Formation of NiFe2O4/Expanded Graphite Nanocomposites with Superior Lithium Storage Properties

To meet the demands of high-energy storage for practical applications in electric vehicles (EVs) and hybrid electric vehicles (HEVs), much attention has been paid to lithium-ion batteries (LIBs) because of their distinct advantages, e.g., their large specific capacity, high energy density, long cycle life, and environmental friendliness [ 1 – 3 ]. Today, there is a great demand to design and develop novel and high-performance electrode materials to achieve LIBs with higher energy density, longer cycle life, improved safety, and lower cost. However, it is still urgency to improve the reversible charge capacity of anode materials in commercial LIBs, i.e., graphite [ 4 , 5 ]. Among various anode materials with higher specific capacities than that of the material used in commercial batteries, ternary compounds (e.g., CuFe 2 O 4 [ 6 , 7 ], ZnFe 2 O 4 [ 8 , 9 ], CoFe 2 O 4 [ 10 – 12 ], Zn 2 SnO 4 [ 9 , 13 ], ZnMn 2 O 4 [ 14 – 17 ]) have been considered promising candidates because of their high theoretical capacities, low cost, and safety [ 9 ]. Nevertheless, their poor electrical conductivities and huge volume changes during continuous charge–discharge processes would lead to electrode pulverization. Rapid disintegration of these electrode materials caused by induced mechanical stress is responsible for a decrease in the capacity upon cycling and further hinders their practical applications [ 18 , 19 ]. Expanded graphite (EG) possesses many advantageous properties, including fewer functional groups, better conductivity, higher mechanical strength [ 20 ], and lower cost [ 21 ]. A layered NiFe 2 O 4 /EG composite structure can be fabricated by incorporating nanostructured NiFe 2 O 4 material with EG. This provides outstanding electron conductivity [ 22 – 25 ] and an ideal solution to the aforementioned inherent drawbacks of ternary compounds. However, to the best of our knowledge, there have been few reports on the construction of nanostructured material/EG composites with superior lithium storage properties because it is a challenge to homogenously disperse nanostructured materials into EG nanosheets.