The Importance of Swelling Effects on Cathode Density and Electrochemical Performance of Lithium−Sulfur Battery Cathodes Produced via Dry Processing

Abstract

Lithium−sulfur batteries are promising candidates to satisfy the growing demand for high gravimetric, as well as high volumetric energy density batteries, due to their abundant and cost‐efficient raw‐materials. Consequently, this cell system has become an active subject of academic and industrial research. Therefore, new records for gravimetric, as well as volumetric energy densities have been reported in recent years. To further increase the volumetric energy density of the cells, the electrodes are often densified. Hence, the influence of the cathode density on the performance of lithium−sulfur batteries is still not fully understood. Herein, dry‐processed (DRYtraec) sulfur carbon cathodes with varying electrode densities are tested with ether‐based electrolytes under lean electrolyte (5 μL mg(s)−1) conditions. The electrochemical evaluation reveals that the density does not influence the performance of the cathodes at coin‐cell level as their density is altered upon electrolyte contact due to swelling. To monitor this, dynamic swelling experiments via confocal microscopy are conducted. Subsequently, the findings are transferred to investigate the influence of cathode swelling on the volumetric energy density. The influence of cathode swelling on the volumetric energy density of pouch cells is calculated based on the cathodes investigated at coin‐cell level.

Influence of external stack pressure on the performance of Li-S pouch cell

“…The thickness of the cathode is reduced by 54%, and due to the applied pressure, only submicrometer pores can be observed in figure S6(d). This is in accordance with the literature, demonstrating that the application of external pressure on the cathodes drastically reduces their macro-porosity [44] Contrarily, the pressure-free tested one does not show such compaction. In figures S6(a) and (b), macropores with a length and width of several micrometers can be observed as well as submicrometer pores.…”

“…The surface of both cathodes, tested without or with 0.31 MPa, is fractured. These fractures can be appointed to the swelling and expansion of the dry-film cathodes just after electrolyte contact [44]. The length of the fractures approaches several hundred micrometers, while the width is in the µm-scale.…”

Strategies towards High Performance Lithium‐Sulfur Batteries

“…[21] Therefore, a low E/S ratio withdraws considerable attention for developing high energy density LSBs. [110,111] However, using a low E/S ratio reduces the LiPSs redox mediator formation, eventually leading to sluggish redox kinetics, poor active materials accessibility, large polarization, and poor reversibility of the LSB. [112] Since concerns of E/S are being recognized by researchers, several strategies have been developed for the practical application of LSBs.…”

Sustainable Protein‐Based Binder for Lithium‐Sulfur Cathodes Processed by a Solvent‐Free Dry‐Coating Method

“…[23,25] Numerous published solvent-free electrode processing techniques depend on fluorine-based polymers. [26][27][28] However, the production of these polymers is discussed in regard of health and environmental issues. [29] Consequently, there is a need of a solventfree processable and fluorine-free alternative.…”

“…Herein, for the first time, the biodegradable polypeptide sericin is introduced as a binder in solvent‐free processed S/C cathodes and compared to polytetrafluoroethylene (PTFE) binder, which has been used for the DRYtraec® process so far. [ 13 , 27 , 32 , 33 ] The surface morphology as well as the adhesion properties of these cathodes are characterized. Moreover, their wetting and swelling behavior is studied by confocal microscopy.…”