Revealing the Sulfur Redox Paths in a Li–S Battery by an In Situ Hyphenated Technique of Electrochemistry and Mass Spectrometry

Abstract

The lithium–sulfur (Li–S) battery is one of the most promising next generation energy storage systems due to its high theoretical specific energy. However, the shuttle effect of soluble lithium polysulfides formed during cell operation is a crucial reason for the low cyclability suffered by current Li–S batteries. As a result, an in‐depth mechanistic understanding of the sulfur cathode redox reactions is urgently required for further advancement of Li–S batteries. Herein, the direct observation of polysulfides in a Li‐S battery is reported by an in situ hyphenated technique of electrochemistry and mass spectrometry. Several short‐lived lithium polysulfide intermediates during sulfur redox have been identified. Furthermore, this method is applied to a mechanistic study of an electrocatalyst that has been observed to promote the polysulfides conversion in a Li–S cell. Through the abundance distributions of various polysulfides before and after adding the electrocatalyst, compelling experimental evidences of catalytic selectivity of cobalt phthalocyanine to those long‐chain polysulfide intermediates are obtained. This work can provide guidance for the design of novel cathode to overcome the shuttle effect and facilitate the sulfur redox kinetics.

Synergistic effect between PPy:PSS copolymers and biomass-derived activated carbons: a simple strategy for designing sustainable high-performance Li–S batteries

“…Wu et al 74 observed two and three peaks for the reduction and oxidation process, respectively, and the in situ Raman spectra showed up to ve peaks, assigned to different stretching, and bending modes of polysuldes [S 8 2À , S 4 2À , S 4 À , S 3 À and S x 2À (x ¼ 4-8)], and revealing the complexity of the electrochemical system. More complex proles have been used by Yu et al 75 to understand in depth the mechanism of S redox reaction, combining cyclic voltammetry and mass spectrometry, able to identify numerous short-live LiPSs intermediates during the process. We believe that the prole shape of the electrochemical measurements is an open question due to the reaction complexity and the role played by the different components of the cell.…”

Recent Advances and Strategies toward Polysulfides Shuttle Inhibition for High‐Performance Li–S Batteries

“…Fortunately, with the continuous development of characterization techniques, the mystery of the catalysis mechanism is gradually being unveiled. [ 208 ] In situ characterization techniques such as operando XAS, IR, XPS, and STEM should be developed and optimized to real‐time monitor the instantaneous change and evolution process inside the battery during the operation process, thereby providing accurate guidance for the design of advanced mediators materials for Li–S batteries. Development of polysulfides‐free solid‐state electrolyte: Replacing liquid electrolytes with all solid‐state electrolytes is the most effective strategy to overcome the polysulfides shuttle problem intrinsically.…”

“…Fortunately, with the continuous development of characterization techniques, the mystery of the catalysis mechanism is gradually being unveiled. [ 208 ] In situ characterization techniques such as operando XAS, IR, XPS, and STEM should be developed and optimized to real‐time monitor the instantaneous change and evolution process inside the battery during the operation process, thereby providing accurate guidance for the design of advanced mediators materials for Li–S batteries. 2)Development of polysulfides‐free solid‐state electrolyte: Replacing liquid electrolytes with all solid‐state electrolytes is the most effective strategy to overcome the polysulfides shuttle problem intrinsically. Of which, oxide‐based and solid polymer electrolytes are usually combined with liquid solvent or polymer, resulting in an unavoidable polysulfides formation.…”

Identifying Metal-Oxo/Peroxo Intermediates in Catalytic Water Oxidation by In Situ Electrochemical Mass Spectrometry

“…However, it is hard for them to obtain information on intermediates in electrochemical water oxidation. Another EC-MS method developed by Shao et al combining a hybrid ultramicroelectrode (UME) technique and relay electrospray ionization mass spectrometry realized the detection of short-lived intermediates in a series of complicated EC reactions including electrochemiluminescence, oxygen reduction at liquid/liquid interfaces, and sulfur redox paths in a lithium–sulfur battery. − The in situ EC-MS based on UMEs could be a useful technique to identify intermediates and investigate mechanisms in catalytic water oxidation.…”

“…As illustrated in Scheme , the carbon hybrid UME can be employed as both the micro-EC cell and MS nanospray emitter, which has been demonstrated in our previous work. ,, Using this EC-MS setup, when the potential is applied on the micro-EC cell and the piezoelectric pistol starts to pump, the catalyst and intermediates in water oxidation can be directly sampled from the carbon UME surface into MS and analyzed in real-time. Cell 2 (SI) with 10 mM PB (pH = 7.0) was used in EC-MS measurements to decrease the interference of electrolytes.…”