Refine
Document Type
Language
- English (4)
Has Fulltext
- yes (4)
Is part of the Bibliography
- yes (4)
Keywords
- Hybrid material (1)
- Lithium-ion-battery (1)
- Mechanochemistry (1)
- Titanium niobium oxide (1)
- adamantane (1)
- amorphous carbon (1)
- carbon characterization (1)
- carbon onions (1)
- nanodiamond (1)
Scientific Unit
- Energy Materials (4)
The preparation of carbons for technical applications is typically based on a treatment of a precursor, which is transformed into the carbon phase with the desired structural properties. During such treatment the material passes through several different structural stages, for example, starting from precursor molecules via an amorphous phase into crystalline-like phases. While the structure of non-graphitic and graphitic carbon has been well studied, the transformation stages from molecular to amorphous and non-graphitic carbon are still not fully understood. Disordered carbon often contains a mixture of sp3-, sp2-and sp1-hybridized bonds, whose analysis is difficult to interpret. We systematically address this issue by studying the transformation of purely sp3-hybridized carbons, that is, nanodiamond and adamantane, into sp2-hybridized non-graphitic and graphitic carbon. The precursor materials are thermally treated at different temperatures and the transformation stages are monitored. We employ Raman spectroscopy, WAXS and TEM to characterize the structural changes. We correlate the intensities and positions of the Raman bands with the lateral crystallite size La estimated by WAXS analysis. The behavior of the D and G Raman bands characteristic for sp2-type material formed by transforming the sp3-hybridized precursors into non-graphitic and graphitic carbon agrees well with that observed using sp2-structured precursors.
The growing use of portable devices and a global transition to electric vehicles has tremendously increased the demand for energy storage devices such as lithium-ion batteries and supercapacitors. Especially the interest is established for better devices exceeding the energy and power performance of current technology. The hybrid supercapacitor (HSC) concept addresses the limits of each device and utilizes the distinct electrochemical features of lithium-ion batteries and supercapacitors. The focus of this Ph.D. thesis is the nano-design of hybrid materials of metal oxides and carbon for better electrochemical performance in lithium- and sodium-ion hybrid energy storage devices. The hybridization of metal oxide and carbon substrate can be achieved by tailored sol-gel synthesis, yielding a homogeneous distribution of nanosized metal oxide domain in the hybrid material. The performance of the hybrids was superior to the composite concept electrodes, but this is not a statement that can be generalized for all sorts of (nano)composites. In addition to the electrode material, also the electrolyte choice has a strong impact on the device operation and safety. The use of alternative solvents and Li- or Na-containing ionic liquids allows to increase the upper temperature and cell voltage at which Li- and Na-based systems can be safely operated at.
This study demonstrates the hybridization of Li4Ti5O12 (LTO) with different types of carbon onions synthesized from nanodiamonds. The carbon onions mixed with a Li4Ti5Ox precursor for sol–gel synthesis. These hybrid materials are tested as anodes for both lithium-ion battery (LIB) and sodium-ion battery (SIB). Electrochemical characterization for LIB application is carried out using 1 m LiPF6 in a 1:1 (by volume) ethylene carbonate and dimethyl carbonate as the electrolyte. For lithium-ion intercalation, LTO hybridized with carbon onions from the inert-gas route achieves an excellent electrochemical performance of 188 mAh g−1 at 10 mA g−1, which maintains 100 mAh g−1 at 1 A g−1 and has a cycling stability of 96% of initial capacity after 400 cycles, thereby outperforming both neat LTO and LTO with onions obtained via vacuum treatment. The performance of the best-performing hybrid material (LTO with carbon onions from argon annealing) in an SIB is tested, using 1 m NaClO4 in ethylene/dimethyl/fluoroethylene carbonate (19:19:2 by mass) as the electrolyte. A maximum capacity of 102 mAh g−1 for the SIB system is obtained, with a capacity retention of 96% after 500 cycles.
This work introduces the facile and scalable two-step synthesis of Ti 2 Nb 10 O 29 (TNO)/carbon hybrid material as a promising anode for lithium-ion batteries (LIBs). The first step uses a mechanically-induced self-sustaining reaction via ball-milling at room temperature to produce titanium niobium carbide with a stoichiometric ratio of Ti and Nb of 1 to 5. The second step involves the oxidation of as-synthesized titanium niobium carbide to produce TNO. Synthetic air yields fully oxidized TNO, while annealing in CO 2 results in TNO/carbon hybrids. The electrochemical performance for the hybrid and non-hybrid electrodes was surveyed for a narrow potential window (1.0-2.5 V vs. Li/Li + ) and a large potential window (0.05-2.5 V vs. Li/Li + ). The best hybrid material displayed a specific capacity of 350 mAh/g at a rate of 0.01 A/g (144 mAh/g at 1 A/g) in the large potential window regime. The electrochemical performance of hybrid materials is superior compared to non-hybrid materials for operation within the large potential window. Due to the advantage of carbon in hybrid material, the rate handling is faster than that of the non-hybrid one. The hybrid materials display robust cycling stability and maintain ca. 70% of their initial capacities after 500 cycles. In contrast, only ca. 26% of the initial capacity is maintained after the first 40 cycles for non-hybrid materials. We also applied our hybrid material as an anode in a full-cell lithium-ion battery by coupling it with commercial LiMn 2 O 4 .
