Morphological Tunability and Surface Reactivity Control of Single‐Crystal Sodium Layered Oxides Employing Spinel Ni1+xMn2−xO4 (x = 0 and 0.5) Precursor

Abstract Development of single‐crystal sodium layered oxide materials has garnered interest in recent years due to the success of analogous materials for lithium‐ion batteries. Methods utilizing single crystal precursors of transition‐metal spinel materials with the form TaMbO4 (T, M = Fe, Mn, Ni, Ti, Al, etc…, and a + b = 3) have been shown to yield materials that suppress intergranular cracking, but morphological control of sodium layered oxides has not been demonstrated with this method. Herein, tunable morphology of NaNi1/2Mn1/2O2 is demonstrated with materials that achieve 130 mA h g−1 at C/5 rate, with capacity retention ranging from 16% to 71% after 200 cycles depending on the morphology. Cycling with a localized high concentration electrolyte (LHCE) controls the influence of surface reactivity and underscores the critical role of the surface in capacity degradation. The impact that transition‐metal chemistry has on the tunability of particle morphology is explored, with the growth kinetics of the terminal and intermediate phases during calcination of the sodium layered oxide compositions having the largest effect on tunability from the single‐crystal templates. By understanding the factors that determine tunability, this work can be extended to offer morphological control without coprecipitation for sodium layered oxides broadly.