Anionic Redox Reaction of Rechargeable Battery Cathodes Investigated by Advanced Characterization Techniques

The rapid growth of new energy industry has created an urgent demand for high-energy-density rechargeable batteries. Notably, the limited energy density provided by cationic redox process of rechargeable batteries can be overcome by triggering anionic redox reaction (ARR), which has emerged as a transformative paradigm for breaking through the energy density bottleneck and garnered widespread attention over the past decade. However, the activity of ARR is usually accompanied by multiple issues and consequent electrochemical setbacks, mainly including irreversible oxygen release, sluggish reaction kinetics, and serious voltage decay/hysteresis. To gain a holistic understanding and harness the full potential of ARR for practical rechargeable batteries, significant research efforts have centered on the oxidized oxygen identification and their associated degradation pathways. However, due to the lack of recognition and inherent limitations of current characterization techniques, comprehensive and accurate research approaches for investigating ARR remain scare. Here, by combining advanced characterization techniques that utilize different energy sources (e.g., electrons, X-rays, and neutrons) for specific research purposes, we provide a systematic multi-scale overview in which the intrinsic characteristics, degradation mechanisms, and regulation strategies related to ARR are comprehensively presented. This perspective concludes with a discussion on developing advanced characterization techniques for ARR and cautioning for its practical application.