Synthesis Control of Layered Oxide Cathodes for Sodium-Ion Batteries: A Necessary Step Toward Practicality

Interest in sodium-ion battery cathode materials, particularly for grid-scale energy-storage applications, has considerably increased in the last few years, sparking a push toward industrially practical research. In addition to more full-cell and pouch-cell research, there has also been more study on the use of an industrial synthesis technique for producing sodium-based cathode materials. Hydroxide coprecipitation is the industry standard for synthesizing lithium-based layered-oxide cathode materials because it is scalable and produces materials with highly tunable particle morphology with low impurity. The tuning of particle morphology allows for improved energy density and reduced surface reactivity, leading to better stability in air and electrolyte. Despite these benefits, the ability to synthesize sodium-based layered-oxide cathode materials with beneficial particle morphology is considerably more challenging than it is for lithium-based layered oxides due to the complexity of numerous interconnected variables. We herein provide a review of the hydroxide coprecipitation method for both sodium- and lithium-based cathode materials, highlighting its benefits and the need for further studies on utilizing coprecipitated sodium-based layered-oxide materials. We then perform an in-depth analysis utilizing a combination of literature, fundamental chemistry, and experimental data to discuss the challenges of hydroxide coprecipitation and provide a framework for overcoming these challenges.