The good, the bad and the ugly in tuning the MAX phase oxidation as a strategy for the production of negative electrode materials for Li- and Na-ion batteries.

The demand for high-capacity, stable negative electrodes for lithium- and sodium-ion batteries supporting fast charging has led to the exploration of conversion and alloying materials. Although these systems offer superior theoretical capacities, their practical application is hindered by dramatic volume changes during cycling. This review rationalizes the thermal oxidation of selected MAX phases, demonstrating how the bottom-up formation of oxide/MAX phase nanocomposites provides a credible solution to these challenges. By tuning oxidation parameters and precursor stoichiometry, we show that it is possible to achieve a synergistic effect between the electroactive oxide shell and the conductive, buffering MAX phase core, ensuring mechanical stability and high-rate capability in both half-cell and full-cell configurations.