A Polyaniline-coated Li-rich Oxide Cathode for Li-ion Batteries

Lithium-rich transition metal oxide (LMO) is one of the most potential candidates for next generation lithium ion batteries cathode for its high capacity and high voltage. However, poor cycling ability, which arisen from unstable structure and Mn dissolution, has been hindering practical applications of this material. Polyaniline (PANi), as a conductive polymer, is coated on the surface of oxide in order to prevent dissolution and improve the conductivity of the material. Oxidative polymerization has been employed in this coating process, using manganese ions (Mn4+) in the pristine oxide as oxidants. In this research, reaction time was examined as a parameter. A close observation under TEM reveals that, as the reaction proceeds, the surface of particles become rough, implying that some parts of particles are dissolved in the acidic environment during reaction. A coating layer of PANi is formed on the surface of particle, with a thickness of about 5nm (Fig. 1a). Electrochemical tests indicate that the material is able to deliver a higher capacity after 30 minutes of coating, despite that lithium concentration is reduced. This sample retains 85% of its original capacity after 200 cycles (Fig. 1b), implying that the stability of the electrode is improved with proper PANi coating. Charge-discharge tests under different current density also suggest that the PANi layer facilitates the diffusion of lithium ions during electrochemical reaction.