Battery, electrical system, and energy storage system

Abstract

A battery, an electrical system, and an energy storage system. The battery comprises: an electrolyte, the electrolyte comprising lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, and the mass ratio in the electrolyte of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide being γ; and a positive electrode plate, the positive electrode plate being at least partially immersed in the electrolyte, and the positive electrode plate comprising a positive electrode current collector and a positive electrode active layer. The positive electrode active layer is disposed on a surface of the positive electrode current collector, and the positive electrode active layer comprises a positive electrode active material and a carbon material, the mass fraction of the carbon material in the positive electrode active layer being B. The battery satisfies the relational expression: 1.31 wt% ≤ γB ≤ 10.74 wt%. The present battery has high dynamic performance and safety performance.

Description

Batteries, power systems and energy storage systems

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 26, 2024, with application number 2024103474408 and application name “Battery, Power System and Energy Storage System”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage, and specifically to a battery, a power system, and an energy storage system. Background Art

[0003] With the continuous development of lithium-ion battery technology, lithium-ion batteries have advantages over other types of batteries such as lead-acid and nickel-cadmium batteries, such as high specific capacity, no memory effect, high operating voltage, fast charging speed, wide operating temperature range, long cycle life, small size, and light weight. Currently, lithium-ion batteries are widely used in mobile phones, laptops, electric vehicles, energy storage cabinets and other fields, and their application range is becoming increasingly wider.

[0004] With the development of the energy storage industry, higher requirements are placed on the fast charging and safety performance of lithium-ion batteries. However, existing lithium-ion batteries are difficult to achieve both dynamic performance and safety performance.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide a battery having high dynamic performance and safety performance.

[0007] In a first aspect, the present application provides a battery comprising:

[0008] an electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the electrolyte is γ; and

[0009] A positive electrode sheet, wherein the positive electrode sheet is at least partially immersed in the electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer, the positive electrode active layer is disposed on the surface of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material and a carbon material, and the mass fraction of the carbon material in the positive electrode active layer is B;

[0010] The battery satisfies the relationship: 1.31 wt%≤γB≤10.74 wt%.

[0011] In a second aspect, the present application further provides an electricity system, comprising:

[0012] Electrical equipment, and

[0013] An energy storage device, which supplies power to the electrical equipment, and the energy storage device includes at least one battery described in an embodiment of the present application.

[0014] In a third aspect, the present application further provides an energy storage system, comprising:

[0015] An electric energy conversion device, the electric energy conversion device is used to convert other forms of energy into electric energy;

[0016] an energy storage device, the energy storage device being electrically connected to the electric energy conversion device and configured to store the electric energy of the electric energy conversion device, the energy storage device comprising at least one battery as described in an embodiment of the present application; and

[0017] An electrical load is electrically connected to the power conversion device and the energy storage device, respectively, and is used to utilize the electrical energy of the power conversion device or the energy storage device to work.

[0018] The electrolyte of the battery of the embodiment of the present application includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The addition of lithium bis(fluorosulfonyl)imide can reduce the hexafluorophosphate ion (PF6 - ) decomposition, thereby reducing the side reactions of the battery and improving the safety performance of the battery. In addition, reducing the hexafluorophosphate ion (PF6 - ) decomposition, can better maintain the conductivity of the electrolyte, so that the battery has better dynamic performance. The positive electrode active layer includes a positive electrode active material and a carbon material. The addition of carbon material to the positive electrode active layer can improve the conductivity of the positive electrode sheet, thereby further improving the dynamic performance of the battery. However, if the content of carbon material is too high, it will increase side reactions and reduce the safety performance of the battery. The embodiment of the present application controls by making 1.31wt%≤γB≤10.74wt%, and by using the combination of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and carbon material, so that the battery has higher dynamic performance, can also effectively reduce the side reactions of the battery, and improve the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] FIG1 is a diagram showing an application scenario of an energy storage system according to an embodiment of the present application.

[0021] FIG2 is a schematic structural diagram of an energy storage system according to an embodiment of the present application.

[0022] FIG3 is a circuit block diagram of an energy storage system according to an embodiment of the present application.

[0023] FIG4 is a partial perspective structural diagram of an electric power system according to an embodiment of the present application.

[0024] FIG5 is a schematic structural diagram of an energy storage device according to an embodiment of the present application.

[0025] FIG6 is a schematic structural diagram of a battery according to an embodiment of the present application.

[0026] FIG. 7 is a schematic cross-sectional view of a battery according to an embodiment of the present application along the AA direction in FIG. 6 .

[0027] FIG8 is a schematic cross-sectional view of the positive electrode sheet according to an embodiment of the present application along the AA direction in FIG6 .

[0028] FIG9 is a schematic cross-sectional view of the negative electrode sheet according to an embodiment of the present application along the AA direction in FIG6 .

[0029] Description of reference numerals:

[0030] 100-Energy storage system, 110-Electric energy conversion device, 130-Electric load, 200-Energy storage device, 210-Case, 300-Electric system, 310-Electric equipment, 400-Battery, 410-Positive electrode sheet, 411-Positive current collector, 412-Positive active layer, 420-Separator, 430-Negative electrode sheet, 431-Negative current collector, 432-Negative active layer, 440-Case. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0033] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0034] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0035] Currently, the generation of green electricity generally relies on photovoltaics, wind power, and hydropower. However, wind and solar energy are generally intermittent and highly volatile, which can cause grid instability, insufficient electricity during peak hours, and excessive electricity during off-peak hours. Unstable voltage can also damage electricity. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar power curtailment". To solve these problems, we must rely on energy storage. This means converting electrical energy into other forms of energy through physical or chemical means and storing them. When needed, this energy is converted into electrical energy and released. Simply put, energy storage is like a large "power bank", storing electricity when photovoltaic and wind energy are sufficient and releasing the stored electricity when needed.

[0036] Taking electrochemical energy storage as an example, the present application provides an energy storage device, which is equipped with a chemical battery. The chemical elements in the battery are mainly used as energy storage media. The charging and discharging process is accompanied by chemical reactions or changes in the energy storage medium. Simply put, the electricity generated by wind and solar energy is stored in the chemical battery. When the use of external electricity reaches its peak, the stored electricity is released for use, or transferred to places where electricity is scarce for use.

[0037] Currently, energy storage (i.e., energy storage) has a wide range of application scenarios, including power generation-side energy storage, grid-side energy storage, renewable energy grid-connected energy storage, and user-side energy storage. The corresponding types of energy storage devices include:

[0038] (1) Large energy storage containers used in grid-side energy storage scenarios can serve as high-quality active and reactive power regulation power sources in the grid, achieving load matching of electricity in time and space, enhancing the ability to absorb renewable energy, and are of great significance in grid system backup, alleviating peak load power supply pressure, and peak and frequency regulation.

[0039] (2) The main operating mode of small and medium-sized energy storage cabinets used in industrial and commercial energy storage scenarios (banks, shopping malls, etc.) on the user side and small household energy storage boxes used in home energy storage scenarios on the user side is "peak shaving and valley filling". Since there is a large price difference in electricity prices at peak and valley locations according to electricity demand, after users have energy storage equipment, in order to reduce costs, they usually charge the energy storage cabinets / boxes during the low electricity price period; during the peak electricity price period, the electricity in the energy storage equipment is discharged for use to achieve the purpose of saving electricity bills. In addition, in remote areas and areas with high incidence of natural disasters such as earthquakes and hurricanes, the existence of household energy storage devices is equivalent to users providing themselves and the power grid with backup power, eliminating the inconvenience caused by frequent power outages due to disasters or other reasons.

[0040] Figure 1 is a diagram illustrating an application scenario of an energy storage system 100 provided in an embodiment of the present application. The embodiment of Figure 1 of the present application uses a household energy storage scenario in user-side energy storage as an example. The energy storage device 200 of the present application is not limited to household energy storage scenarios. Figure 2 is a schematic diagram illustrating the structure of the energy storage system 100 according to an embodiment of the present application. Figure 3 is a circuit block diagram of the energy storage system 100 according to an embodiment of the present application.

[0041] Please refer to Figures 1 to 3. The present application provides an energy storage system 100, which is a household energy storage system 100. The energy storage system 100 includes an electric energy conversion device 110, an energy storage device 200, and an electrical load 130. The electric energy conversion device 110 is used to convert other forms of energy into electric energy; the energy storage device 200 is electrically connected to the electric energy conversion device 110 and is used to store the electric energy of the electric energy conversion device 110; the electric load 130 is electrically connected to the electric energy conversion device 110 and the energy storage device 200, respectively, and is used to use the electric energy of the electric energy conversion device 110 or the energy storage device 200 to work. It can be understood that part of the electric energy converted by the electric energy conversion device 110 is stored in the energy storage device 200, and part is used to power the electric load 130. The energy storage device 200 is used to store electric energy and supply the electric load 130 when the electricity price is peak. The energy storage system 100 can convert other generated energy into electrical energy and store the electrical energy in the energy storage device 200 to supply sufficient electrical energy to the electrical load 130 .

[0042] Optionally, the electric energy conversion device 110 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy, providing a stable power supply for the electrical load 130 and the energy storage device 200.

[0043] Optionally, the power conversion device 110 may be, but is not limited to, a photovoltaic panel, which can convert solar energy into electrical energy during periods of low electricity prices and store the energy in the energy storage device 200. In other embodiments, the power conversion device 110 may be at least one of a wind power generation device, a thermal power generation device, a tidal power generation device, a biomass power generation device, and a mechanical power generation device.

[0044] Optionally, the energy storage device 200 is a small energy storage box that can be mounted on an outdoor wall. In other embodiments, the energy storage device 200 can also be a large energy storage container, a battery used in electronic equipment, etc.

[0045] Optionally, the electrical load 130 may be a street lamp, household appliance, motor vehicle, etc. The energy storage device 200 is used to store the electrical energy and supply it to street lamps and household appliances for use when electricity prices are high, or to supply power when the grid is out of power.

[0046] It is understood that the energy storage device 200 may include but is not limited to at least one of a single cell, a battery module, a battery pack, a battery system, etc. The single cell may be but is not limited to at least one of a cylindrical battery, a square battery, etc.

[0047] It is understandable that the drawings in this embodiment illustrate only one form of the energy storage system 100 and should not be understood as limiting the energy storage system 100 provided in this application, nor should they be understood as limiting the energy storage device 200 provided in each embodiment of this application.

[0048] 4 is a partial perspective structural diagram of an electric system 300 according to an embodiment of the present application. This embodiment of the present application further provides an electric system 300 comprising: an electric device 310 and an energy storage device 200 , wherein the energy storage device 200 supplies power to the electric device 310 .

[0049] The power-consuming device 310 in the embodiments of the present application may be, but is not limited to, a portable electronic device such as a mobile phone, tablet computer, laptop computer, desktop computer, smart bracelet, smart watch, e-reader, game console, etc. The power-consuming device 310 may also be a vehicle such as a car, truck, sedan, van, truck, train, high-speed train, electric vehicle, etc. In addition, the power-consuming device 310 may also be various household appliances such as refrigerators, electric lights, air conditioners, etc. It is understandable that the power-consuming device 310 illustrated in the drawings of this application is only one form of the power-consuming device 310 and should not be understood as limiting the power-consuming device 310 provided in this application.

[0050] 5 , an embodiment of the present application further provides an energy storage device 200 , which includes a box 210 and a plurality of batteries 400 . The plurality of batteries 400 are stacked and accommodated in the box 210 .

[0051] Optionally, the battery 400 may be, but is not limited to, a lithium-ion secondary battery, a lithium-ion primary battery, a lithium-sulfur battery, a sodium-lithium-ion battery, a sodium-ion battery or a magnesium-ion battery, an energy storage battery, or the like.

[0052] The term "plurality" means greater than or equal to two.

[0053] It can be understood that the multiple batteries 400 of the energy storage device 200 can be connected in parallel with each other; or in series with each other; or partially in parallel and partially in series (in other words, mixed connection). This application does not specifically limit the connection method of the multiple batteries 400 of the same energy storage device 200.

[0054] It is understood that the housing 210 has a receiving cavity (not shown) in which multiple batteries 400 are received. In some embodiments, each receiving cavity receives one battery 400. In other embodiments, each receiving cavity receives multiple batteries 400.

[0055] 6 and 7 , an embodiment of the present application further provides a battery 400, which includes an electrolyte, a positive electrode sheet 410, a separator 420, and a negative electrode sheet 430. The positive electrode sheet 410 is at least partially immersed in the electrolyte; the separator 420 is located on one side of the positive electrode sheet 410; and the negative electrode sheet 430 is disposed on a side of the separator 420 facing away from the positive electrode sheet 410 and is at least partially immersed in the electrolyte.

[0056] Please refer to Figure 8. In some embodiments, the electrolyte includes an electrolyte salt, and the electrolyte salt includes lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonyl imide (LiFSI). In the electrolyte, the mass ratio of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is γ; the positive electrode plate 410 includes a positive electrode collector 411 and a positive electrode active layer 412, and the positive electrode active layer 412 is arranged on the surface of the positive electrode collector 411. The positive electrode active layer 412 includes a positive electrode active material and a carbon material, and the mass fraction of the carbon material in the positive electrode active layer 412 is B; wherein, the battery 400 satisfies the relationship: 1.31wt%≤γB≤10.74wt%.

[0057] It is understood that the positive electrode sheet 410, the separator 420 and the negative electrode sheet 430 are stacked in sequence to form an electrode assembly. The electrode assembly can be, but is not limited to, a wound structure, a laminated structure, etc., which is not specifically limited in this application.

[0058] It should be noted that the positive electrode sheet 410 and the negative electrode sheet 430 may be collectively referred to as electrode sheets. In other words, the electrode sheets include the positive electrode sheet 410 and the negative electrode sheet 430 .

[0059] Optionally, the battery 400 further includes a housing 440 , and the housing 440 is used to accommodate the electrolyte, the positive electrode plate 410 , the separator 420 and the negative electrode plate 430 .

[0060] It can be understood that the positive electrode active layer 412 may cover one surface of the positive electrode current collector 411 or may cover two opposite surfaces of the positive electrode current collector 411 .

[0061] Specifically, the value of γB can be but is not limited to 1.31wt%, 1.5wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 10.74wt%, etc. When γB is too small, it may be that the mass ratio γ of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is too small or the mass fraction B of the carbon material in the positive electrode active layer 412 is too small; when the mass ratio γ of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is too small, it indicates that the content of lithium hexafluorophosphate in the electrolyte is too small and the content of lithium bisfluorosulfonyl imide is too high. When the battery 400 is in a high-temperature, high-voltage working environment, the excessively high content of lithium bisfluorosulfonyl imide is likely to corrode the aluminum foil, thereby damaging the positive electrode sheet 410, reducing the life of the battery 400, affecting the normal operation of the battery 400, and increasing the cost of the electrolyte; when the mass fraction B of the carbon material in the positive electrode active layer 412 is too small, it is easy to make the positive electrode sheet 410 insufficient in its electron conductivity, increase the impedance of the positive electrode sheet 410, and reduce the rate performance and cycle performance of the battery 400. When γB is too large, it may be that the mass ratio γ of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is too large or the mass fraction B of the carbon material in the positive electrode active layer 412 is too large; when the mass ratio γ of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is too large, it indicates that the content of lithium hexafluorophosphate in the electrolyte is too high and the content of lithium bisfluorosulfonyl imide is too low, then the battery 400 is in the overcharge stage, and the hexafluorophosphate ion (PF6 -) is prone to decomposition to produce acid. Excessive side reactions can easily increase the temperature of the battery 400, reducing the safety performance of the battery 400. In addition, the decomposition of hexafluorophosphate ions reduces the conductivity of the electrolyte, thereby reducing the kinetic performance of the battery 400. When the mass fraction B of the carbon material in the positive electrode active layer 412 is too large, the energy density of the positive electrode plate 410 is reduced. In addition, when the battery 400 is overcharged (for example, when the overcharge voltage is 4.8V), the side reactions between the electrolyte and the surface of the positive electrode active layer 412 are exacerbated, which can easily increase the temperature of the battery 400 and reduce the safety performance of the battery 400. In this embodiment, by ensuring that 1.31wt%≤γB≤10.74wt%, the electrolyte of the battery 400 has higher conductivity and the battery 400 has higher kinetic performance. In addition, the side reactions within the battery 400, especially those during overcharge, can be reduced, thereby reducing the temperature of the battery 400 during the overcharge stage and significantly improving the safety performance of the battery 400.

[0062] Furthermore, the battery 400 satisfies the relationship: 1.8 wt% ≤ γB ≤ 10 wt%. When γB is within this range, the battery 400 can better have higher dynamic performance while reducing side reactions, thereby having higher safety performance.

[0063] Furthermore, the battery 400 satisfies the relationship: 2wt%≤γB≤9wt%. When γB is within this range, the battery 400 can better have higher dynamic performance while reducing side reactions, thereby having higher safety performance.

[0064] The electrolyte of the battery 400 of the embodiment of the present application includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The addition of lithium bis(fluorosulfonyl)imide can reduce the hexafluorophosphate ion (PF6 - ) decomposition, thereby reducing the side reactions of the battery 400 and improving the safety performance of the battery 400. In addition, the hexafluorophosphate ion (PF6 -) decomposition, can better maintain the conductivity of the electrolyte, so that the battery 400 has better dynamic performance. The positive electrode active layer 412 includes a positive electrode active material and a carbon material. The addition of the carbon material in the positive electrode active layer 412 can improve the conductivity of the positive electrode plate 410, thereby further improving the dynamic performance of the battery 400. However, if the content of the carbon material is too high, it will increase the side reactions and reduce the safety performance of the battery 400. The embodiment of the present application controls by making 1.31wt%≤γB≤10.74wt%, and by using the combination of the contents of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and carbon material, so that the battery 400 has higher dynamic performance while greatly reducing the side reactions of the battery 400 and improving the safety performance of the battery 400.

[0065] Optionally, the positive electrode current collector 411 may be, but is not limited to, an aluminum sheet.

[0066] Optionally, the positive electrode active material may be, but is not limited to, lithium iron phosphate.

[0067] In some embodiments, the mass fraction B of the carbon material in the positive electrode active layer 412 is in the range of 1.073 wt% ≤ B ≤ 1.653 wt%. Specifically, in the positive electrode active layer 412, the mass fraction B of the carbon material can be, but is not limited to, 1.073 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.25 wt%, 1.3 wt%, 1.35 wt%, 1.4 wt%, 1.45 wt%, 1.5 wt%, 1.55 wt%, 1.6 wt%, 1.653 wt%, etc. The carbon material helps form a conductive network, increases the electron transport path, and improves the dynamics of the positive electrode plate 410. When the mass fraction B of the carbon material in the positive electrode active layer 412 is too low, the positive electrode plate 410 may have insufficient electron conductivity, increase the impedance of the positive electrode plate 410, and reduce the rate performance and cycle performance of the battery 400. When the mass fraction B of the carbon material in the positive electrode active layer 412 is too large, the energy density of the positive electrode sheet 410 is reduced. In addition, when the battery 400 is overcharged (for example, when the overcharge voltage is 4.8V), the side reaction between the electrolyte and the surface of the positive electrode active layer 412 is aggravated, which easily causes the temperature of the battery 400 to rise, thereby reducing the safety performance of the battery 400. In this embodiment, by setting the mass fraction B of the carbon material within the range of 1.073wt%≤B≤1.653wt%, the electrolyte of the battery 400 has higher electron conductivity and lower impedance, thereby improving the rate performance and cycle performance of the battery 400. In addition, the battery 400 can have fewer side reactions when overcharged, reducing the overcharge temperature of the battery 400, and thus reducing the safety performance of the battery 400.

[0068] Furthermore, the mass fraction B of the carbon material in the positive electrode active layer 412 is in the range of 1.2 wt% ≤ B ≤ 1.6 wt%. When the mass fraction B of the carbon material in the positive electrode active layer 412 is within this range, the electrolyte of the battery 400 can have higher electron conductivity and lower impedance, thereby further improving the rate performance and cycle performance of the battery 400. In addition, the battery 400 can have fewer side reactions during overcharging, reducing the overcharge temperature of the battery 400, thereby further reducing the safety performance of the battery 400.

[0069] In some embodiments, the carbon material includes a carbon coating layer (also referred to as coated carbon) and conductive carbon, the carbon coating layer is wrapped around the surface of the positive electrode active material, and the conductive carbon is dispersed in the positive electrode active layer 412; in the positive electrode active layer 412, the mass ratio of the carbon coating layer to the conductive carbon is in the range of: 2.57≤B1 / B2≤4.5.

[0070] Specifically, in the positive electrode active layer 412 , the mass ratio B1 / B2 of the carbon coating layer to the conductive carbon may be, but is not limited to, 2.57, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.5, etc.

[0071] When the mass ratio B1 / B2 of the carbon coating layer to the conductive carbon is too small, the interface dynamics of the positive electrode active layer 412 of the positive electrode plate 410 will be deteriorated, so that the lithium ion extraction and insertion rate will be reduced and the interface polarization will be increased; when the mass ratio B1 / B2 of the carbon coating layer to the conductive carbon is too large, the gram capacity of the positive electrode active layer 412 will be insufficient, the energy density will be reduced, and in addition, the side reaction at the interface between the electrolyte and the carbon coating layer of the positive electrode plate 410 under high voltage will be deteriorated.

[0072] Optionally, in the positive electrode active layer 412 , the mass fraction B1 of the carbon coating layer is in the range of: 0.77 wt % ≤ B1 ≤ 1.35 wt %.

[0073] Specifically, in the positive electrode active layer 412, the mass fraction B1 of the carbon coating layer can be, but is not limited to, 0.77 wt%, 0.8 wt%, 0.87 wt%, 0.9 wt%, 0.95 wt%, 1.04 wt%, 1.1 wt%, 1.15 wt%, 1.20 wt%, 1.25 wt%, 1.30 wt%, 1.35 wt%, etc. When the mass fraction B1 of the carbon coating layer in the positive electrode active layer 412 is too low, the carbon coating layer cannot completely cover the positive electrode active material, causing part of the positive electrode active material to directly contact the electrolyte, increasing the side reaction between the electrolyte and the positive electrode active layer 412, thereby increasing the consumption of the electrolyte and reducing the cycle capacity retention rate of the battery 400; in addition, the carbon coating layer also affects the construction of the conductive network at the interface of the positive electrode active layer 412. If the mass fraction of the carbon coating layer is too low, the conductive performance will be deteriorated, affecting the kinetics.

[0074] Optionally, in the positive electrode active layer 412, the mass fraction B2 of the conductive carbon is in the range of: 0≤B2≤0.3wt%. Specifically, in the positive electrode active layer 412, the mass fraction B2 of the conductive carbon can be, but is not limited to, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, etc. In the positive electrode active layer 412, if the mass fraction B2 of the conductive carbon is too small, the conductive network of the positive electrode active material (such as lithium iron phosphate) between the binders is insufficient, thereby reducing the electronic conductivity of the positive electrode active layer 412 and thus reducing the kinetic performance of the positive electrode active layer 412; in the positive electrode active layer 412, if the mass fraction B2 of the conductive carbon is too large, the viscosity of the positive electrode active layer 412 is too high during the slurrying process, increasing the difficulty of coating the positive electrode active layer 412 and affecting the performance of the gram capacity of the positive electrode active layer 412.

[0075] Optionally, the conductive carbon may be, but is not limited to, at least one of conductive carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0076] Alternatively, the carbon coating layer can be obtained by sintering a carbon source through a carbothermal reduction method.

[0077] Optionally, the carbon source may be, but is not limited to, at least one of glucose, sucrose, starch, and a high molecular weight carbon source such as PEG.

[0078] Optionally, the positive electrode active layer 412 further includes a first binder and a first thickener.

[0079] Optionally, the first binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0080] Optionally, the mass fraction of the first binder in the positive electrode active layer 412 ranges from 2 wt% to 4 wt%. Specifically, the mass fraction of the first binder in the positive electrode active layer 412 may be, but is not limited to, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, etc. If the mass fraction of the first binder is too low, the positive electrode active layer 412 may easily pulverize or slag. If the mass fraction of the first binder is too high, the energy density of the positive electrode sheet 410 may be reduced.

[0081] Optionally, the first thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethacrylate (PMA).

[0082] Optionally, the diaphragm 420 may be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic diaphragm 420 , and the like.

[0083] Optionally, the thickness of the diaphragm 420 is 14 μm to 18 μm. Specifically, the thickness of the diaphragm 420 may be, but is not limited to, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, and 18 μm.

[0084] In some embodiments, the mass ratio γ of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the electrolyte is in the range of 1.22≤γ≤6.5. Specifically, the mass ratio γ of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the electrolyte can be, but is not limited to, 1.22, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, etc. When the mass ratio γ of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is too small, it indicates that the content of lithium hexafluorophosphate in the electrolyte is too small and the content of lithium bisfluorosulfonyl imide is too high. When the battery 400 is in a high temperature and high voltage working environment, the excessively high content of lithium bisfluorosulfonyl imide is likely to corrode the aluminum foil, thereby damaging the positive electrode sheet 410, reducing the life of the battery 400, affecting the normal operation of the battery 400, and increasing the cost of the electrolyte; when the mass ratio γ of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is too large, it indicates that the content of lithium hexafluorophosphate in the electrolyte is too high and the content of lithium bisfluorosulfonyl imide is too small. In the overcharge stage of the battery 400, the hexafluorophosphate ion (PF6 - ) is prone to decomposition to produce acid. Excessive side reactions can easily increase the temperature of battery 400, reducing the safety performance of battery 400. In addition, the decomposition of hexafluorophosphate ions reduces the conductivity of the electrolyte, thereby reducing the dynamic performance of battery 400. When the mass ratio γ of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is within the range of 1.22≤γ≤6.5, battery 400 can have a lower cost and a longer service life, while also having higher safety and dynamic performance.

[0085] Furthermore, in the electrolyte, the mass ratio γ of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is in the range of 1.5 ≤ γ ≤ 6. When the mass ratio γ of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the electrolyte is within this range, the battery 400 can have a lower cost and a longer service life while also having better overcharge resistance, safety, and dynamic performance.

[0086] In some embodiments, the total molar concentration M of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide in the electrolyte is in the range of 0.7 mol / L≤M≤1.4 mol / L. The total molar concentration M of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide in the electrolyte can be, but is not limited to, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, etc. If the total molar concentration M of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide is too low, the concentration of free ions in the electrolyte is too low, which reduces the conductivity of the electrolyte and thus reduces the kinetic performance of battery 400. If the total molar concentration M of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide is too high, a portion of the electrolyte salt is likely to remain undissociated, and the viscosity of the electrolyte will increase, which in turn reduces the conductivity of the electrolyte and also reduces the kinetic performance of battery 400. When the total molar concentration M of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the electrolyte is in the range of 0.7 mol / L≤M≤1.4 mol / L, the electrolyte can have a higher conductivity, thereby enabling the battery 400 to have better kinetic performance.

[0087] Furthermore, in the electrolyte, the total molar concentration M of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide is in the range of 0.8 mol / L ≤ M ≤ 1.3 mol / L. When the total molar concentration M of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the electrolyte is within this range, the electrolyte can have better conductivity, thereby enabling the battery 400 to have better kinetic performance.

[0088] In some embodiments, the electrolyte further includes a sulfur-containing additive. The sulfur-containing additive can form lithium sulfate or alkyl lithium sulfate in the positive electrode plate 410, further stabilizing the solid electrolyte interface (SEI) film of the positive electrode plate 410 and making the SEI film thinner, thereby further reducing the impedance of the positive electrode plate 410, thereby reducing the high-temperature heat generation of the positive electrode plate 410 and improving the safety performance of the battery 400.

[0089] Optionally, the sulfur-containing additive may be, but is not limited to, a positive electrode sulfur-containing additive.

[0090] Optionally, in the electrolyte, the mass fraction w1 of the sulfur-containing additive is in the range of 0.1 wt% ≤ w1 ≤ 1 wt%. Specifically, in the electrolyte, the mass fraction w1 of the sulfur-containing additive may be, but is not limited to, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, etc. If the mass fraction w1 of the sulfur-containing additive in the electrolyte is too low, the stability of the interface film of the positive electrode plate 410 is limited, and the safety performance of the battery 400 cannot be effectively improved. If the mass fraction w1 of the sulfur-containing additive in the electrolyte is too high, the sulfur-containing additive easily decomposes and produces acid at high temperatures, destroying the interface film of the positive electrode plate 410, causing the positive active layer 412 of the positive electrode plate 410 to directly contact the electrolyte, increasing side reactions between the positive active layer 412 and the electrolyte, thereby increasing electrolyte consumption and reducing the cycle capacity retention rate of the battery 400. When the mass fraction of the sulfur-containing additive in the electrolyte is 0.1wt%≤w1≤1wt%, the safety performance of the battery 400 can be better improved while maintaining a high cycle capacity retention rate.

[0091] In some embodiments, the sulfur-containing additive includes at least one of methylene methanedisulfonate (MMDS), ethylene sulfate (DTD), tris(trimethylsilyl) phosphite (TMSP), propene sultone (PST), butane sultone (BS), and propene sulfite (PS). In this embodiment, the use of these sulfur-containing additives can better stabilize the interface film of the positive electrode plate 410, reduce the impedance of the positive electrode plate 410, reduce the high-temperature heat generation of the positive electrode plate 410, and improve the safety performance of the battery 400. In addition, these substances are less likely to decompose and produce acid when the battery 400 is exposed to high temperatures, which can better reduce the consumption of electrolyte at high temperatures, thereby maintaining a high cycle capacity retention rate of the battery 400.

[0092] In some embodiments, the electrolyte further includes a lithium salt additive to replenish lithium ions in the electrolyte. In addition, the lithium salt additive can improve the impedance of the positive electrode plate 410 or the negative electrode plate 430 and enhance the dynamic performance of the battery 400 .

[0093] Optionally, in the electrolyte, the mass fraction w2 of the lithium salt additive is 0.2wt%≤w2≤2wt%. Specifically, the mass fraction w2 of the lithium salt additive can be, but is not limited to, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, etc. If the mass fraction w2 of the lithium salt additive is too small, the reduction in the impedance of the positive electrode sheet 410 or the negative electrode sheet 430 is limited, and it is difficult to improve the dynamic performance of the positive electrode sheet 410 or the negative electrode sheet 430. If the mass fraction w2 of the lithium salt additive is too large, due to the limited solubility of the lithium salt additive, when the concentration of the lithium salt additive reaches a certain level, the dynamic performance of the positive electrode sheet 410 or the negative electrode sheet 430 will no longer be improved, but the cost of the battery 400 will be greatly increased. When the mass fraction w2 of the lithium salt additive is 0.2 wt%≤w2≤2 wt%, the dynamic performance of the positive electrode sheet 410 or the negative electrode sheet 430 can be improved while the cost of the battery 400 can be lowered.

[0094] Optionally, the lithium salt additive includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiODFB), and lithium difluorooxalatophosphate. In this embodiment, the use of these lithium salt additives can better form an inorganic salt structure or film on the surface of the positive electrode plate 410 or the negative electrode plate 430, thereby reducing the impedance of the positive electrode plate 410 or the negative electrode plate 430 and better improving the dynamic performance of the positive electrode plate 410 or the negative electrode plate 430. For example, lithium difluorophosphate can form an inorganic salt structure such as lithium fluoride on the negative electrode plate 430, which can reduce the impedance of the negative electrode plate 430 and improve the dynamic performance of the negative electrode plate 430. For another example, lithium difluorooxalatoborate can form a film on the surface of the positive electrode sheet 410 and the negative electrode sheet 430 , thereby reducing the impedance of the positive electrode sheet 410 and the negative electrode sheet 430 and improving the dynamic performance of the positive electrode sheet 410 and the negative electrode sheet 430 .

[0095] Optionally, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of a cyclic carbonate and a chain carbonate. Cyclic carbonate has a high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode plate 430, but its viscosity is relatively large. Chain carbonate has a lower viscosity than cyclic carbonate, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, when a mixed solvent of cyclic carbonate and chain carbonate is used, the electrolyte can have a more suitable viscosity and low-temperature stability, and the battery 400 using the electrolyte can also form a better film.

[0096] Optionally, the cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), etc. The dielectric constant of ethylene carbonate is much greater than that of propylene carbonate, and ethylene carbonate can better promote the formation of SEI film.

[0097] Optionally, the linear carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Dimethyl carbonate (DMC) and diethyl carbonate (DEC) can better improve the conductivity and solubility of the electrolyte.

[0098] Optionally, in the electrolyte, the mass fraction of the organic solvent is 60 wt % to 85 wt %, specifically, but not limited to, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, etc.

[0099] Optionally, the organic solvent further comprises at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0100] Optionally, the electrolyte further includes a film-forming additive. When the electrolyte is applied to the lithium-ion battery 400, the film-forming additive can be used to promote the formation of an interface film of at least one of the positive electrode plate 410 and the negative electrode plate 430 and maintain the stability of the interface film.

[0101] Optionally, the film-forming additive includes at least one of fluoroethylene carbonate (FEC), vinyl sulfate (PST), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, adiponitrile, succinonitrile, and 1,3,6-hexanonitrile.

[0102] Optionally, the mass fraction of the film-forming additive ranges from 1% to 3%. Specifically, the mass fraction of the film-forming additive can be, but is not limited to, 1%, 1.2%, 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%, etc.

[0103] 9 , optionally, the negative electrode sheet 430 includes a negative electrode current collector 431 and a negative electrode active layer 432 , wherein the negative electrode active layer 432 is disposed on the surface of the negative electrode current collector 431 . It is understood that the negative electrode active layer 432 may cover one surface or two opposite surfaces of the negative electrode current collector 431 .

[0104] Optionally, the negative electrode current collector 431 may be, but is not limited to, a copper sheet.

[0105] Optionally, the negative electrode active layer 432 includes a negative electrode active material, a negative electrode conductor, a second binder, and a second thickener.

[0106] Optionally, the negative electrode active material may be, but is not limited to, graphite. Optionally, the graphite may be natural graphite or artificial graphite, which is not specifically limited in this application.

[0107] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0108] Optionally, the second binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0109] Optionally, the mass fraction of the second binder in the negative electrode active layer 432 ranges from 2 wt% to 4 wt%. Specifically, the mass fraction of the second binder in the negative electrode active layer 432 may be, but is not limited to, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, etc. If the mass fraction of the second binder is too low, the negative electrode active layer 432 may easily pulverize or slag. If the mass fraction of the second binder is too high, the energy density of the negative electrode sheet 430 may be reduced.

[0110] Optionally, the second thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethacrylate (PMA).

[0111] After testing, the battery 400 of the embodiment of the present application has a cycle capacity retention rate of greater than or equal to 95.32% at a 1C discharge rate, and specifically, it can be, but not limited to, 95.32%, 96%, 97%, 98%, 99%, etc. The battery 400 of the embodiment of the present application has a cycle capacity retention rate of greater than or equal to 88.13% at a 2C discharge rate, and specifically, it can be, but not limited to, 88.13%, 90%, 91%, 92%, 93%, 94%, 95%, 95.32%, 96%, 97%, 98%, 99%, etc.

[0112] The battery 400 of the present application is further described below through specific embodiments.

[0113] Examples 1 to 23, Comparative Examples 1 to 5

[0114] The preparation method of the battery 400 of each embodiment and comparative example includes:

[0115] (1) Preparation of positive electrode sheet 410: dry-mix positive electrode particles (positive electrode particles including lithium iron phosphate positive electrode active material and a carbon coating layer coated on the surface of the lithium iron phosphate), conductive carbon black SP (conductive carbon), and PVDF (first binder) in a mass ratio of 97.4:0.3:2.3, mix evenly, add to N-methylpyrrolidone (NMP) solvent and stir and knead, the kneaded solid content is 72% to 74%; then continue to add N-methylpyrrolidone for high-speed dispersion, and then form a positive electrode slurry with uniform viscosity and fineness through the processes of viscosity adjustment, vacuum slow stirring to remove bubbles, and filtration; the positive electrode slurry is coated on aluminum foil (positive electrode current collector 411), and the coating thickness of the positive electrode slurry is controlled to be 0.5g / 1540.25mm 2 Up to 0.6g / 1540.25mm 2 ; Then, the positive electrode sheet 410 is made by baking, rolling, slitting and cutting; at the same time, the carbon material content of the positive electrode sheet 410 can be detected using a carbon-sulfur analyzer by scraping the powder from the material area of ​​the positive electrode sheet 410. For detailed data of each embodiment and comparative example, please refer to Table 1 below.

[0116] (2) Preparation of the negative electrode sheet 430: The negative electrode active material artificial graphite, conductive carbon black SP (second conductive agent), and sodium carboxymethyl cellulose CMC (second thickener) are mixed in a preset mass ratio, a certain amount of deionized water is added and stirred, and styrene-butadiene rubber (SBR second binder) is added and stirred and dispersed, so that the mass ratio of artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber is 96.9:0.1:1:2; after vacuum slow stirring to remove bubbles and filtering, a negative electrode slurry with uniform viscosity and fineness is formed; then the negative electrode slurry is coated on copper foil (negative electrode current collector 431) so that the coating thickness of the negative electrode slurry is controlled to 0.24g / 1540.25mm2 Up to 0.3g / 1540.25mm 2 ; Then, the negative electrode sheet 430 is made through processes such as baking, rolling, slitting, and cutting.

[0117] (3) Electrolyte preparation: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC) are dehydrated with molecular sieves to reduce the water content of the solvent to less than 10 ppm; in an argon atmosphere glove box with a water content of ≤1 ppm, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC) are mixed in a certain ratio to obtain a mixed solvent, and then dry electrolyte salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are dissolved in the mixed solvent and stirred until completely dissolved and uniformly dissolved, and fluoroethylene carbonate (FEC), vinylene carbonate (VC) and methylene disulfonate (sulfur-containing additive MMDS) are added and mixed uniformly to obtain the electrolyte.

[0118] In the electrolytes of Examples 1 to 16, Examples 20 to 23, and Comparative Examples 1 to 7, the mass ratio of dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate was 1:1:1. In Examples 17 to 19, the mass ratios of dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate were 1.1:0.9:1, 0.9:1.1:0.9, and 1:1.1:0.9, respectively.

[0119] In the electrolytes of Examples 1 to 19, Example 23, and Comparative Examples 1 to 7, the amount of fluoroethylene carbonate added was 1 wt%, the amount of vinylene carbonate added was 2 wt%, and the amount of methylene methanedisulfonate added was 0.5 wt%. In the electrolytes of Examples 20 to 22, the amount of fluoroethylene carbonate added was 1.01 wt%, the amount of vinylene carbonate added was 2.01 wt%, and the amount of methylene methanedisulfonate added was 0.51 wt%.

[0120] In the electrolytes of Examples 1 to 22 and Comparative Examples 1 to 7, the total molar concentration of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide was 1 mol / L. In the electrolyte of Example 23, the total molar concentration of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide was 1.01 mol / L.

[0121] The mass ratio γ of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in each embodiment and comparative example is shown in Table 1 below.

[0122] (4) Providing a separator 420: A 16 μm polyethylene film is used as the separator 420.

[0123] (5) Assembly of battery 400: The positive electrode sheet 410, the separator 420, and the negative electrode sheet 430 are stacked in sequence to form an electrode assembly. The electrode assembly is wound to obtain a bare cell. After welding the tabs, the cell is assembled into an outer package. After injecting the prepared electrolyte, the cell is packaged, allowed to stand, formed, shaped, and capacity tested, and finally a 3.2Ah battery 400 is prepared.

[0124] Comparative Example 6

[0125] The difference between Comparative Example 6 and Example 13 is that the carbon material of the positive electrode active layer 412 of this comparative example only includes a carbon coating layer and does not contain conductive carbon.

[0126] Comparative Example 7

[0127] The difference between Comparative Example 7 and Example 1 is that the carbon material of the positive electrode active layer 412 of this comparative example only includes a carbon coating layer and does not contain conductive carbon.

[0128] The battery 400 of each embodiment and comparative example was subjected to an overcharge test and a discharge capacity retention rate test at different rates. The performance parameters of the battery 400 of each embodiment and comparative example are shown in Table 1 below.

[0129] (1) Overcharge test of battery 400: Take the fresh battery 400 prepared as described above, and attach a temperature sensor to the surface of the battery 400 to monitor the temperature of the battery 400 during the overcharge process. First, pre-treat the battery 400 and cycle charge and discharge at a rate of 1C for 3 cycles at 45°C. Then, cycle charge and discharge at a rate of 1C for one cycle at room temperature. Then, charge at a constant current of 1C to 3.65V, and then charge at a constant voltage of 3.65V to 0.05C. Then, charge the battery 400 continuously at a current of 1C until it reaches 5.475V (1.5 times the full-charge voltage, i.e., 1.5×3.65V) or the charging time reaches 1h, and then observe for 1h after the charging is completed, monitoring the surface temperature of the battery 400. The overcharge temperature and overcharge time of each embodiment and comparative example are shown in Table 1 below. The “overcharge time” refers to the time required for the battery 400 to continue charging to a voltage of 1.5 times the full-charge voltage (5.475V) after being fully charged (voltage is 3.65V).

[0130] (2) Rate performance test of battery 400: Battery 400 is charged at a constant current of 0.5C in the voltage range of 2.5-3.65V, with a cut-off current of 0.05C, and the discharge capacity retention rate of battery 400 at different discharge rates (e.g., 1C discharge rate, 2C discharge rate) is tested.

[0131] The discharge capacity retention rate is calculated as follows: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0132] Table 1 Performance parameters of battery 400 in various embodiments and comparative examples

[0133] It can be seen from the test data of Examples 1 to 16 in Table 1 that when the battery 400 of the embodiment of the present application satisfies 1.31wt%≤γB≤10.74wt%, at a 1C discharge rate, the cycle capacity retention rate of the battery 400 is above 95.32%, and at a 2C discharge rate, the cycle capacity retention rate of the battery 400 is above 88.13%. The battery 400 of the embodiment of the present application has a high cycle capacity retention rate at both the 1C discharge rate and the 2C discharge rate, which indicates that the battery 400 of the embodiment of the present application has good dynamic performance.

[0134] In addition, it can be seen from the test data of Examples 1 to 16 in Table 1 that when the battery 400 of the embodiment of the present application satisfies 1.31wt%≤γB≤10.74wt%, when the battery 400 is overcharged (overcharged to 1.5 times the full-charge voltage), the overcharge temperature on the surface of the battery 400 is less than or equal to 79°C, which has a lower overcharge temperature; the overcharge time of each embodiment is less than or equal to 13.9min, which has a shorter overcharge time, which indicates that the battery 400 generates less heat during the overcharge stage, has better overcharge resistance, and thus has better safety performance.

[0135] From the test results of Example 1, Example 5, Example 9 and Example 13, it can be seen that when the battery 400 of the embodiment of the present application satisfies 1.31wt%≤γB≤10.74wt%, the battery 400 of the embodiment of the present application has a high cycle capacity retention rate at both the 1C discharge rate and the 2C discharge rate, and has good rate performance. From the test results of Comparative Example 3, it can be seen that when γ<1.22 and γB<1.31wt%, although the battery 400 still has a high cycle capacity retention rate at the 1C discharge rate, the cycle capacity retention rate decreases significantly at the 2C discharge rate. From the test results of Comparative Example 5, it can be seen that when γ>6.5, although the battery 400 still has a high cycle capacity retention rate at the 1C discharge rate, the cycle capacity retention rate also decreases significantly at the 2C discharge rate. Furthermore, Comparative Example 4 shows that when γ>6.5 and γB>10.74wt%, the cycle capacity retention rate at a 1C discharge rate and the cycle capacity retention rate at a 2C discharge rate of Comparative Example 4 are both reduced compared to Comparative Example 5. Furthermore, Comparative Examples 4 and 5 also show that when γ>6.5, or γ>6.5 and γB>10.74wt%, the overcharge temperature of the battery 400 increases significantly and the overcharge time becomes significantly longer, indicating that the charge resistance and safety performance of the battery 400 are reduced.

[0136] It can be seen from the test results of Examples 1 to 4 that when the value of γ is fixed and 1.073wt%≤B≤1.653wt%, as the content of carbon material (i.e., B=B1+B2) increases, the cycle capacity retention rate of battery 400 at a discharge rate of 1C and the cycle capacity retention rate at a discharge rate of 2C both increase.

[0137] The test results of Example 1 and Comparative Example 7 show that when the carbon material of the positive electrode active layer 412 is entirely a carbon coating layer without conductive carbon (i.e., Comparative Example 7), the cycle capacity retention rate of the battery 400 at a 1C discharge rate and the cycle capacity retention rate at a 2C discharge rate remain essentially unchanged. In addition, the overcharge temperature of the battery 400 increases significantly, and the overcharge time also increases, indicating that the overcharge resistance and safety performance of the battery 400 are reduced.

[0138] The test results of Example 13 and Comparative Example 6 show that when the carbon material of the positive electrode active layer 412 is entirely a carbon coating layer without conductive carbon (i.e., Comparative Example 6), the cycle capacity retention rate of battery 400 at a 1C discharge rate and the cycle capacity retention rate at a 2C discharge rate remain essentially unchanged. In addition, the overcharge temperature of battery 400 increases significantly, and the overcharge time also increases, indicating that the overcharge resistance and safety performance of battery 400 are reduced.

[0139] It can be seen from the test results of Examples 5 and 17 to 19 that when γ, B1, B2 and B are the same, only the solvent ratio of the electrolyte is changed, and the cycle capacity retention rate of the battery at a 1C discharge rate and the cycle capacity retention rate at a 2C discharge rate have almost no change, and the overcharge temperature and overcharge time also change very little.

[0140] It can be seen from the test results of Examples 5 and 20 to 22 that when γ, B1, B2 and B are the same, only by changing the ratio of the film-forming additives in the electrolyte, there is almost no change in the cycle capacity retention rate of the battery at a 1C discharge rate and a 2C discharge rate, and the overcharge temperature and overcharge time also change very little.

[0141] It can be seen from the test results of Examples 5 and 20 to 22 that when γ, B1, B2 and B are the same, only the total molar concentration of the lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the electrolyte is changed, and the cycle capacity retention rate of the battery at a 1C discharge rate and the cycle capacity retention rate of a 2C discharge rate are almost unchanged, and the overcharge temperature and overcharge time also change very little.

[0142] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of the present application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application, unless there is a contradiction between them.

[0143] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit them. Although the present application has been described in detail with reference to the above preferred implementation modes, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.

Claims

1. A battery, wherein: include: An electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the electrolyte is γ; as well as A positive electrode sheet, wherein the positive electrode sheet is at least partially immersed in the electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer, the positive electrode active layer is disposed on the surface of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material and a carbon material, and the mass fraction of the carbon material in the positive electrode active layer is B; The battery satisfies the relationship: 1.31 wt%≤γB≤10.74 wt%.

2. The battery according to claim 1, wherein In the positive electrode active layer, the mass fraction B of the carbon material is in the range of 1.073 wt%≤B≤1.653 wt%.

3. The battery according to claim 2, wherein The carbon material includes a carbon coating layer and conductive carbon, the carbon coating layer is wrapped around the surface of the positive electrode active material, and the conductive carbon is dispersed in the positive electrode active layer; in the positive electrode active layer, the mass ratio of the carbon coating layer to the conductive carbon is in the range of: 2.57≤B1 / B2≤4.

5.

4. The battery according to claim 1, wherein In the electrolyte, the mass ratio γ of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is in the range of 1.22≤γ≤6.

5.

5. The battery according to claim 1, wherein In the electrolyte, the total molar concentration M of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide is in the range of 0.7 mol / L≤M≤1.4 mol / L.

6. The battery according to claim 1, wherein The electrolyte further includes a sulfur-containing additive, and the mass fraction w1 of the sulfur-containing additive is in the range of 0.1 wt%≤w1≤1 wt%.

7. The battery according to claim 6, wherein The sulfur-containing additive includes at least one of methylene methanedisulfonate, ethylene sulfate, tris(trimethylsilyl)phosphite, propylene sultone, butyl sultone, and propylene sulfite.

8. The battery according to any one of claims 1 to 7, wherein: The electrolyte also includes a lithium salt additive. In the electrolyte, the mass fraction w2 of the lithium salt additive is 0.2wt%≤w2≤2wt%; the lithium salt additive includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate, and lithium difluorooxalatophosphate.

9. An electricity system, wherein: include: Electrical equipment, and An energy storage device, wherein the energy storage device supplies power to the electrical equipment, and the energy storage device comprises at least one battery according to any one of claims 1 to 8.

10. An energy storage system, wherein: include: An electric energy conversion device, the electric energy conversion device is used to convert other forms of energy into electric energy; an energy storage device, the energy storage device being electrically connected to the electric energy conversion device and configured to store the electric energy of the electric energy conversion device, the energy storage device comprising at least one battery according to any one of claims 1 to 8; as well as An electrical load is electrically connected to the power conversion device and the energy storage device, respectively, and is used to utilize the electrical energy of the power conversion device or the energy storage device to work.

Images