Rechargeable lithium-ion batteries (LIBs) have the potential to meet DOE’s energy and cost goals for transportation applications but significant barriers to commercialization remain. Performance limitations in cathode materials are currently considered as the bottleneck even after decades of intense developmental effort in this area. In order to increase energy density of the state-of-the-art lithium transition-metal oxide (Li-TM oxide) cathodes, strategies for either increasing the operating voltage window or the charge density/capacity of the oxides are needed. It is well-known that when cycled at high voltages (> 4.3 V), Li-TM oxides suffer from structural instability, extensive side reactions with the electrolyte, poor cyclability and severe thermal runaway reactions [1, 2]. Utilizing a unique diagnostic approach combining carefully prepared cathode model samples and advanced analytical techniques with high spatial resolution and chemical specificity, we recently obtained important insights on the relationships among oxide’s specific physical properties, reaction mechanisms and its reactivities. The results suggest that majority of the high-voltage stability issues are associated with the physical and chemical properties of the oxide surface, both pristine and changes associated with the cycling [3, 4]. In this presentation, we will discuss these relationships and explore surface modification approaches in addressing the instabilities. Furthermore, recent reports suggested that drastic increase in oxide capacity is possible by utilizing both cationic and anionic redox activities in Li-excess oxides [5, 6]. Insights on the physical and chemical processes occurring during the charge and discharge of these unique oxides will be presented.
References:
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Acknowledgment
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
