Electrochemical Performance Study Of Iron Oxide-based Lithium-ion Battery Anode Materials

Lithium ion batteries have been widely used due to the advantages of no memory effect,high capacity and long cycle life.With the rapid upgrading of electronic products,the rise of new energy industry and the era of"carbon peak"and"carbon neutrality",the performance of lithium ion battery is required to be further improved.Among them,one of the critical factors affecting its performance is the electrode material.Graphite is a typical anode material for large-scale commercial use.However it has a low theoretical specific capacity(372 m Ah g^-1),which make it difficult to satisfy higher requirements for application.In addition,iron oxide has the advantages of high theoretical specific capacity,low cost,safety,non-toxicity and abundant reserves in nature,which make it a promising new material to replace graphite.But when iron oxide is used as a anode material,the volume expansion phenomenon and low conductivity of need to be solved.The morphology and size control and its composite materials are usually used to surmount above problems.In this paper,unitary Fe₂O₃ and binary Zn Fe₂O₄ iron oxides are investiged,and the main research contents are litsted as follows:（1）Fe₂O₃ samples with hollow spheres,cubes and nanoparticles were prepared by carbon sphere template method,hydrothermal method and coprecipitation method,respectively.The effect of morphology on lithium storage performance was investigated.The results showed that the electrochemical properties of nanoparticles Fe₂O₃ was better than those of hollow sphere Fe₂O₃ and cube Fe₂O₃.The discharge/charge specific capacity was at 866.4/855.7 m Ah g^-1 at 500 m A g^-1 for200 cycles and remained 511.4/495.3 m Ah g^-1 at 2 A g^-1.Due to the smaller particle size and grain size,the uniformly dispersed Fe₂O₃ nanoparticles improve the electrochemical reaction activity,shorten the transmission path of Li⁺,and alleviate the volume expansion effect.（2）Fe₂O₃/NC（N-doped Carbon nanosheets）nanocomposites were prepared by two-step hydrothermal method using melamine and formaldehyde as carbon and nitrogen sources.The results showed that when Fe₂O₃/NC was used as anode material of lithium ion battery,the discharge/charge specific capacity of 1059.3/1046.1 m Ah g^-1 when cycled for 500 times at 500 m Ah g^-1,and even at a high current density of 15 A g^-1,its specific capacity was 348.6/340.3 m Ah g^-1.Compared with pure nanoparticles Fe₂O₃,the electrochemical performance was improved dramatically.The excellent electrochemical performance of Fe₂O₃/NC was due to the unique"sandwich"structure,nanoscale size and the combination of nitrogen and carbon elements.These advantages can enhance the structural stability,increase the surface area,reduce the volume effect and agglomeration phenomenon,improve the electrical/ion conductivity of the electrodes.（3）Zn Fe₂O₄-Fe₂O₃/NC nanocomposite materials were designed and assembled by sol-gel and hydrothermal methods.The electrochemical test results showed that the discharge/charge specific capacity of Zn Fe₂O₄-Fe₂O₃/NC was 1518.5/1504.5 m Ah g^-1 after 300 cycles at 500 m A g^-1;at a high current density of 10 A g^-1,the discharge/charge specific capacity of Zn Fe₂O₄-Fe₂O₃/NC was639.2/628.1 m Ah g^-1.The excellent performance of Zn Fe₂O₄-Fe₂O₃/NC materials was attributed to the three-dimensional structure of Zn Fe₂O₄-Fe₂O₃ nanosheets embedded in the nitrogen-carbon nanosheets and the introduction of Fe₂O₃ and NC.