Lithium ion capacity of single wall carbon nanotube paper electrodes

The electrochemical cycling performance of high purity single wall carbon nanotube (SWCNT) paper electrodes has been measured vs lithium metal for a series of electrolyte solvent compositions. The addition of propylene carbonate (PC) into the conventional ethylene carbonate (EC):dimethyl carbonate (DMC) cosolvent mixture enabled a reversible lithium ion capacity of 520 mAh/g for high purity SWCNTs. The free-standing SWCNT electrode (absent of polymer binder or metal substrate support) with this electrolyte combination demonstrates enhanced cycleability, retaining > 95 % of the initial capacity after 10 cycles. The first cycle hysteresis, common in these materials, is shown to vary dramatically with solvent selection and illustrates the importance of the solid-electrolyte-interface (SEI) formation on SWCNT capacity. The effect of galvanostatic charge rate (i.e., C-rate) on lithium ion capacity shows a 2 x improvement [in capacity per current] over reported values for conventional graphite anode materials. These electrochemical results are complemented by a postmortem analysis of the purified SWCNT electrode after lithiation using scanning electron microscopy, X-ray diffraction, Raman, and optical absorption spectroscopy. The results show that the structural integrity and carbonaceous purity of individual SWCNTs is maintained during cycling, while the lithium insertion is accommodated by bundle channel expansion.