Novel spinel nanocomposites of Ni _x Co _1−x Fe ₂ O ₄ nanoparticles with N-doped graphene for lithium ion batteries

A dual-doping strategy was applied to fabricate the novel electrode materials. For the first time, the spinel hybrids of nanosized Ni _x Co _1−x Fe ₂ O ₄ with N-doped graphene (N _x -NG) were synthesized by a hydrothermal co-precipitation method. The size of Ni _x Co _1−x Fe ₂ O ₄ (N _x ) nanoparticles on N-doped graphene can be tuned with the regulation of Ni/Co content. Among these nanocomposites, the Ni _0.4 Co _0.6 Fe ₂ O ₄ nanoparticles with the smallest average size of 10 nm are uniformly anchored on the N-doped graphene. The electrochemical characterizations display that the N _0.4 -NG exhibits the best electrochemical lithium storage performance compared to other five nanocomposites. It delivers a high capacity of 1367.0 mA h g ⁻¹ at the first discharge process，and the reversible capacity retention of 87% (2nd to 50th) at 0.1 A g ⁻¹ . The excellent electrochemical performance of N _0.4 -NG can be owing to the small size of nanoparticles and its well-combination with N-doped graphene, which provide the large surface area and promote the ion/electron transfer rate. The synergistic effect resulted from the strong interaction between N _0.4 and N-doped graphene is contributed to the enhanced electrochemical performance of N _0.4 -NG. This study not only extends graphene-based electrode materials for lithium ion battery, but also promotes the development of energy resources.