Single-Crystal Growth of P2-Type Layered Oxides with Increased Exposure of {010} Planes for High-Performance Sodium-Ion Batteries

An increase in the size of single-crystal particles can effectively reduce the interfacial side reactions of layered oxides for sodium-ion batteries at high voltages but may result in sluggish Na+ transport. Herein, single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 with increased proportions of {010} planes is synthesized by adding low-cost NaCl as the molten salt. With the assistance of a NaCl molten salt, the median diameter (D50) of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 increases to 10.46 μm relative to that of the comparison sample without NaCl (6.57 μm). Electrolyte decomposition on the surface of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 is considerably suppressed, owing to a decrease in the specific surface area. Moreover, the increased exposure of {010} planes is favorable for improving the Na+ transport kinetics of single-crystal particles. Therefore, at 100 mA g–1, single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 exhibits a high-capacity retention of 96.6% after 100 cycles, which is considerably greater than that of the comparison sample (86.8%). Moreover, the rate performance of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 (average discharge capacity of 81.2 mAh g–1) is superior to that of the comparison sample (average discharge capacity of 61.2 mAh g–1) at 2000 mA g–1. This work provides a new approach for promoting the single-crystal growth of layered oxides for highly stable interfaces at high voltages without compromising Na+ transport kinetics.