Synthesis, Morphology Control And Electrochemical Performance Of Fe₂Ti₃O₉Solid Solution

The researchers develop and study a new type of lithium-ion batteryanode material actively to obtain the ideal material with high capacity,good cycle stability, high safety performance. Reducing the size of thematerial, increasing its specific surface area, and preparing the specialstructure of the anode material （hollow nanotubes, thin films, nanowires,etc.） can increase the intercalation and deintercalation of lithium ion, andthus improve its electrochemical properties.In this paper, Fe₂Ti₃O₉solid solution was prepared via thehydrothermal method and studies its electrochemical performance. Thesheet and nano-rod materials were prepared via treating the Fe₂Ti₃O₉solidsolution with solvothermal method and further expoded the transitionmechanism of different morphologies and their electrochemical properties.The influence of conductive agent to the electrochemical properties ofanode materials was studied by adding different ratio of acetylene black.The results show that the Fe₂Ti₃O₉solid solution electrode holds the discharge capacity of334.6mAh/g and the charge capacity of330.7mAh/g after50cycles, and its coulombic efficiency is98.8%. The chargecapacity-keeping rate of the battery is as high as93.7%, which is only0.446mAh/g loss for each cycle. The charge capacity of Fe₂Ti₃O₉solidsolution electrode is330.7mAh/g after50cycles, which is much higherthan TiO₂（theoretical value of168mAh/g）. The Fe₂Ti₃O₉solid solutionelectrode possesses not only the high reversible capacity of Fe2O3electrode, but also the better cycling performance of TiO₂, which will be apromising anode material for lithium ion batteries.The samples were synthetized by keeping the hydrothermaltemperature at200℃and changing the reaction time （12h,24h,36h,48h）.A series of sample test results showed that the morphology of the sampletransformed from graininess to lamellae and then to spherical structuresassembled by layers, and afterward to a rod-like structure assembled bylayers, and finally to the nano-rods. Electrochemical tests show thatsamples with reaction time of12h and24h hold higher specific capacitythan Fe₂Ti₃O₉solid solution electrode. The morphology of the sampletransformed to lamellae and spherical structures assembled by layers afterhydrothermal reaction, which increased the specific surface area, therefor,the capacity was improved. Samples with reaction time of36h and48hhold lower specific capacity than Fe₂Ti₃O₉solid solution electrode, whichis due to the solid nano-rods unfavorable to lithium ion intercalation and deintercalation.The samples were synthetized by keeping reaction time at48h andchanging the hydrothermal temperature （140℃,160℃,180℃,200℃）.A series of sample test results showed that the morphology of the sampletransformed from lamellae to nano-rods with the increase of reactiontemperature. Electrochemical tests show that samples with reactiontemperature of140℃and200℃have high stability and lower specificcapacity. This is because the sample with reaction temperature of140℃has large packing density and the sample with reaction temperature of200℃has the solid structure, which are all unfavorable to lithium ionintercalation and deintercalation. Samples with reaction temperature of160℃and180℃have higher specific capacity, which is because theexistence of nanowires increase the distance between the layers andsample specific surface area to some extent.The impact of the amount of conductive agent （acetylene black） toelectrochemical properties of lithium-ion battery was researched. Theresults show that the capacity of the electrode raised200mAh/g byincreasing the amount of acetylene black from10%to35%, which ismore than150mAh/g above the theoretical capacity. This suggests themain fuction of acetylene black is to enhance the conductivity of theanode material and to make the active material release more capacities.