Phase Engineering of Lithium Silicate in SiO_x Anodes for Fast-Charging Lithium-Ion Batteries

The development of high-energy-density anodes capable of withstanding fast-charging conditions remains a significant challenge for lithium-ion batteries. Silicon monoxide (SiO_x) is a promising candidate, yet its performance intrinsically depends on the structure of the lithium silicate matrix formed during the initial lithiation. Herein, we demonstrate that the lithiation method, chemical versus electrochemical, serves as a powerful tool for the precise phase engineering of this silicate component. We selectively synthesized Li₂Si₂O₅, Li₂SiO₃, and Li₄SiO₄, establishing that the [NBO]/[Si] ratio is the key descriptor for Li-ion transport kinetics. Multiscale simulations confirm that nonbridging oxygen (NBO) sites provide low-energy migration pathways, whereas bridging oxygen (BO) sites impede ion mobility. The electrochemically derived Li₄SiO₄ phase, which possesses the highest [NBO]/[Si] ratio, consequently enables a superior fast-charging performance. Practical validation using 2-Ah pouch cells demonstrates 85% capacity retention after 300 cycles at 4C (15-min charging). This work establishes lithiation engineering as a fundamental strategy for developing high-performance SiO_x anodes, transforming it from a simple pretreatment into a critical design parameter for fast-charging batteries.