Highly Stable Anode-free Sodium Batteries Enabled by Mechanically Deformable Nucleation Interface

Abstract

Anode-free sodium metal batteries (AFNMBs) with zero excess sodium offer superior energy density, lower cell cost, and design practicality for next-generation EVs and other applications. However, reaching consistent high Coulombic efficiency (CE) greater than 99.9% remains a challenge for this battery architecture. In this study, our findings support that using a soft Li metal interface under a current collector coated with a thin carbon black nucleation layer facilitates extremely stable nucleation and growth of Na metal by locally distributing pressure to mitigate SEI or dead sodium formation. Specifically, our findings demonstrate Na half cells with stable CE of 99.98% over 500 cycles at 0.5 mA/cm². Further, zero-excess sodium full cell AFNMBs with Na₃V₂(PO₄)₃ cathodes exhibit total first cycle formation loss of only 5.4% at C/10 rates, which is over two times lower than commercial Li-ion cells, with capacity retention of 97.4% after 100 cycles at 0.5 mA cm^-2 (∼ C/3) and average round-trip energy efficiency of 99.97%.