具有核壳结构的FeS_2微米球与碳纳米管原位复合介孔材料的构建及其在锂离子电池中的应用

Mesoporous composite of core-shell FeS_2 micron spheres with multi-walled CNTs and its application in lithium ion batteries

通过简单的水热反应原位合成了具有核壳结构的FeS_2微米球与多壁碳纳米管复合的介孔材料(C-S-FeS_2@MWCNT). FeS_2微米球表面由纳米片状颗粒堆叠形成的厚度为～350 nm壳层,以及以化学键的形式吸附在微球表面的碳纳米管共同构成了材料保护层.保护层具有丰富的官能团和大量的孔隙结构,保证了锂离子扩散通道,并有效抑制了体积膨胀. C-SFeS_2@MWCNT在200 mA·g^(-1)的电流密度下,250次循环可逆容量达到638 mA·h·g^(-1),倍率性能也得到明显改善,为过渡金属硫化物电极材料的微米化设计和体积能量密度的提升提供了可能.

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 m A·h·g-1 based on conversiontype reactions.However,transition metal sulfides(TMSs),including FeS2,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 m A·h·g-1 in250 cycles at a current density of 200 m A·g-1 and exhibits a significantly improved rate performance.This work demonstrates a new method to develop TMS micron electrode material with high volumetric energy density.