Negative electrode sheet, battery, and electric device

Abstract

The application relates to a negative electrode sheet, a battery and an electric device. The negative electrode sheet comprises a negative electrode current collector layer and a negative electrode material layer which are arranged in a stack, the negative electrode material layer comprises a carbon-based negative electrode material, a negative electrode binder and a first additive, the negative electrode binder comprises lithium polyacrylate, and the structural formula of the first additive is

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode sheet, a battery, and an electrical device. Background Technology

[0002] In the field of energy storage technology, adding polyacrylic acid (PAA) binder to the negative electrode formulation is a common method to improve the cycle life of battery cells. This is because PAA molecules have a large number of carboxyl groups, which can form strong hydrogen bonds with the negative electrode surface, encapsulating the negative electrode interface and suppressing the expansion of the negative electrode sheet during cycling, thus improving the cycle stability of the cell. However, the protons (H) on the carboxyl groups can easily attack solvent molecules in the electrolyte, leading to electrolyte decomposition and side reactions, which in turn worsens the cycle performance of the cell. Therefore, the polyacrylic acid is currently pre-lithiated to remove proton hydrogen from the molecules, resulting in lithium polyacrylate molecules, which reduces the reaction of proton hydrogen with the electrolyte. Although lithium polyacrylate (PAA-Li) coating on the negative electrode surface has a good inhibitory effect on the expansion of the negative electrode graphite, its good coating effect also reduces the direct contact area between the electrolyte and the negative electrode particles, resulting in poor negative electrode wettability, which further hinders lithium-ion migration and deteriorates the battery's kinetic performance. Summary of the Invention

[0003] In view of this, this application provides a negative electrode sheet, a battery, and an electrical device, wherein when the negative electrode sheet is applied to a battery, the battery has better dynamic performance and cycle performance.

[0004] This application provides a negative electrode sheet, which includes a negative electrode current collector layer and a negative electrode material layer stacked together. The negative electrode material layer includes a carbon-based negative electrode material, a negative electrode binder, and a first additive. The negative electrode binder includes lithium polyacrylate, and the first additive has the following structural formula: .

[0005] Furthermore, in the negative electrode material layer, the mass fraction of lithium polyacrylate is a, the mass ratio of the first additive is b, the mass of the negative electrode material layer is A1, the mass of the first additive is A2, and the mass ratio of the first additive b satisfies the relationship: b=A2 / (A1-A2). Then, the negative electrode material layer satisfies the relationship: 0.05≤10b / a≤40.

[0006] Furthermore, in the negative electrode material layer, the mass fraction 'a' of lithium polyacrylate is in the range of 0.5% ≤ a ≤ 3%.

[0007] Furthermore, in the negative electrode material layer, the mass percentage b of the first additive is in the range of 0.01% ≤ b ≤ 2%.

[0008] This application provides a battery comprising a negative electrode, a separator, a positive electrode, and an electrolyte, wherein the separator is disposed on one side of the negative electrode; the positive electrode is disposed on the side of the separator opposite to the negative electrode; and the electrolyte is used to wet at least a portion of the negative electrode, the separator, and the positive electrode.

[0009] Furthermore, in the negative electrode material layer, the mass percentage of the first additive is b; the electrolyte includes lithium salt, and the mass fraction of lithium salt in the electrolyte is c. Then the battery satisfies the relationship: 0.05≤100b / c≤20.

[0010] Furthermore, the electrolyte includes a lithium salt, and the mass fraction c of the lithium salt in the electrolyte is in the range of 5% ≤ c ≤ 20%.

[0011] Furthermore, the electrolyte further includes a second additive, which includes at least one of the following: fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, ethylene sulfate, ethylene disulfate, ethylene sulfite, methylene disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, adiponitrile, succinate, 1,3,6-hexanetrionitrile, 2-fluoropyridine, and hexamethylene diisocyanate.

[0012] Furthermore, in the electrolyte, the mass fraction of the second additive is d, and the range of the mass fraction d of the second additive is: 0.5%≤d≤5%.

[0013] This application provides an electrical device, which includes: a device body and a battery provided in this application, wherein the battery supplies power to the device body.

[0014] In this application, the negative electrode binder of the negative electrode sheet is lithium polyacrylate (PAA-Li). On the one hand, compared to polyacrylic acid, the lithium polyacrylate has been pre-lithiated, which can prevent the negative electrode binder from attacking solvent molecules in the electrolyte due to the presence of protonated hydrogen. This reduces side reactions and improves the cycle performance of the battery when the negative electrode sheet is used in a battery. On the other hand, the carbon-based negative electrode material has a negatively charged surface, and the lithium polyacrylate, after dissociation, has a large number of negatively charged carboxylic acid groups. The two repel each other due to the same charge, making it difficult for the negative electrode binder to stably adhere to the surface of the negative electrode sheet. The negative electrode sheet also includes the first additive, in which the negatively charged phosphate ester anion terminal tends to combine with the lithium ions in the lithium polyacrylate, so that the negative electrode binder is adsorbed on the surface of the negative electrode sheet. When the negative electrode sheet is applied to the battery and the electrolyte is injected, the first additive dissolves in the electrolyte. The first additive combines with the negative electrode binder and leaves empty sites on the surface of the negative electrode sheet, which is beneficial for the electrolyte to wet the negative electrode sheet. This solves the problem of poor wettability of the negative electrode sheet caused by the application of lithium polyacrylate in the negative electrode sheet, further improving lithium-ion transport efficiency and enhancing the kinetic performance and long-cycle performance of the battery.

[0015] Furthermore, when the negative electrode is applied to the battery and dissolved in the electrolyte, on the one hand, the first additive includes a quaternary ammonium salt cation terminal and a phosphate ester anion terminal. The first additive is adsorbed onto the surface of the negative electrode due to electrostatic adsorption, and is closer to the negative electrode than other components in the electrolyte. Further, since the first additive also includes polymerizable double bond terminals, it can undergo in-situ polymerization under electrochemical or thermal conditions to form a cross-linked polymer film, and the first additive has a low reduction potential. During battery formation, the first additive preferentially forms an SEI film (Solid Electrolyte Interphase) on the surface of the negative electrode compared to other components in the electrolyte. On the other hand, the quaternary ammonium salt cation terminal contains nitrogen, and the phosphate ester anion terminal contains phosphorus, so that the generated solid electrolyte interphase film includes inorganic components such as nitrogen and phosphorus. These inorganic components can improve the stability and density of the SEI film, effectively suppressing side reactions in the electrolyte. Furthermore, the polymerizable double bond ends decompose to form organic components, which improve the flexibility and adaptability of the SEI film to accommodate volume changes in the negative electrode during charging and discharging, preventing cracking of the SEI film after a period of use. The quaternary ammonium salt cation end, phosphate ester anion end, and polymerizable double bond end work together to construct an SEI film rich in inorganic and organic components, ultimately giving the SEI film excellent structural stability, mechanical toughness, and ionic conductivity. This is beneficial for improving the cycle performance of the battery when the negative electrode is used, and extending the battery's lifespan. On another front, the quaternary ammonium salt cation end and phosphate ester anion end in the first additive form a zwitterionic structure, which can construct efficient lithium-ion transport channels within the SEI film through electrostatic and coordination interactions, promoting rapid lithium-ion conduction. Furthermore, the phosphate ester group contains a phosphoryl oxygen atom with a lone pair of electrons. This oxygen atom has strong electronegativity and coordination ability, enabling it to coordinate with lithium ions, facilitating lithium ion dissociation, reducing lithium ion association, lowering the lithium ion transition energy barrier, and making it easier for ions to move forward within the ion transport channels in the SEI film. Moreover, the polymerizable double bond end is a methacrylate group, which can undergo in-situ polymerization on the surface of the negative electrode to form a thin, uniform, and flexible organic film. The first additive provided in this application forms a thin and uniform SEI film on the surface of the negative electrode, avoiding increased impedance due to excessive film thickness. Simultaneously, the SEI film formed by the first additive constructs lithium ion transport channels, which also helps improve lithium ion transport performance.In summary, the SEI film formed by the first additive provided in this application has both excellent stability and high ion conductivity. While achieving effective film formation protection, it significantly reduces interfacial impedance, thereby improving the long-cycle performance and kinetic performance of the negative electrode sheet when applied to the battery, and extending the service life of the battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the implementation will be briefly introduced below. Obviously, the drawings described below are some implementations of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of an energy storage system according to an embodiment of this application; Figure 2 This is a schematic diagram of the structure of an energy storage system according to another embodiment of this application; Figure 3 This is a schematic diagram of the structure of an energy storage system according to another embodiment of this application; Figure 4 This is a partial cross-sectional structural diagram of a battery according to an embodiment of this application; Figure 5 This is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of this application; Figure 6 This is a schematic diagram of the structure of an electrical device according to an embodiment of this application; Figure 7 This is a circuit block diagram of an electrical device according to an embodiment of this application.

[0018] Explanation of reference numerals in the attached figures: 100 - Energy storage system; 110 - First power conversion device; 120 - First user load; 130 - Second user load; 140 - Energy storage device; 150 - High-voltage cable; 160 - Second power conversion device; 170 - Photovoltaic-energy storage-charging station; 180 - Automobile; 200 - Battery; 210 - Electrolyte; 220 - Electrode assembly; 221 - Positive electrode sheet; 222 - Separator; 223 - Negative electrode sheet; 2231 - Negative current collector layer; 2232 - Negative electrode material layer; 300 - Electrical equipment; 310 - Equipment body. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0021] In this document, references to "embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with an embodiment or implementation may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] In the field of energy storage technology, adding polyacrylic acid (PAA) binder to the negative electrode formulation is a common method to improve the cycle life of battery cells. This is because PAA molecules have a large number of carboxyl groups, which can form strong hydrogen bonds with the negative electrode surface, encapsulating the negative electrode interface and suppressing the expansion of the negative electrode sheet during cycling, thus improving the cycle stability of the cell. However, the protons (H) on the carboxyl groups can easily attack solvent molecules in the electrolyte, leading to electrolyte decomposition and side reactions, which in turn worsens the cycle performance of the cell. Therefore, the polyacrylic acid is currently pre-lithiated to remove proton hydrogen from the molecules, resulting in lithium polyacrylate molecules, which reduces the reaction of proton hydrogen with the electrolyte. Although lithium polyacrylate (PAA-Li) coating on the negative electrode surface has a good inhibitory effect on the expansion of the negative electrode graphite, its good coating effect also reduces the direct contact area between the electrolyte and the negative electrode particles, resulting in poor negative electrode wettability, which further hinders lithium-ion migration and deteriorates the battery's kinetic performance and long-cycle performance.

[0023] In the terminology of this application, long cycle performance refers to the ability of a battery cell to maintain stable and slow capacity decay, slow internal resistance growth, and stable interface structure without damage during long-term, repeated charge-discharge use, thereby achieving a longer cycle life and more durable performance.

[0024] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form for future applications. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels. Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0025] Taking electrochemical energy storage as an example, this solution provides an energy storage device 140, which is applied to the energy storage system 100. The energy storage device 140 is equipped with a set of chemical batteries, which mainly use the chemical elements in the battery 200 as the energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical battery. When the use of external electrical energy reaches its peak, the stored electrical energy is released for use, or transferred to places with a shortage of electricity for use.

[0026] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding energy storage devices (140 types) include: (1) Large-scale energy storage power stations (including multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, the energy storage power station can realize the load matching of power in time and space, enhance the renewable energy absorption capacity, reduce instantaneous power changes, reduce the impact on the power grid, improve the problem of new energy power generation absorption, and is of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation.

[0027] (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption.

[0028] (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices 140, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system 100 when the electricity price is low and discharging the energy storage system 100 when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use the energy storage system 100 to store energy during the low electricity consumption period and discharge during the peak load period, thereby reducing peak power and the maximum demand declared, and achieving the goal of reducing capacity electricity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0029] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 100 according to an embodiment of this application. Figure 1 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 140 in this application is not limited to an energy storage box in a home energy storage scenario.

[0030] This application provides an energy storage system 100, which includes a first power conversion device 110 (photovoltaic panel), a first user load 120 (household lighting fixtures), a second user load 130 (e.g., household appliances such as air conditioners), and the energy storage device 140 of this application. The energy storage device 140 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 140 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 140 is used to store this electrical energy and supply it to lighting fixtures and household appliances during periods of high electricity prices, or to provide power during power outages / power failures.

[0031] Optionally, the first power conversion device 110 may include, but is not limited to, a photovoltaic panel, and the first power 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 electrical energy.

[0032] In some embodiments, see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 100 according to another embodiment of this application, and this application Figure 2 The embodiments are illustrated using a shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 140 in this application is not limited to a prefabricated energy storage module in a power generation / distribution energy storage scenario.

[0033] This application provides an energy storage system 100, which includes: a high-voltage cable 150, a first power conversion device 110, a second power conversion device 160, and an energy storage device 140 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 160 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 140 through grid connection. The energy storage device 140 is connected to the high-voltage cable and outputs smooth electricity to supply the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and ensuring stable grid operation; or, wind power... The conversion device is always connected to the high-voltage cable. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 140 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 140 together with the high-voltage cable 150 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0034] In some embodiments on the distribution network side, the first power conversion device 110 can be a photovoltaic panel, and the energy storage device 140 is connected to the high-voltage cable 150 and installed downstream of the high-voltage cable 150 between the user load and the user load. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 140, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 150 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0035] Optionally, the first power conversion device 110 may include, but is not limited to, a wind power conversion device, and the second power conversion device 160 may include, but is not limited to, a photovoltaic panel. The first power conversion device 110 and the second power conversion device 160 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0036] In some embodiments, see Figure 3 , Figure 3This is a schematic diagram of the structure of an energy storage system 100 according to another embodiment of this application, and this application Figure 3 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 140 of this application is not limited to an energy storage cabinet in an industrial and commercial energy storage scenario.

[0037] This application provides an energy storage system 100, which includes: an energy storage device 140, a high-voltage cable 150, a factory equipped with a first power conversion device 110, a photovoltaic-energy storage-charging station 170 equipped with a second power conversion device 160, and a vehicle 180. In some embodiments of industrial and commercial scenarios, the first power conversion device 110 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 140 in the factory. In the event of a power grid failure, the energy storage device 140 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 140 in conjunction with the high-voltage cable 150 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the second power conversion device 160 can also be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 140 of the photovoltaic-energy storage-charging station 170, directly charging the vehicle 180 through the photovoltaic-energy storage-charging station 170, which is fast and convenient.

[0038] Optionally, the first power conversion device 110 and the second power conversion device 160 may include, but are not limited to, photovoltaic panels. The first power 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 electrical energy.

[0039] Optionally, the energy storage device 140 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0040] Optionally, the energy storage device 140 may include, but is not limited to, single-cell batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / prefabricated energy storage compartments, and other battery integrated systems composed of single-cell batteries. The actual application form of the energy storage device 140 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 140. This application embodiment only uses a multi-cell battery of the energy storage device 140 as an example for illustration.

[0041] Optionally, the individual battery cells constituting the energy storage device 140 can be, but are not limited to, at least one of cylindrical, prismatic, prismatic, or other shaped batteries.

[0042] Optionally, the energy storage device 140 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0043] Optionally, the energy storage device 140 may include battery modules, battery packs, battery clusters, mobile power supplies, energy storage cabinets / prefabricated energy storage compartments, and other battery integrated systems composed of individual batteries. The actual application form of the energy storage device 140 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 140.

[0044] Alternatively, the single cell is not limited to at least one of cylindrical, square, prismatic, or other shaped cells.

[0045] Optionally, the single cell can be a rechargeable battery, which refers to a single cell that can be recharged after discharge to activate the active materials and continue to be used. The single cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0046] Please see Figure 4 and Figure 5 This application provides a negative electrode sheet 223, which includes a negative electrode current collector layer 2231 and a negative electrode material layer 2232 stacked together. The negative electrode material layer 2232 includes a carbon-based negative electrode material, a negative electrode binder, and a first additive. The negative electrode binder includes lithium polyacrylate, and the first additive has the following structural formula: .

[0047] Understandably, the negative electrode 223 is used in the battery 200. When the negative electrode 223 is assembled in the battery 200, the battery 200 also includes an electrolyte 210. The first additive in the negative electrode 223 will combine with the electrolyte 210 and dissolve in the electrolyte 210.

[0048] Optionally, the carbon-based anode material includes, but is not limited to, graphite, soft carbon, hard carbon, porous carbon, etc.

[0049] Understandably, the first additive comprises a quaternary ammonium salt cationic terminal, a phosphate ester anionic terminal, and a polymerizable double bond terminal. Specifically, the quaternary ammonium salt cationic terminal is a trimethylethylammonium cation, the phosphate ester anionic terminal has a phosphate diester structure, and the polymerizable double bond terminal is a methacrylate group.

[0050] Understandably, the negative electrode binder also includes styrene-butadiene rubber (SBR).

[0051] In this embodiment, the negative electrode binder of the negative electrode sheet 223 is lithium polyacrylate (PAA-Li). On the one hand, compared to polyacrylic acid, the lithium polyacrylate has been pre-lithiated, which can prevent the negative electrode binder from attacking solvent molecules in the electrolyte 210 due to the presence of protonated hydrogen. This reduces side reactions and improves the cycle performance of the battery 200 when the negative electrode sheet 223 is used. On the other hand, the carbon-based negative electrode material has a negatively charged surface, and the lithium polyacrylate, after dissociation, has a large number of negatively charged carboxylic acid groups. The two repel each other due to the same charge, making it difficult for the negative electrode binder to stably adhere to the surface of the negative electrode sheet 223. The negative electrode sheet 223 also includes the first additive, in which the negatively charged phosphate ester anion terminal tends to combine with the lithium ions in the lithium polyacrylate, so that the negative electrode binder is adsorbed on the surface of the negative electrode sheet 223. When the negative electrode 223 is applied to the battery 200 and the electrolyte 210 is filled, the first additive dissolves in the electrolyte 210. The first additive combines with the negative electrode binder and leaves empty sites on the surface of the negative electrode 223, which is beneficial for the electrolyte 210 to wet the negative electrode 223. This solves the problem of poor wettability of the negative electrode 223 caused by the application of lithium polyacrylate to the negative electrode 223, further improving lithium-ion transport efficiency and enhancing the kinetic performance and long-cycle performance of the battery 200.

[0052] Furthermore, when the negative electrode 223 is applied to the battery 200 and dissolved in the electrolyte 210, the first additive, comprising a quaternary ammonium salt cation terminal and a phosphate ester anion terminal, adsorbs onto the surface of the negative electrode 223 due to electrostatic adsorption. The first additive is closer to the negative electrode 223 than other components in the electrolyte 210. Further, since the first additive also includes polymerizable double bond terminals, it can undergo in-situ polymerization under electrochemical or thermal conditions to form a cross-linked polymer film, and the first additive has a low reduction potential. When the battery 200 is formed, the first additive preferentially forms an SEI film (Solid Electrolyte Interphase) on the surface of the negative electrode 223 compared to other components in the electrolyte 210. On the other hand, the quaternary ammonium salt cation end contains nitrogen, and the phosphate ester anion end contains phosphorus, so that the generated solid electrolyte interphase (SEI) film includes inorganic components such as nitrogen and phosphorus. These inorganic components improve the stability and density of the SEI film, effectively suppressing side reactions in the electrolyte 210. Furthermore, the polymerizable double bond ends decompose to form organic components, which improve the flexibility and adaptability of the SEI film to accommodate volume changes in the negative electrode 223 during charging and discharging, preventing cracking of the SEI film after a period of use. The quaternary ammonium salt cation end, the phosphate ester anion end, and the polymerizable double bond ends work together to construct an SEI film rich in both inorganic and organic components, ultimately giving the SEI film excellent structural stability, mechanical toughness, and ionic conductivity. This is beneficial for improving the cycle performance of the battery 200 when the negative electrode 223 is used in the battery 200, extending the battery's lifespan. On the other hand, the quaternary ammonium salt cation end and the phosphate ester anion end in the first additive form an amphoteric structure, which can construct a highly efficient lithium-ion transport channel within the SEI film through electrostatic and coordination interactions, promoting rapid lithium-ion conduction. Furthermore, the phosphate ester group contains a phosphoryl oxygen atom with a lone pair of electrons. This oxygen atom has strong negative charge and coordination ability, enabling it to coordinate with lithium ions, helping lithium ion dissociation and reducing lithium-ion association, resulting in a lower lithium-ion transition energy barrier and easier forward movement of lithium ions within the ion transport channel of the SEI film. Moreover, the polymerizable double bond end is a methacrylate group, which can undergo in-situ polymerization on the surface of the negative electrode 223 to form a thin, uniform, and flexible organic film layer. The SEI film formed on the surface of the negative electrode 223 by the first additive provided in this embodiment is thin and uniform, avoiding increased impedance due to excessive film thickness. Simultaneously, the lithium-ion transport channel constructed within the SEI film formed by the first additive also contributes to improving lithium-ion transport performance.In summary, the SEI film formed by the first additive provided in this application embodiment has both excellent stability and high ion conductivity. While achieving effective film formation protection, it significantly reduces interfacial impedance, thereby improving the long-cycle performance and kinetic performance of the negative electrode 223 when applied to the battery 200, and extending the service life of the battery 200.

[0053] Understandably, in the terminology of this application, formation refers to the first charge-discharge activation process of the battery 200 after assembly, during which an SEI film is formed on the surface of the negative electrode 223.

[0054] Understandably, the zwitterionic structure formed by the quaternary ammonium salt cation end and the phosphate ester anion end can construct a highly efficient lithium-ion transport channel because: the phosphate ester anion end has negatively charged oxygen sites, which can weakly coordinate with lithium ions, adsorbing and guiding the orderly migration of lithium ions; in addition, the quaternary ammonium salt cation end reduces the aggregation and hindrance of lithium ions during transport through electrostatic repulsion, lowering the lithium-ion transition energy barrier. The combination of the phosphate ester anion end and the quaternary ammonium salt cation end enables the construction of a continuous and efficient lithium-ion transport channel within the SEI film, significantly improving the ion conductivity of the SEI film and thus significantly reducing interfacial impedance.

[0055] Understandably, the negative electrode 223 comprises lithium polyacrylate and the first additive. Before the negative electrode 223 is applied to the battery 200 and before electrolyte is injected, the lithium polyacrylate combines with the first additive and occupies sites on the surface of the negative electrode 223. After the battery 200 is injected with electrolyte 210, on the one hand, the first additive dissolves in the electrolyte 210 to free up sites on the surface of the negative electrode 223, thereby improving the wetting of the negative electrode 223 by the electrolyte 210. On the other hand, the first additive can also serve as a film-forming additive, preferentially forming a film on the surface of the negative electrode 223, and the formed SEI film has good stability and density. Furthermore, the positively charged quaternary ammonium salt cation end in the first additive combines with the lithium salt anions in the electrolyte 210 to promote the dissociation of lithium salt, increase the conductivity of the electrolyte 210, improve the migration rate of lithium ions in the electrolyte 210, and ultimately improve the kinetic performance of the battery 200.

[0056] In some optional embodiments, in the negative electrode material layer 2232, the mass fraction of lithium polyacrylate is a, the mass of the negative electrode material layer 2232 is A1, the mass of the first additive is A2, and the mass percentage b of the first additive satisfies the relationship: b=A2 / (A1-A2), then the negative electrode material layer 2232 satisfies the relationship: 0.05≤10b / a≤40.

[0057] Optionally, the value of 10b / a can be, but is not limited to, 0.05, 0.1, 0.5, 1, 1.5, 4, 5, 8, 10, 12, 14, 16, 18, 20, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 36, 37, 38 and 40.

[0058] Understandably, b is the mass ratio of the first additive to the other components in the negative electrode material layer 2232.

[0059] Understandably, the mass fraction of the lithium polyacrylate is the ratio of the mass of the lithium polyacrylate to the mass of the negative electrode material layer 2232.

[0060] In this embodiment, when the negative electrode material layer 2232 satisfies the relationship 0.05≤10b / a≤40, the mass fraction of lithium polyacrylate and the mass ratio of the first additive in the negative electrode material layer 2232 are both within a reasonable range. On one hand, the negative electrode binder and the first additive work together to form sufficient sites on the surface of the negative electrode sheet 223. When the first additive dissolves in the electrolyte 210, the sites formed by the negative electrode binder and the first additive on the surface of the negative electrode sheet 223 are released, thereby improving the wetting performance of the electrolyte 210 on the negative electrode sheet 223. When the value of 10b / a is too large, the mass ratio b of the first additive is too large or the mass fraction a of lithium polyacrylate is too small. If the mass ratio b of the first additive is too large, it may cause the SEI film formed by the first additive on the surface of the negative electrode sheet 223 to be thick enough, which may increase the interfacial impedance and deteriorate the rate performance and charge / discharge efficiency of the battery 200. If the mass fraction of lithium polyacrylate is too small, the negative electrode binder will have difficulty effectively bonding the carbon-based negative electrode material and the first additive, causing the negative electrode sheet 223 to easily shed powder and material during rolling, slitting, or winding, thus reducing the processing performance of the negative electrode sheet 223. When the value of 10b / a is too small, the mass percentage b of the first additive is too small or the mass fraction a of the lithium polyacrylate is too large. If the mass percentage b of the first additive is too small, the first additive will have difficulty fully combining with the lithium polyacrylate, making it difficult for the negative electrode binder to adsorb onto the surface of the negative electrode sheet 223, resulting in fewer sites formed on the surface of the negative electrode sheet 223 after the first additive combines with the lithium polyacrylate. When the negative electrode sheet 223 is wetted by the electrolyte 210 and the first additive dissolves in the electrolyte 210, the sites formed on the surface of the negative electrode sheet 223 after the first additive combines with the lithium polyacrylate are released, but still few, making it difficult to effectively improve the wetting performance of the negative electrode sheet 223. If the mass fraction of lithium polyacrylate is too high, there will be too many negatively charged carboxylate ions in the negative electrode binder. Even with the presence of the first additive, a large number of free carboxylate ions will still accumulate on the surface of the negative electrode sheet 223, and many sites will be continuously occupied by the negative electrode binder. When the first additive dissolves in the electrolyte 210 and releases some sites, the remaining negative electrode binder will still hinder the wetting of the negative electrode sheet 223 by the electrolyte 210, increasing the conduction resistance of lithium ions, thereby resulting in poor rate performance and severe polarization of the battery 200.

[0061] In some optional embodiments, the mass fraction a of lithium polyacrylate in the negative electrode material layer 2232 ranges from 0.5% to a ≤ 3%.

[0062] Specifically, the value of a can be, but is not limited to, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.5%, 2.6%, 2.8%, and 3%.

[0063] In the negative electrode material layer 2232 provided in this embodiment, when the mass fraction a of lithium polyacrylate is within the range of 0.5% ≤ a ≤ 3%, the mass fraction of lithium polyacrylate is within a reasonable range. On the one hand, the negative electrode binder can fully exert its performance in bonding the carbon-based negative electrode material with the first additive, thereby preventing the negative electrode sheet 223 from shedding powder or material during rolling, slitting, or winding, and improving the performance of the negative electrode sheet 223. On the other hand, the number of sites formed by the negative electrode binder and the first additive on the surface of the negative electrode sheet 223 is within a reasonable range. When the first additive dissolves in the electrolyte 210, the sites formed by the negative electrode binder and the first additive on the surface of the negative electrode sheet 223 are released, thereby improving the wetting performance of the electrolyte 210 on the negative electrode sheet 223. When the mass fraction 'a' of lithium polyacrylate is too high, there are too many negatively charged carboxylate ions in the negative electrode binder. Even with the first additive present, a large number of free carboxylate ions will accumulate on the surface of the negative electrode sheet 223, and a large number of sites will be continuously occupied by the negative electrode binder. When the first additive dissolves in the electrolyte 210 and releases some sites, the negative electrode binder residue is still too high, which still hinders the wetting of the negative electrode sheet 223 by the electrolyte 210, increasing the lithium-ion conduction resistance, thereby resulting in poor rate performance and severe polarization of the battery 200. When the mass fraction 'a' of lithium polyacrylate is too low, the negative electrode binder has difficulty effectively bonding the carbon-based negative electrode material and the first additive in the negative electrode material layer 2232, thereby making the negative electrode sheet 223 prone to powder and material shedding during rolling, slitting, or winding, reducing the processing performance of the negative electrode sheet 223. Meanwhile, the carbon-based negative electrode material lacking the negative electrode binder coating may come into direct contact with the electrolyte 210, increasing side reactions and potentially continuously consuming the lithium salt in the electrolyte 210, causing the battery 200 to experience cycle degradation.

[0064] In some optional embodiments, the mass percentage b of the first additive in the negative electrode material layer 2232 is in the range of 0.01% ≤ b ≤ 2%.

[0065] Specifically, the value of b can be, but is not limited to, 0.01%, 0.03%, 0.08%, 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2%.

[0066] In this embodiment, when the mass percentage b of the first additive is within the range of 0.01% ≤ b ≤ 2%, the mass percentage b of the first additive is within a reasonable range. On one hand, the first additive fully binds to the lithium polyacrylate to form a sufficient number of sites on the surface of the negative electrode 223. When the negative electrode 223 is wetted by the electrolyte 210 and the first additive dissolves in the electrolyte 210, the sites formed on the surface of the negative electrode 223 after the first additive binds to the lithium polyacrylate are released, which can effectively improve the wetting performance of the electrolyte 210 on the negative electrode 223. On the other hand, the first additive preferentially adheres to the surface of the negative electrode 223 and forms a thin, uniform, high-quality SEI film on the surface of the negative electrode 223, containing both inorganic and organic components and with efficient lithium-ion transport channels. This SEI film effectively blocks direct contact between the negative electrode 223 and the electrolyte 210, reduces the continuous reduction and decomposition of other components in the electrolyte 210, suppresses side reactions in the electrolyte 210, and improves the initial capacity of the battery 200. Simultaneously, the SEI film has high lithium-ion transport efficiency, which reduces interfacial impedance, thereby significantly improving the cycle stability of the battery 200. Furthermore, it avoids the increase in viscosity and decrease in ion conduction rate of the electrolyte 210 due to excessive use of the first additive, while preventing excessive thickness of the interfacial film from increasing interfacial impedance, ensuring that the electrolyte 210 possesses excellent kinetic performance, and enabling the battery 200 to achieve a good balance between long cycle life and low impedance, high rate performance. When the mass percentage of the first additive is too high, the mass fraction of the negative electrode binder and carbon-based negative electrode material in the negative electrode sheet 223 is correspondingly too low, reducing the bonding performance and energy density of the negative electrode sheet 223. When the first additive dissolves in the electrolyte 210, it may cause the viscosity of the electrolyte 210 to be too high, reducing the migration rate of lithium ions in the electrolyte 210, thus weakening the ion conduction capacity and kinetic performance of the electrolyte 210. In addition, it may also cause the SEI film formed by the first additive on the surface of the negative electrode sheet 223 to be too thick, thereby increasing the interfacial impedance and deteriorating the rate performance and charge / discharge efficiency of the battery 200. When the mass percentage of the first additive is too low, on the one hand, the first additive is difficult to fully combine with the lithium polyacrylate, thus making it difficult for the negative electrode binder to adsorb onto the surface of the negative electrode sheet 223, and the number of sites formed on the surface of the negative electrode sheet 223 after the first additive combines with the lithium polyacrylate is small. When the negative electrode 223 is wetted by the electrolyte 210 and the first additive is dissolved in the electrolyte 210, the sites formed on the surface of the negative electrode 223 after the first additive combines with the lithium polyacrylate are released, but still in small quantities, making it difficult to effectively improve the wettability of the negative electrode 223.On the other hand, after the first additive dissolves in the electrolyte 210, it is difficult for the first additive to form a thin and uniform SEI film with lithium-ion transport channels inside on the surface of the negative electrode 223. As a result, it cannot effectively suppress the side reactions of the electrolyte 210, nor can it significantly reduce the interface impedance. It is difficult to effectively improve the cycle performance of the battery 200, and the cycle stability of the battery 200 is poor.

[0067] This application also provides a battery 200, which includes: a negative electrode 223, a separator 222, a positive electrode 221, and an electrolyte 210 provided in this application. The separator 222 is disposed on one side of the negative electrode 223; the positive electrode 221 is disposed on the side of the separator 222 opposite to the negative electrode 223; and the electrolyte 210 is used to wet at least a portion of the negative electrode 223, the separator 222, and the positive electrode 221.

[0068] Understandably, the battery 200 includes an electrode assembly 220, which includes a positive electrode 221, a separator 222 and a negative electrode 223 stacked together, and the electrolyte 210 is used to wet at least a portion of the electrode assembly 220.

[0069] Optionally, the battery 200 can be, but is not limited to, a square battery, a round battery, etc.

[0070] In this embodiment, the battery 200 includes a negative electrode 223 provided in this application. The negative electrode 223 includes lithium polyacrylate and a first additive. The lithium polyacrylate and the first additive are combined to occupy sites on the surface of the negative electrode 223. When the electrolyte 210 wets the electrode assembly 220, the first additive dissolves in the electrolyte 210 and vacates sites, so that the electrolyte 210 can fully wet the negative electrode 223, improving lithium-ion transport efficiency and enhancing the kinetic performance and long-cycle performance of the battery 200. Furthermore, compared to other components in the electrolyte 210, the first additive preferentially undergoes a reduction reaction on the surface of the negative electrode 223 to form a thin, uniform, high-quality SEI film containing both inorganic and organic components and with efficient lithium-ion transport channels. This SEI film effectively blocks direct contact between the negative electrode 223 and the electrolyte 210, reduces the continuous reduction and decomposition of other components in the electrolyte 210, suppresses side reactions in the electrolyte 210, and improves the initial capacity of the battery 200. Simultaneously, the SEI film has high lithium-ion transport efficiency, which reduces interfacial impedance, thereby significantly improving the cycle stability of the battery 200.

[0071] In some optional embodiments, the electrolyte 210 further includes a lithium salt, wherein the mass fraction c of the lithium salt in the electrolyte 210 is in the range of 5% ≤ c ≤ 20%.

[0072] Understandably, the mass fraction c of the lithium salt can be, but is not limited to, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 14.5%, 15%, and 20%.

[0073] Understandably, the mass fraction c of the lithium salt is the ratio of the mass of the lithium salt to the mass of the electrolyte 210.

[0074] In the electrolyte 210 provided in this embodiment, when the mass fraction c of the lithium salt meets the range of 5%≤c≤20%, the mass fraction of the lithium salt is within a reasonable range. On the one hand, this ensures that there are sufficient lithium ions in the electrolyte 210, giving the electrolyte 210 a high ionic conductivity. At the same time, it ensures that lithium ions can migrate quickly and stably in the electrolyte 210, improving the rate performance and charge / discharge efficiency of the battery 200 when the electrolyte 210 is applied. On the other hand, it also allows the lithium salt to fully dissociate, ensuring that the electrolyte 210 system is uniform and stable, avoiding problems such as excessive viscosity, salting out, and crystallization. Thus, the electrolyte 210 has good kinetic performance and electrochemical stability. When the mass fraction of the lithium salt is too high, it may increase the viscosity of the electrolyte 210, exacerbating the migration resistance of lithium ions in the electrolyte 210. Simultaneously, it may cause insufficient dissociation of the lithium salt, reducing the uniformity and stability of the electrolyte 210. The electrolyte 210 is prone to salting out, crystallization, and system inhomogeneity, easily triggering side reactions and leading to a decline in the cycle performance of the battery 200. When the mass fraction of the lithium salt is too low, the concentration of lithium ions in the electrolyte 210 is insufficient, reducing the ionic conductivity of the electrolyte 210, thereby affecting the rate performance and cycle stability of the battery 200 when the electrolyte 210 is used.

[0075] In some optional embodiments, the electrolyte 210 satisfies the relationship: 0.05 ≤ 100b / c ≤ 20.

[0076] Specifically, the value of 100b / c can be, but is not limited to, 0.05, 0.08, 0.1, 0.15, 0.2, 0.5, 0.8, 1, 5, 6, 8, 10, 12, 15, 16, 18 and 20.

[0077] In the electrolyte 210 provided in this embodiment, when the 100b / c ratio meets the range of 0.05≤100b / c≤20, the mass ratio of the first additive and the mass fraction of the lithium salt are both within a reasonable range, and the first additive and the lithium salt form a good synergistic effect. On the one hand, the quaternary ammonium salt cation terminal in the first additive is easy to combine with the negatively charged anion in the lithium salt, and the phosphoryl oxygen atom with lone pair electrons in the phosphate ester group is easy to coordinate with lithium ions, thereby promoting the dissociation of lithium salt, increasing the migration number of lithium ions in the electrolyte 210, enabling more lithium ions to participate in the insertion / extraction and migration during the charging and discharging process, improving the lithium ion transport efficiency and utilization rate, and improving the rate performance, charge / discharge efficiency and cycle stability of the battery 200. On the other hand, under the action of the first additive, the anions in the lithium salt have higher reduction activity and are more likely to undergo reduction reaction on the surface of the negative electrode 223, thereby forming an SEI film rich in inorganic components, which blocks the direct contact between the electrolyte 210 and the negative electrode 223 and further enhances the interfacial stability of the negative electrode 223. When the b / c value is too large, the mass ratio of the first additive is too large, or the mass fraction of the lithium salt is too small, which may increase the viscosity of the electrolyte 210, resulting in insufficient lithium ion concentration and decreased ionic conductivity in the electrolyte 210. At the same time, it will cause the formed SEI film to be too thick and the interfacial impedance to increase, which is not conducive to lithium salt dissociation and synergistic film formation, and reduces the rate performance and cycle stability of the battery 200. When the b / c value is too small, the mass percentage of the first additive is too small, or the mass fraction of the lithium salt is too large, the first additive is difficult to effectively promote the dissociation of the lithium salt, increase the migration number of lithium ions in the electrolyte 210, and is also difficult to fully improve the reduction activity of anions in the lithium salt. Ultimately, it is difficult to form a well-structured SEI film on the surface of the negative electrode 223. When the electrolyte 210 is applied to the battery 200, the cycle stability of the battery 200 is poor.

[0078] In some optional embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorodioxalate phosphate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfinate, and lithium 4,5-dicyano-2-trifluoromethyl-imidazolium.

[0079] In this embodiment, when the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorodioxalate phosphate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfinate, and lithium 4,5-dicyano-2-trifluoromethyl-imidazolium, the lithium salt has the characteristics of strong dissociation ability, high ionic conductivity, and good electrochemical stability, which can provide a sufficient and stable source of lithium ions for the electrolyte 210 and improve the ion conduction performance of the electrolyte 210. When the lithium salt is compounded with the first additive, the interaction between the quaternary ammonium salt cation and anion and the coordination between the phosphate ester group and the lithium ion can further promote the dissociation of the lithium salt, increase the lithium ion transference number, and optimize the film structure, so that the electrolyte 210 has high ionic conductivity, excellent film formation and good cycle stability, thereby significantly improving the comprehensive electrochemical performance of the battery 200.

[0080] In some optional embodiments, the electrolyte 210 further includes a second additive, which includes at least one selected from fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, ethylene sulfate, ethylene disulfate, ethylene sulfite, methylene disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, adiponitrile, succinate, 1,3,6-hexanetrionitrile, 2-fluoropyridine, and hexamethylene diisocyanate.

[0081] Understandably, the second additive is a film-forming additive.

[0082] In this embodiment, when the second additive includes at least one of fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, ethylene sulfate, ethylene disulfate, ethylene sulfite, methylene disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, adiponitrile, succinate, 1,3,6-hexanetrionitrile, 2-fluoropyridine, and hexamethylene diisocyanate, the second additive works in conjunction with the first additive to form a dense, stable, and low-resistance SEI film on the surface of the negative electrode 223, effectively suppressing the side reactions of the electrolyte 210, improving the interfacial stability of the negative electrode 223, and improving the cycle performance of the battery 200.

[0083] In some optional embodiments, the mass fraction of the second additive in the electrolyte 210 is d, and the mass fraction d of the second additive is in the range of 0.5% ≤ d ≤ 5%.

[0084] Specifically, the mass fraction d of the second additive can be, but is not limited to, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, and 5%.

[0085] In the electrolyte 210 provided in this embodiment, when the mass fraction d of the second additive is within the range of 0.5% ≤ d ≤ 5%, the mass fraction of the second additive is within a reasonable range. The second additive, in combination with the first additive, can form a dense, stable, and low-resistance solid interface protective film on the surface of the negative electrode 223, effectively suppressing side reactions in the electrolyte 210, improving the interface stability of the negative electrode 223, and extending the cycle life of the battery 200. When the mass fraction of the second additive is too high, it may cause the viscosity of the electrolyte 210 to increase, increasing the transport impedance of lithium ions in the electrolyte 210. Simultaneously, it may cause the thickness of the SEI film formed on the surface of the negative electrode 223 to be too large, increasing the interface impedance and weakening the cycle performance of the battery 200. When the mass fraction of the second additive is too low, even when combined with the first additive, it is difficult for the second additive to form a complete and effective protective film on the surface of the negative electrode 223, thus making it difficult for the second additive to fully exert its interface modification and stabilizing effects.

[0086] In some optional embodiments, the electrolyte 210 further includes a solvent comprising at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethylene glycol dimethyl ether.

[0087] In this embodiment, the solvent provides a stable dissolution environment for the first and second additives, ensuring that the first and second additives form an orderly film on the surface of the negative electrode 223. The solvent, lithium salt, first additive, and second additive form a multi-component synergistic effect, ultimately enabling the electrolyte 210 to possess excellent ion conductivity, wide temperature range adaptability, and high electrochemical stability, comprehensively improving the rate performance and high and low temperature operating capabilities of the battery 200, while extending the cycle life of the battery 200.

[0088] The technical solution of this application will be further described below with reference to several embodiments: Examples 1 to 17, Comparative Examples 1 to 7: 1. Preparation of electrolyte 210: In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were uniformly mixed at a mass ratio of 1:1:1. The dried electrolyte lithium salt lithium hexafluorophosphate was dissolved in the solvent and fully dissolved. Then, the lithium salt and the second additive were added and mixed thoroughly to obtain the electrolyte 210 of Examples 1 to 17 and Comparative Examples 1 to 7.

[0089] The types of the second additive, the mass fraction d of the second additive, and the mass fraction c of the lithium salt are shown in Table 1.

[0090] 2. Fabrication of electrode assembly 220: (1) Preparation of positive electrode 221: Lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and PVDF binder were mixed at a mass ratio of 97.2:2.3:0.5. Then, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 60 wt%, which was stirred evenly. The positive electrode slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil current collector. After drying, cold pressing, slitting, and cutting, positive electrode sheet 221 was obtained. The single-sided thickness of the positive electrode active material layer was 100 μm.

[0091] (2) Preparation of negative electrode 223: With a specific surface area of ​​1.1m 2 A mixture of artificial graphite (a negative electrode active material), sodium carboxymethyl cellulose (CMC) thickener, conductive carbon black (Super-P), and negative electrode binder in a mass ratio of 96:0.5:0.5:3, wherein the negative electrode binder comprises styrene-butadiene rubber latex (SBR) and lithium polyacrylate, is further mixed with a first additive and deionized water to form a negative electrode slurry with a solid content of 50 wt%, and stirred evenly. The negative electrode slurry is uniformly coated on one surface of a 6 μm thick copper foil for the negative electrode current collector. After drying, cold pressing, slitting, and cutting, negative electrode sheet 223 is obtained. The single-sided thickness of the negative electrode active material layer is 70 μm.

[0092] The structural formula of the first additive is as follows: The mass percentage b of the first additive, the mass fraction a of the negative electrode binder lithium polyacrylate, 10b / a, and 100b / c are shown in Table 1. The mass fraction of the styrene-butadiene rubber latex varies with the mass fraction of lithium polyacrylate.

[0093] (3) Preparation of diaphragm 222: A 16µm polypropylene (PP) film is used as the separator 222.

[0094] 3. Assembly of battery 200: The positive electrode 221, separator 222, and negative electrode 223 are stacked in sequence, with the separator 222 acting as a separator between the positive electrode 221 and the negative electrode 223. Then, they are wound into a bare cell. After welding the tabs, the bare cell 200 is placed in an outer packaging shell, dried, and then injected with the electrolyte 210. After vacuum sealing, standing, formation, and shaping, the implementation cells 1 to 17 and the comparative cells 1 to 7 are finally prepared.

[0095] In this embodiment, the negative electrode 223 and electrolyte 210 of Example 1 are used in the experimental battery 1, the negative electrode 223 and electrolyte 210 of Example 2 are used in the experimental battery 2, the negative electrode 223 and electrolyte 210 of Comparative Example 1 are used in the control battery 1, and so on.

[0096] Table 1 below shows the component parameters of the negative electrode 223 and electrolyte 210 of Examples 1 to 17 and Comparative Examples 1 to 7.

[0097] Table 1: Component parameters of negative electrode 223 and electrolyte 210 in Examples 1 to 17 and Comparative Examples 1 to 7.

[0098]

[0099] Understandably, as shown in Table 1, the negative electrode 223 in Comparative Examples 1 to 5 does not include the first additive, and the mass percentage of the first additive in the negative electrode 223 in Comparative Examples 1 to 5 is 0.

[0100] Battery 200 performance test: 1. Charge-discharge cycle tests were performed on batteries 1 to 17 and control batteries 1 to 7. The experimental batteries 1 to 17 and the control batteries 1 to 7 were sequentially placed on a charge / discharge apparatus for constant current charge / discharge cycle testing. The test temperature was 45℃, and the charge / discharge rate was 0.5C (the magnitude of the charge / discharge current is usually expressed by the charge / discharge rate, and the calculation formula for the charge / discharge current is: charge / discharge current = charge / discharge rate × rated capacity of battery 200). The charge / discharge voltage window was 2.5V~3.65V (that is, the charging cut-off voltage of battery 200 is 3.65V, and the discharging cut-off voltage of battery 200 is 2.5V). The capacity retention rate after 500 cycles was calculated using the formula: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%. One complete charge / discharge cycle is usually referred to as one charge / discharge cycle, meaning that battery 200 is first charged from 2.5V to 3.65V, and then discharged from 3.65V to 2.5V, thus forming one charge / discharge cycle. N cycles are performed by repeating the above process N times.

[0101] Table 2 shows the capacity retention rates of implementation batteries 1 to 17 and control batteries 1 to 7 after 500 cycles at 45°C.

[0102] Understandably, this application uses the capacity retention rate of the battery 200 after 500 cycles at 45°C as the standard for evaluating the cycle performance of the battery 200. Compared with the performance test of the battery 200 at room temperature, the interface stability of the negative electrode 223 of the battery 200 will be more severely damaged at high temperature, which is a better characterization of the cycle performance of the battery 200.

[0103] 2. Energy efficiency tests were conducted on batteries 1 to 17 and control batteries 1 to 7. The experimental batteries 1 to 17 and the control batteries 1 to 7 were placed sequentially on the charge / discharge meter for two cycles of constant power charge / discharge testing. The test temperature was 25℃. The batteries were charged at a constant power of 0.5P (0.5P = 0.5 × rated capacity of battery 200 × median battery voltage of 3.2V). The charge / discharge voltage window was 2.5V~3.65V (i.e., the charging cutoff voltage of battery 200 is 3.65V, and the discharging cutoff voltage of battery 200 is 2.5V; the energy efficiency of the second cycle = the discharge energy of the battery / the charging energy of the battery).

[0104] The efficiency values ​​of the implementation batteries 1 to 17 and the comparative batteries 1 to 7 in the second cycle at 25°C are shown in Table 2.

[0105] Table 2: Performance parameters of implementation batteries 1 to 17 and comparison batteries 1 to 7.

[0106]

[0107] Please refer to Tables 1 and 2. From the data of Examples 1 to 7 and Comparative Examples 1 to 7, it can be seen that the negative electrode 223 of Examples 1 to 7 all include the first additive and the mass percentage of the first additive meets the reasonable range of 0.01% ≤ b ≤ 2%. The negative electrode 223 of Comparative Examples 1 to 5 does not include the first additive. The mass fraction of the first additive in the negative electrode 223 of Comparative Example 6 is too small, so that the value of 10b / a is too small. The mass fraction of the first additive in the negative electrode 223 of Comparative Example 7 is too large. Therefore, the capacity retention rate of Implemented Battery 1 to Implemented Battery 10 after 500 cycles at 45°C is higher than that of Comparative Battery 1 to Comparative Battery 7 after 500 cycles at 45°C. Moreover, the capacity retention rate of Comparative Battery 6 and Comparative Battery 7 after 500 cycles at 45°C is higher than that of Comparative Battery 1 to Comparative Battery 5 after 500 cycles at 45°C. This is because: when the negative electrode 223 is applied to the battery 200 before electrolyte is injected, the lithium polyacrylate combines with the first additive and occupies sites on the surface of the negative electrode 223. When the battery 200 is injected with electrolyte 210, on the one hand, the first additive dissolves in the electrolyte 210, thereby freeing up the sites occupied on the surface of the negative electrode 223 and improving the wetting of the negative electrode 223 by the electrolyte 210. On the other hand, the first additive can also serve as a film-forming additive. Due to electrostatic adsorption, the first additive is adsorbed onto the surface of the negative electrode 223. Furthermore, compared to other components in the electrolyte 210, the first additive preferentially undergoes a reduction reaction on the surface of the negative electrode 223 to form a thin, uniform, high-quality SEI film containing both inorganic and organic components and with efficient lithium-ion transport channels. This SEI film effectively blocks direct contact between the negative electrode 223 and the electrolyte 210, reduces side reactions in the electrolyte 210, and ultimately gives the corresponding battery 200 better cycle stability. The SEI film preferentially forms on the surface of the negative electrode 223 and exhibits good stability and density. On the other hand, the positively charged quaternary ammonium salt cation in the first additive combines with the lithium salt anions in the electrolyte 210 to promote the dissociation of lithium salt, increase the conductivity of the electrolyte 210, enhance the migration rate of lithium ions in the electrolyte 210, and ultimately improve the kinetic performance of the battery 200. Furthermore, data from Comparative Examples 1 to 7 show that adding the first additive to the negative electrode 223 improves the kinetic performance of the corresponding battery 200.

[0108] Further, please refer to Examples 1 to 7. Under the same conditions, as the mass ratio of the first additive gradually increases, the values ​​of 10b / a and 100b / c also gradually increase. The capacity retention rate of the corresponding battery 200 after 500 cycles at 45°C shows a trend of first increasing and then decreasing. The energy efficiency of the corresponding battery 200 after the second cycle at 25°C gradually decreases. This is because the negatively charged phosphate ester anion terminal in the first additive tends to combine with lithium ions in lithium polyacrylate, so that the negative electrode binder is adsorbed on the surface of the negative electrode sheet 223. When the negative electrode 223 is applied to the battery 200 and the electrolyte 210 is filled, the first additive dissolves in the electrolyte 210. The first additive combines with the negative electrode binder and leaves empty sites on the surface of the negative electrode 223, which is beneficial for the electrolyte 210 to wet the negative electrode 223. This solves the problem of poor wettability of the negative electrode 223 caused by the application of lithium polyacrylate to the negative electrode 223, further improving lithium-ion transport efficiency and enhancing the kinetic performance and long-cycle performance of the battery 200. Furthermore, when the first additive dissolves in the electrolyte 210, it preferentially adheres to the surface of the negative electrode 223, forming a thin, uniform, high-quality SEI film on the surface of the negative electrode 223. This SEI film contains both inorganic and organic components and has an efficient lithium-ion transport channel. This SEI film effectively blocks direct contact between the negative electrode 223 and the electrolyte 210, reducing the continuous reduction and decomposition of other components in the electrolyte 210, suppressing side reactions in the electrolyte 210, and improving the initial capacity of the battery 200 when the electrolyte 210 is applied. Simultaneously, the SEI film has high lithium-ion transport efficiency and can reduce interfacial impedance, thereby significantly improving the cycle stability of the battery 200. However, as the mass percentage of the first additive increases, the viscosity of the electrolyte 210 may increase, which in turn reduces the migration rate of lithium ions in the electrolyte 210, weakens the ion conduction capacity and kinetic performance of the electrolyte 210, thereby reducing the energy efficiency of the corresponding battery 200 and decreasing the cycle stability of the corresponding battery 200.

[0109] Furthermore, please refer to Examples 5, 8 to 11. Under the same conditions, the cycle performance of the corresponding battery 200 can be improved by adjusting the type of the second additive. The second additive forms a film after the first additive reacts and decomposes. When the second additive is vinylene carbonate or ethylene ethylene carbonate, it will work with the first additive to form a "film of inorganic components containing N / P - polymerized organic components - polymerized organic components", that is, an inner inorganic component film and an outer double organic component film. When the second additive is fluoroethylene carbonate, ethylene sulfate, ethylene disulfate, or other additives, it will work with the first additive to form a "film of inorganic components containing N / P - polymerized organic components - inorganic components containing F or S" on the negative electrode surface, that is, an inner inorganic component, a middle organic component, and an outer inorganic component film. Compared with the inner inorganic and outer double organic component film, this inorganic-organic component alternating interface film has a more compact component connection and a more stable interface, resulting in better cycle performance. However, at the same time, this compact interface film will lead to an increase in interface impedance and hinder lithium-ion transport, resulting in a decrease in cell efficiency. Further data from Examples 9 and 10 show that if the second additive is a sulfur-containing sulfate ester additive and the outermost layer is an inorganic component film containing sulfate, it can accelerate lithium-ion transport and improve the energy efficiency of the battery cell to a certain extent.

[0110] Further, referring to Examples 12 to 15, under the same conditions, as the mass fraction of lithium salt gradually increases, the value of 100b / c gradually decreases. The capacity retention rate of the corresponding battery 200 after 500 cycles at 45°C shows a trend of first increasing and then decreasing. This is because: as the mass fraction of lithium salt increases, the number of lithium ions in the electrolyte 210 increases, resulting in higher ionic conductivity of the electrolyte 210. However, as the mass fraction of lithium salt gradually increases, the viscosity of the electrolyte 210 increases, exacerbating the migration resistance of lithium ions in the electrolyte 210, which in turn reduces the ionic conductivity of the electrolyte 210 and causes a decrease in the cycle performance of the corresponding battery 200.

[0111] Furthermore, please refer to Examples 7, 16, and 17. Under the same conditions, adjusting the mass fraction 'a' of the lithium polyacrylate can correspondingly adjust the value of 10b / a. When the value of 10b / a satisfies the range 0.05 ≤ 10b / a ≤ 40, the corresponding battery 200 has better cycle performance.

[0112] Please see Figure 6 and Figure 7 This application also provides an electrical device 300, which includes a device body 310 and a battery 200 provided in this application, wherein the battery 200 supplies power to the device body 310.

[0113] Understandably, the device body 310 and the battery 200 are electrically connected.

[0114] In this embodiment, the battery 200 includes the negative electrode 223 provided in this application, and the battery 200 has good cycle stability and high rate efficiency. When the battery 200 is applied to the electrical device 300, the battery 200 can provide stable power to the device body 310, which is beneficial to improving the user experience.

[0115] Optionally, the electrical device 300 in this application embodiment can be, but is not limited to, portable electronic devices such as mobile phones, tablets, laptops, desktop computers, smart bracelets, smartwatches, e-readers, and game consoles. It can also be a vehicle such as a car, truck, sedan, van, freight train, high-speed train, or electric vehicle. Furthermore, it can be various household appliances. Figure 6 In this embodiment, the electrical equipment 300 is an energy storage battery cabinet.

[0116] It is understood that the electrical equipment described in this embodiment is merely one form of electrical equipment used with the battery, and should not be construed as a limitation on the electrical equipment provided in this application, nor should it be construed as a limitation on the electrical equipment provided in various embodiments of this application.

[0117] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet comprises a negative electrode current collector layer and a negative electrode material layer arranged in a stack, the negative electrode material layer comprises a carbon-based negative electrode material, a negative electrode binder and a first additive, the negative electrode binder comprises lithium polyacrylate, and the structural formula of the first additive is .

2. The negative electrode sheet according to claim 1, characterized in that, In the negative electrode material layer, the mass fraction of lithium polyacrylate is a, the mass of the negative electrode material layer is A1, the mass of the first additive is A2, and the mass ratio of the first additive is b, which satisfies the relationship: b=A2 / (A1-A2). Then, the negative electrode material layer satisfies the relationship: 0.05≤10b / a≤40.

3. The negative electrode sheet according to claim 1, characterized in that, In the negative electrode material layer, the mass fraction 'a' of lithium polyacrylate is in the range of 0.5% ≤ a ≤ 3%.

4. The negative electrode sheet according to claim 1, characterized in that, In the negative electrode material layer, the mass percentage b of the first additive is in the range of 0.01% ≤ b ≤ 2%.

5. A battery, characterized in that, The battery includes: The negative electrode sheet according to any one of claims 1 to 4; A diaphragm is disposed on one side of the negative electrode sheet; A positive electrode, wherein the positive electrode is disposed on the side of the separator opposite to the negative electrode; and An electrolyte used to wet at least a portion of the negative electrode, the diaphragm, and the positive electrode.

6. The battery according to claim 5, characterized in that, In the negative electrode material layer, the mass percentage of the first additive is b; the electrolyte includes lithium salt, and the mass fraction of lithium salt in the electrolyte is c. Then the battery satisfies the relationship: 0.05≤100b / c≤20.

7. The battery according to claim 6, characterized in that, In the electrolyte, the mass fraction c of the lithium salt is in the range of 5% ≤ c ≤ 20%.

8. The battery according to claim 5, characterized in that, The electrolyte includes a second additive, which includes at least one of the following: fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, ethylene sulfate, ethylene disulfate, ethylene sulfite, methylene disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, adiponitrile, succinate, 1,3,6-hexanetrionitrile, 2-fluoropyridine, and hexamethylene diisocyanate.

9. The battery according to claim 8, characterized in that, In the electrolyte, the mass fraction of the second additive is d, and the range of the mass fraction d of the second additive is: 0.5%≤d≤5%.

10. An electrical appliance, characterized in that, The electrical equipment includes: The equipment itself; and The battery of claim 9, wherein the battery supplies power to the device body.

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