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Rational design and synthesis of hybrid structures consisting with multiple pseudocapacitive components are challenging to develop materials with a high energy density for conversion and storage applications. Herein, a novel and cost-effective two-step method has been developed to synthesize three-dimensional (3D) nickel cobalt sulfides (Ni-Co-S)/Co(OH) 2 nanocomposite with synergistic effect to provide an excellent comprehensive electrochemical performance, which shows a high specific capacitance (1560.8 Fg −1 at 1 A g −1 ) and outstanding rate capability (953.3 Fg −1 at 30 A g −1 ). Subsequently, an all-solid-state asymmetric supercapacitor (ASC) was successfully assembled using Ni1-Co2-S/Co(OH) 2 nanocomposite as the positive electrode, activated carbon (AC) as the negative electrode and an alkaline PVA gel (PVA/KOH) as electrolyte. The Ni1-Co2-S/Co(OH) 2 //AC all-solid-state ASC device with a voltage window of 1.6 V delivered a maximum energy density of 48.8 W h kg −1 at a power density of 800 W kg −1 with excellent cycle stability. Excitedly, two all-solid-state ASCs assembled in series under fully charged can effectively light up four parallel connected light-emitting diodes (LEDs) for around 10 min, and can power a white LED (working voltage, 3.0–3.4 V) effectively. These remarkable electrochemical performances of Ni1-Co2-S/Co(OH) 2 //AC are beneficial to their practical applications for high-performance energy storage. [ABSTRACT FROM AUTHOR]

Due to their reliability, affordability and high safety, rechargeable aqueous zinc ion batteries (ZIBs) have garnered a lot of attention. Nevertheless, undesirable long-term cycle performance and the inadequate energy density of cathode materials impede the development of ZIBs. Herein, we report a layered CaV4O9-MXene (Ti3C2Tx) composite assembled using CaV4O9 nanosheets on Ti3C2Tx and investigate its electrochemical performance as a new cathode for ZIBs, where CaV4O9 nanosheets attached on the surface of MXene and interlamination create a layered 2D structure, efficiently improving the electrical conductivity of CaV4O9 and avoiding the stacking of MXene nanosheets. The structure also enables fast ion and electron transport. Further discussion is conducted on the effects of adding MXene in various amounts on the morphology and electrochemical properties. The composite shows an improved reversible capacity of 274.3 mA h g−1 at 0.1 A g−1, superior rate capabilities at 7 A g−1, and a high specific capacity of 107.6 mA h g−1 can be delivered after 2000 cycles at a current density of 1 A g−1. The improvement of the electrochemical performance is due to its unique layered structure, high electrical conductivity, and pseudo capacitance behavior. [ABSTRACT FROM AUTHOR]

CoZn layered double hydroxide (LDH) or Co(OH)2 pseudocapacitive material has been prepared on the current collector of carbon fiber paper (CFP) using an eco-friendly one-step electrodeposition. Benefiting from its unique structural feature, the binder-free CoZn LDH/CFP electrode material realizes high specific capacitance of 1156 Fg−1 at a current density of 1 Ag−1 and excellent rate capability of 80% retention with 16 fold current density increment, which is much better than that of Co(OH)2 (617 Fg−1, 65%). Notably, the CoZn LDH/CFP can retain an outstanding electrochemical stability with a capacitance degradation of only 6% after 6000 charge–discharge cycles at 32 Ag−1. Moreover, an asymmetric supercapacitor (ASC) using CoZn LDH/CFP as a positive electrode and AC/CFP as a negative electrode has been assembled. The ASC exhibits a superior energy density of 30.0 Whkg−1 at a power density of 800 Wkg−1 with a specific capacitance up to 84.4 Fg−1 and a potential window wide to 1.6 V. These encouraging results indicate that CoZn LDH/CFP composite material has a great potential for next-generation energy conversion/storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Composites of polyimide derived carbon nanofibers and MnO 2 nanosheets are reported. • The structure effectively suppresses Jahn-Teller effect and promotes fast Zn2+ ion diffusion. • The combination of delicate fiber and salty ice electrolyte enables excellent electrochemical performance. • A potential low temperature electrolyte is demonstrated. • The cell can work at a low temperature of −20 °C and 500 cycles is achieved under 0 °C. Mn-based aqueous zinc-ion batteries are potential candidates for energy storage owing to the low cost, high efficiency, and safety. Nevertheless, the Jahn–Teller effect induces Mn2+ dissolution and irreversible phase changes, seriously deteriorating the cycling life. Herein, the facile construction and low temperature performance of the core–shell composites of polyimide derived nitrogen-doped carbon nanofibers and δ-MnO 2 (δ-MnO 2 -CNFs) are reported, where ultrafine MnO 2 arrays are tightly anchored on carbon nanofibers. The hybrid effect of nitrogen doping, porous structure, and abundant active sites effectively inhibits the structural damage of MnO 2. The as-prepared δ-MnO 2 -CNFs cathode achieves a high specific capacity of 232.9 mAh g−1 and energy density of 450.7 Wh kg−1 at a current density of 100 mA g−1, and could be stably cycled for 500 cycles at a high current rate of 1 A g−1. The density functional theory calculation results show that the synergistic effect in δ-MnO 2 -CNFs is more conducive to the transfer of zinc ions. Furthermore, a salty ice electrolyte Zn(ClO 4) 2 has been used for the Zn//δ-MnO 2 -CNFs cell, which can work at a low temperature of −20 °C, and a stable low temperature (0 °C) cycle of 500 cycles is achieved at 1 A g−1. [ABSTRACT FROM AUTHOR]

Hybrid ion capacitors show promise to bridge the gap between rechargeable batteries with high energy density and supercapacitors of high power. However, research efforts primarily focus on lithium-ion and/or sodium-ion based capacitors, potassium ion capacitor (KIC) is theoretically more sustainable and promising owing to the high abundance, low standard redox potential and low cost of the K sources. Herein, nitrogen-doped porous carbon submicrospheres derived from hierarchical micro-flowerlike polyimide superstructure are fabricated and investigated as novel anodes for excellent K ion storage. The effect of different electrolytes on potassium storage properties and the reaction kinetics are successfully revealed. A low cost nonaqueous KIC is assembled with commercial activated carbon as cathode and the polyimide derived carbon as anode. Benefiting from the unique structure characteristics of enriched active sites, high electronic conductivity, and the conspicuous pseudocapacitive effect of polyimide carbon, the as-fabricated device manifests the maximum energy density and power density of 90.1 Wh kg−1 and 3000 W kg−1, respectively. Even at 1540 W kg−1, the energy density still remains at 43.5 Wh kg−1. Moreover, the device achieves a near 100% Coulombic efficiency and favorable cycling stability over 5000 cycles at a current density 500 mA g−1. Image 1 • Polyimide derived N-doped carbon as new anodes for K ion capacitors. • The effect of different electrolytes on potassium storage properties. • High electronic/ionic conductivity and conspicuous pseudocapacitive effect. • The device demonstrates high energy density and exceptional cycling stability. [ABSTRACT FROM AUTHOR]