Surface Modification of NaCrO₂ Positive Electrode Material with an Aluminium-Based Precursor

Sodium-ion batteries are promising successors to lithium-ion batteries, with NaCrO 2 being particularly interesting given its decent capacity and high thermal stability. However, improvements in cyclic stability are still necessary. Metal oxide coatings are a well-established method for enhancing these properties in lithium-ion batteries, but are not yet widely explored for NaCrO 2 . We show that volatile (H 2 AlO t Bu) 2 as a precursor forms an artificial cathode-electrolyte interface containing Al 2 O 3 and the sodium-ion conductor NaAlO 2 . The coating forms in a simple batch process in an autoclave at 180°C and significantly enhances capacity retention by reducing the material’s resistance and improving its cycling stability. When used with an electrolyte mixture of EC and DMC with 1 m NaPF 6 and 3 wt% FEC as an additive, initial discharge capacity improves from 92.7 to 97.3 mAh −1 . During cycling, this difference increases, resulting in a discharge capacity/capacity retention of 85.2 mAh −1 /with a state of health (SoH) of 91.8% for pristine and 91.2 mAh −1 /SoH 93.7% for the coated material after 150 cycles. The coating drastically reduces side reactions during initial cycles, resulting in a smaller layer of decomposed electrolyte on the surface, as evident in scanning electron microscopy imaging, accounting for the observed improvements.