The acceptance of electric vehicles (EVs) by the general public is strongly coupled to key parameters like the driving range and charging time. To this extent, the decarbonization of the private transport sector has been fueled by the development of lithium ion batteries (LIBs). Layered mixed transition metal oxide cathode (LOC) materials like Li[NixCoyMnz]O2 (NCM) have emerged as the dominant material class in EVs. Over the past decade, a steady increase in Ni-content has pushed the energy output of LOCs and thus enabled longer driving ranges. The drawback of these Ni-rich formulations is a loss of cycling stability. In this regard, the intergranular cracking of secondary particles caused by the anisotropic volume change of the individual crystal grains during cycling has been identified as a major failure mechanism.
‘Single-crystal’ (SC) NCMs are highly promising candidates to mitigate this issue. In contrast to their polycrystalline (PC) counterparts, SC-NCMs are comprised of non agglomerated micron-sized primary particles which maintain their structural integrity during cycling. Surface-related degradation phenomena like cathode electrolyte interphase (CEI) growth, transition metal dissolution, electrolyte decomposition and surface reconstruction can therefore be suppressed endowing SC-NCMs with an enhanced cycling stability especially at high cell voltages.
Although the aforementioned challenges are exacerbated with increasing Ni content, the literature on Ni-rich SC-NCMs (> 80% Ni) is still scarce. This is likely because the synthesis can be quite challenging. In this work, a systematic study on the synthesis of SC-NCM811 is carried out. Parameters like the ratio of lithium to transition metals, calcination temperature and lithium source are investigated in terms of their impact on the crystal structure, particle size and particle morphology.