Wenjing Lu

A Highly Ion‐Selective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications

Zeolites are crystalline microporous aluminosilicates with periodic arrangements of cages and well-defined channels, which make them very suitable for separating ions of different sizes, and thus also for use in battery applications. Herein, an ultra-thin ZSM-35 zeolite flake was introduced onto a poly(ether sulfone) based porous membrane. The pore size of the zeolite (ca. 0.5u2005nm) is intermediary between that of hydrated vanadium ions (>0.6u2005nm) and protons (<0.24u2005nm). The resultant membrane can thus be used to perfectly separate vanadium ions and protons, making this technology useful in vanadium flow batteries (VFB). A VFB with a zeolite-coated membrane exhibits a columbic efficiency of >99u2009% and an energy efficiency of >81u2009% at 200u2005mAu2009cm(-2), which is by far the highest value ever reported. These convincing results indicate that zeolite-coated membranes are promising in battery applications.

High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces

A simple and effective solvent treatment method was developed to prepare porous membranes with a tunable morphology for vanadium flow battery applications. The solvent treatment method can effectively create poly(ether sulfone) (PES) membranes with a well-controllable pore size and pore size distribution. An impressive vanadium flow battery (VFB) performance with a coulombic efficiency of over 99% and an energy efficiency of over 90% was obtained, which are the highest values ever reported for porous uncharged membranes. The concept provides an entirely novel, simple and cost-effective way to fabricate high-performance porous membranes for VFB applications.

Polypyrrole modified porous poly(ether sulfone) membranes with high performance for vanadium flow batteries

Polypyrrole (PPY) modified porous poly(ether sulfone) (PPY/PES) membranes with excellent ion conductivity and high ion selectivity are prepared and employed in vanadium flow batteries (VFBs). The porous PES membranes are modified through in situ polymerization of pyrrole (PR) by using VO2+ as the oxidizing agent. The positively charged PPY nanoparticles can effectively retain vanadium ions via the Donnan exclusion and afford excellent ion conductivity through the interaction between the sulfuric acid in electrolytes and the nitrogen elements in PPY. As a consequence, the designed PPY/PES porous membranes demonstrate high ion selectivity and excellent ion conductivity along with exceptional chemical stability under VFB operation conditions. The PPY/PES porous membranes exhibited a very prospective performance for vanadium flow applications, showing a coulombic efficiency (CE) of 96.30% and an energy efficiency (EE) of 87.20% at a current density of 80 mA cm−2, which are much better than those of a VFB with a Nafion 115 membrane (coulombic efficiency of 93.16% and energy efficiency of 82.29%). Furthermore, a VFB using the PPY/PES porous membranes delivers a stable battery efficiency after continuously operating for more than 100 cycles, displaying good potential usage in VFB applications.

Advanced charged porous membranes with flexible internal crosslinking structures for vanadium flow batteries

Advanced charged porous membranes with flexible internal crosslinking networks were designed and fabricated for vanadium flow battery application. Flexible 1,4-diaminobutane was introduced in CMPSF spongy porous membranes to build flexible crosslinking networks on the pore walls. The flexible segments could induce relatively highly micro-phase separated structures (hydrophilic and hydrophobic phase) and effectively enhance the mobility of hydrophilic and hydrophobic domains, which is highly beneficial for proton transportation. At the same time, the positively charged crosslinking networks can ensure the high chemical stability of resulting membranes. As a result, porous membranes with flexible crosslinking networks could meet the requirement of VFB application owing to their excellent conductivity, high selectivity and high chemical stability. A VFB single cell with the prepared charged porous membrane exhibits a coulombic efficiency (CE) of more than 99% and an energy efficiency (EE) of about 87% at 80 mA cm−2, showing much higher performance than commercial Nafion 115 (CE = 92.5%, EE = 83.7%). A VFB employing the prepared membrane maintains a stable performance after more than 4000 charge–discharge cycles, showing impressive potential for VFB application.

Solvent treatment: the formation mechanism of advanced porous membranes for flow batteries

Solvent treatment has been proved to be a very simple and efficient method to prepare high-performance porous membranes for flow batteries. In this article, the process parameters of solvent treatment were regulated to further investigate the formation mechanism of porous membranes. The effect of the solvent evaporation temperature, the solvent immersion time and the solvent composition on the morphology and performance of porous membranes was studied systematically. The adjustment of these process parameters made the acting mechanisms of the polymer–solvent interaction and the cohesive force of polymers more clear. The factors affecting the polymer–solvent interaction and the cohesive force, along with the acting principles of process parameters, were also elucidated in detail. The formation mechanism of porous membranes during solvent treatment was accordingly clarified distinctly. As a result, an optimized VFB performance of treated membranes with a coulombic efficiency of 98.33%, and an energy efficiency of 81.17% at 160 mA cm−2 was achieved, which was much higher than that of Nafion 115 and among the highest values ever reported. Moreover, this VFB could continually run over 2600 cycles at 200 mA cm−2, without obvious efficiency fade. Thus, this paper provides a simpler, quicker and more economical method to prepare high-performance porous membranes for flow batteries.