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V₄C₃T_x MXene-derived chemically preintercalated bilayered vanadium oxides with nanoflower-like morphology as cathodes in aqueous zinc-ion batteries
Thesis   Open access

V₄C₃T_x MXene-derived chemically preintercalated bilayered vanadium oxides with nanoflower-like morphology as cathodes in aqueous zinc-ion batteries

Maxwell John MacEachern
Master of Science (M.S.), Drexel University
May 2026
DOI:
https://doi.org/10.17918/00011438
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Abstract

Aqueous zinc-ion batteries Chemical preintercalation Energy storage Materials electrochemistry Vanadium oxides Materials Chemistry
Hydrated layered frameworks have emerged as a promising class of materials for high-performance aqueous zinc-ion batteries (AZIBs) due to their large interlayer regions and high theoretical capacities. Among these materials, bilayered vanadium oxide (BVO) has become a major research focus because of its high oxidation state V⁵⁺ atoms and ability to have the interlayer structure tuned through chemical preintercalation. This synthesis strategy inserts chemical pillars, in the form of inorganic or organic ions, alongside structural water into the interlayer galleries, providing structure stabilization and charge screening upon electrochemical cycling. Recent developments have demonstrated significant improvements in the electrochemical properties of chemically preintercalated bilayered vanadium oxides (CP-BVOs) utilizing MXene precursors, attributed to the unique 2D nanoflake morphologies of MXene-derived oxides obtained through this conversion pathway. However, prior literature has focused exclusively on V₂CT_x-derived oxides. Utilizing a structurally thicker V₄C₃T_x MXene precursor may allow for greater flexibility in controlling the oxidation kinetics to preserve a residual carbon containing motif. This would enable pathways for electron transfer in the partially oxidized product. Therefore, demonstrating V₄C₃T_x MXene transformation into oxides with 2D nanoflake morphology assembled into nanoflower-like particles is desirable for advancing AZIBs. Here, in this thesis, nanoflower-like V₄C₃T_x-derived CP-BVOs with Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and Zn²⁺ were first reported using an adapted synthesis consisting of the reaction of MXene precursor with hydrogen peroxide followed by a settling step and hydrothermal treatment. The synthesized materials were characterized by XRD, demonstrating (001) d-spacings of 9.69 Å to 13.97 Å depending on the preintercalated cation. The BVO composition was determined using atomic absorption spectroscopy and thermogravimetric analysis as: Li_[0.016]V₂O₅·0.53H₂O (LVO), Na_[0.45]V₂O₅·0.14H₂O (NVO), K_[0.40]V₂O₅·0.17H₂O (KVO), Mg_[0.21]V₂O₅·0.89H₂O (MVO), Ca_[0.25]V₂O₅·0.94H₂O (CVO), and Zn_[0.17]V₂O₅·0.76H₂O (ZVO). Under electrochemical cycling, LVO demonstrated the poorest performance, due to the dense film formed by the 2D particles instead of the open nanoflower-like architecture. While the other singly charged ion preintercalated BVOs, NVO and KVO, delivered high initial capacities (478 and 473 mAh g⁻¹, respectively), they experienced significant instability over extended cycling attributed to the large cations hindering ion diffusion revealed by electrochemical impedance spectroscopy (EIS). In contrast, the doubly charged ion preintercalated BVOs (MVO, CVO, and ZVO) demonstrated superior electrochemical stability. At low current densities, ZVO demonstrated high capacity and capacity retention (454 mAh g⁻¹ and 73%) because the sites from chemically preintercalated zinc ions are favorable for subsequent intercalation of electrochemically cycled Zn²⁺ ions, effectively improving diffusion. However, under high currents, MVO emerged as the superior electrode, achieving high capacity and capacity retention (235 mAh g⁻¹ and 123%) through long-term cycling due to the large interlayer regions and high water content in the material structure lowering the charge transfer resistance, as shown in EIS, thereby drastically reducing electrochemically induced strain on the BVO lattice. To elucidate the underlying charge storage mechanism governing the electrochemical performance of CP-BVOs, in situ pH evolution measurements were conducted, revealing that redox activity at higher potentials (0.8 - 1.6 V vs. Zn/Zn²⁺) is dominated by reversible proton intercalation, whereas electrochemical activity at lower potentials (below 0.8 V vs Zn/Zn²⁺) might exhibit significant reversible zinc ion intercalation. Complementary, ex situ XRD and SEM demonstrate the reversible formation of basic zinc salts (BZS, Zn_xOTf_y(OH)_[2x-y]·nH₂O) on the surface of the cathode during discharge and subsequent dissolution during charge. This result was further corroborated by EIS, revealing a significant increase in impedance at the end of the discharge across multiple cycles, attributed to the reversible formation of BZS on the cathode. In conclusion, ZVO showed highest performance at lowest current densities, while MVO outperformed all materials at higher current densities highlighting the significance of preintercalated ion selection in BVOs in AZIBs.

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