KR20140038676A - Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery prepared with the same, capable of reducing the generation of HF by including fluorinated alcohol into the electrolyte, while increasing the capacity, low-temperature properties, and lifespan properties of the battery. The lithium secondary battery using non-aqueous electrolyte of the present invention, unlike LiFSI lithium salt, does not have problems regarding low anode oxidation resistance and erosion of an aluminum cathode collector, but is excellent in low temperature discharge characteristics, the capacity, and lifespan of the battery, corresponding to the LiFSI lithium salt. [Reference numerals] (AA) Differential capacitance; (BB) Comparative example 2-1; (CC) Example 2-1; (DD) Comparative example 2-3; (EE) Example 2-2; (FF) Comparative example 2-2; (GG) Voltage(V)

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising the same}

The present invention relates to a nonaqueous electrolyte for a lithium secondary battery and a lithium secondary battery having the same. More particularly, the fluorinated alcohol is included in the electrolyte to reduce HF generation, while improving the capacity, low temperature, and lifetime characteristics of the battery. It relates to a nonaqueous electrolyte solution for a lithium secondary battery and to a lithium secondary battery provided with the electrolyte.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs, and electric vehicles further expand, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet these demands, and researches on them are actively under way.

The lithium secondary battery is composed of an anode such as a carbon material capable of occluding and releasing lithium ions, a cathode made of a lithium-containing oxide, and the like, and a nonaqueous electrolyte in which an appropriate amount of lithium salt is dissolved in a mixed organic solvent.

The average discharge voltage of the lithium secondary battery is about 3.6 to 3.7 V, which is one of the advantages of higher discharge voltage than other alkaline batteries, nickel-cadmium batteries, and the like. In order to achieve such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge and discharge voltage range of 0 to 4.2 V. For this purpose, a mixed solvent in which a cyclic carbonate compound such as ethylene carbonate or propylene carbonate and a linear carbonate compound such as dimethyl carbonate, ethylmethyl carbonate or diethyl carbonate are appropriately mixed is used as a solvent for the electrolyte solution. LiPF ₆ , LiBF ₄ , LiClO ₄ and the like are commonly used as lithium salts as the solute of the electrolyte, and these act as a source of lithium ions in the battery to enable operation of the lithium battery.

Among these, LiPF ₆ is a lithium salt currently widely used in the lithium secondary battery electrolyte. LiPF ₆ has the advantage of exhibiting higher ionic conductivity than other lithium salts such as LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , but is thermally decomposed at 80-100 ° C. during normal operation. Produces highly toxic alkyl fluorophosphates. The decomposition generates PF ₅ through a self-catalytic mechanism initiated by a small amount of water or alcohol at a ppm level present in the manufacture of a lithium secondary battery, and the generated PF ₅ reacts with water as shown in Scheme 1 below. Or react with alcohol as in Scheme 2 to generate HF:

Scheme 1

PF ₅ + H ₂ O → 2HF + POF ₃

Scheme 2

HF not only destroys the SEI film of the anode, but also acts as a catalyst in the decomposition reaction of the electrolyte solvent and affects corrosion of electrode materials such as current collectors, binders, and active materials, and in particular, decreases the capacity of lithium secondary batteries and deteriorates low temperature characteristics. This results in a decrease in lifespan and ultimately deteriorates battery performance.

In order to solve the problems as described above, KR 10-2008-0047642 A discloses a non-aqueous lithium electrolyte containing a Lewis base which stabilizes by providing a non-covalent electron pair to PF ₅ , whereby side reactions by alcohol There is a limit that cannot be suppressed.

In addition, KR 10-2010-0039010 A describes the inclusion of LiWF ₇ in a lithium salt, and CN101383433 A describes the addition of a phosphite ester compound and an amine compound to a nonaqueous electrolyte to inhibit LiPF ₆ degradation and to reduce HF production. However, there was a problem that it was not satisfactory in terms of low temperature characteristics, capacity and life characteristics of the obtained battery.

On the other hand, LiFSI (lithium bis (fluorosulfonyl) imide, Li (FSO ₂ ) ₂ N), unlike LiPF ₆ , does not generate HF even in a nonaqueous electrolytic solution in which impurities including active hydrogen such as water are present. Although there is a stable advantage, since the oxidation resistance is low at the anode and has a problem of corroding the aluminum of the cathode current collector, there is a problem that must be used mixed with other salts in order to apply to the actual battery.

Accordingly, the problem to be solved by the present invention is to suppress the inappropriate decomposition of fluorine-based lithium salts by a small amount of water or alcohol, to reduce HF production, to reduce the reactivity of the anode coating SEI coating, to reduce the low temperature characteristics, capacity and lifetime of the battery. The characteristics provide an improved novel nonaqueous electrolyte for lithium secondary batteries and a lithium secondary battery having the same.

According to an aspect of the present invention, a non-aqueous electrolyte for a lithium secondary battery comprising a fluorine-based lithium salt and an organic solvent, there is provided a non-aqueous electrolyte for a lithium secondary battery, characterized in that it further comprises a C 2-6 halogenated alcohol.

The fluorine-containing lithium salt anion ^{_{PF 6 -, (FSO 2)}} 2 N -, F -, BF 4 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 ^{_{-, (CF 3) 5 PF}} -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, CF 3 CF 2 (CF 3) ^{_{2 CO -, (CF 3 SO}} 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 - and ( CF ₃ CF ₂ SO ₂ ) ₂ N ^-It is characterized in that it is selected from the group consisting of.

The halogenated alcohol is characterized in that the fluorinated alcohol having 2 to 6 carbon atoms.

The fluorinated alcohol is characterized in that the fluorinated ethanol.

The fluorinated ethanol is characterized in that at least one member selected from the group consisting of 2-fluoroethanol and 2,2,2-trifluoroethanol.

The content of the halogenated alcohol is characterized in that 0.01 to 10 parts by weight or 0.1 to 5 parts by weight based on 100 parts by weight of the organic solvent.

The organic solvent is any one selected from the group consisting of linear carbonates, cyclic carbonates, ethers, esters and amides, or a mixture of two or more thereof.

The linear carbonate is characterized in that it comprises any one or a mixture of two or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate.

The cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and It characterized in that it comprises any one selected from the group consisting of halides thereof or a mixture of two or more thereof.

The ether is characterized in that it comprises any one or a mixture of two or more selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether.

The nonaqueous electrolyte is characterized in that it further comprises any one or a mixture of two or more selected from the group consisting of cyclic sulfite, saturated sultone, unsaturated sultone and acyclic sulfone.

In addition, according to an aspect of the present invention, in the lithium secondary battery having an electrode assembly consisting of an anode, a cathode, and a separator interposed between the cathode and the anode and a nonaqueous electrolyte injected into the electrode assembly, the nonaqueous electrolyte is Provided is a lithium secondary battery, which is a nonaqueous electrolyte solution for a lithium secondary battery described above.

The lithium secondary battery using the nonaqueous electrolyte of the present invention has low oxidation resistance at the anode and does not have a problem of corroding aluminum, which is a cathode current collector, and exhibits excellent low-temperature discharge characteristics, battery capacity, and lifespan characteristics by decreasing the SEI film reactivity of the anode. Has an effect.

1 and 2 are voltage-capacity graphs showing the basic capacity of the lithium secondary battery measured in Test Example 1.
3 and 4 are voltage-capacity graphs showing low-temperature charging characteristics of the lithium secondary battery measured in Test Example 2.
5 is a graph illustrating dQ / dV of the graphs 3 and 4 described above.
6 and 7 are voltage-capacity graphs showing low-temperature discharge characteristics of the lithium secondary battery measured in Test Example 3.
8 is a capacity-cycle number graph showing the life characteristics of a lithium secondary battery measured at 23 ° C in Test Example 4.
9 is a capacity-cycle number graph showing the life characteristics of the lithium secondary battery measured at 55 ℃ in Test Example 4.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

According to one aspect of the present invention, in a nonaqueous electrolyte solution for a lithium secondary battery comprising a fluorine-based lithium salt and an organic solvent, there is provided a nonaqueous electrolyte solution for a lithium secondary battery, further comprising a halogenated alcohol.

In the non-aqueous electrolyte of the lithium secondary battery of the present invention, the fluorine-based lithium salt may be used without limitation as long as those used in the lithium secondary battery electrolyte. For example, an anion wherein the fluorine-containing lithium salt is ^{_{PF 6 -, (FSO 2)}} 2 N -, F -, BF 4 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) ^{_{4 PF 2 -, (CF 3}} ) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, CF 3 CF 2 ( ^{_{CF 3) 2 CO -, (}} CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 ^- , And (CF ₃ CF ₂ SO ₂ ) ₂ N ^- It can be selected from the group consisting of.

In this case, as the fluorine-based lithium salt, LiPF ₆ or Li (FSO ₂ ) ₂ N and the like can be used as a representative, in addition to lithium salts commonly used for lithium secondary batteries, for example, LiSbF ₆ , LiAsF ₆ , LiClO ₄ , and LiC ₄ BO ₈ may be further included.

In the present invention, 'alcohol' refers to an alcohol commonly referred to in the art, for example, monohydric alcohols such as methanol, ethanol, isopropyl alcohol, butyl alcohol, pentanol, and hexadecane-1-ol. alcohol); Ethane-1,2-diol, propane-1,2,3-triol, butane-1,2,3,4-tetraol, pentane-1,2,3,4,5-pentol, hexane-1 Polyhydric alcohols such as 2,3,4,5,6-hexole; Unsaturated aliphatic alcohols such as prop-2-en-1-ol, 3,7-dimethylocta-2,6-dien-1-ol, prop-2-yn-1-ol ; And alicyclic alcohols such as cyclohexane-1,2,3,4,5,6-hexole, 2- (2-propyl) -5-methyl-cyclohexan-1-ol, and the like. It is not limited.

In the present invention, the term "halogenated alcohol" means that at least one hydrogen atom bonded to an alcohol carbon atom is substituted with at least one halogen selected from the group consisting of fluorine, bromine, chlorine and iodine.

The halogenated alcohol may preferably be a fluorinated alcohol selected from the group consisting of fluorinated alcohols having 2 to 6 carbon atoms, more preferably a halogenated alcohol is fluorinated ethanol, particularly preferred halogenated alcohols are 2-fluoroethanol and 2, At least one selected from the group consisting of 2,2-trifluoroethanol.

The content of the halogenated alcohol may be 0.01 to 10 parts by weight or 0.1 to 5 parts by weight based on 100 parts by weight of the organic solvent. When the content of the halogenated alcohol satisfies this range, the basic capacity, low temperature characteristics and lifespan characteristics may be improved in proportion to the content, and the reactivity of the anode SEI film may be reduced.

Examples of the organic solvent included in the above-mentioned non-aqueous electrolyte include those commonly used in electrolytic solutions for lithium secondary batteries, such as ether, ester, amide, linear carbonate, cyclic carbonate, etc., Can be mixed and used.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Any one selected or a mixture of two or more thereof may be representatively used, but is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, are high-viscosity organic solvents having a high dielectric constant and can dissociate the lithium salt in the electrolyte more easily. In addition, such cyclic carbonates can be used as dimethyl carbonate and diethyl carbonate When a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher electric conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone, ε-caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

The nonaqueous electrolyte solution for a lithium secondary battery according to an aspect of the present invention may further include an additive for forming a known SEI layer within the scope of the present invention. As the additive for forming the SEI layer usable in the present invention, a cyclic sulfite, a saturated sulphone, an unsaturated sulphone, and a non-cyclic sulfone may be used singly or in combination of two or more, but the present invention is not limited thereto. In addition, among the aforementioned cyclic carbonates, vinylene carbonate and vinylethylene carbonate may also be used as additives for forming an SEI layer for improving battery life.

The cyclic sulfites include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfide Pite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, and the like. 1,3-propane sultone, 1,4-butane sultone, and the like, and unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-prop Pen sulfone etc. are mentioned, As acyclic sulfone, divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl vinyl sulfone, etc. are mentioned.

The additive for forming the SEI layer may be contained in an appropriate amount depending on the specific kind of the additive, for example, 0.01 to 10 parts by weight relative to 100 parts by weight of the non-aqueous electrolyte.

According to an aspect of the present invention, there is provided a lithium secondary battery comprising an electrode assembly comprising an anode, a cathode, and a separator interposed between the cathode and the anode, and a non-aqueous electrolyte injected into the electrode assembly, There is provided a lithium secondary battery which is a nonaqueous electrolyte solution for the lithium secondary battery.

The cathode, the anode and the separator constituting the electrode assembly may be those conventionally used in the manufacture of a lithium secondary battery.

The cathode has a structure in which a cathode layer including a cathode active material, a conductive material and a binder is supported on one or both surfaces of the current collector.

Lithium-containing transition metal oxide may be preferably used as the cathode active material, for example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO ₂ (0.5 <x <1.3), Li _x Mn ₂ O ₄ (0.5 <x <1.3), Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5 <x <1.3, 0 <a <1, 0 <b <1 , 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _{1 -y} Mn _y O ₂ (0.5 <x <1.3, 0≤y <1), Li _x Ni _{1- y} Mn _y O ₂ (0.5 <x <1.3, O≤y <1), Li _x (Ni _a Co _b Mn _c ) O ₄ (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _{2 -z} Ni _z O ₄ (0.5 <x <1.3 , 0 <z <2), Li _x Mn _{2 -z} Co _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ (0.5 <x <1.3), any one selected from the group consisting of, or a mixture of two or more thereof may be used, and the lithium-containing transition metal oxide may be coated with a metal or metal oxide such as aluminum (Al). In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

The conductive material is not particularly limited as long as it is an electronic conductive material that does not cause chemical change in the electrochemical device. In general, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material and the like can be used. Commercially available products as the conductive material include acetylene black series (manufactured by Chevron Chemical Co., (Chevron Chemical Company or Gulf Oil Company products), Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (MM (MMM)). For example, acetylene black, carbon black and graphite.

The anode has a structure in which the anode layer including the anode active material and the binder is supported on one or both surfaces of the current collector.

As the anode active material, a carbon material, a lithium metal, a metal compound, or a mixture thereof, in which lithium ions can be occluded and released, can be used.

Concretely, as the carbon material, low-crystallinity carbon and high-crystallinity carbon may be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

Examples of the metal compound include metal elements such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, , And the like. These metal compounds may be a single substance, an alloy, an oxide (TiO ₂ , SnO ₂ Or the like), a nitride, a sulfide, a boride, an alloy with lithium, or the like, but an alloy with a single substance, an alloy, an oxide, and lithium can be increased in capacity. Among them, it may contain at least one element selected from Si, Ge and Sn, and it may further increase the capacity of the battery including at least one element selected from Si and Sn.

The binder used for the cathode and the anode has a function of holding the cathode active material and the anode active material in the current collector and also connecting the active materials, and a commonly used binder may be used without limitation.

For example, it is possible to use vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, styrene Various types of binder polymers such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like can be used.

The current collectors used for the cathode and the anode are metals of high conductivity, and metals to which the slurry of the active material can easily adhere can be used as long as they are not reactive in the voltage range of the battery. Specifically, examples of the current collector for a cathode include aluminum, nickel, or a combination thereof. Examples of the current collector for an anode include copper, gold, nickel, or a copper alloy or a combination thereof And the like. In addition, the current collector may be used by laminating the substrates made of the above materials.

The cathode and the anode are kneaded using an active material, a conductive agent, a binder, and a high boiling point solvent to form an electrode mixture, and then the mixture is applied to a copper foil of a current collector, dried, and press-molded, then about 50 ° C to 250 ° C. It may be produced by heat treatment under vacuum at a temperature of about 2 hours.

The thickness of the electrode layer of the cathode may be 30 to 120 占 퐉 or 50 to 100 占 퐉, and the thickness of the electrode layer of the anode may be 1 to 100 占 퐉, or 3 to 70 占 퐉. When the cathode and the anode satisfy this thickness range, the amount of active material in the electrode material layer is sufficiently secured to prevent the battery capacity from decreasing and the cycle characteristics and rate characteristics can be improved.

The separator may be a conventional porous polymer film conventionally used as a separator, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer The porous polymer film made of a polyolefin-based polymer may be used alone or in a laminate thereof, or a nonwoven fabric made of a conventional porous nonwoven fabric, for example, a glass fiber having a high melting point, polyethylene terephthalate fiber or the like may be used. It is not.

The lithium secondary battery of the present invention is not limited in its outer shape, but may be cylindrical, square, pouch type or coin type using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Preparation of nonaqueous electrolyte

Example  1-1

3 parts by weight of vinylene carbonate and 1.5 parts by weight of propanesultone (PS) are added to 100 parts by weight of an organic solvent composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 1: 2 volume ratio, and LiPF ₆ is dissolved to a concentration of 1 M. 100 g of the solution was prepared, and 0.5 g of 2,2,2-trifluoroethanol (trade name JH-F2, available from Aldrich) was added thereto to prepare a nonaqueous electrolyte.

Example  1-2

A non-aqueous electrolyte was prepared in the same manner as in Example 1-1 except that LiFSI was used instead of LiPF ₆ .

Comparative Example  1-1

A nonaqueous electrolyte was prepared in the same manner as in Example 1-1 except that 2,2,2-trifluoroethanol was not added.

Comparative Example  1-2

A nonaqueous electrolyte was prepared in the same manner as in Example 1-1, except that ethanol was added instead of 2,2,2-trifluoroethanol.

Comparative Example  1-3

A nonaqueous electrolyte was prepared in the same manner as in Comparative Example 1-1 except that LiFSI was used instead of LiPF ₆ .

Manufacture of lithium secondary battery

Example  2-1

An electrode was prepared by blending LiCoO ₂ as a cathode and Si oxide (5-10 wt% SiO, 90-95 wt% graphite, prepared using a non-aqueous binder) as an anode, followed by Example 1-1. A rectangular lithium secondary battery was manufactured by a conventional method of injecting a nonaqueous electrolyte prepared in the above.

Example  2-2

A square lithium secondary battery was manufactured in the same manner as in Example 2-1 except for using the nonaqueous electrolyte prepared in Example 1-2.

Comparative Example  2-1

A square lithium secondary battery was manufactured in the same manner as in Example 2-1 except for using the nonaqueous electrolyte prepared in Comparative Example 1-1.

Comparative Example  2-2

A square lithium secondary battery was manufactured in the same manner as in Example 2-1 except for using the nonaqueous electrolyte prepared in Comparative Example 1-2.

Comparative Example  2-3

A square lithium secondary battery was manufactured in the same manner as in Example 2-1 except for using the nonaqueous electrolyte prepared in Comparative Example 1-3.

Characterization of Lithium Secondary Battery

Test Example  1: Basic capacity assessment

After charging the lithium secondary batteries prepared in Example 2-1 and Comparative Examples 2-1 to 2-2 at 854 mA and 4.2 V constant current / constant voltage conditions for 5 minutes at room temperature, the final current is charged to 60 mA, The voltage-capacity graph then discharged at 0.5 C under 610 mA and 3 V constant current / constant voltage conditions is shown in FIG. 1.

From FIG. 1, the basic capacity of the lithium secondary battery prepared in Example 2-1 is comparable to that of the lithium secondary battery of Comparative Example 2-1 in which ethanol is not added to the electrolyte, and Comparative Example 2-2 in which ethanol is added to the electrolyte Is much higher than lithium secondary batteries.

In the same manner as above, the voltage-capacity graph discharged after charging the lithium secondary batteries prepared in Examples 2-2 and Comparative Examples 2-1 to 2-3 is shown in FIG. 2.

From FIG. 2, the basic capacity of the lithium secondary battery of Example 2-2 is comparable to the lithium secondary battery of Comparative Example 2-3 using LiFSI as the lithium secondary battery of Comparative Example 2-1 without ethanol and the electrolyte lithium salt. In addition, it was found to be much higher than the lithium secondary battery of Comparative Example 2-2 in which ethanol was added to the electrolyte.

Test Example  2: low temperature charging characteristics

When the lithium secondary batteries of Example 2-1 and Comparative Examples 2-1 to 2-2 were left at -30 ° C. for 1 hour, charged to 3.8 V, and then the capacity became 200 mAh at a constant voltage of 3.8 V. Figure 3 shows the voltage-capacity graph charged up to.

In the same manner as above, the voltage-capacity graphs obtained for the lithium secondary batteries of Example 2-2 and Comparative Example 2-3 are shown in FIG. 4.

FIG. 5 is a dQ / dV graph of the graphs obtained in FIGS. 3 and 4, in which the capacity change suddenly increases at around 2.75 V only in the lithium secondary battery of Comparative Example 2-2 in which ethanol is added to the electrolyte solution. While the embodiments are shown, in the lithium secondary batteries of Examples 2-1 and 2-2 to which fluorinated ethanol was added, the lithium secondary batteries of Comparative Example 2-2 to which ethanol was added and Comparative Examples 2-1 and ethanol were not added Compared with the lithium secondary battery of 2-3, the capacity was increased rapidly and stably. This means that the charging speed of the lithium secondary battery according to the present invention to which ethanol fluoride is added is increased.

Test Example  3: low temperature discharge characteristics

The lithium secondary batteries prepared in Example 2-1 and Comparative Examples 2-1 to 2-2 and charged to 3.8V were discharged to 3.0V after being left at −30 ° C. for 1 hour, and the results are shown in FIG. 6. It was.

As can be seen in Figure 6, the lithium secondary battery of Example 2-1 to which 2,2,2-trifluoroethanol is added, the lithium secondary battery of Comparative Example 2-1 without the alcohol compound and ethanol is added It showed greater resistance reduction and excellent low temperature discharge characteristics than the lithium secondary battery of Comparative Example 2-2.

Similarly, the lithium secondary batteries prepared in Example 2-2 and Comparative Examples 2-1 and 2-3 were also discharged to 3.0V in the same manner as above, and the results are shown in FIG. 7.

As can be seen in FIG. 7, the lithium secondary battery of Example 2-2 to which 2,2,2-trifluoroethanol was added, the lithium secondary battery of Comparative Example 2-1 to which no alcohol compound was added and ethanol were added It showed greater resistance reduction and excellent low temperature discharge characteristics than the lithium secondary battery of Comparative Example 2-2.

6 and 7, the lithium secondary battery of Example 2-2 in which LiFSI was used as the lithium salt in the electrolyte was more discharged than in the lithium secondary battery of Example 2-1 in which LiPF ₆ was used as the lithium salt. High capacity and low resistance. In addition, in the lithium secondary battery to which 2,2,2-trifluoroethanol was added, the capacity increase and the resistance decrease were large.

Test Example  4: Life characteristics

After the initial charging and discharging of the lithium secondary batteries of Examples 2-1 and 2-2 and Comparative Examples 2-1 to 2-3, the basic charging and discharging was performed 100 times at room temperature (23 ° C.), The battery capacity is shown in FIG. 8, and the battery capacity measured by the same method at 55 ° C. is shown in FIG. 9.

As can be seen from Figures 8 and 9, only the lithium secondary battery of Comparative Example 2-2 in which ethanol was added to the electrolyte solution, a significant decrease in life characteristics was observed.

Test Example  5: gas generation and thickness change

Gas generation and thickness change after the formation / aging process step were performed using the electrolyte solutions of Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-3.

As a result, in Examples 1-1 and 1-2, gas generation similar to that in Comparative Examples 1-1 and 1-3 without HF gas generation by alcohol was observed, and ethanol-added comparative example In the case of 1-2, the largest change in thickness was observed compared to Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-3.

Claims (12)

A nonaqueous electrolyte for lithium secondary batteries containing a fluorine-based lithium salt and an organic solvent, the nonaqueous electrolyte for lithium secondary batteries further comprising a halogenated alcohol having 2 to 6 carbon atoms.
The method according to claim 1,
Wherein the fluorine-containing lithium salt of the anion ^{_{PF 6 -, (FSO 2)}} 2 N -, F -, BF 4 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 ^{_{-, (CF 3) 5 PF}} -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, CF 3 CF 2 (CF 3) ^{_{2 CO -, (CF 3 SO}} 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, and _{(CF 3 CF 2 SO 2)} 2 N - non-aqueous electrolyte lithium secondary battery, characterized in that selected from the group consisting of.
The method according to claim 1,
The halogenated alcohol is a non-aqueous electrolyte lithium secondary battery, characterized in that the fluorinated alcohol having 2 to 6 carbon atoms.
The method of claim 3,
The non-aqueous electrolyte solution for lithium secondary batteries, wherein the fluorinated alcohol is fluorinated ethanol.
5. The method of claim 4,
The non-aqueous electrolyte solution for lithium secondary batteries, characterized in that the fluorinated ethanol is at least one selected from the group consisting of 2-fluoroethanol and 2,2,2-trifluoroethanol.
The method according to claim 1,
The content of the halogenated alcohol is a non-aqueous electrolyte lithium secondary battery, characterized in that 0.01 to 10 parts by weight based on 100 parts by weight of the organic solvent.
The method according to claim 1,
The organic solvent is any one selected from the group consisting of linear carbonate, cyclic carbonate, ether, ester and amide or a mixture of two or more thereof.
8. The method of claim 7,
Lithium secondary characterized in that the linear carbonate comprises any one or a mixture of two or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate Non-aqueous electrolyte solution for batteries.
8. The method of claim 7,
The cyclic carbonates are ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and A nonaqueous electrolyte solution for a lithium secondary battery comprising any one selected from the group consisting of halides thereof or a mixture of two or more thereof.
8. The method of claim 7,
The lithium secondary battery, characterized in that the ether comprises any one or a mixture of two or more selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether. Nonaqueous electrolyte.
The method according to claim 1,
Wherein the non-aqueous electrolyte further comprises any one selected from the group consisting of a cyclic sulfite, a saturated sulphone, an unsaturated sulphone, and a non-cyclic sulphone, or a mixture of two or more thereof.
12. A lithium secondary battery comprising an anode, a cathode, and an electrode assembly composed of a separator interposed between the cathode and the anode, and a nonaqueous electrolyte injected into the electrode assembly, wherein the nonaqueous electrolyte is any one of claims 1 to 11. It is a nonaqueous electrolyte solution for secondary batteries of Claim, The lithium secondary battery characterized by the above-mentioned.

Images