Understanding Performance Fade in High Energy Density Li Batteries

The desire to develop higher performing batteries can be linked with greater demand for long range electric vehicles, longer lasting consumer electronics, and increased use of energy storage technologies in applications such as grid storage. A key to enhancing battery energy density and specific energy for many of these applications is to reduce battery pack size while maintaining or even increasing total capacity. The first attempts at commercializing secondary Li metal batteries occurred over three decades ago. 1,2 However, despite this long history there is still a significant gap between desired high energy density Li metal batteries and what can be effectively achieved. One potential route to enhance energy density is the use of a high energy cathode such as nickel-rich lithium nickel manganese cobalt oxide (NMC) in conjunction with a liquid electrolyte and a Li metal negative electrode. In such a configuration, high theoretical energy densities of at least 500 Wh/kg can be realized with optimal utilization of active materials in both the positive and negative electrodes and minimized electrolyte volume. With increased utilization of active materials, there is a respective decrease in volume of electrolyte and other non-active components such as conductive carbon and binder. Each of these reductions has the potential to shift the equilibrium of degradation processes and alter the accumulation of degradation byproducts in higher energy battery systems. This presentation will discuss some of the implications associated with this shift in degradation as the balance of materials transitions from having multiple components in excess to a more energy dense setting with minimal excesses. 1. Whittingham, M. S. History, Evolution, and Future Status of Energy Storage. Proc. IEEE 100, 1518–1534 (2012). 2. Brandt, K. Historical development of secondary lithium batteries. Solid State Ion. 69, 173–183 (1994).