Hybrid bilayered vanadium oxide electrodes with large and tunable interlayer distances in lithium-ion batteries

Tunable interlayer distance in graphene oxide through alkylamine surface coverage and chain length

Layered materials have unique structures that can be modified by adjusting the space between layers through pillaring or surface functionalization. Unlike typical crystalline layered materials, graphene oxide (GO) possesses reactive oxygenated functional groups, which lead to spontaneous reduction and stacking upon thermal treatment. Here, we investigated the functionalization of GO with different amounts of hexylamine to control the degree of surface coverage. Furthermore, octylamine and dodecylamine were employed to confirm the effect of the alkyl chain length on the interlayer distance of the resultant GO derivatives. Subsequent thermal treatment produced reduced GO (rGO) functionalized with alkylamines, demonstrating the retention of the interlayer distance. Additionally, amine-functionalized rGOs exhibited varying porous structures.

Piperazine-Linked Phthalocyanine Covalent Organic Frameworks for Efficient Anodic Lithium Storage

Organic anode materials have been considered as promising electrodes for achieving low-cost and sustainable lithium-ion batteries (LIBs). However, organic materials face challenges, such as inadequate cycling stability and sluggish reaction kinetics, leading to an unsatisfactory LIB performance. Covalent organic frameworks (COFs) possess a porous and designable structure coupled with exceptional stability, making them promising candidates for anode electrodes in LIBs to address the challenges. Herein, two piperazine-linked conjugated phthalocyanine-based COFs (named CoPc-BTM-COF and CoPc-DAB-COF) were fabricated from reacting hexafluorophthalocyanine cobalt(II) (CoPcF16) with 1,2,4,5-benzenetetramine (BTM) and 3,3'-diaminobenzidine (DAB), respectively. Powder X-ray diffraction and electron microscopy analyses in combination with theoretical simulation reveal their crystalline nature with sql net and AA arranged stacking pattern. The pore sizes of these two Pc-COFs are 1.62 and 1.90 nm according to theoretical simulation and N2 sorption measurement, which facilitates their rapid transport of Li+ ions. The immersion experiments disclose their remarkable stability. These advantages, together with their conjugated nitrogen-rich skeletal structures, lead to outstanding anodic Li+ storage capabilities, exceptional rate performance, and favorable cycling stability. In particular, both Pc-COFs exhibit high capacities of 877 and 669 mAh g-1 at 100 mA g-1, superior to most reported organic LIB anodes, showing promising application potential in high-performance LIBs.

MXene-Derived Potassium-Preintercalated Bilayered Vanadium Oxide Nanostructures for Cathodes in Nonaqueous K-Ion Batteries

Bilayered vanadium oxides (BVOs) are promising cathode materials for beyond-Li-ion batteries due to their tunable chemistries and high theoretical capacities. However, the large size of beyond-Li+ ions limits electrochemical cycling and rate capability of BVO electrodes. Recent reports of MXene-derived BVOs with nanoscale flower-like morphology have shown improved electrochemical stability at high rates up to 5C in nonaqueous lithium-ion batteries. Here, we report how morphological stabilization can lead to improved rate capability in potassium-ion batteries (PIBs) through the synthesis and electrochemical characterization of MXene-derived K-preintercalated BVOs (MD-KVOs), which were derived from two V2CT x precursor materials prepared using two different etching protocols. We show that the etching conditions affect the surface chemistry of the MXene, which plays a role in the MXene-to-oxide transformation process. MXene derived from a milder etchant transformed into a nanoflower MD-KVO with two-dimensional (2D) nanosheet petals (KVO-DMAE) while a more aggressive etchant produced a MXene that transformed into a MD-KVO with one-dimensional (1D) nanorod morphology (KVO-CMAE). Electrochemical cycling of the produced MD-KVOs after drying at 200 °C under vacuum (KVO-DMAE-200 and KVO-CMAE-200) in PIBs showed that electrochemical stability of MD-KVO at high rates improved through the morphological stabilization of 2D particles combined with the control of interlayer water and K+ ion content. Structure refinement of KVO-DMAE-200 further corroborates the behavior observed during K+ ion cycling, connecting structural and compositional characteristics to the improved rate capability. This work demonstrates how proper synthetic methodology can cause downstream effects in the control of structure, chemical composition, and morphology of nanostructured layered oxide materials, which is necessary for development of future materials for beyond-Li-ion battery technologies.