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

Abstract To improve the electrochemical properties of Li(Ni 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 (Ni 0.37 Mn 0.18 Co 0.32 )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 °C. Correlations between process parameters, microstructure and electrical behaviour are discussed in detail.