Structural Stability of Quaternary ACuFeS2 (A = Li, K) Phases: A Computational Approach

Mixed Cu-Fe Sulfides Derived from Polydopamine-Coated Prussian Blue Analogue as a Lithium-Ion Battery Electrode

Batteries employing transition-metal sulfides enable high-charge storage capacities, but polysulfide shuttling and volume expansion cause structural disintegration and early capacity fading. The design of heterostructures combining metal sulfides and carbon with an optimized morphology can effectively address these issues. Our work introduces dopamine-coated copper Prussian blue (CuPB) analogue as a template to prepare nanostructured mixed copper-iron sulfide electrodes. The material was prepared by coprecipitation of CuPB with in situ dopamine polymerization, followed by thermal sulfidation. Dopamine controls the particle size and favors K-rich CuPB due to its polymerization mechanism. While the presence of the coating prevents particle agglomeration during thermal sulfidation, its thickness demonstrates a key effect on the electrochemical performance of the derived sulfides. After a two-step activation process during cycling, the C-coated KCuFeS₂ electrodes showed capacities up to 800 mAh/g at 10 mA/g with nearly 100% capacity recovery after rate handling and a capacity of 380 mAh/g at 250 mA/g after 500 cycles.

Electronic Structure and Magnetic Properties of CuFeS2

Chalcopyrite (CuFeS2) is an antiferromagnetic semiconductor with unusual magnetic and electrical properties, which are still not clearly understood. Neutron diffraction experiments reveal a phase transition at ∼50 K that has been attributed to an unexpected appearance of magnetic moments on Cu ions, having a paramagnetic arrangement down to 50 K and then ordering to an antiferromagnetic state at lower temperatures. In this study we use DFT-based computational methods to investigate the electronic structure and magnetic properties of CuFeS2 in order to obtain a reliable source of information for the interpretation of the observed magnetic behavior, and in particular to shed some light on the magnetic behavior of copper atoms in this compound. We have calculated the electronic structure of the ground and low-energy magnetically excited states and deduced a set of exchange coupling constants that are used afterward in classical Monte Carlo simulations to obtain magnetic susceptibility data, which compare successfully with our experimental results above ∼170 K. From our results it can be inferred that copper atoms remain in a diamagnetic state in this temperature range, although spin delocalization from neighboring iron atoms results in a non-negligible spin density on the copper atoms at high temperatures.