Abstract
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) (NiCp2) 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 NiCp2 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 NiCp2 and oxygen plasma at 300 °C using optimal ALD condition consisted mainly of stoichiometric polycrystalline NiO with high density (6.6 g/cm3) 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)).
Highlights
In recent years, a large number of studies have been actively conducted to study the possibility of using nickel oxide (NiO) nanofilms as electrocatalysts for water decomposition [1], chemical sensors [2], active components of solar cells [3], and antiferromagnetic layers [4]
The necessary condition for correct Atomic layer deposition (ALD) is the use of an excess of reagent vapors to saturate the surface during chemical reactions
This excess can be achieved by increasing the vapor pressure by heating the evaporator or/and by increasing the pulse time
Summary
A large number of studies have been actively conducted to study the possibility of using nickel oxide (NiO) nanofilms as electrocatalysts for water decomposition [1], chemical sensors [2], active components of solar cells [3], and antiferromagnetic layers [4]. The value of the theoretical electrochemical capacity for NiO (718 mAh/g [6]) is close to the values for several other promising anode materials, such as SnO2 (790 mAh/g) [7], CoO (715 mAh/g) [8], and MnO (650 mAh/g) [8]. The capacity of these oxide materials is more than twice the capacity of graphite (372 mAh/g) used in the industry of lithium-ion batteries [9]. The stability of NiO nanofilms during charge/discharge cycling at high current densities [10] allows us to consider NiO as promising material for creating negative electrodes of portable energy sources of biosensors, microchips, pacemakers, and other devices. [11].
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