Optimizing micrometer-sized Sn powder composite electrodes for sodium-ion batteries

Abstract

A nanometer-sized Sn (nano-Sn) powder composite electrode with polyacrylate binder delivers a discharge capacity of 600mAhg −1 with a good capacity retention for 100 cycles in non-aqueous Na cells, however, a micrometer-sized Sn (micro-Sn) composite electrode exhibits an insufficient cycle performance under the same condition. Although surface analysis of cycled electrodes reveals no apparent difference in solid electrolyte interphase layer formed on the nano- and micro-Sn electrodes, we found that in the case of nano-Sn electrodes the moderately porous composite layers and thin binder coating on Sn particles are responsible for a favorable cycle performance. On the other hand, the dense and less-porous micro-Sn electrode having a relatively thicker coating of binder on micro-Sn particles deteriorates the reversibility of sodium alloying reaction. Therefore, we optimize the electrode preparation process to introduce the suitable porosity and properly thin binder coating in the micro-Sn composite electrodes. The optimization enables the micro-Sn electrode to demonstrate high reversible sodiation capacity of 676–470mAhg −1 with much improved capacity retention over 100 cycles.