Alginate/r-GO assisted synthesis of ultrathin LiFePO4 nanosheets with oriented (0 1 0) facet and ultralow antisite defect

Abstract

Li4Ti5O12/LiFePO4 (LTO/LFP) is a promising lithium ion batteries (LIBs) configuration due to its high safety and circularity. However, three factors result in the low capacity at high current density and low energy density in LTO/LFP: (i) low intrinsic electronic and ionic conductivities; (ii) long one-dimensional (1D) pathway along the [0 1 0] channel; (iii) Fe-Li antisite defect in LFP. It is still a great challenge to address the three problems simultaneously in LTO/LFP cell. Herein, we synthesized LFP ultrathin nanosheets (∼5–10 nm) with oriented (0 1 0) facet and ultralow Fe-Li antisite defects with the assistance of alginate and 2D reduced graphene oxide (LFP NS/r-GO). The novel “egg-box” structure in alginate is the key to restrain the Fe-Li antisites. The sandwich structure, which is formed by long range Van der Waals forces and hydrogen bond between the Li-Fe-P-alginate molecules and 2D r-GO nanosheets, results in the formation of ultrathin LFP NSs with oriented (0 1 0) facet. The density functional theory (DFT) calculations reveal that the tacking of LFP ultrathin NS with oriented (0 1 0) facet on the r-GO has a strong ability of Li+ ion deintercalation. When evaluating LFP NS/r-GO as cathode materials for LIBs, the sample displays outstanding rate capacity of 98.6 mA h g−1 at 100 C and its full cell with LTO anode achieves remarkable specific energy (265 W h kg−1) and power density (6.81 kW kg−1).