Mg–Ti co-doping behavior of porous LiFePO4 microspheres for high-rate lithium-ion batteries

Abstract

The development of fast-charging lithium-ion batteries (LIBs) is an urgent necessity. Nevertheless, it is still a huge challenge to prepare superior high-rate cathode materials for LIBs. In this work, porous Mg–Ti co-doped LiFe_0.985Mg_0.005Ti_0.01PO₄ microspheres are successfully synthesized via a carbothermic reduction reaction in combination with a spray drying process, with FePO₄ as the Fe and P source. Through X-ray diffraction (XRD) combined with X-ray photoelectron spectroscopy (XPS) Ar⁺-sputtering technology, it confirms that Mg and Ti are in the form of doping rather than surface recombination inside LiFePO₄ microspheres, and the existence of Fe³⁺ inside the samples is confirmed as residual FePO₄. Compared to the undoped sample, the porous Mg–Ti co-doped LiFePO₄ microspheres show great improvement in electronic conductivity (1.58 × 10⁻³ S cm⁻¹) and diffusion coefficient (5.97 × 10⁻⁹ cm s⁻¹ for charging and 4.30 × 10⁻⁹ cm s⁻¹ for discharging). More importantly, the porous Mg–Ti co-doped LiFe_0.985Mg_0.005Ti_0.01PO₄ microspheres show excellent high-rate capabilities, delivering a discharge capacity of 161.5, 160.3, 156.7, 147.5, 139.8 and 131.5 mA h g⁻¹ at 0.2C, 0.5C, 1C, 3C, 5C and 8C, respectively.