Redox Reactions in Prussian Blue Analogue Films with Fast Na+ Intercalation

Electronic state of cobalt and manganese Prussian blue analogues were systematically investigated against Na+ intercalation by means of the infrared and X-ray absorption spectroscopies. The spectroscopies revealed that 3.8 and 3.4 V plateaus in the discharge curve of NaxCo[Fe(CN)(6)](0.90)2.9H(2)O (denoted as NCF90) are ascribed to the reduction processes of Fe3+ and Co3+, respectively. On the other hand, 3.6 and 3.2V plateaus of NaxMn[Fe(CN)(6)](0.83)3.5H(2)O (NMF83) are ascribed to the reduction processes of Mn3+ and Fe3+, respectively. We found that the film electrodes with a thickness of 1.1 mu m exhibit fast Na+ intercalations: the discharge capacity at 60 C of the NCF90 (NFM83) film was 90% (45%) of the open-circuit-voltage (OCV) value. Thus, Prussian blue analogue films are promising cathode candidates for sodium-ion secondary batteries. (C) 2013 The Japan Society of Applied Physics