Effect of various ratios of poly(3-hexylthiophene) with polyvinyl alcohol gel-polymer electrolytes in flexible sodium-ion batteries using Samanea saman tree-leaf-derived carbon quantum dots decorated with SnO2 and NaVO3

Abstract

Abstract Gel-polymer electrolytes with high thermal stability and mechanical properties were considered suitable in rechargeable batteries so as to overcome the problems encountered in liquid electrolytes. In a previous study, flexible sodium-ion batteries (FSIBs) were fabricated using electrodes made of carbon quantum dots (CQDs) decorated with SnO2 and NaVO3 utilizing a polyvinyl alcohol (PVA)/P3HT gel-polymer electrolyte at a ratio of 1:0.05. In addition, 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) were tested in flexible Na-ion batteries. The SIL SH delivered a high specific discharge capacity of 4246 mAh g–1 in the initial cycle at 2 V and maintained a value of 71 mAh g–1 in the 50th cycle. With the aim of improving the cyclic ability of FSIBs, different weight ratios of PVA/P3HT (1:0.025, 1:0.05, 1:0.1, 1:0.15, 1:0.2) were tried in this work using the electrodes CQDs@SnO2 and CQDs@NaVO3. The above ratios were referred to as B25, B50, B100, B150 and B200, respectively. SIL SH was used as a separator. Cyclic voltammetry studies indicated that B150 had a high specific capacitance of 13 062 F g–1. B25 and B100 exhibited high discharge capacities (171 mAh g–1) and (151 mAh g–1) compared to that of other ratios B50 (75 mAh g–1), B150 (88 mAh g–1) and B200 (54 mAh g–1) in the 50th cycle at 2.0 V. This study reveals the scope of developing FSIBs of high capacity and cyclability at different voltages using carbonaceous electrodes and gel-polymer electrolytes with different ratios of PVA/P3HT. The focus of the present study is to bring out the optimum ratio of PVA/P3HT for maximizing the cyclic ability of FSIBs.