Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device, and belongs to the technical field of energy storage. The secondary battery comprises an electrolyte and a shell; the electrolyte comprises a cyclic sulfate compound and a fluorosulfonylamide compound; the mass content of the cyclic sulfate compound and the fluorosulfonylamide compound is a% and b% respectively based on the total mass of the electrolyte, 0.01≤a≤5, 1≤b≤15; the shell comprises a shell body and a pressure relief assembly; the material of the shell body is a steel shell, the pressure relief assembly comprises a sealing element and a first through hole; the area of the first through hole is c mm 2 , 1≤c≤9; the pressure relief assembly is configured such that when the temperature inside the shell body reaches a threshold temperature, the sealing element of the pressure relief assembly loses the sealing effect, the first through hole is connected to the external environment, the internal pressure of the battery is released, and heat is taken out; the threshold temperature is d℃, 100≤d≤130. Through the above arrangement, the high-temperature cycle performance and the hot box pass rate of the secondary battery can be improved.

Description

Technical Field

[0001] This application belongs to the field of energy storage technology, specifically relating to a secondary battery and electronic device. Background Technology

[0002] As rechargeable energy storage devices, secondary batteries can store and release electrical energy through electrochemical reactions, making them an indispensable key component in electronic devices, electric vehicles, and energy storage systems. With continuous technological iteration and upgrades, lithium-ion batteries have been widely used due to their high energy density, long cycle life, and environmental friendliness.

[0003] Lithium-ion batteries with steel-cased packaging hold a significant position in the battery industry due to their high structural strength and excellent sealing properties. However, compared to pouch batteries packaged with aluminum-plastic film, steel-cased materials have higher thermal conductivity, resulting in a faster internal thermal response and a steeper temperature gradient within the cell during thermal abuse tests (such as nail penetration, heating, and external thermal shock). This characteristic makes steel-cased batteries more prone to triggering a chain reaction of internal thermal runaway within a short time under the influence of external heat sources, deteriorating the high-temperature cycling performance and thermal chamber pass-through rate of the secondary battery. This poses a systemic challenge to the coordinated design of electrolyte flame retardant design and thermal diffusion strategies for the steel-cased structure. Summary of the Invention

[0004] In view of this, this application provides a secondary battery and electronic device that improves the high-temperature cycle performance and hot box pass rate of the secondary battery by controlling the composition of the electrolyte and setting up a pressure relief component.

[0005] In a first aspect, this application provides a secondary battery, which includes an electrolyte and a casing;

[0006] The electrolyte contains cyclic sulfate compounds, and the mass content of the cyclic sulfate compounds is a% based on the total mass of the electrolyte, with a content of 0.01 ≤ a ≤ 5%.

[0007] The electrolyte also includes fluorosulfonamide compounds, as shown in Formula II:

[0008] Formula II;

[0009] Wherein, R1 is selected from fluorine atoms, wholly or partially fluorinated C1 to C5 alkyl groups, wholly or partially fluorinated C1 to C5 oxyalkyl groups, wholly or partially fluorinated C6 to C10 aryl groups, and wholly or partially fluorinated C6 to C10 oxyaryl groups; and when R1 contains an O atom, the O atom in R1 is not directly connected to the S atom; R2 and R3 are selected from fluorinated or unsubstituted C1 to C5 alkyl groups and fluorinated or unsubstituted C6 to C10 aryl groups; and when R2 and R3 are selected from fluorinated or unsubstituted C1 to C5 alkyl groups, R2 and R3 are independent of each other;

[0010] Based on the total mass of the electrolyte, the mass content of the fluorosulfonamide compound is b%, 1≤b≤15;

[0011] The outer casing includes a housing and a pressure relief assembly; the housing is made of steel, and the pressure relief assembly includes a seal and a first through-hole; the area of ​​the first through-hole is c mm. 2 , 1≤c≤9;

[0012] The pressure relief assembly is configured such that when the internal temperature of the casing reaches a threshold temperature, the seal of the pressure relief assembly loses its sealing function, allowing the first through-hole to connect to the external environment, thereby releasing the internal pressure of the battery and carrying away heat. The threshold temperature is d℃, where 100≤d≤130. This application introduces specific amounts of cyclic sulfate compounds and fluorosulfonamide compounds into the electrolyte to form a stable interfacial film on the positive and negative electrode surfaces, effectively suppressing side reactions at the positive and negative electrode interfaces and reducing heat and gas generation under high temperature or abuse conditions. Simultaneously, the pressure relief assembly with a specific first through-hole area can synergistically work with the cyclic sulfate compounds and fluorosulfonamide compounds, opening promptly through its first through-hole when the internal pressure reaches the threshold, allowing gas to escape and carrying away heat, preventing heat accumulation inside the cell from causing casing deformation and short circuits, and simultaneously suppressing the increased electrolyte activity under overheating conditions that would lead to aggravated side reactions with the electrode materials and casing. Among the three components—cyclic sulfate compounds, fluorosulfonamide compounds, and pressure relief components—if the content of cyclic sulfate compounds or fluorosulfonamide compounds is too low, the interfacial film protection is insufficient, leading to large amounts of heat and gas generated by solvent side reactions. Even if the pressure relief components are activated, the rapid pressure rise can still cause deformation of the steel shell, resulting in obstruction or sealing failure of the pressure relief channel. If the area of ​​the first through-hole of the pressure relief components is too small, it may affect the smooth discharge of gas, increasing the risk of steel shell battery deformation, increasing the probability of short circuit, and exacerbating the risk of thermal runaway. Conversely, if there is too much cyclic sulfate compounds or fluorosulfonamide compounds, the battery impedance will increase after the formation of the interfacial film, leading to more side reactions and deteriorating high-temperature cycling performance. If the area of ​​the first through-hole of the pressure relief components is too large, the shell rigidity will decrease, making it more prone to deformation, which will affect the venting efficiency and worsen the hot box throughput. Through the synergistic effect of the cyclic sulfate compounds, fluorosulfonamide compounds, and pressure relief components, the heat accumulation temperature of the secondary battery is effectively reduced, improving the high-temperature cycling performance and hot box throughput of the secondary battery.

[0013] In this application, "R2 and R3 are independent of each other" means that the substitution choices of R2 and R3 are unrelated to each other, and each can be independently selected from the defined range of groups. They can be the same or different.

[0014] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) 0.2 ≤ a ≤ 4; (2) 2 ≤ b ≤ 12; (3) 0.15 ≤ (a + b) / c ≤ 10; (4) 100 ≤ d ≤ 120. In the above embodiments, the present application regulates the mass content of cyclic sulfate compounds to meet the above ranges, which can effectively improve the stability of the positive and negative electrode interface films at high temperatures, reduce the high-temperature heat generation side reactions of the positive and negative electrodes, and thus further improve the high-temperature cycle performance and hot box throughput of the secondary battery.

[0015] In the above embodiments, the present application regulates the mass content of the fluorosulfonamide compound to meet the above range, which can suppress the degree of side reaction at the positive and negative electrode interface, effectively reduce the gas production and heat generation in the high temperature environment of the battery, thereby further improving the high temperature cycle performance and hot box pass rate of the secondary battery.

[0016] In the above embodiments, the ratio of the sum of the mass contents of cyclic sulfate compounds and fluorosulfonamide compounds to the area of ​​the first through hole is controlled to meet the above range, which can effectively balance the gas expansion and heat failure of the cell. This ensures that the cyclic sulfate compounds and fluorosulfonamide compounds fully suppress the electrochemical side reactions, and also ensures that the pressure relief channel is unobstructed and efficient, thereby significantly improving the thermal safety performance of the steel-cased battery.

[0017] In the above embodiments, if the threshold temperature of this application meets the above range, pressure can be released within a suitable temperature range to release the internal pressure of the steel shell and remove heat, reduce the degree of deformation of the steel shell, reduce the probability of short circuit of the cells inside the steel shell, and effectively reduce the rapid heat accumulation of the steel shell caused by short circuit, thereby further improving the high-temperature cycle performance and heat box pass rate of the secondary battery.

[0018] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) 0.3 ≤ a ≤ 3; (2) 2 ≤ b ≤ 8; (3) 0.3 ≤ (a+b) / c ≤ 8; (4) 105 ≤ d ≤ 115. Further adjusting the mass content of cyclic sulfate compounds, the mass content of fluorosulfonamide compounds, the ratio of the sum of the mass contents of cyclic sulfate compounds and fluorosulfonamide compounds to the area of ​​the first through-hole, and ensuring that the threshold temperature meets the above ranges, can further improve the high-temperature cycling performance and hot box throughput of the secondary battery.

[0019] In some embodiments, the cyclic sulfate compound includes at least one of the following compounds:

[0020] Formula I-1, Formula I-2, Formula I-3, Formula I-4, Formula I-5, Formula I-6, Formula I-7, Formula I-8, Formula I-9. The selection of cyclic sulfate compounds in this application can further improve the high-temperature cycle performance and hot box throughput of secondary batteries.

[0021] In some embodiments, the fluorosulfonamide compound includes at least one of the following compounds:

[0022] Formula II-1 Formula II-2 Formula II-3 Formula II-4 Formula II-5 Formula II-6 Formula II-7 Formula II-8 Formula II-9 Formula II-10 Formula II-11 Formula II-12 Formula II-13 Formula II-14 Formula II-15 Formula II-16 Formula II-17 Formula II-18 Formula II-19. The selection of fluorosulfonamide compounds in this application can further improve the high-temperature cycle performance and hot box pass rate of secondary batteries.

[0023] In some implementations, the first through hole can be a pressure relief hole or a liquid injection hole.

[0024] In some implementations, the seal may be elliptical or circular in shape.

[0025] In some embodiments, the electrolyte includes a first substance, which includes at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate. This application uses the first substance in conjunction with the above-mentioned electrolyte system to further improve the high-temperature cycle performance and hot box throughput of the secondary battery.

[0026] In some embodiments, the electrolyte includes a lithium salt, which includes at least one selected from LiPF6, LiBF4, LiB(C2O4)2, LiBF2C2O4, Li[(CF3SO2)2N], or Li[(FSO2)2N]. Based on the total mass of the electrolyte, the mass content of the lithium salt is e%, 5 ≤ e ≤ 20%. This application uses lithium salt in conjunction with the above-mentioned electrolyte system and controls the mass content of the lithium salt to meet the above range, which can further improve the high-temperature cycle performance and hot box throughput of the secondary battery.

[0027] In some embodiments, the seal comprises a polymer, including at least one selected from polyethylene, polypropylene, polyvinyl chloride, polypropylene chloride, polyvinylidene fluoride, polyacrylic acid, polyacrylate, polystyrene, polyacrylonitrile, or polymaleic anhydride. By selecting the aforementioned polymers, the seal's adhesion in the electrolyte can be improved, reducing potential seal failure problems caused by contact between the seal and the electrolyte.

[0028] In some embodiments, the secondary battery includes a positive electrode sheet, which includes a positive electrode active material, including lithium cobalt oxide; the single-sided coating weight of the positive electrode sheet is mg / cm³. 2 The coating weight of the positive electrode sheet is 13 ≤ m ≤ 26. This application regulates the coating weight on one side of the positive electrode to meet the above range, enabling it to synergistically form a dense and uniform CEI film on the positive electrode surface with cyclic sulfate compounds and fluorosulfonamide compounds in the electrolyte. This suppresses gas generation and side reactions at high temperatures, reduces the risk of heat accumulation, and further improves the high-temperature cycle performance and thermal conductivity of the secondary battery. If the coating weight is too high, the active material layer is too thick, and the electrolyte wetting is insufficient. Cyclic sulfate compounds and fluorosulfonamide compounds cannot effectively migrate to the interface, resulting in an incomplete CEI film coverage and inability to effectively suppress side reactions of the positive electrode at extreme temperatures. If the coating weight is too low, there is insufficient active material per unit area, leading to an increase in local current density. This causes excessive decomposition of cyclic sulfate compounds and fluorosulfonamide compounds, forming an excessively thick CEI film, hindering lithium-ion transport, and exacerbating polarization and heat generation.

[0029] The single-sided coating weight in this application refers to the mass of the material layer coated on one side of the current collector per unit area.

[0030] Based on the above implementation methods, the single-sided coating weight of the positive electrode sheet refers to the mass of the positive electrode material layer coated on one side of the current collector per unit area.

[0031] In some embodiments, lithium cobalt oxide includes Li x Co y M z N w O2, wherein 0.84≤x≤1.2, 0.84≤y<1, 0<z≤0.12, 0≤w<0.12, M is selected from at least one of aluminum, lanthanum, nickel, manganese, magnesium, titanium, zirconium, fluorine, tungsten, boron or yttrium, and N is selected from at least one of sodium, iron, silicon, zinc or phosphorus.

[0032] In some embodiments, the secondary battery includes a negative electrode sheet; the negative electrode sheet includes a negative electrode material layer containing silicon, and the mass content of silicon is h% based on the total mass of the negative electrode material layer, 1≤h≤25%. This application controls the mass content of silicon in the negative electrode material layer to meet the above range, which can improve the capacity of the negative electrode sheet while controlling the volume expansion of silicon and the accompanying heat generation effect during charging and discharging within a safe threshold. On the one hand, it enables cyclic sulfate compounds and fluorosulfonamide compounds to form a dense SEI film on the silicon surface, effectively suppressing electrolyte reduction decomposition and gas generation at high temperatures; on the other hand, it significantly reduces the pressure relief load on the pressure relief component, ensuring that internal pressure can be smoothly released through the first through-hole under thermal abuse conditions, avoiding casing deformation or short circuit.

[0033] In some embodiments, the coating weight on one side of the negative electrode sheet is n mg / cm³. 2 6.5≤n≤13. This application regulates the single-sided coating weight of the negative electrode sheet to meet the above range, enabling it to synergistically interact with cyclic sulfate esters and fluorosulfonamides in the electrolyte to form a dense, uniform, and thermally stable SEI film on the negative electrode surface. This significantly suppresses side reactions, gas generation, and heat accumulation during high-temperature cycling, further improving the high-temperature cycling performance and thermal pack throughput of the secondary battery. If the coating weight is too high, the active material layer is too thick, and the electrolyte wetting is insufficient, making it difficult for additives to effectively diffuse to the electrode / electrolyte interface. The resulting SEI film coverage is incomplete, failing to effectively suppress side reactions and gas evolution at high temperatures. If the coating weight is too low, the active material per unit area is insufficient, leading to excessively high local current density. This causes excessive decomposition of cyclic sulfate esters and fluorosulfonamides, generating an excessively thick, high-resistivity SEI film that hinders lithium-ion transport and exacerbates polarization and heat generation.

[0034] Further improve the high-temperature cycle performance and hot box pass rate of secondary batteries.

[0035] Based on the above implementation methods, the single-sided coating weight of the negative electrode sheet refers to the mass of the negative electrode material layer coated on one side of the current collector per unit area.

[0036] In some implementations, the volumetric energy density of the secondary battery is V Wh / L, where 700 ≤ V ≤ 1200.

[0037] Secondly, this application provides an electronic device including any of the aforementioned secondary batteries. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0039] In order to solve the problems of the prior art, this application provides a secondary battery in a first aspect, the secondary battery including an electrolyte and a casing;

[0040] The electrolyte contains cyclic sulfate compounds, and the mass content of the cyclic sulfate compounds is a% based on the total mass of the electrolyte, with a content of 0.01 ≤ a ≤ 5%.

[0041] The electrolyte also includes fluorosulfonamide compounds, as shown in Formula II:

[0042] Formula II;

[0043] Wherein, R1 is selected from fluorine atoms, wholly or partially fluorinated C1 to C5 alkyl groups, wholly or partially fluorinated C1 to C5 oxyalkyl groups, wholly or partially fluorinated C6 to C10 aryl groups, and wholly or partially fluorinated C6 to C10 oxyaryl groups; and when R1 contains an O atom, the O atom in R1 is not directly connected to the S atom; R2 and R3 are selected from fluorinated or unsubstituted C1 to C5 alkyl groups and fluorinated or unsubstituted C6 to C10 aryl groups; and when R2 and R3 are selected from fluorinated or unsubstituted C1 to C5 alkyl groups, R2 and R3 are independent of each other;

[0044] Based on the total mass of the electrolyte, the mass content of the fluorosulfonamide compound is b%, 1≤b≤15;

[0045] The outer casing includes a housing and a pressure relief assembly; the housing is made of steel, and the pressure relief assembly includes a seal and a first through-hole; the area of ​​the first through-hole is c mm. 2 , 1≤c≤9;

[0046] The pressure relief assembly is configured such that when the internal temperature of the casing reaches a threshold temperature, the seal of the pressure relief assembly loses its sealing function, allowing the first through-hole to connect to the external environment, thereby releasing the internal pressure of the battery and carrying away heat. The threshold temperature is d℃, where 100≤d≤130. The inventors discovered that this application, by synergistically introducing specific amounts of cyclic sulfate compounds and fluorosulfonamide compounds into the electrolyte, can suppress interfacial side reactions and heat and gas generation at high temperatures. Specifically, the excellent high-temperature stability of the cyclic sulfate compounds allows for the formation of thermally stable interfacial films on the positive and negative electrode surfaces, significantly reducing side reactions and associated heat generation during high-temperature cycling. Simultaneously, due to their excellent low reactivity and low heat generation, the addition of a certain amount of fluorosulfonamide compounds can further reduce gas generation and heat generation in the high-temperature environment of the battery without affecting its high-temperature cycling performance. The two compounds complement each other in terms of film-forming ability and thermochemical stability, jointly improving the high-temperature cycling performance and thermal chamber test pass rate of the battery. Furthermore, this application incorporates a pressure relief component with a specific first through-hole area, which can synergistically work with cyclic sulfate compounds and fluorosulfonamide compounds. Through its first through-hole, it opens promptly when the internal pressure reaches a threshold, allowing gas to escape and carrying away heat. This prevents heat accumulation inside the cell from causing casing deformation and short circuits, while simultaneously suppressing the increased electrolyte activity under overheating conditions, which could exacerbate side reactions with the electrode materials and casing. If the content of the cyclic sulfate compound or fluorosulfonamide compound is too low, the interfacial film protection is insufficient, leading to large amounts of heat and gas generated by solvent side reactions. Even if the pressure relief component opens, the rapid pressure increase can still cause deformation of the steel casing, resulting in obstruction or sealing failure of the pressure relief channel. If the first through-hole area of ​​the pressure relief component is too small, it may affect the smooth escape of gas, increasing the risk of steel casing battery deformation, raising the probability of short circuits, and exacerbating the risk of thermal runaway. Conversely, excessive amounts of cyclic sulfate compounds or fluorosulfonamide compounds can lead to increased battery impedance, more side reactions, and deteriorated high-temperature cycling performance after the formation of an interfacial film. Furthermore, an excessively large first through-hole area in the pressure relief component reduces the rigidity of the casing, making it more prone to deformation and affecting venting efficiency, thus worsening the hot box throughput. Through the synergistic effect of the aforementioned cyclic sulfate compounds, fluorosulfonamide compounds, and pressure relief components, the heat accumulation temperature of the secondary battery is effectively reduced, improving its high-temperature cycling performance and hot box throughput.

[0047] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) 0.2 ≤ a ≤ 4; (2) 2 ≤ b ≤ 12; (3) 0.15 ≤ (a + b) / c ≤ 10; (4) 100 ≤ d ≤ 120. This application regulates the mass content of cyclic sulfate compounds, the mass content of fluorosulfonamide compounds, the ratio of the sum of the mass contents of cyclic sulfate compounds and fluorosulfonamide compounds to the area of ​​the first through-hole, and ensures that the threshold temperature meets the above ranges, thereby synergistically improving the high-temperature cycling performance and hot box throughput of the secondary battery.

[0048] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) 0.3 ≤ a ≤ 3; (2) 2 ≤ b ≤ 8; (3) 0.3 ≤ (a+b) / c ≤ 8; (4) 105 ≤ d ≤ 115. This application adjusts the above parameters to further satisfy the above ranges, which can synergistically improve the high-temperature cycling performance and hot box pass rate of the secondary battery.

[0049] In some embodiments, 0.01 ≤ a ≤ 5, preferably 0.2 ≤ a ≤ 4, and more preferably 0.3 ≤ a ≤ 3. For example, the value of a can be 0.01, 0.1, 0.2, 0.3, 0.7, 1.2, 1.9, 2.4, 3, 3.5, 3.8, 4, 4.6, 4.9, 5, or any value within the range of any two of these values. This application regulates the mass content of the cyclic sulfate ester compound to meet the above range, which can effectively improve the stability of the positive and negative electrode interface film at high temperatures, reduce high-temperature heat-generating side reactions of the positive and negative electrodes, and thus further improve the high-temperature cycle performance and hot box throughput of the secondary battery. If the amount added is too low, an effective interface film cannot be formed, and the high-temperature cycle performance of the battery cannot be improved. If the amount added is too high, the viscosity of the electrolyte will be significantly increased, leading to reduced electrolyte wettability and deterioration of battery cycle performance.

[0050] In some embodiments, 1 ≤ b ≤ 15, preferably 2 ≤ b ≤ 12, and more preferably 2 ≤ b ≤ 8. For example, the value of b can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or any combination of these values. This application regulates the mass content of the fluorosulfonamide compound to meet the above range, which can suppress the degree of side reactions at the positive and negative electrode interfaces, effectively reduce the gas production and heat generation in the high-temperature environment of the battery, thereby further improving the high-temperature cycle performance and heat box throughput of the secondary battery. If the amount added is too low, it will not be able to suppress the side reactions; if the amount added is too high, it will reduce the solubility of the lithium salt, leading to lithium salt precipitation.

[0051] In some embodiments, 1≤c≤9, preferably 3≤c≤7. For example, the value of c can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or any combination of these values. This application controls the area of ​​the first through-hole to meet the above range, effectively balancing pressure relief capacity and shell structural strength. If the area of ​​the first through-hole is too large, although it facilitates rapid gas discharge, it will reduce the local mechanical strength of the steel shell, making it prone to deformation under internal battery pressure or thermal stress, leading to failure of the pressure relief component or loss of sealing. If the area of ​​the first through-hole is too small, it will affect the pressure relief efficiency, preventing timely release of internal gas during thermal runaway or abnormal gas generation, causing a sharp increase in internal pressure, which in turn causes the steel shell to bulge and deform. Therefore, controlling the area of ​​the first through-hole to 1mm... 2 Up to 9mm 2 This ensures efficient gas discharge under high temperature or abuse conditions while maintaining sufficient structural rigidity of the steel shell to resist deformation, thereby further improving the heat box pass rate of the secondary battery.

[0052] In some embodiments, 100≤d≤130, preferably 100≤d≤120, and more preferably 105≤d≤115. For example, the value of d can be 100, 105, 110, 111, 112, 113, 115, 117, 118, 119, 120, 123, 124, 125, 127, 130, or any value within the range of any two of these values. By controlling the threshold temperature to meet the above range, pressure relief can be performed within a suitable temperature range, releasing the internal pressure of the steel shell and carrying away heat, reducing the degree of deformation of the steel shell, reducing the probability of short circuits in the cells inside the steel shell, and effectively reducing the rapid heat accumulation in the steel shell caused by short circuits, thereby further improving the high-temperature cycle performance and heat box pass rate of the secondary battery. In the threshold temperature range above 130°C, pressure relief failure is likely to occur; while in the threshold temperature range below 110°C, leakage may occur, neither of which achieves the ideal pressure relief effect and leads to a deterioration in the thermal safety performance of the cells.

[0053] In some embodiments, 0.15 ≤ (a+b) / c ≤ 10, preferably 0.3 ≤ (a+b) / c ≤ 8. For example, the value of (a+b) / c can be 0.15, 0.3, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any combination of these values. This application regulates the ratio of the sum of the mass contents of cyclic sulfate compounds and fluorosulfonamide compounds to the area of ​​the first through-hole to meet the above range, effectively balancing the gas expansion and heat generation failure of the battery cell. This ensures both the sufficient suppression of electrochemical side reactions by cyclic sulfate compounds and fluorosulfonamide compounds and the unobstructed and efficient pressure relief channel, thereby significantly improving the thermal safety performance of the steel-cased battery. If the ratio is too small, the total amount of cyclic sulfate compounds and fluorosulfonamide compounds is insufficient to effectively suppress heat and gas generation in the battery, causing a sudden increase in internal pressure. This leads to the steel shell bulging and deforming, resulting in the pressure relief components being unable to effectively relieve pressure due to deformation, and the thermal safety test of the steel-shell battery is at risk of failure. If the ratio is too large, the battery venting is not smooth enough, and the effective venting area of ​​the through holes is relatively insufficient, leading to gas accumulation and stress concentration in the shell. This increases the risk of steel shell deformation and the probability of internal short circuits, and the thermal safety performance of the steel-shell battery cannot be guaranteed.

[0054] In some embodiments, cyclic sulfate compounds include at least one of the following compounds:

[0055] Formula I-1, Formula I-2, Formula I-3, Formula I-4, Formula I-5, Formula I-6, Formula I-7, Formula I-8, Formula I-9. The cyclic sulfate compounds of this application can form an interfacial film with excellent thermal stability at the positive and negative electrodes, reduce side reactions at the positive and negative electrodes in high temperature and high pressure environments, suppress heat generation in the battery, and thus improve the high temperature cycle performance and heat box throughput of the secondary battery.

[0056] In some embodiments, the fluorosulfonamide compound includes at least one of the following compounds:

[0057] Formula II-1 Formula II-2 Formula II-3 Formula II-4 Formula II-5 Formula II-6 Formula II-7 Formula II-8 Formula II-9 Formula II-10 Formula II-11 Formula II-12 Formula II-13 Formula II-14 Formula II-15 Formula II-16 Formula II-17 Formula II-18 Formula II-19. The fluorosulfonamide compound of this application has excellent low reactivity and low heat generation, which can suppress the degree of side reaction at the positive and negative electrode interface, effectively reduce the gas generation and heat generation in the high temperature environment of the battery, thereby improving the high temperature cycle performance and heat box throughput of the secondary battery.

[0058] In some embodiments, the first through hole can be a pressure relief hole or a liquid injection hole. The first through hole of this application can both connect to the external environment and relieve pressure when the seal loses its sealing function, and can also be used for liquid injection before formation, thereby simplifying the manufacturing process of the battery cell with the casing and reducing the production cost of the battery cell.

[0059] In some embodiments, the seal may be elliptical or circular in shape.

[0060] In some embodiments, the seal may include a polymer covering the first through-hole and bonded to the housing by thermoforming, making the connection simple and convenient. During thermal abuse, the polymer loses its viscosity upon heating and easily separates from the housing, thereby opening the first through-hole to release pressure and achieve timely pressure relief, improving the safety performance of the battery cell equipped with this housing. In some embodiments, the polymer includes at least one of polyethylene, polypropylene, polyvinyl chloride, polypropylene chloride, polyvinylidene fluoride, polyacrylic acid, polyacrylate, polystyrene, polyacrylonitrile, or polymaleic anhydride. Using the above polymers can improve the stability of the seal when in contact with the electrolyte and reduce the risk of loss of viscosity and leakage due to electrolyte immersion.

[0061] In some embodiments, the seal may further include a first metal sheet; a polymer is disposed between the first metal sheet and the housing, the first metal sheet being connected to the housing via the polymer and covering the first through-hole. In some embodiments, the first metal sheet is made of one or more of nickel, aluminum, or stainless steel.

[0062] In some embodiments, the seal further includes a second metal sheet having a second through hole; the second metal sheet is connected between the first metal sheet and the housing, the second through hole communicates with the first through hole, and the second metal sheet is attached to the outer surface of the housing by a polymer. In some embodiments, the material of the second metal sheet is one or more of nickel, aluminum, or stainless steel.

[0063] In the above technical solution, the sealing element is provided with a second through hole that communicates with the first through hole, thereby further improving the pressure relief efficiency of the pressure relief assembly.

[0064] In some embodiments, the electrolyte includes a first substance, which includes at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate. This application introduces a first substance that, in conjunction with the aforementioned electrolyte system, possesses a considerable dielectric constant and high-voltage stability, can dissolve lithium salts, effectively optimizes the conductivity and viscosity of the electrolyte, thereby improving the overall cycle stability of the battery, and further enhancing the high-temperature cycle performance and thermal conductivity of the secondary battery.

[0065] In some embodiments, the electrolyte comprises a lithium salt, which includes at least one of LiPF6, LiBF4, LiB(C2O4)2, LiBF2C2O4, Li[(CF3SO2)2N], or Li[(FSO2)2N]. The mass content of the lithium salt is e% based on the total mass of the electrolyte, 5 ≤ e ≤ 20. For example, the value of e can be 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 20, or a value within the range of any two of these values.

[0066] In some embodiments, the secondary battery includes a positive electrode sheet, which includes a positive electrode active material, including lithium cobalt oxide; the single-sided coating weight of the positive electrode sheet is m mg / cm³. 2 The value of m is 13 ≤ m ≤ 26, preferably 16 ≤ m ≤ 23, and more preferably 17 ≤ m ≤ 21. For example, the value of m can be 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, or any combination of these values. This application controls the single-sided coating weight of the positive electrode sheet to meet the above range, enabling it to synergistically form a dense and uniform CEI film on the positive electrode surface with cyclic sulfate compounds and fluorosulfonamide compounds in the electrolyte. This suppresses gas generation and side reactions at high temperatures, reduces the risk of heat accumulation, and further improves the high-temperature cycle performance and hot box pass rate of the secondary battery. If the coating weight is too high, the active material layer will be too thick, and the electrolyte will not wet sufficiently. Cyclic sulfate compounds and fluorosulfonamide compounds will have difficulty migrating to the interface effectively, resulting in an incomplete CEI film that cannot effectively suppress side reactions of the positive electrode at extreme temperatures. If the coating weight is too low, there will be insufficient active material per unit area, leading to an increase in local current density. This will cause excessive decomposition of cyclic sulfate compounds and fluorosulfonamide compounds, resulting in an excessively thick CEI film that hinders lithium-ion transport and exacerbates polarization and heat generation.

[0067] In some embodiments, lithium cobalt oxide includes Lix Co y M z N w O2, wherein 0.84≤x≤1.2, 0.84≤y<1, 0<z≤0.12, 0≤w<0.12, M is selected from at least one of aluminum, lanthanum, nickel, manganese, magnesium, titanium, zirconium, fluorine, tungsten, boron, or yttrium, and N is selected from at least one of sodium, iron, silicon, zinc, or phosphorus. This application controls the composition of the lithium cobalt oxide to meet the above ranges, effectively stabilizing its structure under high voltage and high temperature conditions, suppressing lattice distortion, phase transition, and lattice oxygen release caused by deep delithiation during charging and discharging, and reducing structural collapse. Simultaneously, the lithium cobalt oxide of this composition synergistically interacts with cyclic sulfate compounds and fluorosulfonamide compounds in the electrolyte to form a dense, high-temperature stable CEI film in situ on the positive electrode surface, effectively passivating the interface, preventing electrolyte oxidative decomposition, and significantly reducing side reaction heat generation and gas generation. By using the aforementioned lithium cobalt oxide as the positive electrode active material, the charging voltage and volumetric energy density of the secondary battery are further improved, and the high-temperature cycle performance and thermal pack pass rate of the battery are significantly enhanced while ensuring safety.

[0068] In some embodiments, the secondary battery includes a negative electrode sheet; the negative electrode sheet includes a negative electrode material layer containing silicon. Based on the total mass of the negative electrode material layer, the mass content of silicon is h%, 1≤h≤25. For example, the value of h can be 1, 2, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 17, 18, 20, 22, 25, or any value within the range of any two of these values. This application regulates the mass content of silicon in the negative electrode active material layer to meet the above range, which can improve the capacity of the negative electrode sheet while controlling the volume expansion of silicon and the accompanying heat generation effect during charging and discharging within a safe threshold. On the one hand, it allows cyclic sulfate ester compounds and fluorosulfonamide compounds to form a dense SEI film on the silicon surface, effectively suppressing electrolyte reduction decomposition and gas generation at high temperatures; on the other hand, it significantly reduces the pressure relief load on the pressure relief component, ensuring that internal pressure can be smoothly released through the first through-hole under thermal abuse conditions, avoiding casing deformation or short circuit.

[0069] In some embodiments, the coating weight on one side of the negative electrode sheet is n mg / cm³. 2The value of n is 6.5 ≤ n ≤ 13, preferably 7.5 ≤ n ≤ 10.5, and more preferably 8 ≤ n ≤ 9.5. For example, the value of n can be 6.5, 6.8, 7, 7.3, 8, 8.5, 9, 9.2, 10, 10.5, 11, 12, 12.6, 13, or any value within the range of any two of these values. This application controls the single-sided coating weight of the negative electrode sheet to meet the above range, enabling it to synergistically interact with cyclic sulfate ester compounds and fluorosulfonamide compounds in the electrolyte to form a dense, uniform, and thermally stable SEI film on the negative electrode surface. This significantly suppresses side reactions, gas generation, and heat accumulation during high-temperature cycling, further improving the high-temperature cycling performance and hot box throughput of the secondary battery. If the coating weight is too high, the active material layer will be too thick, and the electrolyte will not be sufficiently wetted, making it difficult for the additives to effectively diffuse to the electrode / electrolyte interface. The resulting SEI film will not cover the entire surface and will not be able to effectively suppress the side reactions and gas evolution of the negative electrode at high temperatures. If the coating weight is too low, there will be insufficient active material per unit area, and the local current density will be too high, which will promote the excessive decomposition of cyclic sulfate compounds and fluorosulfonamide compounds, generating an excessively thick, high-resistivity SEI film that hinders lithium-ion transport and exacerbates polarization and heat generation.

[0070] In some embodiments, the volumetric energy density of the secondary battery is V Wh / L, where 700 ≤ V ≤ 1200. This application, through the above-described scheme, enables the secondary battery to have a volumetric energy density of 700 ≤ V ≤ 1200, thereby better meeting the needs of consumer electronics, wearable devices, and other applications for high volumetric energy density energy storage devices.

[0071] In this application, the electrolyte also includes a non-aqueous solvent. This application does not particularly limit the non-aqueous solvent, as long as it can serve as a medium for the movement of ions participating in the electrochemical reaction of the battery cell. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dipropyl carbonate, methyl propyl carbonate, or ethyl propyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of butylene carbonate or vinyl ethylene carbonate. The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, ethyl methyl-2,2-difluoroethylene, ethyl 2,2,2-trifluoroethylene, ethyl 2,2-difluoroethylene, and methyl 2,2-difluoroacetate. The aforementioned ether compounds may include, but are not limited to, at least one of 1,3-dioxapentane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, ketone solvents such as 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, and cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; alcohol solvents such as ethanol and isopropanol; nitrile solvents such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds) (e.g., acetonitrile); amide solvents such as dimethylformamide; dioxolane solvents such as 1,2-dioxolane and 1,3-dioxolane; or sulfone solvents such as dimethyl sulfoxide, sulfolane, and methyl sulfolane; or phosphate solvents such as trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. In the above text, the hydrocarbon group may be selected from one or more of alkyl, alkenyl, or alkynyl groups.

[0072] The lithium salt in the electrolyte of this application may also include, but is not limited to, at least one of: lithium difluorophosphate (LiPO2F2), LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6 or lithium difluoroborate.

[0073] The electrolyte of this application may also include functional additives, which may be cyclic carbonate compounds, nitrile compounds, boron-containing compounds, nitrogen-containing lithium salt compounds, sulfonate compounds, sulfate ester compounds, phosphate ester compounds, silane compounds, ether compounds, pyridine compounds, or other compounds.

[0074] Preferably, the functional additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), trans-difluoroethylene carbonate (DFEC), vinyl sulfite (ES), succinate (SN), glutaronitrile, adiponitrile (ADN), heptanonitrile, caprylyl nitrile, sebaconitrile, triaconitrile glycerol (TCP), 1,2-di(cyanoethoxy)ethane, 1,3,6-hexanetricarbonyl (HTCN), ethylene glycol bis(propionitrile) ether (DENE), 1,2,3-tris(2-cyanoethoxy)propane, 1,4-dicyano-2-butene, 1,3-propanesulfonyl lactone (PS), propenyl-1,3-sulfonyl lactone (PST), lithium trioxamate phosphate (LiTOP), tri(trimethylsilane) phosphate (TMSP), tri(trimethylsilane) phosphite, tri(2,2,2-trifluoroethylene) phosphate, etc. The following are at least one of the following: trimethyl phosphite (TFEP), trimethyl phosphite (TMP), triethyl phosphate (TEP), tris(pentafluorophenyl)phosphine (TPFPP), pentafluoroethoxycyclotriphosphazene (PFPN), fluorotris(trimethylsilane) phosphate, dimethyldimethoxysilane (DODSi), tetravinylsilane (TVS), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium monofluorophosphate, 1,2-bis(difluorophosphoxy)ethane, lithium fluorosulfonate, tris(trimethylsilane)borate (TMSB), hexamethyldisilazane (HMDS), fluorobenzene (FB), cyclohexylbenzene, biphenyl (BP), maleic anhydride (MA), acetamide (EA), polyamide (PA), pyridine, 2-methylpyridine, 2-fluoropyridine, 2-cyanopyridine, or 3-vinylpyridine.

[0075] There are no particular restrictions on the selection and content of the aforementioned functional additives in the electrolyte; they can be chosen according to actual needs. For example, specific components can be selected as film-forming additives, flame-retardant additives, overcharge protection additives, water / acid removal additives, passivating agents for protecting Al current collectors or battery casings, and wetting agents to improve wetting properties to meet the battery's needs for different application scenarios and positive and negative electrode matching.

[0076] positive electrode

[0077] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be located on one surface of the positive current collector along its thickness direction, or it can be located on two surfaces of the positive current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the positive current collector, or it can refer to a portion of the surface area of ​​the positive current collector. This application does not have any particular limitations, as long as the purpose of this application is achieved.

[0078] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors). Composite current collectors can be formed by forming metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer substrate.

[0079] The positive current collector of this application can have an appropriate thickness as needed. Although there are no particular limitations, the positive current collector can have a thickness in the range of 1 μm to 500 μm, or a thickness in the range of 1 μm to 300 μm, or a thickness in the range of 1 μm to 100 μm, or a thickness in the range of 1 μm to 50 μm, or a thickness in the range of 1 μm to 20 μm.

[0080] Unless otherwise specified, the terms thickness (or height), width, and length used in this invention refer to average values ​​and can be measured by a measuring instrument capable of measuring thickness (or height), width, and length separately and in accordance with methods in the art.

[0081] The positive electrode current collector can form fine irregularities on its surface, thereby further enhancing its adhesion to the positive electrode material layer. For example, the positive electrode current collector can be selected from one or more of the following: membrane, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0082] The positive electrode material layer of this application includes a positive electrode active material, and the positive electrode active material of this application may also include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05 At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate.

[0083] In this application, the positive electrode material layer may further include a positive electrode binder and a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode binder in the positive electrode material layer, as long as it achieves the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR), or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0084] This application does not impose any particular limitation on the type of positive electrode conductive agent in the positive electrode material layer, as long as it can achieve the purpose of this application. In some embodiments, the positive electrode conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. This application does not impose any particular limitation on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as it can achieve the purpose of this application. For example, the loading of positive electrode active material in the positive electrode sheet is 4.0 mg / cm³. 2 Up to 10.0 mg / cm 2 .

[0085] In this application, the positive electrode material layer can be formed by coating a positive electrode slurry onto at least one side of the positive electrode current collector and drying it, and calendering can be performed after drying if necessary. The positive electrode slurry includes the aforementioned positive electrode material and a positive electrode binder, and may further include a conductive agent if necessary. In addition, the positive electrode slurry may also contain a solvent. This application does not have any particular limitation on the type of solvent, as long as it can achieve the purpose of this application. For example, the solvent may be an organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, methyl propionate, alcohol, or ethyl propionate, or an aqueous solvent such as water, or a mixed solvent composed of two or more of the above solvents.

[0086] This application does not impose any particular restrictions on the mass ratio of the positive electrode material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. These mass ratios can be those that are known to be applicable.

[0087] negative electrode

[0088] This application does not impose any particular limitation on the negative electrode, as long as the purpose of this application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application does not impose any particular limitation, as long as the purpose of this application can be achieved.

[0089] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.).

[0090] The negative electrode current collector of this application can have an appropriate thickness as needed. Although there are no particular limitations, the negative electrode current collector can have a thickness in the range of 1 μm to 500 μm, or in the range of 1 μm to 300 μm, or in the range of 1 μm to 100 μm, or in the range of 1 μm to 50 μm, or in the range of 1 μm to 20 μm, or in the range of 5 μm to 10 μm.

[0091] The negative electrode current collector can form fine irregularities on its surface, thereby further enhancing its adhesion to the negative electrode material layer. For example, the negative electrode current collector can be selected from one or more of the following forms: membrane, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0092] The negative electrode material layer of this application includes a negative electrode active material, which may include, but is not limited to, graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, and SiO2. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate lithiation TiO2-Li4Ti5O 12The material comprises at least one of Li-Al alloy and metallic lithium. In some embodiments, the negative electrode active material includes silicon-carbon material. In some embodiments, the silicon particles in the silicon-carbon material are selected to be spherical with a sphericity ≥0.66, which is beneficial for reducing side reactions. In some embodiments, the silicon particles in the silicon-carbon material are selected to be bulk silicon, which is beneficial for capacity utilization. In some embodiments, the Dv10 of the silicon-carbon material is in the range of 2μm-7μm. In some embodiments, the Dv50 of the silicon-carbon material is in the range of 6μm-12μm. In some embodiments, the Dv90 of the silicon-carbon material is in the range of 10μm-20μm. In some embodiments, the Dv99 of the silicon-carbon material is in the range of 15μm-30μm.

[0093] The negative electrode material layer in this application may further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode material layer may further include a negative electrode binder, a negative electrode conductive agent, and a thickener. This application does not impose any particular limitation on the type of negative electrode binder in the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of the following: polyvinylidene fluoride (PVDF), polyvinyl alcohol, styrene-butadiene rubber (SBR), polyethylene oxide, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, cellulose acetate, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyarylate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin, or nylon.

[0094] This application does not impose any particular limitation on the type of negative electrode conductive agent in the negative electrode material layer, as long as it can achieve the purpose of this application. In some embodiments, the negative electrode conductive agent includes carbon-based materials, such as graphite such as natural graphite or artificial graphite, carbon black, acetylene black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, and other carbon materials; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or mixtures formed by any combination of these substances.

[0095] This application does not impose any particular limitation on the type of thickener, as long as it can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0096] In this application, the negative electrode material layer can be formed by coating a negative electrode slurry onto at least one side of the negative electrode current collector and drying it, and calendering can be performed after drying if necessary. The negative electrode slurry includes the aforementioned negative electrode material and negative electrode binder, and may further include a negative electrode conductive agent if necessary. In addition, the negative electrode slurry may also contain a solvent. This application does not have any particular limitation on the type of solvent, as long as it can achieve the purpose of this application. For example, the solvent may be an organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, methyl propionate, alcohol, or ethyl propionate, or an aqueous solvent such as water, or a mixed solvent composed of two or more of the above solvents.

[0097] diaphragm

[0098] The separator in this application refers to a membrane that prevents short circuits between the positive and negative electrodes while allowing electron transport substances to pass through. This application does not impose any particular limitations on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, and spun membrane.

[0099] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0100] Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the inorganic particles, which may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. This application does not have any particular limitation on the binder, which may be at least one of the above-mentioned positive electrode binders or negative electrode binders. The polymer layer contains a polymer. This application does not have any particular limitation on the polymer, which may include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene). In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 5 μm to 500 μm.

[0101] Secondly, this application provides an electronic device including any of the aforementioned secondary batteries.

[0102] In some embodiments, the electronic devices of this application include, but are not limited to, laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0103] The following uses a lithium-ion battery as an example to illustrate the solution of this application with specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels. Various tests and evaluations are carried out according to the methods described below. In addition, unless otherwise specified, "parts" and "%" are quality bases.

[0104] Test methods

[0105] Elemental mass content test (silicon):

[0106] The mass percentage of silicon was determined using microwave digestion and a PE ICP-OES Optima 7000DV instrument.

[0107] High-temperature cycling performance test:

[0108] The lithium-ion battery was placed in a constant temperature environment of 45℃ and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 0.5C to 4.53V, followed by constant voltage charging at 4.53V to a current of 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V, and this initial discharge capacity C0 was recorded. The same process was repeated 600 times, including charging at a constant current of 0.5C to 4.53V, followed by constant voltage charging at 4.53V to a current of 0.025C, standing for 5 minutes, and then discharging at a constant current of 0.5C to 3.0V. The discharge capacity C1 after 600 cycles was recorded. The high-temperature cycle capacity retention rate was calculated and used as an indicator to evaluate the high-temperature cycle performance of the lithium-ion battery.

[0109] High-temperature cycling capacity retention % = C1 / C0 × 100%.

[0110] Hot box pass rate test:

[0111] Take a lithium-ion battery and place it in a constant temperature environment of 25℃ for 30 minutes to allow it to reach a constant temperature. Charge it at a constant current of 0.5C to 4.53V, then charge it at a constant voltage of 4.53V to a current of 0.025C, and let it stand for 5 minutes. Before testing, take photos and measure the internal resistance. Then, attach a temperature sensing wire to the battery surface, place the sample in the heating furnace, and raise the temperature to 130±2℃ at a rate of 5±2℃ / min and maintain it for 60 minutes. After the test, take photos and measure the internal resistance. The criterion for passing the hot chamber test is that the battery does not catch fire or explode. Perform parallel tests on 20 cells to calculate the pass rate of the hot chamber test, which is used as an indicator to evaluate the safety performance of lithium-ion batteries.

[0112] Hot box test pass rate % = number of samples that passed the test / 20 × 100%.

[0113] Example 1-1

[0114] <Preparation of Electrolyte>

[0115] In an argon-atmosphere glove box with a water content of less than 10 ppm, a base solvent was prepared by mixing ethylene carbonate, propylene carbonate, propyl acetate, and ethyl propionate in a ratio of 1:1:2:1.5 (mass ratio). Lithium hexafluorophosphate (LiPF6), cyclic sulfate compounds, and fluorosulfonamide compounds were then added and stirred until homogeneous to obtain the electrolyte. Based on the total mass of the electrolyte, the mass content of lithium hexafluorophosphate was 12.5%. The types and mass contents of the cyclic sulfate compounds and fluorosulfonamide compounds are shown in Table 1 below. The remainder was the base solvent.

[0116] <Preparation of Negative Electrode Sheets>

[0117] Silicon carbon particles, graphite particles, conductive agent (acetylene black), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 2:95.4:1.4:1.2. Deionized water was then added, and the mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 51 wt% was obtained. The negative electrode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 85°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer (60 μm thick). (The single-sided coating weight of the negative electrode sheet was 6.5 mg / cm².) 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode active material. After cold pressing and cutting, the negative electrode sheet is ready for use.

[0118] <Preparation of the positive electrode>

[0119] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), and conductive carbon black were mixed at a mass ratio of 97:2:1. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was then uniformly coated onto one surface of a 30 μm thick aluminum foil current collector and dried at 90 °C to obtain a positive electrode sheet with a single-sided coating of positive active material (40 μm thick). (The single-sided coating weight of the positive electrode sheet was 13 mg / cm³.) 2 Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material. After cold pressing and cutting, the positive electrode sheet is ready for use.

[0120] <Septum>

[0121] A 5 μm thick polyethylene-polypropylene composite film was used as the base film. PVDF slurry and inorganic particle slurry (a mass ratio of lamellar boehmite and Al2O3 of 70:30) were coated on the two surfaces of the base film, respectively, and then dried to obtain the separator film. The coating thickness on each surface of the separator film was 3 μm.

[0122] <Preparation of Lithium-ion Batteries>

[0123] The prepared positive and negative electrode sheets are stacked sequentially, with the separator positioned between them to act as a barrier. These are then stacked alternately in sequence and fixed to obtain a stacked electrode assembly. This assembly is placed in a steel shell equipped with a pressure relief component, dried, and then injected with electrolyte. After processes including electrolyte injection, formation, pressure relief, electrolyte replenishment, and sealing, a lithium-ion battery cell is obtained. The pressure relief component includes a seal and a first through-hole, the area of ​​which is shown in Table 1 below.

[0124] Comparative Examples 1-9

[0125] Comparative Examples 1-9 differ from Examples 1-1 in that the electrolyte is prepared according to a method including the following steps:

[0126] In an argon-atmospheric glove box with a water content of less than 10 ppm, a base solvent was prepared by mixing ethylene carbonate, propylene carbonate, propyl acetate, and ethyl propionate in a ratio of 1:1:2:1.5 (mass ratio). Lithium hexafluorophosphate (LiPF6), formula I-8, and sulfonamide were then added and stirred until homogeneous to obtain the electrolyte. The electrolyte contained, based on its total mass, 12.5% ​​lithium hexafluorophosphate, 1.5% formula I-8, and 1% sulfonamide, with the remainder being the base solvent.

[0127] The main difference between the embodiments and comparative examples in Table 1 and Example 1-1 is that the parameters shown in Table 1 are adjusted accordingly.

[0128] Table 1

[0129]

[0130] Note: In Table 1, " / " indicates that the corresponding substance or parameter does not exist. The (a+b) / c values ​​of Examples 1-23 to 1-25 are rounded to one decimal place.

[0131] As shown in Table 1, this application, by controlling the inclusion of cyclic sulfate compounds and fluorosulfonamide compounds in the electrolyte and controlling the mass content of each component to meet the requirements of 0.01≤a≤5 and 1≤b≤15, can suppress side reactions at the positive and negative electrode interfaces and improve the high-temperature cycle performance and thermal pack throughput of the battery. In particular, when the mass content of each component is adjusted to meet the requirements of 0.3≤a≤3 and 2≤b≤8, the high-temperature cycle performance and thermal pack throughput of the battery can be further improved.

[0132] This application can further improve the high-temperature cycle performance and hot box throughput of the battery by adjusting the area of ​​the first through hole to satisfy 1≤c≤9 and the threshold temperature to satisfy 100≤d≤130.

[0133] The main differences between the embodiments in Table 2 and embodiments 1-30 are as follows: the single-sided coating weight of the positive electrode, the single-sided coating weight of the negative electrode, the mass content of silicon, and the volumetric energy density of the secondary battery are shown in Table 2.

[0134] Table 2

[0135]

[0136] As shown in Table 2, this application achieves improved high-temperature cycle performance of the secondary battery by adjusting the single-sided coating weight of the positive electrode sheet to satisfy 13≤m≤26, preferably 16≤m≤23. Similarly, this application further improves the high-temperature cycle performance of the secondary battery by adjusting the single-sided coating weight of the negative electrode sheet to satisfy 6.5≤n≤13, preferably 7.5≤n≤10.5.

[0137] This application controls the mass content h% of silicon in the negative electrode material layer to satisfy 1≤h≤25, which can improve the capacity of the negative electrode sheet while controlling the volume expansion and heat generation effect of silicon during charging and discharging within a safe threshold.

[0138] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes an electrolyte and a casing; The electrolyte includes cyclic sulfate compounds, and based on the total mass of the electrolyte, the mass content of the cyclic sulfate compounds is a%, 0.2≤a≤4%. The cyclic sulfate compounds include at least one of the following compounds: Equation I-1, Formula I-6, Formula I-7, Formula I-8; The electrolyte comprises a fluorosulfonamide compound, as shown in Formula II: Formula II; Wherein, R1 is selected from fluorine atoms, or C1 to C5 alkyl groups that are wholly or partially fluorine-substituted; R2 and R3 are selected from fluorine-substituted or unsubstituted C1 to C5 alkyl groups; and when R2 and R3 are selected from fluorine-substituted or unsubstituted C1 to C5 alkyl groups, R2 and R3 are independent of each other. Based on the total mass of the electrolyte, the mass content of the fluorosulfonamide compound is b%, 2≤b≤12; The outer casing includes a housing and a pressure relief assembly; the housing is made of steel, and the pressure relief assembly includes a seal and a first through-hole; the area of ​​the first through-hole is c mm. 2 , 1≤c≤9; 0.7≤(a+b) / c≤10; The pressure relief assembly is configured such that when the internal temperature of the housing reaches a threshold temperature, the seal of the pressure relief assembly loses its sealing function, allowing the first through hole to connect to the external environment, thereby releasing the internal pressure of the battery and carrying away heat. The threshold temperature is d℃, where 100≤d≤120.

2. The secondary battery according to claim 1, characterized in that, The secondary battery satisfies at least one of the following conditions: （1）0.3≤a≤3； （2）2≤b≤8； (3) 0.7≤(a+b) / c≤8; （4）105≤d≤115。 3. The secondary battery according to any one of claims 1-2, characterized in that, The fluorosulfonamide compound includes at least one of the following compounds: Formula II-1 Formula II-2 Formula II-3 Formula II-4 Formula II-5 Formula II-6 Formula II-7 Formula II-8 Formula II-14 Formula II-15 Formula II-16 Formula II-17 Formula II-18 Formula II-19.

4. The secondary battery according to any one of claims 1-2, characterized in that, The secondary battery includes a positive electrode sheet, which includes a positive electrode active material, including lithium cobalt oxide; the single-sided coating weight of the positive electrode sheet is mg / cm³. 2 , 13≤m≤26.

5. The secondary battery according to any one of claims 1-2, characterized in that, The secondary battery includes a negative electrode sheet; the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer contains silicon element, and based on the total mass of the negative electrode material layer, the mass content of the silicon element is h%, 1≤h≤25%.

6. The secondary battery according to claim 5, characterized in that, The single-sided coating weight of the negative electrode sheet is nmg / cm³. 2 , 6.5≤n≤13.

7. The secondary battery according to any one of claims 1-2, characterized in that, The volumetric energy density of the secondary battery is V Wh / L, where 700≤V≤1200.

8. An electronic device, characterized in that, The secondary battery includes any one of claims 1 to 7.

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