Sodium-compensating electrolyte additive stabilizes interfaces for highly reversible anode-free sodium batteries

Abstract

Anode-free sodium batteries (AFSBs) offer superior cost, energy density, and manufacturing advantages over sodium-ion batteries (SIBs) by eliminating the conventional anode. However, their development is fundamentally hindered by dead sodium formation and interfacial side reactions that severely limit cycle life. To address these issues, for the first time, we report sodium bis(trimethylsilyl)amide (NaHMDS) as a non-invasive, gas-free electrolyte additive for sodium compensation, which operates at a low compensation potential of 2.82 V (vs. Na + /Na). This multifunctional additive enables Ah-level AFSB pouch cells to retain 89.6% capacity after 500 cycles at 1C rate by compensating active sodium loss, stabilizing electrode interphases, and improving sodium stripping/plating reversibility. In contrast, the sodium-compensating additives sodium thiocyanate (NaSCN) and NaNO 2 induce irreversible side reactions, electrode degradation, and dendrite growth while failing to provide effective sodium compensation for AFSBs. This work presents a promising sodium-compensating additive with commercial viability, redefining AFSB additive design principles by prioritizing interfacial stability over conventional metrics such as compensation capacity and potential.