Effect of annealing on the morphology evolution and densification of LiMn2O4 film from chitosan-containing solution

Dense LiMn2O4 films deposited on a Pt-coated silicon substrate were obtained by annealing the deposited Li–Mn–O-chitosan films under a two-stage heat-treatment procedure. It was demonstrated that the heat-treatment at 300 °C plays an important role in the subsequent densification of LiMn2O4 films. This is attributed to the formation and rearrangement of the nano-sized LiMn2O4 crystallites. The surface morphology of the calcined Li–Mn–O-chitosan films was highly related to the annealing temperature. Ridge-like bumps formed on the surface of the films after being heated at 200 °C for 1 h. With calcination at 400 °C or higher, the surface morphology turned into a wrinkle-like microstructure. This morphology transformation is ascribed to the flowing characteristics of the Li–Mn–O-chitosan films during heat-treatment and subsequent thermal decomposition of the precursor at higher temperatures. Moreover, the electrochemical tests showed that the 700 °C-annealed LiMn2O4 film possesses the highest discharge capacity of 56.3 μA h/(cm2 μm) and best capacity retention of 90.7% after 50 charge/discharge cycles of all annealed films.