Decarbonating layered double hydroxides using a carbonated salt solution.

Layered double hydroxides (LDHs) intercalated with tunable anionic species are finding increasingly wide applications. While LDHs with intercalated CO32- anions (LDH-CO3) are usually synthesized to achieve high crystallinity, the substitution of the intercalated CO32- with other desired anions is rather difficult because of the ultra-high affinity of CO32- to LDHs' main plates. Herein, we report a novel and facile method to overcome this difficulty. LDH-CO3 is decarbonated via submerging in a carbonated NaCl solution with CO2 bubbling. Complete deintercalation of CO32- is achieved quickly without damaging the main plates, i.e., the hydroxide layers, even in the case of Mg2Al-LDH-CO3 having the most stable CO32- anions. It is shown that carbonic acid H2CO3 in the salt solution reacts with intercalated CO32- to form bicarbonate (HCO3-), which exhibits a much lower affinity to the main plates and thus is easily substituted by chloride ions (Cl-) from the salt solution.

Engineering CoP Alloy Foil to a Well-Designed Integrated Electrode Toward High-Performance Electrochemical Energy Storage.

Nanostructured integrated electrodes with binder-free design show great potential to solve the ever-growing problems faced by currently commercial lithium-ion batteries such as insufficient power and energy densities. However, there are still many challenging problems limiting practical application of this emerging technology, in particular complex manufacturing process, high fabrication cost, and low loading mass of active material. Different from existing fabrication strategies, here using a CoP alloy foil as a precursor  a simple neutral salt solution-mediated electrochemical dealloying method to well address the above issues is demonstrated. The resultant freestanding mesoporous np-Co(OH)x /Co2 P product possesses not only active compositions of high specific capacity and large electrode packing density (>3.0 g cm-3 ) to meet practical capacity requirements, high-conductivity and well-developed nanoporous framework to achieve simultaneously fast ion and electron transfer, but also interconnected ligaments and suitable free space to ensure strong structural stability. Its comprehensively excellent electrochemical energy storage (EES) performances in both lithium/sodium-ion batteries and lithium-ion capacitors can further illustrate the effectiveness of the integrated electrode preparation strategy, such as remarkable reversible specific capacities/capacitances, dominated pseudo-capacitive EES mechanism, and ultra-long cycling life. This study provides new insights into preparation and design of high-performance integrated electrodes for practical applications.

Efficient, scalable, closed-loop synthesis of highly crystalline pure phase MgAl-layered double hydroxides intercalated with hydroxyl anions.

Layered double hydroxides (LDHs) can play an important role in various areas, but conventional LDHs synthesis often causes product agglomeration and generates plenty of high-salt wastewater, and requires a time-consuming aging process to reach the desired purity and crystalline state. Herein, we report the synthesis of MgAl-LDH, a representative of these kinds of ionic lamellar inorganic solids, with a novel method involving the reaction of magnesium oxide (MgO) with aluminate ions (Al(OH)4-) in a strongly alkaline environment. The formation of MgAl-LDH follows a mechanism of interfacial dissolution-reprecipitation (IDR), i.e., Mg2+ ions released at the interface of dissolved MgO react immediately with Al(OH)4- ions to reprecipitate as MgAl-LDH. The obtained MgAl-LDH has no impurity phases and shows high crystallinity, high specific surface area, and a narrow particle size distribution. Moreover, MgAl-LDH is intercalated with OH- anions, so it can be directly used as a Brønsted base catalyst and ion exchanger. The novel method requires no time-consuming aging process and is highly scalable. It is also shown that a closed-loop synthesis of MgAl-LDH without waste discharge can be achieved with an appropriate Al source, e.g., Al(OH)3, and a recycled NaOH solution.

Unveiling a bimetallic FeCo-coupled MoS2 composite for enhanced energy storage.

Sodium and potassium-ion batteries are promising for energy storage owing to their source abundance and low cost; however, most active materials still suffer from sluggish kinetics, huge volume variations, and poor conductivity and cycle stability. It remains a great challenge to explore appropriate electrode materials for scaled practical applications. Herein, mesoporous FeCo-incorporated MoS2 nanosheets encapsulated into a porous carbon framework (FeCo@C@MoS2) are smartly designed, artistically fabricated and evaluated for sodium and potassium storage. The FeCo@C@MoS2 electrode displays high reversible capacities of 380 mA h g-1 and 147 mA h g-1 at 500 mA g-1 for sodium and potassium storage, respectively. FeCo derived from a Prussian blue analogue promotes fast reaction kinetics of Na+/K+ transport, introduces the formation of a stable solid electrolyte interphase layer (SEI) in both the interior and exterior of the cube-like porous nanostructure and controls the Na+/K+ fluxes, suppressing the growth of metal dendrites. The porous carbon framework with large interstitial voids can effectively buffer volume variations and mitigate mechanical stress, contributing significantly to alleviate strain intensification on the surface layer between MoS2 and FeCo during repeated plating/stripping processes. Density functional theoretical calculations (DFT) further confirm that the synthesized nanostructure shows an intensified electron state, elevated anti-stress ability, high-quality SEI film and preferable Na+/K+ adsorption energies. This in-depth investigation of the electrochemical performance and the extended energy storage mechanism based on metal alloy/sulfide nanostructures for sodium and potassium storage provides guidance for the smart design of heterojunctions for remarkable energy storage.

Magnetic Field Facilitated Resilient Chain-like Fe3O4/C/Red P with Superior Sodium Storage Performance.

Red phosphorus (P) has recently attracted lots of interest due to its extraordinary theoretical capacity of 2596 mAh g-1 in sodium-ion batteries (SIBs). However, it is challenging to solve the stability in the preparation process, while enhancing its low conductivity and solving the structural degradation caused by the enormous volume expansion (>490%) during cycling have become the targeted pursuits. Here, we creatively introduced the magnetic stimuli source to solve both of the preparation and the volume swelling force issues. In the precedence of magnetic field, the increased pressure in the sample room drives the homogeneous red P particles to finely deposit on the surface of Fe3O4/C. The chain-like Fe3O4/C/red P was successfully prepared assisted by the magnetic field. Simultaneously, considering that the speeded up movements for both electrons and sodium ions depended on Lorentz force, the electrochemical performance of such anode material is optimized by tuning the arrays in collector. It is noted that the nanostructure is elastically rearranged for the resistance of volume swelling force. Compared with the single Fe3O4/C/red P particles, for the magnetic fabricated Fe3O4/C/P chain structure, the electrostatic potential for reconstructing the chain-like Fe3O4/C/P is the largest. Such configured chain-like anode material exhibits an extraordinary cyclic performance and superior rate capability (692 mAh g-1 at 2000 mA g-1). The magnetic stimuli source bridges both the preparation optimization and the electrochemical performance enhancements for the red P based anode materials.

Ultraviolet Irradiation Treatment for Enhanced Sodium Storage Performance Based on Wide-Interlayer-Spacing Hollow C@MoS2@CN Nanospheres.

The photochemistry and sodium storage process have been generally considered as two separated approaches without strong connection. Here, ultraviolet (UV) irradiation was applied to sodium-ion batteries to improve the electrochemical performance of MoS2-based composites. C@MoS2@CN nanospheres consist of double protective structures, including inner hollow carbon spheres with a thin wall (C) and outer N-doping carbon nanosheets (CNs) derived from polydopamine. The special nanostructure possesses the virtues such as wide-interlayer spacing, flexible feature with great structure integrity, and rich active sites, which endow the fast electron transfer and shorten the ion diffusion pathways. Under the excitation of UV-light, intense electrons and holes are accumulated within MoS2-based composites. The excited electrons can promote the preinsertion of Na+. More importantly, dense electrons promote the electrolyte to decompose and hence form a stable solid electrolyte interphase in advance. After UV-light irradiation treatment in the electrolyte, the initial Coulombic efficiency of C@MoS2@CN electrodes increased from 48.2 to 79.6%, and benefiting from the fine nanostructure, the C@MoS2@CN electrode with UV irradiation treatment delivered a great rate performance 116  mAh g-1 in 20 s and  super cycling stability that 87.6% capacity was retained after 500 cycles at 500 mA g-1. When employed as anode for sodium-ion hybrid capacitors, it delivered a maximum power density of 6.84 kW kg-1 (with 114.07  Wh kg-1 energy density) and a maximum energy density of 244.15 Wh g-1 (with 152.59 W kg-1 power density). This work sheds new viewpoints into the applications of photochemistry in the development of energy storage devices.