Dynamically Responsive Interfaces (Task 2)
Above, (a) Autonomic shutdown concept using a triggered microcapsule to coat a separator or electrode after thermal activation. (b) Microscope image of polymerized poly(divinylbenzene) after thermally induced rupture of a microcapsule. (c) SEM image of a polypropylene separator partially covered with wax after melting.
The goals of the Dynamically Responsive Interfaces task include the safe shutdown of lithium-ion batteries and the extension of battery lifetime through electronic self-healing. Electrochemical processes in batteries inevitably have unintended or unwanted side reactions at the electrode/electrolyte interface that negatively affect electrochemical performance. Electrode and electrolyte materials and their interfaces, which respond to the initiation of damage, can ensure stabilization of, or increases in, storage capacity, safety, and lifetime.
In this task, recent developments in the concepts of “self-repair” and “activated shutdown” have been exploited. For example, nanoscale materials with packets of repair compounds that open as damage occurs mitigate the inherent decay of the electrodes. This concept is novel in its application to battery materials and is a unique feature of the Center’s research. For battery shutdown at elevated operating temperatures, the concept is to thermally trigger the release of additives from microcapsules that can polymerize, and thus, prevent ionic conductivity and further battery operation. For life extension, encapsulated suspensions of conductive materials, when released, may be used to bridge gaps in cracked electrodes. Redox shuttles are being investigated to prevent overcharge.
This activity complements a second focus on fundamental studies of electrolyte additives that have been shown to respond to damaging electrochemical potential and thermal events at the electrode surface either by self-repair or by termination of cell operation in a non-catastrophic way. Task 2 is strongly supported by Theory, in which quantum chemical modeling is used to investigate how these additives react to the damaging electrochemical events by carrying out fundamental studies of fragmentation of the additives upon oxidation at the surfaces. The Dynamically Responsive Interfaces task is also well-integrated with the Control of Interfacial Processes task, in which repair and shutdown mechanisms are studied.