Dependence of the constitution, microstructure and electrochemical behaviour of magnetron sputtered Li–Ni–Mn–Co–O thin film cathodes for lithium-ion batteries on the working gas pressure and annealing conditions

Abstract

AbstractLi(Ni1/3Mn1/3Co1/3)O2 as a cathode material for lithium ion batteries shows good thermal stability, high reversible capacity (290 mAh g−1), good rate capability and better results in terms of environmental friendliness. In this paper thin film cathodes in the material system Li–Ni–Mn–Co–O were deposited onto silicon and stainless steel substrates, by non-reactive r.f. magnetron sputtering from a ceramic Li1.18(Ni0.39Mn0.19Co0.35)O1.97 target at various argon working gas pressures between 0.2 Pa and 20 Pa. A comprehensive study on the composition and microstructure was carried out. The results showed that the elemental composition varies depending on argon working gas pressure. The elemental composition was determined by inductively coupled plasma optical emission spectroscopy in combination with carrier gas hot extraction. The films showed different grain orientations depending argon working gas pressures. The degree of cation order in the lattice structure of the films deposited at 0.5 Pa and 7 Pa argon working gas pressure, was increased by annealing in an argon/oxygen atmosphere at different pressures for one hour. The microstructure of the films varies with annealing gas pressure and is characterized using X-ray diffraction and unpolarized micro-Raman spectroscopy at room temperature. Electrochemical characterization of as-deposited and annealed films was carried out by galvanostatic cycling in Li–Ni–Mn–Co–O half-cells against metallic lithium. Correlations between process parameters, constitution, microstructure and electrochemical behaviour are discussed in detail.