Electrolyte, secondary battery, and device

Abstract

The invention relates to an electrolyte, a secondary battery and a device, the electrolyte comprises a lithium salt, a solvent, a first additive and a second additive, the first additive comprises at least one of compounds shown as a formula I, and the second additive comprises at least one of compounds shown as a formula II; the second additive comprises at least one of compounds as shown in a formula II and a formula III: # imgabs0 #. By using the electrolyte provided by the invention, the reaction speed of the electrolyte and a positive electrode under a mechanical abuse condition can be effectively reduced, the thermal runaway of the battery can be delayed, and the capacity retention ratio of the battery can be effectively improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of energy storage materials, and in particular to an electrolyte, a secondary battery and a device. Background Art

[0002] In recent years, lithium batteries have been widely used in smart phones, unmanned aerial vehicles, hybrid electric vehicles, etc., but with the development of society, low energy density lithium batteries have been unable to meet the demand. The development of high-capacity high-nickel ternary material positive electrode and silicon-carbon negative electrode has become the development direction of high energy density lithium batteries. Due to the increase in nickel content in the positive electrode, although the battery capacity continues to increase, the safety and stability continue to decline.

[0003] The electrolyte is an important component of lithium batteries. The solvents, lithium salts and additives in the electrolyte play a vital role in the storage, circulation and safety performance of lithium-ion batteries. Under extreme conditions (such as puncture, overcharging, hot box testing, etc.), the safety of the battery is closely related to the electrolyte. For example, at extreme temperatures (for example, greater than 150°C), due to the continuous intensification of the internal chemical reaction of the battery, the heat cannot be released, causing the lithium battery to catch fire or even explode, posing a serious safety hazard. At present, researchers generally believe that the cause of thermal runaway comes from the reaction of cyclic carbonates in the electrolyte with the oxygen released at high temperature of the positive electrode, so it is very important to find an electrolyte composition that can both reduce the side reactions of the positive electrode and replace the cyclic carbonates. Summary of the invention

[0004] In view of the problems existing in the prior art, the present application provides an electrolyte, a secondary battery and a device.

[0005] In a first aspect, the present application provides an electrolyte, the electrolyte comprising: a lithium salt, a solvent, a first additive and a second additive, wherein the first additive comprises at least one of the compounds shown in formula I, and the second additive comprises at least one of the compounds shown in formula II and formula III:

[0006]

[0007] Wherein, in Formula I, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted C3-C6 cycloalkyl, or substituted or unsubstituted C6-C12 aryl; wherein the substituted substituents are independently selected from fluorine;

[0008] In formula II and formula III, R5, R6, R7, and R8 are independently selected from substituted or unsubstituted C1-C6 alkyl, L1 is selected from substituted or unsubstituted C1-C6 alkylene, and L2 is selected from substituted or unsubstituted C1-C6 alkylene or substituted or unsubstituted C3-C8 cycloalkyl; wherein the substituted substituents are independently selected from fluorine, C1-C4 alkyl, =O or -NR9R 10 , R9 and R 10 are independently selected from C1-C4 alkyl.

[0009] In a second aspect, the present application provides a secondary battery, wherein the secondary battery comprises the electrolyte described in the first aspect.

[0010] In a third aspect, the present application provides a device, comprising the secondary battery described in the second aspect.

[0011] Beneficial effects of this application:

[0012] By using the electrolyte provided by the present disclosure, especially the synergistic effect of the first additive and the second additive, the storage, cycle and safety performance of the lithium-ion battery are well regulated, especially the reaction speed of the electrolyte and the positive electrode under mechanical abuse conditions can be effectively reduced, the thermal runaway of the battery can be delayed, and the hot box safety performance can be improved. At the same time, by using the electrolyte, the capacity retention rate of the battery containing the electrolyte can be effectively improved. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present disclosure clearer, the technical solution of the present disclosure will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present disclosure. The embodiments of the present disclosure should not be interpreted as limiting the present disclosure.

[0014] the term:

[0015] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0016] In this article, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0017] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0018] Unless otherwise specified, the terms used in this disclosure have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this disclosure can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this disclosure).

[0019] A list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0020] The term "C1-C6 alkyl" includes, but is not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, and the like.

[0021] The term "C1-C6 alkoxy" includes, but is not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentyloxy or n-hexyloxy, etc.

[0022] The term "C2-C6 alkenyl" includes, but is not limited to, ethenyl, propenyl, butenyl, pentenyl or hexenyl and the like.

[0023] The term "C2-C6 alkynyl" includes, but is not limited to, ethynyl, propynyl, butynyl, pentynyl or hexynyl and the like.

[0024] The term "C3-C6 cycloalkyl" includes, but is not limited to, cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl and the like.

[0025] The term "C6-C12 aryl" includes, but is not limited to, phenyl or naphthyl, and the like.

[0026] The term "substituted or unsubstituted" means that the functional group recorded after the term may or may not have a substituent. For example, "substituted or unsubstituted C1-C6 alkyl" refers to a C1-C6 alkyl with a substituent or an unsubstituted C1-C6 alkyl. The number of substituents may be 1 or more than 2, and the substituents include at least one of halogen, carbonyl and amino. It should be understood that when the number of substituents is greater than 1, each substituent may be the same or different.

[0027] The present disclosure is further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present disclosure and are not used to limit the scope of the present disclosure.

[0028] Electrolyte:

[0029] The electrolyte provided in the present application includes: a lithium salt, a solvent, a first additive and a second additive, wherein the first additive includes at least one of the compounds shown in Formula I, and the second additive includes at least one of the compounds shown in Formula II and Formula III:

[0030]

[0031] Wherein, in Formula I, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted C3-C6 cycloalkyl, or substituted or unsubstituted C6-C12 aryl; wherein the substituted substituents are independently selected from fluorine;

[0032] In formula II and formula III, R5, R6, R7, and R8 are independently selected from substituted or unsubstituted C1-C6 alkyl, L1 is selected from substituted or unsubstituted C1-C6 alkylene, and L2 is selected from substituted or unsubstituted C1-C6 alkylene or substituted or unsubstituted C3-C8 cycloalkyl; wherein the substituted substituents are independently selected from fluorine, C1-C4 alkyl, =O or -NR9R 10 , R9 and R 10 are independently selected from C1-C4 alkyl.

[0033] By using the electrolyte provided by the present disclosure, especially the synergistic effect of the first additive and the second additive, the storage, cycle and safety performance of the lithium-ion battery are well regulated, especially the reaction rate of the electrolyte and the positive electrode under mechanical abuse conditions can be effectively reduced, the thermal runaway of the battery can be delayed, and the hot box safety performance can be improved. At the same time, by using the electrolyte, the capacity retention rate of the battery containing the electrolyte can be effectively improved.

[0034] In some embodiments, in Formula I, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, C1-C6 alkyl, and fluorine-substituted C1-C6 alkyl.

[0035] In some embodiments, the first additive includes at least one of the following compounds:

[0036]

[0037] In some embodiments, the first additive includes ethylene carbonate and / or fluoroethylene carbonate.

[0038] In some embodiments, in Formula II and Formula III, R5, R6, R7, and R8 are independently selected from methyl or ethyl, L1 is selected from methylene or ethylene, and L2 is selected from substituted or unsubstituted C1-C4 alkylene or substituted or unsubstituted C4-C6 cycloalkyl; wherein the substituted substituents are each independently selected from methyl, ethyl, =O or -NR9R 10 , R9 and R 10 are independently selected from methyl or ethyl.

[0039] In some embodiments, the second additive includes at least one of the following compounds:

[0040]

[0041] In some embodiments, the second additive includes dimethyl 2,5-dioxaadipate and / or dimethyl 2,5-dimethyladipate.

[0042] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the first additive is Y%, and the mass percentage of the second additive is X%, wherein -3≤0.0037×X 2 -0.0229×X+Y-10.12≤3. When the contents of the first additive and the second additive satisfy this relationship, the reaction rate of the electrolyte and the positive electrode under mechanical abuse conditions can be effectively reduced, the thermal runaway of the battery can be delayed, and the hot box safety performance can be improved. At the same time, the first additive and the second additive have a synergistic effect and can also effectively improve the capacity retention rate of the battery containing the electrolyte.

[0043] In some embodiments, 0.0037×X 2 -0.0229×X+Y-10.12 is -2.5, -2, -1.5, -1, -0.5, 0, 0.5, 1, 1.5, 2, 2.5 or any value therebetween. In some embodiments, -2.1≤0.0037×X 2 -0.0229×X+Y-10.12≤1.7. In some embodiments, -0.5≤0.0037×X 2 -0.0229×X+Y-10.12≤0.

[0044] In some embodiments, 0.01≤Y≤15. In some embodiments, Y is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5 or any value therebetween. In some embodiments, 5≤Y≤10. When the content of the first additive is too high, the electrolyte and the positive electrode plate will react violently at the beginning of thermal runaway, generating a large amount of Joule heat and causing the battery to heat up rapidly.

[0045] In some embodiments, 10≤X≤50. In some embodiments, X is 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48 or any value therebetween. In some embodiments, 20≤X≤40. Among them, the second additive can partially replace the first additive, so that the battery cell can perform normal film formation and charge and discharge cycles at a low cyclic ester content, while improving the thermal safety performance of the battery. When the content of the second additive is too low, the synergistic effect will be reduced and the capacity retention rate of the battery will be reduced; when the content of the second additive is too high, the electrolyte conductivity will be too low and the battery will not be able to circulate normally.

[0046] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium, and lithium difluorooxalatoborate. The lithium salt is lithium hexafluorophosphate.

[0047] In some embodiments, the molar concentration of the lithium salt is 0.2mol / L to 3mol / L. In some embodiments, the molar concentration of the lithium salt can be 0.4mol / L, 0.6mol / L, 0.8mol / L, 1.0mol / L, 1.2mol / L, 1.4mol / L, 1.6mol / L, 1.8mol / L, 2.0mol / L, 2.2mol / L, 2.4mol / L, 2.6mol / L, 2.8mol / L or any value therebetween. In some embodiments, the molar concentration of the lithium salt is 0.5mol / L to 1.5mol / L; specifically 0.75mol / L to 1.25mol / L, more specifically 1mol / L.

[0048] In some embodiments, the solvent includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and butyl propionate. Specifically, the solvent is diethyl carbonate.

[0049] In some embodiments, based on the mass of the electrolyte, the mass percentage of the solvent is 50% to 90%.

[0050] In some embodiments, the electrolyte further comprises a third additive, the third additive comprising at least one of a cyclic carbonate containing a carbon-carbon double bond, a silyl-containing phosphate, a silyl-containing borate, a nitrile compound, and a propanesulfonic acid pyridinium salt. In some embodiments, the third additive comprises at least one of vinylene carbonate (VC), tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, succinonitrile, adiponitrile, glutaronitrile, and hexanetrinitrile.

[0051] In some embodiments, based on the mass of the electrolyte, the mass percentage of the third additive is 0.05% to 10%. In some embodiments, the mass percentage of the third additive is 0.05%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10% or any value therebetween. In some embodiments, the mass percentage of the third additive is 0.1% to 5%.

[0052] Positive electrode:

[0053] In some embodiments, the secondary battery provided in the present application further includes a positive electrode plate, the positive electrode plate includes a positive electrode active material layer, and the positive electrode active material of the positive electrode active material layer includes at least one of lithium nickel transition metal oxide and phosphate-based materials.

[0054] In some embodiments, the lithium nickel transition metal oxide comprises LiNi x Co y M (1-x-y) O2, M includes at least one of cobalt, manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, copper, yttrium, lanthanum, gallium, silver and niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1.

[0055] In some embodiments, the phosphate-based material includes LiMn k B (1-k) PO4, 0≤k≤1, and the B element includes at least one of iron, cobalt, magnesium, calcium, zinc, chromium and lead.

[0056] In some embodiments, the positive electrode active material includes lithium nickel transition metal oxide.

[0057] In some embodiments, the positive electrode active material may have a coating layer on the surface, or may be mixed with another compound having a coating layer.

[0058] In some embodiments, the coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound for the coating may be amorphous or crystalline. The coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating may be applied by any method as long as the method does not adversely affect the performance of the positive active material. For example, the method may include any coating method well known to those of ordinary skill in the art, such as spraying, dipping, etc.

[0059] In some embodiments, the positive electrode active material further includes a binder, and optionally a conductive agent. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0060] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0061] In some embodiments, the positive electrode active material includes a conductive agent to impart conductivity to the electrode. The conductive agent may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0062] In some embodiments, the positive electrode plate further includes a positive current collector, and the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0063] Negative electrode:

[0064] In some embodiments, the secondary battery provided in the present application also includes a negative electrode plate, which includes a negative electrode active material layer, and the negative electrode active material of the negative electrode active material layer includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from a carbon-based material, a tin-based material, a phosphorus-based material and metallic lithium.

[0065] In some embodiments, the silicon-based material includes at least one of silicon, silicon alloy, silicon oxide and silicon carbon compound. In some embodiments, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotube and graphene. In some embodiments, the tin-based material includes at least one of tin, tin oxide and tin alloy. In some embodiments, the phosphorus-based material includes phosphorus and / or phosphorus-carbon composite.

[0066] In some embodiments, based on the mass of the second active material, the mass percentage of the silicon-based material is 10% to 100%.

[0067] In some embodiments, the negative electrode active material includes a silicon-carbon composite.

[0068] In some embodiments, the negative electrode active material layer may include a binder and optionally a conductive material. The binder improves the bonding of the negative electrode active material particles to each other and to the current collector.

[0069] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, and the like.

[0070] In some embodiments, the negative electrode active material layer includes a conductive material so that the electrode has conductivity. The conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0071] In some embodiments, a negative electrode sheet of the present disclosure includes a negative electrode active material, a binder, and a conductive agent.

[0072] In some embodiments, the negative electrode active material of the present disclosure may also be selected from other materials that can electrochemically absorb and release metal ions such as lithium ions. Specifically, it can be selected from carbonaceous materials, silicon materials, alloy materials, lithium-containing metal oxide materials, etc. They can be used alone or in any combination of two or more.

[0073] In some embodiments, the negative electrode plate further includes a negative electrode current collector, and the negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0074] Diaphragm:

[0075] In some embodiments, the secondary battery and device of the present disclosure are provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the device of the present disclosure are not particularly limited, and can be any technology disclosed in the prior art.

[0076] In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0077] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0078] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0079] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0080] The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

[0081] Secondary battery:

[0082] In some embodiments, the secondary battery involved in the present disclosure is a lithium secondary battery, which includes the above-mentioned positive electrode, negative electrode, separator, electrolyte, etc., but is not limited thereto. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0083] In some embodiments, the secondary battery involved in the present disclosure may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0084] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0085] In some embodiments, the present disclosure further provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present disclosure uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present disclosure can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0086] In some embodiments, the present disclosure further provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0087] Device:

[0088] The present disclosure also provides a device, which includes at least one of the above-mentioned secondary battery, battery module and battery pack.

[0089] In some embodiments of the present disclosure, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0090] In some other embodiments of the present disclosure, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0091] The present disclosure is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present disclosure and are not used to limit the scope of the present disclosure.

[0092] Examples and Comparative Examples

[0093] Embodiment 1:

[0094] (1) Preparation of electrolyte:

[0095] In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dioxadipic acid were mixed in a mass ratio of 5:45:50, 2% by mass of vinylene carbonate was added, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. After stirring evenly, the lithium battery electrolyte of Example 1 was obtained.

[0096] (2) Preparation of positive electrode:

[0097] The positive electrode ternary high-nickel active material, conductive carbon black and binder polyvinylidene chloride are mixed in a mass ratio of 97.5:1.5:1.0, and the mixture is dispersed in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry, and then the positive electrode slurry is evenly coated on both surfaces of the aluminum foil, and after drying, calendering and vacuum drying, a positive electrode sheet is obtained.

[0098] (3) Preparation of negative electrode:

[0099] Mixed silicon-carbon material, conductive carbon black, binder (styrene-butadiene rubber, polyacrylic acid) and sodium carboxymethyl cellulose are mixed in a mass ratio of 96.0:1.0:2.4:0.6, and the mixture is dispersed in deionized water to obtain a negative electrode slurry, and the negative electrode slurry is coated on both surfaces of a copper foil, and a negative electrode sheet is obtained after drying, calendering and vacuum drying.

[0100] (4) Preparation of lithium-ion batteries:

[0101] A three-layer diaphragm with a thickness of 11 μm (polyethylene PE porous polymer film is used as a diaphragm) is placed between the above positive electrode and the negative electrode, and then the sandwich structure composed of the positive electrode, the diaphragm and the negative electrode is subjected to a lamination process, and then the sandwich structure is placed in an aluminum-plastic film packaging bag, and vacuum baked at 75° C. for 48 hours to obtain a battery cell to be injected with liquid, and the above-prepared electrolyte is injected into the battery cell, vacuum packaged, and left to stand at room temperature for 12 hours, and left to stand at a high temperature of 45° C. for 12 hours, and then subjected to a capacity conversion step to obtain a lithium ion battery; wherein the capacity conversion step is: constant current charging at 0.05C for 120 minutes, constant current and constant voltage charging at 0.1C to 4.2V, and discharging at 0.2C to 2.5V, the formation is completed, high temperature is left to stand for 24 hours, constant current and constant voltage charging at 0.1C to 4.2V, and constant current and constant voltage charging at 0.2C to 2.5V, and the battery cell is charged to 4.2V at 0.1C and discharged to 2.5V at 0.2C, and the capacity conversion is completed after two cycles.

[0102] Embodiment 2:

[0103] The steps of Example 2 are the same as those of Example 1, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dimethyladipate are mixed in a mass ratio of 7:63:30, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 2 is obtained after stirring evenly.

[0104] Embodiment 3:

[0105] The steps of Example 3 are the same as those of Example 1, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dioxadipic acid are mixed in a mass ratio of 5:65:30, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 3 is obtained after stirring evenly.

[0106] Embodiment 4:

[0107] The steps of Example 4 are the same as those of Example 1, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and diethyl 2,5-dioxadipic acid are mixed in a mass ratio of 8:57:35, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 4 is obtained after stirring evenly.

[0108] Embodiment 5:

[0109] The steps of Example 5 are the same as those of Example 1, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and diethyl 2,5-dioxadipic acid are mixed in a mass ratio of 7:73:20, 2% mass fraction of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 5 is obtained after stirring evenly.

[0110] Embodiment 6:

[0111] The steps of Example 6 are the same as those of Example 1, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dioxadipic acid are mixed in a mass ratio of 12.5:77.5:10, 2% mass fraction of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 6 is obtained after stirring evenly.

[0112] Embodiment 7:

[0113] The steps of Example 7 are the same as those of Example 1, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), and diethyl 2,5-dioxadipic acid are mixed in a mass ratio of 5:67:28, 2% mass fraction of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 7 is obtained after stirring evenly.

[0114] Embodiment 8:

[0115] (1) Preparation of electrolyte:

[0116] In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dioxadipic acid were mixed in a mass ratio of 30:20:50, 2% by mass of vinylene carbonate was added, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. After stirring evenly, the lithium battery electrolyte of Example 8 was obtained.

[0117] (2) Preparation of positive electrode:

[0118] The positive electrode ternary high-nickel active material, conductive carbon black and binder polyvinylidene chloride are mixed in a mass ratio of 97.5:1.5:1.0, and the mixture is dispersed in NMP to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on both surfaces of an aluminum foil, and the positive electrode is obtained after drying, calendering and vacuum drying.

[0119] (3) Preparation of negative electrode:

[0120] A mixed silicon-carbon material, conductive carbon black, a binder (styrene-butadiene rubber, polyacrylic acid) and sodium carboxymethyl cellulose are mixed in a mass ratio of 96.0:1.0:2.4:0.6, and the mixture is dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both surfaces of a copper foil, and a negative electrode is obtained after drying, calendering and vacuum drying.

[0121] (4) Preparation of lithium-ion batteries:

[0122] A three-layer diaphragm with a thickness of 11 μm (a PE porous polymer film is used as a diaphragm) is placed between the above positive electrode and the negative electrode, and then the sandwich structure composed of the positive electrode, the diaphragm and the negative electrode is subjected to a lamination process, and then the sandwich structure is placed in an aluminum-plastic film packaging bag, and vacuum-baked at 75° C. for 48 hours to obtain a battery cell to be injected with liquid, and the above-prepared electrolyte is injected into the battery cell, vacuum-packaged, and left to stand at room temperature for 12 hours, and left to stand at a high temperature of 45° C. for 12 hours, and then subjected to a capacity-splitting step to obtain a lithium-ion battery; wherein the capacity-splitting step is: constant current charging at 0.05C for 120 minutes, constant current and constant voltage charging at 0.1C to 4.2V, and discharging at 0.2C to 2.5V, the formation is completed, high temperature is left to stand for 24 hours, constant current and constant voltage charging at 0.1C to 4.2V, and constant current and constant voltage charging at 0.2C to 2.5V, and the battery cell is charged to 4.2V at 0.1C and discharged to 2.5V at 0.2C, and the capacity is split twice to complete the capacity splitting.

[0123] Embodiment 9:

[0124] The steps of Example 9 are the same as those of Example 8, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and diethyl 2,5-dioxadipic acid are mixed in a mass ratio of 10:55:35, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 9 is obtained after stirring evenly.

[0125] Embodiment 10:

[0126] The steps of Example 10 are the same as those of Example 8, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and diethyl 2,5-dioxadipic acid are mixed in a mass ratio of 3:77:20, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Example 10 is obtained after stirring evenly.

[0127] Comparative Example 1:

[0128] The steps of Comparative Example 1 are the same as those of Example 8, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dimethyladipate are mixed in a mass ratio of 7:93:0, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Comparative Example 1 is obtained after stirring evenly.

[0129] Comparative Example 2:

[0130] The steps of Comparative Example 2 are the same as those of Example 8, except that, in the preparation of the electrolyte: in an argon-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl 2,5-dioxadipic acid are mixed in a mass ratio of 0:70:30, 2% by mass of vinylene carbonate is added, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the lithium battery electrolyte of Comparative Example 2 is obtained after stirring evenly.

[0131] Test method:

[0132] Cycle capacity retention test:

[0133] At 25°C, the prepared lithium-ion secondary battery was charged to 4.2V at a constant current rate of 1C, and then charged at a constant voltage until the current was less than 0.05C. After standing for 5 minutes, it was discharged to 2.5V at a rate of 1C, and the initial discharge capacity was recorded. The lithium-ion secondary battery was charged and discharged 500 times by the above method, and the discharge capacity was recorded each time. The capacity retention rate of the lithium-ion secondary battery after 500 cycles at 25°C = the discharge capacity of the 500th time / initial discharge capacity × 100%.

[0134] Hot box test:

[0135] Preparation stage: place the prepared lithium-ion secondary battery at 25±2°C for 5 minutes; then charge to 4.25V at 1 / 3C with a cut-off current of 1 / 20C; place for 30 minutes; then charge to 2.5V at 1 / 3C; place for another 30 minutes; repeat the above steps, and finally charge to 4.25V at 1 / 3C with a cut-off current of 1 / 20C to end charging.

[0136] Testing phase: Use a fixture to clamp the above processed battery with a preload of 1.5Nm (using 6 bolts); put the battery into a temperature box, and heat the temperature box from ambient temperature to 130±2℃ at a rate of 5℃ / min, and maintain this temperature for 60 minutes; then repeat the above steps to increase the temperature of the temperature box continuously until the battery experiences thermal runaway.

[0137] The lithium ion batteries of Examples 1 to 10 and Comparative Examples 1 to 2 were subjected to electrochemical tests, and the obtained data are shown in Table 1. The 180°C hot box pass rate represents the number of times the battery passed the puncture test in 5 times, for example, 1 / 5 represents one time of passing the hot box test in 5 times.

[0138] Table 1

[0139]

[0140] By comparing Examples 1 to 10 and Comparative Examples 1 to 2, it is shown that the synergistic effect of adding the first additive and the second additive at the same time has a good regulatory effect on the storage, cycle and safety performance of the lithium-ion battery, effectively reducing the reaction rate of the electrolyte and the positive electrode under mechanical abuse conditions, delaying the thermal runaway of the battery, and improving the hot box safety performance. At the same time, by using the electrolyte, the capacity retention rate of the battery containing the electrolyte can be effectively improved. Further, satisfying -3≤Y+0.0037×X 2-0.0229×X-10.12≤3, the battery capacity retention rate and thermal safety performance are further improved in Examples 1 to 7. Example 8 shows that the battery capacity retention rate of the comparison example that the first additive is higher than the set range requirement and does not satisfy the above relationship will be affected to a certain extent, and the thermal safety performance is poor due to excessive increase in EC. Examples 9 and 10 show that even if the content of the first additive and the second additive meets the set range, if the above relationship is not satisfied, the thermal safety performance or battery capacity retention rate will be affected to a certain extent. Comparative Example 1 shows that the battery capacity retention rate of the comparison example that does not add the second additive and does not satisfy the above relationship is poor. Comparative Example 2 shows that the battery capacity retention rate of the comparison example that does not add the first additive and does not satisfy the above relationship is poor.

[0141] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present disclosure, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present disclosure.

Claims

1. An electrolyte, characterized in that: include: A lithium salt, a solvent, a first additive and a second additive, wherein the first additive includes at least one of the compounds shown in Formula I, and the second additive includes at least one of the compounds shown in Formula II and Formula III: Wherein, in Formula I, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted C3-C6 cycloalkyl, or substituted or unsubstituted C6-C12 aryl; wherein the substituted substituents are independently selected from fluorine; In formula II and formula III, R5, R6, R7, and R8 are independently selected from substituted or unsubstituted C1-C6 alkyl, L1 is selected from substituted or unsubstituted C1-C6 alkylene, and L2 is selected from substituted or unsubstituted C1-C6 alkylene or substituted or unsubstituted C3-C8 cycloalkyl; wherein the substituted substituents are independently selected from fluorine, C1-C4 alkyl, =O or -NR9R 10 , R9 and R 10 are independently selected from C1-C4 alkyl.

2. The electrolyte according to claim 1, characterized in that In formula I, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, C1-C6 alkyl, and fluorine-substituted C1-C6 alkyl; and / or In formula II and formula III, R5, R6, R7, and R8 are independently selected from methyl or ethyl, L1 is selected from methylene or ethylene, and L2 is selected from substituted or unsubstituted C1-C4 alkylene or substituted or unsubstituted C4-C6 cycloalkyl; wherein the substituted substituents are independently selected from methyl, ethyl, =O or -NR9R 10 , R9 and R 10 are independently selected from methyl or ethyl.

3. The electrolyte according to claim 1 or 2, characterized in that The first additive comprises at least one of the following compounds: And / or the second additive comprises at least one of the following compounds:

4. The electrolyte according to claim 1 or 2, characterized in that Based on the total mass of the electrolyte, the mass percentage of the first additive is Y%, and the mass percentage of the second additive is X%, wherein: -3≤0.0037×X 2 -0.0229×X+Y-10.12≤3。 5. The electrolyte according to claim 4, characterized in that -2.1≤0.0037×X 2 -0.0229×X+Y-10.12≤1.7; and / or 0.01≤Y≤15; and / or 10≤X≤50。 6. The electrolyte according to claim 5, characterized in that 5≤Y≤10; and / or, 20≤X≤40.

7. The electrolyte according to claim 1, characterized in that The lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole and lithium difluorooxalatoborate; the molar concentration of the lithium salt is 0.2 mol / L to 3 mol / L; and / or The solvent comprises at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and butyl propionate; based on the mass of the electrolyte, the mass percentage of the solvent is 50% to 90%; and / or The electrolyte also includes a third additive, which includes at least one of a cyclic carbonate containing a carbon-carbon double bond, a silyl-containing phosphate, a silyl-containing borate, a nitrile compound and pyridinium propanesulfonate; based on the mass of the electrolyte, the mass percentage of the third additive is 0.05% to 10%.

8. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that: The positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material of the positive electrode active material layer comprises at least one of a lithium nickel transition metal oxide and a phosphate-based material; the lithium nickel transition metal oxide comprises LiNi x Co y M (1-x-y) O2, M includes at least one of cobalt, manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, copper, yttrium, lanthanum, gallium, silver and niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1; the phosphate material includes LiMn k B (1-k) PO4, 0≤k≤1, the B element includes at least one of iron, cobalt, magnesium, calcium, zinc, chromium and lead; and / or The negative electrode plate includes a negative electrode active material layer, the negative electrode active material of the negative electrode active material layer includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from a carbon-based material, a tin-based material, a phosphorus-based material and metallic lithium; the silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide compound and a silicon-carbon compound, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes and graphene, the tin-based material includes at least one of tin, tin oxide and a tin alloy, and the phosphorus-based material includes phosphorus and / or a phosphorus-carbon complex; based on the mass of the second active material, the mass percentage of the silicon-based material is 10% to 100%.

10. A device, characterized in that: A secondary battery comprising the secondary battery according to claim 8 or 9.

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