Ultra-Long-Term Cyclability of Ge/C Nanocomposite Anode for Li-Ion Batteries

Germanium (Ge) is the potential candidate to replace graphite anode material for lithium ion batteries (LIB). Graphite has been used until now as a main anode material in LIB. However, its limited specific capacity cannot meet the world’s growing demand for energy. The volumetric capacity of Ge (7366 Ah/l) is relatively smaller than that of Si (8344 Ahl^-1), but Ge has more advantage over Si: the diffusion coefficient of Li in Ge is approximately two orders of magnitude greater than that in Si, intrinsically electrical conductivity of Ge is four order higher than that of Si due to its smaller band gap, and the volume expansion during lithium insertion-deinsertion into Ge is smaller compared with Si. Despite these of promising characteristic, the capacity fading of Ge after some charge/discharge cycles is main problem to be addressed. To improve the cyclability of Ge most studies so far have focused on the use of buffer layer or reducing particle size of Ge. The use of buffer layer has negligible effect on specific capacity of Ge but it will improve significantly the performance of Ge at high rate of charge-discharge owing to improvement in mechanical properties, contact between active material with electrode, and diffusivity of Li.

In this study, we introduced a simple method for synthesis of Ge nano particles interconnected by carbon (GEC). The GEC electrode showed a high specific capacity up to 1339 mAh/g at the rate of C/2, after 50 cycles the specific capacity retained at value of 1321 mA h/g. Even with increasing the charge-discharge rate up to 10C, the specific capacity only decreased about 30 % compared with that at the rate of C/10. The excellent electrochemical performance of GEC electrode was not only due to the buffer layer of carbon but also the interface layer of Ge-carbon. The formation of Ge-C bonding at interface layer is believed to improve the contact between Ge and C, increase the stability during charge-discharge process and reduce stress tension during volume expansion.

The cyclic life of GEC electrode is under-investigation and it can be observed from its initial data that the electrode shows steady performance till the obtained data. However, further cycling data is necessary for making any stamen about the stability in its performance. The initial results demonstrate that the synthesized GEC can be used as an active Li storage material for lithium ion batteries.