AbstractCompensating the irreversible loss of limited active lithium (Li) is essentially important for improving the energy‐density and cycle‐life of practical Li‐ion battery full‐cell, especially after employing high‐capacity but low initial coulombic efficiency anode candidates. Introducing prelithiation agent can provide additional Li source for such compensation. Herein, we precisely implant trace Co (extracted from transition metal oxide) into the Li site of Li₂O, obtaining (Li_0.66Co_0.11□_0.23)₂O (CLO) cathode prelithiation agent. The synergistic formation of Li vacancies and Co‐derived catalysis efficiently enhance the inherent conductivity and weaken the Li−O interaction of Li₂O, which facilitates its anionic oxidation to peroxo/superoxo species and gaseous O₂, achieving 1642.7 mAh/g_~Li2O prelithiation capacity (≈980 mAh/g for prelithiation agent). Coupled 6.5 wt % CLO‐based prelithiation agent with LiCoO₂ cathode, substantial additional Li source stored within CLO is efficiently released to compensate the Li consumption on the SiO/C anode, achieving 270 Wh/kg pouch‐type full‐cell with 92 % capacity retention after 1000 cycles.