Mallory Clites

Effect of aging and hydrothermal treatment on electrochemical performance of chemically pre-intercalated Na–V–O nanowires for Na-ion batteries

A chemical pre-intercalation approach was used to synthesize Na-containing vanadium oxide nanowires for use as Na-ion battery cathodes. The synthesis method was based on a sol–gel process followed by aging and/or hydrothermal treatment. We have for the first time shown that addition of sodium salt into the hydrothermally treated precursor mixture leads to a higher content of chemically pre-intercalated Na+ ions in the crystal structure of produced layered vanadium oxides. Further, the inclusion of an aging step was found to be crucial for the formation of bilayered NaxV2O5 phase with high capacity in Na-ion cells. Single-phase bilayered NaxV2O5 nanowires, obtained after the hydrothermal treatment of four-day aged precursor, demonstrated a record high initial discharge capacity of 365 mA h g−1. The hydrothermal treatment was shown to improve crystallinity of nanowires, leading to the better electrochemical stability of electrodes. Our results demonstrate the potential of chemical pre-intercalation synthesis method to develop high-capacity Na-ion battery cathodes. The ability to control various parameters in the multi-step chemical pre-intercalation approach opens a door to employing this method for the synthesis of electrode materials for other beyond lithium-ion electrochemical systems, such as Mg-ion and K-ion batteries.

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

ABSTRACT 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. GRAPHICAL ABSTRACT IMPACT STATEMENT By simply decreasing the pH of a Ti3C2Tx colloidal suspension, we induce the 2D flakes flocculate into mesoporous crumpled flakes, that we then show can be used as Na-ion battery anodes.

Stabilization of Battery Electrodes through Chemical Pre-Intercalation of Layered Materials

Vanadium oxide with bilayered crystal structure shows high specific capacity in intercalation-based energy storage systems, such as Li-ion and Na-ion batteries. The enhanced charge storage ability is attributed to the high oxidation state of vanadium enabling intercalation of more than one Li+ (or Na+) ion per V2O5 unit cell. In addition, large interlayer spacing of ∼10–13 Å, typical for the bilayered vanadium oxide, is believed to lead to the facilitated diffusion of charge carrying ions further improving specific capacity of this material. However, we found that initial high capacity of the bilayered V2O5 notably decreases only after a few cycles. In this work, we show results of the capacity stabilization strategy based on inclusion of inorganic ions, other than lithium ion, between the structural layers using chemical pre-intercalation approach. These ions are believed to form bonds with the V–O layered framework improving structural stability of the material during electrochemical cycling, and therefore they are often called stabilizing ions. In this paper we report how electrochemical stability of the AxV2O5 (A = Na, K, Mg, Ca) cathode materials is correlated with the size and charge of the stabilizing ions. Li-preintercalated vanadium oxide (LixV2O5) served as the reference material in this study. We found that chemical insertion of doubly charged, small (r = 0.86 Å) Mg2+ stabilizing ion results in the highest capacity retention.

Improved electrochemical cycling stability of intercalation battery electrodes via control of material morphology

AbstractUsing a model tunnel manganese oxide with the todorokite crystal structure (T-MnO2), we demonstrate that controlling the morphology of the active material can improve the cycling stability of intercalation battery electrodes. The T-MnO2 structure is built from tunnels that provide spacious 1D diffusion channels for charge-carrying ions. Taking advantage of the unique ability to synthesize T-MnO2 in the form of both highly crystalline two-dimensional (2D) nanoplatelets and one-dimensional (1D) nanowires through a facile hydrothermal growth method, we investigated the effect of nanoscale particle dimensions on reversible battery cycling. Insertion of ions into the tunnels results in anisotropic expansion of the structure, making T-MnO2 with different morphologies an excellent model platform to understand how intercalation-induced volume change, typically leading to the deterioration of the electrode performance over extended cycling, can be controlled through synthesis of targeted morphologies. T-MnO2 nanowires showed not only significantly improved capacity retention but also substantially higher specific capacity than the T-MnO2 nanoplatelets. The enhanced electrochemical properties of the nanowire electrodes could be attributed to the larger surface-to-volume ratio than that of nanoplatelets, resulting in higher contact area with electrolyte for the nanowires. Moreover, due to the smaller cross-sectional area of the nanowires, volume expansion and contraction perpendicular to the structural tunnels induced by reversible ion intercalation occurs in a more facile fashion. This work shows that chemically controlling morphology and producing particles with nanostructure dimensionality replicating that of atomic structure (i.e., 1D morphology and 1D structure) makes it possible to enhance material performance. Graphical abstractᅟ

Synthesis of hybrid layered electrode materials via chemical pre-intercalation of linear organic molecules

Chemical pre-intercalation is a low-temperature, scalable synthesis method that utilizes a sol-gel process to form layered oxides with positively-charged species inserted between the layers. We have shown that this approach can be used to successfully intercalate Li+ , Na+ , K+ , Mg2+, and Ca2+ ions into the crystal structure of bilayered vanadium oxide (δV2O5).1 Through this ion-intercalation, the interlayer spacing of the δ-MgxV2O5 (M=Li, Na, K, Mg, and Ca) structure can be controlled between 9.6 Å (δ-KxV2O5) and 13.4 Å (δ-MgxV2O5).1 Moreover, the expanded spacing achieved for the δ-MgxV2O5 phase corresponded to increased electrochemical stability in both Li- and Na-ion cells.[1] While this study identified a correlation between expanded interlayer spacing and improved electrochemical stability over cycling, chemical pre-intercalation of ions does not allow for expansion beyond that exhibited by the δ-MgxV2O5 structure. In this work, we show that further expansion of the interlayer spacing can be achieved via pre-intercalation of positivelycharged linear, organic cations. We report synthesis of hybrid inorganic/organic materials with a 1D nanobelt morphology. The layered structure of the hybrids is confirmed by both XRD and TEM analysis. δ-V2O5 preintercalated with cetyltrimethylammonia ions, CTA+ , demonstrated the interlayer spacings of all samples (31 Å), more than twice larger than the largest interlayer spacing achieved via pre-intercalation of inorganic ions. The effects of carbon chainlength and positively charged nitrogen termini on the interlayer spacing and electrochemical stability is investigated, with two N-termini on the cation (DMO+) resulting in increased electrochemical stability of the preintercalated phase.

The ion dependent change in the mechanism of charge storage of chemically preintercalated bilayered vanadium oxide electrodes

Chemical pre-intercalation is a soft chemistry synthesis approach that allows for the insertion of inorganic ions into the interlayer space of layered battery electrode materials prior to electrochemical cycling. Previously, we have demonstrated that chemical pre-intercalation of Na+ ions into the structure of bilayered vanadium oxide (δ-V2O5) results in record high initial capacities above 350 mAh g-1 in Na-ion cells. This performance is attributed to the expanded interlayer spacing and predefined diffusion pathways achieved by the insertion of charge-carrying ions. However, the effect of chemical pre-intercalation of δ-V2O5 has not been studied for other ion-based systems beyond sodium. In this work, we report the effect of the chemically preintercalated alkali ion size on the mechanism of charge storage of δ- MxV2O5 (M = Li, Na, K) in Li-ion, Na-ion, and K-ion batteries, respectively. The interlayer spacing of the δ-MxV2O5 varied depending on inserted ion, with 11.1 Å achieved for Li-preintercalated δ-V2O5, 11.4 Å for Na-preintercalated δ- V2O5, and 9.6 Å for K-preintercalated δ-V2O5. Electrochemical performance of each material has been studied in its respective ion-based system (δ-LixV2O5 in Li-ion cells, δ-NaxV2O5 in Na-ion cells, and δ-KxV2O5 in K-ion cells). All materials demonstrated high initial capacities above 200 mAh g-1. However, the mechanism of charge storage differed depending on the charge-carrying ion, with Li-ion cells demonstrating predominantly pseudocapacitive behavior and Naion and K-ion cells demonstrating a significant portion of capacity from diffusion-limited intercalation processes. In this study, the combination of increased ionic radii of the charge-carrying ions and decreased synthesized interlayer spacing of the bilayered vanadium oxide phase correlates to an increase in the portion of capacity attributed diffusion-limited charge-storage processes.

Chemical modification approaches for improved performance of Na-ion battery electrodes

Na-ion batteries have received considerable attention in recent years but still face performance challenges such as limited cycle lifetime and low capacities at high current rates. In this work, we propose novel combinations of preand post-synthesis treatments to modify known Na-ion battery electrode materials to achieve enhanced electrochemical performance. We work with two model metal oxide materials to demonstrate the effectiveness of the different treatments. First, wet chemical preintercalation is combined with post-synthesis aging, hydrothermal treatment, and annealing of α-V2O5, resulting in enhanced capacity retention in a Na-ion battery system. The hydrothermal treatment resulted in an increased specific capacity of nearly 300 mAh/g. Second, post-synthesis acid leaching is performed on α- MnO2, also resulting in improved electrochemical capacity. The chemical, structural, and morphological changes brought about by the modifications are fully characterized.