Microcapsule-based techniques for improving the safety of lithium-ion batteries

Microcapsules;safety;batteries

Baginska, Marta

关键词: Microcapsules;    safety;    batteries;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/50686/Marta_Baginska.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Lithium-ion batteries are vital energy storage devices due to their high specific energy density, lack of memory effect, and long cycle life. While they are predominantlyused in small consumer electronics, new strategies for improving battery safety and lifetime are critical to the successful implementation of high-capacity, fast-charging materials required for advanced Li-ion battery applications. Currently, the presence of a volatile, combustible electrolyte and an oxidizing agent (Lithium oxide cathodes) makethe Li-ion cell susceptible to fire and explosions. Thermal overheating, electrical overcharging, or mechanical damage can trigger thermal runaway, and if left unchecked, combustion of battery materials.To improve battery safety, autonomic, thermally-induced shutdown of Li-ion batteries is demonstrated by depositing thermoresponsive polymer microspheres onto battery anodes. When the internal temperature of the cell reaches a critical value, the microspheres melt and conformally coat the anode and/or separator with an ion insulatingbarrier, halting Li-ion transport and shutting down the cell permanently. Charge and discharge capacity is measured for Li-ion coin cells containing microsphere-coated anodes or separators as a function of capsule coverage. Scanning electron microscopyimages of electrode surfaces from cells that have undergone autonomic shutdown provides evidence of melting, wetting, and re-solidification of polyethylene (PE) into the anode and polymer film formation at the anode/separator interface.As an extension of this autonomic shutdown approach, a particle-based separator capable of performing autonomic shutdown, but which reduces the shorting hazard posed by current bi- and tri-polymer commercial separators, is presented. This dual-particleseparator is composed of hollow glass microspheres acting as a physical spacer between electrodes, and PE microspheres to impart autonomic shutdown functionality. An oil immersion technique is developed to simulate an overheating condition while the cell is cycling. Experimental protocols are developed to assess the performance of the separatorin terms of its ability to perform autonomic shutdown and examine tested battery materials using scanning electron microscopy.Another approach to improving battery functionality is via the microencapsulation of battery additives. Currently, additives are added directly into a battery electrolyte, and while they typically perform their function given a sufficient loading, these additives often do so at the expense of battery performance. Microencapsulation allows for a high loading of additives to be incorporated into the cell and their release triggered only whenand where they are needed. In this work, microencapsulation techniques are developed to successfully encapsulate 3-hexylthiophene, a stabilizing agent for high-voltage cathodes in Li-ion batteries and conductive polymer precursor, as well as the flame retardantTris(2-choloroethyl phosphate) (TCP). Microcapsules containing 3-hexylthiophene are coated onto model battery electrodes and immersed in electrolyte. The microcapsule shell wall insulates the 3-hexylthiophene until the microcapsules are mechanically crushed and electropolymerization of the released core to form poly(3-ht) occurs under cyclicvoltammetry. In addition, TCP was encapsulated using in situ polymerization. TCP-containingmicrocapsules are stable in electrolyte at room temperature, but are thermally triggered to release their payload at elevated temperatures. Experimental protocols are developed to study the in situ triggering and release of microencapsulated additives.