Structural Analysis of Submicrometer LiCoO[sub 2] Films

Abstract

Submicrometer LiCoO 2 films were prepared with pulsed laser deposition ͑PLD͒ and rf sputtering using stoichiometric targets. The influences of both substrate material and annealing procedure on the polycrystalline microstructure of the LiCoO 2 films were investigated. XRD analysis revealed strong preferential orientation: annealed films deposited with PLD had their ͑00l͒ planes parallel to the surface, while rf sputtered films had their ͑110͒ planes in this orientation. The rf-film also developed the ͑003͒ reflection typical of PLD-films, but only after prolonged annealing at 600°C. The degree of preferential orientation is influenced significantly by the annealing procedure and only little by the substrate material and the thickness of the deposited film. Pulsed laser deposition on an rf-sputtered seed layer revealed the PLD-film reflections. Extinction of the otherwise dominating ͑003͒ reflection indicated a random cationic distribution in LiCoO 2 with an NaCl-type structure.The lithium intercalation ability of LiCoO 2 was discovered 20 years ago by Goodenough and has been exploited by Sony with the introduction of their rechargeable C/LiCoO 2 battery in 1991. Presently, this technology finds large-scale commercial application as a power source for numerous handheld devices. Extensive research has been conducted to explore alternative materials, which are more cost effective and less toxic. 1 Until now, lithium cobalt oxide based electrodes exhibit superior properties in terms of cycle stability and energy density, a favorable combination for a reliable power source. 2,3 There is a growing interest in the production of secondary lithium batteries of smaller dimensions; microbatteries are very suitable to provide backup power for on-chip static memory modules. Integrated memory is encountered frequently due to a growing tendency in the microelectronics industry toward complete integration of all functions onto a single chip designed for one specific purpose. For example, a motor controller chip will contain everything from controller to the power regulation in one module called a multichip module ͑MCM͒. The functions can subsequently be implemented on a separate silicon substrate, interconnected, and stacked in a single housing. 4 The addition of a single microbattery allows the digital memory states to remain unaffected during power failure or long time storage.The common composite powder electrodes are unsuitable for microbattery application due to their porosity and the necessity for additives. The indistinct characteristics of powder-based electrodes also make modeling of the electrochemical intercalation behavior difficult. The present paper describes preparation and properties of dense, submicron films of polycrystalline LiCoO 2 on a silicon wafer with pulsed laser deposition ͑PLD͒ and rf sputtering. The welldefined composition, microstructure, and dimensions of the deposited layers make these samples suitable for fundamental electrochemical studies of the lithium intercalation process. Eventually, these f...

Nanoanalysis and Ion Conductivity of Thin Film Battery Materials

“…As before, a clear enrichment of Li is detected close to the surface. But in the case of the glass here, the enrichment of Li is balanced by a joint decrease of the second metal and oxygen as well, in obvious contrast to the previous case of LiCoO 2 in which the increase of Li was accompanied by an increase of the oxygen content. Furthermore, the elevated Li content at the surface is counterbalanced by an obvious loss of Li at the opposite side of the glass layer towards the tungsten substrate, as marked by light and dark shaded areas in Fig.…”

“…Therefore, the growth of thin films has attracted considerable attention recently, see e.g. [1][2][3][4][5].…”

All‐Solid‐State Lithium‐Ion Microbatteries: A Review of Various Three‐Dimensional Concepts

“…However, the formation of HT-LiCoO 2 has also been reported by the application of relatively low temperature wet-chemical processes. [ 25 ] The same two polymorphs of LiCoO 2 are also observed when depositing solid-state thinfi lms which can, amongst other methods, be achieved by RF sputtering, [26][27][28][29] sol-gel deposition, [ 27 , 30-32 ] chemical vapor deposition [ 33 , 34 ] and pulsed laser deposition. [ 29 ] HT-LiCoO 2 is well-known for its layered hexagonal structure.…”

The film growth and electrochemical properties of rf-sputtered LiCoO2 thin films

“…In this work, HT-LiCoO 2 was deposited on Pt-coated silicon by rf sputtering. Although the electrochemical properties and some fabrication parameters of rf-sputtered LiCoO 2 thin films have been investigated [3][4][5][6][7][8][9][10][11][12], the film growth of HT-LiCoO 2 under various sputtering parameters and the dependence of Li + diffusion coefficient (D Li + ) in rf-sputtered HT-LiCoO 2 films on various annealing temperatures were not yet reported. Thus, * Corresponding author.…”