Although graphite is the most commonly used anode material for Li-ion batteries, its low capacity (372 mAh/g) limits the energy storage performance. Recently, graphene has demonstrated great promise as a candidate to replace graphite due to its high power and high energy densities.^1-3 Here, we prepared Li-ion battery anodes based on reduced graphene oxide (rGO) powder obtained from an established company and investigated effects of oxygen contents in the rGO on the energy storage properties. The oxygen content of rGO could be controlled by heat-treating the rGO at 500 ^oC and 800 ^oC under Ar condition. The O/C atomic ratios from XPS were 0.208, 0.126, and 0.031 for the pristine rGO, the rGO heat-treated at 500 ^oC (rGO-HT500) and the 800 ^oC (rGO-HT800), respectively. We employed Dr. Blade method to prepare the electrodes using the pristine and heat-treated rGO. While the loading density of the electrodes were kept in the range of 1.68−1.75 mg_rGO/cm²_electrode, the density gradually decreased with the heat-treatment from 0.62 to 0.21 g/cm³. We then fabricated a Li coin-type cell (CR2032) with the rGO electrode in an Ar-filled glovebox. Li metal foil, Celgard 2500 membrane, and 1 M LiPF₆ (in EC/DMC) were used as a counter electrode, a separator, and an electrolyte, respectively. For evaluating energy storage performance of the rGO-based electrode, we conducted galvanostatic charge/discharge test at different current densities in the range of 37.2–3720 mA/g. At the current density of 37.2 mA/g, both electrodes based on the pristine rGO and rGO-HT500 showed ~1000 mAh/g_rGO, which is greatly enhanced capacity by 2−3 folds relative to the theoretical capacity of graphite (Fig. 1). However, the rGO-HT800-based electrode exhibited only showed a capacity of 579 mAh/g_rGO, indicating the minor oxygen content could contribute to the charge capacity of rGO in the Li-ion battery.

1. J. Hassoun et al., An advanced lithium-ion battery based on a graphene anode and a lithium iron phosphate cathode. Nano letters 14, 4901-4906 (2014).
2. G. Wang, X. Shen, J. Yao, J. Park, Graphene nanosheets for enhanced lithium storage in lithium ion batteries. Carbon 47, 2049-2053 (2009).
3. F. J. Sonia et al., Understanding the Li-storage in few layers graphene with respect to bulk graphite: experimental, analytical and computational study. Journal of Materials Chemistry A 5, 8662-8679 (2017).

Figure 1. (a) Charge/discharge profiles of pristine rGO at difference current densities from 37.5 to 3750 mA/g. (b) Comparison of charge/discharge profiles of pristine and heat-treated rGO electrodes obtained at 37.5 mA/g.