No abstract

The yolk‐shell structure exhibits fascinating and important properties for energy storage devices. The carbon shell significantly improves the good electrical conductivity and the stable micro‐/nanostructures of the active material increases utilization. MnO2@C with a yolk‐shell structure shows high reversibility, good rate performance, and excellent cycling stability for aqueous Zn‐ion batteries. The Zn‐ion battery with MnO2@C could realize a high reversible capacity of 239 mAh g−1 at 0.1 A g−1. In particular, at a quite high current density of 2 A g−1, it achieves capacity of 91 mAh g−1. The Zn‐ion battery has excellent capacity retention of up to 1000 cycles at 1 A g−1. The yolk‐shell structure plays an important role in improving the battery performance.

Selenium exhibits smaller volume expansion and much higher electrical conductivity compared with sulfur, which makes it considered as a potential cathode material. In order to improve electrochemical performance of potassium-selenium (KÀ Se) batteries, we prepared porous carbon/Se (PC/Se) composite via carbonization, KOH activation and melt diffusion and synthesized a novel porous carbon/Se/graphene oxide (PC/Se/GO) composite with the Se content of~40 % via controlling the ionic strength of the solution as cathode material in the work. The combination of porous carbon structure and graphene can effectively relieve the volume expansion of selenium during the charge and discharge process, and provide excellent conductivity. The one-step conversion without polyselenides between the PC/Se/GO composite and metal potassium further improves the capacity and cycling stability. Therefore, the PC/Se/GO delivers high discharge capacities of 426.3 and 316.8 mAh g À 1 in the 2nd and 150th cycles at 0.5 C. This work plays an important reference role for the exploration of advanced potassiumselenium batteries.

P2-type Na 0.65 Mn 0.6 Ni 0.35 Cu 0.05 O 2 microspheres assembled irregularly with massive primary nanoparticles are prepared via hydrothermal method and subsequent two-step calcination process. As expected, the P2-type Na 0.65 Mn 0.6 Ni 0.35 Cu 0.05 O 2 microspheres show superior electrochemical performance in terms of high-rate capability and long-period cycling stability. This material exhibits a reversible capacity of 81 mA h g −1 and exceptional capacity retention up to 79% over 150 cycles even at the high current density of 1 A g -1 . The distinctive spherical structure with high specific surface area can be accountable to the excellent electrochemical properties, which offers abundant surface sodium storage sites and shortened diffusion paths of sodium ions. Therefore, this work puts forward a feasible method to design nanoparticles assembled microspheres for layered oxides with high-rate performance as a promising cathode material for sodium ion batteries.

Aqueous zinc‐ion hybrid capacitors (ZIHCs) attract widespread attention due to their excellent electrochemical performance, safety, and low cost. Here, a honeycomb‐like porous carbon is synthesized as the cathode of ZIHCs via facile pre‐oxidation in combination with an activation process. The pre‐oxidized porous carbon (PPC) displays a larger specific surface area and faster electrochemical kinetics compared to porous carbon without pre‐oxidation (PC), realizing a superior electrochemical performance. The PPC cathode can deliver a capacity of 238 mAh g−1 at 0.1 A g−1. Besides, the hybrid capacitors can achieve a high energy density of 193.6 Wh kg−1 at 76.6 W kg−1 and 109.5 Wh kg−1 at a maximum power density of 3981 W kg−1. More importantly, the hybrid capacitor exhibits a good cycling stability with a capacity retention of 83 % after 20000 cycles at a high current density of 2 A g−1. This cathode material – with an excellent electrochemical performance – could pave the way for application of ZIHCs.