Comparative study of LiMnPO4/C cathodes synthesized by polyol and solid-state reaction methods for Li-ion batteries

A systematic comparison of LMP prepared by solid-state reaction (SSR) and polyol methods was carried out through detailed analyses that included: X-ray and neutron powder diffractions, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical characterization. The LMP synthesized by the two different methods had a similar amount of Li/Mn cation mixing, ca. 4–5%. The polyol method provided a flower-like morphology to the LMP particles, in the form of platelet of which growth direction is parallel to the bc-plane. The LMP prepared by the polyol method was further optimized by carbon composite using two different kinds of carbon sources: Shawinigan acetylene black (AB) and Super-P Li carbon black (SP). With the smallest crystallite size and a homogeneous carbon particle network, the LMP processed with SP delivered better cathode performance than both the AB – mixed LMP and that prepared by the SSR method. AC-impedance spectroscopy of the LMP composite with SP showed an abrupt increase in impedance after 50% delithiation. Because of this difficulty of charging, the capacity of the LMP composite with SP was strongly influenced by the upper cut-off voltage used.

► Effect of synthetic methods on LMP was investigated. ► LMP had 4–5% cation mixing from powder neutron diffraction data. ► TEM analysis showed that polyol method grows LMP platelets parallel to bc-plane. ► Polyol method with super-P composite offered the best performances. ► Capacity of LMP was strongly influenced by upper cut-off voltage used.