Ge/C Composite Electrodeposits As an Anode Material for Lithium Ion Batteries

Recently, lithium ion batteries have received considerable attention due to the increased demand for energy storage medium in portable electronic devices. Graphite has been extensively used as a commercial anode material for Li-ion batteries due to its excellent cycling behavior during charge and discharge cycles. However, the theoretical specific capacity of graphite is limited to 339 mAh×g^-1. Therefore, it is essential to develop new anode materials with larger capacity as well as good cyclability. In particular, Ge has been reported to a promising anode material due to its large theoretical capacity (1624 mAh×g^-1).

However, pure Ge anode suffers from a poor cyclability due to severe mechanical cracking and pulverization caused by significant volume change during the lithiation/delithiation process. To overcome this problem, various attempts have been reported. In particular, electrodeposition is a versatile bottom-up processing method that can be used for the deposition of metals, polymers, and semiconductors in a wide range of microstructures and nanostructures. The method is inexpensive and relatively simple, and especially it can support a good interface strength and electronic conductivity between the coating metals and the substrate.

In this study, the Ge/C composite was prepared by an electrodeposition process on Cu foil in ethylene glycol containing GeCl₄ and carbon black. The Ge/C electrode showed better cyclic performance and higher charge capacity than Ge electrode. The improved electrochemical performance of the Ge/C electrode is due to the carbon black. Ge/C is preferable to endure pulverization of active materials by accommodating severe volume expansion during charge-discharge cycling.

The initially deposited Ge grains are relatively uniform with an average size of 20-30 nm. On the other hand, Ge grains with C are regularly deposited, forming clusters. The specific capacities of Ge and Ge/C at 0.1C-rate were about 1100 and 950 mAh×g^-1respectively at the first cycle. Furthermore, the Ge/C retains a charge capacity of 860 mAh×g^-1 after 40th cycle. The results confirm the Ge/C is more suitable than Ge in the cyclic performance and reversible charge capacity.