LAUSR

Enhancing the energy density of lithium‐ion batteries (LIBs) remains a critical challenge for advancing next‐generation energy storage technologies. Silicon‐based anodes offer significantly higher theoretical capacitites, but their practical application is hindered by low initial coulombic efficiency (ICE), leading to substantial lithium loss and rapid full cell performance degradation. Herein, a novel prelithiation agent, lithium borate (LBO), based on the ultralight, cost‐effective, and d‐orbital‐free non‐metallic element boron (B) is presented. LBO features a core–shell architecture, consisting of a crystalline Li3BO3 core encapsulated by Li2CO3 and amorphous carbon, delivering an exceptional initial charge capacity of 692 mAh g−1 and superior atmospheric stability with 70% capacity retention after 8 days of ambient exposure. When applied in SiOx||LRLO (Li‐rich layered oxide) pouch cells, LBO enhances the gravimetric and volumetric energy density by 14.7% and 21.8%, respectively, while effectively suppressing the irreversible LRLO degradation caused by Li deficiency. This work introduces an element‐centric design methodology for prelithiation agents, providing a promising route to propel the development of high‐energy‐density LIBs.