Studies On The Preperation And Performance Of Fe3O₄/Carbon Nanomaterial Composite Anodes

With the vigorous development and promotion of electric vehicles in recent years,the performance requirements for power system-chemical energy storage device have been more and more severe.The conventional li-ion batteries have been unable to meet the growing market demands,as a consequence,there is an urgent need for the development of new-type lithium-ion batteries with high capacity and energy density.Fe₃O₄ has been regarded as a potential anode material and received the widespread attention,because of its high theoretical specific capacity(926mAh·g^-1),non-toxicity,eco-friendly property and low cost.However,similar to other transition metal oxides,Fe3O4 anode suffers large volume change during cycling,resulting in the destroy of structure and poor cycle stability,which greatly affects the practical application.Aiming at these problems,hybridization of Fe₃O₄ with carbon materials was fulfilled by a solvothermal method while ferric trichloride hexahydrate as the iron source and different nanomaterials as carbon matrixes,including 1D functionalized MWCNTs（f-WCNTs）,3D cellulose nanofibril（CNF）-based carbon aerogel and CNF/MWCNTs compound carbon aerogel.This paper aims to explore a new-type of Fe₃O₄/carbon nanomaterials composite anode systems with high specific capacity and excellent cycle stability.（1）Functionalized MWCNTs were synthesized by chemical oxidation in a mixture of concentrated acids,and three components of Fe₃O₄/f-MWCNTs composites were prepared by solvothermal method.Compared to pure Fe3O4 anode,the electrochemical properties of the synthesized nanomaterials have been greatly improved,f-MWCNTs not only increases the electrical conductivity of the anode material,but also promotes the charge transfer to allow the active material to be fully utilized.While the ratio of Fe3O4 is 40 wt%in the composite,nanoparticles uniformly distribute throughout the compound system,and the nanocomposite delivers a reversible specific capacity of 550.7 mAh·g^-1 after 100 cycles.（2）Fe₃O₄/C-CNFA nanocomposite was prepared by a solvothermal method while ferric trichloride hexahydrate as the iron source and CNF aerogel as the carrier.Meanwhile,the electrochemical performance of Fe3O4/C-CNFA anode was also measured.Nanocomposite demonstrates an excellent cycling stability with a reversible capacity of 750 mAh·g^-1 over 100 cycles at a current density of 100mA·g^-1,as well as an initial specific discharge capacity of 912.4 mAh·g^-1.However,its capacity needs to be further improved.（3）MWCNTs/CNF composite aerogels were prepared by freeze-drying method,and the mass fraction of MWCNTs was 30%,40%and 50%respectively.The porous carbon aerogels CA-1,CA-2 and CA-3 were synthesized by high-temperature carbonization and served as carbon matrixes to fabricate Fe₃O₄/CA-1,Fe₃O₄/CA-2and Fe₃O₄/CA-3 composites.Fe₃O₄/CA-2 processes better electrochemical performance than two other composites,which delivers an initial specific discharge capacity of 1181.2 mAh·g^-11 and an reversible specific capacity of 825.1 mAh·g^-1 after100 cycles at a current density of 100 mA·g^-1.Carbon nanotubes can further enhance the conductivity of carbon aerogel,providing an excellent conductive network for charge transmission.Meanwhile,CA-2 aerogel with porous structure could facilitate the uniform load of Fe3O4 nanoparticle,promoting capacity deallocation and preserving the structural integrity of the electrode.On the other hand,this 3D network could effectively restrain volume expansion of active material during cyclic process,improving the cycle stability of anode material.