Secondary battery and electronic equipment

Abstract

The invention provides a secondary battery and an electronic device. The secondary battery comprises a negative plate and an electrolyte, the negative plate comprises a negative active layer, the negative active layer comprises a negative active material, the negative active material comprises a silicon-based material, and the silicon-based material comprises a calcium element; the electrolyte comprises a boron additive as shown in a formula 1; and the mass percentage content WB% of the boron additive in the electrolyte is 0.1%-5%. The secondary battery comprises the calcium-doped silicon-based negative electrode active material and the specially-composed boron additive, and the calcium-doped silicon-based negative electrode active material and the specially-composed boron additive are matched and cooperated with each other in special content, so that the electronic conductivity and the ionic conductivity of the silicon-based material are effectively improved, the low-temperature discharge performance of the secondary battery is improved, and the lithium precipitation risk is reduced.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to a secondary battery and an electronic device. Background Technology

[0002] Lithium-ion batteries, as the core of modern electrochemical energy storage technology, have been widely used in new energy vehicles, consumer electronics, portable tools, and large-scale energy storage systems. With the increasing demands for energy density and power density, developing higher-performance electrode materials has become crucial for driving industrial upgrading.

[0003] Among numerous novel anode active materials, silicon-based materials exhibit enormous application potential. Based on their high theoretical specific capacity, silicon-based materials are considered the most promising alternative to traditional graphite. However, silicon-based anodes still face a series of severe challenges in practical industrial applications. First, the intrinsic electronic conductivity and ion diffusion rate of silicon-based materials are low, resulting in poor overall conductivity of the anodes they form. Especially at low temperatures, ion migration resistance increases significantly, leading to a sharp decline in battery discharge capacity and deterioration in power performance, making it difficult to meet the application requirements of high-altitude or low-temperature environments. More critically, at low temperatures, due to kinetic lag, lithium ions cannot be inserted into the silicon lattice or carbon phase in time, resulting in irreversible deposition on the anode surface, a phenomenon known as "lithium plating." Lithium plating not only irreversibly consumes the active lithium source, leading to rapid capacity decay, but may also grow dendrites that pierce the separator, causing internal short circuits and posing serious safety hazards. These inherent defects severely restrict the performance and practical application of silicon-carbon anodes.

[0004] Therefore, overcoming the two major technological bottlenecks of poor low-temperature performance and high lithium plating risk of silicon anode active materials is of paramount importance for promoting the development of the next generation of high-performance lithium-ion batteries. Summary of the Invention

[0005] This application provides a secondary battery and an electronic device. The secondary battery includes a silicon-based negative electrode active material containing calcium and a boron-based additive with a special composition, which effectively improves the electronic conductivity and ionic conductivity of the silicon-based material, thereby improving the low-temperature discharge performance of the secondary battery and reducing the risk of lithium plating.

[0006] This application provides a secondary battery, including a negative electrode and an electrolyte;

[0007] The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the silicon-based material includes calcium.

[0008] The electrolyte includes boron-based additives as shown in Formula 1;

[0009] The boron-based additive in the electrolyte has a mass percentage W B The percentage ranges from 0.1% to 5%.

[0010] Formula 1

[0011] In Formula 1, R is absent or selected from C1-C20 substituted or unsubstituted alkyl, C1-C20 substituted or unsubstituted alkoxy, halogen. When substituted, the substituent is selected from C1-C5 alkyl, C1-C5 alkenyl, cyano, halogen, and 1≤n≤3.

[0012] In the secondary battery described above, the boron-based additive includes at least one of the following compounds:

[0013] I-1, I-2, I-3, I-4, I-5, I-6, I-7, I-8, I-9.

[0014] In the secondary battery described above, the calcium content W in the silicon-based material is... Ca ppm ranges from 5 to 300 ppm;

[0015] And / or, 3≤W Ca / W B ≤2000, where W Ca % represents the calcium content in the silicon-based material; preferably, 5 ≤ W Ca / W B ≤1500.

[0016] In the secondary battery described above, the electrolyte further includes a nitrogen-containing solvent as shown in Formula 2, wherein the nitrogen-containing solvent has a mass percentage content of 3%-20% in the electrolyte;

[0017] Formula 2

[0018] In Formula 2, R1, R2, and R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C5 alkyl, fluorinated or C1-C5 alkyl-substituted sulfone groups, and include at least one sulfone group.

[0019] In the secondary battery described above, the nitrogen-containing solvent includes at least one of the following compounds:

[0020] Equation 2-1, Equation 2-2, Equation 2-3, Equation 2-4.

[0021] In the secondary battery described above, the electrolyte further includes a nitrile additive, wherein the nitrile additive comprises 0.5%-6% by mass in the electrolyte; and / or,

[0022] The electrolyte further includes lithium salts; the lithium salts include lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide, wherein the lithium bis(trifluoromethanesulfonyl)imide has a mass percentage content of 2%-13% in the electrolyte; and / or,

[0023] The electrolyte also includes fluoroethylene carbonate, wherein the fluoroethylene carbonate has a mass percentage of 7%-22% in the electrolyte.

[0024] In the secondary battery described above, the particle size Dv50 of the silicon-based material is 5-15 μm; and / or,

[0025] In the negative electrode active layer, the silicon-based material has a mass percentage content of 3-80%; and / or,

[0026] The silicon-based material includes a carbon coating layer with a thickness of 1-25 nm; and / or,

[0027] The silicon-based material includes at least one of silicon-carbon materials, silicon-oxygen materials, elemental silicon, and silicon alloys; and / or,

[0028] The negative electrode active material further includes carbon-based materials, preferably including at least one of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0029] In the secondary battery described above, the negative electrode active layer further includes a carbon nanotube conductive agent, wherein the outer diameter of the carbon nanotube conductive agent is 1-40 nm and the aspect ratio is 200-10000.

[0030] In the secondary battery described above, the surface of the negative electrode active layer includes grooves, and the number of grooves N≥2;

[0031] Wherein, the minimum distance between two adjacent grooves is 0.1-10mm; and / or, the depth of the groove is 5-35μm; and / or, the width of the groove is 20-1000μm.

[0032] This application also provides an electronic device including any of the secondary batteries described above.

[0033] The negative electrode active material of the secondary battery in this application uses a silicon-based material containing calcium, combined with a specially formulated boron-based additive. Calcium regulates the crystal structure of the silicon-based material and promotes the formation of more ordered and stable electron transport channels, significantly improving the electronic conductivity of the silicon-based material. The introduction of boron-based additives (as shown in Formula 1) at a specific mass percentage optimizes the ion insertion / extraction process on the electrode material surface, significantly enhancing ionic conductivity. The synergistic effect of calcium and boron-based additives effectively improves the charge transport efficiency within the battery, significantly enhancing the cycle performance of the secondary battery at low temperatures, enabling it to maintain stable charge / discharge capabilities under cold conditions, and also greatly reducing the risk of lithium plating, ensuring the safety and reliability of the battery. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] In the research and development of silicon-based anode materials, improving their low-temperature conductivity has always been a key technical concern for those skilled in the art. Existing technologies typically employ methods such as conductive coating, element doping, or structural design to attempt to enhance the electronic conductivity of silicon-based materials. However, practice has shown that simply enhancing electronic conductivity often fails to achieve the expected improvement in low-temperature performance. In fact, after implementing some solutions, lithium plating on the anode surface becomes even more severe during low-temperature cycling.

[0036] After in-depth analysis, the inventors believe that the above-mentioned problems may stem from an imbalance between electronic conductivity and ionic conductivity in the battery system. Under low-temperature conditions, only the electronic conduction rate is increased, while the lithium-ion transport rate is significantly delayed. This mismatch between the two causes lithium ions to be unable to be inserted into the silicon anode active material in a timely and uniform manner, resulting in uncontrolled deposition on the anode surface, exacerbating the risk of lithium plating, and limiting capacity utilization and cycle life.

[0037] Therefore, the inventors intend to improve the electronic conductivity of silicon-based anodes and significantly enhance the interfacial migration and intercalation kinetics of lithium ions at low temperatures by synergistically regulating the electron-ion conductivity matching. This will improve the low-temperature discharge performance of secondary batteries while effectively suppressing lithium plating, thus achieving a synergistic improvement in capacity retention and safety.

[0038] Based on this, the first aspect of this application provides a secondary battery, including a negative electrode and an electrolyte; the negative electrode includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the silicon-based material includes calcium; the electrolyte includes a boron-based additive as shown in Formula 1; the mass percentage W of the boron-based additive in the electrolyte is... B The percentage ranges from 0.1% to 5%.

[0039] Formula 1

[0040] In Formula 1, R is absent or selected from C1-C20 substituted or unsubstituted alkyl, C1-C20 substituted or unsubstituted alkoxy, halogen. When substituted, the substituent is selected from C1-C5 alkyl, C1-C5 alkenyl, cyano, halogen, and 1≤n≤3.

[0041] The secondary battery of this application includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. In addition to the negative electrode active material, the negative electrode active layer may also include other additives commonly used in the art, such as conductive agents and binders. For example, the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; the material of the negative electrode current collector layer may be at least one of copper foil, nickel foam, and copper foam.

[0042] In the specific preparation of the negative electrode, the negative electrode active material, conductive agent, and binder can be dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained. In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0043] In addition to the boron-based additives shown in Formula 1, the electrolyte may also include non-aqueous solvents, lithium salts, and further, other additives.

[0044] In Formula 1, it can be understood that when R is absent, that is, the hydrogen atoms in the benzene ring, except for the carbon atom bonded to the boron atom, are not substituted to the other five carbon atoms; when R is selected from C1-C20 substituted or unsubstituted alkyl, C1-C20 substituted or unsubstituted alkoxy, or halogen, the number of R on each benzene ring can be any number from 1 to 3, and this application does not limit the substitution position of R. In addition, the number of substitutions and substitution positions of R between each benzene ring can be the same or different from each other.

[0045] For example, C1-C20 substituted or unsubstituted alkyl means that R can be selected from straight-chain alkyl or branched alkyl with C1 to C20 carbon atoms (i.e., R is selected from straight-chain alkyl with 1 to 20 carbon atoms or branched alkyl with 1 to 20 carbon atoms), and the number of carbon atoms in R is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, and the hydrogen atoms in the alkyl group may be unsubstituted or substituted. For example, R can be methyl, ethyl, n-propyl, n-butyl, isopropyl, tert-butyl, isobutyl, etc.

[0046] For example, C1-C20 substituted or unsubstituted alkoxy groups refer to the fact that R can be selected from straight-chain alkoxy groups with C1 to C20 carbon atoms or branched alkoxy groups (i.e., R is selected from straight-chain alkoxy groups with 1 to 20 carbon atoms or branched alkoxy groups with 1 to 20 carbon atoms). The number of carbon atoms in R is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, and the hydrogen atoms in the alkoxy group may be unsubstituted or substituted. For example, R can be methoxy, ethoxy, n-propoxy, n-butoxy, isopropoxy, tert-butoxy, isobutoxy, etc.

[0047] For example, when R is a halogen, it can be a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom.

[0048] Furthermore, when R is a substituted alkyl or substituted alkoxy group, the substituent is selected from C1-C5 alkyl, C1-C5 alkenyl, cyano, or halogen.

[0049] The secondary battery of this application exhibits excellent electrical performance during application, especially at low temperatures, where it demonstrates a higher discharge capacity ratio and lower lithium plating. This is because the silicon-based active material of this application includes chemically stable calcium, which forms a highly conductive second phase, optimizing the efficient electron conduction network of the negative electrode and effectively compensating for the inherent poor conductivity of silicon-based materials. This improvement significantly enhances the electron transport rate from the negative electrode current collector to the negative electrode active material, providing a foundation for improving the discharge capacity ratio at low temperatures. Simultaneously, boron-based additives, as shown in Formula 1, are added to the electrolyte, with their mass percentage strictly controlled within an optimal range. Specifically, these additives exhibit a higher binding energy with lithium ions than conventional solvent molecules, preferentially coordinating with lithium ions. This significantly reduces the desolvation energy barrier of lithium ions at the electrode / electrolyte interface, directly enhancing the interfacial migration kinetics of lithium ions at low temperatures and substantially increasing their insertion / extraction rate. At the same time, this dosage can also avoid a series of negative effects caused by excessive additives, such as excessively thick interfacial film, excessive consumption of active lithium and increased electrolyte viscosity, further ensuring the smooth ion conduction path.

[0050] Through the aforementioned synergistic effect, the imbalance between electron conduction and ion migration within the battery at low temperatures is effectively resolved. Electrons and lithium ions achieve kinetic matching, ensuring that lithium ions can be promptly and uniformly embedded into the negative electrode active material, rather than remaining on the surface and undergoing reduction reactions. This fundamentally suppresses lithium plating and significantly improves safety during low-temperature charging. Ultimately, the rechargeable battery of this application exhibits an excellent low-temperature discharge capacity ratio, and lithium plating is significantly suppressed.

[0051] It is understood that, in addition to the negative electrode and the electrolyte, the secondary battery of this application also includes a positive electrode. Specifically, the positive electrode includes a positive current collector and a positive active layer comprising a positive active material disposed on at least one surface of the positive current collector.

[0052] In the specific preparation of the positive electrode sheet, for example, the positive electrode active material of this application can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder, and more specifically, 80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0053] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0054] Generally, a secondary battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0055] In this application, the separator is used to separate the positive and negative electrode plates, preventing short circuits caused by contact between them. Conventional separators in the art can be used in this application, and there are no particular limitations. For example, the separator material can be a separator made of one or more of the following substances: high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0056] In this application, conventional housing materials in the art can be used to encapsulate the battery cell. The housing may include flexible packaging materials such as aluminum-plastic film, but is not limited to this.

[0057] This application allows for the assembly of components such as positive electrode, separator, and negative electrode into a battery using conventional methods in the field. For example, positive electrode, separator, and negative electrode can be stacked alternately to produce a stacked cell (or wound into a wound cell). The cell is then placed in a casing (outer packaging) and subjected to conventional processes such as electrolyte injection and encapsulation to produce a secondary battery.

[0058] This invention does not limit the method of adding calcium to silicon-based materials. It can be a simple physical mixing of silicon-based materials and calcium-containing compounds during the preparation of secondary batteries, or it can be residual calcium impurities from the silicon-based material preparation process. For qualitative detection of calcium in silicon-based materials in secondary batteries, for example, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), or X-ray diffraction (XRD) can be used to determine whether calcium is present.

[0059] Furthermore, the secondary battery exhibits particularly superior performance when the boron-based additives include at least one of the following nine compounds.

[0060] I-1, I-2, I-3, I-4, I-5, I-6, I-7, I-8, I-9.

[0061] The inventors analyzed that the nine specific boron-based additives exhibit higher interfacial reactivity in the electrolyte, preferentially participating in the formation of a thinner, more stable, and more ionicly conductive SEI film. Their unique molecular structure further optimizes the coordination ability of BO bonds with lithium ions, thereby more effectively reducing the desolvation energy barrier. Therefore, this specific additive can significantly improve the low-temperature capacity retention of the battery even at extremely low concentrations and more effectively suppress lithium plating at the negative electrode, demonstrating a better synergistic enhancement effect.

[0062] In one specific embodiment, the calcium content W in the silicon-based material Ca The concentration ranges from 5 to 300 ppm. When the calcium content is within the optimized range, it can increase the integrity and continuity of the three-dimensional conductive network in the silicon matrix, significantly improving the electron transport efficiency between particles of the negative electrode active material and between it and the current collector. Simultaneously, it can further enhance the smoothness of the lithium-ion diffusion path, thereby making the conductivity and ion-conductivity of the silicon-based material more compatible, resulting in a more significant improvement in the low-temperature cycle performance and safety performance of the secondary battery.

[0063] In addition, this application also addresses W Ca and W B The relationship between them was further specified; specifically, 3 ≤ W Ca / W B ≤2000. When the contents of both are within this ratio range, the efficient electron conduction network constructed by calcium and the lithium-ion interfacial migration kinetics optimized by the additives achieve a more suitable match. This ratio control ensures that the improvement in electron conduction rate is synchronized with the enhancement of lithium-ion desolvation and insertion rates, solving the fundamental problem of electron-ion conduction imbalance under low-temperature conditions at the molecular scale. At this point, the discharge capacity ratio of the secondary battery under low-temperature conditions is significantly improved, while the lithium plating phenomenon at the negative electrode caused by kinetic mismatch is more significantly suppressed, achieving a balance between high energy density and safety and reliability. Furthermore, 5≤W Ca / W B ≤1500, more preferably 50≤W Ca / W B ≤100.

[0064] It needs to be explained that in calculating W...Ca / W B At that time, W Ca The unit is ppm, W B This refers to values ​​without the percentage sign. For example, when W... B It is 0.1%, W Ca At 100 ppm, W Ca / W B =100 / 0.1=1000.

[0065] Specifically, when detecting the calcium content in silicon-based materials, inductively coupled plasma optical emission spectrometry (ICP-OES) can be used.

[0066] In addition to the boron-based additives shown in Formula 1, the electrolyte in the secondary battery of this application may also include a nitrogen-containing solvent shown in Formula 2, wherein the mass percentage of the nitrogen-containing solvent in the electrolyte is 3%-20%.

[0067] Formula 2

[0068] In Formula 2, R1, R2, and R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C5 alkyl, fluorinated or C1-C5 alkyl-substituted sulfone groups, and include at least one sulfone group.

[0069] Specifically, C1-C5 alkyl groups refer to straight-chain or branched alkyl groups with 1 to 5 carbon atoms, and they may be substituted or unsubstituted. When substituents are included, this application does not limit the specific selection of the substituents. Fluorine-substituted or C1-C5 alkyl-substituted sulfone groups refer to sulfone groups where the sulfur atom and the N atom in Formula 2 are connected, and then connected to a fluorine atom or a C1-C5 alkyl group, wherein C1-C5 alkyl groups refer to straight-chain or branched alkyl groups with 1 to 5 carbon atoms. It should be noted that although R1, R2, and R3 can be chosen independently, at least one of R1, R2, and R3 must include a fluorine-substituted or C1-C5 alkyl-substituted sulfone group.

[0070] This nitrogen-containing solvent, with its low oxidation potential, preferentially forms a film at the positive electrode interface, effectively suppressing the continuous oxidative decomposition of the electrolyte under high voltage, thereby enhancing the high-voltage cycle stability of the battery. Simultaneously, its high reduction potential allows it to preferentially reduce at the negative electrode surface, decomposing to form a stable SEI film rich in LiF and S and N species. LiF imparts excellent thermal stability to the interface, improving high-temperature performance; while the S and N components further enhance the ionic conductivity of the SEI. By controlling the mass percentage of the nitrogen-containing solvent in the electrolyte within an appropriate range, it is possible to ensure the formation of a protective layer with ideal composition and thickness at the positive and negative electrode interfaces, while avoiding the negative impact of excessive decomposition on the active lithium and the bulk properties of the electrolyte. Ultimately, this synergistically enhances interfacial ion transport kinetics, improving high-voltage and high-temperature performance while further promoting electrode process kinetic matching, effectively suppressing lithium plating and improving low-temperature performance.

[0071] Furthermore, when the nitrogen-containing solvent includes at least one of the following compounds, the battery's cycle stability at high voltage, capacity retention at high temperature, and rate performance at low temperature are all significantly improved, while the risk of lithium plating under all operating conditions is further reduced.

[0072] Equation 2-1, Equation 2-2, Equation 2-3, Equation 2-4.

[0073] In one specific embodiment, the electrolyte further includes nitrile additives, with a mass percentage of 0.5%-6% in the electrolyte. At this mass percentage, the nitrile and boron additives work synergistically. Specifically, while nitrile additives can improve the positive electrode stability and high-temperature stability of the secondary battery and suppress the gas generation problem of boron additives, they tend to introduce high impedance, leading to a decrease in low-temperature performance and charging kinetics. On the other hand, boron additives can weaken the solvation effect of nitrile additives, reducing the impact of nitrile additives at low temperatures. Therefore, the combination of the two can balance the high and low temperature performance of the secondary battery, resulting in superior performance over a wide temperature range.

[0074] The nitrile additives in this application include at least one of oxadionitrile, butadionitrile, adiponitrile, glutaronitrile, 3-methoxypropionitrile, malononitrile, benzonitrile, 4-fluorobenzonitrile, 4-trifluoromethylbenzonitrile, 2-methylglutaronitrile, 1,3,6-hexanetrionitrile, phosphate trinitrile, and ethylene glycol bis(propionitrile) ether.

[0075] In one specific embodiment, the electrolyte further includes a lithium salt. The lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium hexafluoroarsenate (LiAsF6), and lithium trifluoromethanesulfonate (LiCF3SO3).

[0076] Furthermore, when the lithium salt includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide, and the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 2%-13%, the electrolyte has a stronger chelating effect, which can reduce the lithium-ion desolvation energy, increase the lithium-ion migration rate, further improve the matching degree between electronic conductivity and ionic conductivity, and further reduce the risk of lithium plating.

[0077] Furthermore, the electrolyte of the secondary battery in this application also includes fluoroethylene carbonate, wherein the mass percentage of fluoroethylene carbonate in the electrolyte is 7%-22%. Fluoroethylene carbonate can form a stable interfacial film on the surfaces of the positive and negative electrodes, and can continuously repair damage to the interfacial film of the silicon-based negative electrode during long-term cycling, preventing further reaction between the negative electrode activity and the electrolyte. When controlled at the above-mentioned percentage, through synergy with boron-based additives, it can effectively improve long-term cycling stability, suppress impedance growth during cycling, and improve cycle capacity retention.

[0078] This application also includes non-aqueous solvents, including carbonates and / or carboxylic esters, wherein the carbonates are selected from one or more of the following solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and methyl ethyl carbonate; and the carboxylic esters are selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl butyrate.

[0079] In one specific embodiment, when the particle size Dv50 of the silicon-based material is controlled to be 5-15 μm, it means that the solid-state diffusion path of lithium ions inside the silicon particles is shorter, which can significantly reduce the ion transport impedance at low temperatures, making it easier for lithium ions to be inserted and extracted in the active material. On the other hand, it helps to buffer the internal stress caused by volume changes, reduce particle breakage and pulverization of electrode structures, and reduce the interface area where side reactions occur, thereby improving the cycle stability at high temperatures.

[0080] In addition, when the mass percentage of silicon-based materials in the negative electrode active material is 3-80%, the energy density can be significantly improved while minimizing the negative impact on the cycle performance of the battery caused by the expansion and deformation of silicon-based materials.

[0081] To further suppress the deformation of silicon-based materials and improve their conductivity, a carbon coating layer can be formed on at least a portion of the silicon-based material's surface. It is important to note that when the thickness of the carbon coating layer is 1-25 nm, the proportion of inactive materials can be minimized, thereby significantly reducing the adverse effects of the carbon coating layer on the energy density of the secondary battery.

[0082] The silicon-based materials described in this application include at least one of silicon-carbon materials, silicon-oxygen materials, elemental silicon, and silicon alloys. Furthermore, to simultaneously consider the energy density and cycle stability of the secondary battery, the silicon-based material can be a silicon-carbon material, which includes a porous carbon matrix and silicon material deposited on the porous carbon matrix.

[0083] In addition to silicon-based materials, the negative electrode active material in the secondary battery of this application may also include carbon-based materials to further improve the cycle stability of the secondary battery. Furthermore, the carbon-based material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon. This application does not limit the coexistence of silicon-based and carbon-based materials; they can be a physical mixture of the two.

[0084] The inventors discovered that when the negative electrode active material includes carbon nanotube conductive agents with an outer diameter of 1-40 nm and an aspect ratio of 200-10000, the unique fibrous one-dimensional structure of the carbon nanotube conductive agents can form a highly efficient and stable three-dimensional conductive network between the negative electrode active materials. This network not only significantly improves the macroscopic electronic conductivity of the negative electrode active material, but also allows for deep contact with silicon particles, ensuring the uniformity of electron transport and avoiding excessively high local current densities. This, in turn, activates more lithium intercalation sites on the surface of the negative electrode active material, greatly increasing the effective reaction interface available for ion-electron exchange and significantly improving the low-temperature performance of the secondary battery.

[0085] Furthermore, this application further improves the electrical performance of the secondary battery by controlling the surface structure of the negative electrode. Specifically, the surface of the negative electrode active layer includes grooves, the number of which N ≥ 2; the minimum spacing between two adjacent grooves is 0.1-10 mm. By performing groove formation treatment with the above-mentioned spacing on the surface of the negative electrode, multiple ion transport paths can be established, effectively shortening the diffusion distance of lithium ions in the electrolyte, improving ion migration kinetics, and thus reducing the risk of lithium plating caused by uneven ion distribution during high-rate charging.

[0086] Furthermore, when the groove size satisfies at least one of the following: depth of 5-35μm and width of 20-1000μm, the negative electrode active layer can orderly accommodate the volume change of silicon-based material without significantly sacrificing energy density. This significantly reduces SEI film rupture and regeneration side reactions caused by repeated expansion and contraction, helps maintain the integrity of the interface structure and low impedance characteristics, thereby improving battery cycle performance while also ensuring effective discharge capability under low temperature conditions.

[0087] Specifically, grooves can be formed on the surface of the negative electrode active layer through laser processing. The localized thermal effect during laser processing can promote the localized graphitization transformation of carbon materials in the adjacent area, further enhancing the interfacial electronic conductivity.

[0088] A second aspect of this application also provides an electronic device including the secondary battery described in the first aspect. This electronic device has advantages corresponding to the aforementioned secondary battery, which will not be elaborated further.

[0089] The secondary battery of this application can be widely used in various electronic devices that require electrochemical energy storage technology to operate. Specifically, typical application areas for electronic devices include, but are not limited to: power equipment, such as electric vehicles, electric bicycles, and drones; consumer electronics, such as smartphones, tablets, laptops, portable speakers, and digital cameras; wearable smart devices, such as smartwatches, smart bracelets, and augmented reality (AR) or virtual reality (VR) glasses; and fixed or mobile energy storage devices, such as home energy storage systems, backup power supplies for communication base stations, and large-scale grid energy storage power stations.

[0090] The secondary battery of this application will be described in detail below through specific embodiments.

[0091] Example 1

[0092] The secondary battery preparation method of this embodiment includes the following steps:

[0093] 1. Preparation of positive electrode sheet

[0094] Lithium cobalt oxide (Dv50 of 10 μm), polyvinylidene fluoride, conductive carbon black (SP), and carbon nanotubes were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a uniform and fluid positive electrode slurry (with a solid content of 65 wt%) was formed. The positive electrode slurry was uniformly coated on both surfaces of an aluminum foil, the coated aluminum foil was dried, and then rolled and slit to obtain the positive electrode sheet.

[0095] 2. Preparation of negative electrode sheet

[0096] Silicon-carbon material (containing calcium, with a Dv50 of 10 μm), artificial graphite, carbon nanotube conductive agent, styrene-butadiene rubber, and sodium carboxymethyl cellulose were placed in deionized water at a mass ratio of 10:87.2:0.5:1.3:1. The slurry was stirred evenly to obtain a negative electrode slurry. This negative electrode slurry was uniformly coated onto a copper foil current collector, and then subjected to drying, rolling, and slitting processes. The slitting negative electrode sheets were then laser-grooved, creating a matrix of grooves on the entire surface of the negative electrode sheet. The minimum spacing between adjacent grooves was set to 1.2 mm, the groove depth was 18 μm, and the groove width was 100 μm. After laser treatment, the negative electrode sheets were cleaned and prepared into a sheet to obtain the final negative electrode sheet.

[0097] 3. Battery manufacturing

[0098] The diaphragm in this application uses a 9μm thick substrate + ceramic + adhesive-coated diaphragm.

[0099] The electrolyte comprises lithium salt, solvent, and additives. The electrolyte, by mass percentage, includes: lithium salt including LiPF6 (14%) and lithium bis(trifluoromethanesulfonylimide) (6%); additives including nitrile additives, fluoroethylene carbonate, and boron additives (the specific composition of the additives is shown in Table 1); and the balance is solvent, which includes ethylene carbonate (EC), ethyl propylene carbonate (PC), propyl propionate (PP), and nitrogen-containing solvents. The molar ratio of EC:PC:PP is 1:1:3.

[0100] After the above-mentioned diced positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, they are wound into a wound cell structure. The cell is then encapsulated, injected with electrolyte, formed, and resealed to obtain a secondary battery. The specific composition of the secondary battery in this embodiment is shown in Tables 1A, 1B, and 1C.

[0101] Examples 2-35 and Comparative Examples 1-3 are basically the same as Example 1, with differences shown in Table 1. The negative electrode active material in the examples and comparative examples is a mixture of silicon carbide and artificial graphite. In Example 26, conductive carbon black was used to replace the nanotube conductive agent.

[0102] Experimental Example 1

[0103] 1. W Ca :

[0104] Silicon-carbon materials were detected using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0105] 2. Silicon-based material Dv50:

[0106] The battery was disassembled in an argon-filled glove box. The negative electrode was removed and rinsed with the inert solvent DMC to remove residual electrolyte. The solvent and trace amounts of moisture were removed in the glove box. The negative electrode active material was scraped off from the current collector. The scraped negative electrode active material was placed in a centrifuge tube, and N-methylpyrrolidone (NMP) was added. The mixture was then thoroughly dispersed by ultrasonic vibration and stirring, followed by high-speed centrifugation. The binder dissolved in the supernatant, while the negative electrode active material and conductive agent precipitated at the bottom of the tube. The supernatant was discarded, and the mixture was washed and centrifuged three times with fresh solvent. Finally, it was vacuum dried to obtain a mixture of negative electrode active material and conductive agent.

[0107] After sputter-coating the mixture with gold to improve conductivity, the field of view was first located at low magnification using SEM. Since silicon-based materials are typically brighter than artificial graphite in SEM images, initial localization was possible. Energy dispersive spectroscopy (EDS) was then used for Si elemental distribution analysis. The Si elemental distribution map clearly and unambiguously identified which particles were silicon-based. Guided by the Si elemental distribution map, multiple random, Si-rich regions were photographed at magnifications above 10,000x, ensuring clear images and distinct particle boundaries. The captured SEM images were imported into professional image analysis software to determine the Dv50 of the silicon-based material.

[0108] 3. Silicon-based material content:

[0109] Taking the mass content of silicon-carbon composite material in the negative electrode active layer as an example, calculations were performed using ash content and EDS test results. EDS test: The battery was discharged to 0% SOC, disassembled, and the negative electrode sheet was removed. The negative electrode sheet containing the silicon-carbon composite material was treated with an argon ion polisher to obtain its cross-section. Then, it was tested using a scanning electron microscope in backscatter mode at a magnification of 10K. A single silicon-carbon particle was selected, and EDS was used to test the location points within the particle. The silicon content (wt%) at that point was calculated using standard-free analysis. EDS sampling tests were performed on the silicon content at five points in different regions within a single particle, and the average value was calculated as the silicon content of the single particle. The silicon content of 10 different silicon-carbon composite material particles was statistically analyzed, and the average value was taken as the silicon content of the silicon-carbon composite material. Ash content test: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode sheet is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove lithium salts adhering to the electrode sheet. After drying, the electrode sheet is subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active material layer can then be peeled off from the current collector, and the negative electrode active material is collected. In the silicon content test, a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer) is used. The sample size is 10 mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 minutes. This allows the non-silicon components in the negative electrode material active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content of the negative electrode active layer. Ignoring the mass percentage of trace impurities that may be present in the ash, and treating all ash as silicon dioxide, the mass of silicon in the negative electrode active material can be calculated using the following formula: Mass percentage of silicon in the negative electrode active layer = 7 × Mass of ash / (15 × Mass of test sample). Based on the EDS and ash test results above, and according to the silicon content percentage of the silicon-carbon composite material and the mass percentage of silicon in the negative electrode active material, the mass content of the silicon-carbon composite material in the negative electrode active layer can be calculated in reverse.

[0110] 4. Depth, width, and spacing of the grooves in the negative electrode: The batteries of the examples and comparative examples were disassembled, and the negative electrode was separated from the batteries. The depth, width, and spacing of the grooves in the negative electrode were tested using SEM.

[0111] 5. Qualitative and quantitative detection of nitrogen-containing solvents: Battery disassembly and electrolyte extraction were performed in an argon-protected glove box. A certain mass of electrolyte sample was accurately weighed using a precision balance as the basis for all subsequent quantitative calculations. The sample was transferred to a volumetric flask, diluted and brought to volume with anhydrous dimethyl carbonate, and then detected using nuclear magnetic resonance (NMR) and GC-MC (gas chromatography-mass spectrometry).

[0112] 6. Qualitative and quantitative detection of boron-based solvents: Battery disassembly and electrolyte extraction were performed in an argon-protected glove box. A precise mass of electrolyte sample was accurately weighed using a precision balance as the basis for all subsequent quantitative calculations. The sample was transferred to a volumetric flask, diluted and brought to volume with anhydrous dimethyl carbonate, and then detected using nuclear magnetic resonance (NMR) and GC-MC (gas chromatography-mass spectrometry).

[0113] 7. Qualitative and quantitative detection of lithium salts: Battery disassembly and electrolyte extraction were performed in an argon-protected glove box. A certain mass of electrolyte sample was accurately weighed using a precision balance as the basis for all subsequent quantitative calculations. The sample was transferred to a volumetric flask, diluted and brought to volume with anhydrous dimethyl carbonate, and then detected using ion chromatography (IC) with inductively coupled plasma optical emission spectrometry (ICP-OES).

[0114] 8. Qualitative and quantitative detection of other additives (FEC, nitrile additives): Battery disassembly and electrolyte extraction were performed in an argon-protected glove box. A certain mass of electrolyte sample was accurately weighed using a precision balance as the basis for all subsequent quantitative calculations. The sample was transferred to a volumetric flask, diluted and brought to volume with anhydrous dimethyl carbonate, and then detected using nuclear magnetic resonance and GC-MC (gas chromatography-mass spectrometry).

[0115] 9. Detection of carbon nanotube dimensions (outer diameter and aspect ratio):

[0116] The battery was disassembled in an argon-filled glove box, and the negative electrode was removed. A cross-section of the negative electrode was selected and scanned at a low magnification of 5,000x using a scanning electron microscope (SEM) to locate the edges or surface of the artificial graphite particles. The magnification was then switched to a high magnification of 30,000x to clearly distinguish each carbon nanotube. Ten high-resolution SEM images were randomly taken at different locations and analyzed using the built-in measurement software of the SEM images.

[0117] The results are shown in Tables 1A, 1B, and 1C.

[0118] Experimental Example 2

[0119] 1. 45℃ Cyclic Performance Test

[0120] The batteries prepared in the examples and comparative examples were subjected to 500 charge-discharge cycles at 45°C at a 1C rate within the charge-discharge cutoff voltage range (3.0V-4.5V). The discharge capacity of the first cycle was measured as x2 mAh, and the discharge capacity of the 500th cycle was measured as y2 mAh. The capacity of the 500th cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = y2 / x2. The results are shown in Table 2.

[0121] 2. Low-temperature discharge capacity ratio

[0122] Under 25°C conditions, the batteries of the examples and comparative examples were discharged to 3.0V with a given current of 0.2C; left to rest for 5 minutes; then charged to 4.5V with a charging current of 0.2C. When the cell voltage reached 4.5V, the charging was switched to 4.5V constant voltage charging with a cutoff current of 0.02C. The batteries were then discharged to 3.0V with a given current of 0.2C. The discharge capacity of the last step was taken as the room temperature capacity. The batteries were first charged to 4.5V with a charging current of 0.2C. When the cell voltage reached 4.5V, the charging was switched to 4.5V constant voltage charging with a cutoff current of 0.02C. The batteries were then placed in a -20°C temperature chamber and left to stand for 1 hour. The batteries were then discharged to 3.4V with a given current of 0.2C. The discharge capacity was taken as the low temperature capacity.

[0123] Low-temperature discharge capacity ratio = (low-temperature capacity / room-temperature capacity) * 100%

[0124] The results are shown in Table 2.

[0125] 3. Lithium plating situation

[0126] After the batteries prepared in the examples and comparative examples were subjected to capacity testing in a constant temperature environment of 25°C, the following steps were followed:

[0127] ① Let stand for 10 minutes, ② Discharge to 3.0V at 0.2C, ③ Let stand for 10 minutes, ④ Charge to 4.5V at a 3C rate with a cutoff current of 0.02C, ⑤ Repeat cycles ①-④ 10 times, and disassemble the fully charged battery to confirm lithium plating. The results are shown in Table 2.

[0128] Table 1A

[0129]

[0130] Table 1B

[0131]

[0132] Table 1C

[0133]

[0134] Table 2

[0135]

[0136] As shown in Table 2, the battery described in this application is beneficial for improving the low-temperature discharge performance of secondary batteries and reducing the risk of lithium plating.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A secondary battery, characterized in that, Includes the negative electrode and the electrolyte; The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the silicon-based material includes calcium. The electrolyte includes boron-based additives as shown in Formula 1; The boron-based additive in the electrolyte has a mass percentage W B The percentage ranges from 0.1% to 5%. Formula 1 In Formula 1, R is absent or selected from C1-C20 substituted or unsubstituted alkyl, C1-C20 substituted or unsubstituted alkoxy, halogen. When substituted, the substituent is selected from C1-C5 alkyl, C1-C5 alkenyl, cyano, halogen, and 1≤n≤3.

2. The secondary battery according to claim 1, characterized in that, The boron-based additives include at least one of the following compounds. I-1, I-2, I-3, I-4, I-5, I-6, I-7, I-8, I-9。 3. The secondary battery according to claim 1 or 2, characterized in that, In the silicon-based material, the calcium content W Ca ppm ranges from 5 to 300 ppm; And / or, 3≤W Ca / W B ≤2000, where W Ca % represents the calcium content in the silicon-based material; preferably, 5 ≤ W Ca / W B ≤1500.

4. The secondary battery according to any one of claims 1-3, characterized in that, The electrolyte also includes a nitrogen-containing solvent as shown in Formula 2, wherein the mass percentage of the nitrogen-containing solvent in the electrolyte is 3%-20%. Formula 2 In Formula 2, R1, R2, and R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C5 alkyl, fluorinated or C1-C5 alkyl-substituted sulfone groups, and include at least one sulfone group.

5. The secondary battery according to claim 4, characterized in that, The nitrogen-containing solvent includes at least one of the following compounds. Equation 2-1, Equation 2-2, Equation 2-3, Equation 2-4.

6. The secondary battery according to any one of claims 1-5, characterized in that, The electrolyte further includes nitrile additives, wherein the nitrile additives constitute 0.5%-6% by mass in the electrolyte; and / or, The electrolyte further includes lithium salts; the lithium salts include lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide, wherein the lithium bis(trifluoromethanesulfonyl)imide has a mass percentage content of 2%-13% in the electrolyte; and / or, The electrolyte also includes fluoroethylene carbonate, wherein the fluoroethylene carbonate has a mass percentage of 7%-22% in the electrolyte.

7. The secondary battery according to any one of claims 1-6, characterized in that, The silicon-based material has a particle size Dv50 of 5-15 μm; and / or, In the negative electrode active layer, the silicon-based material has a mass percentage content of 3-80%; and / or, The silicon-based material includes a carbon coating layer with a thickness of 1-25 nm; and / or, The silicon-based material includes at least one of silicon-carbon materials, silicon-oxygen materials, elemental silicon, and silicon alloys; and / or, The negative electrode active material further includes carbon-based materials, preferably including at least one of artificial graphite, natural graphite, hard carbon, and soft carbon.

8. The secondary battery according to any one of claims 1-7, characterized in that, The negative electrode active layer also includes a carbon nanotube conductive agent, the outer diameter of which is 1-40 nm and the aspect ratio is 200-10000.

9. The secondary battery according to any one of claims 1-8, characterized in that, The surface of the negative electrode active layer includes grooves, and the number of grooves N≥2; Wherein, the minimum distance between two adjacent grooves is 0.1-10mm; and / or, the depth of the groove is 5-35μm; and / or, the width of the groove is 20-1000μm.

10. An electronic device comprising a secondary battery according to any one of claims 1 to 9.

Images