KR20190054920A - Electrolyte for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a secondary battery, a lithium secondary battery comprising the same, and a method for manufacturing the lithium secondary battery. The electrolyte comprises: a lithium salt; a non-aqueous organic solvent; and an electrolyte additive. The electrolyte additive comprises 1,3-propene sultone, a nitrile-based compound, and a carbonate-based compound. According to the present invention, the residual capacity performance of the battery can be enhanced.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrolyte for a secondary battery, and a lithium secondary battery including the same. BACKGROUND ART [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a secondary battery and a lithium secondary battery including the electrolyte. More particularly, the present invention relates to an electrolyte for a secondary battery improved in high temperature storability and life characteristics, and a lithium secondary battery comprising the electrolyte.

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

Among the electrochemical devices, there is a growing interest in the development of a rechargeable secondary battery. In particular, the lithium secondary battery developed in the early 1990s is attracting attention because of its high operating voltage and energy density.

The lithium secondary battery is generally manufactured through an electrode manufacturing process for manufacturing an anode / cathode, a assembling process for assembling various parts such as the electrodes in the form of a battery, and a forming process for activating the battery.

The forming process is divided into an activation process, a defective cell removal process, and a capacity selection process. At this time, the activation process is a process for stabilizing the cell structure by charging the assembled battery, aging, discharging, etc., and making the battery usable. Specifically, lithium ions from lithium metal oxide, which is a positive electrode active material, are transferred and inserted into the negative electrode during the initial charging. Since lithium ions are highly reactive, Li ₂ CO ₃ , Li ₂ O, LiOH And these compounds form a solid electrolyte interface (SEI) coating on the cathode surface. The SEI coating formed through the above process facilitates the movement of lithium ions at the electrolyte-negative electrode interface and inhibits the decomposition of the electrolyte. Therefore, depending on the degree of activation, various characteristics such as performance, lifetime, and stability of the battery are affected. Meanwhile, the aging process stabilizes the activated battery by allowing it to remain for a certain period of time.

The lithium secondary battery completed through the above-described processes is generally prohibited from being exposed to high temperatures in order to accelerate the decomposition reaction of the electrolyte at a high temperature or decrease the charge / discharge capacity of the lithium secondary battery.

However, recently, in order to manufacture a lithium secondary battery having a high energy density, it is required to operate a secondary battery at a high temperature and a high voltage. Due to an increase in oxidation reaction between the electrolyte and the anode, swelling (swelling) phenomenon occurs, and as the SEI film is collapsed, deterioration of lifetime characteristics of the battery is problematic.

In order to solve such a problem, there is a need for an electrolyte for a secondary battery capable of suppressing the swelling phenomenon through gas reduction under high temperature storage and at the same time preventing deterioration in lifetime performance.

Korean Patent Laid-Open Publication No. 2015-0043298

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an electrolyte for a secondary battery capable of improving high temperature storage characteristics and cycle life characteristics, a secondary battery including the secondary battery, and a method for manufacturing the secondary battery.

In one aspect, the present invention provides a lithium salt; Non-aqueous organic solvent; And an electrolyte additive, wherein the electrolyte additive comprises an electrolyte for a secondary battery comprising 1,3-propenesultone (1,3-propenesultone), a nitrile-based compound and a carbonate-based compound.

Meanwhile, 1,3-propenesultone (1,3-propenesultone) may be contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the electrolyte for a secondary battery.

In another aspect, the present invention provides a battery comprising: a positive electrode; cathode; A separation membrane interposed between the anode and the cathode; And an electrolyte disposed between the anode, the cathode, and the separator, wherein the electrolyte uses the electrolyte according to the present invention.

According to still another aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery, including: preparing a lithium secondary battery having a cathode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte for the rechargeable battery disposed between the cathode and the separator; And performing a degassing process for removing the gas generated in the lithium secondary battery. The present invention also provides a method for manufacturing a lithium secondary battery.

When the secondary battery according to the present invention is applied, even when the secondary battery is driven at a high voltage in order to achieve high energy density, it is possible to suppress the side reaction of oxidation between the anode and the electrolyte through stabilization of the surface of the anode, swelling phenomenon can be suppressed and the residual capacity of the battery can be improved by reducing the resistance increase rate.

In addition, a stable SEI film is formed on the surface of the electrode during the activation process of the secondary battery, thereby realizing a battery having excellent lifetime characteristics even at a high voltage.

Hereinafter, the present invention will be described in more detail.

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

The terminology used herein is for the purpose of describing exemplary 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 this specification, the terms " comprising, " " comprising, " or " having ", and the like are intended to specify the presence of stated features, But do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

<Electrolyte for Secondary Battery>

The electrolyte for a secondary battery according to the present invention comprises a lithium salt; Non-aqueous organic solvent; And an electrolyte additive, wherein the electrolyte additive includes 1,3-propenesultone, a nitrile-based compound, and a carbonate-based compound.

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, the lithium salt, as, and anions including Li + as the cation ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, AlO 4 - _{^{, AlCl 4 -, PF 6 -}} , SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 -, (CF 3) 2 PF 4 -, (CF3) 3 PF 3 -, (CF ^{_{3) 4 PF 2 -, (}} CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2 _{^{) 2 N -, (FSO 2}} ) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 ^- , CH ₃ CO ₂ ^- , SCN ^-, and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- . The lithium salt may be used alone or in admixture of two or more. At this time, the concentration of the lithium salt can be appropriately changed within a usable range. However, in order to obtain an effect of forming an anti-corrosive film on the optimum electrode surface, the concentration of the lithium salt in the electrolyte is preferably 1 M to 1.5 M, M, more preferably in a concentration of 1 M to 1.4 M.

The non-aqueous organic solvent is not particularly limited as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the non-aqueous organic solvent, for example, a linear carbonate compound, a cyclic carbonate compound, an ether compound, or an ester compound may be used alone or as a mixture of two or more thereof. Typically, a cyclic carbonate compound , A linear carbonate compound, or a mixture thereof.

Examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2- Carbonate, and 2,3-pentylene carbonate, or a mixture of two or more thereof, but the present invention is not limited thereto.

The linear carbonate compound may be, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methylethylcarbonate (MEC), ethyl methyl carbonate Propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more thereof, but the present invention is not limited thereto.

As the ether compound, for example, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether, or a mixture of two or more thereof may be used However, the present invention is not limited thereto.

Examples of the ester compound include methyl propionate, ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, iso-propyl propionate, n- Iso-butyl propionate, and tert-butyl propionate; And cyclic esters such as? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or a mixture of two or more thereof However, the present invention is not limited thereto.

Preferably, a cyclic carbonate such as ethylene carbonate and propylene carbonate, which is known to dissociate the lithium salt in the electrolyte well, is used as an organic solvent having a high viscosity in the carbonate-based organic solvent. In addition to the cyclic carbonate, dimethyl carbonate and When a low viscosity, low dielectric constant linear carbonate such as diethyl carbonate is mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be produced. Particularly, it is preferable to use a mixture of the carbonate-based solvent and the propionate-based solvent having a high ionic conductivity and a high dielectric constant, which can improve the charge-discharge performance of the battery.

More preferably, ethylene carbonate, propylene carbonate and propyl propionate can be mixed and used. The mixing ratio may be (0.5 to 30): (0.5 to 20): (1 to 65) , (0.5 to 30): (0.5 to 20): (1 to 60). When the carbonate-based organic solvent is mixed with the carbonate-based organic solvent in the above-described ratio to provide an electrolyte having a proper ionic conductivity and viscosity, the mobility of lithium ions in the battery can be improved and the safety of the battery can be improved. Can be improved.

Meanwhile, the electrolyte additive according to the present invention includes 1,3-propenesultone (1,3-propenesultone), a nitrile-based compound and a carbonate-based compound. In order to achieve a high energy density of a lithium secondary battery, high-voltage driving of the battery is required. The battery is exposed to a high temperature at a high SOC (high state of charge) state while the battery is driven under a high voltage. At this time, the oxidation reaction between the electrolyte and the anode increases to generate gas, . Particularly, since the reactivity between the anode and the electrolyte increases and the generation of gas increases, the battery deforms (for example, swelling phenomenon) under high voltage and high temperature, and there is a risk of explosion.

Accordingly, the present inventors have devised an electrolyte for a secondary battery including an electrolyte additive capable of forming a stable film on the surfaces of the positive electrode and the negative electrode in the activation step of the battery.

If the electrolyte for the secondary battery is used, the reaction between the electrode and the electrolyte can be suppressed even when the battery is driven at a high voltage and a high temperature by the coating formed at the activation step of the battery, It is possible to provide a lithium secondary battery improved in storage characteristics and cycle characteristics.

More specifically, the 1,3-propenesultone (1,3-propenesultone) inhibits the elution of transition metal from the surface of the anode during the activation process of the cell to inhibit electrodeposition of the eluted metal on the surface of the anode , So that the SEI film can be stably formed on the surface of the negative electrode. When the SEI film is stably formed, the SEI film is not collapsed even when the battery is driven at a high voltage and at a high temperature. Therefore, stabilization of the electrode surface and increase in resistance can be suppressed, and side reactions between the electrode and the electrolyte So that swelling phenomenon in which the battery is swollen due to decomposition of the electrolytic solution or gas is also prevented.

On the other hand, the 1,3-propenesultone (1,3-propenesultone) is added in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 5 parts by weight, per 100 parts by weight of the electrolyte for a secondary battery, May be included in an amount of 0.1 to 5 parts by weight. In the case where 1,3-propenesultone is contained within the above range, the SEI film can be stably formed by the reaction with the electrode in the activation step of the secondary battery, and the SEI film is not decomposed even in a high temperature and high voltage environment. , Lifetime characteristics can be improved. However, in the case where 1,3-propenesultone is contained in excess of the above range, remaining 1,3-propenesultone after forming the SEI film may act as a resistance increasing factor. Do.

The nitrile compound may be selected from the group consisting of succinonitrile, SN, ethylene glycol bis (propionitrile) ether, ASA3, adiponitrile, butyronitrile BUTYRONITRILE), 1,4-DICYANO-2-BUTENE, GLUTARONITRILE and 1,3,6-hexanetricarbonitrile (1,3,6- HEXANETRICARBONITRILE). &Lt; / RTI &gt;

Preferably, the nitrile-based compound may include succinonitrile (SN) and ethylene glycol bis (propionitrile) ether (ETHYLENE GLYCOL BIS (PROPIONITRILE) ETHER, ASA3). When the above compounds are used as an electrolyte additive, when the voltage of the battery rises and the high voltage is reached through the activation process, a film is formed on the positive electrode and the negative electrode so that the transition metal contained in the positive electrode and the metal ion The dissolution can be suppressed, and the high-temperature durability of the battery can be improved. The nitrile compound may be added in an amount of 0.01 to 15 parts by weight, preferably 0.05 to 15 parts by weight, more preferably 0.1 to 13 parts by weight based on 100 parts by weight of the electrolyte for a secondary battery.

More specifically, when succinonitrile (SN) is used as the nitrile compound, the succinonitrile is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the electrolyte for a secondary battery. By weight to 10 parts by weight, and more preferably 0.5 part by weight to 8 parts by weight.

When ethylene glycol bis (propionitrile) ether (ETHYLENE GLYCOL BIS (PROPIONITRILE) ETHER, ASA3) is used as the nitrile compound, the ethylene glycol bis (propionitrile) Preferably from 0.05 to 5 parts by weight, more preferably from 0.1 to 5 parts by weight based on 100 parts by weight of the composition.

When the nitrile-based compound is contained in the electrolyte for the secondary battery within the above range, the amount of the nitrile-based compound remaining in the battery can be minimized and the increase of the resistance can be suppressed.

The carbonate compound may include at least one selected from the group consisting of vinylene carbonate (VINYLENECARBONATE, VC) and fluoroethylene carbonate (FEC). When the listed compounds are used as the carbonate compound, the SEI coating can be stably formed on the surface of the negative electrode at the activation step of the battery, so that the lifetime characteristics and safety of the battery can be improved.

The carbonate compound may include 0.01 to 15 parts by weight, preferably 0.05 to 15 parts by weight, more preferably 0.1 to 13 parts by weight based on 100 parts by weight of the electrolyte for a secondary battery.

More specifically, when vinylene carbonate (VINYLENECARBONATE, VC) is used as the carbonate compound, the vinylene carbonate is used in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 5 parts by weight per 100 parts by weight of the electrolyte for a secondary battery To 5 parts by weight, and more preferably 0.1 part by weight to 5 parts by weight.

In the case of using FLUOROETHYLENE CARBONATE (FEC) as the carbonate compound, the fluoroethylene carbonate is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the electrolyte for the secondary battery To 10 parts by weight, and more preferably 0.5 part by weight to 8 parts by weight. When the carbonate compound is contained in the electrolyte for the secondary battery within the above range, the SEI film can be stably formed on the negative electrode, and the amount of the SEI film remaining in the battery can be minimized, and generation of gas even under high temperature conditions can be suppressed .

Meanwhile, the electrolyte additive may further include 1,3-propane sultone (1,3-propane sultone). When 1,3-propane sultone is used as an electrolyte additive, a film can be stably formed on the electrode, and the lifetime characteristics and high-temperature storage performance of the battery can be improved.

Also, the electrolyte additive may further include a borate compound, and the borate compound may include lithium difluoro (oxalato) borate (LITHIUM DIFLUORO (OXALATO) BORATE, LiODFB). In case of using lithium difluoro (oxalato) borate (LITHIUM DIFLUORO (OXALATO) BORATE, LiODFB) as an electrolyte additive, it is possible to form a SEI film having a relatively low resistance on the negative electrode, ) Characteristics can be improved.

The borate compound may include 0.01 to 5 parts by weight, preferably 0.05 to 5 parts by weight, more preferably 0.1 to 5 parts by weight based on 100 parts by weight of the electrolyte for a secondary battery. When the borate compound is contained in the electrolyte for the secondary battery within the above range, a film can be stably formed on the negative electrode, and the residual amount can be minimized, so that generation of gas even under high temperature conditions can be suppressed.

Meanwhile, in one embodiment of the present invention, the electrolyte additive is at least one selected from the group consisting of 1,3-propenesultone, nitrile compounds, carbonate compound borate compounds and 1,3-propane sultone (1 , 3-PROPANE SULTONE), wherein the nitrile compound comprises SUCCINONITRILE and ETHYLENE GLYCOL BIS (PROPIONITRILE) ETHER, wherein the carbonate compound (VINYLENECARBONATE, VC) and FLUOROETHYLENE CARBONATE (FEC), wherein the borate compound is selected from the group consisting of lithium difluoro (oxalato) borate, LiODFB ). When the above listed compounds are used together as an electrolyte additive, a stable film can be simultaneously formed on the cathode and the anode. At this time, the coating formed on the cathode can inhibit the decomposition of the electrolyte even under high temperature and high pressure conditions, as well as inhibiting the elution of the transition metal contained in the anode by the coating formed on the anode, , High-pressure characteristics and stability can be improved.

<Lithium secondary battery>

Next, a lithium secondary battery according to the present invention will be described. The secondary battery according to the present invention includes an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte disposed between the anode and the separator. At this time, since the electrolyte is the same as the above-described electrolyte, a detailed description will be omitted.

The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, a binder, a conductive material, and a solvent on the positive electrode current collector.

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

The cathode active material is a compound capable of reversibly intercalating and deintercalating lithium, and may specifically include a lithium composite metal oxide including lithium and at least one metal such as cobalt, manganese, nickel, or aluminum have. More specifically, the lithium composite metal oxide may be at least one selected from the group consisting of lithium-manganese-based oxides (for example, LiMnO ₂ and LiMn ₂ O ₄ ), lithium-cobalt oxides (for example, LiCoO ₂ ), lithium- (For example, LiNiO ₂ and the like), a lithium-nickel-manganese-based oxide (for example, LiNi ₁ -Y ₁ MnY ₁ O ₂ (where 0 <Y 1 <1), LiMn _{2-z 1} Niz ₁ O ₄ here, 0 <Z1 <2) and the like), lithium-nickel-cobalt oxide (e. g., in _{LiNi 1-Y 2Co Y2 O 2} ( here, 0 <Y2 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y3 Mn _Y3 O ₂ (here, 0 <Y3 <1), LiMn 2-z2 Coz 2 O 4 ( here, 0 <Z2 <2) and the like), lithium-nickel -manganese-cobalt oxide (e.g., Ni _p1 Co _q1 Mn _r1 (Li) O ₂ (here, 0 <p1 <1, 0 <q1 <1, 0 <r1 <1, p1 + q1 + r1 = 1) or Li (Ni _p2 Co _q2 Mn _r2) O ₄ (here, 0 <p2 <2, 0 <q2 <2, 0 <r2 <2, p2 + q2 + r2 = 2) , etc.), or a lithium- nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni Co _{p3 q3} Mn _r3 M _S1) O ₂ ( Wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p3, q3, r3 and s1 are atomic fractions of independent elements, 0 <p3 < 0 <q3 <1, 0 <r3 <1, 0 <s1 <1, p3 + q3 + r3 + s1 = 1), etc., and any one or more of these compounds may be included.

The lithium composite metal oxide may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ ), or lithium nickel cobalt aluminum oxide (such as LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , Li (Ni _0.5 , and the like), and the lithium composite metal oxide may be Li _{Mn 0.3 Co 0.2) O 2,} Li (Ni 0.7 Mn 0.15 Co 0.15) O 2 or _{Li (Ni 0.8 Mn 0.1 Co 0.1} ) O 2 and the like, there is one or a mixture of two or more of them may be used.

The positive electrode active material may include 80 wt% to 99 wt%, preferably 85 wt% to 99 wt%, and more preferably 90 wt% to 98 wt% based on the total weight of the solid material excluding the solvent in the positive electrode active material slurry have.

The binder is a component that assists in binding of the active material and the conductive material and bonding to the current collector. The binder generally contains 1% by weight to 20% by weight, preferably 1% by weight, based on the total weight of the solid content excluding the solvent in the slurry of the cathode active material % To 15 wt%, and more preferably 1 wt% to 10 wt%.

Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The conductive material is a component for further improving the conductivity of the positive electrode active material, and it is preferably 1% by weight to 20% by weight, more preferably 1% by weight to 15% by weight based on the total weight of the solid content excluding the solvent in the positive electrode active material slurry, May be included in an amount of 1 wt% to 10 wt%.

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

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

The negative electrode may be prepared by coating a negative electrode active material slurry including a negative electrode active material, a binder, a conductive material, and a solvent on the negative electrode collector.

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

Examples of the negative electrode active material include natural graphite, artificial graphite, carbonaceous material; Lithium-containing titanium composite oxide (LTO), metals (Me) with Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; An alloy composed of the metal (Me); An oxide of the metal (Me) (MeOx); And a composite of the metal (Me) and the carbon (C).

The negative electrode active material may include 80 wt% to 99 wt%, preferably 85 wt% to 99 wt%, and more preferably 90 wt% to 98 wt% based on the total weight of the solid material excluding the solvent in the negative electrode active material slurry have.

The binder is a component that assists in the bonding between the conductive material, the active material and the current collector. The binder usually contains 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, based on the total weight of solids, %, More preferably from 1 wt% to 10 wt%.

Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and it is preferably 1% by weight to 20% by weight, more preferably 1% by weight to 15% by weight based on the total weight of the solid content excluding the solvent in the negative electrode active material slurry, May be included in an amount of 1 wt% to 10 wt%.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

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

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

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

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the lithium secondary battery having a high capacity, a high rate-limiting characteristic, and a cycling characteristic, the battery module and the battery pack can be suitably used as a middle- or large- And can be used as a power source of the device.

&Lt; Production method of lithium secondary battery >

Next, a method of manufacturing a lithium secondary battery will be described. A method of manufacturing a secondary battery according to another embodiment of the present invention includes the steps of (1) manufacturing a lithium secondary battery, (2) activating the lithium secondary battery, and (3) degassing. Hereinafter, the manufacturing method will be described for each step.

(1) Lithium secondary battery manufacturing step

The above step is a step of manufacturing a lithium secondary battery having an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte disposed between the anode and the separator.

In general, a lithium secondary battery includes: (a) preparing an anode, a cathode, and a separator; (b) inserting the anode assembly, the cathode assembly, and the separator between the anode assembly and the cathode assembly, And (c) supplying an electrolyte to the battery case.

The step (a) may be performed by a method of manufacturing the positive electrode, the negative electrode, and the separator according to the manufacturing method of the positive electrode, the negative electrode and the separator, or a commercially available positive electrode, negative electrode and separator may be purchased and used.

When the anode, the cathode and the separator are prepared, they are assembled according to the step (b) to produce an electrode assembly.

The electrode assembly is largely classified into a jelly-roll type (wound type), a stack type (stacked type), and a stack-fold type, depending on the structure.

 In the case of a jelly-roll (wound type) electrode assembly, a separator is interposed between the positive electrodes and the negative electrodes of a long sheet type, and the separator is wound. In the case of the stacked (stacked) electrode assembly, a plurality of positive electrodes and negative electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween. In the case of a stack-folding type electrode assembly in the form of a jelly-roll type and a stack type, a Bi-cell or a full cell stacked with a predetermined unit of positive electrode, negative electrode, By using a continuous separator sheet.

After the electrode assembly is manufactured, the battery case is inserted into the battery case. The outer shape of the battery case is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, Specifically, it may include a pouch type.

Thereafter, the electrolyte is supplied to the battery case according to the step (c) to manufacture a lithium secondary battery.

When the electrolyte is a liquid electrolyte, it is not necessary to perform any additional treatment after injecting the electrolyte. However, if the electrolyte is a solid electrolyte or a gel electrolyte, the electrolyte may be injected through other methods.

For example, in the case of a gel electrolyte, an electrode and a separation membrane are coated with an electrolyte, cured (gelled) using heat or UV, and then an electrode and / or a separation membrane on which the gel electrolyte is formed are wound or laminated to form an electrode assembly And then inserting it into the battery case, and reusing the existing liquid electrolyte.

(2) Activation phase of lithium secondary battery

Next, the above step is a step of activating the lithium secondary battery by charging and discharging.

Specifically, the activating step includes charging the lithium secondary battery manufactured through the step (1), aging and discharging after the charging step is repeated to stabilize the battery structure, .

During the activation phase, lithium ions from the lithium metal oxide, which is a cathode active material, migrate to the cathode and are inserted. Since the lithium ion is highly reactive, it reacts with the electrolyte on the surface of the cathode to generate compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH And these compounds form a solid electrolyte interface (SEI) coating on the surface of the negative electrode. The SEI coating formed through the above process facilitates the movement of lithium ions at the electrolyte-negative electrode interface and inhibits the decomposition of the electrolyte.

On the other hand, when the electrolyte according to the present invention is used, a stable film is formed not only on the surface of the negative electrode but also on the surface of the positive electrode. Therefore, even when the secondary battery is driven at a high voltage, the side reaction of oxidation between the anode and the electrolyte can be suppressed by the coating on the surface of the anode, and the resistance increase rate can be reduced to improve the high temperature storability.

Meanwhile, since the charging step for activating the battery is the initial charging step of the battery, it is preferable that the activation step is performed under the following charging conditions in order to minimize negative reaction on the negative electrode.

The charging step for the activating step may be performed at a temperature of 40 캜 to 80 캜, preferably 40 캜 to 75 캜, and more preferably 45 캜 to 75 캜. When the charging is performed under the temperature condition within the above range, adverse reaction such as decomposition of lithium salt and generation of gas can be minimized and the activation process can be stably performed.

Further, the filling step for the activation step may be performed under a pressurization condition of 0.5 kgf / cm 2 to 10 kgf / cm 2, preferably 1 kgf / cm 2 to 10 kgf / cm 2, more preferably 1.5 kgf / . When the battery is charged while being pressurized to a pressure within the above range, the electrolyte solution is prevented from being discharged into the battery, so that the remaining electrolyte content in the battery can be maintained at a certain level.

Meanwhile, the charging step for the activation step may be performed by filling the SOC with 50% to 75% SOC, preferably 55% to 75% SOC, and more preferably 55% to 70% SOC.

In the activating step, an aging step may be further performed if necessary. Aging is to stabilize the activated cell by allowing it to remain for a certain period of time.

The aging step is preferably carried out within a temperature range of 60 ° C to 80 ° C. When the aging step is performed within the above-mentioned temperature range, the wettability of the secondary battery is improved and the electrolyte is not evaporated, so that the stability of the battery is maintained at a certain level or more. On the other hand, the remaining capacity (SOC) of the battery may be in any range from 100% which is the fully charged state to 0% due to the discharge. The aging time is not particularly limited, but is preferably about 1 hour to 2 days. When the aging process is performed, components that may cause swelling of the battery are evaporated, thereby minimizing swelling that causes safety and performance degradation of the battery in the course of the battery reaction.

(3) Degassing step

Finally, the step is to remove the gas generated inside the lithium secondary battery.

More specifically, it is a step of removing gas generated after the activation process of the lithium secondary battery. The degassing process can be carried out by a conventional method, and the gas such as carbon dioxide and methane which are generated during the SEI film formation through the activation step, as well as the component which causes the swelling phenomenon Gas and the like can be removed in advance.

Hereinafter, the present invention will be described more specifically by way of specific examples. However, the following examples are provided only to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and it is obvious that such variations and modifications are within the scope of the appended claims.

[Example]

1. Example 1

(1) Preparation of electrolyte

4.2 g of a 1.2 M LiPF ₆ electrolytic solution containing ethyl carbonate (EC): propylene carbonate (PC): propylene propionate (PP) in a 2: 1: 7 mass ratio was prepared. Thereafter, the electrolyte solution was added with vinylene carbonate (VC): 1,3-propane sultone (PS): fluoroethylene carbonate (FEC): succinonitrile (SN): ethylene glycol bis (propionitrile) : 0.8 g of an additive mixed with lithium difluoro (oxalato) borate (LiODFB): 1,3-propensulfone (PRS) in a mass ratio of 0.5: 3: 3: 5: 3: 0.5: Thereby preparing an electrolyte for a battery.

(2) cathode manufacturing

(Polyvinylidene fluoride (PVDF)) as a positive electrode active material (lithium cobalt oxide (LiCoO ₂ ): conductive material (bundled carbon nanotube)) was added to 100 parts by weight of N-methyl-2-pyrrolidone (NMP) Were mixed in a weight ratio of 97.7: 0.3: 2 to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 20 m, followed by drying and roll pressing, .

(3) cathode manufacturing

40 parts by weight of a negative electrode active material slurry prepared by mixing a negative electrode active material (graphite), a conductive material (carbon black) and a binder (polyvinylidene fluoride (PVDF)) at a weight ratio of 97: 0.5: 2.5 was added based on 100 parts by weight of distilled water as a solvent Thereby preparing a negative electrode active material slurry. The negative electrode active material slurry was applied to a negative electrode current collector (Cu thin film) having a thickness of 8 탆, followed by drying and roll pressing to produce a negative electrode.

(4) Production of lithium secondary battery

The positive electrode and the negative electrode fabricated by the above-described method are sequentially laminated together with a polyethylene porous film to produce a stack-folding type electrode assembly, which is then housed in a pouch-type secondary battery case, A nonaqueous electrolyte was injected and an activation process of charging SOC to 65% at a rate of 0.7C while being pressurized to 60 kg / cm2 at 60 DEG C was carried out to prepare a lithium secondary battery. Then, the lithium secondary battery was subjected to a high-temperature aging process at 70 캜 and then subjected to a degassing process to remove generated gases therein.

2. Example 2

(VC): 1,3-propane sultone (PS): fluoroethylene carbonate (FEC): succinonitrile (SN): ethylene glycol bis (propionitrile) in 4.1 g of the electrolytic solution in Example 1, A mixture of 0.9 g of an additive mixed in a ratio of 0.5: 3: 3: 5: 3: 0.5: 3 of the ether (ASA3): lithium difluoro (oxalato) borate (LiODFB) Were mixed to prepare an electrolyte for a secondary battery, a lithium secondary battery was prepared in the same manner as in Example 1 above.

3. Example 3

(VC): 1,3-propane sultone (PS): fluoroethylene carbonate (FEC): succinonitrile (SN): ethylene glycol bis (propionate 3: 3: 5: 3: 0.5: 0.5 mass ratio of lithium dihydrogenphosphate (ASA3): lithium difluoro (oxalato) borate (LiODFB) To prepare an electrolyte for a secondary battery, a lithium secondary battery was produced in the same manner as in Example 1, except that an electrolyte for a secondary battery was prepared.

4. Example 4

A lithium secondary battery was produced in the same manner as in Example 1, except that the temperature of the activation condition was 25 캜 and that no pressure was applied during the production of the lithium secondary battery.

5. Example 5

A lithium secondary battery was produced in the same manner as in Example 1, except that the activation step of charging the battery at an SOC of 65% at a rate of 0.7 C while pressurizing the activation process at a temperature of 25 캜 at a rate of 5 kgf / Thereby preparing a lithium secondary battery.

6. Example 6

A lithium secondary battery was produced in the same manner as in Example 1, except that the activation step of charging the lithium secondary battery at an SOC of 17% at a rate of 0.7 C was carried out at 25 ° C temperature condition, .

7. Example 7

In the same manner as in Example 1, except that the activation step of charging the lithium secondary battery to SOC 65% at a rate of 0.7 C while pressurizing the activation step at a temperature of 60 ° C at 20 kgf / Thereby preparing a lithium secondary battery.

8. Example 8

The same procedure as in Example 1 was carried out except that the activation step of charging the lithium secondary battery at an SOC of 17% at a rate of 0.7 C while pressurizing the activation process at a temperature of 60 ° C at 5 kgf / Thereby preparing a lithium secondary battery.

9. Example 9

(VC): 1,3-propane sultone (PS): fluoroethylene carbonate (FEC): succinonitrile (SN): ethylene glycol bis (propionitrile Except that 1.075 g of the additive mixed at a mass ratio of 0.5: 3: 3: 5: 3: 0.5: 7 was mixed in a mixture of lithium diisopropyl ether (ASA3): lithium difluoro (oxalato) borate (LiODFB) 1, a lithium secondary battery was produced.

[Comparative Example]

1. Comparative Example 1

A lithium secondary battery was produced in the same manner as in Example 1, except that the additive was not used in 5 g of the electrolytic solution in Example 1.

2. Comparative Example 2

(VC): 1,3-propane sultone (PS): fluoroethylene carbonate (FEC): succinonitrile (SN): ethylene glycol bis (propionitrile Except that 0.75 g of an additive mixed at a mass ratio of 0.5: 3: 3: 5: 3: 0.5 was mixed in a mixture of lithium dihydrogenphosphate (ACA3): lithium difluoro (oxalato) borate (LiOHFB) A lithium secondary battery was produced in the same manner.

Table 1 below shows mass ratios of the compounds constituting the additives used in Examples 1 to 8 and Comparative Examples 1 and 2 and activation conditions of lithium secondary batteries.

Additive (weight ratio) Activation condition VC PS FEC SN ASA3 LiODFB PRS Temperature (℃) Pressure (kgf / cm2) SOC (%)
(Speed: 0.7C) Example 1 0.5 3 3 5 3 0.5 One 60 5 65 Example 2 0.5 3 3 5 3 0.5 3 60 5 65 Example 3 0.5 3 3 5 3 0.5 0.5 60 5 65 Example 4 0.5 3 3 5 3 0.5 One 25 Not pressurized 65 Example 5 0.5 3 3 5 3 0.5 One 25 5 65 Example 6 0.5 3 3 5 3 0.5 One 25 Not pressurized 17 Example 7 0.5 3 3 5 3 0.5 One 60 20 65 Example 8 0.5 3 3 5 3 0.5 One 60 5 17 Example 9 0.5 3 3 5 3 0.5 7 60 5 65 Comparative Example 1 - - - - - - - 60 5 65 Comparative Example 2 0.5 3 3 5 3 0.5 - 60 5 65

[Experimental Example]

1. Experimental Example 1: Measurement of high-temperature lifetime characteristics (45 DEG C)

Each of the lithium secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 and 2 was charged and discharged 100 times under a high temperature (45 ° C) temperature condition of 4.45 V and then charged and discharged at the same temperature condition (45 ° C) The retention rate was measured. Here, the capacity retention rate refers to a relative ratio of the discharge capacity after 100 charge / discharge cycles when the measured discharge capacity after one charge / discharge of the secondary cells is 100%. The measurement results are shown in Table 2 below.

Capacity retention rate (%) Example 1 95 Example 2 84 Example 3 92 Example 4 91 Example 5 92 Example 6 91 Example 7 89 Example 8 93 Example 9 71 Comparative Example 1 55 Comparative Example 2 92

As shown in Table 2, it can be confirmed that the PRS was used as the electrolyte additive (Example 1), and the high temperature capacity retention ratio was higher than that of Comparative Examples 1 and 2. However, in Examples 2, 7 and 9, it can be seen that the high-temperature capacity retention ratio is somewhat low as compared with Comparative Example 2. In the case of Examples 2, 7 and 9, Gas reduction effect and the like are improved as compared with the comparative examples.

2. Experimental Example 2: Measurement of high-temperature capacity characteristics (85 DEG C)

Each of the lithium secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 and 2 was charged at 4.45 V, maintained at a high temperature (85 캜) for 8 hours, and discharged to measure a high-temperature discharge capacity. At this time, the discharge capacity when the lithium secondary battery was charged / discharged once was set as the initial discharge capacity (100%), and the capacity retention ratio (%) was measured by comparing the high temperature discharge capacity and the initial discharge capacity. The measurement results are shown in Table 3 below.

 Capacity retention rate (%) Example 1 92 Example 2 87 Example 3 90 Example 4 88 Example 5 89 Example 6 85 Example 7 89 Example 8 88 Example 9 80 Comparative Example 1 79 Comparative Example 2 84

As shown in Table 3, it can be seen that, in the case of using the PRS as the electrolyte additive, the capacity retention ratio after the high-temperature storage is larger than that of the comparative examples not using the PRS. This is because the side reaction between the electrode and the electrolyte is suppressed by the electrolyte additive including PRS, and the stable SEI film is formed on the electrode surface to improve the capacity characteristics of the lithium secondary battery.

3. Experimental Example 3: Measurement of gas reduction effect at high temperature (85 DEG C)

Each of the lithium secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 and 2 was charged at 4.45 V and then heated at 85 ° C. at a rate of 1 ° C./min at room temperature. The test was carried out under the conditions of keeping for a period of time and then warming to room temperature for 24 hours. At this time, the state before the heating to 85 ° C was regarded as an initial lithium secondary battery, and the swelling of the battery was measured by comparing the thickness of the lithium secondary battery with the initial lithium secondary battery. The measured results are shown in Table 4 below.

Battery swelling (%) Example 1 8 Example 2 7 Example 3 9 Example 4 12 Example 5 11 Example 6 13 Example 7 10 Example 8 10 Example 9 15 Comparative Example 1 48 Comparative Example 2 18

Referring to Table 4, it can be seen that, in the case of using PRS as an electrolyte additive, the swelling degree is low even when it is stored at a high temperature for a certain time or more than the comparative examples. This is because, in the high temperature activation step, when an electrolyte additive including PRS is used, SEI film is stably formed on the electrode surface.

Claims (13)

Lithium salts;
Non-aqueous organic solvent; And
An electrolyte additive,
Wherein the electrolyte additive comprises 1,3-propenesultone, a nitrile compound, and a carbonate compound.
The method according to claim 1,
Wherein the 1,3-propenesultone is contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the electrolyte for a secondary battery.
The method according to claim 1,
The electrolyte additive
An electrolyte for a secondary battery, further comprising 1,3-propane sultone (1,3-propane sultone).
The method according to claim 1,
The nitrile-
But are not limited to, succinonitrile, ethylene glycol bis (propionitrile) ether, adiponitrile, butyronitrile, At least one selected from the group consisting of 2-butene (1,4-DICYANO-2-BUTENE), GLUTARONITRILE and 1,3,6-hexanetricarbonitrile Or more of the total weight of the electrolyte.
The method according to claim 1,
The carbonate-
Wherein the electrolyte comprises at least one selected from the group consisting of vinylene carbonate (VINYLENECARBONATE, VC), and fluoroethylene carbonate (FLUOROETHYLENE CARBONATE, FEC).
The method according to claim 1,
Wherein the electrolyte additive further comprises a borate compound,
Wherein the borate compound comprises lithium difluoro (oxalato) borate (LITHIUM DIFLUORO (OXALATO) BORATE).
The method according to claim 6,
Wherein the electrolyte additive further comprises 1,3-propane sultone,
The nitrile-based compound includes succinonitrile and ethylene glycol bis (propionitrile) ether, and the nitrile-
Wherein the carbonate compound includes vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
anode;
cathode;
A separation membrane interposed between the anode and the cathode; And
And an electrolyte disposed between the anode, the cathode, and the separator,
Wherein the electrolyte is the electrolyte for a secondary battery according to claim 1.
A separator interposed between the anode and the cathode, and a lithium secondary battery in which an electrolyte is disposed between the anode and the separator;
Activating the lithium secondary battery; And
And performing a degassing process for removing gas generated inside the lithium secondary battery,
Wherein the electrolyte is the electrolyte for a secondary battery according to claim 1.
10. The method of claim 9,
Wherein the activating step comprises a charging step.
11. The method of claim 10,
And the temperature condition of the charging step is 40 占 폚 to 80 占 폚.
11. The method of claim 10,
Wherein the pressing condition of the charging step is 0.5 kgf / cm 2 to 10 kgf / cm 2.
11. The method of claim 10,
Wherein the charging condition of the charging step is SOC 50% to SOC 75%.