Temperature-Controlled Synthesis of High-Voltage Spinel LiNi_0.5Mn_1.5O₄ Films via Metal-Organic Decomposition:...

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cobalt-free cathode material for lithium-ion batteries, yet its integration as a binder-free thin film on metallic current collectors via simple solution routes remains underexplored. Here, LNMO films were synthesized on 304 stainless steel (SS304) by metal-organic decomposition (MOD) from metal-acetate precursors in ethanol, followed by spin-coating and annealing at 500, 600, and 700 °C under flowing O2. The films were characterized by XRD, FESEM-FIB cross-sectioning, EDS, and XPS, and tested as binder-free cathodes by cyclic voltammetry and galvanostatic charge/discharge. All samples are dense, approximately 1.9 μm thick, and crystallize in the disordered spinel phase. The LNMO crystallite size increases from 21.9 to 43.8 nm between 500 and 700 °C, while the grain size also shows a temperature dependence, increasing the average size from 25 up to 56 nm in diameter. XPS confirms Mn4+ as the dominant manganese surface species (45-49%) across all samples. The films deliver reversible discharge capacities of 92, 92, and 70 mAh g-1 at 0.1 C for LNMO500, LNMO600, and LNMO700, respectively, with well-defined Ni2+/Ni3+ and Ni3+/Ni4+ redox peaks at 4.7 and 4.8 V. DFT calculations independently predict a voltage plateau at ∼4.7 V for 0.2≤x≤1, in agreement with the experimental profiles. These findings establish MOD as a viable, vacuum-free route to the synthesis of nanostructured LNMO cathodes.