Ca pillar effect on the electrochemistry and stability of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mn>P2-Na</mml:mn> </mml:mrow> <mml:mi mathvariant="normal">x</mml:mi> </mml:msub> <mml:mi mathva

Cathode materials for Na-ion batteries often degrade in air and suffer from large lattice mismatch during ion intercalation. This work focuses on the pillaring effect to address these challenges. The authors have used an ion exchange method to introduce Ca ions as structural pillars in the P2-type Na${}_{0.67}$Fe${}_{0.5}$Mn${}_{0.5}$O${}_{2}$ layered oxide Na-ion cathode material. The pillared materials show improved stability in moist and acidic environments and reduced lattice mismatch between phases developed during Na ion (de)intercalation. The ion exchange reaction provides a general method to exploit the pillaring effect in layered metal oxides for electrochemical energy storage.