Sodium reservoir to compensate sodium loss for ultra-stable anode-less sodium metal batteries

The potential application of anode-less sodium metal batteries (ALSBs) is severely affected by the irreversible depletion of sodium ions. Cathode sodium compensation (SC) additive is an effective way for sodium supplement due to its simplicity and flexibility. However, developing SC additives with no toxicity, low cost, low sensitivity to air and humidity is still a huge challenge. In this work, we propose a low-cost, environmentally friendly and air-stable organic sodium salt as sodium reservoir to compensate sodium ion, thus improving the cycle stability of ALSBs. The capacity of ALSBs with N: P as low as 0.5:1 could maintain capacity retention of 91.3% after 100 cycles with this SC additive, while the cell without this SC additive would decline to almost zero after 10 cycles. The inexpensive price and ease of preparation also make it suitable for industrialization. This work provides a realistic SC approach for improving the cycling stability for ALSBs.