▎ 摘　　要

In this study we synthesized LiFePO4/carbon/reduced graphene oxide (LFP/C/rGO) composite cathode materials using a method involving sol-gel processing, spray-drying, and calcination. To improve the electrochemical performance of LFP/C, we tested graphene oxides (GOs) of various morphologies as conductive additives, including pristine GO, three-dimensional GO, and hydrothermal porous GO (HTGO). Among our samples, the cathode material prepared through spray-drying with the addition of 1 wt% of HTGO (denoted SP-LFP/C/1%rHTGO) displayed the best electrochemical performance; its discharge capacities at 0.1C, 1C, 5C, and 10C were 160.5, 151.8, 138.8, and 130.3 mA h g(-1), respectively. From measurements of its long-term cycling performance, the discharge capacity in the first cycle and the capacity retention after 30 cycles at 0.1C were 160.2 mA h g(-1) and 99.6%, respectively; at 10C, these values were 132.2 mA h g(-1) and 91.8%, respectively. The electronic conductivity of SP-LFP/C/1%rHTGO (6.58 x 10(-5) S cm(-1)) was higher than that of the pristine LFP/C (9.24 x 10(-6) S cm(-1)). The Li+ ion diffusivities (D-Li(+)) of the SP-LFP/C/1%HTGO cathode, measured using AC impedance (3.91 x 10(-13) cm(2) s(-1)) and cyclic voltammetry (6.66 x 10(-10) cm(2) s(-1) for discharge), were superior to those of the LFP/C cathode (9.31 x 10(-15) cm(2) s(-1) and 1.79 x 10(-10) cm(2) s(-1) for discharge, respectively). Galvanostatic intermittent titration revealed that the value of D-Li(+) was located in a reasonable range from 1 x 10(-10) to 1 x 10(-17) cm(2) s(-1); its value dropped to its lowest point when the state of charge was close to 50%. Thus, the use of spray-drying and the addition of conductive HTGO (having a 3D wrinkled morphology and interconnected pore structure) can enhance the electronic conductivity and Li+ ion diffusivity of LFP/C cathode materials, thereby improving the electrochemical performance significantly. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.