Reaction kinetics and capacity decay mechanism of NaNi1/3Fe1/3Mn1/3O2@activated carbon cathode of sodium ion batteries

Layered metal oxides are among the primary cathode materials used in sodium-ion batteries (SIBs), but they face limitations mainly in terms of slow reaction kinetics and structural instability with increasing cycles. Activated carbon (AC) is vital in cathode materials for SIBs. In this study, the charge transfer kinetics and reaction mechanisms of NaNi_1/3Fe_1/3Mn_1/3O₂(NFM)/AC composites were investigated. Results showed that the physical doping of AC improved the electrode wettability, provided more conducting channels for ions and reduced the ionic impedance. The addition of AC accelerated the O3–P3 transition of NFM, as observed through ex-situ X-ray diffraction and dQ/dV curves, thus reducing active material consumption during extended cycling processes. COMSOL simulations of the discharge process revealed that AC in NFM created a more homogeneous reactive material, increasing the capacity of NFM/AC composites by nearly three times at 1000 mA g⁻¹ compared to material without AC. In addition, after 100 cycles, the cycle stability increased from 76 % to 81 %. The findings of this study provide a new way to improve the performance of cathode materials for SIBs.