Microstructural Observations of “Single Crystal” Positive Electrode Materials Before and After Long Term Cycling by Cross-section Scanning Electron Microscopy

Abstract

Single crystal LiNi0.5Mn0.3Co0.2O2 (SC532), LiNi0.6Mn0.2Co0.2O2 (SC622) and LiNi0.8Mn0.1Co0.1O2 (SC811) electrodes were retrieved from heavily cycled commercial-grade pouch cells at 4.3 V for cross-section scanning electron microscopy (SEM). SEM images indicated the single crystals showed very little microcracking, thought by many researchers to be one of the main reasons for cell degradation when polycrystalline materials are used. SEM images of electrodes from heavily cycled cells were compared to those from fresh cells which showed little visual difference. Parallel microcracks within very few single crystal particles were observed for both fresh and heavily cycled materials and are thought to be caused during the electrode calendaring process. It is believed by the authors that single crystal materials are highly promising positive electrode materials for high energy density and long cycle life lithium-ion cells.