Investigation of the Relationship between Solvation Structure and Battery Performance in Highly Concentrated Aqueous Nitroxy Radical Catholyte

RD Yang and Y Zhang and K Takechi and EJ Maginn, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 13815-13826 (2018).

DOI: 10.1021/acs.jpcc.8b00915

A new battery catholyte material composed of equimolar 4-methoxy-2,2,6,6-tetramethylpiperidine 1-oxyl (MT) and lithium his (trifluoromethanesulfonyl) imide (LT) and its highly concentrated mixtures with water were studied using experiments and molecular dynamics simulations. It was found that the dynamic properties of the mixture are significantly improved by adding even a small amount of water. Detailed analysis on the solvation structure in the mixtures reveals that water molecules can break the strong interaction between MT and LT, and thus the ions can move more freely. As a result, the ionic conductivity of the catholyte mixtures increases with increasing water molar ratio in the water concentration range covered in the current work. The performance of the catholyte mixture systems was also tested in battery cells. The best utility efficiency of the capacity was found for the mixture of water:MT:LT ratio at 5.3:1:1. Water molar ratios of 5 to 6 were also found to be the lowest concentration at which MT and LT are fully saturated by water. These results provide insightful understanding of the performance of these battery catholytes.

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