Understanding and Passivation of Surface Corrosion of Cu for Stable Low-N/P-Ratio Lithium-Sulfur Battery

The realization of a low negative/positive capacity (N/P) ratio is essential for attaining high energy density in lithium-sulfur batteries (LSBs). However, it has been challenging to maintain the stability of the Li metal anode at low N/P ratios. Herein, it is revealed that the corrosion of the Cu current collector by dissolved intermediates of polysulfides -a largely overlooked perspective- significantly contributes to the instability of Li metal anode at low N/P ratios. The reduced Li/Li⁺ redox rates on the corroded Cu surface result in uneven and porous Li deposits that severely deteriorate cycling stability. To address this issue, an anti-corrosion alloy coating is developed to passivate the Cu surface against polysulfides. LSBs with passivated current collectors at a low N/P ratio (1.5) and lean electrolyte (5 µL mg_s⁻¹) show a ten fold extension in cycle and calendar life. This study not only provides the initial evidence of the impact of Cu corrosion on the failure mechanism of low N/P ratio LSBs but also proposes a practical yet effective strategy to stabilize high-energy-density LSBs.