(Invited) Single Crystal Ni-Rich Cathode Materials: Synthesis, Scaleup and Validation

Abstract

Synthesis of high-performance single crystal Ni-rich NMC, especially when Ni≥0.8, poses a challenge. A conflict exists because as Ni content increase in NMC811, a lower calcination temperature is preferred due to Ni reduction at elevated temperatures, while high temperatures favour single crystal growth.Therefore, molten salt is sometimes employed as the reaction media to promote growth of single crystal NMC811. In general, four approaches for synthesizing of Ni-rich NMC single crystals: molten salt, hydrothermal, direct solid-state synthesis and multi-step lithiation. Molten salt and hydrothermal approaches result in the formation of well-segregated large crystals, but they also increase manufacturing cost. Direct solid-state synthesis, which involves ball milling all precursors together followed by calcination, is a time-saving approach. However, it poses challenge for impurity control due to contamination from milling media, and it can damage the material structure. The calcination of TM(OH)2 precursor with LiOH at very high sintering temperatures forms micron-sized primary particles which, however, still exhibit significantly agglomerated. A post-synthesis milling process is required to break down those NMC811 crystal clusters.This talk will discuss an innovative nanoscale phase separation approach for synthesis of high-performance single crystal NMC811 that is readily adaptable for industry manufacturing. The reaction mechanism of single crystal growth is investigated to understand the synthesis-morphology-performance relationship in growing single crystal NMC811 in the absence of molten salts. The scaled single crystal NMC811 is then further validated in a 2Ah Li-ion pouch cells, demonstrating 1000 stable cycling, confirming the feasibility of this new synthesis approach. This work provides new insights that are broadly applicable for cost-efficient large-scale synthesis of single crystals for different advanced battery technologies to accelerate deep decarbonization process.