Journal
ENERGY STORAGE MATERIALS
Volume 48, Issue -, Pages 290-296Publisher
ELSEVIER
DOI: 10.1016/j.ensm.2022.02.049
Keywords
Voltage hysteresis; Oxygen redox; Na Mn-2 O-3 (7); Operando EPR; Electronic structure
Funding
- National Natural Science Foundation of China [21902049, 21872055]
- Shanghai Sailing Pro-gram [19YF1413000]
- Chenguang Program [20CG30]
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Oxygen redox has both benefits and drawbacks for battery cathodes. This study focuses on Na2Mn3O7, which exhibits an abnormal small voltage hysteresis during oxygen redox. The stable electronic structure and dispersive oxygen redox in Na2Mn3O7 are proposed as the reasons for this abnormal behavior.
Oxygen redox is a double-edged sword for battery cathodes as it furnishes a substantial increase in energy density at the expense of bringing additional detrimental issues, such as irreversible local structural transformation and substantial voltage hysteresis. Intriguingly, Na2Mn3O7 can access an oxygen-redox capacity with an abnormal small voltage hysteresis (~0.05 V), making it a rare model system to identify a reaction mechanism that suitable for engineering oxygen-redox cathodes with high energy efficiency. Herein, we firstly corroborate by operando electron paramagnetic resonance (EPR) that the local electronic structure evolution of Na2Mn3O7 upon oxygen redox is highly reversible. By ex situ low-temperature EPR measurements, we also confirm that O-2 p localized holes (O-.) is the chemical state of oxidized oxygen species in Na2-xMn3O7, contributing to a highly reversible local structural evolution around Na nucleus. The stable electronic structure stimulated by the absence of in-plane Mn migration and the dispersive oxygen redox without O -O dimerization in Na2-xMn3O7, is thus firstly proposed as the origin of abnormal small voltage hysteresis. This study provides the rationale for achieving nonhysteretic behavior in the large family of oxygen-redox cathodes.
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