No abstract

Exploring advanced electrode materials with superb energy/power densities and long lifetime as well as low cost is the recent focus of hybrid solid‐state supercapacitor (HSSC). This study reports a novel hierarchical bimetallic hydroxide (Ni1Co1‐OH) built by nanowire‐lapped bonfire‐like bundles through a facile and scalable method, and provides thorough insights into possible formation mechanism and structural merits of the interesting hierarchical architecture. Benefiting from multistep redox reactions, high accessible surface area and fast kinetics contributed by the unique structure, Ni1Co1‐OH using 2 m KOH electrolyte can achieve highly improved gravimetric capacity/capacitance of 876.8 C g−1/1753.6 F g−1 at active mass loading of 3 mg cm−2 at 1 A g−1, and especially deliver a record‐high areal capacity of 7.6 C cm−2 at 1 A g−1 under a commercial loading of 15 mg cm−2. 1.5 V Ni1Co1‐OH based HSSC with the poly(vinyl alcohol)/KOH gel electrolyte verifies the intriguing performance including high energy/power densities of 27.9 Wh kg−1/13812.9 W kg−1, a long life over 10 000 cycles, and a low self‐discharge rate with a voltage decline of 20% after 24 h. The findings identify the scalable production of high‐performance bimetal compounds, which will boost the development of highly demanding HSSC devices.

The data that supports the findings of this study are available in the Supporting Information of this article.

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.

Despite the physicochemical advantages of two-dimensional (2D) carbons for supercapacitors, the inappropriate texture within 2D carbon materials suppresses the charge storage capability. Reported here are heteroatom-rich carbon sheets with the overall network engineered by molecular structure modulation and subsequent chemical activation of a three-dimensional (3D) cross-linked polymer. The 3D-to-2D reconstruction mechanism is unveiled. The architecture with a large active surface, fully interpenetrating and conductive network, and rich surface heteroatoms relieves well the ionic diffusion restriction within thick sheets and reduces the overall resistance, exhibiting fast transport kinetics and excellent stability. Indeed, high gravimetric capacitance (281.1 F g–1 at 0.5 A g–1), ultrahigh retention rate (92.5% at 100 A g–1), and impressive cyclability (89.7% retention after 20 000 cycles) are achieved by this material. It also possesses a high areal capacitance of 3.56 F cm–2 at 0.5 A g–1 under a high loading of 25 mg cm–2. When coupled with the developed dual cross-linked hydrogel electrolyte (Al-alginate/poly­(acrylamide)/sodium sulfate), a quasi-solid-state supercapacitor delivers an energy density of 28.3 Wh kg–1 at 250.1 W kg–1, which is significantly higher than those of some reported aqueous carbon-based symmetric devices. Moreover, the device displays excellent durability over 10 000 charge/discharge cycles. The proposed cross-linked polymer strategy provides an efficient platform for constructing dynamics-favorable carbon architectures and attractive hydrogel electrolytes toward improved energy supply devices.