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

Abstract 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.