Evaluating electrochemical properties of layered Na x Mn 0.5 Co 0.5 O 2
obtained at different calcined temperatures
Abstract
This work elucidated the structure and electrochemical performance of
the layered cathode material Na xMn
0.5Co 0.5O 2 (NMC) with
x~1 calcined at 650, 800 and 900 oC.
XRD diffraction indicated that the NMC material possessed a phase
transition from P3- to P2-type layered structure with bi-phasic P3/P2 at
medium temperature. The sodium storage performance was evaluated by
constant current charging/discharging. Specifically, P2-NMC exhibits the
highest initial capacity of 156.9 mAh.g -1 with
capacity retention of 76.2% after 100 cycles, which is superior to the
initial discharge capacity is only 149.3 mAh.g -1 and
severe capacity fading per cycle of P3-NMC, indicating high robust
structure stability by calcined at the higher temperature. Additionally,
the best performance of P2-NMC also demonstrated by the high-rate
capability that delivered a capacity of 50 mAh.g -1 at
charge/discharge rate up to 10C. The sodium diffusion coefficient of Na
+ ions into the P2-type layered structure obtained by
Cyclic Voltammetry (CV) was in the range of 10 −13–10
−12 cm 2.s −1,
which is inferior to the others. However, the structure stability of P2
phase contributed to the best prerformance in sodium-ion half-cell.