Lithium-ion battery, battery module, battery pack, and electric device

Abstract

An electric device, comprising a lithium-ion battery, a battery module, or a battery pack. The battery pack comprises the lithium-ion battery or the battery module; the battery module comprises the lithium-ion battery; and the lithium-ion battery comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode active material, and the mass percentage of silicon in the negative electrode active material is greater than 40%. The electrolyte comprises fluoroethylene carbonate and a siloxane additive.

Description

Lithium ion battery, battery pack, battery package and electric device

[0001] Cross-reference to Related Applications

[0002] The present application claims priority to the Chinese patent application No. 202411327960.9, filed on September 23, 2024, entitled “Lithium ion battery, battery pack, battery package and electric device”, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of battery, in particular to a lithium ion battery, a battery pack, a battery package and an electric device. BACKGROUND

[0004] To meet the demand of electric device for high energy density and long cycle life, in the related art, the composition of the positive electrode material and / or the ratio of the composition of the electrolyte are often adjusted. However, the above method has a small improvement effect on the energy density of the battery.

[0005] DISCLOSURE

[0006] The present disclosure aims to at least solve one of the technical problems existing in the prior art. To this end, the first object of the present disclosure is to provide a lithium ion battery, which improves the energy density of the lithium ion battery while inhibiting the volume expansion of the negative electrode, slows down the breaking of the SEI film, and greatly improves the cycle life of the lithium ion battery.

[0007] The second object of the present disclosure is to provide a battery pack.

[0008] The third object of the present disclosure is to provide a battery package.

[0009] The fourth object of the present disclosure is to provide an electric device.

[0010] The lithium ion battery according to the first aspect of the present disclosure comprises: a positive electrode; a negative electrode, the negative electrode comprising a negative electrode active material, the mass percentage of silicon in the negative electrode active material being greater than 40%; and an electrolyte, the electrolyte comprising fluoroethylene carbonate and a siloxane additive.

[0011] The lithium ion battery according to the present disclosure increases the content of silicon in the negative electrode active material, which 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 structure of the positive electrode and reduce the dissolution of lithium ions from the positive electrode. The electrolyte is beneficial to the formation of a large amount of LiF component and Si-O bond component SEI film on the negative electrode, so that the SEI film has elasticity and rigidity, which can effectively inhibit the volume expansion of the negative electrode while slowing down the breaking of the SEI film, greatly improving the cycle life of the lithium ion battery.

[0012] According to some embodiments of the present disclosure, the siloxane additive comprises at least one of the compounds of formula (1) - formula (3):

[0013] R1~R6in formula (1) - formula (3) 13 are each selected from any one of hydrogen, halogen, phenyl, C1~C5halogenated or non-halogenated hydrocarbon group, C1~C5halogenated or non-halogenated alkenyl group, C1~C5halogenated or non-halogenated alkynyl group, C1~C5halogenated or non-halogenated cyano group, C1~C5halogenated or non-halogenated alkylsilyl group, C1~C5halogenated or non-halogenated alkoxy group, C1~C5halogenated or non-halogenated sulfate group, C1~C5halogenated or non-halogenated sulfite group, and C1~C5halogenated or non-halogenated sulfonate group.

[0014] According to some embodiments of the present disclosure, the total additive amount of the compound of formula (1) - formula (3) is 0.01%~10% by mass percentage.

[0015] According to some embodiments of the present disclosure, the total additive amount of the compound of formula (1) - formula (3) is 0.01%~8% by mass percentage.

[0016] According to some embodiments of the present disclosure, the additive amount of the fluoroethylene carbonate is 2%~50% by mass percentage.

[0017] According to some embodiments of the present disclosure, the additive amount of the fluoroethylene carbonate is 3%~40% by mass percentage.

[0018] According to some embodiments of the present disclosure, R1~R6in formula (1) - formula (3) 13 are each selected from any one of C1~C3halogenated or non-halogenated hydrocarbon group, C1~C3halogenated or non-halogenated alkenyl group, C1~C3halogenated or non-halogenated alkynyl group, C1~C3halogenated or non-halogenated cyano group, C1~C3halogenated or non-halogenated alkylsilyl group, C1~C3halogenated or non-halogenated alkoxy group, C1~C3halogenated or non-halogenated sulfate group, C1~C3halogenated or non-halogenated sulfite group, C1~C3halogenated or non-halogenated sulfonate group, and C1~C3halogenated or non-halogenated phenyl group.

[0019] According to some embodiments of the present disclosure, R1~R6in formula (1) - formula (3) 13 are each selected from any one of C1~C3halogenated or non-halogenated hydrocarbon group, C1~C3halogenated or non-halogenated alkenyl group, C1~C3halogenated or non-halogenated alkynyl group, and C1~C3halogenated or non-halogenated cyano group.

[0020] According to some embodiments of the present disclosure, the formula (1) is selected from at least one of the following compounds:

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

[0022] According to some embodiments of the present disclosure, the formula (3) is selected from at least one of the following compounds

[0023] According to some embodiments of the present disclosure, the electrolyte further comprises: a solvent and a lithium salt, wherein the solvent comprises at least one of a carbonate solvent, a carboxylic acid ester solvent, and an ether solvent.

[0024] According to some embodiments of the present disclosure, the carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the carboxylic acid ester solvent comprises 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; and the ether solvent comprises at least one of dimethyl ether of ethylene glycol, diethyl ether of ethylene glycol, 1,3-dioxolane, dimethoxy methane, dimethyl ether of diethylene glycol, dimethyl ether of triethylene glycol, dimethyl ether of tetraethylene glycol, dimethyl ether of polyethylene glycol, dimethyl ether of isosorbide, dimethyl ether of dipropylene glycol, 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-hexafluoroisopropyl methyl ether, and 2,2,2-trifluoroethyl ether.

[0025] According to some embodiments of the present disclosure, the lithium salt comprises 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.

[0026] According to some embodiments of the present disclosure, the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises: LiNi x Co y Mn zL (1-x-y-z) O2, wherein 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.

[0027] According to some embodiments of the present disclosure, the negative electrode further comprises a pre-stored lithium material connected to the negative electrode active material to replenish consumption of active lithium, wherein a capacity of the pre-stored lithium material for releasing lithium ions accounts for 15% to 25% of a capacity of the positive electrode.

[0028] According to some embodiments of the present disclosure, the pre-stored lithium material is a lithium foil strip, the lithium foil strip comprises a plurality of bent segments, and at least part of the lithium foil strip is arranged at an outer periphery of the negative electrode active material.

[0029] According to some embodiments of the present disclosure, a thickness of the lithium foil strip is D, wherein the D satisfies: 5 μm≤D≤20 μm.

[0030] A battery pack according to a second aspect of the present disclosure comprises at least one lithium ion battery according to the first aspect of the present disclosure.

[0031] A battery pack according to a third aspect of the present disclosure comprises at least one lithium ion battery according to the first aspect of the present disclosure, or at least one battery group according to the second aspect of the present disclosure.

[0032] A power consumption device according to a fourth aspect of the present disclosure comprises at least one lithium ion battery according to the first aspect of the present disclosure, or at least one battery group according to the second aspect of the present disclosure, or at least one battery pack according to the third aspect of the present disclosure.

[0033] Additional aspects and advantages of the present disclosure will be made apparent from the following description. DETAILED DESCRIPTION

[0034] A lithium ion battery according to embodiments of the present disclosure is described below.

[0035] A lithium-ion battery according to embodiments of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode is the end where electrons flow out. In a chemical reaction, the positive electrode usually undergoes an oxidation reaction, i.e., loses electrons. The negative electrode is the end where electrons flow in. When the battery is discharging, the negative electrode usually undergoes a reduction reaction, i.e., gains electrons. The electrolyte is a solution that allows ions to move inside the battery, which helps to balance the charge inside the lithium-ion battery. The positive electrode, the negative electrode, and the electrolyte work together to enable current to flow through an external circuit, thereby powering a device. When the battery is discharging, a chemical reaction occurs at the positive and negative electrodes, and the electrons generated flow through the external circuit, while the lithium ions move inside the battery through the electrolyte to maintain charge balance.

[0036] Specifically, the negative electrode includes a negative electrode active material, and the mass percentage of silicon in the negative electrode active material is greater than 40%. The electrolyte includes fluoroethylene carbonate (FEC) and a siloxane-based additive.

[0037] The theoretical gram capacity of the Si material in the negative electrode is 4200 mAh / g, and the theoretical gram capacity of graphite is 372 mAh / g. The theoretical gram capacity of the Si material is much greater than that of graphite, so increasing the silicon content in the negative electrode active material can significantly improve the energy density.

[0038] Fluoroethylene carbonate is conducive to promoting the formation of a stable and effective solid electrolyte interface (SEI) film on the surface of the negative electrode, preventing direct contact between the electrolyte and the negative electrode active material, preventing the continuous decomposition of the electrolyte, while allowing lithium ions to pass freely, thereby helping to maintain the cycle performance of the lithium-ion battery and prolong the life of the lithium-ion battery. The SEI film helps to maintain good ionic conductivity at low temperatures, which helps to improve the performance of the lithium-ion battery under low temperature conditions and reduce safety problems that occur in the lithium-ion battery under excessive charging or high temperature conditions. Fluoroethylene carbonate has high chemical stability and can remain stable during the charging and discharging process of the lithium-ion battery, avoiding rapid degradation of the electrolyte.

[0039] The siloxane-based additive helps to promote the formation of a stable and uniform SEI film on the surface of the negative electrode of the lithium-ion battery, thereby helping to improve the energy density of the lithium-ion battery and enable the lithium-ion battery to store more energy under the same volume or weight. The siloxane-based additive is not easily decomposed at high voltage, which helps to maintain the stability of the electrolyte within the entire voltage range of the lithium-ion battery, avoiding the production of harmful byproducts and thereby improving the overall chemical stability of the electrolyte. At the same time, the siloxane-based additive helps to prevent the lithium-ion battery from experiencing thermal runaway under extreme conditions such as overcharging, overdischarging, or high temperature, while still maintaining good electrochemical performance at low temperatures, thereby helping to enrich the use conditions of the lithium-ion battery.

[0040] In addition, the negative active material is prone to serious volume expansion due to a high silicon content. During the charging and discharging process of the lithium ion battery, the SEI film on the negative electrode surface is continuously broken and reformed, continuously reacts with the electrolyte, consumes active lithium, and accelerates the failure of the lithium ion battery. Under the synergistic effect of the fluorinated ethylene carbonate and siloxane additive in the electrolyte, a large amount of inorganic-organic SEI film with LiF components and Si-O bond components is easily formed on the negative electrode surface. The SEI film has rigidity and elasticity, which is beneficial to inhibit the negative electrode expansion and the SEI film is not easy to break, thereby greatly reducing the side reaction of the negative electrode and the electrolyte. At the same time, the fluorinated ethylene carbonate and siloxane additive can also form a film on the positive electrode to inhibit the dissolution of lithium ions, reduce the deposition of lithium ions on the negative electrode and the damage to the negative electrode, thereby significantly improving the cycle life of the lithium ion battery.

[0041] According to the lithium ion battery of the embodiments of the present disclosure, the silicon content in the negative active material is increased, which can significantly improve the energy density of the lithium ion battery. Meanwhile, the electrolyte can form a film on the positive electrode to protect the structure stability of the positive electrode and reduce the dissolution of lithium ions from the positive electrode. The electrolyte is beneficial to form a large amount of SEI film with LiF components and Si-O bond components on the negative electrode. The SEI film has elasticity and rigidity, which can effectively inhibit the volume expansion of the negative electrode and slow down the breaking of the SEI film, thereby greatly improving the cycle life of the lithium ion battery.

[0042] According to some embodiments of the present disclosure, the siloxane additive includes at least one of the compounds of formula (1) to formula (3):

[0043] R1 to R 13 are each selected from any one of hydrogen, halogen, phenyl, C1 to C5 halogenated or non-halogenated hydrocarbon group, C1 to C5 halogenated or non-halogenated alkenyl group, C1 to C5 halogenated or non-halogenated alkynyl group, C1 to C5 halogenated or non-halogenated cyano group, C1 to C5 halogenated or non-halogenated alkylsilicon group, C1 to C5 halogenated or non-halogenated alkoxy group, C1 to C5 halogenated or non-halogenated sulfate group, C1 to C5 halogenated or non-halogenated sulfite group, and C1 to C5 halogenated or non-halogenated sulfonate group. The siloxane bond in the above-mentioned compound can remove HF generated by the hydrolysis of lithium salt, and the unsaturated bond introduced in the branched chain is beneficial to improve the film forming rate. Therefore, the use of at least one of the above-mentioned compounds of formula (1) to formula (3) is beneficial to form a film of the electrolyte on the positive electrode and the negative electrode, thereby inhibiting the dissolution of lithium ions from the positive electrode, inhibiting the volume expansion of the negative electrode, and reducing the side reaction of the electrolyte at the negative electrode interface.

[0044] Further, the total amount of the compound of formula (1) - formula (3) is 0.01% - 10% by mass. When the total amount of the compound of formula (1) - formula (3) is less than 0.01%, the total amount of the compound of formula (1) - formula (3) is small, so it is difficult to fully meet the needs of the electrolyte, and the side reactions of the negative electrode and the electrolyte are still more; when the total amount of the compound of formula (1) - formula (3) is greater than 10%, the total amount of the compound of formula (1) - formula (3) is large, which increases the cost of the electrolyte, and further increases the cost of the lithium ion battery. Therefore, by controlling the total amount of the compound of formula (1) - formula (3) to be 0.01% - 10%, it is beneficial to fully reduce the side reactions of the negative electrode and the electrolyte, improve the use stability of the lithium ion battery, and control the cost of the lithium ion battery.

[0045] Further, the total amount of the compound of formula (1) - formula (3) is 0.01% - 10% by mass. When the total amount of the compound of formula (1) - formula (3) is less than 0.01%, the total amount of the compound of formula (1) - formula (3) is small, so it is difficult to fully meet the needs of the electrolyte, and the side reactions of the negative electrode and the electrolyte are still more; when the total amount of the compound of formula (1) - formula (3) is greater than 10%, the total amount of the compound of formula (1) - formula (3) is large, which increases the cost of the electrolyte, and further increases the cost of the lithium ion battery. Therefore, by controlling the total amount of the compound of formula (1) - formula (3) to be 0.01% - 10%, it is beneficial to fully reduce the side reactions of the negative electrode and the electrolyte, improve the use stability of the lithium ion battery, and control the cost of the lithium ion battery.

[0046] According to some embodiments of the present disclosure, the amount of fluoroethylene carbonate added is 2% - 50% by mass. When the amount of fluoroethylene carbonate added is less than 2%, the amount of fluoroethylene carbonate added is small, so it is difficult to fully play the role of fluoroethylene carbonate, it is difficult to fully meet the needs of the electrolyte, and the side reactions of the negative electrode and the electrolyte are still more; when the amount of fluoroethylene carbonate added is greater than 50%, the amount of fluoroethylene carbonate added is large, which increases the cost of the electrolyte, and thus increases the cost of the lithium ion battery. Therefore, by controlling the amount of fluoroethylene carbonate added to be 2% - 50%, it is beneficial to reduce the side reactions of 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.

[0047] Further, the amount of fluoroethylene carbonate added is 3% - 40% by mass. Therefore, the amount of fluoroethylene carbonate added is more reasonable, and can fully form a film on the positive electrode and the negative electrode, thereby avoiding the dissolution of lithium ions from the positive electrode and inhibiting the volume expansion of the negative electrode, while it is also beneficial to control the cost of the lithium ion battery.

[0048] In formula (1) - formula (3), R1 - R 13any one selected from C1-C3 halogenated or non-halogenated hydrocarbon group, C1-C3 halogenated or non-halogenated alkenyl group, C1-C3 halogenated or non-halogenated alkynyl group, C1-C3 halogenated or non-halogenated cyano group, C1-C3 halogenated or non-halogenated alkylsilicon group, C1-C3 halogenated or non-halogenated alkoxy group, C1-C3 halogenated or non-halogenated sulfate group, C1-C3 halogenated or non-halogenated sulfite group, C1-C3 halogenated or non-halogenated sulfonate group, and C1-C3 halogenated or non-halogenated phenyl group. The above-mentioned groups all have unsaturated bonds, which are beneficial to improve the film-forming speed of the electrolyte on the positive electrode and the negative electrode, and improve the cycle performance and safety of the lithium ion battery.

[0049] Further, R1-R4 in formula (1)-formula (3) are independently selected from any one of C1-C3 halogenated or non-halogenated hydrocarbon group, C1-C3 halogenated or non-halogenated alkenyl group, C1-C3 halogenated or non-halogenated alkynyl group, and C1-C3 halogenated or non-halogenated cyano group. The branched structure of the above-mentioned compounds is small, so the steric hindrance is small, which is beneficial to improve the film-forming rate. At the same time, the cost of the above-mentioned compounds is low, which is beneficial to control the cost of the lithium ion battery and improve the market competitiveness of the lithium ion battery. 13 Further, R1-R4 in formula (1)-formula (3) are independently selected from any one of C1-C3 halogenated or non-halogenated hydrocarbon group, C1-C3 halogenated or non-halogenated alkenyl group, C1-C3 halogenated or non-halogenated alkynyl group, and C1-C3 halogenated or non-halogenated cyano group. The branched structure of the above-mentioned compounds is small, so the steric hindrance is small, which is beneficial to improve the film-forming rate. At the same time, the cost of the above-mentioned compounds is low, which is beneficial to control the cost of the lithium ion battery and improve the market competitiveness of the lithium ion battery.

[0050] According to some embodiments of the present disclosure, formula (1) is selected from at least one of the following compounds:

[0051] The ring formation of the above-mentioned compounds is beneficial to improve the stability and uniformity of the SEI film, prevent further decomposition of the electrolyte, and ensure efficient transmission of lithium ions. The ring formation of the siloxane compound can improve the chemical stability of the electrolyte, reduce the decomposition of the electrolyte under high voltage or high temperature conditions, thereby reducing the generation of gas inside the battery and improving the safety of the battery. In addition, the network structure formed after the ring formation of the siloxane compound can enhance the mechanical strength of the SEI film, so that it can withstand the volume change of the negative electrode during the charging and / or discharging process of the battery, reduce the separation between the negative electrode and the SEI film, and improve the cycle performance of the lithium ion battery.

[0052] According to some embodiments of the present disclosure, formula (2) is selected from at least one of the following compounds:

[0053] The above-mentioned compounds are beneficial to the uniform deposition of lithium ions on the electrode surface, prevent performance degradation caused by local overcharging or overdischarging, and improve the overall energy density and power density of the lithium ion battery. At the same time, by using at least one of the above-mentioned compounds, it is beneficial to optimize the composition of the SEI film, thereby reducing the side reactions between the electrolyte and the electrode material, such as solvent decomposition and electrode corrosion, and improving the efficiency and life of the battery.

[0054] According to some embodiments of the present disclosure, the formula (3) is selected from at least one of the following compounds

[0055] The above-mentioned compounds have simple structures, improve the interfacial compatibility between the electrolyte and the positive electrode and the negative electrode, promote more stable electrochemical reactions, form a stable and reliable SEI film, improve the overall performance of the battery, and at the same time, are conducive to reducing the cost of lithium ion batteries.

[0056] In addition, the electrolyte further comprises a solvent and a lithium salt, wherein the solvent comprises at least one of a carbonate solvent, a carboxylate solvent, and an ether solvent. The lithium salt has a high dissociation degree, and the role of the lithium salt is to provide charge carriers, i.e., to provide lithium ions, and to affect the electrical 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-based additives and the like, so as to improve the uniformity of the electrolyte, thereby being conducive to improving the stability of the electrochemical performance of the lithium ion battery.

[0057] The carbonate solvent has a high dielectric constant, can effectively dissolve the lithium salt, and thus ensures that the electrolyte has good ionic conductivity. The carboxylate solvent has good solubility and electrochemical stability, can effectively dissolve the lithium salt and promote the transmission of lithium ions. Compared with the carbonate solvent, the carboxylate solvent has a lower dielectric constant and viscosity, which is conducive to improving the flowability and ionic conductivity of the electrolyte. The ether solvent has a low viscosity, can improve the flowability of the electrolyte, and is helpful for the rapid migration of lithium ions between the positive electrode and the negative electrode, thereby improving the power density and low-temperature performance of the battery. At the same time, the ether solvent allows lithium ions to pass freely, and at the same time can promote the formation of a stable and thin SEI film on the surface of the negative electrode, preventing further decomposition of the electrolyte.

[0058] Further, the carbonate solvent comprises at least one of vinyl carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. The dielectric constants of the above-mentioned solvents are relatively high, and the solubility of the lithium salt is good, so that the use of at least one of the above-mentioned solvents is conducive to improving the conductivity of the electrolyte, improving the electrochemical performance of the lithium ion battery, improving the practical stability of the lithium ion battery, and improving the market competitiveness of the lithium ion battery.

[0059] 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 dielectric constant and viscosity of the above-mentioned solvents are low, and the use of at least one of the above-mentioned solvents is beneficial to improve the flowability of the electrolyte, which is helpful to improve the migration of lithium ions, thereby improving the electrochemical performance and cycle performance of the lithium ion battery.

[0060] The ether solvent includes at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, dimethoxy methane, 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-hexafluoroisopropyl methyl ether, and 2,2,2-trifluoroethyl ether. The solubility of the above-mentioned solvents to lithium salt is high, thereby ensuring the ionic conductivity of the electrolyte. At the same time, the above-mentioned solvents have low viscosity, good volatility, and strong electrochemical stability, and the use of at least one of the above-mentioned solvents is beneficial to improve the flowability of the electrolyte, the migration of lithium ions, and the electrochemical performance of the lithium ion battery.

[0061] According to some embodiments of the present disclosure, 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. The lithium ions released by the dissociation of the above-mentioned lithium salt can migrate during charging and discharging, and the lithium ions can participate in the formation of the SEI film on the surface of the negative electrode. At the same time, the above-mentioned lithium salt has good thermal stability, thereby the use of at least one of the above-mentioned lithium salt is beneficial to avoid the decomposition of the lithium salt when the battery is overheated, thereby improving the safety of the battery.

[0062] In addition, the positive electrode includes a positive electrode active material, and the positive electrode active material includes: LiNi x Co y Mn z L (1-x-y-z)O2, wherein 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. The content of Ni in the positive electrode active material is relatively high, which is conducive to improving the gram capacity of the positive electrode active material, i.e., the higher the amount of electric charge that can be stored in the positive electrode active material in the electrochemical reaction per unit mass, thereby facilitating the realization of higher battery energy density of the lithium ion battery. The positive electrode active material can be NCM622, NCM712, NCM811 or NCM9055, but is not limited thereto. For example, NCM622 represents that the ratio of nickel, cobalt and manganese is 6:2:2 (by mole), i.e., nickel accounts for 60%, cobalt accounts for 20%, and manganese accounts for 20%.

[0063] According to some embodiments of the present disclosure, the negative electrode further comprises a pre-stored lithium material connected to the negative electrode active material to supplement the consumption of active lithium. The increase of the content of silicon in the negative electrode active material consumes a large amount of active lithium in the formation stage, which reduces the initial efficiency and energy density of the battery. By providing a pre-stored lithium material in the negative electrode, the initial efficiency of the battery can be improved, for example, the initial efficiency of the lithium ion battery after the pre-stored lithium material is increased from 75%+ to 90%+.

[0064] The capacity of the pre-stored lithium material that can release lithium ions accounts for 15% to 25% of the capacity of the positive electrode. When the ratio of the capacity of the pre-stored lithium material that can release lithium ions to the capacity of the positive electrode is less than 15%, the amount of lithium ions that can be released by the pre-stored lithium material is relatively small, which is difficult to meet the demand for improving the initial efficiency and energy density of the battery. When the ratio of the capacity of the pre-stored lithium material that can release lithium ions to the capacity of the positive electrode is greater than 25%, the capacity of the pre-stored lithium material that can release lithium ions is relatively large, i.e., the amount of the pre-stored lithium material in the negative electrode is relatively large, thereby increasing the volume of the negative electrode and reducing the applicability of the lithium ion battery. Therefore, the capacity of the pre-stored lithium material that can release lithium ions accounts for 15% to 25% of the capacity of the positive electrode, which is conducive to fully utilizing the pre-stored lithium material, increasing the initial efficiency and energy density of the battery, and at the same time, realizing the lightweight design of the lithium ion battery as much as possible, thereby improving the applicability of the lithium ion battery.

[0065] Further, the pre-stored lithium material is a lithium foil strip used to pre-store active lithium for the negative electrode active material. The lithium foil strip comprises a plurality of bending segments. For example, the shape of the lithium foil strip is approximately "Z" shape. Herein, no specific limitation is made. Therefore, the contact area between the lithium foil strip and the negative electrode active material is increased, thereby being conducive to improving the setting reliability of the lithium foil strip. At least part of the lithium foil strip is arranged at the outer periphery of the negative electrode active material, which is conducive to increasing the contact between the lithium foil strip and the substances outside the negative electrode, thereby improving the release rate of lithium ions, improving the use stability of the lithium ion battery, and reducing the cost of the lithium ion battery.

[0066] Further, the thickness of the lithium foil strip is D, wherein D satisfies: 5 μm≤D≤20 μm. When the thickness of the lithium foil strip is less than 5 μm, the capacity of the negative electrode pre-stored active lithium is less, which cannot compensate the loss of active lithium in the formation process and the cycling process, and is not conducive to the performance of the energy density and the cycle life; when the thickness of the lithium foil strip is greater than 20 μm, the pre-stored lithium capacity of the negative electrode is significantly increased, at this time, the negative electrode cannot bear the active lithium from the positive electrode during charging, and the lithium precipitation phenomenon is prone to occur at the negative electrode interface, which greatly increases the side reaction at the negative electrode interface, thereby reducing the cycle life of the battery. Therefore, by making the thickness D of the lithium foil strip satisfy: 5 μm≤D≤20 μm, the cycle life of the battery is prolonged while the initial efficiency of the battery is ensured.

[0067] According to the second aspect of the battery pack of the present disclosure, at least one lithium ion battery according to the first aspect of the present disclosure is included.

[0068] According to the battery pack of the present disclosure, the electrochemical stability of the battery pack is improved, and the cycle life of the battery pack is improved.

[0069] According to the third aspect of the battery pack of the present disclosure, at least one lithium ion battery according to the first aspect of the present disclosure is included, or at least one battery pack according to the second aspect of the present disclosure is included.

[0070] According to the battery pack of the present disclosure, the use stability and reliability of the battery pack are improved, and the reliability of charging and discharging of the battery pack is improved, thereby improving the market competitiveness of the battery pack.

[0071] According to the fourth aspect of the power consumption equipment of the present disclosure, at least one lithium ion battery according to the first aspect of the present disclosure is included, or at least one battery pack according to the second aspect of the present disclosure is included, or at least one battery pack according to the third aspect of the present disclosure is included.

[0072] According to the power consumption equipment of the present disclosure, the power supply of the power consumption equipment is more reliable, thereby improving the use experience and use safety of the power consumption equipment, and further improving the market competitiveness of the power consumption equipment.

[0073] The embodiments of the present disclosure are described in detail below. It should be noted that the embodiments described below are exemplary and are used to explain the present disclosure, and cannot be understood as a limitation of the present disclosure. In addition, if not specifically stated, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also easily obtained by those skilled in the art.

[0074] Preparation of lithium ion battery

[0075] 1. Preparation of non-aqueous electrolyte

[0076] Fluoroethylene carbonate, propylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in proportion to be uniform, and the mixed solvent is 100% by mass, wherein the fluoroethylene carbonate is added in the percentage in the examples, the propylene carbonate is added in a mass ratio of 10%, and the methyl ethyl carbonate and the diethyl carbonate are added to make up 100% of the mixed solvent in a mass ratio of 1:1. Then, 1 mol / L lithium hexafluorophosphate is added, and then the compounds represented by Structural Formulas (1) to (3) are added in the corresponding percentage based on the total mass of the non-aqueous electrolyte to obtain the electrolyte used in the examples.

[0077] 2. Preparation of positive electrode

[0078] The positive electrode active material (NCM523, NCM622, NCM712, NCM811, or NCM9055), the conductive agent (carbon nanotube CNT), and the binder (polyvinylidene fluoride PVDF) are mixed in a mass ratio of 95.8:1.7:2.5, and then they are 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 an aluminum tab is welded on using an ultrasonic welding machine to obtain a positive electrode.

[0079] 3. Preparation of negative electrode

[0080] The negative electrode active material (silicon-carbon material), the conductive agent (CNT), the binder (polyacrylic acid), and the thickening agent (sodium carboxymethyl cellulose CMC) are mixed in a mass ratio of 94.2:1.1:4.7:0.5, and then they are dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil, dried, calendered, and vacuum dried to obtain a negative electrode without pre-stored lithium.

[0081] The lithium foil strip is folded in a "Z" shape, and then the negative electrode is placed in the interstices, ensuring that the outermost side is the lithium foil. After the core package is completed, high-temperature adhesive tape is used for fixation, and then the core package is placed in an aluminum foil packaging bag. The core package is extruded at 105°C and 2Mpa pressure for 16h, and then the heating is stopped and the pressure is unloaded. After the temperature drops to room temperature, the aluminum foil packaging bag is opened, and the pre-stored lithium negative electrode sheet is taken out and welded with a nickel tab using an ultrasonic welding machine to obtain a pre-stored lithium negative electrode.

[0082] 4. Preparation of battery cell

[0083] The separator is folded in a "Z" shape, and then the positive electrode and the pre-stored lithium negative electrode are placed in the interstices, ensuring that the outermost side is the two negative electrodes. Usually, 7 positive electrodes and 8 negative electrodes are used. After the core package is completed, high-temperature adhesive tape is used for fixation, and then the core package is placed in an aluminum foil packaging bag. The core package is vacuum baked at 85°C for 48h to obtain a battery cell ready for liquid injection.

[0084] 5. Liquid injection, formation and capacity equalization of the battery cell

[0085] The electrolyte prepared above was injected into the battery cell in a dry room with dew point controlled below -40°C, vacuum sealed, and left at 45°C for 24 hours. Then the first charge formation was carried out as follows: 0.05C constant current charging for 120 min, 0.2C constant current charging for 240 min, left at 45°C for 36 hours, and vacuum sealed again.

[0086] Then constant current constant voltage charging was carried out at 0.2C to 4.4V (NCM523) / 4.3V (NCM622) / 4.25V (NCM712) / 4.2V (NCM811) / 4.2V (NCM9055), left at room temperature for 24 hours, and then constant current discharging to 3.0V at 0.2C, followed by 2 cycles at the same current size to complete the capacity equalization.

[0087] Performance test

[0088] 1) Room temperature cycle test

[0089] The battery in the example was placed in a thermostat at 25°C, left for more than 4h to ensure that the battery body temperature was stable at 25°C, and then constant current constant voltage charging was carried out at 0.5C to 4.4V (NCM523) / 4.3V (NCM622) / 4.25V (NCM712) / 4.2V (NCM811) / 4.2V (NCM9055), followed by constant current discharging to 3.0V at 0.5C, and the cycle was repeated to record the first discharge capacity and the last discharge capacity. The capacity retention rate was calculated using the following formula:

[0090] Capacity retention rate = last discharge capacity / first discharge capacity x 100%.

[0091] 2) Room temperature cycle gas production test

[0092] The volume of the battery before and after the cycle, i.e. after the capacity equalization, was tested using the drainage method, the volume before the cycle was recorded as V1, and the volume after the cycle was recorded as V2, and the room temperature cycle gas production was calculated using the following formula:

[0093] Room temperature cycle gas production = (V2-V1) / battery rated capacity.

[0094] Table 1: Content and test results of examples 1-47 and comparative examples 1-5

[0095] Result analysis

[0096] As can be seen from Table 1, when the electrolyte contains both fluoroethylene carbonate and at least one of the compounds shown in structural formulas (1)-(3), the cycle capacity retention rate of the battery at room temperature is obviously improved, and the gas production at room temperature is also obviously reduced. This is because when FEC and the compounds shown in structural formulas (1)-(3) are not contained, the negative electrode reacts with the electrolyte due to continuous expansion and contraction, and the SEI film mainly containing inorganic component LiF or the SEI film containing organic component Si-O cannot effectively protect the negative electrode. Only when both are used together can the negative electrode be better protected and the side reaction be inhibited, and the cycle life be improved.

[0097] As can be seen from Comparative Examples 10-31 and Comparative Examples 3-5, different amounts of the compounds shown in structural formulas (1)-(3) can improve the cycle capacity retention rate and the gas production at room temperature of the battery, and the same rule is also applicable when the compounds shown in structural formulas (1)-(3) are mixed, that is, the compounds shown in structural formulas (1)-(3) can all form a film together with FEC to protect the negative electrode, and there is no deterioration when mixed.

[0098] As can be seen from Comparative Examples 32-41 and Comparative Example 4, the addition of 3%-40% content of fluoroethylene carbonate can improve the cycle capacity retention rate and the gas production at room temperature of the battery, and the effect is more obvious when the FEC content is 20%-35%. This is because the FEC in this content range can generate an appropriate amount of LiF to protect the negative electrode, and when the FEC content is too high, it will become a gas source and deteriorate the cycle performance.

[0099] As can be seen from Comparative Example 1, Examples 42-44 and Comparative Example 1, when the content of the positive active material Ni is <60%, the cycle performance of the battery system at room temperature is obviously poor. It is speculated that the electrolyte and the additive have poor high-pressure stability. In order to obtain high capacity, the application voltage of NCM523 positive electrode is usually greater than 4.4V, at this time, the stability of the positive CEI film and the electrolyte is required to be higher, and the electrolyte and the additive in the present disclosure are not suitable for high-voltage battery systems.

[0100] As can be seen from Comparative Example 1, Examples 45-47 and Comparative Example 2, when the content of the negative active material Si is <40%, the cycle performance of the battery system at room temperature is obviously poor. It is speculated that at this time, FEC is in an excessive state, and the excessive FEC has poor stability and is decomposed to produce gas, which deteriorates the cycle performance.

[0101] In the description of the disclosure, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the disclosure. In the description of the disclosure, the exemplary description of the above terms does not necessarily mean the same embodiment or example.

[0102] Although the embodiments of the disclosure have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the disclosure, and the scope of the disclosure is defined by the claims and their equivalents.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises: a positive electrode; a negative electrode comprising a negative electrode active material, the mass percentage of silicon in the negative electrode active material being greater than 40%; and an electrolyte comprising fluoroethylene carbonate and a siloxane additive.

2. The lithium-ion battery of claim 1, wherein, The siloxane-based additive includes at least one of the compounds of formula (1) - formula (3): R1to R3in formulae (1) to (3) are each selected from any one of hydrogen, halogen, phenyl, C1to C5halogenated or non-halogenated hydrocarbon group, C1to C5halogenated or non-halogenated alkenyl group, C1to C5halogenated or non-halogenated alkynyl group, C1to C5halogenated or non-halogenated cyano group, C1to C5halogenated or non-halogenated alkylsilyl group, C1to C5halogenated or non-halogenated alkoxy group, C1to C5halogenated or non-halogenated sulfate group, C1to C5halogenated or non-halogenated sulfite group, and C1to C5halogenated or non-halogenated sulfonate group. 13 R1to R3in formulae (1) to (3) are each selected from any one of hydrogen, halogen, phenyl, C1to C5halogenated or non-halogenated hydrocarbon group, C1to C5halogenated or non-halogenated alkenyl group, C1to C5halogenated or non-halogenated alkynyl group, C1to C5halogenated or non-halogenated cyano group, C1to C5halogenated or non-halogenated alkylsilyl group, C1to C5halogenated or non-halogenated alkoxy group, C1to C5halogenated or non-halogenated sulfate group, C1to C5halogenated or non-halogenated sulfite group, and C1to C5halogenated or non-halogenated sulfonate group.

3. The lithium-ion battery of claim 2, wherein, The total additive amount of the compounds represented by the formulae (1)-(3) is 0.01%-10% by mass.

4. The lithium-ion battery of claim 3, wherein, The total additive amount of the compounds represented by the formulae (1)-(3) is 0.01%-8% by mass.

5. The lithium-ion battery of any one of claims 2-4, wherein, The additive amount of the fluoroethylene carbonate is 2%-50% by mass.

6. The lithium-ion battery of claim 5, wherein, The additive amount of the fluoroethylene carbonate is 3%-40% by mass.

7. The lithium-ion battery of any one of claims 2-6, wherein, R1to R3in the formula (1) to the formula (3) 13 each is selected from any one of C1to C3halogenated or non-halogenated hydrocarbon group, C1to C3halogenated or non-halogenated alkenyl group, C1to C3halogenated or non-halogenated alkynyl group, C1to C3halogenated or non-halogenated cyano group, C1to C3halogenated or non-halogenated alkylsilyl group, C1to C3halogenated or non-halogenated alkoxy group, C1to C3halogenated or non-halogenated sulfate group, C1to C3halogenated or non-halogenated sulfite group, C1to C3halogenated or non-halogenated sulfonate group, and C1to C3halogenated or non-halogenated phenyl group.

8. The lithium-ion battery of claim 7, wherein, R1to R4in the formula (1) - the formula (3) 13 any one selected from the group consisting of C1to C3halogenated or non-halogenated hydrocarbon group, C1to C3halogenated or non-halogenated alkenyl group, C1to C3halogenated or non-halogenated alkynyl group and C1to C3halogenated or non-halogenated cyano group, respectively.

9. The lithium-ion battery of any one of claims 2-8, wherein, The compounds of formula (1) are selected from at least one of the following compounds:

10. The lithium-ion battery of any one of claims 2-9, wherein, The formula (2) is selected from at least one of the following compounds:

11. The lithium-ion battery of any one of claims 2-10, wherein, said formula (3) is selected from at least one of the following compounds 12. The lithium-ion battery of any one of claims 1-11, wherein, The electrolyte further comprises a solvent and a lithium salt, wherein the solvent comprises at least one of a carbonate solvent, a carboxylate solvent, and an ether solvent.

13. The lithium-ion battery of claim 12, wherein, The carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the carboxylate solvent comprises 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; and the ether solvent comprises at least one of dimethyl ether of ethylene glycol, diethyl ether of ethylene glycol, 1,3-dioxolane, dimethoxy methane, dimethyl ether of diethylene glycol, dimethyl ether of triethylene glycol, dimethyl ether of tetraethylene glycol, dimethyl ether of polyethylene glycol, dimethyl ether of isosorbide, dimethyl ether of dipropylene glycol, 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-hexafluoroisopropyl methyl ether, and 2,2,2-trifluoroethyl ether.

14. The lithium-ion battery of claim 12 or 13, wherein, The lithium salt comprises 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 of any one of claims 1-14, wherein, The positive electrode includes a positive electrode active material including: LiNi x Co y Mn z L (1-x-y-z) O2, wherein 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 of any one of claims 1-15, wherein, The negative electrode further comprises a pre-stored lithium material connected to the negative electrode active material to replenish consumption of active lithium, wherein the capacity of the pre-stored lithium material for releasing lithium ions accounts for 15%-25% of the capacity of the positive electrode.

17. The lithium-ion battery of claim 16, wherein, The pre-stored lithium material is a lithium foil strip comprising a plurality of bent segments, and at least part of the lithium foil strip is arranged at the outer periphery of the negative electrode active material.

18. The lithium-ion battery of claim 17, wherein, The thickness of the lithium foil strip is D, wherein the D satisfies 5 μm≤D≤20 μm.

19. A battery pack, characterized by The lithium ion battery comprises at least one lithium ion battery according to any one of claims 1-18.

20. A battery pack, characterized by A lithium ion battery comprising at least one lithium ion battery according to any one of claims 1 to 18, or a battery pack comprising at least one battery according to claim 19.

21. An electrical device, comprising: A lithium ion battery comprising at least one lithium ion battery according to any one of claims 1 to 18, or a battery pack comprising at least one battery according to claim 19, or a battery pack comprising at least one battery pack according to claim 20.

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