A secondary battery

Abstract

This application belongs to the field of batteries and discloses a secondary battery. The secondary battery includes a negative electrode and an electrolyte. The negative electrode includes a silicon-based material containing nitrogen, with a nitrogen content A% satisfying 0.05 ≤ A ≤ 4.8. The electrolyte includes a compound of formula (I), with a mass content B% satisfying 0.01 ≤ B ≤ 6. This application combines an appropriate amount of nitrogen-containing silicon-based material with an electrolyte containing the compound of formula (I). This allows for the utilization of the high specific capacity advantage of silicon-based materials while improving the electron and lithium-ion transport rate in the negative electrode, preventing negative electrode cracking and pulverization. The nitrogen-containing silicon-based material preferentially adsorbs the compound of formula (I) and promotes its reduction and ring-opening, forming a stable organic-inorganic composite SEI film with high ionic conductivity. This synergistically optimizes interfacial lithium-ion transport, suppresses interfacial side reactions and impedance increases at high rates, and thus improves the battery's rate performance and cycle stability. Formula (I)

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery. Background Technology

[0002] With the increasing demands for high energy density and fast charging performance from consumer electronics and electric vehicles, silicon materials, with their theoretical specific capacity far exceeding that of traditional graphite, have become one of the key materials for the next generation of high energy density batteries. Silicon-doped battery systems are currently an important direction for industrial research and development.

[0003] However, the inherent low conductivity and severe interfacial side reactions of silicon materials severely limit the rapid migration of lithium ions, leading to a significant degradation in battery rate performance and becoming a core bottleneck restricting its commercial application. Existing technologies mainly attempt to improve the anode interface kinetics through silicon-based material structure design or doping modification and electrode structure design. However, these methods fail to fundamentally solve the dynamic instability of the electrochemical interface at high rates. As the current increases, interfacial side reactions intensify, impedance rises rapidly, leading to severe voltage polarization and ineffective capacity release during cycling, resulting in limited improvement. Summary of the Invention

[0004] In view of this, the technical problem to be solved by this application is to overcome the defect of poor cycle stability of existing secondary batteries at high rates.

[0005] To achieve the above objectives, this application adopts the following technical solution.

[0006] According to an embodiment of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode active layer, the negative electrode active layer comprises a silicon-based material, the silicon-based material comprises nitrogen, and the mass content A% of the nitrogen, based on the mass of the negative electrode active layer, satisfies 0.05≤A≤4.8. The electrolyte comprises a compound of formula (I), and the mass content B% of the compound of formula (I), based on the mass of the electrolyte, satisfies 0.01≤B≤6.

[0007]

[0008] Formula (I) Wherein, m and n are independently 0, 1 or 2 respectively; R1 and R2 are independently selected from CH2 or O respectively; R3, R4, R5 and R6 are independently selected from any one of H, F, alkyl with 1 to 6 carbon atoms that are fluorinated or unsubstituted, alkenyl with 2 to 6 carbon atoms that are fluorinated or unsubstituted, and alkynyl with 2 to 6 carbon atoms that are fluorinated or unsubstituted.

[0009] Furthermore, in some optional implementations, A satisfies: 0.1 ≤ A ≤ 3.5.

[0010] Furthermore, in some optional implementations, B satisfies: 0.1 ≤ B ≤ 3.

[0011] In some alternative embodiments, the compound of formula I includes at least one of the following structures: .

[0013] In some alternative implementations, A and B satisfy: 0.02 ≤ B / A ≤ 100.

[0014] Furthermore, in some optional implementations, A and B satisfy: 0.05 ≤ B / A ≤ 50.

[0015] In some alternative embodiments, the silicon-based material includes calcium, and the mass content of calcium, C ppm, based on the mass of the silicon-based material, satisfies 5 ≤ ​​C ≤ 300.

[0016] In some optional embodiments, the electrolyte further includes a fluorosulfonamide compound, wherein the mass content D% of the fluorosulfonamide compound, based on the mass of the electrolyte, satisfies 2 ≤ D ≤ 30.

[0017] Furthermore, in some optional embodiments, the mass content D% of the fluorosulfonamide, based on the mass of the electrolyte, satisfies 5 ≤ ​​D ≤ 20.

[0018] Further, in some optional embodiments, the fluorosulfonamide compound includes at least one of N,N-dimethylaminosulfonyl fluoride, N,N-bis(trifluoromethylaminosulfonyl fluoride), piperidine-1-sulfonyl fluoride, morpholine-4-sulfonyl fluoride, N,N-diethylaminosulfonyl fluoride, N-ethyl-N-methylaminosulfonyl fluoride, N,N-di(fluoromethyl)aminosulfonyl fluoride, N,N-di(difluoromethyl)aminosulfonyl fluoride, and 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide.

[0019] In some optional embodiments, the electrolyte further includes a polynitrile compound, wherein the mass content E% of the polynitrile compound, based on the mass of the electrolyte, satisfies 0.5 ≤ E ≤ 6.

[0020] Further, in some optional embodiments, the polynitrile compound includes at least one of 1,3,6-hexanetrionitrile (HTCN), 1,2,4-butanetrionitrile, adiponitrile (ADN), succinic anhydride (SN), ethylene glycol bis(propionitrile) ether (DENE), and tris(2-cyanoethyl) phosphate, compounds of formula (II-1), (II-2), and (II-3): .

[0022] In some alternative embodiments, the electrolyte further includes fluorocarbonate, wherein the mass content F% of the fluorocarbonate, based on the mass of the electrolyte, satisfies 5 ≤ ​​F ≤ 30.

[0023] Furthermore, in some optional embodiments, the fluorocarbonate includes at least one of fluoroethylene carbonate and difluoroethylene carbonate.

[0024] In some optional embodiments, the additive further includes lithium salt additives, wherein the mass content G% of the lithium salt additives, based on the mass of the electrolyte, satisfies 0.01≤G≤3.

[0025] Furthermore, in some optional embodiments, the lithium salt additive includes at least one of lithium difluorooxalate borate and lithium difluorophosphate.

[0026] In some alternative implementations, the negative electrode active layer satisfies at least one of the following conditions: (1) The particle size Dv50 of the silicon-based material is 1μm~15μm; (2) The sphericity of the silicon-based material is 0.5~0.99; (3) The compaction density of the negative electrode active layer is 0.8 g / cm³. 3 ~1.85g / cm 3 .

[0027] In some optional embodiments, the surface of the negative electrode active layer is provided with a recess, and the recess satisfies at least one of the following conditions: (1) The depth of the concave part is 1μm~35μm; (2) The width of the recess is 0.01mm~8mm; (3) The distance between two adjacent recesses is 0.1mm~20mm.

[0028] In some optional embodiments, the positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes lithium cobalt oxide particles, and the particle size Dv50 of the lithium cobalt oxide particles is 5μm~25μm.

[0029] In some alternative implementations, the charging cutoff voltage of the secondary battery is not less than 4.5 V.

[0030] In some alternative embodiments, the diaphragm includes a base membrane and an adhesive layer, the adhesive layer being disposed on at least one side of the base membrane, the adhesive layer comprising polymer particles; the polymer particles comprising secondary particles, the secondary particles being agglomerated from primary particles; the average particle size of the primary particles being 0.1 μm to 3 μm.

[0031] In some alternative embodiments, the polymer particles include at least one of fluoroolefin polymers, acrylate polymers, and acrylonitrile polymers.

[0032] In some alternative embodiments, the thickness of the adhesive layer on one side is 0.5 μm to 8 μm.

[0033] In some alternative embodiments, the projection coverage of the adhesive layer on one side of the base film surface is 15% to 70%.

[0034] The technical solution of this application has the following advantages: This application utilizes nitrogen-containing silicon-based materials, controls the nitrogen content in the negative electrode active layer to be within the range of 0.05% to 4.8%, and combines it with an electrolyte containing 0.01% to 10% of compound (I). This allows for the utilization of the high specific capacity advantage of silicon-based materials, while leveraging the appropriate amount of nitrogen doped in the silicon-based materials to significantly improve the electron and lithium ion transport rate in the negative electrode, prevent cracking and pulverization of the negative electrode active layer, preferentially adsorb compound (I) in the electrolyte and promote its reduction and ring opening, forming a stable organic-inorganic composite SEI film with high ionic conductivity. This synergistically optimizes interfacial lithium ion transport, suppresses interfacial side reactions and impedance rise at high rates, and effectively improves the rate performance and cycle stability of the battery while ensuring high energy density.

[0035] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Detailed Implementation

[0036] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0037] It should be noted that the technical features involved in the different embodiments described below can be combined with each other as long as they do not conflict with each other.

[0038] To address the issues of unstable electrochemical interfaces and poor ion transport kinetics in secondary batteries at high rates in related technologies, this application proposes the following solutions.

[0039] A secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative electrode active layer, the negative electrode active layer includes a silicon-based material, the silicon-based material includes nitrogen, and the mass content A% of the nitrogen is 0.05≤A≤4.8 based on the mass of the negative electrode active layer; the electrolyte includes a compound of formula (I), and the mass content B% of the compound of formula (I) is 0.01≤B≤6 based on the mass of the electrolyte.

[0040] Formula (I) Wherein, m and n are independently 0, 1 or 2 respectively; R1 and R2 are independently selected from CH2 or O respectively; R3, R4, R5 and R6 are independently selected from any one of H, F, alkyl with 1 to 6 carbon atoms that are fluorinated or unsubstituted, alkenyl with 2 to 6 carbon atoms that are fluorinated or unsubstituted, and alkynyl with 2 to 6 carbon atoms that are fluorinated or unsubstituted.

[0041] As an example, the alkyl group includes at least one of methyl, ethyl, and propyl; the alkenyl group includes at least one of vinyl and propenyl; and the alkynyl group includes at least one of ethynyl and propynyl.

[0042] This study found that doping silicon-based materials with an appropriate amount of nitrogen can regulate the electronic structure, valence bond structure, and interface properties of the materials, thereby improving the specific capacity, cycle life, and rate performance of batteries. Specifically, the introduction of nitrogen can increase the carrier concentration, improve the overall conductivity of the material, and the high electronegativity of nitrogen can also regulate the interfacial charge distribution, reduce the lithium ion adsorption energy, and accelerate ion transport. At the same time, nitrogen can form strong covalent bonds such as Si-NC bonds with silicon and carbon in silicon-based materials, effectively anchoring silicon active materials and helping to suppress interfacial cracking and electrode pulverization. The presence of nitrogen can also promote the formation of a solid electrolyte interfacial film (SEI film) rich in inorganic substances such as LiF and Li3N, which can suppress interfacial side reactions and adapt to the volume changes of silicon-based anodes.

[0043] Meanwhile, this application utilizes compound (I) in the electrolyte. Compared to monocyclic sulfonates, monocyclic sulfates, and non-spirobicyclic sulfonates / sulfates, compound (I) has a higher ring strain due to its spirocyclic structure, making it easier to open the ring during electrochemical reduction and resulting in faster reaction kinetics. Furthermore, the reduction potential of compound (I) is significantly higher than that of conventional carbonate solvents and lithium salts. During electrochemical reduction, the presence of nitrogen can also promote the reduction of some substances in the electrolyte. The compound (I) can be preferentially adsorbed by nitrogen sites on the surface of silicon-based materials before other components in the electrolyte, and then completely reduced and decomposed to generate an organic / inorganic crosslinked network that can quickly conduct lithium ions and has high mechanical strength. This ensures the high stability and high ion conductivity of the SEI film on the negative electrode surface, thereby effectively improving the cycle life and interfacial kinetics of the battery.

[0044] In summary, this application, by selecting nitrogen-containing silicon-based materials and controlling the mass content A% of nitrogen in the negative electrode active layer within the range of 0.05% to 4.8%, particularly between 0.1% and 3.5%, and combining it with an electrolyte containing B% (0.01≤B≤6, especially 0.1≤B≤3) of compound (I), can significantly improve the electron and lithium ion transport rate in the negative electrode by utilizing the appropriate amount of nitrogen doped in the silicon-based materials, while leveraging the high specific capacity advantage of silicon-based materials. This prevents cracking and pulverization of the negative electrode active layer, preferentially adsorbs compound (I) in the electrolyte and promotes its reduction and ring opening, forming a stable organic-inorganic composite SEI film with high ionic conductivity. This synergistically optimizes interfacial lithium ion transport, suppresses interfacial side reactions and impedance rise at high rates, and thus improves the rate performance and cycle stability of the battery while ensuring high energy density.

[0045] This study found that if the mass content of compound (I) in the electrolyte is too high (greater than 6%), it may affect the electrochemical performance due to excessive decomposition and consumption of active lithium, increased SEI film impedance, or accumulation of side reactions. Conversely, if the mass content of compound (I) in the electrolyte is too low (less than 0.01%), it is difficult to form a uniform, dense, stable, and highly conductive SEI film on the negative electrode surface, thus failing to promote lithium-ion transport and ensure cycle stability.

[0046] As an example, the mass content of compound (I) in the electrolyte can be obtained by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography (LC). For example, the mass content of compound (I) can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 1%, 2%, 5%, 6%, etc., or a value within any two of the above ranges.

[0047] When the nitrogen content in the negative electrode active layer is too high (greater than 4.8%), excessive doping may lead to a decrease in the structural stability of the silicon-based material and changes in the interface properties, thereby triggering continuous side reactions. Conversely, if the nitrogen content in the negative electrode active layer is too low (less than 0.05%), it cannot effectively improve the transport rate of electrons and lithium ions in the negative electrode sheet, and cannot prevent the negative electrode active layer from cracking and pulverizing, nor can it preferentially adsorb compounds of formula (I) in the electrolyte and promote their reduction and ring opening, thus limiting the improvement of battery dynamic performance and the extension of cycle life.

[0048] As an example, the mass content of nitrogen in the negative electrode active layer can be obtained by energy-dispersive X-ray spectroscopy (EDS) or inductively coupled plasma optical emission spectrometry (ICP-OES). For example, the mass content of nitrogen can be 0.05%, 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.80%, or values ​​within any two of the above ranges.

[0049] This application can introduce nitrogen into silicon-based materials using conventional methods in the prior art. For example, a chemical vapor deposition (CVD) method can be used, such as placing porous carbon in an ammonia atmosphere to dope nitrogen into silicon-carbon materials. Alternatively, nitrogen can be introduced by mixing nitrogen-containing precursors (such as urea, melamine, etc.) with a silicon source and then performing high-temperature heat treatment.

[0050] In some embodiments, the silicon-based material includes at least one of silicon-carbon materials, silicon-oxygen materials, elemental silicon, and silicon alloys.

[0051] In some embodiments, the nitrogen content A% in the negative electrode active layer and the content B% of compound (I) in the electrolyte are controlled to satisfy 0.02 ≤ B / A ≤ 100, particularly 0.05 ≤ B / A ≤ 50. This further enhances the synergistic effect between the two. On the one hand, it can significantly improve the transport rate of electrons and lithium ions in the negative electrode sheet, effectively preventing cracking and pulverization of the negative electrode active layer. On the other hand, an appropriate amount of nitrogen can precisely and preferentially adsorb compound (I) in the electrolyte and promote the complete reduction and ring-opening of compound (I), forming a more stable SEI film with high ionic conductivity. Thus, while ensuring high energy density of the battery, it significantly improves the cycle life and rate performance of the battery. For example, the value of B / A can be 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 30, 40, 50, 80, 100, or a value within any two of the above values.

[0052] If the B / A value is less than 0.1, it indicates that the content of compound (I) in the electrolyte is too low, or the nitrogen content in the negative electrode active layer is too high. Both of these are detrimental to further improving the cycle stability and lithium-ion transport kinetics of the battery. Conversely, if the B / A value is greater than 100, it means that the content of compound (I) in the electrolyte is too high, side reactions are aggravated, the SEI film impedance increases, or it reflects that the nitrogen content in the negative electrode active layer is too low. This will also affect the effect of further improving the cycle life and rate performance of the battery.

[0053] In some embodiments, the compound of formula (I) includes at least one of the following structures: .

[0055] The above-mentioned compounds have high preferential reduction potential and excellent film-forming ability, and can form a good synergistic effect with nitrogen-containing silicon-based materials. Under the strong adsorption of nitrogen, the above-mentioned compounds can be preferentially reduced on the negative electrode surface to generate an SEI film with high ionic conductivity and good mechanical stability, thereby ensuring the efficient transport of lithium ions and maintaining interface stability, and systematically solving the problem of limited cycle life of high-silicon battery systems at high rates.

[0056] It should be noted that other elements may be present in the silicon-based material during its preparation. In some specific embodiments, the silicon-based material includes calcium. The calcium content in the silicon-based material is extremely low and does not participate in electrochemical reactions. However, excessive calcium may damage the integrity of the initial SEI interface of the electrode, occupy active sites, form local high impedance regions, thereby hindering the normal migration of lithium ions, and even inducing problems such as lithium plating during cycling.

[0057] In view of this, in some embodiments, by controlling the mass content of calcium in the silicon-based material within the range of 5 ppm to 300 ppm, the negative impact of calcium can be reduced, ensuring the electrochemical stability of the negative electrode interface and the rapid transport of lithium ions. On the other hand, the high-quality organic-inorganic composite SEI film formed by preferentially polymerizing and decomposing the compound of formula (I) in the electrolyte on the negative electrode surface can effectively block the contact between calcium in the silicon-based material and the electrolyte, suppressing the occurrence of side reactions. At the same time, the decomposition products of the compound of formula (I) include an interface layer rich in inorganic lithium salts such as Li2SO3, reducing the lithium ion transport resistance caused by the presence of calcium, thereby improving the cycle stability and rate performance of the battery.

[0058] As an example, the mass content of calcium in silicon-based materials can be obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES). For instance, the mass content of calcium can be 5 ppm, 10 ppm, 30 ppm, 50 ppm, 80 ppm, 100 ppm, 130 ppm, 150 ppm, 180 ppm, 200 ppm, 220 ppm, 260 ppm, 300 ppm, or a value within any range of two of the above values.

[0059] It is understood that the electrolyte composition in this application includes organic solvents, additives, and lithium salts. The organic solvents provide a good dissolution and transport medium for the ion conductors and other functional additives, synergistically constructing a stable electrochemical environment. Based on the mass of the electrolyte, the mass content (H%) of the organic solvent satisfies 30% ≤ H ≤ 90%, and the mass content of the organic solvent can be determined by gas chromatography-mass spectrometry (GC-MS). As an example, the organic solvent includes at least one of carbonates and carboxylic acid esters; the carbonates include at least one of diethyl carbonate, methyl ethyl carbonate, propylene carbonate, and ethylene carbonate; and the carboxylic acid esters include at least one of propyl propionate, ethyl propionate, and ethyl butyrate.

[0060] The addition of an appropriate amount of lithium salt ensures that the electrolyte has high ionic conductivity, supporting efficient charge transport and stable interfacial reactions in the battery. Based on the mass of the electrolyte, the mass content J% of the lithium salt satisfies 5% ≤ J ≤ 30%; the mass content of the ionic conductor can be obtained by ion chromatography (IC). As an example, the ionic conductor includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, and lithium perchlorate.

[0061] In addition to the compound of formula (I) mentioned above, in some embodiments of this application, the electrolyte also includes a fluorosulfonamide compound. Based on the mass of the electrolyte, by controlling the mass content D% of the fluorosulfonamide compound within the range of 2%-30%, the high reducing activity and interfacial affinity of the sulfonyl group (-SO2-) and fluorine atom in the fluorosulfonamide molecule can be fully utilized, enabling it to undergo a synergistic reduction reaction with the compound of formula (I) on the negative electrode surface during electrochemical processes. The decomposition products of the fluorosulfonamide compound can introduce high-quality inorganic SEI components such as LiF and Li3N to the interface. The organic polymer network formed by the fluorosulfonamide compound and the compound of formula (I) intertwines to construct a composite SEI film with higher mechanical strength, lower solubility, and better lithium-ion conductivity. Therefore, the combined use of fluorosulfonamide compounds and the compound of formula (I) can achieve more comprehensive protection of the negative electrode interface and synergistically improve the lithium-ion transport rate. This more effectively inhibits the continuous decomposition of the electrolyte under high voltage and high rate, reduces active lithium loss and interfacial impedance increase, and enhances the structural integrity of the SEI film during long-term cycling, thereby significantly improving the battery's cycle life, rate performance, and safety performance under high voltage and high temperature conditions. In particular, when the mass content D% of the fluorosulfonamide compound is in the range of 5%-20%, the battery's rate performance and cycle life can be further enhanced.

[0062] If the mass content of fluorosulfonamide compounds is too high (greater than 30%), it may lead to a significant increase in electrolyte viscosity, hinder lithium-ion migration, or excessive decomposition that consumes a large amount of active lithium, affecting battery capacity and first-time efficiency. If the mass content of fluorosulfonamide compounds is too low (less than 2%), it will be difficult to form a sufficient and stable sulfur / fluorine synergistic protective layer at the negative electrode interface, which will not effectively suppress electrolyte decomposition and interfacial side reactions, thereby weakening the improvement effect on battery cycle life and safety performance.

[0063] It should be noted that the mass content of fluorosulfonamide compounds can be obtained by gas chromatography-mass spectrometry (GC-MS). For example, the mass content of fluorosulfonamide compounds can be 2%, 4%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or values ​​within any two of the above ranges.

[0064] For example, the fluorosulfonamide compounds include at least one selected from N,N-dimethylaminosulfonyl fluoride, N,N-bis(trifluoromethylaminosulfonyl fluoride), piperidine-1-sulfonyl fluoride, morpholine-4-sulfonyl fluoride, N,N-diethylaminosulfonyl fluoride, N-ethyl-N-methylaminosulfonyl fluoride, N,N-di(fluoromethyl)aminosulfonyl fluoride, N,N-di(difluoromethyl)aminosulfonyl fluoride, and 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide. The CAS number of N,N-bis(trifluoromethyl)aminosulfonyl fluoride is 141577-86-8, and the CAS number of N,N-di(fluoromethyl)aminosulfonyl fluoride is 141596-52-3.

[0065] In some embodiments, the electrolyte further includes a polynitrile compound. By controlling the mass content of the polynitrile compound within the range of 0.5%-6% based on the mass of the electrolyte, the polynitrile compound can be effectively complexed on the surface of the lithium cobalt oxide cathode, stabilizing the cathode structure and suppressing interfacial side reactions under high voltage. Although the polynitrile compound may negatively affect the SEI film of the anode, the compound of formula (I) in the electrolyte can preferentially form a film on the anode surface and construct a stable interfacial layer to counteract the negative effects of the polynitrile compound, thereby further improving the interfacial stability and cycle life of the battery under high voltage.

[0066] It should be noted that the mass content of polynitrile compounds can be obtained by gas chromatography-mass spectrometry (GC-MS). For example, the mass content of polynitrile compounds can be 0.5%, 1.1%, 1.7%, 2.3%, 2.9%, 3.5%, 4.1%, 4.7%, 5.3%, 5.9%, 6.0%, or values ​​within any two of the above ranges.

[0067] For example, the polynitrile compound includes at least one of 1,3,6-hexanetrionitrile (abbreviated as HTCN), 1,2,4-butanetrionitrile, adiponitrile (abbreviated as ADN), succinic anionyl (abbreviated as SN), ethylene glycol bis(propionitrile) ether (abbreviated as DENE), tris(2-cyanoethyl) phosphate, and compounds shown in formula (II-1), formula (II-2), and formula (II-3): .

[0068] The CAS number for 1,2,4-butanetrionitrile is 5238-65-3.

[0069] In some embodiments, the electrolyte further includes fluorocarbonate. Based on the mass of the electrolyte, by controlling the mass content F% of fluorocarbonate within the range of 5%-30%, the fluorocarbonate can further participate in the reaction and introduce stable components rich in LiF on the basis of the interfacial film constructed by the compound of formula (I). This allows it to form a more compact, tougher, and lower impedance composite SEI structure together with the decomposition products of the compound of formula (I), significantly improving the structural stability of the negative electrode interface and the uniformity of lithium-ion conduction, and further improving the cycle performance and rate performance of the battery.

[0070] It should be noted that the mass content of fluorocarbonate can be obtained by gas chromatography-mass spectrometry (GC-MS). For example, the mass content of fluorocarbonate can be 5.0%, 6.8%, 8.6%, 10.4%, 12.1%, 13.9%, 15.7%, 17.5%, 19.3%, 21.1%, 22.9%, 24.6%, 26.4%, 28.2%, 30.0%, or values ​​within any two of the above ranges.

[0071] For example, the fluorocarbonate includes at least one of fluoroethylene carbonate and difluoroethylene carbonate.

[0072] In some embodiments, the additives also include lithium salt additives. Based on the mass of the electrolyte, by controlling the mass content G% of the lithium salt additives within the range of 0.01% to 3%, these additives can effectively participate in the construction of the interfacial film, introduce stable components such as boron and phosphorus to optimize ion conduction, and maintain the bulk properties of the electrolyte without damage.

[0073] It should be noted that the mass content of lithium salt additives can be obtained by testing with an ion chromatograph. For example, the mass content of lithium salt additives can be 0.01%, 0.02%, 0.03%, 0.05%, 0.07%, 0.1%, 0.15%, 0.2%, 0.3%, 0.5%, 0.7%, 1.0%, 1.5%, 2.0%, 3.0%, or values ​​within any two of the above ranges.

[0074] For example, the lithium salt additive includes at least one of lithium difluorooxalate borate and lithium difluorophosphate.

[0075] In some implementations, by controlling the particle size Dv50 of the silicon-based material between 1 μm and 15 μm, the lithium-ion transport kinetics and structural durability of the negative electrode are optimized while maintaining high tap density and interface stability, thereby enabling the battery to achieve better rate performance and cycle life.

[0076] It is understood that the particle size Dv50 of silicon-based materials refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, that is, the volume content of particles smaller than or equal to this size accounts for 50% of the total particle volume. For testing the particle size Dv50 of silicon-based materials, refer to GB / T19077-2016 / ISO 13320:2009, and use a laser particle size analyzer (MalvernMaster Size 3000) for measurement. For example, the particle size Dv50 of silicon-based materials can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc., or a value within any two of the above ranges.

[0077] In some implementations, by controlling the sphericity of silicon-based materials to be between 0.5 and 0.99, it is possible to ensure good contact and a uniform conductive network between silicon-based materials while taking into account both electrode processing performance and structural stability. This prevents uneven stacking, local stress concentration, and aggravated interfacial side reactions caused by excessively low sphericity (below 0.5).

[0078] For example, the sphericity S of the silicon-based material can be 0.50, 0.54, 0.57, 0.61, 0.64, 0.68, 0.71, 0.75, 0.78, 0.82, 0.85, 0.89, 0.92, 0.96, 0.99, or a value within any two of the above values.

[0079] In this application, the sphericity of silicon-based materials can be tested using conventional methods in the art. For example, using image processing software (e.g., Image Pro Plus), in a scanning electron microscope (SEM) image of silicon-based materials at a certain magnification (e.g., 2500x), 100 silicon-based material particles are selected, and the perimeter and area of ​​each particle are measured. The perimeter equivalent radius r1 and area equivalent radius r2 of each particle are calculated respectively. The sphericity is then r2 / r1, and the average value is taken to obtain the sphericity of the silicon-based material.

[0080] In some embodiments, the compaction density of the negative electrode active layer is maintained at 0.8 g / cm³. 3 ~1.785g / cm 3 Within this range, it further enhances excellent rate performance, energy density, and cycle life.

[0081] It should be noted that the test method for the compaction density of the negative electrode active layer includes: a cut area of ​​15.0425 cm². 2The negative electrode wafer is weighed, and the weight of the wafer is subtracted from the weight of the foil of the same area to obtain the coating weight. The areal density is calculated by dividing the coating weight by the wafer area; then, the areal density is divided by the coating thickness to calculate the compaction density of the negative electrode active layer. For example, the compaction density of the negative electrode active layer can be, for example, 0.80 g / cm³. 3 0.87 g / cm 3 0.94 g / cm 3 1.01 g / cm 3 1.08 g / cm 3 1.15 g / cm 3 1.22 g / cm 3 1.29 g / cm 3 1.36 g / cm 3 1.43 g / cm 3 1.50 g / cm 3 1.57 g / cm 3 1.64 g / cm 3 1.71 g / cm 3 1.85 g / cm 3 Values ​​equal to or within the range of any two of the above values.

[0082] In some embodiments, the negative electrode active material layer includes recesses. By controlling the depth of the recesses on the surface of the negative electrode active layer to 1 μm to 35 μm, and / or controlling the width of the recesses on the surface of the negative electrode active layer to 0.01 mm to 8 mm, and / or controlling the spacing between two adjacent recesses on the surface of the negative electrode active layer to 0.1 mm to 20 mm, the volumetric stress during cycling can be uniformly released, maintaining the stability of the electrode structure. While improving wettability and reducing interfacial impedance, it also increases the contact area between the active material and the electrolyte. The compound of formula (I) contained in the electrolyte can preferentially form a film on the negative electrode surface, effectively suppressing possible aggravated side reactions.

[0083] The shape of the recess on the electrode surface includes at least one of the following: circular, linear, square, rectangular, and trapezoidal, preferably circular or linear. The circular recess can be formed by embossing roller pressing, while the linear recess can be processed by laser scanning.

[0084] It should be noted that the depth, width, and spacing between adjacent recesses on the surface of the negative electrode active layer can all be obtained by conventional methods in this field.

[0085] For example, when the recess is a hole, the width of the recess refers to the diameter of the hole. If the orthographic projection of the hole on the surface of the negative electrode is a regular circle, then the diameter is the diameter of the circle; if the orthographic projection is an irregular circle (such as an ellipse), then the diameter is the diameter of an equivalent circle with the same area as the shape. The spacing between the recesses refers to the shortest distance between the edges of two adjacent holes. The diameter of the hole can be tested using a 3D profilometer, measuring the diameter of at least 20 holes on the surface of the negative electrode active coating and taking the average value; the spacing between the holes can be tested using a scanning electron microscope (SEM), selecting at least 10 groups of adjacent holes in the field of view of the SEM, measuring the spacing and taking the average value.

[0086] When the recess is a groove, the width of the recess refers to the width of the groove, that is, the average distance from one long side to another long side in the length or width direction of the negative electrode sheet. The spacing of the recess refers to the average distance between the two adjacent long sides of two adjacent grooves. The width and spacing of the grooves can be tested by a 3D profilometer. The width and spacing of all or at least 5 grooves on the surface of the negative electrode active coating are tested and the average value is taken.

[0087] For example, the depth of the recess on the surface of the negative electrode active layer can be, for example, 1.0 μm, 3.4 μm, 5.9 μm, 8.3 μm, 10.7 μm, 13.1 μm, 15.6 μm, 18.0 μm, 20.4 μm, 22.9 μm, 25.3 μm, 27.7 μm, 30.1 μm, 32.6 μm, 35.0 μm, or a value within the range of any two of the above values.

[0088] The width of the recess on the surface of the negative electrode active layer can be, for example, 0.0 mm, 0.6 mm, 1.2 mm, 1.7 mm, 2.3 mm, 2.9 mm, 3.4 mm, 4.0 mm, 4.6 mm, 5.2 mm, 5.7 mm, 6.3 mm, 6.9 mm, 7.4 mm, 8.0 mm, or a value within any two of the above ranges.

[0089] The spacing between two adjacent recesses on the surface of the negative electrode active layer can be, for example, 0.1mm, 1.5mm, 2.9mm, 4.4mm, 5.9mm, 7.4mm, 8.9mm, 10.4mm, 11.9mm, 13.4mm, 14.9mm, 16.4mm, 17.9mm, 19.4mm, 20.0mm, or a value within any range of two of the above values.

[0090] In some embodiments, the positive electrode sheet includes a positive electrode active layer, which includes lithium cobalt oxide particles. By controlling the particle size Dv50 of the lithium cobalt oxide particles within the range of 5μm to 25μm, it can be ensured that the lithium cobalt oxide particles have a shorter lithium-ion solid-phase diffusion path and higher interfacial reaction activity, thereby ensuring the battery's excellent rate performance.

[0091] It should be noted that the particle size Dv50 of lithium cobalt oxide particles can be measured using a laser particle size analyzer (Malvern Master Size 3000) in accordance with GB / T19077-2016 / ISO13320:2009. For example, the particle size Dv50 of lithium cobalt oxide particles can be 5.0 μm, 6.4 μm, 7.9 μm, 9.3 μm, 10.7 μm, 12.1 μm, 13.6 μm, 15.0 μm, 16.4 μm, 17.9 μm, 19.3 μm, 20.7 μm, 22.1 μm, 23.6 μm, 25.0 μm, or values ​​within any two of the above ranges.

[0092] In some embodiments, the charging cutoff voltage of the secondary battery is not less than 4.5 V.

[0093] In some embodiments, the diaphragm includes a base membrane and an adhesive layer, the adhesive layer being disposed on at least one surface of the base membrane; the adhesive layer includes polymer particles; the polymer particles include secondary particles, which are formed by the aggregation of primary particles; the average particle size of the primary particles is 0.1 μm to 3 μm.

[0094] In some specific embodiments, a coating layer is further included between the adhesive layer facing the positive and / or negative electrode and the base film. The coating layer includes ceramic particles, which include at least one of alumina, boehmite, aluminum hydroxide, barium carbonate, magnesium oxide, silicon oxide, and titanium oxide.

[0095] It should be noted that the term "primary particle" also refers to the original particles formed during the material preparation process. They are the smallest solid units that can exist independently without agglomeration.

[0096] This application achieves a stable functional layer in the adhesive layer by controlling the average particle size of the primary polymer particles to be between 0.1 μm and 3 μm. This allows the secondary particles formed after agglomeration to have a suitable pore structure, high surface wettability, and good adhesion to the electrode. This prevents the primary particles from being too large (greater than 3 μm), which would lead to coarsening of the aggregate pores and a rough coating, thereby weakening the tight contact with the electrode and the uniformity of interfacial ion transport. It also prevents the particles from being too small (less than 3 μm), which would cause excessive agglomeration and low porosity, affecting electrolyte wetting and the construction of lithium-ion transport channels. Ultimately, this ensures that the adhesive layer can effectively play its role in pre-setting a high-conductivity lithium interface and improving the rate performance of the battery.

[0097] It should be noted that the average particle size of the primary polymer particles described in this application can be obtained by scanning electron microscopy (SEM). The specific testing method includes: arbitrarily selecting a 100μm × 100μm region in the SEM image of the adhesive layer surface, identifying and randomly selecting 100 primary polymer particles; for each selected primary particle, drawing the smallest rectangle or square that completely encloses the particle and is tangent to its four sides, the length of the longer side of the rectangle or the side length of the square being the particle size of that primary particle; if the number of particles in a single image is less than 100, multiple images can be taken until the cumulative number of observed primary polymer particles reaches 100; the arithmetic mean of the measured particle sizes of the 100 primary particles is calculated, which is the average particle size of the primary polymer particles. For example, the average particle size of a primary particle can be 0.1μm, 0.3μm, 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 3.0μm, or a value within the range of any two of the above values.

[0098] For example, the polymer particles include at least one of fluorinated olefin polymers, acrylate polymers, and acrylonitrile polymers; the fluorinated olefin polymers include at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluorinated vinyl-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer; the acrylate polymers include at least one of polybutyl acrylate, polyethyl acrylate, polybutyl methacrylate, polymethyl methacrylate, methacrylate-acrylonitrile copolymer, methacrylate-ethylene copolymer, methacrylate-styrene copolymer, butadiene, and isobutyl acrylate copolymer.

[0099] In some implementations, by controlling the thickness of the adhesive layer on one side to be between 0.5 μm and 8 μm, it is possible to ensure that the adhesive layer fully and continuously covers the surface of the negative electrode active material, thereby optimizing the interfacial lithium-ion transport kinetics and electrode structure stability, and improving the rate performance of the battery.

[0100] It should be noted that the thickness of the single-sided adhesive layer can be obtained by scanning electron microscopy. For example, the thickness of the single-sided adhesive layer can be 0.5μm, 1.0μm, 1.6μm, 2.1μm, 2.6μm, 3.2μm, 3.7μm, 4.3μm, 4.8μm, 5.3μm, 5.9μm, 6.4μm, 6.9μm, 7.5μm, 8.0μm, or a value within any two of the above ranges.

[0101] In some embodiments, by controlling the projection coverage of the adhesive layer on the surface of the base film to be within the range of 15%-70%, the electrolyte can be fully penetrated while the adhesive layer performs its function, thereby optimizing the interface wettability and ion transport rate.

[0102] It should be noted that the projection coverage of the adhesive layer on the surface of the base film on one side can be obtained by scanning electron microscopy (SEM). The specific testing method includes: acquiring a microscopic image of the surface of the carrier layer using SEM, and randomly dividing the image into areas with a surface area of ​​10000 µm. 2 A detection area (e.g., 100 µm × 100 µm) is defined; this area is uniformly divided into 200 × 200 squares. If the projected area of ​​a square covered by the coating exceeds half of the square's area, the square is considered to be occupied by the coating; otherwise, it is considered not occupied by the coating. The total number of squares occupied by the coating is counted and recorded as X3. The coverage rate is calculated according to the following formula: Coverage rate = (X3 / (200 × 200)) × 100%. The above operation is repeated 5 times, and the arithmetic mean of the 5 calculation results is taken as the coverage rate of the adhesive layer on the surface of the carrier layer. For example, the projection coverage of the adhesive layer on the surface of the base film on one side can be, for example, 15.0%, 18.9%, 22.9%, 26.8%, 30.7%, 34.6%, 38.6%, 42.5%, 46.4%, 50.4%, 54.3%, 58.2%, 62.1%, 66.1%, 70.0%m, or a value within the range of any two of the above values.

[0103] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0104] Example 1 This embodiment provides a method for preparing a secondary battery, including the following steps: Step 1: Preparation of the positive electrode sheet Lithium cobalt oxide (LiCoO2) positive electrode active material, polyvinylidene fluoride (PVDF) binder, conductive carbon black (Super P) and carbon nanotubes (CNT) were weighed and mixed in a mass ratio of 96:2:1.5:0.5. An appropriate amount of N-methylpyrrolidone (NMP) was added as a dispersion medium. The mixture was continuously stirred in a vacuum mixer until a uniform positive electrode slurry with suitable fluidity was formed. The slurry was then uniformly coated on both sides of an aluminum foil. After drying, rolling and slitting, the desired positive electrode sheet was obtained.

[0105] Step 2: Preparation of the negative electrode Artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber (SBR), conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were weighed out according to the mass ratio (94.5-A):A:2.5:1.5:1:0.5. After being mixed evenly, an appropriate amount of deionized water was added, and the mixture was continuously stirred in a vacuum mixer until a uniform and fluid negative electrode slurry was formed. The slurry was then evenly coated on both sides of a copper foil, allowed to stand and dry at room temperature, and then dried in an 80°C oven for 10 hours. After cold pressing and slitting, the required negative electrode sheet was obtained.

[0106] Step 3: Preparation of electrolyte In an argon-protected glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed uniformly at a mass ratio of 10:10:80 to obtain a mixed solvent. Under continuous stirring, 14 wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte was slowly added to the mixed solvent. The required additives (specifically, at least one of fluorosulfonamide, polynitrile compound, fluorocarbonate, and lithium salt additive) were added according to the additive dosages in Tables 1-2. After stirring until the system was homogeneous, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0107] Step 4: Preparation of secondary batteries The positive electrode sheet obtained in the first step, the negative electrode sheet obtained in the second step, and the separator are stacked and wound in the order of positive electrode sheet / separator / negative electrode sheet to obtain a battery cell. Then, the battery cell is placed in an aluminum-plastic film packaging bag, and the electrolyte prepared in the third step is injected. After vacuum sealing, standing, formation, shaping and sorting processes, a secondary battery is obtained. The charge and discharge voltage range of the battery is 3.0 V~4.5 V. The separator includes a polyethylene base film with a thickness of 8 μm, an alumina coating on both sides of the base film, and a polyvinylidene fluoride adhesive layer on both sides of the separator. Specific parameters are shown in Table 2.

[0108] The preparation methods of Examples 2-24 are basically the same as those of Example 1. The differences are shown in Tables 1-2.

[0109] The preparation method of Example 25 differs from that of Example 1 in the preparation of the negative electrode sheet: Artificial graphite, silicon-carbon anode, sodium carboxymethyl cellulose, styrene-butadiene rubber (SBR), conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were weighed out according to the mass ratio (94.5-A):A:2.5:1.5:1:0.5. After being mixed evenly, an appropriate amount of deionized water was added, and the mixture was continuously stirred in a vacuum mixer until a uniform and fluid anode slurry was formed. The slurry was then evenly coated on both sides of a copper foil, allowed to stand and dry at room temperature, and then placed in an 80°C oven to dry for 10 hours. Then, a laser was used to scribing lines on the surface of the anode sheet to form multiple equally spaced recesses with a recess spacing of 20 mm, a recess depth of 1 μm, and a recess width of 4 mm. After cold pressing and slitting, the desired anode sheet was obtained.

[0110] The preparation methods of Examples 26 and 27 are basically the same as those of Example 25. The differences are shown in Tables 1 and 2.

[0111] The preparation methods of Comparative Examples 1-6 are basically the same as those of Example 1. The differences are shown in Tables 1-2.

[0112] Table 1

[0113] Table 2

[0114] It should be noted that the mass content of each additive in the electrolyte mentioned in Tables 1 and 2 is calculated based on the total mass of the electrolyte. In Example 1, the E value corresponding to the polynitrile compound being HTCN+ADN is 2+1, which means that the mass content of HTCN in the electrolyte is 2% and the mass content of ADN is 1%; all expressions of this kind in Tables 1 and 2 should be understood in the same way as described above.

[0115] Test case 1. Ratio Performance Test Under a test environment of 25℃±2℃, the battery was discharged at a constant current of 0.2C to the lower discharge limit voltage and allowed to stand for 10 minutes. Then, it was charged at a constant current of 0.7C to the upper charging limit voltage, followed by constant voltage charging at the upper charging limit voltage until the current dropped to 0.05C, and allowed to stand for 10 minutes. Next, it was discharged at constant current to the lower discharge limit voltage at 0.2C and 5C rates respectively, and the discharge capacity at each rate was recorded. Using the discharge capacity at 0.2C as a benchmark, the ratio of the discharge capacity at 5C to that at 0.2C was calculated. The resulting percentage is the capacity retention rate of the battery at the 5C discharge rate, used to evaluate the battery's rate performance.

[0116] 2. Room temperature cycling performance test Place the battery in a 25°C environment and perform a cycle test at a 4C rate within the set charge / discharge cutoff voltage range. Record the discharge capacity of the first cycle as x1mAh and the discharge capacity of the Nth cycle as y1mAh. Calculate the capacity retention rate R1 of the Nth cycle as R1 = y1 / x1 × 100%. Record the number of cycles T1 when the capacity retention rate R1 drops to 80%.

[0117] 3. Volumetric energy density test Under a test environment of 25℃±2℃, the formed batteries were charged at a constant current of 0.2C to the upper charging limit voltage of 4.5V, and then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then left to rest for 10 minutes. They were then discharged at a constant current of 0.2C to the lower discharge limit voltage of 3.0V, and the discharge energy was recorded. Five batteries were tested in each group, and the arithmetic mean was taken as the discharge energy of that group. The volumetric energy density of the battery was calculated using the following formula: Volumetric energy density (Wh / L) = Average discharge energy of battery (Wh) / Battery volume (L) The test results are shown in Table 3.

[0118] Table 3

[0119] As can be seen from Tables 1-3, this application, by selecting nitrogen-containing silicon-based materials and controlling the mass content A% of nitrogen element in the negative electrode active layer within the range of 0.05% to 4.8%, and using it in combination with an electrolyte containing B% (0.01≤B≤6) of compound (I), can significantly improve the electron and lithium ion transport rate in the negative electrode by utilizing the appropriate amount of nitrogen element doped in the silicon-based materials, while leveraging the high specific capacity advantage of silicon-based materials. This prevents the cracking and pulverization of the negative electrode active layer, preferentially adsorbs compound (I) in the electrolyte and promotes its reduction and ring opening, forming a stable organic-inorganic composite SEI film with high ionic conductivity. This synergistically optimizes interfacial lithium ion transport, suppresses interfacial side reactions and impedance rise at high rates, and thus improves the rate performance and cycle stability of the battery while ensuring high energy density.

[0120] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; characterized in that, The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a silicon-based material, the silicon-based material includes nitrogen element, and based on the mass of the negative electrode active layer, the mass content A% of nitrogen element satisfies 0.05≤A≤4.8; The electrolyte includes a compound of formula (I), and the mass content B% of the compound of formula (I) satisfies 0.01≤B≤6 based on the mass of the electrolyte; Formula (I) Wherein, m and n are independently 0, 1 or 2 respectively; R1 and R2 are independently selected from CH2 or O respectively; R3, R4, R5 and R6 are independently selected from any one of H, F, alkyl with 1 to 6 carbon atoms that are fluorinated or unsubstituted, alkenyl with 2 to 6 carbon atoms that are fluorinated or unsubstituted, and alkynyl with 2 to 6 carbon atoms that are fluorinated or unsubstituted.

2. The secondary battery according to claim 1, characterized in that, The condition A satisfies: 0.1 ≤ A ≤ 3.5; And / or, the B satisfies: 0.1 ≤ B ≤ 3; And / or, A and B satisfy: 0.02 ≤ B / A ≤ 100; And / or, the compound of formula (I) comprises at least one of the following structures: 。 3. The secondary battery according to claim 2, characterized in that, The condition A and B satisfy: 0.05 ≤ B / A ≤ 50.

4. The secondary battery according to claim 1, characterized in that, The silicon-based material includes calcium, and the mass content of calcium, C ppm, based on the mass of the silicon-based material, satisfies 5 ≤ ​​C ≤ 300.

5. The secondary battery according to claim 1, characterized in that, The electrolyte also includes fluorosulfonamide compounds. Based on the mass of the electrolyte, the mass content D% of the fluorosulfonamide compounds satisfies 2≤D≤30, preferably 5≤D≤20. And / or, the electrolyte further includes a polynitrile compound, wherein the mass content E% of the polynitrile compound, based on the mass of the electrolyte, satisfies 0.5≤E≤6; And / or, the electrolyte further includes fluorocarbonate, and the mass content F% of the fluorocarbonate, based on the mass of the electrolyte, satisfies 5 ≤ ​​F ≤ 30; And / or, the electrolyte further includes lithium salt additives, and the mass content G% of the lithium salt additives, based on the mass of the electrolyte, satisfies 0.01≤G≤3.

6. The secondary battery according to claim 5, characterized in that, The fluorosulfonamide compounds include at least one of N,N-dimethylaminosulfonyl fluoride, N,N-bis(trifluoromethylaminosulfonyl fluoride), piperidine-1-sulfonyl fluoride, morpholine-4-sulfonyl fluoride, N,N-diethylaminosulfonyl fluoride, N-ethyl-N-methylaminosulfonyl fluoride, N,N-bis(difluoromethyl)aminosulfonyl fluoride, and 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide; And / or, the polynitrile compound includes at least one of the following: 1,3,6-hexanetrionitrile, 1,2,4-butanetrionitrile, adiponitrile, succinic anhydride, ethylene glycol bis(propionitrile) ether, tris(2-cyanoethyl) phosphate, and compounds of formula (II-1), (II-2), and (II-3): ； And / or, the fluorocarbonate includes at least one of fluoroethylene carbonate and difluoroethylene carbonate; And / or, the lithium salt additive includes at least one of lithium difluorooxalate borate and lithium difluorophosphate.

7. The secondary battery according to claim 1, characterized in that, The negative electrode active layer satisfies at least one of the following conditions: (1) The particle size Dv50 of the silicon-based material is 1μm~15μm; (2) The sphericity of the silicon-based material is 0.5~0.99; (3) The compaction density of the negative electrode active layer is 0.8 g / cm³. 3 ~1.85g / cm 3 .

8. The secondary battery according to any one of claims 1 or 7, characterized in that, The surface of the negative electrode active layer is provided with a recess, and the recess satisfies at least one of the following conditions: (1) The depth of the concave part is 1μm~35μm; (2) The width of the recess is 0.01mm~8mm; (3) The distance between two adjacent recesses is 0.1mm~20mm.

9. The secondary battery according to claim 1, characterized in that, The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes lithium cobalt oxide particles, wherein the particle size Dv50 of the lithium cobalt oxide particles is 5μm~25μm; And / or, the charging cut-off voltage of the secondary battery is not less than 4.5 V.

10. The secondary battery according to claim 1, characterized in that, The diaphragm includes a base membrane and an adhesive layer, the adhesive layer being disposed on at least one side of the base membrane; the adhesive layer includes polymer particles; The polymer particles include secondary particles, which are formed by the aggregation of primary particles; the average particle size of the primary particles is 0.1 μm to 3 μm. And / or, the polymer particles include at least one of fluoroolefin polymers, acrylate polymers, and acrylonitrile polymers; And / or, the thickness of the adhesive layer on one side is 0.5 μm to 8 μm; And / or, the projection coverage of the adhesive layer on the surface of the base film on one side is 15% to 70%.

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