Ion-exchange is an important route to achieve partial or complete substitution of alkali ions into intercalation cathodes for alkali-ion batteries. In Na-ion cathodes, the partial substitution of Na for large, charge dense pillar ions, such as Ca2+, could help alleviate the detrimental structural transitions that these cathodes undergo during desodiation. Typically, ion-exchange is achieved by heating the cathode powder in the presence of a substantial molar excess of alkali halide salt in solution. Here, we successfully demonstrate ion-exchange of Ca2+ for Na+ in Na0.67Mn0.72Mg0.28O2 by simple mechanical mixing of powders with the proper molar amount of CaI2 under ambient conditions. The reaction proceeds in the solid-state at room temperature via the formation of crystalline hydrates of CaI2 which form spontaneously with moisture in the air. Ca2+ is uniformly incorporated into the layered cathode up to a limit of about 0.1 Ca (i.e. Na0.47Ca0.1Mn0.72Mg0.28O2). These findings point to the intriguing possibility of achieving facile room temperature, solid-state ion-exchange in other alkali-ion systems.
34 Chemical Sciences
,3406 Physical Chemistry
