In situ polyaniline modified cathode material Li [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 with high rate capacity for lithium ion batteries

摘要

Lithium-rich layered [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 is prepared by a fast co-precipitation method and surface modified with conducting polyaniline (PANI, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt% theoretically) via in situ chemical oxidation polymerization to optimize the electrochemical properties. The uniform PANI layer with a thickness of 5 nm (10 wt%) has been successfully coated on the surface of [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 particles, as observed by field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). The X-ray powder diffraction (XRD) results show that all the prepared samples have a typical layered hexagonal α-NaFeO2 structure. The PANI layer maintains the integrity of the surface material crystal structure of the [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 particles by protecting the electrodes from external erosion during continuous charge-discharge cycles. PANI-coated [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 electrodes present excellent electrochemical properties at room temperature. The initial discharge capacity is 313.5 mA h g~(-1) (0.05 C) with a coulombic efficiency of 89.01% (PANI, 10 wt%), compared with 291.9 mA h g~(-1) (0.05 C) for the pristine [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 with a coulombic efficiency of 81.31% in the potential range 2.0-4.8 V (vs. Li/Li~+). The discharge capacity is retained at 282.1 mA h g~(-1) after 80 cycles at 0.1 C. Moreover, the PANI-coated Li [Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O2 exhibits an excellent high rate capacity of 198.6 mA h g~(-1) at 10 C. The electrochemical impedance spectra (EIS) measurements reveal that the thin PANI coating layer significantly optimizes the interfacial electrochemical reaction activity by reducing the charge transfer resistance. Moreover, the special H~+/Li~+ exchange reaction during the proton acid doping procedure also promotes the improvement of the electrochemical performance.