Synthesis and design of NaNi1/3Fe1/3Mn1/3O2 cathode materials for long-life sodium-ion batteries

To enable the widespread adoption of residential energy storage, sustainable, low-cost, long-life, and energy-dense battery technologies are required. Sodium-ion offers many of these characteristics, however often the system is tailored for energy rather than cycle life. In this work, the effect of synthesis conditions upon the primary and agglomerated secondary particle size and shape of the sodium-ion cathode material NaNi_1/3Fe_1/3Mn_1/3O₂ was investigated for optimization of energy and cycle life. A two-level full factorial experimental design was utilized to examine how the synthesis parameters (pH, molar ratio of ammonia/metal precursor salt, and stirring speed) affect the physical and electrochemical properties. This approach enabled a comprehensive investigation of the main effects and interactions of these parameters. The data from multiple synthesis runs were analyzed using statistical methods and regression analysis. This experimental design provided valuable insights into the relationship between synthesis parameters and material properties. Statistical analysis indicates that both physical and electrochemical properties are mainly controlled through pH and NH₄OH, while the effects of stirring speed are less pronounced. The optimal synthetic conditions producing the highest cycling performance were extrapolated from the statistical analysis. A validation experiment showed that particles synthesized with optimum parameters displayed a threefold increase in cycling performance together with uniformly distributed particle size and a high tap density.