Void-rich layered SiGex alloys via in situ molten salt electrochemistry for high-performance lithium-ion battery anodes

Abstract

Silicon (Si) has emerged as a highly promising anode material for next-generation lithium-ion batteries owing to its exceptional high theoretical capacity, natural abundance, and low (de)lithiation potential. However, its practical implementation faces significant challenges, including poor conductivity and substantial volume expansion (∼300%) during cycling. In this study, we present an innovative in situ molten salt electrochemical approach for the direct synthesis of silicon–germanium alloys (SiGe_x) using commercial SiO and Ge precursors. Through meticulous optimization of the SiO/Ge molar ratio, three SiGe_x alloys (SiGe, SiGe_0.67 and SiGe_0.5) are successfully synthesized, and their structural and electrochemical performance are systematically investigated. Among them, the optimally designed SiGe_0.67 alloy, electrolyzed at a voltage of 2.5 V with a SiO/Ge ratio of 1 : 0.67, shows a well-defined lamellar structure with an expanded lattice and abundant interlamellar voids. The typical lamellar structure of the SiGe_0.67 alloy with high electrical conductivity facilitates rapid electron and lithium-ion transportation while accommodating the volume expansion, thereby improving both rate performance and structural stability of the SiGe_x host. Benefiting from these merits, the optimized SiGe_0.67 electrode delivers a high initial discharge capacity of 2046 mAh g⁻¹ with an impressive initial coulombic efficiency (ICE) of 82.6%. The electrode also exhibits remarkable cycling stability, retaining 1090.4 mAh g⁻¹ at 1 A g⁻¹ after 200 cycles with 82.7% of capacity retention. Furthermore, it maintains a competitive capacity of 870 mAh g⁻¹ even at a high current density of 4 A g⁻¹, demonstrating its superior rate performance. These results highlight the potential of structure-guided Si–Ge alloy design in developing high-capacity, long-cycle-life, and fast-charging anodes for next-generation energy storage systems.