Effect of Electrolyte Concentration on the Electrochemical Performance of Spray Deposited LiFePO₄

LiFePO₄ is a common electrode cathode material that still needs some improvements regarding its electronic conductivity and the synthesis process in order to be easily scalable. In this work, a simple, multiple-pass deposition technique was utilized in which the spray-gun was moved across the substrate creating a "wet film", in which-after thermal annealing at very mild temperatures (i.e., 65 °C)-a LiFePO₄ cathode was formed on graphite. The growth of the LiFePO₄ layer was confirmed via X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The layer was thick, consisting of agglomerated non-uniform flake-like particles with an average diameter of 1.5 to 3 μm. The cathode was tested in different LiOH concentrations of 0.5 M, 1 M, and 2 M, indicating an quasi-rectangular and nearly symmetric shape ascribed to non-faradaic charging processes, with the highest ion transfer for 2 M LiOH (i.e., 6.2 × 10^-9 cm²/cm). Nevertheless, the 1 M aqueous LiOH electrolyte presented both satisfactory ion storage and stability. In particular, the diffusion coefficient was estimated to be 5.46 × 10^-9 cm²/s, with 12 mAh/g and a 99% capacity retention rate after 100 cycles.