Azo-Group-Containing Organic Compounds as Electrode Materials in Full-Cell Lithium-Ion Batteries

Inorganic compounds, including graphite, transition metal oxides, and chalcogenides, are widely used as electrode materials in rechargeable lithium-ion batteries (LIBs). However, environmentally friendly and cost-effective alternatives are pursued by focusing on the molecular design of organic materials that could be potential electrode materials in next-generation LIBs. Herein, we study the utilization of an organic compound, azobenzene 4,4-dicarboxylate lithium (ADL), as a negative electrode in full-cell LIBs. The full-cell LIBs are assembled by using ADL as the negative electrode, LiCoO₂ (LCO/ADL) or LiFePO₄ (LFP/ADL) as the positive electrode, and 1 M LiPF₆ dissolved in ethylene carbonate/diethylene carbonate (EC : DEC=1 : 1 by volume) as the electrolyte. Then, ex situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were carried out to understand the charge storage mechanism and structural changes during the electrochemical reaction. From the charge/discharge measurements, LFP/ADL rendered a higher specific capacity retention (88.05 %) than LCO/ADL full-cells (73.79 %) after 200 cycles at a current density of 100 mA g⁻¹. The XPS analysis revealed that the deposition of metallic Li on the ADL anode in LCO/ADL full-cells led to rapid capacity decay and inferior cyclic performance, whereas Li-free metal deposition had been observed on the ADL anode in LFP/ADL full cells, which explained the higher cyclic stability and capacity retention rate in LFP/ADL full-cells. The present study provides useful insights into the development and practical utilization of organic electrodes in next-generation Li-ion battery technology.