Microwave-assisted hydrometallurgical extraction of LiTiO and LiFePO from ilmenite: effect of PPy-Br derived C-coating with N, Br, and Nb Co-doping on electrodes for high-rate energy storage performance.

Microwave-driven hydrometallurgical (MW-HM) method has been adopted to extract spinel-type Li4Ti5O12 (LTO) and orthorhombic-type LiFePO4 (LFP) from naturally occurring Ilmenite (FeTiO3) within 2 h unlike the conventional process that requires >30 h. We have successfully demonstrated aliovalent-Nb5+ doping and carbon coating with N, Br co-doping upon the pyrolysis of a polypyrrole-(PPy)-Br2 charge-transfer-(CT)-complex via MW-hydrothermal and MW-solid state heating within 30 min. Further, we also investigated the effect of carbon coating and co-doping of LTO and LFP electrodes at high C-rate performance of the lithium battery. XRD, XPS, FTIR, and Raman spectroscopy results confirmed the co-existence of dual-phase Li4Ti5O12/rutile-TiO2 (LTO-RTO) with substitution-induced transition of Ti4+ → Ti3+ in spinel-LTO due to Nb5+ and N, Br co-doping, which facilitates fast Li+ ion and electron transfer at the electrode-electrolyte interface. Conversely, in situ Nb5+ doped LiFePO4 combined with ex situ carbon-coating with N, Br co-doping improved the overall electronic conductive behavior. The UV-Visible absorption spectra and Tauc plots further support the decrease in the band gap upon co-doping, thus promoting n-type electronic behavior of the electrodes. A significant enhancement in the discharge-capacities of the carbon-coated N, Br co-doped Li4Ti4.97 Nb0.03O12/rutile-TiO2 (NBC-LTNO-RTO) and pristine anode in the range of 174-148 mA h g-1 and 167-125 mA h g-1 was exhibited at different rates in the range of 0.2 C-20 C with 97% and 94% capacity retention, respectively. Instead, the carbon-coated N, Br co-doped LiFe0.99 Nb0.01PO4 (NBC-LFNP) and pristine cathode exhibited discharge capacities in the range of 169-73 mA h g-1 and 136-65 mA h g-1 at different rates in the range of 0.2 C-20 C with 92% and 40% capacity retention for 500 cycles, respectively. Hence, this innovative, rapid, and sustainable chemical process for the fabrication of the modified cathode and anode from the earth abundant ilmenite ore as the single source with high-rate capability and ultra-stability can be used for high-power and safer lithium-ion energy storage.