First-Principles Study on Cathode Properties of Li2MTiO4 and Na2MTiO4 (M = V, Cr, Mn, Fe, Co, Ni)

TL;DR

This study uses density functional theory to compare the stability and electrochemical properties of layered and disordered structures in Na2MTiO4 and Li2MTiO4 cathodes, revealing stability differences and factors influencing voltage profiles.

Contribution

It provides the first-principles comparison of structural stability and electrochemical behavior of Na2MTiO4 and Li2MTiO4 cathodes, highlighting the role of ionic radii and structure type.

Findings

Layered Na2MTiO4 is more stable than disordered form.

Intermediate compounds in Na2MTiO4 have low formation enthalpies.

Ionic radii influence the energy difference between structures.

Abstract

The cathode properties of Na2MTiO4 (M: transition-metal element) are investigated by means of density-functional-theory calculations. The stability between the layered structure and the disordered structure are focused in comparison with the Li2MTiO4 prototypical case. It is found that the layered structure is more stable than the disordered structure in Na2MTiO4 while those structure shows the similar stability in Li2MTiO4. In layered-structure Na2MTiO4, the formation enthalpies at the intermediate compounds during charge/discharge reactions are significantly low, leading to the unstable voltage-capacity profiles. A machine-learning analysis reveals that the total-energy difference between these structures can be described by a simple function of ionic radii.