1. A compound represented by the following formula 1: [Formula 1] LiMP1-xAxO4 wherein M is a transition metal selected from the group consisting of Fe and Mn having an oxidation number of +2 to +3, A is an element having an oxidation number of +4 or less, wherein A substituting for P is at least one element selected from the group consisting of Ti(4+), Al(3+) ,B(3+), Zr(4+), Sn(4+), V(4+), Pb(4+) and Ge(4+) and 0

Description [1] The present invention relates to a novel electrode active material that can be used in a lithium secondary battery and has improved conductivity. Background Art [2] Due to the structural stability of LiMPO4 resulting from covalent bonds therein, many attempts are made to develop LiMPO4 as advanced cathode active material for a lithium secondary battery. However, because LiMPO4 has very low conductivity, con- ductivity of LiMPO should be improved in order to commonly use it as electrode active material. Therefore, research and development are made intensively to improve the conductivity of LiMPO4 . [3] Typically, two types of methods are used to improve the conductivity of LiMPO4 . One method that is used generally includes a step of adding carbon during a mixing step preceding heat treatment in preparing LiMPO4 . By doing so, carbon is coated on surfaces of active material particles formed of LiMPO4 to provide LiMPO4 having improved conductivity. Another method that is used recently includes substituting Li or M sites of LiMPO4 with a metal having a different oxidation number. JP 2002-117903 discloses an electrode active material comprising a compound represented by the formula of Li Fe M PO , wherein M is Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B or Nb; x is a number of between 0.05 and 1.2; and y is a number of between 0 and 0.8. Disclosure [4] Therefore, the present invention has been made in order to improve low con- ductivity of LiMPO . It is an object of the present invention to provide a novel electrode active material comprising LiMPO in which P atoms in the polyanionic PO sites are partially substituted with a different element instead of substituting Li or M sites with a different element. [5] According to an aspect of the present invention, there is provided a compound represented by the following formula 1. There is also provided a lithium secondary battery using the same compound as electrode active material, preferably as cathode active material. [6] [Formula 1] [7] LiMP AO [8] wherein M is a transition metal. A is an element having an oxidation number of +4 or less and 0 M>+2). By doing so, it can be expected that the novel compound according to the present invention has improved conductivity in a similar manner to the prior art. [15] Such conversion of the transition metal M of LiMPO into a multivalent state may 4 be exemplified as follows. [16] LiMPO (M= 2+) => LiM2+ M3+ P Ti O (M=2+or3+) 4 v (1-x) x (1-x) x 4 [17] wherein M is at least one transition metal selected from the group consisting of Fe, Co, Mn, Ni, V, Cu, Ti, etc., and 0 [39] Co-acetate, Li-carbonate and ammonium dihydrogen phosphate were introduced into a mortar mixer in a desired equivalent ratio and then mixed to obtain a mixture. The resultant powder was introduced into an electric furnace under nitrogen atmosphere and reacted at 300 °C for 12 hours to remove impurities. The powder free from impurities was mixed again in a mortar mixer. Then, the mixed powder was introduced into an electric furnace under nitrogen atmosphere and reacted at 700 °C for 24 hours to obtain a final product (LiCoPO ). [40] [41] The final product, LiCoPO was used as cathode active material. Slurry was formed by mixing the cathode active material, a conductive agent and binder in the ratio of 90:5:5 and the resultant slurry was applied onto Al foil to provide an electrode. As counter electrode, lithium metal was used. An electrolyte containing EGEMC (1:2) in which 1M LiPF was dissolved was used along with the cathode and anode to provide a coin type battery. [42] Example 1: Synthesis of LiCoP Ti O and Manufacture of Battery 0.98 0.02 4 J [43] Comparative Example 1 was repeated to obtain a final product (LiCoP Ti 0 ), except that Co-acetate, Li-carbonate, ammonium dihydrogen phosphate and Li Ti04 were used in a desired equivalent ratio. Additionally, a coin type battery was man- ufactured in the same manner as Comparative Example 1, except that the final product, LiCoP Ti 0 was used as cathode active material. 0.9S 0.02 4 [44] Comparative Example 2: Synthesis of LiFePO and Manufacture of Battery [45] Comparative Example 1 was repeated to obtain a final product (LiFePO ), except that Fe-acetate was used instead of Co-acetate. Additionally, a coin type battery was manufactured in the same manner as Comparative Example 1, except that the final product, LiFePO was used as cathode active material. [46] Example 2: Synthesis of LiFeP Ti O and Manufacture of Battery L r- j 09g QQ2 4 [47] Example 1 was repeated to obtain a final product (LiFeP Ti O ), except that Fe- acetate was used instead of Co-acetate. Additionally, a coin type battery was man- ufactured in the same manner as Comparative Example 1, except that the final product, LiFeP Ti O was used as cathode active material. 0.98 0.02 4 [48] Experimental Example 1: Electrochemical Test [49] Each of the batteries obtained from Comparative Example 1 and Example 1 was subjected to a charge/discharge cycle in a voltage range of 3-5.2V under constant current (CC) conditions of 0.1C (15 rhAh/g). The results are shown in FIGs. 1 and 2. [50] As can be seen from FIG. 1 (Comparative Example 1) and FIG. 2 (Example 1), the battery according to Example 1 showed a significant drop in the gap between charge profile and discharge profile, as compared to the battery according to Comparative Example 1. This indicates that the cathode active material according to the present invention shows an increased conductivity and decreased resistance. Further, the battery according to Example 1 showed an increase in charge/discharge capacity. When conductivity of an electrode active material increases, the gap between charge profile and discharge profile of the battery using the same material decreases. This results from a drop in overvoltage appearing in charge/discharge cycles, wherein the overvoltage increases in proportion to the resistance of an electrode active material. [51] Meanwhile, each of the batteries obtained from Comparative Example 2 and Example 2 was subjected to a charge/discharge cycle in a voltage range of 3-4V under constant current (CC) conditions of 0.1C. The results are shown in FIGs. 3 and 4. [52] Similarly, as can be seen from FIG. 3 (Comparative Example 2) and FIG. 4 (Example 2), the battery according to Example 2 showed a significant drop in the gap between charge profile and discharge profile, as compared to the battery according to Comparative Example 2. This indicates mat the cathode active material according to the present invention shows an increased conductivity and decreased resistance. Further, the battery according to Example 2 showed an increase in charge/discharge capacity. [53] Therefore, it can be seen from FIGs. 2 and 4 that each of the batteries using the cathode active materials according to Examples 1 and 2 operates as a battery and provides excellent battery quality compared to the batteries using the cathode active materials according to Comparative Examples 1 and 2. Industrial Applicability [54] As can be seen from the foregoing, the electrode active material comprising LiMP A O according to the present invention shows improved conductivity and charge/ discharge capacity compared to LiMPO . [55] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings. On the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims. WE CLAIM: 1. A compound represented by the following formula 1: [Formula 1] LiMP1-xAxO4 wherein M is a transition metal selected from the group consisting of Fe and Mn having an oxidation number of +2 to +3, A is an element having an oxidation number of +4 or less, wherein A substituting for P is at least one element selected from the group consisting of Ti(4+), Al(3+) ,B(3+), Zr(4+), Sn(4+), V(4+), Pb(4+) and Ge(4+) and 0