A process for preparing a stable Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 is provided. The general formula of the potassium “A” site and Group VIII Period 4 (Fe, Co and Ni) “B” site modified lithium manganese-based AB.sub.2O.sub.4 spinel is Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 where Me is Fe, Co, or Ni. In addition, a Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 cathode material for electrochemical systems is provided. Furthermore, a lithium or lithium-ion rechargeable electrochemical cell is provided, incorporating the Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 cathode material in a positive electrode.

Provided is a material that can be used as a potassium secondary battery positive electrode active material (particularly a potassium ion secondary battery positive electrode active material), other than Prussian blue, by using a potassium compound and a potassium ion secondary battery positive electrode active material comprising the potassium compound, the potassium compound being represented by general formula (1):
K.sub.nA.sub.kBO.sub.m,
wherein A is a positive divalent element in groups 7 to 11 of the periodic table; B is positive tetravalent silicon, germanium, titanium or manganese, excluding a case in which A is manganese and B is titanium, and a case in which A is cobalt and B is silicon; n is 1.5 to 2.5; and m is 3.5 to 4.5.

Provided are a method of manufacturing a cathode active material including a first step of preparing a metal glycolate solution, a second step of mixing lithium-containing transition metal oxide particles and the metal glycolate solution and stirring in a paste state, a third step of drying the paste-state mixture, and a fourth step of performing a heat treatment on the dried mixture, a cathode active material including a metal oxide layer which is manufactured by the above method, and a secondary battery composed of a cathode including the cathode active material.

A process for preparing a stable Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 is provided. The general formula of the potassium A site and Group VIII Period 4 (Fe, Co and Ni) B site modified lithium manganese-based AB.sub.2O.sub.4 spinel is Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 where Me is Fe, Co, or Ni. In addition, a Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 cathode material for electrochemical systems is provided. Furthermore, a lithium or lithium-ion rechargeable electrochemical cell is provided, incorporating the Li.sub.xK.sub.yMn.sub.2-zMe.sub.zO.sub.4 cathode material in a positive electrode.

Provided is a material that can be used as a potassium secondary battery positive electrode active material (particularly a potassium ion secondary battery positive electrode active material), other than Prussian blue, by using a potassium compound and a potassium ion secondary battery positive electrode active material comprising the potassium compound, the potassium compound being represented by general formula (1):

K.sub.nA.sub.kBO.sub.m,

wherein A is a positive divalent element in groups 7 to 11 of the periodic table; B is positive tetravalent silicon, germanium, titanium or manganese, excluding a case in which A is manganese and B is titanium, and a case in which A is cobalt and B is silicon; n is 1.5 to 2.5; and m is 3.5 to 4.5.