Electrolyte, battery cell, battery and electrical apparatus

Abstract

An electrolyte, a battery cell, a battery and an electrical apparatus, belonging to the technical field of batteries. Fluorophosphate and / or borate is added into an electrolyte containing a low-viscosity solvent, and due to low LUMO energy levels, the fluorophosphate and the borate readily accept electrons and undergo reduction after being added into the electrolyte, so as to form a stable SEI film on the surface of a negative electrode active material, thus blocking contact between the low-viscosity solvent and the surface of the negative electrode active material, reducing the reduction of the low-viscosity solvent, and inhibiting further side reactions on the negative electrode sheet side. Meanwhile, the fluorophosphate and the borate can be combined with metal ions on the surface of a positive electrode active material to form ionic bonds, such that the phenomenon of surface overdelithiation of the positive electrode active material is reduced, thus effectively reducing structural damage to the positive electrode active material, and reducing side reactions between the electrolyte and the positive electrode sheet side. Reducing side reactions between electrolytes and both the negative electrode sheet side and the positive electrode sheet side is conductive to the service life of batteries.

Description

Electrolyte, battery cell, battery and electrical device

[0001] Cross-references

[0002] This application cites Chinese Patent Application No. 2024102821980 filed on March 12, 2024, entitled “An electrolyte, a battery cell, a battery and an electrical device”, Chinese Patent Application No. 2024115402576 filed on October 30, 2024, entitled “An electrolyte, a battery cell, a battery and an electrical device”, and Chinese Patent Application No. 202411540228X filed on October 30, 2024, entitled “An electrolyte, a battery cell, a battery and an electrical device”, all of which are incorporated into this application by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to an electrolyte, a battery cell, a battery, and an electrical device. Background Art

[0004] Secondary batteries, such as lithium batteries, are increasingly being used due to their clean and renewable nature. They also boast high specific energy density and long cycle life, and have been widely applied in consumer electronics, electric vehicles, energy storage, and other fields. As the scope of secondary battery applications expands, the need for better fast-charging performance is increasing, placing increasing demands on the kinetic performance of secondary batteries. Fast-charging batteries typically improve the liquid-phase transport of lithium ions by introducing low-viscosity solvents into the electrolyte, thereby improving the kinetic performance of the secondary battery. However, the introduction of low-viscosity solvents can reduce the lifespan of fast-charging batteries. Summary of the Invention

[0005] In view of the above problems, the present application provides an electrolyte, a battery cell, a battery and an electrical device, which can reduce the impact of low-viscosity solvents introduced into fast-charging batteries on battery life.

[0006] In a first aspect, the present application provides an electrolyte, the components of which include a solvent, an electrolyte, and a first additive, the solvent includes a low-viscosity solvent, the viscosity of the low-viscosity solvent is <0.6 mPa·s, and the first additive includes at least one of a fluorophosphate and a borate.

[0007] In the technical solution of the embodiment of the present application, by adding fluorophosphate and / or borate to the electrolyte containing a low viscosity solvent, since fluorophosphate and borate have a lower LUMO energy level, when added to the electrolyte, they are more likely to obtain electrons and be reduced, forming a stable SEI film on the surface of the negative active material, which can block the contact between the low viscosity solvent and the negative active material, thereby reducing the occurrence of the low viscosity solvent being reduced, thereby inhibiting further side reactions on the negative electrode side. At the same time, fluorophosphate and borate can combine with the metal ions on the surface of the positive active material to form ionic bonds, reducing the phenomenon of lithium over-delithiation on the surface of the positive active material, thereby effectively reducing the occurrence of structural destruction of the positive active material and reducing the side reaction of the electrolyte on the positive electrode side. By reducing the side reactions between the negative and positive electrode sides and the electrolyte, it is beneficial to the life of the battery.

[0008] In some embodiments, the viscosity of the electrolyte is ≤5 mPa·s.

[0009] In the above implementation process, the reduced viscosity of the electrolyte facilitates the diffusion of lithium ions in the electrolyte, thereby effectively improving the battery's fast charging and power performance. By controlling the viscosity of the electrolyte to ≤5mPa·s, the battery containing this electrolyte has better fast charging and power performance.

[0010] In some embodiments, the mass content a1 of the low-viscosity solvent in the electrolyte is 10%-70%; and / or the mass content b1 of the first additive in the electrolyte is 0.15%-2.5%.

[0011] In the above implementation process, the greater the mass content of the low-viscosity solvent in the electrolyte, the more conducive it is to reducing the viscosity of the electrolyte, and thus to the diffusion of lithium ions in the electrolyte, thereby improving the fast charging and power performance of the battery. The greater the mass content of the first additive in the electrolyte, the more conducive it is to the formation of ionic bonds between the cathode SEI film and the anode sheet, thereby reducing the side reactions between the negative and positive electrode sheets and the electrolyte, which is beneficial to the life of the battery. The smaller the mass content of the first additive in the electrolyte, the more conducive it is to reducing the viscosity of the electrolyte. By controlling the mass content a1 of the low-viscosity solvent to 10%-70% and the mass content b1 of the first additive to 0.15%-2.5%, the dynamic performance and life of the battery can be taken into account.

[0012] In some embodiments, the mass content a1 of the low-viscosity solvent in the electrolyte is 20%-60%; and / or

[0013] The mass content b1 of the first additive in the electrolyte is 0.5%-1.5%.

[0014] By controlling the mass content a1 of the low-viscosity solvent to 20%-60% and the mass content b1 of the first additive to 0.5%-1.5%, the dynamic performance and life of the battery can be better balanced.

[0015] In some embodiments, the fluorophosphate comprises at least one of monofluorophosphate and difluorophosphate; and / or

[0016] The borate includes at least one of tetrafluoroborate, bisoxalatoborate, and fluorine-containing oxalatoborate; and / or

[0017] The fluorophosphate and borate each independently include at least one of a lithium salt, a sodium salt and a potassium salt.

[0018] In some embodiments, the low viscosity solvent comprises: R1-COO-R2, wherein R1 comprises H, methoxy and C1-C5 alkyl, and R2 comprises C1-C5 alkyl.

[0019] In some embodiments, the low viscosity solvent includes at least one of dimethyl carbonate, ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0020] In some embodiments, the low viscosity solvent includes at least one of ethyl acetate, methyl acetate, and dimethyl carbonate.

[0021] The above solvents have low viscosity, which is conducive to the diffusion of lithium ions in the electrolyte and improves the battery's fast charging and power performance.

[0022] In some embodiments, the electrolyte further comprises a second additive, wherein the second additive comprises a sulfur-containing compound.

[0023] In the above implementation process, the sulfur-containing compound is also beneficial to the film formation on the surface of the cathode active material and the anode active material. By adding the sulfur-containing compound to the electrolyte, it can be beneficial to the life of the battery and improve the gas production of the battery.

[0024] In some embodiments, the mass content c1 of the second additive in the electrolyte is 0.1%-4%.

[0025] In the above implementation, a higher sulfur-containing compound content in the electrolyte facilitates film formation on the surfaces of the cathode and anode active materials, thereby improving battery life and gas production. A lower sulfur-containing compound content in the electrolyte also contributes to lowering battery impedance. By controlling the second additive content c1 in the electrolyte to between 0.1% and 4%, battery performance, including life, gas production, and impedance, can be balanced.

[0026] In some embodiments, the mass content c1 of the second additive in the electrolyte is 0.5%-3%.

[0027] In the above implementation process, by controlling the mass content c1 of the second additive in the electrolyte to be 0.5%-3%, the battery performance of long life, low gas generation and low impedance can be better taken into account.

[0028] In some embodiments, the sulfur-containing compound includes at least one of a sulfonate compound and a vinyl sulfate compound. In the above implementation, both the sulfonate compound and the vinyl sulfate compound are rich in cyclic sulfate groups, which can form a lithium sulfate-rich SEI film on the negative electrode active material layer, exhibiting good thermal stability, thereby improving battery life.

[0029] In some embodiments, the mass content of the vinyl sulfate compound in the electrolyte is 0.05%-3.5%. Alternatively, the mass content of the vinyl sulfate compound in the electrolyte is 0.1%-2.5%. And / or,

[0030] The mass content of the sulfonate compound in the electrolyte is 0.05%-0.5%.

[0031] In the above embodiments, the mass ratio of sulfonate compounds and vinyl sulfate compounds is within an appropriate range, and their combined effect can promote the formation of a more uniform, dense and stable SEI film, which can effectively reduce the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0032] In some embodiments, the vinyl sulfate compound includes At least one of; and / or

[0033] Sulfonate compounds include At least one of .

[0034] In some embodiments, the second additive comprises described With the The mass ratio is 1:(0.25-7); or

[0035] The additives include described The mass ratio is 1:(0.25-7).

[0036] In the above embodiments, the mass ratio of sulfonate compounds and vinyl sulfate compounds is within an appropriate range, and their combined effect can promote the formation of a more uniform, dense and stable SEI film, which can effectively reduce the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0037] In some embodiments, the first additive includes at least one of lithium difluorophosphate and lithium difluorooxalatoborate; and / or

[0038] The second additive includes At least one of .

[0039] In some embodiments, the mass ratio of lithium difluorophosphate to lithium difluorooxalatoborate is 1:(0.05-15).

[0040] In the above embodiment, the mass ratio of lithium difluorophosphate and lithium difluorooxalatoborate is within an appropriate range, and their combined effect can promote the formation of a more uniform, dense and stable SEI film, which can effectively reduce the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0041] In some embodiments, the electrolyte comprises a lithium salt; and / or

[0042] The lithium salt includes at least one of LiPF6 and LiFSI.

[0043] In some embodiments, the electrolyte comprises LiPF6 and LiFSI, the molar ratio of LiFSI to LiPF6 is 0.1-5; and / or the mass ratio of LiPF6 to LiFSI is 0.1-10.

[0044] In the above implementation process, the higher the content of LiFSI, the more favorable it is for Li + The migration of LiFSI improves the battery's fast-charging performance. Lower LiFSI content also helps reduce corrosion of the negative electrode current collector, which in turn improves battery safety. By controlling the ratio of LiFSI to LiPF6, both fast-charging performance and safety can be achieved.

[0045] In a second aspect, the present application provides a battery cell, which includes the electrolyte provided in the first aspect.

[0046] In the technical solution of the embodiment of the present application, by adding fluorophosphate and / or borate to the electrolyte containing a low-viscosity solvent, since fluorophosphate and borate have a lower LUMO energy level, they are more likely to obtain electrons and be reduced, forming a stable SEI film on the negative electrode sheet, which can block the contact between the low-viscosity solvent and the negative electrode sheet, thereby reducing the occurrence of the low-viscosity solvent being reduced, thereby inhibiting further side reactions on the negative electrode sheet side. At the same time, fluorophosphate and borate can combine with the metal ions on the surface of the positive electrode sheet to form ionic bonds, reducing the phenomenon of lithium over-deionization on the surface of the positive electrode sheet, thereby effectively reducing the occurrence of structural destruction of the positive electrode active material and reducing the side reaction of the electrolyte on the positive electrode sheet side. By reducing the side reactions between the negative electrode sheet side and the positive electrode sheet side and the electrolyte, it is beneficial to the life of the battery.

[0047] In some embodiments, the mass content a2 of the low-viscosity solvent in the electrolyte is 10%-70%; and / or

[0048] The mass content b2 of the first additive in the electrolyte is 0%-1%.

[0049] In some embodiments, the fluorophosphate comprises at least one of monofluorophosphate and difluorophosphate; and / or

[0050] The borate includes at least one of tetrafluoroborate, bisoxalatoborate, and fluorine-containing oxalatoborate; and / or

[0051] The fluorophosphate and borate each independently include at least one of a lithium salt, a sodium salt and a potassium salt.

[0052] In some embodiments, the mass content c2 of the second additive in the electrolyte is 0%-2%.

[0053] In some embodiments, the battery cell further comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material comprises lithium nickel cobalt manganese oxide, and the Dv50 of the lithium nickel cobalt manganese oxide is 2 μm-15 μm; or, the positive electrode active material comprises a lithium-containing phosphate, and the Dv50 of the lithium-containing phosphate is 0.3 μm-2 μm.

[0054] In batteries where the positive active material of the positive electrode sheet is a ternary system material, the first additive can combine with the metal ions on the surface of the positive electrode sheet to form ionic bonds, reducing the phenomenon of over-delithiation on the surface of the positive electrode sheet, thereby effectively reducing the occurrence of structural destruction of the positive electrode active material, reducing the side reaction of the electrolyte on the positive electrode sheet side and the gas production problem caused by the side reaction. When the second additive is added to the electrolyte, a CEI film can be further formed on the surface of the positive electrode active material, improving the structural stability of the positive electrode sheet side, reducing the risk of gas production, and improving the life of the battery. In batteries where the positive active material of the positive electrode sheet is a lithium phosphate material (including lithium manganese iron phosphate materials), the additive can form a stable SEI film on the negative electrode sheet, blocking the contact between the solvent, especially the low-viscosity solvent, and the negative electrode sheet, reducing the reduction gas production side reaction of the solvent on the negative electrode sheet side, and improving the life of the battery. In a low-viscosity system, the smaller the particle size of the positive electrode active material, the greater the impact on the interfacial side reaction. In the above embodiment, the Dv50 of the lithium nickel cobalt manganese oxide positive electrode active material is controlled to be 2μm-15μm, or the Dv50 of the lithium phosphate positive electrode active material is controlled to be 0.3μm-2μm. The positive electrode active material has many reaction sites, and the deintercalation speed of lithium ions is improved, which can match the transmission speed of lithium ions in the electrolyte, helping to reduce the lithium ion transmission impedance and the temperature rise of the battery under the fast charging system. At the same time, it can reduce the interfacial side reactions caused by the small particle size of the positive electrode active material, reduce the gas production caused by the side reactions and the impact of the side reactions on the battery life, and better balance the fast charging performance and service life of the battery.

[0055] In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide, the molar content of nickel element is less than 80% based on the total molar number of transition metals in the positive electrode active material, the Dv50 of the positive electrode active material is 2μm-5μm, and the positive electrode active material includes unagglomerated primary particles.

[0056] The molar content of nickel element is less than 80%, which is beneficial to reducing the probability of nickel dissolution of the positive electrode active material under high voltage (charging cut-off voltage ≥ 4.3V) and improving the withstand voltage of the positive electrode active material. The combination of low nickel components and unagglomerated primary particles can further reduce the degree of side reactions between the positive electrode active material and the low viscosity solvent, reduce the probability of cracking of the positive electrode active material during high voltage charging and discharging, and improve the cycle performance of the battery cell. At the same time, the primary particles have a higher specific surface area and a smaller particle size, which is beneficial to increase the rate of lithium ion insertion / extraction process and improve the fast charging performance of the battery. The Dv50 of the primary particles is 2μm-5μm. While improving the fast charging performance of the battery, it also takes into account the structural stability of the positive electrode active material, which is beneficial to the battery maintaining stable cycle performance.

[0057] In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide, based on the total molar number of transition metals in the positive electrode active material, the molar content of nickel element is greater than or equal to 80%, the Dv50 of the positive electrode active material is 6μm-15μm, and the positive electrode active material includes secondary particles formed by agglomeration of primary particles, and the average particle size of the primary particles in the secondary particles is 0.1μm-1.5μm.

[0058] Molding high-nickel materials into large-sized secondary particles is beneficial for simultaneously improving the specific capacity of the positive electrode active material and the gradation of the positive electrode sheet, thereby improving the energy density of the battery. At the same time, the secondary particles are composed of primary particles with small particle sizes, which can shorten the transmission distance of lithium ions, increase the number of embedded end faces, reduce the DC impedance of the battery cells, and improve the power performance of the battery cells. The Dv50 of the secondary particles is 6μm-15μm, which can improve the energy density of the battery while taking into account the transmission distance of lithium ions and improving the fast charging performance of the battery. Controlling the average particle size of the primary particles in the secondary particles can shorten the transmission distance of lithium ions, increase the number of embedded end faces, reduce the DC impedance of the battery cells, and improve the power performance of the battery cells.

[0059] In some embodiments, the positive electrode active material comprises unagglomerated primary particles and / or secondary particles agglomerated from primary particles, and the average particle size of the primary particles of the positive electrode active material is between 50 nm and 300 nm. Lithium-containing phosphates with an average primary particle size within this range have both a short ion transport path and low lithium ion transfer impedance, matching the liquid-phase transfer rate of lithium ions in the electrolyte while also extending the cycle life of the battery cell.

[0060] In some embodiments, the battery cell further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material and lithium metal.

[0061] In some embodiments, the negative electrode active material includes artificial graphite; and / or

[0062] The negative electrode active material comprises secondary particles formed by agglomeration of primary particles, and the Dv50 of the negative electrode active material is 5 μm-18 μm; and / or

[0063] The air oxidation temperature T0 of the negative electrode active material is 630℃-730℃.

[0064] In the above embodiment, the artificial graphite has fewer defects, which can reduce side reactions with low-viscosity solvents, lower gas production, and improve the gas production defects of the battery.

[0065] In the above-mentioned embodiment, the secondary particles help increase the reactive sites of the negative electrode active material, providing suitable end surfaces for lithium ions to embed, increasing the rate of lithium ion embedding and deintercalation, and improving fast-charging performance. The secondary particles have a Dv50 of 5μm-18μm, which not only improves the battery's fast-charging performance but also reduces side reactions between the negative electrode active material and the electrolyte, thereby improving the battery's cycle life.

[0066] In the above embodiment, the air oxidation temperature T0 of the negative electrode active material is 630°C-730°C. The negative electrode active material has good surface quality and a suitable end surface for lithium ion embedding, which can match the lithium ion transfer rate of the electrolyte, thereby improving the battery's fast-charging performance. At the same time, the negative electrode active material has a large number of lithium embedding sites, which is conducive to improving the battery's energy density. The negative electrode active material works synergistically with the first and second additives to form a dense SEI film on the surface of the negative electrode active material, improving the battery's fast-charging performance while also taking into account the battery's cycle performance and service life.

[0067] In some embodiments, the negative electrode active material includes a silicon-based material, and the silicon-based material accounts for no more than 25% by mass of the negative electrode active material layer.

[0068] In a third aspect, the present application provides a battery comprising the battery cell provided in the second aspect.

[0069] In some embodiments, the charging time t for charging the battery from 0% SOC to 80% SOC satisfies: t≤15.2 min.

[0070] In a fourth aspect, the present application provides an electrical device, which includes the battery provided in the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0072] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present application;

[0073] FIG2 is a schematic diagram of the exploded structure of a secondary battery provided in some embodiments of the present application;

[0074] FIG3 is a schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0075] FIG4 is an exploded view of a battery cell provided in some embodiments of the present application.

[0076] The figure numbers in the specific implementation manner are as follows: 1000-vehicle; 100-secondary battery; 200-motor; 300-controller; 10-housing; 11-accommodating space; 12-first part; 13-second part; 20-battery cell; 21-housing; 211-opening; 22-end cover assembly; 221-end cover; 222-electrode terminal; 23-electrode assembly; 24-current collecting member; 25-insulating protection part. DETAILED DESCRIPTION

[0077] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0078] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0079] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0080] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0081] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0082] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0083] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0084] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0085] Currently, market developments indicate that power batteries are becoming increasingly widely used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. As power battery applications continue to expand, market demand is also growing.

[0086] Power batteries can be sodium-ion batteries and lithium-ion batteries. As the application scope of secondary batteries expands, better fast-charging performance is required, so the dynamic performance of secondary batteries is increasingly required. Usually, fast-charging batteries improve the liquid-phase transmission capacity of lithium ions by introducing low-viscosity solvents into the electrolyte, thereby improving the dynamic performance of secondary batteries.

[0087] However, low-viscosity solvents have a larger diffusion coefficient and a smaller molecular radius, which makes it easier for them to penetrate the SEI film, diffuse to the surface of the positive and negative electrodes, and contact the active materials; and the low-viscosity solvents themselves are not resistant to redox and have poor compatibility with the positive and negative electrodes. Therefore, the introduction of low-viscosity solvents will lead to the deterioration of the life and gas production performance of fast-charging batteries, and increase the internal pressure of the battery cells.

[0088] It should be noted that fast-charging batteries generally refer to batteries whose charging time t from 10% SOC to 80% SOC satisfies: t≤15min. That is, when the current density of a lithium-ion battery is greater than or equal to 2.8C, the charging time from 10% SOC to 80% SOC is less than or equal to 15min. This current density is the equivalent current density of the lithium-ion battery during the process of charging from 10% SOC to 80% SOC. In other words, in the process of charging from 10% SOC to 80% SOC, the current density I may gradually decrease from greater than 2.8C to less than 2.8C. In this process, the lithium-ion battery may undergo a transition from constant current charging to constant voltage charging, and thus, the current density is not constant. For example: start charging the lithium-ion battery at room temperature of 25°C, charge from 10% SOC to 80% SOC, and the charging time is 10 minutes (equivalent current I≥4C). The charging process is as follows: initially at 5C from 10% SOC to 45% SOC, then at 4.6C from 45% SOC to 50% SOC, 4.3C from 50% SOC to 55% SOC, 3.9C from 55% SOC to 60% SOC, 3.6C from 60% SOC to 65% SOC, 3.3C from 65% SOC to 70% SOC, 3.1C from 70% SOC to 75% SOC, and 2.9C from 75% SOC to 80% SOC, and then charging ends. The charging time for the lithium-ion battery to charge from 0% SOC to 100% SOC at 1C is 60 minutes. Therefore, when it is measured that the charging time of the lithium-ion battery from 10% SOC to 80% SOC is 10 minutes, the equivalent current density of the process can be calculated as: [(80% SOC-10% SOC) / (100% SOC-0% SOC)]×[(1C×60min) / 10min]=4.2C. Under the charging conditions of the lithium-ion battery, the time it takes to charge from 0% SOC to 100% SOC can also be directly recorded. For example, if the time is around 15 minutes (the error does not exceed 1 minute), it is generally considered to be a 4C fast-charging battery. For another example, if the time is around 12 minutes (the error does not exceed 1 minute), it is generally considered to be a 5C fast-charging battery. For another example, if the time is around 10 minutes (the error does not exceed 1 minute), it is generally considered to be a 6C fast-charging battery.

[0089] In order to reduce the impact of the introduction of low-viscosity solvents in fast-charging batteries on battery life, the present application proposes an electrolyte, the components of which include a solvent, an electrolyte and a first additive. The solvent includes a low-viscosity solvent, the viscosity of the low-viscosity solvent is <0.6mPa·s, and the first additive includes at least one of a fluorophosphate and a borate.

[0090] In such an electrolyte, by adding fluorophosphate and / or borate to an electrolyte containing a low-viscosity solvent, since fluorophosphate and borate have lower LUMO energy levels, they are more likely to obtain electrons and be reduced when added to the electrolyte, forming a stable SEI film on the surface of the negative electrode active material, which can block the contact between the low-viscosity solvent and the negative electrode active material, thereby reducing the occurrence of the low-viscosity solvent being reduced, thereby inhibiting further side reactions on the negative electrode sheet side. At the same time, fluorophosphate and borate can combine with metal ions on the surface of the positive electrode active material to form ionic bonds, reducing the phenomenon of over-delithiation on the surface of the positive electrode active material, thereby effectively reducing the occurrence of structural destruction of the positive electrode active material and reducing side reactions of the electrolyte on the positive electrode sheet side. By reducing side reactions between the negative and positive electrode sheets and the electrolyte, the battery life is improved.

[0091] The electrolyte can be used to prepare battery cells, which can be used in, but not limited to, electrical devices such as vehicles, ships, or aircraft. A power supply system comprising the battery cells and batteries disclosed in this application can be used to form the electrical device.

[0092] The present application provides an electric device that uses the above-mentioned battery as a power source. The electric device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, etc. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc. The spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0093] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0094] Please refer to Figure 1, which is a structural schematic diagram of a vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A secondary battery 100 is provided inside the vehicle 1000, and the secondary battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000. For example, the secondary battery 100 can serve as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to power the motor 200, for example, for starting, navigating and driving the vehicle 1000.

[0095] In some embodiments of the present application, the secondary battery 100 can serve not only as an operating power source for the vehicle 1000 , but also as a driving power source for the vehicle 1000 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000 .

[0096] In this application, a secondary battery 100 may refer to a single battery cell 20, or it may refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which may be in the form of a battery pack, a battery module, etc. The secondary battery 100 may include a housing 10 for enclosing the multiple battery cells 20. The housing 10 may prevent liquids or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0097] FIG2 is a schematic diagram of the exploded structure of a secondary battery 100 provided in some embodiments of the present application. Referring to FIG2 , the secondary battery 100 includes a housing 10 and a battery cell 20 , wherein the battery cell 20 is housed in the housing 10 .

[0098] The housing 10 is used to provide a storage space 11 for the battery cells 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap to define the storage space 11 for accommodating the battery cells 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a seal (not shown), such as a sealing ring, sealant, or the like.

[0099] The first portion 12 and the second portion 13 can have various shapes, such as a rectangular parallelepiped, a cylinder, etc. The first portion 12 can be a hollow structure with an opening on one side to form a receiving cavity for accommodating the battery cell 20. The second portion 13 can also be a hollow structure with an opening on one side to form a receiving cavity for accommodating the battery cell 20. The open side of the second portion 13 covers the open side of the first portion 12, thereby forming the box 10 with the receiving space 11. Of course, as shown in Figure 2, the first portion 12 can also be a hollow structure with an opening on one side, and the second portion 13 can be a plate-like structure. The second portion 13 covers the open side of the first portion 12, thereby forming the box 10 with the receiving space 11.

[0100] In the secondary battery 100, there are multiple battery cells 20. These multiple battery cells 20 can be connected in series, in parallel, or in a hybrid connection. Hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 20. Multiple battery cells 20 can be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery cell 20 is housed within the housing 10. Alternatively, multiple battery cells 20 can be first connected in series, in parallel, or in a hybrid connection to form a battery module, and then the multiple battery modules are further connected in series, in parallel, or in a hybrid connection to form an entire battery module, which is then housed within the housing 10. The battery cells 20 can be cylindrical, flat, rectangular, or in other shapes. Figure 2 exemplifies a case where the battery cells 20 are square.

[0101] In some embodiments, the secondary battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or hybrid connection of the multiple battery cells 20 .

[0102] Figure 3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of the present application, and Figure 4 is an exploded view of a battery cell 20 provided in some embodiments of the present application. Referring to Figures 3 and 4, the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, and the electrode assembly 23 is accommodated within the housing 21. The end cap assembly 22 is used to seal the opening 211.

[0103] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a rectangular parallelepiped structure, the housing 21 can be a rectangular parallelepiped structure. Figures 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0104] The shell 21 may be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0105] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the outer shell 21 to form a sealed installation space (not shown), which is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 serves as a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to electrically connect to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0106] It should be noted that the number of openings 211 of the outer shell 21 can be one or two. If the number of openings 211 of the outer shell 21 is one, the number of end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are respectively used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23. If the number of openings 211 of the outer shell 21 is two, for example, the two openings 211 are provided on opposite sides of the outer shell 21, the number of end cap assemblies 22 can also be two, and the two end cap assemblies 22 are respectively covered on the two openings 211 of the outer shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal 222, which is used to electrically connect to the positive electrode tab of the electrode assembly 23; and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal 222, which is used to electrically connect to the negative electrode sheet of the electrode assembly 23.

[0107] In some embodiments, as shown in FIG4 , the battery cell 20 may further include an insulating protective member 25 secured to the periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is a tape adhered to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is disposed around the periphery of the multiple electrode assemblies 23, forming the multiple electrode assemblies 23 into a single integrated structure to maintain structural stability.

[0108] The electrode assembly 23 includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode current collector. The positive electrode current collector not coated with the positive electrode active material layer protrudes from the positive electrode current collector coated with the positive electrode active material layer. The positive electrode current collector not coated with the positive electrode active material layer serves as the positive electrode tab. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector. The negative electrode current collector not coated with the negative electrode active material layer protrudes from the negative electrode current collector coated with the negative electrode active material layer. The negative electrode current collector not coated with the negative electrode active material layer serves as the negative electrode tab. The negative electrode current collector can be made of copper, and the negative electrode active material can be carbon, silicon, or other materials. To ensure that high currents can pass without melting, multiple positive electrode tabs are stacked together, and multiple negative electrode tabs are stacked together. The separator can be made of materials such as PP (polypropylene) or PE (polyethylene). In addition, the electrode assembly 23 may be a laminated electrode assembly, but the embodiments of the present application are not limited thereto.

[0109] In the electrolyte, the solvent may include ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate (EMC), methyl formate, ethyl formate, methyl acetate (MA), ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate (EA), acid anhydride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, dimethyl sulfite, tetrahydrofuran, fluorine-containing cyclic organic esters, and sulfur-containing cyclic organic esters.

[0110] The electrolyte may be selected from one or more of an organic electrolyte or an inorganic electrolyte. The electrolyte may contain one or more of nitrogen, sulfur, fluorine, boron, and phosphorus. The type of electrolyte is related to the type of secondary battery to which the electrolyte of the present application is applied. For example, when used in a lithium-ion battery, the electrolyte may be a lithium salt, which may be selected from one or more of an organic lithium salt or an inorganic lithium salt. Specifically, the lithium salt may be selected from one or more of lithium hexafluorophosphate LiPF6, lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (abbreviated as LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (abbreviated as LiBOB), lithium difluorooxalatoborate LiBF2(C2O4) (abbreviated as LiDFOB), LiBF4, LiClO4, and LiAsF6. When used in a sodium ion battery, the electrolyte may be a sodium salt, which may be selected from one or more of an organic sodium salt or an inorganic sodium salt.

[0111] A low-viscosity solvent refers to a solvent with a viscosity of <0.6 mPa·s. The specific viscosity of the low-viscosity solvent can be determined according to its type, and the type of solvent in the electrolyte (including the low-viscosity solvent) and its content can be determined according to methods known in the art. For example, it can be determined by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and inductively coupled plasma optical emission spectrometry (ICP-OES). In other words, the presence of a low-viscosity solvent can be determined by testing the type of solvent in the electrolyte. The specific determination process can refer to the standard GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" for qualitative and quantitative analysis of organic components in the electrolyte by gas chromatography.

[0112] The type and content of additives (including fluorophosphates and borates) in the electrolyte can be tested using the following method: In a nitrogen-filled glove box, 500 μl of a deuterated reagent is added to an NMR tube. A 100 μl non-aqueous electrolyte sample is then added to the NMR tube. The tube is shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The test is then performed using an Oxford Instruments X-Pulse desktop NMR spectrometer. Because non-aqueous electrolytes are very sensitive to moisture, NMR testing and sample preparation are performed in a nitrogen atmosphere (H2O content less than 0.1 ppm, O2 content less than 0.1 ppm). Furthermore, the test instruments must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent is prepared as follows: deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene are dried over 4A molecular sieves at a temperature above 25°C for at least 3 days to ensure that the water content of all reagents is less than 3 ppm. The moisture tester can be a Swiss Metrohm Coulometric Moisture Tester Model 831KF. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene are mixed to obtain a first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene are mixed to obtain a second solution. The first and second solutions are then mixed to obtain the deuterated reagent.

[0113] In some embodiments of the present application, the electrolyte may optionally include other additives.

[0114] In some embodiments of the present application, the viscosity of the electrolyte is ≤5 mPa·s.

[0115] The viscosity of the electrolyte can be measured using instruments and methods known in the art. For example, non-Newtonian fluids can refer to the rotational viscometer method provided in the national standard GB / T22235-2008 "Determination of Liquid Viscosity". Specifically, a certain mass of electrolyte sample is placed in a sample container and tested using a rotational viscometer model DV2TLV produced by Brookfield. At a certain temperature, the shear force exerted on the rotor when it rotates continuously at a constant speed in the sample causes the spring to generate torque, and the torque is proportional to the viscosity, and the viscosity value is obtained. The test equipment meets the following test environmental conditions: 1. External environment of the equipment: temperature is 15-28°C, humidity is RH<80%; 2. Internal environment of the equipment: 2 / 3 of the sample container is immersed in a water bath, the medium is water, and water is used to keep the sample at a constant temperature.

[0116] Lowering the electrolyte's viscosity facilitates the diffusion of lithium ions within the electrolyte, effectively improving the battery's fast-charging and power performance. By controlling the electrolyte's viscosity to ≤5mPa·s, batteries containing this electrolyte exhibit improved fast-charging and power performance.

[0117] For example, the viscosity of the electrolyte can be 1 mPa·s, 1.5 mPa·s, 2 mPa·s, 2.5 mPa·s, 3 mPa·s, 3.5 mPa·s, 4 mPa·s, 4.5 mPa·s, or 5 mPa·s, etc., and can also be any value within the range of ≤5 mPa·s. Generally, the viscosity of the electrolyte is negatively correlated with the amount of the low-viscosity solvent used, that is, the greater the amount of the low-viscosity solvent used, the lower the viscosity of the entire electrolyte, and conversely, the smaller the amount of the low-viscosity solvent used, the greater the viscosity of the entire electrolyte.

[0118] In some embodiments of the present application, the relationship between the mass content a1 of the low-viscosity solvent in the electrolyte and the mass content b1 of the first additive in the electrolyte satisfies: 17≤a1 / b1≤390.

[0119] By controlling the relationship between the mass content a1 of the low-viscosity solvent in the electrolyte and the mass content b1 of the first additive in the electrolyte to satisfy: 17≤a1 / b1≤390, the battery can meet the following requirements: the charging time required for 0-80% SOC is within 15.2 minutes, and the number of cycles with a cycle capacity retention rate of 80% is more than 1200 cycles.

[0120] Furthermore, the relationship between the mass content a1 of the low-viscosity solvent in the electrolyte and the mass content b1 of the first additive in the electrolyte satisfies the following conditions: 20≤a1 / b1≤292. By controlling the relationship between the mass content a1 of the low-viscosity solvent in the electrolyte and the mass content b1 of the first additive in the electrolyte to satisfy the following conditions: 20≤a1 / b1≤292, and by controlling the relationship between the mass content a1 of the low-viscosity solvent in the electrolyte and the mass content b1 of the first additive in the electrolyte to satisfy the following conditions: 20≤a1 / b1≤292, the battery can meet the following conditions: the charging time required for 0-80% SOC is within 14.2 minutes, and the number of cycles to achieve a cycle capacity retention rate of 80% is greater than 1320 cycles.

[0121] For example, the value of the relationship a1 / b1 between the mass content a1 of the low viscosity solvent in the electrolyte and the mass content b1 of the first additive in the electrolyte can be 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 233, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390 or 390, etc., and it can also be any value in the range of 17-390.

[0122] In some embodiments of the present application, the mass content a1 of the low-viscosity solvent in the electrolyte is 10%-70%; the mass content b1 of the first additive in the electrolyte is 0.15%-2.5%.

[0123] The mass content of the low-viscosity solvent in the electrolyte is defined as: the mass of the low-viscosity solvent in the electrolyte divided by the mass of the entire electrolyte. The mass content of the first additive in the electrolyte is defined as: the mass of the first additive divided by the mass of the entire electrolyte. The masses of the low-viscosity solvent and the first additive can be measured by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), or inductively coupled plasma optical emission spectrometry (ICP-OES).

[0124] The greater the mass content of the low-viscosity solvent in the electrolyte, the more conducive it is to reducing the viscosity of the electrolyte, and thus to the diffusion of lithium ions in the electrolyte, thereby improving the battery's fast charging and power performance. The lower the content of the low-viscosity solvent in the electrolyte, the greater the electrolyte viscosity, but the gas production and life problems will be alleviated. The greater the mass content of the first additive in the electrolyte, the more conducive it is to the formation of the SEI film on the surface of the cathode active material and the ionic bond on the surface of the anode active material, thereby reducing the side reactions between the negative and positive electrode sheets and the electrolyte, which is beneficial to the battery life. The lower the mass content of the first additive in the electrolyte, the more conducive it is to reducing the viscosity of the electrolyte. Controlling the mass content a1 of the low-viscosity solvent to 10%-70% and the mass content b1 of the first additive to 0.15%-2.5% can take into account both the battery's kinetic performance and life.

[0125] For example, the mass content a1 of the low viscosity solvent in the electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, etc., and can also be any value within the range of 10%-70%. The mass content b1 of the first additive in the electrolyte can be 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, or 2.5%, etc., and can also be any value within the range of 0.15%-2.5%.

[0126] Furthermore, the mass content a1 of the low-viscosity solvent in the electrolyte is 20%-60%, and the mass content b1 of the first additive in the electrolyte is 0.5%-1.5%. Controlling the mass content a1 of the low-viscosity solvent to 20%-60% and the mass content b1 of the first additive to 0.5%-1.5% can better balance the dynamic performance and life of the battery.

[0127] In some embodiments of the present application, the fluorophosphate includes at least one of monofluorophosphate and difluorophosphate; the borate includes at least one of tetrafluoroborate, bisoxalatoborate, and fluorine-containing oxalatoborate; and the fluorophosphate and borate each independently include at least one of lithium salt, sodium salt, and potassium salt.

[0128] Exemplarily, the fluorophosphate can be selected from lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, potassium difluorophosphate; the borate can be selected from at least one of lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, lithium bisoxalatoborate, sodium bisoxalatoborate, potassium bisoxalatoborate, fluorine-containing lithium oxalatoborate (e.g., lithium difluorooxalatoborate), fluorine-containing sodium oxalatoborate (e.g., sodium difluorooxalatoborate) or fluorine-containing potassium oxalatoborate (e.g., potassium difluorooxalatoborate), etc.

[0129] In some embodiments of the present application, the borate may be selected from lithium difluorooxalatoborate (LIODFB); the fluorophosphate may be selected from lithium difluorophosphate (LIPO2F2).

[0130] Lithium difluorooxalatoborate added to the electrolyte may be converted into lithium tetrafluoroborate. A simplified reaction equation can be expressed as: LiDFOB → LiBF4 + CO2 + H2O. This process is very complex and may involve multiple intermediate steps. Therefore, when the first additive contains lithium difluorooxalatoborate, the electrolyte may contain 100ppm-3000ppm of lithium tetrafluoroborate by weight.

[0131] Illustratively, in the electrolyte of the present application, the mass content of lithium tetrafluoroborate is 100 ppm, 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 1200 ppm, 1400 ppm, 1600 ppm, 1800 ppm, 2000 ppm, 2200 ppm, 2400 ppm, 2600 ppm, 2800 ppm or 3000 ppm, and it can also be any value within the range of 100 ppm-3000 ppm.

[0132] In some embodiments of the present application, the first additive includes lithium tetrafluoroborate, and the amount of lithium tetrafluoroborate added to the electrolyte is b1. It is understood that the amount of lithium tetrafluoroborate in the electrolyte, when added as an additive, and the amount converted from lithium difluorooxalatoborate, can be the same or different.

[0133] In some embodiments of the present application, the low viscosity solvent includes: R1-COO-R2, wherein R1 includes H, methoxy and C1-C5 alkyl, and R2 includes C1-C5 alkyl.

[0134] As used herein, the term "alkyl" refers to a saturated hydrocarbon group, which is formed by removing a hydrogen atom from an alkane molecule. Alkyl groups are chain-like organic groups that contain only carbon and hydrogen atoms.

[0135] In some embodiments of the present application, R1 is selected from hydrogen, methoxy, methyl, ethyl, and n-propyl. In some embodiments of the present application, R2 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl.

[0136] In some embodiments of the present application, the low-viscosity solvent includes at least one of dimethyl carbonate, ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate. In some embodiments of the present application, the low-viscosity solvent includes at least one of dimethyl carbonate, ethyl acetate, and methyl acetate.

[0137] The above solvents have low viscosity, which is conducive to the diffusion of lithium ions in the electrolyte and improves the battery's fast charging and power performance.

[0138] In some embodiments of the present application, the electrolyte further comprises a second additive comprising a sulfur-containing compound. The sulfur-containing compound also facilitates film formation on the surfaces of the cathode active material and the anode active material. Adding the sulfur-containing compound to the electrolyte can improve battery life and gas production.

[0139] In some embodiments of the present application, the mass content c1 of the second additive in the electrolyte is 0.1%-4%.

[0140] The mass content of the second additive in the electrolyte is defined as: the mass of the second additive divided by the mass of the entire electrolyte. The mass of the second additive can be measured by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), or inductively coupled plasma optical emission spectrometry (ICP-OES).

[0141] A higher sulfur-containing compound content in the electrolyte facilitates film formation on the surfaces of the cathode and anode active materials, thereby improving battery life and gas production. A lower sulfur-containing compound content in the electrolyte also contributes to lower battery impedance. By controlling the second additive's content (c1) in the electrolyte to between 0.1% and 4%, it can synergize with the first additive to achieve both low electrolyte viscosity and long battery life, reduced gas production, and low impedance.

[0142] Furthermore, the mass content c1 of the second additive in the electrolyte is 0.5%-3%. By controlling the mass content c1 of the second additive in the electrolyte to 0.5%-3%, the battery performance of long life, low gas generation and low impedance can be better taken into account.

[0143] Illustratively, the mass content c1 of the second additive in the electrolyte can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, etc., and can also be any value within the range of 0.1%-4%.

[0144] In some embodiments of the present application, the sulfur-containing compound includes at least one of a sulfonate compound and a vinyl sulfate compound. Both sulfonate compounds and vinyl sulfate compounds are rich in cyclic sulfate groups and can form a lithium sulfate-rich SEI film on the negative electrode active material layer, which has good thermal stability, thereby improving battery life.

[0145] In some embodiments of the present application, the mass content of the vinyl sulfate compound in the electrolyte is 0.05%-3.5%.

[0146] In some embodiments of the present application, the mass content of the vinyl sulfate compound in the electrolyte is 0.1%-2.5%.

[0147] Exemplarily, the mass content of vinyl sulfate compounds in the electrolyte is 0.05%, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, etc., and it can also be any value in the range of 0.05%-2.5%.

[0148] In some embodiments of the present application, the mass content of the sulfonate compound in the electrolyte is 0.05%-0.5%.

[0149] For example, the mass content of the sulfonate compound in the electrolyte is 0.05%-0.4%, 0.05%-0.3%, 0.05%-0.2%, or 0.05%-0.1%. The mass content of the sulfonate compound in the electrolyte is 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%, etc. It can also be any value within the range of 0.05%-0.5%.

[0150] When the mass ratio of sulfonate compounds and vinyl sulfate compounds is within an appropriate range, their combined effect can promote the formation of a more uniform, dense and stable SEI film, which can effectively reduce the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0151] For example, the sulfonate compound may be a sultone compound, and its structural formula may be: Wherein, p is 1, 2 or 3, and optionally 1; R 11 and R 12 are each independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group and a C1-C3 haloalkoxy group; optionally, R 11 and R 12 are independently selected from hydrogen atoms, halogen atoms, C1-C3 alkyl groups, C1-C3 haloalkyl groups; more optionally, R 11 is a hydrogen atom, and R 12 is a hydrogen atom, a C1-C3 alkyl group or a halogen atom; R 13 and R 14 are each independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group and a C1-C3 haloalkoxy group; optionally, R 13 and R14 Each is independently selected from a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group and a C1-C3 haloalkoxy group, and more optionally R 13 and R 14 are each independently a hydrogen atom or a C1-C3 alkyl group; R 15 and R 16 Each is independently selected from a hydrogen atom, a halogen atom, a C2-C6 alkenyl group, an ester group, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, and a C1-C6 haloalkoxy group, and optionally selected from a hydrogen atom, a C1-C3 alkyl group, a C1-C3 fluoroalkyl group, and a C2-C3 alkenyl group; or R15 and R16 together form a carbonyl group. The structural formula of the vinyl sulfate compound can be: Wherein, q is 1, 2 or 3, optionally 1, R 17 and R 18 Each is independently selected from a hydrogen atom, a halogen atom, a C2-C6 alkenyl group, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 alkyloxyacyl group, a C1-C6 haloalkoxyacyloxy group, a C1-6 alkyl group and a 4-6 membered cyclic sulfate group; optionally R 17 and R 18 are each independently selected from a hydrogen atom, a halogen atom, a C2-C4 alkenyl group, a C1-C4 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy acyloxy group, a C1-C3 alkyl group and a 4-6 membered cyclic sulfate group; more optionally, R 17 and R 18 Each is independently selected from a hydrogen atom, a C1-C4 alkyl group, a C1-C3 alkyloxyacyl group; R 19 and R 20 are each independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group and an aryl group; optionally, R 19 and R 20 Each is independently selected from a hydrogen atom, a halogen atom and a C1-C6 alkyl group.

[0152] In some embodiments of the present application, the vinyl sulfate compound includes vinyl sulfate Vinyl disulfate and ethylene trisulfate At least one of; Sulfonate compounds include 1,3-propane sultone and methylene methanedisulfonate At least one of .

[0153] In some embodiments of the present application, the second additive includes and The mass ratio is 1:(0.25-7).

[0154] In the above embodiments, the mass ratio of the sulfonate compound and the vinyl disulfate compound is within an appropriate range, and their combined effect can promote the formation of a more uniform, dense and stable SEI film, which can effectively reduce the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0155] For example, and The mass ratio is 1:0.25, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5 or 1:7, etc., and it can also be any value in the range of 1:(0.25-7).

[0156] In some implementations of the present application, the electrolyte includes and The mass ratio is 1:(0.25-7).

[0157] For example, and The mass ratio is 1:0.25, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5 or 1:7, etc., and it can also be any value in the range of 1:(0.25-7).

[0158] In the above embodiments, the mass ratio of the sulfonate compound and the ethylene trisulfate compound is within an appropriate range, and their combined effect can promote the formation of a more uniform, dense and stable SEI film, which can effectively reduce the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0159] In some embodiments of the present application, the first additive includes at least one of lithium difluorophosphate and lithium difluorooxalatoborate; and / or

[0160] The second additive includes At least one of .

[0161] In some embodiments of the present application, the mass ratio of lithium difluorophosphate to lithium difluorooxalatoborate is 1:(0.05-15).

[0162] When the mass ratio of lithium difluorophosphate and lithium difluorooxalatoborate is within an appropriate range, their combined effect can promote the formation of a more uniform, dense and stable SEI film, effectively reducing the decomposition of the electrolyte on the negative electrode side, thereby improving the cycle life and long-term stability of the battery.

[0163] Exemplarily, the mass ratio of lithium difluorophosphate and lithium difluorooxalatoborate is 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.7, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, etc., and it can also be any value in the range of 1:(0.05-15).

[0164] In some embodiments of the present application, the electrolyte includes a lithium salt; further, the lithium salt includes at least one of LiPF6 and LiFSI.

[0165] In some embodiments of the present application, the electrolyte includes LiPF6 and LiFSI, and the molar ratio of LiFSI to LiPF6 is 0.1-5. In some embodiments of the present application, the molar concentration of LiFSI in the electrolyte is 0.1-1 mol / L, and the molar concentration of LiPF6 in the electrolyte is 0.2-1.2 mol / L. The higher the content of LiFSI, the more favorable it is for Li + The migration of LiFSI improves the battery's fast-charging performance. Lower LiFSI content also reduces corrosion of the negative electrode current collector, which in turn improves battery safety. By controlling the molar ratio of LiFSI to LiPF6 to 0.1-5, both fast-charging performance and safety can be achieved.

[0166] Exemplarily, the molar ratio of LiFSI to LiPF6 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, etc., and it can also be any value in the range of 0.1 to 5. The molar concentration of LiFSI in the electrolyte can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L, etc., and it can also be any value in the range of 0.1 to 1 mol / L. The molar concentration of LiPF6 in the electrolyte can be 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L or 1.2mol / L, etc., and it can also be any value within the range of 0.2-1.2mol / L.

[0167] In some embodiments of the present application, the mass ratio of LiPF6 to LiFSI is 0.1-10, which is beneficial to taking into account both the fast charging performance and safety of the battery. Exemplarily, the mass ratio of LiPF6 to LiFSI can be 0.1, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10, and it can also be any value in the range of 0.1-10.

[0168] After the above introduction to the composition of the electrolyte, its application in the battery cell 20 will be described in detail below.

[0169] The method for preparing the battery cell 20 includes the following steps:

[0170] S101. Preparation of positive electrode sheet: The positive electrode active material, conductive agent, and binder are mixed to obtain a mixture. The mixture is added to a solvent and stirred to obtain a positive electrode active slurry. The positive electrode active slurry is then evenly coated on the positive electrode current collector. The positive electrode sheet is obtained after drying, cold pressing, and slitting.

[0171] Among them, the positive electrode active material can be lithium nickel cobalt manganese oxide, such as: LiNi 0.6 Co 0.2 Mn 0.2O2, the positive electrode active material can be a lithium-containing phosphate, such as LiFePO4, and a small amount of other positive electrode active materials can be optionally added. The binder can be one or more of styrene-butadiene rubber, water-based acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol and polyvinyl butyral. The conductive agent can be at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene or acetylene black. The solvent can be one or more of dimethyl glutarate and N-methylpyrrolidone. Leveling agents, dispersants, etc. can also be added to the positive electrode active slurry. The positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0172] The coating method may be: blade coating, roller coating, slit coating, etc., which is not limited in this application.

[0173] S102, dissolving the negative electrode active material, conductive agent, binder, and thickener in a solvent, and mixing them evenly to prepare a negative electrode active slurry; coating the negative electrode active slurry evenly on the negative electrode current collector once or multiple times, and obtaining a negative electrode sheet through drying, cold pressing, and slitting.

[0174] Among them, the negative electrode active material can adopt the negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more. The conductive agent can include but is not limited to one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). The negative electrode active material layer may optionally include other additives. As an example, other additives may include, but are not limited to, thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. The negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. As the metal foil, copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil may be used. As the three-dimensional porous current collector, copper mesh, nickel mesh, foam copper, foam nickel, and foam aluminum may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, aluminum, aluminum alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0175] S103. The prepared positive electrode sheet, negative electrode sheet, and separator (e.g., polyethylene (PE) porous polymer film) are formed into corresponding electrode assemblies according to a Z-shaped stacking structure. The electrode assembly is vacuum-dried at 90°C for 12 hours, and then the positive and negative electrode tabs are ultrasonically welded. The positive electrode uses aluminum tabs, and the negative electrode uses nickel tabs. The positive and negative electrode tabs are located on the same side of the electrode assembly. The electrode assembly after the tabs are welded is placed in an aluminum-plastic film of appropriate size and top-side sealed at a top-side sealing temperature of 145°C. The electrolyte is then injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes static standing, hot and cold pressing, formation, aging, shaping, capacity testing, and other processes to obtain a battery cell.

[0176] Among them, the isolation membrane is arranged between the positive electrode sheet and the negative electrode sheet, and its main function is to prevent internal short circuits. The present application has no particular restrictions on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected. The material of the isolation membrane can include but is not limited to one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0177] Since the additive participates in the formation of the SEI film and the like during the battery cell preparation process, such as the formation and aging steps, its usage will be reduced to a certain extent. It has been determined that after the above-mentioned electrolyte (i.e., in the electrolyte, the mass content a1 of the low-viscosity solvent is 10%-70%, and the mass content b1 of the first additive is 0.2%-2%, recorded as fresh electrolyte) is applied to a secondary battery and the formation and aging steps are completed, the mass content b2 of the first additive in the electrolyte at this time is 0%-1%, and is positively correlated to a certain extent with the usage of the first additive in the fresh electrolyte; illustratively, the mass content b2 of the first additive in the product battery electrolyte can be 0, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., and can also be any value within the range of 0-1%. The mass content of the low-viscosity solvent remains almost unchanged, ranging from 10% to 70%. For example, the mass content a2 of the low-viscosity solvent in the product battery electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%, etc., and can also be any value within the range of 10% to 70%.

[0178] Similarly, if the original electrolyte contains a second additive, and the mass content c1 of the second additive in the electrolyte is 0.1%-4%. After being applied to a secondary battery and completing the formation, aging and other steps, the mass content c2 of the second additive in the electrolyte at this time is 0%-2%, and to a certain extent, it is positively correlated with the amount of the second additive in the fresh electrolyte. Exemplarily, the mass content c2 of the second additive in the product battery electrolyte can be 0, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, etc., and it can also be any value within the range of 0-2%.

[0179] In fresh electrolyte, the relationship between the mass content a1 of the low-viscosity solvent and the mass content b1 of the first additive satisfies the following relationship: 17 ≤ a1 / b1 ≤ 390, achieving optimal results. Furthermore, the first additive is consumed during the production of the battery product, and the content of the low-viscosity solvent remains essentially unchanged. Accordingly, in the battery product, the relationship between the mass content a2 of the low-viscosity solvent and the mass content b2 of the first additive satisfies the following relationship: 102 ≤ a2 / b2 ≤ 2918. Similarly, 20 ≤ a1 / b1 ≤ 292 in fresh electrolyte corresponds to 70 ≤ a2 / b2 ≤ 1944 in the battery product.

[0180] Exemplarily, the value of a2 / b2 of the relationship between the mass content a2 of the low viscosity solvent in the electrolyte and the mass content b2 of the first additive in the electrolyte can be 70, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900 or 2918, etc., and it can also be any value within the range of 70-2918.

[0181] In some embodiments of the present application, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes lithium nickel cobalt manganese oxide, and the Dv50 of the lithium nickel cobalt manganese oxide is 2μm-15μm.

[0182] In batteries where the positive electrode active material of the positive electrode sheet is lithium nickel cobalt manganese oxide, the first additive can combine with the metal ions on the surface of the positive electrode sheet to form ionic bonds, reducing the phenomenon of over-delithiation on the surface of the positive electrode sheet, thereby effectively reducing the occurrence of structural destruction of the positive electrode active material, reducing the side reaction of the electrolyte on the positive electrode sheet side and the gas production problem caused by the side reaction. When the second additive is added to the electrolyte, a CEI film can be further formed on the surface of the positive electrode active material, thereby improving the structural stability of the positive electrode sheet side, reducing the risk of gas production, and improving the life of the battery. Compared with other positive electrode active materials, ternary system materials are more unstable and will bring more electrolyte reactions, and the battery life and gas production problems are more obvious. In batteries where the positive electrode active material of the positive electrode sheet is a ternary system material, the electrolyte containing a low viscosity solvent and the first additive provided above is used, which significantly improves the life of the battery.

[0183] In this application, Dv50 represents the particle size corresponding to the 50% cumulative volume distribution percentage of a material. It can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd. in the United Kingdom, in accordance with the particle size distribution laser diffraction method described in GB / T 19077-2016.

[0184] For example, the Dv50 of the lithium nickel cobalt manganese oxide is 2 μm-3 μm, 2 μm-5 μm, 2 μm-7 μm, 2 μm-9 μm, 2 μm-10 μm, or 2 μm-12 μm. For example, the Dv50 of the lithium nickel cobalt manganese oxide is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, etc. It can also be any value within the range of 2 μm-15 μm.

[0185] The smaller the particle size of lithium nickel cobalt manganese oxide, the more reactive sites there are on the surface of the lithium nickel cobalt manganese oxide, the faster the lithium ion deintercalation rate, and the better match with the lithium ion transmission rate in the electrolyte. In addition, reducing the particle size of the ternary material is conducive to reducing the lithium ion transmission impedance and reducing the temperature rise of the battery under the fast charging system. The battery temperature rise will cause more side reactions in the low viscosity solvent in the electrolyte, affecting the battery cycle performance. However, if the particle size is too small, it will lead to an increase in the interface side reactions between the ternary material and the electrolyte, worsening gas production and affecting the battery life. Controlling the Dv50 of the ternary material to 2μm-15μm can reduce the side reactions of the electrolyte on the positive electrode side, taking into account the fast charging performance and service life of the battery.

[0186] Furthermore, in some embodiments of the present application, the positive electrode active material includes lithium nickel cobalt manganese oxide, the molar content of nickel element is less than 80% based on the total molar number of transition metals in the positive electrode active material, the Dv50 of the positive electrode active material is 2μm-5μm, and the positive electrode active material includes non-agglomerated primary particles.

[0187] In the present application, primary particles refer to the smallest unit of particles within a certain identification range. The interior of the primary particles may include defects of any form, but it is impossible to define smaller particles in the primary particles. The primary particles can be in an unagglomerated state or an agglomerated state. The aggregate of the primary particles after agglomeration is called a secondary particle. The secondary particles have a clear surface and boundary, but after cutting the cross section of the secondary particles, it can be seen that the secondary particles are formed by the agglomeration of many primary particles. Unagglomerated primary particles refer to the phenomenon that there is no obvious agglomeration between these primary particles to form secondary particles. The state of the positive electrode active material in the positive electrode active material layer can be judged by observing the particle morphology of the cross section in the thickness direction of the positive electrode sheet.

[0188] For example, the molar content of nickel in lithium nickel cobalt manganese oxide can be selected as 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 79% or any range of values ​​therebetween.

[0189] For example, the Dv50 of lithium nickel cobalt manganese oxide with a molar content of nickel element less than 80% is 2μm-4μm, 2μm-3μm, for example, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, and it can also be any value in the range of 2μm-5μm.

[0190] A nickel content of less than 80% by mole helps reduce the probability of nickel dissolution in the positive electrode active material at high voltages (charge cut-off voltage ≥ 4.3V), thereby increasing the withstand voltage of the positive electrode active material. The combination of low-nickel components with unagglomerated primary particles can further reduce the degree of side reactions between the positive electrode active material and the carboxylate solvent, lowering the probability of cracking in the positive electrode active material during high-voltage charge and discharge, and improving the cycling performance of the battery cell.

[0191] In some embodiments of the present application, the positive electrode active material includes lithium nickel cobalt manganese oxide, based on the total molar number of transition metals in the positive electrode active material, the molar content of nickel element is greater than or equal to 80%, the Dv50 of the positive electrode active material is 6μm-15μm, and the positive electrode active material includes secondary particles formed by agglomeration of primary particles.

[0192] Illustratively, the molar content of nickel in lithium nickel cobalt manganese oxide is 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or any range therebetween.

[0193] In some embodiments of the present application, lithium nickel cobalt manganese oxide includes LiNi 0.83 Co 0.07 Mn 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0194] For example, the Dv50 of lithium nickel cobalt manganese oxide having a molar content of nickel element greater than or equal to 80% is 6μm-14μm, 6μm-13μm, 6μm-12μm, 6μm-11μm, 6μm-10μm, 6μm-9μm, 6μm-8μm, 6μm-7μm, for example, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm or 14μm, and it can also be any value in the range of 6μm-15μm.

[0195] In some embodiments of the present application, the positive electrode active material lithium nickel cobalt manganese oxide includes secondary particles, and the average particle size of the primary particles in the secondary particles can be 0.1μm-1.5μm, as an example, 0.1μm, 0.3μm, 0.5μm, 0.7μm, 0.9μm, 0.11μm, 0.13μm, 0.15μm, and it can also be any value in the range of 0.1μm-1.5μm.

[0196] The average particle size of the primary particles in the secondary particles can be tested by any known method in the art. As an example, a cross section in the thickness direction of the positive electrode sheet is obtained, and particles in any 10 areas of the same size and shape are observed in the same scanning electron microscope image (SEM) under 10kv and 30k magnifications. The 10 areas are then each subdivided into 5 positions in the four corners and the center, and the mean particle size of any primary particle at each position under the magnification is selected, and the mean particle size results of the 5 positions in the four corners and the center are averaged to obtain the mean particle size of the primary particles in the area, and then the particle size of the primary particles obtained in the 10 areas is averaged as the average particle size of the primary particles. Specifically, the average value of the major diameter and minor diameter of each particle is taken as the mean particle size of the particle.

[0197] Forming high-nickel materials into large-sized secondary particles helps increase both the specific capacity of the positive electrode active material and the gradation of the positive electrode sheet, improving the battery's energy density. Furthermore, the secondary particles, composed of small-sized primary particles, can shorten the lithium ion transmission distance, increase the number of embedded end faces, reduce the DC impedance of the battery cell, and improve the power performance of the battery cell.

[0198] In some embodiments of the present application, the positive electrode active material includes LiNi 0.6 Co 0.2 Mn 0.2 O2, the Dv50 of the positive electrode active material is 2μm-4μm. In some embodiments of the present application, the positive electrode active material includes LiNi 0.83 Co 0.07 Mn 0.1 O2, the Dv50 of the positive electrode active material is 7μm-10μm.

[0199] In some embodiments of the present application, lithium nickel cobalt manganese oxide can be doped with at least one metal element including Fe, Mg, Fe, Al, Cu, and Ti. Doping metal elements in lithium nickel cobalt manganese oxide can form more conduction paths inside the positive electrode active material, thereby increasing the deintercalation speed of lithium ions, which can match the transmission speed of lithium ions in the electrolyte, and help reduce the lithium ion transmission impedance and the temperature rise of the battery under the fast charging system. At the same time, during the charging and discharging process, especially when the battery is in a high voltage state, the transition metals (such as nickel, cobalt, manganese, etc.) in the positive electrode active material may dissolve into the electrolyte, and the lithium nickel cobalt manganese oxide doped with metal elements can improve the structural stability of the positive electrode active material and ensure the smooth deintercalation of lithium ions.

[0200] In some embodiments of the present application, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes a lithium-containing phosphate, and the Dv50 of the positive electrode active material is 0.3 μm-2 μm. In batteries where the positive electrode active material of the positive electrode sheet is a lithium-containing phosphate material, the additive can form a stable SEI film on the negative electrode sheet, blocking contact between the solvent, especially a low-viscosity solvent, and the negative electrode sheet, reducing the occurrence of solvent reduction, inhibiting further side reactions on the negative electrode side, and improving the battery life.

[0201] In some embodiments of the present application, the general formula of the lithium-containing phosphate is as follows:

[0202] Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 ,

[0203] Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.7≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; and Y includes one or more of O and F.

[0204] The lithium-containing phosphate having the above components has good structural stability and low irreversible loss during fast charging, thereby improving the cycle stability of the battery cell.

[0205] In some embodiments of the present application, the lithium-containing phosphate has an olivine structure, including but not limited to lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate and one or more of their respective doped modified materials, coated modified materials, and composite modified materials.

[0206] In some embodiments of the present application, the Dv50 of the positive electrode active material containing lithium phosphate can be 0.3μm, 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm or 2.0μm, and it can also be any value within the range of 0.3μm-2.0μm.

[0207] The smaller the particle size of the lithium-phosphate material, the more reaction sites it has, the faster the lithium-ion deintercalation rate, and the better match between it and the lithium-ion transfer rate in the electrolyte. Furthermore, reducing the particle size of the lithium-ion iron material helps reduce the lithium-ion transfer impedance and the temperature rise of the battery under fast-charging conditions. This temperature rise can cause more side reactions in the low-viscosity solvent in the electrolyte, affecting the battery's cycle life. However, if the particle size is too small, the lithium-phosphate material will absorb more water, which will not only hydrolyze the low-viscosity solvent in the electrolyte, increasing the battery's internal resistance and affecting the battery's cycle life, but also destabilize the SEI film, leading to continuous electrolyte decomposition and irreversible consumption of lithium ions, which in turn affects the battery's cycle performance. Controlling the Dv50 of the lithium-phosphate material to 0.3μm-2μm can reduce electrolyte hydrolysis, improving the battery's fast-charging performance while also taking into account the battery's cycle performance and service life.

[0208] In some embodiments, the positive electrode active material containing lithium phosphate includes unagglomerated primary particles and / or secondary particles formed by agglomeration of primary particles. The average particle size of the primary particles of the positive electrode active material containing lithium phosphate is 50 nm to 300 nm.

[0209] In some embodiments, the average particle size of the primary particles of the positive electrode active material containing lithium phosphate can be selected to be 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, 300nm or any numerical range therebetween.

[0210] Lithium-containing phosphates with an average primary particle size within this range combine a short ion transport path with low lithium-ion transfer impedance, matching the liquid-phase transfer rate of lithium ions in the electrolyte while maintaining the cycle life of the battery cells. Small primary particles of positive electrode active materials are detrimental to increasing the active material layer density. Aggregation of these particles into secondary particles results in a Dv50 within the 0.3μm-2μm range, further improving the battery's cycle performance and service life.

[0211] In this application, for the positive electrode active material (such as lithium-containing phosphate or lithium nickel cobalt manganese oxide), the statistics of its primary particle size can be carried out in the following way. As an example, the battery is disassembled to obtain the positive electrode sheet, the active material layer of the positive electrode sheet is peeled off, acetone is fully washed, filtered and dried to obtain a powder. Take 0.05g of the evenly mixed powder and dissolve it in 40mL of anhydrous ethanol, then add an appropriate amount of dispersant, stir evenly to obtain a suspension, take 2mL of the suspension and 2mL of anhydrous ethanol and mix them and perform ultrasonic treatment, the ultrasonic power is 480W, the ultrasonic time is 5min, to obtain a uniformly dispersed suspension, take an appropriate amount of the middle layer suspension for transmission electron microscopy test, and obtain a transmission electron microscope image. Select 5-10 transmission electron microscope images with a number of 50 to 100 particles as the sampling area, ensure that at least 500 particles are tested, and then use Avizo 3D software image processing software to count the projected area of ​​each primary particle in each sampling area, which is the primary particle cross-sectional area S. When identifying primary particles, a combination of manual and software identification can be used to determine whether the particle is a single primary particle or two secondary particles. The equivalent circle method is used to obtain the equivalent circle diameter of the primary particle, which is the primary particle size.

[0212] In some embodiments of the present application, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material and lithium metal.

[0213] In some embodiments of the present application, the graphite comprises artificial graphite. Artificial graphite has fewer defects, which can reduce side reactions between the electrolyte and the artificial graphite, alleviate negative electrode gassing, and improve battery gassing defects. Furthermore, artificial graphite has a small specific surface area. When the electrolyte forms a CEI film on the artificial graphite surface, the amount of the first and second additives can be reduced compared to using natural graphite as the negative electrode active material.

[0214] In some embodiments of the present application, the negative electrode active material includes secondary particles, and the Dv50 of the secondary particles is 5 μm to 18 μm. The particle state of the negative electrode active material in the negative electrode active material layer can be determined by observing the particle morphology of a cross section along the thickness direction of the negative electrode sheet. The Dv50 of the negative electrode active material graphite can be measured using a laser particle size analyzer.

[0215] Secondary particles are composed of many small crystals, each with a grain boundary between them, which can provide additional paths for lithium ions, increase the reactive sites of the negative electrode active material, and provide a suitable embedding end face for lithium ions, thereby increasing the rate of lithium ion deintercalation and improving fast charging performance. If the Dv50 of the negative electrode active material is too small, the side reactions between the negative electrode active material and the electrolyte will increase, affecting the battery cycle life. If the Dv50 of the negative electrode active material is too large, the process will be more difficult to implement and will also affect the compaction density of the electrode sheet. Controlling the negative electrode active material to be a secondary particle and the Dv50 of the negative electrode active material to be 5μm to 18μm can make the lithium ion embedding end face of the negative electrode active material suitable, matching the lithium ion transfer rate of the electrolyte, and improving the fast charging performance of the battery. At the same time, the negative electrode active material and the first and second additives work synergistically to form a dense SEI film on the surface of the negative electrode active material, thereby increasing the life of the battery.

[0216] For example, the negative electrode active material secondary particle Dv50 is 5 μm-12 μm, 5 μm-15 μm, or 5 μm-17 μm. The secondary particle Dv50 is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm, etc., and can also be any value within the range of 5 μm-18 μm.

[0217] In some embodiments of the present application, the air oxidation temperature T0 of the negative electrode active material is 630°C-730°C.

[0218] “Air oxidation temperature” refers to the air oxidation temperature T0, which is the temperature corresponding to the intersection of two tangent lines at two points corresponding to 500°C and T1 temperature on the thermogravimetric curve of the negative electrode active material, and T1 temperature is the peak top temperature of the maximum area peak in the differential thermogravimetric curve of the negative electrode active material.

[0219] Thermogravimetric curves and differential thermogravimetric curves can be obtained by thermogravimetric analysis under the following conditions: weigh the sample mass 10±0.05 mg, set the relevant parameters of the thermogravimetric analyzer: the purge gas is air with an air flow rate of 60 mL / min, the heating rate is 5°C / min, and the test temperature range is 35°C-950°C.

[0220] The air oxidation temperature of the negative electrode active material can accurately indicate the temperature at which the negative electrode active material begins to lose weight due to air oxidation, and thus can accurately reflect the end faces and number of defects of the negative electrode active material. When the air oxidation temperature T0 of the negative electrode active material is 630°C-730°C, the negative electrode active material contains a moderate number of end faces and defects, has good lithium ion and electron transport properties, can match the lithium ion transport rate of the electrolyte, and improve the fast charging performance of the battery. At the same time, the negative electrode active material can have more lithium insertion sites, which is beneficial to improving the energy density of the battery. It can also allow the first additive and the second additive to adhere to the surface of the negative electrode active material earlier and more efficiently, forming a dense SEI film, reducing the side reactions between the solvent and the negative electrode, and improving the fast charging performance of the battery while taking into account the cycle performance and service life of the battery.

[0221] Illustratively, the air oxidation temperature T0 of the negative electrode active material is 640° C.-730° C., 660° C.-730° C., 680° C.-730° C., 700° C.-730° C., or 710° C.-730° C. Illustratively, the air oxidation temperature T0 of the negative electrode active material is 630° C., 640° C., 650° C., 660° C., 670° C., 680° C., 690° C., 700° C., 710° C., 720° C., or 730° C., etc., and may also be any value within the range of 630° C. to 730° C.

[0222] In some embodiments of the present application, the negative electrode active material includes a silicon-based material, with the silicon-based material comprising no more than 25% by weight of the negative electrode active material layer. Silicon-based materials contribute to battery performance, such as energy density. However, low-viscosity solvents are prone to generating protonated hydrogen, to which silicon-based materials are sensitive. Therefore, controlling the silicon-based material's proportion to no more than 25% by weight improves the battery's cycle life.

[0223] In some embodiments of the present application, the charging time t for charging the battery from 0% SOC to 80% SOC satisfies: t≤15.2 min. The battery has a short charging time and a strong fast charging capability.

[0224] Exemplarily, the charging time for charging the battery from 0% SOC to 80% SOC is t≤14.1 min, t≤13.3 min, t≤12.6 min, and t≤11.1 min.

[0225] In some embodiments of the present application, the charging time t for charging the battery from 0% SOC to 80% SOC is 11.1 min-15.2 min.

[0226] Exemplarily, the charging time t for the battery to charge from 0% SOC to 80% SOC is 15.2 min, 14.8 min, 14.4 min, 14.0 min, 13.6 min, 13.2 min, 12.8 min, 12.4 min, 12.0 min, 11.6 min, 11.4 min or 11.1 min, etc., and it can also be any value within the range of 11.1 min-15.2 min.

[0227] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0228] 1. Implementation Methods

[0229] Implementation 1-37 and Comparative Example 1-2

[0230]

Preparation of positive electrode sheet

[0231] The positive electrode active material ternary material LiNi 0.6 Co 0.2 Mn 0.2 O2, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a weight ratio of 98:1:1 and dissolved in solvent N-methylpyrrolidone (NMP) to form a positive electrode slurry. The slurry is then coated on the current collector aluminum foil. After drying, it is cold pressed, trimmed, cut into pieces, and slit into strips to make the positive electrode sheet of the lithium-ion battery.

[0232]

Preparation of negative electrode sheet

[0233] The negative electrode active material artificial graphite, conductive agent carbon black, thickener CMC-Na, and adhesive styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:2:1:1 and dissolved in solvent deionized water to form a negative electrode slurry; the slurry is then coated on the current collector copper foil, dried, cold pressed, trimmed, cut into pieces, and slit into strips to form the negative electrode sheet of the lithium-ion battery.

[0234] Preparation of electrolyte

[0235] The electrolyte is prepared in an argon atmosphere glove box with a water content of <10 ppm. First, a non-low-viscosity solvent and a low-viscosity solvent are mixed in a specific ratio. Then, a lithium salt is added, followed by the additives. The percentages of each organic solvent are expressed as weight percentages based on the total weight of the organic solvent, and the percentages of each lithium salt are expressed as weight percentages based on the total weight of the electrolyte.

[0236]

Isolation film

[0237] Polypropylene film is used as the isolation film.

[0238] Preparation of battery cells

[0239] The prepared positive and negative electrodes, along with the separator, are stacked in a Z-shaped configuration to form the corresponding electrode assembly. The electrode assembly is then vacuum-dried at 90°C for 12 hours. The positive and negative electrode tabs are then ultrasonically welded together. The positive electrode tabs are aluminum, while the negative electrode tabs are nickel, located on the same side of the electrode assembly. The electrode assembly, after the tabs are welded, is then enclosed in aluminum-plastic film of appropriate size and sealed top and side at a temperature of 145°C. Electrolyte is then injected and sealed to produce an uncharged battery. The uncharged battery then undergoes a series of processes, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain a single battery cell.

[0240] The preparation methods of Examples 35 to 37 are basically the same as those of Example 1, except that the steps for preparing the positive electrode sheet are changed to: the positive electrode active material containing lithium phosphate LiFePO4, the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a weight ratio of 96:2:2 and dissolved in the solvent N-methylpyrrolidone (NMP) to form a positive electrode slurry, and then the slurry is coated on the current collector aluminum foil, and after drying, it is cold pressed, trimmed, cut into pieces, and stripped to make the positive electrode sheet of the lithium-ion battery.

[0241] The main parameter controls of Examples 1 to 37 and Comparative Examples 1 to 3 are shown in the following table:

[0242] The main parameter controls of Examples 1 to 37 and Comparative Examples 1 to 3 are shown in the following table:

[0243] In the table, “ / ” indicates that the substance is not present. Dv50 and air oxidation temperature T0 are tested using the following method:

[0244] Dv50 test of positive electrode active materials and negative electrode active materials: The average particle size (Dv50) of the positive electrode active materials and negative electrode active materials was measured using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0245] Air oxidation temperature T0 test: The test was performed using a German NETZSCH STA449F3 synchronous thermal analyzer. First, 10±0.05mg of artificial graphite sample was weighed into a flat-bottomed Al2O3 crucible without the lid. The instrument parameters were set as follows: the purge gas was air with a flow rate of 60mL / min, and the shielding gas was nitrogen with a flow rate of 20mL / min. The heating rate was set to 5°C / min, and the test temperature range was 35°C to 950°C. When the temperature was below 500°C, since there were no characteristic peaks at this stage, a rapid heating rate of, for example, 10°C / min was suitable. After the thermogravimetric test, the thermogravimetric curve (TG) and differential thermogravimetric curve (DTG) of the composite graphite material were obtained. The peak top temperature T1 of the maximum area peak was read from the differential thermogravimetric curve. The intersection of the two tangent lines corresponding to the two points corresponding to the temperatures of 500°C and T1, respectively, was determined on the thermogravimetric curve. The temperature corresponding to this intersection on the thermogravimetric curve was the air oxidation temperature T0 of the artificial graphite sample.

[0246] The batteries provided in each embodiment and comparative example were subjected to performance testing, which specifically included the following: Electrolyte viscosity test: A certain mass of electrolyte sample was placed in a sample container and tested using a rotational viscometer model DV2TLV produced by Brookfield. At a certain temperature, the shear force exerted on the rotor as it continuously rotates at a constant speed in the sample causes the spring to generate torque, which is proportional to the viscosity, and the viscosity value is obtained. The test equipment meets the following test environmental conditions: 1. External environment of the equipment: temperature is 15-28°C, humidity is RH<80%; 2. Internal environment of the equipment: 2 / 3 of the sample container is immersed in a water bath, the medium is water, and water is used to maintain a constant temperature for the sample.

[0247] Fast charging capability test: The batteries of the above-mentioned embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 35°C, the battery was charged at a constant current rate of 1C to a voltage of 4.4V, then charged at a constant voltage to a current of ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. The actual capacity was recorded as C0. Then each battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 in sequence to the full battery charge cut-off voltage of 4.4V or the negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is discharged with 1C0 to the full battery discharge cut-off voltage of 2.8V. Record the state of charge (SOC) at different charge rates to 10%, 20%, 30%, ..., 80%. Charge, state of charge, when "SOC = 0" means the battery is fully discharged, when "SOC = 100%" means the battery is fully charged) the corresponding negative electrode potential, draw the charge rate-negative electrode potential curve under different SOC states, and obtain the charge rate corresponding to the negative electrode potential of 0V under different SOC states after linear fitting. The charge rate is the charging window under the SOC state, which is recorded as C(10% SOC), C(20% SOC), C(30% SOC), C(40% SOC), C(5 The charging time T for the battery from 0 to 80% SOC is calculated according to the formula (60 / C(10%SOC)+60 / C(20%SOC)+60 / C(30%SOC)+60 / C(40%SOC)+60 / C(50%SOC)+60 / C(60%SOC)+60 / C(70%SOC)+60 / (C80%SOC))×10%, in minutes. The shorter the time, the better the battery's fast charging performance.

[0248] The cycling performance test procedure is as follows: At 45°C, the prepared battery was charged at a constant current of 1C to 4.25V. Then, it was charged at a constant voltage of 4.25V until the current dropped to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V. This was the first charge / discharge cycle of the battery. The discharge capacity of this cycle was recorded as the discharge capacity of the battery in the first cycle (C1). The above steps were repeated for the same battery. The process capacity of the battery after the nth cycle (Cn) was the process capacity of the battery after the nth cycle. The capacity retention rate after n cycles = Cn / C1×100%. The number of cycles at which the cycle capacity retention rate reached 80% was recorded.

[0249] The test results are shown in the following table:

[0250] By comparing the data of the examples and comparative examples, it can be seen that the examples of the present application use a low-viscosity solvent in combination with a first additive such as fluorophosphate and / or borate in the electrolyte, so that the battery has better fast charging performance and longer life. Among them, the charging time required for 0-80% SOC is within 15.2 minutes, and the number of cycles with a cycle capacity retention rate of 80% is more than 1200 cycles.

[0251] By comparing the data of Examples 1 to 3, it can be seen that as the content of low-viscosity solvent in the electrolyte increases, the fast charging performance of the battery shows a trend of getting better and better, while the life of the battery shows a trend of gradually getting worse. Based on this trend change, it is inferred that when the mass content a1 of the low-viscosity solvent is in the range of 10%-70%, the fast charging performance and life of the battery can meet the requirements.

[0252] By comparing the data of Example 1 and Examples 4 to 9, it can be seen that with the increase of the content of the first additive in the electrolyte, the fast charging performance of the battery shows a trend of gradually deteriorating, while the life of the battery shows a trend of getting better and better. When the content of the first additive is 0.15%-2.5%, the performance of the battery meets the following requirements: the charging time required for 0-80% SOC is 13.1min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1200 cycles; further, when the content of the first additive is 0.5%-1.5%, the performance of the battery meets the following requirements: the charging time required for 0-80% SOC is within 12.7min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1430 cycles.

[0253] By comparing the data of Example 2 and Examples 10 to 14, it can be seen that with the increase of the content of the second additive in the electrolyte, the fast charging performance of the battery shows a trend of gradually deteriorating, while the life of the battery shows a trend of getting better and better. When the content of the second additive is 0.1%-4.0%, the performance of the battery meets the following requirements: the charging time required for 0-80% SOC is within 14.2min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1580 cycles; further, when the content of the second additive is 0.5%-3.0%, the performance of the battery meets the following requirements: the charging time required for 0-80% SOC is within 14min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1640 cycles.

[0254] By comparing the data of Example 2 with those of Comparative Examples 1 and 2, it can be seen that the inclusion of the first additive in the electrolyte can improve the fast charging performance of the battery.

[0255] By comparing the data of Example 1 and Examples 15 to 26, it can be seen that using different first additives or low-viscosity solvents or second additives can achieve better fast charging performance and longer life.

[0256] According to the data of Example 1, Example 27 to Example 28, based on the total molar number of transition metals in the lithium nickel cobalt manganese oxide, the molar content of nickel element is less than 80%, and when the Dv50 of the positive electrode active material is 2μm-4μm, as the Dv50 of the lithium nickel cobalt manganese oxide increases, the fast charging performance of the battery shows a trend of gradually getting worse, while the life of the battery shows a trend of getting better and better. The performance of the battery meets the following requirements: the charging time required for 0-80% SOC is within 12.6min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1340 cycles. According to the trend, it is speculated that based on the total molar number of transition metals in the positive electrode active material, the positive electrode active material with a molar content of nickel element less than 80% Dv50 of 2μm-5μm can achieve better fast charging performance and longer life.

[0257] According to the data of Examples 29 to 30, based on the total molar number of transition metals in the lithium nickel cobalt manganese oxide, the molar content of nickel element accounts for greater than or equal to 80%, and when the Dv50 of the positive electrode active material is 7μm-10μm, as the Dv50 of the lithium nickel cobalt manganese oxide increases, the fast charging performance of the battery shows a trend of gradually getting worse, while the battery life shows a trend of getting better and better. The performance of the battery meets the following requirements: the charging time required for 0-80% SOC is within 12.8min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1680 cycles. According to the trend, it is speculated that based on the total molar number of transition metals in the positive electrode active material, the positive electrode active material with a molar content of nickel element greater than or equal to 80% Dv50 of 6μm-18μm can achieve better fast charging performance and longer life.

[0258] Comparing the data from Example 1 with Examples 31 and 32 shows that as the Dv50 of the negative electrode active material secondary particles increases, the battery's fast-charging performance gradually deteriorates, while the battery's lifespan improves. When the Dv50 of the negative electrode active material secondary particles is between 6μm and 15μm, the battery's performance meets the following requirements: a charge time from 0 to 80% SOC is within 13.1 minutes, and the number of cycles required to maintain a cycle capacity of 80% is greater than 1360. Based on this trend, it is speculated that a Dv50 of the negative electrode active material secondary particles between 6μm and 18μm can achieve better fast-charging performance and a longer battery life.

[0259] By comparing the data of Example 1 with those of Examples 33 to 34, it can be seen that as the air oxidation temperature of the negative electrode active material increases, the fast charging performance of the battery shows a trend of gradually deteriorating, while the battery life shows a trend of getting better and better. When the air oxidation temperature of the negative electrode active material is 630°C-730°C, the performance of the battery meets the following requirements: the charging time required for 0-80% SOC is within 13.2min, and the number of cycles with a cycle capacity retention rate of 80% is more than 1460 cycles.

[0260] From the data of Examples 35 to 37, it can be seen that the use of a low-viscosity solvent in combination with a first additive such as fluorophosphate and borate in a lithium-phosphate-containing positive electrode active material system can achieve better fast charging performance and a longer life.

[0261] The batteries provided in each embodiment and comparative example were applied to an automobile, and the contents of the first additive and the second additive in the electrolyte were tested after the automobile had been driven for 10,000 kilometers. Alternatively, the batteries provided in each embodiment and comparative example were cycled for 25 cycles and the contents of the first additive and the second additive in the electrolyte were tested. The testing method is as follows:

[0262] In a nitrogen-filled glove box, 500 μl of deuterated reagent was added to an NMR tube. A 100 μl sample of the non-aqueous electrolyte was then added to the tube. The tube was shaken to dissolve the non-aqueous electrolyte into the deuterated reagent. The spectrometer was then used on an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because non-aqueous electrolytes are highly sensitive to moisture, NMR measurements and sample preparation were performed under a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). The instrumentation involved in the measurement was pre-washed with pure water and dried in a vacuum at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: deuterated dimethyl sulfoxide (DMSO-d₆), deuterated acetonitrile, and trifluoromethylbenzene were dried over 4A molecular sieves at a temperature above 25°C for at least three days, ensuring that the water content of all reagents was less than 3 ppm. A coulometric moisture analyzer (Model 831KF, available from Metrohm GmbH, Switzerland) was used for moisture measurement. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed evenly to obtain a first solution, 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were mixed evenly to obtain a second solution, and the first solution and the second solution were mixed evenly to obtain a deuterated reagent.

[0263] The results are shown in the following table (since the contents of the first additive and the second additive after operation are positively correlated with the contents of the first additive and the second additive in the fresh electrolyte, only some of the example data are shown to illustrate the trend):

[0264] In the table, “ / ” indicates that the value was not detected.

[0265] The above are merely specific embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a solvent, an electrolyte and a first additive. The solvent comprises a low-viscosity solvent having a viscosity less than 0.6 mPa·s. The first additive comprises at least one of fluorophosphate and borate.

2. The electrolyte according to claim 1, characterized in that The viscosity of the electrolyte is ≤5 mPa·s.

3. The electrolyte according to any one of claims 1 to 2, characterized in that The mass content a1 of the low-viscosity solvent in the electrolyte is 10%-70%; and / or The mass content b1 of the first additive in the electrolyte is 0.15%-2.5%.

4. The electrolyte according to claim 3, characterized in that The mass content a1 of the low-viscosity solvent in the electrolyte is 20%-60%; and / or The mass content b1 of the first additive in the electrolyte is 0.5%-1.5%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The fluorophosphate comprises at least one of monofluorophosphate and difluorophosphate; and / or The borate comprises at least one of tetrafluoroborate, bisoxalatoborate, and fluorine-containing oxalatoborate; and / or The fluorophosphate and borate each independently include at least one of a lithium salt, a sodium salt and a potassium salt.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The low-viscosity solvent includes: R1-COO-R2, wherein R1 includes H, methoxy and C1-C5 alkyl, and R2 includes C1-C5 alkyl.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The low-viscosity solvent includes at least one of dimethyl carbonate, ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate and isoamyl acetate.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The low-viscosity solvent includes at least one of ethyl acetate, methyl acetate and dimethyl carbonate.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The electrolyte further comprises a second additive, wherein the second additive comprises a sulfur-containing compound.

10. The electrolyte according to claim 9, characterized in that The mass content c1 of the second additive in the electrolyte is 0.1%-4%.

11. The electrolyte according to claim 10, characterized in that The mass content c1 of the second additive in the electrolyte is 0.5%-3%.

12. The electrolyte according to any one of claims 9 to 11, characterized in that The sulfur-containing compound includes at least one of a sulfonate compound and a vinyl sulfate compound.

13. The electrolyte according to claim 12, characterized in that The mass content of the vinyl sulfate compound in the electrolyte is 0.05%-3.5%. Optionally, the mass content of the vinyl sulfate compound in the electrolyte is 0.1%-2.5%; and / or, The mass content of the sulfonate compound in the electrolyte is 0.05%-0.5%.

14. The electrolyte according to claim 12 or 13, characterized in that The vinyl sulfate compounds include At least one of; and / or The sulfonate compounds include At least one of .

15. The electrolyte according to any one of claims 12 to 14, characterized in that The second additive includes described With the The mass ratio is 1:(0.25-7); or The additives include described The mass ratio is 1:(0.25-7).

16. The electrolyte according to any one of claims 12 to 15, characterized in that The first additive includes at least one of lithium difluorophosphate and lithium difluorooxalatoborate; and / or The second additive includes At least one of .

17. The electrolyte according to claim 16, characterized in that The mass ratio of the lithium difluorophosphate to lithium difluorooxalatoborate is 1:(0.05-15).

18. The electrolyte according to any one of claims 1 to 17, characterized in that The electrolyte comprises a lithium salt; and / or The lithium salt includes at least one of LiPF6 and LiFSI.

19. The electrolyte according to claim 18, characterized in that The electrolyte comprises LiPF6 and LiFSI, wherein the molar ratio of LiFSI to LiPF6 is 0.1-5; and / or the mass ratio of LiPF6 to LiFSI is 0.1-10.

20. A battery cell, characterized in that: The battery cell uses the electrolyte according to any one of claims 1 to 19.

21. The battery cell according to claim 20, characterized in that The mass content a2 of the low-viscosity solvent in the electrolyte is 10%-70%; and / or The mass content b2 of the first additive in the electrolyte is 0%-1%.

22. The battery cell according to claim 20 or 21, characterized in that: The fluorophosphate comprises at least one of monofluorophosphate and difluorophosphate; and / or The borate comprises at least one of tetrafluoroborate, bisoxalatoborate, and fluorine-containing oxalatoborate; and / or The fluorophosphate and borate each independently include at least one of a lithium salt, a sodium salt and a potassium salt.

23. The battery cell according to any one of claims 20 to 22, characterized in that: The mass content c2 of the second additive in the electrolyte is 0%-2%.

24. The battery cell according to any one of claims 20 to 23, characterized in that: The battery cell further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes lithium nickel cobalt manganese oxide, and the Dv50 of the lithium nickel cobalt manganese oxide is 2 μm-15 μm; or the positive electrode active material includes lithium-containing phosphate, and the Dv50 of the lithium-containing phosphate is 0.3 μm-2 μm.

25. The battery cell according to claim 24, characterized in that The positive electrode active material comprises lithium nickel cobalt manganese oxide, the molar content of nickel element is less than 80% based on the total molar number of transition metals in the positive electrode active material, the Dv50 of the positive electrode active material is 2 μm-5 μm, and the positive electrode active material comprises unagglomerated primary particles; or The positive electrode active material includes lithium nickel cobalt manganese oxide. Based on the total molar number of transition metals in the positive electrode active material, the molar content of nickel element is greater than or equal to 80%. The Dv50 of the positive electrode active material is 6μm-15μm. The positive electrode active material includes secondary particles formed by agglomeration of primary particles, and the average particle size of the primary particles in the secondary particles is 0.1μm-1.5μm.

26. The battery cell according to claim 24, characterized in that The positive electrode active material includes unagglomerated primary particles and / or lithium-containing phosphate formed by agglomerating primary particles into secondary particles. The average particle size of the primary particles of the positive electrode active material is 50 nm to 300 nm.

27. The battery cell according to any one of claims 20 to 26, characterized in that: The battery cell further includes a negative electrode sheet including a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, and lithium metal.

28. The battery cell according to any one of claims 20 to 27, characterized in that: The negative electrode active material includes artificial graphite; The negative electrode active material comprises secondary particles, wherein the Dv50 of the secondary particles is 5 μm-18 μm; and / or The air oxidation temperature T0 of the negative electrode active material is 630°C-730°C.

29. The battery cell according to claim 27 or 28, characterized in that: The negative electrode active material includes a silicon-based material, and the mass proportion of the silicon-based material in the negative electrode active material layer does not exceed 25%.

30. A battery, characterized in that: The battery comprises the battery cell according to any one of claims 20 to 29.

31. The battery according to claim 30, characterized in that The charging time t of the battery from 0% SOC to 80% SOC satisfies: t≤15.2 min.

32. An electrical device, characterized in that: The electrical device includes the battery cell according to any one of claims 20 to 29 or the battery according to any one of claims 30 to 31.

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