Ge-based Lithium Battery Anode Material By Ionic Liquid Electrodeposition Method

Artificial graphite and modified natural graphite are the main commercialized lithium battery anode materials.And a small amount use of lithium titanate is also applied in lithium batteries.These anode material can basically meet the requirements of general electronics and energy storage batteries.However,for the capacity of the commercial ones is not so high that cannot meet the rapid development of electric cars,we need to find more electrode material with high capacity to improve the battery energy density.We choose germanium as the research object for its theoretical capacity as high as 1600 mAh g-1,more than the graphite(372 mAh g-1),making it as an attractive electrode material for lithium batteries.However,the key drawback of the Ge is the large volume change(up to 370%)during Li+ insertion/extraction,which leads to the pulverization of the electrode material and peeling off from the current collector.In this research,we syntheses the Ge-based material by ionic liquid electrodeposition method,to electrodeposit Ge from an ionic liquid on different current collector with special structure.Compared with the common method that by mixing adhesive,conductive material and electrode material together and then coating on the current collector,the Ge-based anode material by the ionic liquid electrodeposition method can be directly used as the integrated anode without using the adhesive and conductive material,which also simply the process of the synthesis of the electrode.The electrochemical tests show that this method can greatly improve the electrochemical performance of Ge-based material.The main research contents and achievements were summarized as follows:(1)A Ge/copper wire mesh anode has been successfully synthesized and characterized.The germanium layer deposited on the copper wire mesh is dense and consists of Ge nanoparticles.There is a firm contact between the Ge film and the surface of the copper wire mesh.Electrochemical tests shows that from the 2nd cycle to 55th cycle,the capacity drops from 873 mAh g-1 to 672 mAh g-1 slowly,remain at a rate of 76.9%.(2)The carbon cloth is also used as current collector to prepare the integrated anode by electro depositing germanium on carbon cloth.The scanning electron microscopy(SEM)characterization shows that the Ge film on the surface of the carbon fiber has a double-layered structure:a porous inner layer of Ge island arrays and a compact Ge film outer layer.The double-layer structure can effectively buffer the volume change in the process of charging and discharging caused by the Li+ insertion/extraction,which further improves the cycle stability of the electrode.Electrochemical tests show that after 100th cycle,the capacity of the battery is still as high as 989 mAh g-1,with a high retention of capacity.