Electrolyte, preparation method thereof and battery

Abstract

The invention provides an electrolyte, a preparation method thereof and a battery. The electrolyte comprises an electrolyte, an organic solvent and an additive, the additive comprises a functional additive, the functional additive meets the structural general formula (I): # imgabs 0 #, at least one of R3 and R4 in the structural general formula (I) meets the structural general formula (II): # imgabs 1 #, n is a natural number, and n is a natural number. R1, R2, R3, R4 and R5 are independently selected from any one of hydrogen, halogen, a cyano group, an isocyanate group, an alkyl group, an alkoxy group, a carboxylic ester group, an alkenyl group, an alkynyl group, an aryl group and a benzyl group. The electrolyte has stable electrochemical performance in a relatively wide temperature range, and the problem that the performance of the battery is reduced at an extreme temperature is relieved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte, a method for preparing the electrolyte, and a battery. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, energy storage and many other fields due to their advantages such as high energy density, long cycle life and low self-discharge. However, with the deepening development of the lithium-ion battery industry and the continuous expansion of battery application scenarios, the performance indicators related to startup and operation that lithium-ion batteries need to meet under service conditions are becoming more and more stringent, especially in terms of wide temperature range working ability. Taking power batteries as an example, under low temperature conditions in winter, there is a general situation where the discharge capacity is rapidly attenuated or even unable to discharge due to the decrease in electrolyte conductivity; and under high temperature conditions in summer, there will be battery performance degradation due to side reactions at the interface between electrolyte and electrode materials. Under the above extreme temperature conditions, the attenuation of battery performance will affect the battery life and even lead to the problem of weakened battery safety performance. Therefore, the development of a wide-temperature range lithium battery that can operate in a large temperature range and has stable electrochemical performance has become an important issue in promoting the development of the battery industry. Summary of the invention

[0003] The embodiments of the present application provide an electrolyte and a preparation method thereof, as well as a battery, which can improve the technical problem of poor performance of the battery at extreme temperatures.

[0004] In a first aspect, an embodiment of the present application provides an electrolyte, comprising: an electrolyte, an organic solvent and an additive, wherein the additive comprises a functional additive, and the functional additive satisfies the general structural formula (I):

[0005]

[0006] In the general structural formula (I), at least one of R3 and R4 satisfies the general structural formula (II):

[0007]

[0008] Wherein, n is a natural number, and R1, R2, R3, R4, and R5 are each independently selected from any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl, and benzyl.

[0009] In one embodiment, the alkyl group includes C 1-10 Alkyl; and / or, the alkoxy group includes C 1-10 Alkoxy; and / or, the carboxylate group comprises C 3-10 carboxylate group; and / or, the alkenyl group comprises C 3-10Alkenyl; and / or, the alkynyl group comprises C 3-10 Alkynyl; and / or, the aryl group comprises C 6-26 Aryl; and / or, the benzyl group includes C 7-27 Benzyl.

[0010] In one embodiment, the alkyl group includes at least one of a straight-chain alkyl group and a branched-chain alkyl group; and / or, the alkyl group includes at least one of a halogenated alkyl group and an unsubstituted alkyl group; and / or, the alkoxy group includes at least one of a straight-chain alkoxy group and a branched-chain alkoxy group; and / or, the alkoxy group includes at least one of a halogenated alkoxy group and an unsubstituted alkoxy group; and / or, the carboxylate group includes at least one of a straight-chain carboxylate group and a branched-chain carboxylate group; and / or, the alkenyl group includes at least one of a straight-chain alkenyl group and a branched-chain alkenyl group; and / or, the alkynyl group includes at least one of a straight-chain alkynyl group and a branched-chain alkynyl group; and / or, the aryl group includes at least one of an alkyl-substituted aryl group, a hydroxyl-substituted aryl group, a halogen-substituted aryl group and an unsubstituted aryl group; and / or, the benzyl group includes at least one of an alkyl-substituted benzyl group, a hydroxyl-substituted benzyl group, a halogen-substituted benzyl group and an unsubstituted benzyl group.

[0011] In one embodiment, the functional additive includes ethyl benzothiadiazole-5-acetate; or, n is less than 2.

[0012] In one embodiment, in the electrolyte, the content of the functional additive is 0.2-2 wt %.

[0013] In one embodiment, the additive further includes a carbonate additive.

[0014] In one embodiment, the carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate.

[0015] In one embodiment, in the electrolyte, the content of the carbonate additive is 0.2-3.0 wt %.

[0016] In one embodiment, the additive further includes a lithium salt additive.

[0017] In one embodiment, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate) and lithium difluorobis(oxalatophosphate).

[0018] In one embodiment, in the electrolyte, the content of the lithium salt additive is 0.5-1.5 wt %.

[0019] In one embodiment, the electrolyte includes LiPF6; and / or, in the electrolyte solution, the concentration of the electrolyte is 0.9 to 1.4 mol / L.

[0020] In one embodiment, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0021] In one embodiment, the organic solvent includes at least three of the ethylene carbonate, the propylene carbonate, the dimethyl carbonate, the diethyl carbonate and the ethyl methyl carbonate, and the volume percentage ratio of the ethylene carbonate, the propylene carbonate, the dimethyl carbonate, the diethyl carbonate and the ethyl methyl carbonate is (20-40): (0-5): (0-20): (30-50): (5-40).

[0022] In a second aspect, an embodiment of the present application further provides a method for preparing an electrolyte, wherein the electrolyte is the electrolyte described in the first aspect, comprising: adding an additive and an electrolyte to an organic solvent under a protective atmosphere, and mixing to obtain an electrolyte.

[0023] In a third aspect, an embodiment of the present application further provides a battery, comprising the electrolyte described in the first aspect, or the electrolyte prepared by the method described in the second aspect.

[0024] Beneficial effects of the embodiments of the present application:

[0025] In an embodiment of the present application, the electrolyte provided in the embodiment of the present application includes an electrolyte, an organic solvent and an additive, and the additive includes a functional additive, and the functional additive can promote the growth of a solid SEI film and a CEI film on the electrode surface. The functional additive contains at least a benzene ring, a heterocyclic ring and a chain carboxylic acid ester group, wherein the heterocyclic structure containing a delocalized conjugated double bond and a heteroatom can be oxidized and reduced during the charge and discharge process, and participates in the positive and negative electrode film formation (CEI film and SEI film, respectively); in this way, the N and S heteroatoms containing lone pairs of electrons in the heterocyclic ring can enter the film layer, so that the film layer has organic or inorganic N, and organic or inorganic S components, which can not only reduce the impedance of the film layer, but also improve the thermal stability of the film layer, reduce the side reactions occurring at the electrolyte / electrode interface under high temperature conditions, and improve the electrochemical performance of the electrolyte at high temperatures. The benzene ring and the chain carboxylate group in the functional additive are relatively stable. The functional additive will continue to remain in the electrolyte after losing the heterocyclic ring. The presence of the chain carboxylate group can reduce the freezing point of the organic solvent, and the chain carboxylate group is connected to the benzene ring, and the steric hindrance increases, which makes the electrolyte have a lower desolvation energy at low temperatures and improves the electrochemical performance of the electrolyte at low temperatures. The electrolyte provided by the embodiment of the present application has stable electrochemical performance in a wide temperature range, which can alleviate the problem of battery performance degradation at extreme temperatures. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0027] In this application, unless otherwise stated, directional words such as "upper" and "lower" generally refer to the upper and lower parts of a device in actual use or working state; while "inner" and "outer" refer to the outline of the device. In addition, in the description of this application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as labels and do not impose numerical requirements or establish an order.

[0028] In this application, "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0029] In the present application, "at least one" means one or more, and "plurality" means two or more. "One or several", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0030] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0031] As an important component of lithium-ion batteries, the performance of electrolyte directly affects the operating efficiency and stability of the battery. In the context of complex modification processes for positive and negative electrode materials of lithium-ion batteries, limited improvement space and high cost, the use of electrolyte additive technology with both high efficiency and cost advantages to develop wide-temperature range electrolytes with stable electrochemical performance over a large temperature range is expected to become a feasible way to solve the technical problems of the industry.

[0032] In a first aspect, an embodiment of the present application provides an electrolyte, comprising: an electrolyte, an organic solvent and an additive, wherein the additive comprises a functional additive, and the functional additive satisfies the general structural formula (I):

[0033]

[0034] In the general structural formula (I), R 2、 At least one of R3 and R4 satisfies the general structural formula (II):

[0035]

[0036] Wherein, n is a natural number, and R1, R2, R3, R4, and R5 are each independently selected from any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl, and benzyl.

[0037] In the general structural formula (I), R2 may satisfy the general structural formula (II), R3 may satisfy the general structural formula (II), R4 may satisfy the general structural formula (II), or both R3 and R4 may satisfy the general structural formula (II).

[0038] n is a natural number, and optionally, n is less than 2. As an example, n is 0 or 1.

[0039] R1 is any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl and benzyl.

[0040] When R2 does not satisfy the general structural formula (II), R2 is any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl and benzyl.

[0041] When R3 does not satisfy the general structural formula (II), R3 is any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl and benzyl.

[0042] When R4 does not satisfy the general structural formula (II), R4 is any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl and benzyl.

[0043] R5 is any one of hydrogen, alkyl, carboxylate, alkenyl, alkynyl, aryl and benzyl.

[0044] Here, the alkyl group may include at least one of a straight chain alkyl group and a branched chain alkyl group. Of course, the alkyl group may also include at least one of a halogenated alkyl group and an unsubstituted alkyl group. For example, the alkyl group includes C 1-10 Alkyl, that is, the number of C atoms in the alkyl is any one of 1 to 10. For example, the number of C atoms in the alkyl is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0045] The alkoxy group may include at least one of a straight chain alkoxy group and a branched chain alkoxy group. The alkoxy group may also include at least one of a halogenated alkoxy group and an unsubstituted alkoxy group. 1-10 The number of C atoms in the alkoxy group is any one of 1 to 10. For example, the number of C atoms in the alkoxy group is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0046] The carboxylate group may include at least one of a linear carboxylate group and a branched carboxylate group. 3-10 The carboxylate group, that is, the number of C atoms in the carboxylate group is any one of 3 to 10. For example, the number of C atoms in the carboxylate group is 3, 4, 5, 6, 7, 8, 9 or 10.

[0047] The alkenyl group may include at least one of a straight chain alkenyl group and a branched chain alkenyl group. 3-10 The number of C atoms in the alkenyl group is any one of 3 to 10. For example, the number of C atoms in the alkenyl group is 3, 4, 5, 6, 7, 8, 9 or 10.

[0048] The alkynyl group may include at least one of a straight chain alkynyl group and a branched chain alkynyl group. 3-10 Alkynyl, that is, the number of C atoms in the alkynyl is any one of 3 to 10. For example, the number of C atoms in the alkynyl is 3, 4, 5, 6, 7, 8, 9 or 10.

[0049] The aryl group may include at least one of an alkyl-substituted aryl group, a hydroxy-substituted aryl group, a halogen-substituted aryl group, and an unsubstituted aryl group. 6-26 Aryl, i.e., the number of C atoms in the aryl is any one of 6 to 26. For example, the number of C atoms in the aryl is 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 or 26.

[0050] The benzyl group may include at least one of an alkyl-substituted benzyl group, a hydroxy-substituted benzyl group, a halogen-substituted benzyl group, and an unsubstituted benzyl group. 7-27Benzyl, i.e., the number of C atoms in the benzyl group is any one of 7 to 27. For example, the number of C atoms in the benzyl group is 7, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26 or 27.

[0051] The electrolyte provided in the embodiment of the present application includes an electrolyte, an organic solvent and an additive, wherein the additive includes a functional additive, and the functional additive can promote the growth of a solid SEI (Solid Electrolyte Interface) film and a CEI (Cathode Electrolyte Interface) film on the electrode surface. The functional additive contains at least a benzene ring, a heterocyclic ring and a chain carboxylic acid ester group, wherein the heteroatoms in the heterocyclic structure containing a delocalized conjugated double bond can be oxidized and reduced during the charge and discharge process, and participate in the positive and negative electrode film formation (CEI film and SEI film, respectively); so that the film layer has organic or inorganic N, and organic or inorganic S components, these components can not only reduce the impedance of the film layer, but also improve the thermal stability of the film layer, reduce the side reactions occurring at the electrolyte / electrode interface under high temperature conditions, and improve the electrochemical performance of the electrolyte at high temperatures. The benzene ring and chain carboxylate group in the functional additive are relatively stable. The functional additive will continue to remain in the electrolyte after losing the heterocyclic ring. The presence of the chain carboxylate group can lower the freezing point of the organic solvent, and the chain carboxylate group is connected to the benzene ring, and the steric hindrance increases, which makes the electrolyte have a lower desolvation energy at low temperature and improves the electrochemical performance of the electrolyte at low temperature.

[0052] In addition, in functional additives, heteroatoms such as N and S containing lone pair electrons interact with SP 2 The planar conjugated structure formed by direct bonding of hybrid C can also capture H2O and corrosive acids such as PF5 and HF to inhibit the increase of electrolyte acidity during battery service, weaken the corrosion of acidic impurities on electrode materials, ensure the stability of CEI film or SEI film under service conditions, and effectively improve battery performance.

[0053] In some embodiments, the functional additive includes at least one of benzothiadiazole-5-acetic acid ethyl ester and benzothiadiazole-5-carboxylic acid methyl ester.

[0054] In some embodiments, the content of the functional additive in the electrolyte is 0.2wt% to 2wt%. Too little addition of the functional additive makes it difficult to form a dense SEI film or CEI film on the negative electrode, and too much addition of the functional additive will lead to excessive film formation, which will reduce the low-temperature discharge and high-temperature cycle performance of the battery. As an example, the content of the functional additive is 0.2wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt% or 2wt%.

[0055] In some embodiments, the additive further includes a carbonate additive. Carbonate additives can obtain electrons in preference to organic solvents in the electrolyte and form compounds to cover the surface of the negative electrode, thereby protecting the electrode material and increasing the battery capacity. In other words, carbonate additives can form a film at the negative electrode of the battery. In the present application, carbonate additives can be combined with functional additives to promote the formation of a dense SEI film on the surface of the negative electrode and enhance the thermal stability of the SEI film. Here, the carbonate additive can be at least one of a cyclic carbonate and a chain carbonate. As an example, the carbonate additive includes at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0056] In some embodiments, in the electrolyte, the content of carbonate additives is 0.2-3.0wt%. Too little addition of carbonate additives cannot form a dense SEI film, and too much addition of carbonate additives will lead to an increase in the impedance of the SEI film, poor low-temperature performance, and increased gas production under high-temperature conditions. As an example, the content of carbonate additives is 0.2wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt% or 3wt%.

[0057] In some embodiments, the additive also includes a lithium salt additive. Lithium salt additives refer to lithium salt substances. By adding lithium salt additives to the electrolyte, the conductivity and stability of the electrolyte can be effectively enhanced, the electrochemical properties of the electrolyte at low temperatures can be improved, and the energy density of the battery can be increased. In addition, lithium salt additives also have the function of positive and negative electrode film formation. In the present application, lithium salt additives can be combined with functional additives to promote the formation of dense film layers on the surfaces of the positive and negative electrodes, especially the generated film layers are relatively dense, which can inhibit the dissolution of positive electrode metal ions, weaken the damage of metal ions to the negative electrode film layer, and improve the thermal stability of film formation. As an example, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB) and lithium difluorobis(oxalatophosphate) (LiODFP).

[0058] In some embodiments, the content of the lithium salt additive in the electrolyte is 0.5-1.5wt%. Too little addition of the lithium salt additive cannot form a dense film layer, and too much addition of the lithium salt additive will lead to gas production and high temperature and / or low temperature performance degradation. As an example, the content of the lithium salt additive is 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%.

[0059] The electrolyte also includes electrolytes. The electrolyte can dissociate lithium ions in the solvent to move freely and participate in electrochemical reactions. In lithium-ion batteries, the electrolyte can include at least one of inorganic electrolyte salts (such as LiBF4, LiClO4, LiAlF4, etc.), fluorophosphate electrolyte salts (such as LiPF6, etc.), carboxylic acid electrolyte salts (such as HCO2Li, CH3CO2Li, etc.) and imide electrolyte salts (such as cyclic 1,2-perfluoroethanedisulfonyl imide lithium, etc.).

[0060] In some embodiments, the electrolyte includes lithium hexafluorophosphate (LiPF6). LiPF6 has a wide electrochemical stability window and high thermal stability, can form a SEI film on the negative electrode, and can effectively passivate the positive electrode current collector to prevent it from dissolving. Thanks to these properties, lithium hexafluorophosphate is widely used in lithium-ion battery electrolytes.

[0061] In some embodiments, in the electrolyte solution, the concentration of the electrolyte is 0.9 to 1.4 mol / L. As an example, the concentration of the electrolyte is 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L or 1.4 mol / L.

[0062] The electrolyte also includes a non-aqueous solvent. The non-aqueous solvent is an organic solvent. Optionally, the organic solvent includes an organic carbonate solvent, and the functional additive can better cooperate with the organic carbonate solvent to reduce the freezing point and desolvation energy of the electrolyte, and improve the electrochemical performance of the electrolyte at high and low temperatures. As an example, the organic carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0063] In some embodiments, the organic solvent includes at least three of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The volume percentage ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate is (20-40): (0-5): (0-20): (30-50): (5-40). As an example, in the organic solvent, the volume percentage of ethylene carbonate is 20 vol%, 25 vol%, 30 vol%, 35 vol% or 40 vol%; the volume percentage of propylene carbonate is 0 vol%, 1 vol%, 2 vol%, 3 vol%, 4 vol% or 5 vol%; the volume percentage of dimethyl carbonate is 0 vol%, 5 vol%, 10 vol%, 15 vol% or 20 vol%; the volume percentage of diethyl carbonate is 30 vol%, 35 vol%, 40 vol%, 45 vol% or 50 vol%; the volume percentage of ethyl methyl carbonate is 5 vol%, 10 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol%, 35 vol% or 40 vol%.

[0064] In some embodiments, in the electrolyte, the additives include functional additives, carbonate additives and lithium salt additives, the content of the functional additives is 0.2-2wt%, the content of the carbonate additives is 0.2-3.0wt%, and the content of the lithium salt additives is 0.5-1.5wt%. Specifically, the additives include functional additives, carbonate additives and lithium salt additives, carbonate additives can form a film on the negative electrode of the battery, and functional additives and lithium salt additives have the function of forming a film on the positive and negative electrodes. By utilizing the synergistic effect between the above-mentioned different additives, the generated SEI film and CEI film can have low impedance and good thermal stability, and the electrolyte has stable electrochemical properties in a wide temperature range of -20°C to 45°C, and the cycle performance and discharge capacity of the battery are improved.

[0065] In a second aspect, an embodiment of the present application further provides a method for preparing an electrolyte, which is used to prepare the electrolyte provided in the first aspect and comprises: adding additives and electrolytes to an organic solvent under a protective atmosphere, and mixing to obtain an electrolyte.

[0066] The preparation method of the electrolyte provided in the embodiment of the present application is simple and easy to implement.

[0067] In some embodiments, the preparation method of the electrolyte is specifically as follows: in an argon atmosphere, a carbonate additive, a lithium salt additive and a functional additive are added to an organic solvent, and finally lithium hexafluorophosphate is added and stirred at low temperature to mix evenly. Optionally, the carbonate additive includes one or both of VC and FEC. Optionally, the lithium salt additive includes one or both of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate) and lithium difluorobis(oxalatophosphate). Optionally, the functional additive includes ethyl benzothiadiazole-5-acetate.

[0068] In a third aspect, an embodiment of the present application further provides a battery, comprising the electrolyte provided in the first aspect, or the electrolyte prepared by the method provided in the second aspect.

[0069] The battery provided in the embodiments of the present application has stable electrochemical performance within a wide temperature range.

[0070] In some embodiments, the battery is a lithium-ion battery. The lithium-ion battery also includes a positive electrode, a negative electrode and a separator. As an example, the positive electrode includes a positive electrode active material, and the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium iron manganese phosphate and lithium-rich manganese-based positive electrode materials. As an example, the negative electrode includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, silicon and silicon carbon. In other embodiments, the battery may also be a sodium-ion battery.

[0071] The following describes it in detail with reference to specific embodiments.

[0072] Example 1

[0073] Preparation of electrolyte: Under an argon atmosphere, add a formulated amount of carbonate additives, lithium salt additives and functional additives to an organic solvent, then add an electrolyte salt, stir and mix at a temperature of 10°C to obtain an electrolyte. That is to say, the prepared electrolyte includes an organic solvent, an electrolyte salt and an additive. Specifically, the electrolyte salt is lithium hexafluorophosphate (LiPF6), and the concentration of lithium hexafluorophosphate in the electrolyte is 1.0 mol / L. The organic solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC. Based on the total volume of the organic solvent as 100 vol%, the volume fraction of ethylene carbonate is 30 vol%, the volume fraction of diethyl carbonate is 40 vol%, and the volume fraction of ethyl methyl carbonate is 30 vol%.

[0074] The additives include carbonate additives, lithium salt additives and functional additives. Among them, the carbonate additive is vinylene carbonate (VC), and its mass fraction in the electrolyte is 2wt%; the lithium salt additive is lithium difluorophosphate (LiPO2F2), and its mass fraction in the electrolyte is 1.0wt%; the functional additive is benzothiadiazole-5-ethyl acetate (CAS No. 195505-47-6), and the structural formula of benzothiadiazole-5-ethyl acetate is as follows:

[0075]

[0076] The mass fraction of ethyl benzothiadiazole-5-acetate in the electrolyte is 0.5wt%.

[0077] Preparation of lithium-ion battery: negative electrode material graphite, conductive agent acetylene black, binder carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) are prepared into slurry at a mass ratio of 94:1:2:3 and coated on copper foil current collector, vacuum dried to obtain negative electrode plate; positive electrode material lithium iron phosphate, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) are prepared into slurry at a mass ratio of 94:3:3 and coated on aluminum foil current collector, vacuum dried to obtain positive electrode plate. Positive electrode plate, negative electrode plate, Celgard2400 separator and the above electrolyte are assembled into soft pack battery.

[0078] Example 2

[0079] The mass fraction of ethyl benzothiadiazole-5-acetate in the electrolyte is 0.2 wt %, and the rest is the same as in Example 1.

[0080] Example 3

[0081] The mass fraction of ethyl benzothiadiazole-5-acetate in the electrolyte is 1.0 wt %, and the rest is the same as in Example 1.

[0082] Example 4

[0083] The mass fraction of ethyl benzothiadiazole-5-acetate in the electrolyte is 2.0 wt %, and the rest is the same as in Example 1.

[0084] Example 5

[0085] The mass fraction of vinylene carbonate (VC) in the electrolyte is 1 wt %, and the rest is the same as in Example 1.

[0086] Example 6

[0087] The mass fraction of vinylene carbonate (VC) in the electrolyte is 0.2 wt %, and the rest is the same as in Example 1.

[0088] Example 7

[0089] The mass fraction of vinylene carbonate (VC) in the electrolyte is 3.0 wt %, and the rest is the same as in Example 1.

[0090] Example 8

[0091] The mass fraction of lithium difluorophosphate (LiPO2F2) in the electrolyte is 0.5wt%, and the rest is the same as in Example 1.

[0092] Example 9

[0093] The mass fraction of lithium difluorophosphate (LiPO2F2) in the electrolyte is 1.5wt%, and the rest is the same as in Example 1.

[0094] Example 10

[0095] The carbonate additive in the electrolyte was replaced with fluoroethylene carbonate (FEC), and the rest was the same as in Example 1.

[0096] Embodiment 11

[0097] The lithium salt additive in the electrolyte was replaced with lithium bis(fluorosulfonyl)imide (LiFSI), and the rest was the same as in Example 1.

[0098] Example 12

[0099] The lithium salt additive in the electrolyte was replaced with lithium bis(oxalatoborate) (LiBOB), and the rest was the same as in Example 1.

[0100] Embodiment 13

[0101] The lithium salt additive in the electrolyte was replaced with lithium difluorobis(oxalyl)phosphate (LiODFP), and the rest was the same as in Example 1.

[0102] Embodiment 14

[0103] The functional additive in the electrolyte was replaced with 0.5 wt% benzothiadiazole-5-carboxylic acid methyl ester (CAS No. 175204-21-4).

[0104]

[0105] The rest is the same as Example 1.

[0106] Embodiment 15

[0107] Lithium difluorophosphate (LiPO2F2) and vinylene carbonate (VC) are not added to the electrolyte, and the content of ethyl benzothiadiazole-5-acetate in the electrolyte is 1.5 wt %. The rest is the same as in Example 1.

[0108] Example 16

[0109] Lithium difluorophosphate (LiPO2F2) is not added to the electrolyte, the content of ethyl benzothiadiazole-5-acetate in the electrolyte is 0.5wt%, the content of vinylene carbonate (VC) in the electrolyte is 1wt%, and the rest is the same as in Example 1.

[0110] Embodiment 17

[0111] No vinylene carbonate (VC) is added to the electrolyte, the content of ethyl benzothiadiazole-5-acetate in the electrolyte is 0.5wt%, the content of lithium difluorophosphate (LiPO2F2) in the electrolyte is 1wt%, and the rest is the same as in Example 1.

[0112] Embodiment 18

[0113] The content of benzothiadiazole-5-acetic acid ethyl ester in the electrolyte is 0.5wt%, the content of vinylene carbonate (VC) in the electrolyte is 0.5wt%, the content of lithium difluorophosphate (LiPO2F2) in the electrolyte is 0.5wt%, and the rest is the same as Example 1.

[0114] Comparative Example 1

[0115] No additives were added to the electrolyte, and the rest was the same as in Example 1.

[0116] Comparative Example 2

[0117] No benzothiadiazole-5-acetic acid ethyl ester and lithium difluorophosphate (LiPO2F2) are added to the electrolyte, and the content of vinylene carbonate (VC) in the electrolyte is 2 wt %. The rest is the same as in Example 1.

[0118] Comparative Example 3

[0119] No benzothiadiazole-5-acetic acid ethyl ester and vinylene carbonate (VC) are added to the electrolyte, and the content of lithium difluorophosphate (LiPO2F2) in the electrolyte is 1 wt %. The rest is the same as in Example 1.

[0120] Table 1

[0121]

[0122] The following electrochemical tests were performed on the lithium-ion batteries prepared in the above embodiments and comparative examples using a charge and discharge test cabinet. The test results are recorded in Table 2.

[0123] 1. Cycle performance test of lithium-ion battery: At 45°C, charge the lithium-ion battery at 1C (nominal capacity) constant current to 3.7V, then charge at 3.7V constant voltage to current ≤0.02C, leave for 10 minutes, and then discharge at 1C constant current to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times at 45°C under the above conditions.

[0124] 2. Low temperature discharge performance test of lithium-ion battery: After placing the lithium-ion battery in a 25℃ constant temperature box, discharge the lithium-ion battery to 2.5V at a nominal rate of 0.33C and let it stand for 10 minutes. Then, use the constant current and constant voltage method to charge the battery to 3.7V at a rate of 0.33C and cut off the current at 0.02C. Then adjust the temperature of the constant temperature box to -20℃. After the temperature stabilizes and the battery cell is left for 4 hours, discharge it to 2.5V at a constant current of 0.33C and record the discharge capacity C2. The -20℃ discharge capacity retention rate = C2 / C.

[0125] Table 2

[0126]

[0127]

[0128] Result analysis:

[0129] Generally, the lithium ion transfer process is fast under high temperature conditions, the film formation is denser and more stable, the corresponding interface side reactions are smaller under high temperature conditions, and the cycle performance is better; while the lithium ion mass transfer process is limited under low temperature conditions, and the processes such as lithium ions passing through the SEI membrane and desolvation energy become the rate-limiting steps. The slower the lithium ion transfer kinetics, the worse the low temperature performance.

[0130] The mass fraction of the functional additive benzothiadiazole-5-ethyl acetate in Examples 1 to 4 is different. As the content of benzothiadiazole-5-ethyl acetate increases, the capacity of the battery at 45°C for 1000 cycles increases first and then decreases slightly, and the discharge capacity of the battery at -20°C also increases first and then decreases significantly. This is because when the amount of benzothiadiazole-5-ethyl acetate added is small, the thickness of the solid SEI film and / or CEI film formed on the electrode surface is also relatively thin. As the amount of benzothiadiazole-5-ethyl acetate added increases slightly, the density of the solid SEI film and / or CEI film on the electrode surface increases, so that the less the interface side reaction under high temperature conditions, the better the cycle performance of the battery; and benzothiadiazole-5-ethyl acetate introduces N and S heteroatoms to the SEI film and / or CEI film, so that the impedance of the SEI film and / or CEI film is reduced, and the electrolyte has a lower desolvation energy at low temperature, so that the low temperature performance of the battery is also improved. However, as the amount of benzothiadiazole-5-ethyl acetate continues to increase, the thickness of the solid SEI film and / or CEI film will increase rapidly, the stability of the SEI film and / or CEI film will be improved, and the battery cycle performance is still relatively good, but the increase in the thickness of the SEI film and / or CEI film will cause the impedance to increase rapidly, thereby causing the low temperature performance of the battery to deteriorate. In Example 1, Implementation 5 to Example 7, the mass fraction of carbonate additive vinyl carbonate (VC) is different. As the content of VC increases, the capacity of the battery for 1000 cycles at 45°C increases first and then decreases, and the discharge capacity of the battery at -20°C also increases first and then decreases. Vinyl carbonate (VC) can promote the formation of a dense SEI film on the negative electrode surface and improve the thermal stability of the SEI film. Therefore, as the content of VC increases, the film quality of the SEI film is improved, and the cycle performance and low temperature performance of the battery are improved, but too much VC content will cause the organic content in the SEI film to increase, the impedance increases, and the low temperature performance of the battery deteriorates.

[0131] In Example 1, Implementation 8 to Example 9, the mass fraction of lithium salt additive lithium difluorophosphate (LiPO2F2) is different. As the content of LiPO2F2 increases, the capacity of the battery at 45°C for 1000 cycles first increases and then remains unchanged, while the discharge capacity of the battery at -20°C also increases first and then decreases. Lithium difluorophosphate can effectively enhance the conductivity of the electrolyte, and increasing the amount of lithium difluorophosphate added can improve the electrochemical properties of the electrolyte at low temperatures. Moreover, lithium difluorophosphate can also promote the formation of dense SEI and CEI films on the surfaces of the positive and negative electrodes, improve the thermal stability of the film layer, and improve the cycle performance of the battery. However, excessive addition of lithium difluorophosphate can also lead to an excessively thick film layer, which in turn leads to an increase in impedance and a decrease in low-temperature performance.

[0132] In Example 1, Implementation 10 to Example 14, the types of carbonate additives, lithium salt additives or functional additives were changed. From the results, it can be seen that the capacity retention rate of the battery after 1000 cycles at 45°C and the discharge capacity at -20°C are both good.

[0133] In Examples 15 to 18, the total amount of additives is kept equal, and the performance of the battery using a single type of additive is not as good as that of the battery using a combination of multiple additives, especially the discharge capacity of the battery at low temperature is significantly improved, which shows that there is a synergistic effect between the functional additive ethyl benzothiadiazole-5-acetate, the carbonate additive vinylene carbonate and the lithium salt additive lithium difluorophosphate, and the three together improve the discharge performance of the battery at high and low temperatures.

[0134] Comparison of Example 1 with Comparative Examples 1 to 3 shows that when no additive is added to the electrolyte (Comparative Example 1) and when no functional additive benzothiadiazole-5-ethyl acetate is added (Comparative Example 2 and Comparative Example 3), the cycle performance of the battery under high temperature conditions is significantly deteriorated, and the discharge performance of the battery under low temperature conditions is also deteriorated. This shows that the functional additive benzothiadiazole-5-ethyl acetate has the effect of improving the high and low temperature performance of the battery. The above is a detailed introduction to the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte, characterized in that: include: Electrolyte, organic solvent and additives, wherein the additives include functional additives, and the functional additives satisfy the general structural formula (I): In the general structural formula (I), at least one of R3 and R4 satisfies the general structural formula (II): Wherein, n is a natural number, and R1, R2, R3, R4, and R5 are each independently selected from any one of hydrogen, halogen, cyano, isocyanate, alkyl, alkoxy, carboxylate, alkenyl, alkynyl, aryl, and benzyl.

2. The electrolyte according to claim 1, characterized in that The alkyl group includes C 1-10 Alkyl; and / or, the alkoxy group includes C 1-10 Alkoxy; and / or, the carboxylate group comprises C 3-10 carboxylate group; and / or, the alkenyl group comprises C 3-10 Alkenyl; and / or, the alkynyl group comprises C 3-10 Alkynyl; and / or, the aryl group comprises C 6-26 Aryl; and / or, the benzyl group includes C 7-27 Benzyl.

3. The electrolyte according to claim 1, characterized in that The alkyl group includes at least one of a straight-chain alkyl group and a branched-chain alkyl group; and / or, the alkyl group includes at least one of a halogenated alkyl group and an unsubstituted alkyl group; and / or, the alkoxy group includes at least one of a straight-chain alkoxy group and a branched-chain alkoxy group; and / or, the alkoxy group includes at least one of a halogenated alkoxy group and an unsubstituted alkoxy group; and / or, the carboxylate group includes at least one of a straight-chain carboxylate group and a branched-chain carboxylate group; and / or, the alkenyl group includes at least one of a straight-chain alkenyl group and a branched-chain alkenyl group; and / or, the alkynyl group includes at least one of a straight-chain alkynyl group and a branched-chain alkynyl group; and / or, the aryl group includes at least one of an alkyl-substituted aryl group, a hydroxyl-substituted aryl group, a halogen-substituted aryl group and an unsubstituted aryl group; and / or, the benzyl group includes at least one of an alkyl-substituted benzyl group, a hydroxyl-substituted benzyl group, a halogen-substituted benzyl group and an unsubstituted benzyl group.

4. The electrolyte according to claim 1, characterized in that The functional additive includes ethyl benzothiadiazole-5-acetate; or, n is less than 2.

5. The electrolyte according to claim 1, characterized in that In the electrolyte, the content of the functional additive is 0.2-2 wt %.

6. The electrolyte according to claim 1, characterized in that The additives also include carbonate additives.

7. The electrolyte according to claim 6, characterized in that In the electrolyte, the content of the carbonate additive is 0.2-3.0 wt %; and / or the carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate.

8. The electrolyte according to claim 1, characterized in that The additives also include lithium salt additives.

9. The electrolyte according to claim 8, characterized in that In the electrolyte, the content of the lithium salt additive is 0.5-1.5 wt %; and / or the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate) and lithium difluorobis(oxalatophosphate).

10. The electrolyte according to any one of claims 1 to 9, characterized in that: The electrolyte includes LiPF6; and / or, in the electrolyte solution, the concentration of the electrolyte is 0.9 to 1.4 mol / L.

11. The electrolyte according to any one of claims 1 to 9, characterized in that: The organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

12. The electrolyte according to claim 11, characterized in that The organic solvent comprises at least three of the ethylene carbonate, the propylene carbonate, the dimethyl carbonate, the diethyl carbonate and the ethyl methyl carbonate, and the volume ratio of the ethylene carbonate, the propylene carbonate, the dimethyl carbonate, the diethyl carbonate and the ethyl methyl carbonate is (20-40): (0-5): (0-20): (30-50: (5-40).

13. A method for preparing an electrolyte, wherein the electrolyte is the electrolyte according to any one of claims 1 to 12, characterized in that: include: Under a protective atmosphere, additives and electrolytes are added to an organic solvent and mixed to obtain an electrolyte.

14. A battery, characterized in that: The invention comprises the electrolyte according to any one of claims 1 to 12, or the electrolyte prepared by the method according to claim 13.

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