Lithium-Ion Storage in Hybrid Bilayered Vanadium Oxide Electrodes with Large and Tunable Interlayer Distances

In this work, we demonstrate the hybrid bilayered vanadium oxide (BVO) electrode materials with large and tunable interlayer distances achieved through chemical preintercalation of decyltrimethylammonium (DTA⁺) and cetyltrimethylammonium (CTA⁺) cations. By varying the concentration of these linear organic cations during chemical preintercalation synthesis, we found that the interlayer distance of hybrid BVOs can be tuned from 11.1 Å to 35.6 Å, which is controlled by the amount of the linear organic cations and structural water confined in the interlayer regions. Thermogravimetric analysis (TGA) confirmed that the increased amounts of DTA⁺ or CTA⁺ bromide salt added in the chemical preintercalation synthesis led to a higher fraction of DTA⁺ or CTA⁺ cations confined in the interlayer regions, in agreement with the reduction of the vanadium oxidation state observed via X-ray photoelectron spectroscopy (XPS). We also observed that the bending and disordering of the vanadium oxide bilayers intensified with the increase of alkylammonium cations concentration. Galvanostatic cycling of the hybrid (DTA)<i>_x</i>V₂O₅ and (CTA)<i>_x</i>V₂O₅ electrodes in non-aqueous lithium-ion cells showed that the specific capacities decrease as the interlayer regions expand, suggesting the confined linear organic cations might be densely packed in the interlayer regions and obstruct the intercalation and transport pathways of the electrochemically cycled ions. We confirmed this hypothesis by showing differences in Li⁺ ions diffusion coefficients and charge transfer resistances in hybrid BVO electrodes evaluated by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS), respectively. Among the hybrid phases reported in this study, the CTA-preintercalated BVO with the smallest interlayer distance of 11.1 Å delivered the highest initial specific capacity of 274 mAh g^-1, which retained about 80% of its initial capacity after 50 cycles. We utilized atomic absorption spectroscopy (AAS) to reveal that a greater layer separation enhances hybrid BVO dissolution in the electrolyte, which leads to capacity decay in cycle life and rate capability tests. Our study sheds light on the rational structural design of hybrid layered electrode materials, which require both spacious interlayer regions and high stability in the electrolyte. This work emphasizes that the chemical composition of the interlayer region needs to be considered for structural engineering of layered material, and provides guidelines for the development of novel hybrid electrode materials for energy storage applications.