Understanding the Li Storage Sites in MWCNTs: SEI, the Key for Delithiation at High Potential

Abstract

To study the Li storage mechanism in multiwalled carbon nanotubes (MWCNTs), MWCNTs were coated with pyrolytic carbon, prepared by dipping the MWCNT paper into sucrose solution and annealing at 1100°C in Ar atmosphere. Different coating degree was achieved by varying the concentration of sucrose solution. From the charge-discharge characteristics, we found that limiting the formation of SEI by increasing the pyrolytic carbon coverage could supress the Li extraction occurs at high potential (1.5 to 3.0 V), which long has been considered as delithiation from Li bonded functional groups. Furthermore, such capacity eventually disappeared while the surface of nanotubes is fully covered. These suggest that the SEI formed on the nanotubes is responsible for Li storage of MWCNTs.