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Engineering Multifunctional Separators and Electrodes to Improve Battery Safety and Lifetimes

  • Author(s): Gonzalez, Matthew Stephens
  • Advisor(s): Liu, Ping
  • et al.

To meet the demand for applications ranging from cell phones to electric vehicles, battery energy density continues to rise. With the use of highly energetic materials such as Li-metal anodes coupled with a reduction of the inactive components generally tasked with safety, failure events from misuse or manufacturing defects will inevitably increase. Furthermore, catastrophic battery failures due to internal short are extremely difficult to detect and can occur even under normal working conditions. To enable next generation Li-metal batteries, an inexpensive “fail safe” mechanism for internal shorting that does not sacrifice energy density is highly desirable. In this dissertation two novel battery separator designs and an easily implementable cathode design modification have been developed to improve battery safety, control, and lifetimes by approaching these problems from both the ionic and the electronic pathways. Firstly, an iongate separator was developed to increase battery calendar life and improve inherent safety by using a rapid and reversible battery shut-off mechanism enabled by a 10x increase in internal ionic resistance. Secondly, a nano-composite Janus separator was implemented to intercept dendrites with a high-resistance interlayer, now controlling the internal electronic resistance of the cell. This separator provides protection and early failure detection, nearly completely eliminating short circuit current and the accompanying cell temperature rise. Lastly, this concept was simplified by using a gradient-conductivity cathode that directly utilizes the inherent resistive properties of the battery active material to create the protection mechanism, halving short circuit current and cell temperature during shorting events. This simplified approach is broadly applicable and results in a particularly inexpensive protection scheme without incurring penalty to energy density. In summary, this dissertation introduces three novel approaches to improve battery safety by controlling both the internal ionic and electronic pathways that are at fault for often catastrophic battery failures.

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