Electrolyte additive, electrolyte, and battery

Abstract

The present disclosure provides an electrolyte additive, an electrolyte, and a battery. The electrolyte additive comprises: a first additive and a second additive. The structure of the first additive is as represented by formula 1, and the second additive comprises a trinitrile substance.

Description

Electrolyte additive, electrolyte, battery

[0001] The present application claims priority to the Chinese patent application No. 202410475714.1, filed on April 19, 2024, and entitled "Electrolyte additive, electrolyte, battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of electrolyte, in particular, to an electrolyte additive, an electrolyte, and a battery. BACKGROUND

[0003] With the rapid development of markets such as pure electric vehicles, smart homes, electric tools, and intelligent transportation, consumers' requirements for the performance of batteries are constantly increasing. Metal ion batteries, such as lithium ion batteries, sodium ion batteries, etc., are widely used in consumer electronics and energy storage and power batteries due to their high energy density, long cycle life, and small self-discharge. Generally, a battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte includes a solvent, an electrolyte salt, and an electrolyte additive. By adding an electrolyte additive to the electrolyte, the performance of the battery in terms of fast charging and discharging, cycle life, storage stability, etc. can be improved to some extent. However, the current electrolyte additive is not sufficient to meet the needs of consumers in terms of battery performance improvement, and further improvement is still needed.

[0004] SUMMARY

[0005] In a first aspect of the present application, an electrolyte additive is provided, comprising: a first additive and a second additive, the structure of the first additive satisfies formula 1,

[0006] The second additive includes a tricyanide substance. In this way, the high-temperature cycle performance of the battery using the electrolyte additive can be effectively improved.

[0007] In some embodiments, the mass fraction of the first additive in the electrolyte additive is w1, the mass fraction of the second additive in the electrolyte additive is w2, and w1 / w2 is 0.9-1.1. In this way, the high-temperature cycle performance of the battery can be further improved.

[0008] In some embodiments, the second additive includes at least one of 1,3,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, and 1,2,3-tris(2-cyanooxy)propane. In this way, the electrical performance of the electrolyte can be improved.

[0009] In some embodiments, a third additive is further included, and the third additive includes at least one of hexamethylene diisocyanate and trimethylsilyl isothiocyanate. Thereby, the cycle life of the battery is further improved.

[0010] In some embodiments, a fourth additive is further included, and the fourth additive includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, 1,3- propene sultone, 1,3-propane sultone, ethylene sulfate, and methane dimesylate. Thereby, the formation of SEI film on the surface of the negative active material is facilitated.

[0011] In a second aspect of the present application, an electrolyte is provided, which includes the aforementioned electrolyte additive. Thereby, the electrolyte has all the features and advantages of the aforementioned electrolyte additive, which will not be repeated here.

[0012] In some embodiments, the mass fraction of the first additive in the electrolyte is 0.1%-2%. Thereby, the cycle life of the battery is improved, and the internal resistance of the battery is reduced.

[0013] In some embodiments, the mass fraction of the second additive in the electrolyte is 0.1%-2%. Thereby, the electrical performance of the battery is improved.

[0014] In some embodiments, the mass fraction of the third additive in the electrolyte is 0.1%-0.3%. Thereby, the cycle life of the battery is further improved.

[0015] In some embodiments, the mass fraction of the fourth additive in the electrolyte is 0.1%-10%. Thereby, the cycle performance of the battery is improved.

[0016] In some embodiments, an electrolyte salt is further included, and the electrolyte salt includes at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, LiPF4C2O4, and NaFP6. Thereby, the ionic conductivity of the electrolyte is improved.

[0017] In some embodiments, the mass fraction of the electrolyte salt in the electrolyte is 8wt%-20wt%. Thereby, the electrolyte has both high ionic conductivity and low cost.

[0018] In a third aspect of the present application, a battery is provided, which includes the aforementioned electrolyte additive, and / or, the aforementioned electrolyte. Thereby, the battery has all the features and advantages of the aforementioned electrolyte additive and electrolyte, which will not be repeated here.

[0019] In some embodiments, further comprising a positive electrode tab, the positive electrode tab comprising a positive electrode current collector and a positive electrode active material layer located at least on one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a mass fraction of manganese element in the positive electrode active material being greater than or equal to 25%. Thus, the cost of the positive electrode active material can be reduced, and the discharge voltage platform of the battery can be improved.

[0020] In some embodiments, the positive electrode active material satisfies the general formula LiMn x Fe 1－x PO4, 0.25 < x < 1; and / or, LiNi 1-y Mn y O, 0.25 < y < 1; and / or, Na z MnO2, 0.5 < z < 1. DETAILED DESCRIPTION

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application; and various parameters mentioned in the application can be measured by various means commonly used in the art (for example, can be tested according to the methods given in the embodiments of the application), unless otherwise specified.

[0022] The terms "comprising" and "having" and any variations thereof used in the specification and claims herein are open-ended, that is, they mean including, but not limited to, the contents of the application.

[0023] In the description of the application, all the numbers disclosed herein are approximate values. The value of each number can vary by 10% or less, or a reasonable value recognized by those skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

[0024] In the description of the application, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implying the number of the indicated technical features. "First feature", "second feature" can include one or more of the features.

[0025] In the description of the application, "A and / or B" can include any one of the cases of A alone, B alone, A and B, where A and B are only used as examples, which can be any technical feature connected by "and / or" in the application.

[0026] Manganese is a common element on earth, and its resource reserves are sufficient, so that manganese-based positive active materials become an alternative solution to alleviate resource pressure. Manganese-based positive active materials also become an important research direction in the field of metal-ion batteries due to their advantages such as high specific capacity, low cost, good thermal stability, etc. Taking lithium-ion batteries as an example, during the charging and discharging process of the battery, the Mn 4+ in the manganese-based positive active material will undergo disproportionation reaction and dissolve into the electrolyte in the form of Mn 2+ . The manganese ions dissolved in the electrolyte will migrate and deposit on the surface of the negative active material, damaging the SEI film (Solid Electrolyte Interface) on the surface of the negative active material. After the SEI film is broken, the exposed negative active material will react with the electrolyte, causing the decomposition of lithium salt to generate HF, causing the positive material to be corroded, and further causing the dissolution of Mn. This process is repeated, not only causing irreversible loss of lithium ions, but also causing consumption of electrolyte, and the cycle performance of the battery is significantly reduced. In addition, when the battery is under high temperature conditions, the positive active material may undergo lattice collapse or structure transformation, causing manganese ions to be released from the structure, and the movement rate of manganese ions increases significantly, causing the speed of manganese ions to be released from the crystal structure to increase, and the chemical reaction rate of manganese dissolution to increase significantly.

[0027] In the present application, the first additive and the second additive are used in combination, wherein the second additive is a tricyanide substance. The molecular structure of the tricyanide additive is stable, and it has good oxidation resistance. The cyanide group of the tricyanide substance can complex with the manganese ions dissolved from the positive active material, reducing the damage of the manganese ions to the SEI film on the surface of the negative active material. Further, since the first additive has a symmetrical structure, and there is an intermolecular force between the first additive and the second additive, the triangular structure of the second additive (i.e. the triangular structure formed by the connecting lines between adjacent cyanide groups in the second additive) and the symmetrical structure of the first additive together realize the surrounding of the manganese ions. Specifically, the cyanide group of the second additive is used to complex with the manganese ions, and the interaction between the first additive and the second additive is used to fix the manganese ions in the surrounding structure formed by the first additive and the second additive, so as to effectively enhance the complexing effect of the electrolyte additive on the free manganese ions, effectively reduce the migration of the manganese ions to the surface of the negative active material, reduce the side reaction of the manganese ions with other substances in the electrolyte, and help the positive and negative electrodes of the battery to obtain good interface stability, and improve the cycle performance of the battery, especially the high-temperature cycle performance.

[0028] In the first aspect of the present application, an electrolyte additive is provided, comprising: a first additive and a second additive, the structure of the first additive satisfies formula 1,

[0029] The second additive comprises a tricyanide substance. Thus, by the synergistic effect of the first additive and the second additive, the dissolved transition metal ions, for example manganese ions, in the positive electrode active material can be effectively captured, thereby the deposition of the transition metal ions on the surface of the negative electrode active material can be effectively reduced, the structural stability of the SEI film on the surface of the negative electrode active material can be improved, and thus the cycle performance, especially the high-temperature cycle performance, of the battery using the electrolyte additive can be effectively improved.

[0030] In some embodiments, the first additive can participate in the formation of the SEI film on the surface of the negative electrode active material as a film-forming additive, and thus the first additive can not only capture the transition metal ions together with the second additive in the electrolyte, but also capture the transition metal ions in the SEI film on the surface of the negative electrode active material, thereby reducing the damage of the transition metal ions to the negative electrode active material.

[0031] In some embodiments, the mass fraction of the first additive in the electrolyte additive is w1, the mass fraction of the second additive in the electrolyte additive is w2, and w1 / w2 is 0.9-1.1. Thus, the high-temperature cycle performance of the battery can be further improved.

[0032] As an example, w1 / w2 can be 0.9, 0.95, 1.0, 1.05, or 1.1.

[0033] The cyano group in the second additive can complex with the transition metal ions, for example manganese ions, dissolved in the positive electrode active material, and weaken the damage of the manganese ions to the SEI film on the surface of the negative electrode active material. However, when the content of the cyano group in the electrolyte additive is too large, the internal resistance of the battery will increase, which will deteriorate the performance of the battery. The weak intermolecular force between the sulfur-oxygen double bond in the first additive and the transition metal ions can bind the transition metal ions to some extent. By using the first additive and the second additive satisfying the aforementioned ratio, and by partially replacing the second additive with the first additive, the amount of the second additive can be reduced, the internal resistance of the battery can be reduced, and the synergistic effect of the first additive and the second additive can be utilized to further reduce the deposition of free transition metal ions on the surface of the negative electrode active material.

[0034] In some embodiments, the second additive can comprise at least one of 1,3,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, and 1,2,3-tris(2-cyanato)propane. Thus, the electrical performance of the battery can be improved.

[0035] When the second additive comprises the aforementioned substances, the carbon chain length of the second additive is moderate, the molecular weight is moderate, the cyano group density is high, the complexing ability for the transition metal ions is high, and the electrochemical performance is excellent.

[0036] In some embodiments, a third additive is further included, the third additive including at least one of hexamethylene diisocyanate, trimethylsilyl isothiocyanate. Thereby, the cycle life of the battery is further improved.

[0037] The moisture in the battery will have an irreversible reaction with lithium salt (such as lithium hexafluorophosphate) in the electrolyte inside the battery to generate hydrofluoric acid (HF) and other harmful byproducts. The trace amount of acidic substances (such as hydrofluoric acid HF) in the electrolyte will corrode the positive active material and accelerate the dissolution of transition metal ions in the positive active material, further reducing the cycle performance of the battery. The addition of the third additive can have physical adsorption or chemical reaction with the water and acidic substances in the battery, thereby reducing the acidic substances in the electrolyte to a low level and slowing down the dissolution of transition metal ions in the positive active material.

[0038] In some embodiments, a fourth additive is further included, the fourth additive including at least one of fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propylene sulfite, 1,3-propane sulfite, ethylene sulfate, methane disulfite. Thereby, the cycle performance of the battery is improved.

[0039] The addition of the fourth additive can form SEI (Solid Electrolyte Interface) on the surface of the negative active material and CEI (Cathode Electrolyte Interface) on the surface of the positive active material. SEI and CEI respectively form films on the surfaces of the negative active material and the positive active material, which can effectively alleviate the problem of side reactions occurring after the active material directly contacts with the electrolyte.

[0040] In the second aspect of the present application, an electrolyte is provided, including the electrolyte additive described above. Thereby, the electrolyte has all the characteristics and advantages of the electrolyte additive described above, which will not be repeated here.

[0041] In some embodiments, the mass fraction of the first additive in the electrolyte is 0.1%-2%. Thereby, the cycle life of the battery is improved and the internal resistance of the battery is reduced.

[0042] For example, the mass fraction of the first additive in the electrolyte can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0%.

[0043] In some embodiments, the mass fraction of the second additive in the electrolyte is 0.1%-2%. In this way, the electrical performance of the battery can be improved.

[0044] For example, the mass fraction of the second additive in the electrolyte can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0045] When the mass fractions of the first additive and the second additive are within the aforementioned ranges, the mass fraction w1 of the first additive and the mass fraction w2 of the second additive can satisfy w1 / w2 is 0.9-1.1. By partially replacing the second additive with the first additive, the amount of the second additive can be reduced, the internal resistance of the battery can be reduced, and the deposition of free transition metal ions on the surface of the negative active material can be effectively reduced by the synergistic effect of the first additive and the second additive, thereby improving the cycle performance of the battery.

[0046] In some embodiments, the mass fraction of the third additive in the electrolyte is 0.1%-0.3%. In this way, the cycle life of the battery can be further improved.

[0047] For example, the mass fraction of the third additive in the electrolyte can be 0.1%, 0.15%, 0.2%, 0.25%, or 0.3%.

[0048] When the mass fraction of the third additive is within the aforementioned range, the dissolution of transition metal ions in the positive active material can be effectively slowed down by adding a small amount of water and acid inhibitor, thereby reducing the manufacturing cost.

[0049] In some embodiments, the mass fraction of the fourth additive in the electrolyte is 0.1%-10%. In this way, the cycle performance of the battery can be improved.

[0050] For example, the mass fraction of the fourth additive in the electrolyte can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, or 10.0%.

[0051] When the mass fraction of the fourth additive is within the aforementioned range, it is helpful to form a uniform and dense SEI (Solid Electrolyte Interface) on the surface of the negative active material, and form a uniform and dense CEI (Cathode Electrolyte Interface) on the surface of the positive active material, and alleviate the problem of side reactions after the active material directly contacts with the electrolyte.

[0052] In some embodiments, further comprising an electrolyte salt, the electrolyte salt comprising at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, LiPF4C2O4, and NaFP6. In this way, the ionic conductivity of the electrolyte can be improved.

[0053] In some embodiments, the mass fraction of the electrolyte salt in the electrolyte is 8wt%-20wt%. In this way, the electrolyte can have both higher ionic conductivity and lower cost.

[0054] The cost proportion of the electrolyte salt in the electrolyte is high, when the mass fraction of the electrolyte salt in the electrolyte is within the aforementioned range, the electrolyte salt can be fully dissolved in the solvent, and the electrolyte can have both higher ionic conductivity and lower manufacturing cost.

[0055] In some embodiments, the solvent of the electrolyte comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

[0056] The solvent in the electrolyte is an important carrier for ion transmission, and when the electrolyte salt is dissolved, it can have higher ionic conductivity, and then by selecting the aforementioned solvent, the cycle life, charge-discharge rate, high-temperature performance, low-temperature performance, and energy density of the battery can be improved.

[0057] In some embodiments, the mass fraction of the solvent in the electrolyte can be 50wt%-80wt%. In this way, it is helpful to fully dissolve the electrolyte salt and improve the conductivity of the electrolyte.

[0058] In a third aspect of the present application, a battery is provided, comprising the aforementioned electrolyte additive, and / or, the aforementioned electrolyte. In this way, the battery has all the characteristics and advantages of the aforementioned electrolyte additive and electrolyte, which are not repeated here.

[0059] Generally, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting between the positive electrode and the negative electrode, while allowing ions to pass through.

[0060] In some embodiments, further comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer located at least on one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a mass fraction of manganese element in the positive electrode active material being greater than or equal to 25%. In this way, the cost of the positive electrode active material can be reduced, and the discharge voltage platform of the battery can be improved.

[0061] When the mass fraction of manganese element in the positive electrode active material is within the aforementioned range, the positive electrode active material has a relatively high specific capacity, thereby effectively improving the energy density of the battery, and the charging cutoff voltage of the battery can reach 4.35V, with a relatively high discharge platform and good cycle stability under a conventional voltage window. In addition, the use of the aforementioned positive electrode active material with rich manganese element and low or no cobalt and nickel can help reduce the cost and dependence on limited resources, as compared to the use of rare and expensive metals such as cobalt and nickel. Furthermore, the use of the positive electrode active material with rich manganese element and low or no cobalt and nickel can also help reduce the environmental impact during battery production and improve environmental protection.

[0062] In the present application, through the combined use of the first additive and the second additive, the symmetric structure of the first additive and the triangular structure of the second additive (i.e., the triangular structure formed by the connecting lines between adjacent cyano groups in the second additive) together surround the manganese ions, thereby effectively enhancing the complexing effect of the electrolyte additive on the free manganese ions, effectively reducing the migration of manganese ions to the surface of the negative electrode active material, reducing the side reactions of manganese ions with other substances in the electrolyte, and helping to obtain better interface stability of the positive electrode and the negative electrode of the battery, thereby improving the cycle performance of the battery, especially the high-temperature cycle performance.

[0063] In some embodiments, the positive electrode active material satisfies the general formula LiMn x Fe 1－x PO4, 0.25 < x < 1.

[0064] In some embodiments, the positive electrode active material satisfies the general formula LiNi 1-y Mn y O4, 0.25 < y < 1.

[0065] In some embodiments, the positive active material satisfies the general formula Na z Mn02, 0.5 < z < 1.

[0066] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] In some embodiments, the positive active material layer can further optionally include a binder. For example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0068] In some embodiments, the positive active material layer can further optionally include a conductive agent. For example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] In some embodiments, the negative electrode tab includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material. The negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, a silicon-based material, a tin-based material, and lithium titanate.

[0070] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming a metal material (copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] In some embodiments, the negative active material layer can further include a binder, a conductive agent, and other additives. For example, the binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the conductive agent can include at least one of super-p carbon, acetylene black, carbon black, ketjen black, carbon dots, single-walled carbon nanotubes, graphene, and carbon nanofibers; and the additive can include a thickening agent such as sodium carboxymethyl cellulose (CMC-Na) or the like.

[0072] The type of the separator film is not particularly limited in the present application, and any porous structure separator film having good chemical stability and mechanical stability can be selected. For example, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film.

[0073] The battery of the present application can include a battery cell, a battery module, and a battery pack.

[0074] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as polypropylene, polybutylene terephthalate, polybutylene succinate, or the like.

[0075] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0076] In some embodiments, the battery module can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0077] The battery cell, the battery module, and the battery pack can be used as a power source of an electric device or as an energy storage unit of an electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, or the like), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, or the like), an electric train, a ship, a satellite, an energy storage system, or the like, but is not limited thereto. As the electric device, the battery, the battery module, or the battery pack can be selected according to the usage requirement thereof.

[0078] The application will be described in detail below through specific examples. It should be noted that the following examples are only used to illustrate the application and should not be regarded as limiting the scope of the application. If the specific technology or conditions are not specified in the examples, the technology or conditions described in the literature in the art or according to the product manual are used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0079] Example 1

[0080] Preparation of positive electrode sheet: the positive electrode active material LiMn 0.6 Fe 0.4 O4, the binder polyvinylidene fluoride (PVDF), the conductive agent carbon black, and the conductive agent carbon nanotube are mixed uniformly at a weight ratio of 95:2.5:2:0.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and the coating amount is 35 g / m 2 , and after drying at 85°C, cold pressing is performed, and edge cutting, sheet cutting, and strip cutting are performed; after strip cutting, drying is performed at 85°C under vacuum conditions for 4 hours, and the tab is welded to obtain the positive electrode sheet.

[0081] Preparation of negative electrode sheet: the negative electrode active material graphite, the conductive agent carbon black, the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber are mixed at a weight ratio of 95:1.5:1:2.5, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and the coating amount is 20 g / m 2 , and after drying at 85°C, cold pressing is performed, and edge cutting, sheet cutting, and strip cutting are performed; after strip cutting, drying is performed at 85°C under vacuum conditions for 4 hours, and the tab is welded to obtain the negative electrode sheet.

[0082] Preparation of electrolyte: in an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), the solvent ethylene carbonate, propylene carbonate, and diethyl carbonate are mixed uniformly at a mass ratio of 3:5:2, fully dried lithium hexafluorophosphate is quickly added to the mixed solvent, the mass fraction of lithium hexafluorophosphate in the electrolyte is 12.5wt%, and the following electrolyte additives are added, wherein the mass fraction is the mass fraction of the corresponding substance based on the mass fraction of the electrolyte: the first additive: 0.5wt% of the compound represented by formula 1; the second additive: 0.5wt% of 1,3,6-hexanetricarbonitrile; and the fourth additive: 5wt% of fluoroethylene carbonate.

[0083] Preparation of separator film: a polyethylene separator film with a thickness of 8μm is selected.

[0084] Preparation of lithium ion battery: the positive electrode sheet, the negative electrode sheet and the separator film prepared according to the above process were made into a lithium ion battery with a thickness of 4.7 mm, a width of 55 mm and a length of 60 mm by a lamination process, vacuum baked at 75°C for 10 hours, and injected with the electrolyte prepared as described above. After standing for 24 hours, the battery was placed in an environment at 45°C, and a pressure of 3 kg was applied. After charging to 4.0V at 0.1C (160 mA), the battery was allowed to stand for 2 days (to fully activate the battery) to obtain the battery.

[0085] Other embodiments, comparative examples and differences from Example 1 are shown in Table 1. In Example 2, 3 and 13, different triazides were used compared to Example 1. In Example 4 and 5, different positive electrode active materials were used. In Example 6, 7 and 8, a third additive was added. In Example 9, 10, 11 and 12, the mass fractions of the first additive and the second additive were different. In Example 14, the positive electrode active material was different, and lithium hexafluorophosphate was replaced with sodium hexafluorophosphate. In Comparative Example 1, the first additive was not added. In Comparative Example 2, the second additive was not added.

[0086] Table 1

[0087] The batteries in the above examples and comparative examples were tested as follows, and the test results are shown in Table 2.

[0088] High temperature cycle performance test: the lithium ion battery was subjected to 500 charge-discharge cycles at 0.5C current at 45°C, and the capacity retention rate (%) = (500th discharge capacity / 1st discharge capacity) x 100%.

[0089] Manganese dissolution test: for the negative electrode sheet: the battery after 500 cycles was disassembled, the negative electrode sheet was taken out, the negative electrode sheet was washed with 30 g of DMC (dimethyl carbonate) for 3 times, and then the negative electrode sheet was soaked with 20 g of water. After the negative active material was separated from the copper foil, the negative active material was filtered and dried. 0.5 g of the negative active material was weighed, 10 mL of nitric acid and 10 mL of sulfuric acid were slowly added thereto, heated until the sample was dissolved (the solution was milky white), cooled, 10 mL of hydrochloric acid was added and heated until the salts were dissolved (the solution was clear), the solution was cooled and filtered with filter paper with a pore size of 50 μm, the filter paper and beaker were washed clean and transferred to a 250 mL volumetric flask, and finally ICP test was performed to record the content of manganese x1; for the electrolyte: the battery after 500 cycles was disassembled, the battery cell was taken out and centrifuged at high speed, 0.5 g of electrolyte was taken, 10 mL of nitric acid and 10 mL of sulfuric acid were slowly added thereto, heated until the sample was dissolved (the solution was milky white), cooled, 10 mL of hydrochloric acid was added and heated until the salts were dissolved (the solution was clear), the solution was cooled and filtered with filter paper with a pore size of 50 μm, the filter paper and beaker were washed clean and transferred to a 250 mL volumetric flask, and finally ICP test was performed to record the content of manganese x2. The manganese dissolution amount on the electrolyte + negative electrode sheet is x1+x2.

[0090] Table 2

[0091] As can be seen from Table 2, it can be seen from Comparative Examples 1-5 and Comparative Examples 1-2 that the second additive in the application has a good synergistic effect with the first additive, which significantly reduces the dissolution of manganese ions in the battery, effectively reduces the SEI film rupture and recombination caused by the deposition of manganese ions on the surface of the SEI film, and effectively improves the cycle performance of the battery.

[0092] As can be seen from Examples 6-8, the third additive is easy to react with water and acid after being added, thereby reducing the generation of hydrofluoric acid, and further reducing the corrosion of HF on the positive active material, effectively inhibiting the dissolution of manganese ions in the positive active material, and improving the cycle performance of the battery.

[0093] It should be noted that the application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the application are all included in the technical scope of the application. In addition, within the scope of the main idea of the application, various modifications of the embodiments, combination of part of the components in the embodiments to construct other ways can also be included in the scope of the application.

Claims

1. An electrolyte additive, wherein, The second additive comprises a tricyanide. a first additive and a second additive, a structure of the first additive satisfying formula 1, The mass fraction of the first additive in the electrolyte additive is w1, the mass fraction of the second additive in the electrolyte additive is w2, and w1 / w2 is 0.9-1.

1.

2. The electrolyte additive according to claim 1, wherein, The second additive comprises at least one of 1,3,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, and 1,2,3-tris(2-cyanato)propane.

3. The electrolyte additive according to claim 1 or 2, wherein, The third additive comprises at least one of hexamethylene diisocyanate and trimethylsilylisothiocyanate.

4. The electrolyte additive according to any one of claims 1 to 3, wherein, The fourth additive comprises at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, 1,3-propene sultone, 1,3-propane sultone, ethylene sulfate, and methanedi sulfonate.

5. The electrolyte additive according to any one of claims 1 to 4, wherein, The electrolyte additive according to any one of claims 1-5.

6. An electrolyte, wherein, The mass fraction of the first additive in the electrolyte is 0.1%-2%.

7. The electrolyte of claim 6, wherein, The mass fraction of the second additive in the electrolyte is 0.1%-2%.

8. The electrolyte of claim 6 or 7, wherein, The mass fraction of the third additive in the electrolyte is 0.1%-0.3%.

9. The electrolyte of any one of claims 6-8, wherein, The mass fraction of the fourth additive in the electrolyte is 0.1%-10%.

10. The electrolyte of any one of claims 6-9, wherein, The electrolyte further comprises an electrolyte salt, which comprises at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, LiPF4C2O4, and NaFP6.

11. The electrolyte of any one of claims 6-10, wherein, The mass fraction of the electrolyte salt in the electrolyte is 8wt%-20wt%.

12. The electrolyte of claim 11, wherein, The electrolyte additive according to any one of claims 1-5, and / or the electrolyte according to any one of claims 6-12.

13. A battery, wherein, The positive electrode sheet further comprises a positive electrode current collector and a positive electrode active material layer at least on one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, and the mass fraction of manganese in the positive electrode active material is greater than or equal to 25%.

14. The battery of claim 13, wherein, ​ 15. The battery of claim 14, wherein, The positive electrode active material satisfies the general formula LiMn x Fe 1－x PO4, 0.25 < x < 1; and / or, LiNi 1-y Mn y O, 0.25 < y < 1; and / or, Na z MnO2, 0.5 < z < 1.

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