Flexible sodium-ion batteries using electrodes from Samanea saman tree leaf-derived carbon quantum dots decorated with SnO2 and NaVO3

Carbonaceous materials with large interlayer spacing and disordered structure are considered suitable as electrodes in sodium-ion batteries so as to overcome the problem encountered in conventional electrodes. In this study, carbon quantum dots (CQDs) decorated with SnO2 and NaVO3 are used as electrodes in the fabrication of flexible Na-ion batteries. CQDs are prepared from dead leaves of the Samanea saman tree through alkaline-peroxide treatment and hydrothermal carbonization. As-prepared CQDs exhibit a quantum yield of 21.03% at an excitation wavelength of 360 nm. Various separators such as indium-doped tin oxide/polyoxyethylene tridecyl ether (ITO/PTE), rice paper (RP), silicone with three big holes (SIL BH), silicone with many small holes (SIL SH) and cellulose paper (CP) have been tried in flexible Na-ion batteries. SIL SH achieved higher specific capacitance (881 F g–1) than other separators due to the function of many small holes on the surface of the silicone. The SIL SH separator delivered higher discharge capacities of 141 and 114 mC g–1 at 1.5 and 2.5 V than SIL BH. The RP separator delivered specific discharge capacities of 1087 and 347 mC g–1 in the 1st and 50th cycles, respectively, at 1 V. The RP separator delivered a high initial specific discharge capacity of 698 mC g–1 at 2 V and maintained a good discharge capacity of 222 mC g–1 in the 50th cycle. As compared to RP, SIL SH delivered high specific discharge capacity of 4246 in 1st cycle at 2 V but maintained a capacity of 71 mC g–1 in the 50th cycle. This study reveals the scope of developing flexible Na-ion batteries with high capacity and cyclability using carbonaceous materials derived from the leaves of the S. saman tree. Carbon quantum dots (CQDs)-decorated with SnO2 and NaVO3 are used as electrodes in the fabrication of flexible Na-ion batteries. CQDs exhibit a quantum yield of 21% at the excitation wavelength of 360 nm. The electrochemical performances of fabricated batteries are investigated by cyclic voltammetry.