Lithium-Sulfur Batteries with a Block Copolymer Electrolyte Analyzed by X-ray Microtomography

Abstract

Most of the work on Lithium-sulfur (LiS) batteries use liquid electrolytes that have limited stability when coupled with Li metal anodes. We have studied LiS batteries with a solid block copolymer electrolyte which exhibits improved stability against Li anodes. The electrolyte comprises a polystyrene-b-poly(ethylene oxide) (SEO) copolymer doped with a Li salt. Hollow carbon nanospheres impregnated with sulfur were used to build a composite cathode. Two types of sulfur-impregnated functionalized carbon nanospheres were used: one with carboxylic acid groups and the other with short lithium poly(4-styrenesulfonyl (trifluoromethylsulfonyl)imide) (PSTFSI-Li) chains. Cells with Li 2 S 8 dissolved in the SEO based electrolyte served as the baseline. After cycling, the reason for capacity fade was determined by imaging the batteries using synchrotron hard X-ray microtomography. It is generally assumed that LiS cells fail due to dissolution of polysulfide into the liquid electrolyte, i.e., the main problems related to the cathode. In our all-solid cells, failure was primarily due to delamination of the Li foil from the polymer electrolyte layer. Delamination is also observed at the sulfur cathode. It is likely that the large changes in volume of the active materials during cycling induce delamination in all-solid LiS cells.

A Highly Sensitive Electrochemical Sensor of Polysulfides in Polymer Lithium-Sulfur Batteries

“…Zaghib and coworkers 23 used operando SEM and UV-vis spectroscopy to study the transformation of solid sulfur into soluble polysulfide species, and vice versa, during discharge and charge, respectively, of a polyether polymer Li-S battery. Balsara and coworkers used XAS [24][25][26] to characterise the various polysulfide species formed during the discharge of a polystyrene-poly(ethylene oxide) diblock copolymer (SEO) Li-S battery, and X-ray microtomography 27 to monitor structural changes with cycling. Wan and coworkers 28 used realtime optical microscopy, and ex situ XPS and Raman to study the degradation of a Li-S battery with a polymer-ceramic composite electrolyte made with poly(ethylene oxide) and Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 .…”

100th Anniversary of Macromolecular Science Viewpoint: Solid Polymer Electrolytes in Cathode Electrodes for Lithium Batteries. Current Challenges and Future Opportunities

“…SEO = salt-containing PS- b -PEO. Reproduced with permission from ref . Copyright 2020 IOP Publishing.…”

“…These large volume changes can lead to delamination of the electrode composite. For example, X-ray tomography experiments revealed the formation of void spaces and delamination failure between PS- b -PEO/LiTFSI SPE and all-solid sulfur electrode interface after cycling (Figure d) …”

“…For example, X-ray tomography experiments revealed the formation of void spaces and delamination failure between PS-b-PEO/LiTFSI SPE and all-solid sulfur electrode interface after cycling (Figure 1d). 55 The common method to mitigate poor interfacial contact issues involves operating under compressive pressure; however, this approach is likely of limited practical utility. Alternative methods include heat treatment, which leverages the melt-flow properties of polymers to improve the interfacial compatibility between SSE/interface within a battery cell.…”

History and recent developments in divergent electrolytes towards high-efficiency lithium–sulfur batteries – a review

“…Additionally, it shows a stable interface with the lithium metal anode. 101,102 The phase behavior of SEO/Li 2 S x mixtures could be better than mixtures of SEO and other lithium salts. The thermal properties of the SEO copolymers with Li 2 S x were investigated in Fig.…”