PRIMARY AND SECONDARY BATTERIES

High Capacity Materials for Li-ion Batteries

Li-ion batteries have transformed energy mobility since their commercialization in the 1990s.  Until now, conventional materials (graphite anodes and spinel oxide cathodes) have been sufficient since the energy density of these batteries has been more than enough to enable the desired applications.  However, the power demand of mobile devices is rapidly increasing as the public’s demand for enhanced functionality shows no sign of stopping.  The automotive industry is also putting considerable pressure on traditional materials as increased energy storage is needed to enable an acceptable vehicle range.  Both these applications demand lightweight, small footprint solutions that can only be accomplished by transitioning both the anode and cathode to newer materials with much higher energy density. 

At the anode, our primary focus has been the replacement of graphite to transition metal oxides (TMOs) and Si.  Both of these materials are promising because they allow for multiple electron transfer steps per mol of active material.  Unfortunately, these materials undergo alloying or chemical conversion reactions that change the bonding of active materials, and sometimes even forming electrochemically inactive materials, limiting both cycle retention and rate capability.  Related to TMOs, our primary focus has been understanding the roles of structure and conductivity on reaction reversibility during charge and discharge, with NiO being our primary probing compound, though we have done a lot of work with Co, Mn and Sn oxides as well.  To date, We have been able to achieve anodes with > 700 mAh/g capacity over 1000's of cycles and excellent rate capability (up to a 10C rate).  For Si, we have focused on understanding the mechanisms behind material stability and instability.  More specifically, we are using advanced techniques to probe the structure of the solid electrolyte interphase, and learn how that structure is dictated by the in-cell environment and operating conditions.  Our team is also investigating performance of Si anodes with different structures and binders, with the goal of determining how the Li diffusion coefficient is changed.  We are further pushing these materials to more realistic formats and systems, with the hopes of reducing their cost and helping to commercialize their use in the next generation of Li-ion batteries.

Primary Alkaline Batteries

Zn-MnO2 primary alkaline batteries have dominated the portable power market for nearly half a century. Zn alkaline batteries are primarily composed of electrolytic manganese dioxide as the cathode and a Zn slurry as the anode.  The performance of these batteries is limited by the zinc anode - where many unwanted processes occur such as passivation and corrosion.  Our work in this area focuses on understanding the reaction mechanisms and material structures that are responsible for these negative responses and developing new approaches to mitigate them.  This includes engineering solutions as well as new active materials, electrolytes, additives, etc.  We want to make advances that enable long operating life, long shelf life, high energy density, high power density, and intrinsic safety.  

Recycling

Batteries are a critical enabler for our energy future that provide a means to ensure the resiliency and reliability of energy systems while also increasing efficiency and enabling widespread electrification.  Battery recycling is also an issue of national security.  For example, today only 6% of the critical materials in Li-ion batteries are sourced from the United States.  Therefore, there is a need for the United States to improve its ability to supply active battery materials - not only for Li-based batteries, but Zn-alkaline, flow batteries, etc.  One possible pathway is to increase mining activities, though it should be noted that this would require billions of tons of new ore to be processed with a significant environmental footprint.  Another pathway with a potentially low environmental footprint is recycling.  End-of-life batteries already contain the necessary elements and, if recovered, could help the United States to control its own supply chain.  Unfortunately, modern battery recycling processes are inefficient, energy-consuming, and environmentally taxing.  Our team has active projects that advance the science and engineering of battery recycling.