Performance of Nitrogen-Doped Carbon Nanoparticles Carrying FeNiCu as Bifunctional Electrocatalyst for Rechargeable Zinc-Air Battery.

Catalysts for zinc-air batteries (ZABs) must be stable over long-term charging-discharging cycles and exhibit bifunctional catalytic activity. In this study, by doping nitrogen-doped carbon (NC) materials with three metal atoms (Fe, Ni, and Cu), a single-atom-distributed FeNiCu-NC bifunctional catalyst is prepared. The catalyst includes Fe(Ni-doped)-N4 for the oxygen evolution reaction (OER), Fe(Cu-doped)-N4 for the oxygen reduction reaction (ORR), and the NiCu-NC catalytic structure for the oxygen reduction reaction (ORR) in the nitrogen-doped carbon nanoparticles. This single-atom distribution catalyst structure enhances the bifunctional catalytic activity. If a trimetallic single-atom catalyst is designed, it will surpass the typical bimetallic single-atom catcalyst. FeNiCu-NC exhibits outstanding performance as an electrocatalyst, with a half-wave potential (E1/2) of 0.876 V versus RHE, overpotential (Ej = 10) of 253 mV versus RHE at 10 mA cm-2, and a small potential gap (ΔE = 0.61 V). As the anode in a ZAB, FeNiCu-NC can undergo continuous charge-discharged cycles for 575 h without significant attenuation. This study presents a new method for achieving high-performance, low-cost ZABs via trimetallic single-atom doping.

RE-doped (RE = La, Ce and Er) Ni2P porous nanostructures as promising electrocatalysts for hydrogen evolution reaction.

The construction of an efficient non-noble-metal electrocatalyst towards alkaline hydrogen evolution is challenging but in great demand. The fabrication of a porous nanostructure and heteroatom doping are two productive strategies for developing effective electrocatalysts. In this contribution, we report the preparation of La, Ce and Er-doped Ni2P porous nanostructures through a facile water bath method and phosphorization strategy. The Er-doped Ni2P porous nanostructure exhibits superb hydrogen evolution reaction (HER) catalytic performance under alkaline conditions with a low cathodic overpotential of 87 mV (10 mA cm-2, glassy carbon) and a small Tafel slope of 65.4 mV dec-1. It also displays excellent electrochemical stability in alkaline electrolytes. First-principles density functional theory (DFT) calculations disclosed the mechanism of the alkaline HER catalysis. For pristine Ni2P, the P site acts as the optimal active site with the Gibbs free energy of H* absorption (ΔGH*) of 0.48 eV. After La, Ce and Er are doped, respectively, the P site is still the active center of the three doping systems. Notably, the ΔGH* value is reduced from 0.48 eV to 0.23 eV (P site in La-doped Ni2P), 0.20 eV (P site in Ce-doped Ni2P) and 0.18 eV (P site in Er-doped Ni2P), suggesting that doping with La, Ce and Er atoms plays a crucial role in decreasing the H* absorption energy on optimal P sites and the optimum active site with a smaller ΔGH* can expedite the charge transfer rate for H* midbody and H2 generation. This is particularly noticeable for Er doping, which is in accordance with the experimental result.

Design strategy for high-performance bifunctional electrode materials with heterogeneous structures formed by hydrothermal sulfur etching.

The synthesis of efficient, stable, and green multifunctional electrode materials is a long-standing challenge for modern society in the field of energy storage and conversion. To this end, we successfully synthesized five bimetallic precursor materials with excellent performance by hydrothermal reaction with the assistance of a high concentration of polyvinylpyrrolidone (PVP), and then, sulfide etched the lamellar precursor materials among them to obtain the one-dimensional heterostructured samples. Benefiting from the synergistic effect of the bimetal and the continuous electron/ion transport structure, the samples displayed excellent bifunctional activity in supercapacitor and oxygen evolution reaction (OER). Regarding supercapacitors, the exceptional performance of 2817.2 F g-1 at 1 A g-1 was demonstrated, while the asymmetric supercapacitors made showed an extraordinary energy density of 150.2 Wh kg-1 at a power density of 618.5 W kg-1 and outstanding cycling performance (94.74% capacity retention after 20,000 cycles at 10 A g-1). Simultaneously, a wearable flexible electrode that can be wrapped around a finger was coated on a carbon cloth and was found to light up a 0.5-m-long strip of light. Moreover, it exhibited an ultralow oxygen reduction overpotential of 249 mV at 10 mA cm-2. Hence, our work provides a facile strategy to modulate the synthesis of heterogeneous structured sulfides with a continuous electron/ion transport pathway, which possesses excellent oxygen reduction electrocatalytic performance while meeting superior supercapacitor performance. Such work provides an effective approach for the construction of multifunctional electrochemical energy materials.

Formation of LiF-rich Cathode-Electrolyte Interphase by Electrolyte Reduction.

The capacity of transition metal oxide cathode for Li-ion batteries can be further enhanced by increasing the charging potential. However, these high voltage cathodes suffer from fast capacity decay because the large volume change of cathode breaks the active materials and cathode-electrolyte interphase (CEI), resulting in electrolyte penetration into broken active materials and continuous side reactions between cathode and electrolytes. Herein, a robust LiF-rich CEI was formed by potentiostatic reduction of fluorinated electrolyte at a low potential of 1.7 V. By taking LiCoO2 as a model cathode, we demonstrate that the LiF-rich CEI maintains the structural integrity and suppresses electrolyte penetration at a high cut-off potential of 4.6 V. The LiCoO2 with LiF-rich CEI exhibited a capacity of 198 mAh g-1 at 0.5C and an enhanced capacity retention of 63.5 % over 400 cycles as compared to the LiF-free LiCoO2 with only 17.4 % of capacity retention.

Interfacial-engineering-enabled practical low-temperature sodium metal battery.

Solid-state sodium (Na) batteries have received extensive attention as a promising alternative to room-temperature liquid electrolyte Na-ion batteries and high-temperature liquid electrode Na-S batteries because of safety concerns. However, the major issues for solid-state Na batteries are a high interfacial resistance between solid electrolytes and electrodes, and Na dendrite growth. Here we report that a yttria-stabilized zirconia (YSZ)-enhanced beta-alumina solid electrolyte (YSZ@BASE) has an extremely low interface impedance of 3.6 Ω cm2 with the Na metal anode at 80 °C, and also exhibits an extremely high critical current density of ~7.0 mA cm-2 compared with those of other Li- and Na-ion solid electrolytes reported so far. With a trace amount of eutectic NaFSI-KFSI molten salt at the electrolyte/cathode interface, a quasi-solid-state Na/YSZ@BASE/NaNi0.45Cu0.05Mn0.4Ti0.1O2 full cell achieves a high capacity of 110 mAh g-1 with a Coulombic efficiency >99.99% and retains 73% of the cell capacity over 500 cycles at 4C and 80 °C. Extensive characterizations and theoretical calculations prove that the stable ß-NaAlO2-rich solid-electrolyte interphase and strong YSZ support matrix play a critical role in suppressing the Na dendrite as they maintain robust interfacial contacts, lower electronic conduction and prevent the continual reduction of BASE through oxygen-ion compensation.

Ultrahigh Water Permeance of Reduced Graphene Oxide Membrane for Radioactive Liquid Waste Treatment.

Membrane methods exhibit great potential for application in radioactive liquid waste treatment. In this work, we prepared a reduced graphene oxide using the amino-hydrothermal method (AH-rGO) that exhibited effective rejection rates of 99.9% for CoCl2, ZnCl2, NiCl2, and radionuclide 60Co solutions with an ultrahigh water permeance of >71.9 L m-2 h-1 bar-1. The thickness of the AH-rGO membranes affects the water permeance, as the membrane with a thickness of ≈250 nm has the highest water permeance of up to 125.1 L m-2 h-1 bar-1 with the corresponding rejection rate of 86.8%. Importantly, this is the most permeable membrane with a satisfactory level of the rejection rate for typical radioactive ions of Co2+, Zn2+, and Ni2+. Moreover, the AH-rGO membranes presented excellent stability. These findings demonstrate the potential of reduced graphene oxide (rGO) membranes for radioactive liquid waste treatment.

Highly Reversible Aqueous Zinc Batteries enabled by Zincophilic-Zincophobic Interfacial Layers and Interrupted Hydrogen-Bond Electrolytes.

Aqueous Zn batteries promise high energy density but suffer from Zn dendritic growth and poor low-temperature performance. Here, we overcome both challenges by using an eutectic 7.6 m ZnCl2 aqueous electrolyte with 0.05 m SnCl2 additive, which in situ forms a zincophilic/zincophobic Sn/Zn5 (OH)8 Cl2 ⋅H2 O bilayer interphase and enables low temperature operation. Zincophilic Sn decreases Zn plating/stripping overpotential and promotes uniform Zn plating, while zincophobic Zn5 (OH)8 Cl2 ⋅H2 O top-layer suppresses Zn dendrite growth. The eutectic electrolyte has a high ionic conductivity of ≈0.8 mS cm-1 even at -70 °C due to the distortion of hydrogen bond network by solvated Zn2+ and Cl- . The eutectic electrolyte enables Zn∥Ti half-cell a high Coulombic efficiency (CE) of >99.7 % for 200 cycles and Zn∥Zn cell steady charge/discharge for 500 h with a low overpotential of 8 mV at 3 mA cm-2 . Practically, Zn∥VOPO4 batteries maintain >95 % capacity with a CE of >99.9 % for 200 cycles at -50 °C, and retain ≈30 % capacity at -70 °C of that at 20 °C.

Fluorinated interphase enables reversible aqueous zinc battery chemistries.

Metallic zinc is an ideal anode due to its high theoretical capacity (820 mAh g-1), low redox potential (-0.762 V versus the standard hydrogen electrode), high abundance and low toxicity. When used in aqueous electrolyte, it also brings intrinsic safety, but suffers from severe irreversibility. This is best exemplified by low coulombic efficiency, dendrite growth and water consumption. This is thought to be due to severe hydrogen evolution during zinc plating and stripping, hitherto making the in-situ formation of a solid-electrolyte interphase (SEI) impossible. Here, we report an aqueous zinc battery in which a dilute and acidic aqueous electrolyte with an alkylammonium salt additive assists the formation of a robust, Zn2+-conducting and waterproof SEI. The presence of this SEI enables excellent performance: dendrite-free zinc plating/stripping at 99.9% coulombic efficiency in a Ti||Zn asymmetric cell for 1,000 cycles; steady charge-discharge in a Zn||Zn symmetric cell for 6,000 cycles (6,000 h); and high energy densities (136 Wh kg-1 in a Zn||VOPO4 full battery with 88.7% retention for >6,000 cycles, 325 Wh kg-1 in a Zn||O2 full battery for >300 cycles and 218 Wh kg-1 in a Zn||MnO2 full battery with 88.5% retention for 1,000 cycles) using limited zinc. The SEI-forming electrolyte also allows the reversible operation of an anode-free pouch cell of Ti||ZnxVOPO4 at 100% depth of discharge for 100 cycles, thus establishing aqueous zinc batteries as viable cell systems for practical applications.

Design of a Solid Electrolyte Interphase for Aqueous Zn Batteries.

Aqueous Zn batteries are challenged by water decomposition and dendrite growth due to the absence of a dense Zn-ion conductive solid electrolyte interphase (SEI) to inhibit the hydrogen evolution reaction (HER). Here, we design a low-concentration aqueous Zn(OTF)2 -Zn(NO3 )2 electrolyte to in situ form a robust inorganic ZnF2 -Zn5 (CO3 )2 (OH)6 -organic bilayer SEI, where the inorganic inner layer promotes Zn-ion diffusion while the organic outer layer suppresses water penetration. We found that the insulating Zn5 (OH)8 (NO3 )2 ⋅2 H2 O layer is first formed on the Zn anode surface by the self-terminated chemical reaction of NO3 - with Zn2+ and OH- generated via HER, and then it transforms into Zn-ion conducting Zn5 (CO3 )2 (OH)6 , which in turn promotes the formation of ZnF2 as the inner layer. The organic-dominated outer layer is formed by the reduction of OTF- . The in situ formed SEI enables a high Coulombic efficiency (CE) of 99.8 % for 200 h in Ti∥Zn cells, and a high energy density (168 Wh kg-1 ) with 96.5 % retention for 700 cycles in Zn∥MnO2 cells with a low Zn/MnO2 capacity ratio of 2:1.

High-Energy Aqueous Sodium-Ion Batteries.

Water-in-salt electrolytes (WISE) have largely widened the electrochemical stability window (ESW) of aqueous electrolytes by formation of passivating solid electrolyte interphase (SEI) on anode and also absorption of the hydrophobic anion-rich double layer on cathode. However, the cathodic limiting potential of WISE is still too high for most high-capacity anodes in aqueous sodium-ion batteries (ASIBs), and the cost of WISE is also too high for practical application. Herein, a low-cost 19 m (m: mol kg-1 ) bi-salts WISE with a wide ESW of 2.8 V was designed, where the low-cost 17 m NaClO4 extends the anodic limiting potential to 4.4 V, while the fluorine-containing salt (2 m NaOTF) extends the cathodic limiting potential to 1.6 V by forming the NaF-Na2 O-NaOH SEI on anode. The 19 m NaClO4 -NaOTF-H2 O electrolyte enables a 1.75 V Na3 V2 (PO4 )3 ∥Na3 V2 (PO4 )3 full cell to deliver an appreciable energy density of 70 Wh kg-1 at 1 C with a capacity retention of 87.5 % after 100 cycles.

Solvation Structure Design for Aqueous Zn Metal Batteries.

Aqueous Zn batteries are promising energy storage devices for large-scale energy-storage due to low cost and high energy density. However, their lifespan is limited by the water decomposition and Zn dendrite growth. Here, we suppress water reduction and Zn dendrite growth in dilute aqueous electrolyte by adding dimethyl sulfoxide (DMSO) into ZnCl2-H2O, in which DMSO replaces the H2O in Zn2+ solvation sheath due to a higher Gutmann donor number (29.8) of DMSO than that (18) of H2O. The preferential solvation of DMSO with Zn2+ and strong H2O-DMSO interaction inhibit the decomposition of solvated H2O. In addition, the decomposition of solvated DMSO forms Zn12(SO4)3Cl3(OH)15·5H2O, ZnSO3, and ZnS enriched-solid electrolyte interphase (SEI) preventing Zn dendrite and further suppressing water decomposition. The ZnCl2-H2O-DMSO electrolyte enables Zn anodes in Zn||Ti half-cell to achieve a high average Coulombic efficiency of 99.5% for 400 cycles (400 h), and the Zn||MnO2 full cell with a low capacity ratio of Zn:MnO2 at 2:1 to deliver a high energy density of 212 Wh/kg (based on both cathode and anode) and maitain 95.3% of the capacity over 500 cycles at 8 C.

Hydrophobic Organic-Electrolyte-Protected Zinc Anodes for Aqueous Zinc Batteries.

Aqueous Zn batteries are promising energy-storage devices. However, their lifespan is limited by irreversible Zn anodes owing to water decomposition and Zn dendrite growth. Here, we separate aqueous electrolyte from Zn anode by coating a thin MOF layer on anode and filling the pores of MOF with hydrophobic Zn(TFSI)2 -tris(2,2,2-trifluoroethyl)phosphate (TFEP) organic electrolyte that is immiscible with aqueous Zn(TFSI)2 -H2 O bulk electrolyte. The MOF encapsulated Zn(TFSI)2 -TFEP forms a ZnF2 -Zn3 (PO4 )2 solid electrolyte interphase (SEI) preventing Zn dendrite and water decomposition. The Zn(TFSI)2 -TFEP@MOF electrolyte protected Zn anode enables a Zn||Ti cell to achieve a high average Coulombic efficiency of 99.1 % for 350 cycles. The highly reversible Zn anode brings a high energy density of 210 Wh kg-1 (of cathode and anode mass) and a low capacity decay rate of 0.0047 % per cycle over 600 cycles in a Zn||MnO2 full cell with a low capacity ratio of Zn:MnO2 at 2:1.

Water-Pillared Sodium Vanadium Bronze Nanowires for Enhanced Rechargeable Magnesium Ion Storage.

Owing to the advantages of high safety, low cost, high theoretical volumetric capacities, and environmental friendliness, magnesium-ion batteries (MIBs) have more feasibility for large-scale energy storage compared to lithium-ion batteries. However, lack of suitable cathode materials due to sluggish kinetics of magnesium ion is one of the biggest challenges. Herein, water-pillared sodium vanadium bronze nanowires (Na2 V6 O16 ·1.63H2 O) are reported as cathode material for MIBs, which display high performance in magnesium storage. The hydrated sodium ions provide excellent structural stability. The charge shielding effect of lattice water enables fast Mg2+ diffusion. It exhibits high specific capacity of 175 mAh g-1 , long cycle life (450 cycles), and high coulombic efficiency (≈100%). At high current density of 200 mA g-1 , the capacity retention is up to 71% even after 450 cycles (compared to the highest capacity), demonstrating excellent long-term cycling performance. The nature of charge storage kinetics is explored. Furthermore, a highly reversible structure change during the electrochemical process is proved by comprehensive electrochemical analysis. The remarkable electrochemical performance makes Na2 V6 O16 ·1.63H2 O a promising cathode material for low-cost and safe MIBs.

Tuning the Anode-Electrolyte Interface Chemistry for Garnet-Based Solid-State Li Metal Batteries.

Lithium (Li) metal is a promising candidate as the anode for high-energy-density solid-state batteries. However, interface issues, including large interfacial resistance and the generation of Li dendrites, have always frustrated the attempt to commercialize solid-state Li metal batteries (SSLBs). Here, it is reported that infusing garnet-type solid electrolytes (GSEs) with the air-stable electrolyte Li3 PO4 (LPO) dramatically reduces the interfacial resistance to ≈1 Ω cm2 and achieves a high critical current density of 2.2 mA cm-2 under ambient conditions due to the enhanced interfacial stability to the Li metal anode. The coated and infused LPO electrolytes not only improve the mechanical strength and Li-ion conductivity of the grain boundaries, but also form a stable Li-ion conductive but electron-insulating LPO-derived solid-electrolyte interphase between the Li metal and the GSE. Consequently, the growth of Li dendrites is eliminated and the direct reduction of the GSE by Li metal over a long cycle life is prevented. This interface engineering approach together with grain-boundary modification on GSEs represents a promising strategy to revolutionize the anode-electrolyte interface chemistry for SSLBs and provides a new design strategy for other types of solid-state batteries.

Enabling safe aqueous lithium ion open batteries by suppressing oxygen reduction reaction.

Due to the non-flammable nature of water-based electrolytes, aqueous lithium-ion batteries are resistant to catching fire. However, they are not immune to the risk of explosion, since the sealing structure adopted by current batteries limits the dissipation of heat and pressure within the cells. Here, we report a safe aqueous lithium-ion battery with an open configuration using water-in-salt electrolytes and aluminum oxide coated anodes. The design can inhibit the self-discharge by substantially suppressing the oxygen reduction reaction on lithiated anodes and enable good cycle performance over 1000 times. Our study may open a pathway towards safer lithium-ion battery designs.