New　tin-based　metal-phosphine　complexes　of　[Sn(OH)(4)(PPh3)(2)]　and　[Sn(OH)(2)(PPh3)(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)(PPh3)(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).　(C)　2021　Published　by　Elsevier　Inc.