The energy-storage mechanism of a battery-type coordination polymer electrode material for hybrid supercapacitors

Abstract

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 (CP) electrode material for hybrid supercapacitors, specifically [Ni(III)₄Ni(II)₂K₂K_0.726Li_0.274(mba)₆(S)₂(C₂H₅O)₃·2(H₂O)]_n (Ni-mba-K(Li), where H₂mba is 2-mercaptobenzoic acid). As a hybrid capacitor electrode material, Ni-mba-K(Li) exhibits the characteristics of battery-type electrode materials but demonstrates a capacitor-level power density and cycling stability. When the power density is 475 W kg⁻¹, the energy density reaches 39.2 Wh kg⁻¹. When the power density is increased to 17 647 W kg⁻¹, the energy density is 8.3 Wh kg⁻¹. Through examination of the crystal structure and analyzing the X-ray photoelectron spectroscopy and in situ Raman spectra at different charge-storage states, the energy storage mechanism of the CP is explored at the molecular level. A preliminary investigation of the factors affecting the specific capacity, energy density, power density, and cycling stability of the electrode material is conducted. This study deepens our understanding of energy storage mechanisms and provides new strategies for improving the power densities of battery-type electrode materials.