| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Wednesday Sessions |
| Session EN+NS-WeA |
| Session: | Nanostructures for Energy Conversion & Storage I |
| Presenter: | C.S. Nimisha, Indian Institute of Science, India |
| Authors: | C.S. Nimisha, Indian Institute of Science, India G. Venkatesh, Indian Institute of Science, India T. Dhivya, Indian Institute of Science, India G. Mohan Rao, Indian Institute of Science, India N. Munichandraiah, Indian Institute of Science, India |
| Correspondent: | Click to Email |
Nanostructured Sn thin films have been prepared by rf sputtering and thermal evaporation on to silicon substrates for evaluating the electrochemical performance to use as anode layer of thin film Li-ion battery. The scanning electron microscopy (SEM) shows different film morphologies for evaporated and sputtered films which directly control the electrochemical performance. Crystallinity of the deposited films were ensured by X-ray diffraction(XRD). Bio-Logic SA potentiostat / Galvanostat (model:VPM3) is used for testing electrochemical performances. Sn thin films prepared by thermal evaporation from Sn granules of 99.99% purity resulted in films with nanograins of ~200nm size homogeneously distributed over the surface. Whereas films made by rf sputtering from Sn target (99.99% purity) with Ar as sputtering gas at a pressure of 5x10-3mbar, resulted in highly porous film surface with ‘nanobead’ (~50nm size) formation inside the edges.
For electrochemical studies half cells were assembled using lithium as counter and reference electrodes in 1M LiAsF6 dissolved in ethylene carbonate and dimethyl carbonate electrolyte. Charging was done with a constant current density of 10 µA / cm2 up to 1.2 V, followed by discharging at 10µA / cm2 down to 0.2 V. The capacity obtained from both evaporated and sputtered films clearly shows the three plateau regions of lithiation and delithiation for both evaporated and sputtered films. From the evaporated film, a discharge capacity of 83.6 µAh/cm2 is obtained, whereas from sputtered film a much higher capacity of 886 µAh/cm2 is obtained.
We speculate that the increased surface area of the rf sputtered Sn film due to the porous nature and the presence of nano beads, resulted in higher capacities than the evaporated Sn films, which have relatively bigger sized grains. Also the presence of more nano sized features in the sputtered film surface reduces the pulverization of Sn films during cycling since the absolute volume change would be minimized. The reduction in diffusion length for Li-ion and increased effective surface area ensures higher discharge capacity from rf sputtered Sn films compared to evaporated films. The higher discharge capacity obtained from rf sputtered Sn thin films makes it ideal candidate for integrating as anode layer of thin film Li-ion battery.