Unveiling the electrochemical supercapacitor dynamics in lead-free Cs3Bi2X9 (Cl/Br) perovskite: Impact of halogen alteration

The research community has recently focused especially on all inorganic lead-free perovskites as possible materials for energy storage in electrochemical systems. Here, a low-cost solution-based facile synthesis approach is adopted to prepare Cs3Bi2(Br/Cl)(9) perovskite for energy storage applications. These perovskites are crystallized in hexagonal phase with P3m1 space group, as confirmed by XRD analysis. The pseudo-capacitance arises in the Cs3Bi2(Br/Cl)(9) perovskites due to the redox transition between Bi3+ and Bi5+ and OH-- ion intercalation/de-intercalation through the electrode material. The specific capacitances of 1617 F g(-1) and 613 F g(-1) at a scan rate of 2 mV s(-1) have been delivered by Cs3Bi2Cl9 and Cs3Bi2Br9 perovskites, respectively. We have also fabricated an asymmetric device using optimized perovskite with the configuration of Cs3Bi2Cl9//PVA-KOH gel/activated carbon (AC), which exhibits an energy density of 27 Whkg(-1) and a power density of 689 W kg(-1) at a current density of 1 Ag-1 with a capacitive retention of similar to 80 % even after 5000 charging/discharging cycles. In our opinion, such promising findings are poised to unlock new horizons for the forthcoming generation in the development of lead-free perovskite-based, non-toxic, sustainable energy storage systems.