Few-Layered Tin Sulfide Nanosheets Supported on Reduced Graphene Oxide as a High-Performance Anode for Potassium-Ion Batteries.

Anodes involving conversion and alloying reaction mechanisms are attractive for potassium-ion batteries (PIBs) due to their high theoretical capacities. However, serious volume change and metal aggregation upon potassiation/depotassiation usually cause poor electrochemical performance. Herein, few-layered SnS2 nanosheets supported on reduced graphene oxide (SnS2 @rGO) are fabricated and investigated as anode material for PIBs, showing high specific capacity (448 mAh g-1 at 0.05 A g-1 ), high rate capability (247 mAh g-1 at 1 A g-1 ), and improved cycle performance (73% capacity retention after 300 cycles). In this composite electrode, SnS2 nanosheets undergo sequential conversion (SnS2 to Sn) and alloying (Sn to K4 Sn23 , KSn) reactions during potassiation/depotassiation, giving rise to a high specific capacity. Meanwhile, the hybrid ultrathin nanosheets enable fast K storage kinetics and excellent structure integrity because of fast electron/ionic transportation, surface capacitive-dominated charge storage mechanism, and effective accommodation for volume variation. This work demonstrates that K storage performance of alloy and conversion-based anodes can be remarkably promoted by subtle structure engineering.

Birnessite Nanosheet Arrays with High K Content as a High-Capacity and Ultrastable Cathode for K-Ion Batteries.

Potassium-ion batteries (PIBs) are one of the emerging energy-storage technologies due to the low cost of potassium and theoretically high energy density. However, the development of PIBs is hindered by the poor K+ transport kinetics and the structural instability of the cathode materials during K+ intercalation/deintercalation. In this work, birnessite nanosheet arrays with high K content (K0.77 MnO2 ⋅0.23H2 O) are prepared by "hydrothermal potassiation" as a potential cathode for PIBs, demonstrating ultrahigh reversible specific capacity of about 134 mAh g-1 at a current density of 100 mA g-1 , as well as great rate capability (77 mAh g-1 at 1000 mA g-1 ) and superior cycling stability (80.5% capacity retention after 1000 cycles at 1000 mA g-1 ). With the introduction of adequate K+ ions in the interlayer, the K-birnessite exhibits highly stabilized layered structure with highly reversible structure variation upon K+ intercalation/deintercalation. The practical feasibility of the K-birnessite cathode in PIBs is further demonstrated by constructing full cells with a hard-soft composite carbon anode. This study highlights effective K+ -intercalation for birnessite to achieve superior K-storage performance for PIBs, making it a general strategy for developing high-performance cathodes in rechargeable batteries beyond lithium-ion batteries.