Electrolyte, secondary battery, and electric device

Abstract

The embodiment of the application discloses an electrolyte, a secondary battery and an electric device. The electrolyte is obtained by adding acetonitrile in a solvent system of a carbonate compound. The acetonitrile has a high dielectric constant and a low viscosity, can reduce the viscosity of the electrolyte system, improve the conductivity, and significantly improve the low-temperature performance of the secondary battery. By selecting an acid anhydride compound and a compound A as additives, the acid anhydride additive has excellent water-removing and acid-removing effects, can timely remove HF generated by the decomposition of acetonitrile, inhibit the decomposition of LiPF6, and optimize the formation of SEI film by cooperating with the acid anhydride compound, which is beneficial to Li + The compound A can inhibit the reduction and decomposition of acetonitrile at the negative electrode through the diffusion of the SEI film on the graphite surface, solve the risk of easy decomposition of the acetonitrile-based electrolyte, and finally realize the play of excellent low-temperature performance, and also consider the cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to an electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] Driven by environmental and carbon emission pressures, research into new energy sources is actively underway. Among these, lithium-ion batteries have garnered significant attention in energy storage and power applications due to their high specific energy, long cycle life, low self-discharge, and good safety performance. As market demands become increasingly stringent and diverse, lithium-ion batteries need to meet the requirements of numerous application scenarios while maintaining excellent performance. Extremely cold regions place extremely high demands on the low-temperature performance of lithium-ion batteries; therefore, improving the low-temperature performance of lithium-ion batteries has become a crucial research direction in the field. Summary of the Invention

[0003] This application provides an electrolyte, a secondary battery, and an electrical device that can solve the problem that the viscosity of existing lithium-ion batteries increases sharply and the conductivity decreases under low temperature conditions, affecting battery life and safety.

[0004] A first aspect of this application provides an electrolyte comprising a lithium salt, an organic solvent, and an additive; the organic solvent comprising acetonitrile and a carbonate compound; the additive comprising an anhydride compound and compound A conforming to the following structural formula:

[0005] The X includes halogens, benzene rings, toluene, alkyl groups, and alkenyl groups.

[0006] Optionally, compound A includes at least one of p-toluenesulfonyl isocyanate, chlorosulfonyl isocyanate, and benzenesulfonyl isocyanate.

[0007] Optionally, the acetonitrile in the electrolyte has a mass percentage of 5% to 30%; the acid anhydride compound in the electrolyte has a mass percentage of 0.2% to 0.6%; and compound A in the electrolyte has a mass percentage of 0.5% to 1.5%.

[0008] Optionally, the carbonate compound includes ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate; the ethylene carbonate has a mass percentage of 20% to 30% in the organic solvent; the methyl ethyl carbonate has a mass percentage of 30% to 40% in the organic solvent; and the diethyl carbonate has a mass percentage of 10% to 20% in the organic solvent.

[0009] Optionally, the ratio of the acetonitrile and the carbonate compound in the organic solvent is acetonitrile: ethylene carbonate: methyl ethyl carbonate: diethyl carbonate = (1-4): (2-3): (2-4): (2-3).

[0010] Optionally, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium difluorodi(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; the lithium salt accounts for 10% to 15% of the total mass of the electrolyte.

[0011] Optionally, the mass ratio of the acid anhydride compound to compound A is 0.2 to 1.1; the acid anhydride compound includes at least one of succinic anhydride, glutaric anhydride, adipic anhydride, pimelic anhydride, phthalic anhydride, maleic anhydride, citrate anhydride, citric anhydride, and 2,3-dimethylmaleic anhydride.

[0012] Optionally, the acid anhydride compound is glutaric anhydride.

[0013] Optionally, the additive further includes boron trifluoride-pyridine, wherein the boron trifluoride-pyridine accounts for 0.2% to 0.6% of the total mass of the electrolyte.

[0014] Optionally, the additives further include vinyl sulfite and vinylene sulfate; the vinyl sulfite accounts for 0.5% to 1% of the total mass of the electrolyte; the vinylene sulfate accounts for 0.5% to 1% of the total mass of the electrolyte.

[0015] A second aspect of this application provides a method for preparing the electrolyte as described above, comprising the following steps:

[0016] S1) Mix lithium salt and organic solvent, controlling the temperature change during mixing to be less than 2°C, to obtain a mixture;

[0017] S2) Mix the additive and the mixture to obtain an electrolyte.

[0018] A third aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0019] A fourth aspect of this application provides an electrical device including a secondary battery as described above, the secondary battery serving as a power supply for the electrical device.

[0020] The beneficial effects of this application are that it provides an electrolyte, a secondary battery having the electrolyte, and an electrical device having the secondary battery. The electrolyte, by adding acetonitrile to a carbonate compound solvent system, utilizes acetonitrile's high dielectric constant and low viscosity to reduce the electrolyte system viscosity, increase conductivity, and significantly improve the low-temperature performance of the secondary battery. By selecting anhydride compounds and compound A as additives, the anhydride additives exhibit excellent dehydration and deacidification effects, effectively removing HF generated from acetonitrile decomposition and inhibiting LiPF6 decomposition. The combination of compound A and the anhydride compounds optimizes the formation of the SEI film, which is beneficial for Li… + By diffusing through the SEI film on the graphite surface, and by using compound A to suppress the reduction and decomposition of acetonitrile at the negative electrode, the risk of easy decomposition of acetonitrile-based electrolytes is resolved, ultimately achieving excellent low-temperature performance while also ensuring good cycle performance. Detailed Implementation

[0021] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0022] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then 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, then 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 element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of".

[0023] In this specification, the range of values ​​indicated by “~” represents the range containing the minimum and maximum values ​​recorded before and after “~”, respectively.

[0024] Conventionally used electrolyte solvents are mostly combinations of carbonate solvents. Cyclic carbonates such as EC (ethylene carbonate) have extremely high dielectric constants (89.78), which can reduce the association between anions and cations and effectively dissociate lithium salts. However, EC has a high viscosity and a high melting point, which greatly limits the low-temperature power performance of EC-based electrolytes. PC (propylene carbonate) has a low melting point and good low-temperature performance, but it carries the risk of graphite stripping. Chain carbonates such as EMC (ethyl methyl carbonate) or DMC (dimethyl carbonate) have lower viscosity and dielectric constants than cyclic carbonates. Therefore, in practical applications, it is often necessary to mix organic solvents with high dielectric constants and low viscosity to obtain electrolytes with relatively high dielectric constants and relatively low viscosity, which can meet the battery performance requirements, but cannot meet more stringent low-temperature conditions. Under harsh low-temperature conditions, the viscosity of lithium-ion batteries increases sharply, and the conductivity decreases, causing lithium ions in the electrolyte to be unable to properly intercalate into the negative electrode, resulting in lithium plating and affecting battery life and safety.

[0025] To overcome the problem that conventional electrolytes affect the electrochemical and safety performance of batteries at low temperatures, this application provides an electrolyte, a method for preparing the electrolyte, a secondary battery, and an electrical device. The electrolyte is prepared by adding acetonitrile to a carbonate compound solvent system. Acetonitrile has a high dielectric constant and low viscosity, which reduces the viscosity of the electrolyte system, increases conductivity, and significantly improves the low-temperature performance of the secondary battery. An anhydride compound and compound A are selected as additives, wherein compound A has the following structural formula:

[0026] Wherein, X includes at least one of halogen, benzene ring, toluene, alkyl, and alkenyl groups.

[0027] Anhydride additives exhibit excellent dehydration and deacidification effects, effectively removing HF produced by acetonitrile decomposition and inhibiting LiPF6 decomposition. Compound A, when combined with anhydride compounds, can optimize SEI film formation, which is beneficial for Li... + Through diffusion of the SEI film on the graphite surface, and by inhibiting the reductive decomposition of acetonitrile at the negative electrode, the risk of easy decomposition of acetonitrile-based electrolytes is mitigated, ultimately achieving excellent low-temperature performance while maintaining good cycle performance. In some embodiments, compound A includes at least one of p-toluenesulfonyl isocyanate, chlorosulfonyl isocyanate, and benzenesulfonyl isocyanate.

[0028] In one embodiment of this application, a secondary battery is provided, the secondary battery including a positive electrode, a negative electrode, a separator, an electrolyte, and a casing.

[0029] I. Electrolyte

[0030] In some embodiments, the electrolyte includes lithium salt, organic solvent, and additives.

[0031] lithium salts

[0032] In some embodiments, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium difluorodioxalato)phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Considering both performance and cost, lithium hexafluorophosphate (LiPF6) is preferred.

[0033] The lithium salt constitutes 10% to 15% of the total mass of the electrolyte. Specifically, the lithium salt content can be 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or any two of these values. Preferably, the lithium salt content is 12% to 13% of the total mass of the electrolyte. Too low a concentration will affect the conductivity of the electrolyte, while too high a concentration will increase the viscosity of the electrolyte.

[0034] organic solvents

[0035] In some embodiments, the organic solvent includes acetonitrile and carbonate compounds.

[0036] The acetonitrile content in the electrolyte is 5% to 30% by mass. Specifically, the acetonitrile content in the organic solvent can be 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, or any two of these values. Excessive acetonitrile may require the addition of large amounts of film-forming additives, and even with sufficient additives, side reactions may not be adequately suppressed. Insufficient acetonitrile will not fully utilize its low viscosity advantage, and carbonate compounds will still dominate the electrolyte system. Preferably, the acetonitrile content is 15% to 25%.

[0037] Carbonate compounds include ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0038] To ensure sufficient dissociation of the lithium salt and guarantee high-temperature performance, a certain amount of ethylene carbonate (EC) needs to be used. The mass percentage of ethylene carbonate (EC) in the organic solvent is 20% to 30%. Specifically, the mass percentage of ethylene carbonate (EC) in the organic solvent can be 20%, 20.5%, 21%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, 26%, 27%, 28%, 29%, 30%, or any two of these values.

[0039] The mass percentage of ethyl methyl carbonate (EMC) in the organic solvent is 30% to 40%. Specifically, the mass percentage of ethyl methyl carbonate (EMC) in the organic solvent can be 30%, 30.5%, 31%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 36%, 37%, 38%, 39%, 40%, or any two of these values.

[0040] The mass percentage of diethyl carbonate (DEC) in the organic solvent is 10% to 20%. Specifically, the mass percentage of diethyl carbonate (DEC) in the organic solvent can be 10%, 10.5%, 11%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 16%, 17%, 18%, 19%, 20%, or any two of these values.

[0041] The ratio of acetonitrile and carbonate compound in the organic solvent is acetonitrile: ethylene carbonate: methyl ethyl carbonate: diethyl carbonate = (1-4): (2-3): (2-4): (2-3).

[0042] Acetonitrile has a high dielectric constant and low viscosity. Its addition to carbonate compound solvent systems can reduce electrolyte viscosity, improve conductivity, and enhance the low-temperature performance of secondary batteries. However, acetonitrile is readily reduced on the negative electrode and readily reacts with PF6. - The reaction generates a large amount of HF, which etches the positive electrode material, causing the positive electrode structure to collapse and exacerbating the dissolution of transition metals, leading to deactivation of the secondary battery. Therefore, it is necessary to form an excellent SEI film (Solid Electrolyte Interface) to inhibit the reductive decomposition of acetonitrile. Simultaneously, the addition of dehydrating and deacidifying additives can effectively remove acetonitrile and PF6. - The HF produced by the (hexafluorophosphate) reaction inhibits the continued occurrence of side reactions. Therefore, acetonitrile is combined with cyclic carbonates (ethylene carbonate) and linear carbonates (methyl ethyl carbonate, diethyl carbonate) to form a mixed solvent.

[0043] additive

[0044] In some embodiments, the additive includes an anhydride compound and compound A, wherein the structural formula of compound A is:

[0045] Wherein, X includes at least one of halogen, benzene ring, toluene, alkyl, and alkenyl. In some embodiments, compound A includes at least one of p-toluenesulfonyl isocyanate, chlorosulfonyl isocyanate, and benzenesulfonyl isocyanate, preferably p-toluenesulfonyl isocyanate.

[0046] In some embodiments, the mass percentage of the acid anhydride compound in the electrolyte is 0.2% to 0.6%. Specifically, the mass percentage of the acid anhydride compound in the electrolyte may be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, or any two of these ranges.

[0047] In some embodiments, the mass ratio of the anhydride compound to compound A is 0.2 to 1.1, and the anhydride compound includes at least one of succinic anhydride, glutaric anhydride, adipic anhydride, pimelic anhydride, phthalic anhydride, maleic anhydride, citrate anhydride, citric anhydride, and 2,3-dimethylmaleic anhydride. Anhydride additives have been shown to have excellent dehydration and deacidification effects. Glutaric anhydride is preferred as it can promptly remove HF generated from acetonitrile decomposition and inhibit the decomposition of LiPF6. The preferred addition amount of glutaric anhydride is 0.2% to 0.6%.

[0048] Compound A, such as p-toluenesulfonyl isocyanate (PTSI), has a mass percentage content of 0.5% to 1.5% in the electrolyte. Specifically, the mass percentage content of p-toluenesulfonyl isocyanate (PTSI) in the electrolyte can be 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any two of these ranges.

[0049] p-Toluenesulfonyl isocyanate (PTSI) acts on the negative electrode to form a film, inhibiting the reductive decomposition of acetonitrile at the negative electrode. The main components of the decomposition products of p-toluenesulfonyl isocyanate (PTSI) are Li₂SO₃, Li₂S, and ROSO₂Li. These decomposition components can improve the ionic conductivity of the interfacial film, which is beneficial to Li₂... + By improving the SEI film on the graphite surface, Li +The diffusion rate is reduced. Furthermore, the aforementioned decomposition components do not react with HF to produce LiF, thus lowering the interfacial impedance. p-Toluenesulfonyl isocyanate (PTSI) is an electron-rich compound containing S=O groups. The S=O bond can delocalize the nitrogen nucleus, which is a weak base site. The detached nitrogen nucleus can inhibit and hinder the PF5 reaction to generate HF, reducing the amount of LiF in the SEI film. This forms a modified film on the electrode and reduces the resistance of the graphite / electrolyte, lowering the interfacial impedance. Therefore, p-Toluenesulfonyl isocyanate (PTSI) not only assists in the removal of HF by acid anhydrides but also alleviates the high impedance problem caused by acid anhydrides.

[0050] In some embodiments, the additive further includes boron trifluoride-pyridine (PBF), wherein the boron trifluoride-pyridine accounts for 0.2% to 0.6% of the total mass of the electrolyte. Specifically, the boron trifluoride-pyridine (PBF) may account for 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or any two of these numbers, of the total mass of the electrolyte. Boron trifluoride-pyridine (PBF) contains two functional groups: the organic base pyridine-Py and -PF3. -Py can coordinate with metallic Mn, inhibiting its reduction at the negative electrode surface and neutralizing acidic substances PF5 and HF in the electrolyte. -BF3 acts as a Lewis acid and anion acceptor, dissolving LiF and reducing interfacial impedance.

[0051] In some embodiments, the additive further includes vinyl sulfite (ES) and vinyl sulfite (VC).

[0052] The vinyl sulfite (ES) comprises 0.5% to 1% of the total mass of the electrolyte. Specifically, the vinyl sulfite (ES) may comprise 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these values. The vinylene sulfate (VC) comprises 0.5% to 1% of the total mass of the electrolyte. Specifically, the vinylene sulfate (VC) may comprise 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these values. The synergistic effect of vinyl sulfite (ES) and vinylene sulfate (VC) can mitigate the risk of easy decomposition of acetonitrile-based electrolytes and leverage their low-temperature performance advantages.

[0053] If the additive content is too low, it cannot exert its respective advantages to suppress the side reactions of the acetonitrile-based electrolyte; if the additive content is too high, it will increase the film-forming resistance and increase the cost.

[0054] Electrolyte preparation method

[0055] In some embodiments, the method for preparing the electrolyte includes the following steps:

[0056] S1) Mix lithium salt and organic solvent, controlling the temperature change during mixing to be less than 2°C, to obtain a mixture;

[0057] S2) Mix the additive and the mixture to obtain an electrolyte.

[0058] Specifically, in step S1), under inert gas protection, lithium salt and organic solvent are mixed, with the temperature rise not exceeding 2°C during the mixing process, to obtain a colorless and transparent liquid (i.e., the mixture); in step S2), the additive and the colorless and transparent liquid are mixed to obtain the electrolyte. In step S1), since adding lithium salt will cause the electrolyte temperature to rise, resulting in a certain degree of thermal decomposition of the lithium salt, the electrolyte temperature is controlled when adding lithium salt. When the electrolyte temperature rises above 2°C, the addition of lithium salt is stopped, and when the electrolyte temperature is below 2°C, the addition of lithium salt can continue.

[0059] The electrolyte temperature can be controlled using common temperature control methods in this field, such as ice bath, dry ice circulation cooling, and liquid nitrogen cooling.

[0060] The water content needs to be strictly controlled during the preparation of the electrolyte. In some embodiments, the preparation method includes: step S1', mixing and removing water from the organic solvent to obtain a mixed solvent; step S2', mixing the lithium salt and the mixed solvent under inert gas protection, with the temperature rise not exceeding 2°C during the mixing process, to obtain a colorless and transparent liquid; step S3', mixing the additive A with the colorless and transparent liquid to obtain the electrolyte. Molecular sieve adsorption can be used to remove water from the organic solvent.

[0061] The electrolyte comprises lithium salt, acetonitrile, cyclic carbonate, linear carbonate, p-toluenesulfonyl isocyanate (PTSI), glutaric anhydride, and boron trifluoride-pyridine (PBF), and also contains ES and VC to further optimize film formation. This electrolyte incorporates a low-viscosity acetonitrile solvent, and the design of additives addresses the risk of acetonitrile-based electrolyte decomposition, ultimately achieving excellent low-temperature performance while maintaining good cycle performance.

[0062] II. Negative electrode plate

[0063] The negative electrode sheet 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 containing a negative active material, the negative active material containing graphite.

[0064] The negative electrode can be a single-sided electrode or a double-sided electrode. When the negative electrode is a single-sided electrode, the negative active material layer is disposed on one surface of the negative current collector. When the negative electrode is a double-sided electrode, the negative active material layer is disposed on both surfaces of the negative current collector.

[0065] Negative current collector

[0066] In some embodiments, the negative electrode current collector includes, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal foil. In some embodiments, the negative electrode current collector is a nickel foil, stainless steel foil, or copper foil, preferably copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0067] In some embodiments, the negative current collector is a conductive resin. In some embodiments, the conductive resin includes a film obtained by depositing copper onto a polypropylene film.

[0068] Negative electrode active material layer

[0069] The negative electrode active material layer can be one or more layers, and each layer in a multilayer negative electrode active material layer can contain the same or different negative electrode active materials. The negative electrode active material is any material capable of reversibly inserting and deintercalating metal ions such as lithium ions. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0070] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a dispersant.

[0071] Negative electrode active material

[0072] In some embodiments, the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, amorphous carbon, carbon nanotubes, and mesophase carbon microspheres.

[0073] conductive agent

[0074] In some embodiments, the conductive agent includes one or more of carbon black, graphite, carbon fiber, carbon nanotubes, or graphene, preferably carbon black.

[0075] adhesive

[0076] Binders can improve the adhesion between the negative electrode active materials. There are no particular limitations on the type of binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, binders include sodium carboxymethyl cellulose and styrene-butadiene rubber.

[0077] dispersant

[0078] In some embodiments, the dispersant comprises diethylhexanol, an environmentally friendly organic compound that is inexpensive and widely available. It has low surface tension, making it easy to adsorb and spread on the liquid surface. The material is subjected to mechanical shearing and friction, as well as internal friction between particles. Under the influence of these forces, the raw material particles tend to be highly dispersed, resulting in a more uniform slurry and better dispersion. This leads to a uniform thickness of the prepared dry electrode sheet, avoiding wrinkling and other issues that could affect electrical performance, enhancing electrode stability, improving lithium-ion transport efficiency between the positive and negative electrodes, reducing electrochemical polarization, accelerating the non-Radida reaction process, and meeting the requirements for rate performance and cycle life of power batteries.

[0079] III. Positive electrode plate

[0080] The positive electrode includes a positive current collector and a layer of positive active material disposed on the positive current collector.

[0081] Positive electrode active material layer

[0082] The positive electrode active material layer can be one or more layers. Each layer in a multilayer positive electrode active material can contain the same or different positive electrode active materials. The positive electrode active material is any material capable of reversibly inserting and deintercalating metal ions such as lithium ions.

[0083] In some embodiments, the positive electrode active material comprises at least one of lithium manganese oxide, lithium iron phosphate (LFP), and ternary materials.

[0084] In some embodiments, the positive electrode active material comprises a ternary material, which may comprise lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0085] In some embodiments, the positive electrode active material comprises lithium nickel cobalt manganese oxide, wherein the content of nickel is greater than or equal to 0.5, based on a molar ratio of nickel, cobalt and manganese of 1.

[0086] In some embodiments, the positive electrode active material contains doping elements and / or coating elements. There are no special requirements for the doping elements and / or coating elements, as long as they can make the positive electrode active material more stable.

[0087] In addition, positive electrode active materials also include positive electrode conductive agents, positive electrode binders, and solvents.

[0088] Positive conductive agent

[0089] There are no restrictions on the type of positive electrode conductive agent; any known conductive agent can be used. Examples of positive electrode conductive agents include, but are not limited to, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive agents can be used alone or in any combination.

[0090] Positive electrode binder

[0091] There are no particular restrictions on the type of positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or their hydrides, and ethylene-propylene-diene terpolymers (EPDM). The above-mentioned positive electrode binders include thermoplastic elastomers such as styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers, or their hydrides; soft resinous polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymeric compositions with ion conductivity of alkali metal ions (especially lithium ions). These positive electrode binders can be used alone or in any combination.

[0092] solvent

[0093] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it can dissolve or disperse the positive electrode active material, positive electrode conductive agent, and positive electrode binder. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media can include, but are not limited to, water and mixtures of alcohol and water. Examples of organic media can include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0094] Positive current collector

[0095] There are no particular limitations on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and composite materials formed by polymers and metal layers. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0096] There are no particular limitations on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, its form may include, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, its form may include, but is not limited to, carbon plate, carbon film, carbon cylinder, etc. In some embodiments, the positive electrode current collector is a metal foil. In some embodiments, the metal foil is a mesh. There are no particular limitations on the thickness of the metal foil. In some embodiments, the thickness of the metal foil is greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the thickness of the metal foil is less than 1 mm, less than 100 μm, or less than 50 μm. In some embodiments, the thickness of the metal foil is within the range of any two of the above values.

[0097] IV. Separating membrane

[0098] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0099] V. Application

[0100] This application also provides an electrical device including the aforementioned secondary battery, which serves as the power supply for the electrical device. As a typical application, the electrical device can be used, but is not limited to, in electric toys, power tools, electric vehicles, electric cars, energy storage devices, ships, spacecraft, etc.

[0101] The preparation method of the secondary battery provided in this application is described below with reference to specific embodiments:

[0102] Example 1

[0103] (1) Preparation of electrolyte

[0104] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), acetonitrile, EC, EMC, and DEC were mixed thoroughly in a mass ratio of 20:30:30:20 (i.e., 2:3:3:2). Molecular sieves are used to remove water, resulting in a mixed solvent. LiPF6 is added to the mixed solvent in batches while continuously stirring and cooling with dry ice. When the electrolyte temperature rise is ensured to be no more than 2°C, LiPF6 can be added further. The mass fraction of LiPF6 in the electrolyte is controlled to be 12.5 wt%, and a colorless and transparent liquid is finally obtained. Additives PTSI: 1 wt%, glutaric anhydride: 0.3 wt%, PBF: 0.3 wt%, ES: 0.5 wt%, and VC: 0.5 wt% are added and stirred evenly to obtain the electrolyte.

[0105] (2) Preparation of positive electrode sheet.

[0106] The positive electrode active material Li(Ni) 0.6 Mn 0.2 Co 0.2 O2 (NMC622), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NMC622:Super P:PVDF = 94:3:3, and then evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry is coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet is obtained.

[0107] (3) Preparation of negative electrode sheet

[0108] The negative electrode active material graphite, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of graphite:SuperP:SBR = 94:3:3, and then evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0109] (4) Making a secondary battery

[0110] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode. After winding, hot pressing and shaping, and electrode tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 80±10℃ for 24 hours. The electrolyte prepared above is injected into the dried aluminum-plastic film, and the cell is allowed to stand, form, and be capacity tested to complete the preparation of the lithium-ion secondary battery.

[0111] Example 2

[0112] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0113] Acetonitrile:EC:EMC:DEC = 3:3:2:2, additives include PTSI: 1wt%, glutaric anhydride: 0.3wt%, PBF: 0.3wt%, ES: 0.5wt%, VC: 0.5wt%.

[0114] Example 3

[0115] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0116] Acetonitrile:EC:EMC:DEC = 1:3:4:2, additives include PTSI: 1wt%, glutaric anhydride: 0.3wt%, PBF: 0.3wt%, ES: 0.5wt%, VC: 0.5wt%.

[0117] Example 4

[0118] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0119] Acetonitrile:EC:EMC:DEC = 3:3:2:2, additives include PTSI: 1.5wt%, glutaric anhydride: 0.5wt%, PBF: 0.5wt%, ES: 0.5wt%, VC: 0.5wt%.

[0120] Example 5

[0121] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0122] Acetonitrile:EC:EMC:DEC = 2:2:4:2, additives include PTSI: 1wt%, glutaric anhydride: 0.3wt%, PBF: 0.3wt%, ES: 0.5wt%, VC: 0.5wt%.

[0123] Example 6

[0124] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0125] Acetonitrile:EC:EMC:DEC = 2:3:3:2, additives include PTSI: 0.5wt%, glutaric anhydride: 0.2wt%, PBF: 0.2wt%, ES: 0.5wt%, VC: 0.5wt%.

[0126] Example 7

[0127] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0128] Acetonitrile:EC:EMC:DEC = 2:3:3:2, additives include PTSI: 1.5wt%, glutaric anhydride: 0.5wt%, PBF: 0.5wt%, ES: 0.5wt%, VC: 0.5wt%.

[0129] Example 8

[0130] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0131] The lithium salt LiPF6 has a mass fraction of 10 wt%, and the ratio of acetonitrile:EC:EMC:DEC is 2:3:3:2. Additives include PTSI: 1 wt%, glutaric anhydride: 0.3 wt%, PBF: 0.3 wt%, ES: 0.5 wt%, and VC: 0.5 wt%.

[0132] Example 9

[0133] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0134] The lithium salt LiPF6 has a mass fraction of 15 wt%, and the ratio of acetonitrile:EC:EMC:DEC is 3:3:2:2. Additives include PTSI: 1 wt%, glutaric anhydride: 0.3 wt%, PBF: 0.3 wt%, ES: 0.5 wt%, and VC: 0.5 wt%.

[0135] Example 10

[0136] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0137] Acetonitrile:EC:EMC:DEC = 2:3:3:2, additives include PTSI: 1.2wt%, phthalic anhydride: 0.3wt%, PBF: 0.6wt%, ES: 0.6wt%, VC: 0.8wt%.

[0138] Example 11

[0139] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0140] Acetonitrile:EC:EMC:DEC = 2:3:3:2, additives include PTSI: 1.5wt%, maleic anhydride: 0.6wt%, PBF: 0.4wt%, ES: 1.0wt%, VC: 0.5wt%.

[0141] Example 12

[0142] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0143] Acetonitrile:EC:EMC:DEC = 2:3:3:2, additives include PTSI:0.8wt%, citrate anhydride:0.2wt%, PBF:0.5wt%, ES:0.5wt%, VC:1.0wt%.

[0144] Example 13

[0145] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0146] Acetonitrile: EC:EMC:DEC = 3:3:2:2, additives include PTSI: 1.2wt%, citric anhydride: 0.3wt%, PBF: 0.6wt%, ES: 0.8wt%, VC: 0.6wt%.

[0147] Example 14

[0148] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0149] Acetonitrile: EC:EMC:DEC = 1:3:4:2, additives include PTSI: 1wt%, 2,3-dimethylmaleic anhydride: 0.6wt%, PBF: 0.5wt%, ES: 0.8wt%, VC: 0.6wt%.

[0150] Example 15

[0151] The secondary battery was prepared according to the method of Example 1, except for the following difference: PTSI was replaced with benzenesulfonyl isocyanate.

[0152] Comparative Example 1

[0153] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0154] EC:EMC:DEC = 3:5:2, with additives including PTSI: 1wt%, glutaric anhydride: 0.3wt%, PBF: 0.3wt%, ES: 0.5wt%, and VC: 0.5wt%.

[0155] Comparative Example 2

[0156] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0157] Acetonitrile:EC:EMC:DEC = 2:3:3:2, additives include ES: 0.5wt%, VC: 0.5wt%.

[0158] Comparative Example 3

[0159] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0160] Acetonitrile:EC:EMC:DEC = 2:3:3:2, no additives.

[0161] Comparative Example 4

[0162] The secondary battery was prepared according to the method of Example 1, except for the following differences, otherwise it was the same as in Example 1:

[0163] EC:EMC:DEC = 3:5:2, with additives including ES: 0.5% and VC: 0.5%.

[0164] Battery performance test

[0165] 1. Room temperature DCR test: At 25±2℃, the secondary batteries obtained from each implementation case and comparative example were charged to 4.2V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, they were pulsed at 10C constant current for 10 seconds. The SOC was then adjusted to 50% according to the above method, and then charged for 10 seconds. The DCR was calculated as follows: DCR = (voltage before pulse discharge - voltage after pulse discharge) / discharge current * 100%.

[0166] 2. Low-Temperature DCR Test: At -30±2℃, the secondary batteries obtained from each implementation case and comparative example were charged to 4.2V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, a 3C constant current pulse discharge was performed for 10 seconds. The SOC was then adjusted to 50% using the same method, and charged again for 10 seconds. The DCR was calculated as: DCR = (Voltage before pulse discharge - Voltage after pulse discharge) / Discharge current * 100%. Here, SOC (state of charge) refers to the current capacity state of the secondary battery. 100% SOC means fully charged within the design operating range.

[0167] 3. High-Temperature Cycling Performance Test: At 60±2℃, the secondary batteries obtained from each implementation case and comparative example were subjected to charge-discharge cycle tests within the range of 2.8~4.2V at a charge-discharge rate of 5C / 5C. The discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle * 100%. The recorded data are shown in Table 1.

[0168] 4. Low-temperature cycle performance test: At -10±2℃, the secondary batteries obtained from each implementation case and comparative example were charged at a constant current of 0.2C to a voltage of 4.2V, charged at a constant voltage of 4.2V to a current of 0.05C, left to stand for 5 minutes, and discharged at 0.2C to 2.8V. 100 charge-discharge cycles were performed, and the discharge capacity of the 100th cycle was measured.

[0169] -10℃ cycle capacity retention rate = (100th discharge capacity / 1st discharge capacity) × 100%, and the recorded data are shown in Table 1.

[0170] Table 1

[0171]

[0172]

[0173]

[0174] Results analysis:

[0175] (1) By comparing the experimental results of Examples 1, 2, 3, 4, and 14 with those of Example 1, it can be seen that, based on the same additive formulation, the addition of acetonitrile to the solvent system to replace EMC significantly improves the DCR of the battery at both room temperature and low temperature. Among them, Example 2 shows the most significant improvement, but its cycle performance is poor. Even if the additive content is further increased (Example 4), it is still not enough to fully suppress the rapid decay of its cycle performance. The DCR of Example 1 is between that of Examples 1 and 3, and its high cycle performance is not significantly different from that of Example 3. At the same time, because the impedance of Example 1 at low temperature is significantly lower than that of Example 3, its low temperature cycle performance is better than that of Example 3. Therefore, considering both cycle and DCR performance, Example 1 is the optimal solution.

[0176] (2) By comparing the experimental results of implementation cases 1 and 5, it can be seen that when acetonitrile is added to the solvent system to replace part of EC and EMC, the impedance will be further reduced, but the high-temperature cycling performance will deteriorate. This is mainly because EC has high viscosity and high melting point. Reducing its content is beneficial to improving kinetic performance and reducing impedance. However, EC not only plays a dominant role in the dissociation of lithium salt, but also has a very important film-forming effect and plays a very important role in high-temperature performance. Therefore, it is necessary to ensure a certain content of EC to balance kinetic and high-temperature cycling performance.

[0177] (3) By comparing the experimental results of Example 1 with those of Comparative Examples 2 and 3, it can be seen that the cycling performance of Comparative Example 3 is extremely poor, and the initial DCR is not improved. This is because without the presence of film-forming additives, a large amount of solvent will be consumed to participate in film formation, and the film formation is not stable enough, with more by-products and increased impedance. Comparative Example 2 contains only additives ES and VC, which can improve the cycling performance to a certain extent, but it is still at a poor level. Compared with the conventional electrolyte of Comparative Example 4, there is still a large gap. This shows that the presence of only ES and VC cannot suppress the occurrence of side reactions at the acetonitrile interface.

[0178] (4) By comparing the experimental results of Examples 1, 6, 7, 11, and 12, it can be seen that under the same solvent formulation, Example 6 exhibits worse high-temperature cycling performance compared to Example 1. This is mainly because there are insufficient additives to form a stable SEI film to inhibit the occurrence of side reactions of acetonitrile at the interface. Furthermore, the SEI film cannot be repaired in time during cycling, leading to the continued occurrence of side reactions and resulting in capacity loss. Example 7 shows increased impedance compared to Example 1, and the cycling performance was not further improved. This is mainly attributed to the fact that the additive combination in Example 1 already met the usage requirements, and excessive additives would increase film-forming impedance.

[0179] (5) The experimental results of Examples 1, 8, 9, and 13 show that both excessively high and low lithium salt content will cause performance degradation. In particular, excessively low lithium salt content results in low electrolyte conductivity, while excessively high lithium salt content increases electrolyte viscosity. Furthermore, changes in lithium salt content will also cause differences in solvation structure, affecting solvation energy barrier and film formation during desolvation, thereby altering the interfacial film composition. Therefore, it is necessary to optimize the lithium salt content.

[0180] This application combines additives within a preferred range and conducts DOE experiments on the additive combinations. The results show that Example 1 is the optimal combination, and other combinations are not listed in Examples. Furthermore, this application does not list examples where acetonitrile replaces DEC because the viscosity difference between EMC and DEC is small, far less than the difference between EMC and acetonitrile. Additionally, DEC exhibits better high-temperature performance than EMC. To ensure good high-temperature performance, a certain amount of DEC needs to be maintained, as confirmed by the DOE experiment results. In summary, the secondary battery using the electrolyte provided in this application not only has excellent low-temperature performance but also maintains cycle performance comparable to conventional solutions (Comparative Example 4). It should be noted that the formulation can be fine-tuned later according to the application scenario.

[0181] The present application provides a detailed description of an electrolyte, a secondary battery, and an electrical device according to its embodiments. Specific examples have been used to illustrate the principles and implementation methods of the present application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of the present application. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of the present application. Therefore, the content of this specification should not be construed as a limitation of the present application.

Claims

1. An electrolyte, characterized in that, Including lithium salts, organic solvents, and additives; The organic solvents include acetonitrile and carbonate compounds; The additives include acid anhydride compounds and compound A, which conforms to the following structural formula: ； The X includes at least one of halogen, benzene ring, toluene, alkyl, and alkenyl groups; The mass ratio of the acid anhydride compound to compound A is 0.2 to 1.1; The mass percentage of compound A in the electrolyte is 0.5% to 1.5%; The lithium salt accounts for 10% to 15% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, Compound A includes at least one of p-toluenesulfonyl isocyanate, chlorosulfonyl isocyanate, and benzenesulfonyl isocyanate.

3. The electrolyte as described in claim 1, characterized in that, The acetonitrile content in the electrolyte is 5% to 30% by mass. The anhydride compound has a mass percentage of 0.2% to 0.6% in the electrolyte.

4. The electrolyte as described in claim 1, characterized in that, The carbonate compound includes ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate; the ethylene carbonate has a mass percentage of 20% to 30% in the organic solvent. The methyl ethyl carbonate in the organic solvent has a mass percentage content of 30% to 40%. The diethyl carbonate has a mass percentage content of 10% to 20% in the organic solvent.

5. The electrolyte as described in claim 4, characterized in that, The ratio of acetonitrile and carbonate compound in the organic solvent is acetonitrile: ethylene carbonate: methyl ethyl carbonate: diethyl carbonate = (1~4): (2~3): (2~4): (2~3).

6. The electrolyte as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium difluorodi(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

7. The electrolyte as described in claim 1, characterized in that, The acid anhydride compounds include at least one of succinic anhydride, glutaric anhydride, adipic anhydride, pimelic anhydride, phthalic anhydride, maleic anhydride, citrate anhydride, citric anhydride, and 2,3-dimethylmaleic anhydride.

8. The electrolyte as described in claim 7, characterized in that, The acid anhydride compound is glutaric anhydride.

9. The electrolyte as described in claim 1, characterized in that, The additive also includes boron trifluoride-pyridine, wherein the boron trifluoride-pyridine accounts for 0.2% to 0.6% of the total mass of the electrolyte.

10. The electrolyte as described in claim 9, characterized in that, The additives also include vinylite and vinylite sulfate; The vinyl sulfite accounts for 0.5% to 1% of the total mass of the electrolyte; The vinylene sulfate accounts for 0.5% to 1% of the total mass of the electrolyte.

11. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1 to 10.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11, wherein the secondary battery serves as the power supply for the electrical device.

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