Electrospun Spinel LiNi_0.5 Mn_1.5 O₄ Hierarchical Nanofibers as 5 V Cathode Materials for Lithium-Ion Batteries

Spinel LiNi_0.5 Mn_1.5 O₄ hierarchical nanofibers with diameters of 200-500 nm and lengths of up to several tens of micrometers were synthesized using low-cost starting materials by electrospinning combined with annealing. Well-separated nanofiber precursors impede the growth and agglomeration of LiNi_0.5 Mn_1.5 O₄ particles. The hierarchical nanofibers were constructed from attached LiNi_0.5 Mn_1.5 O₄ nanooctahedrons with sizes ranging from 200 to 400 nm. It is proven that these LiNi_0.5 Mn_1.5 O₄ hierarchical nanofibers exhibit a favorable electrochemical performance. At a 0.5 C (coulombic) rate, it shows an initial discharge capacity of 133 mA h g^-1 with a capacity retention over 94 % after 30 cycles. Even at 2, 5, 10, and 15 C rates, it can still deliver a discharge capacity of 115, 100, 90, and 80 mA h g^-1 , respectively. Compared with self-aggregated nanooctahedrons synthesized using common sol-gel methods, the LiNi_0.5 Mn_1.5 O₄ hierarchical nanofibers exhibit a much higher capacity. This is owing to the fact that the self-aggregation of the unique nanooctahedron-in-nanofiber structure has been greatly reduced because of the attachment of nanopolyhedrons in the long nanofibers. This unique microstructured cathode results in the large effective contact areas of the active materials, conductive additives and fully realize the advantage of nanomaterial-based cathodes.