Hongzhang Zhang

Nanofiltration (NF) membranes: the next generation separators for all vanadium redox flow batteries (VRBs)?

NF membranes, as an alternative to traditional ion exchange membranes, were first proposed and successfully prepared for VRBs based on a totally new concept of tuning the vanadium/proton selectivity viapore size exclusion. The results showed that membranes show increasing vanadium ion/proton (V/H) selectivity with decreasing pore size distribution. VRBs assembled with prepared NF membranes exhibited comparable performance to that of commercialized Nafion. The concept could potentially overcome the traditional restriction from ion exchange membranes and provide much more material options for VRB membranes.

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.

Anion‐Conductive Membranes with Ultralow Vanadium Permeability and Excellent Performance in Vanadium Flow Batteries

Anion exchange membranes prepared from quaternized poly(tetramethyl diphenyl ether sulfone) (QAPES) were first investigated in the context of vanadium flow battery (VFB) applications. The membranes showed an impressive suppression effect on vanadium ions. The recorded vanadium permeability was 0.02×10(-7)-0.09×10(-7) cm(2) min(-1), which was two orders of magnitude lower than that of Nafion 115. The self-discharge duration of a VFB single cell with a QAPES membrane is four times longer than that of Nafion 115. The morphological difference in hydrophilic domains between QAPES and Nafion was confirmed by TEM. After soaking the membranes in VO(2)(+) solution, adsorbed vanadium ions can barely be found in QAPES, whereas the hydrophilic domains of Nafion were stained. In the ex situ chemical stability test, QAPES showed a high tolerance to VO(2)(+) and remained intact after immersion in VO(2)(+) solution for over 250 h. The performance of a VFB single cell assembled with QAPES membranes is equal to or even better than that of Nafion 115 and remains stable in a long-term cycle test. These results indicate that QAPES membranes can be an ideal option in the fabrication of high-performance VFBs with low electric capacity loss.

Hierarchical Micron-Sized Mesoporous/Macroporous Graphene with Well-Tuned Surface Oxygen Chemistry for High Capacity and Cycling Stability Li–O2 Battery

Nonaqueous Li-O2 battery is recognized as one of the most promising energy storage devices for electric vehicles due to its super-high energy density. At present, carbon or catalyst-supporting carbon materials are widely used for cathode materials of Li-O2 battery. However, the unique electrode reaction and complex side reactions lead to numerous hurdles that have to be overcome. The pore blocking caused by the solid products and the byproducts generated from the side reactions severely limit the capacity performance and cycling stability. Thus, there is a great need to develop carbon materials with optimized pore structure and tunable surface chemistry to meet the special requirement of Li-O2 battery. Here, we propose a strategy of vacuum-promoted thermal expansion to fabricate one micron-sized graphene matrix with a hierarchical meso-/macroporous structure, combining with a following deoxygenation treatment to adjust the surface chemistry by reducing the amount of oxygen and selectively removing partial unstable groups. The as-made graphene demonstrates dramatically tailored pore characteristics and a well-tuned surface chemical environment. When applied in Li-O2 battery as cathode, it exhibits an outstanding capacity up to 19 800 mA h g(-1) and is capable of enduring over 50 cycles with a curtaining capacity of 1000 mA h g(-1) at a current density of 1000 mA g(-1). This will provide a novel pathway for the design of cathodes for Li-O2 battery.

Studies on Iron (Fe3+/Fe2+)-Complex/Bromine (Br2/Br-) Redox Flow Cell in Sodium Acetate Solution

bResearch Institute of Chemical Defense, Beijing 100083, China The formal potential of the FeIII/FeII couple shifts markedly in the negative direction by complexation with ethylenediamine tetraacetate EDTA, oxalate, and citrate. The potentials of the complexes with EDTA and oxalate are less pH-dependent than with citrate. But, the relatively high pH of around 6.0 is favorable electrochemically due to high corresponding currents. Complexation of FeIII/FeII couple can provide fast electrode kinetics except for the complex with citrate. But, the solubility of the complex with citrate is up to 0.8 M. Charge–discharge measurements were conducted with the iron-complex/Br2 redox cells. The results show that performance of the cells with 0.1 M FeIII/FeII-oxalate or FeIII/FeII-citrate is relatively poor due to slow kinetics for the FeIII/FeII-citrate and the unstability of the ferric form for the FeIII/FeII-oxalate, whereas performance of the iron-citrate/Br2 cell is improved considerably by increasing concentration of the FeIII-citrate complex. Also, energy efficiencies of up to approximately 80 and 70% could be obtained for the cell with 0.1 M FeIII/FeII-EDTA and 0.8 M FeIII/FeII-citrate, respectively. The preliminary study shows that novel Br2/iron-complex cells are technically feasible in redox flow batteries but need further investigation.

Lithium Sulfur Primary Battery with Super High Energy Density: Based on the Cauliflower-like Structured C/S Cathode

The lithium-sulfur primary batteries, as seldom reported in the previous literatures, were developed in this work. In order to maximize its practical energy density, a novel cauliflower-like hierarchical porous C/S cathode was designed, for facilitating the lithium-ions transport and sulfur accommodation. This kind of cathode could release about 1300 mAh g−1 (S) capacity at sulfur loading of 6 ~ 14 mg cm−2, and showed excellent shelf stability during a month test at room temperature. As a result, the assembled Li-S soft package battery achieved an energy density of 504 Wh kg−1 (654 Wh L−1), which was the highest value ever reported to the best of our knowledge. This work might arouse the interests on developing primary Li-S batteries, with great potential for practical application.

1-D oriented cross-linking hierarchical porous carbon fibers as a sulfur immobilizer for high performance lithium–sulfur batteries

One-dimensional (1D) oriented cross-linking hierarchical porous carbon fibers (CHPCF) were designed and proposed as the sulfur immobilizer for application in lithium–sulfur (Li–S) batteries. The CHPCFs exhibit a large length/diameter (L/D) ratio, a cross-linked structure and a reasonable hierarchical porous distribution, which provides “green channels” for both e− and Li+ transport. Besides, the CHPCFs possess large micro-porous surfaces to confine the polysulfide (PS) diffusion. As a result, the S/CHPCF cathodes simultaneously achieve excellent C-rate performance and cycling stability of 535 mA h g−1 at 15C (1C = 1672 mA g−1), and 0.076% capacity attenuation per cycle at 5C during 500 cycles. The structure–performance relationship of the carbon materials and Li–S batteries was studied in detail. This research work sheds light on material design for Li–S batteries with excellent C-rate performance.

Sulfur embedded in one-dimensional French fries-like hierarchical porous carbon derived from a metal–organic framework for high performance lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries suffer from poor cycling stability mainly caused by one of their own drawbacks, namely, the shuttle effect, which makes them far from conquering the marketplace. To tackle this problem, a novel French fries-like hierarchical porous carbon (FLHPC) with a one-dimensional (1D) structure was constructed by carbonizing an aluminum metal–organic framework (Al-MOF). In FLHPC, sulfur was infiltrated mainly into the micro- and mesopores, while macro-pores were used to facilitate the transportation of Li ions (Li+). On the basis of this concept, even without LiNO3 as additive, Li–S batteries not only delivered a high initial discharge capacity of nearly 1200 mA h g−1 at 0.1 C (1 C = 1672 mA h g−1) but also showed good cycling stability with a capacity retention of 68% at 0.5 C after 200 cycles. In addition, when the capacity rate (C-rate) was increased to 2 C, a high discharge capacity of 763 mA h g−1 was obtained after 20 cycles, proving their excellent C-rate performance.

Steam-Etched Spherical Carbon/Sulfur Composite with High Sulfur Capacity and Long Cycle Life for Li/S Battery Application

Spherical carbon material with large pore volume and specific area was designed for lithium/sulfur (Li/S) soft package battery cathode with sulfur loading over 75%, exhibiting good capacity output (about 1300 mAh g(-1)-S) and excellent capacity retention (70% after 600 cycles) at 0.1 C. The spherical carbon is prepared via in situ steam etching method, which has the advantages of low cost and easy scale up.

Carbon-Free CoO Mesoporous Nanowire Array Cathode for High-Performance Aprotic Li-O2 Batteries.

Although various kinds of catalysts have been developed for aprotic Li-O2 battery application, the carbon-based cathodes are still vulnerable to attacks from the discharge intermediates or products, as well as the accompanying electrolyte decomposition. To ameliorate this problem, the free-standing and carbon-free CoO nanowire array cathode was purposely designed for Li-O2 batteries. The single CoO nanowire formed as a special mesoporous structure, owing even comparable specific surface area and pore volume to the typical Super-P carbon particles. In addition to the highly selective oxygen reduction/evolution reactions catalytic activity of CoO cathodes, both excellent discharge specific capacity and cycling efficiency of Li-O2 batteries were obtained, with 4888 mAh gCoO(-1) and 50 cycles during 500 h period. Owing to the synergistic effect between elaborate porous structure and selective intermediate absorption on CoO crystal, a unique bimodal growth phenomenon of discharge products was occasionally observed, which further offers a novel mechanism to control the formation/decomposition morphology of discharge products in nanoscale. This research work is believed to shed light on the future development of high-performance aprotic Li-O2 batteries.