A new nickel coordination polymer electrode material for hybrid supercapacitors

Battery-type electrode materials store charge through chemical reactions, leading to low power densities and rendering it difficult to reach the performance levels associated with capacitors. This study introduces a coordination polymer electrode material for hybrid supercapacitors, specifically, poly[[tri-μ-ethanolato-di-μ 3 -sulfido-hexakis(μ 4 -2-sulfidobenzoato)dinickel(II)tetranickel(III)dipotassium(I)[potassium(I)/sodium(I)(0.60/0.40)]] quaterhydrate], {[Ni III 4 Ni II 2 K 2.60 Na 0.40 (C 2 H 5 O) 3 (C 7 H 4 O 2 S) 6 S 2 ]·0.25H 2 O} n or Ni–mba–K(Na), where H 2 mba is 2-mercaptobenzoic acid, ( 1 ). As a hybrid capacitor electrode material, Ni–mba–K(Na) exhibits the characteristics of battery-type electrode materials but demonstrates a capacitor-level power density and cycling stability. The microstructure, element composition, phase structure and thermodynamic stability of Ni–mba–K(Na) are characterized through techniques such as crystal structure determination and X-ray photoelectron spectroscopy. Single-crystal X-ray diffraction shows that compound ( 1 ) consists of a hexanuclear nickel cluster, two mononuclear K nodes and a mononuclear K 0.60 /Na 0.40 shared node, resulting in the formation of a complex covalent three-dimensional network. Due to this novel structure, Ni–mba–K(Na) exhibits supercapacitor performance that combines high energy density and high power density.