Reduced air sensitivity and improved electrochemical stability of P2–Na2/3Mn1/2Fe1/4Co1/4O2 through atomic layer deposition-assisted Al2O3 coating

Considering the abundance and low price of sodium , sodium-ion batteries (SIBs) are of particular attractiveness for large-scale electrochemical energy storage . Layered P2–Na 2/3 Mn 1/2 Fe 1/4 Co 1/4 O 2 (NMFC) is a promising cathode material for SIBs because of its large theoretical capacity, however, its high air sensitivity and poor cycling stability seriously limits the practical use. Here, we report nanometre-thick Al 2 O 3 coating of NMFC electrode through atomic layer deposition (ALD) technique can effectively alleviate such deficiencies to obtain an air-insensitive electrode, which was realized by effectively preventing the direct exposure of NMFC to H 2 O and CO 2 present in the air atmosphere. Interestingly, the ultrathin Al 2 O 3 coating did not cause a block for sodium ion intercalation, and a high capacity of 217.9 mA h g −1 at a high cut-off potential of 4.5 V was achieved. More attractively, a capacity retention rate as high as 84.8% was obtained after cycling at a current density of 0.5C over 100 cycles, demonstrating improved electrochemical stability. Based on CV and EIS characterizations, such good cycling stability is associated with the use of the Al 2 O 3 coating layer as well, which effectively avoided the side reactions at the interface of the liquid electrolyte and the active material under high potential.