[DESCRIPTION] HIGH VOLTAGE CATHODE ACTIVE MATERIAL AND METHOD FOR PREPARING THE SAME [TECHNICAL FIELD] 5 The present invention relates to a high voltage cathode active material and a method for preparing the same and, more particularly, to a cathode active material and a method for preparing the same, wherein the cathode active material includes particles of a spinel-type compound having a composition represented by Formula (1) and a carbonbased material present on surfaces of the particles of the spinel-type compound: 10 Li1+aMxMn2-x04-zAz (1) where a, x, and z are defined as in the detailed description. [BACKGROUND ART] Along with major advances in Information Technology (IT), various mobile information communication devices have entered widespread use and the 21st century 15 marks the dawn of a ubiquitous society in which high quality information services are available anywhere and anytime. -1- Lithium secondary batteries play an important role in the evolution of such a ubiquitous society. As compared to other secondary batteries, lithium secondary batteries have high operating voltage and energy density and can be used for a long time, thus 5 satisfying complex requirements for the needs of an increasing variety of complex devices. Recently, many attempts have been made worldwide to develop existing lithium secondary battery technologies to extend their application not only to ecofriendly transport systems such as electric vehicles but also to power storage. 10 Secondary batteries used for middle or large-scale power sources such as electric vehicles or power storage systems (or energy storage systems (ESS)) require high power, high energy density and high energy efficiency. Despite advantages such as low price and high power, LiMn204 has a disadvantage in that the energy density thereof is lower than those of lithium cobalt oxides. 15 [DISCLOSURE] [TECHNICAL PROBLEM] -2- While developing a compound of LiMn2(>4 in which manganese (Mn) is partially replaced by a metal such as nickel (Ni) to improve upon the low energy density of LiMn204 having an operating potential in the 4V range (from about 3.7V to about 4.5V), the present inventors discovered that, since the compound of LiMn204 5 with manganese being partially replaced by a metal such as nickel has a high operating potential of 4.6V or higher, the electrolyte decomposes even when the battery is in a normal operating range and performance thereof is reduced due to side reaction of the compound with the electrolyte. The present inventors also found that Mn ions suffer elution. LiMn204 having an operating potential in the 4V range does 10 not suffer from this problem. Therefore, the present invention has been made to solve the above problems and it is an object to provide a cathode active material for a high voltage in a 5 V range and a method for preparing the same. [TECHNICAL SOLUTION] 15 In accordance with the present invention, the above and other objects can be accomplished by the provision of a cathode active material including particles of a spinel-type compound having a composition represented by Formula (1) and a carbonbased material present on surfaces of the particles of the spinel-type compound: -3- Lii+aMxMn2-x04-zAz (1) where M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a monoanion or dianion, and 5 -0.1 < a< 0.1, 0.3< x< 0.8 and OS z< 0.1. The spinel-type compound of Formula (1) is different from LiM^C^ in that the spinel-type compound of Formula (1) lias an operating potential of equal to or higher than 4.6V and equal to or less than 4.9V whereas LiMn204 has an operating potential in the 4V range (from about 3.7V to about 4.3V). The spinel-type 0 compound of Formula (1) exhibits high energy density characteristics as compared to LiMn204 since the spinel-type compound of Formula (1) has an operating potential of equal to or higher than 4.6V and equal to or less than 4.9V. The carbon-based material may cover all or part of the surface of particles of the spinel-type compound. Specifically, the carbon-based material may cover equal 5 to or greater than 20% and equal to or less than 100% of the entire surface of the particles of the spinel-type compound. In a non-limiting embodiment, the carbonbased material may cover equal to or greater than 50% and equal to or less than 80% of the entire surface of the particles of the spinel-type compound. Thus, elution of manganese is inhibited due to change in the surface energy of parts of the particles of the spinel-type compound covered with the carbon-based material. The carbon-based material may serve as a protective layer to inhibit reaction with an electrolyte. The protective layer may block direct contact between the 5 electrolyte and the compound of Formula (1) upon charge and discharge at high voltage to inhibit side reaction of the electrolyte. As a result, the cathode active material according to the present invention may exhibit stable charge/discharge cycle characteristics, thereby increasing reversible charge/discharge capacity. In addition, since the carbon-based material has high electron conductivity, 10 the carbon-based material reduces interfacial resistance of the spinel-type compound represented by Formula (1), thereby improving output (or power) characteristics. In a non-limiting embodiment of the present invention, the compound of Formula (1) may comprise a compound represented by Formula (2): LinaNibMcMn2.(b+c)0,j-zAz (2) 15 where M is at least one selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a monoanion or dianion and is at least one selected from the group -5- consisting of S, N and halogens such as F, CI, Br, and I. -0.1< a< 0.1, 0.3< b< 0.6, 0< c< 0.2, and 0< z< 0.1. The carbon-based material may be physically, chemically, or physicochemically bonded to the surfaces of the particles of the spinel-type compound. 5 An average particle diameter (D50) of the carbon-based material may be equal to or greater than 2 nm and equal to or less than 500 nm. Average particle diameters (D50) outside the above range are not preferred since it is not possible to effectively inhibit elution of manganese and side reaction with the electrolyte when the average particle diameter (D50) is less than 2 nm, and the carbon-based material 10 may block the diffusion path of lithium ions, reducing high rate characteristics, when the average particle diameter (D50) is greater than 500 nm. The cathode active material may be prepared through a liquid method in which a liquid coating solution is prepared and mixed with a cathode material, a mechano-chemical method using high mechanical energy of ball milling, a fluidized 15 bed coating method, a spray drying method, a precipitation method in which a coating material is precipitated onto the surface of an active material in an aqueous solution, a method that utilizes reaction between a vapor coating material and a cathode material, a sputtering method and a mechanofusion, method using static electricity. -6- In a specific example, the cathode active material may be prepared according to a method including mixing a spinel-type compound having a composition represented by the above Formula (1) and a carbon precursor, and thermally treating the mixture under an inert atmosphere or an oxygen deficient atmosphere with an 5 oxygen concentration of 35% by volume or less. In a specific example, the spinel-type compound and the carbon precursor may be mixed using dry mixing. In a specific example, the heat treatment may be performed at a temperature of 400 to 800°C, the carbon precursor may include at least one selected from the group 10 consisting of petroleum-based pitch, tar, phenolic resin, furan resin, and carbohydrate, and the inert atmosphere may be a nitrogen (N2) or argon (Ar) atmosphere. The cathode active material according to the present invention may be mixed with other lithium-containing transition metal oxides than those of the cathode active material described above. 15 Examples of the other lithium-containing transition metal oxides include, but are not limited to, layered compounds such as lithium cobalt oxide (LiCoOi) and lithium nickel oxide (LiNiCy alone or substituted by one or more transition metals; lithium manganese oxides such as Lii+yMn2.y04 (in which 02; lithium copper oxide (Li2Cu02); vanadium oxides such as LiVsOs, LiFe304, V2O5 and CU2V2O7; Ni-site type lithium nickel oxides represented by LiNii.yMy02 (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and 0.01 -15- LiNio.5Mn1.5O4 and petroleum-based pitch were introduced in a weight ratio of 100:5 into a conical agitator and were then mixed at 400 rpm for 1 hour. Thereafter, the mixture was thermally treated for 20 hours at a temperature of 500°C under a nitrogen atmosphere, thereby preparing LiNio.5Mn1.5O4 surface-modified with a carbon- 5 based material. LiNio.5Mn1.5O4 surface-modified with a carbon-based material, a conductive material and a binder were weighed in a ratio of 97:2.5:2.5 and then added to NMP, followed by mixing, to form a cathode mix. The cathode mix was applied to an aluminum foil with a thickness of 20 pm, followed by rolling and drying, to form a 10 cathode for lithium secondary batteries. A 2016 coin battery was then fabricated using the formed cathode for lithium secondary batteries, a lithium metal film as a counter electrode (i.e., an anode), a polyethylene membrane (Celgard, thickness: 20 pm) as a separator, and a liquid electrolyte including 1M LiPFg dissolved in a solvent in which ethylene carbonate, 15 dimethylene carbonate and diethyl carbonate were mixed in a ratio of 1:2:1. A coin battery was fabricated in the same manner as in Example 1, except that LiNio.5Mnj.5O4, which was not surface-modified with a carbon-based material, was used -16- as a cathode active material. Experimental Example 1 > Initial Charge/Discharge Characteristics Coin batteries fabricated in Example 1 and Comparative Example 1 were 5 charged and discharged once at a current of 0.1 C within a voltage range of 3.5 to 4.9 V and charge/discharge characteristics were estimated. Estimation results are shown in Table 1 below. 10 Experimental Example 2> Rapid charging Characteristics Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged at a current of 0.1 C and were then charged at a current of 5.0 C, and rapid charging characteristics were estimated. Estimation results are shown in -17- Experimental Example 3> Service life Characteristics Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged 100 times at a current of 1.0 C and service life characteristics were estimated. Estimation results are shown in Table 3 below. Experimental Example 4> Eluted Manganese Amount Measurement Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged once at a current of 0.1 C within a voltage range of 3.5 to 4.9 V and were charged at a current of 0.1 C to 4.9 V. The batteries were then disassembled. A cathode obtained from each of the disassembled batteries was dipped in a container 5 containing 15 mL of an electrolyte and was stored in an 80°C constant temperature bath for 2 weeks. Then, the content of manganese eluted into the electrolyte was analyzed using an ICP (PerkinElmer, Model 7100). 10 Experimental Example 5> High Temperature Storage Characteristics Estimation Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged once at a current of 0.1 C within a voltage range of 3.5 to 4.9 V and were charged at a current of 0.1 C to 4.9 V. The batteries were then stored in a 15 60aC constant temperature bath for 1 week and the amount of self-discharge and the capacity recovery rate of each of the batteries were measured. When a battery is stored -19- in a fully charged state at high temperature, decomposition of electrolyte on the surface of a cathode active material is accelerated, increasing self-discharge. This causes destruction of the structure of the cathode active material. This experiment was devised to observe this phenomenon. According to the present invention, all or part of the surface of particles of a spinel-type compound of the above Formula 1 are coated with a carbon-based material. This inhibits elution of manganese and electrolyte side reaction at a high 10 voltage, thereby enabling provision of improved high-voltage lithium secondary batteries. [CLAIMS] [Claim 1 ] A cathode active material comprising: particles of a spinel-type compound having a composition represented by Formula (1); and a carbon-based material present on surfaces of the particles of the spinel-type compound: Lii+aMxMn2-x04.zAz (1) where M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a monoanion or dianion, and -0.1< a< 0.1, 0.3* x< 0.8 and 0< z< 0.1. [Claim 2] The cathode active material according to claim 1, wherein the spineltype compound comprises a compound represented by Formula (2): Li1+aNibMcMn2-(b+c)04-zAz (2) 15 where M is at least one selected from the group consisting of Ti, Co, Al, Cu, -21- Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a monoanion or dianion, and -0.1< a< 0.1,0.3* b< 0.6,0* c< 0.2, and 0< z< 0.1. [Claim 3] The cathode active material according to claim 1, wherein the 5 carbon-based material is physically and/or chemically bonded to the surfaces of the particles of the spinel-type compound of Formula (1). [Claim 4] The cathode active material according to claim 1, wherein an average particle diameter (D50) of the carbon-based material is equal to or greater than 2 nm and equal to or less than 500 nm. 10 [Claim 5] The cathode active material according to claim 1, wherein the carbon-based material covers equal to or greater than 20% and equal to or less than 100% of the entire surface of the spinel-type compound of Formula (1). [Claim 6] The cathode active material according to claim 5, wherein the carbon-based material covers equal to or greater than 50% and equal to or less than 15 80% of the entire surface of the spinel-type compound of Formula (1), [Claim 7] A method for preparing a cathode active material, the method comprising: mixing a spinel-type compound having a composition represented by Formula (1) and a carbon precursor; and thermally treating the resulting mixture under an inert atmosphere or an oxygen deficient atmosphere with an oxygen concentration of 35% by volume or less: 5 Li!+aMxMn2-x04-zAz (1) where M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a nionoanion or dianion, and -0.1< a< 0.1,0.3< x< 0.8 and 0< z< 0.1. 10 [Claim 8] The method according to claim 7, wherein the spinel-type compound comprises a compound represented by Formula (2): Li i+a NibMcMn2-(b+C)04-zAz (2) where M is at least one selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, 15 A is a nionoanion or dianion, and -0.1< a< 0.1, 0.3< b< 0.6, 0< c< 0.2, and 0< z< 0.1. [Claim 9] The method according to claim 7, wherein the thermal treatment is performed at a temperature of 400 to 800 C. [Claim 10] The method according to claim 7, wherein the carbon precursor 5 comprises at least one selected from the group consisting of petroleum-based pitfch, tar, phenolic resin, furan resin and carbohydrate. [Claim 11 ] The method according to claim 7, wherein the inert atmosphere is a nitrogen (N2) or argon (Ar) atmosphere. [Claim 12] The method according to claim 7, wherein the carbon precursor and 10 the spinel-type compound are mixed using dry mixing. [Claim 13] A lithium secondary battery comprising the cathode active material according to claim 1. [Claim 14] A battery pack comprising the lithium secondary battery according to claim 13. 15 [Claim 15] An electric vehicle comprising the battery pack according to claim 14.