Influence of substrate surface roughness on microstructural and electrical properties of Lithium-rich Li-Ni-Mn-Co-O thin film cathodes

To improve the electrochemical properties of Li(Nn(1/3)Mn(1/3)Co(1/3))O-2 (NMC) like Lithium-diffusion rate or rate capability one way is to increase the surface between the cathode and electrolyte. By sputter etching of stainless steel substrates the surface topography is varied. Lithium-rich Li-Ni-Mn-Co-O thin film cathodes are deposited onto these modified stainless steel substrates by non-reactive r.f. magnetron sputtering from a ceramic Li-1.14(Ni0.37Mn0.18Co0.32)O-1.19 target. Microstructure and electrical properties were characterized by X-ray diffraction (GIXRD), Raman spectroscopy, Atomic-force microscopy (AFM) and impedance spectroscopy (IS). The substrate roughness was increased from R-a = 4 nm to R-a = 63 nm after 180 min of sputter etching. The crystal orientation wasn't influenced significant by the pre deposition surface topography modification. The results show that the activation energy E-A of the conductivity mechanism is 0.23 eV, independent of the pre-deposition sputter etching treatment. Also the pre deposition sputter etching increases the conductivity from 1.49.10(-11) Scm(-1) to 1.75.10(-10) Scm(-1) at 20 degrees C. Correlations between process parameters, microstructure and electrical behaviour are discussed in detail. (C) 2016 Elsevier Ltd. All rights reserved.