KR20180023570A - Electrolyte and Lithium ion batteries - Google Patents

Abstract

The present invention provides an electrolyte containing two kinds of electrolyte additive and a lithium secondary battery comprising the same. A lithium secondary battery using an electrolyte containing an electrolyte additive according to the present invention is excellent in cycle life characteristics due to the combined use of a first additive and a second additive, and can prolong the life of the battery and increase discharging capability of the battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte and a lithium secondary battery including the same.

The present invention relates to an electrolytic solution containing a second electrolyte additive and a lithium secondary battery comprising the same, and more particularly, to a lithium secondary battery comprising a first additive and a second additive, And to provide a lithium secondary battery including the electrolytic solution having an effect of increasing discharge capacity.

In the lithium secondary battery, an electrolyte is interposed between the positive electrode and the negative electrode to enable smooth movement of lithium ions, and electricity is generated or consumed by redox reaction caused by insertion and desorption in the positive electrode and negative electrode.

Lithium secondary batteries, which are mainly used as power sources for mobile IT devices and power tools, such as mobile phones, are being used for applications such as automobiles and energy storage due to the development of large-capacity technologies.

As such an application field is widened and demand is increased, battery performance and stability that are better than those required in conventional small batteries are required. In recent years, battery characteristics such as output characteristics, cycle characteristics, storage characteristics, Various investigations have been made on organic solvents and additives as components for electrolytic solution.

It has been difficult to expect improvement in low-temperature output characteristics due to the formation of a non-uniform SEI film in the case of an electrolyte solution which does not contain an electrolyte additive or contains an electrolyte additive having poor characteristics. Further, even when the amount of the electrolyte additive is included, if the amount of the electrolyte additive can not be adjusted to the required amount, the surface of the anode may be decomposed or the oxidation reaction may occur at the high temperature due to the electrolyte additive, thereby ultimately increasing the irreversible capacity of the secondary battery, There is a problem in that it is lowered.

Patent Document 1: Korean Patent Publication No. 2002-0088963 Patent Document 2: Korean Patent Publication No. 2008-0034938

It is an object of the present invention to provide an electrolyte solution having excellent cycle life characteristics, prolonging the life of the battery, and increasing the discharge capacity, and a lithium secondary battery including the electrolyte solution.

These and other objects of the present invention can be achieved by the present invention described below.

In order to accomplish the above object, the present invention provides a nonaqueous organic solvent; Lithium salts; An electrolyte additive comprising a first additive and a second additive,

The first additive may be represented by the following general formula

[Chemical Formula 1]

Wherein R ₁ and R ₃ are each independently selected from the group consisting of hydrogen or an alkyl group having 1 to 20 carbon atoms and R ₂ is a bond or an alkylene group having 1 to 20 carbon atoms) And the second additive is tetrafluoro (oxalato) lithium phosphate (lithium tetrafluoro (oxalato) phosphate; LiTFOP).

According to such an electrolytic solution, an electrolytic solution having a high capacity and a high initial charging / discharging efficiency, and a gas generation inside the cell also have higher safety and reliability than a conventional nonaqueous electrolyte secondary battery.

In addition, cathode; A separator; And a non-aqueous electrolyte, wherein the anode is a manganese spinel-based active material or a lithium metal oxide, and the cathode is a carbon-based anode active material selected from the group consisting of crystalline carbon, amorphous carbon, artificial graphite, and natural graphite, The present invention provides a lithium secondary battery characterized by being the above-described electrolyte.

By using the lithium secondary battery using the above-described electrolyte solution, it is possible to provide a lithium secondary battery having high safety and high reliability because it has a high capacity, excellent initial charge / discharge efficiency and cycle characteristics, and can reduce gas generation inside the battery .

According to the present invention, it is an object of the present invention to provide an electrolytic solution having excellent room temperature and high temperature service life characteristics, prolonging the life of the battery, and increasing the discharge capacity. Therefore, in the case of a lithium secondary battery including a positive electrode manufactured using the positive electrode, it is advantageous in that capacity can be increased and lifetime characteristics of an excellent battery can be secured.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

The electrolytic solution of the present invention includes a non-aqueous organic solvent; Lithium salts; And an electrolyte additive comprising a first additive and a second additive,

[Chemical Formula 1]

Wherein R ₁ and R ₃ are each independently hydrogen or an alkyl group having 1 to 20 carbon atoms, preferably hydrogen or an alkyl group having 1 to 10 carbon atoms, more preferably hydrogen or an alkyl group having 1 to 5 carbon atoms And R ₂ is a bond or an alkylene having 1 to 20 carbon atoms, preferably a bond or an alkylene having 1 to 10 carbon atoms, more preferably a bond or an alkylene having 1 to 5 carbon atoms Lt; / RTI > may be the same or different,

And the second additive is tetrafluoro (oxalato) lithium phosphate.

When the first additive is included as an additive in the electrolyte to constitute a lithium secondary battery, a coating of an organic material is formed on the anode during charging / discharging, so that the first additive has a higher capacity than conventional ones, And can be provided as a secondary battery.

Specifically, the use of at least one selected from the compounds represented by the general formulas (2) to (4) is preferable as the first additive because it has excellent hydrolytic decomposability at a high temperature of 45 ° C or higher and can effectively control decomposition of the lithium salt into HF .

(2)

Each of R ₄ and R ₅ is independently hydrogen or an alkyl group having 1 to 20 carbon atoms, preferably hydrogen or an alkyl group having 1 to 10 carbon atoms, more preferably hydrogen or a carbon number of 1 to 5.

 (3)

R ₆ is hydrogen or an alkyl group having 1 to 20 carbon atoms, preferably hydrogen or an alkyl group having 1 to 10 carbon atoms, more preferably hydrogen or a carbon number of 1 to 5,

[Chemical Formula 4]

R ₇ and R ₈ are each independently hydrogen or an alkyl group having 1 to 20 carbon atoms, preferably hydrogen or an alkyl group having 1 to 10 carbon atoms, more preferably hydrogen or a carbon number of 2 to 5.

The first additive may be prepared by various known techniques.

As a specific example, the first additive may be 2-methyl-1,3-butadiene, 2-methyl-1,5-hexadiene, And 2,3-dimethyl-1,3-butadiene.

The second additive may be tetrafluoro (oxalato) lithium phosphate. Commercial products may also be used as the second additive. In the case of commercial products, however, compatibility with the above-mentioned first additive may be poor as well as toxicity. Thus, lithium salts such as LiPF ₆ And an oxalic acid compound containing an alkylsilyl group as a reaction product.

The oxysilane compound containing the alkylsilyl group is a silicon compound having a functional group having a different reactivity in the electrolyte solution of the present invention even if remaining in the reactant. The alkyl group acts as an organic substance and the silicon (Si) Thereby forming a stable film on the surface of the anode during charging and discharging, thereby contributing to an improvement in the lifetime performance of the battery.

The oxalic acid compound containing the alkylsilyl group is not limited thereto, but it is preferable to use the compound represented by the following general formula (5) in view of compatibility with the above-described toxicity and the first additive.

[Chemical Formula 5]

In Formula 5, for example, R ₁ , R _2, and R ₃ may each independently be hydrogen or a C ₁ -C ₆ alkyl group.

In another example, R ₁ , R ₂ and R ₃ may each independently be hydrogen, methyl or ethyl.

As another example, R ₁ , R _2, and R ₃ may all be methyl.

Specifically, the preparation of the reaction product may be such that the molar ratio of the compound represented by the general formula (5) to LiPF ₆ as the lithium salt (R ₁ , R ₂ and R ₃ is methyl) is 1: 0.90 to 1: 1.10. If the molar ratio is exceeded, lithium difluorobis (oxalato) phosphate is more chemically synthesized than lithium tetrafluoro (oxalato) phosphate, which is not preferable. For example, a mixture of lithium difluorobis (oxalato) phosphate and lithium tetrafluoro (oxalato) phosphate is formed in a range where the molar ratio is in the range of more than 1: 1.10 and less than 1: 1.90.

The reaction can be carried out in a non-aqueous organic solvent within the range of 20 to 110 ° C.

The organic substance contained in the above-mentioned species can form an SEI coating of a stable organic layer on the anode surface of a carbon material with an oxygen atom as a functional group, and Si, which is a functional group, as an inorganic substance forms an SEI coating of the inorganic layer, It is possible to prevent fusion of the metal ions to the surface of the positive electrode to improve lifetime characteristics of the battery and to form a SEI film more stably in a high temperature environment.

For example, when maintained at a high temperature for a certain time, the lithium salt of conventional LiPF ₆ decomposes according to the following reaction formulas 1 and 2 to generate HF.

[Reaction Scheme 1]

LiPF ₆ → LiF + PF ₅

[Reaction Scheme 2]

PF ₅ + H ₂ O - > 2HF + OPF ₃

Due to the HF generated by the decomposition of the lithium salt as described above, the elution of the metal contained in the cathode active material and the precipitation of metal ions on the surface of the anode continue to occur, and the electrode cycle may be degraded due to the increase of the potential. The electrolytic solution additive can suppress the decomposition reaction of PF ₅ by the property of being hydrolyzed before the reaction according to the reaction formula 2, thereby enhancing the high-temperature stability of the lithium salt contained in the electrolytic solution and suppressing the decrease of the discharge capacity of the secondary battery .

For example, the first additive and the second additive can be used in a weight ratio of 0.2: 1 to 2: 1, more preferably 0.2: 1 to 1: 1, or 1: 1 to 2: And has an excellent initial capacity and cycle life within the above range, and has an effect of suppressing a decrease in the overall life-time maintenance rate.

As another example, the first additive and the second additive may be included in a total amount of 0.1 to 10 parts by weight, preferably 0.3 to 7 parts by weight, based on 100 parts by weight of the electrolytic solution of the lithium salt and the non-aqueous organic solvent , And more preferably 0.5 to 5 parts by weight in total. The effect including the electrolyte additive and the effect of increasing the charge / discharge efficiency are excellent within the above range.

Examples of the lithium salt that can be included in the electrolyte solution of the present invention include LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiSbF ₆ , LiAlO 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 (CaF _{2a + 1} SO ₂ ) (C _b F _{2b + 1} SO ₂ ) , LiCl, LiI, and LiB (C ₂ O ₄ ) ₂ , and preferably LiPF ₆ can be used.

For example, the lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.6M to 2.0M or 0.7M to 1.6M, and the electrolytic solution has a high conductivity in the range, and the viscosity of the electrolyte is low, There is an effect of excellent mobility.

The electrolyte solution may have a lithium ion conductivity of 0.3 S / m or 0.3 SIMILAR 10 S / m under 25 DEG C, for example, and the cycle life characteristics of the lithium secondary battery may be further improved within the above range.

The non-aqueous organic solvent which can be contained in the electrolyte solution is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the battery and can exhibit desired properties together with the additives. For example, Compounds, propionate compounds, and the like. These may be used alone, or two or more of them may be used in combination.

Examples of the organic solvent of the carbonate compound in the non-aqueous organic solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate And may be any one selected from the group consisting of ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC) or a mixture of two 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 the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof, and an organic solvent having a low viscosity selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, Can be mixed and used.

More preferably, the organic solvent having a high dielectric constant and the organic solvent having a low viscosity are mixed in a volume ratio or weight ratio of 2: 8 to 8: 2, and more specifically, ethylene carbonate or propylene carbonate; Ethyl methyl carbonate; And dimethyl carbonate or diethyl carbonate may be mixed in a volume ratio or weight ratio of 5: 1: 1 to 2: 5: 3, preferably 3: 5: 2 by volume or weight ratio.

Examples of the carbonate compound include 10 to 30% by weight or 15 to 25% by weight of ethylene carbonate (EC), 0 to 30% by weight or 1 to 10% by weight of fluoroethylene carbonate (FEC) ), 10 to 50 wt%, or 25 to 40 wt%, and diethyl carbonate (DEC) 10 to 40 wt%, or 20 to 30 wt%.

The organic solvent may be one having a dielectric constant of 3 to 90 epsilon, preferably having a dielectric constant of 3 to 90 epsilon. Within the above range, the cycle life characteristics of the battery can be further improved.

The electrolytic solution further includes an additive (hereinafter referred to as "other additive") which can be generally used for electrolytic solution for the purpose of improving lifetime characteristics of the battery, suppressing reduction in battery capacity, improving discharge capacity of the battery, etc. can do.

The other additives may be, for example, metal fluoride. When the metal fluoride is further included as the other additives, the influence of acid generated in the vicinity of the cathode active material is reduced, and the effect of the cathode active material and the electrolyte The reaction can be suppressed and the phenomenon that the capacity of the battery is sharply reduced can be improved.

The metal fluoride is specifically, LiF, RbF, TiF, AgF , AgF 2, BaF 2, CaF 2, CdF 2, FeF 2, HgF 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} , ZrF 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 .

Examples of the other additives include glutaronitrile (GN), succinonitrile (SN), adiponitrile (AN), 4-tolunitrile, 1, 3,6-hexanetricarbonitrile, 3,3'-thiodipropionitrile (TPN), difluoroethylenecarbonate, fluoro (3,3'-thiodipropionitrile) (Malonato oxalato) borate, LiMOB), LiPF ₂ C ₄ O ₈ , LiSO ₃ CF ₃ , LiPF ₄ (also referred to as LiPF ₂ ), and the like. _{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, Biphenayl, cyclohexyl benzene, 4-fluorotoluene, ethylene sulfate anhydride, tris (trimethylsilyl) aniline, (Oxalate) borate (LiBOB), lithium difluoro (oxalate) borate (Oxalato), and the like. ) Borate, LiDFOB, ethylene sulfate (ESA), Fluoro Ethylene Carbonate (FEC), Vinyl Ethylene Carbonate (VEC), Vinylene Carbonate (VC) 1,3-propane sultone (PRS), 1,3-propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium bis LiFSI), Lithium Bis (trifluoromethane) sulfonamide, LiTFSi, maleic anhydride (MA), 1,1,1,2-tetrafluoroborate , 2,2,3,3-hexafluoropropane-1,3-disulfonamide lithium (1,1,2,2,3,3-hexafluoropropane-1,3-disulfoni mide lithium salt, LiHFP, perfluorohexane-1,6-dinitrile (PFDN), 3-fluoro-1,3-propansultone (FPS) Butyrolactone (GBL), Fluorized? -Butyrolactone (F-GBL), 2-methyl-1,3-butadiene, , And 2-methyl-1,5-hexadiene.

The electrolyte solution may contain 0.1 to 10 parts by weight, or 0.2 to 5 parts by weight, based on 100 parts by weight of the total amount of the electrolyte solution, and the cycle life characteristics of the lithium secondary battery may be further improved have.

The electrolyte according to the present invention having the above composition has excellent stability in a temperature range of -20 ° C to 60 ° C and can be electrochemically stable even at a voltage of about 4V range so that when the battery is applied to a lithium secondary battery, Can be extended.

In addition, the lithium secondary battery according to the present invention includes a positive electrode; cathode; A separator provided between the anode and the cathode; And a nonaqueous electrolytic solution. The non-aqueous electrolyte may include the non-aqueous electrolyte, and the positive electrode and the negative electrode may include a positive electrode active material and a negative electrode active material, respectively.

The anode may be prepared by preparing a composition for forming a cathode active material layer by mixing a cathode active material, a binder and an optional conductive agent, and then applying the composition to a cathode current collector such as an aluminum foil.

As the cathode active material, for example, a conventional NCM cathode active material used in a lithium secondary battery may be used. Specific examples thereof include Li [Ni _x Co _{1-x y} Mn _y ] O ₂ where 0 <x < 0.5). &Lt; / RTI &gt; The variables x and y of the lithium composite metal oxide Li [Ni _x Co _{1-x y} Mn _y ] O ₂ are 0.0001 <x <0.5, 0.0001 <y <0.5, or 0.001 <x <0.3 and 0.001 <y &Lt; 0.3.

As another example of the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used. 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 LiMl _x M2 _y O ₂ (However, 0≤x≤1, 0≤y≤1, 0≤x + y≤1 , M1 and M2 is any selected from the group consisting of each independently selected from Al, Sr, Mg and La ) Is preferable.

The cathode active material may be, for example, a manganese spinel-based active material or a nickel-cobalt manganese phase-based lithium metal oxide.

The negative electrode may be prepared by mixing a negative electrode active material, a binder and optionally a conductive agent 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, for example, a compound capable of reversible intercalation and deintercalation of lithium may be used.

Specific examples of the negative electrode active material may 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. For example, it may be graphite.

At least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or 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, at least one selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite, lithium metal and lithium-containing alloy may be used in view of high stability.

The positive electrode is preferably coated with a coating of the first additive and the second additive. The coating film may be a polymer film having a thickness of 1 to 100 nm. The secondary battery may have a high capacity within the range, a high initial charging / discharging efficiency, and a gas generation inside the battery as compared with a conventional nonaqueous electrolyte secondary battery. There is an effect to provide.

The coating film of the first additive and the second additive may be 0.1 wt% or more and 5 wt% or less with respect to the cathode substrate, and it is possible to increase the initial charge / discharge efficiency while maintaining a high capacity within this range, The occurrence can be suppressed. The content of the coating can be measured, for example, by TEM analysis.

For example, the battery assembly may be completed by inserting a separator between the positive electrode and the negative electrode, inserting the separator into the cell, injecting and sealing the electrolyte. Here, the lithium secondary battery including the electrolyte, anode, cathode, and separator may be a unit cell having a structure of anode / separator / cathode, a bi-cell having a structure of anode / separator / cathode / separator / anode, The structure of the laminated cell in which the structure of the laminated cell is repeated is obvious.

The lithium secondary battery according to 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 electrolytic solution used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin film type. The electrolytic solution according to the embodiment of the present invention is particularly excellent for application to a lithium ion battery, an aluminum laminated battery and a lithium polymer battery.

The lithium secondary battery comprising the electrolytic solution according to the present invention has a lifetime characteristic particularly at a high temperature of 45 占 폚 or higher, for example 45 占 폚 to 60 占 폚, and a high charging voltage (reduction potential) of 4.3 V to 5.0 V And can be used in a portable device such as a mobile phone, a notebook computer, a digital camera, a camcorder, an electric vehicle field such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (plug-in HEV, PHEV) And may be useful for medium to large energy storage systems.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

 [Example]

The following examples and experimental examples further illustrate the present invention, but the present invention is not limited thereto.

Examples 1-1 to 1-8

Preparation of first additive

As the first additive,

(3)

(Corresponding to 2-methyl-1,3-butadiene) having a structure represented by the following formula (wherein R ₆ is a methyl group).

Preparation of second additive

In a glove box, 7.60 g (0.05 mol) of LiPF6 was added to a 250 mL 1-necked round bottom flask (RB) flask equipped with a magnetic stirrer, and 40.4 g of anhydrous ethylmethyl carbonate was added to dissolve and then left to stand at room temperature for a while. To the obtained LiPF6 solution,

[Chemical Formula 5]

11.72 g (0.05 mol) of a compound represented by the following formula (wherein R ₁ , R ₂ and R ₃ are methyl groups) was added and dissolved. After reflux condenser and gas bubbler were installed, the mixture was stirred at room temperature for 23 hours And the mixture was warm-stirred for about 2 to 3 hours until the release of the Me ₃ SiF gas stopped in an oil bath at 80 to 85 캜. The slightly cloudy reaction solution obtained after the reaction was cooled to room temperature and then filtered to obtain 49 g of a transparent colorless filtrate, which was purified to prepare a second additive.

Preparation of electrolytic solution

15 wt% of LiPF ₆ as a lithium salt, 85 wt% of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DEC) (volume ratio: EC / EMC / DEC = 25/45/30) % Of the first additive and the second additive were added to 100 parts by weight of the mixed solution as shown in Table 1 below to prepare an electrolytic solution.

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) The second additive (parts by weight) Example 1-1 EC / EMC / DEC 25/45/30 One One Examples 1-2 EC / EMC / DEC 25/45/30 1.2 One Example 1-3 EC / EMC / DEC 25/45/30 1.5 One Examples 1-4 EC / EMC / DEC 25/45/30 1.8 One Examples 1-5 EC / EMC / DEC 25/45/30 2 One Examples 1-6 EC / EMC / DEC 25/45/30 0.8 One Examples 1-7 EC / EMC / DEC 25/45/30 0.5 One Examples 1-8 EC / EMC / DEC 25/45/30 0.2 One

Manufacture of lithium secondary battery

96% by weight of an NCM-based positive electrode active material containing Li [Ni _x Co _1-xy Mn _y ] O ₂ where 0 <x <0.5 and 0 <y <0.5, 2% by weight of carbon black as a conductive agent, 2% by weight of vinylidene fluoride (PVdF) was added to the solvent N-methyl-2-pyrrolidone (NMP) to prepare a cathode active material slurry. The positive electrode active material slurry was applied to an aluminum foil as a current collector having a thickness of about 20 탆 and dried to prepare a positive electrode, followed by preparing a positive electrode through a roll press process.

The negative electrode mixture slurry was prepared by adding graphite as an anode active material, PVdF as a binder and carbon black as a conductive agent to solvent NMP at 96 wt%, 3 wt% and 1 wt%, respectively. The negative electrode mixture slurry was applied to a copper (Cu) thin film as a negative electrode current collector having a thickness of 10 mu m and dried to prepare a negative electrode. Then, a negative electrode was prepared through a roll press process.

A lithium rechargeable battery for evaluation was prepared using the prepared positive electrode and negative electrode, the electrolyte prepared according to the contents of Table 1, and the separator of the microporous polypropylene film having a thickness of 20 탆.

Example 2

In Example 1-8, as a first additive,

[Chemical Formula 4]

Was replaced with 0.2 part by weight of a compound represented by the following formula (wherein R ₇ is a methyl group and R ₈ is hydrogen): &lt; tb &gt;&lt; TABLE &gt;

Example 3

In the same manner as in Example 1-1 except that, as the first additive,

(2)

(R &lt; ₄ &gt; is a methyl group and R &lt; ₅ &gt; is hydrogen) was carried out in the same manner as in Example 1-1 using the contents and compositions shown in the following Table 2, A battery was prepared.

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) Example 3-1 EC / EMC / DEC 25/45/30 One One Example 3-2 EC / EMC / DEC 25/45/30 1.2 One Example 3-3 EC / EMC / DEC 25/45/30 1.5 One Example 3-4 EC / EMC / DEC 25/45/30 1.8 One Example 3-5 EC / EMC / DEC 25/45/30 2 One Examples 3-6 EC / EMC / DEC 25/45/30 0.8 One Examples 3-7 EC / EMC / DEC 25/45/30 0.5 One Examples 3-8 EC / EMC / DEC 25/45/30 0.2 One

Comparative Examples 1-1 to 1-12

A lithium secondary battery was produced in the same manner as in Example 3, except that the first additive alone or the second additive alone was used according to the contents shown in Table 3 below.

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) Comparative Example 1-1 EC / EMC / DEC 25/45/30 0 One Comparative Example 1-2 EC / EMC / DEC / PP 25/45/15/15 0 One Comparative Example 1-3 EC / EMC / PP 25/45/30 0 One Comparative Example 1-4 EC / EMC / DEC / EP 25/45/15/15 0 One Comparative Example 1-5 EC / EMC / EP 25/45/30 0 One Comparative Example 1-6 EC / EMC / DEC / DMC 25/45/15/15 0 One Comparative Example 1-7 EC / EMC / DEC 25/45/30 0.2 0 Comparative Example 1-8 EC / EMC / DEC / PP 25/45/15/15 0.2 0 Comparative Example 1-9 EC / EMC / PP 25/45/30 0.2 0 Comparative Example 1-10 EC / EMC / DEC / EP 25/45/15/15 0.2 0 Comparative Example 1-11 EC / EMC / EP 25/45/30 0.2 0 Comparative Example 1-12 EC / EMC / DEC / DMC 25/45/15/15 0.2 0

Reference Examples 2-1 to 2-9

A lithium secondary battery was produced in the same manner as in Example 3 except that the first additive and the second additive were used in combination as shown in Table 4 below.

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) Reference Example 2-1 EC / EMC / DEC 25/45/30 0.1 One Reference Example 2-2 EC / EMC / DEC 25/45/30 One 1.5 Reference Example 2-3 EC / EMC / DEC 25/45/30 One 1.8 Reference Example 2-4 EC / EMC / DEC 25/45/30 One 2 Reference Example 2-5 EC / EMC / DEC 25/45/30 2.1 One Reference Example 2-6 EC / EMC / DEC 25/45/30 2.2 One Reference Example 2-7 EC / EMC / DEC 25/45/30 2.5 One Reference Example 2-8 EC / EMC / DEC 25/45/30 2.8 One Reference Example 2-9 EC / EMC / DEC 25/45/30 3 One

<Battery Evaluation>

The produced lithium secondary battery was allowed to stand at room temperature overnight, and then charged and discharged using a secondary battery charge / discharge test apparatus. First, the battery was charged at 4.2 V (0.5 C rate) under the condition of CC (Constant current) / CV (Constant voltage) at 25 ° C and discharged to 2.7 V at CC (0.5 C rate) condition after 10 minutes of dormancy. At this time, the normal capacity was 1000 mAh. The charge and discharge were repeated one cycle, and the charge and discharge capacities were measured. The maintenance rate of the discharge capacity after 300 cycles of one cycle discharge capacity is shown in the following Table 5 to Table 8 as the efficiency (%).

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) efficiency
(%) Examples 1-8 EC / EMC / DEC 25/45/30 0.2 One 85.0 Example 2 EC / EMC / DEC 25/45/30 0.2 One 87.0

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) efficiency
(%) Example 3-1 EC / EMC / DEC 25/45/30 One One 76.7 Example 3-2 EC / EMC / DEC 25/45/30 1.2 One 75.5 Example 3-3 EC / EMC / DEC 25/45/30 1.5 One 75.0 Example 3-4 EC / EMC / DEC 25/45/30 1.8 One 74.0 Example 3-5 EC / EMC / DEC 25/45/30 2 One 73.0 Examples 3-6 EC / EMC / DEC 25/45/30 0.8 One 78.0 Examples 3-7 EC / EMC / DEC 25/45/30 0.5 One 80.0 Examples 3-8 EC / EMC / DEC 25/45/30 0.2 One 85.0

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) efficiency
(%) Comparative Example 1-1 EC / EMC / DEC 25/45/30 0 One 60 Comparative Example 1-2 EC / EMC / DEC / PP 25/45/15/15 0 One 61.2 Comparative Example 1-3 EC / EMC / PP 25/45/30 0 One 58 Comparative Example 1-4 EC / EMC / DEC / EP 25/45/15/15 0 One 60.5 Comparative Example 1-5 EC / EMC / EP 25/45/30 0 One 58.5 Comparative Example 1-6 EC / EMC / DEC / DMC 25/45/15/15 0 One 59 Comparative Example 1-7 EC / EMC / DEC 25/45/30 0.2 0 75.5 Comparative Example 1-8 EC / EMC / DEC / PP 25/45/15/15 0.2 0 74.3 Comparative Example 1-9 EC / EMC / PP 25/45/30 0.2 0 73.6 Comparative Example 1-10 EC / EMC / DEC / EP 25/45/15/15 0.2 0 75.8 Comparative Example 1-11 EC / EMC / EP 25/45/30 0.2 0 74 Comparative Example 1-12 EC / EMC / DEC / DMC 25/45/15/15 0.2 0 74

division Non-aqueous organic solvent Non-aqueous organic solvent
(Volume ratio) The first additive
(Parts by weight) Second additive
(Parts by weight) efficiency
(%) Reference Example 2-1 EC / EMC / DEC 25/45/30 0.1 One 73 Reference Example 2-2 EC / EMC / DEC 25/45/30 One 1.5 78 Reference Example 2-3 EC / EMC / DEC 25/45/30 One 1.8 80 Reference Example 2-4 EC / EMC / DEC 25/45/30 One 2 83 Reference Example 2-5 EC / EMC / DEC 25/45/30 2.1 One 83.4 Reference Example 2-6 EC / EMC / DEC 25/45/30 2.2 One 82 Reference Example 2-7 EC / EMC / DEC 25/45/30 2.5 One 80 Reference Example 2-8 EC / EMC / DEC 25/45/30 2.8 One 78 Reference Example 2-9 EC / EMC / DEC 25/45/30 3 One 70

Referring to Tables 5 to 8, when the battery is charged / discharged at a high voltage, the embodiments using the first additive and the second additive of the present invention may be used alone or in a comparatively large amount or a small amount, And significantly increased capacity and capacity maintenance rates compared to the examples.

Claims (11)

Non-aqueous organic solvent; Lithium salts; An electrolyte additive comprising a first additive and a second additive,
The first additive may be represented by the following general formula
[Chemical Formula 1]

Wherein R ₁ and R ₃ are each independently selected from the group consisting of hydrogen or an alkyl group having 1 to 20 carbon atoms and R ₂ is a bond or an alkylene group having 1 to 20 carbon atoms) , And the second additive is lithium tetrafluoro (oxalato) phosphate (LiTFOP) tetrafluoro (oxalato) phosphate. The method according to claim 1,
Wherein the structure represented by the formula (1) is at least one selected from compounds represented by the following formulas (2) to (4):
(2)

(Wherein R ₄ and R ₅ are independent of each other and are hydrogen or an alkyl group having 1 to 20 carbon atoms)
(3)

(Wherein R ₆ is hydrogen or an alkyl group having 1 to 20 carbon atoms, which is not the same as in the formula (2)
[Chemical Formula 4]

(Wherein R ₇ and R ₈ are independent of each other and are hydrogen or an alkyl group having 1 to 20 carbon atoms) The method according to claim 1,
The compound represented by the formula (1) includes at least one selected from 2-methyl-1,3-butadiene, 2-methyl-1,5-hexadiene and 2,3-dimethyl-1,3-butadiene . The method according to claim 1,
The second additive is an electrolyte, characterized in that the reaction of the oxalic acid compound containing a lithium salt, LiPF ₆ and alkylsilyl. The method according to claim 1,
Wherein the weight ratio of the first additive to the second additive is 0.2: 1 to 2: 1. The method according to claim 1,
Wherein the content of the electrolyte additive is 0.1 to 10 parts by weight based on 100 parts by weight of the electrolyte solution of the lithium salt and the non-aqueous organic solvent. The method according to claim 1,
The lithium salt is _{LiPF 6, 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 (CaF 2a + 1 SO 2} ) (C b F 2b + 1 SO 2) ( However, a and b are natural numbers), LiCl, LiI, and LiB (C ₂ O ₄₎ at least one selected from the group consisting of ₂ And the electrolyte solution. The method according to claim 1,
The non-aqueous organic solvent may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC) MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and butylene carbonate (BC). The method according to claim 1,
The non-aqueous organic solvent may include 10 to 30% by weight of ethylene carbonate (EC), 0 to 30% by weight of fluoroethylene carbonate (FEC), 10 to 50% by weight of ethylmethyl carbonate (EMC) DEC) in an amount of 10 to 40% by weight. anode; cathode; A separator; And a nonaqueous electrolytic solution,
Wherein the anode is a manganese spinel-based active material or a lithium metal oxide,
The negative electrode is a carbon-based negative electrode active material selected from the group consisting of crystalline carbon, amorphous carbon, artificial graphite, and natural graphite,
The lithium secondary battery according to any one of claims 1 to 9, wherein the non-aqueous electrolyte is an electrolyte solution. 11. The method of claim 10,
Wherein the lithium secondary battery is a lithium ion secondary battery or a lithium polymer secondary battery.