High Sulfur Content, Fast Charging, and Extended Life Cathode for Lithium Sulfur Battery
Date
2022-06-22
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Abstract
Beyond lithium-ion batteries (LIB) are required to meet high energy density applications of modern society. Lithium-sulfur (Li-S) battery technology offers a theoretical energy density of 2500 Wh kg-1, which is around 5 times that of existing LIBs. However, at a cell level energy density of >350 Wh kg-1 (where sulfur loading >5 mg cm-2) at room temperature, the Li-S battery demonstrates severe capacity fade, limited cyclability, and poor rate performance. In this thesis, in-situ sulfur cathodes, MoS3 and WS3, are explored as solutions to improve the rate performance of Li-S batteries. Presence of S22- disulfide ligands in MoS3 or WS3, provides an alternative sulfur source to electronically insulating S8. The Li-S battery with MoS3 cathode demonstrated a high reversible capacity of ~1500 mAh g-1 in the first cycle at a rate of 0.3 C, indicating a high sulfur utilization percent of ~89%. Furthermore, when cycled long term at a rate of 2 C (~1000 mAh g-1 in the first cycle), the device was cyclable close to 200 cycles with a capacity fade rate of 0.13% per cycle. The analogous WS3 cathode delivered similar performance. The device was rate capable up to a C-rate of 2C with a specific capacity of ~600 mAh g-1. On long-term cycling the WS3 cathode exhibited a capacity fade rate of ~0.02% per cycle. To increase the sulfur loading tolerance of cathode architecture, a freestanding electrode is investigated. Into this electrode matrix a hybrid MoS2-WS2 anchoring material is incorporated. The novel cathode design maximizes the geometric coverage for anchoring-conversion of polysulfides to restrain shuttle effect at practical sulfur (S) loadings. The strategy presented in chapter 6 prevents the accumulation of polysulfide molecules at a localized site of the anchoring surface. Our systematic analysis (5 – 50 mg cm-2 of S-loadings) reveals that the unique cathode architecture exhibits reversible S-loading tolerance up to 28 mg cm-2. A high initial areal capacity of 32 mAh cm-2 with an area specific energy density of 67 mWh cm-2 is achieved, which is highest among the hybrid composites reported till date. The approach can unlock high S-loading Li-S cells with extended cyclability and rate performance. Finally, we propose a computational aided design principle to screen an ideal surface for polysulfide electrocatalysis.
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Keywords
Battery, sulfur, energy, lithium, metal sulfides, electrocatalysis, energy densitry
Citation
Abraham, A. M. (2022). High Sulfur Content, Fast Charging, and Extended Life Cathode for Lithium Sulfur Battery (Doctoral thesis). University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca .