Ge Nanoparticles Encapsulated in Interconnected Hollow Carbon Boxes as Anodes for Sodium Ion and Lithium Ion Batteries with Enhanced Electrochemical Performance

A carbothermal reaction route to Ge nanoparticle homogeneously encapsulated hollow carbon boxes from NH4H3Ge2O6/resorcinol formaldehyde precursors is designed, using NH4H3Ge2O6 as a Ge precursor from commercial GeO2 and NH4OH. The Ge/C hybrid anode for sodium ion battery displays a higher Na+ storage capacity of 346 mA h g(-1) after 500 cycles at a current density of 100 mA h g(-1), almost approaching the theoretical capacity of Ge. Furthermore, Ge/C anode shows significantly improved electro-chemical performance for Li+ storage, showing a higher initial Coulombic efficiency of 85.1% and a superior reversible capacity of 1336 mA h g(-1) at a high current density of 200 mA g(-1) after 150 cycles. An excellent rate capability with a capacity of 825 mA h g(-1) at a current density of 4.0 A g(-1) can be obtained based on Ge/C anodes. The enhanced electrochemical performance can be attributed to the unique microstructures of Ge/C hybrid anode. The internal void space of hollow carbon boxes can accommodate the volume expansion of Ge during lithiation or sodiation process, thus preserving the structural integrity of electrode material. The interconnected carbon shell can increase the electronic conductivity of the electrode, resulting in the high rate capability and cycling stability.