Electrolyte and method for its preparation, and lithium-ion battery

Abstract

The application discloses an electrolyte, a preparation method thereof, and a lithium ion battery. The electrolyte comprises a lithium salt, a nonaqueous organic solvent, and a first additive and a second additive. The first additive is selected from one or more of borate esters with ether chain structures, and the second additive is selected from one or more of sulfonic acid lactones. The application introduces the borate esters with ether chain structures and the sulfonic acid lactones as the additives in the electrolyte, so that an excellent composite CEI film is produced on the surface of a positive electrode, and the electrical performance of the lithium ion battery is improved.

Description

Electrolyte and its preparation method, and lithium-ion battery Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrolyte and a method for preparing the same, as well as a lithium-ion battery having the electrolyte. Background Technology

[0002] Increasing the operating voltage is one of the key paths to breaking through the energy density bottleneck of lithium-ion batteries. For example, using high-nickel ternary cathodes (such as LiNi) 0.8 Co 0.1 Mn 0.1 The charging voltage of O2 (NCM811) is increased to 4.6V and above, which can release more reversible capacity.

[0003] However, existing electrolyte systems face significant challenges under such harsh high-voltage conditions. First, there are severe interfacial side reactions. Conventional carbonate solvents readily undergo oxidative decomposition on the cathode surface under high voltage, leading to a surge in interfacial impedance, gas production and expansion, and rapid capacity decay. Second, there is HF acid corrosion and transition metal dissolution. The HF produced by the water decomposition of lithium salt LiPF6 corrodes the cathode active material, triggering the dissolution of transition metal ions, damaging the material's crystal structure, and further catalyzing electrolyte decomposition, creating a vicious cycle. Finally, there is the unstable CEI film at the cathode-electrolyte interface. The CEI film formed on the high-voltage cathode in traditional electrolyte systems is often loose and unstable, failing to effectively prevent continuous interfacial side reactions. Summary of the Invention

[0004] To address at least one of the aforementioned technical problems, this application discloses an electrolyte, a method for preparing the same, and a lithium-ion battery having the electrolyte. The electrolyte incorporates borate esters and sulfonyl lactones with ether chain structures as additives to produce an excellent composite CEI film on the positive electrode surface, thereby improving the electrical performance of the lithium-ion battery.

[0005] The first aspect of this application provides an electrolyte that may include lithium salt and a non-aqueous organic solvent, and may further include: a first additive and a second additive; wherein the first additive is selected from one or more borate esters having an ether chain structure, and the second additive is selected from one or more sulfonyl lactones.

[0006] According to some embodiments of this application, the mass percentage of the first additive is 0.5%–3.0%. Alternatively, the mass percentage of the first additive is 1.0%–2.0%.

[0007] According to some embodiments of this application, the mass percentage of the second additive is 0.5%–3.0%; or, the mass percentage of the second additive is 1.0%–2.0%.

[0008] According to some embodiments of this application, the mass ratio between the first additive and the second additive is 1:1–3:1.

[0009] According to some embodiments of this application, the redox potential of the first additive is greater than 4.6 V vs. Li. + / Li, the redox potential of the second additive is less than 4.5 Vvs. Li + / Li.

[0010] According to some embodiments of this application, the first additive is selected from at least one of diethylene glycol methyl ether borate, triethylene glycol methyl ether borate, tetraethylene glycol methyl ether borate, or triethylene glycol methyl ether borate.

[0011] According to some embodiments of this application, the second additive is selected from at least one of 3-fluoro-1,3-propanesulfonate lactone or 1,3-propenesulfonate lactone.

[0012] A second aspect of this application provides a method for preparing the electrolyte as described above. The preparation method may include: dissolving the lithium salt in the non-aqueous organic solvent under an inert atmosphere, then adding the first additive and the second additive and mixing them evenly to obtain the electrolyte.

[0013] A third aspect of this application provides a lithium-ion battery, the lithium-ion battery comprising the electrolyte as described above, or the electrolyte obtained by the preparation method described above.

[0014] According to some embodiments of this application, the charging cutoff voltage of the positive electrode active material of the lithium-ion battery is not less than 4.6V.

[0015] The electrolyte provided in this application incorporates a borate ester with an ether chain structure as a first additive and a sulfonyl lactone as a second additive. Through the synergistic effect of the first and second additives, a gradient composite CEI film is formed on the positive electrode surface, which can simultaneously meet multiple requirements such as high ionic conductivity, high electronic insulation, excellent mechanical strength, and chemical / electrochemical stability, thereby effectively improving the high-voltage cycle performance and high-temperature storage performance of lithium-ion batteries containing this electrolyte.

[0016] Additional aspects and advantages of the invention 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 the invention. Detailed Implementation

[0017] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The terms “comprising” or “including” and similar terms used herein mean that an element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “and / or” or “and / or” as used herein include any and all combinations of one or more of the associated listed items.

[0019] As described in the background section, to address the problems existing in current high-voltage lithium-ion batteries, the common methods are to add film-forming additives to the electrolyte or to coat the surface of the positive electrode material to alleviate these problems. However, simple physical coating processes are complex, costly, and may hinder lithium-ion transport. Conventional film-forming additives (such as vinylene carbonate, VC, etc.) mainly act on the negative electrode, and have limited protective effects on the high-voltage positive electrode.

[0020] Based on this, this application provides an electrolyte that can form a composite protective layer on the surface of the positive electrode, effectively improving the electrical performance of lithium-ion batteries under high voltage.

[0021] The following describes some preferred embodiments of this application. It should be noted that the following description is for illustrative purposes and is not intended to limit the scope of protection of this application.

[0022] The electrolyte provided in this application may include lithium salts and non-aqueous organic solvents, as well as a first additive and a second additive. The first additive may be selected from one or more borate esters having an ether chain structure, and the second additive may be selected from one or more sulfonyl lactones.

[0023] For example, the boronic ester having an ether chain structure may include, but is not limited to, tris(2-methoxyethyl)boronic ester, tris(2-ethoxyethyl)boronic ester, tris(3-methoxypropyl)boronic ester, di(2-methoxyethyl)butylboronic ester, 2-methoxyethylphenylboronic ester, tris(4-methoxybutyl)boronic ester, di(2-ethoxyethyl)phenylboronic ester, 3-methoxypropyl n-octylboronic ester, tris(2-(2-methoxyethoxy)ethyl)boronic ester, tris[2-(2-methoxyethoxy)ethoxy]boronic ester, tris(2-(2-ethoxyethoxy)ethyl)boronic ester, tris(2-(2-methoxyethoxy)ethoxy) Ethyl borate, tris[2–(2–(2–methoxyethoxy)ethoxy)ethoxy]boronic acid ester, di(2–(2–methoxyethoxy)ethyl)hexyl borate, 2–(2–methoxyethoxy)ethyl p-methoxyphenyl borate, tris(5–(2–ethoxyethoxy)pentyl)boronic acid ester, 2–(2–(2–ethoxyethoxy)ethoxy)ethyl borate, di(2–(2–ethoxyethoxy)ethyl)p-fluorophenyl borate, tris[2–(2–(2–(2–methoxyethoxy)ethoxy)ethoxy)ethoxy]boronic acid ester, tris[2–(2–(2–(2–methoxyethoxy)ethoxy)ethoxy]boronic acid ester, etc. or any combination thereof. Optionally or preferably, the borate ester having an ether chain structure is selected from one or more of tris[2–(2–methoxyethoxy)ethoxy]borate (or diethylene glycol methyl ether borate), tris[2–(2–(2–methoxyethoxy)ethoxy)ethoxy]borate (or triethylene glycol methyl ether borate), tris[2–(2–(2–(2–methoxyethoxy)ethoxy)ethoxy)ethoxy]borate (or tetraethylene glycol methyl ether borate), and tris[2–(2–(–methoxyethoxy)ethoxy)ethoxy]borate (or triethylene glycol methyl ether borate triester). Optionally or preferably, the borate ester having an ether chain structure is triethylene glycol methyl ether borate.

[0024] The first additive includes an ether chain that enhances its solubility in the electrolyte, and its boron center possesses strong Lewis acidity, preferentially reacting with trace amounts of water and HF in the electrolyte to inhibit HF corrosion of the positive electrode at its source. This not only improves the electrolyte's oxidation resistance but also allows it to undergo electrochemical oxidation / polymerization on the positive electrode surface at higher charging potentials, forming an inorganic-organic composite protective layer with a boron-oxygen network as its framework. This protective layer not only physically prevents direct contact between the electrolyte and the positive electrode but its Lewis acidity also anchors free anions, effectively increasing the lithium-ion transference number and suppressing concentration polarization in the battery.

[0025] In some embodiments, the mass percentage of the first additive in the electrolyte can be 0.5%–3.0%. Optionally or preferably, the mass percentage of the first additive in the electrolyte can be 1.0%–2.0%. For example, the mass percentage of the first additive is 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc., or any value within any of the above ranges, or any increment or decrement of that value.

[0026] The sulfonyl lactone can refer to a cyclic sulfonate compound having a sulfonic acid group (–SO2O–) and a lactone ring. Exemplary but not limiting, the sulfonyl lactone may include, but is not limited to, 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,5-pentanesulfonyl lactone, 2-methyl-1,3-propanesulfonyl lactone, 3-hydroxy-1-propanesulfonyl lactone, 3-chloro-1,3-propanesulfonyl lactone, 2,2-dimethyl-1,3-propanesulfonyl lactone, 4-hydroxy-2-butanesulfonic acid γ-lactone, 3-ethyl-1 3-Propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 4,4-dimethyl-1,4-butanesulfonate lactone, 1,3-propenesulfonate lactone, 1,3-ethylenepropanesulfonate lactone, 1,3-butenesulfonate lactone, 1,8-naphthalenesulfonate lactone, 2,7-naphthalenedisulfonate lactone, anthracene-9,10-sulfonate lactone, trifluoromethyl-1,3-propanesulfonate lactone, perfluorobutanesulfonate lactone, etc., or any combination thereof. Optionally or preferably, the sulfonate lactone may be 3-fluoro-1,3-propanesulfonate lactone and / or 1,3-propenesulfonate lactone.

[0027] The sulfonyl lactone can polymerize on the positive electrode surface to form an organic polymer layer rich in lithium sulfonate groups (–SO3Li), exhibiting good flexibility and ionic conductivity, and providing abundant lithium-ion transport sites. Furthermore, when 3-fluoro-1,3-propane sulfonyl lactone is used, the introduction of fluorine atoms enhances its antioxidant capacity. 3-fluoro-1,3-propane sulfonyl lactone can form a more stable interfacial film on both the positive and negative electrode surfaces, making it suitable for high-voltage applications. When 1,3-propene sulfonyl lactone is selected, its intramolecular double bonds polymerize on the electrode surface, forming a dense, flexible organic polymer protective layer, thereby further improving interfacial stability.

[0028] In some embodiments, the mass percentage of the second additive in the electrolyte can be 0.5%–3.0%. Optionally or preferably, the mass percentage of the second additive in the electrolyte can be 1.0%–2.0%. For example, the mass percentage of the second additive is 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc., or any value within any of the above ranges, or any increment or decrement of that value.

[0029] In some embodiments, the mass ratio between the first additive and the second additive may be 1:1–3:1. For example, the mass ratio between the first additive and the second additive may be 1:1, 2:1, 3:1, or an adjustment thereof, which does not limit the scope of this application.

[0030] When selecting between the first additive and the second additive, the redox potential of the first additive can be greater than 4.6V vs. Li. + / Li, the redox potential of the second additive can be less than 4.5V vs. Li. + / Li. Thus, the first additive and the second additive can sequentially form an inorganic protective layer (or inner layer) with a boron-oxygen network framework and an organic polymer protective layer (or outer layer) on the positive electrode surface. Instead, the formation of the inner and outer layers occurs simultaneously or in reverse order, thereby preventing failure.

[0031] For the selection of other components of the electrolyte, the lithium salt may include, but is not limited to, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiOTF), lithium hexafluorophosphate (LiPF6), lithium hexafluoroborate (LiBF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium hexafluoroarsenate, and tris(pentafluoroethyl) Lithium trifluorophosphate, lithium perchlorate, lithium tetrafluoroborate, cyclodifluoromethane 1,1 Lithium bis(sulfonyl)imide, cyclodifluoromethane 1,1 Lithium bis(sulfonyl)imide, lithium bis(perfluoroethanesulfonyl)imide, lithium bis(fluoromalonic acid)borate, lithium tetracyanoborate, lithium dicyanotriazole salt, dicyano Trifluoromethyl Imidazole lithium salt, dicyano Pentafluoroethyl) One or more of imidazole lithium salts or others. Optionally or preferably, the lithium salt may comprise a mixture of lithium hexafluoroborate (LiBF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0032] The non-aqueous organic solvent may include, but is not limited to, one or more of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl acetate (EA), and propyl propionate (PP). Optionally or preferably, the non-aqueous organic solvent is a mixture of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC).

[0033] The electrolyte provided in this application incorporates a borate ester with an ether chain structure as a first additive and a sulfonyl lactone as a second additive. Through the synergistic effect of the first and second additives, a gradient composite CEI film is formed on the positive electrode surface, which can simultaneously meet multiple requirements such as high ionic conductivity, high electronic insulation, excellent mechanical strength, and chemical / electrochemical stability, thereby effectively improving the high-voltage cycle performance and high-temperature storage performance of lithium-ion batteries containing this electrolyte.

[0034] This application also provides a method for preparing the above-mentioned electrolyte. Exemplary but not limiting, the method for preparing the electrolyte may include: dissolving the lithium salt in the non-aqueous organic solvent under an inert atmosphere, then adding the first additive and the second additive and mixing them uniformly to obtain the electrolyte. The inert atmosphere is used to isolate interfering components, such as oxygen, water / water vapor, etc. Gases such as argon, nitrogen, helium, neon, or combinations thereof can be used to provide the inert atmosphere. In some implementations, a glove box can be used to provide the above-mentioned preparation scenario. For example, the box is filled with high-purity inert gas (Ar / N2) and has a built-in circulating purification system to remove O2 / H2O (down to ppm level, e.g., <0.1ppm). The lithium salt may be selected from one or more of the above-mentioned lithium salts, such as a mixture of lithium hexafluorophosphate and lithium difluorosulfonylimide. If multiple types are used, they can be weighed and used according to a predetermined ratio. The non-aqueous organic solvent may also be selected from one or more of the above-mentioned non-aqueous organic solvents. For example, the non-aqueous organic solvent is a mixture of fluoroethylene carbonate, ethylene carbonate, and methyl ethyl carbonate. After the lithium salt is dissolved in the non-aqueous organic solvent, a predetermined amount of a first additive and a second additive can be added, and the mixture can be stirred or otherwise mixed evenly to finally obtain the electrolyte.

[0035] This application also provides a lithium-ion battery. The lithium-ion battery includes a cell, a package for encapsulating the cell, and an electrolyte injected into the package.

[0036] The battery cell includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrodes to prevent short circuits caused by contact between them. It also allows active lithium ions to pass through during charging and discharging. The separator may include a polyolefin porous membrane, such as a polyethylene (PE) membrane or a polypropylene (PP) membrane. Alternatively, a modified polyolefin porous membrane can also be used as the separator. For example, a ceramic coating or organic coating, such as an alumina (α-Al₂O₃) coating, a boehmite (γ-AlOOH) coating, a silica (SiO₂) coating, a titanium dioxide (TiO₂) coating, a polyvinylidene fluoride (PVDF) coating, a polyamide (PA) coating, or a polyimide (PI) coating, can be applied to the polyolefin porous membrane.

[0037] The positive electrode includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive current collector can be implemented using a metal plate with electronic conductivity. Currently known positive current collectors can all be used in this application. For example, the positive current collector is aluminum foil.

[0038] The positive electrode active layer may include a positive electrode active material, and at least one of a first binder and a first conductive agent. The positive electrode active material may include, but is not limited to, layered compounds such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel cobalt manganese oxide (LiNiO2). x Co y Mn 1–x–y O2, NCM), lithium nickel cobalt aluminum oxide (LiNi x Al y Mn 1–x–y O2, NCA, etc., or compounds substituted by one or more transition metals; lithium manganese oxides such as Li 1+x Mn 2–x O4 (x is 0~0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxides such as Li2CuO2; vanadium compounds such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; with the molecular formula LiNi 1–x M x Lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, including at least one of the above elements, and x is 0.01~0.3); LiMn 2–x M xLithium-manganese composite oxides represented by O2 (where M is Co, Ni, Fe, Cr, Zn, or Ta and x is 0.01~0.1) or the molecular formula Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); LiNi x Mn 2–x Spinel-type lithium-manganese composite oxides represented by O4; LiMn2O4 in which the Li part is replaced by alkaline earth metal ions; lithium disulfide compounds; Fe2(MoO4)3; lithium iron phosphate; lithium-rich manganese-based (xLi2MnO3) (1–x)LiMO2, M=Ni, Co, Mn); Li2Sn (n=1), lithium organosulfur compounds or carbon-sulfur polymers ((C2S x ) n (where x is 2.5~50, n is 2), etc. In addition, other lithium-containing transition metal oxides, transition metal fluorides, transition metal sulfides, transition metal fluorides, transition metal sulfides, or transition metal nitrides, as well as materials that are surface-coated or ion-doped with the above materials, can also be used as the positive electrode active material.

[0039] In some embodiments, the positive electrode active material may further include a solid electrolyte. For example, inorganic solid electrolytes, including but not limited to halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolyte materials, nitride solid electrolytes, hydride solid electrolytes, borate solid electrolytes, etc.

[0040] Suitable, but not limited, halide solid electrolytes may include, but are not limited to, LaF3, LiCl, LiI, etc., or those with the chemical formula Li a MX b This refers to lithium halide solid electrolytes, where M represents a metallic element or metalloid element, including one or more of B, Si, Ge, As, Sb, Te, Al, Zn, Mg, Ca, Ba, Mn, Cd, Co, Yb, Y, Cr, In, Ga, Sr, Hf, Ti, Ta, Sn, Nb, Er, Sc, etc., and X represents a halogen element such as F, Cl, Br, I, etc. For example, derivatives produced by doping or coating Li₂CdCl₄, Li₂MgCl₄, Li₂CdI₄, Li₂ZnI₄, Li₂ZrCl₆, Li₃YCl₆, Li₃InCl₆, or related materials.

[0041] Suitable, but not limited, sulfide solid electrolytes may include, but are not limited to, Li2S. P2S5, Li2S P2S5–MS x (M=Si, Ge, Sn, 0≤x≤2), Li 9.6 P3S12 、Li7P3S 11 、Li7P2S8I、Li 10 SnP2S 12 、The 10 SiP2S 12 、Li9P3S9O3、LGPS(Li 10 GeP2S 12 )、Thio–LISICON(Li 3.25 Here 0.25 P 0.75 S4)、Li6PS5–X(X=Cl、Br、I),Li3PS4–X(X=Cl、Br、I)、Li4SnS4–X(X=Cl,Br)、Li 3.25 Here 0.25 P 0.75 S4、The 3.4 If 0.4 P 0.6 S4、The 10 GeP2S 11.7 O 0.3 、The 9.54 If 1.74 P 1.44 S 11.7 Cl 0.3 、The 10.35 Here 1.35 P 1.65 S 12 、The 10.35 If 1.35 P 1.65 S 12 、The 9.81 Sn 0.81 P 2.19 S 12 、The 10 (The 0.5 Here 0.5 )P2S 12 、The 10 (Here 0.5 Sn 0.5 )P2S 12 、The 10 (The 0.5 Sn 0.5 )P2S 12 、Li6(PS5) 0.7 (GeS4) 0.3 Cl、Li 7.5 P 2.5 Sn 0.5 S 10.5 Cl 1.5 、Li6PS5Cl 0.5Br 0.5 、Li6PS5I 0.2 Cl 0.8 、Li5SnS2C l3 、Li 10 P3S 12 Cl2、Li7P2S 8.5 Cl 0.5 and derivatives produced by doping or coating improvement with the like, any combination thereof, or related materials.

[0042] Some suitable but non-limiting oxide solid electrolytes may include, but are not limited to, NASICON-type solid electrolytes such as LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3, LiHf2(PO4)3, Li 1+x Al x Ge2 x (PO4)3 (LAGP, where 0 ≤ x ≤ 2), Li 1+x Al x Ti2 x (PO4)3 (LATP, where 0 ≤ x ≤ 2), Li 1+x Y x Zr2 x (PO4)3 (LYZP, where 0 ≤ x ≤ 2), Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc., perovskite-type solid electrolytes such as Li 3x La( 2 / 3 x )TiO3 (LLTO, where 0 < x < 0.25), LiSr 1.65 Zr 1.3 Ta 1.7 O9, Li 2x y Sr1 x Ta y Zr1 y O3 (where x = 0.75y and 0.60 < y < 0.75), etc., LISICON-type solid electrolytes such as Li 14 ZnGe4O 16 、Li4SiO4、LiGeO4, etc., garnet-type solid electrolytes such as Li7La3Zr2O 12 、Li 6.5 La3Zr 1.75 Te0.25 O 12 Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La3Zr2O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Derivatives produced by doping or coating with materials such as, etc., or any combination thereof or related materials.

[0043] Suitable, but not limited, nitride solid electrolytes may include, but are not limited to, Li3N, Li7PN4, LiSi2N3, and Li9N2Cl3. Suitable, but not limited, hydride solid electrolytes may include, but are not limited to, LiBH4 and LiBH4–Li X (X = Cl, Br, or I), LiNH2, Li2NH, LiBH4–LiNH2, Li3AlH6, etc. Some suitable but not limited borate solid electrolytes may include, but are not limited to, Li2B4O7, Li2O–B2O3–P2O5, Li2B... 10 H 10 –Li2B 12 H 12 Li7N2I–0.5LiOH, etc.

[0044] Derivatives of the above electrolytes obtained through substitution, doping, modification, and compositing can also be used as inorganic solid electrolytes in this application. For example, bromine (Br)-substituted or partially substituted Li₂ZrCl₆, such as Li₂ZrCl₆... 6–x Br x Rare earth metals such as lanthanum or yttrium-doped Li6PS5Br, and LLZO deposited on indium (In) surfaces, etc. It should be noted that the above examples are for illustrative purposes only and are not intended to limit the scope of this application.

[0045] The first adhesive can be any known adhesive, including but not limited to polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc., or any combination thereof, which can be used in this application. Copolymers can also be used as adhesives, exemplary of which are copolymers of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, trifluorochloroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, hexadiene, etc. Alternatively, mixtures of two or more materials in the above examples can also be used as adhesives. In some implementations, the adhesive may include a fiberizable adhesive. For example, the adhesive may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polymethyl methacrylate (PMMA), polyacrylonitrile (PANO), polyvinyl alcohol (PVA), polyaniline (PANI), polypyrrole (PPy), seaweed nanofibers (CNF), sodium alginate (Alg), β-cyclodextrin polymer (β-CDp), polypropylene emulsion (LA132), etc., or any combination thereof, or functionalized derivatives of the above polymers or copolymers between monomers.

[0046] The first conductive agent may include, but is not limited to, carbon-based materials such as graphite (natural or artificial graphite), carbon black (acetylene black, Ketjen black, Super P, etc.), carbon nanotubes, graphene, etc.; metal-based materials such as metal powders (aluminum powder, nickel powder, etc.), metal oxides (titanium oxide, etc.), metal whiskers (alumina, oxidizing agents, etc.); conductive polymers such as polyaniline, polypyrrole, polythiophene, etc.; conductive fibers such as carbon fibers, metal fibers, metal compound fibers, polymer fibers, etc.; or other known conductive agents.

[0047] The negative electrode includes a negative current collector and a negative active layer located on at least one side of the negative current collector. The negative current collector can be implemented using a metal plate with electronic conductivity. Currently known negative current collectors can all be used in this application. For example, the negative current collector is copper foil.

[0048] The negative electrode active layer may include a negative electrode active material and at least one of a second binder and a second conductive agent. The negative electrode active material may also be a material containing metal ions capable of intercalating or deintercalating lithium ions, exemplarily, it may be a metallic material (such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, Zn, etc., or alloys or compounds of the above metals, such as Li...). Sn alloys, Li Sn O alloy, Sn, SnO, SnO2, TiO2 Li4Ti5O 12 Li Al alloys, Ag Carbon materials (such as graphite, including natural / artificial graphite, carbon fiber, soft carbon, hard carbon, crystalline carbon, amorphous carbon, etc.), silicon compounds (such as silicon, silicon-carbon composites), or composite materials formed from metals and carbon / silicon. In some embodiments, the negative electrode active layer may be a graphite layer, and the negative electrode sheet may be a graphite electrode sheet.

[0049] The second adhesive may be the same as or similar to the first adhesive, and the second conductive agent may be the same as or similar to the first conductive agent. Please refer to the foregoing descriptions for details.

[0050] The battery cell can be a wound battery cell, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode. The battery cell can also be a laminated battery cell, comprising multiple stacked positive and negative electrode plates, which are alternately placed and separated by the separator.

[0051] The encapsulation body may include, but is not limited to, flexible packaging materials, such as aluminum-plastic film. The encapsulation body may also be other suitable materials, and this application is not limited thereto.

[0052] The electrolyte can be the electrolyte described above, and you can refer to the foregoing description for details.

[0053] The lithium-ion battery can be manufactured by assembling the positive electrode, the separator, and the negative electrode into a cell, encapsulating the cell in a package, and then performing processes such as electrolyte injection, formation, aging, and capacity testing. Alternatively, other manufacturing processes in the art can be applied here, and no particular limitation is made.

[0054] In some embodiments, the charging cut-off voltage of the positive electrode active material selected for the lithium-ion battery may not be lower than 4.6V. As an example, the positive electrode active material may be lithium cobalt oxide (LiCoO2), lithium-rich manganese-based, high-nickel ternary positive electrode (NCM811), or a modified material for lithium nickel cobalt manganese oxide. For example, surface coating (e.g., using inorganic materials such as Al2O3, LiNbO3, LiAlO2 to coat the surface of the positive electrode particles to isolate the electrolyte from direct contact with the active material) or bulk doping (e.g., introducing Mg) may be employed. 2+ Zr 4+ Ti 4+ Methods include using heterovalent ions to enhance the stability of the layered structure, and single-crystallization treatment (e.g., preparing granular lithium nickel cobalt manganese oxide into single-crystal particles to eliminate intergranular grain boundary stress). Using a positive electrode active material with a charging cutoff voltage of not less than 4.6V can improve the energy density of the lithium-ion battery. This is suitable for high-voltage lithium-ion batteries (operating voltage > 4.4V vs. Li / Li). + With the electrolyte provided in this application, it has significantly improved cycle stability, high-temperature storage performance and safety.

[0055] This application also discloses a lithium-ion battery module, comprising multiple lithium-ion batteries arranged in a folded, stacked, or combined manner as described above. This lithium-ion battery module can be applied to electrically driven vehicles, including but not limited to electric vehicles, hybrid vehicles, and energy storage devices such as energy storage systems.

[0056] The present application will be further described in detail below with reference to embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection claimed in this application.

[0057] Example 1 – Preparation of Lithium-ion Batteries

[0058] 1. Preparation of electrolyte

[0059] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% by mass of triethylene glycol methyl ether borate and 1.5% by mass of 3-fluoro-1,3-propanesulfonate lactone were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0060] 2. Preparation of lithium-ion batteries

[0061] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0062] Example 2 – Preparation of Lithium-ion Batteries

[0063] 1. Preparation of electrolyte

[0064] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 0.5% of triethylene glycol methyl ether borate and 1.5% of 3-fluoro-1,3-propanesulfonate lactone (by mass of the total electrolyte) were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0065] 2. Preparation of lithium-ion batteries

[0066] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0067] Example 3 – Preparation of Lithium-ion Batteries

[0068] 1. Preparation of electrolyte

[0069] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 3.0% by mass of triethylene glycol methyl ether borate and 1.5% by mass of 3-fluoro-1,3-propanesulfonate lactone were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0070] 2. Preparation of lithium-ion batteries

[0071] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0072] Example 4 – Preparation of Lithium-ion Batteries

[0073] 1. Preparation of electrolyte

[0074] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% of triethylene glycol methyl ether borate and 0.5% of 3-fluoro-1,3-propanesulfonate lactone (by mass of the total electrolyte) were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0075] 2. Preparation of lithium-ion batteries

[0076] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0077] Example 5 – Preparation of Lithium-ion Batteries

[0078] 1. Preparation of electrolyte

[0079] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% by mass of triethylene glycol methyl ether borate and 3.0% by mass of 3-fluoro-1,3-propanesulfonate lactone were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0080] 2. Preparation of lithium-ion batteries

[0081] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0082] Example 6 – Preparation of Lithium-ion Batteries

[0083] 1. Preparation of electrolyte

[0084] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% of triethylene glycol methyl ether borate and 1.0% of 3-fluoro-1,3-propanesulfonate lactone (by mass of the total electrolyte) were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0085] 2. Preparation of lithium-ion batteries

[0086] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0087] Example 7 – Preparation of Lithium-ion Batteries

[0088] 1. Preparation of electrolyte

[0089] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and methyl ethyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 2.7% (by mass) of triethylene glycol methyl ether borate and 0.27% (by mass) of 3-fluoro-1,3-propanesulfonate lactone were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0090] 2. Preparation of lithium-ion batteries

[0091] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0092] Example 8 – Preparation of Lithium-ion Batteries

[0093] 1. Preparation of electrolyte

[0094] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% by mass of diethylene glycol methyl ether borate and 1.5% by mass of 1,3-propylene sulfonate lactone were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0095] 2. Preparation of lithium-ion batteries

[0096] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0097] Comparative Example 1 – Preparation of Lithium-ion Batteries

[0098] Neither the first additive nor the second additive was added to the electrolyte of Comparative Example 1. Details are as follows:

[0099] 1. Preparation of electrolyte

[0100] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and methyl ethyl carbonate (EMC) at a molar ratio of 1:0.2 (FEC / EC / EMC volume ratio of 0.5:1:0.5). The solution was stirred until homogeneous to obtain the electrolyte. The total lithium salt concentration was 1.2 mol / L.

[0101] 2. Preparation of lithium-ion batteries

[0102] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0103] Comparative Example 2 – Preparation of Lithium-ion Batteries

[0104] In Comparative Example 2, only the first additive was added to the electrolyte, without the second additive. Details are as follows:

[0105] 1. Preparation of electrolyte

[0106] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% (by mass) of triethylene glycol methyl ether borate and 1.5% (by mass) of the electrolyte were added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0107] 2. Preparation of lithium-ion batteries

[0108] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0109] Comparative Example 3 – Preparation of Lithium-ion Batteries

[0110] In Comparative Example 3, only the second additive was added to the electrolyte, without the first additive. Details are as follows:

[0111] 1. Preparation of electrolyte

[0112] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, 1.5% (by mass) of 3-fluoro-1,3-propanesulfonate lactone was added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0113] 2. Preparation of lithium-ion batteries

[0114] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0115] Comparative Example 4 – Preparation of Lithium-ion Batteries

[0116] The electrolyte in Comparative Example 4 did not contain the first or second additive. Instead, 1.5% lithium difluoroborate containing sulfonate groups was added. Details are as follows:

[0117] 1. Preparation of electrolyte

[0118] In an argon-filled glove box (H2O, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) were dissolved at a molar ratio of 1:0.2 in a mixed solvent of fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (FEC / EC / EMC volume ratio of 0.5:1:0.5), resulting in a total lithium salt concentration of 1.2 mol / L. Then, lithium difluoroborate containing sulfonate groups (1.5% by mass of the total electrolyte) was added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0119] 2. Preparation of lithium-ion batteries

[0120] NMC11 was selected as the positive electrode, graphite as the negative electrode, and a polyethylene porous membrane coated with an alumina coating was used as the separator. The cells were then assembled into a pouch cell in the aforementioned glove box.

[0121] The relevant parameters of Examples 1 to Comparative Examples 4 are shown in Table 1.

[0122] Table 1 Parameter Comparison

[0123]

[0124] Test Example 1 – Cyclic Performance Test

[0125] The pouch cells were subjected to cycle performance testing: 500 cycles were performed at 45℃ with a 1C rate within a voltage range of 2.75V–4.6V, and the capacity retention rate was calculated. The test results are shown in Table 2.

[0126] Test Example 2 – High Temperature Storage Performance Test

[0127] A fully charged battery (100% SOC) was stored at 60°C for 90 days, then discharged at 25°C using a 1C method. The remaining capacity was recorded and the residual capacity rate was calculated. The test results are shown in Table 2.

[0128] Table 2 Test Results

[0129]

[0130] Table 1 shows that Example 1 exhibits the best synergistic effect, indicating the advantages of the bilayer structure. In Example 2, the reduced content of the first additive results in an incomplete boron-oxygen network skeleton. Reducing the amount of borate esters prevents the formation of a stable boron-oxygen network skeleton, leading to weak anchoring and ion conduction of the inner CEI layer. Simultaneously, it causes the outer layer to lose support. The decomposition products of sulfonyl lactones may form a loose, unstable organic layer in the absence of a solid underlying layer, further reducing the performance of the lithium-ion battery. In Example 3, the increased content of the first additive may lead to an imbalance in the film formation process. Excessive borate esters may decompose prematurely and excessively, forming an overly thick or prematurely covered initial layer, interfering with the uniform "filling" of subsequent sulfonyl lactones. Simultaneously, the film layer may become brittle due to excessive inorganic / organic-inorganic components, easily cracking during cycling and resulting in poor mechanical properties. Furthermore, excessive additive decomposition will irreversibly consume more lithium source. In Example 4, the reduced content of the second additive may result in incomplete outer layer "encapsulation." Insufficient sulfonyl lactone will prevent adequate filling and encapsulation of the inner B-O framework, potentially resulting in an incomplete and defective CEI membrane. Simultaneously, the membrane's mechanical toughness may be insufficient. Lacking sufficient flexible organic components to buffer volume changes, the membrane is prone to breakage. In Example 5, the increased content of the second additive led to an excessively thick outer layer. Excessive sulfonyl lactone may generate an excessively thick organic polymer outer layer, increasing ion conduction resistance. It may also trigger side reactions; certain sulfonyl lactones or their decomposition intermediates, when locally concentrated excessively, may adversely affect the stability of the electrode or electrolyte. Comparative Example 1, lacking additives, exhibited severe interfacial side reactions and the worst performance. Comparing Examples 1-6 with Example 7, when the ratio of the first to second additive is within the preferred range of 1:3 to 3:1, the battery performance improvement is more significant. Beyond this range, the improvement in capacity and high-temperature performance is limited. Comparative Examples 2 and 3, due to the introduction of only the first or second additive, only possess a single layer and cannot achieve dual-layer synergy, resulting in lower performance. Comparative Example 4 shows that traditional additives cannot improve the performance of high-voltage lithium-ion batteries, and this application has superior characteristics compared with existing solutions.

[0131] This application has described the basic concepts. Obviously, for those skilled in the art, the above detailed disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this application.

[0132] Furthermore, this application uses specific terms to describe its embodiments. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this application do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined.

[0133] Similarly, it should be noted that, in order to simplify the description of this application and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of the embodiments of this application sometimes combines multiple features into one embodiment or its description. However, this disclosure method does not imply that the subject matter of this application requires more features than those mentioned in the claims. In fact, the embodiments have fewer features than all the features of the single embodiments disclosed above.

[0134] Finally, it should be understood that the embodiments described in this application are merely illustrative of the principles of the embodiments of this application. Other modifications may also fall within the scope of this application. Therefore, alternative configurations of the embodiments of this application are considered as examples and not limitations, and are regarded as consistent with the teachings of this application. Accordingly, the embodiments of this application are not limited to the embodiments explicitly described and illustrated in this application.

Claims

1. An electrolyte comprising a lithium salt and a non-aqueous organic solvent; characterized in that, The electrolyte further comprises: a first additive and a second additive; wherein the first additive is a borate ester with an ether chain structure, and the second additive is a sulfonyl lactone; the mass percentage of the first additive is 0.5%–3.0%, and the mass percentage of the second additive is 0.5%–3.0%; the mass ratio of the first additive to the second additive is 1:1–3:1; and the redox potential of the first additive is greater than 4.6 Vvs. Li + / Li, the redox potential of the second additive is less than 4.5 Vvs. Li + / Li.

2. The electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of diethylene glycol methyl ether borate, triethylene glycol methyl ether borate, tetraethylene glycol methyl ether borate, or triethylene glycol methyl ether borate.

3. The electrolyte according to claim 1, characterized in that, The second additive is selected from at least one of 3-fluoro-1,3-propanesulfonate lactone or 1,3-propenesulfonate lactone.

4. A method for preparing an electrolyte as described in any one of claims 1-3, characterized in that, The preparation method includes: dissolving the lithium salt in the non-aqueous organic solvent under an inert atmosphere, adding the first additive and the second additive, and mixing them evenly to obtain the electrolyte.

5. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1–3, or the electrolyte obtained by the preparation method described in claim 4.

6. The lithium-ion battery according to claim 5, characterized in that, The charging cutoff voltage of the positive electrode active material of the lithium-ion battery is not less than 4.6V.

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