Co-Free Layered Oxide Cathode Material with Stable Anionic Redox Reaction for Sodium-Ion Batteries

摘要

Co shows excellent performance in the high voltage range for layered oxidecathode materials for sodium ion batteries (SIBs). However, its high cost andtoxicity are significant disadvantages.Co-free cathodes with high performanceare urgently needed for development. Herein, cheap Mg and Ti elements arepreferred to replace Co elements. A P2-Na_(0.67)Mn_(0.53)Ni_(0.30)Mg_(0.085)Ti_(0.085)O_2(Ni30MgTi) cathode shows a high reversible specific capacity of 118 mA h g~(-1)at a current density of 50 mA g~(-1) in 2.0-4.25 V, which is even higher than thatin the base sample with Co. Moreover, Mg and Ti raise the median dischargevoltage from 3.21 to 3.59 V, which raises the energy density from 325 to410 Wh kg~(-1). On the other hand, ex situ XPS and in situ differentialelectrochemical mass spectrometry tests indicate that Ni30MgTi has a stableanionic redox reaction with reversible capacity in the high voltage range. Theconcept of bimetallic co-substitution offers a simple and effective Co-freestrategy to reduce the cost and increase the energy density of layered oxidecathode materials simultaneously for SIBs.