Mediating the alloying depth to tune silicon's morphology and lithium-storage performance

Abstract

Regulating the morphology and structure of Si by alloying/dealloying has been proven as an effective way to leverage the Li-storage performance of Si the anode in Li-ion batteries (LIBs). However, the alloying depth is difficult to control and thus the alloy depth-structure relationship is still unclear. Here, we employ the molten-salt electrochemical alloying/dealloying approach to regulate the Li/Si atom ratio (Li_x–Si, where x refers to the Li/Si atom ratio and ranges from 1 to 9) to prepare a series of three-dimensional nanoporous Si materials. The obtained nanoporous Si (np-Si-5) shows an outstanding charge capacity of 3276.6 mA h g⁻¹ at 1 A g⁻¹, a high initial coulombic efficiency of 77.5%, excellent rate performance (reversible capacity of 1074.1 mA h g⁻¹ at 7 A g⁻¹), and long cycle stability (reversible capacity of 1012.1 mA h g⁻¹ and capacity retention of 83% at 5 A g⁻¹ after 1000 cycles). Moreover, the np-Si-5 ‖ LiNi_0.6Co_0.2Mn_0.2O₂ full cell delivers a high capacity of 101.2 mA h g⁻¹ and capacity retention of 89% after 150 cycles at 5C. Hence, controlling the Li/Si ratio can mediate the morphology and structure of Si so as to control the Li-storage performance of the Si anode, which sheds light on designing Si-based anodes for high-performance LIBs.