Pillar and Pinning Effects in Sodium Oxide Cathodes: Atomic‐Level Strategies for Structural Stability

ABSTRACT Among available cathode materials of sodium ion batteries (SIBs), the sodium layered transition metal oxides (Na x TMO 2 ) stand out owing to their high specific capacity and suitable working voltage. However, they are commonly plagued by lattice collapse, irreversible phase transition, and poor air stability, which severely limit their cycle durability and rate capability. To address the persistent challenges of Na x TMO 2 , structural regulation strategies based on the pillar and pinning effects have emerged as effective approaches. The ions serving as pillars in the alkali metal layer can expand the interslab spacing and strengthen interlayer interactions, thus constructing efficient Na + migration pathways and establishing a robust lattice framework. Similarly, the pinning ions in the TM and/or alkali metal layers acting as nails help to stabilize phase configuration, especially in deeply sodiated and desodiated states. Both pillar and pinning effects are extensively employed to optimize the structural stability, phase evolution behavior, and electrochemical properties of Na x TMO 2 . This review systematically summarizes recent advances in Na x TMO 2 regulated by pillar and pinning effects, primarily focusing on their construction approaches and underlying enhancement mechanisms. Finally, we outline the ongoing challenges and future research directions for Na x TMO 2 modified by the pillar or pinning effects.