▎ 摘　　要

LiFePO4@C/G composite is successfully prepared by a simple spray drying and subsequent high temperature calcination reaction. Two different ferric sources, ferric nitrate and ferric citrate, are first used together in order to conveniently tune the pH of spray solution and carbon content of LiFePO4@C/G product. As-prepared LiFePO4@C/G is pure phase and has an orthorhombic olivine-type structure. SEM and TEM reveal that the LiFePO4@C/G composite is composed of regularly spherical secondary aggregations with particle size of several micrometers. In the secondary aggregation, LiFePO4 nano-crystallites are homogeneously and thoroughly coated by carbon layer and nano-LiFePO4@C is interconnected by homogeneously dispersed graphene sheets. The LiFePO4@C/G composite delivers a high reversible capacity, superior cycling stability and excellent rate capability. The first discharge capacity of LiFePO4@C/G composite is 167.6 (near to the theoretical capacity of LiFePO4: 170 mAh g(-1)), 147.3, and 118.3 mAh g(-1) at 0.1 C, 1 C, and 10 C, respectively. And at 0.1, 1, and 10 C, the discharge capacity retention is 100, 99, and 96.7% after 50, 150, and 200 cycles, respectively. Through in situ electrochemical delithiation and sodiation, NaFePO4@C/G has been first obtained; as-prepared NaFePO4@C/G displays a high reversible capacity and good cycling stability. At 0.1 C, the second discharge capacity of NaFePO4@C/G is 138.8 mAh g(-1) and the discharge capacity still keeps 133.2 mAh g(-1) at 51th cycle.