Solid‐State Hybrid Supercapacitor Assembled from a Heterostructured Co−Ni Battery‐like Cathode and Supercapacitor‐Type Highly Disordered Carbon Nanosheets

Oriented Nanosheet-Assembled CoNi-LDH Cages with Efficient Ion Diffusion for Quasi-Solid-State Hybrid Supercapacitors

Fast-charged energy-storage technologies have become important nowadays as they are required by many applications, including automobiles. This inspires the exploitation of hybrid supercapacitors (HSCs) with the advantages of fast charge offered by the capacitor characters and high energy density from the property of battery technology. The challenges lay in the construction of advanced materials with high pseudocapacitive activity. Herein, a metal-organic framework derivative is utilized to address the problems. Specifically, polyhedral CoNi layered double hydroxide (CoNi-LDH_x) cages assembled in the form of nanosheet arrays are prepared from ZIF-67 using a facile ion-exchange approach. Based on the control over the mass ratio of ZIF-67 to Ni salt, the optimal CoNi-LDH₂ is attained. It exhibits ultrahigh capacities ranging from 1031.4 to 667.3 C g^-1 under 1-25 A g^-1, thanks to rich Faradaic active spots and the accelerated kinetics provided by the synergy between nanosheet arrays and the hollow structure. The CoNi-LDH₂-based HSC with the gel electrolyte shares remarkable energy output of 49 Wh kg^-1 and approving cyclability with almost no capacity decay after 12 000 cycles. This is an advancement vs many related studies and can arouse tremendous interests of researchers in solving the main problems of energy storage.

Phosphate-modified Co-Ni phosphide heterostructure formed by interfacial and electronic tuning for boosted faradaic properties

Rational structural and compositional modulation endows electrode materials with unique physicochemical characteristics due to their adjustable electronic properties. Herein, a phosphate-modified hierarchical nanoarray consisting of a heterojunction with a well-aligned cobalt phosphide nanowire core and nickel phosphide nanosheet shell on flexible carbon cloth (denoted as CoP@Ni₂P-CC) is engineered. The phosphate-modulated heterogeneous phosphide with a tuned electronic structure, additional heterojunction interfaces, and high degree of covalency in the chemical bonds accelerates the reaction kinetics and enhances the energy storage performance. Due to these reasons, the as-obtained phosphide-based heterostructured CoP@Ni₂P-CC electrode delivers a capacity of 475.9 C g^-1 at 0.5 A g^-1 with a satisfying rate capability, which is greatly superior to that of its transition metal counterparts (sulfide, selenide, and oxide). After being assembled into a flexible hybrid supercapacitor (FHSC), a wide operating voltage (1.8 V), high energy/power densities (49.8 W h kg^-1/8.6 kW kg^-1), and long-term stability (85.1% capacity retention after 10 000 cycles) were achieved. This work may provide a general method from multiple strategies for designing reliable pseudocapacitive materials for flexible electronics.