Electrolyte and secondary battery

Abstract

The present application provides an electrolyte and a secondary battery, the electrolyte comprises a solvent, an electrolyte and an additive, the additive comprises a compound represented by formula 1, based on the mass of the electrolyte, the mass percentage of the compound represented by formula I is W1, and 0.05% < = W1 < = 1%. Through the arrangement, the compound shown in the formula 1 has excellent film forming characteristic, C-N bonds in molecules are easy to break, formation of a stable electrolyte interface film on a positive electrode is facilitated, formation of a stable solid electrolyte interface film on a negative electrode is facilitated, further decomposition of an electrolyte is inhibited, an electrode material is protected, and impedance of the interface film is reduced; the imidazole group in the compound shown in the formula I is beneficial to removal of H2O and HF in the electrolyte, side reaction is further inhibited, and the high-temperature cycle performance, low-temperature cycle performance and normal-temperature cycle performance of the secondary battery are improved, so that the wide-temperature-range working capability of the secondary battery is improved.

Description

Technical Field

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

[0002] Rechargeable batteries (such as lithium-ion batteries) are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life, and environmental friendliness. As the application scope of rechargeable batteries continues to expand and their usage scenarios become more diverse, the market is placing higher demands on their electrochemical performance. For example, with the diversification of usage scenarios, rechargeable batteries must adapt to various climatic conditions; therefore, they are required to maintain good electrochemical performance over a wide temperature range, such as balancing room temperature cycling performance, high temperature cycling performance, and low temperature cycling performance.

[0003] However, under high-temperature conditions, side reactions easily occur between the electrolyte and the positive and negative electrode materials, leading to a decrease in the high-temperature performance of the secondary battery. Under low-temperature conditions, the impedance of the interfacial film is high, hindering charge transfer and lithium-ion diffusion, resulting in a decrease in the low-temperature performance of the secondary battery. Therefore, how to improve the room-temperature cycle performance, high-temperature cycle performance, and low-temperature cycle performance of secondary batteries, and enhance their wide-temperature-range operating capability, has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte and a secondary battery to improve the wide-temperature-range operating capability of the secondary battery, while also improving its cycling performance at room temperature, high temperature, and low temperature. The specific technical solution is as follows:

[0005] A first aspect of this application provides an electrolyte comprising a solvent, an electrolyte, and an additive, the additive comprising a first additive selected from compounds shown in Formula 1:

[0006]

[0007] Wherein, based on the mass of the electrolyte, the mass percentage of the compound shown in Formula I is W1, 0.05%≤W1≤1%, preferably 0.1%≤W1≤0.5%.

[0008] In some embodiments of this application, the additive includes a second additive selected from at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorodi(oxalate)phosphate. Based on the mass of the electrolyte, the mass percentage of the second additive is W2, 0.1% ≤ W2 ≤ 2%, preferably 0.1% ≤ W2 ≤ 1%.

[0009] In some embodiments of this application, the additive includes a third additive selected from at least one of vinylene carbonate, ethylene ethylene carbonate, ethylene ethylene sulfate, 1,3-propane sulfonyl lactone, 1,3-propene sulfonate lactone, and vinyl sulfite. Based on the mass of the electrolyte, the mass percentage of the third additive is W3, 0.5% ≤ W3 ≤ 2%, preferably 0.5% ≤ W3 ≤ 1%.

[0010] In some embodiments of this application, the additive includes a fourth additive selected from at least one of tris(trimethylsilane)borate, tris(vinyldimethylsilane)borate, tris(trimethylsilane)phosphate, and tris(vinyldimethylsilane)phosphate, wherein the mass percentage of the fourth additive is W4 based on the mass of the electrolyte, and 0.5% ≤ W4 ≤ 1%.

[0011] In some embodiments of this application, the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the mass percentage of the electrolyte is W5 based on the mass of the electrolyte, 12% ≤ W5 ≤ 17%.

[0012] In some embodiments of this application, the solvent is selected from at least one of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, sulfolane, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate. Based on the mass of the electrolyte, the mass percentage of the solvent is W6, where 80% ≤ W6 ≤ 88%.

[0013] The second aspect of this application provides a secondary battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte provided in the first aspect of this application.

[0014] The beneficial effects of this application are:

[0015] This application provides an electrolyte and a secondary battery. The electrolyte includes a solvent, an electrolyte, and an additive. The additive includes a first additive selected from compounds shown in Formula 1. Based on the mass of the electrolyte, the mass percentage of the compound shown in Formula 1 is W1, where 0.05% ≤ W1 ≤ 1%. The electrolyte includes the compound shown in Formula 1, and the mass percentage of the compound shown in Formula 1 is controlled within the scope of this application. The compound shown in Formula 1 has excellent film-forming properties. The CN bonds in the molecule are easily broken, which is beneficial for forming a stable electrolyte interphase (CEI) film at the positive electrode and a stable solid electrolyte interphase (SEI) film at the negative electrode. This inhibits further decomposition of the electrolyte, protects the electrode materials, and reduces the interfacial film impedance. Furthermore, the imidazole group in the compound shown in Formula 1 is beneficial for removing H2O and HF from the electrolyte, further inhibiting the occurrence of side reactions and improving the high-temperature cycle performance, low-temperature cycle performance, and room-temperature cycle performance of the secondary battery, thereby improving the wide-temperature range operation capability of the secondary battery.

[0016] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0017] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0018] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0019] A first aspect of this application provides an electrolyte comprising a solvent, an electrolyte, and an additive, the additive comprising a first additive selected from compounds shown in Formula 1:

[0020]

[0021] Wherein, based on the mass of the electrolyte, the mass percentage content of the compound shown in Formula I is W1, where 0.05% ≤ W1 ≤ 1%, preferably 0.1% ≤ W1 ≤ 0.5%. For example, the value of W1 can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range of any two of these values.

[0022] The inventors discovered that the electrolyte contains the compound shown in Formula 1, and the mass percentage of the compound shown in Formula 1 is controlled within the scope of this application. The compound shown in Formula 1 has excellent film-forming properties. The CN bond in the molecule is easily broken, especially the amide group between the two imidazole groups, which is easily broken after gaining or losing electrons. During charging and discharging, the molecule will decompose and participate in film formation by breaking the CN bond, introducing the N-containing component into the interface film. This is beneficial for forming a stable electrolyte interface film (CEI film) at the positive electrode, and also beneficial for forming a stable solid electrolyte interface film (SEI film) at the negative electrode. This inhibits further decomposition of the electrolyte, protects the electrode material, and reduces the interface film impedance. Furthermore, the imidazole group in the compound shown in Formula 1 is beneficial for removing H2O and HF from the electrolyte, further inhibiting the occurrence of side reactions, improving the stability of the electrode structure, reducing impedance, and improving the high-temperature cycle performance, low-temperature cycle performance, and room-temperature cycle performance of the secondary battery, thereby improving the wide-temperature range operation capability of the secondary battery. When the value of W1 is too small, for example, less than 0.05%, the content of the compound shown in Formula 1 is too low, resulting in less nitrogen content in the formed CEI and SEI films. This leads to poor stability of the CEI and SEI films, making them prone to damage during the charging and discharging process of the secondary battery, thus affecting the cycle performance. Conversely, when the value of W1 is too large, for example, greater than 1%, the formed SEI and CEI films become thicker, increasing impedance and further affecting the cycle performance of the secondary battery. The inclusion of the compound shown in Formula 1 in the electrolyte of this application, and the control of its mass percentage within the range of this application, is beneficial for improving the high-temperature, low-temperature, and room-temperature cycle performance of the secondary battery, thereby enhancing its wide-temperature-range operating capability. In this application, high temperature refers to a temperature greater than or equal to 45°C, and low temperature refers to a temperature less than or equal to 0°C.

[0023] In some embodiments of this application, the additive includes a second additive selected from at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorodi(oxalate)phosphate. Based on the mass of the electrolyte, the mass percentage of the second additive is W2, where 0.1% ≤ W2 ≤ 2%, preferably 0.1% ≤ W2 ≤ 1%. For example, the value of W2 can be 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%, 2%, or a range consisting of any two of these values. Within the scope of this application, the inclusion of a second additive in the electrolyte and the control of its mass percentage are as follows: On one hand, the second additive facilitates the formation of a lithium-containing interfacial film at the interface between the positive and negative electrodes, thereby improving the diffusion capacity of lithium ions at the electrode interface. Simultaneously, the nitrogen-containing component in the first additive possesses lone pairs of electrons, which can further enhance lithium ion transport at the electrode interface. The synergistic effect of both additives improves the low-temperature conductivity of the secondary battery. On the other hand, the lithium-containing component serves as the framework of the interfacial film, further enhancing its stability. Furthermore, the first additive's dehydration and deacidification properties further reduce interfacial film damage, synergistically improving its stability. The synergistic effect of the first and second additives further enhances lithium ion transport performance and interfacial film stability, thereby further improving the low-temperature, high-temperature, and room-temperature cycling performance of the secondary battery.

[0024] In some embodiments of this application, the additive includes a third additive selected from at least one of vinylene carbonate, ethylene ethylene carbonate, ethylene ethylene sulfate, 1,3-propane sulfonyl lactone, 1,3-propene sulfonate lactone, and vinyl sulfite. Based on the mass of the electrolyte, the mass percentage of the third additive is W3, 0.5% ≤ W3 ≤ 2%, preferably 0.5% ≤ W3 ≤ 1%. For example, the value of W3 can be 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%, 2%, or a range consisting of any two of these values. The electrolyte includes a third additive, and the content of the third additive is controlled within the scope of this application. On the one hand, the third additive is beneficial for forming a denser CEI and SEI film, further reducing side reactions and protecting electrode materials. However, in actual operation of secondary batteries, if the third additive is used alone, the resulting interfacial film is easily damaged by HF and other ions. This application uses the first and third additives together. The first additive has the function of removing water and acid, which can reduce HF attack on the interfacial film. The two work synergistically to maintain the stability of the interfacial film. In addition, although the third additive is beneficial for forming a dense interfacial film at the positive and negative electrodes and improving the stability of the interfacial film, it is not conducive to lithium-ion transport. This application uses the first and third additives together. The nitrogen-containing component in the first additive also participates in the construction of the interfacial film. The lone pair electrons of nitrogen are beneficial for lithium-ion transport, thereby making up for the problem of lithium-ion transport difficulties caused by the third additive being used alone. The synergistic effect of the first and third additives further improves the stability of the interfacial film and takes into account the lithium-ion transport performance at the interface, further improving the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0025] In some embodiments of this application, the additive includes a fourth additive selected from at least one of tris(trimethylsilane)borate, tris(vinyldimethylsilane)borate, tris(trimethylsilane)phosphate, and tris(vinyldimethylsilane)phosphate. Based on the mass of the electrolyte, the mass percentage of the fourth additive is W4, where 0.5% ≤ W4 ≤ 1%. For example, the value of W4 can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range of any two of these values. In addition to the first additive in the electrolyte, the fourth additive is further introduced. This fourth additive is beneficial for improving the stability and ionic conductivity of the SEI and CEI films, reducing impedance. Simultaneously, the fourth additive can react with water or acid in the electrolyte, working synergistically with the first additive to further remove water or acid from the electrolyte. The synergistic effect of the first and fourth additives further removes water and acid from the electrolyte, jointly improving the stability of the interfacial films and further enhancing the low-temperature, high-temperature, and room-temperature cycling performance of the secondary battery.

[0026] In some embodiments of this application, the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. Based on the mass of the electrolyte, the mass percentage of the electrolyte is W5, where 12% ≤ W5 ≤ 17%. For example, the value of W5 can be 12%, 13%, 14%, 15%, 16%, 17%, or a range of any two of these values. The electrolyte includes electrolytes within the above range, and by controlling the mass percentage of the electrolyte within the range of this application, the electrolyte can have higher ionic conductivity and better electrochemical stability, which can further improve the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0027] In some embodiments of this application, the solvent is selected from at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, sulfolane, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate. Based on the mass of the electrolyte, the mass percentage of the solvent is W6, where 80% ≤ W6 ≤ 88%. For example, the value of W6 can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or a range of any two of these values. The electrolyte includes solvents within the above-mentioned range, and by adjusting the mass percentage of the solvent within the scope of this application, the electrolyte can have suitable viscosity, high ionic conductivity, and good electrochemical stability, which can further improve the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0028] In some embodiments of this application, the electrolyte includes a first additive, a second additive, and a third additive, and satisfies the following conditions: 0.05% ≤ W1 ≤ 1%, 0.1% ≤ W2 ≤ 2%, and 0.5% ≤ W3 ≤ 2%, which is beneficial for further improving the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0029] In some embodiments of this application, the electrolyte includes a first additive, a second additive, and a fourth additive, and satisfies the following conditions: 0.05% ≤ W1 ≤ 1%, 0.1% ≤ W2 ≤ 2%, and 0.5% ≤ W4 ≤ 1%, which is beneficial for further improving the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0030] In some embodiments of this application, the electrolyte includes a first additive, a third additive, and a fourth additive, and satisfies the following conditions: 0.05% ≤ W1 ≤ 1%, 0.5% ≤ W3 ≤ 2%, and 0.5% ≤ W4 ≤ 1%, which is beneficial for further improving the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0031] In some embodiments of this application, the electrolyte includes a first additive, a second additive, a third additive, and a fourth additive, and satisfies the following conditions: 0.05% ≤ W1 ≤ 1%, 0.1% ≤ W2 ≤ 2%, 0.5% ≤ W3 ≤ 2%, and 0.5% ≤ W4 ≤ 1%, which is beneficial for further improving the low-temperature cycle performance, high-temperature cycle performance, and room-temperature cycle performance of the secondary battery.

[0032] The second aspect of this application provides a secondary battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte provided in the first aspect of this application.

[0033] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved; for example, the negative electrode current collector can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel or foamed copper, aluminum foil, or a composite negative electrode current collector. The aforementioned composite negative electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of copper, copper alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the negative electrode material layer and the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be from 50 μm to 180 μm, and the thickness of the negative electrode current collector can be from 3 μm to 10 μm.

[0034] The negative electrode material layer includes a negative electrode active material. This application does not have a particular limitation on the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, lithium metal, etc. Graphite may include, but is not limited to, at least one of natural graphite or artificial graphite; the aforementioned silicon-based materials may include, but are not limited to, at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys; the aforementioned tin-based materials may include, at least one of elemental tin, tin oxide compounds, or tin alloys.

[0035] The negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder. This application does not impose any particular limitation on the types of negative electrode conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), sodium carboxymethyl cellulose (CMC-Na), polymethyl methacrylate (PMAA), or carboxymethyl chitosan (CMCS). This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode conductive agent, and negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0036] In this application, the secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved. This application does not have any particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, the positive current collector can be an aluminum foil, an aluminum alloy foil, or a composite positive current collector. The aforementioned composite positive electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of aluminum, aluminum alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer can be from 50 μm to 250 μm, and the thickness of the positive electrode current collector can be from 7 μm to 20 μm.

[0037] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0038] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fiber. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0039] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), glass fiber, polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of separator may include at least one of woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, or spun membrane. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the separator thickness may be from 4 μm to 20 μm.

[0040] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0041] In some embodiments of this application, the secondary battery may include, but is not limited to: lithium metal secondary battery, lithium-ion secondary battery (lithium-ion battery), lithium polymer secondary battery or lithium-ion polymer secondary battery, etc.

[0042] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0043] Example

[0044] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0045] Test methods and equipment:

[0046] ambient temperature cycling performance test

[0047] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V. The discharge capacity was recorded as C1, constituting one charge-discharge cycle. This charge-discharge cycle was repeated for 1000 cycles. The discharge capacity C2 after 1000 cycles was recorded, and the cycle capacity retention rate of the lithium-ion battery was calculated.

[0048] Capacity retention rate during ambient temperature cycling = C2 / C1 × 100%.

[0049] High-temperature cycling performance test

[0050] The lithium-ion battery was placed in a 45°C constant temperature test chamber and left to stand for 60 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V. The discharge capacity was recorded as Q1, constituting one charge-discharge cycle. This charge-discharge cycle was repeated for 700 cycles. The discharge capacity after 700 cycles was recorded as Q2, and the cycle capacity retention rate of the lithium-ion battery was calculated. High-temperature cycle capacity retention rate = Q2 / Q1 × 100%.

[0051] Low temperature cycling performance test

[0052] The lithium-ion battery was placed in a -10℃ constant temperature test chamber and left to stand for 240 minutes to reach a constant temperature. It was then charged at a constant current of 0.5C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.2C to 2.75V. The discharge capacity was recorded as R1, constituting one charge-discharge cycle. This charge-discharge cycle was repeated for 300 cycles. The discharge capacity R2 after 300 cycles was recorded, and the cycle capacity retention rate of the lithium-ion battery was calculated. Low-temperature cycle capacity retention rate = R2 / R1 × 100%.

[0053] Example 1

[0054] <Preparation of Electrolyte>

[0055] In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 1:2 to obtain a solvent. Then, the first additive compound (Formula 1) and the electrolyte LiPF6 were added to the solvent. Based on the total mass of the electrolyte, the mass percentage of LiPF6 (W5) was 12.5%, the mass percentage of the first additive (W1) was 0.05%, and the remainder was solvent, with a solvent mass percentage (W6) of 87.45%.

[0056] <Preparation of Negative Electrode Sheets>

[0057] Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (binder), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 95:1.5:2:1.5. Deionized water was added as a solvent, and the mixture was stirred evenly in a vacuum mixer to obtain a negative electrode slurry with a solid content of 49 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After drying at 85°C, the sheet was rolled, then slit and had tabs welded to obtain a negative electrode sheet with a size of 708 mm × 59 mm for later use. The thickness of the single-sided negative electrode material layer was 46.5 μm, and the compaction density was 1.65 g / cm³. 3 .

[0058] <Preparation of the positive electrode>

[0059] Lithium nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride (PVDF), and acetylene black were mixed at a mass ratio of 96.8:2:1.2. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred evenly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 55 wt%. This slurry was uniformly coated onto one surface of a 7 μm thick aluminum foil used as a positive electrode current collector. The foil was then baked in ovens at different temperature gradients (90℃, 100℃, and 85℃) at a speed of 2200 mm / min, followed by drying in a 120℃ oven for 8 hours to obtain a single-sided coated positive electrode sheet. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After drying at 90℃, the sheet was rolled, slit, and had tabs welded to obtain a 558 mm × 55 mm positive electrode sheet for later use. The thickness of the single-sided positive electrode material layer is 59 μm, and the compaction density is 3.5 g / cm³. 3 .

[0060] <Preparation of the diaphragm>

[0061] A porous polyethylene (PE) membrane with a thickness of 8μm (provided by Shenzhen Xingyuan Material Technology Co., Ltd.) was used as the separator.

[0062] <Preparation of Lithium-ion Batteries>

[0063] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The electrode assembly is then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 85°C. The electrolyte prepared above is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and sorting processes to obtain a lithium-ion battery.

[0064] Examples 1 to 5

[0065] Except for the adjustment of the mass percentage W1 of the compound of formula 1 shown in Table 1 in the <Preparation of Electrolyte>, and the change of the mass percentage W6 of the solvent accordingly, the rest is the same as in Example 1.

[0066] Examples 6 to 13

[0067] Except for the addition of a second additive to the electrolyte in the <Electrolyte Preparation> section, where the type and mass percentage W2 of the second additive are adjusted according to Table 1, and the mass percentage W6 of the solvent is changed accordingly, the rest is the same as in Example 2. In the table, LiODFP is lithium difluorodioxalate phosphate, LiBF4 is lithium tetrafluoroborate, LiODFB is lithium difluorodioxalate borate, and LiDFP is lithium difluorophosphate.

[0068] Examples 14 to 23

[0069] Except for the addition of a third additive to the electrolyte in the <Preparation of Electrolyte> section, where the type and mass percentage W3 of the third additive are adjusted according to Table 1, and the mass percentage W6 of the solvent is changed accordingly, the rest is the same as in Example 2. In the table, DTD is ethylene sulfate, VC is vinylene carbonate, VEC is ethylene ethylene carbonate, and PS is 1,3-propanesulfonyl lactone.

[0070] Examples 24 to 30

[0071] Except for the addition of a fourth additive to the electrolyte in the <Preparation of Electrolyte> section, where the type and mass percentage W4 of the fourth additive are adjusted according to Table 1, and the mass percentage W6 of the solvent is changed accordingly, the rest is the same as in Example 2. In the table, TMVSB is tris(vinyldimethylsilane)borate, TMSB is tris(trimethylsilane)borate, and TMSP is tris(trimethylsilane)phosphate.

[0072] Examples 31 to 35

[0073] Except for adjusting the relevant parameters according to Table 1 in the <Preparation of Electrolyte> section, the rest is the same as in Example 2.

[0074] Comparative Example 1

[0075] Except for the fact that the first additive is not added in the <Preparation of Electrolyte>, and the mass percentage of solvent W6 is changed accordingly, the rest is the same as in Example 1.

[0076] Comparative Example 2

[0077] Except for the adjustment of the mass percentage of the first additive according to Table 1 in the <Preparation of Electrolyte>, and the change of the mass percentage of the solvent W6 accordingly, the rest is the same as in Example 1.

[0078] Comparative Example 3

[0079] Except for the fact that the first additive is not added in the <Preparation of Electrolyte>, and the mass percentage of solvent W6 is changed accordingly, the rest is the same as in Example 7.

[0080] Comparative Example 4

[0081] Except that the first additive is not added in the <Preparation of Electrolyte>, and the mass percentage of solvent W6 is changed accordingly, the rest is the same as in Example 16.

[0082] Comparative Example 5

[0083] Except for the fact that the first additive is not added in the <Preparation of Electrolyte>, and the mass percentage of solvent W6 is changed accordingly, the rest is the same as in Example 26.

[0084]

[0085]

[0086] As can be seen from Examples 1 to 5 and Comparative Examples 1 to 5, when the electrolyte includes the first additive within the scope of this application and the mass percentage content W1 of the first additive is controlled within the scope of this application, the lithium-ion battery can have a higher room temperature cycle retention rate, a higher high temperature cycle retention rate, and a higher low temperature cycle retention rate. This indicates that the lithium-ion battery has good room temperature cycle performance, good high temperature cycle performance, and good low temperature cycle performance, that is, the lithium-ion battery has good wide temperature range operating capability.

[0087] The type and mass percentage W2 of the second additive typically affect the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of lithium-ion batteries. As can be seen from Examples 2, 6 to 13 and Comparative Example 3, when the electrolyte includes the first additive within the scope of this application, and a second additive is further introduced and the mass percentage W2 of the second additive is controlled within the scope of this application, the resulting lithium-ion battery exhibits higher room temperature capacity retention, higher high temperature cycle retention, and higher low temperature cycle retention. This indicates that the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of the lithium-ion battery are further improved, that is, the wide temperature range operating capability of the lithium-ion battery is further enhanced.

[0088] The type and mass percentage W3 of the third additive typically affect the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of lithium-ion batteries. As can be seen from Examples 2, 14 to 23, and Comparative Example 4, when a third additive is further introduced into the electrolyte based on the first additive within the scope of this application, and the mass percentage W3 of the third additive is controlled within the scope of this application, the resulting lithium-ion battery exhibits higher room temperature capacity retention, higher high temperature cycle retention, and higher low temperature cycle retention. This indicates that the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of the lithium-ion battery are further improved, that is, the wide temperature range operating capability of the lithium-ion battery is further enhanced.

[0089] The type and mass percentage W4 of the fourth additive typically affect the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of lithium-ion batteries. As can be seen from Examples 2, 24 to 30, and Comparative Example 5, when the electrolyte includes the first additive within the scope of this application, the introduction of a fourth additive and the adjustment of the mass percentage W4 of the fourth additive within the scope of this application result in a lithium-ion battery with higher room temperature capacity retention, higher high temperature cycle retention, and higher low temperature cycle retention. This indicates that the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of the lithium-ion battery are further improved, that is, the wide temperature range operating capability of the lithium-ion battery is further enhanced.

[0090] As can be seen from Examples 31 to 35, the electrolyte, based on the first additive, further introduces at least two of the second, third, and fourth additives, which has a good synergistic effect and further improves the room temperature cycle performance, high temperature cycle performance, and low temperature cycle performance of the lithium-ion battery.

[0091] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrolyte comprising a solvent, an electrolyte, and an additive, said additive comprising a first additive selected from compounds of Formula 1: in, Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is W1, where 0.05% ≤ W1 ≤ 1%.

2. The electrolyte according to claim 1, wherein, 0.1％≤W1≤0.5％。 3. The electrolyte according to claim 1, wherein, The additive includes a second additive selected from at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorodi(oxalate)phosphate. Based on the mass of the electrolyte, the mass percentage of the second additive is W2, where 0.1% ≤ W2 ≤ 2%.

4. The electrolyte according to claim 3, wherein, 0.1％≤W2≤1％。 5. The electrolyte according to claim 1, wherein, The additive includes a third additive selected from at least one of vinylene carbonate, ethylene ethylene carbonate, ethylene ethylene sulfate, 1,3-propane sulfonyl lactone, 1,3-propene sulfonate lactone, and vinyl sulfite. Based on the mass of the electrolyte, the mass percentage of the third additive is W3, where 0.5% ≤ W3 ≤ 2%.

6. The electrolyte according to claim 5, wherein, 0.5％≤W3≤1％。 7. The electrolyte according to any one of claims 1 to 6, wherein, The additive includes a fourth additive selected from at least one of tris(trimethylsilane)borate, tris(vinyldimethylsilane)borate, tris(trimethylsilane)phosphate, and tris(vinyldimethylsilane)phosphate, wherein the mass percentage of the fourth additive is W4 based on the mass of the electrolyte, and 0.5% ≤ W4 ≤ 1%.

8. The electrolyte according to any one of claims 1 to 6, wherein, The electrolyte is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. Based on the mass of the electrolyte, the mass percentage of the electrolyte is W5, where 12% ≤ W5 ≤ 17%.

9. The electrolyte according to any one of claims 1 to 6, wherein, The solvent is selected from at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, sulfolane, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate. Based on the mass of the electrolyte, the mass percentage of the solvent is W6, where 80% ≤ W6 ≤ 88%.

10. A secondary battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte according to any one of claims 1 to 9.

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