Electrolyte, battery and electric equipment

Abstract

The invention provides an electrolyte, a battery and electric equipment. The electrolyte provided by the invention comprises a lithium salt and a solvent, wherein the lithium salt comprises lithium bis (fluorosulfonyl) imide; the solvent comprises ethyl acetate. The lithium bis (fluorosulfonyl) imide and the ethyl acetate in the electrolyte are accurately proportioned, so that the quick charging performance of the battery and the cycling stability at high temperature are improved.

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used in mobile devices and electric vehicles due to their significant advantages such as high voltage, high energy density, long charge-discharge life, and safety and environmental friendliness. Fast-charging technology for lithium-ion batteries allows users to quickly restore most of their device's power, thus reducing interruptions caused by insufficient battery power.

[0003] To enhance fast-charging performance, current fast-charging lithium-ion batteries often use lithium hexafluorophosphate (LiPF6) as the lithium salt in their electrolytes. LiPF6 has a high degree of lithium-ion dissociation and can form a stable SEI film on the negative electrode. Fast-charging lithium-ion batteries need to withstand high current densities during charging and discharging. Therefore, the SEI film covering the surface of the negative electrode active material is more prone to damage. The subsequent repair process of the SEI film consumes electrolyte, severely affecting the battery's cycle life. Furthermore, during fast charging, the current density increases significantly, leading to a faster electrochemical reaction rate inside the battery and generating more heat. This increased internal temperature affects the stability of the electrolyte.

[0004] Therefore, there is an urgent need for an electrolyte that can remain stable during the fast charging process of lithium-ion batteries, so that the batteries can have a high cycle life. Summary of the Invention

[0005] This invention provides an electrolyte that supports the fast charging process of lithium-ion batteries, enabling lithium-ion batteries to simultaneously achieve good kinetic performance and long cycle life.

[0006] The present invention also provides a battery comprising the electrolyte as described above, wherein the battery has good fast-charging performance and long cycle life.

[0007] The present invention also provides a battery pack including the battery as described above. The battery pack can be quickly charged in a short time and maintain stable performance over multiple charge and discharge cycles, reducing the need for frequent replacements due to capacity degradation and lowering maintenance costs.

[0008] The present invention also provides an electrical device, including the battery or battery pack described above, which can maintain stable operation for a long period of time and has high reliability.

[0009] This invention provides an electrolyte, wherein the electrolyte comprises a lithium salt and a solvent:

[0010] The lithium salt includes lithium bis(fluorosulfonyl)imide;

[0011] The solvent includes ethyl acetate;

[0012] The electrolyte satisfies the following:

[0013] 0.45 / c≤m2 / m1≤2 / c,

[0014] Wherein, m1 is the mass of the lithium difluorosulfonylimide in the electrolyte;

[0015] m2 is the mass of the ethyl acetate in the electrolyte;

[0016] c represents the molar concentration ratio of the lithium bis(fluorosulfonyl)imide in the lithium salt, where 0.24 ≤ c ≤ 1.

[0017] The electrolyte as described above, wherein 0.25 < c < 0.7.

[0018] The electrolyte as described above, wherein the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is 4.1% to 9.5%.

[0019] The electrolyte as described above, wherein the mass percentage of ethyl acetate in the electrolyte is 9.1% to 29.1%.

[0020] In the electrolyte described above, the coordination ratio of ethyl acetate molecules to lithium ions is (1-4):1.

[0021] The electrolyte as described above, wherein the lithium salt further includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide.

[0022] The electrolyte as described above, wherein the lithium salt is lithium hexafluorophosphate.

[0023] The electrolyte as described above, wherein the solvent further includes at least one of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, N-methylpyrrolidone, and dimethylacetamide.

[0024] The electrolyte as described above, wherein the solvent further includes ethylene carbonate.

[0025] The electrolyte as described above further includes additives, the additives including at least one of vinylene carbonate, fluoroethylene carbonate, and methylene disulfonate.

[0026] The present invention also provides a battery, wherein the battery comprises the electrolyte as described above.

[0027] The battery as described above further includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material, the positive electrode active material including one or more of lithium iron phosphate, lithium manganese iron phosphate and ternary materials, the ternary material including lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide;

[0028] And / or, the battery further includes a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising graphite and / or silicon carbon.

[0029] In the battery described above, the graphite includes at least one of natural graphite and artificial graphite.

[0030] The present invention also provides a battery pack, wherein the battery pack includes the battery as described above.

[0031] The present invention also provides an electrical device, wherein the electrical device includes a battery as described above or a battery pack as described above.

[0032] This invention provides an electrolyte in which the content of lithium bis(fluorosulfonyl)imide and ethyl acetate is precisely proportioned, enabling the electrode solution to support rapid charging of the battery. Furthermore, the electrolyte is relatively stable, allowing the battery to have a long cycle life. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] To meet the lithium-ion concentration requirements during fast charging, lithium hexafluorophosphate is often used as the source of lithium ions in the electrolyte. This substance can ionize a large number of lithium ions in the electrolyte, giving the battery a high energy density.

[0035] The inventors discovered that adding lithium bis(fluorosulfonyl)imide to the electrolyte of lithium-ion batteries improves their fast-charging performance. Furthermore, the ratio of lithium bis(fluorosulfonyl)imide to ethyl acetate has a crucial impact on fast-charging performance. A low ratio results in a high concentration of free ethyl acetate molecules in the electrolyte, leading to severe gas generation within the cell and shortening battery life. Conversely, a high ratio causes a sharp increase in electrolyte viscosity, hindering lithium-ion migration and reducing ionic conductivity, thus affecting the battery's power output. Therefore, a well-designed electrolyte composition is key to achieving good power and cycle performance in lithium-ion fast-charging batteries.

[0036] Furthermore, the current density of lithium-ion batteries increases significantly during fast charging, leading to excessively high internal temperatures and affecting electrolyte stability. Therefore, there is an urgent need for an electrolyte that maintains high stability at high temperatures, enabling the battery to retain high energy density even after multiple rapid charge-discharge cycles.

[0037] Based on this, the first aspect of the present invention provides an electrolyte comprising a lithium salt and a solvent: the lithium salt comprises lithium bis(fluorosulfonyl)imide; the solvent comprises ethyl acetate; the electrolyte satisfies the following conditions:

[0038] 0.45 / c≤m2 / m1≤2 / c,

[0039] Where m1 is the mass of lithium bis(fluorosulfonyl)imide in the electrolyte;

[0040] m2 is the mass of ethyl acetate in the electrolyte;

[0041] c represents the molar concentration of lithium bis(fluorosulfonyl)imide in the lithium salt, where 0.24 ≤ c ≤ 1.

[0042] In detail, the electrolyte provided by this invention may contain only lithium bis(fluorosulfonyl)imide, in which case the molar concentration of lithium bis(fluorosulfonyl)imide in the lithium salt is 100%; alternatively, the lithium salt may include other lithium salts besides lithium bis(fluorosulfonyl)imide, in which case the molar concentration of lithium bis(fluorosulfonyl)imide in the lithium salt is less than 100%. This invention does not impose any special limitations on lithium salts other than lithium bis(fluorosulfonyl)imide, as long as they can provide a source of lithium ions for the electrolyte. For example, the lithium salt can be an organic lithium salt or an inorganic lithium salt.

[0043] In this embodiment of the invention, the solvent in the electrolyte may consist only of ethyl acetate, or it may include other solvents besides ethyl acetate. The inventors have discovered that ethyl acetate has a lower melting point, which can improve the lithium-ion transport efficiency. Furthermore, using ethyl acetate as a solvent can reduce the viscosity of the electrolyte, allowing lithium ions to migrate freely within the electrolyte.

[0044] Furthermore, in this invention, ethyl acetate can form a solvated structure with lithium bis(fluorosulfonyl)imide. A solvated structure refers to a stable structure formed by the interaction between ions and solvent molecules in an electrolyte. In this structure, solvent molecules surround the ions through electrostatic interactions or hydrogen bonds, forming one or more solvated shells, which can significantly optimize the ionic conductivity of the electrolyte. The solvated structure can also improve the thermal and chemical stability of the electrolyte, enabling it to maintain stable properties even in the high-temperature environment generated during fast charging.

[0045] As mentioned above, in order to improve the solvation of the electrolyte, the electrolyte in this invention satisfies the following:

[0046] 0.45 / c≤m 2 / m1≤2 / c

[0047] Where m1 is the mass of lithium bis(fluorosulfonyl)imide in the electrolyte and m2 is the mass of ethyl acetate in the electrolyte. The two masses are of the same order of magnitude. For example, the units of their masses can be mg, g, or kg.

[0048] Furthermore, the molar concentration ratio (c) of lithium bis(fluorosulfonyl)imide in the electrolyte of this invention is in the range of 0.25 ≤ c ≤ 1. When the molar concentration ratio of lithium bis(fluorosulfonyl)imide in the electrolyte meets the above range, the electrolyte can have good conductivity.

[0049] When the electrolyte satisfies 0.45 / c≤m2 / m1≤2 / c, the solvation structure of the electrolyte is relatively complete, with good electrical conductivity and thermal stability, enabling the battery to perform rapid charge and discharge and have a high cycle life.

[0050] Preferably, the molar concentration ratio c of lithium bis(fluorosulfonyl)imide in the electrolyte of the present invention in the lithium salt is in the range of 0.25 < c < 0.7. The electrolyte has higher conductivity and thermal stability, reduces the DC battery capacity, and increases cycle performance.

[0051] In this embodiment of the invention, the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is 4.1% to 9.5%. For example, the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte includes, but is not limited to, 4.1%, 4.7%, 4.9%, 5%, 5.2%, 6%, 7%, 8%, 9%, 9.41%, 9.5%, or any combination thereof. When the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is within the above range, it is beneficial to balance the viscosity and conductivity of the electrolyte.

[0052] Considering the viscosity and solvation structure of the electrolyte, this invention further controls the mass percentage of ethyl acetate in the electrolyte to be between 9.1% and 29.1%. For example, the mass percentage of ethyl acetate in the electrolyte includes, but is not limited to, 9.1%, 9.14%, 10%, 15%, 20%, 25%, 28%, 28.19%, 29.1%, or any combination thereof. When the mass percentage of ethyl acetate in the electrolyte is within the above range, the electrolyte has a suitable viscosity, which is beneficial for the migration of lithium ions in the electrolyte, and the electrolyte has a superior solvation structure, which can improve the stability of the electrolyte.

[0053] Specifically, in every 100g of electrolyte, the mass m1 of lithium difluorosulfonylimide is 4.1–9.5g, and the mass m1 of ethyl acetate is 9.1–29.1g.

[0054] As mentioned above, an electrolyte exhibits a high level of solvation when 0.45 / c ≤ m2 / m1 ≤ 2 / c. When lithium ions from lithium salts participate in solvation in the electrolyte, one lithium ion coordinates with four solvent molecules. The electrolyte in this invention comprises lithium ions and ethyl acetate molecules. When the electrolyte meets the above conditions, the coordination ratio of ethyl acetate molecules to lithium ions is (1–4):1. Specifically, when m2 / m1 = 0.45 / c, ethyl acetate molecules can participate in the solvation structure with lithium ions through a 1:1 coordination; when m2 / m1 = 2 / c, ethyl acetate molecules can participate in the solvation structure with lithium ions through a 4:1 coordination. The above coordination can be determined using molecular dynamics simulations.

[0055] In practice, to characterize the composition of the electrolyte inside the battery cell, it can be cut open and a standard solvent (such as ethyl propionate (EP)) can be injected. After shaking evenly (generally for 3-7 days), the supernatant is taken out, and the lithium salt content is tested by inductively coupled plasma (ICP) technology and by gas chromatography-mass spectrometry (GC-MS) technology. The relative proportions of anions, cations and solvent components in the electrolyte can be obtained.

[0056] Furthermore, the coordination between lithium ions and solvent in the electrolyte can be determined using nuclear magnetic resonance (NMR), Raman spectroscopy, and molecular dynamics simulation (MD). Specifically, NMR spectroscopy can analyze the solvation structure of lithium ions by measuring the chemical environment of lithium ions and the chemical shift of the solvent; Raman spectroscopy can determine the solvation structure of lithium ions by measuring the vibrational shift of functional groups caused by the interaction between the solvent and lithium ions, as well as the intensity of the interaction peak between lithium ions and the solvent; molecular dynamics simulation constructs a force field by using potential energy functions and lithium ion parameterization to simulate the interaction process between lithium ions and solvent, and analyzes the solvation structure of lithium ions from the temporal, spatial, and energy dimensions.

[0057] As mentioned above, the lithium salts in the electrolyte also include other lithium salts besides lithium bis(fluorosulfonyl)imide. These lithium salts can be inorganic or organic. Inorganic lithium salts include, but are not limited to, one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium perchlorate; organic lithium salts include, but are not limited to, one or more of lithium bis(oxalato)borate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide. Adding the above lithium salts to the electrolyte is beneficial for further improving the ionic conductivity of the electrolyte.

[0058] Preferably, when the lithium salt also includes lithium hexafluorophosphate, it is beneficial to further improve the ionic conductivity of the electrolyte, thereby improving the fast charging performance of the battery.

[0059] In addition, the solvent in the electrolyte also includes at least one selected from ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, N-methylpyrrolidone, and dimethylacetamide. Adding these solvents helps to better adjust the viscosity of the electrolyte. It should be noted that the solvent in this invention is a non-aqueous solvent, and the electrolyte is a non-aqueous electrolyte.

[0060] Preferably, when the electrolyte solvent also includes ethylene carbonate, it can further promote the ionization of lithium salts in the electrolyte, allowing more lithium ions to participate in the battery charging and discharging process in ionic form, thereby increasing the battery's energy density. This invention does not impose a specific limit on the mass percentage of ethylene carbonate in the electrolyte; it can be selected according to actual conditions. In specific implementations, the mass percentage of ethylene carbonate in the electrolyte is 15% to 30%.

[0061] In one embodiment, the electrolyte further includes additives, including at least one of vinylene carbonate, fluoroethylene carbonate, and methylene disulfonate.

[0062] Specifically, vinylene carbonate and fluoroethylene carbonate, as film-forming additives, decompose on the surface of the negative electrode during the first charge-discharge process, generating a thin and dense solid electrolyte interphase (SEI) layer. This SEI layer not only effectively prevents further reactions between the electrolyte and the negative electrode active material, but also reduces the loss of active lithium and lowers the interfacial resistance.

[0063] Methylene methane disulfonate can form a sulfur-containing SEI layer on the negative electrode surface. These sulfur compounds possess good conductivity and chemical stability, effectively reducing side reactions and improving the mechanical strength of the SEI layer. Furthermore, methylene methane disulfonate can effectively reduce lithium dendrite growth, prevent internal short circuits, and extend battery cycle life. In addition, methylene methane disulfonate can also improve the CEI (cathode electrolyte interface) layer on the positive electrode surface, reducing corrosion and structural damage to the positive electrode active material.

[0064] The present invention does not impose a special limitation on the mass percentage of the additive in the electrolyte, but can select it according to the specific situation. For example, the mass percentage of the additive in the electrolyte is 2 to 20%.

[0065] In practice, the additives in the electrolyte include vinylene carbonate (VC), fluoroethylene carbonate (FEC), and methylene methane disulfonate. The mass percentage of vinylene carbonate (VC) in the electrolyte is 2-15%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 0.5-5%, and the mass percentage of methylene methane disulfonate in the electrolyte is 0.5-3%.

[0066] The electrolyte preparation method provided by this invention is a common method used by those skilled in the art, which simply involves mixing the components (including lithium salt, non-aqueous solvent and additives) evenly. This invention does not have any special limitations on the mixing method and order.

[0067] A second aspect of this invention provides a battery comprising the aforementioned electrolyte. The battery provided by this invention exhibits high charge / discharge rates and power output capabilities, enabling it to maintain efficient energy conversion even under high-rate conditions. Furthermore, the battery provided by this invention demonstrates reliability, safety, and cycle stability under various environments due to the relatively stable electrolyte.

[0068] In detail, the battery also includes a positive electrode sheet, which includes a positive electrode active material. The positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, and ternary materials. The ternary materials include lithium nickel cobalt manganese oxide (nickel cobalt manganese ternary material (NCM)) and / or lithium nickel cobalt aluminum oxide (nickel cobalt aluminum ternary material (NCA)).

[0069] The positive electrode sheet also includes a positive current collector and a positive active layer on at least one side surface of the positive current collector. Specifically, the positive active layer can be provided on one side surface in the thickness direction of the positive current collector, or positive active layers can be provided on both opposite sides surface in the thickness direction of the positive current collector.

[0070] Specifically, the positive electrode active layer may include a positive electrode active material, a conductive agent, and a binder. In the positive electrode active layer, the mass percentage of the positive electrode active material may be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the binder may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0071] In this embodiment of the invention, the binder in the positive electrode active layer can be a conventional adhesive material in the art. For example, the binder in the positive electrode active layer may include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0072] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0073] In this embodiment of the invention, 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 active layer can be dispersed in a 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.

[0074] In one embodiment, the battery further includes a negative electrode sheet, which includes a negative electrode active material, including at least one of graphite and silicon-carbon.

[0075] Preferably, the negative electrode active material includes graphite, which includes at least one of artificial graphite and natural graphite.

[0076] Preferably, the artificial graphite includes a core matrix and a coating layer. The coating layer is amorphous carbon, and the core is a carbon material made from petroleum coke, pitch coke, coal tar, etc., through high-temperature (2800–3300℃) graphitization treatment. This invention does not impose a specific limitation on the mass percentage of amorphous carbon-coated artificial graphite in the negative electrode active material; it can be selected according to actual needs. For example, the mass percentage of amorphous carbon-coated artificial graphite in the negative electrode active material can be 20%–100%. In specific implementations, the mass percentage of amorphous carbon-coated artificial graphite in the negative electrode active material can be 50%.

[0077] This invention utilizes amorphous carbon-coated artificial graphite as the negative electrode active material, which facilitates better compatibility with the aforementioned electrolyte to improve the battery's fast-charging performance. After extensive experimentation, the inventors concluded that the reason may be that the carbon lattice on the surface of amorphous carbon-coated artificial graphite exhibits anisotropy, providing more diverse insertion paths and positions for lithium ions, thus facilitating lithium ion intercalation in the negative electrode. Simultaneously, the electrolyte in this invention more readily forms a stable SEI film on the surface of amorphous carbon-coated artificial graphite, thereby increasing the battery's cycle performance.

[0078] Generally, the mass percentage of the negative electrode active material in the negative electrode active layer can be 80% to 100%, including but not limited to 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof.

[0079] In the above-mentioned negative electrode sheet, the current collector is a negative electrode current collector. A negative electrode active layer can be provided on one side surface of the negative electrode current collector in the thickness direction, or a negative electrode active layer can be provided on both opposite sides surface in the thickness direction of the negative electrode current collector.

[0080] In this embodiment of the invention, the negative electrode active layer further includes an adhesive. The adhesive of the negative electrode active layer can be any adhesive suitable for negative electrodes known in the art. For example, the adhesive of the negative electrode active layer includes at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene-polyethylene glycol block copolymers), polyethers and their copolymers (e.g., polyethylene oxide), polyphenylene ethers and their copolymers, polysiloxanes and their copolymers (e.g., polydimethylsiloxane, poly(dimethylsiloxane-co-alkylmethylsiloxane)), polyesters and their copolymers (e.g., polyethylene ester, polyvinyl acetate, polyacrylate), carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA). Specifically, polyolefins include one or more of polyethylene, polypropylene, ethylene / propylene copolymer, ethylene / vinylidene fluoride copolymer, and propylene / vinylidene fluoride copolymer; polytetrafluoroethylene and its copolymers may be at least one of tetrafluoroethylene / ethylene copolymer, tetrafluoroethylene / propylene copolymer, tetrafluoroethylene / vinylidene fluoride copolymer, tetrafluoroethylene / ether copolymer, tetrafluoroethylene / branched polyether copolymer, tetrafluoroethylene / vinyl ether copolymer, tetrafluoroethylene / branched polyether / vinyl ether copolymer, and tetrafluoroethylene / siloxane copolymer.

[0081] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0082] In embodiments of the present invention, the negative electrode sheet can be prepared by a dry process (i.e., rolling the material used to form the negative electrode active layer into a film and then combining it with the negative electrode current collector to obtain the negative electrode sheet), or by a wet process (coating method) (i.e., coating the negative electrode slurry used to form the negative electrode active layer onto the surface of the negative electrode current collector, and then drying, rolling and other processes to form the negative electrode active layer on the surface of the negative electrode sheet to obtain the negative electrode sheet).

[0083] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0084] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0085] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0086] In this embodiment of the invention, components such as positive electrode, separator and negative electrode can be assembled into a battery using 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 (outer packaging) and after conventional processes such as electrolyte injection (i.e., injection of electrolyte) and encapsulation, a battery is obtained.

[0087] In practice, the battery can be manufactured through the following process:

[0088] Preparation of positive electrode sheet: Lithium iron phosphate, binder, carbon black and NMP are mixed in a mass ratio of 100:3:7 to prepare a slurry. The slurry is coated on aluminum foil, baked at 60°C and rolled and die-cut to prepare the required positive electrode sheet.

[0089] Preparation of negative electrode sheet: The negative electrode active material (artificial graphite, natural graphite and silicon carbide), binder and conductive agent are mixed with deionized water at a mass ratio of 100:5:1 to prepare a slurry. The slurry is coated on copper foil, baked at 60°C and rolled and die-cut to prepare the required negative electrode sheet.

[0090] Cell preparation: The positive and negative electrode sheets prepared above are stacked with a PP separator of 14 micrometer thickness of the corresponding size in a stacking machine to prepare a soft pack battery with a capacity of 1.8Ah. After being packaged with aluminum-plastic film, the tabs are welded on. After baking at 85℃ for 24 hours, the battery is formed by liquid injection and encapsulation.

[0091] The battery assembled by the present invention using the above-mentioned positive electrode active material and negative electrode active material in the above manner has high cycle stability and energy density.

[0092] A fifth aspect of the present invention provides a battery pack including the battery described above, which has advantages corresponding to the battery described above, and will not be described in detail hereafter.

[0093] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0094] The present invention also provides an electrical device, including the battery or battery pack described above. By using the battery or battery pack described above in the electrical device, the electrical energy can be continuously and stably output to supply the electrical device, so that the electrical device has a longer service life. At the same time, the maintenance of the battery in the electrical device can be reduced, which is beneficial to saving costs.

[0095] The electrical equipment provided by this invention can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars), electrical equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without any particular limitation.

[0096] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0097] Example 1

[0098] The preparation process of the electrolyte in this embodiment is as follows:

[0099] Lithium hexafluorophosphate (LiPF6, 7.65 g) and lithium difluorosulfonyl imide (LiFSI, 9.41 g) were fully dissolved in an argon glove box in a mixed solvent of ethylene carbonate (EC, 20 g), dimethyl carbonate (DMC, 25.5 g), ethyl methyl carbonate (EMC, 25 g), and ethyl acetate (EA, 9.14 g). 3.3 g of additives (including 2 g of vinylene carbonate (VC), 0.8 g of fluoroethylene carbonate (FEC), and 0.5 g of methanedisulfonate) were added to prepare an electrolyte with a total mass of 100 g. Specific parameters for each component are shown in Tables 1 and 2.

[0100] The preparation process of the positive electrode sheet is as follows: lithium iron phosphate, binder, carbon black and NMP are mixed in a mass ratio of 100:3:7 to prepare a positive electrode slurry. The positive electrode slurry is coated on aluminum foil, baked at 60°C, and rolled and die-cut to prepare a positive electrode sheet. The positive electrode sheet is aluminum foil.

[0101] The preparation process of the negative electrode sheet is as follows: artificial graphite (the core is carbon material that has undergone high-temperature graphitization treatment, and the coating layer is amorphous carbon) coated with amorphous carbon, binder, and conductive agent are mixed with deionized water at a mass ratio of 100:5:1 to prepare a negative electrode slurry. The negative electrode slurry is coated on copper foil, baked at 60°C, and then rolled and die-cut to prepare the required negative electrode sheet.

[0102] Cell preparation: The positive and negative electrode sheets prepared above are stacked with PP separators of corresponding size and thickness of 14 micrometers in a stacking machine to prepare a soft pack battery with a capacity of 1.8Ah. After being packaged with aluminum-plastic film, the tabs are welded on. After baking at 85°C for 24 hours, electrolyte injection (using the above-mentioned electrolyte) is performed, followed by encapsulation and formation to obtain the battery.

[0103] Example 2

[0104] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 11.46g, the amount of LiFSI added is 4.7g, the amount of EA added is 28.19g, the amount of DMC added is 16.35g, and the amount of EMC added is 16g.

[0105] Example 3

[0106] This embodiment is basically the same as Example 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 3.05g, the amount of LiFSI added is 15.06g, the amount of ethyl acetate (EA) added is 9.1g, the amount of DMC added is 24.99g, and the amount of EMC added is 24.51g.

[0107] Example 4

[0108] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 6.1g, the amount of LiFSI added is 11.3g, the amount of EA added is 28g, the amount of DMC added is 15.81g, and the amount of EMC added is 15.5g.

[0109] Example 5

[0110] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 9g, the amount of LiFSI added is 4g, the amount of EA added is 28g, the amount of DMC added is 18g, and the amount of EMC added is 17.7g.

[0111] Example 6

[0112] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 11g, the amount of LiFSI added is 4.9g, the amount of EA added is 8.5g, the amount of DMC added is 26.3g, and the amount of EMC added is 26g.

[0113] Example 7

[0114] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 11.6g, the amount of LiFSI added is 5.2g, the amount of EA added is 32g, the amount of DMC added is 14.1g, and the amount of EMC added is 13.8g.

[0115] Example 8

[0116] This embodiment is basically the same as Embodiment 1, except that the artificial graphite in the negative electrode includes artificial graphite with amorphous carbon coating. The mass percentage of the artificial graphite with amorphous carbon coating in the negative electrode active material is 50%, and the remainder is natural graphite.

[0117] Example 9

[0118] This embodiment is basically the same as Embodiment 1, except that LiPF6 is not added during the electrolyte preparation process in this embodiment, and the amount of LiFSI added is 17.06g.

[0119] Example 10

[0120] This embodiment is basically the same as Embodiment 1, except that ethylene carbonate is not added during the preparation of the electrolyte in this embodiment, and the electrolyte includes dimethyl carbonate (DMC, 36g) and ethyl methyl carbonate (EMC, 34.5g).

[0121] Example 11

[0122] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the additives include 2.35g of vinylene carbonate (VC) and 0.95g of fluoroethylene carbonate (FEC).

[0123] Example 12

[0124] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the additives include 2.64g of vinylene carbonate (VC) and 0.66g of methanedisulfonate.

[0125] Example 13

[0126] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the additives include 2g of methylene disulfonate and 1.3g of fluoroethylene carbonate.

[0127] Example 14

[0128] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 5.65g, the amount of EA added is 8.5g, the amount of DMC added is 26.84g, and the amount of EMC added is 26.3g.

[0129] Example 15

[0130] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of EA added is 35g, the amount of DMC added is 12.57g, and the amount of EMC added is 12.07g.

[0131] Example 16

[0132] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 5.86g and the amount of LiFSI added is 11.2g.

[0133] Example 17

[0134] This embodiment is basically the same as Embodiment 1, except that in the electrolyte preparation process of this embodiment, the amount of LiPF6 added is 8.61g, the amount of LiFSI added is 3.45g, the amount of DMC added is 28g, and the amount of EMC added is 27.5g.

[0135] Comparative Example 1

[0136] The difference between this comparative example and Example 1 is that in the electrolyte preparation process of this comparative example, the amount of LiPF6 added is 17.06g, LiFSI and EA are not added, the amount of DMC added is 30.12g, and the amount of EMC added is 29.52g.

[0137] Comparative Example 2

[0138] The difference between this comparative example and Example 1 is that in the electrolyte preparation process of this comparative example, the amount of LiPF6 added is 17.06g, while no LiFSI is added. The amount of EA added is 9.38g, the amount of DMC added is 25.38g, and the amount of EMC added is 24.88g.

[0139] Comparative Example 3

[0140] The difference between this comparative example and Example 1 is that, in the electrolyte preparation process of this comparative example, the amount of LiPF6 added is 4.9g, the amount of LiFSI added is 9.19g with a concentration percentage of 0.6%, the amount of EA added is 74g, the amount of EC added is 2.4g, the amount of DMC added is 3.41g, and the amount of EMC added is 2.8g.

[0141] Comparative Example 4

[0142] The difference between this comparative example and Example 1 is that, in the electrolyte preparation process of this comparative example, the amount of LiPF6 added is 5.6g, the amount of LiFSI added is 3g with a concentration percentage of 0.3%, the amount of EA added is 43g, the amount of DMC added is 13.1g, and the amount of EMC added is 12g.

[0143] Comparative Example 5

[0144] The difference between this comparative example and Example 1 is that, in the electrolyte preparation process of this comparative example, the amount of LiPF6 added is 6.44g, the amount of LiFSI added is 2g with a concentration percentage of 0.2%, the amount of EA added is 4g, the amount of DMC added is 32.68g, and the amount of EMC added is 31.58g.

[0145] Test case

[0146] Battery DC internal resistance test:

[0147] The batteries of the examples and comparative examples were discharged at a constant current of 0.33C (0.6A) to 2.0V at room temperature, and then charged at a constant current of 0.33C to 50% SOC (charging capacity 0.9A). They were then discharged at a constant current of 1.5C (2.7A) for 30 seconds, and the voltage before and after discharge was recorded. The formula for calculating the battery's DC internal resistance (discharge DCIR) is as follows:

[0148] Discharge DCIR (mΩ) = (voltage before discharge - voltage after discharge) / discharge current * 1000. The test results are shown in Table 3.

[0149] Battery high-temperature cycle test:

[0150] The batteries of the examples and comparative examples were charged to 3.8V at a constant current rate of 1C (approximately 1.8A) at 60°C, and then discharged to 2.0V at a constant current rate of 1.8A. The initial charge capacity and discharge capacity were recorded. After repeating this charge-discharge cycle 400 times, the discharge capacity of the 200th cycle was recorded. The formula for calculating the capacity retention rate after the cycle is as follows:

[0151] The capacity retention rate after cycling (%) = discharge capacity after 400 cycles / initial discharge capacity × 100%. The test results are shown in Table 3.

[0152] Table 1

[0153]

[0154] Table 2

[0155]

[0156] "-" indicates that this value does not need to be calculated.

[0157] Table 3

[0158] Discharge DCIR / mΩ Capacity retention rate / % Example 1 62.3 92.46 Example 2 64.7 91.85 Example 3 66.4 90.28 Example 4 63.4 92.33 Example 5 68.8 88.15 Example 6 67.5 89.28 Example 7 69.6 87.72 Example 8 60.7 93.26 Example 9 63.8 86.55 Example 10 64.1 86.82 Example 11 63.5 90.68 Example 12 67.3 91.76 Example 13 61.6 87.22 Example 14 65.9 88.75 Example 15 65.7 90.34 Example 16 64.4 90.38 Example 17 68.1 88.13 Comparative Example 1 72.3 82.43 Comparative Example 2 70.5 84.32 Comparative Example 3 71.2 84.76 Comparative Example 4 71.8 85.11 Comparative Example 5 72.6 83.81

[0159] As shown in the table, compared to Comparative Examples 1-5, Examples 1-17 of the present invention, by precisely proportioning the content of lithium difluorosulfonylimide and ethyl acetate in the electrolyte, effectively reduced the DC internal resistance of the battery, improved the fast-charging performance of the battery, and also gave the battery a longer cycle life at high temperatures. Compared to Example 5, Examples 1-4 further improved the fast-charging performance and cycle life of the battery by controlling the mass percentage of lithium difluorosulfonylimide in the electrolyte to 4.1%–9.5%. Compared to Example 9, Examples 1-4 used both lithium difluorosulfonylimide and lithium hexafluorophosphate, resulting in batteries with both good fast-charging performance and cycle life. Compared to Examples 6-7, Examples 1-4 further reduced the DC internal resistance of the battery and improved the capacity retention rate by further limiting the mass percentage of ethyl acetate in the electrolyte to 9.1%–29.1%, resulting in batteries with higher fast-charging performance and cycle life.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized by, The electrolyte comprises a lithium salt, a solvent: The lithium salt comprises lithium bisfluorosulfonylimide; The solvent comprises ethyl acetate; The electrolyte satisfies: 0.45 / c≤m2 / m1≤2 / c, wherein m1 is the mass of the lithium bisfluorosulfonylimide in the electrolyte; m2 is the mass of the ethyl acetate in the electrolyte; c is the molar concentration ratio of the lithium bisfluorosulfonylimide in the lithium salt, 0.24≤c≤1.

2. The electrolyte according to claim 1, characterized in that, 0.25＜c＜0.7。 3. The electrolyte of claim 1, wherein The mass percentage of the lithium bisfluorosulfonylimide in the electrolyte is 4.1% to 9.5%.

4. The electrolyte of claim 1, wherein The mass percentage of the ethyl acetate in the electrolyte is 9.1% to 29.1%.

5. The electrolyte of claim 1, wherein The coordination ratio of ethyl acetate molecules to lithium ions is (1-4):

1.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The lithium salt further comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalate borate, lithium trifluoromethylsulfonate, lithium bis-trifluoromethylsulfonylimide.

7. The electrolyte according to any one of claims 1 to 6, characterized in that, The lithium salt further comprises lithium hexafluorophosphate.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, The solvent further comprises at least one of vinyl carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, N-methyl pyrrolidone, dimethylacetamide.

9. The electrolyte according to any one of claims 1 to 8, characterized in that, The solvent further comprises vinyl carbonate.

10. The electrolyte according to any one of claims 1 to 9, characterized in that, The electrolyte further comprises an additive, the additive comprising at least one of vinylene carbonate, fluoro-vinylene carbonate, and methylene methanedisulfonate.

11. A battery, characterized by The battery comprises the electrolyte of any one of claims 1-10.

12. The battery of claim 11, wherein, The battery further comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising one or more of lithium iron phosphate, lithium iron manganese phosphate, and a ternary material, the ternary material comprising lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide; And / or, the battery further comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising graphite and / or silicon-carbon.

13. The battery of claim 12, wherein, The graphite comprises at least one of natural graphite and artificial graphite.

14. A battery pack, characterized by The battery pack comprises the battery of any one of claims 11-13.

15. An electrical device, characterized by The electrical equipment comprises the battery of any one of claims 11-13 or the battery pack of claim 14.

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