Powder target; rf sputtering; thin film cathodes; LiCoO2 thin films.

Investigations On Sputter Deposited LiCoO2 Thin Films From Powder Target

Yellareswara Rao Kosuri¹, Tirupathi Rao Penki², Munichandraiah Nookala², Per Morgen³, Mohan Rao Gowravaram^1*

¹Department of instrumentation and applied physics, Indian institute of science, Bangalore 560012, India

²Department of inorganic and physical chemistry, Indian institute of science, Bangalore 560012, India

³Department of physics, chemistry and pharmacy, University of Southern Denmark, Campusvej 55 DK 5230 Odense, Denmark

Adv. Mater. Lett., 2013, Current Issue, 4 (8), pp 615-620

DOI: 10.5185/amlett.2012.12479

Publication Date (Web): Jul 13, 2013

E-mail: gmrao@isu.iisc.ernet.in

Full Article

Abstract

LiCoO2 thin films used as cathode layers in thin-film solid-state batteries have been deposited from LiCoO₂ powder target using radio frequency (rf) magnetron sputtering in a cost effective approach in terms of material consumption and processing time. X-ray diffraction (XRD) studies of the films after post deposition annealing treatment revealed (104) orientation, which is the characteristic of rf sputtered LiCoO2 films. Raman spectroscopy was used to identify the different modes of vibration of atoms in the film. The surface morphology and cross-section of the samples were characterized using field emission scanning electron microscopy (SEM). The chemical analysis of LiCoO₂ thin films was examined by X-ray photoelectron spectroscopy (XPS) showed atomic ratio of Li/Co as 0.9 which is close to the ideal value 1. Electrochemical characterization such as charge – discharge and cyclic voltammetry were conducted for LiCoO₂ films deposited on platinized silicon substrates in the potential range 3.0 to 4.2 V vs Li/Li⁺. The maximum discharge capacity of 64 µAh.µm^-1. cm^-2 and 52 µAh. µm^-1.cm^-2 were achieved when discharged at a current of 5 µA and 50 µA for the first discharge cycle respectively. Moreover the electrochemical investigations of LiCoO₂ thin films on flexible copper substrates also investigated and achieved an initial discharge capacity of 83 mAh/g. The possible reasons for degradation in the electrochemical properties have been discussed. The present work indicates suitability of sputtering from powder targets for thin film battery fabrication.