Abstract
A facile and selective hydrothermal synthesis is performed to control the crystalline phases of cobalt hydroxides into α-Co(OH)2 and β-Co(OH)2: α-Co(OH)2, consisting of both octahedral and tetrahedral Co sites, is produced without ionic liquids, whereas β-Co(OH)2, containing octahedral Co sites, is synthesized in the presence of ionic liquids. The ionic liquids play significant role as co-solvent and template to tune the morphology of Co(OH)2. α-Co(OH)2 reveals flake-like structure, whereas β-Co(OH)2 exhibits nanorod-like network structure. The interlayer spacing of α-Co(OH)2 is 8.24 Å, which is larger than 4.63 Å of β-Co(OH)2 due to the expansion of interlayer by the precursor Cl─ anions. The presence of Cl─ anions hinders the insertion of hydroxide ion into α-Co(OH)2 interlayers, which shows the specific capacitance of 613 F g─1 less than 1066 F g─1 of β-Co(OH)2 at 2 A g─1. When the current density increases up to 20 A g─1, the capacitance retention of β-Co(OH)2 is 80%, greater than 70% of α-Co(OH)2. Configuring β-Co(OH)2 and reduced graphene oxide as positive and negative electrodes, asymmetric supercapacitor delivers the maximum energy and power densities of 20.05 W h kg─1 and 13.40 kW kg─1 with the capacitance retention of 93% over 10,000 cycles.
Original language | English |
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Pages (from-to) | 9-17 |
Number of pages | 9 |
Journal | Journal of Power Sources |
Volume | 422 |
DOIs | |
State | Published - 15 May 2019 |
Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2019 Elsevier B.V.
Funding
This research was supported by both Korea Electric Power Corporation (Grant number: R17XA05-52) and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF- 2017R1D1A1B03036362). This research was supported by both Korea Electric Power Corporation (Grant number: R17XA05-52 ) and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education ( NRF- 2017R1D1A1B03036362 ).
Funders | Funder number |
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Ministry of Education | - 2017R1D1A1B03036362 |
National Research Foundation of Korea | NRF- 2017R1D1A1B03036362 |
Korea Electric Power Corporation | R17XA05-52 |
Keywords
- Asymmetric device
- Cobalt hydroxide
- Hybrid supercapacitors
- Ionic liquid
- Nanostructure
- Redox capacitor