initial discharge capacity Co. The battery was tested for 1000 cycles of constant-power charging at 0.5P / constant-power discharging at 0.5P, and the discharge capacity of the 1000th cycle was recorded. P refers to the rated charge or discharge power of the battery, which is the product of the nominal voltage U of the battery and the current density of 1C. The nominal voltage of the iron phosphate battery is 3.2V, and 0.5P refers to 0.5 times the rated power. The cycle capacity retention rate = (discharge capacity of the 1000th cycle / initial discharge capacity Co) x 100%. The cycle capacity retention rate of the battery 100 of each example and the comparative example after 1000 cycles at a charge-discharge rate of 1P at 45°C is shown in Table 1 below.

[0101] The cycle capacity retention rates of the batteries 100 of the examples and the comparative examples after 1000 cycles at 45°C and 1P are shown in Table 1 below.

[0102] (2) The test temperature was 25°C, the lithium ion battery 100 was charged at 0.5C constant current to 3.65V, then charged at constant voltage to 0.05C, and then discharged at 0.5C to 2.5V after standing for 10 minutes. The capacity obtained in this step was the initial discharge capacity Co. After standing for 10 minutes, the lithium ion battery 100 was again charged at 0.5C constant current to 3.65V, then charged at constant voltage to 0.05C, and then placed in a 45°C oven for storage for 30 days. After 3 cycles of charge-discharge at 0.5C, the recovered capacity was recorded. The remaining capacity recovery rate was: the recovered capacity of the lithium ion battery 100 after standing / the initial discharge capacity Co x 100%. The capacity retention rates of the batteries 100 of the examples and the comparative examples after 30 days of storage at 45°C are shown in Table 1 below.

[0103] Table 1 Test data of the examples and the comparative examples

[0104] From the test data of Examples 1 to 28, it can be seen that when the mass fraction of the xanthine compound added in the electrolyte is 0.1% to 5%, the battery 100 using the electrolyte has higher high-temperature cycle capacity retention rate and high-temperature storage capacity retention rate, and has higher cycle performance and storage performance. In addition, compared with other substituent groups, when the xanthine compound includes a trimethylsilyl substituent group (such as 1,3-bis(trimethylsilyl) xanthine, 1,3-dimethyl-9-trimethylsilyl xanthine), the high-temperature cycle capacity retention rate and high-temperature storage performance of the battery 100 using the electrolyte are further improved, which is mainly due to the Si group can react with HF in the electrolyte, removing the acid in the electrolyte, improving the high-temperature cycle performance and high-temperature storage performance of the battery 100.

[0105] From the test results of Comparative Example 1, it can be seen that when the electrolyte does not add a xanthine compound, the high-temperature capacity retention rate of the lithium ion battery 100 after 1000 cycles and the remaining capacity retention rate after 30 days of high-temperature storage are both low. This may be due to the expansion and contraction of the SEI film during the electrochemical process of charging and discharging of the lithium ion battery 100 during the cycle process. At this time, the SEI film has poor cycle stability at high temperature, so the SEI film is constantly damaged and repaired, and the process of generating the SEI film is the process of the components of the electrolyte losing and gaining electrons on the surface of the active material. In this process, active lithium is lost, and it is irreversible loss. The decrease in the content of active lithium leads to the deterioration of the charge-discharge cycle capability and storage performance of the lithium ion battery 100.

[0106] When a small amount of 1,3-dimethylxanthine (Comparative Example 2) is added to the electrolyte, the cycle performance and high-temperature storage of the lithium ion battery 100 are slightly improved, but when the content is too low, the SEI film formed on the surface of the negative electrode sheet 130 cannot effectively protect the negative electrode sheet 130, so although the high-temperature capacity retention rate after 1000 cycles and the residual capacity retention rate after 30 days of high-temperature storage are increased, they are still low.

[0107] When the amount of 1,3-dimethylxanthine added to the electrolyte is too high (Comparative Example 3), the SEI film formed on the surface of the negative electrode sheet 130 of the battery 100 is too thick, increasing the impedance of lithium intercalation, affecting the kinetic performance of the lithium ion battery 100, and in addition, lithium precipitation occurs during the cycle, consuming active lithium, thereby greatly reducing the high-temperature capacity retention rate after 1000 cycles and the residual capacity retention rate after 30 days of high-temperature storage of the battery 100.

[0108] Examples 29 to 31

[0109] Examples 29 to 31 differ from Example 3 in that Examples 29 to 31 further add fluoroethylene carbonate, and the amount of fluoroethylene carbonate added in each example is shown in Table 2.

[0110] Comparative Example 4

[0111] This comparative example differs from Example 31 in that this comparative example only adds fluoroethylene carbonate without adding 1,3-dimethylxanthine.

[0112] Test data of each example and comparative example in Table 2

[0113] As can be seen from the test results in Table 2, compared with using xanthine compounds or fluoroethylene carbonate alone, the combination of xanthine compounds and fluoroethylene carbonate in the examples of the present application makes the battery 100 have higher high-temperature cycle capacity retention rate and high-temperature storage capacity retention rate.

[0114] Referring to FIG. 5, the example of the present application further provides an energy storage device 200, which comprises a box 210 and a plurality of batteries 100 described in the example of the present application, wherein the plurality of batteries 100 are stacked and accommodated in the box 210.

[0115] The term "a plurality of" means greater than or equal to two.

[0116] It can be understood that the plurality of batteries 100 of the energy storage device 200 can be connected in parallel with each other, or connected in series with each other, or partially connected in parallel and partially connected in series (in other words, connected in hybrid mode), and the connection mode of the plurality of batteries 100 of the same energy storage device 200 is not specifically limited in the present application.

[0117] Optionally, the energy storage device can be at least one of a small energy storage box, a large energy storage cabinet, an energy storage module, etc. The shape of the energy storage device is not limited in the present application. The shape of the energy storage device in the present application is only one of its many shapes, and should not be understood as a limitation of the energy storage device in the present application.

[0118] It can be understood that the box 210 has a receiving cavity, and the plurality of 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 a plurality of batteries 100.

[0119] Referring to FIGS. 6 and 7, the present application also provides an energy storage system 300, which comprises an energy conversion device 310 and the energy storage device 200 described in the present application. The energy conversion device 310 is electrically connected to the energy storage device 200. The energy conversion device 310 is used to convert other forms of energy into electrical energy. The energy storage device 200 is used to store the electrical energy.

[0120] Optionally, the energy conversion device 310 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0121] Optionally, the number of energy conversion devices 310 can be one or more. When there are multiple energy conversion devices 310, the multiple energy conversion devices 310 can be connected in series or in parallel, which is not limited in the present application.

[0122] Optionally, the energy conversion device 310 can be, but is not limited to, at least one of a photovoltaic panel, a wind power generation device, a water power generation device, etc.

[0123] Optionally, the number of energy storage devices 200 can be one or more. When the number of energy storage devices 200 is multiple, the multiple energy storage devices 200 can be connected in series or in parallel with each other, which is not limited in the present application.

[0124] In operation, the energy 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 used to supply power to streetlights and household appliances during peak electricity prices, or to supply power when the power grid is off. The electrical energy generated by the energy conversion device 310 can also be supplied to the power grid through high-voltage cables to alleviate the power supply pressure during peak power grid.

[0125] The term "in an embodiment" or "in embodiments" appearing in various locations throughout this application refers to various embodiments of the application described in the specification. The presence of this term in a given location does not necessarily refer to the same embodiment in every instance. It is explicitly contemplated that one or more embodiments of the application can include some features, structures, or characteristics described in connection with one or more embodiments while excluding others. Furthermore, it is also contemplated that one or more embodiments of the application can include some features, structures, or characteristics of the disclosure while excluding others. Accordingly, no limitation - expressed or implied - is placed on the scope of the application described in the claims.

[0126] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, but not to limit the present application. Although the present application is described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

An electrolyte, wherein, The electrolyte comprises a lithium salt and an additive, the structural formula of the additive is: Wherein, R1 is one of hydrogen, alkyl, trifluoromethyl, acyl, or alkylsilyl groups having 1 to 5 carbon atoms; R2 is one of hydrogen, alkyl, trifluoromethyl, acyl, or alkylsilyl groups having 1 to 5 carbon atoms; and R3 is one of hydrogen, alkyl, trifluoromethyl, acyl, or alkylsilyl groups having 1 to 5 carbon atoms. The electrolyte according to claim 1, wherein The additives include at least one of the following structural formulas: The electrolyte according to claim 1, wherein In the electrolyte, the mass fraction of the additive is 0.1% to 5%. The electrolyte according to claim 1, wherein, In the electrolyte, the mass fraction of the additive is 0.2% to 1%. The electrolyte according to claim 1, wherein, The electrolyte also includes fluoroethylene carbonate, wherein the mass fraction of the fluoroethylene carbonate in the electrolyte ranges from 0.1% to 4%. The electrolyte according to any one of claims 1 to 5, wherein The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorodioxalate phosphate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium trifluoromethanesulfonate. The electrolyte according to any one of claims 1 to 5, wherein The electrolyte also includes sulfur-containing additives, which include at least one of methylene disulfonate, ethylene sulfate, tris(trimethylsilyl)phosphite, propylene sulfonate lactone, butyl sulfonate lactone, and propylene sulfite. A battery, wherein, include: The electrolyte according to any one of claims 1-7; Positive electrode sheet; A diaphragm, the diaphragm being located on one side of the positive electrode; as well as The negative electrode is disposed on the side of the diaphragm opposite to the positive electrode. An energy storage device, wherein, include: Box; as well as The batteries of claims 8, wherein the plurality of batteries are housed within the housing. An energy storage system, wherein, include: An energy conversion device and an energy storage device as described in claim 9, wherein the energy conversion device is electrically connected to the energy storage device, the energy conversion device is used to convert other forms of energy into electrical energy, and the energy storage device is used to store the electrical energy.

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