(ECS Toyota Young Investigator Fellowship Program Address) Structure-Property Relationships of Silylamine Switchable Electrolytes As a Thermally Controlled Safety Switch
Authors: Biddinger Elizabeth J , Jung Sungyup , Podder Showmik 
Published: February 2020

Over the past few decades, rechargeable energy-storage devices have allowed for the development of portable devices and electric vehicles. Ideal characteristics of those devices are high capacity, fast charge/discharge capability and low cost while maintaining safe operating conditions. However, the drawback of increased capacity is that there is an increased safety risk. Runaway reactions are a common concern in such energy-storage devices including secondary batteries and supercapacitors. These uncontrolled reactions often result from in situ heat generation that increases the safety risks of the devices and further causes device failure [1]. To take advantage of safe energy-storage devices, durable thermally-activated safety components that do not interrupt normal operation are required.

Our work explores the potential of using switchable electrolytes that will provide a thermally-controlled safety mechanism in batteries. This switchable electrolyte system would minimize the need for any extra material or sub-devices that become necessary for thermal safety management in energy storage devices. The switchable electrolytes used are part of a larger class of switchable solvents that can switch between two states with the introduction of an external stimulus, such as carbon dioxide or heat[2]. Silylamine-based reversible ionic liquids (RevILs)[4, 5] are investigated here as the switchable electrolyte. In this case, the silylamine is in an ionic liquid-like state (RevIL state) that when dissolved in an organic solvent has shown to have substantial conductivity[3]. With heating, the RevIL will release CO2 and drop in conductivity substantially (and be in what is termed a molecular liquid (ML) state). Upon cooling, the silylamine can re-react with the CO2 and return back to its conductive state (RevIL state). This dramatic difference between two states may enable a device to reversibly shut off when heat is generated in the system. It is known that by altering the structure of the silylamine, the thermo-physical properties can be tuned[4, 5]. The impact of the structure of (3-aminopropyl)trialkylsilanes on the safety-switch relevant properties including ionic conductivity of both RevIL+solvent and ML+solvent, and reversal temperature of RevIL+solvent to ML+solvent will be reported in the presence of metallic salts and in the absence of metallic salts. The switch rates between the conductive RevIL and non-conductive ML states will also be reported.

References

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