Interaction of FeS₂and Sulfur in Li-S Battery System

Abstract

Many transition metal sulfides are electronically conductive, electrochemically active and reversible in reactions with lithium. However, the application of transition metal sulfides as sulfur cathode additives in lithium-sulfur (Li-S) batteries has not been fully explored. In this study, Pyrite (FeS 2 ) is studied as a capacity contributing conductive additive in sulfur cathode for Li-S batteries. Electrochemically discharging the S-FeS 2 composite electrodes to 1.0 V activates the FeS 2 component, contributing to the improved Li-S cell discharge energy density. However, direct activation of the FeS 2 component in a fresh S-FeS 2 cell results in a significant shuttling effect in the subsequent charging process, preventing further cell cycling. The slight FeS 2 solubility in electrolyte and its activation alone in S-FeS 2 cells are not the root causes of the severe shuttling effect. The observed severe shuttling effect is strongly correlated to the 1 st charging of the activated S-FeS 2 electrode that promotes iron dissolution in electrolyte and the deposition of electronically conductive FeS on the anode SEI. Pre-cycling of the S-FeS 2 cell prior to the FeS 2 activation or the use of LiNO 3 electrolyte additive help to prevent the severe shuttling effect and allow the cell to cycle between 2.6 V to 1.0 V with an extra capacity contribution from the FeS 2 components. However, a more effective method of anode pre-passivation is still needed to fully protect the lithium surface from FeS deposition and allow the S-FeS 2 electrode to maintain high energy density over extended cycles. A mechanism explaining the observed phenomena based on the experimental data is proposed and discussed.

Formation of a Surficial Bifunctional Nanolayer on Nb2O5 for Ultrastable Electrodes for Lithium‐Ion Battery

“…Additionally, in terms of overpotential, N-Nb 2 O 5 exhibits the smallest overpotential, while Nb 2 O 5 exhibits the highest overpotential, which highlights the effect of surficial nanolayer. Generally, it is widely reported that a surficial nanolayer helps to minimize the excess free energy and interfacial energy [42,47] and it has been further confirmed that such surficial films reduce the polarization at the interface, [48] which then also helps to lower the overpotential. Similar trend was also shown in the previous literature.…”

“…Moreover, it is interesting to note that N-Nb 2 O 5 shows minimal contact resistance but has higher charge transfer resistance compared with Nb 2 O 5 . The minimal contact resistance of N-Nb 2 O 5 is based on the previous claim [48] that surficial nanolayer/film helps to reduce the polarization at the interface, resulting in decreased contact resistance. On the other hand, as for the charge transfer of electrons, electron transport pathway is increased for N-Nb 2 O 5 with the creation of additional nanolayer, making it more difficult for electrons to transport to Nb 2 O 5 .…”

Rational Design of a Dual‐Function Hybrid Cathode Substrate for Lithium–Sulfur Batteries

“…[3] Additionally, the degradation of anode and volume changes of sulfur species during reaction also undermine the electrochemical stability and cycle life of Li-S batteries, challenging the practical use of Li-S technology. [27] For instance, cobalt disulfide (CoS 2 ), [21] titanium disulfide (TiS 2 ), [28,29] and iron disulfide (FeS 2 ) [30] have been applied as sulfur hosts and have been demonstrated with a strong chemical interaction capability toward migrating polysulfides. [17][18][19][20] In view of cathode modification, it has been demonstrated that nonpolar carbon matrix with only physical polysulfide confinement may not be enough for high-loading cell performance during long cycle life.…”

Determination of Cyclability of Li/FeS2 Batteries Based on Measurement of Coulombic Efficiency

“…To evaluate comparable end points, the testing process follows a specific pattern during the data collection, as shown in the left side of the figure. The increase, decrease, and stabilization of the end discharge capacity points observed during the first 15 cycles can be attributed to the conditioning of the half-cells, a period that occurs after the electrolyte penetrates the electrode [17]. This increases the contact area between the electrode, electrolyte, and Cu foil, which yields an increment in the capacity.…”