Tin-based metal-phosphine complexes nanoparticles as long-cycle life electrodes for high-performance hybrid supercapacitors

New tin-based metal-phosphine complexes of [Sn(OH) 4 (PPh 3 ) 2 ] and [Sn(OH) 2 (PPh 3 ) 2 ] have been successfully synthesized and used as supercapacitor electrodes for the first time, exhibiting a high specific capacitance, a good rate capability, and an excellent cycling stability. The specific capacitances (highest specific capacitance for tin-based materials) of 1204F g −1 and 764F g −1 for two samples at a current density of 1 A g −1 in 6 M KOH can respectively be achieved, and their capacitance retention remained at 95.1% and 89.2% even after 15,000 cycles at a current density of 10 A g −1 . Furthermore, a flexible quasi-solid-state asymmetric supercapacitor composed of Sn(OH) 2 (PPh 3 ) 2 and activated carbon was assembled and exhibited a specific capacitance of 290.6 mF cm −2 at a current density of 1 mA cm −2 . More importantly, this device also displayed excellent cyclic stability of ∼100% for 1800 cycles during the galvanostatic charge/discharge process at 5 mF cm −2 .