A study of the electrochemical kinetics of sodium intercalation in P2/O1/O3-NaNi1/3Mn1/3Co1/3O2

Sodium ternary layered oxides, typically NaNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC), are layered structures analogous to LiNi 1/3 Mn 1/3 Co 1/3 O 2 , and have been utilized extensively in sodium-ion batteries (SIBs). The cathode material was successfully synthesized by a sol-gel process followed by a calcination step at 900 °C for 12 h. The triple-phase integration denoted as P2, O1 and O3 in the NMC sample was evidently revealed on XRD diagrams. The composite cathode material acted as an O3 purity phase that exhibited relatively good performance that delivered an initial capacity of 140 mAh g −1 and sustained reversible capacities of nearly 110 mAh g −1 after 100 cycles. The kinetics of sodium intercalation of sol-gel NMC upon reversible Na + insertion/de-insertion was evaluated via galvanostatic intermittence titration technique (GITT) and electrochemical impedance spectroscopy (EIS). The diffusion coefficients of Na + deduced from the GITT curve were found to lie within a wide range, 10 −9 –10 −12 cm 2 s −1 for the charge process and 10 −13 –10 −17 cm 2 s −1 for the discharge process. This implies that the kinetics of Na + extraction out of the Na x Ni 1/3 Mn 1/3 Co 1/3 O 2 host could be much more favored than Na + insertion. Additionally, the evolution of diffusion coefficient and charge transfer resistance are consistent with the complex phase transition generally observed in sodium layered oxides.