A facile synthesis of a novel mesoporous Ge@C sphere anode with stable and high capacity for lithium ion batteries

Abstract

Tremendous volume expansion of germanium during cycling causes much difficulty to its use in high performance anodes for lithium ion batteries (LIBs). In this paper, we report a facile synthesis of novel mesoporous Ge@C spheres as stable and high capacity LIB anodes. A Ge–catechol complex obtained via a simple chelation reaction was introduced into resorcinol–formaldehyde polymer spheres prepared by the extended Stöber method. After carbonization and carbothermic reduction at 800 °C in an Ar atmosphere, carbon spheres loaded with Ge nanoparticles (∼8 nm) were fabricated. The Ge@C spheres have a uniform diameter of ∼500 nm, a mesopore size of ∼14 nm and a specific surface area of 348 m² g⁻¹. Mesoporosity between Ge particles and the carbon matrix creates a buffer layer that effectively stabilizes the encapsulated Ge particles for huge volume change and mitigates the aggregation of active particles during the lithiation/delithiation process. The mesoporous Ge@C sphere anode shows initial discharge and charge specific capacities of 1653 and 1440 mA h g⁻¹ at 0.1 C. Even at a high rate of 10 C, the Ge@C electrode still has a reasonable discharge–charge specific capacity of 753/708 mA h g⁻¹, exhibiting excellent high-rate discharge–charge performance. The Ge@C anode maintains a high discharge capacity of 1099 mA h g⁻¹ at 0.1 C with a coulombic efficiency of 99% after 100 cycles. The simple method for the design of mesoporous Ge@C spheres with a high capacity coupled with an excellent cycling stability opens up a new opportunity of Ge-based anode materials for widespread applications in LIBs.