Electrolyte and battery

Abstract

The present invention provides an electrolyte and a battery, the electrolyte comprising: a first additive, the first additive comprising a cyclic phosphate compound having a structure represented by formula 1; and the second additive comprises a fluorosulfonyl compound with a structure as shown in a formula 2. According to the invention, lithium precipitation and generation of lithium dendrites can be effectively inhibited, and the fast charging performance is improved.

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 the core competitive track in the fields of consumer electronics, electric vehicles, etc. While pursuing the fast charging experience, we need to pay attention to the internal risks of the battery that it may bring. When the battery, especially the lithium-ion battery, is applied with too large a charging current (i.e., fast charging), the lithium ions on the surface of the negative electrode material (such as graphite) may not be able to be timely and completely embedded in its layered structure. This will cause the lithium ions to accumulate excessively on the surface of the negative electrode, and eventually precipitate in the form of metallic lithium, a process called "lithium precipitation". The precipitated metallic lithium tends to form sharp, tree-like crystals, namely "lithium dendrites". The growth of lithium dendrites will not only irreversibly consume active lithium ions and reduce battery capacity and life, but more seriously, they may pierce the diaphragm inside the battery, causing a direct short circuit between the positive and negative electrodes. This internal short circuit will instantly generate a lot of heat, which can easily cause thermal runaway, leading to serious safety accidents such as battery fire and explosion. Therefore, how to effectively inhibit the formation of lithium precipitation and lithium dendrites is the key content that fast charging technology needs to overcome. Summary of the invention

[0003] The embodiments of the present invention provide an electrolyte and a battery, which can effectively inhibit lithium deposition and the formation of lithium dendrites and improve 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 are replaced by F, an ethyl group in which 1 to 3 H are replaced by F, or a propyl group in which 1 to 3 H are replaced by F.

[0011] According to an 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 saturated hydrocarbon group having 1 to 10 carbon atoms, an olefin group having 2 to 10 carbon atoms, an alkyne group having 2 to 10 carbon atoms, and a halogenated saturated hydrocarbon group having 1 to 10 carbon atoms.

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

[0013]

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

[0015]

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

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

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

[0019] According to an embodiment of the present application, the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl 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 difluoro(oxalato)phosphate, lithium tetrafluoroborate, lithium tetrafluoro(oxalato)phosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole.

[0020] On the other hand, the present application provides a battery including the above electrolyte.

[0021] According to one embodiment of the present application, the battery also includes a positive electrode plate, a negative electrode plate and a separator, the positive electrode plate 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 implementation methods 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 implementation methods obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0024] The factors that affect the fast charging of batteries mainly include battery temperature, lithium precipitation, material pulverization, etc. Among them, lithium precipitation is an important factor affecting the fast charging performance of lithium-ion batteries. During lithium precipitation, metallic lithium often grows in a unique dendritic form (i.e., lithium dendrites). Lithium dendrites gradually accumulate on the surface of the negative electrode, which is like constantly piling up obstacles on the "road" for lithium ion transmission, making the path for lithium ion transmission inside the electrode longer and full of obstacles. What's more serious is that lithium dendrites may pierce the diaphragm, which is like creating a short circuit in the circuit, instantly causing the internal resistance of the battery to rise sharply. If the heat is not properly controlled, it may cause battery overheating, expansion and thermal runaway problems, 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 urgently solved in this field.

[0026] In view of this, an embodiment of the present invention provides an electrolyte, including: a first additive, the first additive including 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 groups, C2-C10 alkenyl groups, C2-C10 alkynyl groups, C1-C10 halogenated saturated hydrocarbon groups, C2-C10 halogenated alkenyl groups, and C2-C10 halogenated alkynyl groups.

[0029] The second additive, and the second additive includes a fluorosulfonyl compound having the structure shown in Formula 2:

[0030]

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

[0032] The first additive is a cage-like phosphate compound having a three-dimensional skeleton structure. There is a strong interaction between this compound and PF6. This interaction not only helps to dissociate the LiPF6 salt, but also can significantly improve the ionic conductivity in the electrolyte and promote the migration of lithium ions in the electrolyte. At the same time, the phosphorus-oxygen double bond in this compound has lone pair electrons and is a Lewis base, which can react on the surface of the battery cathode material to form a protective film, and the formed protective film can partially retain its three-dimensional rigid skeleton, increasing the porosity of the SEI film, thereby being beneficial to improving the fast charging performance.

[0033] However, when the first additive is used alone, under fast charging conditions, especially when the working voltage increases, the first additive is easily oxidized and its three-dimensional skeleton is damaged, resulting in changes in the composition of the interfacial film (such as the SEI film) and a decrease in the ion conduction performance. After multiple charges, lithium ions will precipitate and form lithium dendrites, ultimately affecting the fast charging performance. To solve this problem, the second additive is introduced. The second additive is a fluorosulfonyl compound having the structure shown in Formula 2 (such as fluorinated alkylsulfonylimide compounds). The N atom of this substance is connected to two adjacent -SO2R (such as -SO2F) groups, and since there is also a benzene ring connected to the N atom, the π electrons in the conjugated system can stabilize the formation of intermediates, effectively reducing the chemical reaction energy barrier. This makes the two S-N bonds more easily broken and can be preferentially oxidized before the compound of Formula 1 is oxidized, so that the three-dimensional skeleton structure of the compound of Formula 1 can be maintained. And when the benzene ring is replaced by other groups, such as a -CH3 with a smaller steric hindrance, the above effects cannot be achieved. More importantly, the SEI film formed by the two additives can effectively shrink the film pores and reduce the occurrence of side reactions; and the three P=O bonds evenly distributed on the film and a pair of lone pair electrons on N and Li +The weak interaction between them helps lithium ions form a stable four-coordination structure, thus promoting their rapid transmission inside the battery without precipitating in the form of lithium dendrites and ensuring the 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 existing in lithium-ion batteries during high-speed discharge, such as sharp increase in battery polarization, decrease in discharge platform, and decrease in discharge capacity, effectively reducing the impedance of lithium-ion batteries and improving the cycle stability and other performances 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, saturated hydrocarbon groups with 1 to 10 carbon atoms, olefin groups with 2 to 10 carbon atoms, alkyne groups with 2 to 10 carbon atoms, and halogenated saturated hydrocarbon groups with 1 to 10 carbon atoms, which is more conducive to synergistic cooperation with the second additive to improve the stability of interfacial films such as the formed SEI film, taking into account the improvement of the fast charging performance, cycle performance of the battery and the reduction of battery impedance.

[0036] In some embodiments, the first additive includes one or more of the following compounds of formula 1-1 to formula 1-8, which is conducive to further 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:

[0037]

[0038] In the embodiment of the present invention, the cyclic phosphate compound can be obtained by conventional methods, such as commercially available or self-made by conventional methods, and no special limitation is made thereto. Specifically, the CAS number of the compound shown in formula 1-1 is 62958-36-5, the CAS number of the compound shown in formula 1-2 is 51486-74-9, the CAS number of the compound shown in formula 1-3 is 60027-99-8, the CAS number of the compound shown in formula 1-4 is 3066478-04-1, the CAS number of the compound shown in formula 1-5 is 3066478-05-2, the CAS number of the compound shown in formula 1-6 is 3066478-06-3, the CAS number of the compound shown in formula 1-7 is 3059548-77-2, and the CAS number of the compound shown in 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 the fast charging performance and battery rate performance, and at the same time improve the high-temperature performance of the battery:

[0040]

[0041] In the embodiments of the present invention, the fluoro sulfonyl compound (the second additive) can be obtained by conventional methods, such as commercially available or self-made by conventional methods, and there is no special limitation on this. Specifically, the CAS number of the compound shown in Formula 2-1 is 1622206-83-0, and the CAS number of the compound shown in Formula 2-4 is 37595-74-7.

[0042] For further example, the compounds such as Formula 2-2, Formula 2-3, Formula 2-5 to Formula 2-8 can be prepared by referring to the preparation method of N-phenyl bis(trifluoromethanesulfonyl)imide in Scheme 3 of Patent CN115028557A with the corresponding fluoro sulfonyl raw materials. For example, the raw materials shown in the following Formula 3-1 (CAS number is 1401527-57-8), Formula 3-2 (1426573-49-0), Formula 3-3 (358-79-2), Formula 3-4 (CAS number is 1401527-61-4) can be respectively used to replace trifluoromethanesulfonyl fluoride in Scheme 3 of Patent CN115028557A to prepare the corresponding second additive.

[0043]

[0044] After further research, in the above electrolyte, the mass ratio of the first additive to the second additive can be 1:(0.05~3.5), such as 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 the range composed of any two of them. Preferably, it is 1:(0.2~2), which is beneficial to improving the fast charging performance, enhancing the cycle stability of the battery, and taking into account the improvement of the high-temperature performance of the battery.

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

[0046] After further research, in the above electrolyte, the mass percentage content of the second additive (that is, the ratio of the mass of the second additive to the total mass of the electrolyte) is 0.2%~3%, such as 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or the range composed of any two of them, which is beneficial to improving the fast charging performance, reducing the battery impedance, enhancing the cycle stability of the battery, and taking into account the improvement of the high-temperature performance of the battery.

[0047] In the embodiments 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 beneficial for adapting to the above-mentioned first additive and second additive, improving the fast charging performance, reducing the battery impedance, enhancing the cycle stability of the battery, and taking into account the improvement of the high-temperature performance of the battery.

[0049] Exemplarily, 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 the range composed of any two of them.

[0050] In some embodiments, in the above-mentioned electrolyte, the mass percentage content of the organic solvent (i.e., the ratio of the mass of the organic solvent to the total mass of the electrolyte) may be 60% - 95%, such as 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or the range composed of any two of them, which is beneficial for synergistically cooperating with the above-mentioned first additive, second additive, and film-forming additive, improving the fast charging performance, reducing the battery impedance, enhancing the cycle stability of the battery, and taking into account the improvement of 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(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide, which is beneficial for adapting to the above-mentioned first additive and second additive, improving the fast charging performance, reducing the battery impedance, enhancing 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 content of the electrolyte salt (i.e., the ratio of the mass of the electrolyte salt to the total mass of the electrolyte) may be 5% - 30%, such as 5%, 10%, 15%, 20%, 25%, 30%, or the range composed of any two of them, which is beneficial for synergistically cooperating with the above-mentioned first additive, second additive, and film-forming additive, improving the fast charging performance, reducing the battery impedance, enhancing the cycle stability of the battery, and taking into account the improvement of the high-temperature performance of the battery.

[0053] The embodiments of the present invention further provide a battery, which includes the above-mentioned electrolyte, and the battery has the corresponding advantages as the above-mentioned electrolyte, which will not be elaborated herein.

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

[0055] Generally, the battery includes a battery cell and a housing encapsulating the battery cell, an electrolyte is injected into the battery cell within the housing, and the battery cell includes a positive electrode sheet (or positive electrode plate), a negative electrode sheet (or negative electrode plate), and a separator located between the positive electrode sheet and the negative electrode sheet. Among them, the battery cell may be a wound battery cell, that is, after the positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked, they are wound to form a wound battery cell structure.

[0056] Specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating on at least one surface of the positive electrode current collector. Specifically, the positive electrode coating may be provided on one surface of the positive electrode current collector, or positive electrode coatings are respectively provided on opposite surfaces in the thickness direction of the positive electrode current collector. Among them, the positive electrode coating (positive electrode active material layer) includes a positive electrode active material, and the positive electrode active material includes a transition metal oxide of lithium.

[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 manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, and lithium-rich manganese-based material. The ternary positive electrode material includes lithium nickel cobalt manganese oxide (NCM), and 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 one or more of LiMn2O4, Li 1+a Mn 1-x M x O2, LiE 1-y M y O2, Li2Mn 1-b O4, wherein, Li 1+a Mn 1-x M x O2 and LiE 1-y M y O2, and E and M in LiE

[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-bOne 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 In PO4, each M is independently selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0 ≤ a < 0.2, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 ≤ b < 1.

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

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

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

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

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

[0065] The above nickel-cobalt-manganese ternary material (NCM) has a high specific capacity and can improve the performance of the battery such as capacity. However, there are still some problems with the NCM positive electrode. For example, the traditional carbonate-based electrolyte degrades on the surface of the delithiated cathode, resulting in problems such as the accumulation of by-products, lithium depletion, and the dissolution of transition metal (TM) ions. At the same time, it further consumes a large amount of electrolyte, the thickness of the SEI film further increases, resulting in a decrease in battery capacity and an increase in impedance. Especially during high-speed discharge, the battery polarization increases sharply, the discharge platform decreases, the discharge capacity decreases, and even safety problems occur. In the embodiments of the present invention, by using the electrolyte containing the above first additive and second additive, not only can the production of lithium deposition and lithium dendrites be inhibited, but also these problems can be effectively overcome, the battery impedance can be reduced, the fast charging performance of the battery can be improved, the high-rate charge and discharge requirements of the battery can be met, and at the same time, the cycle performance of the battery can be improved. In particular, the impedance change rate of the battery under high-temperature conditions can be reduced and the cycle life of the battery under high-temperature conditions can be improved, etc.

[0066] In addition, the positive electrode coating further includes a conductive agent and a binder, both of which can be conventional materials in the art. For example, the conductive agent can include one or more of conductive carbon black (Super P), carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder can 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, polyvinylpyrrolidone, polyurethane, etc.

[0067] Generally, in the positive electrode coating, the mass percentage content of the positive electrode active material can be 70% - 99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or the range composed of any two of them; the mass percentage content of the conductive agent can be 0.5% - 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them; the mass percentage content of the binder can be 0.5% - 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them.

[0068] In the embodiments of the present invention, a conventional positive electrode current collector in the art can be used. For example, the positive electrode current collector includes aluminum foil.

[0069] In the embodiments of the present invention, the positive electrode sheet can be prepared by a conventional method in the art. For example, it can be prepared by a coating method. Specifically, components for forming the positive electrode coating such as the positive electrode active material, conductive agent, and binder can be dispersed in a first solvent. The first solvent includes, for example, N-methylpyrrolidone (NMP) to prepare a positive electrode slurry, and then it is coated on the surface of the positive electrode current collector. After processes such as drying, rolling (cold pressing), trimming, slitting, and welding the tab, the positive electrode sheet is prepared.

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

[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 are not limited to, one or more of graphite, soft carbon, hard carbon, silicon, silicon oxides, silicon-carbon composites, and lithium titanate, etc.

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

[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, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, and sodium polyacrylate.

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

[0076] Generally, in the negative electrode coating, the mass percentage content of the negative electrode active material may be 70% - 98.5%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 98.5% or the range composed of any two of them; the mass percentage content of the conductive agent may be 0.5% - 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them; the mass percentage content of the binder may be 0.5% - 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them; the mass percentage content of the thickener may be 0.5% - 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them.

[0077] The embodiments 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 the embodiments of the present invention, the negative electrode sheet can be prepared by conventional methods in the art. For example, it can be prepared by a coating method. Specifically, components such as negative electrode active material, conductive agent, and binder for forming the negative electrode coating can be dispersed in a second solvent. The second solvent includes, for example, water, and specifically deionized water can be used. A negative electrode slurry is prepared, and then it is coated on the surface of the negative electrode current collector. After processes such as drying, rolling (cold pressing), trimming, slitting, and welding the tab, the negative electrode sheet is obtained.

[0079] In the embodiments of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from contacting and short - circuiting. The separator can be a separator known in the art that can be used in a battery and is stable to the electrolyte. For example, the separator can include one or more of polyolefin, aromatic polyamide, polytetrafluoroethylene, and polyethersulfone, and can be specifically set according to needs.

[0080] In the embodiments of the present invention, conventional housing materials in the art can be used to encapsulate the battery cell. The housing includes, for example, aluminum foil (outer packaging aluminum foil), but is not limited thereto.

[0081] The battery in the embodiments of the present invention can be prepared by conventional methods in the art. For example, after stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, it is wound into a wound battery cell (naked battery cell) through a winding process. Then, the wound battery cell is placed in a housing, vacuum - baked, and electrolyte is injected into it. Then, through processes such as vacuum packaging, standing, formation, aging, and grading, the battery is obtained. These steps / processes are all conventional operations in the art, and the present invention does not make special limitations on them and will not be elaborated further.

[0082] The present invention will be further introduced through specific embodiments below.

[0083] 1. Preparation of NCM positive electrode sheet

[0084] Mix LiNi 0.5 Co 0.2 Mn 0.3 O2 positive electrode material (NCM523), SuperP, and PVDF evenly at a mass ratio of 96.8:2:1.2, and stir in vacuum until the fluidity is uniform to obtain a positive electrode slurry;

[0085] Then, the positive electrode slurry is evenly coated on both the front and back surfaces of the aluminum foil, and is successively dried at 85 °C, cold - pressed, trimmed, sliced, slit, and vacuum - dried at 95 o °C for 12 hours to form positive electrode coatings on both the front and back surfaces of the aluminum foil respectively. After welding the tab, a positive electrode sheet is obtained; among them, the areal density of the positive electrode coating is 33 mg / cm 2 .

[0086] 2. Preparation of negative electrode sheet

[0087] Mix graphite, Super P, CMC, and SBR (styrene-butadiene rubber latex) evenly in a mass ratio of 95:1.5:1.5:2 to obtain the negative electrode slurry.

[0088] Coat the negative electrode slurry on both the front and back surfaces of the copper foil, dry it at 85 °C, and then perform cold pressing, edge trimming, slicing, and slitting. Then, dry it in a vacuum at 85 o °C for 12 hours to form negative electrode coatings on both the front and back surfaces of the copper foil. After welding the electrode tabs, negative electrode sheets are obtained. Among them, the surface density of the negative electrode coating is 20.1 mg / cm 2 .

[0089] 3. Preparation of Lithium-Ion Batteries

[0090] Stack the above-mentioned positive electrode sheets, separators, and negative electrode sheets in sequence, and then fabricate a bare cell (wound cell) with a theoretical capacity of 1700 mAh through a winding process. Place the bare cell in an outer packaging aluminum foil, vacuum bake it at 75 °C for 10 hours, inject the electrolyte, and then obtain the lithium-ion battery after processes such as vacuum packaging, standing, formation, aging, and grading.

[0091] Among them, the used electrolyte is composed of an organic solvent, LiPF6, a first additive (1,1,1-trimethylolpropane phosphate (Formula 1-1)), and a second additive (N-phenylbis(fluorosulfonyl)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 content of LiPF6 in the electrolyte is 12.5%, the mass percentage content of the first additive in the electrolyte is 1%, and the mass percentage content of the second additive in the electrolyte is 1%.

[0092] Examples 2 to 32, Comparative Examples 1 to 5: The differences from Example 1 lie in different conditions such as the type of the first additive, the mass percentage content w1 of the first additive in the electrolyte, the type of the second additive, and the mass percentage content w2 of the second additive in the electrolyte. Specifically, see Table 1. Except for the differences shown in Table 1, the other conditions are the same as those in Example 1.

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

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

[0095] Among them, the difference between Comparative Example 3 and Example 1 is that the electrolyte does not contain both additives.

[0096] Among them, 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] Among them, the difference between Comparative Example 5 and Example 1 is that the electrolyte does not contain the second additive, and the mass percentage content w1 of the first additive in the electrolyte is 2%.

[0098] Example 33: The difference from Example 1 lies in the different cathode materials. During the preparation of the cathode sheet, Example 33 uses lithium iron phosphate (LFP) to replace NCM523 to obtain an LFP cathode sheet. The preparation process of the LFP cathode sheet in Example 33 is as follows: Mix the cathode material (LFP), SuperP, CNT, and PVDF evenly according to a mass ratio of 94.5:1.5:1:3.0, and stir in vacuum until the fluidity is uniform to obtain the cathode slurry; then evenly coat the cathode slurry on both the front and back surfaces of the aluminum foil, and successively dry at 85 °C, cold press, trim the edges, cut into pieces, cut into strips, and o vacuum dry at 95 2 °C for 12 hours to form a cathode coating on both the front and back surfaces of the aluminum foil, and then obtain the cathode sheet after welding the electrode tabs; among them, the surface density of the cathode coating is 33 mg / cm

[0099] The difference between Comparative Example 6 and Example 33 is that the electrolyte does not contain the first additive, the mass percentage content w2 of the second additive in the electrolyte is 2%, and the remaining 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 content w1 of the first additive in the electrolyte is 2%, and the remaining conditions are the same as those in Example 33.

[0101] Test the battery performance of each example and comparative example respectively according to the following process, and the results are shown in Table 2; among them, the cathode materials of Examples 1 to 32 and Comparative Examples 1 to 5 are NCM523, and the voltage test range is 2.75 V to 4.2 V (that is, the upper charging cut-off voltage V T is 4.2 V, and the lower discharging cut-off voltage V L is 2.75 V); the cathode materials of Example 33, Comparative Example 6 and Comparative Example 7 are LFP, and the voltage test range is 2.5 V - 3.65 V (that is, the upper charging cut-off voltage V T is 3.65 V, and the lower discharging cut-off voltage V L is 2.5 V), and the remaining test steps of Examples 1 to 33 and Comparative Examples 1 to 7 are the same. The following takes the battery performance test process of Examples 1 to 32 and Comparative Examples 1 to 5 as an example for specific description.

[0102] (1) 25 o C Normal Temperature Cycling Test: Charge the lithium-ion battery at a constant current of 4.0 C to 4.2 V at 25 o °C, then charge at a constant voltage of 4.2 V until the cut-off current is 0.05 C, and then discharge the battery at a constant current of 1.0 C to 2.75 V. Repeat this cycle. Record the discharge capacity Q2 of the 300th cycle and the discharge capacity Q1 of the first cycle. Then, the capacity retention rate after 300 cycles at 25 °C = Q2 / Q1 × 100%. (2) 45 o C High Temperature Cycling Test: Charge the lithium-ion battery at a constant current of 4.0 C to 4.2 V at 45 o °C, then charge at a constant voltage of 4.2 V until the cut-off current is 0.05 C, and then discharge the battery at a constant current of 1.0 C to 2.75 V. Repeat this cycle and record the discharge capacity Q4 of the 300th cycle and the discharge capacity Q3 of the first cycle. Then, the capacity retention rate of the battery after 300 cycles at 45 °C = Q4 / Q3 × 100%.

[0103] (3) 60 o C High Temperature Storage for 30 Days Performance Test: Charge the lithium-ion battery at a constant current of 1.0 C to 4.2 V at 25 o °C, then charge at a constant voltage of 4.2 V until the cut-off current is 0.05 C, and then discharge the battery at a constant current of 1.0 C to 2.75 V. Record the discharge capacity as Q5. At 25 o °C, charge the battery at a constant current of 1.0 C to 4.2 V, then charge at a constant voltage of 4.2 V until the cut-off current is 0.05 C, and then transfer the battery to 60 o °C and leave it for 30 days. Then, discharge the battery at a constant current of 1.0 C to 2.75 V. Record the discharge capacity as Q6. Then, the capacity retention rate after storage at 60 o °C for 30 days = Q6 / Q5 × 100%.

[0104] (4) Initial DCIR Test: Charge the lithium-ion battery at a constant current of 1.0 C to 4.2 V at 25 o °C, then charge at a constant voltage of 4.2 V until the cut-off current is 0.05 C, and then discharge the battery at a constant current of 1.0 C for 30 min. After leaving it for 1 h, discharge it at a constant current of 2.0 C for 10 s. Calculate the DCIR impedance value at 50% SOC of the battery, which is the initial DCIR value.

[0105] (5) High Temperature DCIR Test: Charge the lithium-ion battery at a constant current of 1.0 C to 4.2 V at 25 o °C, then charge at a constant voltage of 4.2 V until the cut-off current is 0.05 C, and then discharge the battery at a constant current of 1.0 C for 30 min. After leaving it for 1 h, discharge it at a constant current of 2.0 C for 10 s. Calculate the DCIR at 50% SOC of the battery and record the value as D1. After completing 60o The battery for the 30-day storage test at high temperature of 30 °C, at 25 o °C, is charged at a constant current of 1.0 C to 4.2 V, charged at a constant voltage of 4.2 V until the cut-off current of 0.05 C, then discharged at a constant current of 1.0 C for 30 min. After standing for 1 h, it is discharged at a constant current of 2.0 C for 10 s, and the DCIR at 50% SOC of the battery is calculated, and the recorded value is D2. Then, for the battery stored at 60 o °C for 30 days, the impedance change rate = D2 / D1 * 100%.

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

[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] As can be seen from Table 2, compared with Comparative Examples 1 to 7, Examples 1 to 33 can take into account improving the room temperature ionic conductivity of the electrolyte, the capacity retention rate after 300 cycles at 25 °C with 4 C, the capacity retention rate after 300 cycles at 45 °C with 4 C, the capacity retention rate after storage at 60 °C for 30 days, the initial DCIR value, and the impedance change rate after storage at 60 °C for 30 days by adding the first additive with the structure of Formula 1 and the second additive with the structure of Formula 2 in the electrolyte at the same time. Thus, it can be shown that the solution of the present application realizes the improvement of the fast charging performance and can take into account improving the low impedance and high cycle life and other performances of the battery at high temperature.

[0112] Furthermore, compared with Examples 2 and 7, Examples 1, 4 to 6 can further improve the fast charging performance and take into account improving the low impedance and high cycle life and other performances of the battery at high temperature by further controlling the mass percentage content of the first additive in the electrolyte within the range of 0.1% to 4%.

[0113] Furthermore, compared with Examples 8 and 12, Examples 1, 9 to 11 can further improve the fast charging performance and take into account improving the low impedance and high cycle life and other performances of the battery at high temperature by further controlling the mass percentage content of the second additive in the electrolyte within the range of 0.2% to 3%.

[0114] Furthermore, compared with Embodiment 13 and Embodiment 14, in Embodiment 1, Embodiments 4 to 6, and Embodiments 9 to 11, by further controlling the mass ratio of the first additive and the second additive in the electrolyte within the range of 1:(0.05 to 3.5), it is beneficial to more significantly improve the fast charging performance, improve the high-temperature performance of the battery, while maintaining a relatively high room-temperature ionic conductivity and normal-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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, Comprising: A first additive, the first additive comprising a cyclic phosphate compound having the 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, a C1-C10 saturated hydrocarbon group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C1-C10 halogenated saturated hydrocarbon group, a C2-C10 halogenated alkenyl group, and a C2-C10 halogenated alkynyl group; A second additive, the second additive comprising a fluorosulfonyl compound having the 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 are replaced by F, an ethyl group in which 1 to 3 H are replaced by F, or a propyl group in which 1 to 3 H are replaced by F.

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

6. The electrolyte according to any one of claims 1-4, characterized in that, The mass ratio of the first additive to the second additive is 1:(0.05 to 3.5).

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

8. The electrolyte according to claim 7, 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 comprises a lithium salt, and the lithium salt comprises one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoroborate, lithium tetrafluoro(oxalato)phosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole.

9. A battery, characterized in that, Comprising the electrolyte according to any one of claims 1-8.

10. The battery according to claim 9, characterized in that, The battery further comprises a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises one or more of a ternary positive electrode material, lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel manganate, and a lithium-rich manganese-based material. The ternary positive electrode material comprises lithium nickel cobalt manganate, and the lithium nickel cobalt manganate comprises one or more of NCM811, NCM613, and NCM523.

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