Lithium ion battery and electric device

Abstract

The invention provides a lithium ion battery and a power utilization device, the lithium ion battery comprises a positive electrode, a negative electrode and an electrolyte, the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material is silicon particles, and the silicon particles contain carbon elements; the electrolyte comprises a first additive and a second additive, the first additive comprises a nitrobenzenesulfonyl fluoride compound, and the second additive comprises a fluoroether diluent; the lithium ion battery satisfies the following formula: (A + B) / X is greater than or equal to 0.0056, A% is 0.5%-4%, and B% is 5%-40%. According to the lithium ion battery provided by the invention, the first additive and the second additive are combined for use, and the formed SEI film has flexible self-repairing capability and rigid framework characteristics, can adapt to the volume change of silicon, can block the electron transfer path of carbon and electrolyte, and improves the high-temperature cycling stability and storage performance of the lithium ion battery; and when (A + B) / X is greater than or equal to 0.0056, A% is 0.5%-4%, and B% is 5%-40%, a synergistic effect can be better exerted to realize synergistic improvement of high-temperature stability and high-temperature storage of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a lithium ion battery and an electric device. BACKGROUND

[0002] Lithium ion batteries are widely used in electronic devices and new energy vehicles due to their high energy density, low self-discharge and long cycle life. Their working principle relies on the synergistic effect of the four parts of the positive electrode, negative electrode, electrolyte and separator. The negative electrode material is responsible for the reversible storage of lithium ions during charging and discharging, and its structure and interface stability directly affect the battery performance. By lattice regulation and layered structure design, the ion transport path can be optimized, and the lithium storage efficiency can be improved. For silicon-based negative electrodes, element doping and coating technology can alleviate volume expansion, and interface modification can reduce side reactions, thereby improving battery capacity and cycle stability.

[0003] In the silicon-based negative electrode battery system, the introduction of carbon elements can alleviate volume expansion, but its high conductivity can exacerbate interface side reactions at high temperatures. Carbon surface defect sites catalyze the decomposition of ester solvents to generate organic lithium compounds with poor thermal stability, resulting in SEI film reconstruction failure and impedance increase. SUMMARY

[0004] In view of the problem of high-temperature storage and cycle performance degradation caused by carbon element doping in the prior art silicon-based negative electrode, a lithium ion battery and an electric device are provided.

[0005] The technical solution adopted by the present application to solve the above technical problems is as follows: The present application provides a lithium ion battery, comprising a positive electrode, a negative electrode and an electrolyte, the negative electrode comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material being silicon particles, the silicon particles containing carbon elements; The electrolyte comprises a first additive and a second additive, the first additive comprising a nitrobenzenesulfonyl fluoride compound, and the second additive comprising a fluorinated ether diluent; The lithium ion battery satisfies the following conditions: Formula 1: (A+B) / X≥0.0056, A% is 0.5% to 4%, and B% is 5% to 40%; Wherein, A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage content of the second additive in the electrolyte; X is the content of carbon elements in the negative electrode active material, unit: ppm.

[0006] Optionally, the lithium ion battery satisfies the following conditions: Formula 2: 0.024≤(A+B) / X≤2.4.

[0007] Optionally, based on the total mass of the electrolyte (100%), the mass percentage A% of the first additive is 1% to 4%; and / or, Based on the total mass of the electrolyte as 100%, the mass percentage B% of the second additive is 10%~30%.

[0008] Optionally, the first additive and the second additive satisfy the following conditions: A / B ≥ 0.015.

[0009] Optionally, the first additive and the second additive satisfy the following conditions: A / B ≥ 0.025.

[0010] Optionally, the carbon content X in the negative electrode active material is 10~2000 ppm.

[0011] Optionally, the first additive comprises one or more of the following compounds: Structure 1, Structure 2, Structure 3; Among them, R1~R 12 Each atom is independently selected from one or more of the following: methyl, fluorine, and hydrogen atoms.

[0012] Optionally, the first additive comprises one or more of the following compounds: Compound 1 Compound 2 Compound 3 Compound 4, Compound 5, Compound 6.

[0013] Optionally, the second additive includes one or more of 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, methyl nonafluorobutyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0014] Optionally, the electrolyte further includes a third additive, which includes carbonate compounds; Based on the total mass of the electrolyte as 100%, the third additive has a mass percentage content of 5% to 15% in the electrolyte.

[0015] Optionally, the third additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 3,3,3-trifluoropropylene carbonate, tetrafluoroethylene carbonate, and vinyl ethylene carbonate.

[0016] Optionally, the positive electrode includes a positive electrode active material, which includes one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate. The chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr; wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1.

[0017] On the other hand, this application provides an electrical device including a lithium-ion battery as described above.

[0018] The beneficial effects of this application are as follows: In the lithium-ion battery provided in this application, the nitro group in the first additive (nitrobenzenesulfonyl fluoride compound) preferentially reduces at the electrode interface to form a flexible lithium nitride network, buffering the volume deformation of silicon-carbon materials. At the same time, its sulfonyl fluoride group decomposes to generate a high-mechanical-strength lithium fluoride layer, covering the catalytic active sites on the carbon surface to inhibit the decomposition of ester solvents. The second additive (fluorinated ether diluent) reduces the corrosiveness of the electrolyte through a weak solvation effect and promotes the formation of a fluoride-rich lithium interface. However, the SEI film formed when the second additive is used alone is too thin. Furthermore, when the first and second additives are used together, the benzene ring conjugation effect enhances the compatibility of the additives. The decomposition products of the nitro group and sulfonyl fluoride construct a gradient "lithium nitride-lithium fluoride" composite structure, while the fluorinated ether group continuously enhances the degree of fluorination at the interface. The SEI film formed by the synergistic mechanism of the two has both flexible self-healing ability and rigid framework characteristics. It can adapt to the volume change of silicon and block the electron transfer path between carbon and electrolyte, thereby simultaneously improving the high-temperature cycle stability and storage performance of the lithium-ion battery. Furthermore, this application achieves a better synergistic effect by controlling the mass percentage content of the first additive A and the second additive B, as well as the mass of carbon element X in the negative electrode active material, to satisfy the relationship (A+B) / X≥0.0056, and when A% is 0.5%~4% and B% is 5%~40%, thereby achieving a synergistic improvement in the high-temperature stability and high-temperature storage of lithium-ion batteries. Detailed Implementation

[0019] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material layer, which includes a negative electrode active material. The negative electrode active material is silicon particles, and the silicon particles contain carbon elements. The electrolyte includes a first additive and a second additive, wherein the first additive includes nitrobenzenesulfonyl fluoride compounds and the second additive includes fluoroether diluents. The lithium-ion battery meets the following conditions: Formula 1: (A+B) / X≥0.0056, A% is 0.5%~4%, B% is 5%~40%; Wherein, A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage of the second additive in the electrolyte; X represents the carbon content in the negative electrode active material, expressed in ppm.

[0021] It should be noted that while the introduction of carbon into silicon-based anode battery systems can improve conductivity and buffer volume expansion, its high conductivity brings significant negative effects: carbon surface defect sites catalyze the decomposition of ester solvents in the electrolyte, generating thermally unstable organic lithium compounds. This catalytic effect can damage the stability of the SEI film, leading to a surge in interfacial impedance and capacity decay. Furthermore, carbon materials accelerate electrolyte decomposition at high temperatures, generating gaseous byproducts and triggering SEI film reconstruction failure. Although carbon coating can alleviate the volume expansion problem of silicon, its inherent catalytic activity exacerbates interfacial side reactions at high temperatures, which is the main reason for the performance degradation of pure silicon anodes after the introduction of carbon.

[0022] Specifically, in the lithium-ion battery provided in this application, the nitro group in the first additive (nitrobenzenesulfonyl fluoride compound) preferentially reduces at the electrode interface to form a flexible lithium nitride network, buffering the volume deformation of silicon-carbon materials. At the same time, its sulfonyl fluoride group decomposes to generate a lithium fluoride layer with high mechanical strength, covering the catalytic active sites on the carbon surface to inhibit the decomposition of ester solvents. The second additive (fluorinated ether diluent) reduces the corrosiveness of the electrolyte through a weak solvation effect and promotes the formation of a lithium fluoride-rich interface. However, the SEI film formed when the second additive is used alone is too thin. Furthermore, when the first additive and the second additive are used together, the benzene ring conjugation effect enhances the compatibility of the additives. The decomposition products of the nitro group and the sulfonyl fluoride construct a gradient "lithium nitride-lithium fluoride" composite structure, while the fluorinated ether group continuously enhances the degree of fluorination at the interface. The SEI film formed by the synergistic mechanism of the two has both flexible self-healing ability and rigid framework characteristics. It can adapt to the volume change of silicon and block the electron transfer path between carbon and electrolyte, thereby simultaneously improving the high-temperature cycle stability and storage performance of the lithium-ion battery. Furthermore, this application controls the mass percentage content of the first additive A and the second additive B, as well as the mass of carbon element X in the negative electrode active material, to achieve a better synergistic effect when the relationship (A+B) / X≥0.0056 is met, and A% is 0.5%~4% and B% is 5%~40%, thus achieving a synergistic improvement in the high-temperature stability and high-temperature storage of lithium-ion batteries. If the (A+B) / X ratio is lower than 0.0056, insufficient concentrations of the first and second additives in the electrolyte will lead to dual performance defects: on the one hand, insufficient interface protection causes the defect sites on the carbon-doped silicon negative electrode surface to continuously catalyze the decomposition of ester solvents, generating unstable organic lithium compounds and causing SEI film reconstruction failure; on the other hand, the incomplete film formation of the lithium nitride and lithium fluoride composite SEI makes it difficult to effectively buffer the silicon volume expansion stress, resulting in rapid decay of high-temperature cycling capacity.

[0023] Furthermore, the mass percentage A% of the first additive in the electrolyte can be 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.4%, 2.8%, 3.0%, 3.5%, or 4.0%, that is, A% can be in the range of 0.5% to 4%.

[0024] Specifically, the mass percentage of the second additive, B%, can be 5%, 15%, 20%, 25%, 30%, 35%, 40%, etc., that is, B% can be in the range of 0.5% to 4%.

[0025] Specifically, the carbon content in the silicon particles, the negative electrode active material of this application, can be detected by the following methods: Take 5 mg of negative electrode active material (pure silicon particles) and add 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid in sequence. Heat to 180°C until the solution is clear and transparent. After cooling, add water to make up to 50 mL and send the sample for testing. Use an ICP (Inductively Coupled Plasma Emission Spectrometer) to test the carbon content.

[0026] Specifically, in silicon-based lithium-ion batteries, nitrobenzenesulfonyl fluoride additives (the first additive) synergistically work with fluorinated ether diluents (the second additive) to construct a gradient nitrogen-fluorine composite interface layer, achieving dual optimization of the silicon anode and cathode interfaces. The nitro groups (-NO2) preferentially reduce to form a flexible Li3N network, buffering silicon volume expansion and mitigating mechanical stress on the solid electrolyte interface (SEI). Simultaneously, the sulfonyl fluoride groups (-SO2F) decompose to form a LiF layer with high ionic conductivity, covering carbon defects on the silicon anode surface and inhibiting electrolyte catalytic side reactions and lithium dendrite growth. The conjugated structure of the benzene ring coupled with the molecular orbitals of the fluorinated ether further optimizes the wettability of the electrolyte to silicon particles, reducing lithium-ion diffusion resistance. At the cathode interface, the strong electron-withdrawing effect of nitrobenzenesulfonyl fluoride promotes the coordination reconstruction of the fluorinated ether solvent and lithium salt, forming a dense LiF-LixPOy composite CEI film, effectively inhibiting transition metal dissolution and electrolyte oxidative decomposition.

[0027] When the mass percentage of the first additive, nitrobenzenesulfonyl fluoride, is less than 0.5%, the discontinuity of the Li3N network at the negative electrode interface leads to a significant decrease in the mechanical strength of the SEI, which fails to disperse the expansion stress of silicon particles, causing interface cracking and uneven lithium metal deposition. At the positive electrode interface, due to insufficient fluorination, the CEI film exhibits a porous structure, leading to accelerated dissolution of transition metals at high temperatures and a surge in electrolyte oxidation gas production. Simultaneously, the wettability of the electrolyte to the silicon negative electrode deteriorates, hindering lithium-ion transport kinetics and significantly increasing low-temperature charge-discharge polarization. When its mass percentage exceeds 4%, excessive LiF layer accumulation thickens the SEI film, prolonging the lithium-ion migration path and resulting in decreased low-temperature charging efficiency. Furthermore, an excessively high proportion of rigid LiF weakens the dynamic adaptability of the interface layer against volume expansion. Imbalance in the intermolecular forces of the additive causes an abnormal increase in electrolyte viscosity, reducing the lithium-ion transference number and exacerbating transport polarization over a wide temperature range. In addition, excessive adsorption of nitrobenzenesulfonyl fluoride at the positive electrode interface interferes with the uniform formation of the CEI film, creating localized stress concentration points and accelerating interface degradation and capacity decay.

[0028] In summary, when the mass percentage of the first additive is 0.5% to 4%, by balancing the interfacial chemical composition and the physical properties of the electrolyte, the mechanical stability and ion transport efficiency of the nitrogen-fluorine composite interfacial layer are synergistically optimized, thereby achieving a simultaneous improvement in the high-temperature cycle stability and low-temperature performance of silicon-based batteries.

[0029] In silicon-based lithium-ion batteries, fluorinated ether diluents (secondary additives) synergistically interact with electrolyte components to construct a gradient fluorine-based ion transport network, achieving dual regulation of electrode interface stability and electrolyte physicochemical properties. The fluorinated ether groups at the ends of their molecular chains preferentially adsorb onto the silicon anode surface, inducing the formation of a LiF-rich inorganic layer. This layer, through mechanical interlocking, suppresses SEI film rupture caused by silicon volume expansion. Simultaneously, the lone pair electrons of the ether oxygen atoms form weak coordination with lithium ions, optimizing the electrolyte solvation structure and enhancing lithium-ion migration rate. At the cathode interface, the strong electron-retardant properties of fluorinated ethers promote the formation of a uniform LiF-Li₂CO₃ composite CEI film on the transition metal oxide surface, effectively blocking lattice oxygen loss and deep electrolyte oxidation.

[0030] When the content of fluorinated ether diluent is less than 5%, excessive association of lithium ions in the solvation structure leads to an increase in the desolvation energy barrier, and the lithium deposition kinetics deteriorate significantly at low temperatures. The coverage of the LiF layer at the negative electrode interface is insufficient, and the stress concentration of silicon particle expansion causes the SEI film to delaminate and fall off, accelerating the loss of active lithium. The degree of fluorination of the positive electrode CEI film is insufficient, and the dissolution of transition metal ions is aggravated during high-temperature cycling, triggering a chain decomposition reaction of the electrolyte. At the same time, the high viscosity of the electrolyte leads to a decrease in wettability, and the electrode polarization voltage increases significantly at low temperatures.

[0031] When the content of fluorinated ether diluent exceeds 40%, over-fluorination triggers thermodynamic instability in the electrolyte system. During high-temperature storage, defluorination of fluorinated ether molecules occurs, generating corrosive HF and damaging the integrity of the SEI / CEI film. Excessive thickening of the LiF layer at the negative electrode interface significantly increases the lithium-ion diffusion barrier, resulting in low-temperature charging capacity decay. Simultaneously, the decrease in the electrolyte dielectric constant leads to a decrease in lithium salt dissociation and a significant decline in ionic conductivity, exacerbating concentration polarization over a wide temperature range.

[0032] In summary, when the mass percentage of the second additive is 5% to 40%, by balancing the construction of the fluorination interface and the stability of the electrolyte, the irreversible decomposition of fluorination products during storage is suppressed while maintaining high ion migration efficiency, ultimately achieving a synergistic improvement in the wide temperature range performance and long-term storage stability of silicon-based batteries.

[0033] In some embodiments, the lithium-ion battery satisfies the following conditions: Equation 2: 0.024≤(A+B) / X≤2.4.

[0034] Specifically, when the lithium-ion battery further satisfies the relationship 0.024≤(A+B) / X≤2.4, the synergistic effect of the first additive and the second additive is better, which in turn helps to improve the high-temperature cycling and high-temperature storage performance of the lithium-ion battery.

[0035] In some embodiments, based on the total mass of the electrolyte (100%), the mass percentage A% of the first additive is 1% to 4%; and / or, Based on the total mass of the electrolyte as 100%, the mass percentage B% of the second additive is 10%~30%.

[0036] Furthermore, the mass percentage A% of the first additive can be 1%, 2%, 3% or 4%, and the mass percentage B% of the second additive can be 10%, 15%, 20% or 30%.

[0037] In some embodiments, the first additive and the second additive satisfy the following conditions: A / B ≥ 0.015.

[0038] When the A / B ratio is less than 0.015, the content of the first additive is insufficient, which leads to interface failure. Specifically, the poor supply of film-forming precursors will result in insufficient SEI film growth kinetics, forming a discontinuous passivation layer with high porosity, which cannot effectively prevent the electrolyte from continuously corroding the silicon anode. On the other hand, the insufficient crystallinity of inorganic components (such as Li2O and Li2CO3) in the thin SEI layer will cause grain boundary migration and phase separation under high temperature, exposing fresh silicon surfaces and triggering side reactions. This structural defect will accelerate the irreversible consumption of active lithium, resulting in increased interfacial impedance and a stepwise decrease in coulombic efficiency under storage conditions.

[0039] Furthermore, the first additive and the second additive satisfy the following conditions: A / B ≥ 0.025, meaning that extensive previous verification has shown that when A / B ≥ 0.025, it is beneficial to better leverage the system effects of both components, thereby further improving the high-temperature cycling and high-temperature storage performance of lithium-ion batteries.

[0040] In some embodiments, the carbon content X in the negative electrode active material is 10~2000 ppm.

[0041] Specifically, the carbon content X in the negative electrode active material is limited to 10~2000 ppm. This feature is compatible with the first additive and the second additive, and further exerts a synergistic effect to optimize the performance of lithium-ion batteries. When X is within this range, the content of the first and second additives, which satisfy (A+B) / X≥0.0056, can ensure that the total amount of the two additives and the carbon content are in a suitable ratio. If the carbon content exceeds 2000ppm, the excess carbon will form a local conductive network heterogeneous region in the silicon anode, resulting in uneven distribution of lithium-ion insertion / extraction kinetics and exacerbating the volume effect stress concentration of silicon particles. At the same time, the defect state density at the interface between the carbon phase and the silicon matrix increases, promoting the occurrence of electrolyte side reactions and forming an unstable SEI film composite structure. Carbon impurities can also hinder the diffusion channels of lithium ions in the silicon lattice, causing a significant increase in charge transfer impedance, especially under high-rate charge-discharge conditions where the capacity decay rate doubles. In summary, the carbon content within the above range avoids both excessive carbon content leading to too many catalytic active sites and insufficient coverage by additives to suppress solvent decomposition, and insufficient carbon content leading to insufficient conductivity of the negative electrode active material, and excessive additives leading to increased costs or side reactions. This ensures that the "lithium nitride-lithium fluoride" composite SEI film can effectively adapt to the effects of carbon, further enhancing the synergistic mechanism's effect on improving high-temperature cycling stability and storage performance.

[0042] In some embodiments, the first additive comprises one or more of the following compounds: Structure 1, Structure 2, Structure 3; Among them, R1~R 12 Each atom is independently selected from one or more of the following: methyl, fluorine, and hydrogen atoms.

[0043] Specifically, the first additive mentioned above, based on satisfying structural formula 1, structural formula 2 or structural formula 3, can synergize with the second additive to improve the performance of lithium-ion batteries in high-temperature cycling and high-temperature storage.

[0044] In some embodiments, the first additive comprises one or more of the following compounds: Compound 1 Compound 2 Compound 3 Compound 4, Compound 5, Compound 6.

[0045] Specifically, compound 1 is 4-nitrobenzenesulfonyl fluoride (CAS: 349-96-2), compound 2 is 2-nitrobenzenesulfonyl fluoride (CAS: 433-98-7), compound 3 is 3-nitrobenzenesulfonyl fluoride (CAS: 349-78-0), compound 4 is 2-methyl-4-nitrobenzenesulfonyl fluoride (CAS: 21320-93-4), compound 5 is 3-methyl-4-nitrobenzenesulfonyl fluoride (CAS: 1936664-02-6), and compound 6 is 2-fluoro-4-nitrobenzenesulfonyl fluoride (CAS: 2092078-42-5). 4-Nitrobenzenesulfonyl fluoride (CAS: 349-96-2), when used as a second additive, possesses a nitro group (-NO2) with strong electron-withdrawing properties, readily undergoing reduction reactions at the electrode interface; the benzene ring structure endows the molecule with certain conjugated stability, enhancing its compatibility with other additives; the sulfonyl fluoride group (-SO2F) exhibits high chemical activity, readily decomposing on the electrode surface to generate inorganic substances such as lithium fluoride, and the molecule as a whole possesses both polarity and a certain degree of hydrophobicity, enabling it to participate in electrode interface reactions and form good interactions with other components in the electrolyte; 2-Nitrobenzenesulfonyl fluoride... Both acyl fluoride and 3-nitrobenzenesulfonyl fluoride contain nitro and sulfonyl fluoride groups in their molecules. The nitro group can be reduced at the electrode interface, and the sulfonyl fluoride group can decompose to generate lithium fluoride. The presence of methyl groups alters the molecular polarity and spatial structure of 2-methyl-4-nitrobenzenesulfonyl fluoride and 3-methyl-4-nitrobenzenesulfonyl fluoride, which may affect their solubility and reactivity in the electrolyte. The methyl group also gives them a certain degree of hydrophobicity. The introduction of fluorine atoms into 2-fluoro-4-nitrobenzenesulfonyl fluoride enhances its electronegativity, which may change the molecular electron cloud distribution and make the compound more likely to participate in the electrode interface reaction, promoting the formation of a more stable SEI film. In summary, the first additive described in this application may be selected from one or more of the above-mentioned compounds 1-6. When the first additive is preferably one of the above-mentioned compounds, it is more beneficial to improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0046] In some embodiments, the second additive includes a diluent that is one or more of 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether (HFE), bis(2,2,2-trifluoroethyl) ether (BTFE), methyl nonafluorobutyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

[0047] In some embodiments, the electrolyte further includes a third additive, which includes carbonate compounds; Based on the total mass of the electrolyte as 100%, the third additive has a mass percentage content of 5% to 15% in the electrolyte.

[0048] Specifically, the third additive, as a functional additive, optimizes the construction process of the SEI film at the negative electrode interface through intermolecular interactions with the main film-forming additive (first additive). When the mass percentage of the additive is controlled within the optimal range (5%~15%), its active functional groups can selectively react with other components in the electrolyte to form a multilayer composite interface film with both mechanical toughness and lithium-ion conductivity. This optimized interface structure can not only effectively inhibit the continuous decomposition of the electrolyte, but also significantly improve the cycling stability of the electrode. However, when the mass percentage of the third additive is too high, its excessive reactive sites will cause an imbalance in the redox reaction of the electrolyte, resulting in a large accumulation of gaseous byproducts. Conversely, if the amount added is insufficient, it will lead to insufficient SEI film coverage, making it difficult to effectively control the uniform deposition behavior of lithium ions.

[0049] Furthermore, the mass percentage of the third additive in the electrolyte can be 5%, 8%, 10%, 12%, 13%, 14%, or 16%.

[0050] In some embodiments, the third additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 3,3,3-trifluoropropylene carbonate, tetrafluoroethylene carbonate, and vinyl ethylene carbonate.

[0051] Specifically, the third additive is preferably one of the types mentioned above, which helps to form an interface-stable SEI film.

[0052] In some embodiments, the electrolyte further includes a solvent comprising at least one of ethylene carbonate, propylene carbonate, butenyl 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.

[0053] Specifically, the solvents mentioned above are mainly used to dissolve the first additive, the second additive, the third additive, and the lithium salt.

[0054] In some embodiments, the electrolyte further includes a lithium salt.

[0055] Lithium salts are existing technology and are not limited in this application. For example, the lithium salt can be 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.

[0056] It should be noted that 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 some embodiments, the positive electrode includes a positive electrode active material, which includes one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate. The chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr; wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1.

[0058] Specifically, the highly active substance may be one or more of the above-mentioned substances.

[0059] In this invention, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc.

[0060] In some preferred embodiments, the negative current collector comprises copper foil.

[0061] In some embodiments, the negative electrode further includes a negative electrode active material layer disposed on at least one side surface of the current collector, and the negative electrode active material layer further includes a negative electrode conductive agent, a negative electrode binder, a thickener, and a solvent.

[0062] The negative electrode conductive agent includes at least one of the following carbon materials: natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The negative electrode binder includes styrene-butadiene latex, and the thickener includes CMC. The solvent includes deionized water.

[0063] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active substance.

[0064] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material.

[0065] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent, a positive electrode binder, and a solvent.

[0066] In some embodiments, the type of positive conductive agent mentioned in this invention is not limited, and any known conductive agent can be used.

[0067] In some embodiments, the positive electrode conductive agent mentioned in this invention includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0068] In one embodiment, the type of positive electrode binder mentioned in this invention is not limited, and any known positive electrode binder can be used.

[0069] In some embodiments, the positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0070] In the lithium-ion batteries mentioned in this application, a separator is typically provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0071] In some embodiments, the diaphragm includes a porous sheet-like or non-woven material with excellent liquid retention properties. The diaphragm includes resin or glass fiber diaphragm materials, including but not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc.

[0072] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0073] In some implementations, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0074] 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.

[0075] On the other hand, one embodiment of this application provides an electrical device including the lithium-ion battery described above.

[0076] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0077] The present invention will be further illustrated by the following examples.

[0078] The method for testing the carbon content in silicon particles is as follows: Take 5 mg of the negative electrode active material and add it to 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid in sequence. Heat to 180°C until the solution is clear and transparent. After cooling, add water to make up to 50 mL and send the sample for testing. Use an ICP (Inductively Coupled Plasma Emission Spectrometer) to test the carbon content.

[0079] Table 1 Example 1 This embodiment illustrates the lithium-ion battery disclosed in this invention, and includes the following operational steps: Preparation of positive electrode sheet The positive electrode active material lithium cobalt oxide, the positive electrode conductive agent acetylene black (SuperP) and polyvinylidene fluoride (PVDF) binder are mixed evenly at a mass ratio of 97:1.5:1.5, and then evenly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The mixed slurry is coated on both sides of the aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0080] Preparation of negative electrode sheet The negative electrode active material silicon particles, negative electrode conductive agent acetylene black (Super P), thickener CMC, and negative electrode binder SBR were mixed evenly at a mass ratio of 94:2:1.2:2.8, and then uniformly dispersed with deionized water to form a uniform negative electrode slurry. The mixed slurry was coated on both sides of a copper foil current collector, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet. The specific carbon content of the added negative electrode active material pure silicon is shown in Table 1.

[0081] Preparation of electrolyte a. Mix ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (EP), and diethyl carbonate (DEC) in a mass ratio of 10:20:40:30 to form a mixed solvent. Remove water using a molecular sieve and set aside. Add 1M LiPF6 and mix thoroughly. b. Add additives (the types and amounts of additives are shown in Table 1) to the colorless and transparent liquid obtained in step a to obtain the electrolyte.

[0082] Manufacturing of lithium-ion batteries The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes. After winding and welding the tabs, a bare cell is obtained. The bare cell is placed in an aluminum-plastic film for liquid injection and encapsulation to obtain a lithium-ion battery.

[0083] Examples 2-29 Examples 2-29 illustrate the lithium-ion battery disclosed in this invention. Examples 2-29 include most of the operations in Example 1, with the following differences: In Examples 2-29, the type of the first additive, the mass percentage A% of the first additive in the electrolyte, the type of the second additive, the mass percentage B% of the second additive in the electrolyte, the mass X of carbon in the negative electrode active material, the ratio of the first additive to the second additive, and the value of (A+B) / X are all taken from Table 1.

[0084] Example 27 Example 27 illustrates the lithium-ion battery disclosed in this invention, including most of the operations in Example 1, except that: A third additive, fluoroethylene carbonate, was also added to the electrolyte, with a mass content of 10% in the electrolyte.

[0085] Comparative Examples 1-16 The types of the first additive, the mass percentage A% of the first additive in the electrolyte, the types of the second additive, the mass percentage B% of the second additive in the electrolyte, the mass X of carbon in the negative electrode active material, the ratio of the first additive to the second additive, and the value of (A+B) / X in Comparative Examples 1 to 16 are all referenced in Table 1.

[0086] Performance testing The following performance tests were performed on Examples 1-29 and Comparative Examples 1-16 prepared above: 60℃ Storage Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged at 25°C at a rate of 1C to the cutoff voltage, with a cutoff current of 0.025C, and left to stand for 5 minutes. The thickness H1 of the lithium-ion battery was then measured. After that, the batteries were stored at 60°C for 60 days, and the thickness H2 of the lithium-ion battery was measured after the storage period.

[0087] Thickness expansion rate = [(H2-H1) / H1]×100%.

[0088] 45℃ Cyclic Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged and discharged at 45°C at a rate of 1C / 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was recorded as C1, and the discharge capacity of the Nth cycle was recorded as C2. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = C2 / C1. The number of cycles of the lithium-ion battery when the cycle capacity retention rate R2 was 70% was recorded.

[0089] The test results are entered into Table 2.

[0090] Table 2 As can be seen from the test results in Table 2, compared with Comparative Examples 1 to 3, Comparative Example 1 had no first additive and no second additive, resulting in a high thickness expansion rate and low cycle life of the battery. Comparative Example 2 had the first additive added, and Comparative Example 3 had the second additive added, but the performance improvement of the battery was not significant. As can be seen from the test results of Example 5 and Comparative Examples 9-12, the performance of Example 5 is better than that of Comparative Examples 9-12. Further comparison shows that Comparative Examples 9-12 added additives other than those described in this application or did not add the first additive and the second additive described in this application at the same time. This shows that only when the first additive and the second additive described in this application are added at the same time can an effective synergistic effect be achieved to improve the storage performance of lithium-ion batteries during high-temperature cycling. The test results of Examples 1-15 and Comparative Examples 4-8 show that the overall test performance of Examples 1-15 is better than that of Comparative Examples 4-8. The test data shows that when the content of the first additive is 0.5%-4%, the content of the second additive is 5%-40%, and the carbon content in the negative electrode active material is less than 2000ppm, it is more helpful to improve the cycle and high-temperature storage performance of silicon-based negative electrode batteries. Comparing the test results of Examples 1-19 with those of Comparative Examples 13-16, it can be seen that when A / B≥0.015 and (A+B) / X≥0.0056 are satisfied, the synergistic effect of the first additive and the second additive can be exerted. Examples 16-19 satisfy A / B≥0.025 and simultaneously satisfy 0.024≤(A+B) / X≤2.4, which further enhances the synergistic effect of the first and second additives, resulting in better overall performance of the lithium-ion battery. Comparing the test results of Example 5 and Examples 20-26, when the first additive and the second additive are other compounds described in this application, they can also exert the corresponding effects to improve the high-temperature cycling and high-temperature storage performance of lithium-ion batteries. In Example 27, a third additive (fluoroethylene carbonate) was added during the preparation of the electrolyte. Compared with Example 1, the thickness expansion rate at 60°C was 9.3%, and the cycle capacity retention rate at 45°C was increased to 70% with 823 cycles. Therefore, it can be concluded that adding the third additive in the technical solution of this application is beneficial to further improve the overall performance of the battery.

[0091] Comparing Examples 24 and 28-29, the TTE mass percentage of the second additive in Example 24 was 20%, in Example 28 it was 10%, and in Example 29 it was 30%. Further comparison of the test data shows that, under the same conditions of the type of first additive, the mass percentage of the first additive, the type of second additive, and the carbon content, when the content of the second additive increased from 10% to 20%, the storage expansion rate slightly increased, but the number of cycles increased significantly. When it increased from 20% to 30%, the increase in storage expansion rate was more significant, and the number of cycles also increased slightly. This indicates that when the second additive is in the 10%-30% range, 20% better balances storage and cycling performance, while 30% results in slightly better cycling performance but decreased storage performance.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material layer, which includes a negative electrode active material. The negative electrode active material is silicon particles, and the silicon particles contain carbon. The electrolyte includes a first additive and a second additive, wherein the first additive includes nitrobenzenesulfonyl fluoride compounds and the second additive includes fluoroether diluents. The lithium-ion battery meets the following conditions: Formula 1: (A+B) / X≥0.0056, A% is 0.5%~4%, B% is 5%~40%; Wherein, A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage of the second additive in the electrolyte; X represents the carbon content in the negative electrode active material, expressed in ppm.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following conditions: Equation 2: 0.024≤(A+B) / X≤2.

4.

3. The lithium-ion battery according to claim 1, characterized in that, Based on the total mass of the electrolyte as 100%, the mass percentage A% of the first additive is 1%~4%; and / or, Based on the total mass of the electrolyte as 100%, the mass percentage B% of the second additive is 10%~30%.

4. The lithium-ion battery according to claim 1, characterized in that, The first additive and the second additive satisfy the following conditions: A / B ≥ 0.

015.

5. The lithium-ion battery according to claim 1, characterized in that, The first additive and the second additive satisfy the following conditions: A / B ≥ 0.

025.

6. The lithium-ion battery according to claim 1, characterized in that, The carbon content X in the negative electrode active material is 10~2000 ppm.

7. The lithium-ion battery according to claim 1, characterized in that, The first additive includes one or more of the following compounds: Structure 1, Structure 2, Structure 3; Among them, R1~R 12 Each atom is independently selected from one or more of the following: methyl, fluorine, and hydrogen atoms.

8. The lithium-ion battery according to claim 1, characterized in that, The first additive includes one or more of the following compounds: Compound 1 Compound 2 Compound 3 Compound 4, Compound 5, Compound 6.

9. The lithium-ion battery according to claim 1, characterized in that, The second additive includes one or more of 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, methyl nonafluorobutyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

10. The lithium-ion battery according to claim 1, characterized in that, The electrolyte also includes a third additive, which includes carbonate compounds; Based on the total mass of the electrolyte as 100%, the third additive has a mass percentage content of 5% to 15% in the electrolyte.

11. The lithium-ion battery according to claim 10, characterized in that, The third additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 3,3,3-trifluoropropylene carbonate, tetrafluoroethylene carbonate, and vinyl ethylene carbonate.

12. The lithium-ion battery according to claim 1, characterized in that, The positive electrode includes a positive electrode active material, which includes one or more of the following: lithium transition metal oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate. The chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr; wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1.

13. An electrical appliance, characterized in that, The lithium-ion battery includes any one of claims 1 to 12.

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