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Thesis
Improvement of electron transport in cathodes via integration of nanostructured carbons with layered oxides for high power Li-ion batteries
Master of Science (M.S.), Drexel University
Jun 2020
DOI:
https://doi.org/10.17918/00000156
Abstract
The need for efficient energy storage is quickly becoming a limiting factor of the advancements being made in infrastructure and transportation. Li-ion batteries have become one of the most ubiquitous technologies in the world, but their performance is limited by the availability of efficient cathode materials. In most Li-ion batteries, layered transition metal oxides (TMOs) are used as cathodes. The presence of two-dimensional channels in these layered cathodes enables facilitated diffusion of electrochemically cycled ions. However due to the low electronic conductivity of oxides, the transfer of electrons is limited, and the power density of the battery suffers. While most commercial batteries incorporate carbon additives to increase the interparticle electronic conductivity in the electrode, this solution does not address the issue of low intraparticle conductivity. The focus of this thesis research is to explore the possibility of improving the conductivity of oxide materials by integration of nanostructured carbon at the point of synthesis and understand the effects of carbon structure and dimensionality on the conductivity and electrochemical performance of the synthesized composites. Chemically preintercalated bilayered vanadium oxide ([delta]-Li[x]V₂O₅·nH₂O) was chosen as the candidate TMO, due to its high capacity enabled by the large interlayer distance and high oxidation state of vanadium that can undergo multiple reductions steps when lithium is intercalated. The synthesis approach developed by the Materials Electrochemistry Group involves an aqueous method that is followed by aging and hydrothermal treatment. Due to the hydrophobic nature of carbon, integration into the synthesis of bilayered vanadium oxide is challenging. In this work methods to improve hydrophilicity of carbons are explored. First, the effects of surface functionalization of the carbons were investigated as a method of increasing compatibility with aqueous systems. Hydrophilicity was improved through the use of acid treatment and "flash oxidation". Conductivity measurements demonstrated that flash-oxidized carbon retained at least 90% of the original conductivity while the acid-treated carbon retained at most 50% of the conductivity. As a result, the flash oxidation method was chosen for carbon functionalization. Next, the flash-oxidized carbons were incorporated into the synthesis of bilayered vanadium oxide and homogeneous nanostructured composites were obtained after aging for four days required to achieve lamellar stacking of vanadium oxide layers. However, hydrothermal treatment of the aged precipitates resulted in phase separation and agglomerates of carbon nanoparticles and bilayered vanadium oxide nanobelts were observed. Electrochemical performance was evaluated for both sets of composites to better understand the role of morphological homogeneity. Galvanostatic cycling revealed the appropriate scaling of specific capacity in agreement with the mass ratio of carbon and vanadium oxide in composite electrodes. Four-point conductivity measurements showed that conductivity of the composites was 3-4 orders of magnitude higher than that of the pristine vanadium oxide. However, rate capability testing is necessary to confirm that higher electronic conductivity leads to improved power density of the cells containing composite electrodes. Overall, this research demonstrated a facile method for developing nanostructured composite materials for energy storage. The improvements in conductivity offer valuable insights into the tunability of layered oxides for high power cathode applications.
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Details
- Title
- Improvement of electron transport in cathodes via integration of nanostructured carbons with layered oxides for high power Li-ion batteries
- Creators
- Timofey Averianov
- Contributors
- Bahram Nabet (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xii, 61 pages
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- College of Engineering (1970-2026); Electrical (and Computer) Engineering [Historical]; Drexel University
- Other Identifier
- 991014695234904721