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Aqueous‐ion batteries have received much attention owing to the merits of high safety, low cost, and environmental friendliness. Among potential cathode candidates, transition metal sulfides drew little attention since they suffer from low capacity, low working potential, and fast capacity fading. Here, advantage is taken of the chemical instability of VS2 in aqueous electrolyte to in situ fabricate a heterostructural VS2/VOx material. Benefiting from the internal electric field at heterointerfaces, high conductivity of vanadium sulfide and high chemical stability of vanadium oxides, heterostructural VS2/VOx delivers an enhanced working potential by 0.25 V, superior rate capability with specific capacity of 156 mA h g−1 at 10 A g−1, and long‐term stability over 3000 cycles as Zn2+ storage electrode. In addition, heterostructural VS2/VOx is employed as the cathode for aqueous NH4+ ion storage with high reversible capacity over 150 mA h g−1 and long lifespan over 1000 cycles, surpassing the state‐of‐the‐art materials. VS2/VOx is proved to demonstrate a (de)intercalation process for Zn2+ storage, while a conversion reaction accompanied by insertion is responsible for nonmetal NH4+. The strong insight obtained in this study sheds light on a new methodology of exploring the potential of transition metal sulfides‐based cathode materials for aqueous ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid potassium‐ion capacitors (KICs) show great promise for large‐scale storage on the power grid because of cost advantages, the weaker Lewis acidity of K+ and low redox potential of K+/K. However, a huge challenge remains for designing high‐performance K+ storage materials since K+ ions are heavier and larger than Li+ and Na+. Herein, the synthesis of hierarchical Ca0.5Ti2(PO4)3@C microspheres by use of the electrospraying method is reported. Benefiting from the rich vacancies in the crystal structure and rational nanostructural design, the hybrid Ca0.5Ti2(PO4)3@C electrode delivers a high reversible capacity (239 mA h g−1) and superior rate performance (63 mA h g−1 at 5 A g−1). Moreover, the KIC employing a Ca0.5Ti2(PO4)3@C anode and activated carbon cathode, affords a high energy/power density (80 W h kg−1 and 5144 W kg−1) in a potential window of 1.0–4.0 V, as well as a long lifespan of over 4000 cycles. In addition, in situ X‐ray diffraction is used to unravel the structural transition in Ca0.5Ti2(PO4)3, suggesting a two‐phase transition above 0.5 V during the initial discharge and solid solution processes during the subsequent K+ insertion/extraction. The present study demonstrates a low‐cost potassium‐based energy storage device with high energy/power densities and a long lifespan. [ABSTRACT FROM AUTHOR]

Potassium‐ion batteries (KIBs) are emerging as one of the most promising candidates for large‐scale energy storage owing to the natural abundance of the materials required for their fabrication and the fact that their intercalation mechanism is identical to that of lithium‐ion batteries. However, the larger ionic radius of K+ is likely to induce larger volume expansion and sluggish kinetics, resulting in low specific capacity and unsatisfactory cycle stability. A new Ni/Mn‐based layered oxide, P2‐type K0.44Ni0.22Mn0.78O2, is designed and synthesized. A cathode designed using this material delivers a high specific capacity of 125.5 mAh g−1 at 10 mA g−1, good cycle stability with capacity retention of 67% over 500 cycles and fast kinetic properties. In situ X‐ray diffraction recorded for the initial two cycles reveals single solid‐solution processes under P2‐type framework with small volume change of 1.5%. Moreover, a cathode electrolyte interphase layer is observed on the surface of the electrode after cycling with possible components of K2CO3, RCO2K, KOR, KF, etc. A full cell using K0.44Ni0.22Mn0.78O2 as the cathode and soft carbon as the anode also exhibits exceptional performance, with capacity retention of 90% over 500 cycles as well as superior rate performance. These findings suggest P2‐K0.44Ni0.22Mn0.78O2 is a promising candidate as a high‐performance cathode for KIBs. [ABSTRACT FROM AUTHOR]