With increasing need for batteries and energy storage, sodium batteries are of increasing demand. Lithium batteries are very popular but focus is being placed on sodium due to its higher abundance and subsequently, its lower cost.  The human body also has a higher threshold for ingesting sodium than lithium as a nutrient, making it more biocompatible in ingestible battery¹. The main focus of the study is to improve the electrolyte^2,3. We test the electrolyte in a coin cell battery with sodium metal as the anode and the cathode. 

A variety of solvents, electrolytes, and additives are tested to optimize the electrolyte. Several different solvents were tested: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dimethoxyethane (DME), and dioxolane.  These solvents were tested in different combinations with three electrolytes: sodium perchlorate (NaClO₄), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium hexafluorophosphate (NaPF₆). Lastly additives were tested in combination with above cases to test how they improve the electrolyte. The ionic liquid, 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI) and lithium nitrate (LiNO₃) were tested as additives.

We look at the overpotential to gauge the effectiveness of the electrolytes by cycling symmetrical Na/Na cells. An example of the cycling with EC/PC/DEC and NaClO₄ electrolyte is shown in the below Figure 1.

References:

1. L. Xin, X. Huang, H. Xu, Y. Zhang, J. Lam, J. Cheng and J. A. Rogers, Adv Mater 26, 3879-3884 (2014).

2. A. Ponrouch, D. Monti, A. Boschin, B. Steen, P. Johansson and M. R. Palacin, J. Mater. Chem. A, 3, 22 (2015).

3. Monti, Damien, Alexandre Ponrouch, M. Rosa Palacín, and Patrik Johansson. Journal of Power Sources, 324, 712-721 (2016).