Effect of radio frequency power and thickness on the electrochemical properties of Li_2−x MnO_3−y thin films

In the present work, Li_2−xMnO_3−y (LMO) thin films have been deposited by radio frequency (RF) reactive magnetron sputtering using acid-treated Li₂MnO₃ powder target. Systematic investigations have been carried out to study the effect of RF power on the physicochemical properties of LMO thin films deposited on platinized silicon substrates. X-ray diffraction, electron microscopy, surface chemical analysis and electrochemical studies were carried out for the LMO films after post deposition annealing treatment at 500 °C for 1 h in air ambience. Galvanostatic charge discharge studies carried out using the LMO thin film electrodes, delivered a highest discharge capacity of 139 μAh μm⁻¹ cm⁻² in the potential window 2.0–3.5 V vs. Li/Li⁺ at 100 W RF power and lowest discharge capacity of 80 μAh μm⁻¹ cm⁻² at 75 W RF power. Thereafter, the physicochemical properties of LMO films deposited using optimized RF power 100 W on stainless steel substrates has been studied in the thickness range of 70 to 300 nm as a case study. From the galvanostatic charge discharge experiments, a stable discharge capacity of 68 μAh μm⁻¹ cm⁻² was achieved in the potential window 2.0–4.2 V vs. Li/Li⁺ tested up to 30 cycles. As the thickness increased, the specific discharge capacity started reducing with higher magnitude of capacity fading.