Theoretical Understanding
and Prediction of Lithiated Sodium Hexatitanates
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Abstract
Sodium hexatitanates (Na<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub>) with tunnelled structures have been experimentally proposed
to be good candidates for anode materials of lithium ion batteries
because of their low potential, small shape transformation, and good
reversibility. The understanding of the properties of this lithiated
titanate is significant for their development. To this end, the first-principle
calculations were performed to investigate the interaction between
Li ions and Na<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> at the atomic
level. After structural optimization with various Li:Ti ratios, the
Li ions are found to energetically prefer to stay at the small rhombic
tunnels of Na<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub>, where the diffusion
energy barrier of Li ions is also lower. Such preference is determined
by the chemical environment around Li ions. Our theoretical intercalation
potential and volume change on the basis of the optimized atomic structures
agree with the experimental observations. The analysis of the electronic
properties reveals the Burstein–Moss effect in lithiated Na<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> due to the heavy n-type doping.
Such materials possess high conductivity, which can benefit their
applications in photoelectrochemical or electrochemical areas