KR20180065755A - non-aqueous liquid electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte liquid with improved ion transfer properties of an electrolyte, and a lithium secondary battery including the same. The non-aqueous electrolyte liquid for a secondary battery includes a lithium salt and an organic solvent. Capacity and cycle characteristics are improved.

Description

[0001] The present invention relates to a non-aqueous electrolyte solution and a lithium secondary battery comprising the same,

The present invention relates to a non-aqueous electrolytic solution improved in ion transport properties and a lithium secondary battery comprising the same.

In recent years, interest in energy storage technology has been increasing, and efforts for research and development of electrochemical devices are becoming more and more specific as the applications of cell phones, camcorders, notebook PCs, and electric vehicles are expanded.

The electrochemical device is one of the most attracting fields in this respect, and attention is focused on a rechargeable secondary battery. Particularly, among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s are attracting attention because of their high operating voltage and energy density.

The lithium secondary battery includes a negative electrode made of a carbon material capable of absorbing and desorbing lithium ions, a positive electrode made of a lithium-containing oxide or the like, and a nonaqueous electrolyte solution in which an appropriate amount of a lithium salt is dissolved in a mixed organic solvent. The lithium ions are intercalated into the graphite electrode of the negative electrode and deintercalated.

On the other hand, since a lithium secondary battery is usually driven at a high operating voltage, a conventional aqueous electrolyte can not be used because the lithium ion reacts violently with an aqueous solution. In recent years, a non-aqueous organic electrolyte solution in which a lithium salt is dissolved in an organic solvent is used in a lithium secondary battery.

When a carbonate-based polar solvent is used as such an organic solvent, an excess amount of charge is used because the carbon of the cathode reacts with the electrolyte at the time of initial charging. By this irreversible reaction, a passivation layer such as a solid electrolyte interface (SEI) film is formed on the surface of the cathode.

The SEI film allows the electrolyte solution to maintain stable charge / discharge without further decomposition, passes through only lithium ions by acting as an ion tunnel, solubilizes lithium ions, Can be prevented from being co-intercalated together with the carbon cathode, thereby preventing the cathode structure from being collapsed.

However, when a high voltage of 4V or more is repeatedly applied during charging and discharging, the SEI film produced by the polar solvent and the lithium salt cracks, and the reduction reaction of the solvent is continued so that the insoluble salt precipitates inside and outside of the cathode, A crack is generated in the substrate. If the electronic connection is deteriorated by such a crack, the internal resistance of the cathode increases, and the battery capacity decreases. Further, there is also a problem that the electrolyte is depleted due to the decomposition of the solvent, making it difficult to transfer ions.

Accordingly, there is a growing need for the development of a lithium secondary battery capable of improving ion transfer characteristics of an electrolyte while maintaining excellent cycle life characteristics even under harsh environments such as high temperature and low temperature environments and high voltage charging.

Korean Patent Publication No. 2012-0099013

In order to solve the above-mentioned problems, a first technical object of the present invention is to provide a non-aqueous electrolytic solution improved in ion transport properties of an electrolyte.

Another object of the present invention is to provide a lithium secondary battery having improved capacity and cycle characteristics by including the nonaqueous electrolyte solution.

In order to solve the problem to be solved,

In one embodiment of the invention,

Lithium salts; And a nonaqueous electrolyte solution for a secondary battery comprising an organic solvent,

The organic solvent may be an ether compound; Ester compounds; Nitrile-based compounds; Linear carbonate compounds; And a second organic solvent comprising at least one first organic solvent selected from the group consisting of a cyclic carbonate compound and a compound represented by the following formula 1,

Wherein the second organic solvent comprises less than 20% by volume based on the total volume of the first organic solvent and the second organic solvent.

[Chemical Formula 1]

Specifically, in the nonaqueous electrolyte solution for a secondary battery, a mixing volume ratio of the first organic solvent to the second organic solvent may be 81: 19 to 99: 1.

In an embodiment of the present invention,

There is provided a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a lithium secondary battery comprising the nonaqueous electrolyte of the present invention.

The present invention provides a nonaqueous electrolyte solution which further comprises a second organic solvent capable of improving ion transfer characteristics of the electrolyte impregnated in the separator, thereby enabling more uniform movement of lithium ions, This improved lithium secondary battery can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a graph showing battery life characteristics results according to Experimental Example 2 of the present invention.

Hereinafter, the present invention will be described in more 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.

Specifically, in one embodiment of the present invention

Lithium salts; And a nonaqueous electrolyte solution for a secondary battery comprising an organic solvent,

The organic solvent may be an ether compound; Ester compounds; Nitrile-based compounds; Linear carbonate compounds; And a second organic solvent comprising at least one first organic solvent selected from the group consisting of a cyclic carbonate compound and a compound represented by the following formula 1,

Wherein the second organic solvent comprises less than 20% by volume based on the total volume of the first organic solvent and the second organic solvent.

[Chemical Formula 1]

Generally, when the secondary battery is repeatedly charged and discharged, the cathode undergoes rapid expansion and contraction, and when the SEI film collapses, a new SEI film is regenerated by electrolytic decomposition. As a result, the electrolyte is gradually depleted and lithium ions present in the electrolyte are consumed, so the capacity of the secondary battery decreases as the cycle progresses.

Such electrolyte depletion can be seen to occur mainly in cyclic carbonate in organic solvents. This can be deduced from the fact that the life of the secondary battery is shortened during the life test, and the secondary battery is disassembled and the electrolyte is analyzed. As a result, all the fluoroethylene carbonate used as the cyclic carbonate solvent is consumed.

Accordingly, in the present invention, by further including the second organic solvent as the organic solvent of the non-aqueous electrolyte, it is possible to improve the ion transfer characteristic of the electrolyte solution impregnated in the separator, thereby improving the uniformity of lithium ion movement, It is possible to give an increased effect.

At this time, in the nonaqueous electrolyte for a secondary battery of the present invention, the mixing volume ratio of the first organic solvent to the second organic solvent may be 81:19 to 99: 1. If the volume ratio of the second organic solvent is less than 1, the effect of increasing the conductivity can be reduced. If the volume ratio of the second organic solvent is more than 19, the bulk and the impregnation conductivity are lowered due to the low conductivity of the compound itself, Ion transport properties can be rather reduced.

On the other hand, in the non-aqueous liquid electrolyte of the present invention, the lithium salt is in can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example comprising a Li ⁺ as the cation, the anion is F ^-, Cl ^{-, _{Br -, I -, NO 3}} -, N (CN) 2 -, BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O _{^{4 -, BC 4 O 8 -}} , (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 -,}} C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (F 2 SO 2) 2 N -, CF 3 CF 2 (CF ^{_{3) 2 CO -, (CF}} 3 SO 2) 2 CH -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and (CF ₃ CF ₂ SO _{2) 2} N ^- , or at least two or more of them. Specifically, the lithium salt may be at least one selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , LiN CF ₃ SO ₂ ) ₂ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF _3, and LiClO ₄ , or at least two or more of them.

The lithium salt may be contained in the non-aqueous electrolyte for lithium secondary battery at 0.5M to 3M. If the concentration of the lithium salt is less than 0.5M, the effect of improving the low-temperature power of the battery and improving the high-temperature cycle characteristics may not be sufficient. If the concentration exceeds 3M, side reactions in the electrolyte occur excessively during charging / discharging of the battery, A swelling phenomenon may occur, or corrosion of a positive electrode or negative electrode current collector made of a metal in an electrolyte solution may occur.

In the nonaqueous electrolyte solution of the present invention, the first organic solvent may be any of those conventionally used for an electrolyte for a lithium secondary battery without limitation, and examples thereof include ether compounds, ester compounds, nitrile compounds, linear carbonate compounds, Cyclic carbonate compounds, etc. may be used alone or in combination of two or more. Among them, typical examples include a cyclic carbonate compound, a linear carbonate compound, or a mixture thereof.

The ether compound in the organic solvent may be 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. But is not limited thereto.

The ester compound may be a linear ester such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate; And a cyclic ester compound such as? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone,? -Caprolactone, or a mixture of two or more thereof But is not limited thereto.

The nitrile compound may be at least one compound selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile , At least one selected from the group consisting of difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

Specific examples of the linear carbonate compound are selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate Or a mixture of two or more of them may be used. However, the present invention is not limited thereto.

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 A carbonate, a carbonate, a 2,3-pentylene carbonate, a vinylene carbonate, and a fluoroethylene carbonate (FEC), or a mixture of two or more thereof.

Particularly, the above-mentioned cyclic carbonates such as ethylene carbonate and propylene carbonate are high-viscosity organic solvents having a high dielectric constant and can dissociate the lithium salt in the electrolyte well. Therefore, cyclic carbonates and ethylmethyl carbonate, dimethyl carbonate or When a low viscosity, low dielectric constant linear carbonate such as diethyl carbonate is mixed in an appropriate ratio, an electrolytic solution having a high electric conductivity can be prepared, which is more preferably used.

In an embodiment of the present invention,

A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode,

A lithium secondary battery comprising the non-aqueous electrolyte of the present invention is provided.

Specifically, the lithium secondary battery of the present invention can be manufactured by injecting the non-aqueous electrolyte of the present invention into an electrode structure composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

At this time, the positive electrode may be manufactured by coating a positive electrode active material on the positive electrode current collector, and optionally a positive electrode material mixture including a binder, a conductive material, and a solvent.

The positive electrode collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, the positive electrode collector may be formed of a metal such as carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used.

The cathode active material is a compound capable of reversibly intercalating and deintercalating lithium, and may specifically include a lithium composite metal oxide including lithium and at least one metal such as cobalt, manganese, nickel, or aluminum have. More specifically, the lithium composite metal oxide may be at least one selected from the group consisting of lithium-manganese-based oxides (for example, LiMnO ₂ and LiMn ₂ O ₄ ), lithium-cobalt oxides (for example, LiCoO ₂ ), lithium- (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( here, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn 2 - z1 Co z1 O 4 ( here, 0 <z1 <2) and the like), lithium-nickel -manganese-cobalt oxide (e.g., Ni _p Co _q Mn _r1 (Li) O ₂ (here, 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co _q1 Mn _r2) O ₄ (here, 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2) , etc.), or a lithium- nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni Co _{p2 q2} Mn _r3 M _s2) O ₂ (here Wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r3 and s2 are atomic fractions of independent elements, 0 <p2 < Q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), etc., and any one or more of these compounds may be included. The lithium composite metal oxide may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , _{Li (Ni 0.5 Mn 0.3 Co 0.2} ) O 2, Li (Ni 0.7 Mn 0.15 Co 0.15) O 2 or _{Li (Ni 0.8 Mn 0.1 Co 0.1} ) O 2 ), or lithium nickel cobalt aluminum oxide (e.g., LiNi _0.8 Co _0.15 Al _0.05 O _2, etc.), and considering the remarkable improvement effect according to the kind and content ratio control of constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide is Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , _{Li (Ni 0.5 Mn 0.3 Co 0.2} ) O 2, Li (Ni 0.7 Mn 0.15 Co 0.15) O 2 or _{Li (Ni 0.8 Mn 0.1 Co 0.1} ) O 2 and the like, any one or a mixture of two or more may be used of which have.

The cathode active material may include 80 wt% to 99 wt% based on the total weight of each cathode mix.

The binder is a component that assists in bonding of the active material and the conductive material to the binder and the binder, and is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene (Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and includes, for example, graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that is preferred to contain the cathode active material, and optionally, a binder and a conductive material. For example, the concentration of the solid material including the cathode active material, and optionally the binder and the conductive material may be 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

The negative electrode may be prepared, for example, by coating a negative electrode current collector with a negative electrode mixture including a negative electrode active material, a binder, a conductive material, and a solvent.

The anode current collector generally has a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Examples of the negative electrode active material include carbonaceous materials such as natural graphite or artificial graphite; Lithium-containing titanium composite oxide (LTO); Cu, Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; An alloy composed of the above metals; Oxides of the metals; And a composite of the above metals and carbon.

The negative electrode active material may include 80% by weight to 99% by weight based on the total weight of the negative electrode material mixture.

The binder is a component for assisting the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the negative electrode material mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the negative electrode material mixture. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that makes it desirable to contain the negative electrode active material, and optionally, a binder and a conductive material . For example, the concentration of the solid material including the negative electrode active material, and optionally the binder and the conductive material may be 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

The separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions. The separator can be used without particular limitation as long as it is used as a separator in a lithium secondary battery. Especially, the separator has low resistance against electrolyte migration, It is preferable that the ability is excellent.

Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used.

The thickness of the separator may be in the range of 10 to 60 占 퐉, and more specifically in the range of 10 to 40 占 퐉. When the thickness is within the above range, the energy density can be enhanced.

At this time, an organic / inorganic composite separator coated with an inorganic material may be used for securing heat resistance or mechanical strength, and it may be selectively used as a single layer or a multilayer structure.

The inorganic material is not particularly limited as long as it is a material capable of uniformly controlling the pores of the organic / inorganic composite separator and improving the heat resistance. For example, the inorganic material is a non-limiting example is _{SiO 2, Al 2 O 3,} TiO 2, BaTiO 3, Li 2 O, LiF, LiOH, Li 3 N, BaO, Na 2 O, Li 2 CO 3, CaCO 3, At least one selected from the group consisting of LiAlO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiC and their derivatives and mixtures thereof.

The average diameter of the inorganic material may be 0.001 탆 to 10 탆, and more specifically 0.001 탆 to 1 탆. If the average diameter of the inorganic materials is within the above range, the dispersibility in the coating solution is improved and the occurrence of problems in the coating process can be minimized. In addition, the physical properties of the final separator can be made uniform, the inorganic particles can be uniformly distributed in the pores of the nonwoven fabric to improve the mechanical properties of the nonwoven fabric, and the advantage of easily controlling the size of the pores of the non- .

The average diameter of the pores of the organic / inorganic composite separator may be in the range of 0.001 to 10 탆, more specifically 0.001 to 1 탆. When the average diameter of the pores of the organic / inorganic hybrid separator is within the above range, gas permeability and ion conductivity can be controlled within a desired range, and when the battery is manufactured using the organic / inorganic composite separator, It is possible to eliminate the possibility of an internal short circuit of the battery by the battery.

The porosity of the organic / inorganic composite separator may be in the range of 30 to 90% by volume. When the porosity is within the above range, the ion conductivity can be increased and the mechanical strength can be enhanced.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like 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.

Example

Example  One.

(Preparation of electrolytic solution)

A first organic solvent prepared by mixing ethylene carbonate (EC): ethyl methyl carbonate (EMC) at a weight ratio of 30:70 and a second organic solvent containing a compound represented by the following general formula (1) were mixed at a volume ratio of 95: . Next, LiPF ₆ was dissolved in the mixed organic solvent to a concentration of 1.0 M to prepare a non-aqueous electrolyte of the present invention.

[Chemical Formula 1]

(anode)

(Positive electrode active material (LiCoO ₂ ): conductive material (carbon black): binder (PVDF)) in a weight ratio of 96: 2: 2 based on 100 parts by weight of N-methyl- Were added to prepare a positive electrode material mixture. The positive electrode mixture was applied to a positive electrode current collector (Al thin film) having a thickness of 20 占 퐉, followed by drying and roll pressing to prepare a positive electrode.

(Cathode manufacture)

A 20 mu m-thick lithium metal was rolled on a copper collector having a thickness of 20 mu m to prepare a negative electrode.

(Secondary Battery Manufacturing)

A secondary battery was produced by sequentially laminating the positive electrode and the negative electrode manufactured by the above-described method together with a porous polyethylene (PE) separator in sequence, and then pouring an excess amount of the prepared nonaqueous electrolyte solution to prepare a pouch type lithium secondary battery.

Example  2.

Except that the first organic solvent and the second organic solvent were mixed at a ratio of 90:10 by volume in the preparation of the electrolytic solution in Example 1 to prepare a mixed organic solvent, And a secondary battery including the same was manufactured.

Comparative Example  One.

A non-aqueous electrolyte and a lithium secondary battery including the non-aqueous electrolyte were prepared in the same manner as in Example 1, except that the second organic solvent was not included in the preparation of the non-aqueous electrolyte in Example 1.

Comparative Example  2.

A non-aqueous electrolyte and a non-aqueous electrolyte were prepared in the same manner as in Example 1, except that the first organic solvent and the second organic solvent were mixed at a ratio of 80:20 by volume in the preparation of the non-aqueous electrolyte in Example 1, And a lithium secondary battery containing the same was prepared.

Experimental Example

Experimental Example  One.

The bulk and impregnation conductivities of the nonaqueous electrolyte prepared in Examples 1 and 2 and the nonaqueous electrolyte prepared in Comparative Examples 1 and 2 were measured. Impregnation Conductivity is the ion transfer characteristic that appears when the electrolyte is impregnated in the separator. After the electrolyte is sufficiently impregnated into the separator, the bulk resistance is measured and converted into the conductivity.

The first solvent content Second solvent content Bulk conductivity
(10 &lt; ^-3 &gt; S / m) Impregnation conductivity
(10 &lt; ^-3 &gt; S / m) Conductivity rate
(%) Example 1 95 vol% 5 vol% 8.83 1.38 15.63 Example 2 90% 10 vol% 8.33 1.21 14.53 Comparative Example 1 100 vol% - 9.03 1.13 12.51 Comparative Example 2 80 vol% 20 vol% 7.38 0.99 13.41

In Table 1, the conductivity developing rate is the ratio of the impregnation conductivity, which is the conductivity when the separator is impregnated with the electrolyte, and the bulk conductivity of the liquid electrolyte itself. At this time, a high rate of occurrence of conductivity indicates that the pores of the separator are efficiently used, and the effect of increasing the movement uniformity of lithium ions can be obtained.

As shown in Table 1, in the case of the non-aqueous electrolyte of Examples 1 and 2 including the second organic solvent and the non-aqueous electrolyte of Comparative Example 2, compared with the non-aqueous electrolyte of Comparative Example 1 which did not include the second organic solvent The bulk conductivity is decreased, and the impregnation conductivity and the conductivity expression ratio are improved. From these results, it can be predicted that when the second organic solvent is contained in the non-aqueous electrolyte, the pores of the separator can be efficiently used to improve the movement uniformity of lithium ions.

On the other hand, in the case of the nonaqueous electrolyte solution of Comparative Example 2 containing 20% by volume of the second organic solvent, the bulk conductivity, the impregnation conductivity and the conductivity rate were significantly lowered compared to Examples 1 and 2 due to the low conductivity of the compound itself Able to know.

Experimental Example  2. Evaluation of battery life characteristics

The lithium secondary battery prepared in Example 2 and the lithium secondary batteries prepared in Comparative Examples 1 and 2 were charged at 0.2 C / 4.2 V constant current / constant voltage until the current reached 1/20 mA of 0.2 C current Then, discharge was performed under the condition of 0.5 C / 3 V constant current. The results are shown in Fig.

Referring to FIG. 1, the secondary battery manufactured in Example 2 has improved lifetime performance as compared with the secondary batteries of Comparative Examples 1 and 2. From these results, it can be seen that the secondary battery of Example 2 having the non-aqueous electrolyte containing the second organic solvent of the present invention has improved lifetime performance due to improved uniformity of lithium ion transfer and improved impregnation conductivity. In addition, the secondary battery of Comparative Example 2 containing 20 vol% of the second organic solvent showed a deterioration in the lifetime characteristics due to the decrease in bulk and impregnation conductivity.

Claims (9)

Lithium salts; And a nonaqueous electrolyte solution for a secondary battery comprising an organic solvent,
The organic solvent may be an ether compound; Ester compounds; Nitrile-based compounds; Linear carbonate compounds; And a second organic solvent comprising at least one first organic solvent selected from the group consisting of a cyclic carbonate compound and a compound represented by the following formula 1,
Wherein the second organic solvent comprises less than 20% by volume based on the total volume of the first organic solvent and the second organic solvent.
[Chemical Formula 1]

The method according to claim 1,
Wherein the mixing ratio of the first organic solvent to the second organic solvent is 81:19 to 99: 1.
The method according to claim 1,
Wherein the lithium salt comprises Li ^{&lt; +} &gt; as a cation,
As the anion, it is possible to use F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , AlO ₄ ^- , AlCl ₄ ^- , PF ₆ ^- , SbF ₆ ^{- _{6 -, BF 2 C 2 O}} 4 -, BC 4 O 8 -, (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 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (F 2 SO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .
The method according to claim 1,
Wherein the ether compound comprises 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.
The method according to claim 1,
Wherein the ester compound is at least one linear ester selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate; And at least one cyclic ester compound selected from the group consisting of? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone, and? -Caprolactone, &Lt; / RTI &gt; and mixtures thereof.
The method according to claim 1,
The nitrile compound may be at least one compound selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile , At least one compound selected from the group consisting of fluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.
The method according to claim 1,
The cyclic carbonate compound may be at least one selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate and fluoroethylene A carbonate, and mixtures of two or more thereof.
The method according to claim 1,
Wherein the linear carbonate compound comprises any one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, or a mixture of two or more thereof.
A lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte,
And the nonaqueous electrolyte solution comprises the nonaqueous electrolyte solution of claim 1.

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