Redox reaction of Sn-polyacrylate electrodes in aprotic Na cell

Sn powder electrodes with polyacrylate binder are examined in aprotic Na cells. The Sn electrodes demonstrate electrochemical redox reaction to reversibly form Sn-Na intermetallic phases, such as Na15Sn4 in the voltage region between 0.0 and 0.7 V vs. Na whereas Si, Ge, and Pb electrodes show less or no specific capacity in Na cells. The reversibility of the Sn electrodes is improved by polyacrylate as a binder and restriction of potential range between 0.0 and 0.8 V. When fluoroethylene carbonate is added to propylene carbonate solution containing NaClO4, the Sn electrode performance with polyacrylate is further improved. The Sn electrode delivers ca. 500 mAh g− 1 for more than 20 cycles, which is about two times larger reversible capacity compared with a hard-carbon negative electrode for Na-ion batteries.

► Sn shows highest redox activity in Na cell among C, Si, Ge, Sn, and Pb. ► The redox reaction is based on reversible formation of Sn-Na alloy phase. ► Composite Sn electrode with polyacrylate binder delivers ca. 500 mAh g− 1. ► The capacity retention is improved by fluoroethylene carbonate electrolyte additive.