The Use of Redox Mediators for Enhancing Utilization of Li₂S Cathodes for Advanced Li–S Battery Systems

Abstract

The development of Li2S electrodes is a crucial step toward industrial manufacturing of Li-S batteries, a promising alternative to Li-ion batteries due to their projected two times higher specific capacity. However, the high voltages needed to activate Li2S electrodes, and the consequent electrolyte solution degradation, represent the main challenge. We present a novel concept that could make feasible the widespread application of Li2S electrodes for Li-S cell assembly. In this concept, the addition of redox mediators as additives to the standard electrolyte solution allows us to recover most of Li2S theoretical capacity in the activation cycle at potentials as low as 2.9 VLi, substantially lower than the typical potentials >4 VLi needed with standard electrolyte solution. Those novel additives permit us to preserve the electrolyte solution from being degraded, allowing us to achieve capacity as high as 500 mAhg(-1)Li2S after 150 cycles with no major structural optimization of the electrodes.

A highly efficient polysulfide mediator for lithium–sulfur batteries

“…Organometallic redox mediators are shown to provide better utilization of Li 2 S (ref. 34). Additives such as P 2 S 5 also effectively control Li 2 S deposition and aid in elimination of the polysulfide shuttle 35 .…”

Keggin-type Polyoxometalates as Bidirectional Redox Mediators for Rechargeable Batteries

“…Figure 2d shows that the redox reaction of SiW itself contributed only slightly to the cell capacity, confirming the role of the POM as a mediator. While some organometallic compounds have previously shown mediation effects for the charging process, 6 it is here demonstrated that Keggin-type POMs improve the capacity as redox mediators for both charging and discharging reactions and allow long-term cycling performance in Li-S cells without any physical modification of the carbon supports.…”

“…The cathode electrolytes consisted of 10 µL of sulfolane containing 10 mM of the relevant POM and 1 M LiTFSI, as sulfolane allowed stable operation at high temperatures due to its high boiling point (>280°C) while ether-based liquid electrolytes would not. 6,12,[21][22][23][24][25] Hence, each cell contained 0.1 µmol of POM and approximately 28 µmol of sulfur atoms. A standard electrolyte that did not contain POM was also used as a control sample.…”

“…Redox mediators (RMs) have long been used in electrochemical studies [1][2][3][4] and in devices such as biosensors, 5 solar cells, 6 photocatalysis, 7 and batteries. [8][9][10][11][12][13][14][15] They facilitate the electrochemical reactions of redox compounds that are located away from the electrodes and are not electrically connected to them.…”

Redox-Active Supramolecular Polymer Binders for Lithium–Sulfur Batteries That Adapt Their Transport Properties in Operando

“…[40][41][42][43] Those consisting of polycyclic aromatic hydrocarbons, and in particular perylene bisimide 44,45 (PBI) and benzo[ghi]perylene imide (BPI), as reported by us, are amenable to supramolecular polymerization via π-stacking. Whereas our previous accounts focused on the action of soluble redox mediators in Li-S cells, our focus here is instead on their action in the solid state as a binder.…”