Ge nanocrystals tightly and uniformly distributed in a carbon matrix through nitrogen and oxygen bridging bonds for fast-charging high-energy-density lithium-ion batteries

Abstract

Germanium (Ge) has come into the public interest as a high-capacity and high-rate lithium-ion battery anode. However, its unsatisfactory cycling life is caused by its large volume expansion (∼230%) upon cycling. In order to settle this intractable problem, a highly mesoporous Ge/C nanocomposite, in which Ge nanocrystals (∼20 nm) are evenly dispersed into a N,O co-doped carbon matrix, can be prepared via the pyrolysis of a mixture of bis[2-carboxyethylgermanium(IV)] sesquioxide and dimethylformamide. Vast phase boundaries are induced due to the homogeneously dispersed structure, in which the N and O atoms effectively bridge Ge and C through Ge–O–C and Ge–N–C bonds, to achieve a highly robust structure and a fast ion transport route. Consequently, the Ge/C anode shows a high specific/volumetric capacity of 1607.8 mA h g⁻¹/2090.1 mA h cm⁻³, prominent cyclability, and a striking rate capability in half cells. Remarkably, a high specific energy density of 481.5/358.7 W h kg⁻¹ at 0.1/5C, and a high volumetric energy density of 1019.1 W h l⁻¹ are obtained in full cells with LiFePO₄ as the cathode.