Structure and Electrochemistry of NaxFexMn1-xO2 (1.0 ≤ x ≤ 0.5) for Na-Ion Battery Positive Electrodes

The primary objective of research activities in Na-ion battery development is the implementation of inexpensive, sustainable and environmentally friendly battery materials. Here we report an investigation of NaxFexMn1-xO2 electrode materials which contain elements commonly found in the earth's crust, have very low toxicity and cost, and can be prepared in open air atmosphere using simple procedures. Samples with x > 0.65 were found to have the same structure as O-3 alpha-NaFeO2 under selected synthesis conditions. Samples with x < 0.65 did not have the P2 or O3 structures, but retained a layered structure in which staging likely occurs. Samples having x = 0.5 were found to cycle reversibly at a capacity over 170 mAh/g (corresponding to a theoretical energy density of approximately 460 Wh/kg) with 85% capacity retention after 20 cycles. When the capacity is restricted to 135 mAh/g (340 Wh/kg), capacity retention approaches 95% after 20 cycles. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.058302jes] All rights reserved.