Chemical pre-intercalation synthesis approach for novel layered cathode materials for Li-ion and beyond Li-ion batteries

Mallory Clites

doi:10.17918/b951-rm74

Beyond-lithium ion (BLI) alkali ion-based batteries are rising in interest among researchers because of their utilization of more abundant, cost-effective charge carriers, including Na⁺ and K⁺ ions, compared to traditionally used Li⁺ ions. However, because such systems utilize electrochemically cycling ions with larger ionic radii, achieving fast diffusion and high insertion rates of the BLI carriers into traditional, close-packed electrode materials is challenging. As such, these new systems require the development of novel electrode materials with high capacity, rapid charge transfer, and stable behavior over extended cycling. Materials with open, layered crystal structures have proven themselves among the most reliable electrode materials for Na-ion and K-ion based batteries, enabling high performance in these emerging systems. Tuning and control of interlayer spacing and chemical composition in open layered structures, can be accomplished via simple wet chemical modification approaches. Such tailoring has the capability to increase ion insertion and movement as well as electrochemical stability, which may lead to improvements in electrochemical performance of these electrode structures. Layered vanadium pentoxide (V₂O₅) phases are promising candidates for BLI batteries in part because vanadium can be present in its highest oxidation state, 5+, and can undergo multiple reduction steps down to a 3+ state, allowing for the transfer of up to two electrons per vanadium ion. In particular, bilayered [delta]-V₂O₅·nH₂O is an ideal phase for Li-ion and BLI systems due to its large open-layered structure offering facile movement of larger charge-carrying ions. The bilayered structure is built from double layers of VO_x polyhedra which are separated by a large interlayer spacing of 11.5 Å which is stabilized only by intercalated water molecules. When this [delta]-V₂O₅·nH₂O phase is synthesized via scalable sol-gel and hydrothermal treatment capacity typically decays over extended cycling, due to lattice breathing and the gradual breakdown of the lamellar stacking of the V-O layers. This dissertation focuses on a novel chemical pre-intercalation synthesis approach as a means to improve electrochemical performance of bilayered vanadium oxide electrodes in Na- and K-ion systems. Via this approach, ion-containing [delta]-M_xV₂O₅, where M represents alkali (Li⁺, Na⁺, K⁺), alkali-earth (Mg²⁺ and Ca²⁺) ions, phases can be synthesized. This synthesis technique allows for the tunability of the interlayer spacing from 9.65 to 13.4 Å depending on the nature of the inserted ion. Further, synthesis of the electrode materials via chemical pre-intercalation approach can lead to increased capacities and electrochemical stability in Li-ion, Na-ion, and K-ion cells. Electrochemical performance of [delta]-M_xV₂O₅ (M = Li, Na, K, Mg, Ca) in Li-ion cells will also be presented as a reference. Further, it will be demonstrated that this synthesis approach can lead to improved electrochemical performance of [delta]-V₂O₅ electrodes in intercalation-based batteries through three modes: (1) pre-intercalation of charge-carrying into the bilayered [delta]-V₂O₅ phase can lead to tailored ion transport and increase overall specific capacities, (2) optimization of interlayer water content, improvement of structural order, and increase of intralayer bonding via low-temperature vacuum annealing to improve electrochemical stability, and (3) pre-intercalation of electrochemically inactive organic and inorganic ions in order to stabilize the bilayered structure and improve capacity retention in both Li⁺ ion and BLI ion cycling. While this pre-intercalation synthesis route may lead to the partial reduction of the oxidation state of vanadium present in the structure, high discharge capacities over 200 mAh·g⁻¹ are observed in all three ion-based systems in the voltage range of 2.0 - 4.3 V and a higher discharge capacity of 365 mAh·g⁻¹ observed for the [delta]-Na_xV₂O₅ electrodes in the Na-ion system in an expanded voltage range of 1.0 - 4.3 V. A detailed study of the mechanism of charge storage and the effect of charge-carrying ion size on experimentally achieved specific capacities and electrochemical stability in Li-ion, Na-ion and K-ion batteries will also be discussed. Additionally, organic cation-intercalated [delta]-Org_xV₂O₅ (DTA, DMO, CTA) phases can be synthesized via this approach, with interlayer spacings from 12.5 to 30.5 Å depending on the cation and precursor concentration. The electrochemical performance of [delta]-Org_xV₂O₅ phases in Li-ion and Na-ion will be determined.

Chemical pre-intercalation synthesis approach for novel layered cathode materials for Li-ion and beyond Li-ion batteries

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Chemical pre-intercalation synthesis approach for novel layered cathode materials for Li-ion and beyond Li-ion batteries

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