Judicious design of lithium iron phosphate electrodes using poly(3,4-ethylenedioxythiophene) for high performance batteries

Abstract

LiFePO₄ electrodes were built in different architectures using a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) mixed conductor as an additive. Conductivity enhancement of PEDOT:PSS was achieved by the addition of ethylene glycol and dimethyl sulfoxide solvents. The amounts of conducting polymer and solvent additives strongly influence the discharge capacity and potential of LiFePO₄ electrodes at high rates. The initial impedance and the direct current resistance were correlated with the discharge performance at high rates. The optimized amount of PEDOT:PSS added within the bulk resulted in a lower value of impedance, lower load resistance and higher capacity as compared to the standard preparation. Furthermore ⁵⁷Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy were employed to probe the bulk transformation of the LiFePO₄ active material and the surface changes of the composite electrodes with the conducting polymer upon lithiation. The electrode with PEDOT:PSS coated on the aluminium current collector and doped with ethylene glycol showed highly competitive performance (132 mA h g⁻¹ at 5 C and 145 mA h g⁻¹ at 2 C for 50 cycles).