Influence of grain size on lithium storage performance of germanium oxide films

Abstract

Germanium oxide (GeO 2) films with two different grain sizes of 10 nm (GeO 2 (10 nm)) and 100 nm (GeO 2 (100 nm)) were grown via reactive radio frequency sputtering at different temperatures. Electrochemical measurements of the GeO 2 (10 nm) thin film used as an anode in Li ion rechargeable batteries show superior capacity retention and rate capability compared to those of GeO 2 (100 nm). The GeO 2 (10 nm) thin film possesses an initial capacity of 930 mAh g −1 with 89% capacity retention after 100 cycles, compared with 455 mAh g −1 with 53% of GeO 2 (100 nm) and 225 mAh g −1, 30% (10 cycles) of common macro-size GeO 2. Microstructural studies reveal that the GeO 2 (10 nm) thin film can better accommodate volume changes during Li–Ge alloying and de-alloying processes.