Electrolyte composition comprising a fluorinated acyclic carbonate and a fluorinated cyclic carbonate

Abstract

Disclosed herein is an electrochemical cell comprising an anode, a cathode, and an electrolyte composition, wherein the anode comprises a combination of at least a carbon material and a silicon material as an anode active material, and the electrolyte composition comprises a solvent, 0.5 wt % to 70 wt % of a fluorinated acyclic carbonate compound based on the total weight of the electrolyte, 0.5 wt % to 10 wt % of a fluorinated cyclic carbonate compound based on the total weight of the electrolyte, and an electrolyte salt.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. 19213036.7, filed December 3, 2019, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to an electrolyte composition comprising a combination of a fluorinated acyclic carbonate compound and a fluorinated cyclic carbonate compound.

[0003] The electrolyte compositions are particularly useful in electrochemical cells such as lithium ion batteries that contain silicon and its derivatives as the anode material. [Background technology]

[0004] Lithium-ion batteries have been the dominant battery technology in recent years because they exhibit not only high power density but also efficient and high energy storage, and therefore dominate the market for batteries used in portable electronic devices. However, next-generation large-scale applications such as power storage devices and electric vehicles still require further improvements over existing technologies in terms of energy density, power supply, and cycle life.

[0005] The use of silicon as an anode material for lithium-ion batteries has attracted significant attention due to its high theoretical specific capacity (3580 mAh / g, nearly 10 times that of typical graphite anode materials (372 mAh / g)), reasonable lithium intercalation voltage, and cost-effectiveness. One of the drawbacks of silicon as an anode material is its large volume expansion (over 300%) during repeated cycling, which causes cracking and pulverization of silicon particles, resulting in slow kinetics and poor cycle life due to loss of active material and poor electrical contact.

[0006] By using silicon mixed with other elements, a composite material is provided that exhibits a lower anode capacity value than when using high-purity silicon alone, which shows a better capacity retention rate as well as a good cycle life. Representative silicon composite materials are silicon-carbon (Si / C) and silicon oxide-carbon (SiO / C, where 0 < a < 2). Carbon can be regarded as a diluent / buffer that alleviates the overall volume expansion of the silicon composite material. This solution has received very favorable reviews among researchers and battery manufacturers.

[0007] The use of fluoroethylene carbonate (FEC) as an electrolyte component introduced into a carbon-coated porous Si anode has been reported by Myung-Jin Chun, Hyungmin Park, Soojin Park and Nam-Soon Choi, RSC Adv., 2013, 3, 21320. The repeated performance at temperatures of 30 °C and 60 °C was improved. However, FEC decomposes more rapidly at temperatures above ambient temperature. Thus, firstly, the addition of FEC is not efficient enough to improve the repetition of high-temperature cycles. Thus, secondly, when FEC decomposes, gas is generated, which can cause expansion problems.

[0008] Therefore, it is highly desirable to provide an electrolyte composition that improves the cycle performance of a lithium-ion battery, particularly a lithium-ion battery containing a silicon-carbon composite as an anode material. The technical requirement is that the improvement of the cycle performance at high temperature (typically 45 °C) continues while maintaining the cycle performance at ambient temperature (typically 25 °C). Summary of the Invention

[0009] One subject of the present invention is an electrochemical cell comprising an anode, a cathode, and an electrolyte composition, wherein the anode comprises at least a combination of a carbon material and a silicon material as an anode active material, and the electrolyte composition comprises - a solvent, - based on the total weight of the electrolyte, the general formula R1 -OCOO-R 2 (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group), and - 0.5 wt% to 10 wt% of a fluorinated cyclic carbonate compound based on the total weight of the electrolyte; - Electrolyte salts and Includes:

[0010] In another aspect, an electronic device, a transport device, or a telecommunications device is disclosed that includes an electrochemical cell as defined above.

[0011] Furthermore, another subject of the present invention is a method for improving the high temperature cycling performance of an electrochemical cell comprising a combination of at least a carbon material and a silicon material as an anode active material, - Based on the total weight of the electrolyte, the general formula R 1 -OCOO-R 2 (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group), and - 0.5% by weight to 10% by weight of a fluorinated cyclic carbonate compound based on the total weight of the electrolyte as an additive in an electrolyte composition. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows the cycling performance (discharge capacity and capacity retention) of cells containing the electrolyte formulations of the examples at room temperature (25° C.). [Figure 2] 1 shows the cycling performance (discharge capacity and capacity retention) of cells containing example electrolyte formulations at high temperature (45° C.). [Figure 3]1 shows the capacity retention and capacity recovery of a cell according to an example after storage at 60° C. DETAILED DESCRIPTION OF THE INVENTION

[0013] The term "alkyl group," as used herein, unless otherwise specified, means a linear or branched, straight-chain or cyclic hydrocarbon group containing 1 to 20 carbons, preferably 1 to 6 carbons, and more preferably 1 to 4 carbons, and containing no unsaturation. Examples of straight-chain alkyl radicals include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl. Examples of branched-chain isomers of straight-chain alkyl groups include isopropyl, isobutyl, tert-butyl, sec-butyl, isopentyl, neopentyl, isohexyl, neohexyl, and isooctyl. Examples of cyclic alkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.

[0014] As used herein, unless otherwise specified, the term "fluoroalkyl group" means an alkyl group in which at least one hydrogen has been replaced by fluorine.

[0015] As used herein, unless otherwise specified, the term "alkenyl group" refers to a linear or branched, straight-chain or cyclic group as described for an alkyl group as defined herein, except that at least one double bond exists between two carbon atoms. Examples of alkenyl groups include vinyl, cyclohexenyl, cyclopentenyl, cyclohexadienyl, and butadienyl.

[0016] As used herein, unless otherwise specified, the term "alkynyl group" means a linear or branched, straight-chain or cyclic group as described for an alkyl group as defined herein, except that at least one triple bond exists between two carbon atoms.

[0017] Unless otherwise specified, all percentages are by weight and are based on the total weight of the electrolyte composition.

[0018] The equilibrium potential between lithium and lithium ions is the potential of a reference electrode using lithium metal in contact with an electrolyte composition containing a lithium salt at a concentration sufficient to provide a lithium ion concentration of about 1 mole / liter, and is determined by the equation: + ) is passed through. Such a current is small enough that it does not significantly change the + The potential of the reference electrode is assigned a value of 0.0 V here. The potential of the anode or cathode is the potential of the anode or cathode and the potential of the Li / Li + The voltage refers to the potential difference between the cathode and anode of a cell, neither of whose electrodes can be operated at a potential of 0.0 V.

[0019] As used herein, the term "SEI" refers to a solid electrolyte interfacial layer formed on the active materials of an electrode. Lithium-ion secondary electrochemical cells are assembled in an uncharged state and must be charged for use (a process called formation). During the first few charging events (cell formation) of a lithium-ion secondary electrochemical cell, electrolyte components are reduced or otherwise decomposed or incorporated on the surface of the negative electrode active material and oxidized or otherwise decomposed or incorporated on the surface of the positive electrode active material, electrochemically forming a solid electrolyte interface on the active materials. These electrically insulating but ionically conductive layers help prevent electrolyte decomposition and can extend cycle life and improve battery performance. On the anode, the SEI can inhibit reductive decomposition of the electrolyte, and on the cathode, the SEI can inhibit oxidation of the electrolyte components.

[0020] One subject of the present invention is an electrochemical cell comprising an anode, a cathode, and an electrolyte composition.

[0021] The term "electrochemical cell" refers to a basic functional unit that is a power source obtained by the direct conversion of chemical energy. Typically, an electrochemical cell can include or consist of a housing, an anode and a cathode disposed within the housing and in ionically conductive contact with each other, an electrolyte composition disposed within the housing and providing an ionically conductive pathway between the anode and the cathode, and a porous separator between the anode and the cathode.

[0022] In a preferred embodiment, the electrochemical cell is a lithium ion battery.

[0023] The term "lithium-ion battery" refers to a type of rechargeable battery in which lithium ions move from the anode to the cathode during discharge and from the cathode to the anode during charge.

[0024] The housing may be any suitable container for containing the electrochemical cell components. Housing materials are well known in the art and may include, for example, metal and polymer housings. The shape of the housing is not particularly important, although suitable housings may be fabricated in the shape of a cylinder, a prismatic case, or a pouch.

[0025] The porous separator helps prevent short circuits between the anode and cathode. Porous separators typically consist of single- or multi-layer sheets of microporous materials such as polyethylene, polypropylene, polyamide, polyimide, glass fiber, nonwoven cellulosic, or combinations thereof. The porous system may be coated with a ceramic or polymer layer. The pore size of the porous separator is large enough to allow ion transport and provide ionically conductive contact between the anode and cathode, but small enough to prevent contact between the anode and cathode, either directly or through particle penetration, or dendrites that may form on the anode and cathode.

[0026] The term "anode" means the electrode of an electrochemical cell where oxidation occurs. In a secondary (i.e., rechargeable) battery, the anode is the electrode where oxidation occurs during discharge and reduction occurs during charging.

[0027] According to the present invention, the anode contains at least a combination of a carbon material and a silicon material as an anode active material.

[0028] The carbon material (denoted as "C") is preferably one that can absorb and desorb lithium ions. The carbon material can be selected from the group consisting of graphite, amorphous carbon, carbon such as diamond, carbon nanotubes or their composites. Materials typically commercialized for anodes are mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MCF), vapor-grown carbon fibers (VGCF), and massive artificial graphite (MAG). The carbon material can preferably consist of 2 wt% to 99 wt%, more preferably 2 wt% to 97 wt% of the anode active material. The carbon material can consist of any of 2 wt% to 30 wt%, or 30 wt% to 50 wt%, or 50 wt% to 97 wt% of the anode active material.

[0029] The silicon material is preferably one that can absorb and desorb lithium ions and / or can form an alloy with lithium. The silicon material can be silicon metal (denoted as "Si") or silicon oxide (denoted as "SiO a " where 0 < a < 2), or a mixture thereof. Silicon metal Si can preferably consist of 3 wt% to 90 wt%, more preferably 3 wt% to 50 wt% of the anode active material. Silicon metal Si can consist of any of 3 wt% to 20 wt%, or 20 wt% to 50 wt%, or 50 wt% to 90 wt% of the anode active material. Silicon oxide SiO a (0 < a < 2) can preferably consist of 3 wt% to 90 wt%, more preferably 3 wt% to 50 wt% of the anode active material. Silicon oxide SiO a can consist of any of 3 wt% to 40 wt%, or 40 wt% to 70 wt%, or 70 wt% to 90 wt% of the anode active material.

[0030] The anode can be a composite material selected from Si / C, SiO a / C, and Si / SiO a / C (0 < a < 2).

[0031] A method for manufacturing such a composite material is based on mixing individual components (such as C and Si and / or SiO a , or precursors of the desired matrix material) during the preparation of the electrode paste formulation, or by dry grinding / mixing at least a carbon material and a silicon material (followed by a firing step that may be present), or by wet grinding / mixing at least a carbon material and a silicon material (followed by removal of the liquid medium and a firing step that may be present), or by a separate composite manufacturing process further implemented by wet grinding / mixing at least a carbon material and a silicon material (followed by removal of the liquid medium and a firing step that may be present).

[0032] In addition to the anode active material described above, an anode active material composition in which a binder and a solvent are mixed therein can be prepared. Water can be used as the solvent. Carboxymethyl cellulose (CMC), butadiene styrene rubber (SBR), acrylate, and methacrylate copolymer can be used as the binder. The anode active material composition can further contain a conductive agent and / or a filler. Carbon black, acetylene black, and graphite can be used as the conductive agent and / or the filler. For example, 94% by weight of the anode active material containing the Si / C composite material, 3% by weight of the binder, and 3% by weight of the conductive agent can be mixed in powder form, and water is added as the solvent to prepare a slurry having a solid content of 70% by weight. Next, the slurry can be coated on the anode current collector, dried, and pressed to produce an anode electrode plate.

[0033] The anode can be fabricated by forming an anode active material layer containing an anode active material and an anode binder on an anode current collector. The anode current collector is not particularly limited, as long as it does not cause chemical changes in the battery and has high electrical conductivity. For example, the anode current collector can be formed from copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper, stainless steel surface-treated with carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy. Examples of shapes include foil, flat plate, and mesh. The anode electrode current collector typically has a thickness of about 3 μm to about 500 μm. Examples of methods for forming the anode active material layer include doctor blade, die coater, CVD, and sputtering. The anode active material layer can then be dried and pressed to obtain the anode component of the device.

[0034] The term "cathode" means the electrode of an electrochemical cell at which reduction occurs. In secondary (i.e., rechargeable) batteries, the cathode is the electrode at which reduction occurs during discharge and oxidation occurs during charge.

[0035] In some embodiments, the cathode is, for example, LiCoO2, LiNiO2, LiMn2O4, LiCo 0,2 Ni 0,2 O2, LiV3O8, LiNi 0,5 Mn 1,5 O4, LiFePO4, LiMnPO4, LiCoPO4, LiVPO4F, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi a Co b Mn cIt may include a cathode active material containing lithium and a transition metal such as O2 (where a + b + c = 1).

[0036] In other embodiments, examples of the cathode active material include Li a A 1-b ,R b D2 (where 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); Li a CoG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Ni 1-b-c Co b R c O 2-d Z d (where 0.9 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.05, and 0 ≤ d ≤ 0.05); Li 1+z Ni 1-x-y Co x Al y O2 (where 0 < x < 0.3, 0 < y < 0.1, and 0 < z < 0.06); Li a Ni b Mn c Co d ​​​​​​​​​​​​In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, Zr, Ti, a rare earth element, or a combination thereof; and Z is F, S, P, or a combination thereof.

[0038] "Rare earth elements" means the lanthanide elements La to Lu, as well as Y and Sc.

[0039] In another embodiment, the cathode active material is a material that exhibits a capacity greater than 120 mAh / g at an operating voltage in the range of 3.0V to 4.2V.

[0040] A cathode having a cathode active material contained therein can be prepared by mixing an effective amount, for example, about 70 weight percent to about 97 weight percent, of the cathode active material with a polymer binder, such as polyvinylidene difluoride (PVdF), in a suitable solvent, such as N-methylpyrrolidone (NMP), and conductive carbon to form a paste, which is then coated onto a current collector, such as aluminum foil, and dried to form the cathode. The weight percentages are based on the total weight of the cathode.

[0041] The electrochemical cell according to the present invention further comprises an electrolyte composition. The term "electrolyte composition" as used herein means a chemical composition capable of providing an electrolyte in an electrochemical cell. The electrolytic cell of the present invention comprises at least a solvent, an electrolyte salt, and - Based on the total weight of the electrolyte, the general formula R 1 -OCOO-R 2 (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group), and - The electrolyte contains a combination of 0.5 wt % to 10 wt % of a fluorinated cyclic carbonate compound based on the total weight of the electrolyte.

[0042] The electrolyte composition according to the present invention comprises a fluorinated acyclic carbonate. Suitable fluorinated acyclic carbonates include those having the formula: R 1 -OCOO-R 2 (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group).

[0043] In one embodiment, R 1 contains 1 carbon atom. In another embodiment, R 1 contains 2 carbon atoms. In another embodiment, R 1 and R 2 is as defined hereinabove, and R 1 and R 2 as a set, contain at least 2 carbon atoms but not more than 7 carbon atoms and further contain at least 2 fluorine atoms, with the proviso that R 1 MoR 2 provided that the aryl group does not contain any FCH2- or -FCH- groups.

[0044] Examples of suitable fluorinated acyclic carbonates include, but are not limited to, CH3-OC(O)O-CH2CF2H (methyl 2,2-difluoroethyl carbonate, CAS No. 916678-13-2), CH3-OC(O)O-CH2CF3 (methyl 2,2,2-trifluoroethyl carbonate, CAS No. 156783-95-8), CH3-OC(O)O-CH2CF2CF2H (methyl 2,2,3,3-tetrafluoropropyl carbonate, CAS No. 156783-98-1), CH3CH2-OCOO-CH2CF2H (ethyl 2,2-difluoroethyl carbonate, CAS No. 916678-14-3), and CH3CH2-OCOO-CH2CF3 (ethyl 2,2,2-trifluoroethyl carbonate, CAS No. 156783-96-9).

[0045] The electrolyte composition according to the present invention may contain one fluorinated acyclic carbonate as defined above, or a mixture of two or more fluorinated carbonates.

[0046] Fluorinated acyclic carbonates suitable for use herein can be prepared using known methods. For example, methyl chloroformate can be reacted with 2,2-difluoroethanol to form methyl 2,2-difluoroethyl carbonate. Alternatively, some of these fluorinated solvents can be purchased from companies such as Matrix Scientific (Columbia, SC). For best results, it is desirable to purify the fluorinated acyclic carbonates to a purity level of at least about 99.9%, more particularly at least about 99.99%. These fluorinated solvents can be purified using distillation methods such as vacuum distillation or spinning band distillation.

[0047] The content of the fluorinated acyclic carbonate compound is 0.5 wt % to 70 wt % based on the total weight of the electrolyte. In one embodiment, the content of the fluorinated acyclic carbonate compound is 10 wt % to 70 wt %, preferably 15 wt % to 60 wt %, and more preferably 20 wt % to 50 wt %, based on the total weight of the electrolyte. However, lower amounts of the fluorinated acyclic carbonate compound are believed to be advantageous. In another embodiment, the content of the fluorinated acyclic carbonate compound is 0.5 wt % to 10 wt % based on the total weight of the electrolyte. Preferably, the content of the fluorinated acyclic carbonate is strictly less than 10%. More preferably, the content of the fluorinated acyclic carbonate is 1 wt % to 9 wt %, and even more preferably 2 wt % to 5 wt %.

[0048] The electrolyte composition according to the present invention includes a fluorinated cyclic carbonate. The fluorinated cyclic carbonate may be selected from the group consisting of 4-fluoroethylene carbonate, 4,5-difluoro-1,3-dioxolan-2-one, 4,5-difluoro-4-methyl-1,3-dioxolan-2-one, 4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, tetrafluoroethylene carbonate, or a mixture thereof. 4-Fluoroethylene carbonate is also known as 4-fluoro-1,3-dioxolan-2-one or fluoroethylene carbonate. Preferably, the fluorinated cyclic carbonate may be selected from the group consisting of 4-fluoroethylene carbonate; 4,5-difluoro-1,3-dioxolan-2-one; and a mixture thereof. In one preferred embodiment, the fluorinated cyclic carbonate compound is fluoroethylene carbonate.

[0049] It is desirable to use fluorinated cyclic carbonates that are battery grade or have a purity level of at least about 99.9%, more particularly at least about 99.99%. Such fluorinated cyclic carbonates are typically commercially available.

[0050] The content of the fluorinated cyclic carbonate compound is 0.5% to 10% by weight based on the total weight of the electrolyte. Preferably, the content of the fluorinated cyclic carbonate is strictly less than 10%. More preferably, the content of the fluorinated cyclic carbonate is 1% to 9% by weight, and even more preferably, 2% to 5% by weight.

[0051] The solvent in the electrolyte composition according to the present invention may be any suitable solvent typically used in this technical field. Preferably, the solvent may further comprise one or more organic carbonates, which may be fluorinated or non-fluorinated, linear or cyclic. Obviously, the components of the solvent may be different from the fluorinated acyclic carbonate compounds and fluorinated cyclic carbonate compounds defined herein as additives of the electrolyte composition according to the present invention.

[0052] Suitable non-fluorinated cyclic organic carbonates can include, for example: ethylene carbonate (also known as 1,3-dioxalane-2-one); propylene carbonate; vinylene carbonate; ethyl propyl vinylene carbonate; vinyl ethylene carbonate; dimethyl vinylene carbonate.

[0053] Suitable non-fluorinated acyclic organic carbonates may include, for example: ethyl methyl carbonate; dimethyl carbonate; diethyl carbonate; di-tert-butyl carbonate; dipropyl carbonate; methyl propyl carbonate; methyl butyl carbonate; ethyl butyl carbonate; propyl butyl carbonate; and dibutyl carbonate.

[0054] Suitable fluorinated acyclic organic carbonates can include, for example: bis(2,2,3,3-tetrafluoropropyl)carbonate; bis(2,2,2-trifluoroethyl)carbonate; bis(2,2-difluoroethyl)carbonate; 2,3,3-trifluoroallylmethyl carbonate; or mixtures thereof.

[0055] It is desirable to use carbonates that are battery grade or have a purity level of at least about 99.9%, for example at least about 99.99%. Organic carbonates are commercially available or may be prepared by methods known in the art.

[0056] In a preferred embodiment, the solvent of the electrolyte composition comprises a non-fluorinated cyclic carbonate, which may be preferably selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof. In one embodiment, the cyclic carbonate comprises ethylene carbonate. In one embodiment, the cyclic carbonate comprises propylene carbonate. The content of the non-fluorinated cyclic carbonate may be 5% to 95% by volume, preferably 8% to 50% by volume, and more preferably 10% to 30% by volume, based on the total volume of the solvent.

[0057] In another preferred embodiment, the solvent of the electrolyte composition contains a non-fluorinated acyclic carbonate, which may be preferably selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and mixtures thereof. The content of the non-fluorinated acyclic carbonate may be 5% to 95% by volume, preferably 50% to 92% by volume, and more preferably 70% to 90% by volume, based on the total volume of the solvent.

[0058] In another preferred embodiment, the solvent of the electrolyte composition comprises at least one non-fluorinated cyclic carbonate and at least one non-fluorinated acyclic carbonate, such as ethylene carbonate / ethyl methyl carbonate, ethylene carbonate / dimethyl carbonate, ethylene carbonate / diethyl carbonate, ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate, ethylene carbonate / ethyl methyl carbonate / diethyl carbonate, propylene carbonate / ethyl methyl carbonate, propylene carbonate / dimethyl carbonate, propylene carbonate / diethyl carbonate, propylene carbonate / ethyl methyl carbonate / dimethyl carbonate, propylene carbonate / ethyl methyl carbonate / diethyl carbonate.

[0059] In another embodiment, the solvent of the electrolyte composition comprises at least one non-fluorinated acyclic carbonate, such as ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, and mixtures thereof.

[0060] In another embodiment, the solvent of the electrolyte composition comprises at least one fluorinated acyclic ester, such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 2,2-difluoroethyl propionate, 3,3-difluoropropyl acetate, 3,3-difluoropropyl propionate, and mixtures thereof.

[0061] As used herein, the term "electrolyte salt" means an ionic salt that is at least partially soluble in the solvent of the electrolyte composition and that at least partially dissociates into ions in the solvent of the electrolyte composition to form a conductive electrolyte composition.

[0062] The electrolyte composition according to the present invention also includes an electrolyte salt. Suitable electrolyte salts include, but are not limited to: - lithium hexafluorophosphate (LiPF6), - lithium difluorophosphate (LiPO2F2), - lithium bis(trifluoromethyl)tetrafluorophosphate (LiPF4(CF3)2), - lithium bis(pentafluoroethyl)tetrafluorophosphate (LiPF4(C2F5)2), - lithium tris(pentafluoroethyl)trifluorophosphate (LiPF3(C2F5)3), - lithium bis(trifluoromethanesulfonyl)imide, - lithium bis(fluorosulfonyl)imide, - lithium bis(perfluoroethanesulfonyl)imide, - lithium (fluorosulfonyl) (nonafluorobutanesulfonyl) imide, - lithium tetrafluoroborate, - Lithium perchlorate, - lithium hexafluoroarsenate, - lithium trifluoromethanesulfonate, - lithium tris(trifluoromethanesulfonyl)methide, - lithium bis(oxalato)borate, - lithium difluoro(oxalato)borate, - lithium difluorobis(oxalato)phosphate, - Li2B 12 F 12-x H x (x is equal to 0-8), - Lithium fluoride mixed with an anion acceptor such as B(OC6F5)3 Examples include:

[0063] Mixtures of two or more of these or equivalent electrolyte salts can also be used. According to a preferred embodiment, the electrolyte salt includes lithium hexafluorophosphate (LiPF6). Alternatively, the electrolyte salt includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Alternatively, the electrolyte salt includes lithium bis(fluorosulfonyl)imide (LiFSI). The electrolyte salt can be present in the electrolyte composition in an amount of about 0.2 M to about 2.0 M, for example, about 0.3 M to about 1.7 M, or for example, about 0.5 M to about 1.2 M, or for example, 0.5 M to about 1.7 M.

[0064] Optionally, the electrolyte compositions described herein may further include additives such as lithium boron compounds, cyclic sultones, cyclic sulfates, cyclic carboxylic acid anhydrides, or combinations thereof.

[0065] In some embodiments, the electrolyte composition further comprises a lithium boron compound. Suitable lithium boron compounds include lithium terafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, other lithium boron salts, LiB 12 F 12-x H x(x is 0 to 8), a mixture of lithium fluoride and an anion receptor such as B(OC6F5)3, or a mixture thereof. According to a preferred embodiment, the electrolyte composition of the present invention additionally contains at least one lithium borate salt selected from lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, or a mixture thereof, preferably lithium bis(oxalato)borate. The lithium borate compound may be present in the electrolyte composition in a range of 0.1 to about 10 wt %, for example, 0.1 to about 5.0 wt %, or 0.3 to about 4.0 wt %, or 0.5 to 2.0 wt %, based on the total weight of the electrolyte composition. Lithium boron compounds can be commercially available or obtained by methods known in the art.

[0066] In some embodiments, the electrolyte composition further comprises a cyclic sultone. Suitable sultones include those having the formula: [ka]

[0023] In the formula:

[0024] , each A is independently hydrogen, fluorine, or an optionally fluorinated alkyl, vinyl, allyl, acetylene, or propargyl group. The vinyl (HC=CH-), allyl (HC=CH-CH-), acetylene (HC≡C-), or propargyl (HC≡C-CH-) group may each be unsubstituted, partially, or fully fluorinated. Each A may be the same or different from one or more of the other A groups, and two or three of the A groups may together form a ring. Mixtures of two or more sultones may also be used. Suitable sultones include 1,3-propane sultone, 1,3-propene sultone, 3-fluoro-1,3-propane sultone, 4-fluoro-1,3-propane sultone, 5-fluoro-1,3-propane sultone, and 1,8-naphthalene sultone. In a preferred embodiment, the sultone comprises 1,3-propane sultone, 1,3-propene sultone or 3-fluoro-1,3-propane sultone, preferably 1,3-propane sultone or 1,3-propene sultone.

[0067] In one embodiment, the sultone is present at about 0.01% to about 10% by weight, or about 0.1% to about 5% by weight, or about 0.5% to about 3% by weight, or about 1% to about 3% by weight, or about 1.5% to about 2.5% by weight, or about 2% by weight of the total electrolyte composition.

[0068] In some embodiments, the electrolyte composition further comprises a cyclic sulfate. Suitable cyclic sulfates include those represented by the formula: [ka] wherein each B is independently hydrogen or an optionally fluorinated vinyl, allyl, acetylenic, propargyl, or C1-C3 alkyl group. The vinyl (HC=CH-), allyl (HC=CH-CH-), acetylenic (HC≡C-), propargyl (HC≡C-CH-), or C1-C3 alkyl group may each be unsubstituted, partially, or fully fluorinated. Mixtures of two or more cyclic sulfates may also be used. Suitable cyclic sulfates include ethylene sulfate (1,3,2-dioxathiolane-2,2-dioxide), 1,3,2-dioxathiolane-4-ethynyl-2,2-dioxide, 1,3,2-dioxathiolane-4-ethenyl-2,2-dioxide, 1,3,2-dioxathiolane-4,5-diethenyl-2,2-dioxide, 1,3,2-dioxathiolane-4-methyl-2,2-dioxide, and 1,3,2-dioxathiolane-4,5-dimethyl-2,2-dioxide. In a preferred embodiment, the cyclic sulfate is ethylene sulfate.

[0069] In one embodiment, the cyclic sulfate is present at about 0.1 wt % to about 12 wt %, or about 0.5 wt % to less than about 10 wt %, or about 0.5 wt % to less than about 5 wt %, or about 0.5 wt % to about 3 wt %, or about 0.5 wt % to about 2 wt %, or about 2 wt % to about 3 wt % of the total electrolyte composition. In one embodiment, the cyclic sulfate is present at about 1 wt % to about 3 wt %, or about 1.5 wt % to about 2.5 wt %, or about 2 wt % of the total electrolyte composition.

[0070] In some embodiments, the electrolyte composition further comprises a cyclic carboxylic acid anhydride. Suitable cyclic carboxylic acid anhydrides include those represented by formulas (IV) to (XI): [ka] (In the formula, R 7 ~R 14 are each independently a straight or branched C1-C alkyl group optionally substituted with H, F, alkoxy, and / or thioalkyl substituents;10 Alkyl radical, straight or branched chain, C2-C 10 Alkenyl radical, or C6-C 10 The alkoxy substituent can have 1 to 10 carbons and can be straight or branched chain; examples of alkoxy substituents include -OCH3, -OCH2CH3, and -OCH2CH2CH3. The thioalkyl substituent can have 1 to 10 carbons and can be straight or branched chain; examples of thioalkyl substituents include -SCH3, -SCH2CH3, and SCH2CH2CH3. Examples of suitable cyclic carboxylic acid anhydrides include maleic anhydride, succinic anhydride, glutaric anhydride, 2,3-dimethylmaleic anhydride, citraconic anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride, 2,3-diphenylmaleic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 2,3-dihydro-1,4-dithiono-[2,3-c]furan-5,7-dione, and phenylmaleic anhydride. Mixtures of two or more of these cyclic carboxylic acid anhydrides can also be used. In a preferred embodiment, the cyclic carboxylic acid anhydride comprises maleic anhydride. In one embodiment, the cyclic carboxylic acid anhydride comprises maleic anhydride, succinic anhydride, glutaric anhydride, 2,3-dimethylmaleic anhydride, citraconic anhydride, or a mixture thereof. The cyclic carboxylic acid anhydrides can be obtained from specialty chemical companies such as Sigma-Aldrich, Inc. (Milwaukee, WI) or can be prepared using methods known in the art. It is desirable to purify the cyclic carboxylic acid anhydrides to a purity level of at least about 99.0%, for example, at least about 99.9%. Purification can be carried out using methods known in the art.

[0071] In some embodiments, the electrolyte composition comprises from about 0.1% to about 5% by weight of the cyclic carboxylic acid anhydride, based on the total weight of the electrolyte composition.

[0072] In some embodiments, the electrolyte composition, optionally, can further include additives known to those skilled in the art to be useful in conventional electrolyte compositions, particularly for use in lithium-ion batteries. For example, the electrolyte compositions disclosed herein can also include a gas-reducing additive that is useful for reducing the amount of gas generated during charging and discharging of lithium-ion batteries. The gas-reducing additive can be used in any effective amount, but can be present in an amount that accounts for about 0.05% to about 10% by weight of the electrolyte composition, preferably about 0.05% to about 5% by weight, and more preferably about 0.5% to about 2% by weight.

[0073] Suitable gas reducing additives known in the art include, for example: halobenzenes such as fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, or haloalkylbenzenes; 1,3-propane sultone; succinic anhydride; ethynylsulfonylbenzene; 2-sulfobenzoic cyclic anhydride; divinyl sulfone; triphenyl phosphate (TPP); diphenyl monobutyl phosphate (DMP); gamma-butyrolactone; 2,3-dichloro-1,4-naphthoquinone; 1,2-naphthoquinone; 2,3-dibromo-1,4-naphthoquinone; 3-bromo-1,2-naphthoquinone; Quinones; 2-acetylfuran; 2-acetyl-5-methylfuran; 2-methylimidazole 1-(phenylsulfonyl)pyrrole; 2,3-benzofuran; Fluoro-cyclotriphosphazenes such as 2,4,6-trifluoro-2-phenoxy-4,6-dipropoxy-cyclotriphosphazene and 2,4,6-trifluoro-2-(3-(trifluoromethyl)phenoxy)-6-ethoxy-cyclotriphosphazene; Benzotriazole; Perfluoroethylene carbonate; Anisole; Diethylphosphonate; 2-Trifluoromethyldiphosphazene Fluoroalkyl-substituted dioxolanes such as dioxolane and 2,2-bistrifluoromethyl-1,3-dioxolane;Trimethylene borate;Dihydro-3-hydroxy-4,5,5-trimethyl-2(3H)-furanone;Dihydro-2-methoxy-5,5-dimethyl-3(2H)-furanone;Dihydro-5,5-dimethyl-2,3-furandione;Propene sultone;Diglycolic anhydride;Di-2-propynyl oxalate;4-Hydroxy-3-pentenoic acid gamma-lactone;CF3COOCH2C(CH3)(CH2OCOCF3)2;CF3COO CH2CF2CF2CF2CF2CH2OCOCF3;α-Methylene-γ-butyrolactone;3-Methyl-2(5H)-furanone;5,6-Dihydro-2-pyranone;Diethylene glycol diacetate;Triethylene glycol dimethacrylate;Triglycol diacetate;1,2-Ethanedisulfonic anhydride;1,3-Propanedisulfonic anhydride;2,2,7,7-Tetraoxido-1,2,7-oxadithiepane;3-Methyl-2,2,5,5-tetraoxido-1,2,5-oxadithiolane;Hexamethoxycyclotriphosphazene;4,5-Dimethyl-4,5-difluoro-1,3-dioxolan-2-one;2-Ethoxy-2,4,4,6,6-pentafluoro-2,2,4,4,6,6-hexahydro-1,3,5,2,4,6-triazatriphosphorine;2,2,4,4,6-Pentafluoro-2,2,4,4,6,6-hexahydro-6-methoxy-1,3,5,2,4,6-triazatriphosphorine;4,5-Difluoro- 1,3-Dioxolan-2-one; 1,4-bis(ethenylsulfonyl)-butane; bis(vinylsulfonyl)-methane; 1,3-bis(ethenylsulfonyl)-propane; 1,2-bis(ethenylsulfonyl)-ethane; ethylene carbonate; diethyl carbonate; dimethyl carbonate; ethyl methyl carbonate; and 1,1'-[oxybis(methylenesulfonyl)]bis-ethene.

[0074] Optionally, the electrolyte composition according to the present invention can further contain additives known as film-forming additives. Film-forming additives may promote the formation of a solid electrolyte interfacial SEI layer on the anode and / or cathode surfaces by reacting on the electrode surface before the solvent. Therefore, the main components of the SEI include decomposition products of the electrolyte solvent and salts such as Li2CO3, alkyl lithium carbonate, and alkyl lithium oxide, as well as other salt moieties such as LiF for LiPF6-based electrolytes. Typically, the reduction potential of the film-forming additive is higher than the reduction potential of the solvent when the reaction occurs on the anode surface, and the oxidation potential of the film-forming additive is lower than the oxidation potential of the solvent when the reaction occurs on the cathode side. In the present invention, the film-forming additive is typically not a fluorinated compound. Examples of film-forming additives include, but are not limited to, salts based on tetrahedral boron compounds, including lithium (bisoxalatoborate) and lithium difluorooxalatoborate; cyclic sulfite and sulfate compounds, including 1,3-propanesultone, ethylene sulfite, and prop-1-ene-1,3-sultone; sulfone derivatives, including dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone, and isopropyl methyl sulfone; nitrile derivatives, including succinonitrile, adiponitrile glutaronitrile, and 4,4,4-trifluoronitrile; and vinyl acetate, biphenylbenzene, isopropylbenzene, hexafluorobenzene, lithium nitrate (LiNO), tris(trimethylsilyl)phosphate, triphenylphosphine, ethyl diphenylphosphinite, triethyl phosphite, vinylene carbonate, vinyl ethylene carbonate, ethyl propyl vinylene carbonate, dimethyl vinylene carbonate, maleic anhydride, and mixtures thereof. The total amount of all film-forming additives generally comprises 0.05% to 30% by weight, preferably 0.05% to 20% by weight, more preferably 2% to 15% by weight, and even more preferably 2% to 5% by weight, based on the total weight of the electrolyte composition.

[0075] Other suitable additives that can be used are HF scavengers such as silanes, silazanes (Si-NH-Si), epoxides, amines, aziridines (containing two carbons), salts of lithium carbonate oxalate, BO, ZnO, and fluorinated inorganic salts.

[0076] The electrochemical cell as disclosed herein can be used in a variety of applications. It can be used as an energy storage device. An energy storage device is a device designed to provide electrical energy on demand, such as a battery or a capacitor. The energy storage devices contemplated herein provide energy at least in part from an electrochemical source. For example, the electrochemical cell can be used for grid storage or as a power source in various electrically powered or electrically operated devices, such as computers, cameras, radios, power tools, communication equipment, or transportation devices. The present disclosure also relates to an electronic device, communication device, or transportation device comprising the disclosed electrochemical cell.

[0077] Unexpectedly, the inventors have discovered that the combination of a fluorinated acyclic carbonate compound and a fluorinated cyclic carbonate as defined in the present invention provides more than a simple combination of the effects of both compounds. The inventors have discovered that the combination provides a synergistic performance effect in electrochemical cells having silicon-containing anodes. Another subject of the present invention is a method for improving the high temperature cycling performance of electrochemical cells comprising a combination of at least a carbon material and a silicon material as an anode active material: - Based on the total weight of the electrolyte, the general formula R 1 -OCOO-R 2 (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group), and - 0.5% by weight to 10% by weight of a fluorinated cyclic carbonate compound based on the total weight of the electrolyte as an additive in an electrolyte composition.

[0078] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that the term may be unclear, the statements of this application shall control.

[0079] The following examples serve to explain the invention in more detail, but are not intended to limit it. [Example]

[0080] Materials and Methods EC: Ethylene carbonate - battery grade, purchased from Panax ETEC Co. Ltd. in Korea EMC: Ethyl methyl carbonate battery brand, purchased from Enchem Co. Ltd., Korea FEC: Fluoroethylene carbonate - battery grade, purchased from Enchem Co. Ltd., Korea TFEMC: Trifluoroethyl methyl carbonate (CH3-OC(O)O-CH2CF3) - synthesized by Solvay.

[0081] The cathode and anode were manufactured by UTP (Ulsan Techno Park, Korea): -NCA cathode (LiNiCoAlO2 from Ecopro, Korea) -Graphite-silicon composite anode (Si / C from BTR New Energy Materials Inc., China).

[0082] Preparation of electrolyte The electrolyte composition was prepared as follows: A stock solution of EC / EMC 30 / 70 (v / v) solution was prepared in an argon-purged dry box. LiPF6 was added to reach a concentration of 1 M. FEC and TFEMC were added to reach the concentrations listed in Table 1 herein below. The mixture was gently stirred to dissolve the components.

[0083] [Table 1]

[0084] Coin cell fabrication Coin cells were fabricated using electrodes from pouch cells purchased from UTP, with an NCA cathode and a Si / C anode. The electrodes were punched in air and then heated overnight at 100°C under vacuum to remove residual moisture, then transferred to a glove box where the coin cells were assembled with the cathode, anode, and intermediate polyethylene separator. The same volume of electrolyte was used for all of the coin cells.

[0085] Coin Cell Evaluation Procedure Cycling at 25°C: Cells were maintained at 25±0.1°C and cycled at 1C charge / 2C discharge between 2.7 and 4.2V.

[0086] Cycling at 45°C: The cells were maintained at 45±0.1°C and cycled at 1C charge / 2C discharge between 2.7 and 4.2V.

[0087] Storage test: The cells were charged to 4.2 V and transferred to a thermal chamber for storage testing. The cells were kept at 60° C. for 3 days and the capacity retention and recovery were measured.

[0088] result The cycling performance of the electrolyte formulations at room temperature (25°C) and at elevated temperature (45°C) is shown in Figures 1 and 2 and Table 2:

[0089] [Table 2]

[0090] At room temperature (25°C) and at elevated temperatures (45°C), the formulation containing a combination of FEC and TFEMC according to the present invention (EL3) shows unexpectedly good cycling performance when compared to the electrolyte formulation containing only FEC (EL1) or the electrolyte formulation containing only TFEMC (EL2). Particularly at elevated temperatures, after 300 cycles, the performance of the cell containing the formulation according to the present invention (EL3) is significantly improved relative to the cell containing the formulation with only FEC (EL1).

[0091] The storage performance of the electrolyte formulations is shown in FIG.

[0092] The formulation containing a combination of FEC and TFEMC according to the present invention (EL3) exhibits higher capacity retention and recovery after a 3-day storage test at 60°C when compared to the electrolyte formulation containing only FEC (EL1) or only TFEMC (EL2).

Claims

1. 1. An electrochemical cell comprising an anode, a cathode, and an electrolyte composition, wherein the anode comprises a combination of at least a carbon material and a silicon material as an anode active material, and the electrolyte composition comprises: a solvent comprising at least one non-fluorinated cyclic carbonate in an amount of 8 to 50% by volume (vol %) and at least one non-fluorinated acyclic carbonate in an amount of 50 to 92% by volume, based on the total volume of the solvent; - based on the total weight of the electrolyte composition, R １ -OCOO-R ２ (In the formula, R １ is a C1-C4 alkyl group, and R ２ is a C1-C4 fluoroalkyl group), and - 0.5% to 10% by weight of a fluorinated cyclic carbonate compound, based on the total weight of the electrolyte composition; - Lithium hexafluorophosphate as the sole electrolyte salt an electrochemical cell comprising:

2. The anode is made of Si / C, SiO ａ / C and Si / SiO ａ 2. The electrochemical cell of claim 1, wherein the composite material is selected from the group consisting of: ZnO / C (where 0<a<2).

3. 3. The electrochemical cell of claim 1 or 2, wherein the fluorinated acyclic carbonate is selected from the group consisting of methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, methyl 2,2,3,3-tetrafluoropropyl carbonate, ethyl 2,2-difluoroethyl carbonate, ethyl 2,2,2-trifluoroethyl carbonate, and mixtures thereof.

4. 4. The electrochemical cell of claim 3, wherein the fluorinated acyclic carbonate is methyl 2,2,2-trifluoroethyl carbonate.

5. 4. The electrochemical cell of claim 3, wherein the fluorinated acyclic carbonate is methyl 2,2-difluoroethyl carbonate.

6. 6. The electrochemical cell according to claim 1, wherein the content of the fluorinated acyclic carbonate compound is 0.5% by weight to 10% by weight based on the total weight of the electrolyte composition.

7. 7. The electrochemical cell of any one of claims 1 to 6, wherein the fluorinated cyclic carbonate is selected from the group consisting of 4-fluoroethylene carbonate, 4,5-difluoro-1,3-dioxolan-2-one, 4,5-difluoro-4-methyl-1,3-dioxolan-2-one, 4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, tetrafluoroethylene carbonate, and mixtures thereof.

8. 8. The electrochemical cell according to claim 1, wherein the content of the fluorinated cyclic carbonate compound is 1% by weight to 9% by weight.

9. 9. The electrochemical cell of any one of claims 1 to 8, wherein the solvent of the electrolyte composition comprises a non-fluorinated cyclic carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof.

10. 10. The electrochemical cell of any one of claims 1 to 9, wherein the solvent of the electrolyte composition comprises a non-fluorinated acyclic carbonate selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and mixtures thereof.

11. 11. The electrochemical cell of claim 1, wherein the electrolyte composition further comprises an additive selected from a lithium boron compound, a cyclic sultone, a cyclic sulfate ester, a cyclic carboxylic acid anhydride, or a combination thereof.

12. An electronic, transport or telecommunications device comprising an electrochemical cell according to any one of claims 1 to 11.

13. To improve the high temperature cycling performance of an electrochemical cell containing a combination of at least a carbon material and a silicon material as an anode active material, - based on the total weight of the electrolyte composition, R １ -OCOO-R ２ (In the formula, R １ is a C1-C4 alkyl group, and R ２ is a C1-C4 fluoroalkyl group), and 0.5% to 10% by weight of a fluorinated cyclic carbonate compound, based on the total weight of the electrolyte composition; and a combination of lithium hexafluorophosphate (LiPF) as the sole electrolyte salt in the electrolyte composition. ６ ) as an additive in combination with

14. 1. An electrolyte composition for improving high temperature cycling performance of an electrochemical cell, the electrochemical cell comprising a combination of at least a carbon material and a silicon material as an anode active material, the electrolyte composition comprising: a solvent comprising at least one non-fluorinated cyclic carbonate in an amount of 8 to 50% by volume (vol %) and at least one non-fluorinated acyclic carbonate in an amount of 50 to 92% by volume, based on the total volume of the solvent; - based on the total weight of the electrolyte composition, R １ -OCOO-R ２ (In the formula, R １ is a C1-C4 alkyl group, and R ２ is a C1-C4 fluoroalkyl group), - 0.5% to 10% by weight of a fluorinated cyclic carbonate compound, based on the total weight of the electrolyte composition; - Lithium hexafluorophosphate as the sole electrolyte salt 1. An electrolyte composition comprising:

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