LiNi_0.5Mn_1.5O₄ Cathode Deterioration in Lithium-Ion Batteries Tracked through Intermittent Post-Mortem Material Characterizations

Identifying high performing and cobalt-free transition metal-based energy storage solutions are a key feature for a cost-effective transition away from the fossil fuel economy. To inform the design of new materials, and the engineering of existing battery materials, a strong understanding of fundamental processes within the device is required. Lithium-ion batteries (LIB) are periodically evaluated by post-mortem (PM) autopsy, wherein a battery is disassembled and each cell component is analyzed separately, providing insights towards which areas of study are most critical to prevent device failure. When investigating cathodes in this manner, typically only whole-cathodes are studied where active material particles are encased in polymeric binders and adhered to a current collector. This provides some access to PM characterization through surface imaging, but cannot demonstrate a full understanding of the consequences of electrochemical cycling on the inner and base layers of cathode particles. Additionally, completing structural and composition characterizations are challenging due to the organics present. Seeking to develop a more detailed understanding of how cathodes particles deteriorate within an LIB cell, a procedure has previously been developed in the Gates Research Group to non-destructively harvest single cathode particles from their binder matrix for comprehensive post-mortem study. Building on this methodology, a systematic investigation into single cathode particles is presented.<br/><br/>In this work, cobalt-free LiNi_0.5Mn_1.5O₄ cathode particles are harvested at different points in their cycle life and characterized as PM isolated single particles to identify and track trends of cathode deterioration over time. High-resolution scanning electron microscopy images of hundreds of individual particles are systematically assessed for physical features of deterioration from cycling. These assessments are supported by x-ray diffraction and standard electrochemical analyses. With use of statistical analyses applied to the detailed imaging data, a template is created to enhance failure mechanism diagnostics and contribute experimental evidence to models of cathode degradation, informing the design of future cost-effective materials.