Characterizing the Behaviors of Li-O2 Battery in a Stable Electrolyte System

Boston College, Chestnut Hill MA

Investigators

Abstract

Electrochemical energy storage is of paramount importance to a future energy infrastructure that is primarily powered by renewable sources. Currently, the state-of-the-art technology, lithium (Li)-ion batteries, will not sufficiently meet increasing needs in terms of energy densities. Of the new technologies that are being pursued, lithium-oxygen (Li-O2) batteries are prominent as theoretical studies predict that Li-O2 batteries could be 2 to 10 times better than Li-ion batteries. To date, the poor stability of the battery electrolyte is a key factor that limits further advancement of this new technology. This fundamental research project will directly address this critical challenge. This project will research a water-based electrolyte that has a high level of salt so that it is not corrosive or reactive in the presence of the battery electrodes. In this way the project will directly test what key reactions occur at the electrode that limit its overall performance compared to predictions. The research project will then explore how to improve Li-O2 batteries. Upon its completion, the project will advance research on this new promising technology. The research efforts will be complemented by outreach activities designed to broaden the impacts of renewable energy research to diverse audiences including undergraduate researchers, high school student researchers, and pre-college children and their families. The project will contribute significantly to the goals of moving toward a renewable energy-powered society. This project addresses fundamental research on a novel strategy to solve the problem of electrolyte degradation of lithium-O2 batteries by using a H2O-based electrolyte, in which all known electrolyte decomposition pathways are blocked. An electrolyte with high salt concentration (referred to as water in salt, WiS) will be used to minimize potential negative influences by H2O decomposition and H2O-induced oxide decomposition. The project's research goal is to quantitatively study how electrolyte decomposition contributes to the low performance of existing Li-O2 batteries. This information is imperative to the evaluation of the theoretical maximum performance attribute of Li-O2 battery as an electrochemical energy storage technology; however, a knowledge gap exists for this information. The gap exists because previous research on Li-O2 batteries all employed electrolytes that exhibit reactivity toward oxygen species. As a result, parasitic chemical reactions due to electrolyte decomposition have been ubiquitous, greatly undermining efforts designed to understand Li-O2 battery operations. The WiS electrolyte represents a super-concentrated aqueous solution. When the salt concentration is sufficiently high (e.g., 21 mole/1 kg of H2O, or 21 m), all H2O molecules are locked down by solvating the salt ions, and the overall solution acts as an aprotic one within a reasonably wide potential window (e.g., between 1.9 V and 4.9 V vs. Li/Li+). Such a system provides a unique, organic-solvent-free environment for the studies of Li-O2 battery chemistries. WiS electrolytes have proven effective in enabling superior performance for Li-ion, Li-sulfur and, most recently, Li-O2 battery operations. The system provides a unique opportunity to examine Li-O2 battery chemistry without the confounding factors connected to parasitic chemical reactions of the electrolytes. The outcome of the project will be a knowledge base of Li-O2 chemistry without the confounding factors such as electrolyte decomposition. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.