Zhizhang Yuan

Advanced porous membranes with ultra-high selectivity and stability for vanadium flow batteries

Porous polybenzimidazole membranes with ultra-high selectivity and stability were designed and fabricated for vanadium flow batteries. The combination of the facile fabrication procedure, high performance, the low cost of the starting materials and easy up-scaling makes the PBI porous membrane currently by far the most promising candidate for vanadium flow batteries.

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. 0.5 nm) is intermediary between that of hydrated vanadium ions (>0.6 nm) and protons (<0.24 nm). 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 >99 % and an energy efficiency of >81 % at 200 mA cm(-2), which is by far the highest value ever reported. These convincing results indicate that zeolite-coated membranes are promising in battery applications.

Porous membrane with high curvature, three-dimensional heat-resistance skeleton: a new and practical separator candidate for high safety lithium ion battery

Separators with high reliability and security are in urgent demand for the advancement of high performance lithium ion batteries. Here, we present a new and practical porous membrane with three-dimension (3D) heat-resistant skeleton and high curvature pore structure as a promising separator candidate to facilitate advances in battery safety and performances beyond those obtained from the conventional separators. The unique material properties combining with the well-developed structural characteristics enable the 3D porous skeleton to own several favorable properties, including superior thermal stability, good wettability with liquid electrolyte, high ion conductivity and internal short-circuit protection function, etc. which give rise to acceptable battery performances. Considering the simply and cost-effective preparation process, the porous membrane is deemed to be an interesting direction for the future lithium ion battery separator.

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.

Morphology and performance of poly(ether sulfone)/sulfonated poly(ether ether ketone) blend porous membranes for vanadium flow battery application

Poly(ether sulfone) (PES) porous membranes with tunable morphology were fabricated via a phase inversion method and applied in vanadium flow batteries (VFBs). The morphology of the PES membrane was adjusted by changing the polymer concentration and blending with hydrophilic sulfonated poly(ether ether ketone) (SPEEK) in the cast solution. The relationship between the membrane morphology and the performance in VFBs was investigated in detail. The results indicated that with increasing polymer concentration of the cast solution, the number of macrovoids gradually decreased and the finger-like pores became larger. A higher coulombic efficiency (CE) can be obtained due to the lower vanadium permeability, while the voltage efficiency (VE) decreased. In addition, the introduction of SPEEK in cast solution will induce the transformation of membrane structures from finger-like to spongy-like pores. The CE decreased with the higher vanadium permeability, while the VE increased due to the increased proton conductivity. As a result, optimized VFB performance of the PES membranes was obtained, showing a CE of 92.8% and an energy efficiency (EE) of 78.4%. The battery assembled with the prepared membranes showed a stable battery performance after running for more than 200 cycles, showing good oxidation stability. This work presents an effective and facile method to fabricate PES membranes with tunable battery performance.

Highly stable membranes based on sulfonated fluorinated poly(ether ether ketone)s with bifunctional groups for vanadium flow battery application

A facile strategy for fabricating a sulfonated poly (ether ether ketone) ion exchange membrane with high chemical stability, excellent ion selectivity and battery performance is presented. The essence of this strategy lies in the introduction of benzotrifluoride bifunctional groups that function to protect the ether bond (through the conjugation effect of the benzene ring) and restrict swelling behaviour of the membrane (resulting from the -CF3 hydrophobic groups). With the introduction of benzotrifluoride bifunctional groups, the SFPEEK membranes exhibited excellent ion selectivity and cell performance under vanadium flow battery (VFB) operation conditions, exhibiting a columbic efficiency of 98.32% and an energy efficiency of 87.74% at a current density of 80 mA cm(-2), which is much higher than commercial Nafion 115 (CE = 94.83%, EE = 83.25%). A VFB single cell assembled with a SFPEEK membrane shows a stable performance after continuously running more than 1050 cycles, which is by far the longest cycle life reported on sulfonated aromatic cation exchange membranes. These results demonstrated that the sulfonated poly (ether ether ketone) ion exchange membranes with benzotrifluoride bifunctional groups are promising candidates for VFB systems.

Composite membrane with ultra-thin ion exchangeable functional layer: a new separator choice for manganese-based cathode material in lithium ion batteries

A composite membrane with an ultra-thin ion exchangeable layer is specially designed as a separator in lithium ion batteries with manganese-based cathode materials. The composite membrane features a Mn2+ capture function which originates from the ion exchanging process, especially at high temperature, and is proven to help to alleviate the capacity decay of lithium ion batteries effectively. The enhanced thermal stability, improved wettability and higher lithium ion transference number of the composite membrane further suggest its promising application in lithium ion batteries.

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.

Toward a Low-Cost Alkaline Zinc-Iron Flow Battery with a Polybenzimidazole Custom Membrane for Stationary Energy Storage

Summary Alkaline zinc-iron flow battery is a promising technology for electrochemical energy storage. In this study, we present a high-performance alkaline zinc-iron flow battery in combination with a self-made, low-cost membrane with high mechanical stability and a 3D porous carbon felt electrode. The membrane could provide high hydroxyl ion conductivity while resisting zinc dendrites well owing to its high mechanical stability. The 3D porous carbon felt could serve as a guidance for the zinc stripping/plating, which can effectively suppress zinc dendrite/accumulation as well. Thus this battery demonstrates a coulombic efficiency of 99.5% and an energy efficiency of 82.8% at 160 mA cm−2, which is the highest value among recently reported flow battery systems. The battery can stably run for more than 500 cycles, showing very good stability. Most importantly, the practicability of this battery is confirmed by assembling a kilowatt cell stack with capital cost under

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

90/kWh.