Chemical Pre-intercalation Synthesis Approach for Novel Layered Cathode Materials for Li-ion and Beyond Li-ion Batteries

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 VOx polyhedra which are separated by a large interlayer spacing of 11.5 (ANGSTROM SIGN) 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-MxV2O5, 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 (ANGSTROM SIGN) 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-MxV2O5 (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-NaxV2O5 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-OrgxV2O5 (DTA, DMO, CTA) phases can be synthesized via this approach, with interlayer spacings from 12.5 to 30.5 (ANGSTROM SIGN) depending on the cation and precursor concentration. The electrochemical performance of delta-OrgxV2O5 phases in Li-ion and Na-ion will be determined.Ph.D., Materials Science and Engineering -- Drexel University, 201

Mesoporous MXene powders synthesized by acid induced crumpling and their use as Na-ion battery anodes

Manipulating the shapes of, otherwise flat, two-dimensional, 2D, flakes is important in many applications. Herein by simply decreasing the pH of a Ti3C2Tx MXene colloidal suspension, the 2D nanolayers crash out into crumpled flakes, resulting in randomly oriented powders, with a mesoporous architecture. Electrodes made with the latter showed capacities of 250 mAh g−1 at 20 mA g−1 in sodium-ion batteries. The rate performance, 120 mAh g−1 at 500 mA g−1, was also respectable. This acid-induced, reversible, crumpling approach is facile and scalable and could prove important in electrochemical, biological, catalytic, and environmental MXene-based applications

Mesoporous MXene powders synthesized by acid induced crumpling and their use as Na-ion battery anodes

<p>Manipulating the shapes of, otherwise flat, two-dimensional, 2D, flakes is important in many applications. Herein by simply decreasing the pH of a Ti₃C₂T_x MXene colloidal suspension, the 2D nanolayers crash out into crumpled flakes, resulting in randomly oriented powders, with a mesoporous architecture. Electrodes made with the latter showed capacities of 250 mAh g⁻¹ at 20 mA g⁻¹ in sodium-ion batteries. The rate performance, 120 mAh g⁻¹ at 500 mA g⁻¹, was also respectable. This acid-induced, reversible, crumpling approach is facile and scalable and could prove important in electrochemical, biological, catalytic, and environmental MXene-based applications.</p> <p>By simply decreasing the pH of a Ti₃C₂T_x colloidal suspension, we induce the 2D flakes flocculate into mesoporous crumpled flakes, that we then show can be used as Na-ion battery anodes.</p

Chemically Preintercalated Bilayered K_<i>x</i>V₂O₅·<i>n</i>H₂O Nanobelts as a High-Performing Cathode Material for K‑Ion Batteries

Tailoring the structure of the electrode material through chemical insertion of charge-carrying ions emerged as an efficient approach leading to enhanced performance of energy storage devices. Here, we for the first time report the effect of chemically preintercalated K⁺ ions on electrochemical charge storage properties of bilayered vanadium oxide (δ-V₂O₅) as a cathode in nonaqueous K-ion batteries, a low-cost alternative to Li-ion batteries, which is attractive for large-scale energy storage. δ-K_0.42V₂O₅·0.25H₂O with expanded interlayer spacing of 9.65 Å exhibited record high initial discharge capacity of 268 mAh·g^–1 at a current rate of C/50 and 226 mAh·g^–1 at a current rate of C/15. K-preintercalated bilayered vanadium oxide showed capacity retention of 74% after 50 cycles at a constant current of C/15 and 58% capacity retention when the current rate was increased from C/15 to 1C. Analysis of the mechanism of charge storage revealed that diffusion-controlled intercalation dominates over nonfaradaic capacitive contribution. High electrochemical performance of δ-K_0.42V₂O₅·0.25H₂O is attributed to the facilitated diffusion of electrochemically cycled K⁺ ions through well-defined intercalation sites, formed by chemically preintercalated K⁺ ions