Cycling performance of silicon-carbon composite anodes enhanced through phosphate surface treatment

Abstract

Abstract Silicon (Si)‐based anodes have long been viewed as the next promising solution to improve the performance of modern lithium‐ion batteries. However, the poor cycling stability of Si‐based anodes impedes their application and calls for solutions for further improvements. In the present work, the incorporation of phosphate groups on the surface of an amorphous Si‐carbon composite (a‐Si/C) has been achieved by a hydrothermal reaction using phosphoric acid and sodium dihydrogen phosphate at pH = 2. Different levels of the surface P‐doping have been realized using reaction times (2, 4, and 8 h) at two different phosphate concentrations. The presence of phosphate groups on the particle's surface has been confirmed by energy‐dispersive X‐ray, infrared, and Raman spectroscopy. The cycling stability of the P‐treated a‐Si/C composites has been significantly improved when using lithium bis(trifluoromethanesulfonyl)imide as a salt in ether‐based solvents mixture compared to a conventional electrolyte for Si‐based anodes (LiPF 6 in carbonate‐based solvents). Coulombic efficiencies as high as 99% have been reached after five charge/discharge cycles for almost all phosphate‐treated materials. The 4 h P‐treated a‐Si/C composite electrode exhibits the best reversible capacity of 1598 mAh g −1 after 200 cycles demonstrated in half‐cells using an ether‐based electrolyte.