Ternary AlGe_xP alloy compounds for high capacity and rate capability of lithium-ion battery anodes

Despite the high volumetric capacity of Ge-based anodes, their practical applications are still limited by low cycling stability and rate performance. To resolve these challenges, herein, we simultaneously incorporate both Al and P into Ge to synthesize AlGe_xP (x = 6, 2, 2/3) series materials through a facile mechanical ball milling method. Experiments and theoretical calculations confirm that AlGe₂P provides the fastest electronic conductivity and Li-ion diffusion capability, thus providing the best Li-storage performance among AlGe_xP (x = 6, 2, 2/3) series materials. As verified by ex situ characterization, AlGe₂P features a reversible Li-storage mechanism arising from the first intercalation stage followed by conversion reactions, where the electronically conducting Li₁₅GeP₃, Li_4.4Ge, and LiAl and Li-ion conducting Li₃P, Li_4.4Ge and LiAl are simultaneously produced, ensuring fast charge storage kinetics upon cycling. Accordingly, the AlGe₂P/C composite presents a long-term cycling stability of retaining 867 mA h g⁻¹ after 800 cycles at 2000 mA g⁻¹, and a high-rate capacity of 454 mA h g⁻¹ even at 20 000 mA g⁻¹, thus holding promise for real world applications. Broadly, the ternary all-lithium-reactive Ge-based compounds have great application potential in the energy storage field due to their intriguing physiochemical properties.