Abstract
Realizing reversible reduction-oxidation (redox) reactions of lattice oxygen in batteries is a promising way to improve the energy and power density. However, conventional oxygen absorption spectroscopy fails to distinguish the critical oxygen chemistry in oxide-based battery electrodes. Therefore, high-efficiency full-range mapping of resonant inelastic X-ray scattering (mRIXS) has been developed as a reliable probe of oxygen redox reactions. Here, based on mRIXS results collected from a series of Li1.17Ni0.21Co0.08Mn0.54O2 electrodes at different electrochemical states and its comparison with peroxides, we provide a comprehensive analysis of five components observed in the mRIXS results. While all the five components evolve upon electrochemical cycling, only two of them correspond to the critical states associated with oxygen redox reactions. One is a specific feature at 531.0 eV excitation and 523.7 eV emission energy, the other is a low-energy loss feature. We show that both features evolve with electrochemical cycling of Li1.17Ni0.21Co0.08Mn0.54O2 electrodes, and could be used for characterizing oxidized oxygen states in the lattice of battery electrodes. This work provides an important benchmark for a complete assignment of all mRIXS features collected from battery materials, which sets a general foundation for future studies in characterization, analysis, and theoretical calculation for probing and understanding oxygen redox reactions.
Highlights
Developing high energy-density and low-cost energy storage devices has become crucial for effectively addressing energy and environmental challenges, with a projected market expansion for 10 times in this decade [1]
We provide a careful analysis of all the mapping of resonant inelastic X-ray scattering (mRIXS) features observed in a series of Li-rich Li1.17Ni0.21Co0.08Mn0.54O2 (LR-NMC) electrodes and its comparison with Li2O2 results
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Summary
Developing high energy-density and low-cost energy storage devices has become crucial for effectively addressing energy and environmental challenges, with a projected market expansion for 10 times in this decade [1]. Improving battery technology to meet the requirements of modern energy storage remains a formidable challenge, which calls for conceptual breakthroughs and advanced characterizations to explore new solutions beyond conventional systems. Only transition-metal (TM) redox is involved in electrochemical cycling, and introducing oxygen (O) redox was believed to be detrimental to the reversibility and safety of a battery, mainly because of the irreversible O2 release and parasitic surface reactions. Some recent studies suggest that oxygen redox could be reversible and could greatly improve the energy density of battery cathodes [7]. This opens opportunities for developing and optimizing TM oxide materials towards a high energy density beyond conventional TM redox systems
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