Borate-Like Terminations Strengthen MXene-Silicon Coupling for Ultrafast and Durable Lithium Storage

Abstract

Surface terminations play a crucial role in determining the properties of MXene. This study developed a silicon anode composite using borate-terminated MXene (Ti3C2Tx) nanosheets to achieve enhanced electrochemical performance. These borate-like surface terminations (Ti & horbar;O & horbar;B & horbar;O) chemically anchored the MXene to Si nanoparticles, forming strong interfacial bonds. X-ray absorption spectroscopy confirmed that borate functionalization increased the oxidation state of Ti while maintaining the local coordination environment and two-dimensional carbide structure of the MXene, despite modification in surface chemistry. Ex-situ XPS analysis of the borate-terminated MXene nanosheets (B-MXNS)/Si electrode further reveals the formation of a boron-rich, fluorine-regulated solid-electrolyte interphase containing B-F and P-F species with suppressed excessive LiF accumulation, indicating effective HF scavenging and mitigation of continuous electrolyte decomposition. This chemically stabilized interphase rationalizes the higher initial Coulombic efficiency and exceptional long-term cycling stability of the B-MXNS/Si anode at high silicon loading. The composite (60 wt% Si) retained around 80% of the initial capacity after 1200 cycles at 2 A g-1 and delivered approximately 2100 mAh g-1 at 4 A g-1. This study underscores that atomic-level surface engineering with boron effectively addresses long-standing challenges in high-silicon-content anodes and provides a promising route toward high-energy-density lithium-ion batteries with extended cycle life.