Popped rice carbons (PC) were derived from popped rice by using a facile and low-cost technique. PC was then activated by different kinds of activating agents, such as potassium hydroxide (KOH), zinc chloride (ZnCl₂), iron (III) chloride (FeCl₃), and magnesium (Mg), in order to increase the number of pores and specific surface area. The phase formation of porous activated carbon (PAC) products after the activation process suggested that all samples showed mainly graphitic, amorphous carbon, or nanocrystalline graphitic carbon. Microstructure observations showed the interconnected macropore in all samples. Moreover, additional micropores and mesopores were also found in all PAC products. The PAC, which was activated by KOH (PAC-KOH), possessed the largest surface area and pore volume. This contributed to excellent electrochemical performance, as evidenced by the highest capacity value (383 mAh g⁻¹ for 150 cycles at a current density of 100 mA g⁻¹). In addition, the preparation used in this work was very simple and cost-effective, as compared to the graphite preparation. Experimental results demonstrated that the PAC architectures from natural popped rice, which were activated by an optimal agent, are promising materials for use as anodes in LIBs.

The development of lithium-ion batteries (LIBs) has become an important aspect of advanced technologies. Although LIBS have already outperformed other secondary batteries, they still require improvement in various aspects. Most crucially, graphite, the commercial anode, has a lower capacity than emerging materials. The goal of this research is to develop carbon-based materials from sustainable sources. Banana stem waste was employed as a precursor because of its xylem structure and large surface area. In addition, catalytic graphitization of biomass yields both graphitic carbon and metal oxides, which can be converted into higher-capacity Fe₃O₄/C nanocomposites. The nanocomposites consist of nanoparticles distributed on the surface of the carbon sheet. It was found that Fe₃O₄/C nanocomposites not only achieved a superior specific capacity (405.6 mAh/g at 0.1 A/g), but also had good stability in long-term cycling (1000 cycles). Interestingly, they had a significantly greater capacity than graphite at a high current density (2 A/g), 172.8 mAh/g compared to 63.9 mAh/g. For these reasons, the simple preparation approach, with its environmental friendliness and low cost, can be employed to produce Fe₃O₄/C nanocomposites with good electrochemical properties. Thus, this approach may be applicable to varied biomasses. These newly developed Fe₃O₄/C nanocomposites derived from banana waste recycling were found to be suitable to be used as anodes for sustainable LIBs.