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

Germanium oxide (GeO2) films with two different grain sizes of 10 nm (GeO2 (10 nm)) and 100 nm (GeO2 (100 nm)) were grown via reactive radio frequency sputtering at different temperatures. Electrochemical measurements of the GeO2 (10 nm) thin film used as an anode in Li ion rechargeable batteries show superior capacity retention and rate capability compared to those of GeO2 (100 nm). The GeO2 (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 GeO2 (100 nm) and 225 mAh g−1, 30% (10 cycles) of common macro-size GeO2. Microstructural studies reveal that the GeO2 (10 nm) thin film can better accommodate volume changes during Li–Ge alloying and de-alloying processes.

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► We deposited GeO2 thin films at different temperatures to form different grain sizes.
► Li storage of GeO2 as anode was studied, which shows that the GeO2 with grain size of about 10 nm reveals high capacity retention.
► Nanograined GeO2 also shows better rate capability and cyclability.