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We present a novel strategy for constructing three-dimensional (3D) porous Ti3C2Tx (MXene) networks by alkali-induced crumpling of Ti3C2Tx nanosheets. The 3D porous Ti3C2Tx networks display high capacity and outstanding rate performance as anode materials for sodium-ion batteries.

Manipulating the shapes of, otherwise flat, two-dimensional, 2D, flakes is important in many applications. Herein by simply decreasing the pH of a Ti 3 C 2 T x 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. IMPACT STATEMENTBy simply decreasing the pH of a Ti 3 C 2 T x colloidal suspension, we induce the 2D flakes flocculate into mesoporous crumpled flakes, that we then show can be used as Na-ion battery anodes.

Tailoring the structure of the electrode material through chemical insertion of charge-carrying ions emerged as an efficient approach leading to enhanced performance of energy storage devices. Here, we for the first time report the effect of chemically preintercalated K + ions on electrochemical charge storage properties of bilayered vanadium oxide (δ-V 2 O 5 ) as a cathode in nonaqueous K-ion batteries, a low-cost alternative to Li-ion batteries, which is attractive for large-scale energy storage. δ-K 0.42 V 2 O 5 • 0.25H 2 O with expanded interlayer spacing of 9.65 Å exhibited record high initial discharge capacity of 268 mAh•g −1 at a current rate of C/50 and 226 mAh•g −1 at a current rate of C/15. K-preintercalated bilayered vanadium oxide showed capacity retention of 74% after 50 cycles at a constant current of C/15 and 58% capacity retention when the current rate was increased from C/15 to 1C. Analysis of the mechanism of charge storage revealed that diffusion-controlled intercalation dominates over nonfaradaic capacitive contribution. High electrochemical performance of δ-K 0.42 V 2 O 5 •0.25H 2 O is attributed to the facilitated diffusion of electrochemically cycled K + ions through well-defined intercalation sites, formed by chemically preintercalated K + ions.

All-solid-state sodium metal batteries (SSMBs) are of great interest for their high theoretical capacity, non-flammability, relatively low cost owing partially to the abundance of sodium recourses. However, it is challenging to fabricate SSMBs because compared with their lithium metal counterparts, sodium metal is mechanically softer and more reactive towards the electrolyte. Herein, we report the synthesis and electrochemical properties of newly designed sodium-containing hybrid network solid polymer electrolytes (SPEs) and their application in This article is protected by copyright. All rights reserved. 2 SSMBs. The hybrid network was synthesized by controlled crosslinking of octakis(3glycidyloxypropyldimethylsiloxy)octasilsesquioxane (octa-POSS) and amine-terminated PEG in existence with sodium perchlorate (NaClO 4). Plating and stripping experiments using symmetrical cells showed prolonged cycle life of the SPEs, >5150 hours and 3550 hours at current density of 0.1 mA cm-2 and 0.5 mA cm-2 , respectively. Our results for the first time show that the SPE|sodium metal interface migrates into the SPE phase upon cycling. SSMBs fabricated with the hybrid SPE sandwiched between sodium metal anode and bilayered δ-Na x V 2 O 5 cathode exhibited record high specific capacity for solid sodium-ion batteries of 305 mAh g-1 and excellent Coulombic efficiency. Our work demonstrates that the hybrid network SPEs are promising for SSMB applications.

A chemical pre-intercalation approach was used to synthesize Na-containing vanadium oxide nanowires with the bilayered crystal structure for use as Na-ion battery cathodes.

Synthetic strategies for the improvement in electronic conductivities and electrochemical stabilities of transition metal oxide cathodes, which are limiting factors in the performance of commercial intercalation batteries, are required for next-generation, high-performance battery systems. The chemical preintercalation approach, consisting of a combined sequence of a sol−gel process, extended aging, and a hydrothermal treatment, is a versatile, wet synthesis technique that allows for the incorporation of a polar species between the layers of transition metal oxides. Here, formation of a layered 2D δ-C x V 2 O 5 •nH 2 O heterostructure occurs via chemical preintercalation of dopamine molecules between bilayers of vanadium oxide followed by the hydrothermal treatment of the precipitate, leading to carbonization of the organic molecules. The presence of carbon layers within the structure has been confirmed via a combined analysis of scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, four-probe conductivity measurements, and scanning transmission electron microscopy characterization. 2D δ-C x V 2 O 5 •nH 2 O heterostructure electrodes demonstrated significantly improved electrochemical performance, particularly at higher current densities, in Li-ion cells. The heterostructure electrodes exhibited 75% of the capacity retention when the current was changed from 20 mA g −1 (206 mAh g −1 ) to 300 mA g −1 (155 mAh g −1 ), while the reference δ-V 2 O 5 •nH 2 O electrodes exhibited only 10% capacity retention in the same experiment. Remarkably, 2D δ-C x V 2 O 5 •nH 2 O heterostructure electrodes demonstrated significantly improved capacity retention (94% after 30 cycles) for bilayered vanadium oxide electrodes in Li-ion cells during galvanostatic cycling at 20 mA g −1 . The improved electrochemical performance, in both extended cycling and rate capability studies, of the 2D δ-C x V 2 O 5 •nH 2 O heterostructure electrodes in the Li-ion system is ascribed to the intermittent formation of carbon layers within the bilayered structure, which leads to increased electronic conductivity and improved structural stability of the heterostructure compared to the reference δ-V 2 O 5 •nH 2 O electrodes.

Layered transition metal compounds with expanded interlayer regions, stabilized by structural water, often show high initial capacities but suffer from rapid capacity decay and poor rate capability in Na-ion batteries. High-temperature annealing, accompanied by phase transformation with the formation of more dense atomic structures, has been shown to improve electrochemical stability. However, the capacity of annealed materials decreases compared to their original forms. Here, we for the first time demonstrate that low-temperature annealing (260 °C under vacuum) can be used to achieve enhanced electrochemical stability of high capacity Na-preintercalated bilayered vanadium oxide (δ-Na x V2O5·nH2O) nanobelts, while preserving its open layered structure with expanded interlayer region available for insertion and diffusion of a large number of electrochemically cycled Na+ ions. Intriguingly, we demonstrate that using low-temperature vacuum annealing the interlayer water content can be varied in the 0.5 ≤ n ≤ 1.20 range without a significant change in the interlayer spacing. The mechanism of the thermally induced interlayer water loss is discussed. The improved capacity retention exhibited by low-temperature vacuum annealed δ-Na x V2O5·nH2O nanobelts is attributed to the partial removal of the structural water from the interlayer region, formation of additional bonds within the V–O bilayers, and increased stacking order of V–O bilayers. Low-temperature vacuum annealing is proposed as an efficient strategy to control interlayer water and advance electrochemical stability of the growing family of hydrated transition metal compounds used as electrodes in intercalation batteries.