High-Energy-Density LiNi_0.8Co_0.15Al_0.05O₂ and Dual-Phase LTO-R-TiO₂ Materials via a Microwave-Assisted Reaction: Alleviating the Capacity Fading Mechanism by Nanocoating of Al₂O₃ and PEDOT

Here, we report the improved energy storage performance of lithium-ion batteries consisting of a hexagonal-layered LiNi0.8Co0.15Al0.05O2 (LNCA) cathode and a spinel-type Li4Ti5O12-Rutile-TiO2 (LTO-R-TiO2) dual-phase anode upon nanocoating of Al2O3 and electronically conducting poly(3,4-ethylenedioxythiophene) (PEDOT). LNCA and LTO-R-TiO2 were prepared by rapid microwave-assisted hydrothermal (MW-HT) and solid-state (MW-SS) techniques within 10–30 min compared to conventional techniques that require >35 h. The crystal structure, lattice parameters, and microstrain (ε) of the electrode materials induced by microwave irradiation (MW-HT and MW-SS) were determined using the Williamson–Hall equation deduced from X-ray diffraction. The Raman and Fourier transform infrared spectroscopy studies delineated the existence of PEDOT and dual phases of LTO-R-TiO2. Field emission-scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy analyses revealed homogeneous distribution of transition-metal ions along with the polymer and Al2O3 over the electrode surface. The UV–visible and DRS spectroscopies unveiled the reduction in band-gap energies (Eg) of LTO-R-TiO2 after PEDOT coating. Indeed, the LNCA-Al2O3/PEDOT hybrid cathode exhibited an enhanced discharge capacity of 209 mAh g–1 with a Coulombic efficiency of 98% compared to the uncoated pristine cathode with a discharge capacity of 194 mAh g–1 with a Coulombic efficiency of 91%. On the other hand, the optimized LTO-R-TiO2/PEDOT hybrid anodes exhibited a reversible capacity of 174 mAh g–1 at 0.2 C compared to the pristine anode with a reversible capacity of 169 mAh g–1 at 0.2 C vs Li/Li+ in the half-cell configuration. Besides, the LNCA-Al2O3/PEDOT||LTO-R-TiO2/PEDOT full cells delivered an energy density of 156.2 Wh kg–1 with excellent cyclability over 200 cycles at 1 C with a capacity retention of 90%. The FE-SEM image illustrated the absence of structural/mechanical damage in LNCA-Al2O3/PEDOT and LTO-R-TiO2/PEDOT electrodes after 200 cycles in the full-cell configuration. Hence, amorphous phases of the PEDOT matrix and Al2O3-coating layers tend to promote the electrical conductivity and reaction kinetics of both electrodes. Therefore, this work provides an energy-efficient and cost-effective synthesis approach driven by microwave irradiation for the development of high-energy-density lithium-ion batteries.