Secondary battery and electronic device

Abstract

The present invention provides a secondary battery and an electronic device, the secondary battery comprising positive electrode pieces, negative electrode pieces and an electrolyte, the electrolyte comprising vinylene carbonate, the mass percentage a of vinylene carbonate being 0.1%-3% relative to the total mass of the electrolyte, the positive electrode pieces comprising a positive electrode active material, the positive electrode active material comprising elemental carbon, the mass percentage b of elemental carbon being 0.5%-6% relative to the total mass of the positive electrode active material. By satisfying the above characteristics, the secondary battery provided by the present invention can be made to have good cycle characteristics and storage characteristics as well as excellent dynamic characteristics.

Description

[Technical Field]

[0001] The present invention relates to the field of electrochemical technology, and in particular to secondary batteries and electronic devices. [Background technology]

[0002] At present, secondary batteries are widely used in fields such as electric vehicles, consumer electronics, and energy storage devices, and have gradually become the mainstream battery in the above fields due to their advantages such as high energy density and no memory effect. In particular, the electric vehicle, power, and energy storage industries have entered a stage of rapid development, providing a wide range of application prospects for the use of secondary batteries.

[0003] Due to the properties of lithium iron phosphate positive electrode material itself, secondary batteries constructed using it have the characteristics of high safety, long service life, excellent high-temperature characteristics, low cost, and environmental friendliness. Compared with other types of secondary batteries, it has great advantages and good application prospects. Despite these advantages, as the requirements for secondary battery properties in fields such as power and energy storage become increasingly higher, how to further improve the cycle characteristics, storage characteristics, and dynamic characteristics of lithium-ion batteries remains of great value. Summary of the Invention

[0004] The present invention provides a secondary battery and an electronic device that have good cycle characteristics and storage characteristics as well as excellent dynamic characteristics.

[0005] A first aspect of the present invention provides a secondary battery, the secondary battery comprising positive electrode pieces, negative electrode pieces, and an electrolyte, the electrolyte comprising vinylene carbonate, wherein the mass percentage a of the vinylene carbonate is 0.1% to 3% relative to the total mass of the electrolyte, and the positive electrode pieces comprise a positive electrode active material, the positive electrode active material comprising elemental carbon, wherein the mass percentage b of the carbon is 0.5% to 6% relative to the total mass of the positive electrode active material. The electrolyte and positive electrode pieces in the secondary battery provided by the present invention satisfy the above characteristics, thereby simultaneously improving the ionic conductivity and electronic conductivity of the secondary battery and reducing the rate of electrolyte consumption, enabling the secondary battery to have good cycle characteristics and storage characteristics as well as excellent kinetic characteristics.

[0006] In some embodiments of the present invention, the a is 0.1% to 2.5%, preferably 0.5% to 2.5%, and more preferably 0.8% to 2.5%, and / or the b is 0.5% to 5%, preferably 0.5% to 4.5%. By controlling the values ​​of a and b within the above ranges, the cycle characteristics, storage characteristics, and dynamic characteristics of the secondary battery can be further improved.

[0007] In some embodiments of the present invention, the ratio of a to b is 0.22 to 6. By controlling the ratio of a to b within the above range, it is possible to not only form a high-quality electrolyte interfacial film on the surface of the positive electrode, but also to prevent deterioration of the interfacial impedance, thereby further improving the cycle characteristics, storage characteristics, and dynamic characteristics of the secondary battery.

[0008] In some embodiments of the present invention, the electrolyte solution further comprises a nitrogen-containing heterocyclic compound, and the mass percentage c of the nitrogen-containing heterocyclic compound is 0.01% to 1% relative to the total mass of the electrolyte solution. By controlling the mass percentage c of the nitrogen-containing heterocyclic compound within the above range, the cycle characteristics of the secondary battery can be improved.

[0009] In some embodiments of the present invention, the ratio of a to c is 2 to 60. By controlling the ratio of a to c within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0010] In some embodiments of the present invention, the nitrogen-containing heterocyclic compound comprises the following compound (Formula I) or compound (Formula II): [ka]

[0011] where R1, R2, and R3 are each independently selected from the group consisting of a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, a substituted or unsubstituted C2-C5 alkynylene group, and a substituted or unsubstituted C3-C5 allenylene group, and when substituted, the substituent is a halogen atom. By selecting a nitrogen-containing heterocyclic compound within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0012] In some embodiments of the present invention, the electrolyte solution further contains an isocyanate compound, and the mass percentage d of the isocyanate compound is 0.01% to 2% relative to the total mass of the electrolyte solution. By controlling the mass percentage d of the isocyanate compound within the above range, the cycle characteristics of the secondary battery can be improved.

[0013] In some embodiments of the present invention, the ratio of a to d is 2 to 60. By controlling the ratio of a to d within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0014] In some embodiments of the present invention, the isocyanate compound comprises the following compound (Formula III) or compound (Formula IV): [ka]

[0015] The isocyanate compound contains at least one -NCO group, and R3 and R4 are each independently selected from a C1 to C7 hydrocarbon group or a C1 to C7 aromatic hydrocarbon group. By selecting an isocyanate compound within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0016] In some embodiments of the present invention, the electrolyte solution further contains an acid anhydride compound, and the mass percentage e of the acid anhydride compound is 0.01% to 2% relative to the total mass of the electrolyte solution. By controlling the mass percentage e of the acid anhydride compound within the above range, the cycle characteristics of the secondary battery can be improved.

[0017] In some embodiments of the present invention, the ratio of a to e is 2 to 60. By controlling the ratio of a to e within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0018] In some embodiments of the present invention, the acid anhydride compound includes at least one of maleic anhydride, dimethylmaleic anhydride, citraconic anhydride, glutaric anhydride, succinic anhydride, norbornene dicarboxylic anhydride, diphenic anhydride, pyridine dicarboxylic anhydride, pyrazine dicarboxylic anhydride, 2,3-pyridine dicarboxylic anhydride, pyridine-3,4-dicarboxylic anhydride, and 2,3-pyrazine dicarboxylic anhydride. By selecting an acid anhydride compound within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0019] In some embodiments of the present invention, the electrolyte solution further contains a silane compound, and the mass percentage f of the silane compound is 0.01% to 2% relative to the total mass of the electrolyte solution. By controlling the mass percentage f of the silane compound within the above range, the cycle characteristics of the secondary battery can be improved.

[0020] In some embodiments of the present invention, the ratio of a to f is 2 to 60. By controlling the ratio of a to f within the above range, the cycle characteristics, storage characteristics, and dynamic characteristics of the secondary battery can be further improved.

[0021] In some embodiments of the present invention, the silane compound includes at least one of tetramethyldivinyldisiloxane, bis(trimethylsilyl)malonate, diphenyldifluorosilane, heptamethyldisilazane, tetramethyldivinyldisiloxane, tetraethoxysilane, 2-cyanoethyltriethoxysilane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, and vinyltriethoxysilane. By selecting a silane compound within the above range, the cycle characteristics, storage characteristics, and dynamic characteristics of the secondary battery can be further improved.

[0022] In some embodiments of the present invention, the electrolyte solution further comprises a nitrogen-containing heterocyclic boron trifluoride complex, and the mass percentage (g) of the nitrogen-containing heterocyclic boron trifluoride complex is 0.01% to 1% relative to the total mass of the electrolyte solution. By controlling the mass percentage (g) of the nitrogen-containing heterocyclic boron trifluoride complex within the above range, the cycle characteristics of the secondary battery can be improved.

[0023] In some embodiments of the present invention, the ratio of a to g is 2 to 60. By controlling the ratio of a to g within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0024] In some embodiments of the present invention, the nitrogen-containing heterocyclic boron trifluoride complex comprises at least one of boron trifluoride pyridine, boron trifluoride pyrazine, boron trifluoride pyridazine, 2-fluoropyridine boron trifluoride complex, boron trifluoride pyrimidine, boron trifluoride pyrrole, boron trifluoride pyrazole, and boron trifluoride imidazole. By selecting a nitrogen-containing heterocyclic boron trifluoride complex within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0025] In some embodiments of the present invention, the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0026] A second aspect of the present invention provides an electronic device including the secondary battery according to any one of the above embodiments, and therefore the electronic device provided by the present invention has good usage characteristics.

[0027] The beneficial effects of the present invention are as follows: The present invention provides a secondary battery and an electronic device, the secondary battery comprising positive electrode pieces, negative electrode pieces and an electrolyte, the electrolyte comprising vinylene carbonate, the mass percentage a of the vinylene carbonate being 0.1%-3% relative to the total mass of the electrolyte, the positive electrode pieces comprising a positive electrode active material, the positive electrode active material comprising elemental carbon, the mass percentage b of the carbon being 0.5%-6% relative to the total mass of the positive electrode active material. By satisfying the above characteristics, the secondary battery provided by the present invention can simultaneously improve the ionic conductivity and electronic conductivity of the secondary battery and reduce the consumption rate of the electrolyte, allowing the secondary battery to have good cycle characteristics and storage characteristics as well as excellent dynamic characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0029] In the following description, the present invention will be described using a lithium ion battery as an example of a secondary battery, but the secondary battery of the present invention is not limited to a lithium ion battery. Specific technical solutions are as follows:

[0030] A first aspect of the present invention provides a secondary battery, the secondary battery comprising positive electrode pieces, negative electrode pieces and an electrolyte, the electrolyte comprising vinylene carbonate, wherein a mass percentage a of the vinylene carbonate is 0.1% to 3% relative to the total mass of the electrolyte, the positive electrode pieces comprising a positive electrode active material, the positive electrode active material comprising elemental carbon, wherein a mass percentage b of the carbon element is 0.5% to 6% relative to the total mass of the positive electrode active material.

[0031] According to the inventors' research, while carbon coating is typically used to improve the electronic and ionic conductivity of positive electrode active materials, the carbon coating increases the reactive active area between the positive electrode active material and the electrolyte, increasing side reactions. On the other hand, vinylene carbonate has a low oxidation potential and can form a film on the surface of the positive electrode active material at a rapid rate, thereby suppressing side reactions between the positive electrode active material and the electrolyte. By adding a specific amount of vinylene carbonate to a secondary battery and ensuring that the positive electrode active material contains a specific amount of carbon, the ionic and electronic conductivity of the secondary battery can be simultaneously improved and the rate of electrolyte consumption can be reduced, resulting in a secondary battery with good cycle and storage characteristics as well as excellent dynamic characteristics.

[0032] Specifically, the mass percentage a of vinylene carbonate may be 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, or 3%. Alternatively, a may be within a range consisting of any two of the above values. Preferably, a is 0.1% to 2.5%. More preferably, a is 0.5% to 2.5%. More preferably, a is 0.8% to 2.5%. The mass percentage b of carbon element may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6%. Alternatively, b may be within a range consisting of any two of the above values. Preferably, b is 0.5% to 5%. More preferably, b is 0.5% to 4.5%. If the mass percentage of vinylene carbonate is too low (for example, less than 0.1%), the protective film formed on the surfaces of the positive and negative electrodes is insufficient, interfacial side reactions and transition metal elution cannot be suppressed, and the effects of improving the cycle characteristics and high-temperature storage characteristics of the secondary battery are not significant. On the other hand, if the mass percentage of vinylene carbonate is too high (for example, more than 3%), the film formation impedance at the interface between the positive and negative electrodes becomes too high, leading to poor charge-discharge characteristics, particularly at low temperatures. If the mass percentage of carbon element is too low (for example, less than 0.5%), dynamic characteristics will be poor. On the other hand, if the mass percentage of carbon element is too high (for example, more than 6%), cycle characteristics and storage characteristics will be poor. By controlling the mass percentage of vinylene carbonate in the electrolyte and the mass percentage of carbon element in the positive electrode active material within the ranges of the present invention, it is possible to form a film by polymerization on the positive electrode surface, and at the same time, a stable solid electrolyte interfacial film is also formed on the negative electrode interface, so that the secondary battery has good cycle characteristics and storage characteristics as well as excellent kinetic characteristics.

[0033] In the secondary battery provided by the present invention, the electrolyte contains vinylene carbonate, the positive electrode active material contains carbon, and by controlling the mass percentages of vinylene carbonate and carbon within the ranges of the present invention, the vinylene carbonate film formation efficiency is high, a high-quality electrolyte interfacial film is formed on the surface of the carbon-coated positive electrode, and the interface can be effectively protected. The carbon coating also increases the ionic conductivity of the positive electrode active material, thereby preventing deterioration of interfacial impedance. These two factors work synergistically to ensure that the secondary battery has good cycle characteristics and storage characteristics as well as excellent dynamic characteristics.

[0034] In the present invention, the ratio of a to b indicates the content of vinylene carbonate per unit carbon content and further indicates the state of formation of a solid electrolyte interfacial film on the carbon coated on the positive electrode surface. In some embodiments of the present invention, the ratio of a to b is 0.22 to 6. Specifically, the ratio of a to b may be 0.22, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, or 6. Alternatively, the ratio of a to b may be within a range consisting of any two of the above values. By controlling the ratio of a to b within the above range, it is possible to provide a high-quality electrolyte interfacial film on the surface of the positive electrode, thereby reducing the rate of electrolyte consumption and preventing deterioration of the interfacial impedance, thereby providing the secondary battery with good cycle characteristics, storage characteristics, and dynamic characteristics.

[0035] In some embodiments of the present invention, the electrolyte further comprises a nitrogen-containing heterocyclic compound, and the mass percentage c of the nitrogen-containing heterocyclic compound relative to the total mass of the electrolyte is 0.01% to 1%. Specifically, c may be 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1%. Alternatively, c may be in a range consisting of any two of the above values. Adding a nitrogen-containing heterocyclic compound to the electrolyte forms a stable solid electrolyte interfacial film on the negative electrode surface during the formation process, preventing the reduction and decomposition of other components in the electrolyte on the negative electrode surface. This improves the cycle characteristics of the secondary battery and suppresses gas generation during storage and cycling. It also forms a good positive electrode electrolyte interfacial film on the positive electrode interface, preventing electrolyte decomposition and consumption at the positive electrode. Furthermore, the nitrogen-containing heterocyclic compound in the electrolyte reacts with traces of water or HF to remove traces of water and HF from the electrolyte, reducing interfacial side reactions and reducing the elution of positive electrode transition metals, thereby suppressing gas generation and improving cycle characteristics and safety. Controlling the mass percentage c of the nitrogen-containing heterocyclic compound within the above range achieves appropriate negative electrode interfacial impedance and good charge / discharge characteristics. It also strengthens the electrolyte interfacial film on the surfaces of the positive and negative electrodes, improving the cycle characteristics of the secondary battery.

[0036] In some embodiments of the present invention, the ratio of a to c is 2 to 60. By controlling the ratio of a to c within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0037] In some embodiments of the present invention, the nitrogen-containing heterocyclic compound comprises the following compound (Formula I) or compound (Formula II): [ka]

[0038] wherein R1, R2, and R3 are each independently selected from a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, a substituted or unsubstituted C2-C5 alkynylene group, and a substituted or unsubstituted C3-C5 allenylene group, and when substituted, the substituent is a halogen atom.

[0039] By selecting a nitrogen-containing heterocyclic compound within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0040] In some embodiments of the present invention, the electrolyte solution further contains an isocyanate compound, and the mass percentage d of the isocyanate compound relative to the total mass of the electrolyte solution is 0.01% to 2%. Specifically, d may be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. Alternatively, d may be in a range consisting of any two of the above values. Isocyanate compounds are highly active and easily react with water and acid, and therefore can exhibit certain moisture and acid removal effects. Adding an isocyanate compound to the electrolyte can effectively reduce the generation of HF in the electrolyte and reduce the elution of transition metals from the positive electrode, thereby suppressing gas generation and improving cycle characteristics and safety. Controlling the mass percentage d of the isocyanate compound within the above range can achieve appropriate negative electrode interfacial impedance and good charge / discharge characteristics, further strengthening the electrolyte interfacial film on the surfaces of the positive and negative electrodes and improving the cycle characteristics of the secondary battery.

[0041] In some embodiments of the present invention, the ratio of a to d is 2 to 60. By controlling the ratio of a to d within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0042] In some embodiments of the present invention, the isocyanate compound comprises the following compound (Formula III) or compound (Formula IV): [ka]

[0043] Here, the isocyanate compound contains at least one -NCO group, and R3 and R4 are each independently selected from a C1 to C7 hydrocarbon group or a C1 to C7 aromatic hydrocarbon group.

[0044] By selecting an isocyanate compound within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0045] In some embodiments of the present invention, the electrolyte further contains an acid anhydride compound, and the mass percentage e of the acid anhydride compound relative to the total mass of the electrolyte is 0.01% to 2%. Specifically, e may be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. Alternatively, e may be within a range consisting of any two of the above values. The acid anhydride compound neutralizes residual alkaline groups on the surface of the positive electrode material and suppresses the decomposition of the alkali in the carbonate ester-based solvent. In addition, the acid anhydride compound can react with trace amounts of moisture in the secondary battery to produce organic acids, thereby reducing the generation of strong acids and further reducing damage to the material. Therefore, acid anhydride compounds have the effect of improving high-temperature characteristics and reducing gas generation in batteries. Adding an acid anhydride compound to the electrolyte can improve the cycle characteristics of secondary batteries and suppress gas generation during storage and cycling. Controlling the mass percentage e of the acid anhydride compound within the above range can achieve appropriate negative electrode interfacial impedance and good charge / discharge characteristics, and further strengthen the electrolyte interfacial film on the surfaces of the positive and negative electrodes, thereby improving the cycle characteristics of secondary batteries.

[0046] In some embodiments of the present invention, the ratio of a to e is 2 to 60. By controlling the ratio of a to e within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0047] In some embodiments of the present invention, the acid anhydride compound includes at least one of maleic anhydride, dimethylmaleic anhydride, citraconic anhydride, glutaric anhydride, succinic anhydride, norbornene dicarboxylic anhydride, diphenic anhydride, pyridine dicarboxylic anhydride, pyrazine dicarboxylic anhydride, 2,3-pyridine dicarboxylic anhydride, pyridine-3,4-dicarboxylic anhydride, and 2,3-pyrazine dicarboxylic anhydride. By selecting an acid anhydride compound within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0048] In some embodiments of the present invention, the electrolyte further comprises a silane compound, and the mass percentage (f) of the silane compound relative to the total mass of the electrolyte is 0.01% to 2%. Specifically, (f) may be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. Alternatively, (f) may be a range consisting of any two of the above values. Because silane compounds can react with HO or HF, they have excellent moisture and acid removal effects, preventing the continued occurrence of subsequent side reactions. This type of additive also forms a stable, low-impedance interfacial film at the interface, thereby improving the electrochemical characteristics of secondary batteries. Controlling the mass percentage f of the silane compound within the above range is advantageous for film formation of vinylene carbonate, increases the density of the film, strengthens the electrolyte interfacial film on the surfaces of the positive and negative electrodes, improves the effects of moisture removal and acid removal, and improves the cycle characteristics of the secondary battery.

[0049] In some embodiments of the present invention, the ratio of a to f is 2 to 60. By controlling the ratio of a to f within the above range, the cycle characteristics, storage characteristics, and dynamic characteristics of the secondary battery can be further improved.

[0050] In some embodiments of the present invention, the silane compound includes at least one of tetramethyldivinyldisiloxane, bis(trimethylsilyl)malonate, diphenyldifluorosilane, heptamethyldisilazane, tetramethyldivinyldisiloxane, tetraethoxysilane, 2-cyanoethyltriethoxysilane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, and vinyltriethoxysilane. By selecting a silane compound within the above range, the cycle characteristics, storage characteristics, and dynamic characteristics of the secondary battery can be further improved.

[0051] In some embodiments of the present invention, the electrolyte further includes a nitrogen-containing heterocyclic boron trifluoride complex, and the mass percentage (g) of the nitrogen-containing heterocyclic boron trifluoride complex is 0.01% to 1% relative to the total mass of the electrolyte. Specifically, g may be 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1%. Alternatively, g may be in a range consisting of any two of the above values. The nitrogen-containing heterocyclic boron trifluoride complex includes two active functional groups: a Lewis acid (BF3) and a nitrogen-containing heterocyclic organic base. The nitrogen-containing heterocyclic organic base not only neutralizes acidic substances in the electrolyte but also coordinates with transition metal ions in the electrolyte, suppressing side reactions of the transition metal ions at the anode surface. Meanwhile, -BF3 is a boron-containing Lewis acid that acts as an anion receptor, enhancing the dissociation of lithium salts and lithium ion mobility, thereby reducing impedance. Adding a nitrogen-containing heterocyclic boron trifluoride complex to the electrolyte reduces interfacial side reactions and the influence of transition metals on the anode, thereby improving the cycle and storage characteristics of secondary batteries. Controlling the mass percentage (g) of the nitrogen-containing heterocyclic boron trifluoride complex within the above ranges achieves optimal anode interfacial impedance and favorable charge / discharge characteristics. Furthermore, it strengthens the electrolyte interfacial film on the cathode and anode surfaces, improving the cycle characteristics of secondary batteries.

[0052] In some embodiments of the present invention, the ratio of a to g is 2 to 60. By controlling the ratio of a to g within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0053] In some embodiments of the present invention, the nitrogen-containing heterocyclic boron trifluoride complex comprises at least one of boron trifluoride pyridine, boron trifluoride pyrazine, boron trifluoride pyridazine, 2-fluoropyridine boron trifluoride complex, boron trifluoride pyrimidine, boron trifluoride pyrrole, boron trifluoride pyrazole, and boron trifluoride imidazole. By selecting a nitrogen-containing heterocyclic boron trifluoride complex within the above range, the cycle characteristics and storage characteristics of the secondary battery can be further improved.

[0054] The electrolyte of the secondary battery of the present invention further contains a lithium salt and a nonaqueous solvent. The lithium salt may include at least one of various lithium salts commonly used in the art, such as LiPF, LiBF, LiAsF, LiClO, LiB(CH), LiCHSO, LiCFSO, LiN(SOCF), LiC(SOCF), LiSiF, lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate. In the present invention, there are no particular limitations on the concentration of the lithium salt in the electrolyte, as long as the object of the present invention can be achieved. For example, the concentration of the lithium salt in the electrolyte solution is 0.4 mol / L to 2 mol / L, preferably 0.5 mol / L to 1.2 mol / L. For example, the concentration of the lithium salt in the electrolyte solution may be 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2 mol / L. Alternatively, the concentration of the lithium salt in the electrolyte solution may be within a range consisting of any two of the above values. In the present invention, there are no particular limitations on the nonaqueous solvent, as long as the object of the present invention can be achieved. For example, the nonaqueous solvent may include at least one of a carbonate ester compound, a carboxylic acid ester compound, an ether compound, and other organic solvents, but is not limited thereto. The carbonate ester compound may include at least one of a chain carbonate ester compound, a cyclic carbonate ester compound, and a fluorocarbonate ester compound, but is not limited thereto. The chain carbonate compound may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (MEC). The cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC).The fluorocarbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. The carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, and caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. The mass percentage of the nonaqueous solvent in the electrolyte may be 70% to 95%, for example, 70%, 75%, 80%, 85%, 90%, or 95%. Alternatively, the mass percentage of the nonaqueous solvent in the electrolyte may be within a range consisting of any two of the above values.

[0055] In the present invention, the secondary battery further includes a positive electrode piece, which includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The phrase "a positive electrode active material layer provided on at least one surface of the positive electrode current collector" refers to the positive electrode active material layer being provided on one surface of the positive electrode current collector in the thickness direction thereof, or on two surfaces of the positive electrode current collector in the thickness direction thereof. The "surface" here may be the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector, and is not particularly limited in the present invention as long as the objective of the present invention is achieved. In the present invention, the positive electrode current collector is not particularly limited, and may be any material as long as the objective of the present invention is achieved, such as aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0056] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material of the present invention may include at least one of lithium iron phosphate and lithium manganese iron phosphate. The positive electrode active material of the present invention may have a coating layer on its surface or may be mixed with another compound having a coating layer. In the present invention, the other compound is not particularly limited as long as it achieves the objective of the present invention. For example, the other compound may be at least one of nickel cobalt manganese lithium oxide (e.g., common NCM811, NCM622, NCM523, NCM111), nickel cobalt lithium aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO), lithium manganese oxide, lithium manganese iron phosphate, and lithium titanate. The coating layer may include at least one of an oxide of the applied element, a hydroxide of the applied element, an oxyhydroxide of the applied element, an oxycarbonate of the applied element, and a hydroxycarbonate of the applied element. The compound may be amorphous or crystalline. The applied element may include one or more of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, and Zr. In the present invention, there is no particular limitation on the method for applying the coating layer, as long as the object of the present invention can be achieved, and for example, spraying or dipping may be used.

[0057] The positive electrode active material layer further includes a conductive agent and a binder. The present invention does not limit the types of conductive agent and binder as long as the objectives of the present invention can be achieved. For example, the binder may include at least one of polyvinyl alcohol, hydroxypropyl cellulose, polyvinylidene fluoride, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, poly(1,1-difluoroethylene), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, but is not limited to these. The conductive agent may include at least one of carbon-based materials, metal-based materials, conductive polymers, and mixtures of the above-mentioned materials, but is not limited to these. For example, the carbon-based material may include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. The metal-based material may include metal powder, metal fiber, copper, nickel, aluminum, or silver. The conductive polymer may include a polyphenylene derivative. In the present invention, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer is not particularly limited, and those skilled in the art can select it according to their actual needs as long as the objectives of the present invention are achieved. In the present invention, the thickness of the positive electrode current collector and the positive electrode active material layer is not particularly limited, as long as the objectives of the present invention are achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode active material layer is 30 μm to 120 μm. In the present invention, the thickness of the positive electrode pieces is not particularly limited, as long as the objectives of the present invention are achieved. For example, the thickness of the positive electrode pieces is 50 μm to 150 μm. Optionally, the positive electrode piece may further include a conductive layer located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0058] In the present invention, there is no particular limitation on the preparation process of the positive electrode active material, as long as the object of the present invention can be achieved. In one example, the positive electrode active material is prepared by the following method. Li2C2O4, FeC2O4·2H2O, and NH4H2PO4 are blended in the stoichiometric ratio of LiFePO4, and then dry-milled for 40 h to 50 h to obtain a precursor. Carbon sources with different mass percentages are added to the obtained precursor, and wet-milled for 5 h to 6 h. The obtained solid-liquid mixture is dried by a spray dryer, and the dried powder is pre-sintered in a tubular furnace at 500 °C to 600 °C for 5 h to 7 h under a N2 protection atmosphere, and then the temperature is continuously raised and sintered at 600 °C to 700 °C for 10 h to 12 h to obtain a carbon-containing LiFePO4 sample. The carbon source may include at least one of glucose, sucrose, graphite, and starch, but is not limited thereto.

[0059] In the present invention, there is no particular limitation on the method for controlling the content of carbon element in the positive electrode active material, as long as the object of the present invention can be achieved. For example, since the content of carbon element in the positive electrode active material usually increases with the increase of the content of different carbon sources such as glucose, the content of carbon element in the positive electrode active material can be adjusted by adjusting the content of the carbon source in the preparation process.

[0060] In the present invention, the secondary battery further includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. In the present invention, there is no particular limitation on the negative electrode current collector, as long as the object of the present invention can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector, etc. The negative electrode active material layer in the present invention includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material of the present invention is natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate with a spinel structure Li4Ti5O 12, Li-Al alloy, metallic lithium, etc. In the present invention, the type of binder and conductive agent is not particularly limited as long as the objectives of the present invention are achieved. For example, the binder and conductive agent may include at least one of the above-mentioned materials, but are not limited thereto. In the present invention, the thickness of the negative electrode current collector and the negative electrode active material layer is not particularly limited as long as the objectives of the present invention are achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm. In the present invention, the thickness of the negative electrode piece is not particularly limited as long as the objectives of the present invention are achieved. For example, the thickness of the negative electrode piece is 50 μm to 150 μm. Optionally, the negative electrode piece may include a conductive layer located between the negative electrode current collector and the negative electrode active material layer. The composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0061] In the present invention, the secondary battery further includes a separator that separates the positive and negative electrode pieces to prevent short circuits within the secondary battery, allow the free passage of electrolyte ions, and prevent interference with the electrochemical charge and discharge process. The separator is not particularly limited in the present invention, as long as it achieves the objectives of the present invention. For example, the separator material may include, but is not limited to, at least one of polyolefin (PO)-based materials mainly consisting of polyethylene (PE) and polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. The type of separator may include at least one of woven membranes, nonwoven membranes, microporous membranes, composite membranes, rolled membranes, and spun membranes.

[0062] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a porous nonwoven fabric, membrane, or composite membrane, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer may be provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic material. For example, the inorganic layer may include inorganic particles and a binder. The inorganic particles are not particularly limited and may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is not particularly limited and may be, for example, at least one of the binders described above. The polymer layer includes a polymer, and the polymer material may include at least one of polyamide, polyacrylonitrile, acrylic ester polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0063] The secondary battery of the present invention further includes a packaging bag for containing the positive electrode pieces, separator, negative electrode pieces, and electrolyte, as well as other components known in the field of secondary batteries, but the present invention is not limited to these other components. The packaging bag of the present invention is not particularly limited, and any packaging bag known in the art may be used as long as it can achieve the objectives of the present invention.

[0064] The secondary battery of the present invention is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the secondary battery may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0065] The process for preparing the secondary battery of the present invention is well known to those skilled in the art and is not particularly limited in the present invention. For example, the process may include, but is not limited to, the following steps: stacking positive electrode pieces, a separator, and a negative electrode pieces in order, and optionally rolling or folding them to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting an electrolyte into the packaging bag; and sealing the packaging bag to obtain a secondary battery. Alternatively, stacking positive electrode pieces, a separator, and a negative electrode pieces in order, and then securing the four corners of the entire stack with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting an electrolyte into the packaging bag; and sealing the packaging bag to obtain a secondary battery. Furthermore, an overcurrent protection element, lead plates, etc. may be provided in the packaging bag as needed to prevent internal pressure buildup and overcharging / discharging of the secondary battery.

[0066] A second aspect of the present invention provides an electronic device including the secondary battery according to any one of the above embodiments, and therefore the electronic device provided by the present invention has good usage characteristics.

[0067] The electronic device of the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor.

[0068] Example Hereinafter, embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were performed using the following methods. Unless otherwise specified, "parts" and "%" are based on mass.

[0069] Measurement method and equipment: Determination of carbon element content: The carbon element content in the powder of the positive electrode active material was measured directly using a carbon / sulfur analyzer.

[0070] The coated area of ​​the prepared positive electrode pieces or positive electrode pieces removed from the lithium-ion battery was cut into sheets and subjected to ultrasonic vibration in an NMP bath at 100°C for 48 hours. The current collector was then removed, and the remaining material was polished for 1 hour, washed and filtered three times to remove the gelatinous material. The remaining solid material was then dried at 100°C for 8 hours. The resulting powder was then sampled and the carbon content was measured using a carbon / sulfur analyzer.

[0071] Measurement of cycle characteristics: The lithium-ion battery was placed in a thermostatic chamber at 45°C and allowed to stand for 30 minutes to reach a constant temperature of 45°C. The lithium-ion battery was charged to 3.65V at a constant current of 1C, then charged to 0.05C at a constant voltage of 3.65V, and then discharged to 2.5V at a constant current of 1C. This constituted one charge-discharge cycle. The initial discharge capacity was defined as 100%, and the charge-discharge cycle was repeated until the discharge capacity had decayed to 70%. The measurement was then completed, and the number of cycles was recorded and used as an index to evaluate the cycle characteristics of the lithium-ion battery.

[0072] At the same time, the cycle characteristics of the lithium-ion battery at 60°C were measured. The lithium-ion battery was placed in a thermostatic box at 60°C and left to stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature of 60°C. The charge-discharge cycle procedure was the same as the charge-discharge cycle process at 45°C described above.

[0073] 100% State of Charge (SOC) High Temperature Storage Test: The lithium-ion battery was placed in a thermostatic chamber at 25°C and allowed to stand for 30 minutes to reach a constant temperature of 25°C. It was then charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 0.05C, and then discharged at a constant current of 1C to 2.5V. The discharge capacity at this time was recorded as the initial capacity C0. It was then charged at a constant current of 0.5C to 3.65V and then charged at a constant voltage of 0.05C. The battery thickness T0 was measured with a micrometer and recorded. The lithium-ion battery was then transferred to a thermostatic chamber at 60°C and stored for 90 days, during which time the battery thickness was measured and recorded every 30 days. The lithium-ion battery was then transferred to a thermostatic chamber at 25°C, allowed to stand for 60 minutes, and then discharged at a constant current of 1C to 2.5V. The discharge capacity at this time was recorded as the remaining capacity C1. The battery was then charged to 3.65 V at a constant current of 1 C, charged to 0.05 C at a constant voltage, and then discharged to 2.5 V at a constant current of 1 C. The discharge capacity at this point was recorded as the recovered capacity C2, and the thickness T1, open circuit voltage, and impedance of the lithium-ion battery were measured. The remaining capacity retention rate and recovered capacity retention rate of the lithium-ion battery were calculated according to the formula below as indicators for evaluating the high-temperature storage characteristics of the lithium-ion battery at 100% SOC.

[0074] Thickness expansion rate of 100% SOC during high temperature storage = (T1-T0) / T0 × 100%; Residual capacity retention rate during high-temperature storage at 100% SOC = C1 / C0 × 100%; Recovery capacity retention rate during high-temperature storage at 100% SOC = C2 / C0 × 100%.

[0075] 0% SOC high temperature storage test: The lithium-ion battery was placed in a thermostatic chamber at 25°C and allowed to stand for 30 minutes to reach a constant temperature of 25°C. It was charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 0.05C, and then discharged at a constant current of 1C to 2.5V. The discharge capacity at this time was recorded as the initial capacity C3. The battery thickness T2 was measured with a micrometer and recorded. The lithium-ion battery was then transferred to a thermostatic chamber at 60°C and stored for 90 days, during which the battery thickness was measured and recorded every 30 days. The lithium-ion battery was then transferred to a thermostatic chamber at 25°C, allowed to stand for 60 minutes, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 0.05C, and then discharged at a constant current of 1C to 2.5V. The discharge capacity at this time was recorded as the recovery capacity C4. The thickness T3, open-circuit voltage, and impedance of the lithium-ion battery were then measured. As an index for evaluating the high-temperature storage characteristics of a lithium-ion battery at 0% SOC, the thickness expansion rate of the lithium-ion battery was calculated according to the formula below.

[0076] Thickness expansion rate at high temperature storage of 0% SOC = (T3 - T2) / T2 × 100%.

[0077] DC Impedance (DCR) Measurement: The lithium-ion battery was placed in a 0°C thermostatic chamber for 4 hours, charged at a constant current of 0.1C to 3.65V, charged at a constant voltage to 0.05C, left to rest for 10 minutes, discharged at a constant current of 0.1C to 2.5V, left to rest for 10 minutes, charged at a constant current of 0.1C to 3.65V, charged at a constant voltage to 0.05C, left to rest for 10 minutes, discharged at a constant current of 0.1C for 3 hours, and then discharged at a constant current of 1C for 1 second. The DC impedance corresponding to a 70% SOC state of the lithium-ion battery was calculated.

[0078] Charging characteristics measurement: The battery was charged and discharged at 25°C according to the following procedure: 1) Leave the battery to stand for 5 minutes. 2) Discharge to 2.5V at a constant current of 0.5C. 3) Leave the battery to stand for 15 minutes. 4) Charge to 3.65V at a constant current of 1.5C, then charge to 0.05V at a constant voltage. 5) Leave the battery to stand for 60 minutes. 6) Repeat steps 3) to 5) 10 times.

[0079] After the measurement, the fully charged battery was removed and disassembled to observe the degree of lithium deposition at the interface of the negative electrode piece. Severe lithium deposition was defined as obvious lithium deposition over the entire surface of the battery, or a capacity retention rate of less than 90% after 10 cycles. Moderate lithium deposition was defined as lithium deposition in localized areas or corners of the battery, or a capacity retention rate of 90% to 98% after 10 cycles. Mild lithium deposition was defined as lithium deposition only in corners or the edges of the lithium-ion battery, or a capacity retention rate of greater than 98% but less than 99.5% after 10 cycles. No lithium deposition was defined as all areas remaining golden yellow.

[0080] Example 1-1 <Preparation of positive electrode active material> A precursor was obtained by mixing Li2C2O4, FeC2O4·2H2O, and NH4H2PO4 in the stoichiometric ratio of LiFePO4 and then dry-grinding for 40 hours. A certain amount of glucose was added to the resulting precursor, followed by wet-grinding for 5 hours. The resulting solid-liquid mixture was dried in a spray dryer. The dried powder was pre-sintered in a tubular furnace at 500°C for 5 hours under a N2 protective atmosphere, and then heated to 600°C and sintered for 10 hours to obtain a LiFePO4 sample with a carbon content of 1.5%. During the sintering process under N2, some carbon content loss occurred, approximately 50%.

[0081] <Preparation of positive electrode piece> LFP, SuperP, and PVDF were mixed in a weight ratio of 96.3:1.5:2.2, and N-methylpyrrolidone (NMP) was added as a solvent to form a slurry with a solids content of 72 wt%. The mixture was then uniformly stirred under vacuum to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to one surface of a 10 μm-thick aluminum foil current collector and dried at 85°C to obtain a positive electrode piece with a 100 μm-thick coating layer coated on one side. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode piece with a positive electrode active material layer coated on both sides. After cold pressing, cutting, and tab welding, the piece was vacuum dried at 85°C for 4 hours to obtain a positive electrode piece with a specification of 74 mm x 867 mm.

[0082] <Preparation of negative electrode pieces> Artificial graphite, SuperP, sodium carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96.4:1.5:0.5:1.6 and deionized water was added as a solvent to form a slurry with a solids content of 54 wt%. The mixture was then uniformly mixed using a vacuum mixer to obtain anode slurry. The anode slurry was then uniformly coated on one surface of a 10 μm-thick copper foil anode current collector and dried at 85°C to obtain anode pieces with a 100 μm-thick coating layer of anode active material on one side. The same process was then repeated on the other surface of the copper foil to obtain anode pieces with anode active material on both sides. After cold pressing, cutting, and tab welding, the anode pieces were vacuum dried at 120°C for 12 hours to obtain anode pieces with specifications of 78 mm x 875 mm.

[0083] <Preparation of electrolyte> In a glove box filled with dry argon gas, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 35:65 to obtain a base solvent. Then, vinylene carbonate was added and dissolved, and the mixture was thoroughly stirred. After that, a lithium salt, LiPF6, was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, the mass percentage of vinylene carbonate was 0.1%, and the mass percentage of the base solvent was 87.4%.

[0084] <Preparation of separator> A 7 μm thick porous polyethylene film (provided by Celgard) was used.

[0085] <Preparation of lithium-ion batteries> The positive electrode pieces, separator, and negative electrode pieces were stacked in this order, with the separator interposed between them to provide isolation, and then wound to obtain an electrode assembly. The electrode assembly was placed in a foil case, and moisture was removed at 80°C. The electrolyte solution prepared above was then poured into the assembly. The assembly was then vacuum sealed, allowed to stand, and subjected to formation (charging to 3.3 V at a constant current of 0.02 C, and then further charging to 3.6 V at a constant current of 0.1 C), molding, capacity grading, and other processes to obtain a soft-packaged lithium-ion battery (3.3 mm thick, 39 mm wide, and 96 mm long).

[0086] Examples 1-2 to 1-19 The procedure was the same as in Example 1-1, except that in <Preparation of positive electrode active material>, the mass percentage of glucose was controlled to adjust the carbon element content in the positive electrode active material, and in <Preparation of electrolyte solution>, the relevant preparation parameters were adjusted according to Table 1.

[0087] Example 2-1 The electrolyte solution was prepared in the following manner, and the relevant preparation parameters were adjusted according to Table 3, which was the same as in Examples 1-5.

[0088] <Preparation of electrolyte> In a glove box with a dry argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 35:65 to obtain a base solvent. Then, vinylene carbonate and pyridine were added, dissolved, and thoroughly stirred. After that, a lithium salt, LiPF6, was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, the mass percentage of vinylene carbonate was 2%, the mass percentage of pyridine was 0.01%, and the mass percentage of the base solvent was 85.49%.

[0089] Examples 2-2 to 2-11 In <Preparation of Electrolyte Solution>, the same procedure as in Example 2-1 was carried out except that the relevant preparation parameters were adjusted according to Table 3.

[0090] Example 3-1 The electrolyte solution was prepared in the following manner, and the relevant preparation parameters were adjusted according to Table 5, which was the same as in Examples 1-5.

[0091] <Preparation of electrolyte> In a glove box with a dry argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:EMC = 35:65 to obtain a base solvent, followed by the addition of vinylene carbonate and hexamethylene diisocyanate. After dissolving and stirring thoroughly, the lithium salt LiPF6 was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, the mass percentage of vinylene carbonate was 2%, the mass percentage of hexamethylene diisocyanate was 0.01%, and the mass percentage of the base solvent was 85.49%.

[0092] Examples 3-2 to 3-11 In <Preparation of Electrolyte Solution>, the same procedure as in Example 3-1 was carried out except that the relevant preparation parameters were adjusted according to Table 5.

[0093] Example 4-1 The electrolyte solution was prepared in the following manner, and the relevant preparation parameters were adjusted according to Table 7, which was the same as in Examples 1-5.

[0094] <Preparation of electrolyte> In a glove box with a dry argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 35:65 to obtain a base solvent. Then, vinylene carbonate and maleic anhydride were added, dissolved, and thoroughly stirred. After that, a lithium salt, LiPF6, was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, the mass percentage of vinylene carbonate was 2%, the mass percentage of maleic anhydride was 0.01%, and the mass percentage of the base solvent was 85.49%.

[0095] Examples 4-2 to 4-11 In <Preparation of Electrolyte Solution>, the same procedure as in Example 4-1 was carried out except that the relevant preparation parameters were adjusted according to Table 7.

[0096] Example 5-1 The electrolyte solution was prepared in the following manner, and the relevant preparation parameters were adjusted according to Table 9, which was the same as in Examples 1-5.

[0097] <Preparation of electrolyte> In a glove box with a dry argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:EMC = 35:65 to obtain a base solvent, followed by the addition of vinylene carbonate and tetramethyldivinyldisiloxane. After dissolving and stirring thoroughly, the lithium salt LiPF6 was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, the mass percentage of vinylene carbonate was 2%, the mass percentage of tetramethyldivinyldisiloxane was 0.1%, and the mass percentage of the base solvent was 85.4%.

[0098] Examples 5-2 to 5-9 In <Preparation of Electrolyte Solution>, the same procedure as in Example 5-1 was carried out except that the relevant preparation parameters were adjusted according to Table 9.

[0099] Example 6-1 The electrolyte solution was prepared in the following manner, and was the same as in Examples 1-5, except that the relevant preparation parameters were adjusted according to Table 11:

[0100] <Preparation of electrolyte> In a glove box with a dry argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 35:65 to obtain a base solvent. Subsequently, vinylene carbonate and boron trifluoride pyridine were added, dissolved, and thoroughly stirred. After that, a lithium salt, LiPF6, was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, the mass percentage of vinylene carbonate was 2%, the mass percentage of boron trifluoride pyridine was 0.01%, and the mass percentage of the base solvent was 85.49%.

[0101] Examples 6-2 to 6-10 <Preparation of electrolyte solution> was the same as in Example 6-1, except that the relevant preparation parameters were adjusted according to Table 11.

[0102] Comparative Example 1 The procedure was the same as in Example 1-1, except that the electrolyte solution was prepared in the following manner.

[0103] <Preparation of electrolyte> In a glove box with a dry argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:EMC = 35:65 to obtain a base solvent. After sufficient dissolution, lithium salt LiPF6 was added and mixed uniformly to obtain an electrolyte solution. Here, the mass percentage of LiPF6 was 12.5%, and the mass percentage of the base solvent was 87.5%.

[0104] Comparative Examples 2 to 4 The procedure was the same as in Example 1-1, except that in <Preparation of positive electrode active material>, the mass percentage of glucose was controlled to adjust the carbon element content in the positive electrode active material, and in <Preparation of electrolyte solution>, the relevant preparation parameters were adjusted according to Table 1.

[0105] The preparation parameters and property measurements for each of the Examples and Comparative Examples are shown in Tables 1 to 12.

[0106] [Table 1]

[0107] [Table 2]

[0108] As can be seen from Examples 1-1 to 1-19 and Comparative Examples 1 to 4, the mass percentages of vinylene carbonate and carbon element in the Examples are all within the ranges of the present invention, whereas Comparative Examples 1 to 4 do not simultaneously satisfy the above characteristics. The lithium ion batteries in the Examples of the present invention have a higher number of cycles at 45°C and a higher number of cycles at 60°C, a lower thickness expansion rate during high-temperature storage at 100% SOC and a lower thickness expansion rate during high-temperature storage at 0% SOC, a higher remaining capacity retention rate and recovered capacity retention rate during high-temperature storage at 100% SOC, and a lower DCR and degree of lithium precipitation. This demonstrates that lithium ion batteries prepared using the electrolyte and positive electrode active material provided by the present invention have good cycle characteristics and storage characteristics as well as excellent kinetic characteristics.

[0109] [Table 3]

[0110] [Table 4]

[0111] As can be seen from Examples 2-1 to 2-11, when the type and content of the added nitrogen-containing heterocyclic compound are within the range of the present invention, the resulting lithium ion battery has a higher number of cycles at 45°C and 60°C, a lower thickness expansion rate during high-temperature storage at 100% SOC and 0% SOC, and a higher remaining capacity retention rate and recovered capacity retention rate during high-temperature storage at 100% SOC. This demonstrates that the lithium ion battery prepared using the electrolyte provided by the present invention can further improve the cycle characteristics and storage characteristics.

[0112] [Table 5]

[0113] [Table 6]

[0114] As can be seen from Examples 3-1 to 3-11, when the type and content of the added isocyanate compound are within the range of the present invention, the resulting lithium ion battery has a higher number of cycles at 45°C and a higher number of cycles at 60°C, a lower thickness expansion rate during high temperature storage at 100% SOC and a lower thickness expansion rate during high temperature storage at 0% SOC, and a higher remaining capacity retention rate and recovered capacity retention rate during high temperature storage at 100% SOC. This demonstrates that the lithium ion battery prepared using the electrolyte solution provided by the present invention can further improve the cycle characteristics and storage characteristics.

[0115] [Table 7]

[0116] [Table 8]

[0117] As can be seen from Examples 4-1 to 4-11, when the type and content of the added acid anhydride compound are within the range of the present invention, the resulting lithium ion battery has a higher number of cycles at 45°C and a higher number of cycles at 60°C, a lower thickness expansion rate during high-temperature storage at 100% SOC and a lower thickness expansion rate during high-temperature storage at 0% SOC, and a higher remaining capacity retention rate and recovered capacity retention rate during high-temperature storage at 100% SOC. This demonstrates that the lithium ion battery prepared using the electrolyte provided by the present invention can further improve the cycle characteristics and storage characteristics.

[0118] [Table 9]

[0119] [Table 10]

[0120] As can be seen from Examples 5-1 to 5-9, when the type and content of the added silane compound are within the range of the present invention, the resulting lithium ion battery has a higher number of cycles at 45°C and a higher number of cycles at 60°C, a lower thickness expansion rate during high temperature storage at 100% SOC and a lower thickness expansion rate during high temperature storage at 0% SOC, a higher remaining capacity retention rate and recovered capacity retention rate during high temperature storage at 100% SOC, and a lower degree of lithium precipitation. This demonstrates that the lithium ion battery prepared using the electrolyte provided by the present invention has good cycle characteristics and storage characteristics as well as excellent kinetic characteristics.

[0121] [Table 11]

[0122] [Table 12]

[0123] As can be seen from Examples 6-1 to 6-10, when the type and content of the added nitrogen-containing heterocyclic boron trifluoride complex are within the range of the present invention, the resulting lithium ion battery has a higher number of cycles at 45°C and 60°C, a lower thickness expansion rate during high-temperature storage at 100% SOC and a lower thickness expansion rate during high-temperature storage at 0% SOC, and a higher remaining capacity retention rate and recovered capacity retention rate during high-temperature storage at 100% SOC. This demonstrates that the lithium ion battery prepared using the electrolyte provided by the present invention can further improve the cycle characteristics and storage characteristics.

[0124] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A secondary battery comprising a positive electrode piece, a negative electrode piece, and an electrolyte, the electrolytic solution contains vinylene carbonate, and a mass percentage a of the vinylene carbonate is 0.1% to 3% relative to the total mass of the electrolytic solution; The positive electrode piece comprises a positive electrode active material, the positive electrode active material comprises a carbon element, and a mass percentage b of the carbon element is 0.5% to 6% relative to the total mass of the positive electrode active material.

2. 2. The secondary battery according to claim 1, wherein a is 0.1% to 2.5% and / or b is 0.5% to 5%.

3. 2. The secondary battery according to claim 1, wherein a is 0.5% to 2.5% and / or b is 0.5% to 4.5%.

4. 2. The secondary battery according to claim 1, wherein a is 0.8% to 2.5% and / or b is 0.5% to 4.5%.

5. 2. The secondary battery according to claim 1, wherein the ratio of a to b is 0.22 to 6.

6. 2. The secondary battery according to claim 1, wherein the electrolyte solution further contains a nitrogen-containing heterocyclic compound, and a mass percentage c of the nitrogen-containing heterocyclic compound is 0.01% to 1% with respect to the total mass of the electrolyte solution.

7. 7. The secondary battery according to claim 6, wherein the ratio of a to c is 2 to 60.

8. The nitrogen-containing heterocyclic compound includes the following compound (Formula I) or compound (Formula II): 【Chemistry 1】 Here, R １ , R ２ and R ３ are each independently substituted or unsubstituted C １ -C ５ an alkylene group of the formula ２ -C ５ an alkenylene group of the formula: ２ -C ５ and substituted or unsubstituted C ３ -C ５ and when substituted, the substituent is a halogen atom.

9. 2. The secondary battery according to claim 1, wherein the electrolytic solution further contains an isocyanate compound, and a mass percentage d of the isocyanate compound is 0.01% to 2% with respect to the total mass of the electrolytic solution.

10. 10. The secondary battery according to claim 9, wherein the ratio of a to d is 2 to 60.

11. The isocyanate compound includes the following compound (Formula III) or compound (Formula IV): 【Chemistry 2】 wherein the isocyanate compound contains at least one —NCO group, and R ３ and R ４ are each independently C １ ~C ７ or a hydrocarbon group of C １ ~C ７ The secondary battery according to claim 9 , wherein the aromatic hydrocarbon group is selected from the following aromatic hydrocarbon groups:

12. 2. The secondary battery according to claim 1, wherein the electrolyte solution further contains an acid anhydride compound, and a mass percentage e of the acid anhydride compound is 0.01% to 2% with respect to the total mass of the electrolyte solution.

13. 13. The secondary battery according to claim 12, wherein the ratio of a to e is 2 to 60.

14. The secondary battery according to claim 12, wherein the acid anhydride compound includes at least one of maleic anhydride, dimethylmaleic anhydride, citraconic anhydride, glutaric anhydride, succinic anhydride, norbornene dicarboxylic anhydride, diphenic anhydride, pyridine dicarboxylic anhydride, pyrazine dicarboxylic anhydride, 2,3-pyridine dicarboxylic anhydride, pyridine-3,4-dicarboxylic anhydride, and 2,3-pyrazine dicarboxylic anhydride.

15. 2. The secondary battery according to claim 1, wherein the electrolyte solution further contains a silane compound, and a mass percentage f of the silane compound is 0.01% to 2% with respect to the total mass of the electrolyte solution.

16. 16. The secondary battery according to claim 15, wherein the ratio of a to f is 2 to 60.

17. The secondary battery according to claim 15, wherein the silane compound includes at least one of tetramethyldivinyldisiloxane, bis(trimethylsilyl) malonate, diphenyldifluorosilane, heptamethyldisilazane, tetramethyldivinyldisiloxane, tetraethoxysilane, 2-cyanoethyltriethoxysilane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, and vinyltriethoxysilane.

18. 2. The secondary battery according to claim 1, wherein the electrolyte solution further contains a nitrogen-containing heterocyclic boron trifluoride complex, and the mass percentage g of the nitrogen-containing heterocyclic boron trifluoride complex is 0.01% to 1% with respect to the total mass of the electrolyte solution.

19. 19. The secondary battery according to claim 18, wherein the ratio of a to g is 2 to 60.

20. 19. The secondary battery according to claim 18, wherein the nitrogen-containing heterocyclic boron trifluoride complex includes at least one of boron trifluoride pyridine, boron trifluoride pyrazine, boron trifluoride pyridazine, 2-fluoropyridine boron trifluoride complex, boron trifluoride pyrimidine, boron trifluoride pyrrole, boron trifluoride pyrazole, and boron trifluoride imidazole.

21. 2. The secondary battery according to claim 1, wherein the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

22. An electronic device comprising the secondary battery according to any one of claims 1 to 21.

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