Thanks to the low cost of Na precursors and the abundant Na resources, Na-ion batteries have been considered a promising alternative to Li-ion batteries for large-scale energy storage systems. However, the cost decrease of Na-ion batteries relative to that of Li-ion batteries cannot be easily achieved, in spite of the inexpensive Na precursors. Since Na-ion batteries have slightly lower energy densities than Li-ion batteries, the energy density limitations offset the cost savings due to the use of Na. Accordingly, the cost per energy ($/Wh) of Na-ion batteries can be decreased only when the similar energy density of Na-ion batteries to that of Li-ion batteries is obtained. The energy density of Na-ion batteries can be improved by using high-capacity anode materials with appropriately low redox potentials (about <0.4 V vs. Na/Na+). Therefore, in this presentation, we introduce high-capacity anode materials such as phosphorus and tin phosphide in order to improve the energy density of Na-ion batteries.We for the first time introduced amorphous red phosphorus/carbon composites showing excellent electrochemical performance for Na-ion batteries. The P/C composite delivered the highest reversible capacity, 1890 mA h gP-1, among any reported anode materials for Na-ion batteries. The P/C composite also showed good rate performance and stable cycleability over 30 cycles. The improved electrochemical performance of the P/C composite is caused by i) the enhanced electrical conductivity through the intimate nanoscale contact between phosphorus and carbon and ii) the use of the polyacrylic acid (PAA) binder.Recently, we also reported that Sn4P3 as an anode material showed excellent electrochemical performance for Na-ion batteries. The Sn4P3 electrode delivered a reversible capacity of about 700 mA h g-1 and exhibited excellent cycle performance with a negligible capacity fading over 100 cycles.

High-capacity anode materials for sodium ion batteries

248th National Meeting (2014)

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