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This work explores a novel approach for improving the sodium-ion battery performance of coal char using flash pyrolysis and an ether-based electrolyte. Coal char is an ultra-low cost hard carbon with promising application as an anode material in sodium-ion batteries. During flash pyrolysis, char is heated at 1000 °C/s in a drop-tube furnace to create a highly-irregular structure. The larger d-spacing and smaller closed micropore diameter of flash-pyrolyzed char increases anode capacity compared to traditional slow-pyrolyzed char electrodes. The sodium-ion battery anode performance of flash-pyrolyzed char is further improved using an ether-based electrolyte in place of the traditional ester-based electrolyte. Performance improvements include greater initial Coulombic efficiency (58% in ester- vs. 64% in ether-based electrolyte) and improved specific capacity in an ether-based electrolyte. Overall, the combination of flash pyrolysis and ether-based electrolyte increases the sodium-ion battery discharge capacity of coal char by over 50%, from 72.5 mAh g−1 (slow-pyrolyzed char in ester-based electrolyte) to 109.4 mAh g−1 (flash-pyrolyzed char in ether-based electrolyte) (50 mA g−1 discharge rate). The results highlight improvements that can be realized through flash pyrolysis of coal char for battery applications and the numerous processing advantages of flash vs. slow pyrolysis.
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Determination of size and porosity of chars during combustion of biomass particles
This research focused on the size and overall porosity (pore volume) of carbonaceous chars, originating from high-heating rates and high-temperature pyrolysis and/or combustion of biomass. Emphasis was given to torrefied biomass chars. First, the porosity of char residues of single biomass particles of known mass was determined, based on an assumed value of skeletal density and by comparing experimentally observed temperature-time histories with numerical predictions of their burnout times. The average char porosities (effective porosities) of several raw and torrefied biomass particles were calculated to be in the range of 92–95%. Thereafter, these deduced porosity values were input again to the model to calculate the size of chars of other biomass particle precursors, whose initial size and mass were not known. Such biomass particles were sieve-classified to different nominal size ranges. This time, besides the porosity, representative time-temperature profiles of biomass particles in the aforementioned size ranges were also input to the model. Biomass particles are highly irregular with large aspect ratios and, in many cases, they melt and spherodize under high heating rates and elevated temperatures. Knowledge of the initial size of the chars, upon extinction of the volatile flames, is needed for modeling their heterogeneous combustion phase. For this purpose, numerical predictions were in general agreement with measurements of char size obtained from both scanning electron microscopy of captured chars and real-time high-speed, high- magnification cinematographic observations of their combustion. Results showed that the generated chars of the examined biomass types were highly porous with large cavities. The average initial dimension of the chars, upon rapid pyrolysis, was in the range of 50–60% the mid-value of the mesh size of the sieves used to size-classify their highly irregular parent biomass particles.
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- Award ID(s):
- 1810961
- PAR ID:
- 10336356
- Editor(s):
- Egolfopoulos, Fokion
- Date Published:
- Journal Name:
- Combustion and flame
- Volume:
- 242
- ISSN:
- 0010-2180
- Page Range / eLocation ID:
- 112182
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.combustflame.2022.112182
