Electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte and a lithium ion battery. Specifically, through directional adsorption, synergistic reaction and structural coupling of an annular sulfur-oxygen double bond-containing compound and a compound as shown in a formula (I) at an interface, a composite interfacial film with gradient structural characteristics is constructed on the surface of the positive electrode in situ, so that the physicochemical characteristics of an electrolyte-electrode interface are remarkably improved; the technical effect of improving the performance of the lithium ion battery is achieved.

Description

Electrolyte and Lithium-ion Battery Technical Field

[0001] This disclosure relates to the technical field, and more particularly to an electrolyte and a lithium-ion battery. Background Technology

[0002] As lithium-ion batteries develop towards higher specific energy, cathode materials are increasingly employing higher compaction densities and higher loading rates to achieve higher energy density per unit volume. However, the structural characteristics of thick, dense cathodes result in narrower internal channels and lower connectivity, significantly slowing down the wetting, absorption, and penetration processes of the electrolyte on the electrode surface. The inability of the electrolyte to penetrate the electrode quickly not only affects the overall wetting uniformity of the electrode but also leads to the formation of localized dry zones, causing positional shifts in the interfacial reaction and consequently impacting the efficiency of the initial formation of a stable interfacial film. This delayed wetting phenomenon easily leads to uneven film formation and decreased utilization of active materials, becoming a key limiting factor in the production and use of thick, dense cathodes. Due to insufficient initial wetting, thick, dense electrodes result in uneven film formation, making their interfacial films more prone to localized rupture, dissolution, or reconstruction under high-temperature environments, leading to increased impedance, gas generation, and accelerated capacity decay. Summary of the Invention

[0003] In view of this, the purpose of this disclosure is to provide an electrolyte and a lithium-ion battery.

[0004] For the purposes described above, this disclosure provides an electrolyte comprising a cyclic sulfur-oxygen double bond compound and a compound as shown in formula (I):

[0005] Equation (I); where n is an integer from 1 to 8.

[0006] In some embodiments, the cyclic sulfur-containing oxygen double bond compound comprises at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, and vinyl sulfate; and / or the compound represented by formula (I) comprises at least one of the following structural formulas: Formula (II) Formula (Ⅲ), Formula (Ⅳ).

[0007] In some embodiments, the mass fraction of the cyclic sulfur-containing oxygen double bond compound is 0.1% to 3% based on the total mass of the electrolyte; and / or the mass fraction of the compound represented by formula (I) is 0.1% to 3% based on the total mass of the electrolyte.

[0008] In some embodiments, the mass fraction of the cyclic sulfur-oxygen double bond compound is 0.5% to 2% based on the total mass of the electrolyte; and / or the mass fraction of the compound represented by formula (I) is 0.5% to 1% based on the total mass of the electrolyte.

[0009] In some embodiments, the mass ratio of the compound represented by formula (I) to the cyclic sulfur-containing oxygen double bond compound is 1:1 to 1:3.

[0010] In some embodiments, the additive further includes at least one of a first additive and a second additive; wherein the first additive includes at least one of tetravinylsilane, ethyltrivinylsilane, tetramethyldivinyldisiloxane, trimethoxy(3,3,3-trifluoropropyl)silane and tetramethoxysilane; and the second additive includes at least one of lithium difluorophosphate, lithium dioxaborate, lithium tetrafluoroborate and lithium difluorooxaborate.

[0011] In some embodiments, the mass fraction of the first additive is 0.1% to 1% based on the total mass of the electrolyte; and / or the mass fraction of the second additive is 0.2% to 3% based on the total mass of the electrolyte.

[0012] In some embodiments, a solvent is further included; the solvent includes carboxylic acid esters and carbonates; wherein, based on the total mass of the electrolyte, the mass fraction of the solvent is 75% to 85%; and the mass fraction of the carboxylic acid ester is 8% to 16% based on the total mass of the electrolyte.

[0013] In some embodiments, a lithium salt is also included; the lithium salt has a mass fraction of 10% to 20% based on the total mass of the electrolyte.

[0014] Based on the same inventive concept, this disclosure also provides a lithium-ion battery, including the electrolyte, positive electrode, and negative electrode described in any one of the foregoing embodiments; wherein the positive electrode includes a positive active material, the thickness of which on one side of the positive electrode is 70 μm to 170 μm, and the areal density on one side is 25 mg / cm³. 2 ~32mg / cm 2 .

[0015] As can be seen from the above, the electrolyte and lithium-ion battery provided in this disclosure utilize cyclic sulfur-containing oxygen double bond compounds and compounds as shown in formula (I): Formula (I) shows that the directional adsorption, synergistic reaction and structural coupling of these two types of functional molecules at the interface can construct a composite interface film with gradient structure characteristics in situ on the positive electrode surface, thereby significantly improving the physicochemical properties of the electrolyte-electrode interface and achieving the technical effect of improving the performance of lithium-ion batteries. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains.

[0018] In this disclosure, the term "range" is used to define a range in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~130 and 70~120 are listed for a specific parameter, it is expected that ranges of 60~120 and 70~130 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this disclosure, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0020] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0021] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0022] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B".

[0023] In related technologies, the performance of the interfacial film can be improved to some extent by adjusting the solvent composition in the electrolyte, introducing film-forming additives, and optimizing interface engineering strategies. However, such solutions still face many limitations in thick and dense cathode systems and under high temperature conditions.

[0024] On the one hand, the electrolyte has limited wetting ability on the electrode surface, making it difficult to quickly and uniformly penetrate deep into the pores in a cathode structure with high compaction density. The lag in electrolyte absorption and localized dry areas during the wetting process lead to insufficient interface formation and discontinuous film formation, resulting in increased initial irreversible capacity and higher interfacial impedance. This problem becomes more pronounced as the electrode thickness increases, making it difficult for the electrolyte to cover the entire positive electrode active area in a short time, thus affecting battery formation quality and cycle stability.

[0025] On the other hand, due to the uneven distribution of the initial film-forming area, the electrode is more prone to concentrated side reactions such as solvent oxidation, salt decomposition, and metal dissolution at high temperatures. This leads to local rupture or repeated reconstruction of the interfacial film, resulting in a rapid increase in impedance, accelerated capacity decay, and increased gas generation. Although current film-forming additives can improve interfacial thermal stability to some extent, their distribution within thick electrodes is often difficult to control. The film-forming process is limited by the wetting quality of the electrolyte, causing the overall structure of the protective film to easily become unstable under high-temperature conditions. Commonly used interfacial film-forming additives exhibit strong hydrophobic properties. Although they can form a protective layer with a certain degree of thermal stability on the electrode surface, they may also reduce the overall spreading ability of the electrolyte, making it more difficult for the electrolyte to diffuse in the dense porous structure, further exacerbating the wetting problem of thick electrodes. Since wettability and high-temperature stability are often affected by different molecular characteristics, current additive systems cannot simultaneously balance these two key interfacial requirements, thus limiting the effectiveness of improving the performance of thick electrodes.

[0026] In view of this, the present disclosure provides an electrolyte and a lithium-ion battery, which utilize cyclic sulfur-containing oxygen double bond compounds and compounds as shown in formula (I): Formula (I) shows that the directional adsorption, synergistic reaction and structural coupling of these two types of functional molecules at the interface can construct a composite interface film with gradient structure characteristics in situ on the positive electrode surface, thereby significantly improving the physicochemical properties of the electrolyte-electrode interface and achieving the technical effect of improving the performance of lithium-ion batteries.

[0027] To make the technical solutions of this disclosure clearer and easier to understand, the electrolyte and lithium-ion battery provided in this disclosure will be described in detail below with reference to specific embodiments.

[0028] electrolyte In a first aspect, embodiments of this disclosure provide an electrolyte comprising a cyclic sulfur-oxygen double-bonded compound and a compound as shown in formula (I): Equation (I); where n is an integer from 1 to 8, for example 1, 2, 3, 4, 5, 6, 7, 8.

[0029] It should be noted that cyclic compounds containing sulfur-oxygen double bonds are compounds with a cyclic structure that contain sulfur-oxygen double bonds. 'n' represents the number of carbon atoms in the fluorocarbon chain; different 'n' values ​​correspond to fluorocarbon chain structures of different lengths.

[0030] The compound shown in Formula (I) and the cyclic sulfur-oxygen double bond compound exhibit synergistic enrichment and directional adsorption on the polar surface of the positive electrode. Specifically, the highly polar acrylate groups of the compound shown in Formula (I) can be anchored to polar sites on the surface of the positive electrode active material through polarity or chemical interaction, while the fluorocarbon segments it carries spontaneously align towards the electrolyte side at the interface. Simultaneously, the cyclic sulfur-oxygen double bond compound participates in interfacial adsorption and initial film formation reactions through sulfur-oxygen bonds. Together, they form a low surface energy coating layer on the positive electrode surface, significantly reducing the liquid-solid interface energy, promoting the spread and penetration of the electrolyte in the thick and dense positive electrode, thereby improving wettability.

[0031] At high positive electrode potential, the compound shown in formula (I) and the cyclic sulfur-oxygen double bond compound undergo synergistic oxidative decomposition and cross-linking reactions at the interface. The cyclic sulfur-oxygen double bond compound preferentially generates film-forming structural units with inorganic (sulfite) esters; the compound shown in formula (I) participates in the interfacial reaction through its unsaturated bonds, undergoing addition with the active intermediate derived from the sulfoxy group, thus stably introducing the fluorocarbon chain into the forming interfacial membrane network. An in-situ constructed composite cathode-electrolyte interphase (CEI) membrane structure exhibiting a compositional gradient from the inside out, with the inner layer dominated by an organic-inorganic hybrid sulfur-oxygen structure, possesses good mechanical support and Li + Transmission capability; the outer layer is enriched with fluorocarbon segments, which can effectively regulate surface energy and prevent direct contact between electrolyte molecules and the positive electrode surface.

[0032] It can be seen that by introducing the interfacial active properties of formula (I) and the cyclic sulfur-containing oxygen double bond compound that can form a stable protective film on the electrode surface, the electrolyte wetting behavior of the thick cathode can be effectively improved, the interfacial film quality can be enhanced, the interfacial side reactions under high temperature conditions can be suppressed, and the cycle stability and overall performance of lithium-ion batteries can be improved without increasing environmental and toxic risks.

[0033] In some embodiments, the cyclic sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, and vinyl sulfate.

[0034] In some embodiments, the compound represented by formula (I) comprises at least one of the following structural formulas: Formula (II) Formula (Ⅲ), Formula (Ⅳ).

[0035] It should be understood that the value of n for the compound shown in formula (II) is 5, the value of n for the compound shown in formula (III) is 2, and the value of n for the compound shown in formula (IV) is 7.

[0036] In some embodiments, based on the total mass of the electrolyte, the mass fraction of the cyclic sulfur-containing oxygen double bond compound is 0.1% to 3%, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2.1%, 2.5%, 2.8%, 3%, etc. Such an addition range enables the formation of a stable protective film on the electrode surface, which is beneficial to improving the overall performance of the battery.

[0037] Optionally, the mass fraction of the cyclic sulfur-containing oxygen double bond compound is 0.5% to 2%.

[0038] In some embodiments, based on the total mass of the electrolyte, the mass fraction of the compound shown in formula (I) is 0.1% to 3%, for example 0.1%, 0.2%, 0.4%, 0.7%, 1%, 1.3%, 1.5%, 1.7%, 2%, 2.4%, 2.8%, 3%, etc.

[0039] Optionally, the mass fraction of the compound shown in formula (I) is 0.5% to 1%.

[0040] In some embodiments, the mass ratio of the compound shown in formula (I) to the cyclic sulfur-containing oxygen double bond compound is 1:1 to 1:3, for example, 1:1, 1:2, 1:3, etc. Such a ratio range helps the two to work synergistically and improve battery performance.

[0041] In some embodiments, the electrolyte further includes at least one of a first additive and a second additive.

[0042] For example, the first additive includes at least one of tetravinylsilane (TVSi), ethyltrivinylsilane, tetramethyldivinyldisiloxane, trimethoxy(3,3,3-trifluoropropyl)silane and tetramethoxysilane.

[0043] Here, the first additive can participate in the interfacial reaction under high voltage and high temperature conditions. Through its multi-unsaturated functional groups, it forms a cross-linked structure, effectively capturing the active intermediates generated during the interfacial reaction and inhibiting the continuous decomposition and gas production of the electrolyte.

[0044] For example, the second additive includes at least one of lithium difluorophosphate (LiPO2F2), lithium dioxaborate (LiBOB), lithium tetrafluoroborate (LiBF4), and lithium difluorooxaborate (LiODFP).

[0045] In some embodiments, the mass fraction of the first additive is 0.1% to 1% based on the total mass of the electrolyte, for example, 0.1%, 0.2%, 0.5%, 0.7%, 0.9%, 1%, etc. Optionally, the mass fraction of the first additive is 0.1% to 0.5%.

[0046] In some embodiments, the mass fraction of the second additive is 0.2% to 3% based on the total mass of the electrolyte, for example, 0.2%, 0.5%, 0.7%, 0.9%, 1%, 1.5%, 1.8%, 2%, 2.5%, 3%, etc.

[0047] In some embodiments, the electrolyte further includes a solvent. The solvent has a mass fraction of 75% to 85% based on the total mass of the electrolyte, for example, 75%, 78%, 80%, 81%, 82%, 85%, etc.

[0048] In some embodiments, the solvent includes carboxylic esters and carbonates. Here, carboxylic ester solvents have lower viscosity and faster diffusion characteristics, which can further accelerate the penetration and filling process of the electrolyte in the positive electrode channels, thus improving the ion transport kinetics in the thick and dense positive electrode.

[0049] For example, the carboxylic acid ester includes at least one of ethyl acetate (EA), methyl acetate (MA), ethyl formate (EF), and ethyl propionate (EP).

[0050] For example, the carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC).

[0051] In some embodiments, the mass fraction of the carboxylic acid ester is 8% to 16% based on the total mass of the electrolyte, for example, 8%, 10%, 12%, 14%, 15%, 16%, etc. Optionally, the mass fraction of the carboxylic acid ester is 10% to 14%.

[0052] In some embodiments, the electrolyte further includes a lithium salt. Exemplarily, the lithium salt includes at least one of LiPF6, LiFSI, and LiTFSI. Further, based on the total mass of the electrolyte, the lithium salt has a mass fraction of 10% to 20%, such as 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.

[0053] Lithium-ion batteries Secondly, embodiments of this disclosure also provide a lithium-ion battery, including the electrolyte provided above. Here, the lithium-ion battery can be a primary lithium-ion battery or a secondary lithium-ion battery, and this disclosure does not limit it in this regard.

[0054] In some embodiments, a lithium-ion battery includes a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0055] Positive electrode sheet The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0056] For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0057] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (e.g., polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0058] In some embodiments, the positive electrode active material includes Li x Ni y Mn z M m O 0.5x+1.5y+1.5z+1.5m Wherein, 0.9≤x≤1.1, 0.8≤y≤1, 0≤z≤0.2, 0≤m≤0.2; and M is selected from one or more of Fe, Ti, and Co. Optionally, 0.9≤y≤1.

[0059] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0060] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0061] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0062] Optionally, the areal density of the positive electrode slurry coating on one side is 25 mg / cm³. 2 ~32mg / cm 2 The positive electrode coating is applied at a ratio of 3.0 g / cm². 3 ~4.0g / cm 3 The material is rolled to achieve a compaction density of 70µm to 170µm for a single-sided active material layer. It should be noted that the positive electrode sheet prepared based on the above areal density, compaction density, or thickness can be a thick, dense positive electrode.

[0063] Negative electrode sheet The negative electrode includes a negative current collector and a film layer optionally disposed on at least one surface of the negative current collector.

[0064] For example, the film layer may include a negative electrode active material (e.g., artificial graphite), a conductive agent, a thickener, and a binder.

[0065] In some embodiments, the negative electrode active material includes any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbide, silicon carbide composite material, or lithium titanate.

[0066] Optionally, the negative electrode active material is a mixture of silicon-carbon composite material and graphite; wherein, based on the total mass of the negative electrode active material, the mass fraction of the silicon-carbon composite material is 5% to 35%, for example 5%, 7%, 9%, 10%, 12%, 15%, 18%, 28%, 30%, or 35%. Optionally, the mass fraction of the silicon-carbon composite material is 15% to 35%.

[0067] In some embodiments, the negative electrode sheet can be prepared by dispersing the negative electrode active material, conductive agent, thickener, binder and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0068] Separating membrane In some embodiments, the secondary battery further includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0069] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0070] Example The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0071] The secondary lithium-ion battery of Embodiment 1 of this disclosure is prepared by the following specific method: (1) Preparation of lithium nickel cobalt manganese oxygen cathode: The cathode active material (LiNi) is prepared by... 0.9 Co 0.05 Mn 0.05 O2), polyvinylidene fluoride (PVDF) as a binder, and Super P as a conductive agent are mixed in a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until the system becomes homogeneous and transparent, obtaining a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil. After the aluminum foil is dried at room temperature, it is transferred to an oven for further drying, followed by cold pressing and slitting to obtain the positive electrode (electrode sheet). The areal density of the positive electrode can be 29.2 mg / cm³. 2 The thickness of the current collector can be 16µm, and the thickness of the single-layer active material layer can be 105µm.

[0072] (2) Preparation of graphite-silicon-carbon composite negative electrode: artificial graphite and silicon-carbon composite material are mixed at a mass ratio of 8:2. The mixture is used as the negative electrode active material, Super P as the conductive agent, sodium carboxymethyl cellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the binder. The mixture is mixed at a mass ratio of 96:1:1:2. Deionized water is added and the negative electrode slurry is obtained under the action of a vacuum stirrer. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil. After the copper foil is dried at room temperature, it is transferred to an oven for drying. Then, it is cold-pressed and cut to obtain the negative electrode (electrode sheet).

[0073] (3) Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10ppm, battery-grade ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), ethyl acetate (EA), and dimethyl carbonate (DMC) were mixed in a mass percentage ratio of 4:8:8:10:12:(35~40) to form an organic solvent. LiPF6 and LiFSI (mass ratio 14:3) were then slowly added to the organic solvent. After complete dissolution, TVSi, the compound shown in formula (I), and ethylene sulfate (DTD) were added. The amounts of LiPF6, LiFSI, and TVSi used were 17% and 0.3% of the total electrolyte mass, respectively.

[0074] In Tables 1 and 2, the content of each component is a mass percentage calculated based on the total mass of the electrolyte. The electrolytes in other embodiments and comparative examples are prepared in the same manner as in this embodiment, except that the component ratios are as specified in Table 1. It should be noted that if the total content of all components in the electrolyte is less than 100%, it is supplemented by an organic solvent.

[0075] It should be noted that the CF3-terminated compounds in Table 1 are obtained by replacing the CF2-terminated compound in (II) with the CF3-terminated compound.

[0076] (4) Preparation of the isolation membrane: Polypropylene membrane is used as the isolation membrane.

[0077] (5) Preparation of secondary battery: Using a 12μm thick polypropylene film (PP) as the separator, the above-prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film is wrapped around the outer layer, and the battery is dried in a vacuum oven at 120°C. After injecting 3.0g / Ah of the above-prepared electrolyte, the battery is sealed and liquefied to obtain a soft-pack battery (i.e., lithium-ion battery) with a capacity of 1Ah.

[0078] Test conditions (1) Impedance DCR at 25℃: Adjust the temperature of the constant temperature chamber to 25℃, let it stand for 10 min, charge it with a constant current of 0.33C to 4.25V, then charge it with a constant voltage of 4.25V to 0.05C cutoff, let it stand for 30 min, then discharge it with a constant current of 0.33C to 2.5V; repeat the 0.33C charge-discharge cycle twice, and record the discharge capacity of the last discharge as C0; after standing for 30 min, discharge it with 0.33C to 50%C0, adjust the cell SOC to 50%, let it stand for 30 min, record the voltage V1 at the end of the standing period, discharge it with a constant current of 4C for 30 s, record the voltage V2 at the end and the current I, and calculate DCR=(V1-V2) / I. Here, SOC is an abbreviation for State of Charge (SOC).

[0079] (2) Capacity recovery rate after 30 days of storage at 60℃: At 25℃, the battery was charged to 4.25V with a constant current of 1 / 3C, then charged to less than 0.05C with a constant voltage of 4.25V. After resting for 10 minutes, it was discharged to 2.5V with a constant current of 1 / 3C. The discharge capacity of the battery at this time was measured as the discharge capacity C0 of the 0-day cycle. Then the battery was charged to 4.25V with a constant current of 1 / 3C, then charged to less than 0.05C with a constant voltage of 4.25V and placed in a 60℃ oven. The battery was stored fully charged at 60℃ for 30 days. The battery was then discharged to 2.5V with a constant current of 1 / 3C at 25℃, then charged to 4.25V with a constant current of 1 / 3C, then charged to 0.05C with a constant voltage. The battery was then discharged to 2.5V with a constant current of 1 / 3C, and the discharge capacity was recorded as C1. The capacity recovery rate is (C1 / C0)×100%.

[0080] (3) Volume expansion rate after 28 days of storage at 60℃: The secondary battery was fully charged and stored in a 60℃ oven. Its volume was tested every 7 days, and the volume growth rate was recorded and calculated as the volume expansion rate.

[0081] (4) Wetting test: Cut the prepared positive electrode sheet into 2cm×2cm sizes and place it on a clean platform. Use a microsyringe to drop 5μL of the electrolyte to be tested onto the surface of the electrode sheet. Continuously monitor the change of the contact angle over time using a contact angle tester until the droplet is completely spread or stabilized, and record the contact angle.

[0082] (5) Calculation of Young's modulus of CEI: Molecular dynamics simulation was used to theoretically calculate the mechanical properties of positive electrode interphase (CEI) films formed by different electrolyte systems. First, based on the chemical composition of the film-forming components in the electrolyte, a representative CEI model was constructed. This model includes inorganic sulfate / sulfite structural units formed by the decomposition of vinyl sulfate and organic film-forming segments formed by formula (I). Li was also introduced into the model. + To reflect the actual coordination environment of the interfacial membrane, the Optimized Potentials for Liquid Simulations-All-Atom (OPLS-AA) force field was used to perform structural relaxation and equilibrium calculations at an initial temperature of 298 K. After the system reached full equilibrium under the NVT ensemble, small uniaxial tensile strains (range 0–2%) were applied in three orthogonal directions, and the relationship between the total energy of the system and strain was recorded. Based on the second derivative of the energy-strain curve, the equivalent Young's modulus of the interfacial membrane was calculated.

[0083] It should be noted that the NVT ensemble (also known as the canonical ensemble) is a fundamental statistical ensemble in statistical mechanics and molecular dynamics simulations, referring to an ensemble in which the number of particles (N), volume (V), and temperature (T) remain constant.

[0084] Table 1. Partial composition, mass percentage, and battery performance of the electrolytes in the examples and comparative examples.

[0085] Comparing Comparative Examples 1 to 3, it can be seen that, compared to Comparative Example 1, the addition of the compound shown in Formula (II) or DTD alone in Comparative Examples 2 and 3, although able to improve the battery impedance, volume expansion rate, and capacity recovery rate, is to a lesser extent. Comparing Example 1, Comparative Examples 2, and 3, it can be seen that the simultaneous addition of the compound shown in Formula (II) and DTD can significantly improve the battery impedance, volume expansion rate, and capacity recovery rate.

[0086] Comparing Example 1 and Comparative Example 4, it can be seen that the CF3 end group has higher symmetry and stronger hydrophobicity. The molecules tend to form a dense arrangement with high hydrophobicity at the interface. Although this helps to suppress side reactions, it also significantly increases the interfacial energy barrier, weakens the wetting ability of the electrolyte on the thick and dense positive electrode, and makes the CEI more rigid, making it difficult to effectively improve the performance of the battery.

[0087] Table 2. Partial composition, mass percentage, and battery performance of the electrolytes in the examples and comparative examples.

[0088] Comparing Examples 1 to 4, it can be seen that when the DTD addition amount remains constant at 1%, the interfacial film is not fully formed when the amount of Formula (II) is low, making it difficult to effectively suppress side reactions under high temperature conditions. When the addition amount is increased to 0.5% (corresponding to Example 1), the battery impedance and high-temperature performance are significantly improved; the contact angle decreases to 27°, indicating a significant improvement in electrode surface wettability; at the same time, the Young's modulus of CEI increases to 6.5 GPa, indicating that the interfacial film has sufficient mechanical strength while maintaining a certain degree of flexibility. When the addition amount is further increased to 1% (corresponding to Example 3) and 3% (corresponding to Example 4), although the Young's modulus of CEI increases to 9.2 GPa and 12.4 GPa respectively, the overall performance of the battery shows a deterioration trend. This indicates that excessive Formula (II) will lead to an overly dense or overly rigid interfacial film, which is not conducive to the full wetting of the electrolyte in the electrode channels, and at the same time increases the resistance to ion migration, thereby affecting the rate capability and high-temperature stability of the battery. In summary, the amount of formula (II) used is about 0.5%~1.0%, resulting in better overall battery performance.

[0089] Comparing Examples 1 and 5-7, it can be seen that, with the amount of DTD added remaining constant, increasing the amount of DTD improves the battery's impedance and high-temperature performance. Further increasing the amount to 3% leads to a decrease in both battery impedance and high-temperature performance. At 1%, DTD synergistically forms a stable, dense, and somewhat flexible CEI with Formula (II), while significantly improving high-temperature performance. In summary, a DTD content of approximately 0.5% to 2% results in superior overall battery performance.

[0090] Comparing Comparative Examples 1-3, Example 1, Example 8 and Example 9, it can be seen that the compounds shown in Formula (II), Formula (III) and Formula (IV) can all improve battery performance.

[0091] Comparing Example 1 and Example 10, it can be seen that in the presence of TVSi, the increase in film thickness leads to a slight increase in DCR, but it can improve the capacity recovery rate and volume expansion rate of the battery, especially the volume expansion rate is significantly reduced.

[0092] Comparing Examples 1, 11, and 12, it can be seen that adding the second additive can further improve the electrical performance of the battery.

[0093] Comparing Example 1 and Example 13, it can be seen that adding carboxylic acid esters to the electrolyte is beneficial to increasing the wettability of the electrolyte and improving the electrical performance of the battery.

[0094] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0095] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. An electrolyte, characterized in that, This includes cyclic sulfur-containing oxygen double bond compounds and compounds as shown in formula (I): Equation (I); where n is an integer from 1 to 8.

2. The electrolyte according to claim 1, characterized in that, The cyclic sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, and vinyl sulfate; and / or the compound represented by formula (I) includes at least one of the following structural formulas: Formula (II) Formula (Ⅲ), Formula (Ⅳ).

3. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass fraction of the cyclic sulfur-containing oxygen double bond compound is 0.1% to 3%; and / or based on the total mass of the electrolyte, the mass fraction of the compound represented by formula (I) is 0.1% to 3%.

4. The electrolyte according to claim 3, characterized in that, Based on the total mass of the electrolyte, the mass fraction of the cyclic sulfur-oxygen double bond compound is 0.5% to 2%; and / or based on the total mass of the electrolyte, the mass fraction of the compound represented by formula (I) is 0.5% to 1%.

5. The electrolyte according to claim 1, characterized in that, The mass ratio of the compound shown in formula (I) to the cyclic sulfur-containing oxygen double bond compound is 1:1 to 1:

3.

6. The electrolyte according to claim 1, characterized in that, It also includes at least one of a first additive and a second additive; wherein the first additive includes at least one of tetravinylsilane, ethyltrivinylsilane, tetramethyldivinyldisiloxane, trimethoxy(3,3,3-trifluoropropyl)silane and tetramethoxysilane; and the second additive includes at least one of lithium difluorophosphate, lithium dioxaborate, lithium tetrafluoroborate and lithium difluorooxaborate.

7. The electrolyte according to claim 6, characterized in that, Based on the total mass of the electrolyte, the mass fraction of the first additive is 0.1% to 1%; and / or based on the total mass of the electrolyte, the mass fraction of the second additive is 0.2% to 3%.

8. The electrolyte according to claim 1, characterized in that, It also includes solvents; the solvents include carboxylic acid esters and carbonates; wherein, based on the total mass of the electrolyte, the mass fraction of the solvent is 75% to 85%; and based on the total mass of the electrolyte, the mass fraction of the carboxylic acid ester is 8% to 16%.

9. The electrolyte according to claim 1, characterized in that, It also includes lithium salt; the lithium salt has a mass fraction of 10% to 20% based on the total mass of the electrolyte.

10. A lithium-ion battery, characterized in that, The electrode comprises an electrolyte, a positive electrode, and a negative electrode according to any one of claims 1 to 9; wherein the positive electrode comprises a positive active material, the thickness of which on one side of the positive electrode is 70 μm to 170 μm and the areal density on one side is 25 mg / cm³. 2 ~32mg / cm 2 .

Images