In situ polyaniline modified cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 with high rate capacity for lithium ion batteries

Abstract

Lithium-rich layered Li[Li_0.2Mn_0.54Ni_0.13Co_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[Li_0.2Mn_0.54Ni_0.13Co_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[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ particles by protecting the electrodes from external erosion during continuous charge–discharge cycles. PANI-coated Li[Li_0.2Mn_0.54Ni_0.13Co_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[Li_0.2Mn_0.54Ni_0.13Co_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_0.2Mn_0.54Ni_0.13Co_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.