Electrolyte and battery

Abstract

The present invention provides an electrolyte and a battery, the electrolyte comprising: a first additive comprising a cyclic phosphate compound having the structure shown in Formula 1; and a second additive comprising a fluorinated sulfonyl compound having the structure shown in Formula 2. The present invention can effectively inhibit lithium deposition and the formation of lithium dendrites, thereby improving fast-charging performance.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to an electrolyte and a battery. Background Art

[0002] Fast charging technology has become a core competitive advantage in sectors such as consumer electronics and electric vehicles. While pursuing a fast charging experience, it's also crucial to be mindful of the potential internal battery risks. When batteries, especially lithium-ion batteries, are subjected to excessive charging currents (i.e., fast charging), lithium ions on the surface of the negative electrode material (such as graphite) may not be able to fully and promptly embed themselves into its layered structure. This leads to excessive lithium ion accumulation on the negative electrode surface, ultimately precipitating as lithium metal, a process known as "lithiation." The precipitated lithium metal often forms sharp, branch-like crystals known as "lithium dendrites." The growth of lithium dendrites not only irreversibly consumes active lithium ions, reducing battery capacity and lifespan, but more seriously, they can pierce the separator inside the battery, causing a direct short circuit between the positive and negative electrodes. This internal short circuit instantly generates significant heat, easily triggering thermal runaway, leading to serious safety hazards such as battery fires and explosions. Therefore, effectively suppressing lithium deposition and the formation of lithium dendrites is a key challenge in fast charging technology. Summary of the Invention

[0003] Embodiments of the present invention provide an electrolyte and a battery that can effectively inhibit lithium plating and the formation of lithium dendrites, thereby improving fast charging performance.

[0004] In one aspect of the present application, an electrolyte is provided, comprising:

[0005] A first additive, wherein the first additive includes a cyclic phosphate compound having a structure shown in Formula 1:

[0006]

[0007] In Formula 1, R1, R2, R3, R4, R5, R6, and R7 are each independently selected from one of H, phenyl, halogen, C1-C10 saturated hydrocarbon group, C2-C10 olefin group, C2-C10 alkynyl group, C1-C10 halogenated saturated hydrocarbon group, C2-C10 halogenated olefin group, and C2-C10 halogenated alkynyl group.

[0008] The second additive includes a fluorinated sulfonyl compound having a structure shown in Formula 2:

[0009]

[0010] In Formula 2, R8 and R9 are each independently selected from F, a methyl group in which 1 to 3 H groups are replaced by F, an ethyl group in which 1 to 3 H groups are replaced by F, or a propyl group in which 1 to 3 H groups are replaced by F.

[0011] According to one embodiment of the present application, in Formula 1, R1, R2, R3, R4, R5, R6, and R7 are each independently selected from one of H, a C1-C10 saturated hydrocarbon group, a C2-C10 olefin group, a C2-C10 alkyne group, and a C1-C10 halogenated saturated hydrocarbon group.

[0012] According to one embodiment of the present application, the first additive includes one or more of the following compounds of Formula 1-1 to Formula 1-8:

[0013]

[0014] According to one embodiment of the present application, the second additive includes one or more of the following compounds of Formula 2-1 to Formula 2-12:

[0015]

[0016] According to one embodiment of the present application, in the electrolyte, the mass percentage of the first additive is 0.1%~4%; and / or, in the electrolyte, the mass percentage of the second additive is 0.2%~3%.

[0017] According to one embodiment of the present application, the mass ratio of the first additive to the second additive is 1:(0.05-3.5), preferably 1:(0.2-2).

[0018] According to one embodiment of the present application, the electrolyte further includes an organic solvent and an electrolyte salt. In the electrolyte, the mass percentage of the organic solvent is 60% to 95%; the mass percentage of the electrolyte salt is 5% to 30%.

[0019] According to one embodiment of the present application, the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, ethyl acetate, methyl propyl carbonate, halogenated ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone; and / or the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, and lithium 4,5-dicyano-2-trifluoromethylimidazole.

[0020] Another aspect of the present application provides a battery comprising the above-mentioned electrolyte.

[0021] According to one embodiment of the present application, the battery further includes a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet includes a positive electrode collector and a positive electrode active material layer arranged on the surface of the positive electrode collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes one or more of a ternary positive electrode material, lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, and a lithium-rich manganese-based material, the ternary positive electrode material includes lithium nickel cobalt manganese oxide, and the lithium nickel cobalt manganese oxide includes one or more of NCM811, NCM613, and NCM523.

[0022] The implementation of the present invention has at least the following beneficial effects: by introducing a cyclic phosphate compound having a structure shown in Formula 1 (a first additive) and a fluorinated sulfonyl compound having a structure shown in Formula 2 (a second additive) into the electrolyte, the two act synergistically to inhibit lithium precipitation and the formation of lithium dendrites, thereby improving fast charging performance. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0024] Factors affecting battery fast charging primarily include battery temperature, lithium deposition, and material pulverization. Lithium deposition is a significant factor affecting the fast-charging performance of lithium-ion batteries. During lithium deposition, metallic lithium often grows in a distinctive, branch-like structure (lithium dendrites). These dendrites gradually accumulate on the surface of the negative electrode, like a continuous accumulation of obstacles on the "road" for lithium ion transport. This makes the path for lithium ion transport within the electrode longer and more obstructed. More seriously, lithium dendrites can pierce the separator, creating a short circuit and instantly causing a sharp increase in the battery's internal resistance. Improper heat management can lead to battery overheating, expansion, and thermal runaway, further limiting the application of fast charging.

[0025] Therefore, how to inhibit lithium plating and the formation of lithium dendrites and improve fast charging performance remains a technical problem that needs to be solved urgently in this field.

[0026] In view of this, an embodiment of the present invention provides an electrolyte, including: a first additive, wherein the first additive includes a cyclic phosphate compound having a structure shown in Formula 1:

[0027]

[0028] In Formula 1, R1, R2, R3, R4, R5, R6, and R7 are each independently selected from one of H, phenyl, halogen, C1-C10 saturated hydrocarbon group, C2-C10 olefin group, C2-C10 alkynyl group, C1-C10 halogenated saturated hydrocarbon group, C2-C10 halogenated olefin group, and C2-C10 halogenated alkynyl group.

[0029] The second additive includes a fluorinated sulfonyl compound having a structure shown in Formula 2:

[0030]

[0031] In formula 2, R8 and R9 are each independently selected from F, a methyl group in which 1 to 3 H groups are replaced by F, an ethyl group in which 1 to 3 H groups are replaced by F, or a propyl group in which 1 to 3 H groups are replaced by F.

[0032] The first additive is a caged phosphate compound with a three-dimensional skeleton structure. There is a strong interaction between this compound and PF6. This interaction not only helps to dissociate LiPF6 salt, but also significantly improves the ionic conductivity in the electrolyte and promotes the migration of lithium ions in the electrolyte. At the same time, the phosphorus-oxygen double bond in this compound has a lone pair of electrons and is a Lewis base. It can react on the surface of the battery positive electrode material to form a protective film, and the formed protective film can partially retain its three-dimensional rigid skeleton, increase the porosity of the SEI film, and thus help improve the fast charging performance.

[0033] However, when the first additive is used alone, it is easily oxidized under fast-charging conditions, especially when the operating voltage is increased. This can disrupt the three-dimensional structure of the first additive, leading to changes in the composition of the interfacial film (e.g., SEI film) and reduced ion conductivity. After repeated charging, lithium ions may precipitate and form lithium dendrites, ultimately affecting fast-charging performance. To address this issue, a second additive is introduced. The second additive is a fluorinated sulfonyl compound (e.g., a fluorinated alkylsulfonyl imide compound) having the structure shown in Formula 2. The nitrogen atom of this compound has two adjacent -SO2R (e.g., -SO2F) groups attached to it. Because the nitrogen atom is also attached to a benzene ring, the π electrons in the conjugated system stabilize the formation of the intermediate, effectively lowering the chemical reaction energy barrier. This makes the two S-N bonds more easily broken, allowing them to be oxidized preferentially before the compound in Formula 1, thereby maintaining the three-dimensional structure of the compound in Formula 1. However, replacing the benzene ring with other groups, such as the less sterically hindered -CH3, does not achieve this effect. More importantly, the SEI film formed by the two additives can effectively shrink the membrane pores and reduce the occurrence of side reactions; and the three P=O bonds evenly distributed on the membrane and the lone pair of electrons on N interact with Li +The weak interaction between lithium ions helps lithium ions form a stable four-coordinate structure, thereby promoting their rapid transmission inside the battery without precipitation in the form of lithium dendrites, thus ensuring battery performance.

[0034] The electrolyte of the embodiment of the present invention can be applied to lithium-ion batteries, which can not only improve the fast charging performance, but also solve the problems of rapid increase in battery polarization, reduction in discharge platform, and reduction in discharge capacity during high-speed discharge of lithium-ion batteries, effectively reduce the impedance of lithium-ion batteries and improve the cycle stability and other performance of lithium-ion batteries.

[0035] In some embodiments, in Formula 1, R1, R2, R3, R4, R5, R6, and R7 are each independently selected from one of H, a C1-C10 saturated hydrocarbon group, a C2-C10 olefin group, a C2-C10 alkyne group, and a C1-C10 halogenated saturated hydrocarbon group, which is more conducive to synergizing with the second additive to improve the stability of the formed SEI film and other interface films, while taking into account improving the fast charging performance, cycle performance, and reducing the battery impedance of the battery.

[0036] In some embodiments, the first additive includes one or more of the following compounds of Formula 1-1 to Formula 1-8, which can further enhance fast charging performance, reduce battery impedance, improve battery cycle stability, and improve high-temperature performance of the battery:

[0037]

[0038] In the embodiment of the present invention, the cyclic phosphate compound can be obtained by conventional methods, such as commercially available or homemade by conventional methods, and there is no particular limitation on this. Specifically, the CAS number of the compound represented by Formula 1-1 is 62958-36-5, the CAS number of the compound represented by Formula 1-2 is 51486-74-9, the CAS number of the compound represented by Formula 1-3 is 60027-99-8, the CAS number of the compound represented by Formula 1-4 is 3066478-04-1, the CAS number of the compound represented by Formula 1-5 is 3066478-05-2, the CAS number of the compound represented by Formula 1-6 is 3066478-06-3, the CAS number of the compound represented by Formula 1-7 is 3059548-77-2, and the CAS number of the compound represented by Formula 1-8 is 3059548-82-9.

[0039] In some embodiments, the second additive includes one or more of the following compounds of Formula 2-1 to Formula 2-12, which can significantly improve fast charging performance and battery rate performance, while also improving the high-temperature performance of the battery:

[0040]

[0041] In the embodiments of the present invention, the fluorinated sulfonyl compound (second additive) can be obtained by conventional methods, such as commercially available or prepared by conventional methods, without particular limitation. Specifically, the compound represented by Formula 2-1 has a CAS number of 1622206-83-0, and the compound represented by Formula 2-4 has a CAS number of 37595-74-7.

[0042] For further example, the compounds of Formula 2-2, Formula 2-3, Formula 2-5 to Formula 2-8 can be prepared by using the corresponding fluorinated sulfonyl raw materials with reference to the preparation method of N-phenylbistrifluoromethanesulfonimide in Scheme 3 of patent CN115028557A. For example, the raw materials shown in Formula 3-1 (CAS No. 1401527-57-8), Formula 3-2 (1426573-49-0), Formula 3-3 (358-79-2), and Formula 3-4 (CAS No. 1401527-61-4) can be used to replace trifluoromethanesulfonyl fluoride in Scheme 3 of CN115028557A to prepare the corresponding second additive.

[0043]

[0044] After further research, in the above-mentioned electrolyte, the mass ratio of the first additive to the second additive can be 1: (0.05~3.5), for example, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.3, 1:1.5, 1:1.8, 1:2, 1:2.5, 1:3, 1:3.5 or a range composed of any two of them, preferably 1: (0.2~2), which is beneficial to improving the fast charging performance, improving the cycle stability of the battery, and improving the high temperature performance of the battery.

[0045] After further research, the mass percentage of the first additive in the above-mentioned electrolyte (that is, the ratio of the mass of the first additive to the total mass of the electrolyte) can be 0.1%~4%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or a range composed of any two of them, which is beneficial to improving fast charging performance, reducing battery impedance, improving battery cycle stability, and improving the high temperature performance of the battery.

[0046] After further research, the mass percentage of the second additive in the above-mentioned electrolyte (i.e., the ratio of the mass of the second additive to the total mass of the electrolyte) is 0.2%~3%, for example, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range composed of any two of them, which is beneficial to improving fast charging performance, reducing battery impedance, improving battery cycle stability, and improving the high-temperature performance of the battery.

[0047] In the embodiment of the present invention, the electrolyte is a non-aqueous electrolyte, which further includes an organic solvent (or non-aqueous solvent) and an electrolyte salt.

[0048] Specifically, the organic solvent may include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), ethyl acetate (EA), methyl propyl carbonate, halogenated ethylene carbonate, propylene carbonate (PC), γ-butyrolactone and γ-valerolactone, which is conducive to adapting the above-mentioned first additive and the second additive, improving the fast charging performance, reducing the battery impedance, improving the cycle stability of the battery, and taking into account the improvement of the high temperature performance of the battery.

[0049] Illustratively, the organic solvent may include ethylene carbonate and ethyl methyl carbonate, and the mass ratio of ethylene carbonate to ethyl methyl carbonate may be 3:(5-9), such as 3:5, 3:6, 3:7, 3:8, 3:9 or a range consisting of any two thereof.

[0050] In some embodiments, in the above-mentioned electrolyte, the mass percentage of the organic solvent (i.e., the ratio of the mass of the organic solvent to the total mass of the electrolyte) can be 60%~95%, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range composed of any two of them, which is conducive to synergizing with the above-mentioned first additive, second additive and film-forming additive to improve fast charging performance, reduce battery impedance, improve battery cycle stability, and take into account improving the high temperature performance of the battery.

[0051] In addition, the electrolyte salt may include a lithium salt, and the lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide, which is conducive to adapting the above-mentioned first additive and the second additive, improving the fast charging performance, reducing the battery impedance, improving the cycle stability of the battery, and taking into account the improvement of the high temperature performance of the battery.

[0052] In some embodiments, in the above-mentioned electrolyte, the mass percentage of the electrolyte salt (i.e., the ratio of the mass of the electrolyte salt to the total mass of the electrolyte) can be 5%~30%, for example, 5%, 10%, 15%, 20%, 25%, 30% or a range composed of any two of them, which is conducive to synergizing with the above-mentioned first additive, second additive and film-forming additive to enhance fast charging performance, reduce battery impedance, improve battery cycle stability, and take into account improving the high temperature performance of the battery.

[0053] An embodiment of the present invention further provides a battery, which includes the above-mentioned electrolyte. The battery has corresponding advantages to the above-mentioned electrolyte, which will not be described in detail.

[0054] The battery in the embodiment of the present invention may be a lithium-ion battery.

[0055] Generally, a battery consists of a cell and a casing that encapsulates the cell. An electrolyte is injected into the cell within the casing. The cell includes a positive electrode sheet (also called a positive electrode sheet), a negative electrode sheet (also called a negative electrode sheet), and a separator located between the positive and negative electrodes. The cell can be a wound cell, meaning that the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and then wound to form a wound structure.

[0056] Specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating located on at least one side of the positive electrode current collector. Specifically, the positive electrode coating may be provided on one side of the positive electrode current collector, or on two opposite sides of the positive electrode current collector in the thickness direction. The positive electrode coating (positive electrode active material layer) includes a positive electrode active material, which includes a lithium transition metal oxide.

[0057] In some embodiments, the positive electrode active material may include one or more of a ternary positive electrode material, lithium cobalt oxide, lithium iron phosphate (LFP), lithium iron manganese phosphate, lithium manganese oxide, lithium nickel manganese oxide, and a lithium-rich manganese-based material. The ternary positive electrode material includes lithium nickel cobalt manganese oxide (NCM), and the lithium nickel cobalt manganese oxide may include one or more of NCM811, NCM613, and NCM523, but is not limited thereto.

[0058] For example, the positive electrode active material may include LiMn2O4, Li 1+a Mn 1-x M x O2、LiE 1-y M y O2、Li2Mn 1-b One or more of O4, wherein Li 1+a Mn 1-x M x O2 and LiE 1-y M yE and M in O2 independently include one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, Fe, V, Ti, B, and F, with 0<a<0.2, 0≤x<1, 0≤y<1, and 0≤b<1.

[0059] For example, the positive electrode active material may include LiMn2O4, Li 1+a Mn 1-x M x O2、LiCo 1-y M y O2、LiFe 1-z M z PO4, Li2Mn 1-b One or more of O4, wherein Li 1+a Mn 1-x M x O2、LiCo 1-y M y O2 and LiFe 1-z M z M in PO4 is independently selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, with 0≤a<0.2, 0≤x<1, 0≤y<1, 0≤z<1, and 0≤b<1.

[0060] For example, Li 1+a Mn 1-x M x O2 may include LiMnO2 (a=0, x=0).

[0061] For example, Li2Mn 1-b O4 may include Li2MnO4 (b=0).

[0062] For example, LiE 1-y M y O2 may include LiCoO2 (E is Co, y=0).

[0063] For example, LiE 1-y M y O2 may include LiFePO4 (E is Fe, y=0).

[0064] For example, the positive electrode active material is NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O2).

[0065] The above-mentioned nickel-cobalt-manganese ternary material (NCM) has a high specific capacity and can improve the capacity and other performance of the battery. However, there are still some problems with the NCM positive electrode. For example, the traditional carbonate-based electrolyte degrades on the surface of the delithiation cathode, leading to problems such as byproduct accumulation, lithium depletion and transition metal (TM) ion dissolution. At the same time, a large amount of electrolyte is further consumed, and the thickness of the SEI film is further increased, resulting in a decrease in battery capacity and an increase in impedance. In particular, during high-speed discharge, the battery polarization increases sharply, the discharge platform decreases, the discharge capacity decreases, and even safety issues arise. In the embodiment of the present invention, by using an electrolyte containing the above-mentioned first additive and second additive, not only can lithium plating and the production of lithium dendrites be suppressed, but these problems can also be effectively overcome, reducing battery impedance, improving the battery's fast charging performance, meeting the battery's high-rate charge and discharge requirements, and improving the battery's cycle performance. In particular, the impedance change rate of the battery in a high-temperature environment can be reduced and the battery's cycle life under high-temperature conditions can be improved.

[0066] In addition, the positive electrode coating also includes a conductive agent and a binder, both of which can be conventional materials in the field. For example, the conductive agent may include one or more of conductive carbon black (Super P), carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers; the binder may include one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, etc.

[0067] In general, in the positive electrode coating, the mass percentage of the positive electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two thereof, the mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof, and the mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof.

[0068] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0069] In an embodiment of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the components used to form the positive electrode coating, such as the positive electrode active material, the conductive agent, and the binder, can be dispersed in a first solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector. After drying, roller pressing (cold pressing), trimming, striping, and welding the tabs, the positive electrode sheet is obtained.

[0070] Specifically, the negative electrode sheet includes a negative electrode collector and a negative electrode coating located on at least one side surface of the negative electrode collector. Specifically, the negative electrode coating can be provided on one side surface of the negative electrode collector, or on both sides of the negative electrode collector in the thickness direction.

[0071] Specifically, the negative electrode coating (negative electrode active material layer) includes a negative electrode active material, a conductive agent, a binder, and a thickener, all of which can be conventional materials in the art.

[0072] For example, the negative electrode active material may include one or more of carbonaceous materials, silicon-carbon materials, alloy materials, and lithium-containing metal composite oxides, and specifically may include but is not limited to one or more of graphite, soft carbon, hard carbon, silicon, silicon oxides, silicon-carbon composites, and lithium titanate.

[0073] For example, the conductive agent in the negative electrode coating may include one or more of conductive carbon black (Super P), carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers.

[0074] For example, the binder in the negative electrode coating may include one or more of styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0075] For example, the thickener in the negative electrode coating may include a carboxymethyl cellulose thickener, and the carboxymethyl cellulose thickener may include a carboxymethyl cellulose salt, such as sodium carboxymethyl cellulose (CMC).

[0076] In general, in the negative electrode coating, the mass percentage of the negative electrode active material can be 70% to 98.5%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 98.5% or a range consisting of any two thereof, and the mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof, The mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof, and the mass percentage of the thickener can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof.

[0077] The embodiment of the present invention may adopt a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0078] In an embodiment of the present invention, the negative electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, the conductive agent, and the binder, can be dispersed in a second solvent. The second solvent includes, for example, water, specifically deionized water, to prepare a negative electrode slurry, which is then coated on the surface of the negative electrode current collector. After drying, roller pressing (cold pressing), trimming, striping, and welding the tabs, the negative electrode sheet is obtained.

[0079] In the embodiments of the present invention, a separator is used to separate the positive and negative electrodes to prevent contact and short circuits between the positive and negative electrodes. The separator can be any known separator in the art that can be used in batteries and stabilizes the electrolyte. For example, the separator can include one or more of polyolefin, aromatic polyamide, polytetrafluoroethylene, and polyethersulfone, and the specific separator can be configured as needed.

[0080] In the embodiment of the present invention, the battery cell may be encapsulated with conventional shell materials in the art, and the shell may include, for example, aluminum foil (outer packaging aluminum foil), but is not limited thereto.

[0081] The battery of the embodiment of the present invention can be manufactured according to conventional methods in the field. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked in sequence and then wound into a wound battery cell (bare battery cell) through a winding process. The wound battery cell is then placed in a shell and vacuum-baked. The electrolyte is injected into the shell and then vacuum-packaged, allowed to stand, formed, aged, and capacity-separated to obtain a battery. These steps / processes are all conventional operations in the field. The present invention does not impose any special restrictions on this and will not be described in detail.

[0082] The present invention is further described below through specific examples.

[0083] 1. Preparation of NCM positive electrode sheet

[0084] LiNi 0.5 Co 0.2 Mn 0.3 O2 cathode material (NCM523), SuperP, and PVDF were mixed evenly in a mass ratio of 96.8:2:1.2 and vacuum stirred until the fluidity was uniform to obtain a cathode slurry;

[0085] Then the positive electrode slurry is evenly coated on the front and back surfaces of the aluminum foil, and then dried at 85℃, cold pressed, trimmed, cut into pieces, and slit, and then rolled at 95℃. o C vacuum drying for 12 hours to form positive electrode coatings on the front and back surfaces of the aluminum foil, and then welding the tabs to obtain the positive electrode sheet; wherein the surface density of the positive electrode coating is 33mg / cm 2 .

[0086] 2. Preparation of negative electrode sheet

[0087] Graphite, Super P, CMC, and SBR (styrene-butadiene rubber emulsion) were mixed uniformly in a mass ratio of 95:1.5:1.5:2 to obtain a negative electrode slurry;

[0088] The negative electrode slurry is coated on both the front and back surfaces of the copper foil, dried at 85°C, and then cold pressed, trimmed, cut into pieces, and striped. o C under vacuum conditions for 12 hours to form a negative electrode coating on the front and back surfaces of the copper foil, and then weld the tabs to obtain a negative electrode sheet; wherein the surface density of the negative electrode coating is 20.1 mg / cm 2 .

[0089] 3. Preparation of lithium-ion batteries

[0090] The above-mentioned positive electrode sheet, separator and negative electrode sheet are stacked in sequence and wound into a bare cell (wound cell) with a theoretical capacity of 1700mAh. The bare cell is placed in an outer packaging aluminum foil and vacuum-baked at 75°C for 10 hours. The electrolyte is then injected and the lithium-ion battery is produced after vacuum packaging, standing, formation, aging, and capacity separation.

[0091] The electrolyte used is composed of an organic solvent, LiPF6, a first additive (1,1,1-trimethylolpropane phosphoric acid (Formula 1-1)), and a second additive (N-phenylbisfluorosulfonyl imide (PhFSI) (Formula 2-1)). The organic solvent is composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:EMC=3:7. The mass percentage of LiPF6 in the electrolyte is 12.5%, the mass percentage of the first additive in the electrolyte is 1%, and the mass percentage of the second additive in the electrolyte is 1%.

[0092] Example 2 to Example 32, Comparative Example 1 to Comparative Example 5: The difference from Example 1 is that the type of the first additive, the mass percentage w1 of the first additive in the electrolyte, the type of the second additive, the mass percentage w2 of the second additive in the electrolyte, etc. are different. See Table 1 for details. Except for the differences shown in Table 1, the other conditions are the same as those in Example 1.

[0093] The difference between Comparative Example 1 and Example 1 is that the electrolyte does not contain the first additive.

[0094] The difference between Comparative Example 2 and Example 1 is that the electrolyte does not contain the second additive.

[0095] The difference between Comparative Example 3 and Example 1 is that the electrolyte does not contain the two additives.

[0096] The difference between Comparative Example 4 and Example 1 is that the electrolyte does not contain the first additive, and the mass percentage content w2 of the second additive in the electrolyte is 2%.

[0097] The difference between Comparative Example 5 and Example 1 is that the electrolyte does not contain the second additive, and the mass percentage w1 of the first additive in the electrolyte is 2%.

[0098] Example 33: The difference from Example 1 is that the positive electrode material is different. In the preparation process of the positive electrode sheet, Example 33 uses lithium iron phosphate (LFP) instead of NCM523 to prepare the LFP positive electrode sheet. The preparation process of the LFP positive electrode sheet of Example 33 is as follows: the positive electrode material (LFP), SuperP, CNT, and PVDF are mixed evenly in a mass ratio of 94.5:1.5:1:3.0, and vacuum stirred until the fluidity is uniform to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the front and back surfaces of the aluminum foil, and then dried at 85°C, cold pressed, trimmed, cut, slit, 95 o C vacuum drying for 12 hours to form positive electrode coatings on the front and back surfaces of the aluminum foil, and then welding the tabs to obtain the positive electrode sheet; wherein the surface density of the positive electrode coating is 33mg / cm 2 The remaining conditions of Example 33 are the same as those of Example 1.

[0099] The difference between Comparative Example 6 and Example 33 is that the electrolyte does not contain the first additive, the mass percentage w2 of the second additive in the electrolyte is 2%, and the other conditions are the same as those in Example 33.

[0100] The difference between Comparative Example 7 and Example 33 is that the electrolyte does not contain the second additive, the mass percentage w1 of the first additive in the electrolyte is 2%, and the other conditions are the same as those in Example 33.

[0101] The battery performance of each embodiment and comparative example was tested according to the following process. The results are shown in Table 2. Among them, the positive electrode material of Examples 1 to 32 and Comparative Examples 1 to 5 is NCM523, and the voltage test range is 2.75V~4.2V (i.e., the upper limit cut-off voltage V T The lower discharge cut-off voltage is 4.2V. L The positive electrode material of Example 33, Comparative Example 6 and Comparative Example 7 is LFP, and the voltage test range is 2.5V-3.65V (i.e., the upper limit cut-off voltage V T The lower discharge cut-off voltage V L The remaining test steps of Examples 1 to 33 and Comparative Examples 1 to 7 are the same. The battery performance test process of Examples 1 to 32 and Comparative Examples 1 to 5 is described below as an example.

[0102] (1) 25 o C normal temperature cycle test: Li-ion batteries are subjected to o C is charged to 4.2V at a constant current of 4.0C, charged to a cut-off current of 0.05C at a constant voltage of 4.2V, and then discharged to 2.75V at a constant current of 1.0C. The battery is cycled in this way. The discharge capacity Q2 of the 300th cycle and the discharge capacity Q1 of the 1st cycle are recorded. The capacity retention rate after 300 cycles at 25℃ is Q2 / Q1×100%. (2) 45 o C high temperature cycle test: Li-ion batteries are subjected to o C is charged at a constant current of 4.0C to 4.2V, and then charged at a constant voltage of 4.2V to a cut-off current of 0.05C. The battery is then discharged at a constant current of 1.0C to 2.75V. In this cycle test, the discharge capacity of the 300th cycle is Q4, and the discharge capacity of the 1st cycle is Q3. Therefore, the battery capacity retention rate after 300 cycles at 45℃ = Q4 / Q3×100%.

[0103] (3) 60 o C high temperature storage 30 days performance test: Li-ion batteries are stored at 25 oC is charged to 4.2V at a constant current of 1.0C, charged to a cut-off current of 0.05C at a constant voltage of 4.2V, and then discharged to 2.75V at a constant current of 1.0C. The discharge capacity is recorded as Q5. o C, charge at a constant current of 1.0C to 4.2V, charge at a constant voltage of 4.2V to a cut-off current of 0.05C, and then transfer the battery to a 60 o C for 30 days, then discharge the battery to 2.75V at a constant current of 1.0C, and record the discharge capacity as Q6. Then, 60 o C storage 30 days capacity retention rate = Q6 / Q5×100%.

[0104] (4) Initial DCIR test: Li-ion battery is tested at 25 o C is charged at a constant current of 1.0C to 4.2V, and then at a constant voltage of 4.2V to a cutoff current of 0.05C. The battery is then discharged at a constant current of 1.0C for 30min. After standing for 1h, it is discharged at a constant current of 2.0C for 10s. The DCIR impedance value of the battery at 50% SOC is calculated, which is the initial DCIR value.

[0105] (5) High temperature DCIR test: Li-ion batteries are tested at 25 o C is charged to 4.2V at 1.0C constant current, and charged to a cut-off current of 0.05C at 4.2V constant voltage. Then the battery is discharged at 1.0C constant current for 30min. After 1h, it is discharged at 2.0C constant current for 10s. The DCIR of the battery at 50% SOC is calculated and recorded as D1. o C high temperature storage test for 30 days, at 25 o C is charged to 4.2V at a constant current of 1.0C, and then charged to a cut-off current of 0.05C at a constant voltage of 4.2V. Then, the battery is discharged at a constant current of 1.0C for 30min. After standing for 1h, it is discharged at a constant current of 2.0C for 10s. The DCIR of the battery at 50% SOC is calculated and recorded as D2. o C Storage 30-day impedance change rate = D2 / D1*100%.

[0106] (6) Room temperature ionic conductivity test: The conductivity of the electrolyte at 25°C was measured using a conductivity meter (DDS-307A conductivity meter from Shanghai Leici).

[0107] Table 1 The first additive and the second additive in the electrolyte and their contents

[0108]

[0109] Table 2 Performance test results

[0110]

[0111] It can be seen from Table 2 that, relative to Comparative Examples 1 to 7, Examples 1 to 33 can simultaneously improve the room temperature ionic conductivity of the electrolyte, the capacity retention rate of 300 cycles at 25°C 4C, the capacity retention rate of 300 cycles at 45°C 4C, the capacity retention rate of 300 cycles at 60°C, the initial DCIR value, and the impedance change rate of 30 days of storage at 60°C by adding a first additive having a structure of Formula 1 and a second additive having a structure of Formula 2 to the electrolyte. This shows that the scheme of the present application achieves an improvement in fast charging performance, and can also improve the battery's performance such as low impedance and high cycle life at high temperatures.

[0112] Furthermore, relative to Example 2 and Example 7, Example 1 and Example 4 to Example 6 further control the mass percentage of the first additive in the electrolyte within the range of 0.1% to 4%, which is beneficial to further improve the fast charging performance while taking into account the improvement of the battery's low impedance and high cycle life at high temperatures.

[0113] Furthermore, relative to Example 8 and Example 12, Example 1, Example 9 to Example 11 further control the mass percentage of the second additive in the electrolyte within the range of 0.2% to 3%, which is beneficial to further improve the fast charging performance while taking into account the improvement of the battery's low impedance and high cycle life at high temperatures.

[0114] Furthermore, relative to Example 13 and Example 14, Example 1, Example 4 to Example 6, and Example 9 to Example 11 further control the mass ratio of the first additive to the second additive in the electrolyte within the range of 1: (0.05~3.5), which is conducive to more significantly improving the fast charging performance and improving the high temperature performance of the battery, while maintaining a high room temperature ionic conductivity and room temperature cycle capacity retention rate of the battery.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that: include: A first additive, wherein the first additive includes a cyclic phosphate compound having a structure shown in Formula 1: In Formula 1, R1, R2, R3, R4, R5, R6, and R7 are each independently selected from one of H, phenyl, halogen, C1-C10 saturated hydrocarbon group, C2-C10 olefin group, C2-C10 alkynyl group, C1-C10 halogenated saturated hydrocarbon group, C2-C10 halogenated olefin group, and C2-C10 halogenated alkynyl group; The second additive includes a fluorinated sulfonyl compound having a structure shown in Formula 2: In Formula 2, R8 and R9 are each independently selected from F, a methyl group in which 1 to 3 H groups are replaced by F, an ethyl group in which 1 to 3 H groups are replaced by F, or a propyl group in which 1 to 3 H groups are replaced by F; The mass ratio of the first additive to the second additive is 1:(0.05-3.5).

2. The electrolyte according to claim 1, characterized in that In Formula 1, R1, R2, R3, R4, R5, R6, and R7 are each independently selected from one of H, a C1-C10 saturated hydrocarbon group, a C2-C10 olefin group, a C2-C10 alkynyl group, and a C1-C10 halogenated saturated hydrocarbon group.

3. The electrolyte according to claim 1, characterized in that The first additive includes one or more of the following compounds of Formula 1-1 to Formula 1-8: 。 4. The electrolyte according to claim 1, characterized in that The second additive includes one or more of the following compounds of Formula 2-1 to Formula 2-12: 。 5. The electrolyte according to any one of claims 1 to 4, characterized in that In the electrolyte, the mass percentage of the first additive is 0.1% to 4%; And / or, in the electrolyte, the mass percentage of the second additive is 0.2%~3%.

6. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further comprises an organic solvent and an electrolyte salt. In the electrolyte, the mass percentage of the organic solvent is 60% to 95%; the mass percentage of the electrolyte salt is 5% to 30%.

7. The electrolyte according to claim 6, characterized in that The organic solvent comprises one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, ethyl acetate, methyl propyl carbonate, halogenated ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone; And / or, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatephosphate, lithium tetrafluoroborate, lithium tetrafluorooxalatephosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, and lithium 4,5-dicyano-2-trifluoromethylimidazole.

8. A battery, characterized in that: The electrolyte comprises the electrolyte according to any one of claims 1 to 7.

9. The battery according to claim 8, characterized in that The battery also includes a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer arranged on the surface of the positive electrode collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes one or more of a ternary positive electrode material, lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, and a lithium-rich manganese-based material. The ternary positive electrode material includes lithium nickel cobalt manganese oxide, and the lithium nickel cobalt manganese oxide includes one or more of NCM811, NCM613, and NCM523.

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