A novel low cost sodium-ion battery electrolyte additive ZSM-5 nanozeolite, which improves cycle life, is demonstrated in a Na-ion cell. The addition of this zeolitic small molecule scavenger removes electrolyte decomposition products, and has beneficial properties compared to traditional organic additives such as fluoroethylene carbonate (FEC). Capacity retention after 480 cycles improves from 40% (none) compared to 62% (ZSM-5). This is due to the enhanced interface stability over the cell life-time, as shown by XPS.