Effect of Vacancy Defects on the Properties of CoS_(2) and FeS_(2)

In order to explore the effect of vacancy defects on the structural,electronic,magnetic and optical properties of CoS_(2) and FeS_(2),first-principles calculation method was used to investigate the alloys.The calculated results of materials without vacancy are consistent with those reported in the literatures,while the results of materials with vacancy defect were different from those of literatures due to the difference vacancy concentration.The Co vacancy defect hardly changes the half-metallic characteristic of CoS_(2).The Fe vacancy defect changes FeS_(2) from semiconductor to half-metal,and the bottom of the spin-down conduction band changes from the p orbital state of S to the d(t_(2g))orbital state of Fe,while the top of the valence band remains the d orbital d(eg)state of Fe.The half-metallic Co vacancy defects of CoS_(2) and Fe vacancy defects of FeS_(2) are expected to be used in spintronic devices.S vacancy defects make both CoS_(2) and FeS_(2) metallic.Both the Co and S vacancy defects lead to the decrease of the magnetic moment of CoS_(2),while both the Fe and S vacancy defects lead to the obvious magnetic property of FeS_(2).Vacancy defects enhance the absorption coefficient of infrared band and long band of visible light obviously,and produce obvious red shift phenomenon,which is expected to be used in photoelectric devices.

NATURAL AND TREATED FES_2 IN LI/FES_2 COIN CELL

Treated FeS2 samples were prepared by natural FeS2 samples which were ground first, heated in nitrogen and then washed in acid. The levels of impurity elements, primarily present as metallic oxides and sulfides, are higher in the natural FeS2 than those in the treated sample. Scanning electron microscopy shows that the grain sizes of treated FeS2, particles are smaller than those of natural FeS2 particles. The electrochemical performance of Li/treated FeS2 cells is attributed to the smaller grain sizes and higher purity of treated FeS2 particles in comparison to the natural FeS2 sample.

Structure adapting of bulk FeS_(2) micron particles and the corresponding anode for high performance sodium-ion batteries

The practical application of Pyrite iron disulfide (FeS_(2)) as anode material of sodium-ion battery is limitedby its low electronic conductivity, large volume changes during charge/discharge. To overcome thesechallenges, a novel structure design single-walled carbon nanotubes (SWCNTs) composited polyaniline(PANI)-wrapped FeS_(2) (FeS_(2)-PANI-SWCNTs) electrodes are successfully achieved in this work. PANI canprotect the FeS_(2) particles from collapse and offer a protective layer to relive the polysulfides shuttlingeffect, and also promote the electron and Naþ diffusion during the chemical conversion process. Underthe dual protection of PANI and SWCNTs, the FeS_(2)-PANI-SWCNTs film electrode demonstrates a goodstructural integrity, which accounts for the excellent rate capability and long cycling performance. Inaddition, the PANI coating and SWCNT network in the fabricated electrode can synergistically anchorpolysulfides and therefore strongly suppress shuttle effect during the chargeedischarge processes,resulting in less capacity loss. The anode with a loading 3.2 mg cm 2 of FeS_(2) coated with PANI exhibitsthe initial coulombic efficiency of 81.5% and delivers a specific capacity of 625.8 mAh g^(-1) after 100 cyclesat 200 mA g^(-1). High flexible and binder-free FeS_(2)-PANI-SWCNTs film anode demonstrates a reversiblecapacity of 537 mAh g^(-1) after 550 cycles at 1 A g^(-1). This research may offer an efficient method toimprove electrochemical performance of the metal sulfides in sodium-ion batteries.

S-Doped Carbon-Coated FeS_(2)/C@C Nanorods for Potassium Storage

Potassium-ion batteries(PIBs) are promising scalable energy storage system;however,one of the challenges for its potential application is the huge volume variations during cycling due to the insertion/extraction of large size potassium ions.Here,we fabricated the S-doped carbon-coated rod-like FeS2/C@C,which not only effectively alleviate the volume variations upon cycling but also can improve electrical conductivity and maintain the structural integrity.As an anode material for PIBs,the rod-like FeS2/C@C electrodes delivered excellent rate performance(175 mA h g-1 at 0.5 A g-1) and stable cycle performance(262 mA h g-1 after 100 cycles at 0.1 A g-1).The superior excellent performance is associated with the unique structure of FeS2/C@C.The as-synthesized FeS2/C@C is demonstrated to be a potential anode for PIBs.