“Just remove the water?” The real culprit behind battery failure revealed
Pohang University of Science & Technology (POSTECH)
image:
(a) Schematic illustration of the liquid-phase bubbling-assisted crystal water removal process
(b) Surface oxidation and Fe–O bond formation during conventional thermal dehydration
(c) Integrated liquid-phase dehydration–electrode fabrication process minimizing moisture re-absorption
view moreCredit: POSTECH
Like a delicate fabric that becomes damaged during drying, a promising next-generation battery material has faced an unexpected challenge: removing water to improve performance can actually shorten battery life. Now, a Korean research team has identified surface oxidation occurring during the dehydration process as the true cause of performance degradation and developed a new dehydration progress to overcome it.
A research team led by Professor Changshin Jo from the Department of Battery Engineering and the Department of Chemical Engineering at POSTECH (Pohang University of Science and Technology), together with Ph.D. candidate Seunghye Jang from the Department of Battery Engineering, recently published their findings in Advanced Materials, a world-leading journals in materials science.
As the markets for electric vehicles (EVs) and energy storage systems (ESSs) continue to expand, competition for battery raw materials is intensifying. Sodium-ion batteries have attracted significant attention as a next-generation energy storage technology because sodium is more abundant and less expensive than lithium. Among various sodium-ion battery cathode materials, Prussian Blue, an iron-based cathode material, is considered highly promising due to its low production cost and high energy-storage capability.
One major challenge is that Prussian Blue inherently contains a substantial amount of crystal water during its synthesis. This water can trigger undesirable side reactions, including electrolyte decomposition, gas evolution, and iron dissolution, ultimately reducing battery performance and lifespan. To address this issue, high-temperature heat treatment has been widely used to remove the water. However, battery performance often deteriorates after dehydration, and the underlying cause has remained unclear.
The research team focused on the fact that battery performance did not improve as expected even after crystal water had been removed through high-temperature heat treatment. Through detailed analyses of the surface chemical state before and after dehydration, they discovered for the first time that the primary cause of performance degradation is not the crystal water itself, but rather iron–oxygen (Fe–O) bonds that form on the surface of Prussian Blue during heat –treatment. These Fe–O bonds promote surface oxidation, accelerate electrolyte decomposition and gas generation, and ultimately undermine battery performance and stability.
Based on this finding, the researchers developed a new solution: a liquid-phase bubbling dehydration process that continuously injects nitrogen gas into a non-aqueous solvent. As nitrogen bubbles pass through the solution, crystal water is effectively removed while minimizing exposure to oxygen, suppressing surface oxidation. The process is analogous to drying wet clothes with a gentle breeze rather than with excessive heat that can damage the fabric.
Using this approach, the team reduced the crystal water content of Prussian Blue from approximately 12 wt.% to around 1 wt.% while significantly suppressing surface oxidation. The treated material also generated less gas during battery operation and exhibited superior capacity retention after 100 charge-discharge cycles compared with conventionally heat-treated samples.
Importantly, the new process can directly utilize the solvent already employed during electrode fabrication, allowing dehydration and electrode fabrication to be integrated into a single step. This integration minimizes moisture reabsorption, a common issue in conventional processing, and further improves long-term stability.
“This liquid-phase bubbling dehydration process integrates dehydration and electrode fabrication into a single operation while preventing moisture reabsorption,” said Professor Changshin Jo. “We believe this process can contribute to the commercialization of next-generation sodium-ion batteries.”
The study was supported by the Ministry of Trade, Industry and Energy through the Advanced Specialized Graduate School Program for Batteries, the Energy Technology Development Program, and the Industrial Technology Innovation Program.
Journal
Advanced Materials
Article Title
Suppressing Surface Degradation in Na-Rich Prussian Blue Cathodes via Liquid-Phase Dehydration
No comments:
Post a Comment