Lithium ion battery, battery pack, battery pack and electric equipment

Abstract

The invention discloses a lithium ion battery, a battery pack, a battery pack and electric equipment. The lithium ion battery comprises a positive electrode, a negative electrode and electrolyte. The negative electrode comprises a negative electrode active material, and the mass percent of silicon in the negative electrode active material is greater than 40%. An electrolyte solution; and fluoroethylene carbonate and a siloxane additive. According to the lithium ion battery, the silicon content in the negative electrode active material is improved, the energy density of the lithium ion battery can be remarkably improved, and meanwhile, the electrolyte can form a film on the positive electrode to protect the structural stability of the positive electrode and reduce the lithium ion dissolution of the positive electrode; the electrolyte is beneficial to formation of a large number of LiF components and an SEI film containing Si-O bond components on the negative electrode, the SEI film has elasticity and rigidity, the volume expansion of the negative electrode can be effectively inhibited, meanwhile, the breakage of the SEI film is slowed down, and the cycle life of the lithium ion battery is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a lithium-ion battery, battery pack, battery module, and electrical device. Background Technology

[0002] To meet the demands of electrical devices for high energy density and long cycle life, related technologies often adjust the composition and / or electrolyte ratio of the battery's positive electrode material. However, these methods have limited effect on improving the battery's energy density. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, the first objective of this invention is to provide a lithium-ion battery that improves the energy density of the lithium-ion battery while suppressing negative electrode volume expansion, slowing down SEI film breakage, and greatly improving the cycle life of the lithium-ion battery.

[0004] The second objective of this invention is to provide a battery pack.

[0005] The third objective of this invention is to provide a battery pack.

[0006] The fourth objective of this invention is to provide an electrical device.

[0007] A lithium-ion battery according to a first aspect of the present invention includes: a positive electrode; a negative electrode comprising a negative electrode active material, wherein the negative electrode active material contains silicon by mass percentage greater than 40%; and an electrolyte comprising: fluoroethylene carbonate and siloxane additives.

[0008] According to the lithium-ion battery of the present invention, increasing the silicon content in the negative electrode active material can significantly improve the energy density of the lithium-ion battery. At the same time, the electrolyte can form a film on the positive electrode to protect the structural stability of the positive electrode and reduce the dissolution of lithium ions from the positive electrode. The electrolyte is conducive to the formation of a large amount of LiF components and an SEI film containing Si-O bond components on the negative electrode. The SEI film has elasticity and rigidity, which can effectively suppress the volume expansion of the negative electrode while slowing down the breakage of the SEI film, thus greatly improving the cycle life of the lithium-ion battery.

[0009] According to some embodiments of the present invention, the siloxane additive comprises at least one of compounds of formula (1)-(3):

[0010]

[0011] In equations (1) to (3), R1~R 13It is selected from hydrogen, halogen, phenyl, and any one of the following groups: halogenated or non-halogenated hydrocarbon group, alkenyl group, alkynyl group, cyano group, alkanesilyl group, alkoxy group, sulfate ester group, sulfite ester group, and sulfonate ester group, respectively.

[0012] According to some embodiments of the present invention, the total amount of compounds represented by formulas (1) to (3) is 0.01% to 10% by mass percentage.

[0013] According to some embodiments of the present invention, the total amount of compounds represented by formulas (1) to (3) is 0.01% to 8% by mass percentage.

[0014] According to some embodiments of the present invention, the amount of fluoroethylene carbonate added is 2% to 50% by mass percentage.

[0015] According to some embodiments of the present invention, the amount of fluoroethylene carbonate added is 3% to 40% by mass percentage.

[0016] According to some embodiments of the present invention, in equations (1) to (3), R1 to R 13 The group is selected from any one of the following C1-C3 halogenated or non-halogenated hydrocarbon groups, alkenyl groups, alkynyl groups, cyano groups, alkanesilyl groups, alkoxy groups, sulfate groups, sulfite groups, sulfonate groups, and phenyl groups.

[0017] According to some embodiments of the present invention, in equations (1) to (3), R1 to R 13 Each group is selected from any one of the halogenated or non-halogenated hydrocarbon, alkenyl, alkynyl, and cyano groups of C1 to C3.

[0018] According to some embodiments of the present invention, formula (1) is selected from at least one of the following compounds:

[0019]

[0020]

[0021] According to some embodiments of the present invention, formula (2) is selected from at least one of the following compounds:

[0022]

[0023] According to some embodiments of the present invention, formula (3) is selected from at least one of the following compounds.

[0024]

[0025] According to some embodiments of the present invention, the electrolyte further includes a solvent and a lithium salt, wherein the solvent includes at least one of a carbonate solvent, a carboxylic acid ester solvent, and an ether solvent.

[0026] According to some embodiments of the present invention, the carbonate solvent includes at least one selected from ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the carboxylic acid ester solvent includes at least one selected from methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the ether solvent includes ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, and dimethyl... At least one of oxymethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, isosorbide dimethyl ether, dipropylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl dimethyl ether, 1,1,1,3,3,3-hexafluoroisopropylmethyl ether, and 2,2,2-trifluoroethyl ether.

[0027] According to some embodiments of the present invention, the lithium salt includes at least one selected from LiPF6, LiBF4, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2.

[0028] According to some embodiments of the present invention, the positive electrode includes a positive electrode active material, wherein the positive electrode active material includes: LiNi x Co y Mn z L (1-x-y-z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, 0≤x+y+z≤1.

[0029] According to some embodiments of the present invention, the negative electrode further includes a pre-stored lithium material, which is connected to the negative electrode active material to supplement the consumption of active lithium, wherein the capacity of the pre-stored lithium material to extract lithium ions accounts for 15% to 25% of the capacity of the positive electrode.

[0030] According to some embodiments of the present invention, the pre-stored lithium material is a lithium foil strip, the lithium foil strip includes multiple bent sections, and at least a portion of the lithium foil strip is disposed on the outer periphery of the negative electrode active material.

[0031] According to some embodiments of the present invention, the thickness of the lithium foil strip is D, wherein D satisfies: 5μm≤D≤20μm.

[0032] A battery pack according to a second aspect of the present invention includes at least one lithium-ion battery according to the first aspect of the present invention described above.

[0033] A battery pack according to a third aspect of the present invention includes at least one lithium-ion battery according to the first aspect of the present invention, or includes at least one battery pack according to the second aspect of the present invention.

[0034] An electrical device according to a fourth aspect of the present invention includes at least one lithium-ion battery according to the first aspect of the present invention, or includes at least one battery pack according to the second aspect of the present invention, or includes at least one battery pack according to the third aspect of the present invention.

[0035] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0036] The following describes a lithium-ion battery according to an embodiment of the present invention.

[0037] A lithium-ion battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode is the end from which electrons flow out. In a chemical reaction, the positive electrode typically undergoes an oxidation reaction, i.e., loses electrons. The negative electrode is the end from which electrons flow in. During battery discharge, the negative electrode typically undergoes a reduction reaction, i.e., gains electrons. The electrolyte is a solution that allows ions to move within the battery, which helps balance the charge inside the lithium-ion battery. The positive electrode, negative electrode, and electrolyte work together to allow current to flow through an external circuit, thereby powering electrical devices. When the battery discharges, chemical reactions occur at the positive and negative electrodes, the generated electrons flow through the external circuit, while the remaining lithium ions move within the battery through the electrolyte, maintaining charge balance.

[0038] Specifically, the negative electrode includes a negative electrode active material, in which the mass percentage of silicon is greater than 40%. The electrolyte includes fluoroethylene carbonate (FEC) and siloxane additives.

[0039] The theoretical specific capacity of Si material in the negative electrode is 4200 mAh / g, while that of graphite is 372 mAh / g. The theoretical specific capacity of Si material is much greater than that of graphite. Therefore, increasing the silicon content in the negative electrode active material can significantly improve the energy density.

[0040] Fluorinated ethylene carbonate (FE) promotes the formation of a stable and effective solid electrolyte interphase (SEI) film on the negative electrode surface, preventing direct contact between the electrolyte and the negative electrode active material, thus preventing continuous electrolyte decomposition while allowing lithium ions to pass freely. This helps maintain the cycle performance of lithium-ion batteries and extends their lifespan. Simultaneously, the SEI film helps maintain good ionic conductivity at low temperatures, improving the performance of lithium-ion batteries under low-temperature conditions and reducing safety issues caused by overcharging or high temperatures. FE also exhibits high chemical stability, remaining stable during the charge and discharge process of lithium-ion batteries and preventing rapid electrolyte degradation.

[0041] Siloxane additives help promote the formation of a stable and uniform SEI film on the negative electrode surface of lithium-ion batteries, thereby improving the energy density of lithium-ion batteries and enabling them to store more energy in the same volume or weight. Siloxane additives are not easily decomposed at high voltages, which helps maintain the stability of the electrolyte throughout the entire voltage range of lithium-ion battery operation, avoiding the generation of harmful byproducts and thus improving the overall chemical stability of the electrolyte. At the same time, siloxane additives help prevent thermal runaway in lithium-ion batteries under extreme conditions such as overcharging, over-discharging, or high temperatures, and maintain good electrochemical performance at low temperatures, thus contributing to a wider range of operating conditions for lithium-ion batteries.

[0042] Furthermore, the high silicon content of negative electrode active materials easily leads to severe volume expansion. During the charging and discharging process of lithium-ion batteries, the SEI film on the negative electrode surface continuously breaks down and reconstructs, constantly undergoing side reactions with the electrolyte, consuming active lithium, and accelerating lithium-ion battery failure. In contrast, with the synergistic effect of fluoroethylene carbonate and siloxane additives in the electrolyte, the negative electrode active material readily forms a large amount of LiF and an inorganic-organic combined SEI film containing Si-O bonds on the negative electrode surface. This SEI film possesses both rigidity and elasticity, which helps suppress negative electrode expansion while preventing its breakage, greatly reducing side reactions between the negative electrode and the electrolyte. Simultaneously, fluoroethylene carbonate and siloxane additives can also form good films on the positive electrode to inhibit lithium-ion dissolution, reduce lithium-ion deposition on the negative electrode and its damage, thereby significantly improving the cycle life of lithium-ion batteries.

[0043] According to the lithium-ion battery of the present invention, increasing the silicon content in the negative electrode active material can significantly improve the energy density of the lithium-ion battery. At the same time, the electrolyte can form a film on the positive electrode to protect the structural stability of the positive electrode and reduce the dissolution of lithium ions from the positive electrode. The electrolyte is conducive to the formation of a large amount of LiF components and an SEI film containing Si-O bond components on the negative electrode. The SEI film has elasticity and rigidity, which can effectively suppress the volume expansion of the negative electrode while slowing down the breakage of the SEI film, thus greatly improving the cycle life of the lithium-ion battery.

[0044] According to some embodiments of the present invention, the siloxane additives include at least one of the compounds of formula (1)-(3):

[0045]

[0046] In equations (1) to (3), R1~R 13 The compounds are selected from hydrogen, halogen, phenyl, and any one of the following C1-C5 halogenated or non-halogenated hydrocarbon, alkenyl, alkynyl, cyano, alkanesilyl, alkoxy, sulfate, sulfite, and sulfonate groups. The silicon-oxygen bonds in the above compounds can remove HF generated by lithium salt hydrolysis, and the unsaturated bonds introduced on the side chains are beneficial to increasing the film formation rate. Therefore, using at least one of the compounds of formulas (1)-(3) above can help the electrolyte to form films at both the positive and negative electrodes, thereby inhibiting the dissolution of lithium ions at the positive electrode, inhibiting the volume expansion of the negative electrode, and reducing the side reactions of the electrolyte at the negative electrode interface.

[0047] Furthermore, the total amount of compounds shown in formulas (1) to (3) added, by mass percentage, is 0.01% to 10%. When the total amount of compounds shown in formulas (1) to (3) added is less than 0.01%, the total amount of compounds shown in formulas (1) to (3) added is small, which makes it difficult to fully meet the needs of the electrolyte, and there are still many side reactions between the negative electrode and the electrolyte. When the total amount of compounds shown in formulas (1) to (3) added is greater than 10%, the total amount of compounds shown in formulas (1) to (3) added is large, which increases the cost of the electrolyte and thus increases the cost of the lithium-ion battery. Therefore, by controlling the total amount of compounds shown in formulas (1) to (3) added within the range of 0.01% to 10%, it is beneficial to fully reduce the side reactions between the negative electrode and the electrolyte, improve the stability of lithium-ion battery use, and control the cost of lithium-ion battery.

[0048] Furthermore, the total amount of compounds shown in formulas (1) to (3) added is 0.01% to 8% by mass percentage. Thus, the total amount of compounds shown in formulas (1) to (3) is more reasonably controlled, the composition of the electrolyte is optimized, which helps to improve the electrochemical performance of lithium-ion batteries, improve the stability of lithium-ion batteries, and extend the service life of lithium-ion batteries.

[0049] According to some embodiments of the present invention, the amount of fluoroethylene carbonate added is 2% to 50% by mass percentage. When the amount of fluoroethylene carbonate added is less than 2%, the amount is relatively small, making it difficult to fully utilize the function of fluoroethylene carbonate and meet the requirements of the electrolyte, resulting in more side reactions between the negative electrode and the electrolyte. When the amount of fluoroethylene carbonate added is greater than 50%, the amount is relatively large, increasing the cost of the electrolyte and thus the cost of the lithium-ion battery. Therefore, by controlling the amount of fluoroethylene carbonate added to 2% to 50%, it is beneficial to reduce the side reactions between the negative electrode and the electrolyte, while the film formation on the positive electrode can protect the structural stability of the positive electrode and improve the cycle life of the lithium-ion battery.

[0050] Furthermore, the amount of fluoroethylene carbonate added is 3% to 40% by mass percentage. Therefore, the amount of fluoroethylene carbonate added is more reasonable, allowing for sufficient film formation at both the positive and negative electrodes, thus preventing lithium ion dissolution at the positive electrode, suppressing volume expansion at the negative electrode, and simultaneously helping to control the cost of lithium-ion batteries.

[0051] In equations (1) to (3), R1~R 13 The groups are selected from any one of the following C1-C3 halogenated or non-halogenated hydrocarbon groups, alkenyl groups, alkynyl groups, cyano groups, alkanesilyl groups, alkoxy groups, sulfate groups, sulfite groups, sulfonate groups, and phenyl groups. All of these groups have unsaturated bonds, which is beneficial for increasing the film formation rate of the electrolyte at both the positive and negative electrodes, thereby improving the cycle performance and safety of lithium-ion batteries.

[0052] Furthermore, in equations (1) to (3), R1~R 13 These compounds are selected from any one of the following C1-C3 halogenated or non-halogenated hydrocarbon, alkenyl, alkynyl, and cyano groups. The branched structures of these compounds are relatively small, resulting in low steric hindrance, which is beneficial for increasing the film formation rate. At the same time, these compounds have low cost, which helps control the cost of lithium-ion batteries and enhances their market competitiveness.

[0053] According to some embodiments of the present invention, formula (1) is selected from at least one of the following compounds:

[0054]

[0055] The cyclization of the aforementioned compounds improves the stability and uniformity of the SEI film, prevents further electrolyte decomposition, and ensures efficient lithium-ion transport. Cyclic siloxane compounds enhance the chemical stability of the electrolyte, reducing decomposition under high voltage or high temperature conditions, thereby reducing gas generation inside the battery and improving battery safety. Furthermore, the network structure formed by the cyclization of siloxane compounds strengthens the mechanical strength of the SEI film, enabling it to withstand volume changes in the negative electrode during charging and / or discharging, reducing separation between the negative electrode and the SEI film, and improving the cycle performance of the lithium-ion battery.

[0056] According to some embodiments of the present invention, formula (2) is selected from at least one of the following compounds:

[0057]

[0058]

[0059] The aforementioned compounds facilitate uniform deposition of lithium ions on the electrode surface, preventing performance degradation caused by localized overcharging or over-discharging, and improving the overall energy density and power density of lithium-ion batteries. Simultaneously, at least one of these compounds helps optimize the composition of the SEI film, thereby reducing side reactions between the electrolyte and electrode materials, such as solvent decomposition and electrode corrosion, thus improving battery efficiency and lifespan.

[0060] According to some embodiments of the present invention, formula (3) is selected from at least one of the following compounds.

[0061]

[0062] The above compounds all have relatively simple structures, which improve the interfacial compatibility between the electrolyte and the positive and negative electrodes, promote a more stable electrochemical reaction, that is, form a stable and reliable SEI film, improve the overall performance of the battery, and at the same time help reduce the cost of lithium-ion batteries.

[0063] In addition, the electrolyte also includes a solvent and a lithium salt. The solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, and ether solvents. The lithium salt has a high degree of dissociation and its role is to provide charge carriers, i.e., to provide lithium ions, and it also affects the conductivity, thermal stability, and chemical stability of the electrolyte to some extent. The solvent can fully dissolve or mix the lithium salt, fluoroethylene carbonate, and siloxane additives to improve the uniformity of the electrolyte, thereby contributing to the improvement of the electrochemical performance stability of the lithium-ion battery.

[0064] Carbonate solvents possess high dielectric constants, effectively dissolving lithium salts and ensuring good ionic conductivity of the electrolyte. Carboxylic acid ester solvents exhibit good solubility and electrochemical stability, effectively dissolving lithium salts and promoting lithium-ion transport. Compared to carbonate solvents, carboxylic acid ester solvents have lower dielectric constants and viscosities, which are beneficial for improving electrolyte flowability and ionic conductivity. Ether solvents have lower viscosity, improving electrolyte flowability and facilitating rapid migration of lithium ions between the positive and negative electrodes, thereby increasing battery power density and low-temperature performance. Simultaneously, ether solvents allow lithium ions to pass freely and promote the formation of a stable and thin SEI film on the negative electrode surface, preventing further electrolyte decomposition.

[0065] Furthermore, the carbonate solvent includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. These solvents all have high dielectric constants and good solubility for lithium salts. Therefore, using at least one of these solvents is beneficial for improving the conductivity of the electrolyte, enhancing the electrochemical performance of the lithium-ion battery, improving the practical stability of the lithium-ion battery, and increasing the market competitiveness of the lithium-ion battery.

[0066] Carboxylic acid ester solvents include at least one of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate. These solvents have relatively low dielectric constants and viscosities. Using at least one of these solvents is beneficial for improving the fluidity of the electrolyte, which helps to enhance lithium-ion migration, thereby improving the electrochemical performance and cycle performance of lithium-ion batteries.

[0067] Ether solvents include at least one selected from the following: ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, dimethoxymethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, isosorbide dimethyl ether, dipropylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl dimethyl ether, 1,1,1,3,3,3-hexafluoroisopropylmethyl ether, and 2,2,2-trifluoroethyl ether. These solvents have high solubility for lithium salts, which helps ensure the ionic conductivity of the electrolyte. When used, the solvents mentioned above have low viscosity, good volatility and strong electrochemical stability. Using at least one of the solvents mentioned above is beneficial to improve the fluidity of the electrolyte and improve the electrochemical performance of lithium-ion batteries by utilizing the migration of lithium ions.

[0068] According to some embodiments of the present invention, the lithium salt includes at least one selected from LiPF6, LiBF4, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2. The lithium ions released from the dissociation of the above lithium salts can migrate during charging and discharging, and the lithium ions can participate in the formation of an SEI film on the negative electrode surface. Simultaneously, the above lithium salts exhibit good thermal stability; therefore, using at least one of the above lithium salts helps to prevent the lithium salt from decomposing when the battery overheats, thereby improving battery safety.

[0069] In addition, the positive electrode includes positive electrode active materials, which include: LiNi x Co y Mn z L (1-x-y-z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V, or Fe, 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, 0≤x+y+z≤1. A higher Ni content in the positive electrode active material is beneficial for increasing the specific capacity of the positive electrode active material, meaning a higher amount of charge can be stored per unit mass of positive electrode active material during the electrochemical reaction, thus contributing to higher energy density in lithium-ion batteries. The positive electrode active material can be NCM622, NCM712, NCM811, or NCM9055, but is not limited to these. For example, NCM622 indicates a nickel, cobalt, and manganese ratio of 6:2:2 (in molar terms), i.e., 60% nickel, 20% cobalt, and 20% manganese.

[0070] According to some embodiments of the present invention, the negative electrode further includes a pre-stored lithium material, which is connected to the negative electrode active material to supplement the consumption of active lithium. Increasing the silicon content in the negative electrode active material will consume a large amount of active lithium during the formation stage, reducing the battery's initial efficiency and energy density. By setting a pre-stored lithium material in the negative electrode, it is beneficial to improve the battery's initial efficiency; for example, after pre-stored lithium material, the initial efficiency of the lithium-ion battery increases from 75%+ to 90%+.

[0071] The capacity of pre-stored lithium materials to extract lithium ions accounts for 15% to 25% of the positive electrode's capacity. When this ratio is less than 15%, the amount of lithium ions that can be extracted is relatively small, making it difficult to meet the requirements for improving the battery's initial efficiency and energy density. Conversely, when this ratio is greater than 25%, the amount of lithium ions that can be extracted is relatively large, meaning there is a significant amount of pre-stored lithium material in the negative electrode, which increases the negative electrode's volume and reduces the applicability of the lithium-ion battery. Therefore, by ensuring that the capacity of pre-stored lithium materials to extract lithium ions accounts for 15% to 25% of the positive electrode's capacity, it is beneficial to fully utilize the role of pre-stored lithium materials, increase the battery's initial efficiency and energy density, and simultaneously achieve a lightweight design for the lithium-ion battery, thereby improving its applicability.

[0072] Furthermore, the pre-stored lithium material is a lithium foil strip, used to pre-activate lithium in the negative electrode active material. The lithium foil strip includes multiple bends. For example, the shape of the lithium foil strip is roughly "Z" shaped. No specific limitation is made here. This increases the contact area between the lithium foil strip and the negative electrode active material, thereby improving the reliability of the lithium foil strip setup. At least a portion of the lithium foil strip is located on the outer periphery of the negative electrode active material, which helps increase the contact between the lithium foil strip and substances outside the negative electrode, thereby increasing the lithium-ion extraction rate, improving the stability of the lithium-ion battery, and reducing the cost of the lithium-ion battery.

[0073] Furthermore, the thickness of the lithium foil strip is D, where D satisfies: 5μm ≤ D ≤ 20μm. When the thickness of the lithium foil strip is less than 5μm, the capacity of the pre-active lithium in the negative electrode is relatively small, which cannot compensate for the loss of active lithium during formation and cycling, thus negatively impacting energy density and cycle life. When the thickness of the lithium foil strip is greater than 20μm, the pre-stored lithium capacity of the negative electrode increases significantly. At this point, the negative electrode cannot accommodate the active lithium from the positive electrode during charging, making lithium deposition at the negative electrode interface highly likely. This greatly increases side reactions at the negative electrode interface, thereby reducing the battery's cycle life. Therefore, by ensuring that the thickness D of the lithium foil strip satisfies: 5μm ≤ D ≤ 20μm, the battery's cycle life is extended while maintaining its initial efficiency.

[0074] A battery pack according to a second aspect of the present invention includes at least one lithium-ion battery according to the first aspect of the present invention described above.

[0075] The battery pack according to the embodiments of the present invention is beneficial to improving the electrochemical stability and cycle life of the battery pack.

[0076] A battery pack according to a third aspect of the present invention includes at least one lithium-ion battery according to the first aspect of the present invention, or includes at least one battery pack according to the second aspect of the present invention.

[0077] The battery pack according to the embodiments of the present invention is beneficial to improving the stability and reliability of the battery pack in use, improving the reliability of the battery pack's charging and discharging, thereby enhancing the market competitiveness of the battery pack.

[0078] An electrical device according to a fourth aspect of the present invention includes at least one lithium-ion battery according to the first aspect of the present invention, or includes at least one battery pack according to the second aspect of the present invention, or includes at least one battery pack according to the third aspect of the present invention.

[0079] According to the embodiments of the present invention, the power supply of the electrical equipment is more reliable, thereby improving the user experience and safety of the electrical equipment, and thus helping to enhance the market competitiveness of the electrical equipment.

[0080] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0081] Preparation of lithium-ion batteries

[0082] 1. Preparation of non-aqueous electrolytes

[0083] Fluoroethylene carbonate, propylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed uniformly in a specified ratio, with the mixed solvent weight being 100%. Fluoroethylene carbonate was added according to the percentages shown in the examples, propylene carbonate was added at a 10% mass ratio, and methyl ethyl carbonate and diethyl carbonate were added in a 1:1 mass ratio to prepare a 100% mixed solvent. Then, 1 mol / L lithium hexafluorophosphate was added, followed by the compounds represented by structural formulas (1) to (3) in the corresponding percentages based on the total mass of the non-aqueous electrolyte, to obtain the electrolyte used in the examples.

[0084] 2. Preparation of the positive electrode

[0085] A positive electrode active material (NCM523, NCM622, NCM712, NCM811, or NCM9055), a conductive agent (carbon nanotubes, CNTs), and a binder (polyvinylidene fluoride, PVDF) in a mass ratio of 95.8:1.7:2.5 are mixed and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum tabs are welded on using an ultrasonic welder to obtain the positive electrode.

[0086] 3. Preparation of the negative electrode

[0087] A negative electrode active material (silicon-carbon material), a conductive agent (CNT), a binder (polyacrylic acid), and a thickener (sodium carboxymethyl cellulose, CMC) in a mass ratio of 94.2:1.1:4.7:0.5 were mixed and then dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, and after drying, rolling, and vacuum drying, a negative electrode without pre-stored lithium was obtained.

[0088] Fold the lithium foil strip in a "Z" shape, then insert the negative electrode, ensuring that the outermost layer is lithium foil. After the core package is folded, use high-temperature tape to fix it. Then put the core package into an aluminum foil packaging bag and squeeze it at 105℃ and 2Mpa pressure for 16 hours. Then stop heating and unload the pressure. After cooling to room temperature, open the aluminum foil packaging bag, take out the negative electrode sheet with pre-stored lithium, and weld the nickel tabs with an ultrasonic welding machine to obtain the pre-stored lithium negative electrode.

[0089] 4. Cell fabrication

[0090] Fold the separator in a "Z" shape, then interleave the positive electrode and the pre-stored lithium negative electrode, ensuring that the outermost two negative electrodes are used. Usually, 7 positive electrodes and 8 negative electrodes are used. After the core pack is stacked, use high-temperature tape to fix it. Then put the core pack into an aluminum foil packaging bag and vacuum bake it at 85°C for 48 hours to obtain the cell to be injected with electrolyte.

[0091] 5. Electrolyte injection, formation, and capacity testing of battery cells.

[0092] In a dry room with the dew point controlled below -40°C, the electrolyte prepared above was injected into the battery cell, vacuum sealed, and left to stand at 45°C for 24 hours. Then, the first charge was performed according to the following steps: 0.05C constant current charging for 120 min, 0.2C constant current charging for 240 min, left to stand at 45°C for 36 hours, and then vacuum sealed a second time.

[0093] Then, charge at a constant current and constant voltage of 0.2C to 4.4V (NCM523) / 4.3V (NCM622) / 4.25V (NCM712) / 4.2V (NCM811) / 4.2V (NCM9055), let it stand at room temperature for 24 hours, then discharge at a constant current of 0.2C to 3.0V, and then cycle it twice at a current of 0.2C to complete the capacity testing.

[0094] Performance testing

[0095] 1) Room temperature cycling test

[0096] The batteries in this example were placed in a constant temperature chamber at 25°C and left for at least 4 hours to ensure the battery body temperature stabilized at 25°C. They were then charged at a constant current and constant voltage of 0.5C to 4.4V (NCM523) / 4.3V (NCM622) / 4.25V (NCM712) / 4.2V (NCM811) / 4.2V (NCM9055). Then, they were discharged at a constant current of 0.5C to 3.0V. This cycle was repeated, and the discharge capacity of the first and last discharges was recorded. The capacity retention rate was calculated using the following formula:

[0097] Capacity retention rate = (Final discharge capacity / First discharge capacity) × 100%.

[0098] 2) Room temperature circulating gas production test

[0099] The volume of the battery before cycling (i.e., after capacity testing) and the battery with 80% capacity retention after cycling at room temperature were tested using the water displacement method. The volume before cycling was recorded as V1, and the volume after cycling was recorded as V2. The gas production during cycling at room temperature was calculated using the following formula:

[0100] Gas production during normal temperature cycle = (V2-V1) / battery rated capacity.

[0101] Table 1. Content and test results of Examples 1-47 and Comparative Examples 1-5

[0102]

[0103]

[0104]

[0105]

[0106] Results Analysis

[0107] Referring to Table 1, comparing Examples 1-9 and Comparative Examples 3-5, it can be seen that when the electrolyte simultaneously contains fluoroethylene carbonate and at least one of the compounds shown in structural formulas (1)-(3), the room temperature cycle capacity retention rate of the battery is significantly improved, and the room temperature cycle gas production is significantly reduced. This is because without FEC and the compounds shown in structural formulas (1)-(3), the continuous expansion and contraction of the negative electrode reacts severely with the electrolyte. Neither the SEI film mainly composed of inorganic component LiF nor the SEI film containing organic component Si-O can effectively protect the negative electrode. Only when both are used simultaneously can the negative electrode be better protected, side reactions suppressed, and cycle life improved.

[0108] Comparing Examples 10-31 and Comparative Examples 3-5, it can be seen that the compounds represented by structural formulas (1)-(3) with different amounts can improve the battery's room temperature cycle capacity retention and room temperature cycle gas generation. The same rule applies when the compounds represented by structural formulas (1)-(3) are used in combination. That is, the compounds represented by formulas (1)-(3) can synergistically form a film with FEC to protect the negative electrode, and no degradation effect will occur when they are used in combination.

[0109] Comparing Examples 32-41 and Comparative Example 4, it can be seen that adding 3%-40% of fluoroethylene carbonate can improve the battery's room temperature cycle capacity retention and room temperature cycle gas generation. The effect is more obvious when the FEC content is 20%-35%. This is because FEC in this range can generate an appropriate amount of LiF to protect the negative electrode, while too high FEC content will become a gas generation source and degrade the cycle performance.

[0110] Comparing Examples 1, 42-44, and Comparative Example 1, it can be seen that when the Ni content of the positive electrode active material is <60%, the room temperature cycling performance of this battery system is significantly poor. This is presumably due to the poor high-voltage stability of the electrolyte and additives. To obtain high-capacity NCM523 positive electrodes, the application voltage is typically greater than 4.4V, which places high demands on the stability of the positive electrode CEI film and electrolyte. Therefore, the electrolyte and additives in this invention are not suitable for high-voltage battery systems.

[0111] Comparing Examples 1, 45-47, and Comparative Example 2, it can be seen that when the Si content of the negative electrode active material is <40%, the room temperature cycle performance of this battery system is significantly poor. It is speculated that this is because the FEC is in an excess state at this point; the excess FEC has poor stability and decomposes to produce gas, thus degrading the cycle performance.

[0112] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0113] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A lithium-ion battery, characterized in that, include: positive electrode; A negative electrode, wherein the negative electrode comprises a negative electrode active material, wherein the mass percentage of silicon in the negative electrode active material is greater than 40%; The electrolyte comprises fluoroethylene carbonate and siloxane additives.

2. The lithium-ion battery according to claim 1, characterized in that, The siloxane additives include at least one of the compounds of formulas (1) to (3): In equations (1) to (3), R1~R 13 It is selected from hydrogen, halogen, phenyl, and any one of the following groups: halogenated or non-halogenated hydrocarbon group, alkenyl group, alkynyl group, cyano group, alkanesilyl group, alkoxy group, sulfate ester group, sulfite ester group, and sulfonate ester group, respectively.

3. The lithium-ion battery according to claim 2, characterized in that, The total amount of compounds represented by formulas (1) to (3) added, by mass percentage, is 0.01% to 10%.

4. The lithium-ion battery according to claim 3, characterized in that, The total amount of compounds represented by formulas (1) to (3) added, by mass percentage, is 0.01% to 8%.

5. The lithium-ion battery according to claim 3 or 4, characterized in that, The amount of the fluoroethylene carbonate added is 2% to 50% by mass percentage.

6. The lithium-ion battery according to claim 5, characterized in that, The amount of fluoroethylene carbonate added is 3% to 40% by weight.

7. The lithium-ion battery according to claim 2, characterized in that, In equations (1) to (3), R1 to R 13 The group is selected from any one of the following C1-C3 halogenated or non-halogenated hydrocarbon groups, alkenyl groups, alkynyl groups, cyano groups, alkanesilyl groups, alkoxy groups, sulfate groups, sulfite groups, sulfonate groups, and phenyl groups.

8. The lithium-ion battery according to claim 7, characterized in that, In equations (1) to (3), R1 to R 13 Each group is selected from any one of the halogenated or non-halogenated hydrocarbon, alkenyl, alkynyl, and cyano groups of C1 to C3.

9. The lithium-ion battery according to claim 2, characterized in that, Formula (1) is selected from at least one of the following compounds:

10. The lithium-ion battery according to claim 2, characterized in that, Formula (2) is selected from at least one of the following compounds:

11. The lithium-ion battery according to claim 2, characterized in that, Formula (3) is selected from at least one of the following compounds.

12. The lithium-ion battery according to claim 1, characterized in that, The electrolyte further includes a solvent and a lithium salt, wherein the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, and ether solvents.

13. The lithium-ion battery according to claim 12, characterized in that, The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the carboxylic acid ester solvent includes at least one of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the ether solvent includes ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, dimethoxymethane, and diethyl butyrate. At least one of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, isosorbide dimethyl ether, dipropylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl dimethyl ether, 1,1,1,3,3,3-hexafluoroisopropylmethyl ether, and 2,2,2-trifluoroethyl ether.

14. The lithium-ion battery according to claim 12, characterized in that, The lithium salt includes at least one of LiPF6, LiBF4, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2.

15. The lithium-ion battery according to claim 1, characterized in that, The positive electrode includes a positive electrode active material, which includes: LiNi x Co y Mn z L (1-x-y-z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, 0≤x+y+z≤1.

16. The lithium-ion battery according to claim 1, characterized in that, The negative electrode also includes a pre-stored lithium material, which is connected to the negative electrode active material to supplement the consumption of active lithium. The capacity of the pre-stored lithium material to extract lithium ions accounts for 15% to 25% of the capacity of the positive electrode.

17. The lithium-ion battery according to claim 16, characterized in that, The pre-stored lithium material is a lithium foil strip, which includes multiple bent sections, and at least a portion of the lithium foil strip is disposed on the outer periphery of the negative electrode active material.

18. The lithium-ion battery according to claim 17, characterized in that, The thickness of the lithium foil strip is D, wherein D satisfies: 5μm≤D≤20μm.

19. A battery pack, characterized in that, It includes at least one lithium-ion battery according to any one of claims 1-18.

20. A battery pack, characterized in that, It includes at least one lithium-ion battery according to any one of claims 1-18, or includes at least one battery pack according to claim 19.

21. An electrical appliance, characterized in that, It includes at least one lithium-ion battery according to any one of claims 1-18, or includes at least one battery pack according to claim 19, or includes at least one battery pack according to claim 20.

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