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

Abstract

The FeS 2 has abundant reserves and a high specific capacity (894 mAh g −1 ), commonly used to fabricate Li-FeS 2 primary batteries, like LiM x -FeS 2 thermal batteries (working at ≈500 °C). However, Li-FeS 2 batteries struggle to function as rechargeable batteries due to serious issues such as pulverization and polysulfide shuttling. Herein, highly reversible solid-state Li-FeS 2 batteries operating at 300 °C are designed. Molten salt-based FeS 2 slurry cathodes address the notorious electrode pulverization problem by encapsulating pulverized particles in time with e − and Li + flow conductors. In addition, the solid electrolyte LLZTO tube serves as a hard separator and fast Li + channel, effectively separating the molten electrodes to construct a liquid-solid-liquid structure instead of the solid-liquid-solid structure of LiM x -FeS 2 thermal batteries. Most importantly, these high-temperature Li-FeS 2 solid-state batteries achieve FeS 2 conversion to Li 2 S and Fe at discharge and further back to FeS 2 at charge, unlike room-temperature Li-FeS 2 batteries where FeS and S act as oxidation products. Therefore, these new-type Li-FeS 2 batteries have a lower operating temperature than Li-FeS 2 thermal batteries and perform highly reversible electrochemical reactions, which can be cycled stably up to 2000 times with a high specific capacity of ≈750 mAh g −1 in the prototype batteries.

Current Status and Prospects of Research on Cathode Materials for Lithium-Based Thermal Batteries

“…Pyrite (FeS 2 ) is the most widely used cathode for thermal batteries for its good chemical stability, stable discharge performance, and high natural abundance. The theoretical capacity of FeS 2 is 1206 As g −1 and 894 mAh g −1 with an open-circuit voltage at about 2.3 V. 60 It is a typical semiconductor with a bandgap of 0.95 eV and begins to decompose at 550 °C. The self-discharge kinetics of FeS 2 can be studied by the Serin−Ellickson model.…”

“…(a) Reaction mechanism of high-temperature Li–FeS 2 batteries. Panel a was reproduced with permission from ref . Copyright 2023 John Wiley & Sons.…”

Electrode/electrolyte interphases in high-temperature batteries: a review

“…127 The most notable features of MSLBs are high discharge current density, high specific energy and specific power, short activation time as well as wide operating temperature range. 9,128,129 At present, many advanced high-tech weapons in the world have adopted MSLBs as their preferred power source. Lithium system MSLBs is an ideal electrochemical system for MSLBs.…”

Transition Metal Sulfide Conversion: A Promising Approach to Solid-State Batteries

“…91 The high thermodynamic stability of FeS 2 can also be supported by their use as thermal batteries cathodes which are operated at even higher temperatures of 400−500 °C. 92,93 More generally, the use of transition metal sulfides offer the additional safety benefit of circumventing the safety issues of oxygen release as a decomposition product as is the case with oxide-based materials such as NCM. 22,23 While the chemical and thermal stability of each active material and solid electrolyte pairing will be different, understanding of the thermal properties and behavior of conversion chemistries that undergo phase changes are far limited in scope relative to intercalation systems.…”

“…Unlike LiNi 0.8 Co 0.1 Mn 0.1 O 2 , charged LiFePO 4 cathode composites demonstrated greater thermal stability and safety (decomposition but no ignition) with Li 6 PS 5 Cl, and FeS 2 was detected at 350 °C as a decomposition product . The high thermo­dynamic stability of FeS 2 can also be supported by their use as thermal batteries cathodes which are operated at even higher temperatures of 400–500 °C. , More generally, the use of transition metal sulfides offer the additional safety benefit of circumventing the safety issues of oxygen release as a decomposition product as is the case with oxide-based materials such as NCM. , While the chemical and thermal stability of each active material and solid electrolyte pairing will be different, understanding of the thermal properties and behavior of conversion chemistries that undergo phase changes are far limited in scope relative to intercalation systems. Studying the heat signatures of systems such as TiS 2 , which can undergo both intercalation (TiS 2 → LiTiS 2 ) and conversion (LiTiS 2 → 1 Ti + 4 Li 2 S) depending on the potential window, should provide interesting insights on the different heat signatures between the two systems and on the impact moving from intercalation to conversion at the cell and pack level.…”