Tuning the annealing temperature to achieve heterostructured nanofibers for high performance lithium-ion batteries

Heterointerfaces not only provide more sites for lithium ion storage, but also reduce the damage of electrode active materials, which are conducive to boosting the capacity and cycle stability of the electrode. This paper demonstrates for the first time that nanofibers with a NiO/Co3O4/NiCo2O4 heterostructure can be prepared by adjusting the annealing temperature. These heterostructured nanofibers are derived from as-spun Ni/Co nanofibers prepared by using electrospinning through thermal annealing at 500-800 degrees C. The phase formation and decomposition of spinel NiCo2O4 occur during heat treatment, and the composition is dependent on the annealing temperature. The electrochemical properties of the electrodes are correlated with the phase composition, particle size and morphology of the nanofibers. The nanofiber electrode annealed at 650 degrees C exhibits optimal electrochemical performances. Its specific capacity continues to increase at the initial stage of charge-discharge, and the activation cycle reached 61 cycles. The electrode has the largest boost value of 187.6 mA h g(-1) (boost ratio, 21.08%), and its specific capacity reaches 1081.4 mA h g(-1). The charge storage mechanism is analyzed by using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic intermittent titration technique measurements. The contribution of electrode pseudo capacitance increases from 66.27% to 73.09% as the scan rate increases from 0.2 to 1.0 mV s(-1), revealing that both the diffusion- and capacitive-controlled processes contributed. This is a facile and low-cost strategy to prepare high performance electrode materials for lithium-ion batteries, and stimulates the further development of phase-transition-induced synthesis of nanofibrous heterostructures.