Composite Tin Dioxide-Titanium Dioxide Nanostructured Thin Film Electrodes As Lithium-Ion Anodes

Abstract

An aerosol-chemical vapor deposition technique (ACVD) was utilized in order to deposit highly oriented, one-dimensional nanostructured metal-oxide thin films. Film morphology was controlled using various system parameters in order to obtained the desired columnar morphology. Tin dioxide (SnO2) was chosen as an electrode material due to its high theoretical charge capacity (790 mA-h-g-1), and titanium dioxide (TiO2) was chosen for its remarkable stability and low volume change during charging. The columnar morphology is particularly well suited to SnO2 as the space between the columns allows for accommodation of the large volume expansion the material experiences during charging. Electrodes of SnO2 columnar nanostructures were first synthesized using ACVD by depositing the structures directly on to the current collector. Depositing directly onto the current collector eliminates the need for binding agents and conductive additives during battery fabrication. Then a layer of TiO2 was deposited on the surface of the SnO2 columns using atomic layer deposition. A variety of column heights, ranging from 500 nm to 2 um, and TiO2 layer thickness, ranging from no TiO2 to a 100 nm layer, were synthesized and their electrochemical properties investigated. For all electrochemical characterization experiments, Swagelok-type coin cells were fabricated using lithium foil as a counter electrode and 1M LiPF6 in 50/50 (v/v) EC/DEC as an electrolyte. Optimal electrochemical performance was observed in electrodes with a height of 800 nm and a 15 nm layer of TiO2. A rate capability test was performed to determine how the capacity of the electrodes changed at charging rates ranging from 100-2000 mA-g-1. A stable capacity of 410 mA-h-g-1 was obtained at a charge rate 1000 mA-g-1; rapid capacity fade was observed at higher rates. Galvanostatic charge-discharge was performed for each cell for 100 cycles or until failure at a charge rate of 400 mA-g-1, corresponding approximately to a charge rate of C/2. For the optimal electrode an initial irreversible capacity of 1164 mA-h-g-1 was observed as well as a stable capacity of 530 mA-h-g-1 after 100 cycles. This demonstrates a low cost synthesis of high performance anodes which provides an alternative to conventional electrode synthesis.