Three-dimensional macroporous graphene-Li₂FeSiO₄ composite as cathode material for lithium-ion batteries with superior electrochemical performances.

Abstract

Three-dimensional macroporous graphene-based Li2FeSiO4 composites (3D-G/Li2FeSiO4/C) were synthesized and tested as the cathode materials for lithium-ion batteries. To demonstrate the superiority of this structure, the composite's performances were compared with the performances of two-dimensional graphene nanosheets-based Li2FeSiO4 composites (2D-G/Li2FeSiO4/C) and Li2FeSiO4 composites without graphene (Li2FeSiO4/C). Due to the existence of electronic conductive graphene, both 3D-G/Li2FeSiO4/C and 2D-G/Li2FeSiO4/C showed much improved electrochemical performances than the Li2FeSiO4/C composite. When compared with the 2D-G/Li2FeSiO4/C composite, 3D-G/Li2FeSiO4/C exhibited even better performances, with the discharge capacities reaching 313, 255, 215, 180, 150, and 108 mAh g(-1) at the charge-discharge rates of 0.1 C, 1 C, 2 C, 5 C, 10 C and 20 C (1 C = 166 mA g(-1)), respectively. The 3D-G/Li2FeSiO4/C composite also showed excellent cyclability, with capacity retention exceeding 90% after cycling for 100 times at the charge-discharge rate of 1 C. The superior electrochemical properties of the 3D-G/Li2FeSiO4/C composite are attributed to its unique structure. Compared with 2D graphene nanosheets, which tend to assemble into macroscopic paper-like structures, 3D macroporous graphene can not only provide higher accessible surface area for the Li2FeSiO4 nanoparticles in the composite but also allow the electrolyte ions to diffuse inside and through the 3D network of the cathode material. Specially, the fabrication method described in this study is general and thus should be readily applicable to the other energy storage and conversion applications in which efficient ionic and electronic transport is critical.