Reactivating dead sodium for durable and high-rate anode-free sodium batteries

Reactivating dead alkali metal is an effective strategy for extending the lifespan of alkali metal batteries. Until now, relevant works are mainly concentrated in lithium batteries, however, the reactivation of dead Na remains a mystery. Herein, dead Na reactivation is realized by a reverse-pulse-interspersed charging strategy. Transient large reverse currents are incorporated into the battery charging protocol, during which dead Na can be reactivated by the dielectrophoresis effect. Different from those electrochemical protocols for dead lithium reactivation during discharging or rest, this strategy for reactivating dead Na in charging shows practicality. Moreover, this strategy homogenizes Na deposition by mitigating ion concentration polarization, thus further suppressing dead Na accumulation. As a proof of concept, durable and high-rate anode-free sodium batteries are realized by this strategy. Specifically, the Al | |Na₄Fe₃(PO₄)₂(P₂O₇) anode-free coin cell using this strategy achieves a doubled cycle life at 1 C. Meanwhile, an Ah-level Al | |Na₄Fe₃(PO₄)₂(P₂O₇) anode-free pouch battery exhibits high capacity retentions of 80.0% over 830 cycles and 74.6% over 1000 cycles at 2 C. Furthermore, a 180 Wh/kg Al | |Na₄Fe₃(PO₄)₂(P₂O₇) pouch battery delivers a long lifespan at 1 C, demonstrating application potential. This reverse-pulse-interspersed charging strategy paves a practical avenue for high-performance alkali metal batteries.