Lithium ion battery

Abstract

The application relates to the technical field of batteries, in particular to a lithium ion battery. The lithium ion battery comprises an aluminum plastic film and an electrode assembly, the electrode assembly is located in a containing space formed by the aluminum plastic film; the electrode assembly comprises a positive electrode sheet, a diaphragm and a negative electrode sheet which are stacked; the aluminum plastic film comprises a main body part and first and second side covers which are respectively located on the two sides of the main body part, the first side cover comprises a first area and a second area, the thickness of the first area is greater than that of the second area, and the difference between the thickness of the first area and that of the second area is 1-15 mu m; the first area has an endothermic peak at 100-140 DEG C in a differential scanning calorimetry test; the lithium ion battery further comprises an electrolyte, and the electrolyte comprises a fluorosulfonyl amide compound. The lithium ion battery has better furnace temperature safety performance and high-temperature cycle performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a lithium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles and consumer electronics, pouch lithium-ion batteries have become the mainstream choice for power batteries and portable batteries due to their advantages such as high energy density, lightweight design, and flexible shape. The pursuit of furnace temperature safety performance and long cycle life in lithium-ion batteries has also become a current research focus. Summary of the Invention

[0003] The purpose of this invention is to achieve a balance between furnace temperature safety and long cycle life, providing a lithium-ion battery. This lithium-ion battery, by incorporating a first region with specific thermal response characteristics and a thickness different from other regions on the aluminum-plastic film, provides a controllable pressure relief window when abnormal heat or gas generation occurs inside the battery, reducing the probability of thermal runaway under abuse conditions such as furnace temperature testing. Simultaneously, the use of an electrolyte containing a fluorosulfonamide compound effectively mitigates the adverse effects of the specific aluminum-plastic film structure of this invention on high-temperature cycle stability.

[0004] This invention provides a lithium-ion battery, comprising an aluminum-plastic film and an electrode assembly, the electrode assembly being located within a space formed by the aluminum-plastic film; the electrode assembly comprising a positive electrode, a separator, and a negative electrode stacked together; the aluminum-plastic film comprising a main body and a first side cover and a second side cover respectively located on both sides of the main body, the first side cover comprising a first region and a second region, the thickness of the first region being greater than the thickness of the second region, and the difference between the thickness of the first region and the thickness of the second region being 1μm-15μm; the first region exhibiting an endothermic peak at 100℃-140℃ in differential scanning calorimetry; the lithium-ion battery further comprising an electrolyte comprising a fluorosulfonamide compound.

[0005] This invention provides a first region with a low-melting-point layer on at least one side surface of an aluminum-plastic film, creating a thickness difference between the first region and a second region. This first region undergoes a physical state change when the internal temperature of the battery exceeds a set threshold, thereby forming a controllable pressure relief channel in the encapsulation structure, promptly releasing accumulated high-temperature gas and pressure. This effectively improves the battery's pressure release capability and avoids systemic safety risks caused by internal pressure accumulation without significantly sacrificing the original sealing reliability of the encapsulation structure.

[0006] However, in practical applications, it has been found that due to the thickness difference between the first region and other regions (such as the second region), this structure, due to the loose sealing at the edges, allows moisture from the external environment to easily penetrate into the battery during long-term use. As moisture accumulates, under specific operating conditions, this moisture reacts with the electrolyte in the battery to generate corrosive hydrofluoric acid (HF), which corrodes the interfacial film on the positive and negative electrode surfaces, thereby damaging the electrode materials, leading to battery capacity decay and decreased reliability, and severely affecting the battery's high-temperature cycle performance.

[0007] To address the aforementioned problems, this invention further employs fluorosulfonamide compounds. Fluorosulfonamide compounds possess unique chemical properties, enabling them to react with HF and reduce the concentration and activity of HF within the battery through neutralization and complexation mechanisms. This mitigates the corrosive effects of HF on internal battery components, reducing battery malfunctions and performance degradation caused by corrosion. Simultaneously, as alkaline solvents, fluorosulfonamide compounds can regulate the internal chemical environment of the battery, making it more stable and contributing to improved overall battery reliability and lifespan, ensuring stable performance during long-term operation.

[0008] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: the lithium-ion battery of the present invention has better furnace temperature safety performance and high temperature cycle performance.

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0010] Figure 1 The figure shown is a cross-sectional schematic diagram of the gasket along the thickness direction in an embodiment of the present invention.

[0011] Figure 2 The image shown is a front view of a lithium-ion battery in an example of the present invention. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0013] This invention provides a lithium-ion battery comprising an aluminum-plastic film and an electrode assembly. The electrode assembly is located within a space formed by the aluminum-plastic film and includes a positive electrode, a separator, and a negative electrode stacked together. The aluminum-plastic film includes a main body and a first side cover and a second side cover located on both sides of the main body. The first side cover includes a first region and a second region. The thickness of the first region is greater than the thickness of the second region, and the difference between the thickness of the first region and the thickness of the second region is 1μm-15μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, or 15μm.

[0014] This invention improves the aluminum-plastic film structure to achieve both good sealing and furnace temperature safety in lithium-ion batteries. A first region and a second region are formed on the first side cover of the aluminum-plastic film. The first region has a low-melting-point layer. When a large amount of gas or heat is generated inside the battery, this low-melting-point layer melts first, forming an opening. This allows the gas generated inside the battery, carrying heat, to escape through the opening, achieving directional pressure relief at high temperatures. This prevents thermal runaway problems that may be caused by violent gas and heat generation, improving the battery's furnace temperature safety performance. This method does not degrade energy density and ensures sealing performance at room temperature. Furthermore, there is a thickness difference between the first and second regions. Limiting this thickness difference within a suitable range allows the battery to balance energy density and pressure relief capability. When the thickness difference is small (e.g., less than 1 μm), the pressure relief efficiency of the first region is insufficient or fails at high temperatures, which is detrimental to improving the battery's furnace temperature safety performance. Conversely, when the thickness difference is large (e.g., greater than 15 μm), the width of the battery after sealing increases significantly, which is detrimental to improving the battery's energy density.

[0015] In this invention, the first region exhibits an endothermic peak in the differential scanning calorimetry (DSC) range of 80°C to 140°C, for example, at 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C, or any two of these ranges. The method for DSC testing the first region is as follows: the aluminum-plastic film of the battery is disassembled, soaked in alcohol to completely remove residual adhesive, and the endothermic peak position is obtained by DSC testing on the aluminum-plastic film located in the first region. The testing method refers to ISO 11357-1:2021.

[0016] In this invention, the lithium-ion battery further includes an electrolyte, which comprises a fluorosulfonamide compound.

[0017] <Aluminum-plastic film> In one example, the aluminum-plastic film includes an inner layer, an outer layer, and an intermediate layer located between the inner and outer layers. The inner layer comprises polypropylene (PP) and / or polypropylene carbonate (PPC), the intermediate layer comprises element Al, and the outer layer comprises nylon and / or polyurethane resin (PU). The inner layer is located adjacent to the electrode assembly, and the outer layer is located away from the electrode assembly. The polypropylene includes homopolymer polypropylene and / or random copolymer polypropylene.

[0018] In one example, the aluminum-plastic film located in the first region includes a gasket.

[0019] In one example, the gasket includes a first layer having a melting point T1 of 80°C-140°C, for example, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C.

[0020] In one example, the gasket includes a first layer, a second layer, and a third layer stacked in the thickness direction. For example... Figure 1 The figure shows a cross-sectional schematic diagram of the gasket along the thickness direction in an embodiment of the present invention. As can be seen from the figure, the gasket includes a first layer 1, a second layer 2 and a third layer 3 stacked in the thickness direction.

[0021] In one example, the melting point T1 of the first layer is less than the melting point T2 of the second layer. The melting point T3 of the third layer is less than the melting point T2 of the second layer.

[0022] In one example, T1 is 80℃-140℃, for example, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, or 140℃. T2 is 100℃-180℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, or 180℃. T3 is 80℃-140℃, for example, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, or 140℃. The test methods for T1, T2, and T3 can be referred to the first area, and will not be repeated here.

[0023] In one instance, the first layer, the second layer, and the third layer are each independently selected from polyolefins and their derivatives.

[0024] In one example, the polyolefin includes polypropylene and / or polyethylene.

[0025] In one example, the polyolefin and its derivatives include at least one of maleic anhydride-grafted polypropylene resin, ethylene-α-olefin copolymer, and ethylene-vinyl acetate copolymer.

[0026] In one example, the first layer, the second layer, and the third layer may each independently further include an auxiliary agent, such as at least one of polyphthalamide (PPA), fluoropolymer processing aids, antioxidants, slip agents, antiblocking agents, elastomers, ultraviolet absorbers, ultraviolet stabilizers, nucleating agents, and antistatic agents. The melting points of the first layer, the second layer, and the third layer can be achieved by changing the proportion of the polyolefin and its derivatives.

[0027] In the present invention, the polyolefin and its derivatives can be obtained through conventional routes or methods, such as commercially available or prepared by conventional methods in the prior art. For example, the material required for forming any one of the first layer, the second layer, and the third layer can be a composite formed by polypropylene and maleic anhydride grafted polypropylene resin through methods such as thermoplastics. Among them, the melting point of the formed composite can be regulated by controlling conditions such as the mass ratio of polypropylene and maleic anhydride grafted polypropylene resin, so that the layer formed by the composite has a preset melting point.

[0028] In the present invention, the second layer is formed of a high melting point material to form a high melting point layer, and the first layer and the third layer are formed of low melting point materials to form low melting point layers. The gasket can be obtained by conventional preparation processes in the art, such as coextrusion. Among them, the low melting point layer can melt to form an opening when heat is generated and gas is produced inside the battery due to factors such as side reactions between the electrode material and the electrolyte, realizing directional pressure relief, so that the gas inside the battery carries heat and is discharged. The high melting point layer can ensure the overall sealing of the battery. At room temperature, the gasket can rely on the high melting point layer to provide sufficient structural support to maintain the packaging strength and sealing performance. At the same time, during battery preparation (such as the hot pressing stage), the low melting point layer will slightly melt to bond the gasket and the PP layer of the aluminum-plastic film together, while the high melting point layer remains structurally stable to achieve side cover sealing. The high melting point layer forms a high-strength sealing skeleton, improving the heat resistance and structural strength after packaging, and making the sealing layer maintain a stable shape, not shrink, and not delaminate during long-term cycling of the battery.

[0029] In the present invention, the electrode assembly further includes a tab, the tab extends from the upper end surface of the aluminum-plastic film and extends in a direction away from the electrode assembly, the height direction of the electrode assembly is parallel to the extension direction of the tab, and the width direction of the electrode assembly is perpendicular to the extension direction of the tab.

[0030] In the present invention, the thickness of the first region is h1, the thickness of the second region is h2, and 1 < h1 / h2 ≤ 1.5, such as 1.002, 1.004, 1.006, 1.02, 1.05, 1.08, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5. h1 and h2 respectively refer to the dimensions of the first region and the second region in the width direction.

[0031] In one instance, 1.004 ≤ h1 / h2 ≤ 1.15.

[0032] In one instance, 1.006 ≤ h1 / h2 ≤ 1.1.

[0033] In this invention, h1 and h2 have conventional meanings in the art. h1 indicates that after the lithium-ion battery undergoes hot pressing and formation processes, the low-melting-point layer in the first region undergoes slight hot melting and is bonded and sealed with the aluminum-plastic film on both sides. At this time, the thickness of the sealing area of ​​the first side cover in the first region is h1. h2 indicates that after the lithium-ion battery undergoes hot pressing and formation processes, the thickness of the sealing area of ​​the first side cover in the second region is h2.

[0034] Adjusting h1 / h2 within a suitable range enables the battery to maintain both high energy density and safe furnace temperature performance. When h1 / h2 is too large (e.g., greater than 1.5), the thickness h1 of the first region is too large, resulting in a significant increase in the battery width after the aluminum-plastic film on the first surface of the lithium-ion battery is folded, which is detrimental to improving the battery's energy density. Conversely, when h1 / h2 is too small (e.g., less than or equal to 1), the thickness h1 of the first region is too small, and the low-melting-point layer of the gasket may have over-melted during the encapsulation process. The low-melting-point layer may not remain or may be too thin, failing to ensure that the low-melting-point layer in the first region can perform its high-temperature pressure relief function, which is detrimental to further improving the battery's safe furnace temperature performance.

[0035] In one example, h1 is 100μm-250μm, for example, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, or 250μm. h2 is 100μm-250μm, for example, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, or 250μm. h1 and h2 can be obtained through conventional testing methods in the art, such as unfolding the aluminum-plastic film, completely removing the surface adhesive with alcohol, and then measuring it with a measuring instrument.

[0036] In one example, h1 is 150μm-200μm. h2 is 150μm-200μm.

[0037] In one example, in the height direction, the dimension of the first region is h, which is 10cm-45cm, for example, 10cm, 11cm, 12cm, 13cm, 14cm, 16cm, 18cm, 20cm, 22cm, 24cm, 26cm, 30cm, 35cm, 40cm, or 45cm. h can be obtained by conventional testing methods in the art, such as unfolding the aluminum-plastic film, completely removing the surface adhesive with alcohol, and then measuring it with a height gauge.

[0038] In one example, in the height direction, the size of the aluminum-plastic film located on the first side cover is H, where 10% ≤ h / H ≤ 50%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. h / H reflects the proportion of the gasket's size on the aluminum-plastic film in the height direction, indicating the size of the pressure relief opening at high temperatures. When h / H is too small (e.g., less than 10%), it indicates that the opening is too small at high temperatures, leading to insufficient pressure relief and potentially causing battery fires, which is detrimental to further improving the battery's high-temperature safety performance. Conversely, when h / H is too large (e.g., greater than 50%), it indicates that the gasket is too large, potentially causing battery sealing problems, especially under the high-temperature baking before electrolyte injection and the high-temperature, high-pressure environment during formation, where insufficient sealing can lead to batch battery failures.

[0039] In this invention, H can be obtained by conventional testing methods in the art, such as unfolding the aluminum-plastic film, completely removing the surface adhesive with alcohol, and then measuring it with a height gauge.

[0040] In one example, along the height direction of the electrode assembly, the aluminum-plastic film has an upper end face and a lower end face. The shortest distance from the upper edge of the first region to the upper end face is D1, and the shortest distance from the lower edge of the first region to the lower end face is D2, where D1 < D2. The upper end face is closer to the tab, and the lower end face is away from the tab. By placing the gasket closer to the top of the aluminum-plastic film, the furnace temperature safety performance of the battery can be further improved. The top of the aluminum-plastic film is the end closer to the tab in the lithium-ion battery, and the bottom is the end farther from the tab. When the gasket is placed closer to the top of the aluminum-plastic film, the pressure relief efficiency can be improved. This is because the space between the top of the aluminum-plastic film and the electrode assembly is larger, allowing more gas to accumulate. Therefore, the pressure at the top is greater than at the bottom, and the gas has a shorter path and less pressure relief resistance when escaping from the position closer to the top, which is beneficial for further improving the furnace temperature safety performance of the battery.

[0041] In this invention, D1 and D2 can be obtained by conventional testing methods in the art, such as unfolding the aluminum-plastic film, completely removing the surface adhesive with alcohol, and then measuring it with a micrometer.

[0042] In one example, the distance d1 between the top of the electrode assembly and the upper end face is greater than the distance d2 between the bottom of the electrode assembly and the lower end face, where d1>d2.

[0043] like Figure 2 The figure shows a front view of a lithium-ion battery according to an embodiment of the present invention. As can be seen from the figure, the lithium-ion battery includes an electrode assembly 4 and an aluminum-plastic film 5. The electrode assembly 4 is located in the accommodating space formed by the aluminum-plastic film 5. The aluminum-plastic film includes a main body and a first side cover and a second side cover located on both sides of the main body. The first side cover includes a first region 10 and a second region 20. The thickness h1 of the first region 10 and the thickness h2 of the second region 20 are marked in the figure. The distance d1 between the top 41 of the electrode assembly 4 and the upper end face 51 and the distance d2 between the bottom 42 of the electrode assembly 4 and the lower end face 52 are also shown. The shortest distance D1 from the upper edge of the first region to the upper end face 51 and the shortest distance D2 from the lower edge of the first region to the lower end face 52 are also shown.

[0044] In one example, along the width direction of the electrode assembly, the electrode assembly includes a first arc surface and a second arc surface. The first arc surface is close to the first side cover, and the second arc surface is close to the second side cover. The first arc surface is provided with adhesive tape. The adhesive tape provides insulation protection for the electrode assembly, preventing short circuits between the positive and negative electrodes, enhancing the structural stability of the electrode assembly, preventing delamination under external forces, and reducing battery safety hazards.

[0045] In one example, the sum of the distances from the electrode assembly to the inner side of the first side cover and the inner side of the second side cover is 0.05mm-2mm, for example, 0.05mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 1mm, 1.5mm or 2mm.

[0046] Electrolyte In one example, the fluorosulfonamide compound includes (I-1) (I-2) (I-3) (I-4) (I-5) (I-6) (I-7) (I-8) (I-9) (I-10) (I-11) (I-12) (I-13) (I-14) (I-15) (I-16) and At least one of (I-17).

[0047] In one example, the fluorosulfonamide compound includes the substance shown in I-1 and / or the substance shown in I-2.

[0048] In one example, the fluorosulfonamide compound is present in the electrolyte at a mass content of 3%-35%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, or 35%. As mentioned earlier, the fluorosulfonamide compound can reduce the HF content in the electrolyte, thereby improving the high-temperature cycle stability of the lithium-ion battery. Furthermore, due to its unique molecular structure and chemical properties, the fluorosulfonamide compound can serve as a good solvent medium, especially effectively promoting the dissolution of other sulfur-containing additives (such as 1,3-propanesulfonyl lactone (PS)) in the electrolyte, thus allowing these additives to function better and improving the stability and performance consistency of the entire electrolyte system. Simultaneously, it is necessary to control the mass content of the fluorosulfonamide compound in the electrolyte. When the mass content of fluorosulfonamide compound in the electrolyte is low (e.g., below 3%), the solubility of other sulfur-containing additives is significantly reduced, and precipitation will occur in the electrolyte, affecting the battery performance. When the mass content of fluorosulfonamide compound in the electrolyte is high (e.g., above 35%), although the dissolution problem is solved, the electrolyte may not reach its optimal state in certain aspects due to the low content of other components.

[0049] In one example, the fluorosulfonamide compound is present in the electrolyte at a mass content of 5%-22%.

[0050] In one example, the electrolyte further includes: 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), and vinyl sulfate (DTD). (II-1) (II-2) (II-3) (II-4) (II-5) and At least one of (II-6).

[0051] In one example, the electrolyte also includes PS and the substance shown in II-1.

[0052] In one example, the mass content of PS in the electrolyte is less than or equal to 1.5%, for example, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1%.

[0053] In one example, the mass content of PS in the electrolyte is 0.3%-0.7%.

[0054] In one example, the substance shown in II-1 has a mass content of 0.5%-8% in the electrolyte, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%.

[0055] In one example, the substance shown in II-1 has a mass content of 2%-3.5% in the electrolyte.

[0056] In one example, the mass ratio of the substance shown in II-1 to PS in the electrolyte is 1-20, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. When the negative electrode includes silicon-carbon materials, silicon reacts with the electrolyte to easily form an unstable SEI film; especially when the surface of the negative electrode has grooves, the reaction sites between the electrolyte and silicon increase, requiring optimization of the interfacial contact between the electrolyte and the negative electrode to reduce electrolyte consumption and capacity decay. PS can preferentially form an SEI film on the surface of the negative electrode, but the SEI film it forms is prone to rupture and difficult to repair when silicon particles expand, leading to continuous electrolyte consumption and capacity decay. The substance shown in II-1, with polyhydroxymannitol as its backbone, has highly flexible molecular chains and steric hindrance, enabling the SEI film it reduces to form on the surface of the negative electrode to possess a polymer-like elastic network structure. Compared to rigid sulfonate-based SEI films formed by PS, this structure can actively buffer the volumetric expansion stress of silicon particles, significantly reducing SEI crack formation and repeated reconstruction. By adjusting the content ratio of the substance shown in II-1 to PS, the advantages of both substances can be fully utilized to form a high-quality SEI film. If the ratio is too low (e.g., less than 1), the content of the substance shown in II-1 is relatively small, and the structure formed by PS may lack sufficient flexibility and electronic conductivity, leading to a decrease in the performance of the SEI film. If the ratio is too high (e.g., greater than 20), the content of the substance shown in II-1 is relatively excessive, which will also affect the structure formation of PS in the SEI film and is not conducive to improving the quality of the SEI film.

[0057] In one example, the mass ratio of the substance shown in II-1 to PS in the electrolyte is 2-12.

[0058] In one example, the mass ratio of the substance shown in II-1 to PS in the electrolyte is 3-7.

[0059] In one example, the electrolyte further includes carbonate compounds. These carbonate compounds include fluoroethylene carbonate (FEC) and vinylene carbonate (VC). FEC and VC synergistically act on the surface of the anode containing silicon-carbon materials, significantly improving interfacial stability and reducing electrochemical impedance by constructing a bilayer SEI structure of "inorganic inner layer - organic outer layer." The mechanism of action of FEC and VC is as follows: VC has a reduction potential of approximately 0.77V, allowing it to be preferentially reduced compared to FEC. Its carbon-carbon double bonds undergo free radical polymerization at low potentials, generating an organic polymer network rich in polyethylene carbonate. This network possesses high elasticity and ductility, enabling it to encapsulate silicon-carbon material particles and adapt to their volume changes. Below the organic layer formed by VC, FEC decomposes to generate an inorganic inner layer rich in lithium fluoride (LiF). LiF has high ionic conductivity, high modulus, and low solubility, effectively blocking electrolyte penetration, reducing side reactions, and providing a rapid transport channel for lithium ions. The VC polymer layer reduces the overall SEI resistance, while the LiF generated by FEC enhances lithium-ion mobility. Together, they result in a significantly lower overall interfacial impedance compared to systems where either is added alone. The stable bilayer SEI reduces continuous electrolyte decomposition and SEI reconstruction, preventing impedance accumulation caused by repeated film formation.

[0060] In one example, the mass ratio of FEC to VC in the electrolyte is 20-200, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200.

[0061] In one instance, the mass ratio of FEC to VC in the electrolyte is 25-160.

[0062] In one instance, the mass ratio of FEC to VC in the electrolyte is 40-110.

[0063] In one instance, the FEC content in the electrolyte is 5%-20% by mass, for example, 5%, 8%, 10%, 15% or 20%.

[0064] In one instance, the FEC content in the electrolyte is 8%-16% by mass.

[0065] In one example, the mass content of VC in the electrolyte is 0.1%-2%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5% or 2%.

[0066] In one example, the mass content of VC in the electrolyte is 0.1%-0.5%.

[0067] In one instance, the FEC content in the carbonate compound is 30%-90% by mass, for example, 30%, 40%, 50%, 60%, 70%, 80% or 90%.

[0068] In one instance, the FEC content in the carbonate compound is 52%-90% by mass.

[0069] In one example, the ratio of FEC to the content of the fluorosulfonamide compound in the electrolyte is 0.6-1.1, for example, 0.6, 0.7, 0.8, 0.9, 1 or 1.1.

[0070] In one example, the carbonate compound further includes at least one of propylene carbonate (PC), dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and difluoroethylene carbonate.

[0071] In one example, the electrolyte further includes a carboxylic acid ester compound. The carboxylic acid ester compound includes, for example, at least one selected from 2,2-difluoroethyl acetate (DFEA), ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl propionate (EP), propyl propionate (PP), methyl butyrate, and ethyl butyrate.

[0072] In one example, the electrolyte further includes a lithium salt. The lithium salt includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate. Bis(trifluoromethanesulfonyl)imide itself has strong thermal stability and is not easily decomposed under high temperature and high pressure environments, thereby reducing electrolyte gas production and further extending the battery's high-temperature cycle life. Furthermore, bis(trifluoromethanesulfonyl)imide hardly hydrolyzes and does not produce HF. Using bis(trifluoromethanesulfonyl)imide to replace part of the lithium hexafluorophosphate can reduce the amount of HF produced by the hydrolysis of lithium hexafluorophosphate, thereby further improving the battery's high-temperature cycle stability.

[0073] In one example, the lithium salt further includes lithium difluorophosphate and lithium tetrafluoroborate. The combination of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate can balance ionic conductivity and interfacial stability, and further suppress the occurrence of thermal runaway.

[0074] In one example, the lithium salt includes lithium difluorophosphate, lithium tetrafluoroborate, LiTFSI, and lithium hexafluorophosphate.

[0075] In one example, the mass content of lithium hexafluorophosphate in the electrolyte is 10%-15%. The mass content of lithium difluorophosphate in the electrolyte is 0.1%-1%. The mass content of lithium tetrafluoroborate in the electrolyte is 0.1%-1%.

[0076] In one example, the mass content of LiTFSI in the electrolyte is 3%-10%. Within this range, LiTFSI can create a high salt concentration region at the electrode / electrolyte interface, reducing the overall viscosity of the electrolyte while maintaining high ionic conductivity, thus reducing dendrite and gas generation and further improving furnace temperature safety performance.

[0077] In this invention, the mass content of the lithium salt in the electrolyte can be obtained by methods conventional in the art, such as ion chromatography (IC).

[0078] Negative electrode film In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector. The negative electrode active coating includes a silicon-carbon material, and the mass content of elemental Si in the negative electrode active coating is 5%-50%, for example, 5%, 10%, 20%, 30%, 40%, or 50%. The mass content of elemental Si in the negative electrode active coating can be tested by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under a nitrogen or argon atmosphere). The negative electrode active coating can then be peeled off from the negative electrode current collector and collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the sample size is 5-15 mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 min. This allows the non-silicon components in the negative electrode active coating to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode active coating. The mass content of elemental Si in the negative electrode active coating can be calculated based on the mass of the ash, using the following formula: Mass content of elemental Si in the negative electrode active coating = 7 × mass of ash / (15 × mass of test sample).

[0079] In one example, the surface of the negative electrode active coating has grooves. Silicon-carbon materials have higher specific capacity and energy density than carbon-based materials, but their cycle stability is poor. The groove design can effectively alleviate the volume expansion problem of silicon materials and extend the battery cycle life.

[0080] In one example, the depth of the groove is 5μm-35μm, for example, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, or 35μm. The width of the groove is 20μm-1000μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, or 1000μm. The spacing between the grooves is 0.5mm-10mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm. It is understandable that when there is only one groove on the surface of the negative electrode, there is no spacing between the grooves.

[0081] In this invention, the depth of the groove has a conventional meaning in the art, referring to the vertical distance from the lowest point within the groove to the surface of the negative electrode sheet. The depth of the groove can be determined by using a 3D profilometer to test the depth of all grooves or at least five grooves on the surface of the negative electrode sheet and taking the average value. The width of the groove has a conventional meaning in the art. The orthographic projection of the groove onto the surface of the negative electrode sheet includes two long sides, and the width of the groove refers to the average distance from one long side to the other along the length or width direction of the negative electrode sheet. Fifty points are randomly selected along one long side, and the width corresponding to each point is measured; the average value is taken to obtain the width of the groove. The width of the groove can be determined by, for example, using a 3D profilometer to test the width of all grooves or at least five grooves on the surface of the negative electrode sheet and taking the average value. The spacing of the grooves has a conventional meaning in the art, referring to the average distance between the two adjacent long sides of two adjacent grooves along the length or width direction of the negative electrode sheet. Fifty points are randomly selected along one long side, and the width corresponding to each point is measured; the average value is taken to obtain the spacing. The spacing of the grooves can be determined by the following method: using a 3D profilometer, test the spacing of all grooves or at least 5 grooves on the surface of the negative electrode active coating, and take the average value.

[0082] In one example, the silicon-carbon material comprises a porous carbon matrix and silicon particles located in the pores within the porous carbon matrix.

[0083] In one example, the mass content of element Si in the silicon-carbon material is 30%-80%, for example, 30%, 40%, 50%, 60%, 70%, or 80%. The mass content of element Si in the silicon-carbon material can be tested using conventional methods in the art. For example, the battery is discharged to 0% SOC, the negative electrode is disassembled and removed, and its cross-section is polished using an argon-ion polisher. The silicon-carbon material particles are then observed in backscatter imaging mode on an SEM device to maximize magnification. The cross-section of the silicon-carbon material particles is scanned using an energy dispersive spectroscopy (EDS) instrument, with the scanned area not less than 50% of the cross-section of the silicon-carbon material particles, and the scanning range should be completely within the cross-section of the silicon-carbon material particles. The mass content of element Si is then calculated.

[0084] In one example, the median particle size Dv50 of the silicon-carbon material is 1 μm-20 μm, for example, 1 μm, 5 μm, 10 μm, 15 μm, or 20 μm. The median particle size Dv50 of the silicon-carbon material can be measured by methods conventional in the art, such as using a laser particle size analyzer.

[0085] <Septum> In this invention, the electrode assembly includes a diaphragm.

[0086] In one example, the diaphragm includes a carrier layer and a first adhesive layer located on a first surface of the carrier layer, the surface of the first adhesive layer having a plurality of protrusions. The plurality of protrusions refers to a number greater than or equal to two.

[0087] In one example, the protrusion contains element F. The protrusion comprises polyvinylidene fluoride (PVDF). Both the fluorosulfonamide compound in the electrolyte and the PVDF in the protrusion contain element F. During battery charging and discharging, the two can synergistically form a stable fluorinated interface film at the positive electrode interface. This fluorinated interface film has good chemical and thermal stability, effectively preventing direct contact between the electrolyte and the positive electrode material, reducing side reactions, inhibiting the oxidative decomposition of the electrolyte on the positive electrode surface, and reducing gas generation, thereby improving battery safety and cycle life. Furthermore, there is a certain interaction force between PVDF and LiF, enabling LiF to adhere stably to the positive electrode interface and not easily detach or dissolve. Stable LiF can further improve the properties of the positive electrode interface, reduce interface impedance, and improve lithium-ion transport efficiency, thereby improving the battery's charge and discharge performance. The fluorinated interface film and LiF remain stable at high temperatures, preventing excessive decomposition of the electrolyte and gas generation, and reducing the increase in internal battery pressure. Meanwhile, PVDF itself has good thermal stability, which can maintain the structural integrity of the separator at high temperatures, prevent the separator from shrinking or rupturing, and ensure the safe operation of the battery at high temperatures.

[0088] In one example, the height of the protrusion is 1μm-15μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, or 15μm. The diameter of the orthographic projection of the protrusion onto the diaphragm surface is 0.1μm-15μm, for example, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, or 15μm.

[0089] In this invention, the height of the protrusions and the diameter of their orthogonal projection on the separator surface can be controlled by adjusting the particle size of PVDF. When the height of the protrusions and the diameter of their orthogonal projection on the separator surface are within a specific range, the protrusions can be more uniformly distributed on the separator surface, forming a fine protrusion structure. This improves the uniformity of contact between the separator and the electrode, making the fluorinated interface film formed by PVDF and fluorinated organic matter in the electrolyte at the positive electrode interface more uniform. This further helps to prevent direct contact between the electrolyte and the positive electrode material, reduces the occurrence of side reactions, inhibits the oxidative decomposition of the electrolyte on the positive electrode surface, and reduces gas generation, thereby further improving battery safety and cycle life. Furthermore, increasing the height and strength of the protrusions enhances the buffering capacity against electrode expansion, further improving the battery's high-temperature cycle performance.

[0090] In this invention, the height of the protrusion and the diameter of its orthographic projection on the diaphragm surface can be obtained using conventional methods in the art. For example, by using a scanning electron microscope (SEM) to obtain an SEM image of the diaphragm cross-section, a 100μm × 100μm area is taken on the surface, and the height and diameter of the orthographic projection of 20 protrusions within this area are measured. This operation is repeated 5 times, and the average of the 5 test results is taken as the height of the protrusion and the diameter of its orthographic projection on the diaphragm surface. If the number of protrusions in the 100μm × 100μm area is less than 20, the 100μm × 100μm area is continued until 20 protrusions are measured. The height of the protrusion refers to the vertical distance from the apex of the protrusion to the diaphragm surface. When the orthographic projection of the protrusion onto the diaphragm surface is a regular circle, the diameter of the orthographic projection is the diameter of that regular circle. When the orthographic projection of the protrusion onto the diaphragm surface is not a "regular circle," the diameter of the orthographic projection is the equivalent diameter of a circle with the same area as the "irregular circle." The height of the second protrusion and the diameter of its orthographic projection onto the diaphragm surface are determined with reference to the protrusion itself, and will not be elaborated further here.

[0091] In one example, the coverage of the protrusions on the diaphragm surface is 5%-90%, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%. The coverage of the protrusions on the diaphragm surface can be tested using conventional methods in the art, such as using SEM scanning to obtain an SEM image of the diaphragm cross-section, taking a 100μm × 100μm area on the surface, measuring and calculating the coverage of the protrusions within this area; repeating the above operation 5 times and taking the average value.

[0092] In one example, the carrier layer includes a substrate layer and a nitrogen-containing coating located on at least one side surface of the substrate layer.

[0093] In one example, the thickness of the nitrogen-containing coating is 0.5 μm to 4 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or 4 μm.

[0094] In one example, the nitrogen-containing coating comprises at least one of polyacrylonitrile, nitrile rubber, 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, melamine cyanurate, and melamine thiocyanate.

[0095] In one example, the nitrogen-containing coating is located on the first surface, and the nitrogen-containing coating at least faces the positive electrode.

[0096] In one example, the diaphragm further includes a second adhesive layer located on the second surface of the carrier layer.

[0097] <Positive Electrode Tablets> In this invention, the positive electrode sheet includes a positive current collector and a positive active coating located on at least one side of the surface of the positive current collector. The positive active coating includes a positive active material, such as lithium cobalt oxide.

[0098] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0099] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0100] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0101] The following examples illustrate the lithium-ion battery of the present invention.

[0102] Example 1 Lithium-ion batteries are prepared according to the following method: (1) Preparation of electrolyte In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, PC, DFEA, the fluorosulfonamide compound shown in I-1 and the substance shown in II-1 are mixed evenly, and PS, FEC, VC and lithium salts (lithium difluorophosphate, lithium tetrafluoroborate, LiTFSI and lithium hexafluorophosphate) are added to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained. The electrolyte contains the following substances in the following mass contents: 15.2% fluorosulfonamide compound, 3.3% of the substance shown in II-1, 0.5% PS, 12.3% FEC, 0.3% VC, 35% DFEA, 7% LiTFSI, 11% lithium hexafluorophosphate, 0.3% lithium difluorophosphate, 0.2% lithium tetrafluoroborate, and the remainder is PC.

[0103] (2) Preparation of positive electrode sheet Lithium cobalt oxide, PVDF, conductive carbon black, and carbon nanotubes were mixed evenly in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode active slurry. The positive electrode active slurry was uniformly coated onto the surface of an aluminum foil (12 μm thick). The coated aluminum foil was dried, and then rolled and slit to obtain the positive electrode sheet.

[0104] (3) Preparation of negative electrode sheet Artificial graphite, silicon carbide material (median particle size Dv50 of 7.2 μm, silicon carbide material with Si content of 55%), sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black, and carbon nanotubes were mixed uniformly in a mass ratio of 75.5:19:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred under vacuum until a uniform and fluid negative electrode active slurry was formed. The negative electrode active slurry was uniformly coated onto the surface of a copper foil (6 μm thick). The coated copper foil was air-dried at room temperature, then transferred to an 80°C oven for 10 hours. After cold pressing, grooves were etched on the surface of the negative electrode active coating using laser processing technology, and then the negative electrode sheet was obtained by slitting. The silicon-carbon material comprises a porous carbon matrix and silicon particles located within the pores of the porous carbon matrix; the mass content of elemental Si in the negative electrode active coating is 10.5%. The groove has a depth of 27μm, a width of 521μm, and a spacing of 5.1mm.

[0105] (4) Preparation of lithium-ion batteries Stack the positive electrode sheet prepared in step (2), the separator, and the negative electrode sheet prepared in step (3) in sequence, ensuring that the separator is placed between the positive and negative electrode sheets to play an isolation role; then wind it up, with the aluminum foil at the end, and attach adhesive tape; after encapsulation with an aluminum-plastic film, place a gasket with a three-layer structure (where the first, second, and third layers include polypropylene and maleic anhydride grafted polypropylene resin with different ratios, T1 is 97 °C, T2 is 145 °C, T3 is 97 °C) at the sealing position for encapsulation, and then through baking, liquid injection, formation, secondary sealing, sorting, and OCV, a lithium-ion battery is obtained; Among them, in the differential scanning calorimetry test of the first region, there is an endothermic peak at 105 °C; the thickness h1 of the first region is 158 μm, the thickness h2 of the second region is 151 μm, and h1 - h2 is 7 μm; h is 36 cm, and H is 112.5 cm; d1 > d2, D1 < D2; the sum of the distances from the electrode assembly to the inner sides of the first side cover and the second side cover is 1.2 mm; The separator includes a base material layer (a polyethylene film with a thickness of 8 μm), a nitrogen-containing coating (including 1,3,5-triazine-2,4,6-triamine with a thickness of 1.2 μm) on one surface of the base material layer, a first adhesive layer (including PVDF) on the outer surface of the nitrogen-containing coating, and a second adhesive layer on the other surface of the base material layer; there are several protrusions on the outer surface of the first adhesive layer, the protrusions contain element F, the height of the protrusions is 6.7 μm, the diameter of the positive projection of the protrusions on the surface of the separator is 5.8 μm, and the coverage rate of the protrusions on the surface of the separator is 75%; the nitrogen-containing coating faces the positive electrode sheet.

[0106] Example 2 Prepare a lithium-ion battery according to the following method: (1) Prepare the electrolyte In an argon glove box with a water content < 0.1 ppm and an oxygen content < 0.1 ppm, mix PC, DFEA, the fluorosulfonamide compound shown in I-1, and the substance shown in II-1 evenly, add PS, FEC, VC, and lithium salts (lithium difluorophosphate, lithium tetrafluoroborate, LiTFSI, and lithium hexafluorophosphate), and mix to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained; Among them, the mass contents of the following substances in the electrolyte are respectively: the fluorosulfonamide compound is 9.8%, the substance shown in II-1 is 2.1%, PS is 0.3%, FEC is 10.6%, VC is 0.1%, DFEA is 35%, LiTFSI is 8%, lithium hexafluorophosphate is 13%, lithium difluorophosphate is 0.1%, lithium tetrafluoroborate is 0.5%, and the rest is PC. [[ID=I7]]

[0107] (2) Prepare the positive electrode sheet Lithium cobaltate, PVDF, conductive carbon black, and carbon nanotubes are mixed evenly in a mass ratio of 96:2:1.5:0.5, and N-methylpyrrolidone (NMP) is added. Stir under a vacuum mixer until the mixed system becomes a homogeneous and flowable positive electrode active paste; evenly coat the positive electrode active paste on the surface of an aluminum foil (with a thickness of 12 μm); dry the coated aluminum foil, and then obtain the positive electrode sheet through rolling and slitting.

[0108] (3)Prepare the negative electrode sheet Artificial graphite, silicon-carbon material (median particle size Dv50 is 7.2 μm, and the mass content of element Si in the silicon-carbon material is 55%), sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black, and carbon nanotubes are mixed evenly in a mass ratio of 75.5:19:2.5:1.5:1:0.5, and deionized water is added. Stir under a vacuum mixer until the mixed system becomes a homogeneous and flowable negative electrode active paste; evenly coat the negative electrode active paste on the surface of a copper foil (with a thickness of 6 μm); air-dry the coated copper foil at room temperature, then transfer it to an 80 °C oven for drying for 10 h, then perform cold pressing, and then through laser processing technology, etch grooves on the surface of the negative electrode active coating, and then obtain the negative electrode sheet through slitting; Among them, the silicon-carbon material includes a porous carbon matrix and silicon particles located in the pore channels inside the porous carbon matrix; the mass content of element Si in the negative electrode active coating is 10.5%; The depth of the groove is 5 μm, the width of the groove is 22 μm, and the spacing of the grooves is 0.5 mm.

[0109] (4)Prepare the lithium-ion battery Stack the positive electrode sheet prepared in step (2), the separator, and the negative electrode sheet prepared in step (3) in sequence, ensuring that the separator is between the positive and negative electrode sheets to play an isolation role; then through winding, with the aluminum foil at the end, attach adhesive tape; after encapsulation with an aluminum-plastic film, place a three-layer structure gasket (where the first, second, and third layers include different ratios of polypropylene and maleic anhydride grafted polypropylene resin, T1 is 82 °C, T2 is 103 °C, T3 is 82 °C) at the sealing position for encapsulation, and then through baking, liquid injection, formation, second sealing, sorting, and OCV, obtain the lithium-ion battery; Among them, in the differential scanning calorimetry test, the first region has an endothermic peak at 86 °C; the thickness h1 of the first region is 176 μm, the thickness h2 of the second region is 175 μm, and h1 - h2 is 1 μm; h is 10 cm, and H is 100 cm; d1 > d2, D1 < D2; the sum of the distances from the electrode assembly to the inner sides of the first side cover and the second side cover is 1 mm; The separator comprises a substrate layer (a polyethylene film with a thickness of 8 μm), a nitrogen-containing coating (including 1,3,5-triazine-2,4,6-triamine with a thickness of 0.5 μm) on one side of the substrate layer, a first adhesive layer (including PVDF) on the outer surface of the nitrogen-containing coating, and a second adhesive layer on the other side of the substrate layer; the outer surface of the first adhesive layer has a plurality of protrusions, the protrusions contain element F, the height of the protrusions is 1.2 μm, the diameter of the orthographic projection of the protrusions on the separator surface is 0.2 μm, and the coverage of the protrusions on the separator surface is 63%; the nitrogen-containing coating faces the positive electrode.

[0110] Example 3 Lithium-ion batteries are prepared according to the following method: (1) Preparation of electrolyte In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, PC, DFEA, the fluorosulfonamide compound shown in I-2 and the substance shown in II-1 are mixed evenly, and PS, FEC, VC and lithium salts (lithium difluorophosphate, lithium tetrafluoroborate, LiTFSI and lithium hexafluorophosphate) are added to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained. The electrolyte contains the following substances in the following mass contents: 21.3% fluorosulfonamide compound, 2.5% of the substance shown in II-1, 0.7% PS, 15.4% FEC, 0.2% VC, 35% DFEA, 9% LiTFSI, 10% lithium hexafluorophosphate, 0.5% lithium difluorophosphate, 0.3% lithium tetrafluoroborate, and the remainder is PC.

[0111] (2) Preparation of positive electrode sheet Lithium cobalt oxide, PVDF, conductive carbon black, and carbon nanotubes were mixed evenly in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode active slurry. The positive electrode active slurry was uniformly coated onto the surface of an aluminum foil (12 μm thick). The coated aluminum foil was dried, and then rolled and slit to obtain the positive electrode sheet.

[0112] (3) Preparation of negative electrode sheet Mix artificial graphite, silicon-carbon material (median particle size Dv50 is 7.2 μm, and the mass content of element Si in the silicon-carbon material is 55%), sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black and carbon nanotubes evenly according to a mass ratio of 75.5:19:2.5:1.5:1:0.5, add deionized water, and stir under a vacuum mixer until the mixed system becomes a homogeneous and flowable negative electrode active paste; evenly coat the negative electrode active paste on the surface of a copper foil (with a thickness of 6 μm); dry the coated copper foil at room temperature, then transfer it to an 80 °C oven and dry for 10 h, then cold press it, and then through laser processing technology, etch grooves on the surface of the negative electrode active coating, and then obtain a negative electrode sheet through slitting; Among them, the silicon-carbon material includes a porous carbon matrix and silicon particles located in the pore channels inside the porous carbon matrix; the mass content of element Si in the negative electrode active coating is 10.5%; The depth of the groove is 35 μm, the width of the groove is 896 μm, and the spacing of the grooves is 10 mm.

[0113] (4) Prepare a lithium-ion battery Stack the positive electrode sheet prepared in step (2), the separator, and the negative electrode sheet prepared in step (3) in sequence, ensuring that the separator is between the positive and negative electrode sheets to play an isolation role; then wind it up, with the aluminum foil at the end, and attach adhesive tape; after encapsulation with an aluminum-plastic film, place a gasket with a three-layer structure (where the first, second, and third layers include different ratios of polypropylene and maleic anhydride grafted polypropylene resin, T1 is 115 °C, T2 is 158 °C, T3 is 115 °C) at the sealing position for encapsulation, and then through baking, liquid injection, formation, secondary sealing, sorting, and OCV, a lithium-ion battery is obtained; Among them, in the differential scanning calorimetry test of the first region, there is an endothermic peak at 120 °C; the thickness h1 of the first region is 196 μm, the thickness h2 of the second region is 181 μm, and h1 - h2 is 15 μm; h is 45 cm, and H is 90 cm; d1 > d2, D1 < D2; the sum of the distances from the electrode assembly to the inner sides of the first side cover and the second side cover is 1.4 mm; The separator includes a base material layer (a polyethylene film with a thickness of 8 μm), a nitrogen-containing coating (including 1,3,5-triazine-2,4,6-triamine, with a thickness of 3 μm) located on one surface of the base material layer, a first adhesive layer (including PVDF) located on the outer surface of the nitrogen-containing coating, and a second adhesive layer located on the other surface of the base material layer; there are several protrusions on the outer surface of the first adhesive layer, the protrusions contain element F, the height of the protrusions is 10.8 μm, the diameter of the positive projection of the protrusions on the surface of the separator is 12.3 μm, and the coverage rate of the protrusions on the surface of the separator is 87%; the nitrogen-containing coating faces the positive electrode sheet.

[0114] Example 4 This was used to verify the effects of changes to the "fluorosulfonamide compound".

[0115] The procedure was carried out in accordance with Example 1, except that the fluorosulfonamide compound was the substance shown in I-3.

[0116] Example 5 group This set of examples is used to verify the impact of changes to "h1 and h2".

[0117] This set of embodiments is based on Embodiment 1, except that h1 and h2 are changed, as follows: Example 5a, h1 is 115 μm, h2 is 106 μm; Example 5b, h1 is 249 μm, h2 is 242 μm.

[0118] Example 6 group This set of examples is used to verify the impact of changes to "h1 / h2".

[0119] This set of embodiments is based on Embodiment 1, except that h1 / h1 is adjusted by changing h1 and h2, as follows: Example 6a, h1 is 118 μm, h2 is 103 μm, h1 / h2 is 1.146; Example 6b, h1 is 249 μm, h2 is 248 μm, and h1 / h2 is 1.004.

[0120] Example 7 The procedure was carried out in accordance with Example 1, except that PS was replaced with PST of the same quality.

[0121] Example 8 The procedure was carried out in accordance with Example 1, except that the mass content of PS in the electrolyte was 2%.

[0122] Example 9 The procedure was carried out in accordance with Example 1, except that the substance shown in II-1 was replaced with the same mass of the substance shown in II-2.

[0123] Example 10 group This set of examples is used to verify the effect of changing the mass ratio of the substance shown in II-1 to PS in the electrolyte.

[0124] This set of embodiments follows the same procedure as Example 1, except that the ratio of the two substances is changed by altering the mass content of the substance shown in II-1 and PS in the electrolyte, as detailed below: In Example 10a, the mass content of the substance shown in II-1 in the electrolyte is 3.5%, the mass content of PS in the electrolyte is 0.3%, and the ratio of the two is 11.67. In Example 10b, the mass content of the substance shown in II-1 in the electrolyte is 2%, and the mass content of PS in the electrolyte is 0.7%, with a ratio of 2.86.

[0125] Example 11 group This set of examples is used to verify the impact of changing the "ratio of FEC to VC mass content in the electrolyte".

[0126] This set of embodiments follows the same procedure as Embodiment 1, except that the ratio of FEC and VC is changed by altering their mass content in the electrolyte, as detailed below: In Example 11a, the mass content of FEC in the electrolyte was 10.3%, the mass content of VC in the electrolyte was 0.4%, and the ratio of the two was 25.75. In Example 11b, the mass content of FEC in the electrolyte was 15.7%, and the mass content of VC in the electrolyte was 0.1%, with a ratio of 157.

[0127] Example 12 The procedure was carried out in accordance with Example 1, except that no vitamin C was added to the electrolyte.

[0128] Example 13 The procedure was carried out in accordance with Example 1, except that LiTFSI was not added to the electrolyte.

[0129] Example 14 The procedure was carried out in accordance with Example 1, except that lithium tetrafluoroborate was not added to the electrolyte.

[0130] Example 15 group This set of examples is used to verify the impact of changing the "mass content of element Si in the negative electrode active coating".

[0131] This set of embodiments refers to Embodiment 1, except that the mass content of elemental Si in the negative electrode active coating is controlled by changing the mass ratio of silicon-carbon material in the negative electrode active slurry and / or the mass content of elemental Si in the silicon-carbon material, as detailed below: In Example 15a, the mass content of elemental Si in the negative electrode active coating is 5.2%; In Example 15b, the mass content of elemental Si in the negative electrode active coating is 34.7%; In Example 15c, the mass content of elemental Si in the negative electrode active coating is 48.6%.

[0132] Example 16 The procedure was carried out in accordance with Example 1, except that the outer surface of the first adhesive layer did not have protrusions.

[0133] Example 17 The procedure was carried out in accordance with Example 1, except that the height of the protrusion was 18.7 μm and the diameter of the orthographic projection of the protrusion onto the diaphragm surface was 16.2 μm.

[0134] Example 18 group The procedure was carried out in accordance with Example 1, except that the mass content of the fluorosulfonamide compound in the electrolyte was as follows: In Example 18a, the mass content of the fluorosulfonamide compound in the electrolyte was 5.2%; In Example 18b, the mass content of the fluorosulfonamide compound in the electrolyte was 29.2%.

[0135] Comparative Example 1 The procedure is carried out in accordance with Example 1, except that no gasket is provided.

[0136] Comparative Example 2 The procedure was carried out in accordance with Example 1, except that no fluorosulfonamide compound was added to the electrolyte.

[0137] Test case (1) High temperature cycling test The lithium-ion batteries prepared in the examples and comparative examples were discharged at 45°C to 3.0V at 1C, then allowed to stand for 10 minutes, and then charged at 1C to 4.55V with a cutoff current of 0.025C, followed by a 10-minute stand. They were then discharged at 1.2C to the cutoff voltage of 3.0V and allowed to stand for 10 minutes. The discharge capacity at this point was recorded as the initial capacity. This charging and discharging process was repeated until the 400th constant-voltage charging cycle was completed. After standing for 10 minutes, the batteries were discharged at 1.2C to 3.0V and allowed to stand for 10 minutes. The discharge capacity at this point was recorded as the post-cycle capacity. The cycle capacity retention rate was calculated as: post-cycle capacity × 100% / initial capacity. The results are shown in Table 1.

[0138] (2) Furnace temperature test The lithium-ion batteries prepared in the examples and comparative examples were discharged at 0.2C to the lower limit voltage of 3.0V at 25°C, left to stand for 10 minutes, and then charged at 1C to the upper limit voltage of 4.55V with a cutoff current of 0.05C. The fully charged lithium-ion batteries were then placed in an oven and heated to 132°C at a heating rate of 5°C / min. The temperature was kept constant for 60 minutes, and the lithium-ion batteries were observed to see if they caught fire or exploded. If they did not catch fire or explode, they were considered to have passed the test; otherwise, they were considered to have failed the test. Each example and comparative example was tested 10 times, and the results are expressed as n / 10, where n represents the number of times the test was passed. The results are recorded in Table 1.

[0139] (3) Ratio performance test The lithium-ion batteries prepared in the examples and comparative examples were placed at 25°C, charged at 0.7C to 4.5V with a cutoff current of 0.025C, and discharged at 0.2C to a cutoff voltage of 3.0V to obtain the initial capacity. Then, they were charged at 0.7C to 4.5V with a cutoff current of 0.025C and discharged at 2.5C to a cutoff voltage of 3.0V to obtain the 2.5C discharge capacity. The rate performance was calculated as 2.5C discharge capacity / initial capacity × 100%. The results are recorded in Table 1.

[0140] Table 1 As can be seen from Table 1, the battery prepared with the electrolyte of the present invention has better furnace temperature safety performance, high-temperature cycling performance, and rate performance compared with the comparative example. Example 6a has a lower energy density compared with Example 1.

[0141] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes an aluminum-plastic film and an electrode assembly, and the electrode assembly is located in a receiving space formed by the aluminum-plastic film; the electrode assembly includes a stacked positive electrode sheet, a separator, and a negative electrode sheet; The aluminum-plastic film includes a main body portion and a first side cover and a second side cover respectively located on both sides of the main body portion. The first side cover includes a first region and a second region. The thickness of the first region is greater than that of the second region, and the difference between the thickness of the first region and the thickness of the second region is 1 μm - 15 μm; In the differential scanning calorimetry test of the first region, there is an endothermic peak at 100°C - 140°C; The lithium-ion battery further includes an electrolyte, and the electrolyte includes a fluorosulfonamide compound.

2. The lithium-ion battery according to claim 1, wherein, The aluminum-plastic film located in the first region includes a gasket; the gasket includes a first layer, and the melting point T1 of the first layer is 80°C - 140°C; And / or, the gasket includes a first layer, a second layer, and a third layer stacked in the thickness direction; the melting point T1 of the first layer is 80°C - 140°C, the melting point T2 of the second layer is 100°C - 180°C, and the melting point T3 of the third layer is 80°C - 140°C; And / or, the thickness of the first region is h1, the thickness of the second region is h2, 1 < h1 / h2 ≤ 1.5; preferably, h1 is 100 μm - 250 μm, and h2 is 100 μm - 250 μm.

3. The lithium-ion battery according to claim 1 or 2, wherein, The fluorosulfonamide compound includes , , , , , , , , , , , , , , , and At least one of them; And / or, the mass content of the fluorosulfonamide compound in the electrolyte is 3% - 35%; And / or, the electrolyte further includes: 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, , , , , and At least one of them; Preferably, the mass content of 1,3 - propane sultone in the electrolyte is less than or equal to 1.5%; Preferably, the electrolyte comprises and 1,3-propanesulfonate lactone, the The mass ratio of 1,3-propanesulfonate lactone in the electrolyte is 1-20.

4. The lithium-ion battery according to claim 1 or 2, wherein, The electrolyte further includes a carbonate compound, and the carbonate compound includes fluoroethylene carbonate and vinylene carbonate; Preferably, the ratio of the mass content of fluoroethylene carbonate and vinylene carbonate in the electrolyte is 20 - 200; more preferably 25 - 160; Preferably, the mass content of fluoroethylene carbonate in the carbonate compound is 30% - 90%; Preferably, the ratio of the content of fluoroethylene carbonate and the fluorosulfonamide compound in the electrolyte is 0.6 - 1.

1.

5. The lithium-ion battery according to claim 1 or 2, wherein, The electrolyte further includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide; Preferably, the lithium salt further includes lithium difluorophosphate and lithium tetrafluoroborate.

6. The lithium-ion battery according to claim 1 or 2, wherein, Along the height direction of the electrode assembly, the aluminum-plastic film has an upper end face and a lower end face. The shortest distance from the upper edge of the first region to the upper end face is D1, and the shortest distance from the lower edge of the first region to the lower end face is D2, D1 < D2; And / or, the distance d1 between the top of the electrode assembly and the upper end face is greater than the distance d2 between the bottom of the electrode assembly and the lower end face, d1 > d2.

7. The lithium-ion battery according to claim 1 or 2, wherein, In the height direction of the electrode assembly, the size of the first region is h, and the size of the aluminum-plastic film located in the first side cover is H, 10% ≤ h / H ≤ 50%.

8. The lithium-ion battery according to claim 1 or 2, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector, wherein the negative electrode active coating comprises silicon-carbon material; the mass content of elemental Si in the negative electrode active coating is 5%-50%; Preferably, the surface of the negative electrode active coating has grooves; More preferably, the depth of the groove is 5μm-35μm; More preferably, the width of the groove is 20μm-1000μm; More preferably, the spacing between the grooves is 0.5mm-10mm.

9. The lithium-ion battery according to claim 1 or 2, wherein, The separator includes a carrier layer and a first adhesive layer located on a first surface of the carrier layer, the surface of the first adhesive layer having a plurality of protrusions; the first adhesive layer faces the positive electrode sheet. Preferably, the protrusion contains element F; more preferably, the protrusion comprises polyvinylidene fluoride. Preferably, the height of the protrusion is 1μm-15μm; Preferably, the diameter of the orthographic projection of the protrusion on the diaphragm surface is 0.1 μm-15 μm; Preferably, the carrier layer includes a substrate layer and a nitrogen-containing coating located on at least one side surface of the substrate layer; More preferably, the nitrogen-containing coating is located on the first surface, and the nitrogen-containing coating at least faces the positive electrode sheet; More preferably, the thickness of the nitrogen-containing coating is 0.5 μm-4 μm; More preferably, the nitrogen-containing coating comprises at least one of polyacrylonitrile, nitrile rubber, 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, melamine cyanurate, and melamine thiocyanate.

10. The lithium-ion battery according to claim 2, wherein, Along the width direction of the electrode assembly, the electrode assembly includes a first arc surface and a second arc surface, the first arc surface is close to the first side cover, the second arc surface is close to the second side cover, and the first arc surface is provided with adhesive tape; And / or, the sum of the distances from the electrode assembly to the inner side of the first side cover and the inner side of the second side cover is 0.05mm-2mm.

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