Role of the precursor chemistry on the phase composition and electrochemical performance of thin-film LiMn2O4 Li-ion battery cathodes prepared by spray pyrolysis

LiMn2O4-films were prepared by air-blast spray pyrolysis directly onto stainless steel foil substrate. The films were synthesized from various precursor solutions of dissolved nitrates and acetates with and without the addition of polyethylene glycol (PEG). Hereby X-ray diffraction experiments revealed that the phase compositions of the as-prepared and thermally post-treated films were highly dependent on the precursors used, but independent of the addition of PEG. Samples prepared from nitrates yielded phase mixtures of α-Mn2O3, Mn3O4 and LiNO3 as-prepared and LiMn2O4 and α-Mn2O3 after post-thermal treatment. Whereas films sprayed from acetate precursors consisted of LiMn2O4 predominantly before and after heat treatment, as well. Scanning electron microscopy investigations showed that the applied precursor had an effect on the film morphology and the addition of PEG led to film thinning. Galvanostatic cycling tests and post-mortem analyses of the electrochemical cells fabricated from the thermally treated thin layers revealed that the film prepared from acetates and PEG had the highest capacity retention despite the formation of orthorhombic LiMnO2 besides the cubic LiMn2O4 during battery cycling.