Atomic-scale investigation of the reversible α- to ω-phase lithium ion charge – discharge characteristics of electrodeposited vanadium pentoxide nanobelts
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Journal of Materials Chemistry A |
| Authors | Haytham E. M. Hussein, Richard Beanland, Ana M. Sánchez, David Walker, Marc Walker |
| Institutions | University of Warwick |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study successfully synthesized high-aspect-ratio Vanadium Pentoxide (V2O5) nanobelts (NBs) via electrochemical deposition and demonstrated highly reversible, high-capacity lithium intercalation behavior, tracked at the atomic scale.
- Novel Synthesis: Amorphous V2O5 NBs were electrodeposited using a potential pulse methodology on Boron-Doped Diamond (BDD) electrodes in a mixed water-DMF solvent system, followed by thermal annealing to crystalline α-V2O5.
- Phase Reversibility: The highly challenging reversible phase transition between the layered α-V2O5 and the rock-salt ω-Li3V2O5 structure was achieved and confirmed during the first charge/discharge cycle.
- High Capacity: The material delivered a maximum specific capacity of 440 mA h g-1 (discharge) and 439 mA h g-1 (charge) at a C/10 rate, consistent with the theoretical incorporation of three lithium ions (Li+) per V2O5 unit cell.
- Atomic Insight: Aberration-corrected STEM confirmed the complete conversion of the NB structure to the disordered rock-salt ω-Li3V2O5 phase during lithiation and the full restoration of the α-V2O5 phase upon delithiation.
- Surface Structure: A thin (1-2 nm) rock-salt Vanadium Oxide (VO) layer was observed coherently strained at the edges of the pristine and delithiated NBs, though its presence was below the detection limit of bulk XPS.
- Cycling Limitations: Preliminary second-cycle studies showed reformation of the ω phase but were accompanied by a significant morphological change (NBs becoming more equiaxed), indicating structural instability over extended cycling.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Theoretical Capacity | ~440 | mA h g-1 | Based on 3 Li+ intercalation per V2O5 |
| 1st Cycle Discharge Capacity | 440 | mA h g-1 | Galvanostatic cycling (C/10 rate) |
| 1st Cycle Charge Capacity | 439 | mA h g-1 | Galvanostatic cycling (C/10 rate) |
| Li Intercalation Ratio (Max) | ~3.0 | Li+ per V2O5 | Corresponds to ω-Li3V2O5 formation |
| Cycling Rate | C/10 | N/A | 10 hours discharge/10 hours charge |
| Voltage Window | 1.5 - 3.6 | V | vs. Li |
| Crystallization Temperature | 350 | °C | Thermal annealing in air (2 hours) |
| NB Thickness (α-V2O5) | 10-20 | nm | Typical range |
| NB Mean Length (α-V2O5) | 134 (Range 15-221) | nm | Statistical analysis |
| NB Mean Width (α-V2O5) | 9 (Range 5-37) | nm | Statistical analysis |
| α-V2O5 Lattice Parameter (a) | 11.519 | Angstrom | Orthorhombic structure (ICDD 00-041-1426) |
| ω-Li3V2O5 Lattice Parameter | 4.095 | Angstrom | Rock-salt structure after lithiation |
| VO Surface Layer Thickness | 1-2 | nm | Observed on (010) facets of NBs |
Key Methodologies
Section titled “Key Methodologies”The synthesis and characterization relied on a highly controlled electrochemical deposition process followed by advanced atomic-scale imaging.
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Electrochemical Deposition (V2O5 NBs):
- Electrode: Boron-Doped Diamond (BDD) used as the working electrode due to its catalytic inertness, kinetically retarding water oxidation.
- Solvent System: Mixed water (pH 1.87) and Dimethylformamide (DMF) (3:1 ratio) used to widen the electrochemical stability window and promote Li+ diffusion.
- Pulse Sequence: A five-step potential pulse sequence was applied to control nucleation and growth, resulting in amorphous V2O5 NBs.
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Crystallization and Phase Identification:
- Annealing: As-deposited amorphous V2O5 was annealed in air at 350 °C for 2 hours to achieve crystallization.
- In Situ TEM: In situ heating TEM confirmed the crystallization temperature, with the first evidence of α-V2O5 forming at 350 °C and clear spot patterns at 365 °C.
- Bulk Analysis: Grazing Incidence XRD and XPS confirmed the resulting material was the orthorhombic α-V2O5 phase (V5+ dominant).
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Electrochemical Testing:
- Cell Setup: Three-electrode cell using BDD-V2O5 as the working electrode, Pt wire counter, and SCE reference.
- Electrolyte: 1 M LiCl + 1 M LiClO4 in a 1:3 water:acetonitrile (MeCN) mixture, chosen for low viscosity and enhanced Li+ solvation/diffusion.
- Cycling: Galvanostatic discharge/charge performed at a C/10 rate within the 1.5 V to 3.6 V vs. Li|Li+ window.
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Atomic-Scale Characterization (ac-STEM):
- Technique: Aberration-corrected Scanning Transmission Electron Microscopy (ac-STEM) and Electron Energy Loss Spectroscopy (EELS) were used to track structural changes in individual NBs after lithiation and delithiation.
- Phase Tracking: ac-STEM confirmed the conversion of layered α-V2O5 (V5+) to rock-salt ω-Li3V2O5 (V4+/V3+) and back to α-V2O5, providing atomic resolution of the highly disordered ω phase.
Commercial Applications
Section titled “Commercial Applications”The findings regarding high-capacity, reversible phase transitions in nanostructured V2O5 are highly relevant to advanced energy storage technologies.
- High Energy Density Lithium-Ion Batteries (LIBs): V2O5 nanobelts offer a theoretical capacity (440 mA h g-1) significantly greater than commercial cathodes like LiCoO2 (~240 mA h g-1), making them candidates for next-generation high-energy-density LIBs.
- Advanced Cathode Synthesis: The successful use of electrochemical deposition provides a scalable, low-temperature, and potentially cost-effective method for synthesizing high-aspect-ratio nanomaterials directly onto current collectors, bypassing complex powder processing steps.
- Hybrid Aqueous/Nonaqueous Batteries: The use of mixed solvent electrolytes (H2O/MeCN) demonstrates compatibility with hybrid systems, which are being explored for enhanced safety and performance compared to traditional nonaqueous LIBs.
- Multivalent Ion Batteries: V2O5 is a known host for multivalent ions (Zn2+, Mg2+, Al3+). The atomic-scale understanding of structural rearrangement during Li+ insertion provides crucial foundational knowledge for developing high-performance multivalent metal-ion battery cathodes.
- Fundamental Materials Science: The detailed observation of the α ↔ ω phase transition, which requires large structural rearrangement, contributes to the fundamental understanding needed to engineer materials with improved capacity retention and cycling stability.
View Original Abstract
Electrodeposition is used to produce α-V 2 O 5 nanobelts on a boron doped diamond electrode. The nanoscale dimensions facilitate accommodation of three Li + ions during discharge resulting in ω-Li 3 V 2 O 5 , which is reversible over at least one cycle.