Bilayered δ-V₂O₅, built from double layers of VO_x polyhedra separated by a large interlayer spacing of 11.5 Å, demonstrates advanced electrochemical behavior as a cathode material for beyond-Li ion (BLI) batteries. This high capacity is attributed to the large interlayer space of the bilayered structure, which allows facilitated diffusion and intercalation of large, BLI charge-carriers. However, this capacity typically decays over extended cycling, due to the lattice breathing and eventual breakdown of long-range order of the bilayered structure. Therefore, strategies are needed to improve the stability of bilayered vanadium oxide in order to achieve long lifetimes in electrochemical reactions of reversible sodium ion cycling.

Chemical pre-intercalation is a soft chemistry synthesis approach that allows insertion of positively charged water-soluble species into the interlayer space of layered battery electrode materials prior to electrochemical cycling. We have previously demonstrated that inorganic, ions can be inserted into the δ-V₂O₅ to form δ-M_xV₂O₅ (M = Li, Na, K, Mg, and Ca) stabilized phases that demonstrated improved capacity retentions over cycling in Li-ion and Na-ion cells. It was determined that δ-Mg_xV₂O₅ material, which had the largest interlayer spacing of all preintercalated phases, 13.44 Å, demonstrated the greatest capacity retention in both systems over extended cycling.[1]

In this work, we for the first time report on the use of sol-gel based chemical pre-intercalation approach for the synthesis δ-V₂O₅ materials with positively-charged, linear organic species within the interlayer space. We demonstrate that by carefully selecting the nature of the organic molecule, interlayer spacing in δ-V₂O₅ can be expanded substantially further than in case of inorganic ions. We explored cycling performance of the synthesized hybrid layered phases in Li-ion and Na-ion electrochemical energy storage systems. Organic molecules which have at least one amine group terminus, including cetyltrimethylammonium bromide (CTAB) and hexamethonium bromide (HMOB), have been used as preintercalated, pillaring species within the bilayered vanadium oxide structure in order to expand and stabilize the layers for improved electrochemical performance over extended cycling. δ-CTAB_xV₂O₅ phase demonstrated the largest interlayer spacing of 31.24 Å, more than double the largest interlayer spacing achieved via inorganic ion-preintercalation. Initial studies demonstrated that δ-HMOB_xV₂O₅ phase exhibited capacities above 100 mAh g^-1 in Li-ion cells and 150 mAh g^-1 in Na-ion cells. While capacities of all organic/inorganic hybrid phases were lower than that of the pure bilayered and ion-preintercalated phases, they demonstrated improved capacity retentions over extended cycling. This work demonstrates the viability of chemical pre-intercalation of organic species in order to stabilize electrode structures over electrochemical cycling. We will present the correlation between organic species length, synthesized interlayer spacing, and electrochemical performance for these bilayered vanadium oxides preintercalated with organic molecules. Additionally, we will report on the optimization of hybrid materials synthesis conditions and effect of organic molecule:V₂O₅ ratio on electrochemical performance of the hybrids.

1. Clites, M. et al. Energy Storage Mateirals 2018, 11.