Electrochemical properties of Li[Li 0.2 Mn 0.54 Co 0.13 Ni 0.13 ]O 2 cathode thin film by RF sputtering for all-solid-state lithium battery Haena Yim a,b , Woo Yeon Kong a , Young Chul Kim b , Seok-Jin Yoon a , Ji-Won Choi a,n a Electronic Materials Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea b Department of chemical engineering, KyungHee University, Yoingin 449-701, South Korea article info Article history: Received 2 February 2012 Received in revised form 30 April 2012 Accepted 8 June 2012 Available online 28 June 2012 Keywords: Li[Li 0.2 Mn 0.56 Ni 0.13 Co 0.13 ]O 2 Lithium thin film battery RF magnetron sputter Cathode materials abstract The Li[Li 0.2 Mn 0.56 Ni 0.13 Co 0.13 ]O 2 thin films were prepared by radio frequency magnetron sputtering on Pt/Ti/SiO 2 /Si substrate with target contained a 5% excess of lithium precursor. Thin films were deposited under various deposition conditions such as working pressure, gas ratio of Ar and O 2 , and the temperature of in-situ annealing treatment. The thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The electrochemical property was estimated by a WBC3000 cycler with Li9Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 half-type cell at 1C charge/discharge rate. The (0 0 3) and (1 0 4) diffraction peaks which represent layered a-NaFeO 2 type structure (space group R-3m) were observed. Optimal magnetron sputtering conditions were detected. The 500 1C annealed thin film after deposited at 10 m Torr in Ar:O 2 ¼3:1 shows a high discharge capacity of around 62 mAh/cm 2 mm with a high cyclic retention. & 2012 Elsevier Inc. All rights reserved. 1. Introduction The demand for advanced energy storage devices have increased each year in resulted to the increasing prominence of microeletromechanical systems(MEMS), smart cards devices, and microrobotic systems. All-solid-state lithium-ion thin film bat- teries have predominantly drawn attention to energy device because of its small electronegativity, low density, and high energy to mass ratios. Cathode materials, such as transition metal oxides like LiCoO 2 , LiNiO 2 , and LiMn 2 O 4 , play an important role in thin film battery systems and the commercialized lithium battery industry [1–3]. However, the size of micro devices such as MEMS, smart cards, and microelectronic pill are determined by the size of energy supply system, so minimalized thin film battery with high capacity are strongly required. Therefore, researchers have been focused on new cathode materials which could solve the strong demand for higher capacity, high power and good cyclability. Specifically, the transition metal composite, LiMO 2 (M¼ Co, Cr, Ni, Mn, etc.) with its layered structure, is currently paid worldwide attention as an alternative cathode material since it shows high capacity, wide ranged potential, safety, and cost advantage [4–6]. The oxidation state of cathode cations in the transition metal composite was reported as Ni 2 þ , Mn 4 þ , and Co 3 þ , which is concomitant with the lower capacity loss, less first discharge capacity loss, and better cycling retention [7,8]. Although some fabrication process and its conditions of transition metal composite cathode such as LiNiCoO 2 [9] and LiMn 1/3 Ni 1/3 Co 1/3 O 2 [10] has been searched, fabrication parameters of RF-sputtered Li[Li 0.2 Mn 0.54- Ni 0.13 Co 0.13 ]O 2 has not been investigated. Therefore, in this research, we fabricated the Li[Li 0.2 Mn 0.54- Ni 0.13 Co 0.13 ]O 2 film for realization high capacity cathode positive thin film. The Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 cathode material was synthesized, which has the highest initial discharge capacity (253 mAh/g) [11] in the solid solution series (1-z)Li[Li 1/3 Mn 2/3 ] O 2 -zLi[Mn 1/3 Ni 1/3 Co 1/3 ]O 2 with z ¼ 4. This was done by adding excess amounts of lithium from 0% to 20% through the solid-state method. The 5% overlithiated material showed better electroche- mical performance, therefore, a 5% overlithiated Li[Li 0.2 Mn 0.56 Ni 0.13- Co 0.13 ]O 2 target (2 in. diameter) were fabricated. The thin films were deposited on Pt/Ti/SiO 2 /Si substrate using RF magnetron sputtering at different working pressure, gas ratio, and annealing temperature to optimize parameters. 2. Experiment 2.1. Powder preparation for target Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 powders were prepared through a solid-state reaction by using MnO 2 ( Z99%, Aldrich), NiO ( Z99%, Aldrich), and Co 3 O 4 ( Z99%, Aldrich) in a stoichiometric proportion as raw materials with various excess molar ratio (5%, 10%, 15%, 20% more) of Li 2 CO 3 ( Z99%, Aldrich) were used to compensate for the Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jssc Journal of Solid State Chemistry 0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2012.06.006 n Corresponding author. Postal address: 136-791, Korea Institute of Science and Technology, Hawolgok-dong, Seongbuk-gu, Seoul, Korea. Fax: þ82 2958 6720. E-mail address: jwchoi@kist.re.kr (J.-W. Choi). Journal of Solid State Chemistry 196 (2012) 288–292