Electrolyte, lithium ion battery and electric device

Abstract

The embodiment of the invention provides an electrolyte, a lithium ion battery and an electric device, and relates to the field of batteries. The electrolyte comprises an electrolyte additive, and the electrolyte additive comprises a quaternary ammonium salt compound, an unsaturated ester compound and nitrate. The electrolyte can improve the surface dynamics of the negative electrode, promote uniform nucleation of lithium and improve the cycle performance of the lithium ion battery.

Description

Electrolyte, lithium-ion battery and power-consuming device Technical Field

[0001] The present application relates to the field of batteries, and in particular to an electrolyte, a lithium-ion battery, and an electrical device. Background Art

[0002] With the development of lithium-ion battery technology, its application has gradually expanded from its initial consumer applications in digital products to power batteries and energy storage batteries in power grids and power stations. Unlike consumer batteries, power batteries and energy storage batteries are more expensive to use, often requiring high energy density and service cycles of 10 or even 20 years. Therefore, higher requirements are placed on the energy density and cycle life of lithium-ion batteries.

[0003] Lithium-ion batteries offer both high energy density and long life, but they can experience lithium deposition in the later stages of the cycle. Addressing this issue has long been a key challenge in the lithium-ion battery field. Currently, improving the kinetics of negative electrode materials is often employed to address this issue, such as reducing particle size, increasing specific surface area, and enhancing the material's ability to transport lithium ions through the solid phase. However, this approach carries with it higher costs and can lead to increased side reactions on the negative electrode surface, thus deteriorating the battery's cycle life.

[0004] Summary of the Invention

[0005] In view of the above problems, the present application provides an electrolyte, a lithium-ion battery and an electrical device, which have low cost, can reduce the lithium plating problem of the battery and improve the cycle life of the battery.

[0006] In a first aspect, the present application provides an electrolyte comprising an electrolyte additive, wherein the electrolyte additive comprises a quaternary ammonium salt compound, an unsaturated ester compound and a nitrate.

[0007] In the technical scheme of the present application embodiment, by adding quaternary ammonium salt compounds, unsaturated ester compounds and nitrates in the electrolyte, cost is relatively low, and the cycle life of the battery can be improved. The quaternary ammonium root cation provided by the quaternary ammonium salt compounds can be adsorbed around the lithium protrusions of the negative electrode surface, forming a positive charge shielding layer (electrostatic shielding layer) that can play an electrostatic shielding effect, improving the electrode potential there, can reduce the further lithium analysis problem that occurs in the later stage of the cycle, improve the cycle life of the battery; and quaternary ammonium salt compounds are relatively stable within the operating voltage range, are not easily oxidized, and can play a persistent electrostatic shielding effect.

[0008] Combined with unsaturated ester compounds with high reduction potential (which can be reduced preferentially), a complete SEI film is formed on the surface of the negative electrode, which can inhibit the reduction of quaternary ammonium cations and enable the quaternary ammonium cations to play a continuous electrostatic shielding role during the cycle; and the formed SEI film is of good quality and has few side effects.

[0009] Nitrate can fully participate in the formation of lithium ion solvation sheath, and nitrate ions will form a specific inorganic component (Li3N, LiN) on the anode surface. x O y The SEI film with high conductive components (such as ions) can reduce the anode impedance, improve the kinetic performance of the battery cell, and further improve the rate performance and cycle performance of the battery.

[0010] Unsaturated ester compounds and nitrates work synergistically to form an SEI film. This SEI film not only has the high ion conductivity of the inorganic component, but also has the high toughness of the organic component, reducing the possibility of SEI film rupture caused by the shrinkage and expansion of the electrode during charging and discharging, thereby improving the cycle performance of the battery.

[0011] In some embodiments, the mass fraction of the quaternary ammonium salt compound in the electrolyte is 0.005wt% to 0.5wt%, optionally 0.01wt% to 0.4wt%, and optionally 0.013wt% to 0.3wt%. By adding a certain concentration of quaternary ammonium salt compounds to the electrolyte, the quaternary ammonium cations therein can be made to play an effective and continuous electrostatic shielding effect, delaying the lithium precipitation in the late cycle. If the concentration of the quaternary ammonium salt compound in the electrolyte is too low, the electrostatic protection effect of the quaternary ammonium cations at the lithium dendrite protrusions is insufficient, and it is difficult to significantly slow down the lithium precipitation; if the concentration of the quaternary ammonium salt compound is too high, the quaternary ammonium cations are distributed more evenly on the surface of the negative electrode, so that there is no obvious difference between the surface of the protrusion and the surface of its smooth area, thereby weakening the electrostatic shielding effect.

[0012] In some embodiments, the mass fraction of the unsaturated ester compound in the electrolyte is 0.5 wt% to 9 wt%, optionally 1 wt% to 7 wt%, and optionally 2 wt% to 5 wt%. By adding a certain concentration of unsaturated ester compounds to the electrolyte, a complete SEI film can be preferentially formed on the surface of the negative electrode. If the concentration of the unsaturated ester compound in the electrolyte is too low, it is difficult to form a dense SEI film on the surface of the negative electrode, and the reduction process of quaternary ammonium cations may also occur; if the concentration of the unsaturated ester compound is too high, the organic component content of the formed SEI film is high, the ionic conductivity is low, the impedance is high, and the battery cell dynamic performance is poor.

[0013] In some embodiments, the mass fraction of nitrate in the electrolyte is 0.03wt% to 2.03wt%, optionally 0.07wt% to 1.4wt%, and optionally 0.15wt% to 0.7wt%. By adding a certain concentration of nitrate to the electrolyte, a SEI film rich in highly conductive inorganic components can be formed on the surface of the anode. If the concentration of nitrate in the electrolyte is too low, the degree of participation of nitrate ions in film formation is low, the formed SEI film contains too few inorganic components, and the ionic conductivity is low; if the concentration of nitrate is too high, the formed SEI film contains too many inorganic components, the toughness of the SEI film is low, and it is easy to rupture and reform during charging and discharging, which in turn easily consumes active lithium.

[0014] In some embodiments, the nitrate comprises a metal nitrate, and optionally, the nitrate comprises lithium nitrate. Lithium nitrate can avoid the introduction of metal ions other than lithium into lithium-ion metal batteries, and the large size effect of quaternary ammonium ions can promote the full dissolution of lithium nitrate in the ester electrolyte, allowing nitrate to fully participate in forming a solvation sheath of lithium ions, thereby forming a SEI film rich in specific inorganic components on the anode surface.

[0015] In some embodiments, the mass ratio of the quaternary ammonium compound to the nitrate in the electrolyte is 1:(0.5-40), optionally 1:(5-25). The quaternary ammonium compound and the nitrate, when used in certain amounts, can promote each other and thus fully exert their effects. The quaternary ammonium compound promotes the dissolution of the nitrate, and the SEI film formed by the nitrate can protect the quaternary ammonium compound and inhibit the reduction process of the quaternary ammonium cation.

[0016] In some embodiments, the mass ratio of the quaternary ammonium salt compound to the unsaturated ester compound in the electrolyte is 1:(2-800), and can be optionally 1:(10-200).

[0017] In some embodiments, the mass fraction of the electrolyte additive in the electrolyte is no greater than 10 wt %.

[0018] In some embodiments, the quaternary ammonium salt compound comprises a quaternary ammonium cation and an anion, and the chemical formula of the quaternary ammonium cation is Wherein R1, R2, R3, and R4 independently include alkyl groups or alkoxy groups; optionally, the R1 includes a long-chain alkyl group with a carbon number ≥ 10, and the R2, R3, and R4 independently include a short-chain alkyl group with a carbon number ≤ 4. One of the groups in the quaternary ammonium cation is a long-chain alkyl group, which plays a lithium-repelling role, "evacuating" the lithium ions gathered here to other areas, causing normal negative electrode lithium insertion reaction, reducing the continued deposition of lithium ions at lithium dendrite protrusions, and reducing lithium precipitation. At the same time, the other groups in the quaternary ammonium cation are short-chain alkyl groups, which can reduce the problem of kinetic deterioration and poor cycle performance caused by the strong lithium-repelling effect of the quaternary ammonium cation, which hinders the diffusion of lithium ions to the negative electrode surface.

[0019] In some embodiments, the anion comprises chloride, bromide, nitrate, bis(trifluoromethylsulfonyl)imide anion [TFSI] - , bis(fluorosulfonyl)imide anion [FSI] - , difluorooxalatoborate ion and perfluorohexylsulfonate ion; optionally, the anion includes any one of chloride ion, bromide ion, bistrifluoromethylsulfonyl imide anion, bisfluorosulfonyl imide anion and difluorooxalatoborate ion; optionally, the anion includes chloride ion or bromide ion.

[0020] In some embodiments, the unsaturated ester additive includes at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinyl ethylene carbonate, allyl methyl carbonate, and allyl ethyl carbonate; optionally, the unsaturated ester additive includes vinylene carbonate. Unsaturated ester additives have a high reduction potential and can preferentially form an SEI film.

[0021] In some embodiments, the electrolyte further comprises a lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0022] In some embodiments, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, lactone compounds, nitrile compounds and sulfone compounds; optionally, the organic solvent includes at least one of cyclic carbonates and chain carbonates.

[0023] In a second aspect, the present application provides a lithium-ion battery comprising the electrolyte provided in the first aspect.

[0024] In the technical solution of the embodiment of the present application, after multiple cycles of charge and discharge in the lithium-ion battery, the problem of lithium plating of the battery can be reduced and the cycle life of the battery can be improved.

[0025] In a third aspect, the present application provides an electrical device comprising the lithium-ion battery provided in the second aspect, wherein the battery is used to provide electrical energy.

[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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:

[0028] FIG1 is a schematic structural diagram of a vehicle according to some embodiments of the present application;

[0029] FIG2 is a schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0030] FIG3 is a schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0031] FIG4 is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application.

[0032] Icon: 1000-vehicle; 100-battery; 10-housing; 11-accommodation 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 member; 200-controller; 300-motor. DETAILED DESCRIPTION

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In the description of the embodiments of the present application, the term "plurality" refers to more than two (including two), and similarly.

[0038] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "thickness", "up", "down", "front", "back", "top", "bottom", "inside", and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They 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. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0039] In the description of the embodiments of this application, unless otherwise expressly specified or limited, technical terms such as "installation," "connection," and "fixation" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0040] 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.

[0041] Lithium-ion batteries have the characteristics of high energy density and long life, and are suitable for use as power batteries, but they may have lithium plating problems in the late stages of the cycle. In order to solve the problem of lithium plating, the kinetics of the negative electrode material is often improved, but the cost of this method is usually relatively high and may lead to an increase in side reactions on the negative electrode surface. In addition, specific additives can be added to the electrolyte, such as adding non-lithium metal ion compounds to the electrolyte, and using the non-lithium metal ions to play an electrostatic shielding role at the lithium plating tip of the negative electrode surface, thereby reducing the uneven deposition of lithium ions and inhibiting the growth of lithium dendrites to reduce the problem of lithium plating in the late stages of the cycle.

[0042] However, when the lithium-ion battery formed by this electrolyte is charged and discharged at a higher current density, these non-lithium metal ions are also very likely to be deposited due to battery polarization, thereby failing to play a role in continuously slowing down lithium precipitation.

[0043] In order to solve the problem that the substances at the lithium-plating tips acting on the surface of the negative electrode are difficult to play a continuous electrostatic shielding role, an electrolyte can be designed to which a specific combination of electrolyte additives is added, so that the substances at the lithium-plating tips formed on the surface of the negative electrode can play a continuous electrostatic shielding role, reduce lithium plating in the late cycle, and improve the cycle life of the battery.

[0044] The electrolyte can be used to prepare battery cells, which can be used, but not limited to, in electrical devices such as vehicles, ships, or aircraft. A power supply system comprising the battery cells and batteries disclosed herein can be used to construct such electrical devices, thereby increasing the cycle life of the battery.

[0045] The present invention provides an electric device that uses a 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.

[0046] 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.

[0047] Please refer to Figure 1, which is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of the present application. A battery 100 is disposed within vehicle 1000. Battery 100 can be located at the bottom, front, or rear of vehicle 1000. Battery 100 can be used to power vehicle 1000, for example, as an operating power source for vehicle 1000.

[0048] The vehicle 1000 may further include a controller 200 and a motor 300 . The controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of the vehicle 1000 during startup, navigation, and driving.

[0049] In some embodiments of the present application, the battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0050] FIG2 is a schematic diagram of the exploded structure of a battery 100 provided in some embodiments of the present application. Referring to FIG2 , the battery 100 includes a housing 10 and a battery cell 20 , wherein the battery cell 20 is housed in the housing 10 .

[0051] 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.

[0052] 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.

[0053] In the battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, the multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection. Mixed connection means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, it is also possible that the multiple battery cells 20 are first connected in series, in parallel, or in a mixed connection to form a battery module, and the multiple battery modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery cell 20 can be cylindrical, flat, rectangular, or in other shapes. Figure 2 exemplifies the case where the battery cell 20 is square.

[0054] In some embodiments, the 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 mixed connection of the multiple battery cells 20 .

[0055] 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 a schematic diagram of the exploded structure 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] It should be noted that the housing 21 may have one or two openings 211. If the housing 21 has one opening 211, the end cap assembly 22 may also be one, and two electrode terminals 222 may 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 housing 21 has two openings 211, for example, the two openings 211 are provided on opposite sides of the housing 21, the end cap assembly 22 may also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the housing 21. In this case, the electrode terminal 222 in one end cap assembly 22 may be a positive electrode terminal, 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 may be a negative electrode terminal, which is used to electrically connect to the negative electrode sheet of the electrode assembly 23.

[0060] 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.

[0061] According to some embodiments of the present application, the electrolyte includes an electrolyte additive, and the electrolyte additive includes a quaternary ammonium salt compound, an unsaturated ester compound, and a nitrate.

[0062] Among them, quaternary ammonium salt compounds refer to compounds that can be dissolved in the electrolyte and can also provide free quaternary ammonium cations. This application does not specifically limit quaternary ammonium salt compounds. Quaternary ammonium salt compounds can be selected and adjusted accordingly according to the specific type of electrolyte.

[0063] Unsaturated ester compounds refer to esters containing unsaturated bonds, such as esters containing carbon-oxygen double bonds and / or carbon-carbon double bonds and / or carbon-carbon triple bonds, which have the characteristic of high reduction potential, that is, they are easily reduced.

[0064] Nitrate refers to a compound that can dissolve in an electrolyte and can also provide free nitrate ions. This application does not specifically limit the nitrate, and it can be selected and adjusted accordingly according to the specific type of electrolyte.

[0065] In some embodiments of the present application, the nitrate is composed of a metal ion or ammonium ion and a nitrate radical. Exemplarily, the nitrate includes at least one of a metal nitrate, a primary ammonium nitrate (ammonium nitrate), a secondary ammonium nitrate, a tertiary ammonium nitrate, and a quaternary ammonium nitrate. The quaternary ammonium salt compound and the nitrate can be two different compounds, or the quaternary ammonium salt compound and the nitrate can be one compound, such as a quaternary ammonium nitrate.

[0066] By adding quaternary ammonium compounds, unsaturated ester compounds and nitrates to the electrolyte at the same time, the unsaturated ester compounds and nitrates work together to form a complete SEI film on the negative electrode surface. The SEI film contains both organic components and specific inorganic components, thereby improving the cycle performance of the battery. In the later stage of the cycle, the quaternary ammonium cations can be adsorbed around the lithium-plating protrusions on the negative electrode surface, exerting an electrostatic shielding effect, reducing the lithium plating problem, and further improving the cycle performance of the battery.

[0067] According to some embodiments of the present application, the mass fraction of the quaternary ammonium salt compound in the electrolyte is 0.005wt% to 0.5wt%, optionally 0.01wt% to 0.4wt%, optionally 0.013wt% to 0.3wt%, and optionally 0.02wt% to 0.1wt%.

[0068] The mass fraction of the quaternary ammonium compound in the electrolyte refers to the mass proportion of the quaternary ammonium compound dissolved in the electrolyte. As an example, the mass fraction of the quaternary ammonium compound in the electrolyte can be 0.005wt%, 0.01wt%, 0.013wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.12wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.18wt%, 0.2wt%, 0.22wt%, 0.24wt%, 0.25wt%, 0.26wt%, 0.28wt%, 0.3wt%, 0.4wt% or 0.5wt%, or it can be any value within the above two numerical ranges.

[0069] In some embodiments of the present application, the quaternary ammonium salt compounds in the electrolyte begin to be consumed in the late cycle, and the quaternary ammonium cations are adsorbed on the surface of the negative electrode.

[0070] According to some embodiments of the present application, the mass fraction of the unsaturated ester compound in the electrolyte is 0.5 wt% to 9 wt%, optionally 1 wt% to 7 wt%, or optionally 2 wt% to 5 wt%.

[0071] The mass fraction of the unsaturated ester compound in the electrolyte refers to the mass fraction of the unsaturated ester compound dissolved in the electrolyte. As an example, the mass fraction of the unsaturated ester compound in the electrolyte can be 0.5wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 7wt% or 9wt%, or any value within the above two numerical ranges.

[0072] In some embodiments of the present application, the unsaturated ester compound is partially consumed during battery formation to form a SEI film on the anode surface, and the unsaturated ester compound is also required to participate in the charge and discharge cycle process.

[0073] According to some embodiments of the present application, the mass fraction of nitrate in the electrolyte is 0.03wt% to 2.03wt%, optionally 0.07wt% to 1.4wt%, optionally 0.15wt% to 0.7wt%, and optionally 0.2wt% to 0.55wt%.

[0074] The mass fraction of nitrate in the electrolyte refers to the mass proportion of nitrate dissolved in the electrolyte. As an example, the mass fraction of nitrate in the electrolyte can be 0.03wt%, 0.05wt%, 0.07wt%, 0.09wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt%, 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt% or 2.03wt%, or any value within the above two numerical ranges.

[0075] In some embodiments of the present application, nitrate is consumed during battery formation, forming a SEI film on the anode surface. Only a very small amount of nitrate exists in the electrolyte, and the nitrate ions may even be completely consumed and no longer exist.

[0076] According to some embodiments of the present application, the nitrate comprises a metal nitrate, and optionally, the nitrate comprises lithium nitrate. Exemplarily, the nitrate comprises at least one of lithium nitrate, sodium nitrate, potassium nitrate, calcium nitrate, and magnesium nitrate.

[0077] According to some embodiments of the present application, the mass ratio of the quaternary ammonium salt compound (quaternary ammonium ion) to the nitrate (nitrate ion) in the electrolyte is 1:(0.5-40), and can be optionally 1:(5-25). Exemplarily, the mass ratio of the quaternary ammonium salt compound (quaternary ammonium ion) to the nitrate (nitrate ion) is 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35 or 1:40, and can also be any value between the above two ratios.

[0078] According to some embodiments of the present application, the mass ratio of the quaternary ammonium salt compound to the unsaturated ester compound in the electrolyte is 1:(2-800), and can be optionally 1:(10-200). Exemplarily, the mass ratio of the quaternary ammonium salt compound to the unsaturated ester compound is 1:2, 1:5, 1:7, 1:10, 1:30, 1:50, 1:60, 1:80, 1:100, 1:200, 1:300, 1:400, 1:600, or 1:800, and can also be any value between the above two ratios.

[0079] According to some embodiments of the present application, the mass fraction of the electrolyte additive in the electrolyte is no more than 10 wt %.

[0080] According to some embodiments of the present application, the quaternary ammonium salt compound comprises a quaternary ammonium cation and an anion, and the chemical formula of the quaternary ammonium cation is Wherein R1, R2, R3, and R4 independently include alkyl or alkoxy groups; optionally, R1 includes a long-chain alkyl group with a carbon number of ≥10, and R2, R3, and R4 independently include a short-chain alkyl group with a carbon number of ≤4. For example, R1 includes but is not limited to decanyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, etc., R2 includes but is not limited to methyl, ethyl, n-propyl, isopropyl, 1-butyl, 2-butyl, t-butyl, etc., R3 includes but is not limited to methyl, ethyl, n-propyl, isopropyl, 1-butyl, 2-butyl, t-butyl, etc., and R4 includes but is not limited to methyl, ethyl, n-propyl, isopropyl, 1-butyl, 2-butyl, t-butyl, etc. R1 is a long alkyl chain, which plays a role in repelling lithium and reducing the continued deposition of lithium ions on lithium dendrite protrusions.

[0081] According to some embodiments of the present application, the anion includes any one of a chloride ion, a bromide ion, a nitrate, a bis(trifluoromethylsulfonylimide) anion, a bis(fluorosulfonylimide) anion, a difluorooxalatoborate ion, and a perfluorohexylsulfonate ion; alternatively, the anion includes any one of a chloride ion, a bromide ion, a bis(trifluoromethylsulfonylimide) anion, a bis(fluorosulfonylimide) anion, and a difluorooxalatoborate ion; alternatively, includes a chloride ion or a bromide ion.

[0082] According to some embodiments of the present application, the unsaturated ester additive includes but is not limited to one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), allyl methyl carbonate and allyl ethyl carbonate; optionally, the unsaturated ester additive includes vinylene carbonate (VC).

[0083] According to some embodiments of the present application, the electrolyte further includes a lithium salt, and the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluorosulfonyl)imide.

[0084] According to some embodiments of the present application, the electrolyte further includes an organic solvent, including but not limited to at least one of cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, lactone compounds, nitrile compounds, and sulfone compounds; optionally, the organic solvent includes at least one of saturated esters such as cyclic carbonates and chain carbonates. Quaternary ammonium salts can promote the dissolution of lithium nitrate in ester electrolytes.

[0085] Optionally, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone; the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl formate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate; the cyclic ether is selected from one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane; and the chain ether is selected from one or more of dimethoxymethane, 1,2-dimethoxyethane, 1,2-dimethoxypropane, and diethylene glycol dimethyl ether.

[0086] According to some embodiments of the present application, the present application also provides a lithium-ion battery, comprising the electrolyte of any of the above solutions.

[0087] The lithium-ion battery in this application includes any form of a single cell, a battery module and a battery pack.

[0088] The lithium-ion battery provided in the present application also includes a positive electrode sheet, a negative electrode sheet and a separator.

[0089] [Positive electrode]

[0090] According to some embodiments of the present application, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer located on the surface of the positive electrode current collector, and the positive electrode active material layer provides lithium ions.

[0091] In some embodiments, the positive electrode current collector can be a material of various positive electrode current collectors suitable for lithium ion secondary batteries in the art, and a metal foil or a composite current collector can be used. Alternatively, the positive electrode current collector can include but is not limited to metal foil, for example, aluminum foil can be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. 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 (for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other material substrates).

[0092] In some embodiments, the positive electrode active material layer may include a positive electrode active material, a conductive agent, a binder, and any other components, and the positive electrode active material provides lithium ions. The positive electrode active material may be any known positive electrode active material for lithium ion batteries. The positive electrode active material may include, but is not limited to, lithium transition metal composite oxides, etc. The lithium transition metal composite oxide may include, but is not limited to, lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphide, lithium manganese oxide, lithium iron manganese phosphide, or a combination of one or more of these lithium transition metal oxides and compounds obtained by adding other transition metals or non-transition metals.

[0093] [Negative electrode]

[0094] According to some embodiments of the present application, a negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material. As an example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector can be various materials suitable for use as negative electrode current collectors for lithium-ion secondary batteries in the art, and the negative electrode current collector can be a metal foil or a composite current collector. Alternatively, the negative electrode current collector can include but is not limited to metal foil, for example, copper foil can be used. 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 substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the negative electrode active material can be various negative electrode active materials suitable for lithium ion secondary batteries in the art. As an example, the negative electrode active material can be including but not limited to carbon materials (graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, graphene, etc.), titanium oxide-based materials (lithium titanate, titanium dioxide, etc.), alloyed negative electrode materials (silicon-based materials, tin-based materials, germanium-based materials, etc.), conversion-type negative electrode materials (transition metal oxides, phosphides, sulfides, nitrides, etc.). These negative electrode active materials can be used alone or in combination of two or more. Graphite can be selected from one or more combinations of artificial graphite, natural graphite, and modified graphite. Graphite can be further modified, and the modification method of graphite is not specifically limited, such as coating modification on the graphite surface.

[0097] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0100] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0101] [Isolation film]

[0102] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0103] In some embodiments, the separator may be a multilayer composite film formed by combining one or more materials including, but not limited to, polyethylene, polypropylene, non-woven fabric, and polyfiber. The separator may be a single-layer film or a multilayer composite film, without particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, without particular limitation.

[0104] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0105] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0106] In some embodiments, the outer packaging of the lithium-ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the lithium-ion battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0107] According to some embodiments of the present application, the present application further provides an electrical device, comprising a lithium-ion battery according to any of the above schemes, and the lithium-ion battery is used to provide electrical energy to the electrical device.

[0108] The power-consuming device may be any of the aforementioned devices or systems using batteries.

[0109] 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.

[0110] Example 1

[0111] 1) Preparation of electrolyte

[0112] In an argon-filled glove box, the electrolyte was prepared as follows:

[0113] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a mass ratio of EC:DEC=5:5 to obtain an organic solvent.

[0114] Lithium salt, unsaturated ester compound, quaternary ammonium salt compound and nitrate are added to an organic solvent and stirred thoroughly to obtain an electrolyte.

[0115] Among them, the lithium salt is lithium hexafluorophosphate, and the addition amount is 13% based on the total weight of the electrolyte; the unsaturated ester compound is vinylene carbonate (VC), and the addition amount is 3% based on the total weight of the electrolyte; the quaternary ammonium salt compound is hexadecyltrimethylammonium chloride, and the addition amount is 0.05% based on the total weight of the electrolyte; the nitrate is lithium nitrate, and the addition amount is 0.34% based on the total weight of the electrolyte.

[0116] 2) Preparation of positive and negative electrode sheets

[0117] The positive electrode active material, conductive agent, and adhesive selected from lithium iron phosphate (LFP), carbon black, and polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a weight ratio of 8:1:1, and stirred in a drying room to form a slurry; the above slurry is coated on aluminum foil, dried, and cold pressed with a compression of 2.50 and a thickness of 170μm to form a positive electrode sheet.

[0118] The negative electrode sheet was prepared in a similar manner. The negative electrode active material, binder, conductive agent and their contents were: 96.5% graphite + 1.3% SBR + 1.1 CMC% + 0.4% SP, the density was 1.65, and the thickness was 136 μm.

[0119] A polyethylene (PE) porous polymer film is used as the separator.

[0120] 3) Preparation of lithium-ion batteries

[0121] In the drying room, the positive electrode sheet, separator and negative electrode sheet are wound in sequence to obtain a bare battery cell. The bare battery cell is then placed in a shell and vacuum baked until the water content meets the standard.

[0122] The above electrolyte is injected into the shell, sealed and placed at high temperature, and then the battery is obtained after the processes of formation, vacuuming, capacity measurement, aging, etc.

[0123] Example 2

[0124] Except that cetyltrimethylammonium bromide is used instead of cetyltrimethylammonium chloride as the quaternary ammonium salt compound in step 1), the other steps are the same as those in Example 1.

[0125] Example 3

[0126] Except that dodecyltrimethylammonium chloride is used instead of hexadecyltrimethylammonium chloride as the quaternary ammonium salt compound in step 1), the other steps are the same as those in Example 1.

[0127] Example 4

[0128] Except that the amount of vinylene carbonate added to the electrolyte in step 1) is 2% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0129] Example 5

[0130] Except that the amount of vinylene carbonate added to the electrolyte in step 1) is 5% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0131] Example 6

[0132] Except that the amount of lithium nitrate added to the electrolyte in step 1) is 0.21% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0133] Example 7

[0134] Except that the amount of lithium nitrate added to the electrolyte in step 1) is 0.55% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0135] Example 8

[0136] Except that the amount of cetyltrimethylammonium chloride added to the electrolyte in step 1) is 0.01% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0137] Example 9

[0138] Except that the amount of cetyltrimethylammonium chloride added to the electrolyte in step 1) is 0.05% based on the total weight of the electrolyte, the other steps are the same as those in Example 1.

[0139] Example 10

[0140] Except that the amount of vinylene carbonate added to the electrolyte in step 1) is 1% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0141] Example 11

[0142] Except that the amount of vinylene carbonate added to the electrolyte in step 1) is 7% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0143] Example 12

[0144] Except that the amount of vinylene carbonate added to the electrolyte in step 1) is 9% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0145] Example 13

[0146] Except that the amount of lithium nitrate added to the electrolyte in step 1) is 0.07% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0147] Example 14

[0148] Except that the amount of lithium nitrate added to the electrolyte in step 1) is 1.00% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0149] Example 15

[0150] Except that the amount of lithium nitrate added to the electrolyte in step 1) is 2.03% based on the total weight of the electrolyte, the rest is the same as in Example 1.

[0151] Example 16

[0152] The process is the same as in Example 1 except that ammonium nitrate is used instead of lithium nitrate as nitrate in step 1), and the added amount is 0.39% of the total weight of the electrolyte.

[0153] Example 17

[0154] Except that fluorovinylidene carbonate is used instead of vinylene carbonate as the unsaturated ester compound in step 1), other steps are the same as those in Example 1.

[0155] Example 18

[0156] Except that monoethyltrimethylammonium chloride is used in place of hexadecyltrimethylammonium chloride as the quaternary ammonium salt compound in step 1), the other steps are the same as those in Example 1.

[0157] Example 19

[0158] Except that tri-hexadecylmonomethylammonium chloride is used in place of hexadecyltrimethylammonium chloride as the quaternary ammonium salt compound in step 1), the other steps are the same as those in Example 1.

[0159] Example 20

[0160] The process is the same as in Example 1 except that hexadecyltrimethylammonium nitrate is used as both the quaternary ammonium salt compound and the nitrate in step 1), and the added amount is 0.39% of the total weight of the electrolyte.

[0161] Comparative Example 1

[0162] Except that no quaternary ammonium salt compound and nitrate are added to the electrolyte in step 1), the rest is the same as in Example 1.

[0163] Comparative Example 2

[0164] Except that no quaternary ammonium salt compound is added to the electrolyte in step 1), the amount of vinylene carbonate added is 3.29% of the total weight of the electrolyte, the amount of lithium nitrate added is 0.10% of the total weight of the electrolyte, and the total amount of additives remains unchanged. Other aspects are the same as in Example 1.

[0165] Comparative Example 3

[0166] Except that no nitrate is added to the electrolyte in step 1), the amount of vinylene carbonate added is 3.24% of the total weight of the electrolyte, the amount of hexadecyltrimethylammonium chloride added is 0.05% of the total weight of the electrolyte, and the total amount of additives remains unchanged. Other contents are the same as in Example 1.

[0167] Comparative Example 4

[0168] Except that lithium fluoride and cesium fluoride are used to replace the quaternary ammonium salt compound in a mass ratio of 1:1 in step 1), the rest is the same as in Example 1.

[0169] The performance of the batteries prepared in the above embodiments and comparative examples was tested:

[0170] The battery performance of the above embodiments and comparative examples was characterized by a 25° C. cycle test to test the DCR value of the battery at 50% SOC and the number of cycles of the battery to 70% SOH.

[0171] Among them, the DCR test method is:

[0172] (1) At 25°C, charge the battery to 3.65V at 1 / 3C constant current, charge the battery to a current less than 0.05C at constant voltage, and leave it for 5 minutes.

[0173] (2) Discharge at 1C time to adjust the battery's SOC to 50% SOC.

[0174] (3) Perform 1C DC 30s and 1C CC 30s tests.

[0175] (4) Calculate the DC internal resistance of 1C CC for 30s, which is the DCR at 50% SOC.

[0176] The cycle number test method is:

[0177] (1) Charging: Charge at 1C constant current to 3.65V, charge at constant voltage until the current is less than 0.05C, and leave for 5 minutes;

[0178] (2) Discharge: Discharge at 1C constant current to 2.5V, and leave for 5 minutes;

[0179] (3) Termination condition: Cycle until the capacity decays to 70% of the initial capacity. The number of charge and discharge cycles is the number of cycles to 70% SOH.

[0180] The performance of the batteries prepared in the above embodiments and comparative examples was tested:

[0181] The battery performance of the above embodiments and comparative examples was characterized by a 25° C. cycle test to test the DCR value of the battery at 50% SOC and the number of cycles of the battery to 70% SOH.

[0182] Among them, the DCR test method is:

[0183] (1) At 25°C, charge the battery to 3.65V at 1 / 3C constant current, charge the battery to a current less than 0.05C at constant voltage, and leave it for 5 minutes.

[0184] (2) Discharge at 1C time to adjust the battery's SOC to 50% SOC.

[0185] (3) Perform 1C DC 30s and 1C CC 30s tests.

[0186] (4) Calculate the DC internal resistance of 1C CC for 30s, which is the DCR at 50% SOC.

[0187] The cycle number test method is:

[0188] (1) Charging: Charge at 1C constant current to 3.65V, charge at constant voltage until the current is less than 0.05C, and leave for 5 minutes;

[0189] (2) Discharge: Discharge at 1C constant current to 2.5V, and leave for 5 minutes;

[0190] (3) Termination condition: Cycle until the capacity decays to 70%. The number of charge and discharge cycles is the number of cycles to 70% SOH.

[0191] The performance of the battery tested is shown in Table 1:

[0192] Table 1 Battery performance

[0193] Combined with the results in Table 1, we can see that:

[0194] Compared with Comparative Examples 1 to 3, the battery cycle number of Examples 1 to 20 is higher, indicating that compared with the solution of adding one or two of quaternary ammonium salt compounds, unsaturated ester compounds and nitrates to the electrolyte, adding quaternary ammonium salt compounds, unsaturated ester compounds and nitrates to the electrolyte at the same time can improve the cycle life of the battery.

[0195] Compared with Comparative Example 1, the battery of Example 20 can also improve the cycle life of the battery by adding quaternary ammonium nitrate compounds and unsaturated ester compounds to the electrolyte.

[0196] Compared with Comparative Examples 1 to 3, the batteries of Example 1 and Example 17 add unsaturated ester compounds on the basis of the presence of quaternary ammonium salt compounds and nitrates, which can improve the cycle life of the batteries. According to the batteries of Example 1, Examples 4 to 5, and Examples 10 to 12, the mass fraction of the unsaturated ester compound added to the electrolyte is 1% to 9%, optionally 1% to 7%, optionally

[0197] 2% to 5%, which can significantly improve the cycle life of the battery.

[0198] Compared with Comparative Example 4, the battery cycle numbers corresponding to Examples 1 to 3 are higher, indicating that the electrolyte additive combination of quaternary ammonium salt compounds, unsaturated ester compounds, and nitrates can better improve the cycle life of the battery compared to the solution of adding lithium fluoride + cesium fluoride, unsaturated ester compounds, and nitrates to the electrolyte.

[0199] Compared with Comparative Example 2, the batteries of Examples 1 to 3 and Examples 18 to 19 add a combination of a quaternary ammonium salt compound, an unsaturated ester compound, and a nitrate to the electrolyte, and one of the groups of the quaternary ammonium salt compound can be optionally added as a long-chain alkyl group, and the remaining three groups are short-chain alkyl groups, which can significantly improve the cycle life of the battery.

[0200] Compared with Comparative Example 2, the mass fraction of the quaternary ammonium salt compound added to the electrolyte of the batteries of Example 1 and Examples 8-9 is 0.01wt%-0.5wt%, which can significantly improve the cycle life of the battery.

[0201] Compared with Comparative Example 3, the batteries of Example 1 and Example 16, in addition to the presence of the quaternary ammonium salt compound and the unsaturated ester compound, add nitrate, which can improve the cycle life of the battery. According to the batteries of Example 1, Examples 6-7, and Examples 13-15, the mass fraction of nitrate added to the electrolyte is 0.07% to 2.03%, optionally 0.07% to 1%, and optionally 0.21% to 0.55%, which can significantly improve the cycle life of the battery.

[0202] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. An electrolyte, characterized in that: The electrolyte additive comprises a quaternary ammonium salt compound, an unsaturated ester compound and a nitrate.

2. The electrolyte according to claim 1, characterized in that The mass fraction of the quaternary ammonium salt compound in the electrolyte is 0.005wt% to 0.5wt%, optionally 0.01wt% to 0.4wt%, optionally 0.013wt% to 0.3wt%.

3. The electrolyte according to claim 1 or 2, characterized in that The mass fraction of the unsaturated ester compound in the electrolyte is 0.5wt% to 9wt%, optionally 1wt% to 7wt%, optionally 2wt% to 5wt%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The mass fraction of nitrate in the electrolyte is 0.03wt% to 2.03wt%, optionally 0.07wt% to 1.4wt%, optionally 0.15wt% to 0.7wt%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The nitrate comprises a metal nitrate, and optionally, the nitrate comprises lithium nitrate.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The mass ratio of the quaternary ammonium salt compound to the nitrate in the electrolyte is 1:(0.5-40), and can be optionally 1:(5-25).

7. The electrolyte according to any one of claims 1 to 6, characterized in that The mass ratio of the quaternary ammonium salt compound to the unsaturated ester compound in the electrolyte is 1:(2-800), and can be optionally 1:(10-200).

8. The electrolyte according to any one of claims 1 to 7, characterized in that The mass fraction of the electrolyte additive in the electrolyte is not greater than 10 wt %.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The quaternary ammonium salt compound comprises a quaternary ammonium cation and an anion, and the chemical formula of the quaternary ammonium cation is Wherein R1, R2, R3, and R4 independently include alkyl groups or alkoxy groups; optionally, R1 includes a long-chain alkyl group with a carbon number of ≥10, and R2, R3, and R4 independently include a short-chain alkyl group with a carbon number of ≤4.

10. The electrolyte according to claim 9, characterized in that The anion includes any one of chloride, bromide, nitrate, bis(trifluoromethylsulfonylimide) anion, bis(fluorosulfonylimide) anion, difluorooxalate borate ion and perfluorohexylsulfonate ion; optionally, the anion includes any one of chloride, bromide, bis(trifluoromethylsulfonylimide) anion, bis(fluorosulfonylimide) anion and difluorooxalate borate ion; optionally, the anion includes chloride or bromide.

11. The electrolyte according to any one of claims 1 to 10, characterized in that The unsaturated ester additive includes at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylethylene carbonate, allyl methyl carbonate and allyl ethyl carbonate; optionally, the unsaturated ester additive includes vinylene carbonate.

12. The electrolyte according to any one of claims 1 to 11, characterized in that The electrolyte further comprises a lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluorosulfonyl)imide.

13. The electrolyte according to any one of claims 1 to 12, characterized in that The electrolyte also includes an organic solvent, and the organic solvent includes at least one of cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, lactone compounds, nitrile compounds and sulfone compounds; optionally, the organic solvent includes at least one of cyclic carbonates and chain carbonates.

14. A lithium ion battery, characterized in that: The invention comprises the electrolyte according to any one of claims 1 to 13.

15. An electrical device, characterized in that: Includes the lithium ion battery as claimed in claim 14.

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