Tailoring Hard-Base Sites on the Al Current Collector Enables Anode-Free Sodium–Metal Batteries

Anode-free sodium–metal batteries (AFSMBs) with an Al current collector exhibit considerable energy density and cost-effectiveness, making them viable candidates for next-generation energy storage. Unfortunately, scarce Na nucleation sites on the Al current collector result in rapid dendrite growth, triggering rapid capacity decay and a potential safety hazard. Here, a surface reconstruction strategy based on the Hard and Soft Acids and Bases Theory is proposed, where the tetrabutylammonium fluoride solution is employed to construct abundant hard-base sites (F^–) on the Al surface. Owing to the strong affinity between hard-acid (Na⁺) and hard-base (F^–), the Na nucleation barrier is effectively reduced, contributing to the significantly enhanced cycling stability of AFSMBs. Consequently, the pouch cell assembled with a Na₂Fe_0.92Mn_0.08[Fe(CN)₆] cathode exhibits an energy density of 319 Wh kg^–1 (based on electrode plates). This work provides a scalable paradigm for developing AFSMBs.