Energy storage is one of the key technical challenges for the future, especially for electric vehicles. Batteries have been, and remain, the most versatile and widely used technology in response to this technical challenge. Future electric and hybrid vehicles require tremendous scientific and engineering advancements in terms of energy density, charging rates, and service life compared to the current state of art. Inspired by biological systems that routinely accomplish self-healing, thermal regulation, regeneration, and other autonomic responses, we believe that new materials and concepts integrated within the battery cell can enable a variety of critical features including fail-safe or autonomic shutdown, self-healing of battery performance, and greatly extended lifetimes.
The basic premise is to incorporate microcapsules containing a latent core material within the battery environment – within the electrolyte, embedded in the anode, or layered on the separator. Triggering of the microcapsule is accomplished by a variety of external stimuli (e.g. heat, mechanical force) and once trigger, microcapsules release their payload in order to affect performance.
For example, a variety of complex damage mechanisms in Li-ion batteries and microelectronics can lead to a significant loss of conductivity, and eventual system failure. For Li-ion batteries, cracking, deterioration, and electrochemical pulverization occur during the massive volume changes associated with the intercalation/deintercalation of Li+ ions during charge and discharge. As this damage accumulates, there is a significant degradation of the efficiency, and eventually failure of the battery. Polymeric microcapsules containing a liquid metal (Ga, Ga-In, Ga-In-Sn) can release in response to the mechanical forces associated of these damage processes and upon release, locally restore electrical conductivity and system performance, i.e. self-heal.
Alternatively, thermoresponsive microcapsules are designed to melt and/or polymerize at triggering temperatures that are well below unsafe conditions for batteries. Incorporating these microcapsules onto battery electrodes or within battery separators provides a fail-safe autonomic shutdown feature prior to electrical breakdown and potential fires.
Whatever approach and functionality is imparted to Li-ion batteries, the addition of the microencapsulated phase must not lead to degradation in battery performance. Through proper engineering of the materials, capsule design, and integration this objective can also be achieved.
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