Preparation And Performance Research Of Bismuth-based Anode Materials For Lithium Ion Batteries

Nowadays,the energy field is developing day by day,and people are becoming more and more dependent on energy storage equipment.Lithium-ion batteries are considered to be one of the most promising green energy devices in modern society and have become an indispensable part of human life.Because of its high energy density and long cycle performance,lithium-ion batteries have become the best choice for energy storage.However,with the continuous advancement of technology,many products require the use of higher power and higher energy density battery packs.However,it is difficult for graphite anodes to meet current market demands due to their limited capacity.Therefore,it is necessary to find other more advanced anode materials.Metal bismuth has a relatively high volumetric capacity and is environmentally friendly.Therefore,there has been a lot of research on using bismuth-based materials as new anode materials for lithium-ion batteries.However,due to the serious volume expansion of the material during the reaction,the structure collapsed and the cycle performance deteriorated.In this paper,carbon coating method is used to effectively solve the above problems.The specific work is as follows:（1）BiPO₄@C was prepared by a combination of improved molten salt method and mechanical ball milling method..All the initial raw materials are mass-production,such as bismuth nitrate pentahydrate and ammonium phosphate monobasic,which facilitates the high-yield of the target product.The electrochemical properties of BiPO₄@C composites were studied by assembling half-cell.The results showe that BiPO₄@C composite delivers a high capacity and rate performance as 278 m Ah/g with current density of 100 m A/g after 100 discharge-charge cycles and 210 m A/g delithiation capacity at 200 m A/g after 1500 cycles.A superior result as 100 m Ah/g delithiation capacity at 1 A/g after 5000 cycles is obtained with a very low capacity attenuation rate of 0.013%per cycle.The enhanced electrochemical performance of BiPO₄@C nanocomposite for lithium-ion batteries can be attributed to the formation of Bi nanoparticles uniformly dispersed in Li₃PO₄inert matrix and amorphous carbon during the lithium impregnation process in the first cycle.This work revealed that the as-prepared BiPO₄@C nanocomposite can be utilized as promising anode material for Lithium ion batteries.（2）Mass production of 2D layered BiOCl nanoplates and BiOCl@C composite are achieved by using（BiO）₂CO₃as raw material via a simple molten salt method.Those as-prepared 2D BiOCl nanoplates provide feasible pathways for electrons and ions transportation.However,due to the large volume change of the active material during the reaction,the structure is unstable and the cycle is poor,which limits its practical application in rechargeable batteries.Therefore,the BiOCl@C composites fabricated by BiOCl nanoplates anchored on carbon matrix is proposed,the carbon matrix provides a high conductive network as well as a buffer layer alleviating the volumetric expansion and improving the structure stability for BiOCl nanoplate matrix during the Li⁺insertion/extraction processes.The results showed that after 100cycles,the discharge capacity of BiOCl@C composite electrode keeps 410 m Ah/g,the average coulombic efficiencies can keep up to 99%after the first cycle.This work would provide a new approach for preparing BiOCl@C anode material with high volumetric energy density,and these materials are expected to be the potential candidates applied in LIBs.（3）In this work,Bi₂Fe₄O₉@C is prepared by solid state reaction in combination with mechanical ball milling,and its morphology,structure and properties were studied.As expected,the electrochemical performance of Bi₂Fe₄O₉@C is enhanced by composite with graphite.Electrochemical tests show that the reversible charging capacity of Bi₂Fe₄O₉@C is 743 m Ah/g after 80 cycles at a current density of 100m A/g,while the pure Bi₂Fe₄O₉compound retains only 142 m Ah/g.Especially,the reversible delithiation capacity of Bi₂Fe₄O₉@C composite is up to 551 m Ah/g at 2A/g.This work demonstrates the potential application of Bi₂Fe₄O₉@C composite in anode materials for lithium-ion batteries.