Lithium- and sodium-rich layered transition-metal oxides have recently been attracting significant interest because of their large capacity achieved by additional oxygen-redox reactions. However, layered transition-metal oxides exhibit structural degradation such as layer exfoliation or cracks upon deep charge, which is a major obstacle to achieve higher energy-density batteries. Defect are usually considered as a negative factor to realize stable operation of cathode materials. Here we show, by applying optimal design strategies, defect can not only effectively generate redox-active “orphaned” nonbonding oxygen 2p orbitals to “activate” additional oxygen-redox reactions, but also contribute to “stabilizing” reversible phase transformation with its effective negative point charge.