Isotope Effects in a Li−S Battery: A New Concept

Abstract

Lithium‐sulfur battery represents an innovative technology for the next generation electrochemical energy storage, and insight into the fundamentals about its electrochemistry is a key to improved battery storage performance. With years of striving efforts, the interpretation of Li−S reaction mechanism has been extended down to a molecular level. Based on our recent work, we propose to re‐examine the Li−S electrochemistry at a (sub)atomic level. Both Li anode and S cathode are made up of mixtures of stable isotopes. Provided with almost the same nucleus structure yet different neutron numbers (and atomic mass), these isotopes could affect the thermodynamic and kinetic parameters of a chemical reaction, and energy storage capability of a Li−S battery. At the cathode, 34S forms stronger S−S bonds and shows higher tendency to react with Li than 32S, so that it helps to improve cathode reaction kinetics. High‐order polysulfide anions based on 34S show more sluggish migration in the ether electrolyte than the 32S‐based counterparts, which accounts for improved cycling stability of battery. Based on the electrochemical isotope effects of S, a conceptual technology for separating isotopes from natural chalcogen elements was introduced and shows a higher separation factor than the conventional methods.

Nonconventional Electrochemical Reactions in Rechargeable Lithium–Sulfur Batteries

“…In a recent work, we proposed to study the electrochemical conversion reaction between Li and stable S isotopes in a RLSB. 19 6c). 20 The electrochemical data is consistent with the calculation results that cyclo-34 S 8 (or 34 S atoms on a heteroring) is more prone to react with Li than the 32 S-based counterparts and that 34 S-based high-order polysulfides (including Li 2 34 S 8 , Li 2 34 S 6 , and Li 2 34 S 4 ) show higher solvation energy than the 32 S-based counterparts so that they exhibit higher solubility in the electrolyte and favor the discharge reaction.…”

“…Note that the (electro)chemical reaction proceeds with repeated breaking and (re)formation of chemical bonds between the adjacent atoms, and interatomic information collected at a (sub)atomic level would provide more explicit explanations about the reaction mechanism. In a recent work, we proposed to study the electrochemical conversion reaction between Li and stable S isotopes in a RLSB . Natural S consists of four stable isotopes ( 32 S, 33 S, 34 S, and 36 S), among which 32 S and 34 S account for atomic fractions of 94.99% and 4.25%, respectively (Figure a, b).…”