Lithium ion battery and its application

Abstract

The application relates to a lithium ion battery and application thereof. In the battery, a silicon material and a cobalt element are contained in a negative electrode active material layer in a negative electrode sheet; in an electrolyte, an additive comprises vinylene carbonate, vinyl sulfene sulfite and tetraethylenyl silane, and meets the following conditions: 0.002 <= (A+B) / K <= 1.65, 0.09 <= (A+B+C) / H <= 0.77, 0.05 <= C / (A+B) <= 0.8, 5 <= K <= 2000, 15 <= H <= 60; A represents the mass percentage of the vinylene carbonate in the electrolyte; B represents the mass percentage of the vinyl sulfene sulfite in the electrolyte; C represents the mass percentage of the tetraethylenyl silane in the electrolyte; K represents the content of the cobalt element in the negative electrode active material layer; and H represents the thickness of the negative electrode active material layer. In the scheme provided by the application, the three functional additives are synergistic, the volume expansion of the silicon negative electrode is buffered, the stability of the silicon-based negative electrode lithium ion battery under high and low temperature cycle conditions is improved, and the lithium ion battery can still maintain good cycle life under wide temperature range conditions.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage device technology, and in particular to a lithium-ion battery and its application. Background Technology

[0002] Lithium-ion batteries, as a highly efficient electrochemical energy storage device, have been widely used in portable electronic devices, new energy vehicles, and large-scale energy storage systems due to their advantages such as high energy density and long cycle life.

[0003] The overall performance of a lithium-ion battery system highly depends on the synergistic effect of key materials such as the cathode, anode, electrolyte, and separator. Among these, the cathode active material is the core factor determining the battery's energy density, cost, and stability. Currently, cobalt is an indispensable key component in high-performance layered oxide cathode materials (such as lithium cobalt oxide and NCM ternary materials). The introduction of cobalt can effectively stabilize the layered crystal structure of the cathode active material, suppress phase transitions during charge and discharge, and improve the material's electronic conductivity and lithium-ion diffusion kinetics, thereby ensuring the battery's cycle stability and rate performance at high voltages.

[0004] However, cobalt-containing cathode active materials may dissolve and migrate into the electrolyte system during long-term cycling, becoming free active ions inside the battery. At low temperatures, cobalt ions readily coordinate with electrolyte solvent molecules, increasing electrolyte viscosity and hindering interfacial charge transport. Under high temperature or high pressure conditions, cobalt ions catalyze the oxidative decomposition of the electrolyte, generating gas and causing abnormal thickening of the solid electrolyte interphase (SEI) film. Furthermore, cobalt ions may migrate to the anode side, intercalating into the silicon lattice or undergoing heterogeneous deposition on its surface, disrupting the structural integrity of the silicon anode, hindering normal lithium ion insertion / extraction, and exacerbating local stress concentration when silicon particles expand in volume. This ultimately leads to problems such as active material particle breakage, electrode structure pulverization, and electrical contact failure. Therefore, these chemical behaviors of cobalt easily accelerate the capacity decay of silicon-based anodes under high and low temperature cycling conditions, severely limiting the overall performance and lifespan of the battery. Summary of the Invention

[0005] To address or partially address the problems existing in related technologies, this application provides a lithium-ion battery and its application. Through the synergistic effect of three additives in the electrolyte—ethylene carbonate, vinyl ethylene sulfite, and tetraethylenesilane—the volume expansion of the silicon anode is effectively buffered, improving the stability of the silicon-based anode lithium-ion battery under high and low temperature cycling conditions, enabling the lithium-ion battery to maintain good cycle life even when used under wide temperature range conditions.

[0006] The first aspect of this application provides a lithium-ion battery, including a negative electrode sheet, a positive electrode sheet, and an electrolyte. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative active material layer includes a negative active material, which includes silicon material. The negative active material layer contains cobalt. The electrolyte comprises lithium salt, organic solvent, and additives, wherein the additives include vinylene carbonate, vinyl sulfite, and tetraethylenesilane. The lithium-ion battery satisfies the following conditions: 0.002≤(A+B) / K≤1.65, 0.09≤(A+B+C) / H≤0.77, 0.05≤C / (A+B)≤0.8; Wherein, A represents the mass percentage of vinylene carbonate in the electrolyte, in units of %; B represents the mass percentage of vinyl sulfite in the electrolyte, in units of %; C represents the mass percentage of tetraethylenesilane in the electrolyte, in units of %; K represents the cobalt content in the negative electrode active material layer, in units of ppm, 5≤K≤2000; H represents the thickness of the negative electrode active material layer, in units of μm, 15≤H≤60.

[0007] In some implementations, 0.5 ≤ A ≤ 20; preferably, 1 ≤ A ≤ 15.

[0008] In some implementations, 0.1 ≤ B ≤ 10; preferably, 0.5 ≤ B ≤ 5.

[0009] In some implementations, 0.1 ≤ C ≤ 5; preferably, 0.5 ≤ C ≤ 2.5.

[0010] In some implementations, 0.003 ≤ (A+B) / K ≤ 1.4; and / or, 0.13 ≤ (A+B+C) / H ≤ 0.6; and / or, 0.06 ≤ C / (A+B) ≤ 0.36.

[0011] In some embodiments, the silicon material comprises silicon particles, wherein the silicon content in the silicon particles is 80% to 99%.

[0012] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluoroborate, and lithium difluorodi(oxalate)borate.

[0013] In some embodiments, the organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0014] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector; the positive active material layer includes a positive active material, which includes at least one of lithium transition metal oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate.

[0015] In some embodiments, the chemical formula of the transition metal lithium oxide is Li. (1+x) Ni y Co z M (1-y-z) O2; wherein -0.1≤x≤1, 0≤y≤1, 0≤z≤1, 0≤y+z≤1, and M is selected from at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0016] A second aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0017] The technical solution provided in this application can include the following beneficial effects: By synergistically combining three functional additives—ethylene carbonate, vinyl sulfite, and tetraethylenesilane—and controlling the relationship between these three additives and the negative electrode sheet to satisfy "0.002≤(A+B) / K≤1.65, 0.09≤(A+B+C) / H≤0.77, 0.05≤C / (A+B)≤0.8," the additives can construct a composite interface layer with excellent stability on the silicon negative electrode surface, effectively suppressing catalytic side reactions caused by cobalt ion dissolution, while buffering the volume expansion of the silicon negative electrode, and improving the high and low temperature cycle stability and safety performance of the lithium-ion battery. Specifically, vinyl carbonate preferentially polymerizes to form a flexible basic framework rich in polycarbonate, effectively buffering the volume expansion of the silicon negative electrode; vinyl sulfite decomposes to generate a sulfur-containing composite phase with high ionic conductivity, which is embedded in the framework to improve interfacial ion transport efficiency; and tetraethylenesilane constructs a robust silane protective layer on the surface, significantly enhancing the mechanical integrity and thermal stability of the interface. Furthermore, by defining the relationship, the ratio of additives in the electrolyte can be adjusted according to the parameters of the silicon anode, thereby achieving synergistic function of each component in the electrolyte system. This ensures that the SEI film constructed by the additives on the anode surface has excellent flexibility, ionic conductivity, and interfacial density, effectively suppressing side reactions such as electrolyte catalytic decomposition caused by cobalt ion dissolution, abnormal SEI film thickening, and silicon lattice destruction. Consequently, it significantly improves the high-temperature cycle stability, thermal shock safety, and low-temperature discharge performance of lithium-ion batteries, especially pure silicon anode lithium-ion batteries. This makes the silicon-based anode lithium-ion battery have both high energy density and wide temperature range application value, and it can still maintain good cycle life when used under high and low temperature conditions.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0019] The embodiments of this application will now be described in more detail. It should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0020] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While the methods and materials described herein, or any equivalent methods and materials, may also be used in the implementation or testing of the invention, preferred methods and materials are now described.

[0021] It should be understood that although the terms “first,” “second,” “third,” etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. Features defined as “first” or “second” may explicitly or implicitly include one or more of that feature. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0022] Where numerical ranges are provided, it should be understood that every intermediate value between the upper and lower limits of the range and any other specified or intermediate value within the specified range is covered within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also covered within the present invention, subject to any explicitly excluded limits within the specified range. Where a specified range includes one or two limits, the range excluding any or both of those included limits is also included within the present invention. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] In silicon-based anode battery systems, the introduction of cobalt accelerates battery performance degradation through multiple chemical mechanisms. Specifically, cobalt ions exhibit high migration activity in the electrolyte, readily forming coordination structures with solvent molecules at low temperatures, leading to increased electrolyte viscosity and impeded interfacial charge transport. At high temperatures, cobalt catalyzes the oxidative decomposition of ester electrolytes, promoting the formation of gaseous byproducts and causing abnormal thickening of the solid electrolyte interphase (SEI) film. More critically, dissolved cobalt ions migrate towards the anode during charge and discharge, disrupting the structural stability of the anode material through embedding in the silicon lattice or surface deposition. This heterogeneous deposition not only hinders the normal insertion and extraction of lithium ions but also exacerbates stress concentration during the volume expansion of silicon materials, ultimately leading to active particle breakage and interfacial contact failure. These chemical behaviors of cobalt result in pure silicon anodes facing more severe capacity decay problems under high and low temperature cycling conditions.

[0024] This application provides a lithium-ion battery, including a negative electrode, a positive electrode, an electrolyte, and a separator.

[0025] In this embodiment, the negative electrode includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. This embodiment does not impose any particular limitation on the negative current collector, as long as it is conductive and does not cause adverse chemical changes in the battery. Typical enriched current collectors can be, for example, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors; copper foil is preferred.

[0026] The negative electrode active material layer is formed by coating the negative electrode slurry onto the surface of the negative electrode current collector. The negative electrode slurry may contain negative electrode active material, conductive agent, binder and thickener.

[0027] The negative electrode active material includes silicon materials. Further, the silicon material may include silicon particles, silicon-carbon composite materials, or silicon-oxygen composite materials, preferably silicon particles. In particular, this application shows a significant improvement effect on lithium-ion batteries with silicon particle negative electrodes.

[0028] The silicon content in the silicon particles ranges from 80% to 99%. Specific silicon content can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between these values.

[0029] In the embodiments of this application, the negative electrode active material may also include carbon materials, such as at least one of natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, and soft carbon.

[0030] The conductive agent mentioned in the embodiments of this application can be at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The binder mentioned in the embodiments of this application can be one or more of carboxymethyl cellulose, styrene-butadiene rubber, styrene-acrylic emulsion, lithium polyacrylate, polyacrylic acid, and sodium alginate, and the thickener can be carboxymethyl cellulose salt, etc.

[0031] In this embodiment, the electrolyte includes a lithium salt, an organic solvent, and additives. The additives include vinylene carbonate (VC), vinyl sulfite (VES), and tetraethylenesilane (TVSi). The lithium-ion battery in this embodiment meets the following conditions: Equation 1: 0.002≤(A+B) / K≤1.65; Equation 2: 0.09≤(A+B+C) / H≤0.77; Equation 3: 0.05≤C / (A+B)≤0.8.

[0032] Where A represents the mass percentage of vinylene carbonate in the electrolyte, in %; B represents the mass percentage of vinyl sulfite in the electrolyte, in %; C represents the mass percentage of tetraethylenesilane in the electrolyte, in %; K represents the cobalt content in the negative electrode active material layer, in ppm; and H represents the thickness of the negative electrode active material layer, in μm.

[0033] In the embodiments of this application, the electrolyte formulation can be optimized based on the parameters of the negative electrode sheet in the lithium-ion battery through the above-mentioned formulas 1, 2 and 3. This allows the three additives in the electrolyte to effectively exert their synergistic effect, buffering the volume expansion effect of the silicon negative electrode, while effectively suppressing the negative electrode interface side reaction caused by cobalt dissolution and migration, improving the stability of the silicon negative electrode, thereby improving the cycle stability of the lithium-ion battery under high temperature and low temperature conditions, and improving the cycle life of the lithium-ion battery in a wide temperature range.

[0034] In practical applications, the additive content can be designed by first predicting the amount of cobalt ions dissolved and deposited at the negative electrode interface, then the additive content can be adjusted by the thickness of the negative electrode active material layer, and finally the dosage of the three types of functional additives can be adjusted to optimize the complete additive formula in the electrolyte. The optimal design of the additive dosage in the electrolyte can be achieved by following Equations 1, 2, and 3 in that order.

[0035] In this embodiment, vinylene carbonate undergoes polymerization at the electrode interface via its vinyl groups to form a polycarbonate-rich SEI film. This SEI film exhibits good elasticity and can effectively buffer the volume changes of the silicon anode during cycling, thereby significantly improving high-temperature (e.g., 45°C) cycling performance. However, the interface film formed by vinylene carbonate increases the migration resistance of lithium ions to some extent, especially at low temperatures, leading to a significant increase in interface impedance and a noticeable negative impact on low-temperature (e.g., 0°C) cycling performance. Furthermore, the decomposition products of vinylene carbonate may exacerbate interface reactions under extreme thermal shock, negatively affecting battery safety. Vinyl sulfite, as a sulfur-containing additive, can form a stable interface layer on the anode surface. This interface layer has excellent ionic conductivity, significantly improving the low-temperature cycling performance of the battery. Simultaneously, vinyl sulfite can also inhibit the oxidative decomposition of the electrolyte at high voltages, thus having a significant positive impact on high-temperature cycling performance. However, vinyl sulfite may participate in exothermic reactions at high temperatures, thus negatively impacting thermal shock safety performance. Tetraethylenesilane forms a dense protective layer at the electrode interface through its silane groups. This protective layer effectively prevents direct contact between the electrolyte and the highly active surface, inhibiting the thermal decomposition and oxidation of the electrolyte, thus having a strong positive impact on thermal shock safety and high-temperature cycling performance. However, this dense structure also limits the migration rate of lithium ions at low temperatures, leading to a slight decrease in low-temperature performance.

[0036] The synergistic effect of these three additives is particularly significant for negative electrode sheets using silicon particles as the negative electrode active material. This is mainly because, in lithium-ion batteries, especially silicon-based negative electrode lithium-ion battery systems, when these three additives work simultaneously, vinylene carbonate preferentially reduces at the negative electrode to form an elastic SEI basic framework, effectively adapting to the volume changes of the silicon negative electrode; vinyl sulfite, by generating a sulfur-containing composite phase with high ionic conductivity, embeds itself in this framework to improve the ion transport efficiency of the interfacial film; and tetraethylenesilane, by forming a stable silane protective layer, constructs a robust top-layer protective network on top of the existing SEI film, significantly enhancing the mechanical integrity and thermal stability of the interface. Therefore, the flexible matrix provided by vinylene carbonate alleviates the brittleness problem that vinyl sulfite and tetraethylenesilane may cause; the ion channels optimized by vinyl sulfite partially offset the low-temperature impedance caused by vinylene carbonate and tetraethylenesilane; and the stable interface layer constructed by tetraethylenesilane effectively suppresses the catalytic side reactions caused by cobalt. The three work together to achieve gradient and functionalization of the SEI film in terms of composition and structure, ultimately enabling the battery to maintain excellent cycle stability over a wide temperature range, especially in high-temperature and thermal safety scenarios.

[0037] In this embodiment, the cobalt content in the negative electrode active material layer ranges from 5 ppm to 2000 ppm, i.e., 5 ≤ K ≤ 2000. At this level, the cobalt content is moderate. When the cobalt content exceeds 2000 ppm, excessive cobalt impurities form localized catalytic centers in the pure silicon negative electrode. The delocalization effect of cobalt ions' d-orbital electrons catalyzes the oxidative decomposition of the electrolyte and generates an unstable CoF2 / Li2O composite phase. The solid solution of cobalt in the silicon lattice also blocks the lithium ion diffusion channels, causing an increase in charge transfer impedance. At the same time, the dissolved cobalt ions migrate towards the negative electrode during charging and discharging, destroying the structural stability of the material by embedding into the silicon lattice or by surface deposition.

[0038] Understandably, the cobalt element in the negative electrode active material layer mainly originates from the cobalt element in the positive electrode sheet, which migrates and deposits in the negative electrode active material layer due to dissolution. In other words, it mainly originates from the migration and deposition of cobalt impurities into the negative electrode active material layer during the cell manufacturing process and formation stage. The cobalt content in the negative electrode sheet described in this application embodiment can be specifically detected using the following method: concentrated sulfuric acid and concentrated nitric acid are added sequentially to the negative electrode active material, heated until the solution is clear and transparent, cooled, and brought to a constant volume. The cobalt content is then measured using an ICP (Inductively Coupled Plasma Emission Spectrometer). During the experiment, a corresponding mass fraction of elemental cobalt can be added to the negative electrode slurry to achieve the cobalt content range set for the experiment.

[0039] When (A+B) / K < 0.002, the total amount of additives is severely insufficient relative to the cobalt impurity content. On the one hand, insufficient interfacial passivation leads to the continuous catalytic decomposition of the electrolyte by cobalt ions, generating unstable SEI components and causing a surge in interfacial impedance. On the other hand, the basic interfacial film synergistically constructed by VC and VES cannot effectively complex free cobalt ions, making it difficult to inhibit the electrolyte oxidation and decomposition catalyzed by cobalt, and also unable to establish stable ion transport channels, resulting in increased gas production during high-temperature cycling and a sharp decline in low-temperature discharge capacity. When (A+B) / K > 1.65, the total amount of additives is relatively excessive. Excessive VC polymerization products will form an excessively thick insulating layer, severely hindering lithium ion migration. Excessive sulfides generated by the decomposition of VES will be excessively deposited at the interface. Although this improves the high-temperature stability of the interfacial film, it increases the electronic conductivity of the film layer, exacerbating the continuous decomposition of the electrolyte. At the same time, excessive additives increase side reactions, generating gaseous byproducts, which have an additional negative impact on thermal safety.

[0040] The lithium-ion battery in this embodiment further satisfies: 0.003≤(A+B) / K≤1.4.

[0041] By further defining the relationship between the cobalt content in the negative electrode and the electrolyte additive content, the synergistic effect of the above three additives can effectively suppress the side reactions at the negative electrode interface and the instability of the SEI film caused by the dissolution and migration of cobalt, and better enhance the effect of the synergistic mechanism on improving high-temperature cycling stability and storage performance.

[0042] In this embodiment, the thickness of the negative electrode active material layer is maintained between 15 μm and 60 μm, i.e., 15 ≤ H ≤ 60. At this thickness, the negative electrode active material layer is of moderate thickness, ensuring both high energy density and efficient lithium-ion transport. When the thickness of the negative electrode active material layer is less than 15 μm, the electrode interface reaction is intense, the additive concentration is relatively high, and an excessively thick SEI film is easily formed, increasing interfacial impedance. When the thickness of the negative electrode active material layer exceeds 60 μm, the ion transport path is too long, especially at low temperatures where ion migration is hindered, leading to insufficient capacity utilization and decreased cycle performance.

[0043] When (A+B+C) / H < 0.09, the additive concentration allocated per unit thickness in the negative electrode active material layer is insufficient. In batteries with a thicker negative electrode active material layer, the additive cannot fully wet and modify the entire electrode interface, resulting in a large number of unprotected active sites inside the electrode. These areas exhibit uneven SEI film growth and are highly susceptible to local decomposition induced by cobalt ions, leading to uneven internal resistance distribution, rapid capacity decay, and a significant decrease in cycle stability. When (A+B+C) / H > 0.77, the additive concentration allocated per unit thickness is too high. In batteries with a thinner negative electrode active material layer, the excessively high concentration of additive will undergo a violent reduction reaction on the electrode surface, forming an excessively thick and dense initial SEI film. Although this film can effectively block side reactions, its huge ion migration impedance severely limits the rate performance of the battery, especially under low-temperature conditions, where lithium-ion transport is hindered, resulting in a significant reduction in charging capacity.

[0044] The lithium-ion battery in this embodiment further satisfies: 0.13≤(A+B+C) / H≤0.6.

[0045] By further limiting the relationship between the thickness of the negative electrode active material layer and the content of electrolyte additives in the negative electrode sheet, it is possible to match the chemical protection of additives with the thickness of the negative electrode structure, better balance the interface stability and transmission performance of the battery, enhance the adaptability of the synergistic mechanism to all-climate application scenarios, and achieve the optimal balance between multiple performances such as thermal shock safety, low temperature cycling and high temperature cycling.

[0046] In this embodiment, the amounts of the three additives in the electrolyte are synergistically limited to effectively balance the ratio of basic film formation to interface stability protection. The lithium-ion battery in this embodiment further satisfies: 0.06 ≤ C / (A+B) ≤ 0.36.

[0047] When C / (A+B) < 0.05, the relative content of the interface stabilizer tetraethylenesilane is too low. The basic SEI film formed by vinylene carbonate and vinyl sulfite lacks sufficient silane stabilization, resulting in insufficient chemical and thermal stability. Under long-term cycling and thermal shock, it is difficult to maintain structural stability, and the interface film is easily degraded by the catalytic effect of cobalt ions. Its effect on improving high-temperature cycling performance and thermal safety is weak, failing to exert the expected synergistic protective effect. When C / (A+B) > 0.8, the relative content of the interface stabilizer tetraethylenesilane is too high. Excessive tetraethylenesilane forms an overly dense protective layer at the interface. Although thermal stability is improved, this results in an overly rigid and lacking toughness interface layer. This brittle interface layer cannot adapt to the expansion and contraction of the silicon anode, easily generating microcracks during cycling and losing its effective protective function. Simultaneously, the excessively dense interface layer severely blocks ion transport channels, leading to a sharp increase in interface impedance, which has a serious negative impact on low-temperature performance and cycle life.

[0048] In some specific embodiments, vinylene carbonate (VC) can undergo a polymerization reaction at the anode interface through the vinyl groups in its molecules to form an elastic SEI film rich in polycarbonate. This film layer can effectively adapt to the volume changes of the silicon anode and improve interface stability.

[0049] The optimal performance balance is achieved when the VC mass percentage (A%) is between 0.5% and 20%, preferably between 1% and 15%. Specifically, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value within the above range. When the VC mass percentage is below 0.5%, the polymerization reaction is insufficient, resulting in an excessively thin and incomplete SEI film that cannot effectively buffer volume expansion. When it exceeds 20%, the excessive polymerization products form an excessively thick insulating layer, severely hindering lithium-ion migration, and the increased interfacial impedance significantly deteriorates low-temperature performance.

[0050] In some specific embodiments, vinyl sulfite (VES) can decompose at the electrode interface through the sulfur-containing groups therein to form a stable interface layer. This interface layer has excellent ionic conductivity, which can significantly improve the low-temperature performance and high-temperature cycle life of the battery.

[0051] When the mass percentage (B%) of VES is between 0.1% and 10%, preferably between 0.5% and 5%, the synergistic effect of VES's interface modification and ion transport enhancement properties provides a dual benefit of constructing a high ionic conductivity interface layer and improving interface stability. Specifically, the percentage can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value within the above range. When the mass percentage of VES is below 0.1%, the interface modification effect is insufficient, failing to form a continuous and stable high ionic conductivity interface layer. The low sulfur content leads to decreased interface stability. When it exceeds 10%, excessive decomposition products are deposited at the interface, forming an interface film with excessively high electronic conductivity, exacerbating the continuous decomposition of the electrolyte. Simultaneously, incompletely decomposed VES may catalyze side reactions in the electrolyte, negatively impacting the thermal safety of the battery.

[0052] In some specific embodiments, tetraethylenesilane (TVSi) can form a stable interface protective layer at the electrode interface through the silane groups therein, which can effectively inhibit electrolyte decomposition and transition metal dissolution.

[0053] A TVSi mass percentage (C%) of 0.1% to 5%, preferably 0.5% to 2.5%, can significantly enhance the mechanical integrity and thermal stability of the SEI film at the interface. Specifically, it can be 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, or any value within the above range. When the TVSi mass percentage is below 0.1%, the interface stabilization effect is insufficient, the protective layer coverage is incomplete, and it cannot effectively suppress the catalytic side reactions initiated by cobalt ions. When it exceeds 5%, the excessively dense protective layer leads to a significant increase in interfacial impedance, severely hindering ion transport. Simultaneously, excessive silane groups may trigger electrolyte side reactions.

[0054] In the embodiments of this application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluoroborate, and lithium difluorodi(oxalate)borate.

[0055] In the embodiments of this application, the organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0056] This application does not impose any particular limitation on the preparation method of the electrolyte. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing the raw materials evenly according to the specified ratio.

[0057] In this embodiment, the positive electrode includes a positive current collector and a positive electrode material layer, wherein the positive electrode material layer is formed by coating the surface of the positive current collector with a positive electrode slurry. The positive current collector mentioned in this embodiment is not particularly limited, as long as it is conductive and will not cause adverse chemical changes in the battery; it can be any known material suitable for use as a positive current collector. In one embodiment, the positive current collector can be a metal material such as aluminum, stainless steel, nickel plating, titanium, tantalum, or carbon material such as carbon cloth or carbon paper; preferably, it is aluminum foil.

[0058] The positive electrode slurry may contain a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes at least one of transition metal lithium oxides, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate. Among them, the chemical formula of the transition metal lithium oxide is Li. (1+x) Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is selected from at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr. The type of conductive agent mentioned in the embodiments of this application is not limited; any known conductive agent capable of improving the conductivity of the electrode can be used, specifically selected from at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The type of binder mentioned in the embodiments of this application is not limited; any known positive electrode binder can be used, specifically at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0059] In the lithium-ion batteries mentioned in this application, a separator is typically provided between the positive and negative electrode plates to prevent short circuits. There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. In some embodiments, the separator includes a porous sheet-like or non-woven fabric-like material with excellent liquid retention properties. The separator includes materials such as resin or glass fiber separators, which include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0060] In the lithium-ion battery mentioned in this application, the lithium-ion battery may include an outer packaging that can be used to encapsulate the aforementioned electrode components and electrolyte. In some embodiments, the outer packaging of the lithium-ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0061] This application does not impose any particular restrictions on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape.

[0062] The manufacturing process of the lithium-ion battery mentioned in this application may include the following steps: overlapping the positive and negative electrode sheets via a separator, and then, as needed, winding, folding, or performing other operations, placing them into a casing; injecting the electrolyte into the casing and sealing it; and then performing processes such as settling, formation, capacity testing, and inspection to complete the battery manufacturing. In addition, overcurrent protection components, conductive plates, etc., may be placed in the casing as needed to prevent pressure rise and overcharging / discharging within the electrochemical device.

[0063] This application also provides an electrical device including the aforementioned lithium-ion battery. This electronic device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems, etc.

[0064] To make the present invention easier to understand, the present application will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present application. Unless otherwise specified, the raw materials or components used in the present application can be obtained commercially or by conventional methods.

[0065] Example 1 (1) Preparation of negative electrode sheet A mixture of silicon particles (anode active material) and graphite (mass ratio 1:2), acetylene black (Super P) as a conductive agent, sodium carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as a binder in a mass ratio of 94:2:1.2:2.8 was prepared by adding deionized water and dispersing the mixture uniformly to form a homogeneous anode slurry. This anode slurry was then uniformly coated onto both sides of a copper foil current collector. After baking, rolling, and cutting, the anode sheet was obtained.

[0066] (2) Preparation of electrolyte Ethylene carbonate (EC), propyl propionate (EP), and diethyl carbonate (DEC) were mixed evenly in a mass ratio of 30:40:30 to obtain the base solvent. Water was removed using a molecular sieve, and 1M LiPF6 was added and mixed thoroughly. Then, vinylene carbonate (VC), vinyl ethylene sulfite (VES), and tetraethylenesilane (TVSi) were added in the amounts shown in Table 1, and the mixture was stirred until a gel electrolyte prepolymer was obtained.

[0067] (3) Preparation of positive electrode sheet Lithium cobalt oxide (CCO), acetylene black (Super P), and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred until a homogeneous CCO slurry was formed. This slurry was then uniformly coated onto both sides of the aluminum foil used as the CCO current collector. After baking, rolling, and cutting, the CCO electrode sheet was obtained.

[0068] (4) Preparation of lithium-ion batteries PE porous polymer film is used as the separator.

[0069] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. After winding and tab welding, a bare cell is obtained. The bare cell is then placed in a pre-formed aluminum-plastic film for liquid injection, encapsulation, and formation processes to obtain a lithium-ion battery.

[0070] Examples 2-26 and Comparative Examples 1-17 are prepared using the same method as the lithium-ion batteries in Example 1, except that the content of each additive, the content of cobalt in the negative electrode active material layer, and the thickness of the negative electrode active material layer are as shown in Table 1.

[0071] Specifically, the lithium-ion battery of Example 27 is prepared by the same method, except that its negative electrode active material is a silicon-carbon composite material (with a silicon content of 30%).

[0072]

[0073]

[0074] Note: " / " indicates that it was not added.

[0075] Perform the same lithium-ion battery performance tests on the batteries prepared in the above examples and comparative examples, and fill the test results into Table 2.

[0076] (1)Test for cobalt element content in the negative electrode sheet After discharging the prepared lithium-ion battery completely, disassemble the battery. Take 5 mg of the negative electrode active material layer and add 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid in sequence. Heat to 180 °C until the solution becomes clear and transparent. After cooling, add water to make the volume up to 50 mL, send the sample for testing, and use an ICP (Inductive Coupled Plasma Emission Spectrometer) inductively coupled plasma spectrometer to test the content of iron element in it.

[0077] (2)0 °C storage performance test Perform charge-discharge cycling on the lithium-ion battery at 0 °C at a rate of 1C / 1C within the charge-discharge cut-off voltage range. Record the discharge capacity in the first week as Y1, and the discharge capacity in the Nth week as Y n ; Divide the capacity in the Nth week by the capacity in the first week to obtain the cycle capacity retention rate W in the Nth week n =Y n / Y1, and record the cycle capacity retention rate W n The cycle number of the lithium-ion battery when the cycle capacity retention rate W is 70%.

[0078] (3)45 °C cycling test Perform charge-discharge cycling on the lithium-ion battery at 45 °C at a rate of 1C / 1C within the charge-discharge cut-off voltage range. Record the discharge capacity in the first week as C1, and the discharge capacity in the Nth week as C n ; Divide the capacity in the Nth week by the capacity in the first week to obtain the cycle capacity retention rate R in the Nth week n =C n / C1, and record the cycle capacity retention rate R n The cycle number of the lithium-ion battery when the cycle capacity retention rate R is 70%.

[0079] (4)Thermal shock test Charge the lithium-ion battery at a rate of 0.2C to the cut-off voltage at 25 °C, and the cut-off current is 0.025C. Place the fully charged battery in an oven, and the oven is heated to 150 °C at a rate of 5 °C / min. After heating to 150 °C, keep it warm for 60 min. If the battery does not catch fire or explode, it passes. The total number of batteries tested is 20.

[0080] The test results are shown in Table 2.

[0081]

[0082] As can be seen from the test results in Table 2, the synergistic effect of three types of functional additives—ethylene carbonate (VC), vinyl ethylene sulfite (VES), and tetraethylenesilane (TVSi)—can improve the low-temperature cycling, high-temperature cycling, and thermal shock performance of lithium-ion batteries.

[0083] According to the data from Example 1 and Comparative Example 1, when there are no additives in the electrolyte (Comparative Example 1), only 8 batteries passed the thermal shock test (out of 20 tested), only 188 cycles maintained 70% capacity at 0°C, and only 212 cycles maintained 70% capacity at 45°C.

[0084] According to the data from Examples 1 and Comparative Examples 2-7, when one or two of the following additives are present in the electrolyte: vinylene carbonate (VC), vinyl sulfite (VES), and tetraethylenesilane (TVSi), the number of cycles in which the 0°C cycle capacity retention rate reaches 70% is around 200 cycles, and the number of cycles in which the 45°C cycle capacity retention rate reaches 70% is below 285 cycles. Furthermore, it is impossible to simultaneously solve the problem of insufficient cycle capacity retention rate of lithium-ion batteries under both high-temperature and low-temperature conditions.

[0085] Data from Examples 1, 21-25, and Comparative Examples 8-17 show that when three additives are present in the electrolyte, simultaneously satisfying the relationships "0.002≤(A+B) / K≤1.65, 0.09≤(A+B+C) / H≤0.77, 0.05≤C / (A+B)≤0.8, 5≤K≤2000, 15≤H≤60", the synergistic effect of the battery is enhanced, resulting in excellent performance of the lithium-ion battery across a wide temperature range. Specifically, VC preferentially forms the elastic SEI basic framework, VES improves the ion transport efficiency of the interfacial membrane, and TVSi constructs a robust top-layer protective network. The synergistic effect of these three additives enables the SEI membrane to achieve gradient and functionalization in composition and structure, effectively suppressing catalytic side reactions initiated by cobalt, and achieving a synergistic improvement in thermal shock safety, low-temperature cycling, and high-temperature cycling.

[0086] Data from Examples 1-5 show that VC addition in the range of 1% to 15% exhibits excellent thermal shock pass rate, low-temperature cycling performance, and high-temperature cycling performance. When the VC addition is 0.5% (Example 4), the thermal shock pass rate is 9 / 20, the number of cycles at 0°C is 230, and the number of cycles at 45°C is 254, indicating a significant performance decrease. This is presumably because insufficient VC content is not conducive to the formation of a stable SEI film, resulting in poor battery cycling performance. When the VC addition is 20% (Example 5), the thermal shock pass rate is 7 / 20, the number of cycles at 0°C is 198, and the number of cycles at 45°C is 211, indicating a significant performance decrease. This is presumably because excessive VC forms an overly thick SEI film, increasing interfacial impedance, hindering ion migration, and triggering side reactions, thus deteriorating low-temperature performance.

[0087] Data from Examples 6-10 shows that when the VES content is in the range of 0.5% to 5%, it exhibits excellent thermal shock pass rate, low-temperature cycling performance, and high-temperature cycling performance. When the VES content is 0.1% (Example 9), the thermal shock pass rate is 9 / 20, the number of cycles at 0°C is 218, and the number of cycles at 45°C is 242, indicating poor performance and insufficient interface protection when the VES content is insufficient. When the VES content is 10% (Example 10), the thermal shock pass rate is 6 / 20, the number of cycles at 0°C is 294, and the number of cycles at 45°C is 264. Although the low-temperature performance is good, the thermal safety is poor, presumably because excessive VES forms an unstable interface layer.

[0088] Data from Examples 11-14 and Comparative Example 8 show that when the TVSi content is in the range of 0.5% to 2.5%, it exhibits excellent thermal shock pass rate, low-temperature cycling performance, and high-temperature cycling performance. When the TVSi content is 0.1% (Comparative Example 8), the thermal shock pass rate is only 5 / 20, the number of cycles at 0°C is 245, but the number of cycles at 45°C is only 241, indicating poor thermal safety and high-temperature performance when TVSi is insufficient. When the TVSi content is 5% (Example 14), the thermal shock pass rate is 16 / 20, but the number of cycles at 0°C is only 241, and the number of cycles at 45°C is 278, indicating a significant deterioration in low-temperature performance. It is speculated that this is because excessive TVSi forms a rigid interface layer, which is prone to cracking and affects low-temperature cycling performance.

[0089] Data from Examples 15-17 and Comparative Examples 15-16 show that when the thickness H of the negative electrode active material layer increases from 15 μm to 60 μm, the 0°C cycle capacity retention cycles decrease from 468 cycles to 332 cycles, indicating that increasing H prolongs the ion transport path and deteriorates low-temperature performance; however, it has little impact on the 45°C cycle performance. In Comparative Example 15, when H is 3 μm, and in Comparative Example 16, when H is 100 μm, the thermal shock pass rates are only 8 / 20 and 6 / 20, respectively, and the cycle performance is poor, indicating that the thickness H of the negative electrode active material layer needs to be within the range of 15 μm to 60 μm.

[0090] Data from Examples 18-20 and Comparative Example 17 show that when the cobalt content X increases from 5 ppm to 2000 ppm, the thermal shock pass rate decreases from 15 / 20 to 10 / 20, the 0°C cycle capacity retention cycles decrease from 431 cycles to 344 cycles, and the 45°C cycle capacity retention cycles decrease from 485 cycles to 391 cycles. This indicates that excessive cobalt catalyzes electrolyte decomposition and damages SEI membrane stability. In Comparative Example 17, when the cobalt content is 5000 ppm, the thermal shock pass rate decreases to 3 / 20, and the cycling performance further deteriorates.

[0091] In particular, the solutions of this application embodiment have a significant improvement effect on lithium-ion batteries with silicon particle anodes. As shown by the data of Examples 1 and 27, Example 27, using silicon-carbon composite anode material, achieved a thermal shock pass rate of 10 / 20, a cycle life of 322 cycles to retain 70% of the capacity at 0°C, and a cycle life of 367 cycles to retain 70% of the capacity at 45°C, which is significantly lower than that of Example 1.

[0092] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A lithium-ion battery, comprising a negative electrode, a positive electrode, and an electrolyte, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector; the negative active material layer includes a negative active substance, which includes silicon material; the negative active material layer contains cobalt. The electrolyte comprises lithium salt, organic solvent, and additives, wherein the additives include vinylene carbonate, vinyl sulfite, and tetraethylenesilane. The lithium-ion battery satisfies the following conditions: 0.002≤(A+B) / K≤1.65, 0.09≤(A+B+C) / H≤0.77, 0.05≤C / (A+B)≤0.8; Wherein, A represents the mass percentage of vinylene carbonate in the electrolyte, in units of %; B represents the mass percentage of vinyl sulfite in the electrolyte, in units of %; C represents the mass percentage of tetraethylenesilane in the electrolyte, in units of %; K represents the cobalt content in the negative electrode active material layer, in units of ppm, 5≤K≤2000; H represents the thickness of the negative electrode active material layer, in units of μm, 15≤H≤60.

2. The lithium-ion battery according to claim 1, characterized in that, 0.5≤A≤20; preferably, 1≤A≤15.

3. The lithium-ion battery according to claim 1, characterized in that, 0.1≤B≤10; preferably, 0.5≤B≤5.

4. The lithium-ion battery according to claim 1, characterized in that, 0.1≤C≤5; preferably, 0.5≤C≤2.

5.

5. The lithium-ion battery according to claim 1, characterized in that, 0.003≤(A+B) / K≤1.4; and / or, 0.13≤(A+B+C) / H≤0.6; and / or, 0.06≤C / (A+B)≤0.

36.

6. The lithium-ion battery according to claim 1, characterized in that, The silicon material includes silicon particles, wherein the silicon content in the silicon particles is 80% to 99%.

7. The lithium-ion battery according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluoroborate, and lithium difluorodi(oxalate)borate.

8. The lithium-ion battery according to claim 1, characterized in that, The organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

9. The lithium-ion battery according to claim 1, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector; the positive active material layer includes a positive active material, which includes at least one of lithium transition metal oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate. Preferably, the chemical formula of the transition metal lithium oxide is Li. (1+x) Ni y Co z M (1-y-z) O2; Wherein, -0.1≤x≤1, 0≤y≤1, 0≤z≤1, 0≤y+z≤1, and M is selected from at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

10. An electrical device, characterized in that, Includes the lithium-ion battery as described in any one of claims 1 to 9.

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