Thermal Decomposition Study on Li₂O₂ for Li₂NiO₂ Synthesis as a Sacrificing Positive Additive of Lithium-Ion Batteries

Herein, thermal decomposition experiments of lithium peroxide (Li₂O₂) were performed to prepare a precursor (Li₂O) for sacrificing cathode material, Li₂NiO₂. The Li₂O₂ was prepared by a hydrometallurgical reaction between LiOH·H₂O and H₂O₂. The overall reaction during annealing was found to involve the following three steps: (1) dehydration of LiOH·H₂O, (2) decomposition of Li₂O₂, 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 (Li₂NiO₂) 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 Li₂O (45.6% and 177 to 185 mAh g^-1, respectively) due to optimal powder preparation conditions.