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)).NiO nanofilms are produced using various methods [12] such as thermal spraying, pulsed laser deposition, sol-gel, spin-coating, dip-coating, chemical vapor deposition, and atomic layer deposition (ALD). ALD is the most promising technology because it provides control over the thickness and purity of coatings with high precision, and can deposit uniform surface coatings on of complex shape and even porous and high aspect ratio substrates [13][14][15]. This method could be a crucial factor for transition from 2D to 3D solid-state batteries (SSB), which are structured on 3D substrates with high aspect ratio instead of planar substrates. It could increase the energy density of SSB with the same thickness of the electrode to maintain the required conductivity of the layers [16]. ALD is based on a realization of the sequence of chemical reactions between gaseous reagents and the surface species of the substrate, separated in time by purges with an inert gas to prevent uncontrolled reactions between the reactants and the reaction products. Because of the self-limiting nature, this method allows the deposition of films in a layer-by-layer fashion and the control of the thickness with high precision [13].When selecting the deposition conditions via ALD, it is necessary to consider the stability and reactivity of the precursors. Many precursors have been tested for ALD NiO so far, but the most frequently used are shown in Table 1: nickel(II) acetylacetonate (Ni(acac) 2 ), bis(2,2,6,6-tetramethylheptane-3,5dionate)nickel(II) (Ni(thd) 2 ), bis(cyclopentadienyl) nickel(II) (NiCp 2 ), and NiCp 2 -based compounds such as ...
