Large scale energy storage is the key to incorporating renewable resources like wind, tidal, and solar into power grid allowing us to use these resources when power is needed. High cost and less availability of lithium metal hampers the usage of the present reigning energy storage champion-lithium ion batteries (LIBs) in large scale applications. Sodium ion batteries (NIBs) could provide an alternative solution for expensive LIBs because sodium is the 4^th most abundant metal on earth and has worldwide availability. The energy density is not crucial issue in the field of large scale energy storage systems and therefore low cost of NIBs surpasses the lower gravimetric and volumetric densities of NIBs than LIBs¹. Currently electrochemists are involved in the hunting for highly efficient electrode materials for NIBs. Advantages like stability, insolubility in electrolytes, and a high theoretical capacity with its two available anhydride groups attached to the stable aromatic ring makes the polyimide (PI) as a preeminent candidate for cathode active material for NIBs².

In this work we have synthesized naphthalene tetracarboxylic dianhydride (NTCDA) based polyimide/multi-walled carbon nanotube (PI/MWCNT) composite for use as a cathode active material for high performance NIB. PI/MWCNT composite was synthesized in a two-step process and was characterized using field emission scanning electron microscopy (FE-SEM) and Fourier Transform infrared spectroscopy (FTIR). Three-dimensional network of MWCNT inside and between PI particles enhances the conductivity and thereby electrochemical performance of PI/MWCNT composite electrode. A highly porous polyvinylidene fluoride (PVdF) membrane made by phase inversion method was used as the separator for NIB. The electrochemical performance of cells based on PI/MWCNT composite cathode with PVdF membrane delivered high capacity and cycle capability at different C-rates.

Fig. 1: SEM image of cross section of PVdF membrane.

References:

1. Ong, S. P.; Chevrier, V. L.; Hautier, G.; Jain, A.; Moore, C.; Kim, S.; Ma, X.; Ceder, G., Voltage, stability and diffusion barrier differences between sodium-ion and lithiuim-ion intercalation materials. Energy & Environmental Science 2011, 4, 3680-3688.

2. Mazur, S.; Lugg, P. S.; Yarnitzky, C., Electrochemistry of aromatic polyimides. Journal of Electrochemistry (1987), 134, 346-353.