Study On Fe₂O₃ Surface Coating And Electrochemical Performance Of Lithium-ion Battery Anode Material

Energy issues are closely related to the survival of all mankind,in the process of today's globalization.The development of new energy has become the focus of researchers,with non-renewable fossil energy being developed on a large scale and becoming scarce.As a new energy device,lithium-ion battery has a broad application space because of the high reversible specific capacity.The transition metal oxide Fe₂O₃has a high theoretical specific capacity.It is suitable as a lithium ion negative electrode material.In this article,commercial iron oxide is used to design the surface structure of composite materials to synthesize Fe₂O₃-based anode materials for lithium-ion batteries.The structural characterization and electrochemical performance study of composite materials,the main contents are as follows:(1)Use a combination of sol-gel and heat treatment to coat a layer of TiO₂coating around commercial Fe₂O₃.The titanium source uses butyl titanate,and sodium borohydride is used to introduce oxygen vacancies in the TiO₂coating.The electrochemical performance of the composite material labeled Fe₂O₃@0.2TiO₂is the best when the molar ratio of Fe:Ti is 9:1 after the test.After 150 times cycle,the specific discharge capacity is still 405.6 m Ah/g,which far exceeds the cycle life of pure iron oxide.Pure Fe₂O₃shows a cliff-like decay in the first twelve cycles,and only has a specific discharge capacity of about 50 m Ah/g.The rate performance marked as Fe₂O₃@0.1TiO₂is the best when the molar ratio of Fe:Ti is 19:1.The specific discharge capacity can still rise to 509 m Ah/g when the current density changes from 25 to 400 to 25 m A/g.After coating TiO₂and introducing oxygen vacancies,the electrochemical performance is improved.The TiO₂coating layer suppresses the volume expansion of iron oxide during charging and discharging.Introduce oxygen vacancies to further improve cycle stability and rate performance.(2)Based on the composite material Fe₂O₃@0.2TiO₂prepared in(1),using chemical mixing and heat treatment methods,a carbon layer is coated around the TiO₂coating.The carbon source is PVP to form a double coating.Structured new composite material Fe₂O₃@TiO₂@C.The test shows that Fe₂O₃@TiO₂@C-600?has the best electrochemical performance.The specific charge and discharge capacities are 852.6 m Ah/g and 1146.7 m Ah/g during the first cycle of charge and discharge,at a current of 100 m A/g.After 100 cycles,676.0 m Ah/g and 683.9 m Ah/g are the specific charge and discharge capacities,60%is the capacity retention rate.Fe₂O₃@TiO₂@C-600?also has the best rate performance.The charge-discharge specific capacity can still rise to 844.3 m Ah/g and 861.0 m Ah/g when the current density changes from 25 to 400 to 25 m A/g.After Fe₂O₃is reduced to Fe₃O₄,the conductivity of the material itself is higher than Fe₂O₃and the conductivity of the composite material increases.Fe₂O₃materials have improved conductivity,higher than capacity and cyclic stability.Meanwhile,the inner TiO₂and outer carbon layers jointly inhibit the volume expansion of iron oxide during the charge and discharge process,and improve the stability of iron oxide circulation.(3)Based on the composite material Fe₂O₃@0.2TiO₂prepared in(1),using a chemical mixing method,a conductive polymer coating is covered around the TiO₂coating.The polymer is selected as PEDOT to form a double-layer coating Fe₂O₃@TiO₂@PEDOT,a new composite material with covered structure.The test showed that the composite Fe₂O₃@TiO₂@PEDOT-24h polymerized at a polymerization time of 24h showed the best performance.The cycle life is greatly improved compared with pure Fe₂O₃and Fe₂O₃@TiO₂.It can still maintain 588.9m Ah/g after 360 cycles at a current density of 100 m A/g.The first cycle releases a specific capacity of 1543.4 m Ah/g,which is far exceeds the theoretical specific capacity.Fe₂O₃@TiO₂@PEDOT-24h has the best rate performance.The average charge-discharge specific capacity is 588.1 m Ah/g and 652.5 m Ah/g at the current density of 400 m A/g.The discharge specific capacity and charge specific capacity increase to 951.8 m Ah/g and 940.2 m Ah/g when the current density returns to 25m A/g.PEDOT shell ensures the high conductive structure of the composite and provides interpenetrating fast ion channels on the inner and outer surfaces of a single composite element.Conductive polymer increases the conductivity of the composite material and improves the electrochemical performance of iron oxide.The synergistic effect of conductive polymer PEDOT shell and TiO₂inner shell inhibits volume expansion and improves cycle stability.