Electrolytes and batteries

Abstract

The application relates to the technical field of batteries, in particular to an electrolyte and a battery; the electrolyte comprises an organic solvent, a lithium salt and an additive, the additive comprises a first additive; the first additive comprises a silicon-based sulfonate compound and a thiophosphate compound, the silicon-based sulfonate compound has a structure shown in formula I, and the thiophosphate compound has a structure shown in formula II: formula I; formula II. Compared with the prior art, the application adds the additive containing the silicon-based sulfonate compound and the thiophosphate compound, improves the stability and ion conductivity of an interface film, and significantly improves the cycle life, high-temperature performance and low-temperature performance of a high-voltage lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to an electrolyte and a battery. Background Technology

[0002] As a core energy storage technology in the new energy era, lithium-ion batteries directly determine the performance boundaries of applications such as electric vehicles and energy storage systems due to their energy density and safety. Currently, increasing the operating voltage of lithium batteries has become one of the core methods to overcome the energy density bottleneck.

[0003] However, under high voltage, the interfacial stability between traditional electrolyte systems and electrode materials deteriorates sharply, leading to problems such as capacity decay and a significantly increased risk of thermal runaway. Therefore, developing functional electrolytes suitable for high-voltage systems has become a key technological breakthrough for balancing the energy density and safety of lithium-ion batteries. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides an electrolyte and a battery, wherein the electrolyte, by adding additives containing silanolate compounds and thiophosphate compounds, improves the stability and ionic conductivity of the interfacial film, thereby significantly improving the cycle life, high-temperature performance, and low-temperature performance of a high-voltage lithium-ion battery.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt, and an additive, said additive comprising a first additive; the first additive comprising a silyl sulfonate compound and a thiophosphate compound, said silyl sulfonate compound having a structure shown in Formula I, and said thiophosphate compound having a structure shown in Formula II. Formula I; Formula II; R1 to R7 are independently selected from hydrogen, halogen, cyano, isocyanate group, isothiocyanate group, trimethylsilyl, unsubstituted alkyl or alkoxy group of C1 to C10, substituted alkyl or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C20, and at least one of R5 to R7 is an unsubstituted or substituted aryl group of C6 to C20.

[0006] In some embodiments, the silanolate compound comprises at least one of the following structures: Formula I-1; Formula I-2; Formula I-3.

[0007] In some embodiments, the thiophosphate compound comprises at least one of the following structures: Formula II-1; Formula II-2; Formula II-3.

[0008] In some embodiments, the silanolate compound accounts for 0.1% to 5% of the total mass of the electrolyte, preferably 0.5% to 3%.

[0009] In some embodiments, the thiophosphate compound accounts for 0.1% to 3% of the total mass of the electrolyte, preferably 0.5% to 2%.

[0010] In some embodiments, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0011] In some embodiments, the organic solvent includes at least three of ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0012] In some of these embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0013] In some embodiments, the lithium salt includes at least two of lithium hexafluorophosphate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide.

[0014] In some embodiments, the organic solvent accounts for 60% to 85% of the total mass of the electrolyte.

[0015] In some embodiments, the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

[0016] In some embodiments, the additive further includes a second additive; the second additive includes one or more of the following: fluoroethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, vinyl sulfate, vinylene carbonate, ethylene ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinate, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, succinic anhydride, maleic anhydride, citrate anhydride, and methanedisulfonate.

[0017] According to another aspect of the present invention, a battery is provided, including an electrode assembly and an electrolyte, wherein the electrolyte comprises the electrolyte described in the above-described technical solution.

[0018] In some embodiments, the electrode assembly includes a positive electrode, a diaphragm, and a negative electrode stacked sequentially. The positive electrode includes a positive electrode current collector and a positive electrode coating disposed on at least one surface of the positive electrode current collector along its thickness direction; the positive electrode coating includes a positive electrode active material; the positive electrode active material includes LiNi. x Co y Mn z M 1-x-y-z O2 and / or LiNi x Co y Al z N 1-x-y-z O2; wherein M and N are independently selected from one or more of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, and x+y+z≤1; The negative electrode includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector along the thickness direction; the negative electrode coating includes a negative electrode active material; the negative electrode active material includes one or more of natural graphite, artificial graphite, and silicon-carbon composite materials.

[0019] In some of these embodiments, the battery operates at a voltage ≥4.4V.

[0020] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. This invention uses a combination of silicon-based sulfonate compounds and thiophosphate compounds as electrolyte additives, containing Si, P, and S components, which gives the interface film excellent lithium-ion conduction performance, thereby effectively slowing down the occurrence of side reactions at the electrolyte-electrode interface. At the same time, the solid electrolyte interphase (SEI) film and the positive electrode electrolyte interphase (CEI) film formed are more uniform and stable.

[0021] 2. The present invention uses silane sulfonate compounds containing double bonds and trifluoromethane sulfonate as additives, which can promote earlier and more uniform film formation, thereby significantly improving the cycle performance, high temperature performance and low temperature performance of high voltage lithium-ion batteries.

[0022] 3. This invention uses thiophosphate compounds as additives, and the resulting interfacial film contains both S and P elements, resulting in better ionic conductivity. In addition, the S in P=S contains lone pairs of electrons, which have strong coordination ability and can bond with high-valence metal ions in the cathode material, effectively reducing the dissolution of transition metal ions in the cathode, thereby significantly improving cycle performance, high-temperature performance and low-temperature performance.

[0023] 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

[0024] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0027] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0028] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0029] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0030] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0031] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0032] Currently, lithium-ion batteries, as a core energy storage technology in the new energy era, directly determine the performance boundaries of applications such as electric vehicles and energy storage systems based on their energy density and safety. Increasing the operating voltage of lithium batteries has become one of the core methods to overcome the energy density bottleneck; however, at high voltages, the interfacial stability between traditional electrolyte systems and electrode materials deteriorates sharply, leading to problems such as capacity decay and a significantly increased risk of thermal runaway. Therefore, developing functional electrolytes suitable for high-voltage systems has become a key technological breakthrough for balancing the energy density and safety of lithium-ion batteries.

[0033] Chinese patent CN118522940A discloses a high-voltage electrolyte using halophthalonitrile additives. These additives can construct a CEI with high mechanical and thermal stability, as well as a robust SEI rich in inorganic components, thereby effectively improving the high-voltage cycle stability of lithium batteries. However, cyanide-containing additives generally have high impedance, which may exacerbate the degradation of low-temperature performance. Chinese patent CN119361832A discloses a high-voltage electrolyte capable of forming a stable interfacial film, effectively improving the high-temperature cycle and storage performance of batteries. However, this electrolyte includes additives containing two cyclic anhydride groups. The synthesis process of such additives is complex and they have a certain degree of toxicity, hindering their widespread commercial application.

[0034] In summary, although some progress has been made in the research of lithium-ion battery electrolytes, there are still many bottlenecks that need to be overcome, and new functional electrolytes need to be further developed to meet the higher performance requirements and application scenarios of batteries.

[0035] Based on this, the present invention improves the stability and ionic conductivity of the interface film by adding additives containing silyl sulfonate compounds and thiophosphate compounds, thereby significantly improving the cycle life, high-temperature performance and low-temperature performance of high-voltage lithium-ion batteries.

[0036] According to one aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt, and an additive, said additive comprising a first additive; the first additive comprising a silyl sulfonate compound and a thiophosphate compound, said silyl sulfonate compound having a structure shown in Formula I, and said thiophosphate compound having a structure shown in Formula II. Formula I; Formula II; R1 to R7 are independently selected from hydrogen, halogen, cyano, isocyanate group, isothiocyanate group, trimethylsilyl, unsubstituted alkyl or alkoxy group of C1 to C10, substituted alkyl or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C20, and at least one of R5 to R7 is an unsubstituted or substituted aryl group of C6 to C20.

[0037] Specifically, the first additive includes silane sulfonate compounds and thiophosphate compounds, containing Si, P, and S components, which gives the interface film excellent lithium-ion conduction performance, thereby effectively mitigating the occurrence of side reactions at the electrolyte-electrode interface. Furthermore, using both silane sulfonate compounds and thiophosphate compounds as electrolyte additives results in a more uniform and stable solid electrolyte interphase (SEI) film and positive electrode electrolyte interphase (CEI) film.

[0038] In a specific embodiment of the present invention, the silanolate compound includes at least one of the following structures: Formula I-1; Formula I-2; Formula I-3.

[0039] Specifically, the silane sulfonate compounds contain double bonds and trifluoromethanesulfonate, which can promote earlier and more uniform film formation, thereby significantly improving the cycle performance and high and low temperature performance of high-voltage lithium-ion batteries. This invention does not impose any special restrictions on the source of the silane sulfonate compounds; commercially available products or homemade products well known to those skilled in the art can be used.

[0040] The present invention does not impose any special restrictions on the preparation method of the above-mentioned silanolate compounds, and any preparation method known to those skilled in the art can be used; as an example, for the compound of formula I-1, the following preparation method can be used: (di-tert-butylsilyl bis(trifluoromethanesulfonic acid) ester) + ethyl acetate + (trifluoromethanesulfonic acid) → (diethoxysilyl bis(trifluoromethanesulfonic acid) ester) + (isobutylene gas), wherein the reaction conditions are: excess trifluoromethanesulfonic acid, 0°C to room temperature. For compound I-2, the following preparation method can be used: (1) (di-tert-butylsilyl bis(trifluoromethanesulfonate) ester) + (propenyl magnesium bromide) → (tert-butyl(propenyl)silyl trifluoromethanesulfonate) + (magnesium bromotrifluoromethanesulfonate), wherein the reaction conditions are: anhydrous THF, -78°C, inert gas protection; (2) (tert-butyl(propenyl)silyl trifluoromethanesulfonate) + (fluoride ion) → (dipropenylsilyl bis(trifluoromethanesulfonate) ester) + (tert-butyl fluoride), wherein the reaction conditions are: THF, 0°C to room temperature, inert gas protection. For compound I-3, the following preparation method can be used: (di-tert-butylsilyl bis(trifluoromethanesulfonate) ester) + (trifluoromethanesulfonate) → (tetra(trifluoromethanesulfonate)silane) + (isobutylene gas); wherein the reaction conditions are: excess trifluoromethanesulfonate, carried out at room temperature.

[0041] In a specific embodiment of the present invention, the thiophosphate compound includes at least one of the following structures: Formula II-1; Formula II-2; Formula II-3.

[0042] Specifically, the sulfur (S) in the thiophosphate compounds contains a lone pair of electrons, exhibiting strong coordination ability. This allows them to bond with high-valence metal ions in the cathode material, effectively reducing the dissolution of transition metal ions. The compound of formula II-2 contains sulfur (F), resulting in an interfacial film rich in inorganic LiF, further enhancing the stability of the interfacial film and reducing interfacial impedance, thus promoting uniform lithium-ion transport and further improving low-temperature performance. The compound of formula II-3 contains an -NCO group, which has dehydration and deacidification effects, mitigating the adverse effects of HF to some extent. Furthermore, this group participates in the formation of the interfacial film, effectively improving cycle performance and high-temperature performance. This invention does not impose any special restrictions on the source of the thiophosphate compounds; commercially available products or self-made products well-known to those skilled in the art can be used.

[0043] The present invention does not impose any special restrictions on the preparation method of the above-mentioned thiophosphate compounds, and any preparation method known to those skilled in the art can be used to obtain them; as an example, for the compound of formula II-2, the following preparation method can be used: (1) (triphenyl thiophosphate) + (iodine monochloride) → (tris(4-iodophenyl)thiophosphate) + (hydrogen chloride), wherein the reaction conditions are: dichloromethane (DCM) solvent, 0°C to room temperature; (2) (tris(4-iodophenyl)thiophosphate) + (anhydrous potassium fluoride) → (tris(4-fluorophenyl)thiophosphate) + (potassium iodide), wherein the reaction conditions are: N,N-dimethylformamide (DMF) solvent, 150°C to 200°C.

[0044] In a specific embodiment of the present invention, the silicon-based sulfonate compound preferably accounts for 0.1% to 5% of the total mass of the electrolyte, specifically 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, and any value between any two of the above; more preferably, it is 0.5% to 3%, specifically 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, and any value between any two of the above. When the amount of silicon-based sulfonate compound added is too small, the formed SEI film and CEI film are not uniform and dense enough, and the stability is poor; when the amount of silicon-based sulfonate compound added is too large, the formed interface film is too thick, resulting in increased interface impedance and deterioration of cell performance.

[0045] In a specific embodiment of the present invention, the thiophosphate compound preferably accounts for 0.1% to 3% of the total mass of the electrolyte, specifically 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, and any value between any two of the above; more preferably 0.5% to 2%, specifically 0.5%, 1.0%, 1.5%, 2.0%, and any value between any two of the above. When the amount of thiophosphate compound added is too small, the formed SEI film and CEI film are not uniform and dense enough, and the stability is poor; when the amount of thiophosphate compound added is too large, the formed interface film is too thick, resulting in increased interface impedance and deterioration of cell performance.

[0046] In a specific embodiment of the present invention, the additive preferably further includes a second additive; the second additive preferably includes one or more of the following: fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), 1,3-sulfonate lactone (PST), 1,4-butanesulfonate lactone (BS), vinyl sulfate (DTD), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), tris(trimethylsilane)borate (TMSB), tris(trimethylsilane)phosphate (TMSP), adiponitrile (ADN), succinic anhydride (SN), ethylene glycol dipropionitrile ether (DENE), 1,3,6-hexanetrionitrile (HTCN), succinic anhydride (SA), maleic anhydride (MA), citrate anhydride (CTA), and methanedisulfonate methylene (MMDS). The present invention does not impose any special restrictions on the source of the second additive; commercially available products or homemade products well known to those skilled in the art can be used.

[0047] In a specific embodiment of the present invention, the additive preferably accounts for 5% to 20% of the total mass of the electrolyte, specifically 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, and any value between the above two. The present invention selects the above-mentioned suitable additive dosage to ensure that the subsequently obtained electrolyte meets the expectations of the present invention.

[0048] In specific embodiments of the present invention, the organic solvent preferably includes one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyltrifluoroethyl carbonate (FEMC), diethyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), propyl acetate (PA), ethyl acetate (EA), ethyl butyrate (EB), γ-butyrolactone (GBL), γ-valerolactone (GVL), and δ-valerolactone (DVL). More preferably, the organic solvent includes at least three of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The present invention does not impose any particular limitation on the source of the organic solvent; commercially available products or homemade products well known to those skilled in the art can be used.

[0049] In a specific embodiment of the present invention, the organic solvent preferably accounts for 60% to 85% of the total mass of the electrolyte, specifically 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, and any value between the above two. The present invention selects the above-mentioned suitable amount of organic solvent to ensure that the lithium salt and additives are completely dissolved, thereby obtaining an electrolyte that meets the expectations of the present invention.

[0050] In specific embodiments of the present invention, the lithium salt preferably includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate borate) (LiBOB), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). More preferably, the lithium salt includes at least two of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), and lithium bis(fluorosulfonyl)imide (LiFSI). The present invention does not impose any special restrictions on the source of the lithium salt; commercially available products or homemade products well known to those skilled in the art can be used.

[0051] In a specific embodiment of the present invention, the lithium salt preferably accounts for 10% to 20% of the total mass of the electrolyte, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, and any value between the two mentioned above. The present invention selects the above-mentioned suitable amount of lithium salt to ensure that the resulting electrolyte meets the expectations of the present invention.

[0052] According to another aspect of the present invention, a battery is provided, comprising an electrode assembly and an electrolyte, wherein the electrolyte comprises the electrolyte described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the electrolyte described in the above-described technical solution, which will not be repeated here.

[0053] In a specific embodiment of the present invention, the operating voltage of the battery is ≥4.4V. Specifically, the battery preparation process includes: sequentially stacking and assembling a negative electrode, a separator, and a positive electrode into an electrode assembly, then impregnating it with an electrolyte, and finally fabricating the battery through processes such as formation. The specific conditions and parameters for each step in the above preparation process can be achieved using battery preparation techniques well-known to those skilled in the art, and the present invention does not impose any special limitations on them.

[0054] In a specific embodiment of the present invention, the electrode assembly includes a positive electrode, a separator, and a negative electrode stacked sequentially. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode coating disposed on at least one surface of the positive electrode current collector along its thickness direction; the positive electrode coating preferably includes a positive electrode active material; the positive electrode active material preferably includes LiNi. x Co y Mn z M 1-x-y-z O2 and / or LiNi x Co y Al z N 1-x-y-z O2; wherein M and N are independently selected from one or more of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V, and Ti, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, and x+y+z≤1. Specifically, x can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value between any two of the above; y can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, or any value between any two of the above; z can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, or any value between any two of the above. This invention does not impose any special restrictions on the source of the above positive electrode active material; commercially available products well known to those skilled in the art can be used.

[0055] In a specific embodiment of the present invention, the positive electrode coating further includes a conductive agent and a binder. The conductive agent includes, but is not limited to, one or more of conductive carbon, conductive carbon black (SP), carbon black, Ketjen black, carbon dots, carbon nanotubes (CNTs), graphene, and carbon nanofibers, preferably SP and CNTs. The binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), hydroxymethyl cellulose (CMC), 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), preferably PVDF. The present invention does not impose any special restrictions on the source of the above-mentioned binder and conductive agent; commercially available products well known to those skilled in the art can be used.

[0056] In a specific embodiment of the present invention, the positive electrode can be prepared by the following method: First, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the positive electrode slurry is coated onto a positive electrode current collector, and dried and rolled to obtain the positive electrode. The solvent is preferably N-methyl-2-pyrrolidone (NMP), and the positive electrode current collector is preferably aluminum foil.

[0057] In a specific embodiment of the present invention, the diaphragm includes a base membrane and an adhesive layer and a ceramic layer sequentially disposed on at least one side; the base membrane preferably includes at least one of PP (polypropylene), PE (polyethylene), PET (polyethylene terephthalate), and PA (polyamide), and the thickness is preferably 5μm to 10μm; the adhesive layer is preferably a PVDF layer, and the thickness is preferably 1.5μm to 5μm; the ceramic layer is preferably an alumina layer, and the thickness is 1.5μm to 5μm; the present invention does not have any special restrictions on the source of the diaphragm, and commercially available products or self-made products well known to those skilled in the art can be used.

[0058] In a specific embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector along its thickness direction; the negative electrode coating includes a negative electrode active material; the negative electrode active material preferably includes one or more of natural graphite, artificial graphite, and silicon-carbon composite materials. The present invention does not impose any special restrictions on the source of the above-mentioned negative electrode active material, and commercially available products well known to those skilled in the art can be used.

[0059] In a specific embodiment of the present invention, the negative electrode coating further includes a conductive agent, a binder, and a thickener. The conductive agent includes, but is not limited to, one or more of conductive carbon, conductive carbon black (SP), carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, preferably SP. The binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), 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), preferably SBR. The thickener includes, but is not limited to, one or more of carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and styrene-butadiene rubber, preferably carboxymethyl cellulose. The present invention does not impose any special restrictions on the source of the above-mentioned binder, conductive agent, and thickener; commercially available products well known to those skilled in the art can be used.

[0060] In a specific embodiment of the present invention, the negative electrode can be prepared by the following method: First, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the negative electrode slurry is coated onto a negative electrode current collector, and dried and rolled to obtain the negative electrode. The solvent is preferably water, and the negative electrode current collector is preferably copper foil.

[0061] The following detailed description of this application is based on specific embodiments, but the implementation and protection of this invention are not limited thereto. The following embodiments are only some embodiments of this application and are not intended to limit this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1 S1. Preparation of electrolyte: Based on 100wt% of the electrolyte mass, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 2:1:2:5. After thorough mixing, 13.5wt% LiPF6, 1wt% LiFSI, and 1wt% LiPO2F2 are added sequentially. After complete dissolution, the first additive and the second additive are added. The first additive consists of 3wt% of compound I-1 and 2wt% of compound II-1, and the second additive consists of 1wt% FEC and 1wt% PS. After thorough mixing and dissolution, the mixture is ready for use.

[0063] S2, Preparation of the positive electrode: The positive electrode active material NCM622 (LiNi) 0.6 Co 0.2 Mn 0.2 O2, conductive carbon black (SP), carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) are dispersed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of 97:1.4:0.7:0.9. After thorough stirring, a positive electrode slurry is obtained. The positive electrode slurry is uniformly coated onto a positive electrode current collector aluminum foil, dried, and then rolled and die-cut to obtain the positive electrode.

[0064] S3, Preparation of the negative electrode: The negative electrode active material, artificial graphite, conductive carbon black (SP), binder styrene-butadiene rubber (SBR), and thickener carboxymethyl cellulose (CMC) are dispersed in deionized water at a mass ratio of 96.2:1.2:1.6:1 and thoroughly stirred to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil, dried, and then rolled and die-cut to obtain the negative electrode.

[0065] S4. Preparation of lithium-ion batteries: The positive electrode, negative electrode, and separator are wound together and packaged to form a lithium-ion battery with a thickness of 4.0 mm, a length of 150 mm, and a width of 60 mm. The battery is then vacuum-baked at 80°C for 24 hours to obtain the cell ready for electrolyte injection. The electrolyte is then injected into the cell in a glove box with the dew point controlled below -40°C. After formation, secondary sealing, and capacity testing, the lithium-ion battery manufacturing process is complete.

[0066] Example 2 The difference between Example 2 and Example 1 is that in step S1, the compound of formula I-1 is replaced by the compound of formula I-2.

[0067] Example 3 The difference between Example 3 and Example 1 is that in step S1, the compound of formula I-1 is replaced by the compound of formula I-3.

[0068] Example 4 Example 4 differs from Example 1 in that, in step S1, compound II-1 is replaced by compound II-2.

[0069] Example 5 Example 5 differs from Example 1 in that, in step S1, the compound of formula II-1 is replaced by the compound of formula II-3.

[0070] Example 6 The difference between Example 6 and Example 1 is that in step S1, the amount of compound I-1 added is 0.1 wt%.

[0071] Example 7 The difference between Example 7 and Example 1 is that in step S1, the amount of compound I-1 added is 5 wt%.

[0072] Example 8 The difference between Example 8 and Example 1 is that in step S1, the amount of compound II-1 added is 0.1 wt%.

[0073] Example 9 The difference between Example 9 and Example 1 is that in step S1, the amount of compound II-1 added is 3 wt%.

[0074] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that, in step S1, compound I-1 was not added.

[0075] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that, in step S1, compound II-1 was not added.

[0076] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that no first additive was added in step S1.

[0077] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step S1, the compound of Formula II-1 is replaced with triphenyl phosphate.

[0078] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step S1, the compound of Formula I-1 is replaced with trimethylsilyl trifluoromethanesulfonate.

[0079] Performance testing: The performance of the lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-5 was tested, and the specific procedures are as follows: (1) Room temperature cycling performance test: At 25±2℃, charge to 4.4V with 1C constant current and constant voltage, cut off current 0.05C, and then discharge to 2.8V with 1C constant current. Record the initial discharge capacity as C0. Repeat the charge and discharge 500 times and record the discharge capacity of the 500th cycle as C1. The capacity retention rate of room temperature cycling = C1 / C0×100%.

[0080] (2) High temperature cycling performance test: In a constant temperature chamber at 45±2℃, charge to 4.4V with constant current and constant voltage at 1C, cut off current at 0.05C, and then discharge to 2.8V with constant current at 1C. Record the initial discharge capacity as C0. Repeat the charge and discharge 500 times and record the discharge capacity on the 500th cycle as C1. The capacity retention rate of high temperature cycling = C1 / C0×100%.

[0081] (3) Performance test after 14 days of storage at 70℃: At 25±2℃, the battery was charged to 4.4V with a constant current and constant voltage of 1C and the cutoff current was 0.05C. Then, it was discharged to 2.8V with a constant current of 1C. The initial discharge capacity was recorded as C0, and the initial battery volume was measured as V0. At 25±2℃, the battery was charged to 4.4V with a constant current and constant voltage of 1C and the cutoff current was 0.05C. Then, the fully charged battery was transferred to 70±2℃ and left to stand for 14 days. After storage, the battery was left to stand at 25±2℃ for 2 hours. The battery was then discharged to 2.8V with a constant current of 1C and the discharge capacity was recorded as C1. The battery volume V1 after storage was measured. The volume change rate after 14 days of storage at 70℃ = (V1-V0) / V0×100%, and the capacity retention rate after 14 days of storage at 70℃ = C1 / C0×100%.

[0082] (4) Low-temperature performance test: At 25±2℃, charge the battery to 4.4V with a constant current and constant voltage of 1C, cut off the current at 0.05C, and then discharge it to 2.8V with a constant current of 1C. Record the initial discharge capacity as C0. At 25±2℃, charge the battery to 4.4V with a constant current and constant voltage of 1C, cut off the current at 0.05C, and then transfer the fully charged battery to -20±2℃ and leave it for 4 hours. Then discharge it to 2.8V with a constant current of 1C and record the discharge capacity as C1. The discharge ratio of the battery at -20℃ = C1 / C0 × 100%.

[0083] The test data is shown in Table 1.

[0084] Table 1. Performance test results of lithium-ion batteries As shown in Comparative Examples 1-3 and Examples 1-9, the simultaneous addition of silanolate compounds and thiophosphate compounds to the electrolyte is beneficial for improving the cycle life, high-temperature performance, and low-temperature performance of high-voltage lithium-ion batteries. This is because the SEI and CEI films formed when the two are used together are more uniform and stable, and contain Si, P, and S components, giving the interface films superior lithium-ion conductivity and effectively mitigating the occurrence of side reactions at the electrolyte-electrode interface.

[0085] As can be seen from Comparative Examples 3 and Examples 1-9, controlling the addition amount of silanolate compounds and thiophosphate compounds within the range of this invention can significantly improve the cycle life and high and low temperature performance of the battery cell. When the amount of the first additive is too small, the SEI film and CEI film formed by the additive are not uniform and dense enough, and the stability is poor. When the amount of the first additive is too large, on the one hand, it increases the viscosity of the electrolyte and the resulting interfacial film is too thick, leading to an increase in interfacial impedance, thereby degrading the performance of the battery cell. On the other hand, it increases the cost of the electrolyte.

[0086] As shown in Comparative Example 1 and Examples 1-3, adding silicon-based sulfonate compounds of Formula I-1, Formula I-2, or Formula I-3 to the electrolyte can improve the cycle performance, high-temperature performance, and low-temperature performance of high-voltage lithium-ion batteries, with more significant improvement effects. This is due to the presence of double bonds and trifluoromethanesulfonate in the silicon-based sulfonate compounds, which can promote earlier and more uniform film formation.

[0087] As shown in Comparative Example 2, Examples 1, and 4-5, adding Formula II-2 and Formula II-3 to the electrolyte significantly improves cycle performance and high-temperature performance. Because Formula II-2 contains F, the resulting interfacial film is rich in inorganic LiF, further enhancing its stability and reducing interfacial impedance, thus promoting uniform lithium-ion transport and further improving low-temperature performance. The -NCO group in Formula II-3 has dehydration and deacidification effects, which can eliminate the adverse effects of HF to some extent. Furthermore, this group participates in the formation of the interfacial film, effectively improving cycle performance and high-temperature performance. However, because this group has slightly higher film-forming impedance, the low-temperature performance of the battery prepared with Formula II-3 is slightly worse than that of the battery prepared with Formula II-1.

[0088] As shown in Comparative Examples 1 and 5 and Example 1, adding trimethylsilyl trifluoromethanesulfonate to the electrolyte is also beneficial for improving the performance of high-voltage ternary lithium-ion batteries, but the improvement effect is not as good as that of compound I-1. This is because compound I-1 is a symmetrical silicon-based polysulfonate compound, which forms a more uniform and stable interfacial film, which is beneficial for improving the long cycle life of lithium batteries.

[0089] As shown in Comparative Examples 2 and 4 and Example 1, triphenyl phosphate additives can also improve the performance of high-voltage ternary lithium-ion batteries, but the effect is not as significant as that of compound II-1. The reason for this may be that compound II-1 is a thiophosphate compound, and the interfacial film it forms contains both S and P elements, resulting in better ionic conductivity. Furthermore, the S in P=S contains lone pairs of electrons, exhibiting strong coordination ability, which can bond with high-valence metal ions in the cathode material, effectively reducing the dissolution of transition metal ions in the cathode, thus resulting in a more significant improvement in cycle performance, high-temperature performance, and low-temperature performance.

[0090] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0091] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0092] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. 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, 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, without contradiction. Additionally, it should be noted that in this specification, 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 indicated technical features.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, The additives include an organic solvent, a lithium salt, and an additive, wherein the additives include a first additive; the first additive includes a silane sulfonate compound and a thiophosphate compound, wherein the silane sulfonate compound has the structure shown in Formula I, and the thiophosphate compound has the structure shown in Formula II. Formula I; Formula II; R1 to R7 are independently selected from hydrogen, halogen, cyano, isocyanate group, isothiocyanate group, trimethylsilyl, unsubstituted alkyl or alkoxy group of C1 to C10, substituted alkyl or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C20, and at least one of R5 to R7 is an unsubstituted or substituted aryl group of C6 to C20.

2. The electrolyte according to claim 1, characterized in that, The silanol ester compounds include at least one of the following structures: Equation I-1; Equation I-2; Formula I-3.

3. The electrolyte according to claim 1, characterized in that, The thiophosphate compounds include at least one of the following structures: Formula II-1; Formula II-2; Formula II-3.

4. The electrolyte according to claim 1, characterized in that, The silanol ester compound accounts for 0.1% to 5% of the total mass of the electrolyte, preferably 0.5% to 3%; And / or, the thiophosphate compound accounts for 0.1% to 3% of the total mass of the electrolyte, preferably 0.5% to 2%.

5. The electrolyte according to claim 1, characterized in that, The organic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Preferably, the organic solvent includes at least three of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

6. The electrolyte according to claim 1, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate. Preferably, the lithium salt includes at least two of lithium hexafluorophosphate, lithium difluorophosphate, and lithium bisfluorosulfonylimide.

7. The electrolyte according to claim 1, characterized in that, The organic solvent accounts for 60% to 85% of the total mass of the electrolyte; And / or, the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, The additive further includes a second additive; the second additive includes one or more of the following: fluoroethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, ethylene sulfate, vinylene carbonate, ethylene ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinate, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, succinic anhydride, maleic anhydride, citrate anhydride, and methanedisulfonic acid methylene ester.

9. A battery, characterized in that, It includes an electrode assembly and an electrolyte, wherein the electrolyte includes the electrolyte according to any one of claims 1 to 8.

10. The battery according to claim 9, characterized in that, The electrode assembly includes a positive electrode, a diaphragm, and a negative electrode stacked sequentially. The positive electrode includes a positive electrode current collector and a positive electrode coating disposed on at least one surface of the positive electrode current collector along its thickness direction; the positive electrode coating includes a positive electrode active material; the positive electrode active material includes LiNi. x Co y Mn z M 1-x-y-z O2 and / or LiNi x Co y Al z N 1-x-y-z O2; wherein M and N are independently selected from one or more of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, and x+y+z≤1; The negative electrode includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector along the thickness direction; the negative electrode coating includes a negative electrode active material; the negative electrode active material includes one or more of natural graphite, artificial graphite, and silicon-carbon composite materials; And / or, the operating voltage of the battery is ≥4.4V.

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