Three-Dimensional
Macroporous Graphene–Li<sub>2</sub>FeSiO<sub>4</sub> Composite
as Cathode Material for Lithium-Ion
Batteries with Superior Electrochemical Performances
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Abstract
Three-dimensional macroporous graphene-based
Li<sub>2</sub>FeSiO<sub>4</sub> composites (3D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/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 Li<sub>2</sub>FeSiO<sub>4</sub> composites
(2D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/C) and Li<sub>2</sub>FeSiO<sub>4</sub> composites without graphene (Li<sub>2</sub>FeSiO<sub>4</sub>/C). Due to the existence of electronic conductive graphene, both
3D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/C and 2D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/C showed much improved electrochemical performances than
the Li<sub>2</sub>FeSiO<sub>4</sub>/C composite. When compared with
the 2D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/C composite, 3D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/C exhibited even better performances, with
the discharge capacities reaching 313, 255, 215, 180, 150, and 108
mAh g<sup>–1</sup> 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<sup>–1</sup>), respectively. The 3D-G/Li<sub>2</sub>FeSiO<sub>4</sub>/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/Li<sub>2</sub>FeSiO<sub>4</sub>/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 Li<sub>2</sub>FeSiO<sub>4</sub> 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