Mesoporous composite of core-shell FeS₂ micron spheres with multi-walled CNTs and its application in lithium ion batteries

Pyrite (FeS₂) is considered to be an excellent electrode material candidate for energy storage devices because of its abundant resources, cost effectiveness, environmental friendliness and high theoretical capacity of 894 mA·h·g^-1 based on conversiontype reactions.However, transition metal sulfides (TMSs), includingFeS₂, suffer from low electronic conductivity, sluggish Li ion transfer kinetics, and severe volume change while charging and discharging, which contribute to the sharp decline in capacity as well as limit its application as electrode material for secondary batteries.Downsizing TMS powders to the nanoscale becomes a common strategy to mitigate the volume change and maximize the proportion of active material involved in the electrochemical process.However, nanostructures lead to a serious interphase detrimental reaction, dissolution of the polysulfide intermediates, and low volumetric energy density.Therefore, micron particles are critical to the design of high energy density active material in view of industrial applications.In this study, a facile hydrothermal method has been successfully developed to synthesize a novel mesoporous composite of core-shell FeS₂ micron spheres with multi-walled carbon nanotubes (C-S-FeS₂@ MWCNT).The protective layer is constructed on FeS₂ micron spheres consisting of the approximately 350 nm-thickness shell stacked by nanosheet FeS₂ particles and the reticular MWCNTs anchored via chemical binding.The FeS₂ content is determined using thermogravimetric analysis to be 73.4% of the C-S-FeS₂@ MWCNT composite, which is higher than the value of the reported compound material with nanopowder.The unique architecture with abundant functional groups and pore structures not only provides the Li⁺ ion diffusion pathway but also buffers volume expansion during cycling.The galvanostatic circulation tests indicate that the C-S-FeS₂@ MWCNT electrode delivers a high reversible capacity of 638 mA·h·g^-1 in 250 cycles at a current density of 200 mA·g^-1 and exhibits a significantly improved rate performance.This work demonstrates a new method to develop TMSmicron electrode material with high volumetric energy density.