Electrolyte, secondary battery, and electronic device

Abstract

An electrolyte, a secondary battery and an electronic device. The electrolyte comprises a compound A and a compound B; wherein the compound A is at least one phosphorus-containing amine compound as shown in formula I, and the compound B is at least one pyridine ring-containing compound as shown in formula II. The compound B in the electrolyte can form a stable passivation layer on the negative electrode surface by virtue of its pyridine ring structure and the introduction of unsaturated functional groups, effectively reducing the rapid release of active lithium during the thermal runaway process, thereby improving the thermal safety of the battery; however, the use of compound B alone will cause the impedance of the battery to increase, affecting the kinetic performance. Therefore, the introduction of compound A into the electrolyte containing compound B, the phosphorus-containing amine group of which can synergize with compound B, not only alleviates the impedance increase problem caused by the introduction of compound B, but also further improves the thermal box safety performance of the secondary battery and the electronic device.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to an electrolyte, a secondary battery, and an electronic device. Background Technology

[0002] Electronic devices, especially lithium-ion batteries, have been widely used in portable electronic products (such as smartphones, laptops, and digital cameras) and energy storage systems due to their significant advantages such as high energy density, high operating voltage, lightweight, low self-discharge rate, long cycle life, no memory effect, and environmental friendliness. They are also gradually expanding into high-power fields, including electric vehicles, power tools, drones, and electric ships. However, with the increasing complexity of application scenarios and the continuous improvement of performance requirements, developing electronic devices that combine low impedance and excellent thermal safety performance has become a key challenge for the industry. Summary of the Invention

[0003] This application provides an electrolyte, a secondary battery, and an electronic device that achieves superior thermal safety performance while also improving impedance performance.

[0004] In a first aspect, this application provides an electrolyte comprising compound A and compound B;

[0005] Compound A is selected from compounds shown in Formula I;

[0006]

[0007] Wherein, compound A is one or more of the phosphate-containing amine compounds as shown in Formula I, wherein R1, R2, R3 and R4 are each independently selected from hydrogen atoms, substituted or unsubstituted C1-C3 alkyl groups, substituted or unsubstituted C2-C3 alkenyl groups, substituted or unsubstituted C2-C3 alkynyl groups, substituted or unsubstituted C1-C3 alkoxy groups, substituted or unsubstituted C3-C6 heterocyclic groups, substituted or unsubstituted aryl groups, substituted or unsubstituted benzyl groups, and the substituents are selected from at least one of halogen atoms, cyano, trifluoromethyl, alkenyl and alkynyl groups;

[0008] Compound B is selected from compounds shown in Formula II;

[0009]

[0010] Wherein, compound B is one or more of the pyridine ring-containing compounds as shown in Formula II, wherein each of the R5-R9 groups is independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C2-C3 alkenyl, substituted or unsubstituted C2-C3 alkynyl, and the substituent is selected from at least one of fluorine atom, cyano, trifluoromethyl, alkenyl, and alkynyl.

[0011] This application improves the thermal safety of electronic devices and reduces internal resistance by simultaneously adding compound A (containing an amine phosphate compound) and compound B (containing a pyridine ring compound) to the electrolyte. Compound B, with its pyridine ring structure and the introduction of unsaturated functional groups, can form a stable passivation layer on the negative electrode surface, effectively reducing the rapid release of active lithium during thermal runaway, thereby improving battery thermal safety. However, using compound B alone leads to increased battery impedance, affecting kinetic performance. Therefore, this application has discovered that introducing compound A into an electrolyte containing compound B allows its amine phosphate groups to synergistically work with compound B, not only alleviating the impedance increase caused by the introduction of compound B but also further improving thermal safety performance, thus meeting the requirements of high-energy-density batteries for thermal safety and low impedance performance.

[0012] In some embodiments, the compound of formula I is selected from at least one of the following compounds:

[0013]

[0014] This application embodiment achieves significant optimization of electronic device performance by selecting compounds of formula I with specific structures (such as phosphate-containing amine compounds shown in formulas I-1 to I-9) in synergy with compound B. The phosphate-amine groups of these formula I compounds can effectively reduce the interfacial impedance of the secondary battery, alleviating the problem of increased internal resistance caused by the addition of compound B. This synergistic effect enables electronic devices using this electrolyte to improve the thermal stability of lithium-ion batteries while reducing battery internal resistance, thereby meeting the requirements of high-energy-density batteries for thermal safety and low impedance.

[0015] In some embodiments, the compound of formula II is selected from at least one of the following compounds:

[0016]

[0017]

[0018] This application embodiment utilizes compounds of formula II with specific structures (such as pyridine-containing ring compounds shown in formulas II-1 to II-7) to synergize with compounds of formula I, thereby improving the thermal safety of the secondary battery and reducing its internal resistance. Compound B in the electrolyte, due to its pyridine ring structure and the introduction of unsaturated functional groups, can form a stable passivation layer on the negative electrode surface, effectively reducing the rapid release of active lithium during thermal runaway, thus improving the battery's thermal safety. Simultaneously, the unsaturated functional groups in its molecular structure can synergistically interact with the phosphate groups of the compound of formula I, improving interfacial thermal stability while optimizing lithium-ion transport kinetics, achieving a good balance between thermal safety performance and impedance characteristics.

[0019] In some embodiments, the mass content of compound II is B%, satisfying the condition: 0.05 ≤ B ≤ 5%, based on the mass of the electrolyte. This application, by controlling the content of compound II within the range of 0.05% to 5% of the total electrolyte mass, provides sufficient pyridine ring compounds to participate in the construction of the electrode interface protective layer, thereby improving the thermal stability of the battery; it also avoids excessive addition leading to an excessively thick electrolyte interface film that affects battery kinetics, ultimately achieving an optimized balance between the thermal safety and low impedance of the electronic device. Therefore, by controlling the content of compound II within the aforementioned suitable range, this application, when used in conjunction with compound I, can simultaneously ensure thermal box safety and reduce internal resistance, thereby improving the cycle and power performance of the battery.

[0020] In some embodiments, the mass content of compound I is A%, satisfying the condition: 0.05 ≤ A ≤ 5%, based on the mass of the electrolyte. This application controls the mass content of compound I within the range of 0.05% to 5% of the total electrolyte mass. This provides sufficient phosphate-containing amine compounds to participate in interface regulation, effectively mitigating the increase in impedance caused by the addition of compound II. It also avoids changes in the physicochemical properties of the electrolyte due to excessive addition, while maintaining its synergistic effect with compound II. This ensures that compound I reduces impedance without negatively impacting the basic performance of the electrolyte, thus balancing the thermal safety and low impedance performance of the electronic device.

[0021] In some embodiments, the mass content A% of compound I and the mass content B% of compound II satisfy at least one of the following conditions:

[0022] (1) 0.1 ≤ A ≤ 1;

[0023] (2) 0.1≤B≤2;

[0024] (3) 0.05≤A / B≤10. This application, by controlling the mass content of compound I within the above-mentioned suitable range, can effectively improve interfacial lithium-ion transport while avoiding excessive addition that could exacerbate electrolyte side reactions and degrade battery performance. This application, by controlling the mass content of compound II within the above-mentioned suitable range, can improve the thermal box safety performance without excessively increasing interfacial impedance. This application, by controlling the mass ratio of compound I to compound II within the above-mentioned suitable range, can achieve a good balance between thermal safety and low impedance performance in the electrolyte system, providing a feasible technical solution for improving the overall performance of electronic devices.

[0025] In some embodiments, the electrolyte comprises a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(oxalateborate), lithium difluorooxalateborate, lithium difluorophosphate, lithium tetrafluoroborate, lithium nitrate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(pentafluoroethyl)sulfonyl)imide, lithium difluorooxalateborate, or lithium tetrafluorooxalateborate and lithium hexafluorophosphate.

[0026] Based on the mass of the electrolyte, the mass content of the lithium salt is C%, satisfying 1≤C≤20, preferably 5≤C≤15. This application, by controlling the mass content of the lithium salt within the above-mentioned suitable range, can provide sufficient lithium ions, enabling the electronic device to maintain good thermal stability while also possessing low impedance characteristics, thereby meeting the requirements of electronic devices for thermal safety and low impedance performance.

[0027] In some embodiments, the mass content A% of compound I, the mass content B% of compound II, and the mass content C% of lithium salt satisfy the following relationship: 0.053 ≤ (A+B) / C ≤ 0.2. By adjusting the ratio of the mass content A% of compound I, the mass content B% of compound II, and the mass content C% of lithium salt within the aforementioned suitable range, this application can further improve the thermal stability of electronic devices while also exhibiting low impedance characteristics, thereby meeting the requirements of electronic devices for thermal safety and low impedance performance.

[0028] Secondly, this application provides a secondary battery, which includes a negative electrode and an electrolyte provided in any embodiment of the first aspect of this application, wherein the charging cut-off voltage of the secondary battery is greater than or equal to 4.3V to 4.8V. The electrolyte and secondary battery of this application maintain good electrochemical performance at higher voltages (4.3V-4.8V), and possess high operating voltage, high energy density, low internal resistance, and good thermal safety performance.

[0029] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector. The negative electrode material includes silicon-carbon material, and based on the mass of the negative electrode active material layer, the mass content of silicon element in the silicon-carbon material is D%, satisfying: 5 ≤ D ≤ 20. This application, by controlling the mass content of silicon element in the silicon-carbon material within the above-mentioned suitable range, works in conjunction with a specific electrolyte system to form a denser and more elastic passivation film on the negative electrode surface. This mitigates the damage to the SEI film and electrolyte decomposition caused by the expansion and contraction of the negative electrode sheet, enabling the secondary battery to maintain a high operating voltage and energy density while further improving the battery's thermal safety performance and impedance characteristics, meeting the comprehensive performance requirements of high-voltage (≥4.3V) lithium-ion batteries.

[0030] In some embodiments, the mass content of compound I (A%) and the mass content of silicon in silicon-carbon particles (D%) satisfy the following relationship: 0.015 ≤ A / D ≤ 0.03. This application, by controlling the ratio of the mass content of compound I (A%) and the mass content of silicon in silicon-carbon particles (D%) within the aforementioned suitable range, can achieve synergistic optimization of the electrolyte additive and the silicon-based anode material, improving the thermal safety of electronic devices while maintaining low impedance. When the ratio is less than this range, the energy density increases but battery side reactions intensify, deteriorating the thermal performance of the secondary battery; when the ratio is greater than this range, the increased SEI film thickness leads to increased battery impedance, simultaneously deteriorating the thermal performance.

[0031] Thirdly, this application provides an electronic device, which includes the secondary battery provided in this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] This application provides an electrolyte, a secondary battery, and an electronic device that achieves superior thermal safety performance while also improving impedance performance.

[0034] electrolyte

[0035] In a first aspect, this application provides an electrolyte comprising compound A and compound B;

[0036] Compound A is selected from compounds shown in Formula I;

[0037]

[0038] Wherein, compound A is at least one of the phosphate-containing amine compounds as shown in Formula I, wherein R1, R2, R3 and R4 are each independently selected from hydrogen atom, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C2-C3 alkenyl, substituted or unsubstituted C2-C3 alkynyl, substituted or unsubstituted C1-C3 alkoxy, substituted or unsubstituted C3-C6 heterocyclic, substituted or unsubstituted aryl, substituted or unsubstituted benzyl, and the substituent is selected from at least one of halogen atom, cyano, trifluoromethyl, alkenyl, and alkynyl;

[0039] Compound B is selected from compounds shown in Formula II;

[0040]

[0041] Compound B is at least one of the pyridine ring compounds shown in Formula II, wherein the R5-R9 groups are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C2-C3 alkenyl, and substituted or unsubstituted C2-C3 alkynyl, and the substituents are selected from at least one of fluorine, cyano, trifluoromethyl, alkenyl, and alkynyl. The inventors of this application improve the thermal safety of electronic devices and reduce internal resistance by simultaneously adding compound A (containing an ammonium phosphate compound) and compound B (containing a pyridine ring compound) to the electrolyte. Compound B in the electrolyte, due to its pyridine ring structure and the introduction of unsaturated functional groups, can form a stable passivation layer on the negative electrode surface, effectively reducing the rapid release of active lithium during thermal runaway, thereby improving the thermal safety of the battery; however, using compound B alone leads to increased battery impedance and affects kinetic performance. Therefore, this application has found through research that introducing compound A into an electrolyte containing compound B allows the phosphate amine group to work synergistically with compound B, which not only alleviates the impedance increase problem caused by the introduction of compound B, but also further improves the thermal box safety performance, thereby meeting the requirements of high energy density batteries for thermal safety and low impedance performance.

[0042] In some embodiments, the compound of formula I is selected from at least one of the following compounds:

[0043]

[0044]

[0045] This application embodiment achieves significant optimization of electronic device performance by selecting compounds of formula I with specific structures (such as phosphate-containing amine compounds shown in formulas I-1 to I-9) in synergy with compound B. The phosphate-amine groups of these formula I compounds can effectively reduce the interfacial impedance of the electrolyte, alleviating the problem of increased impedance caused by the addition of compound B. This synergistic effect enables electronic devices using this electrolyte to improve the thermal stability of secondary batteries while reducing the internal resistance of the batteries, thereby meeting the requirements of high-energy-density batteries for thermal safety and low impedance.

[0046] In some embodiments, the compound of formula II is selected from at least one of the following compounds:

[0047]

[0048]

[0049] This application embodiment utilizes compounds of formula II with specific structures (such as pyridine-containing ring compounds shown in formulas II-1 to II-7) to synergize with compounds of formula I, thereby improving the thermal safety of the secondary battery and reducing its internal resistance. Compound B in the electrolyte, due to its pyridine ring structure and the introduction of unsaturated functional groups, can form a stable passivation layer on the negative electrode surface, effectively reducing the rapid release of active lithium during thermal runaway, thus improving the battery's thermal safety. Simultaneously, the unsaturated functional groups in its molecular structure can synergistically interact with the phosphate groups of the compound of formula I, improving interfacial thermal stability while optimizing lithium-ion transport kinetics, achieving a good balance between thermal safety performance and impedance characteristics.

[0050] In some embodiments, the mass content of compound II is B%, satisfying the condition: 0.05 ≤ B ≤ 5%, based on the mass of the electrolyte. As an example, the value of B can be 0.05, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, or any combination of these values. This application, by controlling the content of compound II within the range of 0.05% to 5% of the total electrolyte mass, provides sufficient pyridine ring compounds to participate in the construction of the electrode interface protective layer, thereby improving the thermal stability of the battery; it also avoids excessively thick electrolyte interface films due to excessive addition, which could affect battery dynamics, ultimately achieving an optimized balance between the thermal safety and low impedance of the electronic device. Therefore, by controlling the content of compound II within the aforementioned suitable range, this application, when used in conjunction with compound I, can simultaneously ensure thermal safety and reduce internal resistance, thereby improving the cycle and power performance of the battery.

[0051] In some embodiments, the mass content of compound I is A%, based on the mass of the electrolyte, satisfying: 0.05 ≤ A ≤ 5. As an example, the value of A can be 0.05, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, or any two of these values ​​within a range. This application, by controlling the mass content of compound I within the range of 0.05% to 5% of the total electrolyte mass, provides sufficient phosphate-containing amine compounds to participate in interface regulation, effectively mitigating the increase in impedance caused by the addition of compound II; it also avoids changes in the physicochemical properties of the electrolyte due to excessive addition, while maintaining its synergistic effect with compound II. This ensures that compound I reduces impedance without negatively impacting the basic performance of the electrolyte, thereby balancing the thermal safety and low impedance performance of the electronic device.

[0052] In some embodiments, the mass content A% of compound I and the mass content B% of compound II satisfy at least one of the following conditions:

[0053] (1) 0.1 ≤ A ≤ 1;

[0054] (2) 0.1≤B≤2;

[0055] (3) 0.05 ≤ A / B ≤ 10. As an example, the value of A can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any two of these values ​​within a range. As an example, the value of B can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any two of these values ​​within a range. As an example, the value of A / B can be 0.05, 1.5, 2.5, 3.5, 5.5, 6.5, 7.5, 9.5, 10, or any two of these values ​​within a range. This application, by controlling the mass content of compound I within the aforementioned suitable range, can effectively improve interfacial lithium-ion transport while avoiding excessive addition that could exacerbate electrolyte side reactions and degrade battery performance. This application, by controlling the mass content of compound II within the aforementioned suitable range, improves thermal box safety performance without excessively increasing interfacial impedance. This application, by controlling the mass ratio of compound I to compound II within the aforementioned suitable range, achieves a good balance between thermal safety and low impedance performance in the electrolyte system, providing a feasible technical solution for improving the overall performance of electronic devices.

[0056] In some embodiments, the electrolyte comprises a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(oxalateborate), lithium difluorooxalateborate, lithium difluorophosphate, lithium tetrafluoroborate, lithium nitrate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(pentafluoroethyl)sulfonyl)imide, lithium difluorooxalateborate, or lithium tetrafluorooxalateborate and lithium hexafluorophosphate.

[0057] Based on the mass of the electrolyte, the mass content of the lithium salt is C%, satisfying 1 ≤ C ≤ 20, preferably 5 ≤ C ≤ 15. As an example, the value of C can be 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 13, 15, 17, 18, 19, 20, or any two of these values ​​within a range. Preferably, the value of C can be 5, 6, 7, 8, 10, 11, 13, 15, or any two of these values ​​within a range. By controlling the mass content of the lithium salt within the aforementioned suitable range, the application can provide sufficient lithium ions, enabling the electronic device to maintain good thermal stability while also possessing low impedance characteristics, thereby meeting the requirements of electronic devices for thermal safety and low impedance performance.

[0058] In some embodiments, the mass content A% of compound I, the mass content B% of compound II, and the mass content C% of lithium salt satisfy the following relationship: 0.053 ≤ (A+B) / C ≤ 0.2. As an example, the value of (A+B) / C can be 0.053, 0.2, 0.3, 0.4, 0.5, 0.2, or any value within a range of any two of these values. By adjusting the ratio of the mass content A% of compound I, the mass content B% of compound II, and the mass content C% of lithium salt within the aforementioned suitable range, this application can further improve the thermal stability of electronic devices while also exhibiting low impedance characteristics, thereby meeting the requirements of electronic devices for thermal safety and low impedance performance.

[0059] Secondly, this application provides a secondary battery, which includes a negative electrode and an electrolyte provided in any embodiment of the first aspect of this application, wherein the charging cut-off voltage of the secondary battery is greater than or equal to 4.3V to 4.8V. The electrolyte and secondary battery of this application can maintain good electrochemical performance at higher voltages (4.3V-4.8V), and have high operating voltage, high energy density, low internal resistance and good thermal safety performance.

[0060] negative electrode

[0061] The negative electrode includes a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector.

[0062] In some embodiments, the rechargeable capacity of the negative electrode is greater than the discharge capacity of the positive electrode to reduce the occurrence of lithium plating problems.

[0063] In some embodiments, the negative electrode sheet comprises a silicon-carbon material, which includes silicon-carbon particles. Based on the mass of the negative electrode active material layer, the mass content of silicon in the silicon-carbon particles is D%, satisfying: 5 ≤ D ≤ 20. As an example, the value of D can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 19, 20, or any combination of these values. This application, by controlling the mass content of silicon in the silicon-carbon particles within the aforementioned suitable range, works in conjunction with a specific electrolyte system to form a denser and more elastic passivation film on the negative electrode surface. This mitigates the damage to the SEI film and electrolyte decomposition caused by the expansion and contraction of the negative electrode sheet, enabling the secondary battery to maintain a high operating voltage and energy density while further improving the battery's thermal safety performance and impedance characteristics, meeting the comprehensive performance requirements of high-voltage (≥4.3V) lithium-ion batteries.

[0064] In some embodiments, the mass content of the compound of formula I, A%, and the mass content of silicon in the silicon-carbon particles, D%, satisfy the following relationship: 0.015 ≤ A / D ≤ 0.03. The value of A / D can be 0.015, 0.020, 0.025, 0.03, or any value within a range of any two of these values. By controlling the ratio of the mass content of the compound of formula I, A%, and the mass content of silicon in the silicon-carbon particles, D, within the above-mentioned suitable range, this application can achieve synergistic optimization of the electrolyte additive and the silicon-based anode material, improving the thermal safety of electronic devices while maintaining low impedance. When the ratio is less than this range, the energy density increases but the battery side reactions intensify, deteriorating the thermal performance of the secondary battery; when the ratio is greater than this range, the SEI film thickness increases, leading to increased battery impedance and deteriorating thermal performance.

[0065] In some embodiments, the anode material may also include other carbon-based anode materials, metal-based anode materials, and anode materials combining these.

[0066] Here, carbon-based anode materials refer to active materials with carbon as the main framework that can insert lithium. Examples of carbon-based anode materials include carbonaceous materials and graphitic materials.

[0067] Examples of carbonaceous materials include easily graphitized carbon and difficult-to-graphitize carbon. Among easily graphitized carbons are carbon materials derived from petroleum or coal using tar pitch as a raw material; specific examples include coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers, and pyrolysis-grown carbon fibers. Furthermore, examples of difficult-to-graphitize carbons include carbon materials with amorphous structures, such as glassy carbon; specific examples include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0068] Furthermore, examples of graphitic materials include natural graphite and artificial graphite. Among these, examples of artificial graphite include: artificial graphite formed by heat-treating carbon containing easily graphitizable carbon primarily at 2800°C or higher; graphitic MCMB formed by heat-treating MCMB at 2000°C or higher; and graphitic mesophase pitch-based carbon fiber formed by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher. Additionally, in this invention application, as a carbon-based negative electrode material, natural graphite whose surface is at least partially coated with amorphous carbon (amorphously coated natural graphite) can be used.

[0069] In addition, the metal-based negative electrode material is an active material containing a metal, and generally refers to an active material that contains an element capable of inserting lithium or alloying with lithium in its structure, and has a theoretical current capacity per unit mass of 500 mAh / g or more when inserting lithium or alloying with lithium. As the metal-based negative electrode material, for example, lithium metal, a single substance capable of forming a lithium alloy (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, and Ti, etc.), its alloy, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. can be used. Among them, as the metal-based negative electrode material, an active material containing silicon (silicon-based negative electrode material) is preferred. This is because the use of a silicon-based negative electrode material can increase the capacity of the secondary battery.

[0070] In some embodiments, the negative electrode material includes a silicon-based material.

[0071] In some embodiments, the silicon-based material includes at least one of a composite of a silicon-based substance and a carbon-based substance and silicon oxide (SiO x , 0 < x ≤ 2). The silicon-based substance can be silicon particles, silicon alloy particles, etc. The negative electrode material may further include a carbon material, and the carbon material can be crystalline carbon, amorphous carbon or a mixture thereof. The crystalline carbon can be graphite, such as amorphous, plate-shaped, flaky, spherical or fibrous natural graphite and / or artificial graphite, and the amorphous carbon can be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide or calcined coke, etc.

[0072] The composite of the silicon-based substance and the carbon-based substance can be a composite having a structure in which silicon nanoparticles are arranged on the carbon-based substance, a composite in which silicon particles are included on the surface and inside of the carbon-based substance, and a composite in which the silicon particles are coated with the carbon-based substance and are included in the carbon-based substance. In the composite of the silicon-based substance and the carbon-based substance, the carbon-based substance can be graphite, graphene, graphene oxide or a combination thereof.

[0073] The composite of the silicon-based substance and the carbon-based substance can be an active material obtained by dispersing silicon nanoparticles with an average particle size of 200 nm or less on the carbon-based substance particles and then coating them with carbon, an active material in which silicon (Si) particles are present on and inside graphite, etc.

[0074] From the viewpoint of improving the battery capacity, a silicon-carbon material, such as a composite material of porous carbon loaded with silicon, is preferred.

[0075] In addition, the negative electrode material can be used alone or two or more kinds can be used in combination at any ratio.

[0076] The negative electrode material layer may also include a negative electrode binder. The negative electrode binder improves the bonding between negative electrode material particles and the bonding between the negative electrode material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. When using an aqueous solvent to prepare the negative electrode slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, and polyvinyl alcohol.

[0077] As the current collector for retaining the negative electrode material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper. In some embodiments, the negative electrode current collector is a composite current collector, namely a 12μm composite copper foil (commercially available, a composite current collector made by depositing metallic copper layers on both sides of polyethylene terephthalate (PET) as the base material using an advanced vacuum deposition process).

[0078] The negative electrode can be prepared by coating a negative electrode slurry containing negative electrode material, resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0079] positive electrode

[0080] The positive electrode includes a positive current collector and a positive electrode material disposed on the surface of the positive current collector.

[0081] The cathode material can be one or more layers. Each layer in a multilayer cathode material can contain the same or different cathode active materials. The cathode active material is any material capable of reversibly inserting and deintercalating lithium ions.

[0082] Specifically, in some embodiments, the positive electrode active material includes at least one active material selected from the group consisting of: Li-Ni-Co-Al (NCA), Li-Ni-Co-Mn (NCM), lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4) and modified materials thereof.

[0083] Separating membrane

[0084] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0085] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator can be a resin, glass fiber, inorganic material, etc., formed from a material that stabilizes the electrolyte of this application. In some embodiments, the separator includes porous sheets with excellent liquid retention properties and non-woven fabric-like materials. Examples of materials for resin or glass fiber separators include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0086] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0087] Examples of inorganic materials include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in the form of, but are not limited to, particulates and fibrous materials.

[0088] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, and microporous membranes. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes. For example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0089] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, as well as the DC resistance characteristics and energy density of the secondary battery.

[0090] Thirdly, this application provides an electronic device, which includes the secondary battery provided in this application.

[0091] The application of the secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0092] The following examples illustrate embodiments of the secondary battery of this application, but this application is not limited to these embodiments. Unless otherwise stated, reagents, software, and instruments involved in the following examples are all conventional commercially available products or open-source materials. Furthermore, unless otherwise specified, "parts" and "%" refer to mass measurements.

[0093] Preparation of secondary batteries

[0094] 1. Preparation of the positive electrode sheet: The positive electrode active material LiCoO2, conductive agent Super P, and binder polyvinylidene fluoride are mixed in a weight ratio of 97:1.4:1.6, and then added to N-methylpyrrolidone (NMP) solvent. The mixture is stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is uniformly coated onto the positive electrode current collector aluminum foil. The coated aluminum foil is dried at 85℃, and then cold-pressed, cut, and slit. Finally, it is dried under vacuum at 85℃ for 4 hours to obtain the positive electrode.

[0095] 2. Separating Membrane: A polyethylene (PE) film with a thickness of 8 μm and a porosity of 55% was selected as the base membrane. PVDF slurry and an inorganic particulate slurry (a 70:30 mass ratio of platy boehmite and Al2O3) were coated onto both surfaces of the base membrane, and then dried to obtain the separating membrane. The coating thickness on each surface of this separating membrane was 3 μm.

[0096] 3. Fabrication of the negative electrode sheet: A mixture of silicon and carbon (mass ratio 50:50) is used as the negative electrode active material, Super P as the conductive agent, styrene-butadiene rubber as the binder, and sodium carboxymethyl cellulose (CMC, weight average molecular weight 90,000) as the thickener. The active material, Super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a weight ratio of 95.7:0.5:0.8:3, deionized water is added, and a negative electrode slurry is obtained under vacuum stirring. The solid content of the negative electrode slurry is 45 wt%. The active material layer slurry is uniformly coated on one surface of the negative electrode current collector copper foil and dried at 80°C to form the negative electrode active material layer. After cold pressing and slitting, the negative electrode sheet is obtained.

[0097] 4. Electrolyte preparation:

[0098] In a dry argon atmosphere glove box, compound A, compound B, solvent (EC:DEC = 3:7), lithium salt (lithium hexafluorophosphate, LPF6), and other additives were mixed thoroughly according to the proportions shown in Table 1 to obtain the electrolyte.

[0099] Based on the total mass of the electrolyte, the mass content of compound A (Formula I-1) is 0.3%, the mass content of compound B (Formula II-1) is 0.5%, the lithium salt is lithium hexafluorophosphate (LiPF6) with a mass content of 12%, the solvent has a mass content of 78.6%, and the remainder is other additives.

[0100] 5. Battery manufacturing: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. After welding the tabs, the electrode assembly is placed in an outer aluminum-plastic film. After removing the moisture at 80°C, the electrolyte is injected. The battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a lithium-ion battery.

[0101] 6. Testing Methods

[0102] (1) Pass rate of hot boxes at 130℃, 132℃ or 134℃:

[0103] The lithium-ion battery was discharged at 25°C with a constant current of 0.5C to 3.0V, then charged at a constant current of 0.5C to 4.53V, and finally charged at a constant voltage of 0.02C at 4.53V. It was then placed in a high-temperature furnace at 130°C, 132°C, or 134°C for 1 hour. After 1 hour, the lithium-ion battery was observed to see if it ignited; if it did not ignite, it was considered to have passed the test.

[0104] Five hot-box tests were performed on the lithium-ion batteries corresponding to each embodiment and comparative example at the same temperature (130°C, 132°C, or 134°C). Each hot-box test used new lithium-ion batteries that had not undergone hot-box testing. The five hot-box tests performed on the lithium-ion batteries corresponding to each embodiment and comparative example at the same temperature constituted a set of hot-box tests. The number of hot-box tests that passed in a set was recorded. When X batteries passed the hot-box test at the same temperature, the number of passed hot-box tests was recorded as X / 5.

[0105] (2) Impedance DCR test:

[0106] The lithium-ion battery was placed in a 0°C constant temperature chamber for 1 hour to achieve a constant temperature. It was then charged at a constant current of 0.5C to 4.2V, then charged at a constant current of 0.3C to 4.53V, and then charged at a constant voltage of 4.53V until the current reached 0.02C. The battery was then left to stand for 30 minutes. Finally, it was discharged at a constant current of 0.1C to 3.4V and left to stand for 30 minutes. The capacity obtained from this step was used as a baseline. At 0℃, charge the battery to 4.2V with a constant current of 0.5C, then charge it to 4.53V with a constant current of 0.3C, and then charge it to 0.02C with a constant voltage of 4.53V. Let it stand for 30 minutes. Discharge it with a constant current of 0.1C for 60 minutes (the capacity is calculated based on the theoretical capacity of the lithium-ion battery), and record the voltage at this time as U1. Then discharge it with a constant current of 0.1C for 1 second (the capacity is calculated based on the theoretical capacity of the lithium-ion battery), and record the voltage at this time as U2. Calculate the DC resistance corresponding to the 20% SOC state of the lithium-ion battery at 0℃: DCR=(U1-U2) / 0.1C.

[0107] (3) Test method for silicon content in the negative electrode material layer:

[0108] Take a lithium-ion battery, remove the negative electrode sheet, and clean it with dimethyl carbonate to remove electrolyte residue. Then, dry the negative electrode sheet in a vacuum drying oven. Separate the negative electrode material layer from the dried negative electrode sheet with a scraper, grind the resulting film fragments evenly, and take a powder sample. Mix the sample with KOH at a mass ratio of 1:7, place it in a crucible, heat it to 500 degrees Celsius at 5 degrees Celsius / minute in a muffle furnace, and hold it at that temperature for 3 hours. After cooling, immerse the crucible in boiling water for 1 hour, and then determine the silicon content of the solution using the ICP method.

[0109] The lithium-ion batteries in the following examples and comparative examples differ from those in Examples 1-1 only in that the contents and types of compounds A and B in the electrolyte are adjusted according to Table 1, while all other parameters remain unchanged. The performance test results of the lithium-ion batteries in each example and comparative example are shown in Table 1 below.

[0110] Table 1 -

[0111]

[0112] In the table, " / " indicates that the substance was not added.

[0113] Results Analysis: The experimental results in Table 1 show that the simultaneous addition of compound A (containing phosphate amine compounds) and compound B (containing pyridine ring compounds) to the electrolyte in this application, with the content of compound A satisfying 0.05 ≤ A ≤ 5 and the content of compound B satisfying 0.05 ≤ B ≤ 5, can improve the thermal safety performance and low impedance performance of the electronic device. In particular, when the content of compound A satisfies 0.1 ≤ A ≤ 1, the content of compound B satisfies 0.1 ≤ B ≤ 2, and 0.05 ≤ A / B ≤ 10, it can further achieve dual optimization of the electronic device's thermal safety and impedance performance.

[0114] The following examples differ from Examples 1-4 only in that all parameters remain unchanged except for those specified in Table 2. Experimental results are shown in Table 2.

[0115] Table 2-

[0116]

[0117]

[0118] In the table, " / " indicates that the substance was not added.

[0119] Results Analysis: Based on the experimental test results in Table 2, it can be seen that by controlling the ratio of the mass content A% of compound I, the mass content B% of compound II, and the mass content C% of lithium salt within the above range, this application can improve the safety performance and low impedance performance of the hot box.

[0120] In particular, when the range of 0.05≤(A+B) / C≤0.2 is met, the thermal stability of the electronic device can be further improved while maintaining low impedance characteristics, thereby meeting the requirements of the electronic device for thermal safety and low impedance performance.

[0121] The following examples differ from Examples 1-4 only in that all parameters remain unchanged except for those specified in Table 3. Experimental results are shown in Table 3.

[0122] Table 3

[0123]

[0124] In the table, " / " indicates that the substance was not added.

[0125] Results Analysis: Based on the experimental results in Table 3, it can be seen that when the mass content of the compound of Formula I is A% and the mass content of silicon in the silicon-carbon particles is D, which meets the range of 0.004≤A / D≤0.2, the safety performance and low impedance performance of the hot box can be improved.

[0126] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises a compound A and a compound B; The compound A is selected from a compound as shown in formula I; Formula I; wherein R1, R2, R3 and R4 are each independently selected from a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C2-C3 alkenyl group, a substituted or unsubstituted C2-C3 alkynyl group, a substituted or unsubstituted C1-C3 alkoxy group, a substituted or unsubstituted C3-C6 heterocyclic group, a substituted or unsubstituted aryl group, a substituted or unsubstituted benzyl group, and the substituents are selected from at least one of a halogen atom, a cyano group, a trifluoromethyl group, an alkenyl group, and an alkynyl group; The compound B is selected from a compound as shown in formula II; The compound of formula II is selected from at least one of the following compounds: Formula II-1, Formula II-2; Formula II-3, Formula II-4; Formula II-5, Formula II-6; Formula II-7; The mass content of the compound of formula II is B% based on the mass of the electrolyte, satisfying 0.05≤B≤5; The mass content of the compound of formula I is A% based on the mass of the electrolyte, satisfying 0.05≤A≤5.

2. The electrolyte of claim 1, wherein the compound of formula I is selected from at least one of the following compounds: Formula I-1, Formula I-2, Formula I-3; Formula I-4, Formula I-5, Formula I-6; Formula I-7, Formula I-8, Formula I-9.

3. The electrolyte according to any one of claims 1, characterized in that, The mass content A% of the compound of formula I and the mass content B% of the compound of formula II satisfy at least one of the following conditions: （1）0.1≤A≤1； （2）0.1≤B≤2； (3) 0.05≤A / B≤10.

4. The electrolyte of claim 1, wherein The electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium bisoxalato borate, lithium difluoro oxalato borate, lithium difluorophosphate, lithium tetrafluoroborate, lithium nitrate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, lithium difluoro oxalato phosphate, or lithium tetrafluoro oxalato phosphate, lithium hexafluorophosphate; The mass content of the lithium salt is C% based on the mass of the electrolyte, satisfying 1≤C≤20.

5. The electrolyte of claim 1, wherein 5≤C≤15。 6. The electrolyte of claim 4, wherein The mass content A% of the compound of formula I, the mass content B% of the compound of formula II, and the mass content C% of the lithium salt satisfy the following relationship: 0.053≤(A+B) / C≤0.

2.

7. A secondary battery characterized by comprising: The secondary battery comprises a negative electrode sheet and the electrolyte as claimed in any one of claims 1 to 6, wherein the charging cut-off voltage of the secondary battery is 4.3V to 4.8V.

8. The secondary battery according to claim 7, characterized by The negative electrode sheet comprises a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector, and the negative electrode material comprises a silicon-carbon material, and the mass content of silicon element in the silicon-carbon material is D% based on the mass of the negative electrode active material layer, satisfying 5≤D≤20.

9. The secondary battery according to claim 8, characterized by The mass content A% of the compound of formula I and the mass content D% of silicon element in the silicon-carbon particles satisfy the following relationship: 0.015≤A / D≤0.

06.

10. An electronic device, comprising: The electronic device comprises the secondary battery as claimed in any one of claims 7 to 9.

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