A Roadmap to Design Robust Redox Shuttles for Lithium-Ion Batteries

In designing robust, effective redox shuttles for overcharge protection in lithium-ion batteries, a variety of factors are necessary to consider and evaluate. The stability and reactivity of the radical cation form of a redox shuttle candidate are critical to extensive overcharge performance. Radical cations are subject to a variety of reactions because of their unpaired electron and positive charge, making them subject to nucleophilic attack and dimerization, among other reactions including disproportionation or premature reduction. Equally as important is the stability of the neutral form of the redox shuttle, which may decompose through reaction with electrolyte, SEI, and/or be reduced at the anode/electrolyte interface. Neither stability nor reactivity is easy to predict, although an understanding of organic chemistry can lead to some general guidelines for the design of less reactive species. Density functional theory (DFT) calculations can be used to predict energies of reaction and have been employed by Curtiss, Dahn, and our group. DFT calculations can also be used to compute oxidation and reduction potentials, helping to identify promising candidates before synthesizing materials. This presentation focuses on our work using DFT calculations to help us identify promising redox shuttles and to gain a better understanding of their reactivity and includes experimental data in support of some of the proposed mechanisms of decomposition.