Unlocking Ultrahigh Initial Coulombic Efficiency of MXene Anode via Presodiation and Electrolyte Optimization.
basic_science · Level V
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- Record sourced from PubMed, PMID 38924447.
- Also identified by DOI 10.1021/acsnano.4c04909.
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Abstract
The low initial Coulombic efficiency (ICE) greatly hinders the practical application of MXenes in sodium-ion batteries. Herein, theoretical calculations confirm that -F and -OH terminations as well as the tetramethylammonium ion (TMA<sup>+</sup>) intercalator in sediment Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> (s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>) MXene possess strong interaction with Na<sup>+</sup>, which impedes Na<sup>+</sup> desorption during the charging process and results in low ICE. Consequently, Na<sup>+</sup>-intercalated sediment Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> (Na-s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>) is constructed through Na<sub>2</sub>S·9H<sub>2</sub>O treatment of s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>. Specifically, Na<sup>+</sup> can first exchange with TMA<sup>+</sup> of s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> and then combine with -F and -OH terminations, thus leading to the elimination of TMA<sup>+</sup> and preshielding of -F and -OH. As expected, the resulting Na-s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> anode delivers considerably boosted ICE values of around 71% in carbonate-based electrolytes relative to s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>. Furthermore, electrolyte optimization is employed to improve ICE, and the results demonstrate that an ultrahigh ICE value of 94.0% is obtained for Na-s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> in the NaPF<sub>6</sub>-diglyme electrolyte. More importantly, Na-s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> exhibits a lower Na<sup>+</sup> migration barrier and higher electronic conductivity compared with s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> based on theoretical calculations. In addition, the cyclic stability and rate performance of the Na-s-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> anode in various electrolytes are comprehensively explored. The presented simple strategy in boosting ICE significantly enhances the commercialization prospect of MXenes in advanced batteries.