High throughput screening of the effect of carbon coating in LiFePO4 electrodes

Two high throughput methods are described for the synthesis of graded composition electrode arrays of carbon-coated LiFePO4 by anaerobic pyrolysis of solution precursors at 700 C in the presence of sucrose as a carbon-coating additive. In the first method, direct in situ calcination, the array was prepared directly on the current collectors by a one-step heat-treatment of the solutions. In the second method, post-synthesis array transfer (PoSAT) , the samples were first pyrolyzed in an array of individual microtubes, before mixing with solvent, binder solution, and carbon black then depositing onto the current collector array. High throughput X-ray diffraction clearly showed impurity phases for samples containing 0.10 mol sucrose per mol iron (III) nitrate or less, but mainly olivine phase for sucrose contents above 0.18 mol. Superior results from the PoSAT method showed up to 80% theoretical capacity appearing sharply at the point where the sucrose produced a carbon coating and the characteristic decay in capacity with excess carbon. The PoSAT method is not restricted to LiFePO4 and is recommended as a useful method for high throughput screening of positive electrode materials. (c) 2007 The Electrochemical Society.