Sodium ion batteries (SIB) have potential for large scale renewable energy storage due to geopolitical abundance of Na. However, the high capacity Na-ion anodes still suffer from poor cycling stability and low Coulombic efficiency (CE). Herein, uniform Sn4P3@C spheres were synthesized by a facile aerosol spray-pyrolysis-phosphidation method. By tuning the electrolyte, a reversible capacity of ~ 800mAh/g with an extremely low capacity decay rate of 0.09% per cycle was achieved with a record-high initial CE (> 90%) and high cyclic CE (~ 99.9%). The Sn4P3@C in the stable ether-based electrolyte shows the highest accumulated cycling capacities in the reported SIB anodes.