Rational design of high performance lithium iron phosphate positive electrodes with conducting polymer for lithium-ion batteries

Abstract

LiFePO4 has been pointed out as a next-generation active material for lithium-ion (Li-ion) batteries and its performance has been progressively improved mostly by optimizing the synthesis conditions of this cathode material in order to obtain carbon‑coated nano-particles of controlled purity. Nevertheless, there is still the need for improving the composition and the preparation methods of LiFePO4-based electrodes, which is paramount for maximizing the capacity at high charge/discharge rates. In this regard, this thesis was focused on the improvement of the charge transport throughout the different electrode interphases in order to increase the conductivity and to enable higher energy and power output as compared to conventional electrode formulations. The general strategy followed in this thesis consisted in forming composite electrodes of LiFePO4 with intrinsically conducting polymers of the type poly(3,4‑alkylenedioxythiophene) [PXDOT] by electrochemical polymerization, by blending and by coating methods. Although composite battery electrodes with conducting polymers have been described previously,[1] this thesis presents effective means for obtaining composite electrodes by the electrochemical polymerization of monomers directly over LiFePO4-based electrodes, or by combining the cathode material with ready available conducting polymer.