Earth-Abundant Na-Mg-Fe-Mn-O Cathode with Reversible Hybrid Anionic and Cationic Redox

摘要

Na-ion batteries (NIBs) are promising for grid-scale energy storageapplications. However, the lack of Co, Ni-free cathode materials has madethem less cost-effective. In this work, Mg~(2+) is successfully utilized to activatethe oxygen redox reaction in earth-abundant Fe/Mn-based layered cathodes toachieve reversible hybrid anionic and cationic redox capacities. A high firstcharge capacity of ≈210 mAh g~(?1) with balanced charge–discharge efficiencyis achieved without O-loss, showing a promising energy cost of $2.02 kWh~(?1).Full cell against hard carbon anode without pre-sodiation shows energydensity exceeding ≈280 Wh kg~(?1) with a decent capacity retention of 85.6%after 100 cycles. A comprehensive analysis of the charge compensationmechanisms and structural evolution is conducted. Voltage and capacity lossresulting from partially reversible Fe~(3+) migration to the Na layer is confirmed,shedding light on further improvements for low-cost NIB cathodes inapplication scenarios.