Synthesis of Single Crystal LiNi_0.88Co_0.09Al_0.03O₂ with a Two-Step Lithiation Method

Single crystal positive electrode materials for lithium-ion batteries have superior properties compared to their polycrystalline counterparts as has been demonstrated by industry and academia. Single crystal LiNi0.5Mn0.3Co0.2O2 (NMC532), NMC622 and now NMC811 have been successfully commercialized. However, single crystal LiNi1-x-yCoxAlyO2(NCA) materials have not been reported yet. One simple method for producing single crystal NMC material requiring high temperature and excess lithium during synthesis creates Li5AlO4 impurities if applied directly in attempts to synthesize single crystal NCA materials. This work introduces a two-step lithiation method for single crystal LiNi0.88Co0.09Al0.03O2 synthesis, which can prevent the formation of Li5AlO4 impurities. Powder X-ray diffraction, electron backscatter diffraction, and electrochemical measurements show the viability of the two-step lithiation method. Full coin cell cycling shows that the capacity retention of the single crystal NCA samples is at least as good as their polycrystalline counterparts. It is believed that this two-step lithiation method can be used for the synthesis of single crystal NCA and other single crystal Al-containing positive electrode materials. We believe this can lead to longer lived Li-ion cells with Ni-rich positive electrode materials.