Investigations On Sputter Deposited LiCoO2 Thin Films From Powder Target

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. Xray 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 chargedischarge 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.

Optimization of a potential manufacturing process for thin-film LiCoO2 cathodes

“…While the removal of the native oxide layer prior to cell fabrication appeared to improve the performance in the early stages of cycling, the overall performances of both sets of cells compare favourably to previous reports. For example, most studies report the fabrication of significantly thinner LCO films, which have much lower areal capacities [17,19,[22][23][24][25][26]28,33,34,36,49]. In terms of fabrication conditions, mixed argon-oxygen process gases at high pressures, costly Pt/Au-coated substrates with heating or a potential bias applied during deposition and longer, higher temperature, or more complex post-deposition annealing processes are frequently reported [21,[34][35][36].…”

“…For example, most studies report the fabrication of significantly thinner LCO films, which have much lower areal capacities [17,19,[22][23][24][25][26]28,33,34,36,49]. In terms of fabrication conditions, mixed argon-oxygen process gases at high pressures, costly Pt/Au-coated substrates with heating or a potential bias applied during deposition and longer, higher temperature, or more complex post-deposition annealing processes are frequently reported [21,[34][35][36]. Thus, the fabrication, structural, and electrochemical properties reported here for LCO thin films prepared by a rather simple process are very promising.…”

“…Most studies report similar processing conditions: an RF power density of ~2-5 W cm -2 , a deposition pressure of at least 1 Pa, a mixed argon-oxygen process gas, an unheated metalcoated ceramic substrate, and post-deposition annealing in air or an oxygen/argon-oxygen atmosphere at 600-700 ˚C for 1-2 hours. Relatively few studies have explored conditions that deviate significantly from these ranges [19,21,24,29,[33][34][35][36]. Thus, it may be possible to achieve favourable structural and electrochemical properties across a markedly wider variety of processing conditions.…”

Thin Film Fabrication and Characterization of Layered Rock Salt LiCoO2 on Quartz Glass Spray-Coated with an Aqueous Ammonia Solution Involving Metal Acetates

“…The Raman spectra of Fspray and Fss are given in Figure 3. Two peaks at 485 and 595 cm -1 in both spectra are assignable to the LCO [3,25,26]. The additional broad peak at 1169 cm -1 is assignable to the overtone of the A1g mode of the LCO [27].…”

Microstructural and electrochemical properties of LiTi y Co 1-y O2 film cathodes prepared by RF sputtering

“…In recent years, Li ion rechargeable batteries are widely used power sources for many applications in portable electronic devices, electric vehicles, and in biomedical applications [1,2]. Lithium transition metal oxides such as LiNiO 2 [3,4], LiMn 2 O 4 [5], LiMnO 2 [6], LiFePO 4 [7,8], and LiCoO 2 have made significant role in Lithium ion-battery applications [9,20].…”