Lightweight Electrolyte Design for Li/Sulfurized Polyacrylonitrile (SPAN) Batteries.

Sulfurized polyacrylonitrile (SPAN) recently emerges as a promising cathode for high-energy lithium (Li) metal batteries owing to its high capacity, extended cycle life, and liberty from costly transition metals. As the high capacities of both Li metal and SPAN lead to relatively small electrode weights, the weight and specific energy density of Li/SPAN batteries are particularly sensitive to electrolyte weight, highlighting the importance of minimizing electrolyte density. Besides, the large volume changes of Li metal anode and SPAN cathode require inorganic-rich interphases that can guarantee intactness and protectivity throughout long cycles. This work addresses these crucial aspects with an electrolyte design where lightweight dibutyl ether (DBE) is used as a diluent for concentrated lithium bis(fluorosulfonyl)imide (LiFSI)-triethyl phosphate (TEP) solution. The designed electrolyte (d = 1.04 g mL-1) is 40%-50% lighter than conventional localized high-concentration electrolytes (LHCEs), leading to 12%-20% extra energy density at the cell level. Besides, the use of DBE introduces substantial solvent-diluent affinity, resulting in a unique solvation structure with strengthened capability to form favorable anion-derived inorganic-rich interphases, minimize electrolyte consumption, and improve cell cyclability. The electrolyte also exhibits low volatility and offers good protection to both Li metal anode and SPAN cathode under thermal abuse.

A Zinc-Bromine Battery with Deep Eutectic Electrolytes.

A deep eutectic solvent (DES) is an ionic liquid-analog electrolyte, newly emerging due to its low cost, easy preparation, and tunable properties. Herein, a zinc-bromine battery (ZBB) with a Zn-halide-based DES electrolyte prepared by mixing ZnBr2 , ZnCl2 , and a bromine-capturing agent is reported. The water-free DES electrolyte allows a closed-cell configuration for the ZBB owing to the prevention of Br2 evaporation and H2 evolution. It is found that the Cl- anion changes the structure of the zinc-halide complex anions and demonstrated that it improves the ion mobility and electrode reaction kinetics. The DES electrolyte with the optimized ZnCl2 composition shows much higher rate capability and a cycle life 90 times longer than that of a ZnCl2 -free DES electrolyte. A pouch-type flexible ZBB battery based on the DES electrolyte exhibits swelling-free operation for more than 120 cycles and stable operation under a folding test, suggesting its potential in consumer applications such as wearable electronics.

Modulation of Solvation Structure and Electrode Work Function by an Ultrathin Layer of Polymer of Intrinsic Microporosity in Zinc Ion Batteries.

Zinc ion batteries are promising candidates for large-scale energy storage systems. However, they suffer from the critical problems of insufficient cycling stability due to internal short-circuiting by zinc dendrites and zinc metal orphaning. In this work, a polymer of intrinsic microporosity (PIM-1) is reported as an ion regulating layer and an interface modulator, which promotes a uniform Zn plating and stripping process. According to spectroscopic analyses and computational calculations, PIM-1 enhances the reaction kinetics of a Zn metal electrode by altering the solvation structure of Zn2+ ions and increasing the work function of the Zn surface. As a result, the PIM-1 coating significantly improves the cyclability (1700 h at 0.5 mA cm-2 ) and Coulombic efficiency (99.6% at 3 mA cm-2 ) of the Zn/Zn2+ redox reaction. Moreover, the PIM-1 coated Zn operates for more than 200 h at 70% Zn utilization even under 10 mA cm-2 and 110 h at 95% Zn utilization of the Zn metal electrode. A Zn||V2 O5 full cell employing the PIM-1 layer exhibits seven times longer cycle life compared to the cell using bare Zn. The findings in this report demonstrate the potential of microporous materials as a key ingredient in the design of reversible Zn electrodes.

Electrokinetic-Driven Fast Ion Delivery for Reversible Aqueous Zinc Metal Batteries with High Capacity.

Aqueous zinc (Zn) metal batteries (ZMBs) are considered a promising candidate for grid-scale energy storage due to their freedom from fire hazards. However, a limited reversibility of Zn metal electrode caused by dendritic Zn growth has hindered the advent of high-capacity Zn metal batteries (>4 mAh cm-2 ). Herein, it is reported that fast electrokinetic Zn-ion transport extremely improves the Zn metal reversibility. It is revealed that a negatively charged porous layer (NPL) provides the electrokinetic Zn-ion transport by surface conduction, and consequently impedes the depletion of Zn-ion on electrode surface as indicated by numerical simulations and overlimiting current behavior. Due to the quick Zn-ion delivery, a dendrite-free and densely packed Zn metal deposit is accommodated inside its pores. With the introduction of the NPL, the cycling stability of Zn symmetric cell is enhanced by 21 times at 10 mA cm-2 /10 mAh cm-2 . Average Coulombic efficiency of 99.6% is achieved over 500 cycles for electrodeposition/stripping at 30 mA cm-2 /5 mAh cm-2 on NPL-Cu electrode. Furthermore, a high-capacity Zn/V2 O5 full cell with the NPL exhibits an extraordinary stability over 1000 cycles at a capacity of 4.8 mAh cm-2 .

Catalytic production of impurity-free V3.5+ electrolyte for vanadium redox flow batteries.

The vanadium redox flow battery is considered one of the most promising candidates for use in large-scale energy storage systems. However, its commercialization has been hindered due to the high manufacturing cost of the vanadium electrolyte, which is currently prepared using a costly electrolysis method with limited productivity. In this work, we present a simpler method for chemical production of impurity-free V3.5+ electrolyte by utilizing formic acid as a reducing agent and Pt/C as a catalyst. With the catalytic reduction of V4+ electrolyte, a high quality V3.5+ electrolyte was successfully produced and excellent cell performance was achieved. Based on the result, a prototype catalytic reactor employing Pt/C-decorated carbon felt was designed, and high-speed, continuous production of V3.5+ electrolyte in this manner was demonstrated with the reactor. This invention offers a simple but practical strategy to reduce the production cost of V3.5+ electrolyte while retaining quality that is adequate for high-performance operations.

Pore-Size-Tuned Graphene Oxide Frameworks as Ion-Selective and Protective Layers on Hydrocarbon Membranes for Vanadium Redox-Flow Batteries.

The laminated structure of graphene oxide (GO) membranes provides exceptional ion-separation properties due to the regular interlayer spacing ( d) between laminate layers. However, a larger effective pore size of the laminate immersed in water (∼11.1 Å) than the hydrated diameter of vanadium ions (>6.0 Å) prevents its use in vanadium redox-flow batteries (VRFB). In this work, we report an ion-selective graphene oxide framework (GOF) with a d tuned by cross-linking the GO nanosheets. Its effective pore size (∼5.9 Å) excludes vanadium ions by size but allows proton conduction. The GOF membrane is employed as a protective layer to address the poor chemical stability of sulfonated poly(arylene ether sulfone) (SPAES) membranes against VO2+ in VRFB. By effectively blocking vanadium ions, the GOF/SPAES membrane exhibits vanadium-ion permeability 4.2 times lower and a durability 5 times longer than that of the pristine SPAES membrane. Moreover, the VRFB with the GOF/SPAES membrane achieves an energy efficiency of 89% at 80 mA cm-2 and a capacity retention of 88% even after 400 cycles, far exceeding results for Nafion 115 and demonstrating its practical applicability for VRFB.

Ultrathin Nafion-filled porous membrane for zinc/bromine redox flow batteries.

In this work, we present a 16 µm-thick Nafion-filled porous membrane for Zn/Br redox flow batteries (ZBBs). By using molecular dynamics simulation and dynamic light scattering analysis, we rationally design Nafion solution for Nafion impregnation into a porous polypropylene (PP) separator. A void-free Nafion/PP membrane is successfully fabricated by using NMP as a solvent for the Nafion solution. The resulting membrane shows a smaller area specific resistance in comparison with 600 µm-thick, commercial SF-600 porous membrane. Due to its dense morphology, Br2 diffusivity of the Nafion/PP membrane is two orders of magnitude lower than that of SF-600, resulting in a comparable Br2 crossover in spite of 37.5 times smaller membrane thickness. As a result, the ZBB based on the Nafion/PP membrane exhibits a higher energy efficiency, demonstrating that ion exchange membrane can outperform the conventional porous membrane by reducing the membrane thickness with inexpensive porous substrate.

Crystal structure of the mixed-metal thio-phosphate Nb1.18V0.82PS10.

The mixed-metal thio-phosphate, Nb1.18V0.82PS10 (niobium vanadium phospho-rus deca-sulfide), has been prepared though solid state reactions using an alkali-metal halide flux. The title compound is isostructural with two-dimensional Nb2PS10. [M 2S12] (M = Nb or V) dimers built up from two bicapped trigonal prisms and tetra-hedral [PS4] units share sulfur atoms to construct (1) ∞[M 2PS10] chains along the a axis. These chains are linked through the di-sulfide bonds between [PS4] units in adjacent chains to form layers parallel to the ab plane. These layers then stack on top of each other to complete the three-dimensional structure with van der Waals gaps. The M sites are occupied by 59% of Nb and 41% of V and the average M-S and M-M distances in the title compound are in between those of V2PS10 and Nb2PS10. The classical charge balance of the title compound can be represented by [(Nb/V)(4+)]2[P(5+)][S(2-)]3[S(-)]7.