Activation of Sodium Storage Sites in Prussian Blue Analogues via Surface Etching

Sodium-ion battery technologies are known to suffer from kinetic problems associated with the solid-state diffusion of Na⁺ in intercalation electrodes, which results in suppressed specific capacity and degraded rate performance. Here, a controllable selective etching approach is developed for the synthesis of Prussian blue analogue (PBA) with enhanced sodium storage activity. On the basis of time-dependent experiments, a defect-induced morphological evolution mechanism from nanocube to nanoflower structure is proposed. Through in situ X-ray diffraction measurement and computational analysis, this unique structure is revealed to provide higher Na⁺ diffusion dynamics and negligible volume change during the sodiation/desodiation processes. As a sodium ion battery cathode, the PBA exhibits a discharge capacity of 90 mA h g^–1, which is in good agreement with the complete low spin Fe^LS(C) redox reaction. It also demonstrates an outstanding rate capability of 71.0 mA h g^–1 at 44.4 C, as well as an unprecedented cycling reversibility over 5000 times

Phase-Controlled Synthesis of Cobalt Sulfides for Lithium Ion Batteries

The polyhedral CoS₂ with a narrow size distribution was synthesized by a facile solid-state assembly process in a sealed silica tube. The flux of potassium halide (KX; X = Cl, Br, I) plays a crucial role in the formation of polyhedrons and the size distribution. The S₂^2– groups in CoS₂ can be controllably withdrawn during heat treatment in air. The obtained phases and microstructures of CoS₂, Co₃S₄, CoS, Co₉S₈, and CoO depended on heating temperature and time. These cobalt materials, successfully used as the electrodes of lithium ion batteries, possessed good cycling stability in lithium ion batteries. The discharge capacities of 929.1 and 835.2 mAh g^–1 were obtained for CoS₂ and CoS respectively, and 76% and 71% of the capacities remained after 10 cycles. High capacities and good cycle performance make them promising candidates for lithium ion batteries. The approach combining solid-state assembly and heat treatment provides a simple and versatile way to prepare various metal chalcogeides for energy storage applications