Tuning the water-to-methanol ratio to modulate α-phase Ni and Co hydroxides using mixed structure-directing agents for energy storage applications
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Author list: Kuo P.-C.; Kubendhiran S.; Lai Y.-C.; Kongvarhodom C.; Saukani M.; Yougbaré S.; Chen H.-M.; Wu Y.-F.; Lin L.-Y.
Publication year: 2025
Volume number: 46
ISSN: 24685194
Languages: English-Great Britain (EN-GB)
Abstract
Nickel and cobalt hydroxide is one of the most efficient active materials for battery supercapacitor hybrid (BSH), due to multiple oxidation states and high theoretical capacities. The intrinsic property of nickel and cobalt hydroxide is crucial to improve before integrating foreign materials. Synthesizing alpha phase hydroxide is advantageous for energy storage, as it offers larger interlayer spaces and superior electrochemical activities. In this work, α-Ni(OH)2 and α-Co(OH)2 are synthesized as energy storage materials in a precursor solution containing the structure directing agents of NH4F and NH4HF2. The effects of the water-to-methanol ratio in the solvent are investigated. Alpha phase hydroxides are easily achieved by incorporating water into the solvent. With the favorable alpha phase and excellent surface properties, the highest specific capacitance of 921.1 F/g corresponding to the capacity of 644.8 C/g are achieved for the optimal hydroxide (WM11) electrode. The BSH assembled with WM11 and carbon electrodes exhibits a maximum energy density of 25.3 Wh/kg at 800 W/kg, with a capacitance retention of 83.0% and a Coulombic efficiency higher than 94.5% after 10,000 cycles. This work emphasizes the significance of improving the intrinsic properties of active materials rather than merely seeking contributions from foreign materials. © 2025 Elsevier Ltd
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