Electrolyte additive for lithium secondary battery and non-aqueous electrolyte

Abstract

The invention provides an electrolyte additive for a lithium secondary battery and a non-aqueous electrolyte, and relates to the technical field of lithium batteries. The additive is selected from at least one of compounds with the following chemical structural general formula. According to the additive disclosed by the invention, a high-stability and high-conductivity interface film containing sulfur and nitrogen is formed by utilizing a polar group and a heterocyclic structure, so that the problems of high-voltage impedance and gas production are solved, and the circulation and wide-temperature-range performance is improved. The introduced alkali metal cations regulate and control the solvation structure and promote desolvation, the low-temperature / rate performance is improved, lithium dendrites are inhibited by using the electrostatic shielding effect, and the safety is enhanced. The additive has the advantages of environmental protection and low cost.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to an electrolyte additive and a non-aqueous electrolyte for lithium secondary batteries. Background Technology

[0002] Secondary batteries, as an important carrier of modern energy storage, are widely used in new energy vehicles, portable electronic devices, and energy storage systems. Among them, lithium secondary batteries occupy an important market position due to their high energy density and long cycle life. The electrolyte, as the bridge connecting the positive and negative electrodes inside the secondary battery, not only plays a crucial role in ion transport, but its composition and properties also directly determine the battery's cycle stability, lifespan, safety, and wide-temperature-range electrochemical performance. To improve battery performance, small amounts of additives are usually added to the electrolyte. Through chemical or electrochemical reactions on the electrode surface, a stable solid electrolyte interphase (SEI) film is formed, thereby protecting the electrode materials and inhibiting the continuous decomposition of the electrolyte.

[0003] Currently, commonly used film-forming additives in commercial electrolytes mainly include vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propanesulfonate lactone (PS). These additives can improve battery cycle performance to some extent. For example, VC is often used to form a protective film on the negative electrode surface, while FEC is often used in high-voltage or silicon-based negative electrode systems to improve interface stability. However, with the continuous improvement of battery energy density and increasingly stringent application scenarios, these traditional additives are gradually revealing their limitations.

[0004] Specifically, under high voltage conditions (e.g., greater than 4.2V), VC is prone to excessive oxidation, decomposition, and polymerization, leading to a significant increase in the battery's internal impedance and consequently, rapid capacity decay in the later stages of battery cycling. While FEC exhibits good film-forming properties, it suffers from poor thermal stability and incompatibility with widely used lithium hexafluorophosphate (LiPF6) salts, easily undergoing defluorination reactions to generate hydrogen fluoride (HF). This not only corrodes electrode materials but also severely degrades the battery's electrochemical performance at high temperatures. Furthermore, the synthesis processes of traditional fluorinated additives are often complex, and harmful fluorides may be released during waste disposal, posing certain environmental risks. While sulfur-containing additives such as 1,3-propanesulfonate lactone (PS) show acceptable film-forming effects, some of these compounds have been proven to have carcinogenic risks, posing health and safety hazards during production and use.

[0005] In summary, existing electrolyte additives struggle to balance film stability, impedance control, and chemical compatibility when dealing with complex operating conditions such as high voltage and high temperature. Furthermore, some additives pose environmental and safety concerns. Therefore, finding a novel electrolyte additive that remains stable under high voltage, exhibits good compatibility with commonly used lithium salts, is environmentally friendly, and cost-effective, in order to overcome the shortcomings of existing technologies, has become a pressing issue in the field of secondary battery technology.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an electrolyte additive and a non-aqueous electrolyte for lithium secondary batteries. The additive significantly improves the high-voltage cycle stability, wide temperature range / rate performance and safety of the battery by forming a sulfur-nitrogen-containing high-stability interface film and introducing cations to regulate solvation and electrostatic shielding effects, and is also environmentally friendly and low-cost.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides an electrolyte additive for lithium secondary batteries, wherein the additive is selected from at least one compound having the following general chemical structural formula: ; Wherein, R is a cation selected from any one of H, Li, Na, K, Rb, and Cs; X is a substituent at the 6-position selected from halogens, unsubstituted or optionally substituted C1-C5 alkyl groups, unsubstituted or optionally substituted C1-C5 alkoxy groups, unsubstituted or optionally substituted aryl or heteroaryl groups. The substituents are selected from halogen, cyano, alkyl, alkoxy, olefin, and alkyne groups.

[0009] In optional implementations, R is selected from Li, K, Rb, or Cs; and / or, X is selected from fluorine atom, trifluoromethyl, cyano, methyl, ethyl, n-propyl, isopropyl, methoxy, or phenyl.

[0010] In an optional embodiment, the electrolyte additive for lithium secondary batteries is selected from at least one of the following compounds: Lithium salt of 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide, sodium salt of 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide, potassium salt of 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide, rubidium salt of 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide, and cesium salt of 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide; wherein, in the general chemical formula, the cation R is a potassium ion and the 6-substituent X is an ethyl, trifluoromethyl, methoxy, cyano, fluorine atom, or phenyl compound; or... The electrolyte additive for lithium secondary batteries is selected from at least one of the following compounds: .

[0011] In a second aspect, the present invention provides a non-aqueous electrolyte for lithium secondary batteries, comprising a non-aqueous organic solvent, a conductive lithium salt electrolyte, and the electrolyte additive for lithium secondary batteries described in any of the foregoing embodiments.

[0012] In an optional embodiment, based on the total mass percentage of the non-aqueous electrolyte for lithium secondary batteries being 100%, the mass percentage of the non-aqueous organic solvent is 45% to 95%; the mass percentage of the conductive lithium salt electrolyte is 5% to 30%; the mass percentage of the electrolyte additive for lithium secondary batteries is 0.01% to 2%; and / or, the non-aqueous electrolyte for lithium secondary batteries further comprises fluoroethylene carbonate; wherein the mass ratio of the electrolyte additive for lithium secondary batteries to fluoroethylene carbonate is 1:(1 to 10).

[0013] In an optional embodiment, when the non-aqueous electrolyte for lithium secondary batteries contains functional additives, the mass percentage of the functional additive combination is 0% to 20%.

[0014] In an optional embodiment, it further comprises fluoroethylene carbonate; wherein the mass ratio of the electrolyte additive for lithium secondary batteries to fluoroethylene carbonate is 1:(1~10).

[0015] Thirdly, the present invention provides a lithium secondary battery, comprising a positive electrode, a negative electrode, and a separator, as well as a non-aqueous electrolyte for a lithium secondary battery as described in any of the foregoing embodiments.

[0016] In an optional embodiment, the positive electrode sheet includes a positive electrode active material; the positive electrode active material is selected from LiMnO4. z N 1-z PO4, Li 1+x Ni y Mn 2-x-y O4 and Li1+a Ni b Co c M` 1-a-b-c at least one of O2; wherein, M and N are each one of Fe, Mn, Co or Ni; M` is at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Zn, Ga, Y, Zr, Nb, Mo, Sn and Ba; and 0 ≤ z ≤ 1, 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.5, 0 ≤ a ≤ 0.5, 0 ≤ b, c ≤ 1 and 0 ≤ a + b + c ≤ 1; and / or, The negative electrode plate includes a negative electrode active material; the negative electrode active material is selected from at least one of natural graphite, artificial graphite, mesophase carbon microspheres, elemental silicon, silicon oxide compound SiO X , silicon-carbon composite materials, lithium titanate, lithium metal and lithium alloys; wherein 0 < X ≤ 2; and / or, A solid electrolyte interface film is formed on the surface of the negative electrode plate; the solid electrolyte interface film contains at least one inorganic component of Li2SO3, Li2S and Li3N.

[0017] In a fourth aspect, the present invention provides a lithium metal battery, including a positive electrode, a metallic lithium negative electrode and an electrolyte; the electrolyte includes the electrolyte additive for a lithium secondary battery as described in the foregoing embodiments, and the cation R in the electrolyte additive for a lithium secondary battery is selected from Rb or Cs.

[0018] In a fifth aspect, the present invention provides an electrical device, including the lithium secondary battery as described in the foregoing embodiments, or the lithium metal battery as described in the foregoing embodiments.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The electrolyte additive provided by the present invention can selectively decompose on the electrode surface by utilizing the weak coordination effect between polar functional groups such as sulfonyl (-SO2-) and carbonyl (C=O) in the molecular structure and metal ions, as well as the unique heterocyclic structure, to form inorganic interface components containing sulfur (such as Li2SO3, Li2S) and nitrogen (such as Li3N). These inorganic components have excellent chemical / electrochemical stability and high ionic conductivity, can significantly improve the stability of the solid electrolyte interface (SEI) film, thereby effectively inhibiting the continuous decomposition of the electrolyte, improving the cycle life of the battery, and enhancing the electrochemical performance of the battery in a wide temperature range (high temperature and low temperature). In particular, this additive overcomes the defects of traditional additives (such as VC) that are prone to decomposition and polymerization at high voltages to increase impedance, and fluorine-containing additives (such as FEC) that are prone to gas generation and decomposition to produce HF to corrode the electrode, which helps to improve the stability of the battery under high voltage conditions.

[0020] Furthermore, the cations introduced into the additive molecule (especially Na) + K + 、Rb + Cs + Alkali metal ions can regulate the solvation structure of the electrolyte, effectively weakening the interaction between lithium ions and solvent molecules, promoting the rapid desolvation process of lithium ions, and thus significantly improving battery performance under low-temperature environments and high-rate charge-discharge conditions. Meanwhile, Rb... + and Cs + Large-radius cations can form an "electrostatic shielding effect" on the negative electrode surface, guiding the uniform deposition of lithium ions, effectively inhibiting the growth of lithium dendrites and the formation of "dead lithium," reducing interfacial side reactions and product accumulation, thereby improving battery safety and long-cycle stability. Furthermore, these additives (such as acesulfame K and its derivatives) have widely available raw materials, mature synthesis processes, and are environmentally friendly, avoiding the environmental pollution and health risks that may arise from traditional fluorinated or sulfonyl lactone additives, thus demonstrating promising application prospects and economic benefits. Detailed Implementation

[0021] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0022] This application provides an electrolyte additive for lithium secondary batteries, wherein the additive is selected from at least one compound having the following general chemical structural formula: ; Wherein, R is a cation selected from any one of H, Li, Na, K, Rb, and Cs; X is a substituent at the 6-position, selected from halogens, unsubstituted or optionally substituted C1-C5 alkyl groups, unsubstituted or optionally substituted C1-C5 alkoxy groups, unsubstituted or optionally substituted aryl or heteroaryl groups; the substituents are selected from halogens, cyano groups, alkyl groups, alkoxy groups, alkenyl groups, and alkyne groups.

[0023] The additives described above are compounds having the above general formula. This general formula belongs to the salts of acesulfame potassium and its derivatives.

[0024] This includes a heterocyclic skeleton, and the compound contains a six-membered heterocyclic core structure, namely 1,2,3-oxathiazine-4(3H)-one-2,2-dioxide. The skeleton contains specific polar functional groups, specifically a sulfonyl group (-SO2-) and a carbonyl group (C=O), as well as a negatively charged nitrogen (N) center.

[0025] In the above general formula, R represents the cation moiety, selected from any one of hydrogen (H), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). When R is H, the compound is in acid form; when R is Li, Na, K, Rb, or Cs, the compound is in the form of the corresponding alkali metal salt.

[0026] In the above general formula, X represents a substituent located on the carbon atom at the 6-position of the heterocyclic ring. The specific range of choices for X includes: halogen atoms (such as fluorine, chlorine, etc.); unsubstituents (i.e., hydrogen atoms); C1-C5 alkyl groups (such as methyl, ethyl, propyl, etc.), which can be straight-chain or branched and can be optionally substituted by one or more substituents; C1-C5 alkoxy groups (such as methoxy, ethoxy, etc.), which can be optionally substituted by one or more substituents; aryl or heteroaryl groups (such as phenyl, etc.), which can be optionally substituted by one or more substituents.

[0027] The substituents mentioned above do not refer to the substituent at the 6-position, but rather to any optional "substituent" included in the 6-position substituent, such as an alkyl, alkoxy, aryl, or heteroaryl group, which is limited to one or more selected from halogen, cyano, alkyl, alkoxy, alkenyl, and alkynyl groups.

[0028] The additive functions in lithium-ion battery electrolytes primarily based on its unique molecular structure and ionic composition: First, the sulfonyl (-SO2-) and carbonyl (C=O) groups in the molecule possess strong polarity, enabling them to form weak coordination interactions with metal ions (especially lithium ions) in the electrolyte. This interaction can regulate the solvation structure of the electrolyte, weakening the binding force between lithium ions and solvent molecules, thereby promoting lithium ion transport and desolvation processes.

[0029] Secondly, its film formation mechanism lies in the fact that this heterocyclic structure undergoes specific selective decomposition reactions during battery charging and discharging, especially on the electrode surface. The decomposition products mainly include sulfur-containing (such as Li2SO3, Li2S) and nitrogen-containing (such as Li3N) inorganic components. These components are deposited on the electrode surface, forming a stable solid electrolyte interphase (SEI) film.

[0030] When R is a non-lithium alkali metal ion such as Na, K, Rb, or Cs, the differences in ionic radius and charge density of these ions will affect the microstructure of the electrolyte.

[0031] Especially cations with larger radii (such as Rb) + Cs + According to the principle of electrostatic shielding, these ions tend to adsorb on protrusions (such as dendrite tips) on the negative electrode surface, forming an electrostatic shielding layer. Since the reduction potential of these ions is usually lower than that of lithium, they will not be reduced and deposited before lithium ions. Instead, they will repel subsequent lithium ions through electrostatic repulsion, forcing lithium ions to deposit in a relatively flat area, thereby guiding the uniform deposition of lithium ions.

[0032] Based on the above structure and mechanism, this electrolyte additive has the following advantages and beneficial effects: First, the sulfur- and nitrogen-containing inorganic interface components (such as Li₂SO₃, Li₂S, and Li₃N) formed through decomposition possess high chemical stability, electrochemical stability, and ionic conductivity. This makes the resulting SEI film more robust, dense, and with strong ion-conducting ability, effectively suppressing continuous side reactions of the electrolyte on the electrode surface, thereby significantly improving the cycle life of the battery.

[0033] Secondly, the stable interfacial film and the regulatory effect of additives on the solvation structure help improve the battery's stability at high temperatures (reducing gas generation and side reactions) and its ion transport capability at low temperatures, thereby improving the battery's wide-temperature-range electrochemical performance.

[0034] Furthermore, especially those containing Rb + or Cs + The additives, through the "electrostatic shielding effect," can effectively inhibit the formation and growth of lithium dendrites, reduce the generation of "dead lithium," and not only improve battery safety but also further extend battery life.

[0035] Furthermore, the weakening effect of polar functional groups on the lithium-ion solvation layer promotes rapid desolvation of lithium ions and reduces interfacial charge transfer resistance, thereby improving the battery performance under high-rate charge and discharge conditions.

[0036] Furthermore, the parent structure of this additive (such as acesulfame K) is widely available, and the synthesis process is mature and inexpensive. At the same time, compared to traditional fluorinated additives, this type of compound is more environmentally friendly, reducing the potential risk of environmental pollution.

[0037] Furthermore, regarding the combination of cations, a single cation (such as pure potassium salt) can be used alone, or multiple cation salts can be mixed as needed (such as a mixture of lithium salt and cesium salt) to take advantage of the synergistic effect of different cations (for example, lithium salt provides the lithium source, and cesium salt provides the shielding effect).

[0038] By changing the structure of the 6-substituent X (such as introducing an electron-withdrawing halogen or cyano group, or introducing an electron-donating alkyl group), the redox potential (HOMO / LUMO level) of the molecule can be fine-tuned, thereby optimizing the film-forming potential and film-forming quality of the additive for different positive and negative electrode material systems (such as high-voltage positive electrodes or silicon-carbon negative electrodes).

[0039] In some implementations, R is selected from Li, K, Rb, or Cs.

[0040] In this embodiment, the cation R is preferably lithium (Li), potassium (K), rubidium (Rb) or cesium (Cs), and the additive is specifically a lithium salt, potassium salt, rubidium salt or cesium salt of acesulfame (or its derivative).

[0041] The aforementioned Li (lithium ions) directly provides the lithium source, which is consistent with the active ions transported in the battery. It does not introduce impurity cations, ensuring the purity of the electrolyte system and helping to maintain basic electrochemical performance.

[0042] The aforementioned K (potassium ion) is an alkali metal ion with a larger radius than lithium. + It can slightly adjust the solvation shell structure and help form potassium-containing inorganic interface components (such as KF / LiF mixed phases), which often have good ion conductivity.

[0043] The aforementioned Rb (rubidium ion) and Cs (cesium ion) are the key functional cations in this embodiment. Because Rb... + and Cs + The ionic radius is significantly larger than that of Li. + These large-radius cations exhibit unique adsorption behavior on the electrode surface. According to the principle of electrostatic shielding, these cations preferentially adsorb at the tips or protrusions (areas of high charge density) of the negative electrode surface, forming a temporary electrostatic shielding layer. Because their reduction potential is lower than that of lithium, they do not reduce themselves; instead, they force subsequently arriving lithium ions to deposit on the unshielded flat areas through electrostatic repulsion. This mechanism effectively inhibits the growth of lithium dendrite tips and promotes uniform lithium ion deposition, thereby greatly improving battery safety and cycle stability, especially significantly inhibiting the formation of "dead lithium."

[0044] In some embodiments, X is selected from fluorine atom, trifluoromethyl, cyano, methyl, ethyl, n-propyl, isopropyl, methoxy, or phenyl.

[0045] In this embodiment, the range of the 6-position substituent X is specifically defined as fluorine atom (-F), trifluoromethyl (-CF3), cyano (-CN), methyl (-CH3), ethyl (-C2H5), n-propyl (-n-C3H7), isopropyl (-i-C3H7), methoxy (-OCH3), or phenyl (-Ph). These groups encompass electron-withdrawing groups (such as fluorine atom, trifluoromethyl, cyano), electron-donating groups (such as methyl, ethyl, propyl), and conjugated groups (such as phenyl).

[0046] The aforementioned electron-withdrawing groups (fluorine atom, trifluoromethyl, cyano) can reduce the electron cloud density in the molecule, thereby improving the antioxidant capacity of the additive molecule (i.e., improving high-voltage resistance). This makes the additive more stable on the surface of the high-voltage cathode, or allows it to preferentially decompose at specific high potentials to form a dense passivation film, protecting the cathode material from electrolyte corrosion.

[0047] The aforementioned electron-donating groups (methyl, ethyl, propyl, methoxy), by introducing alkyl or alkoxy groups, can adjust the polarity and solubility of the molecule, improving the solubility of the additive in organic solvents. Simultaneously, these groups, upon decomposition, contribute to the formation of a flexible interface film containing organic components, enhancing the mechanical toughness of the SEI film and accommodating the volume expansion of the electrode material during charging and discharging.

[0048] The aforementioned conjugated group (phenyl) can increase the conjugation system of the molecule, which helps to absorb electrons or form π-π stacking, and may further improve the compactness and stability of the film.

[0049] In some embodiments, the electrolyte additive for lithium secondary batteries is selected from at least one of the following compounds: Compounds comprising, and wherein the cation R is a potassium ion and the 6-substituent X is an ethyl, trifluoromethyl, methoxy, cyano, fluorine atom, or phenyl group.

[0050] The core skeleton of these compounds is 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide. The main difference lies in the cation R, specifically including: Lithium acesulfame K: R is lithium ion (Li... + Acesulfame K: R stands for sodium ion (Na+). +Acesulfame potassium: R stands for potassium ion (K). + ), namely acesulfame K, which is the most common commercially available acesulfame K. Acesulfame K rubidium: R stands for rubidium ion (Rb). + Acesulfame K: R is cesium ion (Cs). + ).

[0051] The cations of this type of compound are fixed as potassium ions (K). + The core skeleton remains 1,2,3-oxathiazine-4(3H)-one-2,2-dioxide. The main difference lies in the changes of the substituent X at the 6-position, specifically including: X as ethyl: 6-ethyl-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide potassium salt; X as trifluoromethyl: 6-trifluoromethyl-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide potassium salt; X as methoxy: 6-methoxy-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide potassium salt; X as cyano: 6-cyano-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide potassium salt; X as fluorine: 6-fluoro-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide potassium salt. X is the potassium salt of phenyl: 6-phenyl-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide.

[0052] The electrolyte additive for lithium secondary batteries is selected from at least one of the following compounds: .

[0053] It should be noted that the additives can be obtained in the following ways: (1) Ace-K: You can directly purchase commercially available food-grade or battery-grade products and use them after vacuum drying to remove moisture.

[0054] (2) Preparation of lithium acesulfame (Ace-Li), rubidium acesulfame (Ace-Rb), and cesium acesulfame (Ace-Cs): These can be prepared by ion exchange (or other methods acceptable to the technology provided in this application). Potassium acesulfame is dissolved in deionized water and passed through a hydrogen-form cation exchange resin column to obtain an acesulfame acid solution. Then, aqueous solutions of lithium hydroxide, rubidium carbonate, or cesium carbonate are added to adjust the pH to neutral. After rotary evaporation to remove water, the solutions are recrystallized in anhydrous ethanol and dried under vacuum to obtain the corresponding metal salts.

[0055] (3) Preparation of 6-trifluoromethyl-acesulfame potassium: Following the synthetic route of acesulfame potassium, ethyl trifluoroacetoacetate was used as the starting material, which was reacted with aminosulfonyl fluoride to form a ring, and then neutralized with potassium hydroxide to obtain the product.

[0056] This application also provides a non-aqueous electrolyte for lithium secondary batteries, comprising a non-aqueous organic solvent, a conductive lithium salt electrolyte, and the electrolyte additives for lithium secondary batteries described in any of the foregoing embodiments.

[0057] The aforementioned non-aqueous electrolyte mainly comprises the following three core components: (1) Non-aqueous organic solvents are the main liquid component of the electrolyte. Their main function is to dissolve lithium salts and provide a transport medium for lithium ions. Specifically, they can include commonly used organic solvents such as carbonates (e.g., EC, DMC) and carboxylic acid esters. Their role is to provide a suitable dielectric constant to dissociate lithium salts and to have appropriate viscosity to ensure rapid ion migration.

[0058] (2) Conductive lithium salt electrolyte, which serves as the ion source in the electrolyte, dissolves in an organic solvent and dissociates into lithium ions (Li). + Lithium salts include lithium hexafluorophosphate (LiPF6) and anions. Their main function is to provide sufficient freely moving ions to ensure the electrolyte has high ionic conductivity, thereby maintaining the battery's charge and discharge process.

[0059] (3) The electrolyte additive for lithium secondary batteries is the specific additive (acesulfame potassium and its derivative salts) described in the foregoing embodiments. This additive exists in the electrolyte in a small amount, but plays a key functional regulating role.

[0060] This electrolyte achieves an overall improvement in battery performance through the synergistic effect of its components. During the first charge, a specific additive (acesulfame derivative) in the electrolyte preferentially undergoes reduction and decomposition on the negative electrode surface compared to the solvent. Its unique sulfur- and nitrogen-containing heterocyclic structure decomposes to form an SEI film containing inorganic components such as Li₂SO₃, Li₂S, and Li₃N.

[0061] This inorganic-rich SEI film has high ionic conductivity and high mechanical strength, acting like a dense "shield" that effectively blocks direct contact between solvent molecules (such as EC and DMC) and the negative electrode material, preventing continuous reduction and decomposition of the solvent and excessive consumption, thereby significantly improving the cycle life of the battery.

[0062] Alkali metal cations (such as K) introduced into the additives + 、Rb + Cs + There is a competitive coordination relationship between lithium ions and solvent molecules. These cations can alter the solvation shell structure around lithium ions, weakening the Li-solvation structure. +The binding force between lithium ions and solvent molecules (such as EC) lowers the desolvation barrier before lithium ions intercalate to the negative electrode, making it easier for lithium ions to remove the solvent coating layer and thus accelerating the interfacial charge transfer rate. This mechanism directly leads to improvements in the battery's low-temperature performance and high-rate (fast charge and fast discharge) performance.

[0063] If the additive contains Rb + or Cs + These cations form an electrostatic shielding layer on the negative electrode surface during charging, inhibiting lithium ion aggregation at the tips and forcing lithium deposition to become more uniform. This effectively prevents the risk of short circuits caused by lithium dendrites piercing the separator, significantly improving battery safety.

[0064] In some embodiments, the non-aqueous electrolyte for lithium secondary batteries further includes functional additives; the functional additives are selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), 1,3-propanesulfonyl lactone (PS), 1,3-propenesulfonyl lactone (PST), 1,4-butanesulfonyl lactone (BS), vinyl sulfite (ES), vinyl sulfate (DTD), propylene sulfate (PCS), methanedisulfonate methylene (MMDS), erythrose bicyclic sulfate (BiDTD), pentaerythritol bicyclic sulfate (DTS), 1,3-propanedisulfonic anhydride (ODTO), succinate (SN), adiponitrile (ADN), glutaronitrile (GN), 1,2-bis(2-cyanoethoxy)ethane (DENE), 1,3,6-hexanetrionitrile (HTCN), tris(trimethylsilane) phosphate (… The following are included in the list of at least one: TMSP, tris(trimethylsilane)borate (TMSB), tris(trimethylsilane)phosphite (TMSPi), triallyl phosphate (TAP), triargyl phosphate (TPP), triphenyl phosphite (TPPi), maleic anhydride (SA), maleic anhydride (MAn), citrate anhydride (MMAn), 2,3-dimethylmaleic anhydride (DMMAn), tetravinylsilane (TVSi), hexamethylene diisocyanate (HDI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium difluorobis(oxalate)phosphate (LiODFP), lithium tetrafluorooxalate phosphate (LiOTFP), lithium difluorophosphate (LiPO2F2), and lithium fluorosulfonate (LiFS). In some embodiments, the non-aqueous organic solvent is selected from at least one of carbonates, carboxylic acid esters, ethers, nitriles, furans, phosphate esters, amides, sulfates, and sulfites; preferably, the non-aqueous organic solvent is selected from ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, 1,3-dioxolane, 1,4-dioxane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl 2,5-dioxaadipic acid, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and tert-pentyl acetate. Methyl ester, ethyl pivalate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, acetonitrile, propionitrile, n-butyronitrile, isobutyronitrile, tetrahydrofuran, 2-methyltetrahydrofuran, trimethyl phosphate, triethyl phosphate, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane, methyl sulfolane, dimethyl sulfolane, dimethyl sulfolane, diethyl sulfone, diethyl sulfone, methyl ethyl sulfone, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, diethyl sulfite, methyl ethyl sulfite, dimethyl sulfate, diethyl sulfate, methyl ethyl sulfate, and at least one of the following organic molecules in which some or all of the hydrogen atoms are replaced by fluorine atoms.

[0065] In some embodiments, the conductive lithium salt electrolyte is an inorganic lithium salt and / or an organic lithium salt; and / or, the conductive lithium salt electrolyte includes at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonyate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium tetrafluoroborate, lithium difluorobis(oxalato)phosphate, lithium tetrafluorooxalato)phosphate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethylimidazolium, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium bis(pentafluoroethyl)imide, lithium tri(trifluoromethyl)methyl, lithium tri(pentafluoroethyl)methyl, lithium trifluoromethanesulfonate, and lithium nonafluoro-1-butanesulfonate.

[0066] In some embodiments, with the total mass percentage of the non-aqueous electrolyte for the lithium secondary battery being 100%, the mass percentage of the non-aqueous organic solvent is 45% to 95% (e.g., 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 95%, etc.); and / or, the mass percentage of the conductive lithium salt electrolyte is 5% to 30% (e.g., 5%, 7%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 30%, etc.); and / or, the mass percentage of the electrolyte additive for the lithium secondary battery is 0.01% to 2% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, etc.).

[0067] If the content of the aforementioned additives is too low (<0.01%), it may not be able to form a sufficiently dense and effective interfacial film on the electrode surface, making it difficult to suppress side reactions and dendrite growth; if it is too high (>2%), it may lead to an excessively thick film, increasing interfacial impedance, which in turn reduces the rate performance and cycle efficiency of the battery, and may even cause solubility problems. In particular, if the content of heterosalt additives such as sodium salts and potassium salts is too high, it will cause Na / K to be directly precipitated on the negative electrode surface in the form of metallic elements, exacerbating the side reactions with the electrolyte, and forming a Na / K-rich inferior SEI, which will affect the electrochemical performance of the battery.

[0068] The content of the aforementioned non-aqueous organic solvent is 45% to 95%. As the main solvent, its content needs to ensure sufficient dissolution of lithium salts and additives, while providing appropriate viscosity and wettability to ensure effective wetting of the electrolyte inside the battery and rapid migration of ions.

[0069] The aforementioned conductive lithium salt electrolyte content is 5% to 30%. This concentration range (typically corresponding to approximately 0.5 to 2 mol / L) is crucial for ensuring high ionic conductivity of the electrolyte. Too low a concentration will result in insufficient ion carriers, while too high a concentration will significantly increase viscosity; both will reduce ionic conductivity.

[0070] In some embodiments, when the non-aqueous electrolyte for lithium secondary batteries contains functional additives, the mass percentage of the functional additive combination is no more than 20%. For example, it can be a single additive or a combination of multiple additives, and the total content of the additives can be 2%, 4%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0071] In some embodiments, fluoroethylene carbonate (FEC) is also included; wherein the mass ratio of the electrolyte additive for lithium secondary batteries to fluoroethylene carbonate is 1:(1~10). For example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0072] It should be noted that FEC is an excellent film-forming agent in silicon-based anodes and high-voltage cathodes, rich in fluorine, and can form a LiF-rich interface. The additive (acesulfame derivative) in the embodiments of this application is rich in sulfur and nitrogen.

[0073] When the two coexist in a specific ratio (1:1 to 1:10), the fluorine-rich underlayer (LiF) preferentially formed by FEC complements the sulfur / nitrogen-containing outer layer (containing S / N inorganic salts) formed by the additives of this invention. LiF provides extremely high interfacial energy and chemical stability, while the S / N-containing component provides excellent ion conduction pathways. This "fluorine-rich + sulfur-nitrogen-rich" composite film structure is both robust and high-voltage resistant, and has extremely low interfacial impedance, thereby significantly improving the cycle stability and rate performance of the battery at high voltages, which is difficult to achieve with a single additive.

[0074] This application also provides a lithium secondary battery, including a positive electrode, a negative electrode, and a separator, as well as a non-aqueous electrolyte for lithium secondary batteries as described in any of the foregoing embodiments.

[0075] The lithium secondary battery described above is an energy storage device that utilizes the aforementioned non-aqueous electrolyte to achieve the interconversion of chemical energy and electrical energy. Its main components may include (but are not limited to): a positive electrode sheet (typically made by coating a positive electrode active material, conductive agent, and binder onto a positive electrode current collector), a negative electrode sheet (made by coating a negative electrode active material onto a negative electrode current collector, or directly using lithium metal foil), and a separator located between the positive and negative electrodes to isolate electrons and conduct ions. In addition, the battery may also include an encapsulation shell (such as aluminum-plastic film, steel shell, or aluminum shell), tabs, a cover plate, and other auxiliary components. In terms of specific battery types, this technology is applicable to various forms of lithium secondary batteries, including but not limited to pouch batteries, cylindrical batteries (such as 18650, 21700, etc.), prismatic hard-shell batteries, and button batteries. These batteries are widely used in consumer electronics, electric vehicles, and energy storage systems.

[0076] In some embodiments, the positive electrode sheet includes a positive electrode active material; the positive electrode active material is selected from LiMnO4. z N 1-z PO4, Li 1+x Ni y Mn 2-x-y O4 and Li 1+a Ni b Coc M` 1-a-b-c At least one of O2; Wherein, M and N are one of Fe, Mn, Co or Ni respectively; M` is at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Zn, Ga, Y, Zr, Nb, Mo, Sn and Ba; and 0≤z≤1, 0≤x≤0.05, 0≤y≤0.5, 0≤a≤0.5, 0≤b, c≤1 and 0≤a+b+c≤1.

[0077] The range of values ​​for z (0 ≤ z ≤ 1) is as follows: for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc. The range of values ​​for x (0 ≤ x ≤ 0.5) is as follows: for example, it can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc. The range of values ​​for y (0 ≤ y ≤ 0.5) is as follows: for example, it can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc. The range of values ​​for 'a' (0 ≤ a ≤ 0.5): For example, it can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc. The range of values ​​for 'b' (0 ≤ b ≤ 1): For example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc. The range of values ​​for 'c' (0 ≤ c ≤ 1): For example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc. The range of values ​​for a+b+c (0≤a+b+c≤1): For example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc.

[0078] The above phosphates (LiM) z N 1-z Lithium iron phosphate (LiFePO4) is a lithium phosphate metal compound with an olivine structure. In the general formula, M and N represent transition metals (Fe, Mn, Co, Ni), and z represents the doping ratio. The most typical is lithium iron phosphate (LiFePO4), where M=Fe and z=1. It can also be lithium manganese iron phosphate (LiMnFePO4). x Fe 1-x (PO4). These materials have extremely stable structures, high safety, and long lifespan, but poor conductivity. The electrolyte additive in this embodiment can form a stable CEI film on its surface, preventing the dissolution of Fe / Mn ions, thereby further improving its high-temperature cycle life.

[0079] The above-mentioned spinel (Li1+x Ni y Mn 2-x-y O4) is a spinel-structured oxide with three-dimensional lithium-ion channels. A typical representative is lithium manganate (LiMn2O4) or lithium nickel manganate (LiNi 0.5 Mn 1.5 O4). The x and y in the general formula reflect the adjustment of the Li / Ni / Mn stoichiometric ratio. It has a high voltage plateau (up to 4.7 V or even 5 V) and good rate performance, but manganese is prone to dissolve at high temperatures. In this embodiment, the additive (especially derivatives containing electron-withdrawing groups) has good high-voltage resistance and can effectively passivate the surface of the positive electrode at high voltages, inhibit the oxidation of the electrolyte and the dissolution of manganese, and significantly improve its high-temperature and high-voltage performance.

[0080] The above-mentioned layered oxides (Li 1+a Ni b Co c M` 1-a-b-c O2) are currently the mainstream materials for high-energy-density batteries, including ternary materials (NCM) and lithium-rich manganese-based materials. M' in the general formula represents various doping elements (such as Mg, Al, etc.) used to stabilize the structure. For example, NCM811 (Ni:Co:Mn = 8:1:1). Its characteristics are that this material has a high capacity, but poor thermal stability and high interfacial reaction activity. This electrolyte additive can form a dense protective film rich in inorganic components on its surface, reduce the side reactions between the positive electrode and the electrolyte, and inhibit gas generation, which is crucial for the safety of high-nickel ternary batteries.

[0081] In some embodiments, the negative electrode sheet includes a negative electrode active material; the negative electrode active material is selected from at least one of natural graphite, artificial graphite, mesocarbon microbeads, elemental silicon, silicon oxide SiO X 、 silicon-carbon composite materials, lithium titanate, lithium metal, and lithium alloys; where 0 < X ≤ 2. For example, X can be 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.8, 2.0, etc.

[0082] The above-mentioned negative electrode sheet is the host for lithium-ion insertion (during charging). Among them, carbon-based materials include natural graphite, artificial graphite, and mesocarbon microbeads. This is the most mature negative electrode for commercial applications at present and has a layered structure for lithium-ion insertion. Silicon-based materials can include elemental silicon, silicon oxide (SiO x, where 0 < x ≤ 2) and silicon-carbon composite materials. The silicon-based negative electrode has an extremely high capacity (more than 10 times that of graphite), but it expands greatly in volume during charge and discharge (>300%). The SEI film rich in S / N elements formed by the additive in this embodiment has high mechanical toughness and ion conductivity, can better adapt to the volume expansion of the silicon-based negative electrode, prevent the SEI film from breaking, and thus significantly improve the cycle stability of the silicon-based negative electrode. Also, other materials can include lithium titanate (Li4Ti5O 12 , a zero-strain material), lithium metal (with the highest energy density), and lithium alloys.

[0083] For the lithium metal negative electrode, the Rb + / Cs + cations in this additive can effectively inhibit the growth of lithium dendrites and prevent the formation of dead lithium through the electrostatic shielding effect, which is an advantage that conventional additives hardly have.

[0084] In some embodiments, a solid electrolyte interface film is formed on the surface of the negative electrode sheet; the solid electrolyte interface film contains at least one inorganic component of Li2SO3, Li2S, and Li3N.

[0085] The above components directly come from the reduction decomposition of additives (acesulfame and its derivatives) in the electrolyte on the surface of the negative electrode. For example, the sulfonyl group (-SO2-) in the molecule is reduced and decomposed to produce Li2SO3 and Li2S, and the nitrogen-containing heterocyclic structure is decomposed to produce Li3N.

[0086] It should be noted that Li3N is one of the substances with the highest conductivity among known solid-state lithium ion conductors (fast ion conductors). Li2S and Li2SO3 also have good ion conductivity. The presence of these components greatly reduces the resistance of lithium ions passing through the SEI film (that is, reduces the interfacial impedance), and significantly improves the rate performance and low-temperature discharge capacity of the battery.

[0087] These inorganic lithium salt components have stable chemical properties, are insoluble in organic solvents, and have high mechanical strength. The SEI film formed by them is dense and firm, can effectively block the penetration of solvent molecules, and inhibit the continuous decomposition of the electrolyte, thus ensuring the long cycle life of the battery.

[0088] An embodiment of the present application also provides a lithium metal battery, including a positive electrode, a metallic lithium negative electrode, and an electrolyte; the electrolyte includes the electrolyte additive for a lithium secondary battery as described in the foregoing embodiment, and the cation R in the electrolyte additive for the lithium secondary battery is selected from Rb or Cs.

[0089] This battery design uses a unique "electrostatic shielding effect" to solve the biggest pain point of lithium metal batteries: the growth of lithium dendrites.

[0090] It should be noted that during the charging process of traditional lithium metal batteries, lithium ions tend to preferentially deposit at the protrusions (charge concentration points) on the negative electrode surface, leading to the growth of needle-like or dendritic "lithium dendrites". Dendrites may pierce the separator, causing a short circuit, or break off to form "dead lithium", resulting in rapid capacity decay and safety hazards.

[0091] Rb + and Cs + The effective reduction potential is lower than that of Li + (That is, they are more difficult to reduce than lithium). Therefore, when the battery is charged, these cations are not reduced to metallic Rb or Cs, but instead adsorb as ions at the tips of the negative electrode surface where the charge density is highest (i.e., the budding points of dendrite growth). The Rb accumulated at these tips... + or Cs + This forms a positively charged shielding layer. Because like charges repel each other, this shielding layer repels any subsequently moving Li₂. + To prevent Li + Continue deposition at the tip.

[0092] And, the excluded Li + It is forced to shift to a flat region with lower surface charge density on the negative electrode for deposition.

[0093] Therefore, this mechanism is equivalent to a "self-healing" process that forces lithium metal to deposit in a smooth and uniform manner, thereby fundamentally inhibiting the formation and growth of dendrites.

[0094] In this embodiment, by effectively suppressing lithium dendrites, the risk of internal short circuits caused by separator puncture is greatly reduced, solving the biggest safety hazard of lithium metal batteries. Suppressing dendrite growth reduces the generation of "dead lithium" (dead lithium is metallic lithium that has detached from the conductive network, leading to irreversible capacity loss), thereby significantly improving the coulombic efficiency of the lithium metal anode and the cycle life of the battery. This allows the high capacity advantage of the lithium metal anode to be truly realized, achieving a balance between high energy density and long lifespan.

[0095] The lithium secondary battery is a high-efficiency energy storage device capable of repeatedly converting electrical energy into chemical energy. Internally, it mainly consists of a positive electrode (typically containing active materials such as lithium transition metal oxides or phosphates) that undergoes a redox reaction and a negative electrode (typically containing active materials such as graphite, silicon-based materials, or lithium titanate). A separator between the positive and negative electrodes allows lithium ions to pass through but blocks electrons. The battery is filled with a non-aqueous electrolyte containing specific functional components for ion transport between the positive and negative electrodes. Depending on the packaging and application, the battery can take various forms, including but not limited to pouch cells, cylindrical cells (such as 18650 and 4680 sizes), prismatic hard-shell cells, and button cells, and is widely used in portable electronic products, electric vehicles, and stationary energy storage power stations.

[0096] It should be noted that the electrolyte of this invention is also applicable to positive electrode systems such as LiFePO4 and LiMn2O4, as well as negative electrode systems such as silicon-carbon and lithium titanate, and tests show that it has a similar improvement trend.

[0097] This application also provides an electrical device, including a lithium secondary battery as described in the foregoing embodiments, or a lithium metal battery as described in the foregoing embodiments.

[0098] The term "electrical equipment" refers to any device, appliance, or system that uses electrical energy as a power source or operates via electricity, and is equipped with the aforementioned lithium secondary batteries or lithium metal batteries as power sources or energy storage components. This category of equipment is very broad, specifically including but not limited to: various mobile communication terminals (such as smartphones and walkie-talkies), portable electronic products (such as tablets, laptops, smartwatches, Bluetooth headsets, digital cameras, and portable game consoles), electric vehicles (such as electric cars, hybrid vehicles, electric bicycles, electric motorcycles, electric scooters, and balance bikes), power tools (such as electric drills, chainsaws, and lawnmowers), smart home devices (such as robot vacuums and cordless vacuum cleaners), and various fixed energy storage systems (such as home energy storage cabinets, backup power supplies for communication base stations, and industrial energy storage power stations). These devices, due to the use of the aforementioned high-performance batteries, possess longer battery life, more stable operating performance, and higher safety.

[0099] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0100] 1. Preparation method of lithium-ion battery: To evaluate the effect of different electrolytes on battery performance, pouch lithium-ion batteries were prepared according to the following general steps: (1) Preparation of positive electrode sheet: The positive electrode active material (LiNi) is prepared by... 0.8 Co0.1 Mn 0.1 O2 (NCM811), conductive agent (super acetylene black), and binder (polyvinylidene fluoride PVDF) are mixed in a mass ratio of 96:2:2, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added. The mixture is stirred evenly to prepare a positive electrode slurry. The slurry is then uniformly coated onto an aluminum foil current collector, dried, rolled, and slit to obtain the positive electrode sheet.

[0101] (2) Preparation of negative electrode sheet: The negative electrode active material (such as artificial graphite), conductive agent (super acetylene black), thickener (sodium carboxymethyl cellulose CMC), and binder (styrene-butadiene rubber SBR) are mixed in a mass ratio of 95:2:1.5:1.5, and an appropriate amount of deionized water is added. The mixture is stirred evenly to prepare a negative electrode slurry. The slurry is evenly coated on a copper foil current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained.

[0102] (3) Battery assembly: Stack the positive electrode, separator (PP / PE / PP three-layer composite separator) and negative electrode in sequence, wind them into an electrode core, and pack them into an aluminum-plastic film packaging bag.

[0103] (4) Electrolyte injection and formation: In a glove box filled with argon (water and oxygen content <1ppm), inject the prepared electrolyte (see each example for specific formula) and seal it. After standing and soaking, perform formation (0.1C constant current charging to 3.0V, then 0.1C constant current charging to the cutoff voltage), then perform secondary sealing and capacity testing to obtain the lithium-ion battery to be tested.

[0104] 2. Electrolyte preparation and examples / comparative examples: Example 1 Non-aqueous organic solvent: Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2.

[0105] Conductive lithium salt: Lithium hexafluorophosphate (LiPF6) is dissolved in the above solvent to achieve a concentration of 1.0 mol / L.

[0106] Additives: Add the potassium salt of 6-methyl-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide (acesulfame potassium, Ace-K) as described in this invention, at an amount of 0.3% of the total mass of the electrolyte.

[0107] Functional additives: No additional functional additives were added.

[0108] Example 2 (Lower limit of additive content) The only difference from Example 1 is that the amount of acesulfame potassium (Ace-K) added is 0.01%.

[0109] Example 3 (Upper Limit of Additive Content) The only difference from Example 1 is that the amount of acesulfame potassium (Ace-K) added is 2.0%.

[0110] Example 4 (combination of multiple functional additives) The only difference from Example 1 is that a combination of multiple functional additives, consisting of 0.5% VC, 2% PS, 1% LiPO2F2, 0.5% LiODFB, 1% DTD, and 0.5% TMSP, are added.

[0111] Example 5 (Different Cations Cs) The only difference from Example 1 is that the additive is replaced with 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide cesium salt (Ace-Cs) at an amount of 0.3%.

[0112] Example 6 (Different substituents -CF3) The only difference from Example 1 is that the additive is replaced with 6-trifluoromethyl-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide potassium salt, and the amount added is 0.3%.

[0113] Example 7 (in collaboration with FEC) The difference from Example 1 is that fluoroethylene carbonate (FEC) was added as a synergistic additive. The amount of acesulfame potassium (Ace-K) added was 0.5%, and the amount of FEC added was 2.5%, with a mass ratio of 1:5.

[0114] Example 8 (Lithium Metal Battery Verification) This embodiment aims to verify the effect of rubidium / cesium-containing additives on suppressing dendrites in lithium metal battery systems.

[0115] Battery fabrication: Positive electrode: The same NCM811 positive electrode sheet as in Example 1 is used.

[0116] Negative electrode: Lithium metal foil with a thickness of 50μm is used directly as the negative electrode, without coating with active materials such as graphite.

[0117] Electrolyte: The same formulation as in Example 5 was used, namely, 0.5% of 6-methyl-1,2,3-oxathiazine-4(3H)-one-2,2-dioxide cesium salt (Ace-Cs) was added to the basic electrolyte.

[0118] Assembly: Assemble into a pouch lithium metal battery in the order of positive electrode / separator / lithium metal negative electrode.

[0119] Example 9 (Ace-Li, conventional lithium-ion battery): The preparation of the basic electrolyte and battery is the same as in Example 1, except that the electrolyte additive is 0.3% lithium acesulfame (i.e., R is Li and X is methyl in the structural formula).

[0120] Example 10 (Ace-Rb, lithium metal battery): The preparation of the basic electrolyte and battery is the same as in Example 8 (lithium metal battery system), except that the electrolyte additive is 0.3% acesulfame K (Ace-Rb, i.e., R is Rb and X is methyl in the structural formula).

[0121] Comparative Example 1 (Blank Control) The only difference from Example 1 is that no acesulfame-based additives are added, and the basic electrolyte consists only of solvent and lithium salt.

[0122] Comparative Example 2 (containing only the conventional additive Vitamin C) The only difference from Example 1 is that instead of acesulfame-based additives, 1.0% vinylene carbonate (VC) is added.

[0123] Comparative Example 3 (Additive content too low) The only difference from Example 1 is that the amount of acesulfame potassium (Ace-K) added is 0.005%.

[0124] Comparative Example 4 (Excessive Additive Content) The only difference from Example 1 is that the amount of acesulfame potassium (Ace-K) added is 3.0%.

[0125] Comparative Example 5 (FEC only, no synergy) The only difference from Example 7 is that acesulfame potassium is not added, but only 2.5% of fluoroethylene carbonate (FEC) is added.

[0126] Comparative Example 6 (Lithium Metal Battery Comparison) For comparison, a lithium metal battery with the same structure as in Example 8 was prepared, but the same blank electrolyte as in Comparative Example 1 (without any acesulfame-based additives) was used.

[0127] 3. Performance Testing and Result Analysis: The following performance tests were performed on the batteries prepared in the above embodiments and comparative examples: (1) Test method: 1) High-temperature cycling performance test: Under 45℃, charge-discharge cycles were performed at a 1C / 1C rate within a voltage range of 2.8V~4.2V, and the capacity retention rate (%) was recorded after 500 cycles. Test objective: To evaluate the effect of additives on improving the stability of the interfacial film (SEI / CEI) at high temperatures.

[0128] 2) Low-temperature discharge performance test: Discharge at 0.2C rate at -20℃, and record the ratio of discharge capacity to discharge capacity at room temperature (25℃) (capacity retention rate %). Test objective: To evaluate the improvement effect of additives on lithium-ion desolvation and low-temperature ion transport capability.

[0129] 3) High-Temperature Storage Gas Generation Test: After fully charging the battery, it was stored in a 60°C high-temperature chamber for 7 days. The battery volume change rate (%) and capacity recovery rate (%) before and after storage were measured. Test objective: To evaluate the ability of additives to inhibit electrolyte decomposition and gas generation.

[0130] 4) Cyclic testing was performed on the batteries of Example 8 and Comparative Example 6: at 25°C, the batteries were charged at a constant current of 0.5C to 4.2V, then at a constant voltage of 0.05C, and finally discharged at a constant current of 0.5C to 3.0V. The capacity retention rate was recorded.

[0131] 5) High-voltage and high-temperature cycle performance test: The formed battery was placed in a 45°C constant temperature chamber and charged at a constant current of 1C to 4.4V, followed by constant voltage charging until the current dropped to 0.05C. After resting for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This charge-discharge cycle was repeated, and the discharge capacity of the battery on the 200th cycle was recorded.

[0132] High-pressure high-temperature cycle capacity retention rate (%) = (discharge capacity of the Xth cycle / discharge capacity of the first cycle) × 100%.

[0133] (2) The test results are shown in the table below: Table 1. Performance Test Results

[0134] Table 2. Cycle test results of lithium metal batteries (Li||NMC) (Test conditions: room temperature 25℃, 0.5C / 0.5C charge and discharge, voltage range 2.8V~4.2V)

[0135] (3) Results analysis: 1) In terms of overall performance, compared with Comparative Example 1 (blank), Example 1 (with 0.3% Ace-K added) showed significant improvements in high-temperature cycling, low-temperature discharge, and gas generation suppression. This demonstrates that the S / N-containing inorganic interface film formed by acesulfame-based additives possesses excellent stability and ion-conducting ability, and that the cation K... + It helps improve low-temperature performance.

[0136] 2) Regarding the content range, although Example 2 (0.01%) was better than the blank, it was not as good as Example 1, indicating that the low content led to incomplete film formation. Comparative Example 3 (0.005%) was almost as good as the blank, confirming the rationality of 0.01% as the lower limit.

[0137] Although Example 3 (2.0%) showed good cycling and gas generation suppression, its low-temperature performance decreased due to the increased impedance caused by the excessively thick interfacial film. Comparative Example 4 (3.0%) exhibited further deterioration in low-temperature performance, confirming the rationale for using 2.0% as the upper limit.

[0138] 3) Regarding functional additives, Example 4 (0.3% Ace-K + combination of multiple functional additives) showed significantly improved circulation and gas production performance compared to Example 1, indicating that Ace-K has a good synergistic effect with commercial functional additives.

[0139] 4) In terms of structural optimization, Example 5 (Ace-Cs) exhibits better cycling and low-temperature performance than Ace-K, thanks to Cs. + Not only does it have an electrostatic shielding effect to suppress dendrites (protecting the negative electrode), its larger ionic radius is also more conducive to reducing the desolvation energy barrier.

[0140] Example 6 (containing -CF3) showed excellent performance in suppressing gas production (low volume expansion rate), indicating that the introduction of electron-withdrawing group -CF3 improved the oxidation resistance of the additive and could form a more stable CEI film on the positive electrode surface.

[0141] 5) Regarding the synergistic effect with FEC, Example 7 (Ace-K + FEC, ratio 1:5) exhibited excellent overall performance. Compared with Comparative Example 5 (FEC only), Example 7 showed significant improvements in both cycle life and low-temperature performance. This demonstrates a significant synergistic effect between the additive of this invention (providing a highly conductive ionic component containing S / N) and FEC (providing a stable component rich in LiF), jointly constructing an ideal interface film with "high stability + high conductivity".

[0142] 6) High-voltage cycle stability: Based on the high-voltage (4.4V) test data in Table 1, it can be seen that when the charging cut-off voltage is increased to 4.4V, the capacity retention rate of Comparative Example 1 (blank electrolyte) drops sharply to 62.5%, with severe oxidative decomposition of the electrolyte on the positive electrode surface. Comparative Example 2 (conventional VC additive) also readily undergoes oxidative polymerization under high voltage, resulting in a capacity retention rate of only 65.4%. In contrast, the capacity retention rate of Example 1 is increased to 83.2%, and in particular, Example 6 (introducing a strong electron-withdrawing group -CF3) achieves a capacity retention rate as high as 88.5%. This strongly demonstrates that the additive of this invention can form a stable CEI interface film under high-voltage conditions, effectively suppressing the increase in impedance and electrolyte decomposition caused by high voltage.

[0143] 7) Cycle stability verification of lithium metal batteries: As shown in Table 2, in the lithium metal battery system, Comparative Example 6 (without the additive of this invention) experienced a rapid decrease in capacity retention to 42.1% after 100 cycles due to the continuous growth of lithium dendrites and the consumption of active lithium, with an average coulombic efficiency of only 97.2%. In contrast, Example 8 (containing additive Ace-Cs) achieved a capacity retention of 86.2% after 100 cycles, with an average coulombic efficiency of 99.4%. Upon disassembly, the lithium metal surface of Example 8 was found to be smooth and dense, with no obvious dendrites. The experimental data clearly confirm the effectiveness of the additive Cs. + Large-radius cations exert a significant electrostatic shielding effect, effectively suppressing lithium dendrite growth.

[0144] 8) Verification of the universality of the cation range: Referring to the data from Example 9 (Ace-Li) in Table 1, it can be seen that the lithium salt form using the anionic framework of this invention exhibits significantly better cycling performance at both room temperature and high temperature / high pressure than the blank comparative example 1, confirming the basic film-forming effect of this heterocyclic anionic framework. Meanwhile, referring to the data from Example 10 (Ace-Rb) in Table 2, it can be seen that Rb… + As with Cs + Large alkali metal cations from the same group exhibited a capacity retention rate of 84.5% after 100 cycles in lithium metal batteries, demonstrating excellent anti-dendritic effects. This fully confirms that the cation range (Li, K, Rb, Cs) defined in the claims of this invention can all exert corresponding technical advantages and has a solid scientific basis.

[0145] (4) Characterization analysis of the interfacial membrane (SEI): To verify the film-forming mechanism of the additive of the present invention, X-ray photoelectron spectroscopy (XPS) analysis was performed on the negative electrode surface after cycling.

[0146] 1) Sample preparation: After 50 cycles of the battery in Example 1 (containing 0.3% Ace-K), the battery was disassembled in an argon-filled glove box, the negative electrode was removed, and the residual electrolyte was removed by cleaning with dimethyl carbonate (DMC). After vacuum drying, the battery was tested.

[0147] 2) Test results: In the S 2p spectrum, a distinct characteristic peak was detected at a binding energy of approximately 167.0–169.0 eV, corresponding to lithium sulfite (Li2SO3) and sulfate ester species; a signal corresponding to lithium sulfide (Li2S) was detected at approximately 160.0–162.0 eV.

[0148] In the N 1s spectrum, characteristic peaks corresponding to lithium nitride (Li3N) and its derivatives were detected at binding energies of approximately 398.0–400.0 eV.

[0149] In contrast, no obvious S and N element-related characteristic peaks were detected on the negative electrode surface of Comparative Example 1 (blank electrolyte).

[0150] Conclusion: The characterization results directly confirm that the additives of this invention (acesulfame K and its derivatives) underwent reductive decomposition on the negative electrode surface and participated in the construction of an SEI film rich in inorganic components such as Li2SO3, Li2S, and Li2N. These inorganic components with high ionic conductivity are the key reason why the battery of Example 1 has excellent low-temperature performance and long cycle life, fully supporting the limitations on the SEI film composition in the aforementioned embodiments.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte additive for lithium secondary batteries, characterized in that, The additive is selected from at least one of compounds having the following general chemical structural formula: ； Wherein, R is a cation selected from any one of H, Li, Na, K, Rb, and Cs; X is a substituent at the 6-position selected from halogens, unsubstituted or optionally substituted C1-C5 alkyl groups, unsubstituted or optionally substituted C1-C5 alkoxy groups, unsubstituted or optionally substituted aryl or heteroaryl groups. The substituents are selected from halogen, cyano, alkyl, alkoxy, olefin, and alkyne groups.

2. The electrolyte additive for lithium secondary batteries as described in claim 1, characterized in that, R is selected from H, Li, K, Rb, or Cs; and / or, X is selected from fluorine, trifluoromethyl, cyano, methyl, ethyl, n-propyl, isopropyl, methoxy, or phenyl; and / or, The electrolyte additive for lithium secondary batteries is selected from at least one of the following compounds: Compounds comprising, and wherein the cation R is a potassium ion and the 6-substituent X is an ethyl, trifluoromethyl, methoxy, cyano, fluorine atom, or phenyl group.

3. The electrolyte additive for lithium secondary batteries as described in claim 2, characterized in that, The electrolyte additive for lithium secondary batteries is selected from at least one of the following compounds: 。 4. A non-aqueous electrolyte for lithium secondary batteries, characterized in that, It includes non-aqueous organic solvents, conductive lithium salt electrolytes, and electrolyte additives for lithium secondary batteries as described in any one of claims 1-3.

5. The non-aqueous electrolyte for lithium secondary batteries as described in claim 4, characterized in that, Based on the total mass percentage of the non-aqueous electrolyte for lithium secondary batteries being 100%, the mass percentage of the non-aqueous organic solvent is 45%~95%; the mass percentage of the conductive lithium salt electrolyte is 5%~30%; the mass percentage of the electrolyte additive for lithium secondary batteries is 0.01%~2%; and / or, the non-aqueous electrolyte for lithium secondary batteries further comprises fluoroethylene carbonate; wherein the mass ratio of the electrolyte additive for lithium secondary batteries to fluoroethylene carbonate is 1:(1~10).

6. A lithium secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator, as well as a non-aqueous electrolyte for lithium secondary batteries as described in any one of claims 4-5.

7. The lithium secondary battery as described in claim 6, characterized in that, The positive electrode sheet includes a positive electrode active material; the positive electrode active material is selected from LiMnO4. z N 1-z PO4, Li 1+x Ni y Mn 2-x-y O4 and Li 1+a Ni b Co c M` 1-a-b-c At least one of O2; Wherein, M and N are one of Fe, Mn, Co, or Ni respectively; M` is at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Zn, Ga, Y, Zr, Nb, Mo, Sn, and Ba; and 0≤z≤1, 0≤x≤0.05, 0≤y≤0.5, 0≤a≤0.5, 0≤b, c≤1 and 0≤a+b+c≤1; and / or, The negative electrode sheet includes a negative electrode active material; the negative electrode active material is selected from at least one of natural graphite, artificial graphite, mesocarbon microbeads, elemental silicon, silicon oxide compound SiO X , silicon-carbon composite material, lithium titanate, lithium metal, and lithium alloy; where 0 < X ≤ 2; and / or, A solid electrolyte interface film is formed on the surface of the negative electrode sheet; the solid electrolyte interface film contains at least one inorganic component selected from Li2SO3, Li2S and Li3N.

8. A lithium metal battery, characterized in that, It includes a positive electrode, a lithium metal negative electrode, and an electrolyte; the electrolyte includes the electrolyte additive for lithium secondary batteries as described in claim 1, and the cation R in the electrolyte additive for lithium secondary batteries is selected from Rb or Cs.

9. An electrical appliance, characterized in that, This includes the lithium secondary battery as described in claim 6, or the lithium metal battery as described in claim 8.

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