Layered silicate magadiite–derived three-dimensional honeycomb-like cobalt–nickel silicates as excellent cathode for hybrid supercapacitors

Developing low-cost electrode materials with high performance is the priority among priorities for large-scale application of supercapacitors (SCs). Magadiite, the most ubiquitous material on Earth, is half-abandoned and half-forgotten, and it is extremely valuable for development to useful materials, such as ‘a potential stock’ to be developed. Herein, we conceive the transformation of magadiite to electrode materials, pursuing the aim ‘waste can be turned into treasure’. Fortunately, three-dimensional honeycomb-like cobalt–nickel silicate (Co_xNi_2-xSiO₄) as high-performance electrode material for SCs is achieved via two simple steps of exfoliation and hydrothermal process. The bimetallic synergistic effect derived from Co/Ni can improve the reactivity of the material, and the honeycomb-like morphology can facilitate ion migration, so the electrochemical properties are enhanced. As a consequence, the Co_xNi_2-xSiO₄ electrode exhibited a specific capacitance of 1,097 F/g (548 C/g) at 0.5 A/g, as well as excellent cyclic stability of 101% retention after 10,000 cycles. The hybrid SC device is assembled by Co_xNi_2-xSiO₄ and active carbon (Co_xNi_2-xSiO₄//AC), and it delivers an excellent energy density of 15.5 Wh/m² at a power density of 1.34 W/m² and cycling stability (100% after 10,000 cycles). This work not only realizes the transformation of magadiite to transition metal silicates (TMSs) as electrode materials for high-performance SCs but also broadens the application of magadiite and opens up a novel strategy for synthesizing TMSs.