Electrode-coated alumina separators for lithium-ion batteries - effect of particle size and distribution of alumina powders

Lithium-ion batteries prepared with ceramic, powder-coated electrode separators exhibit improved safety and performance characteristics compared to those with polymeric separators prone to thermal runaway. However, electrode-coated alumina separators are thinner and more flexible than standalone ceramic powder separators. Previous studies demonstrated the success of lithium-ion batteries with an alumina separator prepared by the blade-coating method on metal oxide electrodes. The present work examines the effect of particle size of α-alumina powder on slurry processability, coating formation, and the performance of lithium-titanate/lithium half cells with an alumina powder electrode-coated separator. Alumina powders with large particles (> 10 μm) were unable to form a slurry with the consistency required to fabricate such electrode-coated separators. Alumina powders that formed a consistent slurry were directly coated onto a lithium-titanate electrode, resulting in a good quality, thin electrode-supported separator. However, submicron-sized particles of α-alumina could block the electrode surface, affecting performance and stability of the final cell with the separator. Unimodal, micron-sized particles formed low viscosity slurries that both wet and damaged the electrode. An improved cell performance was observed if the coated separator was made of alumina powder with bimodal distribution of submicron and micron-sized particles, yet good results in terms of separator formation and the performance of the resulting cells were achieved only with alumina powder of a specific bimodal distribution. Interaction of the alumina and binder in the separator was studied to understand the need for the specific bimodal distribution of the alumina powder.