A process for preparing an active material for a battery includes the
steps of preparing a coating liquid by adding a compound comprising an
element X that is capable of forming a double bond with oxygen, and a
compound comprising at least one from the group consisting of an alkali
metal, an alkaline earth metal, a group 13 element, a group 14 element, a
transition metal, and a rare-earth element, to water, adding a metal
source to the coating liquid to surface-treat the metal source material,
drying the surface-treated metal source material to prepare an active
material precursor; mixing the active material precursor with a lithium
source; and heat-treating the resultant mixture to produce an active
material with a surface-treatment layer comprising the compound of the
formula (1): MXO.sub.k (1) wherein M is at least one selected from the
group consisting of an alkali metal, an alkaline earth metal, a group 13
element, a group 14 element, a transition metal, and a rare-earth
element; X is an element that can form a double bond with oxygen; and k
is a numerical value in the range of 2 to 4.