posted on 2023-02-06, 16:04authored byRihuang Nie, Hongxia Chen, Yutian Yang, Cheng Li, Hongming Zhou
P-type layered manganese-based materials are prone to
undergo lattice
oxygen oxidation accompanied by oxygen layer slipping and even unfavorable
phase transitions at around 4.2 V, giving rise to rapid discharge
capacity decline and inferior structural stability, which restricts
their operating voltage and energy density. Here we propose a modification
strategy for layered Na0.67MnO2 material with
K/F co-doping so as to reach the optimization of lattice oxygen oxidation
behavior and structural stability at a high cut-off voltage of 4.4
V. Combining X-ray powder diffraction refinement results, ex situ
X-ray photoelectron spectrometry analysis, high-resolution transmission
electron microscopy, and electrochemical characterization, our work
demonstrates that an appropriate amount of K/F co-doping has a favorable
effect on the formation of well-reversible lattice oxygen oxidation
behavior and the improvement of Na layer spacing. Owing to the synergetic
effect of potassium and fluorine atoms, the initial discharge capacity
is up to 210.2 mA h g–1 at 0.1 C and 140.2 mA h
g–1 at 1 C with 73% capacity retention after 100
cycles and high discharge capacity of 115.0 mA h g–1 at 5 C, with 68.1 mA h g–1 retained after 200
cycles. The kinetic analysis shows that the optimal K0.05Na0.62MnO1.95F0.05 sample exhibits
the largest sodium ion diffusion coefficient and the smallest electrochemical
polarization, which paves a novel path for the application of layered
manganese-based oxides in high-voltage cathode materials for sodium-ion
batteries.