Temperature-Dependent Reaction Pathways in FeS₂: Reversibility and the Electrochemical Formation of Fe₃S₄

Abstract

The present study has used a variety of characterization techniques to determine the products and reaction pathways involved in the rechargeable Li−FeS 2 system. We revisit both the initial lithiation and subsequent cycling of FeS 2 employing an ionic liquid electrolyte to investigate the intermediate and final charge products formed under varying thermal conditions (room temperature to 100 °C). The detection of Li 2 S and hexagonal FeS as the intermediate phases in the initial lithiation and the electrochemical formation of greigite, Fe 3 S 4 , as a charge product in the rechargeable reaction differ significantly from previous reports. The conditions for Fe 3 S 4 formation are shown to be dependent on both the temperature (∼60 °C) and the availability of sulfur to drive a FeS to Fe 3 S 4 transformation. Upon further cycling, Fe 3 S 4 transforms to a lower sulfur content iron sulfide phase, a process which coincides with the loss of sulfur based on the new reaction pathways established in this work. The connection between sulfur loss, capacity fade, and charge product composition highlights the critical need to retain sulfur in the active material upon cycling.

A comprehensive cognition for the capacity fading mechanism of FeS2 in argyrodite‐based all‐solid‐state lithium battery

“…31b Previous works have proposed that the sulfur loss of FeS 2 cathode accounts for the capacity fade in conventional organic electrolyte system, which is caused by the shuttle effect of polysulfide. 11 Obviously, there is no shuttle effect in ASSLB. Hence, we proposed a new insight that the sulfur loss of FeS 2 cathode in ASSLB manifests as accumulation in the form of inactive Li 2 S.…”

“…Therefore, the capacity fade mechanism of FeS 2 gains extensive attention over the past few years. By analyzing the dissolution of polysulfide in 1,3‐dioxolane, Whang et al 11 demonstrated that the sulfur loss caused by shuttle effect accounts for the rapid capacity fade of FeS 2 . Ashby et al 12 pointed out that volume expansion and causing degradation of the conductive matrix is another important factor for the capacity fade.…”

Modulation of the Oxidation End‐Product Toward Polysulfides‐Free and Sustainable Lithium‐Pyrite Thermal Batteries

“…For controversy (ii), researchers have recognized that the FeS 2 structure is not recoverable at 20–100 °C. [ 26–28 ] Researchers were eager to achieve the reproduction of FeS 2 after cycling at a high temperature (>400 °C). [ 29 ] The researchers analyzed this was feasible from the results of calorimetric measurements of chemically delithiated Li 2 FeS 2 and speculated the following reaction: FeS (hexagonal) + S$$\xrightarrow{{{{197}}^ \circ {\rm{C}}}}$$FeS 2 (orthorhombic)$$\xrightarrow{{ > 265{\ }^ \circ {\rm{C}}}}$$FeS 2 (cubic).…”

3D Printing of Ridged FeS2 Cathodes for Improved Rate Capability and Custom-Form Lithium Batteries

“…Alternatively, iron disulfide (FeS 2 ) is another prominent conversion cathode material of interest for Li-primary and thermal batteries due to its high theoretical energy density, low cost, thermal stability, and earth abundance . Li-FeS 2 is a well-known commercial Li-primary system with expansive effort put forth in demonstrating efficient electrochemical reversibility, allowing for high energy density cycling in secondary batteries. , Though it suffers from polysulfide limitations similar to Li–S, the formation of polysulfides in Li-FeS 2 may be mitigated more easily because the sulfur/polysulfide reaction mechanism is only one part of the overall Li-FeS 2 battery reaction mechanism for storing charge. Mitigation of polysulfide formation in Li-FeS 2 batteries is an active area of research, but a common mitigation is to use a limited voltage cycling window .…”