Electrolyte, battery, battery assembly and electric device

Abstract

The application discloses an electrolyte, which comprises a first carbonate solvent, a nitrate-containing compound and a dimethyl ether compound, the mass ratio of the nitrate-containing compound in the electrolyte is x, the mass ratio of the first carbonate solvent in the electrolyte is y, and the mass ratio of the dimethyl ether compound in the electrolyte is z, wherein 0.2%<=x<=0.5%, 15%<=y<=30%, 2<=z / x<=3, and 0.5%<=x / (y+18z)<=1.35%. The electrolyte prepared has the advantages of long service life, high power, low temperature and fast charging performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrolyte, a battery, a battery assembly, and an electrical device. Background Technology

[0002] With the rapid development of new energy technologies, lithium-ion batteries, as a core component of energy storage, are increasingly widely used in electric vehicles, smart grids, portable electronic devices, and other fields. Battery lifespan and fast-charging performance are key indicators for evaluating battery performance, directly affecting its practicality and economy. Introducing nitrate-containing compounds into the electrolyte to modify the SEI film can improve battery fast-charging performance. However, lithium nitrate has extremely low solubility in carbonate electrolytes, requiring the introduction of a co-solvent. Current technologies that introduce nitrate-containing compounds cannot simultaneously achieve optimal battery lifespan, power output, and low-temperature performance. Summary of the Invention

[0003] This application aims to at least address one of the technical problems existing in the prior art. Therefore, one object of the present invention is to provide an electrolyte that balances battery life, power, low-temperature performance, and fast-charging capabilities.

[0004] According to a first aspect of this application, an electrolyte is provided, comprising a first carbonate solvent, a nitrate-containing compound, and a dimethyl ether compound, wherein the nitrate-containing compound accounts for x% of the mass of the electrolyte, the first carbonate solvent accounts for y% of the mass of the electrolyte, and the dimethyl ether compound accounts for z% of the mass of the electrolyte, wherein 0.2%≤x≤0.5%, 15%≤y≤30%, 2≤z / x≤3, and 0.5%≤x / (y+18z)≤1.35%.

[0005] The electrolyte provided in this application uses a first carbonate solvent and a dimethyl ether compound as co-solvents to assist in the dissolution of nitrate-containing compounds in the electrolyte and participate in the formation of a negative electrode film, forming an SEI film containing Li3N and nitrogen oxides. This SEI film has high Li3N content. + Electrical conductivity is beneficial for reducing battery impedance and improving fast-charging performance. Simultaneously, comprehensively controlling the mass content x of nitrate-containing compounds, the mass content y of the first carbonate solvent, and the mass content z of dimethyl ether compounds to satisfy: 0.2%≤x≤0.5%, 15%≤y≤30%, 2≤z / x≤3, 0.5%≤x / (y+18z)≤1.35%, can reduce electrolyte solvent consumption, promote a decrease in organic components and an increase in inorganic components in the SEI film, enhance the density, mechanical strength, and stability of the SEI film, effectively reduce side reactions, improve battery cycle and storage life, and simultaneously improve ionic conductivity in the SEI film and reduce desolvation energy, thereby improving battery power, low-temperature performance, and fast-charging performance.

[0006] According to some embodiments of this application, 0.3% ≤ z ≤ 1.5%.

[0007] According to some embodiments of this application, the first carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, and butene carbonate.

[0008] According to some embodiments of this application, the nitrate-containing compound includes at least one selected from lithium nitrate, 1,2-dimethyl-3-butylimidazolium nitrate, 1-propyl-3-methylimidazolium nitrate, 1-ethyl-3-methylimidazolium nitrate, 1-methyl-3-butylimidazolium nitrate, N-propyl-N-methylpyrrolidine nitrate, N-ethyl,methylpiperidine nitrate, ethyl nitrate, propyl nitrate, and butyl nitrate.

[0009] According to some embodiments of this application, the dimethyl ether compound includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxopentane.

[0010] According to some embodiments of this application, the electrolyte further includes a second carbonate solvent, which includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and diphenyl carbonate, and the second carbonate solvent accounts for 1% to 80% of the mass of the electrolyte.

[0011] According to some embodiments of this application, the electrolyte further includes a carboxylic acid ester solvent, which includes at least one of γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl 2-methylbutyrate, methyl butyrate, butyl butyrate, ethyl butyrate, isobutyl butyrate, isoamyl butyrate, ethyl valerate, butyl acetate, decyl acetate, hexyl acetate, and pentyl acetate, wherein the carboxylic acid ester solvent accounts for 1% to 70% of the mass of the electrolyte.

[0012] According to some embodiments of this application, the electrolyte further includes lithium salts, including lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the mass ratio of lithium hexafluorophosphate to the electrolyte is 7% to 14% and the mass ratio of lithium difluorosulfonylimide to the electrolyte is 0.1% to 7%.

[0013] According to some embodiments of this application, the electrolyte further includes additives, including vinylene carbonate, fluoroethylene carbonate, propylene sulfite, methylene disulfonate, vinyl sulfite, vinyl sulfate, 1,3-propylene sulfonate lactone, 1,4-butane sulfonate lactone, 1,3-propane sulfonate lactone, pentaerythritol dicyclic sulfate, 1,3,2-dioxane, 2,4,8,10-tetraoxa-3,9-dithiaspiro, methyl trifluoroethyl carbonate, and difluoro... The electrolyte contains at least one of the following: ethylene carbonate, propargyl phosphate, triallyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(trimethylsilyl) phosphite, lithium trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate; the additive constitutes 0.5% to 5% of the electrolyte by mass.

[0014] The second aspect of this application provides a battery that, by utilizing the electrolyte described in the first aspect of this application, can balance lifespan, power, low-temperature performance, and fast-charging capabilities.

[0015] A third aspect of this application provides a battery assembly that, by utilizing the battery described in the second aspect of this application, achieves a balance of lifespan, power, low-temperature performance, and fast-charging capabilities.

[0016] The fourth aspect of this application provides an electrical device that, by utilizing the battery according to the second aspect of this application or the battery assembly described in the third aspect, can balance lifespan, power, low-temperature performance, and fast-charging capabilities. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are exemplary and used to explain the invention, and should not be construed as limiting the invention.

[0018] This application is based on the inventor's discovery and understanding of the following facts and problems: According to the inventor's research, a battery typically includes a cell and an electrolyte that wets the cell. The cell includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. During the charging and discharging process of the battery, active ions (such as lithium ions in a lithium-ion battery) are transported between the positive and negative electrodes through the electrolyte and undergo corresponding extraction / intercalation. During the charging and discharging process, components such as solvents, additives, and lithium salts in the electrolyte undergo a reduction reaction on the surface of the negative electrode, generating an SEI film (solid electrolyte interphase). The SEI film conducts ions but not electrons, which can inhibit further reduction and consumption of the electrolyte. However, the SEI film formed by carbonate electrolytes has poor ionic conductivity, hindering the intercalation / extraction process of active ions such as lithium ions (Li+), thus affecting the battery's fast-charging performance. According to the inventors' research, using carbonate solvents and adding nitrate-containing compounds (such as lithium nitrate (LiNO3)) to the electrolyte can form an SEI film with high ionic conductivity, improving the battery's fast-charging performance. However, lithium nitrate has extremely low solubility in carbonate electrolytes, requiring the introduction of a co-solvent. Existing methods that introduce nitrate-containing compounds cannot simultaneously achieve optimal battery life, power, low-temperature performance, and fast-charging performance. How to improve battery performance while avoiding these problems and obtaining a battery with excellent overall performance remains a challenge to overcome.

[0019] In view of the above, the first aspect of this application provides an electrolyte comprising a first carbonate solvent, a nitrate-containing compound, and a dimethyl ether compound, wherein the mass ratio of the nitrate-containing compound to the electrolyte is x, the mass ratio of the first carbonate solvent to the electrolyte is y, and the mass ratio of the dimethyl ether compound to the electrolyte is z, wherein 0.2%≤x≤0.5%, 15%≤y≤30%, 2≤z / x≤3, and 0.5%≤x / (y+18z)≤1.35%.

[0020] The electrolyte provided in this application uses a first carbonate solvent and a dimethyl ether compound as co-solvents to assist in the dissolution of nitrate-containing compounds in the electrolyte and participate in the formation of a negative electrode film, forming an SEI film containing Li3N and nitrogen oxides. This SEI film has high Li3N content. +Electrical conductivity is beneficial for reducing battery impedance and improving fast-charging performance. Simultaneously, comprehensively controlling the mass content x of nitrate-containing compounds, the mass content y of the first carbonate solvent, and the mass content z of dimethyl ether compounds to satisfy: 0.2%≤x≤0.5%, 15%≤y≤30%, 2≤z / x≤3, 0.5%≤x / (y+18z)≤1.35%, can reduce electrolyte solvent consumption, promote a decrease in organic components and an increase in inorganic components in the SEI film, enhance the density, mechanical strength, and stability of the SEI film, effectively reduce side reactions, improve battery cycle and storage life, and simultaneously improve ionic conductivity in the SEI film and reduce desolvation energy, thereby improving battery power, low-temperature performance, and fast-charging performance.

[0021] According to the embodiments of this application, 0.2% ≤ x ≤ 0.5%. x is, for example, a range of 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any combination thereof. By adjusting the amount of nitrate-containing compounds added to the electrolyte to meet the above range, their dissolution in the electrolyte is facilitated, and a high ionic conductivity and stable SEI film is formed on the electrode surface, thereby better balancing the improvement of battery fast-charging performance and cycle / storage life.

[0022] According to the embodiments of this application, 15% ≤ y ≤ 30%. y is, for example, a range consisting of any two of 15%, 18%, 20%, 23%, 25%, 28%, and 30%. By adjusting the amount of the first carbonate solvent added to the electrolyte, the solubility of nitrate-containing compounds in the carbonate-based electrolyte can be promoted, thereby improving the high-temperature performance of the lithium-ion battery.

[0023] According to the embodiments of this application, 2≤z / x≤3, 0.5%≤x / (y+18z)≤1.35%, by comprehensively controlling the amount of first carbonate solvent, nitrate-containing compound and dimethyl ether compound added, the overall performance of the battery can be improved, thereby obtaining a battery with long life, good power performance, low temperature performance and fast charging performance.

[0024] According to the embodiments of this application, 0.3% ≤ z ≤ 1.5%. z is, for example, a range of 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.3%, 1.4%, or any combination thereof. By further controlling the content of dimethyl ether compound z in the electrolyte within this range, it is beneficial to promote the dissolution of nitrate-containing compounds while further avoiding the co-intercalation reaction of dimethyl ether compounds with graphite, thereby better balancing the improvement of battery life performance.

[0025] According to embodiments of this application, the first carbonate solvent includes at least one selected from ethylene carbonate, propylene carbonate, and butene carbonate. This not only promotes the dissolution of nitrate-containing compounds but also provides good electrochemical stability, which is beneficial for improving battery life.

[0026] According to embodiments of this application, the nitrate-containing compound may include at least one of lithium nitrate, 1,2-dimethyl-3-butylimidazolium nitrate, 1-propyl-3-methylimidazolium nitrate, 1-ethyl-3-methylimidazolium nitrate, 1-methyl-3-butylimidazolium nitrate, N-propyl-N-methylpyrrolidine nitrate, N-ethyl,methylpiperidine nitrate, ethyl nitrate, propyl nitrate, and butyl nitrate. This reduces the decomposition of the first carbonate solvent, decreases battery gas production, and improves battery cycle life. Furthermore, the nitrate-containing compound may include lithium nitrate. When the electrolyte is applied to a lithium-ion battery in a system where lithium nitrate and dimethyl ether compounds coexist, it is more conducive to forming a high lithium-ion conductivity and stable SEI film on the electrode surface, thus improving both the fast-charging performance and lifespan of the lithium-ion battery.

[0027] According to embodiments of this application, the dimethyl ether compound includes at least one selected from ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxopentane. These dimethyl ether compounds facilitate the dissolution of nitrate-containing compounds in the electrolyte, forming a high-ionic-conductivity SEI film on the electrode surface. Simultaneously, they can reduce the co-intercalation reaction with graphite, thereby further improving both the fast-charging performance and lifespan of the battery.

[0028] According to embodiments of this application, the electrolyte further includes a second carbonate solvent, which includes at least one selected from dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and diphenyl carbonate. The second carbonate solvent accounts for 1% to 80% of the electrolyte by mass, for example, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, or any combination thereof. The electrolyte is predominantly composed of the first carbonate solvent, meaning it is a carbonate electrolyte. Introducing the aforementioned proportions of nitrate-containing compounds and dimethyl ether compounds into it helps to improve both the fast charging and lifespan performance of the battery. Simultaneously, it also facilitates the preparation of the electrolyte, offering advantages such as low production costs and greater suitability for practical industrial applications.

[0029] According to embodiments of this application, the electrolyte further includes a carboxylic acid ester solvent, which includes at least one selected from γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl 2-methylbutyrate, methyl butyrate, butyl butyrate, ethyl butyrate, isobutyl butyrate, isoamyl butyrate, ethyl valerate, butyl acetate, decyl acetate, hexyl acetate, and amyl acetate. The carboxylic acid ester solvent accounts for 1% to 70% of the mass of the electrolyte. For example, the mass ratio of the carboxylic acid ester solvent to the electrolyte is 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 65%, or any combination thereof. This reduces the electrolyte viscosity and improves lithium-ion transport capacity.

[0030] According to embodiments of this application, the electrolyte may further include a lithium salt, which may include lithium hexafluorophosphate and lithium bisfluorosulfonylimide. The lithium hexafluorophosphate accounts for 7% to 14% of the electrolyte by mass, and the lithium bisfluorosulfonylimide accounts for 0.1% to 7% of the electrolyte by mass. This is beneficial for further improving the electrolyte conductivity, reducing battery internal resistance, and improving battery cycle life and other performance characteristics.

[0031] According to embodiments of this application, the electrolyte further includes additives, including vinylene carbonate, fluoroethylene carbonate, propylene sulfite, methylene disulfonate, vinyl sulfite, vinyl sulfate, 1,3-propylene sulfonate lactone, 1,4-butane sulfonate lactone, 1,3-propane sulfonate lactone, pentaerythritol bicyclic sulfate, 1,3,2-dioxane, 2,4,8,10-tetraoxa-3,9-dithiaspiro, methyl trifluoroethyl carbonate, and difluoroethylene carbonate. The electrolyte contains at least one of the following: lithium trifluoromethyl phosphate, triargyl phosphate, triallyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(trimethylsilyl) phosphite, lithium trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate; the additive constitutes 0.5% to 5% of the electrolyte by mass. By introducing the additive into the electrolyte, it can synergistically form a high lithium-ion conductivity and stable SEI film on the electrode surface with nitrate-containing compounds, thereby improving both the fast-charging performance and high-temperature cycle stability of lithium-ion batteries.

[0032] A second aspect of this application also provides a battery including the electrolyte described above, which has advantages corresponding to the electrolyte described above, which will not be elaborated further.

[0033] According to an embodiment of this application, the battery includes a cell and a casing for encapsulating the cell. Electrolyte is injected into the cell within the casing. The cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The cell can be a stacked cell, meaning it is formed by alternating layers of positive electrode, separator, and negative electrode. Alternatively, it can be a wound cell, meaning it is formed by stacking positive electrode, negative electrode, and separator and then winding them.

[0034] According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive electrode coating located on at least one side of the positive current collector. Specifically, the positive electrode coating may be provided on one side of the positive current collector, or positive electrode coatings may be provided on both opposite sides in the thickness direction of the positive current collector.

[0035] According to embodiments of this application, the positive electrode coating (positive electrode active material layer) may include a positive electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary positive electrode materials. The ternary positive electrode materials may include nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials. The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber. The binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0036] According to embodiments of this application, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.) and a metal layer (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) formed on at least one surface of the polymer material base film.

[0037] According to embodiments of this application, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. This allows for better adhesion of the positive electrode active material to the positive electrode current collector, resulting in stronger adhesion and reducing the likelihood of problems such as positive electrode dressing detachment.

[0038] According to embodiments of this application, the positive electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers. This effectively improves conductivity, reduces internal resistance, and enhances the electrochemical performance of lithium-ion batteries.

[0039] According to the embodiments of this application, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode coating can be dispersed in a positive electrode solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0040] According to embodiments of this application, the positive electrode further includes a lithium replenishing agent, which includes at least one selected from lithium iron phosphate, lithium nickel phosphate, lithium oxide, lithium peroxide, and lithium nitride. This can further improve battery capacity.

[0041] According to an embodiment of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating located on at least one side surface of the negative electrode current collector. Specifically, the negative electrode coating may be provided on one side surface of the negative electrode current collector, or negative electrode coatings may be provided on both opposite sides of the negative electrode current collector in the thickness direction.

[0042] According to embodiments of this application, the negative electrode coating (negative electrode active material layer) may include a negative electrode active material (negative electrode active material), a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include one or more of graphite, silicon, silicon oxide, and lithium metal; the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0043] According to the embodiments of this application, the negative electrode active material includes graphite. By using the above-mentioned electrolyte, it is beneficial to form an SEI film with high ionic conductivity and stability on the surface of the graphite negative electrode, thereby improving the battery's fast charging cycle stability and high temperature cycle stability. Moreover, graphite has high industrial maturity, low cost, and strong compatibility with the positive electrode, making it suitable for large-scale production.

[0044] According to embodiments of this application, the negative electrode current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, copper foil current collectors; composite current collectors may include a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.) and a metal layer (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) formed on at least one surface of the polymer material base layer.

[0045] According to embodiments of this application, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0046] According to embodiments of this application, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0047] According to the embodiments of this application, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a negative electrode solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0048] According to the embodiments of this application, the separator is used to separate the positive electrode and the negative electrode to avoid short circuit between the positive electrode and the negative electrode. The embodiments of the present invention may use conventional separators in the art, such as polypropylene membranes (PP membranes), but are not limited thereto.

[0049] According to the embodiments of this application, the battery cell can be packaged using conventional housing materials in the art, such as aluminum-plastic film and other soft packaging materials (in which case the battery is a soft-pack battery), but is not limited to this.

[0050] According to the embodiments of this application, components such as positive electrode, separator and negative electrode can be assembled into a battery by conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing and subjected to conventional processes such as electrolyte injection (i.e., injection of electrolyte) and formation to obtain a battery.

[0051] The third aspect of this application provides a battery assembly that, by utilizing the battery according to the second aspect of this application, has good fast-charging performance and good high-temperature storage performance.

[0052] According to embodiments of this application, the specific type of battery assembly is not particularly limited; the battery assembly can be a battery module, a battery pack, etc. In some embodiments, the batteries can be assembled into a battery module, and the number of batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, the batteries can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0053] The fourth aspect of this application provides an electrical device that, by utilizing the battery according to the second aspect of this application or the battery assembly described in the third aspect of this application, has good fast charging performance and good high-temperature storage performance.

[0054] According to the embodiments of this application, the specific type of electrical device is not particularly limited, and it can be any device that uses a lithium-ion battery as a power source or energy storage unit. As examples, electrical devices include, but are not limited to, electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc.

[0055] It is understandable that, in addition to the battery mentioned above, the electrical device also includes other necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0056] According to the embodiments of this application, ion chromatography (IC) and gas chromatography-mass spectrometry (GC-MS) can be used to detect the components and their contents in the electrolyte, such as nitrate-containing compounds, boron-containing lithium oxalate, and organic solvents. For example, the content of nitrate-containing compounds and boron-containing lithium oxalate in the electrolyte can be measured by IC, and the content of organic solvents can be measured by GC-MS.

[0057] For example, the content of nitrate-containing compounds in electrolyte can be tested using an ion chromatograph (IC). Taking the IC-2800 ion chromatograph as an example, the test conditions are as follows: anion exchange column, suppressor current 35 mA, flow rate 1 mL / min, eluent 5 mmol / L sodium carbonate solution: acetone = 75:25, injection volume 100 µL; the test process is as follows: (1) First, dilute the sample to be tested: take 1 mL of electrolyte, dilute with acetonitrile and transfer to a 100 mL volumetric flask, dilute to the mark with acetonitrile, shake well and test; (2) Next, prepare the standard solution: take 0.05 mL of NO3- aqueous solution with a concentration of 1 mg / mL (prepared with a nitrate-containing compound (such as lithium nitrate)), dilute to a 10 mL volumetric flask with deionized water to obtain a NO3- aqueous solution with a concentration of 5 µg / mL, take 1 mL, 2 mL, 4 mL and 10 mL of this solution to a 10 mL volumetric flask respectively. (2) Prepare a series of standard solutions with concentration gradients by diluting the volumetric flask with deionized water to the mark; (3) Analyze the standard samples: establish a standard curve with the peak area (y) of NO3- as the ordinate and the concentration of the standard sample as the abscissa (x), and obtain the curve equation and correlation coefficient; (4) Finally, test the electrolyte to be tested, substitute the measured peak area of ​​NO3- into the standard curve equation, and calculate the content of nitrate-containing compounds (such as lithium nitrate) in the electrolyte. The content of other organic solvents can be obtained by gas chromatography-mass spectrometry (GC-MS), which will not be elaborated here.

[0058] Example 1:

[0059] Positive electrode preparation: Polyvinylidene fluoride (binder) is added to N-methylpyrrolidone (solvent) and stirred to dissolve. Then, conductive carbon black (conductive agent) and lithium iron phosphate (positive electrode active material) are added and kneaded thoroughly to obtain a positive electrode slurry (lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a weight ratio of 96.8:0.8:2.4). The above positive electrode slurry is uniformly coated on current collector aluminum foil, and after baking and rolling, a positive electrode sheet is obtained.

[0060] Negative electrode preparation: Graphite (negative electrode active material), conductive carbon black (conductive agent), SBR (binder), and CMC (thickener) are mixed in a mass ratio of 93:1:4:2, deionized water is added as a solvent, and the mixture is kneaded thoroughly to obtain a negative electrode slurry; the above negative electrode slurry is uniformly coated on the current collector copper foil, and after baking and rolling, a negative electrode sheet is obtained.

[0061] Electrolyte: The electrolyte is prepared by uniformly mixing 0.2 wt% lithium nitrate (LiNO3), 2 wt% vinylene carbonate (VC), 30 wt% ethylene carbonate (EC), 1% fluoroethylene carbonate (FEC), 1% methanedisulfonate (MMDS), 0.78 wt% ethylene glycol dimethyl ether (DME), 35.39 wt% methyl ethyl carbonate and dimethyl carbonate (EMC+DMC), 20 wt% ethyl acetate (EA), 10 wt% lithium hexafluorophosphate (LiPF6) and 2% lithium bis(fluorosulfonyl)imide (LiFSI).

[0062] The diaphragm is made of commercially available PE copolymer microporous membrane with a thickness of 11μm.

[0063] Assembly: Positive electrode, separator and negative electrode are alternately stacked to form a stacked cell; the cell is encapsulated with aluminum-plastic film and electrolyte is injected into it, and then the battery is obtained after formation and other processes.

[0064] The preparation of Examples 2-6, 8-11 and Comparative Examples 1-7 is basically the same as that of Example 1. The differences are shown in Table 1.

[0065] The preparation of Example 7 is basically the same as that of Example 1, except that the positive electrode sheet includes a lithium supplement agent. Polyvinylidene fluoride (binder) is added to N-methylpyrrolidone (solvent), stirred and dissolved, and then conductive carbon black (conductive agent), lithium iron phosphate (positive electrode active material), and lithium-rich lithium iron phosphate (lithium supplement agent) are added and fully kneaded to obtain a positive electrode slurry (the weight ratio of lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and lithium-rich lithium iron phosphate is 96.7:0.8:2.4:0.1). The above positive electrode slurry is uniformly coated on the current collector aluminum foil, and after baking and rolling, a positive electrode sheet is obtained.

[0066] Table 1 (Electrolyte Composition)

[0067] Nitrate compounds x First carbonate y dimethyl ether compounds z x / (y+18z) z / x EMC+DMC VC EA FEC MMDS <![CDATA[LiPF6]]> LiFSI Example 1 Lithium nitrate 0.2 EC 30 DME 0.41 0.54% 2.1 33.39 2 20 1 1 10 2 Example 2 Lithium nitrate 0.3 EC 18 DME 0.7 0.98% 2.3 45 2 20 1 1 10 2 Example 3 Lithium nitrate 0.35 EC 25 DME 0.85 0.87% 2.4 37.8 2 20 1 1 10 2 Example 4 Lithium nitrate 0.4 EC 20 DME 1 1.05% 2.5 42.6 2 20 1 1 10 2 Example 5 Lithium nitrate 0.5 EC 15 DME 1.3 1.30% 2.6 47.2 2 20 1 1 10 2 Example 6 Lithium nitrate 0.5 EC 15 Diethylene glycol dimethyl ether 1.3 1.30% 2.6 47.2 2 20 1 1 10 2 Example 7 Lithium nitrate 0.5 EC 15 DME 1.3 1.30% 2.6 47.2 2 20 1 1 12 0 Example 8 Lithium nitrate 0.5 EC 15 DME 1.3 1.30% 2.6 47.2 2 20 1 1 10 2 Example 9 Lithium nitrate 0.5 propylene carbonate 15 DME 1.3 1.30% 2.6 47.2 2 20 1 1 10 2 Example 10 1-Ethyl-3-methyl-imidazolium nitrate 0.5 EC 15 DME 1.3 1.30% 2.6 47.2 2 20 1 1 10 2 Example 11 Ethyl nitrate 0.5 EC 15 DME 1.3 1.30% 2.6 47.2 2 20 1 1 10 2 Comparative Example 1 EC 30 0 0.00% 0 34 2 20 1 1 10 2 Comparative Example 2 Lithium nitrate 0.25 EC 25 DME 0.4 0.78% 1.6 38.35 2 20 1 1 10 2 Comparative Example 3 Lithium nitrate 0.3 EC 20 DME 2 0.54% 6.7 41.7 2 20 1 1 10 2 Comparative Example 4 Lithium nitrate 0.1 EC 30 DME 0.5 0.26% 5 33.4 2 20 1 1 10 2 Comparative Example 5 Lithium nitrate 1 EC 14 DME 1.5 2.44% 1.5 47.5 2 20 1 1 10 2 Comparative Example 6 Lithium nitrate 0.3 EC 35 DME 0.7 0.63% 2.3 28 2 20 1 1 10 2 Comparative Example 7 Lithium nitrate 0.3 EC 10 DME 1 1.07% 3.3 52.7 2 20 1 1 10 2

[0068] Performance testing:

[0069] The performance of the lithium-ion batteries in each embodiment and comparative example was tested using the following process, and the results are shown in Table 2:

[0070] 1. Room Temperature DCIR Test: ① Let stand at room temperature for 5 hours, adjust to 50% SOC (adjust SOC by charging at 0.33C); ② Rest: 2 hours; ③ Charge DCIR: 1.5C constant current charging for 30 seconds; ④ Rest: 30 minutes; ⑤ Discharge DCIR: 1.5C constant current discharging for 30 seconds. Record the last voltage data from steps ② to ⑤, labeling them V1, V2, V3, and V4 respectively. Calculate the DCIR value using the following formula:

[0071] DCIR charging = (V2 - V1) / 1.5C * 1000 (Unit: mΩ)

[0072] DCIR discharge = (V3 - V4) / 1.5C * 1000 (unit: mΩ)

[0073] 2. Low-temperature cycling test: Place the sample in -10℃ and let it rest for 6 hours; charge at -10℃: charge at a constant current of 0.2C to 3.55V, and let it rest for 60 minutes; discharge at -10℃: discharge at a constant current of 1 / 3C to 2.0V, and let it rest for 60 minutes. Termination condition: 100 cycles. Record the charge and discharge capacity. The ratio of the reversible capacity after 100 cycles to the reversible capacity after the first cycle is the capacity retention rate after 100 cycles at -10℃.

[0074] 3. High-temperature cycling test: Place the sample in a 60℃ environmental chamber and let it stand for 4 hours; charge at 60℃: charge at 1C constant current to 3.8V, and let it stand for 10 minutes; discharge at 60℃: discharge at 1C constant current to 2.0V, and let it stand for 10 minutes. Termination condition: cycle 500 times, record the charge and discharge capacity. The ratio of the reversible capacity after 500 cycles to the reversible capacity after the first cycle is the capacity retention rate after 500 cycles at 60℃.

[0075] 4. High-temperature storage performance: Charge to 100% SOC at room temperature using 1 / 3C constant current and constant voltage (cutoff voltage 3.8V, cutoff voltage 0.05C); store at 60℃ for 28 days. After storage, remove the battery and let it rest at room temperature for 4 hours; discharge to 2.0V using 1 / 3C constant current, and record the discharge capacity as the remaining capacity. Then cycle the battery again using 1 / 3C constant current charge and discharge, and use the discharge capacity of the third cycle as the recovery capacity.

[0076] 5. Fast Charging Performance: At 25℃, the battery was fully charged at nC and fully discharged at 1C for 10 charge-discharge cycles. Then, it was fully charged at nC. The negative electrode was then disassembled, and the lithium plating on its surface was observed. If the area of ​​the lithium plating region on the negative electrode surface was less than 5%, it was considered slight lithium plating; if the area was 5%–40%, it was considered moderate lithium plating; and if it was greater than 40%, it was considered severe lithium plating. If no lithium plating occurred on the negative electrode surface (i.e., no lithium plating area), the charging rate was increased from nC in increments of 0.1C, and the test was repeated until slight lithium plating appeared on the negative electrode surface. The test was then stopped. The maximum charging rate of the battery under non-lithium plating conditions was nC minus 0.1C.

[0077] The performance test results of each embodiment and comparative example are shown in Table 2:

[0078] Table 2

[0079] DCIR (mΩ / Ah) at room temperature (1.5C) Capacity retention % after 50 cycles at -10℃ Capacity retention rate (%) after 500 cyc cycles at 60°C 60℃ storage for 28 days: capacity recovery rate % Lithium plating rate / C Example 1 23 91 93 93 4 Example 2 21 92.5 94 94 5 Example 3 20 93 95 96 6 Example 4 19 93.5 95 96 6.5 Example 5 18 94 94 95 7 Example 6 20 93 93 93.5 5.5 Example 7 18 94 94 95 7 Example 8 19 93 93 92 6.5 Example 9 20 92 90 89 4 Example 10 25 91 92 90 3.5 Example 11 24 90 91 90 3.5 Comparative Example 1 30 85 80 80 3 Comparative Example 2 Insoluble in electrolyte Unable to manufacture batteries - - - Comparative Example 3 21 92 86 85 5.5 Comparative Example 4 30 85 80 80 3 Comparative Example 5 15 95 82 83 7 Comparative Example 6 25 79 90 90 3 Comparative Example 7 21 92 79 78 5

[0080] As can be seen from Table 2, Examples 1-11 of this application use a first carbonate solvent and a dimethyl ether compound as a co-solvent to assist the dissolution of nitrate-containing compounds in the electrolyte, and control the mass content x of the nitrate-containing compound, the mass content y of the first carbonate solvent, and the mass content z of the dimethyl ether compound to satisfy: 0.2%≤x≤0.5%, 15%≤y≤30%, 2≤z / x≤3, 0.5%≤x / (y+18z)≤1.35%. The resulting battery can balance lifespan, power, low temperature performance, and fast charging performance.

[0081] In the description of this specification, the references to terms such as "implementation," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0082] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises a first carbonate solvent, a nitrate-containing compound, and a dimethyl ether compound, wherein the nitrate-containing compound accounts for x% of the mass of the electrolyte, the first carbonate solvent accounts for y% of the mass of the electrolyte, and the dimethyl ether compound accounts for z% of the mass of the electrolyte, wherein 0.2%≤x≤0.5%, 15%≤y≤30%, 2≤z / x≤3, and 0.5%≤x / (y+18z)≤1.35%.

2. The battery according to claim 1, characterized in that, 0.3 %≤z≤1.5%。 3. The battery according to claim 1, characterized in that, The first carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, and butene carbonate.

4. The battery according to claim 1, characterized in that, The nitrate-containing compounds include at least one of lithium nitrate, 1,2-dimethyl-3-butylimidazolium nitrate, 1-propyl-3-methylimidazolium nitrate, 1-ethyl-3-methylimidazolium nitrate, 1-methyl-3-butylimidazolium nitrate, N-propyl-N-methylpyrrolidine nitrate, N-ethyl,methylpiperidine nitrate, ethyl nitrate, propyl nitrate, and butyl nitrate.

5. The battery according to claim 1, characterized in that, The dimethyl ether compound includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxopentane.

6. The battery according to any one of claims 1-5, characterized in that, The electrolyte further includes a second carbonate solvent, which includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and diphenyl carbonate, and the second carbonate solvent accounts for 1% to 80% of the mass of the electrolyte.

7. The battery according to claim 6, characterized in that, The electrolyte further includes a carboxylic acid ester solvent, which includes at least one of γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl 2-methylbutyrate, methyl butyrate, butyl butyrate, ethyl butyrate, isobutyl butyrate, isoamyl butyrate, ethyl valerate, butyl acetate, decyl acetate, hexyl acetate, and pentyl acetate. The carboxylic acid ester solvent accounts for 1% to 70% of the mass of the electrolyte.

8. The battery according to any one of claims 1-5, characterized in that, The electrolyte also includes lithium salts, including lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The lithium hexafluorophosphate accounts for 7% to 14% of the mass of the electrolyte, and the lithium bis(fluorosulfonyl)imide accounts for 0.1% to 7% of the mass of the electrolyte.

9. The battery according to any one of claims 1-5, characterized in that, The electrolyte also includes additives. The additives include vinylene carbonate, fluoroethylene carbonate, propylene sulfite, methylene disulfonate, vinyl sulfite, vinyl sulfate, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, 1,3-propanesulfonate lactone, pentaerythritol dicyclic sulfate, 1,3,2-dioxane, 2,4,8,10-tetraoxa-3,9-dithiaspiro, methyltrifluoroethyl carbonate, and difluoro... At least one of the following: ethylene carbonate, triargyl phosphate, triallyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(trimethylsilyl) phosphite, lithium trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate; The additive accounts for 0.5% to 5% of the mass of the electrolyte.

10. A battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte as described in any one of claims 1-9.

11. The battery according to claim 10, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes graphite; the positive electrode sheet includes a positive electrode active material, which includes lithium phosphate.

12. The battery according to claim 11, characterized in that, The positive electrode also includes a lithium replenishing agent, which includes at least one of lithium iron ferrite, lithium nickel oxide, lithium oxide, lithium peroxide, and lithium nitride.

13. A battery assembly, characterized in that, It includes at least two batteries as described in any one of claims 10-12.

14. An electrical appliance, characterized in that, The electrical device includes an electrical appliance and a battery as described in any one of claims 10-12, or a battery assembly as described in claim 13, wherein the battery or the battery assembly is used to supply power to the electrical appliance.