An oxygen-deficient Ge/GeO2/C anode for lithium ion batteries with enhanced reversible energy storage performance

Although GeO2 exhibites a large theoretical capacity (2125 mAh g-1), its large volume change limits its wide application in anode materials. A novel oxygen-deficient and amorphous Ge/GeO2/C composite anode consisted of crystal Ge was synthesized in situ using hydrothermal methods and reductive sintering to improve the specific capacity and long life of GeO2-based anodes. The capacity of the Ge/GeO2/C anode is 1160 mAh g-1 at 0.2 A g-1 for 200 cycles. The reversible specific capacity is retained at 1004 mAh g-1 at A g-1 for 600 cycles, thereby showing excellent stability. The presence of rich oxygen vacancies and crystalline Ge can assist the reversible decomposition of amorphous GeO2 to improve the ionic and electronic conductivity of the anode. In addition, a stable and uniform film thickness of ∼20 nm is formed at the Ge/GeO2/C electrode surfaces after down cycling 200 times, as observed by transmission electron microscopy. These excellent properties are due to the carbon composite, amorphous structure and high oxygen vacancy concentration of the anode and the synergistic effect by crystalline Ge. Micro-nanoscale Ge/GeO2/C spherical composite has been synthesized, exhibited amorphous structure and enriched with crystalline Ge and oxygen vacancies. This composite anode generated a thin and stable SEI film with self-healing capability during the lithium ion embedding/deembedding process, resulting in high performance and long cycle stability. [Display omitted] •Preparation of amorphous Ge/GeO2/C spherical composite with crystalline Ge and oxygen vacancies.•Formation of a thin and stable SEI film on this anode in Li+ embedding/ deembedding process.•The formed SEI film on the anode showed self-healing capability and stable microstructure.•The amorphous Ge/GeO2/C anode showed excellent cycling stability and high rate capability.