Identifying Hidden Li-Si-O Phases for Lithium-Ion Batteries via First-Principle Thermodynamic Calculations

SiO-based materials are promising alloys and conversion-type anode materials for lithium-ion batteries and are recently found to be excellent dendrite-proof layers for lithium-metal batteries. However, only a small fraction of the Li-Si-O compositional space has been reported, significantly impeding the understanding of the phase transition mechanisms and the rational design of these materials both as anodes and as protection layers for lithium-metal anodes. Herein, we identify three new thermodynamically stable phases within the Li-Si-O ternary system (Li2SiO5, Li4SiO6, and Li4SiO8) in addition to the existing records via first-principle calculations. The electronic structure simulation shows that Li2SiO5 and Li4SiO8 phases are metallic in nature, ensuring high electronic conductivity required as electrodes. Moduli calculations demonstrate that the mechanical strength of Li-Si-O phases is much higher than that of lithium metal. The diffusion barriers of interstitial Li range from 0.1 to 0.6 eV and the interstitial Li hopping serves as the dominating diffusion mechanism in the Li-Si-O ternary systems compared with vacancy diffusion. These findings provide a new strategy for future discovery of improved alloying anodes for lithium-ion batteries and offer important insight towards the understanding of the phase transformation mechanism of alloy-type protection layers on lithium-metal anodes.

Automated summary

SiO-based materials have potential applications as alloys and conversion-type anode materials for lithium-ion batteries, as well as excellent dendrite-proof layers for lithium-metal batteries. Through first-principle calculations, three new thermodynamically stable phases (Li2SiO5, Li4SiO6, and Li4SiO8) were discovered, and it was found that Li2SiO5 and Li4SiO8 phases possess metallic properties with high electronic conductivity. The mechanical strength of Li-Si-O phases was also found to be higher than lithium metal, and the dominant diffusion mechanism in the Li-Si-O ternary systems is interstitial Li hopping.