Junxiang Wang

High-Performance Aluminum-Ion Battery with CuS@C Microsphere Composite Cathode

On the basis of low-cost, rich resources, and safety performance, aluminum-ion batteries have been regarded as a promising candidate for next-generation energy storage batteries in large-scale energy applications. A rechargeable aluminum-ion battery has been fabricated based on a 3D hierarchical copper sulfide (CuS) microsphere composed of nanoflakes as cathode material and room-temperature ionic liquid containing AlCl3 and 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) as electrolyte. The aluminum-ion battery with a microsphere electrode exhibits a high average discharge voltage of ∼1.0 V vs Al/AlCl4-, reversible specific capacity of about 90 mA h g-1 at 20 mA g-1, and good cyclability of nearly 100% Coulombic efficiency after 100 cycles. Such remarkable electrochemical performance is attributed to the well-defined nanostructure of the cathode material facilitating the electron and ion transfer, especially for chloroaluminate ions with large size, which is desirable for aluminum-ion battery applications.

A long-life rechargeable Al ion battery based on molten salts

Affordable and scalable energy storage systems are necessary to mitigate the output fluctuation of an electrical power grid integrating intermittent renewable energy sources. Conventional battery technologies are unable to meet the demanding low-cost and long-life span requirements of a grid-scale application, although some of them demonstrated impressive high energy density and capacity. More recently, the prototype of an Al-ion battery has been developed using cheap electrode materials (Al and graphite) in an organic room-temperature ionic liquid electrolyte. Here we implement a different Al-ion battery in an inorganic molten salt electrolyte, which contains only an extremely low-cost and nonflammable sodium chloroaluminate melt working at 120 °C. Due to the superior ionic conductivity of the melt electrolyte and the enhanced Al-ion interaction/deintercalation dynamics at an elevated temperature of 120 °C, the battery delivered a discharge capacity of 190 mA h g−1 at a current density of 100 mA g−1 and showed an excellent cyclic performance even at an extremely high current density of 4000 mA g−1: 60 mA h g−1 capacity after 5000 cycles and 43 mA h g−1 capacity after 9000 cycles, with a coulombic efficiency constantly higher than 99%. The low-cost and safe characteristics, as well as the outstanding long-term cycling capability at high current densities allow the scale-up of this brand-new battery for large-scale energy storage applications.

Direct Conversion of Greenhouse Gas CO2 into Graphene via Molten Salts Electrolysis

Producing graphene through the electrochemical reduction of CO2 remains a great challenge, which requires precise control of the reaction kinetics, such as diffusivities of multiple ions, solubility of various gases, and the nucleation/growth of carbon on a surface. Here, graphene was successfully created from the greenhouse gas CO2 using molten salts. The results showed that CO2 could be effectively fixed by oxygen ions in CaCl2-NaCl-CaO melts to form carbonate ions, and subsequently electrochemically split into graphene on a stainless steel cathode; O2 gas was produced at the RuO2-TiO2 inert anode. The formation of graphene in this manner can be ascribed to the catalysis of active Fe, Ni, and Cu atoms at the surface of the cathode and the microexplosion effect through evolution of CO in between graphite layers. This finding may lead to a new generation of proceedures for the synthesis of high value-added products from CO2, which may also contribute to the establishment of a low-carbon and sustainable world.

Electrochemically depositing titanium(III) ions at liquid tin in a NaCl–KCl melt

The electrochemical behavior of titanium ions at a liquid tin cathode has been investigated by cyclic voltammetry and square wave voltammetry in a NaCl–KCl melt at 1023 K. The results show that the deposition potentials of alkali metals and titanium at liquid tin are more positive than those at a solid tungsten cathode. Meanwhile, the results prove that titanium(III) ions can be reduced at liquid tin with a one-step reduction, Ti3+ + 3e = Ti, which is a quasi-reversible process with diffusion-controlled mass transfer. The diffusion coefficient of titanium(III) ions is 1.05 × 10−5 cm2 s−1. Additionally, galvanostatic electrolysis has been carried out to clarify the effect of the current density on the cathodic products. The result demonstrates that a greater depth of titanium will be diffused into the liquid tin cathode during electrolysis with a lower current density.

Electrochemical self-assembly of nano-polyaniline film by forced convection and its capacitive performance

At present, an in situ synthesis of a conductive polyaniline (PANI) film via self-assembly is particularly of great interest in the supercapacitor field. Herein, we report the discovery a nanostructuring process for PANI electrochemical self-assembly through a forced convection method. It was observed that the morphology and structure of PANI films at the nanometer scale could be controlled by varying the rotation speed of the disk electrode during the electropolymerization process. On increasing the rotation speed from 0 rpm to 1000 rpm, the growth of PANI films successively changes from the nanorods composed porous films to the nanoparticles (diameter of 50 nm) composed dense films. We have also demonstrated the efficient electrochemical properties of the electrochemically assembled nano-PANI film-based electrodes at a rotation speed of 100 rpm, which showed the highest capacitance of 700.50 F g−1 at a current density of 1 A g−1 and good cycle stability after 1000 cycles.