(Invited) Enabling Conversion-Based Metal Oxide Anodes for Li Ion Batteries through Material Confinement

Abstract

The market demand for electric vehicles (EVs) and hybrid electric vehicles (HEVs) have pushed Li-based technologies towards new higher capacity materials. The end goal is to enable full EVs that recharge very quickly (5-10 min) and achieve similar driving range to fossil-fuel cars (400-500 miles). State of the art Li ion batteries can deliver a gravimetric energy density of approximately 250 Wh kg-1, which is equivalent to ~250 miles for an EV. For EVs to truly compete in the market, batteries with an energy density greater than 500 Wh kg-1 must be realized. One family of materials that has been proposed to replace graphite at the anode is conversion metal oxides, which have both higher capacity (700-1200 mAh/g vs. 372 mAh/g) and slightly higher operating potential. This means that metal oxides have the potential to concomitantly increase energy density and improve safety (by avoiding Li plating during fast charge). Unfortunately, many of the metal oxide anodes that have been reported in the literature have shown poor cycle life and low coulombic efficiency. In this presentation, we will discuss each of the degradation mechanisms that act to reduce capacity, capacity retention and coulombic efficiency of conversion metal oxides in Li-ion batteries. We will present new data on the influence of the electronic conductivity of these materials as well as the growth dynamics of the solid electrolyte interphase (SEI). It will be shown that there are two primary degradation pathways for metal oxide anodes in lithiuim ion batteries and a new strategy based on material confinement will be presented to simultaneously mitigate both. A combination of physical (TEM, S/TEM, XPS) and electrochemical (charge/discharge, EIS) characterization will be used to explain the behavior of these materials, and materials combinations that allow for achieved capacity of 800 mAh/g, capacity retention over 1000’s of cycles and coulombic efficiency > 99.5% will be presented.