Electrolyte additive, electrolyte and battery

Abstract

The present disclosure relates to the field of batteries, and particularly relates to an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a first additive and a second additive. The first additive has a structure as represented by formula 1, and the second additive is a nitrile additive, wherein R1, R2 and R3 each independently comprise any one of H, a halogen, a C1-C4 alkyl, a C1-C4 halogenated alkyl, a C2-C4 alkenyl, a C2-C4 halogenated alkenyl, a C2-C4 alkynyl, a C5-C7 cycloalkyl, -Ph-R4 and -CH2-Ph-R5; and R4 and R5 are each independently selected from any one of H, a halogen and a C1-C2 alkyl.

Description

Electrolyte additives, electrolytes and batteries

[0001] Priority information

[0002] This disclosure claims priority and benefits to patent application No. 2024117403380, filed with the China National Intellectual Property Administration on November 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of batteries, and more particularly to an electrolyte additive, an electrolyte, and a battery. Background Technology

[0004] Lithium-ion batteries offer several significant advantages over other battery types, such as high energy density, long cycle life, and low self-discharge rate, leading to their widespread application in various fields. Nitrile compounds, due to their unique functional groups (such as carbon-nitrogen triple bonds), can effectively enhance the overall performance of lithium-ion battery electrolytes. However, at high temperatures, they can cause problems such as increased internal resistance and reduced rate performance. Furthermore, when batteries use cathode materials containing transition metals, these transition metals tend to escape from the cathode material at high temperatures. Therefore, there is an urgent need to develop an electrolyte solution to address these issues.

[0005] Public content

[0006] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, this disclosure provides an electrolyte additive, an electrolyte, and a battery. The electrolyte additive can reduce the dissolution of transition metal ions in the positive electrode material of a lithium-ion battery, thereby improving the room temperature cycling, high temperature storage, high temperature cycling performance, and fast charging performance of the lithium-ion battery.

[0007] Therefore, the first aspect of this disclosure provides an electrolyte additive, including a first additive and a second additive, wherein the first additive has the structure shown in Formula 1; and the second additive is a nitrile additive.

[0008] R1, R2 and R3 each independently include any one of H, halogen, C1-C4 alkyl, C1-C4 haloalkyl, C2-C4 alkenyl, C2-C4 haloalkenyl, C2-C4 alkynyl, C5-C7 cycloalkyl, -Ph-R4 and -CH2-Ph-R5;

[0009] R4 and R5 are each independently selected from any one of H, halogens, and C1-C2 alkyl groups.

[0010] Nitrile additives possess highly energetic carbon-nitrogen triple bonds (cyano groups), making them resistant to oxidation. Therefore, these compounds exhibit excellent stability and strong oxidation resistance at the cathode. Simultaneously, the cyano group has strong coordination ability, allowing it to bind to active sites on the electrode surface (such as high-valence metal ions like nickel, cobalt, and manganese), masking active ions and reducing the decomposition of the electrolyte by the electrode. However, at high temperatures, these additives can lead to increased internal resistance and reduced rate performance. This is because nitrile additives themselves undergo reduction and decomposition at the anode, forming dimers / trimers and oligomers, resulting in increased interfacial impedance. Particularly at high temperatures, their direct current resistance (DCR) increases significantly, severely hindering lithium-ion transport and consequently leading to poor rate performance and limited cycle life improvement. To address this problem, this disclosure introduces a first additive into the electrolyte additive. This first additive exhibits high reactivity and can be reduced before the nitrile additives, thereby increasing the chemical energy barrier for the reduction of the nitrile additives. Simultaneously, the Si-O bonds in the first additive possess high reactivity; after bond breakage, the resulting difluorophosphate ions will react with lithium ions to deposit lithium difluorophosphate salt. This lithium salt will gradually decompose to produce lithium fluoride, lithium phosphate, and Li. x PO y F z Lithium salts that improve lithium-ion transport reduce the impedance of the SEI interface film. Furthermore, compared to similar structures with three or two silicon-oxygen bonds, the single silicon-oxygen bond structure in the first additive exhibits superior steric hindrance, without reducing lithium-ion migration rate, thus improving battery cycle stability and storage performance. HF in the electrolyte reacts with silicon-based fluorophosphates to produce fluorosilane-like gases, leading to severe gas production and battery degradation after storage or cycling. The Lewis base functional group of cyano compounds can capture Lewis acidic phosphorus pentafluoride. Phosphorus pentafluoride is a decomposition product of LiPF6, undergoing the reaction PF5 + H2O → POF3 + HF. Therefore, the cyano functional group stabilizes and deactivates phosphorus pentafluoride, reducing HF formation and significantly decreasing the generation of fluorosilane-like gases during storage or cycling of silicon-based fluorophosphates. Therefore, the first and second additives complement each other. When an electrolyte containing these two additives is applied to a lithium-ion battery, the lithium-ion battery exhibits excellent room temperature cycling, high temperature storage, high temperature cycling performance, and fast charging performance, and can significantly reduce the dissolution of transition metal ions in the cathode material.

[0011] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Detailed Implementation

[0012] The embodiments of this disclosure are described in detail below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure.

[0013] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0014] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0015] To facilitate understanding of this disclosure, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this disclosure, all other technical and scientific terms used in this disclosure shall have the meaning commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0016] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this disclosure but do not exclude other contents.

[0017] The term "nitrile additives" should be understood as additives containing cyano groups.

[0018] The term "halogen" should be understood as one or more of fluorine, chlorine, bromine, and iodine, which can be substituted by one, two, three or more halogens on an alkyl, alkenyl, or alkynyl group.

[0019] The term "C1-C4 alkyl" should be understood to mean a straight-chain or branched saturated monovalent hydrocarbon group having 1, 2, 3, or 4 carbon atoms. The alkyl group is, for example, methyl, ethyl, propyl, butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, etc.

[0020] The term “C2-C4 alkenyl” should be understood to refer to a straight-chain or branched monovalent alkenyl group containing one or more double bonds and having 2, 3 or 4 carbon atoms.

[0021] The term “C2-C4 alkynyl” should be understood to mean a straight-chain or branched monovalent hydrocarbon group that contains one or more triple bonds and has 2, 3 or 4 carbon atoms.

[0022] The term "Ph" should be understood as phenyl.

[0023] The first aspect of this disclosure provides an electrolyte additive, comprising a first additive and a second additive, wherein the first additive has the structure shown in Formula 1; and the second additive is a nitrile additive.

[0024] R1, R2 and R3 each independently include any one of H, halogen, C1-C4 alkyl, C1-C4 haloalkyl, C2-C4 alkenyl, C2-C4 haloalkenyl, C2-C4 alkynyl, C5-C7 cycloalkyl, -Ph-R4 and -CH2-Ph-R5;

[0025] R4 and R5 are each independently selected from any one of H, halogens, and C1-C2 alkyl groups.

[0026] Nitrile additives possess high bond energy of cyano groups in their structure, making them less susceptible to oxidation. Therefore, nitrile additives exhibit excellent stability and strong oxidation resistance at the cathode. Simultaneously, nitrile additives possess strong coordination ability, enabling them to bind to active sites on the electrode surface (such as high-valence metal ions like nickel, cobalt, and manganese), masking these active ions and reducing the decomposition of the electrolyte by the electrode. However, the inventors discovered that nitrile additives themselves undergo reduction and decomposition at the anode, forming dimers / trimers and oligomers. This leads to increased interfacial impedance, particularly at high temperatures, where the DC resistance (DCR) increases significantly, severely hindering lithium-ion transport. Consequently, the battery's rate performance is poor, and cycle life improvement is limited. To address this issue, this disclosure introduces a first additive in the electrolyte additive. This first additive exhibits high reactivity and can be reduced before nitrile additives, thereby increasing the chemical energy barrier for the reduction of nitrile additives, inhibiting their reduction at the negative electrode, and maintaining the complexing ability of the cyano group. This allows any small amount of escaped transition metal to be anchored on the surface of the positive electrode material by the cyano compound, reducing the possibility of transition metal deposition on the negative electrode and poisoning the SEI film. Furthermore, compared to similar structures with three or two silicon-oxygen bonds, a single silicon-oxygen bond structure has superior steric hindrance, does not reduce the lithium-ion migration rate, and thus improves the battery's cycle stability and storage performance. However, the first additive can also cause some problems. For example, when trace amounts of acid are present in the electrolyte, the first additive will react with it, producing fluorosilane-like gas, leading to severe gas production and a drop in battery performance after a period of storage or cycling. The Lewis base functional group (i.e., the cyano functional group) in the structure of the second additive can capture compounds with Lewis acidity in this process, stabilizing and deactivating them, thereby significantly reducing the generation of fluorosilane-like gas by the first additive during storage or cycling. Therefore, the first and second additives complement each other, which can reduce the risk of transition metal ion dissolution in the cathode material while forming a good interfacial film and reducing gas production. This results in batteries containing these two additives having good cycle stability and excellent storage performance at high temperatures.

[0027] According to specific embodiments of this disclosure, R1, R2, and R3 each independently include any one of F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkyl, -Ph-R4, and -CH2-Ph-R5; R4 and R5 are each independently selected from any one of H, F, and C1-C2 alkyl. This further improves the electrochemical performance of the battery.

[0028] According to specific embodiments of this disclosure, R1, R2, and R3 each independently include any one of F, C1-C4 alkyl groups, C1-C2 fluoroalkyl groups, C2 alkenyl groups, C3 fluoroalkenyl groups, C4 alkynyl groups, C6 cycloalkyl groups, -Ph-R4, and -CH2-Ph-R5; R4 and R5 are each independently selected from any one of H, F, and C1 alkyl groups. This further improves the electrochemical performance of the battery.

[0029] According to certain embodiments of this disclosure, specifically, the first additive includes at least one of the following compounds:

[0030] The CAS numbers for compounds 1-1 to 1-17 are as follows:

[0031] Compound 1-1: 2708941-25-5; Compound 1-2: 4419-25-9; Compound 1-3: 13683-39-1; Compound 1-4: 4414-27-1; Compound 1-5: 4414-26-0; Compound 1-6: 4480-02-8; Compound 1-7: 2577172-95-1; Compound 1-8: 13683-40-4; Compound 1-9: 2577172-9 Compounds 3-9; Compounds 1-10: 2708941-27-7; Compounds 1-11: 2287283-36-5; Compounds 1-12: 6231-57-8; Compounds 1-13: 1386-54-9; Compounds 1-14: 2708941-26-6; Compounds 1-15: 6231-58-9; Compounds 1-16: 6231-59-0; Compounds 1-17: 2577172-94-0.

[0032] The synthesis methods of compounds 1-18 to 1-22 can be referred to the preparation method of Example 14 in CN114728992A, specifically, the dichlorophenylsilane in the reference document is replaced with the following raw materials.

[0033] 1-18: Raw material trivinylchlorosilane (1871-21-2);

[0034] 1-19: The raw material is dimethylethynyl butylchlorosilane (2069196-19-4);

[0035] 1-20: The raw material is dimethyl(trifluoropropylene)chlorosilane (89705-02-2);

[0036] 1-21: The raw material is tris(pentafluoroethyl)chlorosilane (1620665-21-5);

[0037] 1-22: The raw material is dimethyl(p-methylphenylmethyl)chlorosilane (1833-28-9).

[0038] According to embodiments of this disclosure, the second additive includes, but is not limited to, at least one of succinic anion, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, and n-butanol 1,2,3,4-tetrapropionitrile ether (CAS: 2465-94-3).

[0039] A second aspect of this disclosure provides an electrolyte comprising the electrolyte additives described in the first aspect. Thus, when applied to lithium-ion batteries, this electrolyte can improve the room-temperature cycling, high-temperature storage, and high-temperature cycling performance of lithium-ion batteries, and can significantly reduce the dissolution of transition metal ions from the cathode material.

[0040] According to embodiments of this disclosure, the amount of the first additive is 0.05%-5% of the total mass of the electrolyte. As some specific examples, the amount of the first additive is 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the total mass of the electrolyte.

[0041] According to embodiments of this disclosure, the amount of the second additive is 0.1%-3% of the total mass of the electrolyte. As some specific examples, the amount of the second additive is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% of the total mass of the electrolyte.

[0042] According to embodiments of this disclosure, the electrolyte further includes lithium salts and non-aqueous organic solvents.

[0043] Specifically, the type of lithium salt is not particularly limited. As some specific examples, the lithium salt includes, but is not limited to, at least one selected from LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4. The lithium salt has a mass percentage content of 8%-20% in the electrolyte. As some specific examples, the mass percentage content of the lithium salt in the electrolyte is 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0044] Specifically, the type of non-aqueous organic solvent is not particularly limited. As some specific examples, the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, and methyl-(2,2,2-trifluoroethyl) carbonate. The non-aqueous organic solvent in the electrolyte contains 69%-91.75% by mass. As some specific examples, the non-aqueous organic solvent in the electrolyte contains 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, and 91.75% by mass.

[0045] This disclosure provides a battery in a third aspect, comprising the electrolyte described in the second aspect. The battery thus exhibits good cycle stability and excellent storage performance.

[0046] According to a specific embodiment of this disclosure, the battery includes the electrolyte additive or the electrolyte described above, a positive electrode, a negative electrode, and a separator; the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0047] The positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and LiNi. x Co y Mn z M 1-x-y-z O2, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-x O4, Na m AO2, at least one of polyanionic compounds and Prussian blue compounds; wherein M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, and A includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr and Cu, 0≤a<0.2, 0≤x<1, 0<m≤1.

[0048] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0049] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material layer includes the aforementioned positive active material.

[0050] In some embodiments of this disclosure, the positive current collector may include a metal foil or a composite positive current collector. For example, the metal foil may be aluminum foil. The composite positive current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. For example, the composite negative current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0051] In some embodiments of this disclosure, the positive electrode active material layer 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.

[0052] In some embodiments of this disclosure, the positive electrode active material 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.

[0053] In some embodiments of this disclosure, 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, and binder, in a solvent (e.g., N-methylpyrrolidone, NMP) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0054] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0055] In some embodiments of this disclosure, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper 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 (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0056] In some embodiments of this disclosure, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano-carbon, elemental silicon, silicon oxide, silicon-carbon composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, and lithium titanate.

[0057] In some embodiments of this disclosure, the negative electrode active material layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0058] In some embodiments of this disclosure, the negative electrode active material layer may optionally include a conductive agent. 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.

[0059] In some embodiments of this disclosure, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0060] In some embodiments of this disclosure, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, 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.

[0061] This disclosure does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0062] In some embodiments of this disclosure, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene separator, polypropylene separator, aromatic polyamide membrane, polytetrafluoroethylene membrane, polyethersulfone membrane, and PE ceramic-coated separator. The thickness of the separator may be 10μm-16μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, etc.

[0063] It should be noted that the features and advantages described above for the electrolyte also apply to this battery, and will not be repeated here.

[0064] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0065] Example 1

[0066] 1. Preparation of electrolyte: The electrolyte in this embodiment is prepared according to the following components by mass fraction: 13% LiPF6, 1% compound 1-1, 0.5% 1,4-dicyano-2-butene, and non-aqueous organic solvent (EC:PC:DEC:EMC mass ratio of 20:4:21:41) to make up to 100%.

[0067] In an argon-filled glove box (moisture content <10ppm, oxygen content <1ppm), solvents EC, PC, diethyl carbonate DEC and EMC are mixed evenly. Lithium salt and electrolyte additives are quickly added to the mixed solvent and mixed thoroughly. The electrolyte is then obtained by stirring.

[0068] 2. Preparation of positive electrode: Lithium manganese iron phosphate material (LiMn) is prepared. 0.4 Fe 0.6 PO4 (LMFP), conductive agent Super P (conductive carbon black), carbon nanotubes, and binder PVDF (polyvinylidene fluoride) were mixed with solvent NMP in a mass ratio of 96.5:1.5:1:1 to prepare a positive electrode slurry of a certain viscosity. This slurry was then coated onto both surfaces of the positive electrode current collector aluminum foil, dried at 85℃, and cold-pressed. The coating weight was 250 g / m². 2 (Neglecting solvent), the compacted density is 2.2 g / cm³. 3 Next, the edges are trimmed, the sheets are cut, and the sheets are slit. After slitting, the sheets are dried at 85°C for 4 hours under vacuum, and the tabs are welded to form the positive electrode sheet.

[0069] 3. Preparation of negative electrode sheet: Artificial graphite negative electrode material, conductive agent Super P, thickener CMC (sodium carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber latex) are mixed evenly with solvent water at a mass ratio of 95:1.5:1:2.5 to prepare a negative electrode slurry of a certain viscosity. The negative electrode slurry is coated onto both sides of the negative electrode current collector copper foil, dried at 85℃, and then cold-pressed. The coating amount is 154 g / m². 2 (Neglecting solvent), the compacted density is 1.6 g / cm³. 3 The negative electrode sheet is prepared by trimming, cutting, and slitting the edges. After slitting, it is dried at 85°C for 4 hours under vacuum.

[0070] 4. Battery fabrication: The positive electrode, negative electrode, and separator (using a 16μm thick polypropylene porous membrane as the separator) prepared according to the above process are stacked to form a lithium-ion battery with a thickness of 4.7mm, a width of 55mm, and a length of 60mm, with a capacity of 1300mAh. The battery is then vacuum baked at 85℃ for 48h and injected with the above electrolyte to complete the battery fabrication.

[0071] The electrolyte formulations provided in Examples 2-38, 40-65 and Comparative Examples 1-7, 10-15 are basically the same as those in Example 1. The specific parameters are shown in Table 1. Examples 40 and Comparative Examples 10-11 are fast charging cycle tests.

[0072] Example 39

[0073] Preparation of electrolyte: The electrolyte in this embodiment is prepared according to the following components by mass fraction: 13% LiPF6, 1% compound 1-2, 1% 1,4-dicyano-2-butene, and non-aqueous organic solvent (fluoroethylene carbonate: methyl-(2,2,2-trifluoroethyl) carbonate in a mass ratio of 3:5) to 100%.

[0074] In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), fluoroethylene carbonate (FEC) and methyl-(2,2,2-trifluoroethyl) carbonate (FEMC) solvents were mixed thoroughly. Lithium salt and additives were then rapidly added to the mixed solvent and thoroughly mixed. The mixture was then stirred to obtain the electrolyte. The preparation of the remaining battery components was the same as in Example 1.

[0075] The electrolyte formulations provided in Comparative Examples 8 and 9 are basically the same as those in Example 39, and the specific parameters are shown in Table 1.

[0076] Table 1

[0077] Continued from Table 1

[0078] Continued from Table 1

[0079] Continued from Table 1

[0080] Continued from Table 1 The " / " indicates that it is not present.

[0081] Test case

[0082] The lithium-ion batteries obtained in the examples and comparative examples were tested as follows, and the results are shown in Table 2.

[0083] 1. High-temperature storage performance test

[0084] The battery was charged at 25℃ with a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V to a cutoff current of 0.05C. It was then discharged at a constant current of 1C to 2.5V, and the discharge capacity was recorded as A0. The battery was then transferred to a high temperature of 60℃ and left to stand for 30 days. It was then discharged at a constant current of 1C, and the discharge capacity was recorded as A1. The capacity retention rate at 60℃ was calculated as (A1 / A0) × 100%.

[0085] 2. High-temperature cycling performance test

[0086] The battery was charged at 45°C with a constant current of 1.0C to 4.3V, then charged with a constant voltage to a cutoff current of 0.05C. It was then discharged at a constant current of 1.0C to 2.5V, and the discharge capacity was recorded as C0. This charge-discharge cycle was repeated for 500 cycles to obtain the discharge capacity C on the 500th cycle. 500 Capacity retention rate = (C 500 / C0)×100%.

[0087] 3. High-temperature fast charging cycle performance test

[0088] The battery was charged at 3.0C constant current to 4.3V at 45℃, then charged at constant voltage to the cutoff current of 0.05C, and then discharged at 1.0C constant current to 2.5V. The discharge capacity was recorded as C0. This charge-discharge cycle was repeated for 500 cycles to obtain the discharge capacity C of the 500th cycle. 500 Capacity retention rate = (C 500 / C0)×100%.

[0089] 4. Measurement of transition metal (Ni, Co, Mn) deposition:

[0090] Disassemble the battery after 500 cycles and remove the negative electrode. Rinse the negative electrode three times with excess DMC (dimethyl carbonate). Then soak the negative electrode in sufficient water until the negative electrode material detaches from the copper foil. Discard the copper foil, filter, and dry the negative electrode material.

[0091] Weigh 0.5g of the negative electrode material and place it in a 300mL glass beaker. Slowly add 10mL of 65wt% nitric acid and 10mL of 98wt% sulfuric acid. Place the beaker on an electric furnace, cover it with a watch glass, and heat until the sample dissolves (becomes milky white). Remove the beaker and cool it. Add 10mL of 36wt% hydrochloric acid and heat until the salts dissolve (the solution becomes clear). Remove the beaker and cool it. Filter the solution using medium-speed quantitative filter paper. Rinse the filter paper and beaker thoroughly and transfer the solution to a 250mL volumetric flask. Then perform ICP injection testing. Specifically, use an inductively coupled plasma atomic emission spectrometer (Agilent ICP-OES 5110) to directly read the Ni, Co, and Mn content in the negative electrode material.

[0092] Table 2

[0093] Continued from Table 2

[0094] Continued from Table 2

[0095] Continued from Table 2

[0096] Continued from Table 2 Note: The manganese / cobalt / nickel content (unit: ppm) in Table 2 is used to quantify the deposition level of dissolved transition metals (Ni, Co, Mn) in the positive electrode material at the negative electrode after 500 battery cycles. The deposition level directly reflects the degree of influence of transition metal ions on the battery. Generally, the lower the deposition level, the more stable the positive electrode structure is during battery cycling, the less the negative electrode is affected, and the longer the battery life.

[0097] Analysis of experimental results:

[0098] As can be seen from Examples 1-65, the present invention combines the first additive and the second additive and adds them to the lithium-ion battery, which can significantly improve the high-temperature cycle stability and storage performance of the battery, and can significantly reduce the dissolution of transition metal ions in the cathode material.

[0099] Comparing Examples 2, 23-27, and Comparative Example 1, it is evident that Comparative Example 1, containing only the first additive, does not improve the battery's high-temperature cycle stability or storage performance, nor does it reduce the dissolution of manganese ions. Similarly, comparing Examples 1-22, 28-34, and Comparative Example 2, it is evident that Comparative Example 2, containing only the second additive, also does not improve the battery's high-temperature cycle stability, storage performance, or reduce the dissolution of manganese ions. The same results were observed when applied to different battery systems (see Examples 39 and 8-9).

[0100] The embodiments and comparative examples disclosed herein tested the effects of different additive types and contents on battery performance, and the specific analysis is as follows:

[0101] (1) Compared with Examples 1-22 and 28-34, Comparative Example 2 lacks the first additive and only contains the second additive (nitrile additive). The second additive will decompose and form dimers / trimers and oligomers on the negative electrode, resulting in increased interfacial impedance, hindering the transport of lithium ions, thereby reducing the rate performance of the battery and limiting the improvement of cycle life. On this basis, adding the first additive to the electrolyte can improve the above situation. Because the first additive used has high reactivity, it can be reduced before the second additive, thereby increasing the chemical energy barrier for the reduction of the second additive, inhibiting the reduction of the second additive on the negative electrode, maintaining the complexing ability of cyano groups, so that a small amount of escaped transition metal can be anchored on the surface of the positive electrode material by the second additive, reducing the possibility of transition metal depositing on the negative electrode and poisoning the SEI film;

[0102] (2) Compared with Examples 2, 23-27 and 35-38, Comparative Example 1 lacks the second additive and only contains the first additive. It has limited effect on improving the high-temperature cycle stability and storage performance of the battery, and also has limited effect on reducing manganese ion dissolution.

[0103] (3) Examples 39 and Comparative Examples 8-9 differed in the battery system and voltage range (LNMO / graphite 3.4-4.85V, where LNMO was LiNi). 0.5 Mn 1.5 Example 45, like Comparative Examples 12-13, also changed the battery system and voltage range (LCO / graphite 3.0-4.48V, where LCO is LiCoO2). Example 46, like Comparative Examples 14-15, also changed the battery system and voltage range (NCM523 / graphite 2.75-4.4V, where NCM523 is LiNi). 0.5 Co 0.2 Mn 0.3 O2) The test investigated the impact of different battery systems and voltage ranges on the test results. The capacity retention test result "459 cycles @ 80%" for Example 39 indicates that the battery's capacity retention rate was 80% after 459 cycles.

[0104] The results show that the combination of the first and second additives in different battery systems is better than the results of using them alone, which also shows that the technical solution provided in this disclosure has a certain degree of universality.

[0105] (4) Comparing the results of Comparative Examples 1 and 2, it can be seen that Comparative Example 1 only added the first additive and Comparative Example 2 only added the second additive. However, the high-temperature cycle stability and storage performance of the battery prepared by Comparative Example 1 are better than those of Comparative Example 2, which also shows that the first additive itself has a certain improving effect on the cycle stability and high-temperature performance of the battery.

[0106] (5) Compared with Comparative Examples 2 and Examples 1-22, Comparative Example 3 replaced the first additive type with di(trimethylsilyl)fluorophosphate, which contains two silicon-oxygen bonds in its structure. Compared with Comparative Example 2, the addition of di(trimethylsilyl)fluorophosphate in Comparative Example 3 can improve high-temperature cycling stability, storage performance, and reduce manganese ion dissolution, but it is still inferior to the performance improvement effect of Examples 1-22. The reason is that the molecular weight of di(trimethylsilyl)fluorophosphate is relatively large, which will increase the viscosity of the electrolyte and reduce the conductivity of the electrolyte when added to it. In addition, the test results of Comparative Examples 4-6 and Examples 23-25 ​​also conform to this conclusion.

[0107] (6) In Comparative Example 7, compared to Comparative Example 2 and Examples 1-22, the first additive type was replaced with tris(trimethylsilyl)phosphate, which contains three silicon-oxygen bonds in its structure. The results showed that the addition of tris(trimethylsilyl)phosphate did not improve battery performance, but rather reduced it and increased the dissolution of manganese ions. This is because tris(trimethylsilyl)phosphate has a large molecular weight, which significantly increases the viscosity of the electrolyte and significantly reduces its conductivity. Furthermore, it does not contain sulfur (F) and is difficult to form SEI film components with good ion-conducting capabilities, such as LiF. Therefore, not any substance or substance similar to the first additive can achieve the same technical effect.

[0108] In summary, using the first additive and the second additive disclosed herein in combination can achieve a better battery performance improvement than not adding the first additive or not adding the second additive.

[0109] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0110] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. An electrolyte additive, comprising a first additive and a second additive, wherein the first additive has the structure shown in Formula 1; and the second additive is a nitrile additive; in, R1, R2, and R3 each independently include any one of H, halogen, C1-C4 alkyl, C1-C4 haloalkyl, C2-C4 alkenyl, C2-C4 haloalkenyl, C2-C4 alkynyl, C5-C7 cycloalkyl, -Ph-R4, and -CH2-Ph-R5. R4 and R5 are each independently selected from any one of H, halogens, and C1-C2 alkyl groups.

2. The electrolyte additive according to claim 1, wherein, R1, R2 and R3 each independently include any one of F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkyl, -Ph-R4 and -CH2-Ph-R5. R4 and R5 are each independently selected from any one of H, F, and C1-C2 alkyl groups.

3. The electrolyte additive according to any one of claims 1-2, wherein, Each of R1, R2, and R3 independently includes any one of F, C1-C4 alkyl, C1-C2 fluoroalkyl, C2 alkenyl, C3 fluoroalkenyl, C4 alkynyl, C6 cycloalkyl, -Ph-R4, and -CH2-Ph-R5. R4 and R5 are each independently selected from any one of the alkyl groups of H, F, and C1.

4. The electrolyte additive according to any one of claims 1-3, wherein, The first additive includes at least one of the following compounds:

5. The electrolyte additive according to any one of claims 1-4, wherein, The second additive includes nitrile additives.

6. The electrolyte additive according to any one of claims 1-5, wherein, The nitrile additives include at least one of succinic anhydride, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, and n-butanol 1,2,3,4-tetrapropionitrile ether.

7. An electrolyte, wherein, The electrolyte additive includes any one of claims 1-6.

8. The electrolyte according to claim 7, wherein, The amount of the first additive is 0.05%-5% of the total mass of the electrolyte.

9. The electrolyte according to any one of claims 7-8, wherein, The amount of the second additive is 0.1%-3% of the total mass of the electrolyte.

10. The electrolyte according to any one of claims 7-9, wherein, It also includes lithium salts and non-aqueous organic solvents, and satisfies at least one of the following conditions: The lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4; The lithium salt has a mass percentage content of 8%-20% in the electrolyte; The non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, and methyl-(2,2,2-trifluoroethyl) carbonate. The non-aqueous organic solvent has a mass percentage content of 69%-91.75% in the electrolyte.

11. A battery, wherein, The electrolyte includes the electrolyte additive of any one of claims 1-6 or the electrolyte of any one of claims 7-10, a positive electrode, a negative electrode, and a separator; the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material; The positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and LiNi. x Co y Mn z M 1-x-y-z O2, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-x O4, Na m At least one of AO2, polyanionic compounds, and Prussian blue compounds; Wherein M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, and A includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr and Cu; 0 ≤ a < 0.2, 0 ≤ x < 1, 0 < m ≤ 1.

Images