Optimization of thin-film Li1.0Ni0.6Co0.2Mn0.2O2 cathodes enabled by rapid thermal processing in oxygen-rich environments for superior lithium-ion battery performance†

Abstract

With the advancement of small electronic devices, thin-film lithium-ion batteries (TF-LiBs) are garnering attention due to their potential for high integration and superior energy density per unit weight and volume compared to conventional LiBs. Research is being actively pursued on cathode materials, which critically influence TF-LiB performance. Lithium nickel cobalt manganese oxide (LiNi_xCo_yMn_zO₂ (NCM), where x + y + z = 1) is a promising high-energy-density TF cathode material, but its application is hindered by its structural instability during the high-temperature annealing required for improved crystallinity. This study investigates the fabrication and optimization of TF Li_1.0Ni_0.6Co_0.2Mn_0.2O₂ (TF-Li_1.0NCM622), deposited via radio frequency (RF) magnetron sputtering and annealed using rapid thermal annealing at 600 °C in an oxygen (O₂) atmosphere (600(O₂)_NCM). Rigorous characterization revealed that O₂-rich annealing mitigates critical issues such as platinum hillock and side product formation while promoting the crystallinity of the nickel (Ni)-rich TF cathode, enabling favorable lithiation and delithiation. The optimized 600(O₂)_NCM exhibited an initial capacity of 646.8 mAh cm⁻³ at 0.1C and significantly enhanced cycling stability, with capacity retention improving from 38% to 81% after 100 cycles at 1C. This work offers critical insights into the post-treatment of TF-NCM cathodes for miniaturized LiBs.