Method for regulating terminal voltage of cathode during overdischarge and cathode active material for lithium secondary battery

1. A method for regulating terminal voltage of a cathode for a lithium secondary battery, comprising forming a cathode by adding to a cathode active material containing a first lithium transition metal oxide capable of lithium ion intercalation/deintercalation, a second lithium transition metal oxide of which an irreversible capacity in the first charge/discharge cycle is greater than that of the first lithium transition metal oxide, as an additive in an amount of 0.1 to 9 parts by weight based on 100 parts by weight of the total cathode active material,

wherein the additive is a lithium nickel oxide represented by the following formula 1 where y is not 0:

Li 2+x Ni 1−y M y O 2+a   [formula 1]

wherein, x is a number satisfying −0.5≦x≦0.5, y is a number satisfying 0<y<1, a is a number satisfying 0≦a<0.3, and M is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo and Cd,

wherein the terminal voltage of the cathode is in the range of from 2 V to 3.6 V when electric potential difference between a cathode and an anode is 0V during overdischarge, and

wherein the lithium nickel oxide represented by formula 1 belongs to a space group Immm, and forms a tetra-coordinated planar structure, (Ni,M)O 4 and two tetra-coordinated planar structures facing to each other share one side formed by O—O so as to form a primary chain.

2. The method according to claim 1 , wherein the amount of additive added irreversibly provides lithium ions to compensate for an irreversible lithium-consuming reaction in an anode caused by the solid electrolyte interface film formation on the surface of an anode during the first charge.