KR20150060065A - Lithium secondary battery of improved output - Google Patents

Abstract

The present invention relates to a lithium secondary battery, including a positive electrode with a positive electrode mixture, a negative electrode with a negative electrode mixture, and a non-aqueous electrolyte solution, wherein the positive electrode is a conductive material and comprises (i) nanosized carbon based particles and (ii) carbon based fibers having a length which is one to three times longer than that of average particle size to directly connect positive electrode particles electrically; and the negative electrode is a negative electrode active material and comprises (i) carbon based active materials and (ii) a lithium titanium oxide (LTO). Therefore, the lithium secondary battery has a high energy density and accordingly has high capacity, thereby having excellent output and lifespan properties.

Description

TECHNICAL FIELD [0001] The present invention relates to a lithium secondary battery having improved output characteristics,

The present invention relates to a lithium secondary battery having improved output characteristics.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out and it is in the stage of commercialization.

Such a lithium secondary battery generally has a structure in which a lithium electrolyte is impregnated into an electrode assembly composed of a cathode including a lithium transition metal oxide as an electrode active material and a cathode and a porous separator including a carbonaceous active material. The positive electrode is prepared by coating a positive electrode mixture containing a lithium transition metal oxide on an aluminum foil, and the negative electrode is prepared by coating a copper foil with a negative electrode mixture containing a carbonaceous active material.

To the positive electrode mixture and the negative electrode mixture, a conductive material is added to improve the electrical conductivity of the active material. In particular, since the lithium transition metal oxide used as the cathode active material is inherently low in electric conductivity, a conductive material is essentially added to the cathode mixture. Among the conductive materials, a particulate conductive material is generally used in order to increase the conductivity of the cathode mixture. Such a particulate conductive material has a disadvantage in that the loading density can not be increased during compression in order to reduce the thickness of the cathode mixture .

On the other hand, the carbonaceous material used as a conventional negative electrode material has irreversible capacity of some lithium ions inserted into the layered structure during charging and discharging, and a lithium compound is generated on the surface of the negative electrode, There is a problem that the discharge capacity decreases and cycle deterioration occurs. In addition, the electrical conductivity at extremely low temperatures is low, which makes it difficult to produce high output, and has a problem of volume expansion.

To solve this problem, attempts have been made to use lithium titanate as a cathode material, but lithium titanium oxide has a disadvantage in that the capacity per unit weight is small and the energy density is low.

In this connection, some prior art proposes a cathode material comprising a carbon-based material and lithium titanium oxide.

For example, some prior arts disclose a technique that includes a carbon material as a main negative electrode material and a lithium titanium composite oxide as an auxiliary active material. In another prior art, at least one non-aqueous solution containing a lactone having a melting point of 0 ° C or lower A lithium secondary battery comprising an electrolytic solution, the lithium secondary battery comprising a negative electrode active material, a carbon material capable of intercalating and deintercalating lithium ions and lithium titanate, wherein the content of the carbon material with respect to the total amount of the negative electrode active material is 80 to 99% Of 1 to 20% by weight based on the total weight of the lithium secondary battery.

However, in the above technologies, since the carbon material and the lithium titanium oxide are simply mixed, the lithium ion mobility of the carbon material is still low, so that the reaction rate is lowered and the large current characteristic is low.

Therefore, a configuration of a secondary battery having a low internal resistance, a high level of electrical conductivity, and an output characteristic at a desired level has not yet been proposed while compensating for the disadvantages of each of the carbon material and the lithium titanium oxide.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have succeeded in various experiments and have succeeded in carrying out the present invention by using nano-sized carbon-based particles and carbon fiber as the positive electrode conductive material, It has been found that when a lithium secondary battery is manufactured using lithium titanium oxide (LTO), the internal resistance is reduced and the output and lifetime characteristics of the battery can be remarkably improved. Thus, the present invention has been accomplished.

Therefore, the lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode containing a positive electrode material mixture, a negative electrode including a negative electrode material mixture, and a nonaqueous electrolyte solution, wherein the positive electrode is a conductive material comprising: (i) And (ii) carbon-based fibers having a length of 1 to 3 times the average particle diameter of the cathode active material so as to electrically connect the cathode active material particles directly; The negative electrode is composed of (i) a carbonaceous active material and (ii) lithium titanium oxide (LTO) as an anode active material.

The carbon-based fiber may have a particle diameter of 1 to 1,000 nanometers and a length of 1 to 10 ⁶ nanometers. In detail, the carbon fiber may have a particle diameter of 10 to 100 nanometers, ^{May be} between 10 nanometers and 10 ⁵ nanometers.

The carbon-based fiber may be at least one selected from the group consisting of carbon nanotubes, carbon nanofhons, and carbon nanofibers, and more specifically carbon nanofibers.

The content of the carbon-based particles is 1 to 30% based on the total weight of the positive electrode mixture, and the content of the carbon-based fiber may be 0.1 to 5% by weight, more specifically 0.2 to 2% Lt; / RTI >

Specifically, the lithium titanate compound may be a compound represented by Li _x Ti _y O ₄ (0.5? X? 3; ₁ ? Y? 2.5), and specifically may be Li _1.33 Ti _1.67 O ₄ .

Such a lithium titanate compound may be contained in an amount of 0.1 to 30% by weight based on the total weight of the negative electrode mixture.

The lithium titanate compound particles may have an average particle size of 0.1 to 20% based on the average particle size of the carbonaceous active material

The anode may be prepared by dispersing the binder and the carbon-based particles together in a solvent, then adding the carbon-based fiber, further dispersing the cathode active material, applying the slurry on the cathode current collector, followed by drying and rolling have.

The present invention also provides a battery module including the lithium secondary battery as a unit cell, and a battery pack including the battery module.

The battery pack can be used as a power source of a device. Specific examples of the device include a small device such as a computer, a mobile phone, a power tool, and a power tool powered by an electric motor. An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; Power storage systems, and the like, but are not limited thereto.

INDUSTRIAL APPLICABILITY As described above, the lithium secondary battery of the present invention improves the electrical conductivity of a positive electrode using nano-sized carbon particles and a carbon fiber having a predetermined length electrically connecting the positive electrode active material, , The use of a carbonaceous active material and lithium titanium oxide (LTO) as a negative electrode active material can increase the ionic conductivity and reduce the internal resistance. Therefore, the lithium secondary battery including the combination has improved output and lifetime characteristics But can represent high energy density.

Therefore, the lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode containing a positive electrode material mixture, a negative electrode including a negative electrode material mixture, and a nonaqueous electrolyte solution, wherein the positive electrode is a conductive material comprising: (i) And (ii) carbon-based fibers having a length of 1 to 3 times the average particle diameter of the cathode active material so as to electrically connect the cathode active material particles directly; The negative electrode is composed of (i) a carbonaceous active material and (ii) lithium titanium oxide (LTO) as an anode active material.

As described above, in the positive electrode material mixture, a conductive material having a generally chain-like shape is added in order to increase the electrical conductivity. However, since the conductive material having the spherical chain shape is difficult to be uniformly mixed with the cathode active material, the electrical conductivity of the anode mixture is varied, resulting in non-uniformity of inter-cell performance. However, in the present invention, as the conductive material, since the carbon-based fiber having a predetermined length is included in addition to the nano-sized carbon-based particles, the conductive material can be uniformly mixed in the positive electrode material mixture so that the positive electrode active material particles are electrically connected, The internal resistance can be reduced.

The carbon-based active material generally used as the negative electrode active material has disadvantages in that the discharge capacity is high, but the high current characteristics and cycle characteristics are low. However, in the present invention, LTO is added as an anode active material, and the LTO has an operating potential of about 1.5 V, which is higher than the decomposition voltage of the electrolyte, so that formation of the SEI film which increases the resistance is not caused, so that the rate characteristic and the high current characteristic can be improved.

Moreover, LTO itself can participate in the reaction as a redox site, so that the LTO particles directly contact with the carbonaceous active material while minimizing the deterioration of the capacity of the battery, so that the ionic conductivity is high and the output characteristic is excellent.

As described above, since the secondary battery according to the present invention improves the electric conductivity by using the carbon fiber having a predetermined length as the positive electrode conductive material and improves the ion conductivity by using LTO as the negative electrode active material, The synergistic effect can effectively reduce the resistance of the battery. Therefore, it is possible to achieve all of the excellent characteristics of the battery which exceed the merits of the rate and lifetime characteristics obtained by using the respective materials and the like.

In the secondary battery according to the present invention, the carbon-based particles may have various sizes at the nanometer level.

The carbon-based fibers may have a particle diameter of 1 nm to 1000 nm and a length of 1 nm to 10 ⁶ nm. More specifically, the carbon-based fiber may have a particle diameter of 10 nanometers to 100 nanometers and a length of 10 nanometers to 10 ⁵ nanometers.

Since the carbonaceous fiber helps the conductive material to be mixed uniformly in the cathode mixture, the carbon fiber may have various particle diameters and lengths within the defined range according to the size of the cathode active material particles.

That is, the cathode active material particles may have various particle diameters depending on the material used, and accordingly, the carbon fiber may have various lengths, so that the cathode active material can be electrically connected efficiently. However, when the size of the particles of the cathode active material is too small, the dispersibility may decrease due to intergranular agglomeration. On the contrary, when the particle size is too large, the contact surface with the conductive material particle surface becomes small, It is preferable to have a nano-size.

The carbon-based fiber may be at least one selected from the group consisting of carbon nanotubes, carbon nanofhons, and carbon nanofibers, and more specifically carbon nanofibers.

The content of the carbon-based particles may be from 1 to 30% based on the total weight of the positive electrode material mixture, and the content of the carbon-based fibers may be from 0.1 to 5% by weight based on the total weight of the positive electrode material mixture, Lt; / RTI >

In particular, in the case of the carbon-based fibers, if the amount is too small, the cathode active material can not be sufficiently connected and the conductivity becomes low. If the amount is too large, the production process may be complicated, and the amount of the cathode active material The capacity of the battery may be lowered.

Such a carbon-based particle is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer 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; Polyphenylene derivatives, and the like. In particular, carbon-based materials can be used.

The cathode active material is not particularly limited and includes, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2-y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

On the other hand, as the negative electrode active material, the carbonaceous active material is not particularly limited as long as it can absorb and desorb lithium ions, and may be a crystalline carbon-based compound, an amorphous carbon-based compound, or a mixture thereof. Examples of the crystalline carbon-based compound include graphite. Examples of the graphite-based crystalline carbon include artificial graphite having a shape of potato or MCMB (Meso Carbon MicroBead) or an edge portion And natural graphite surface-treated to make it gentle. The amorphous carbon-based compound is a substance having carbon atoms in an amorphous crystal structure. For example, the amorphous carbon-based compound may be a hard carbon, a coke, a needle coke, or a pitch coke obtained by pyrolyzing a phenol resin or a furan resin. And soft carbon obtained by carbonizing carbon black.

In one specific example, the carbon-based active material has a high capacity and high energy density due to its excellent density and conductivity, so that natural and artificial graphite having excellent output and rate characteristics, and excellent output and rate characteristics I can be a mixture of graphitized carbon.

The carbonaceous active material may contain an appropriate amount to obtain a desired battery capacity and energy density. For example, the carbonaceous active material may include 1 to 90% by weight, more preferably 10 to 70% by weight based on the total weight of the negative electrode material mixture.

Specifically, the lithium titanium oxide is a compound represented by Li _x Ti _y O ₄ (0.5? X? 3; ₁ ? Y? 2.5), for example, Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , and Li _1.14 Ti _1.71 O ₄ , but the present invention is not limited thereto. More specifically, it may be Li _1.33 Ti _1.67 O ₄ having a spinel structure with less change in crystal structure during charge and discharge and excellent reversibility.

As described above, since the lithium titanate compound is in direct contact with the carbonaceous active material, the lithium titanate compound acts as a transport path of lithium ions to improve ionic conductivity and has a stable crystal structure. As a result, It is possible to suppress cycle deterioration due to lithium desorption.

Since the method for preparing the lithium titanate compound is well known in the art, detailed description thereof will be omitted herein.

When the content of the lithium titanic acid compound is too large, the content of the carbonaceous active material becomes relatively small. As a result, the battery capacity and the energy density may be lowered and the operating potential becomes excessively high. And the discharge capacity may be lowered. On the other hand, when the amount is too small, it is difficult to expect the effect of addition of the lithium titanium oxide. In consideration of this, the lithium titanium oxide may be added in an amount of 0.1 to 30% by weight, more specifically 0.1 to 10% by weight, based on the total weight of the anode mix.

In the present invention, the lithium titanic acid compound particles have an average particle size of 0.1 to 20%, more specifically 0.5 to 15%, based on the average particle size of the carbonaceous active material.

This is because if the ratio of the average particle size of LTO to the average particle size of the carbonaceous active material is too large, the contact area with the carbonaceous active material on the surface of the carbonaceous active material becomes low and it is difficult to exhibit sufficient ion conductivity improvement. The electrolyte solution decomposition reaction and the SEI film formation reaction may occur. On the other hand, if the average particle size ratio of LTO is too small, cohesion between the LTO particles becomes large and uniformly distributed on the surface of the carbonaceous active material It can be difficult.

When the particle diameter of the carbonaceous active material is too large, the bulk density of the negative electrode material decreases. On the contrary, when the average particle diameter is too small, irreversible capacity of the negative electrode material becomes high and it is difficult to expect a desired discharge capacity.

Therefore, in one specific example, the carbon-based active material may have an average particle size of 5 to 25 mu m, and more specifically, an average particle size of 10 to 20 mu m. It is needless to say that the average particle diameter of LTO is selected within a range that satisfies the particle diameter ratio.

In the present invention, the cathode mixture may contain one or more components selected from a binder, a filler, and the like in addition to the cathode active material and the conductive material, and more specifically, it includes both the conductive material and the binder.

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

The filler is optionally used as a component for suppressing expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used. The content of the filler may be 0.1 to 15% by weight based on the total weight of the positive electrode material mixture.

The anode may be prepared by dispersing the binder and the carbon-based particles together in a solvent, then adding the carbon-based fiber, further dispersing the cathode active material, applying the slurry on the cathode current collector, followed by drying and rolling have.

Specific examples of the solvent used in the preparation of the electrode slurry include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), and acetone. Can be used up to 400% by weight and removed in the drying process.

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

The present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, the separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is prepared, for example, by coating a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the mixture. The negative electrode mixture may contain the above-described components as required.

The negative electrode collector is generally made to have 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.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (propene sultone), FEC (fluoro-ethylene carbonate), and the like.

The present invention also provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module.

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. Examples of the battery pack include small devices such as a computer, a mobile phone, and a power tool, A power tool powered by the motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; Power storage systems, and the like, but are not limited thereto.

Such a lithium secondary battery, a middle- or large-sized battery module including the same as a unit battery, and a structure and a manufacturing method of the battery pack are well known in the art, and a detailed description thereof will be omitted herein.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (18)

A lithium secondary battery comprising a positive electrode including a positive electrode mixture, a negative electrode including a negative electrode mixture, and a nonaqueous electrolyte,
The positive electrode is a conductive material which is composed of (i) nano-sized carbon-based particles, and (ii) carbon-based fibers having a length of 1 to 3 times based on the average particle diameter of the positive electrode active material so as to electrically connect the positive- ;
The lithium secondary battery according to any one of claims 1 to 3, wherein the negative electrode comprises an anode active material (i) a carbonaceous active material and (ii) lithium titanium oxide (LTO). The lithium secondary battery according to claim 1, wherein the carbon-based fiber has a particle diameter of 1 nanometer to 1000 nanometers and a length of 1 nanometer to 10 ⁶ nanometers. The lithium secondary battery according to claim 1, wherein the carbon-based fiber has a particle diameter of 10 nanometers to 100 nanometers and a length of 10 nanometers to 10 ⁵ nanometers. The lithium secondary battery according to claim 1, wherein the carbon-based fibers are at least one selected from the group consisting of carbon nanotubes, carbon nanofhons, and carbon nanofibers. The lithium secondary battery according to claim 1, wherein the carbon-based fiber is a carbon nanofiber. The lithium secondary battery according to claim 1, wherein the content of the carbon-based particles is 1 to 30% based on the total weight of the positive electrode material mixture. The lithium secondary battery according to claim 1, wherein the content of the carbon fiber is 0.1 to 5 wt% based on the total weight of the positive electrode material mixture. The lithium secondary battery according to claim 1, wherein the content of the carbon fiber is 0.2 to 2% by weight based on the total weight of the positive electrode material mixture. The lithium secondary battery according to claim 1, wherein the formula of the lithium titanate compound is represented by Li _x Ti _y O ₄ (0.5? X? 3, ₁ ? Y? 2.5). The lithium secondary battery according to claim 1, wherein the formula of the lithium titanate compound is Li _1.33 Ti _1.67 O ₄ . The lithium secondary battery according to claim 1, wherein the lithium titanic acid compound is contained in an amount of 0.1 to 30% by weight based on the total weight of the negative electrode mixture. The lithium secondary battery according to claim 1, wherein the lithium titanic acid compound is contained in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode material mixture. The lithium secondary battery according to claim 1, wherein the lithium titanic acid compound has an average particle diameter of 0.1 to 20% with respect to an average particle diameter of the carbonaceous active material. The positive electrode according to claim 1, wherein the positive electrode is manufactured by dispersing a binder and a carbon-based particle in a solvent, then adding a carbon-based fiber, and further dispersing the positive electrode active material, Lithium secondary battery. A battery module comprising the lithium secondary battery according to claim 1 as a unit cell. A battery pack comprising the battery module according to claim 15. A device comprising a battery pack according to claim 16. 18. The system of claim 17, wherein the device is a computer, a mobile phone, a power tool, an electric vehicle (EV), a hybrid electric vehicle, a plug- Lt; / RTI > system.