Very high power and superior rate capability LiFePO4 nanorods hydrothermally synthesized using tetraglycol as surfactant

Abstract

Small polarizations, i.e. sufficiently good electronic and ionic conductivity is indispensible for high power lithium iron phosphate, especially for its applications to large current power supplies. Here, carbon coated LiFePO₄/C nanorods that were hydrothermally synthesized using tetraglycol as surfactant followed by calcination exhibit very small polarizations (13.0 mV at 0.1 C, 1 C = 170 mA g⁻¹), high power densities (96.5 and 95.4 kW kg⁻¹ at 200 C at RT and 60 °C, respectively), and excellent cycling performance at high rates (92% discharge capacity retention at 100 C after 200 cycles) with only 10 wt% conductive additive. Intermixing between Fe and Li is detected in the as-synthesized, annealed and carbon coated samples. The superior rate capabilities (270.0 W h kg⁻¹ and 43.0 kW kg⁻¹ at 85 C at RT, 310 W h kg⁻¹ and 49.8 kW kg⁻¹ at 96 C at 60 °C) and small polarizations are attributed to the nanoscale size along the [010] plane, the uniform carbon coating and the partial occupation of Li at the Fe sites. The recipe in this study is quite simple, controllable, energy saving and readily up-scalable. The availability of very high power LiFePO₄ with excellent cycling capability at high rates will undoubtedly greatly promote its applications to large current power supplies such as electric and hybrid electric vehicles.