New, Game-Changing Applications of Polymer-Based Coatings in Battery

Abstract

Commercial lithium-ion batteries (265 Wh/kg) provide 6.5× more energy than lead acid and more than 2× that of nickel-metal hydride (NiMH). These large gains in energy density have ushered in the wide proliferation of portable electronics and the commercialization of long-range personal electric vehicles. Car manufacturing companies such as Tesla and Volkswagen propose that large-scale production of electric vehicles will lower the battery pack cost to $100/kWh (currently around $150/kWh). Such large-scale projects have already started and will be more prevalent by 2020. However, the success of the electric vehicle hinges on the safety, durability, and lifetime of the battery pack. These characteristics are critically important because the lithium-ion battery operates outside its electrochemical stability window. During charging, the electrolyte is exposed to potentials beyond its stability, so it reduces on the graphite anode and may oxidize on the cathode. The lowest unoccupied molecular orbital (LUMO) of the electrolyte is below the Fermi level of the anode, and the highest occupied molecular orbital (HOMO) of the electrolyte lies above the Fermi level of the cathode. In addition, cathode discharge products may have increased solubility in the electrolyte and may be lost during cycling. Thus, battery lifetime is governed by the degree with which these undesired reactions are mitigated. Polymers enable the simple deposition of thin and stable coatings on anodes, separators, and cathode materials which improve the electrochemical performance of the battery. The careful selection of polymers can solve many problems associated with promising new batteries, such as inhibiting dissolution of soluble electrode species and stabilizing electrolyte/electrode interfaces during operation. The end result is a higher energy density and longer cycle life for the battery.