Atomic layer deposition of nio to produce active material for thin-film lithium-ion batteries

Atomic layer deposition (ALD) provides a promising route for depositing uniform thin-film electrodes for Li-ion batteries. In this work, bis(methylcyclopentadienyl) nickel(II) (Ni(MeCp) ₂ ) and bis(cyclopentadienyl) nickel(II) (NiCp ₂ ) were used as precursors for NiO ALD. Oxygen plasma was used as a counter-reactant. The films were studied by spectroscopic ellipsometry, scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray reflectometry, and X-ray photoelectron spectroscopy. The results show that the optimal temperature for the deposition for NiCp ₂ was 200-300 °C, but the optimal Ni(MeCp) ₂ growth per ALD cycle was 0.011-0.012 nm for both precursors at 250-300 °C. The films deposited using NiCp ₂ and oxygen plasma at 300 °C using optimal ALD condition consisted mainly of stoichiometric polycrystalline NiO with high density (6.6 g/cm ³ ) and low roughness (0.34 nm). However, the films contain carbon impurities. The NiO films (thickness 28-30 nm) deposited on stainless steel showed a specific capacity above 1300 mAh/g, which is significantly more than the theoretical capacity of bulk NiO (718 mAh/g) because it includes the capacity of the NiO film and the pseudo-capacity of the gel-like solid electrolyte interface film. The presence of pseudo-capacity and its increase during cycling is discussed based on a detailed analysis of cyclic voltammograms and charge-discharge curves (U(C)).