Facile Self-Assembled Monolayer Deposition on Copper Foil for High-Performance Lithium-Metal Batteries

Li metal is widely acknowledged as the optimal negative electrode material for high-energy-density Li rechargeable batteries. However, challenges arise owing to the formation of Li dendrites and poor surface stability, leading to reduced cycle life and energy efficiency, thereby limiting widespread application. In this study, we introduced a novel approach of a molecular single-layer surface modification onto a Cu foil using a selfassembled monolayer with hexamethyldisilane (HMDS) to enhance the performance of Li-metal electrodes. The deposition of a single molecular layer at the & Aring;-level was achieved by a simple combination of precursor casting and heat treatment without greatly affecting the energy and power density. Furthermore, this process was both scalable and cost-effective, making it highly suitable for large-scale battery manufacturing. The molecular deposition of HMDS effectively mitigated electrolyte decomposition and promoted uniform Li deposition by enhancing the surface stability under repeated Li plating-stripping processes. Optical microscopy revealed the homogeneous Li plating even after extended cycling; the first cycle on the modified surface depicted uniform plating without blank spots owing to the reduced gas-phase by-products from electrolyte decomposition. Thus, HMDS modification greatly improved the cycle stability of Li-metal batteries by successfully mitigating polarization due to electrolyte decomposition. Such improvement improved the Coulombic efficiencies and enhanced the energy efficiency, especially over a wide current density range of 1-5 mA cm- 2. Furthermore, full cells with LiFePO4 cathodes and HMDS-modified Cu foils exhibited extended cyclability with increased energy efficiencies.