Biphenyl as overcharge protection additive for nonaqueous sodium batteries

Sodium batteries are considered as a promising low-cost alternative for currently used lithium batteries. However, safety problems such as overcharge may be a key hindrance for their wide-spread applications. In this study, an aromatic compound (biphenyl) is investigated as an overcharge protection additive for sodium batteries. It is found that BP can be electro-polymerized at 4.3 V (vs. Na/Na⁺), which protects the Na_0.44MnO₂/Na batteries from voltage runaway for more than 800% overcharge capacity by consuming the overcharge current. The influence of proper BP addition on the cycling performance and capacity is negligible. Thus, BP can be used as an overcharge additive for sodium batteries. The results may also be helpful for the further research of safer sodium battery systems.