KR20170071893A - Lithium secondary electolyte and lithium secondary battery with the same - Google Patents

Abstract

The present invention relates to an electrolyte and a lithium secondary battery including the electrolyte, wherein the electrolyte includes LiBF ₄ and propenesulfonate (PST) to improve a linear sweep voltametry (LSV) value, The contact angle and the Li ⁺ ion transference number on the surface are not lowered, so that the battery characteristics, particularly the life characteristics and the high output characteristics, of the lithium secondary battery can be satisfied.

Description

TECHNICAL FIELD [0001] The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery including the same,

The present invention relates to an electrolyte and a lithium secondary battery including the same, and more particularly, to a lithium secondary battery including an electrolyte having improved linear sweep voltametry (LSV) values, contact angle and Li- ⁺ ion transference number) and has a life characteristic and a high output characteristic, and a lithium secondary battery using the electrolyte.

Lithium secondary batteries are widely used not only as portable power sources for mobile phones, notebook computers, digital cameras and camcorders but also as power tools, electric bicycles, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles in HEV, and PHEV). As the application field is expanded and demand is increased, the external shape and size of the battery are variously changed, and performance and stability are demanded more than the characteristics required in the conventional small batteries. In order to meet such a demand, the performance of the battery should be stabilized in a condition where battery components are flowing in a large current.

The lithium secondary battery is manufactured by using a material capable of inserting and desorbing lithium ions as a cathode and an anode, providing a porous separator between the two electrodes, and injecting a liquid electrolyte of a lithium salt. Electricity is generated or consumed by the redox reaction by insertion and desorption.

In order to improve the battery characteristics such as the output characteristics, cyclic characteristics, and storage characteristics of the lithium secondary battery, a lithium salt, which is an electrolyte in a co-solvent mixed with a cyclic carbonate system and a chain carbonate system, Various investigations have been made on non-aqueous solvents and additives.

Particularly, as the secondary battery becomes higher output, higher energy density and middle / large size, the reliability, stability and long life characteristics of the cell become important. Since the performance of the organic electrolyte greatly influences the performance characteristics of the secondary battery, development of a new functional electrolyte additive Urgent.

However, such an electrolyte additive is expected to improve the performance of some items among most cell performances, but the performance of other items is rather reduced.

United States Patent No. 6436582 (Aug. 20, 2002)

It is an object of the present invention to provide a lithium secondary battery capable of improving the linear sweep voltametry (LSV) value and reducing the contact angle and the Li ⁺ ion transference number on the surface of the anode relative to the commercial electrolyte, And an electrolyte additive capable of improving properties, particularly life characteristics and high output characteristics, of an electrolyte for a lithium secondary battery.

Another object of the present invention is to provide a lithium secondary battery comprising the electrolyte.

According to one preferred embodiment of the present invention, a lithium secondary battery electrolyte including LiBF ₄ and propenesulfonate (PST) can be provided.

According to another preferred embodiment of the present invention, a first electrolyte system comprising a cyclic carbonate-based solvent and LiPF ₆ , and a second electrolyte system comprising a chain carbonate-based solvent, LiBF ₄ and propenesulfonate (PST) A lithium secondary battery electrolyte including an electrolyte system can be provided.

The second electrolyte system may be included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the first electrolyte system.

The first electrolyte system may include 6 to 30% by weight of the LiPF ₆ based on the entire first electrolyte system.

The second electrolyte system may include LiBF ₄ in an amount of 0.1 to 10 wt% based on the entire second electrolyte system.

The second electrolyte system may include 0.1 to 10% by weight of the propenesulfonate based on the entirety of the second electrolyte system.

The electron density value of the first electrolyte system may be 2.36 to 2.74? * ?.

The upper limit value and the lower limit value of the electron density value of the second electrolyte system may be within ± 10% of the upper limit value and the lower limit value of the electron density value of the first electrolyte system, respectively.

The electron density value of the second electrolyte system may be 2.12 to 2.38? *?, And the electron density value of the electrolyte may be 2.38 to 2.73? * ?.

According to another embodiment of the present invention, there is provided a lithium secondary battery including a cathode including a cathode active material, a cathode disposed opposite to the cathode, including a cathode active material, and an electrolyte according to the first aspect of the present invention can do.

The electrolyte according to the present invention has improved linear sweep voltametry (LSV) value, and the contact angle and the Li ⁺ ion transference number on the surface of the anode relative to the commercial electrolyte are not lowered, It is possible to improve battery characteristics, particularly high output characteristics.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention.

The present invention is capable of various modifications and various embodiments, and it is intended to illustrate and explain the specific embodiments in detail. However, it is to be understood that the present invention may be embodied with many other changes and modifications, and particular embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the present invention is not intended to be limited to any particular embodiment, but is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the specification of the present invention, terms such as "comprises" or "having" are intended to designate the presence of stated features, integers, steps, operations, elements, parts or combinations thereof, But do not preclude the presence or addition of other features, numbers, steps, operations, components, parts, or combinations thereof.

According to an embodiment of the present invention, the lithium secondary battery electrolyte according to an embodiment of the present invention can provide a lithium secondary battery electrolyte including LiBF ₄ and propenesulfonate (PST).

According to another preferred embodiment of the present invention, a first electrolyte system comprising a cyclic carbonate-based solvent and LiPF ₆ , and a second electrolyte system comprising a chain carbonate-based solvent, LiBF ₄ and propenesulfonate (PST) A lithium secondary battery electrolyte including an electrolyte system can be provided.

In the first electrolyte system, the cyclic carbonate-based solvent is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC), fluoroethylene carbonate (FEC) And a mixture thereof, and may include ethylene carbonate which is preferably excellent in battery characteristics.

In the first electrolyte system, LiPF ₆ dissolves in the carbonate-based solvent to function as a source of lithium ions in the lithium secondary battery, and accelerates the movement of lithium ions between the positive electrode and the negative electrode. The LiPF ₆ may be contained in an amount of 6 to 30% by weight, preferably 8 to 20% by weight based on the total weight of the first electrolyte system. When the content of LiPF ₆ is less than 6 wt%, the conductivity of the electrolyte is lowered to deteriorate the electrolyte performance. When the content of LiPF ₆ is more than 30 wt%, the viscosity of the electrolyte increases and the mobility of lithium ions may be lowered.

The second electrolyte system may include at least one selected from the group consisting of dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropyl carbonate (MPC), ethyl (EPC), methylethylcarbonate (MEC), ethylmethyl carbonate (EMC), and mixtures thereof. The solvent may be selected from the group consisting of methyl ethyl ketone, methyl ethyl ketone, methyl ethyl ketone, methyl ethyl ketone,

The first electrolyte system is a commonly used electrolyte system. However, when LiBF ₄ and propenesulfonate are directly added to the first electrolyte system in order to improve the lifetime and output characteristics of the first electrolyte system, there is a problem that the lithium ion transition number of the first electrolyte system is lowered Lt; / RTI >

The inventors of the present invention have found that LiBF ₄ And propenesulfonate are not added directly to the first electrolyte system but LiBF ₄ and propenesulfonate are added to the second electrolyte system satisfying the specific conditions and then the first electrolyte system and the second electrolyte The present inventors have found that the addition of LiBF ₄ and propenesulfonate improves the battery life and output characteristics as well as the problem of lowering the lithium ion transition water.

LiBF ₄ And propenesulfonate is mixed with the first electrolyte system, it is preferable that the electron density of the first electrolyte system and the second electrolyte system is lower than that of the second electrolyte system so that the lithium- It is assumed that the values should be adjusted so that they are almost similar.

In the case where the organic solvent of the second electrolyte system is a chain carbonate solvent and the second electrolyte system comprises propenesulfonate together with LiBF ₄ , 1 < / RTI > electrolyte system.

The LiBF ₄ may be included in an amount of 0.1 to 10% by weight based on the total weight of the second electrolyte system. If LiBF ₄ is contained in an amount of less than 0.1 wt%, the film may not be formed, and if it is more than 10 wt%, an excessive film may be formed and the resistance may be increased.

The propene sulfonate (PST) may be contained in an amount of 0.1 to 10 wt% based on the total weight of the second electrolyte system. When the PST is less than 0.1 wt%, the positive LSV value, the contact angle at the positive electrode surface, There may be a problem that the transition number is not improved satisfactorily. When the amount exceeds 10% by weight, there may be a problem that the ion conductivity decreases due to an increase in the viscosity of the electrolytic solution and the performance of the battery deteriorates.

The electron density value of the electrolyte system can be measured by the Langmuir probe of Hiden Analytical ESPION. The Langmuir probe is a device for measuring plasma characteristics such as ion and electron density values or electron temperature or potential from an I-V curve obtained by changing the probe voltage. The probe can be a single probe rod with a diameter of 1.2 mm and a length of 6 mm.

The electron density value can be measured by gasifying the electrolyte system in a magnetic field, converting the gas into a plasma state, and measuring the relationship between current and voltage using the Langmuir probe. The relationship between the current and the voltage is such that a copper tube antenna wound four times in a cylindrical shape is installed outside the discharge tube so that the high frequency power is effectively absorbed into the plasma region and the RF frequency is 13.56 MHz and the power of the frequency generator is 20 W Can be measured. For reference, when the RF power is 10 W or less, generation of plasma is weak and accurate discharge may not be exhibited.

The sheath potential (VV _p ) and the current measured by the above method are substituted into the following equation (1), and the electron temperature (T _e ) corresponding to the slope is obtained. Then, the saturation current (I _e ) measured using the above method can be substituted into the following equation (2) to calculate the electron density value.

[Equation 1]

&Quot; (2) "

Where E e, k, and T _e are the electron charge, the Boltzmann constant, and the electron temperature, respectively, and _{e e} , I _e , A _p, and m _e are the electron density, the saturation current, the surface area of the probe, and the mass of the electron, respectively.

The electron density value of the first electrolyte system is 2.36 to 2.74? * ?. On the other hand, in the first electrolyte system, LiBF ₄ And propenesulfonate are directly added, the electron density value of the electrolyte is about 1.97 to 2.21? * ?, and the lower limit value thereof is more than -10% of the lower limit value of the electron density value of the first electrolyte system, The upper limit value thereof is more than -10% of the upper limit value of the electron density value of the first electrolyte system. In this case, the improvement of the life and output characteristics of the electrolyte is also insignificant, and the lithium ion transition number is remarkably lowered as compared with the low one electrolyte system.

Meanwhile, LiBF ₄ And propenesulfonate is in the range of 2.12 to 2.38? *?, The lower limit of which is within ± 10% of the lower limit of the electron density of the first electrolyte system, and the upper limit Is also within ± 10% of the upper limit of the electron density value of the first electrolyte system. In this case, the electrolyte in which the first electrolyte system and the second electrolyte system are mixed not only improves battery life and output characteristics, but also does not lower the lithium ion transition water.

That is, the upper limit value and the lower limit value of the electron density value of the second electrolyte system are respectively within ± 10%, preferably within ± 5% of the upper limit value and the lower limit value of the electron density value of the first electrolyte system, As the electron density value of the second electrolyte system is similar to the electron density value of the first electrolyte system, it is possible to prevent the contact angle on the surface of the anode and the decrease of the lithium ion transfer coefficient when the two electrolytic systems are mixed.

Therefore, the electron density value of the second electrolyte system is preferably 2.12 to 3.01? *?, More preferably 2.12 to 2.38? * ?. In addition, the electron density value of the electrolyte in which the first electrolyte system and the second electrolyte system are mixed may be 2.38 to 2.73? *?, More preferably 2.40 to 2.73? * ?.

As described above, since the first electrolyte system and the second electrolyte system have similar electron density values, even when the first electrolyte system and the second electrolyte system are mixed, the lifetime and the output characteristics of the electrolyte are different from those of the first electrolyte It is superior to the lifetime and output characteristics of the system.

In addition, the electrolyte does not lower the positive LSV value, and rather the positive electrode LSV value of the electrolyte is greater than the positive electrode LSV value of the first electrolyte system. The positive electrode LSV value of the first electrolyte system is about 3.86 V, but the positive electrode LSV value of the electrolyte is 4 V or more, preferably 4 to 6 V. It can be seen from the above LSV value that the result relating to battery life related to deterioration of the electrolyte can be calculated. It can be seen that the higher the LSV value, the more stable the electrolyte remains at the higher voltage. It can be inferred that the stability according to the present invention is related to improving the battery life characteristics.

The second electrolyte system may be included in an amount of 5 to 50 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the first electrolyte system. When the second electrolyte system is contained in an amount of less than 5 parts by weight per 100 parts by weight of the first electrolyte system, the LSV may not be improved. When the amount of the second electrolyte system is more than 50 parts by weight, resistance increases due to excessive coatings by LiBF ₄ and PST can do.

In addition to the first electrolyte system and the second electrolyte system, the electrolyte may be generally used for electrolytes for the purpose of improving lifetime characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. A solvent, a lithium salt, and an additive.

The organic solvent can be used as a medium in which ions involved in the electrochemical reaction of a battery can move, without any particular limitation. Specifically, the organic solvent may be an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a propionate solvent or a carbonate solvent, and one or more of them may be mixed Can be used.

Specific examples of the ester solvent include methyl acetate, ethylacetate, n-propylacetate, dimethyl acetate, methyl propionate, ethyl propionate, ethyl propionate, γ-butyrolactone, decanolide, γ-valerolactone, mevalonolactone, γ-caprolactone, δ-valerolactone, ε-caprolactone, and the like.

Specific examples of the ether solvent include dibutylether, tetraglyme, 2-methyltetrahydrofuran, tetrahydrofuran, and the like.

Specific examples of the ketone-based solvents include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, xylene, (xylene), and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane and diethoxy ethane.

More specifically, the propionate-based solvent may include at least one selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate, buthyl propionate, And may include any one of them. The propionate-based solvent can further improve the capacity, low temperature performance and room temperature life of the battery.

Specific examples of the carbonate solvent include dimethyl carbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate (EPC ), Ethylene carbonate (EC), propylene carbonate (ethylene carbonate), ethylene carbonate (Methylene carbonate), ethylmethyl carbonate (EMC) cyclic carbonate solvent selected from the group consisting of propylene carbonate (PC), butylenes carbonate (BC), fluoroethylene carbonate (FEC) and mixtures thereof, and mixtures of one or more thereof .

Among the carbonate-based solvents, more preferred is a carbonate-based organic solvent having a high ionic conductivity capable of improving the charge-discharge performance of the battery, and a carbonate having a viscosity low enough to suitably control the viscosity of the organic solvent having the high- Based organic solvent may be mixed and used. Specifically, an organic solvent having a high dielectric constant selected from a cyclic carbonate solvent group and an organic solvent having a low viscosity selected from a chain carbonate solvent group may be mixed and used. More preferably, the organic solvent having a high dielectric constant and the organic solvent having a low viscosity are mixed at a volume ratio of 2: 8 to 8: 2, and more specifically, ethylene carbonate or propylene carbonate; Ethyl methyl carbonate; And dimethyl carbonate or diethyl carbonate in a volume ratio of 5: 1: 1 to 2: 5: 3, preferably 3: 5: 2.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, LiPF _6, as to the lithium salt _{LiClO 4, LiAsF 6, LiSbF 6} , LiAl0 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2, LiN ( _{C 2 F 5 SO 2) 2} , LiN (CF 3 SO 2) 2, LiN (C a F 2a + 1 SO 2) (C b F 2b + 1 SO 2) ( However, a and b is preferably a natural number, (Li), Li (Li), LiB (C ₂ O ₄ ) _2, and mixtures thereof, and preferably lithium hexafluorophosphate (LiPF ₆ ) is preferably used.

The lithium salt functions as a source of lithium ions in the lithium secondary battery and can promote the movement of lithium ions between the positive and negative electrodes. Accordingly, the lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%. If the concentration of the lithium salt is less than 0.6 mol%, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If the concentration exceeds 2 mol%, the viscosity of the electrolyte may increase and the lithium ion mobility may be lowered. Considering the conductivity of the electrolyte and the mobility of lithium ions, it is more preferable that the lithium salt is controlled to be approximately 0.7 mol% to 1.6 mol% in the electrolyte.

Examples of the other additives include vinylene carbonate (vinylenecarbonate, VC), metal fluoride (metal fluoride, for example, LiF, RbF, TiF, AgF , AgF 2, BaF 2, CaF 2, CdF 2, FeF 2, HF ₂ , Hg ₂ F ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , _{GaF 3, GdF 3, FeF 3} , HoF 3, InF 3, LaF 3, LuF 3, MnF 3, NdF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3 _{, YbF 3, TIF 3, CeF} 4, GeF 4, HfF 4, SiF 4, SnF 4, TiF 4, VF 4, ZrF4 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF ₆ , WF ₆ , CoF ₂ , CoF ₃ , CrF ₂ , CsF, ErF ₃ , PF ₃ , PbF ₃ , PbF ₄ , ThF ₄ , TaF ₅ and SeF ₆ ), glutaronitrile Succinonitrile (SN), adiponitrile (AN), 4-tolunitrile, 1,3,6-hexanetricarbonitrile (1,3,6-hexanetricarbonitrile) , 3,3'-thiodipropionyitrile (3,3'-thiodipro pionitrile, TPN), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylenecarbonate, fluorodimethylcarbonate, fluoroethylmethyl carbonate carbonate, lithium bis (trifluoromethylsulfonyl) imide, lithium tetrafluoroborate (LiBF ₄ ), lithium bis (trifluoromethylsulfonyl) imide, Lithium bis (oxalato) borate, lithium difluoro (oxalato) borate, lithium difluoroborate (LiDFOB), lithium (malonate oxalate) borate malonato oxalato) borate, LiMOB), phosphates of lithium difluoro _{(lithium difluorophosphate, LiPO 2 F 2} ), LiPF 2 C 4 O 8, LiSO 3 CF 3, LiPF 4 (C 2 O 4), LiP (C 2 O 4 _{) 3, LiC (SO 2 CF} 3) 3, LiBF 3 (CF 3 CF 2), LiPF 3 (CF 3 CF 2) 3, Li 2 B 12 F 12, biphenyl (biphenayl), cyclohexylbenzene (cyclohexyl benzene 4-fluorotoluene, succinic anhydride, ethylene sulfate anhydride, tris (methylsilyl) borate, and the like. And one of these may be used singly or two or more of them may be used in combination.

The other additives may be included in an amount of 0.1 to 20% by weight, preferably 0.2 to 5% by weight, based on the total weight of the electrolyte.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the electrolyte. The lithium secondary battery according to an embodiment of the present invention can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the type of the separator and the electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, Etc., and can be divided into a bulk type and a thin film type depending on the size. The electrolyte according to the embodiment of the present invention may be particularly excellent for application to a lithium ion battery, an aluminum laminated battery and a lithium polymer battery.

Specifically, the lithium secondary battery includes a cathode including a cathode active material disposed opposite to each other, a cathode including a cathode active material, and the electrolyte interposed between the anode and the cathode.

1 is an exploded perspective view of a lithium secondary battery 1 according to an embodiment of the present invention. 1, a lithium secondary battery 1 according to another embodiment of the present invention includes a separator 7 between a cathode 3, an anode 5, the cathode 3, and an anode 5, (5) and the separator (7) are impregnated into the electrolyte (15) by injecting a non-aqueous electrolyte into the electrode assembly (9) have.

Conductive lead members 10 and 13 for collecting a current generated during a battery operation can be attached to the cathode 3 and the anode 5 respectively and the lead members 10 and 13 are respectively connected to the anode 5, And the current generated in the cathode (3) can be led to the positive electrode and the negative electrode terminal.

The anode 5 is prepared by mixing a cathode active material, a conductive agent and a binder to prepare a composition for forming a cathode active material layer, applying the composition for forming a cathode active material layer to a cathode current collector such as aluminum foil, can do.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Specifically, an olivine-type lithium metal compound represented by the following formula (1) can be used.

[Chemical Formula 1]

Li _x M _y M ' _z XO _{4 - w} Y _w

M and M 'are independently Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, And X is an element selected from the group consisting of P, As, Bi, Sb, Mo, and combinations thereof, and Y is selected from the group consisting of F, S, and combinations thereof 0 <x? 1, 0 <y? 1, 0 <z? 1, 0 <x + y + z? 2, and 0? W?

Among these compounds, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _x Mn _(1-x) O ₂ (where 0 <x <1) and LiM _lx M _2y O ₂ (However, 0≤x≤1, 0≤y≤1, 0≤x + y≤1 , M 1 and M ₂ is one selected from the group consisting of Al, Sr, Mg and La are each independently One), and a mixture thereof.

The negative electrode 3 is prepared by mixing a negative electrode active material, a binder and an optional conductive agent in the same manner as the positive electrode 5 to prepare a composition for forming a negative electrode active material layer and then applying the composition to a negative electrode current collector such as a copper foil .

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon. Further, in addition to the carbonaceous material, a compound including a metallic compound capable of alloying with lithium or a metallic compound and a carbonaceous material may be used as the negative electrode active material.

At least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys and Al alloys may be used as the metal capable of being alloyed with lithium. Further, a metal lithium thin film may be used as the negative electrode active material.

As the negative electrode active material, any one selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite, lithium metal, lithium-containing alloy, and mixtures thereof may be used in view of high stability.

On the other hand, since the electrolyte is the same as described above with respect to the electrolyte, the description thereof will be omitted. Since the lithium secondary battery can be manufactured by a conventional method, a detailed description thereof will be omitted herein. Although the pouch type lithium secondary battery is described as an example in the present embodiment, the present invention is not limited to the pouch type lithium secondary battery, and any shape can be used as long as it can operate as a battery.

As described above, the lithium secondary battery including the electrolyte according to the embodiment of the present invention can exhibit low DC-IR characteristics, high-temperature storage characteristics, and improved output characteristics, It can be useful for portable devices such as computers, digital cameras, camcorders, electric vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (HEV, PHEV) have.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[Preparation Example: Preparation of electrolyte and lithium secondary battery]

In the following, LiCoO ₂ as a positive electrode active material, carbon black as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, n-methyl-2-pyrrolidone -2-pyrrolidone, NMP) was coated on an aluminum (Al) substrate. As the negative electrode, a slurry prepared by mixing MCFC (mesocarbon microbead) and carbon black, PVDF as a binder, and NMP as a solvent was coated on a copper (Cu) substrate, .

An aluminum pouch-type lithium secondary battery was prepared using the electrolyte prepared in the following Table 1 and the positive electrode and negative electrode.

The first electrolyte system The second electrolyte system The mixing ratio (weight ratio) of the first and second electrolyte systems Organic solvent
(wt%) additive
(wt%) Sum
(wt%) Organic solvent
(wt%) Additive 1
(wt%) Additive 2
(wt%) Sum
(wt%) Comparative Example EC 84, LiPF ₆ (16) 100 - - - - - Example 1 EC 84, LiPF ₆ (16) 100 DEC (80) LiBF ₄ (10) PST (10) 100 80:20 Example 2 EC 84, LiPF ₆ (16) 100 - LiBF ₄ (50) PST (50) 100 95: 5 Example 3 - - - DEC (80) LiBF ₄ (10) PST (10) 100 - Example 4 EC 84, LiPF ₆ (16) 100 DEC (80) LiBF ₄ (10) PST (10) 100 50:50

In Table 1, EC is ethylene carbonate, DEC is diethyl carbonate, and LiPF ₆ is lithium hexafluorophosphate. LiBF ₄ is lithium bis (fluorosulfonyl) imide, and PST is 1,3-Propene sulfonate.

[ Experimental Example 1  : Evaluation of the characteristics of the produced electrolyte]

The properties of the electrolytes prepared in Examples 1 to 4 and Comparative Examples were evaluated, and the results are shown in Table 2 below.

In Table 2, the respective characteristics were measured by the following methods.

1) Electron density (φ * φ): Measured using a Langmuir probe.

2) Contact angle (°): The contact area was measured by measuring the angle.

3) Anode LSV value (V): measured by lenear sweap voltammetry.

4) Lithium ion transition water: Electrochemical impedance spectroscopy (EIS) was measured. Specifically, the lithium ion transfer coefficient can be calculated by the following equation (3). However, I _o R _o and I _ss R _ss are negligible and can be calculated through I _ss / I _o . At this time, the DC polarization induction was applied until the current value stabilized at 10 mV.

&Quot; (3) &quot;

In Equation (3), t ₊ is the lithium ion transition number, I _o is the pre-polarization current, and I _ss is the post-polarization current.

Electron density value
(φ * φ) Contact angle
(°) Anode LSV value
(V) Lithium ion transition number Comparative Example 2.36 ~ 2.74 14.7 3.86 0.38 to 0.43 Example 1 2.38 ~ 2.73 14 4 0.36 to 0.41 Comparative Example 2 1.97-2.21 14.5 3.88 0.19-0.22 Comparative Example 3 2.12 ~ 2.38 14.4 3.89 0.24-0.28 Comparative Example 4 1.98-2.31 14.5 3.99 0.21 to 0.26

Referring to Table 2 above, Example 2 is a case where LiBF ₄ and propenesulfonate (PST) are directly added to the first electrolyte system (Comparative Example), and its electron density value is about 1.97 to 2.21 * the difference between the lower limit value and the upper limit value by -10% of the lower limit value and the upper limit value of the electron density value of the first electrolyte system, respectively, and that only LiBF ₄ and PST were directly added to the first electrolyte system, , There is a problem that the lithium ion transfer rate is lowered.

That is, the upper limit value and the lower limit value of the electron density value of the second electrolyte system are within ± 10%, preferably within ± 5% of the upper limit value and the lower limit value of the electron density value of the first electrolyte system, It can be seen that as the electron density value of the second electrolyte system is similar to the electron density value of the first electrolyte system, the lowering of the lithium ion transition number can be prevented when these two electrolyte systems are mixed.

Therefore, when the first electrolyte system (Comparative Example) and the second electrolyte system (Example 3) having similar electron density values as in Example 1 are mixed, not only the positive electrode LSV value is improved but also the contact angle And the lithium ion transition water does not decrease.

On the other hand, although the first electrolyte system and the second electrolyte system were mixed as in Example 4, it was confirmed that the electron density value and the lithium ion transition number of the electrolyte were lowered when the mixing ratio was outside the range of the present invention.

[ Experimental Example 2  : Evaluation of characteristics of manufactured battery]

The characteristics of the batteries including the electrolytes of Examples 1 to 4 and Comparative Examples were evaluated, and the results are shown in Table 3 below.

In Table 3, the respective characteristics were measured by the following methods.

1) Normal temperature service life (%): After charging 4.2 V, 2.7 V discharging was repeatedly performed, and 300 cycle discharge capacity was measured at room temperature (25 캜).

2) Output resistance increase rate (%): After charging 4.2 V, the resistance value was obtained by EIS (electrochemical impedance spectroscopy) measurement method.

3) Presence or absence of swelling: After charging at 4.2 V and storage at 60 캜 for 4 weeks, swelling of the battery was measured.

4) High temperature service life (%): 4.2 V charging and 2.7 V discharging were repeatedly carried out, and 300 cycle discharge capacity was measured at high temperature (45 캜).

5) High Temperature Recovery Capacity (%): After charging at 4.2 V and storing at 4O &lt; 0 &gt; C for 4 weeks, the remaining discharge capacity of the cell was measured.

Room Temperature Life (%) Output resistance increase rate (%) Presence or absence of swelling High temperature service life (%) High Temperature Recovery Capacity (%) Comparative Example 74 232 U 65 44 Example 1 84 178 radish 81 61 Example 2 76 184 U 68 51 Example 3 76 186 U 69 52 Example 4 76 184 U 68 51

Referring to Table 3, Example 2 is a case where LiBF ₄ and propenesulfonate (PST) are directly added to the first electrolyte system (Comparative Example), and in the case of a battery using the same, life and output characteristics The improvement is also minimal.

On the other hand, when a second electrolyte system (Example 3) having a lower limit value and an upper limit value of an electron density value is manufactured and mixed with the first electrolyte system (Comparative Example) as in Example 1, the life and output characteristics But also exhibits stable battery characteristics even at a high temperature, and swelling does not occur.

However, in the case of Example 4 in which the mixing ratio of the first electrolyte system (Comparative Example) and the second electrolyte system (Example 3) is outside the scope of the present invention, although the two electrolyte systems are used, And the like.

That is, when the second electrolyte system having a value similar to the electron density value of the first electrolyte system is mixed with each other at an appropriate ratio, it is possible to prevent the reduction of the electron density value and the lithium ion transition number, Is also effective in improving battery life and output characteristics.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. And falls within the scope of the invention.

1: Lithium secondary battery
3: cathode 5: anode
7: separator 9: electrode assembly
10, 13: lead member 15: case

Claims (11)

A lithium secondary battery electrolyte comprising LiBF ₄ and propenesulfonate (PST). A first electrolyte system comprising a cyclic carbonate-based solvent and LiPF ₆ , and
A second electrolyte system including a chain carbonate solvent, LiBF _4, and propenesulfonate (PST)
&Lt; / RTI &gt; 3. The method of claim 2,
Wherein the second electrolyte system is included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the first electrolyte system. 3. The method of claim 2,
Wherein the first electrolyte system comprises 6 to 30% by weight of the LiPF ₆ based on the entire first electrolyte system. 3. The method of claim 2,
Wherein the second electrolyte system comprises the LiBF ₄ in an amount of 0.1 to 10 wt% based on the entire second electrolyte system. 3. The method of claim 2,
Wherein the second electrolyte system comprises 0.1 to 10% by weight of the propenesulfonate based on the entire second electrolyte system. 3. The method of claim 2,
Wherein an electron density value of the first electrolyte system is 2.36 to 2.74? * ?. 3. The method of claim 2,
Wherein an upper limit value and a lower limit value of an electron density value of the second electrolyte system are within ± 10% of an upper limit value and a lower limit value of an electron density value of the first electrolyte system, respectively. 3. The method of claim 2,
Wherein the second electrolyte system has an electron density value of 2.12 to 2.38? *?. 3. The method of claim 2,
And the electron density value of the electrolyte is 2.38 to 2.73? * ?. An anode including a cathode active material,
A negative electrode disposed opposite to the positive electrode and including a negative electrode active material, and
A lithium secondary battery comprising the electrolyte according to claim 1.

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