Lanthanum and cerium Co-doped LiFePO4: Morphology, electrochemical performance and kinetic study from −30 - +50 °C

Abstract This paper reports morphology controlled lanthanum and cerium Co-doped LiFePO4@C nanocomposites varying from nanograin, nanorod to nanoflake prepared with a hydrothermal method. Lanthanum and Cerium co-doping can not only downsize particles, enlarge the interplanar spacing d(020), benefit for more (020) exposure, but also transforms the carrier types of nanocomposites from p-type to n-type (La and Ce codoping > 0.1%), contributing to dramatically increase of carrier density and conductivity by a factor of ∼1010 and ∼105, respectively. As a result, the as-prepared LC-LFP@C-5 delivers a capacity up to 112.2 mAh g−1 at 50 C. Even after 500 cycles, it enables a discharge capacity of 101.1 mAh g−1 at ultrahigh current densities of 100 C. Simulation indicates that Lanthanum and Cerium co-doping facilitates electrolyte to penetrate into the active materials, boosts Li+ de-intercalation rate and equalizes Li+ concentration in the electrode. What is more, the kinetic study of impedance and Li+ diffusion from −30 °C - +50 °C at 2.5V–4.3V indicate that lithium ion diffusion process in the electrode is the rate-determining step compared with charge transfer process, which are also confirmed by the higher apparent activation energy compared with that of Arrhenius activation for charge transfer process.