Using Intimate Carbon to Enhance the Performance of NaTi₂(PO₄)₃Anode Materials: Carbon Nanotubes vs Graphite

Abstract

The effect of intermixed carbon nanotubes and graphite on the electrochemical functionality of NaTi2(PO4)3 was examined. Specifically, the performance of NaTi2(PO4)3 made with "intimate carbons" containing carbon nanotubes (or graphite) introduced at the precursor stage was compared to the performance of similar materials made with the carbons added post synthesis. Specifically, different combinations of carbon nanotubes and graphite were used as carbon sources both in the precursor blend prior to sintering as well as conductive additives in the test electrodes. Graphite-coated NaTi2(PO4)3 with additional carbon nanotubes added (post synthesis) as conductive agent exhibited the best overall performance: the first cycle discharge specific capacity is 130 mAh/g (close to theoretical value 133 mAh/g) at 0.1C rate. The combination also exhibits good cycling stability in aqueous electrolyte: 86% capacity retention under continuous charge/discharge without relaxation at 1C rate for 100 cycles. This suggests that fully coating the precursor material with carbon is critical for performance, and that a graphite additive in the precursor phase is more effective than nanotubes at performing this function.