ABSTRACT
The increasing demands from micro-power applications call for the development of the electrode materials for Li-ion microbatteries using thin-film technology. Porous Olivine-type LiFePO4 (LFP) and NASICON-type Li3Fe2(PO4)3 have been successfully fabricated by radio frequency (RF) sputtering and post-annealing treatments of LFP thin films. The microstructures of the LFP films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the LFP films were evaluated by cyclic voltammetry and galvanostatic charge-discharge measurements. The deposited and annealed thin film electrodes were tested as cathodes for Li-ion microbatteries. It was found that the electrochemical performance of the deposited films depends strongly on the annealing temperature. The films annealed at 500 °C showed an operating voltage of the porous LFP film about 3.45 V vs. Li/Li+ with an areal capacity of 17.9 µAh cm-2 µm-1 at C/5 rate after 100 cycles. Porous NASICON-type Li3Fe2(PO4)3 obtained after annealing at 700 °C delivers the most stable capacity of 22.1 µAh cm-2 µm-1 over 100 cycles at C/5 rate, with an operating voltage of 2.8 V vs. Li/Li+. The post-annealing treatment of sputtered LFP at 700 °C showed a drastic increase in the electrochemical reactivity of the thin film cathodes vs. Li+, leading to areal capacity ~9 times higher than as-deposited film (~27 vs. ~3 µAh cm-2 µm-1) at C/10 rate.
ABSTRACT
The electrochemical behavior of thallium was studied on glassy carbon electrodes in sulfate solutions. Cyclic voltammetry was used to study the kinetics of the electrode processes and to determine the nature of the limiting step of the cathodic reduction of thallium ions. According to the dependence of current on stirring rate and scan rate, this process is diffusion limited. Chronocoulometry showed that the electrodeposition can be performed with a current efficiency of up to 96% in the absence of oxygen.
