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Electrospun carbon fibers are featured with abundant electroactive sites but large mass transport resistances as the electrodes for vanadium redox flow battery. To lower mass transport resistances while maintaining large specific areas, electrospun carbon fibers with different structural properties, including pore size and pore distribution, are prepared by varying precursor concentrations. Increasing the polyacrylonitrile concentration from 9 wt% to 18 wt% results in carbonized fibers with an average fiber diameter ranging from 0.28 μm to 1.82 μm. The median pore diameter, in the meantime, almost linearly increases from 1.32 μm to 9.05 μm while maintaining the porosity of higher than 82%. The subsequent electroactivity evaluation and full battery testing demonstrate that the mass transport of vanadium ions through the electrode with larger fiber diameters are significantly improved but not scarifying the electrochemical activity. It is shown that the flow battery with these electrodes obtains an energy efficiency of 79% and electrolyte utilization of 74% at 300 mA cm−2. Hence, all these results eliminate the concern of mass transport when applying electrospun carbon fibers as the electrodes for redox flow batteries and guide the future development of electrospun carbon fibers. © 2020 Hydrogen Energy Publications LLC

Lithium–sulfur batteries are attractive alternatives to lithium-ion batteries because of their high theoretical specific energy and natural abundance of sulfur. However, the practical specific energy and cycle life of Li–S pouch cells are significantly limited by the use of thin sulfur electrodes, flooded electrolytes and Li metal degradation. Here we propose a cathode design concept to achieve good Li–S pouch cell performances. The cathode is composed of uniformly embedded ZnS nanoparticles and Co–N–C single-atom catalyst to form double-end binding sites inside a highly oriented macroporous host, which can effectively immobilize and catalytically convert polysulfide intermediates during cycling, thus eliminating the shuttle effect and lithium metal corrosion. The ordered macropores enhance ionic transport under high sulfur loading by forming sufficient triple-phase boundaries between catalyst, conductive support and electrolyte. This design prevents the formation of inactive sulfur (dead sulfur). Our cathode structure shows improved performances in a pouch cell configuration under high sulfur loading and lean electrolyte operation. A 1-A-h-level pouch cell with only 100% lithium excess can deliver a cell specific energy of >300 W h kg−1 with a Coulombic efficiency >95% for 80 cycles. © 2020, UChicago Argonne, LLC, Operator of Argonne National Laboratory under exclusive licence to Springer Nature Limited.

In the version of this Article originally published online, in affiliation 8, ‘IRMC’ should have been ‘Institute for Research & Medical Consultations’; this has now been corrected in all versions.

Developing functional membrane with high conductivity and excellent stability is critical for improving the performance of vanadium redox flow batteries (VRFBs). Herein, an asymmetric porous polybenzimidazole (PBI) membrane composed of an ultra-thin dense layer and a sponge-like porous layer is proposed and prepared. The dense layer takes the main role of inhibiting vanadium crossover, whereas the porous layer provides not only a fast proton conduction channel but also a mechanical support to the dense layer. Hence, the asymmetric PBI membrane exhibits a high proton conductivity (36.4 mS cm−1 at room temperature) and an extremely low vanadium permeability (0.26 × 10−7 cm2 min−1). The VRFB with this membrane achieves an energy efficiency of 83.17% at 400 mA cm−2 and 78.59% at 500 mA cm−2. Furthermore, the battery enables to be continuously cycled for 1600 times without a significant degradation at 400 mA cm−2. All these results prove that the PBI membrane with an asymmetric porous structure is an ideal membrane for redox flow batteries. © 2020 Wiley-VCH GmbH

Replacing lithium metal in a lithium-sulfur battery with lithiated silicon can enhance safety and reversibility while maintaining the high energy density. However, fabricating lithiated silicon, while protecting it against lithium polysulfides, is difficult. In this work, we design and prepare a protected lithium/carbon nanofiber composite interlayer for simultaneous lithiation and protection of the silicon anode. The interlayer is fabricated via two steps of reactions, first by reacting antimony trifluoride-modified carbon nanofibers with molten lithium, and then by coating it for a tightly anchored solid electrolyte layer on lithium. The interlayer can be directly inserted between a separator and a silicon anode during battery assembly to lithiate and protect the anode, which enables the stable operation of a lithiated silicon/sulfur battery of a practical loading (4.0 mg cm-2 for both silicon and sulfur) at 2.5 mA cm-2 for 200 cycles, with capacity retention up to 94%. This work demonstrates how we can achieve a durable full battery via a scalable structural design strategy, which could be extended for use in other types of (lithium, sodium, potassium)-ion/sulfur batteries. © 2019 Elsevier B.V.

Lithium-sulfur (Li-S) batteries are a promising energy storage device with exceptionally high specific capacities and energy densities. The widespread applications of the technology, however, have been hindered by issues such as sluggish reaction kinetics, polysulfide shuttle effect and Li dendrite growth. This thesis begins with the study of the precipitation process in the sulfur cathode, which is identified as the limiting step to achieve a high rate capability. First, we develop a discharge model of Li-S batteries based on our experimental observations. The surface nucleation and growth kinetics coupled with electrochemical reactions is exploited for describing the Li2S precipitation. It is predicted that promoting the growth of Li2S particles, including lowering the initial nucleation rate and providing a suitable amount of initial nucleation sites, can prolong the battery’s discharge capacity. Guided by the model, we further design the N-TiO2 nanowire decorated carbon cloth electrode. The nitrogen doping in the nanowires allows for a higher electrical conductivity and stronger polysulfide binding ability. During discharge, Li2S can be deposited along the nanowire array, instead of accumulating on the electrode surface like a resistive thin film. The design leads to a prolonged discharge capacity, 180% higher than that achieved by a pristine carbon cloth electrode at 8.0 mA cm-2 (4.8 mgsulfur cm-2). Further, we demonstrate that, in Na-S batteries, the precipitation of Na2S2 follows a nucleation and growth process similar to Li-S. From the thermodynamic calculation and spectroscopic studies, we reveal the difference in the compositions of final solid discharge products between Li and Na-based systems. To enhance the cyclability, we need to prevent the parasitic reactions between Li anode and solvated discharge intermediates (lithium polysulfides, LiPS). We first lo

Featuring high energy density and low cost, lithium sulfur batteries are regarded as one of the most promising next-generation energy storage technologies. However, their widespread adoption is plagued by lithium dendrite growth and parasitic reactions induced by the polysulfide shuttle effect. To address these two issues simultaneously, we propose a bifunctional artificial protective layer, which is composed of graphitic carbon nitride nanosheets joined together by a polyvinylidene fluoride binder. First-principles study results reveal that the coexistence of pyridinic and quaternary nitrogen in the g-C3N4 bulk phase is capable of facilitating a homogeneous Li ionic flux, thus leading to a more uniform lithium deposition. Meanwhile, side reactions are dramatically suppressed due to the elimination of the direct exposure of lithium metal in the liquid electrolyte environment. As a result, a high coulombic efficiency of 98% for over 250 h under the current density of 1 mA cm−2 and a cycle capacity of 1 mAh cm−2 is achieved for a Li/Cu half-cell. More remarkably, it is demonstrated that the lithium-sulfur battery with the protective layer exhibits a much prolonged cycling life (180 cycles) with a reasonable sulfur mass loading of up to 1.5 mg cm−2. © 2019 Elsevier Ltd

A rechargeable lithium anode requires a porous structure for a high capacity, and a stable electrode/electrolyte interface against dendrite formation and polysulfide crossover when used in a lithium-sulfur battery. Here, we design two simple steps of spontaneous reactions for protecting porous lithium electrodes. First, a reaction between molten lithium and sulfur-impregnated carbon nanofiber forms a fibrous network with a lithium shell and a carbon core. Second, we coat the surface of this porous lithium electrode with a composite of lithium bismuth alloys and lithium fluoride through another spontaneous reaction between lithium and bismuth trifluoride, solvated with phosphorous pentasulfide, which also polymerizes with lithium sulfide residual in the electrode to form a solid electrolyte layer. This protected porous lithium electrode enables stable operation of a lithium-sulfur battery with a sulfur loading of 10.2 mg cm−2 at 6.0 mA cm−2 for 200 cycles.

During the discharge process of lithium-sulfur batteries, the nucleation and growth of Li2S precipitates result in a non-uniform Li2S particle size distribution, significantly affecting the charging process. However, a uniform Li2S distribution at the initial state of the charging process of the batteries is assumed in the models reported in the literature, leading to an unrealistic simulation of the charging process. To address this issue, we propose a one-dimensional transient mathematical model, which incorporates the size-dependent Li2S dissolution and redox mediation reaction between dissolved polysulfides and Li 2 S particles into the charging process. Simulation results show that the dissolution rate of large Li2S particles is suppressed at a lower potential due to the small specific surface area, while the smaller Li2S particles are electrochemically oxidized into dissolved polysulfides first, which further act as the redox mediators to promote the oxidation of larger Li2S particles. Capturing these effects enables an excellent agreement between the predicted and measured charging voltage profiles. Moreover, the effects of particle sizes and redox mediation reaction rates are studied. It is revealed that the optimal amount of smaller-sized Li2S particles and suitable redox mediation reaction rate allow for a lower charging over-potential. Furthermore, it is shown that the effect of redox mediation rates on the dissolution of Li2S large particles exerts a significant influence on the charging process. (C) 2018 Elsevier Ltd. All rights reserved.

In this work, a novel aqueous battery consisting of manganese in (Mn Sn) redox chemistries is proposed, where Mn redox reactions occur in the positive electrode and Sn deposition/stripping reactions occur in the negative electrode. The battery exhibits an open circuit voltage of 1.7 V, while a coulombic efficiency of higher than 98.8% is obtained at an operating current density of 30 mA cm−2. Cyclic tests show that the energy efficiency can be kept above 91.5% with no observable decay at a current density of 10 mA cm−2. In addition, due to the high hydrogen overpotential of Sn metal, the parasitic hydrogen evolution reaction can be largely avoided. With decent battery performance, the Mn Sn system offers a promising solution for future energy storage applications.

Lacking effective anchoring materials to suppress the severe shuttle effect is a longstanding issue hindering the development of lithium-sulfur (Li-S) batteries. In this work, a first-principles study is carried out to investigate the potential of borophene and defective borophene, which have high ionic conductivity and adsorbent ability, as anchoring materials for Li-S batteries. Borophene is found to exhibit ultra-high adsorption energies towards lithium polysulfides, but the material facilitates the decomposition of Li-S clusters, leading to an undesirable sulfur loss during battery cycling. For this reason, borophene is not an ideal anchoring material for Li-S batteries. On the contrary, defective borophene is found to show moderate adsorption energies ranging from 1 to 3 eV, which not only effectively anchors lithium polysulfides to suppress the shuttle effect, but also keeps their cyclic structures undecomposed. In addition, defective borophene exhibits a metallic characteristic during the whole reaction process, ensuring the lithium polysulfides be easily charged back and not accumulate on the anchoring materials. Given these advantages, it is expected that defective borophene is a promising anchoring material, leading to a suppressed shuttle effect and enhanced capacity retention for Li-S batteries.

Liquid-electrolyte sodium-sulfur battery operated at room temperature is encountering challenges brought by the complex sulfur redox reactions, including (i) the dissolved polysulfide intermediates trigger serious side reactions on Na anode surface; (ii) the short-chain sulfide precipitation exhibits sluggish kinetics and the sulfur utilization is generally below 50% with unclear reasons. In this work, employing an ion selective polybenzimidazole-based separator we successfully suppress the polysulfide corrosion on the Na anode, which allows the investigation of the precipitation reaction. Combining DFT calculation and characterization techniques, we determine Na2S2 particles as the final discharge product and reveal that Na2S2 passivation is the predominant attributes of large polarization and capacity fading. To address these issues, we present the use of a bifunctional NaI-P2S5 based electrolyte additive, which (i) improves the Na2S2 precipitation kinetics by forming soluble Na2S2-P2S5 complex and (ii) promotes the dissolution of Na2S2 by the chemical mediation of I−/ I3 −. As a result, a much improved capacity retention (92.9% for 50 cycles at 0.2C) is attained, which sheds light on enabling the stable operation of sodium-sulfur batteries via combining advanced separator and electrolyte engineering strategies. © 2018 Elsevier B.V.

Lacking effective anchoring materials to suppress the severe shuttle effect is a longstanding issue hindering the development of lithium-sulfur (Li-S) batteries. In this work, a first-principles study is carried out to investigate the potential of borophene and defective borophene, which have high ionic conductivity and adsorbent ability, as anchoring materials for Li-S batteries. Borophene is found to exhibit ultra-high adsorption energies towards lithium polysulfides, but the material facilitates the decomposition of Li-S clusters, leading to an undesirable sulfur loss during battery cycling. For this reason, borophene is not an ideal anchoring material for Li-S batteries. On the contrary, defective borophene is found to show moderate adsorption energies ranging from 1 to 3 eV, which not only effectively anchors lithium polysulfides to suppress the shuttle effect, but also keeps their cyclic structures undecomposed. In addition, defective borophene exhibits a metallic characteristic during the whole reaction process, ensuring the lithium polysulfides be easily charged back and not accumulate on the anchoring materials. Given these advantages, it is expected that defective borophene is a promising anchoring material, leading to a suppressed shuttle effect and enhanced capacity retention for Li-S batteries.

In this work, a density functional theory (DFT) based first-principles study is carried out to investigate the potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion (Na-ion) batteries. Results show that both SiS and SiSe have large adsorption energies towards single Na atom of −0.94 and −0.43 eV, owing to the charge transfers from Na to SiS or SiSe. In addition, it is found that the highest Na concentration for both SiS and SiSe is x = 1 with the chemical formulas of NaSiS and NaSiSe, corresponding to the high theoretical specific capacities for Na storages of 445.6 and 250.4 mAh g−1, respectively. Moreover, Na diffusions are very fast and show strong directional behaviors on SiS and SiSe monolayers, with the energy barriers of only 0.135 and 0.158 eV, lower than those of conventional anode materials for Na-ion batteries such as Na2Ti3O7 (0.19 eV) and Na3Sb (0.21 eV). Finally, although SiS and SiSe show semiconducting behaviors, they transform to metallic states after adsorbing Na atoms, indicating enhanced electrical conductivity during battery cycling. Given these advantages, it is expected that both SiS and SiSe monolayers are promising anode materials for Na-ion batteries, and in principle, other Na-based batteries as well.

Li-polyiodide batteries are attractive because of their high energy density and excellent rate performance. Nevertheless, the polyiodide shuttle effect and Li dendrite growth over cycling result in fast degradation of the Li anode and a short cycle life. Here we report a facile yet efficient design of high-energy membrane-free Li-polyiodide battery, in which the Li anode is shielded by a pre-deposited indium (In) layer and a graphene paper layer. The proof-of-concept semi-liquid battery with such a dual-protection strategy demonstrates a remarkably enhanced cycling stability for the reasons: (i) the In layer is capable of mitigating the Li dendrite growth and resisting the polyiodide shuttle attack; and (ii) the graphene paper physically suppresses the anode surface evolution and enables the formation of a separated passivation layer. Consequently, the battery can operate with a concentrated catholyte of 6 M I− and achieves a volumetric energy density as high as 165.3 Wh L−1 (1.5 C) for 100 cycles. The high performances achieved suggest the aprotic Li-polyiodide battery with a compact and robust architecture shows the potential for various energy storage applications. © 2017 Elsevier B.V.

The redox flow battery (RFB) is one of the most promising large-scale energy storage technologies for the massive utilization of intermittent renewables especially wind and solar energy. This work presents a novel redox flow battery that utilizes inexpensive and abundant Fe(II)/Fe(III) and Pb/Pb(II) redox couples as redox materials. Experimental results show that both the Fe(II)/Fe(III) and Pb/Pb(II) redox couples have fast electrochemical kinetics in methanesulfonic acid, and that the coulombic efficiency and energy efficiency of the battery are, respectively, as high as 96.2% and 86.2% at 40 mA cm−2. Furthermore, the battery exhibits stable performance in terms of efficiencies and discharge capacities during the cycle test. The inexpensive redox materials, fast electrochemical kinetics and stable cycle performance make the present battery a promising candidate for large-scale energy storage applications. © 2017 Elsevier B.V.

In this paper, we report a high-energy-density lithium/polyiodide (Li/PI) semi-liquid battery with soluble polyiodide in ether-based solvents as the catholyte. The challenge of shuttle effect is addressed by adopting a hybrid membrane coated with negatively charged sulfonate-ended perfluoroalkyl polymer, which allows for inhibition of polyiodide shuttles due to the electrostatic repulsion. The assembled Li/PI battery demonstrates a superior volumetric energy density (170.5 Wh L−1), a stable cycling performance (>100 cycles, averaged decay < 0.16% at 0.2 C), a high energy efficiency (>84%, 100 cycles at 2 C), and a high coulombic efficiency (>95%, 100 cycles at 2 C). These high performances achieved suggest that the aprotic Li/polyiodide battery with a compact architecture has the potential for various energy storage applications. © 2016 Elsevier B.V.

A semi-liquid polysulfide cathode renders a higher sulfur loading for Li-S batteries. However, the aggravated polysulfide shuttle effect and the poor interaction between polysulfide and carbonaceous electrode lower the battery’s cycling stability and performance. Here we report a freestanding N-TiO2 nanowire (NW) decorated carbon cloth electrode for a Li-polysulfide battery, where the nitrogen doping in the formed nanowires allows for a higher electrical conductivity and stronger polysulfide binding ability. Meanwhile, with the facile adsorption of View the MathML source and more active sites provided by the nanowire structure, Li2S precipitation can be improved as well. With the rationally engineered nanostructured polysulfide binding electrode, the battery achieves a remarkably enhanced cycling stability and prolonged discharge capacity (1210 mAh g−1, 0.2C and 600 mAh g−1, 1C), in comparison with the pristine carbon cloth (890 mAh g−1, 0.2C and 210 mAh g−1, 1C). The facile strategy of fabricating conductive and polysulfide binding nanostructure in this work is thus expected to facilitate the design of high-energy sulfur cathode.

This paper reports on a one-dimensional lithium-oxygen (Li-O2) battery model incorporating the competitive uptake of discharge intermediate between the electrode surface and the aprotic electrolyte. Unlike previous models, in which a single-step reaction is assumed for aprotic Li-O2 batteries (2Li+ + 2e− + O2 → Li2O2), the present model more realistically depicts the electrochemical process in a battery system by taking account of multiple-step reactions, including the surface reduction reactions of adsorbed oxygen (Li++O2 ∗+e-→LiO2 ∗) and adsorbed superoxide (LiO2 ∗+Li++e-→Li2O2) along with the dissolution of superoxide into electrolyte. Transient and spatial analyses are performed to identify the limiting steps for the battery's performance, including oxygen transport and final discharge product precipitation. The effects of the kinetics of oxygen reduction reaction and superoxide dissolution are also investigated. In addition, the impact of cathode microstructures on the battery's performance is studied. It is found that the electrolyte's ability to dissolve the discharge intermediate (LiO2) is critically important to improve the discharge capacity. © 2016 Elsevier Ltd

The zinc bromine flow battery (ZBFB) is regarded as one of the most promising candidates for large-scale energy storage attributed to its high energy density and low cost. However, it suffers from low power density, primarily due to large internal resistances caused by the low conductivity of electrolyte and high polarization in the positive electrode. In this work, chloride based salts including KCl and NH4Cl are investigated as supporting electrolyte to enhance electrolyte conductivity, while graphite-felt electrodes are thermally treated to improve electrocatalytic activity. It is found that the use of 4 M NH4Cl as a supporting electrolyte enables the battery to be operated at a current density of 40 mA cm−2 with an energy efficiency of 74.3%, whereas without the addition of a supporting electrolyte the battery only outputs an energy efficiency of 60.4%. In combination with a thermally treated graphite-felt electrode, efficiency further reaches up to 81.8% at the same current density. More impressively, we demonstrate that even at a high current density of up to 80 mA cm−2, the battery is capable of delivering an energy efficiency of 70%, representing one of the highest performances of ZBFBs in the open literature.

The low density associated with low sulfur areal loading in the solid-state sulfur cathode of current Li S batteries is an issue hindering the development of this type of battery. Polysulfide catholyte as a recyclable liquid fuel was proven to enhance both the energy density and power density of the battery. However, a critical barrier with this lithium (LO/polysulfide battery is that the shuttle effect, which is the crossover of polysulfides and side deposition on the Li anode, becomes much more severe than that in conventional Li S batteries with a solidstate sulfur cathode. In this work, we successfully applied an acrylatebased gel polymer electrolyte (GPE) to the Li/polysulfide system. The GPE layer can effectively block the detrimental diffusion of polysulfides and protect the Li metal from the side passivation reaction. Cathode static batteries utilizing 2 M catholyte (areal sulfur loading of 6.4 mg cm(-2)) present superior cycling stability (727.4 mAh g(-1) after 500 cycles at 0.2 C) and high rate capability (814 mAh g(-1) at 2 C) and power density (similar to 10 mW cm(-2)), which also possess replaceable and encapsulated merits for mobile devices. In the cathode-flow mode, the Li/polysulfide system with catholyte supplied from an external tank demonstrates further improved power density (similar to 59 mW cm(-2)) and stable cycling performance. This novel and simple Li/polysulfide system represents a significant advancement of high energy density sulfur-based batteries for future power sources.

To eliminate the adverse impacts of hydrogen evolution on the capacity of iron-chromium redox flow batteries (ICRFBs) during the long-term operation and ensure the safe operation of the battery, a rebalance cell that reduces the excessive Fe(III) ions at the positive electrolyte by using the hydrogen evolved from the negative electrolyte is designed, fabricated and tested. The effects of the flow field, hydrogen concentration and H2/N2 mixture gas flow rate on the performance of the hydrogen-ferric ion rebalance cell have been investigated. Results show that: i) an interdigitated flow field based rebalance cell delivers higher limiting current densities than serpentine flow field based one does; ii) the hydrogen utilization can approach 100% at low hydrogen concentrations (≤5%); iii) the apparent exchange current density of hydrogen oxidation reaction in the rebalance cell is proportional to the square root of the hydrogen concentration at the hydrogen concentration from 1.3% to 50%; iv) a continuous rebalance process is demonstrated at the current density of 60 mA cm−2 and hydrogen concentration of 2.5%. Moreover, the cost analysis shows that the rebalance cell is just approximately 1% of an ICRFB system cost. © 2017 Elsevier B.V.

The polysulfide shuttle effect and lithium dendrite growth in lithium-sulfur (Li-S) batteries can repeatedly breach the anodic solid electrolyte interphase (SEI) over cycling. As a result, irreversible short-chain sulfide side products (Li2Sx, x = 1, 2) keep depositing on the Li anode, leading to the active material loss, increasing the Li+ transport resistance, and thereby reducing the cycle life. In this work, indium iodide (InI3) is investigated as a bifunctional electrolyte additive for Li-S batteries to protect the Li anode and decompose the side products spontaneously. On the one hand, Indium (In) is electrodeposited onto the Li anode prior to Li plating during the initial charging process, forming a chemically and mechanically stable SEI to prevent the Li anode from reacting with soluble polysulfide species to form Li2Sx (x = 1, 2) side products. On the other hand, by adequately overcharging the battery, the triiodide/iodide redox mediator is capable of chemically transforming side products deposited on the Li anode and separator into soluble polysulfides, which can be recycled by the cathode. It is shown that the battery with the InI3 additive exhibits a prolonged cycle life, and is capable of retrieving its capacity by a facile overcharging process. © 2017 Elsevier B.V.