Understanding the Orderliness of Atomic Arrangement toward Enhanced Sodium Storage

In response to the increased demands of available energy storage, sodium ion batteries (SIBs) appear as promising alternatives to widely used lithium ion batteries. However, because of large radius of Na ions, more complex requirements for the intrinsic properties raise the difficulties in finding a suitable material, in particularly for electrodes with intercalation mechanism. Concerning the principle of designing effective electrodes, the ordering of atomic arrangements should be at the heart in SIBs due to its significant influences on various electrochemical processes, such as ion absorption, ion diffusion, electron diffusion, etc. As proof-of-concept, the state-of-the art TiO2 electrodes with different orderliness of atomic arrangement are achieved through colloidal crystal template method assisted by low-temperature atomic layer deposition and post-heating treatment. The disordering at the surface is benefit for the contribution from surface processes, which is particularly significant to the electrode materials with poorer affinity of transporting ions. Meanwhile, the disordering in bulk results in better ion diffusion, but worse electron transport. Understanding this relationship between atomic orderliness and battery performance is of importance for extending the design principle to some traditional electrodes for highly effective energy storage.