Theoretical and Experimental Strategies for New Heterostructures with Improved Stability for Rechargeable Lithium Sulfur Batteries

Abstract

The prowess of Li4SiO4, a known Li-ion conductor for effectively trapping solvents while enabling Li-ion migration contributing to Li-S battery stability was previously demonstrated. Herein Li-ion conductivity enhancement of Li4SiO4 was investigated using first principles calculations and correspondingly, Ca, Mg and F ion substituted Li4SiO4 were shown to yield ∼3–4 order improvement in room temperature Li+ ion conductivities with reduced activation barriers via vacancy mechanism favoring easy diffusion. To demonstrate effects on Li-S battery performance, high sulfur loading cathodes (∼3.8 mg S cm−2) were generated by coating substituted silicates onto sulfur infiltrated copper bipyridine complex framework material (S-Cu-bpy-CFM) electrodes. These ions substituted Li4SiO4 coated sulfur electrodes demonstrated high areal capacities (∼2.21–2.67 mAh cm−2), good capacity retention (∼0.19%–0.33%/cycle) and rate capabilities (∼800 mAh g−1−700 mAh g−1 @100 mA g−1, 600 mAh g−1− 500 mAh g−1 @300 mA g−1, 400 mAh g−1−300 mAh g−1 @ 500 mA g−1 and ∼250 mAh g−1–190 mAh g−1 @1000 mA g−1) contrasted with unsubstituted Li4SiO4. Post cycle electrochemical impedance spectroscopy analysis of the batteries also shows that the difference in charge-transfer resistance (Rct) between the 1st and the 100th cycle is 49.7Ω for the pristine Li4SiO4 coated electrodes while only 2.14Ω is observed for the calcium substituted Li4SiO4 coated cathodes justifying the cycling performance improvements using the ion-substituted Li4SiO4 coating.