Controlling the Microstructure of Cobalt-Free, High-Nickel Cathode Materials with Dopant Solubility for Lithium-Ion Batteries

Microstructural engineering is becoming notably important in the realization of cobalt-free, high-nickel layered oxide cathodes for lithium-ion batteries since it is one of the most effective ways to improve the overall performance by enhancing the mechanical and electrochemical properties of cathodes. In this regard, various dopants have been investigated to improve the structural and interfacial stabilities of cathodes with doping. Yet, there is a lack of a systematic understanding of the effects of dopants on microstructural engineering and cell performances. Herein, we show controlling the primary particle size by adopting dopants with different oxidation states and solubilities in the host structure as an effective way for tuning the cathode microstructure and performance. The reduction in the primary particle size of cobalt-free high-nickel layered oxide cathode materials, e.g., LiNi0.95Mn0.05O2 (NM955), with high-valent dopants, such as Mo6+ and W6+, gives a more homogeneous distribution of Li during cycling with suppressed microcracking, cell resistance, and transition-metal dissolution compared to lower-valent dopants, such as Sn4+ and Zr4+. Accordingly, this approach offers promising electrochemical performance with cobalt-free high-nickel layered oxide cathodes.