Herein, thermal decomposition experiments of lithium peroxide (Li 2 O 2) were performed to prepare a precursor (Li 2 O) for sacrificing cathode material, Li 2 NiO 2. The Li 2 O 2 was prepared by a hydrometallurgical reaction between LiOH· H 2 O and H 2 O 2. The overall reaction during annealing was found to involve the following three steps:(1) dehydration of LiOH· H 2 O,(2) decomposition of Li 2 O 2, and (3) pyrolysis of the remaining anhydrous LiOH. This stepwise reaction was elucidated by thermal gravimetric and quantitative X-ray diffraction analyses. Furthermore, over-lithiated lithium nickel oxide (Li 2 NiO 2) using our lithium precursor was synthesized, which exhibited a larger yield of 90.9% and higher irreversible capacity of 261 to 265 mAh g− 1 than the sample prepared by commercially purchased Li 2 O (45.6% and 177 to 185 mAh g− 1, respectively) due to optimal powder preparation conditions. View Full-Text​