Current collector interphase design for high-energy and stable anode-less sodium batteries

Sodium-ion batteries have emerged as one of the most promising next-generation energy storage systems. However, their widespread application is hindered by the low energy density and high cost of hard carbon anodes. Anode-free designs offer a potential solution but typically suffer from poor cycling performance due to uncontrolled Na plating and inefficient stripping. Here we report a hard-carbon-derived interphase on an aluminium current collector to construct an anode-less sodium battery (ALSB) that maintains high energy density, reduces costs and enhances cycling stability. Remarkably, the interphase layer with a low dielectric constant and strong Na interaction enables homogeneous Na nucleation, crack-free plating and efficient stripping, thereby minimizing active Na loss during cycling. As a result, our ALSB maintains good stability for up to 900 cycles and 2.3-Ah-level ALSBs show an energy density of 203 Wh kg−1. Our findings pave the way for more sustainable batteries with competitive energy density, extended cycle life and lower costs. Anode-free sodium metal batteries without excess sodium achieve high energy density and low cost, but their cycling stability remains poor. Here an optimized current collector interphase enables unprecedented cyclability and energy density.