KR20170008475A - Electrolyte solution and lithium secondary battery comprising the same - Google Patents

Abstract

A lithium secondary battery of the present invention comprises: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; a separation membrane interposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. The nonaqueous electrolyte comprises a fluoride phosphate compound containing a lithium ion and a borate compound having an alkylsilyl group as additives. By applying a nonaqueous electrolyte comprising the additive to a lithium secondary battery, performance such as room temperature output and low temperature resistance can be improved. Further, a lithium titanium-based composite metal oxide is used as a negative electrode material, so a lithium secondary battery having improved performance can be provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to a non-aqueous electrolyte capable of improving the room temperature output and low temperature resistance of a battery and a lithium secondary battery comprising the same.

As the size and weight of electronic equipment are reduced and the use of portable electronic devices is becoming common, researches on secondary batteries having high energy density as their power source have been actively conducted.

Examples of the secondary battery include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among them, the secondary battery exhibits a discharge voltage two times higher than that of a conventional battery using an aqueous alkaline solution In addition, studies have been made on a lithium secondary battery which has a high energy density per unit weight and can be rapidly charged.

The lithium secondary battery is composed of a positive electrode made of a lithium metal oxide, a negative electrode made of a carbon material or a lithium metal alloy, and an electrolyte made of a lithium salt and an organic solvent.

At this time, the organic solvent is easily volatilized and has a high flammability, resulting in short circuit and ignition due to overcharge, internal overheat during over discharge, and lowers the safety of the lithium secondary battery at high temperature.

Therefore, various attempts have been made to develop electrolytes capable of improving the cycle life and high temperature service life of the battery.

In order to improve the performance of the lithium secondary battery such as the room temperature output and the low temperature resistance characteristic, it is necessary to include two specific additives in the non-aqueous electrolyte and to use the specific negative electrode material, Which is capable of preventing side reactions at the negative electrode interface, protecting the negative electrode, promoting ion-pair separation of the lithium salt in the electrolyte, and reducing the electrode interface resistance, and a lithium secondary battery comprising the non-aqueous electrolyte.

In order to accomplish the above object, the present invention provides a lithium secondary battery including a cathode including a cathode active material, a cathode including a cathode active material, a separator disposed between the cathode and the anode, and a non-aqueous electrolyte, A lithium fluoride-based compound containing lithium ions as an additive, and a borate-based compound having an alkylsilyl group.

The negative electrode active material may include a lithium-titanium composite metal oxide represented by the following general formula (1).

[Chemical Formula 1]

LiTi _a M _b O ₂

M may be at least one metal selected from the group consisting of Mn, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Is a real number satisfying 0.5? A? 1.0, 0? B? 0.5 and a + b =

The cathode active material may include a lithium composite metal oxide represented by the following general formula (2).

(2)

LiM1 _a M2 _b M3 _c O ₂

In Formula 2, M1 to M3 each independently represent a transition metal selected from the group consisting of Ni, Ti, Mn, Al, Co, Cu, Fe, Mg, B, Cr, Zr, Metal, and a, b, and c are real numbers satisfying a + b + c = 1.

Each of M1 to M3 may independently include at least one metal selected from the group consisting of Ni, Mn, and Co.

The fluorophosphate-based compound containing lithium ion is a compound composed of lithium difluoro (bisoxalate) phosphate (LiDFOP) and lithium tetrafluoro oxalate phosphate (LiTFOP) ≪ / RTI >

The alkylsilyl group of the borate compound having an alkylsilyl group may be an alkylsilyl group having 1 to 5 carbon atoms and may include 1 to 3 of the alkylsilyl groups.

The borate compound having an alkylsilyl group may include tris (trimethylsilyl) borate (TMSB).

The lithium fluoride-based compound containing a lithium ion and the borate compound having an alkylsilyl group may each be contained in an amount of 0.1 to 1.0% by weight based on the total weight of the non-aqueous electrolyte.

The lithium secondary battery of the present invention includes two specific additives in a non-aqueous electrolyte and uses a specific negative electrode material to prevent side reactions at the negative electrode interface that may occur depending on the driving potential of the corresponding electrode, And the separation of the ion pair of the lithium salt in the electrolyte is promoted to reduce the electrode interface resistance, and the performance of the lithium secondary battery such as the room temperature output and the low temperature resistance characteristic can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the results of measurement of SOC output during discharging of a lithium secondary battery of Example 1 and Comparative Examples 1 to 3, in accordance with the present specification;
FIG. 2 is a graph showing the results of measurement of SOC output during charging of the lithium secondary battery of Example 1 and Comparative Examples 1 to 3 according to the present specification. FIG.
3 is a graph showing the results of measurement of the voltage drop at low temperatures of the lithium secondary batteries of Example 1 and Comparative Example 2 according to the present specification.
FIG. 4 is a graph showing the results of measurement of the output of each of the lithium secondary batteries of Comparative Examples 4 and 5 during SOC discharge according to the present specification. FIG.
FIG. 5 is a graph showing the results of measurement of SOC output during charging of the lithium secondary batteries of Comparative Examples 4 and 5 according to the present specification. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the constitutions shown in the embodiments described herein are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention, so that various equivalents and variations Examples should be understood.

According to the present specification, there is provided a non-aqueous electrolyte containing a fluorophosphate-based compound containing lithium ions and a borate-based compound having an alkylsilyl group as an additive. By applying such a non-aqueous electrolyte, lithium having improved room temperature output and low temperature resistance A secondary battery is provided.

A lithium secondary battery according to an embodiment of the present invention includes a cathode including a cathode active material, a cathode including a cathode active material, a separator disposed between the cathode and the anode, and a non-aqueous electrolyte, The electrolyte includes a fluorophosphate-based compound containing lithium ion as an additive and a borate-based compound having an alkylsilyl group.

The non-aqueous electrolyte may include a lithium salt, an additive, and a non-aqueous organic solvent. When the two compounds are added to the non-aqueous electrolyte as the additive, the lithium secondary battery Performance such as capacity and output can be improved.

The fluorophosphate compound containing lithium ion as an additive of the non-aqueous electrolyte is preferably lithium difluoro (bisoxalate) phosphate (LiDFOP) (hereinafter referred to as LiDFOP) and lithium tetrafluoro And lithium tetrafluoro oxalate phosphate (LiTFOP). Although it is not particularly limited, LiDFOP may be preferable, and LiDFOP may be the following compound.

Since the fluorophosphate compound containing lithium ions contains lithium ions, it can act as a constituent of the SEI coating, improve the mobility of lithium ions at the SEI interface, and protect the negative electrode interface It can serve as an additive.

The alkylsilyl group of the borate compound having an alkylsilyl group as an additive of the non-aqueous electrolyte may be an alkylsilyl group having 1 to 5 carbon atoms and may include 1 to 3 of the alkylsilyl groups. That is, it may mean a compound in which the alkylsilyl group is bonded to a borate having three oxygen atoms, and the alkylsilyl group may include methylsilyl, ethylsilyl, propylsilyl, isopropylsilyl, butylsilyl, isobutylsilyl, (Trimethylsilyl) borate (TMSB) (hereinafter referred to as TMSB) may be preferably used as long as it is an alkylsilyl group having 1 to 5 carbon atoms such as isopentylsilyl and isopentylsilyl.

The boric acid salt-based compound having an alkylsilyl group contains a boron atom having relatively few electrons, and is capable of dissociating lithium ions to form TMSB-PF ₆ or the like by binding with a salt of a lithium salt having a relatively large electron number, Ion pair separation of the lithium salt can be promoted.

In addition, LiF, which may be contained in the electrolyte in the form of a lithium salt or the like, may not be dissociated during initial charging / discharging, and may not be inserted or desorbed into the negative electrode and the positive electrode, thereby failing to contribute to improvement in battery capacity or output. It is possible to cause problems such as generation of hydrofluoric acid gas and increase in electrode surface resistance. By adding a borate compound having an alkylsilyl group, dissociation of LiF can be promoted to prevent side reactions at the electrode interface, .

That is, the borate-based compound having an alkylsilyl group promotes ion-pair separation of the lithium salt to improve the mobility of the lithium ion, reduce the interfacial resistance of the SEI film, By dissociation, problems such as generation of hydrofluoric acid gas can be solved.

The lithium fluoride-based compound containing a lithium ion and the borate compound having an alkylsilyl group may each be contained in an amount of 0.1 to 1.0% by weight based on the total weight of the non-aqueous electrolyte.

The fluorophosphate-based compound containing lithium ions may be contained in an amount of 0.1 to 1.0 wt% based on the total weight of the non-aqueous electrolyte. When the fluorophosphate-based compound is contained in an amount of 0.1 to 1.0 wt%, the lithium salt and the non- The generation of side reactions at the negative electrode interface is reduced, and the problem of the swelling phenomenon or capacity degradation inside the battery due to the generation of gas during the activation process can be prevented.

The borate compound having an alkylsilyl group may be contained in an amount of 0.1 to 1.0 wt% based on the total weight of the non-aqueous electrolyte. When the borate compound is contained in an amount of 0.1 to 1.0 wt%, the amount of the lithium salt and the organic solvent may be appropriate And the ion pair separation of the lithium salt is not promoted sufficiently, so that the effect of reducing the electrode interface resistance and preventing the side reaction can be obtained, and the phenomenon of formation of a thick film on the surface of the cathode can be reduced, and the resistance of the battery can be reduced.

Meanwhile, in the non-aqueous electrolyte according to the present invention, the non-aqueous organic solvent may include an organic solvent usable as a non-aqueous electrolyte in the production of a conventional lithium secondary battery. At this time, their content can also be appropriately changed within a generally usable range.

Specifically, the non-aqueous organic solvent may include conventional organic solvents which can be used as a non-aqueous organic solvent for a lithium secondary battery such as a cyclic carbonate solvent, a linear carbonate solvent, an ester solvent or a ketone solvent. It can be used in combination of species or more.

The cyclic carbonate solvent may be a mixed solution of one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

Examples of the linear carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), fluoroethylene carbonate (MPC) and ethyl propyl carbonate (EPC). These solvents may be used alone or in combination of two or more.

Examples of the ester solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or mixtures of two or more thereof. As the ketone solvent, polymethyl vinyl ketone or the like may be used.

On the other hand, the non-aqueous organic solvent may be a mixed organic solvent in which three kinds of carbonate-based solvents are mixed, and may be more preferable when using a ternary non-aqueous organic solvent. Examples of the compound which can be used include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, vinylene carbonate, fluoroethylene carbonate, methylpropyl carbonate or ethylpropyl carbonate And a mixed solvent obtained by mixing three kinds of the carbonate compounds may be applied.

The lithium salt that can be included in the electrolyte can provide a predetermined lithium ion conductivity and can be applied without limitation as long as it is commonly used in an electrolyte for a lithium secondary battery. For example, the anion of the lithium salt includes F ^{-, Cl -, Br -,} I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 _{^{-, (CF 3) 4 PF}} 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, F 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N - ^{_{, (FSO 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 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - 1 the lithium salt at least one selected from the group can be used consisting of .

According to the present invention, a lithium secondary battery includes a negative electrode including a negative active material, and the negative active material may intercalate and deintercalate lithium.

The negative electrode active material may include a lithium-titanium composite metal oxide represented by the following general formula (1).

[Chemical Formula 1]

LiTi _a M _b O ₂

M may be at least one metal selected from the group consisting of Mn, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, May be a real number satisfying 0.5? A? 1.0, 0? B? 0.5, and a + b =

The negative electrode active material may be a titanium-based lithium composite metal oxide, and may have a higher potential than a negative electrode to which a carbonaceous negative electrode active material is applied.

On the other hand, since the carbon-based anode active material generally used as the anode active material has a wider voltage driving range than that of the titanium-based composite metal oxide, the output value of each SOC may vary greatly, There is a problem that the output of the constant value can not be stably outputted. Unlike the carbon-based anode active material (for example, graphite), which is a layered structure, the titanium-based composite metal oxide having a spinel structure is advantageous for rapid charge / discharge due to easy storage and release of lithium ions, It is possible to have excellent lifetime characteristics because there is almost no volume expansion of the negative electrode occurring in the discharge, and the insertion reaction of lithium ion is performed at 1.5 V, so that the electrolyte solution is stabilized and lithium dendrite may not be generated.

However, the titanium-based composite metal oxide has a lower full-cell operating voltage than the carbon-based anode active material and has a small capacity. The additives used in the battery of the carbon-based anode active material are used for protecting the anode after the reduction reaction In addition, when the titanium composite metal oxide is used, it is difficult to reduce the additive at the cathode, so that it is difficult to form a uniform SEI film and gas is generated. In addition, titanium tetravalent cation is unstable and ternary, When it becomes a cation, there is a fear of promoting a side reaction because it absorbs electrons in the electrolyte solution.

However, the lithium secondary battery according to the present invention can reduce the deviation of the output value by applying a lithium-titanium composite metal oxide which can stably output at a relatively narrow driving voltage, as a negative electrode active material, The above-described disadvantages of the titanium-based composite metal oxide can be compensated for, while taking advantage of advantages such as excellent lifetime characteristics and superiority of no volume expansion.

In other words, the fluorophosphate-based compound containing lithium ions has a low reduction potential, and by adding it, a reaction can be induced even in a titanium-based composite metal oxide having a low operating voltage, thereby forming an SEI film. By protecting the anode, Can be suppressed. Furthermore, by adding a borate compound having an alkylsilyl group to the non-aqueous electrolyte, the anion stabilizing action becomes excellent, and the generation of gas during storage at a high temperature can be reduced.

Hereinafter, in the lithium secondary battery to which the lithium-titanium composite metal oxide is applied, the action of the two additives contained in the non-aqueous electrolyte will be described according to the present specification.

Generally, in the initial charging process of the secondary battery, the electrolyte is decomposed before the lithium ions discharged from the anode are inserted into the negative electrode, thereby forming SEI coating on the negative electrode surface that affects the battery reaction. This coating has a property of allowing lithium ions to pass therethrough and blocking the movement of electrons, and also functions as a protective film to prevent the electrolyte from being decomposed continuously.

Therefore, when a film is formed on the surface of the negative electrode, decomposition of the electrolyte due to electron transfer between the electrode and the electrolyte is suppressed, and only insertion and desorption of lithium ions can be selectively performed. However, the produced SEI coating does not exist stably until the battery life is over, is destroyed by shrinkage and expansion due to repeated charge / discharge cycles, or is destroyed by external heat or impact.

This destroyed SEI film is restored by the subsequent charge and discharge process, resulting in the consumption of additional or irreversible charge resulting in a reduction of the continuous reversible capacity. Particularly, as the thickness of the solid film formed by the decomposition of the electrolytic solution is increased, the interfacial resistance is increased and the performance of the cell deteriorates.

However, when the lithium-based negative electrode active material and the non-aqueous electrolyte containing two additives are applied to the lithium secondary battery according to the present specification, it is possible to increase the driving potential of the negative electrode, It is possible to simultaneously protect the negative electrode interface such as breakage of the coating film, thereby contributing to improvement of the performance of the lithium secondary battery. That is, the fluorophosphate compound containing lithium ion is a compound decomposed at 1.7 V, which is the operating potential when the LTO electrode is used as a negative electrode. The lithium ion generated as a result of decomposition reacts with the reversible capacity Can be canceled, and the negative electrode interface can be more efficiently protected.

When the boric acid salt-based compound having an alkylsilyl group is used together with the lithium-titanium-based negative active material, it is excellent in stabilizing the anion, thereby stabilizing the lithium salt such as LiPF 6 during high-temperature storage.

The negative electrode can be generally manufactured according to a method used in the art, and can be manufactured by mixing the lithium-titanium-based negative electrode active material, the conductive material and the binder in a solvent and applying the mixture to a current collector.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an 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.

In the case of the conductive material, the content of the conductive material can be appropriately adjusted so as to take advantage of both sides in terms of the improvement of the conductivity of the electrode and the prevention of the porosity of the electrode. In the case of the binder, The content can be appropriately adjusted so as to take advantage of both aspects in terms of improvement, peeling of the electrode surface, viscosity control, and the like. The amount of the conductive material and the binder may be adjusted to about 2 to 5 parts by weight based on 100 parts by weight of the negative electrode active material, for example.

Natural graphite, carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, carbon fiber, carbon black, and the like can be used as the conductive material, as long as it can be generally used in the art. Metal, aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, iridium, Polyaniline, polythiophene, polyacetylene, polypyrrole, or a combination thereof. In general, a carbon black-based conductive material may be used.

The binder can be generally used in the art, and can be applied to any kind of known binders without limitation, and generally includes polyvinylidene fluoride (PVdF), polyhexafluoropropylene-polyvinyl (Vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), poly (ethyl Acrylate), polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene propylene diene monomer (EPDM) Can be used.

According to the present specification, a lithium secondary battery includes a positive electrode including a positive electrode active material, and the positive electrode active material may intercalate and deintercalate lithium.

The cathode active material may include a lithium composite metal oxide represented by the following general formula (2).

(2)

LiM1 _a M2 _b M3 _c O ₂

In Formula 2, M1 to M3 each independently represent a transition metal selected from the group consisting of Ni, Ti, Mn, Al, Co, Cu, Fe, Mg, B, Cr, Zr, Metal, and a, b, and c may be real numbers satisfying a + b + c = 1.

Preferably, each of M1 to M3 may independently include at least one metal selected from the group consisting of Ni, Mn, and Co. The cathode active material may be a ternary cathode active material generally used in the art, such as nickel-manganese-cobalt oxide, nickel-aluminum-manganese oxide, nickel-cobalt-aluminum oxide and the like.

In the case of the cathode active material of the ternary composite metal oxide generally applied in the art, the performance of the lithium secondary battery can be further improved when it is applied together with the non-aqueous electrolyte according to the present invention. In particular, in the case of TMSB, When used together with the ternary composite metal oxide, superiority in high temperature storage characteristics can be further maximized.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

Since the kind and content of the conductive material and the binder are not greatly different from those of the negative electrode, the description thereof will be omitted.

As the separator for insulating the electrodes from each other between the anode and the cathode, a polyolefin separator commonly used in the art or a composite separator having an organic-inorganic hybrid layer formed on an olefin based material may be used without particular limitation .

The positive electrode, the negative electrode, and the separator having the above structure are housed in the pouch case, and then the non-aqueous electrolyte is injected to manufacture a battery.

The external shape of the lithium secondary battery according to 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.

Example

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiment 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  One

One) Non-aqueous  Preparation of electrolyte

1M LiPF ₆ solution containing propylene carbonate (PC): ethyl methyl carbonate (EMC): dimethyl carbonate (DEC) as a carbonate solvent in a weight ratio of 1: 1: 1 was prepared, and as a electrolyte additive, lithium difluoro Oxalate) phosphate (LiDFOP) and tris (trimethylsilyl) borate (TMSB) were added so as to be 1.0 wt%, based on the total weight of the solution, to prepare a nonaqueous electrolyte.

2) Preparation of lithium secondary battery

Subsequently, LiCo _{0 . 2} Ni _{0 . 56} Mn _{0 . 27} O ₂ , and Li ₄ Ti ₅ O ₂ was used as the negative electrode active material. A pouch type battery having a capacity of 280 mAh was prepared using the non-aqueous electrolyte, the cathode and the anode.

Comparative Example  One

A nonaqueous electrolyte and a secondary battery comprising the nonaqueous electrolyte were prepared in the same manner as in Example 1, except that LiDFOP and TMSB were not added as electrolyte additives.

Comparative Example  2

A nonaqueous electrolyte and a secondary battery comprising the nonaqueous electrolyte were prepared in the same manner as in Example 1, except that TMSB was not added as an electrolyte additive.

Comparative Example  3

A nonaqueous electrolyte and a secondary battery comprising the nonaqueous electrolyte were prepared in the same manner as in Example 1, except that LiDFOP was not added as an electrolyte additive.

Comparative Example  4

A lithium secondary battery was prepared in the same manner as in Example 1, except that a nonaqueous electrolyte was prepared (LiDFOP and TMSB not added) in the same manner as in Comparative Example 1, and natural graphite was used as a negative electrode active material.

Comparative Example  5

A lithium secondary battery was prepared in the same manner as in Example 1, except that a nonaqueous electrolyte was prepared (LiDFOP and TMSB was added) in the same manner as in Example 1, and natural graphite was used as a negative electrode active material.

Experimental Example  One: TMSB  And LiDFOP Whether to add  Evaluation of room temperature power

To confirm the change in the room temperature output of the lithium secondary battery according to whether or not TMSB and LiDFOP added as additives to the non-aqueous electrolyte were added, charging was carried out at room temperature (about 25 캜) for each of the above Example 1 and Comparative Examples 1 to 3 And the cell output at the time of discharging were measured. The results are shown in Table 1 and Figs. 1 and 2.

TMSB
(weight %) LiDFOP
(weight %) Room temperature output (SOC, W) 20% 40% 60% 80% 100% charge Discharge charge Discharge charge Discharge charge Discharge charge Discharge Example 1 1.0 1.0 47.7 10.8 49.8 13.3 52.8 18.4 52.7 23.8 45.1 28.5 Comparative Example 1 0 0 43.5 10.1 45.2 12.3 47.7 16.6 47.7 21.4 40.8 25.5 Comparative Example 2 0 1.0 45.1 10.7 47.1 13.0 50.1 17.8 50.4 22.9 42.8 27.0 Comparative Example 3 1.0 0 46.2 11.0 48.3 13.3 51.4 17.3 51.3 24.1 43.5 27.8

Referring to Table 1 and FIG. 1 and FIG. 2, the case of Example 1 in which both of TMSB and LiDFOP were not added or Comparative Examples 1 to 3 in which neither TMSB nor LiDFOP was added, It was confirmed that the output was excellent even at the discharge, and it was confirmed that the output difference at the high SOC was more evident.

Thus, TMSB and LiDFOP, which are used as the electrolyte additives, show excellent effects when both of the additives are added, and it is difficult to obtain the effect when only one of the two additives is not added , And the synergistic effect of the simultaneous addition of the two additives, the lithium secondary battery to which the electrolyte including the electrolyte is applied has a room temperature output improved by about 10%.

Experimental Example  2: Evaluation of room temperature power according to changes of anode active material

In order to confirm a negative electrode active material suitable for a non-aqueous electrolyte containing TMSB and LiDFOP, the battery output at the time of charging and discharging by SOC at room temperature (about 25 ° C) was further measured for Comparative Examples 4 and 5, Are shown in Table 2 and Figs. 4 and 5 together with the results of Example 1.

Anode active material additive Room temperature output (SOC, W) 20% 40% 60% 80% charge Discharge charge Discharge charge Discharge charge Discharge Example 1 LTO LiDFOP and
TMSB 47.7 10.8 49.8 13.3 52.8 18.4 52.7 23.8 Comparative Example 4 natural
black smoke None 52.2 27.8 49.0 41.8 39.7 45.6 28.8 50.9 Comparative Example 5 natural
black smoke LiDFOP and
TMSB 51.4 27.8 48.3 41.3 39.0 44.9 28.1 50.3

Referring to Table 2 and FIGS. 4 and 5, when Comparative Examples 4 and 5, in which the negative electrode active material is natural graphite, were compared, lithium secondary batteries to which LiDFOP and TMSB were added, 5) and the non-applied lithium secondary battery (Comparative Example 4) showed no difference in the effect, and the output was slightly lowered at the high SOC.

However, as shown in Table 2, when Example 1 and Comparative Example 5 in which a non-aqueous electrolyte containing LiDFOP and TMSB were applied were compared, the output of the lithium secondary battery of Example 1 in which the negative electrode active material was LTO It was confirmed that the negative electrode active material was significantly improved as compared with the output of the secondary battery of Comparative Example 5 which is natural graphite and the difference in the high SOC was more evident.

As a result, the lithium secondary battery to which the non-aqueous electrolyte including TMSB and LiDFOP are simultaneously added as an electrolyte additive may cause some damage on the discharge output side compared with the case where a carbonaceous negative electrode active material such as natural graphite is applied as the negative electrode active material , It is understood that LTO superior in life characteristics to graphite anode is more preferable from the viewpoint of performance of secondary battery and it is understood that the addition effect of TMSB and LiDFOP is maximized when LTO cathode is applied have.

Experimental Example  3: Low temperature resistance evaluation

TMSB and LiDFOP on the low-temperature resistance of the lithium secondary battery, the low-temperature resistance of the lithium secondary battery of Example 1 and Comparative Example 2 was measured, and the results are shown in Table 3 below. 3.

Electrolyte additive Low temperature resistance Example 1 LiDFOP + TMSB 0.51 Comparative Example 2 LIDFOP 0.89

Referring to Table 3 and FIG. 3, it can be seen that the voltage drop when a pulse is applied at a low temperature of -10 ° C is further reduced when LiDFOP and TMSB are mixed, compared to Comparative Example 2 using LiDFOP alone there was.

As a result, when TMSB and LiDFOP are simultaneously added to the non-aqueous electrolyte, the voltage drop at a low temperature (about -10 ° C) is smaller than that of the lithium secondary battery to which the electrolyte is not added, and TMSB and LiDFOP The non-aqueous electrolyte added to the lithium secondary battery improves the low-temperature resistance of the battery.

Claims (16)

1. A lithium secondary battery comprising a positive electrode comprising a positive electrode active material, a negative electrode including a negative electrode active material, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte,
Wherein the non-aqueous electrolyte comprises a fluorophosphate-based compound containing lithium ion as an additive and a borate-based compound having an alkylsilyl group.
The method according to claim 1,
Wherein the negative electrode active material comprises a lithium-titanium-based composite metal oxide represented by the following Formula 1:
[Chemical Formula 1]
LiTi _a M _b O ₂
In Formula 1,
M is at least one metal selected from the group consisting of Mn, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr,
a and b are real numbers satisfying 0.5? a? 1.0, 0? b? 0.5 and a + b =
The method according to claim 1,
Wherein the positive electrode active material comprises a lithium composite metal oxide represented by the following formula (2): < EMI ID =
(2)
LiM1 _a M2 _b M3 _c O ₂
In Formula 2,
M1 to M3 are each independently at least one metal selected from the group consisting of Ni, Ti, Mn, Al, Co, Cu, Fe, Mg, B, Cr, Zr,
a, b, and c are real numbers satisfying a + b + c = 1.
The method of claim 3,
And each of M1 to M3 independently includes at least one metal selected from the group consisting of Ni, Mn, and Co.
The method according to claim 1,
The fluorophosphate-based compound containing lithium ion is a compound composed of lithium difluoro (bisoxalate) phosphate (LiDFOP) and lithium tetrafluoro oxalate phosphate (LiTFOP) ≪ / RTI > wherein at least one of the compounds is selected from the group consisting of: < RTI ID = 0.0 >
The method according to claim 1,
Wherein the alkylsilyl group of the borate compound having an alkylsilyl group is an alkylsilyl group having 1 to 5 carbon atoms and contains 1 to 3 of the alkylsilyl groups.
The method according to claim 1,
Wherein the boric acid salt compound having an alkylsilyl group comprises tris (trimethylsilyl) borate (TMSB).
The method according to claim 1,
Wherein the lithium fluoride-based compound containing lithium ion and the borate compound having alkylsilyl group are each contained in an amount of 0.1 to 1.0 wt% based on the total weight of the non-aqueous electrolyte.
The method according to claim 1,
Wherein the non-aqueous electrolyte further comprises a non-aqueous organic solvent,
Wherein the non-aqueous organic solvent comprises a mixed solution of at least one selected from the group consisting of a cyclic carbonate solvent, a linear carbonate solvent, an ester solvent, and a ketone solvent.
10. The method of claim 9,
Wherein the cyclic carbonate solvent comprises a mixed solution of at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and butylene carbonate.
10. The method of claim 9,
Wherein the linear carbonate solvent comprises at least one mixed solution selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, vinylene carbonate, fluoroethylene carbonate, methylpropyl carbonate and ethylpropyl carbonate. Lithium secondary battery.
10. The method of claim 9,
The ester solvent is selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone Wherein the electrolyte solution is a mixed solution of one or more selected from the group consisting of lithium,
The method according to claim 1,
Wherein the non-aqueous electrolyte further comprises a non-aqueous organic solvent,
The non-aqueous organic solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, vinylene carbonate, fluorethylene carbonate, methylpropyl carbonate and ethylpropyl carbonate Wherein the lithium secondary battery is a mixed solvent containing three selected compounds.
The method according to claim 1,
Wherein the non-aqueous electrolyte further comprises a lithium salt,
The lithium salt is _{LiPF 6, LiAsF 6, LiCF 3} SO 3, LiN (CF 3 SO 2) 2, LiBF 4, LiSbF 6, LiN (C 2 F 5 SO 2) 2, LiAlO 4, LiAlCl 4, LiCo 0. ₂ Ni _{0 . 56} Mn _{0 . 27} O ₂ , LiCoO ₂ , LiSO ₃ CF _3, and LiClO ₄ .
A battery module comprising the lithium secondary battery of claim 1 as a unit cell.
A battery pack comprising the battery module of claim 15.

Images