Electrochemical, structural, and electronic properties of Mn-Co hexacyanoferrates against Li concentration

Manganese and cobalt hexacyanoferrates are promising candidates for cathode materials for lithium ion secondary batteries (LIBs), because such compounds exhibit high capacity (? approximate to 130-150mAh/g) and good discharge rate properties. Here, we investigated electrochemical, structural, and electronic properties of solid solutions of Mn and Co hexacyanoferrates, LixMn1-gamma Co-y[ Fe(CN)(6)](2)wH(2)O, against Li concentration (x). In all the compounds, we observed two plateaus at 3.8-4.0V (plateau I) and 3.2-3.4V (plateau II). Ex situ X-ray absorption spectroscopy (XAS) revealed that plateau I (II) is ascribed to the reduction of Co3+ (Fe3+) at y <= yc (= 0.33) while plateau I (II) is ascribed to the reduction of Fe3+ (Co3+ and Mn3+) at y >= yc. The lattice constant (a(Fe)) at the Fe redox plateau discontinuously decreases from ? approximate to 10.5 at y : yc and ? approximate to 10.0 at y <= yc. We will discuss the lattice effects on the electrochemical and electronic properties. (C) 2014 The Japan Society of Applied Physics