Interconvertible and rejuvenated Lewis acidic electrolyte additive for lean electrolyte lithium sulfur batteries
Hannah Cho, Jinkwan Jung, Ilju Kim, Jinuk Kim, Sejin Kim, Jonghyun Hyun, Chang Hoon Lee, Hobeom Kwack, Won-Sik Oh, Jinwoo Lee, Hee‐Tak Kim
Abstract
Realizing practical lithium–sulfur batteries with high energy density requires lean electrolyte design. However, under low electrolyte/sulfur (E/S) ratios, highly concentrated lithium polysulfides in the electrolyte phase limit cycling and capacity. Here, we report that a small amount of Lewis acidic calcium cation in the electrolyte addresses the problems of lean electrolyte lithium–sulfur batteries. Because of its Lewis acidity, Ca2+ readily converts lithium polysulfides into CaS and S8, preventing electrolyte jamming, polysulfide shuttle and Li corrosion. The in situ-formed CaS catalyzes the reduction reaction of lithium polysulfides. Ca2+ rejuvenates via electrochemical oxidation of CaS during charging, enabling a sustainable interconversion between Ca2+ and CaS during cycling. Li-S pouch cells with Ca2+ additive delivered an energy density of 493 Wh kg−1 (E/S of 2.4 μL mg−1) based on the total mass of the cell excluding external packaging, with 70% capacity retention at 220 cycle under 1 mA cm−2 discharge, and 346 Wh kg−1 (2.9 μL mg−1) with 77% capacity retention at 360 cycle under 1.0 C 2 mA cm−2 discharge. The judicious integration of lithium-sulfur and calcium-sulfur chemistries offers a handy but effective approach to overcome the long-lasting trade-off between energy density and cycling stability in the development of lithium–sulfur batteries. High-concentration lithium polysulfides in lean electrolyte lithium–sulfur batteries hinder stable cycling. Here, authors introduce a reversible calcium additive that regulates polysulfides chemistry and catalyzes sulfur redox reactions, improving energy density with stable cycling.