Showing papers by "Hong Jin Fan published in 2023"

Protocol in Evaluating Capacity of Zn–Mn Aqueous Batteries: A Clue of pH

Abstract: In the literature, Zn–Mn aqueous batteries (ZMABs) confront abnormal capacity behavior, such as capacity fluctuation and diverse “unprecedented performances.” Because of the electrolyte additive‐induced complexes, various charge/discharge behaviors associated with different mechanisms are being reported. However, the current performance assessment remains unregulated, and only the electrode or the electrolyte is considered. The lack of a comprehensive and impartial performance evaluation protocol for ZMABs hinders forward research and commercialization. Here, a pH clue (proton‐coupled reaction) to understand different mechanisms is proposed and the capacity contribution is normalized. Then, a series of performance metrics, including rated capacity (Cr) and electrolyte contribution ratio from Mn2+ (CfM), are systematically discussed based on diverse energy storage mechanisms. The relationship between Mn (II) ↔ Mn (III) ↔ Mn (IV) conversion chemistry and protons consumption/production is well‐established. Finally, the concrete design concepts of a tunable H+/Zn2+/Mn2+ storage system for customized application scenarios, opening the door for the next‐generation high‐safety and reliable energy storage system, are proposed.

Dielectric–Metallic Double-Gradient Composition Design for Stable Zn Metal Anodes

Abstract: The commercial implementation of aqueous Zn-ion batteries is being impeded by the rampant dendrite growth and exacerbated side reactions on the Zn metal anodes. Herein, a 60 nm artificial protective layer with spatial dielectric–metallic gradient composition (denoted as GZH) is developed via Zn and HfO2 cosputtering. In this design, the top HfO2 layer with high permittivity and low electronic conductivity effectively suppresses hydrogen evolution. The intermediate Zn-rich oxide region promotes the dendrite-free Zn deposition and reinforces the contact between Zn and the sputtered layer. This design allows stable battery operation at high currents. Symmetric cells with Zn-GZH exhibit stable voltage separation over 500 h at 10 mA cm–2 with a cutoff capacity of 5 mAh cm–2. When paired with a vanadate cathode, the full-cell battery delivers a capacity retention of around 75% after 2000 cycles. This design concept may apply to other aqueous metal batteries.

Cooperation between Dual Metal Atoms and Nanoclusters Enhances Activity and Stability for Oxygen Reduction and Evolution.

Abstract: We have achieved the synthesis of dual-metal single atoms and atomic clusters that co-anchor on a highly graphitic carbon support. The catalyst comprises Ni4 (and Fe4) nanoclusters located adjacent to the corresponding NiN4 (and FeN4) single-atom sites, which is verified by systematic X-ray absorption characterization and density functional theory calculations. A distinct cooperation between Fe4 (Ni4) nanoclusters and the corresponding FeN4 (NiN4) atomic sites optimizes the adsorption energy of reaction intermediates and reduces the energy barrier of the potential-determining steps. This catalyst exhibits enhanced oxygen reduction and evolution activity and long-cycle stability compared to counterparts without nanoclusters and commercial Pt/C. The fabricated Zn-air batteries deliver a high power density and long-term cyclability, demonstrating their prospects in energy storage device applications.

Opportunity for eutectic mixtures in metal-ion batteries

Abstract: Breakthroughs in super-concentrated electrolytes have pushed the aqueous solution to the forefront of the high-safety battery devices. An ideal electrolyte system should be cost-effective and stable in a wide electrochemical window. In recent years, eutectic mixtures have emerged as a green, safe, low-cost, and electrochemically stable electrolyte system for rechargeable metal-ion batteries (MIBs). Here, the fundamental understanding of the formation mechanisms, physio-chemical properties, and composition–structure–property relationships of eutectic mixtures are summarized. Our focus is their advanced function and applications in MIBs. Considering that eutectic mixtures in MIBs are still at an early stage, we provide the challenges and perspectives which hopefully may guide the rational design of advanced eutectic mixtures for different electrochemical energy storage and conversion systems.

Atomically Dispersed Fe-N4 and Ni-N4 Independent Sites Enable Bidirectional Sulfur Redox Electrocatalysis.

Abstract: Single-atom catalysts (SACs) with high atom utilization and outstanding catalytic selectivity are useful for improving battery performance. Herein, atomically dispersed Ni-N4 and Fe-N4 dual sites coanchored on porous hollow carbon nanocages (Ni-Fe-NC) are fabricated and deployed as the sulfur host for Li-S battery. The hollow and conductive carbon matrix promotes electron transfer and also accommodates volume fluctuation during cycling. Notably, the high d band center of Fe in Fe-N4 site demonstrates strong polysulfide affinity, leading to an accelerated sulfur reduction reaction. Meanwhile, Li2S on the Ni-N4 site delivers a metallic property with high S 2p electron density of states around the Femi energy level, enabling a low sulfur evolution reaction barrier. The dual catalytic effect on Ni-Fe-NC endows sulfur cathode high energy density, prolonged lifespan, and low polarization.

Oxidation State Engineering in Octahedral Ni by Anchored Sulfate to Boost Intrinsic Oxygen Evolution Activity.

Abstract: Promoting the electron occupancy of active sites to unity is an effective method to enhance the oxygen evolution reaction (OER) performance of spinel oxides, but it remains a great challenge. Here, an in situ approach is developed to modify the valence state of octahedral Ni cations in NiFe2O4 inverse spinel via surface sulfates (SO42-). Different from previous studies, SO42- is directly anchored on the spinel surface instead of forming from uncontrolled conversion or surface reconstruction. Experiment and theoretical calculations reveal the precise adsorption sites and spatial arrangement for SO42- species. As a main promoting factor, surface SO42- effectively converts the crystal field stable Ni state (t2g6eg2) to the near-unity eg electron state (t2g6eg1). Moreover, the inevitable oxygen vacancies (Vo) further optimize the energy barrier of the potential-determining step (from OH* to O*). This co-modification strategy enhances turnover frequency-based electrocatalytic activity about two orders higher than the control sample without surface sulfates. This work may provide insight into the OER activity enhancement mechanism by the oxyanion groups.

Dynamic Balance of Partial Charge for Small Organic Compound in Aqueous Zinc‐Organic Battery

Abstract: Organic cathodes for aqueous zinc-ion batteries (AZIBs) feature intrinsic flexibility and favorable kinetics, but they suffer from high solubility. Herein, a partial charge regulation strategy is deployed by designing a small organic molecule with extended π-conjugated plane, namely benzo[i]benzo[6′,7′]quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine-5,10,16,21-tetraone (PTONQ). The charge equalization of active sites induced by the extended π-conjugated plane of the PTONQ molecule combined with high aromaticity renders the molecule low solubility, fast charge transfer, and high structural stability. The fabricated Zn//PTONQ battery cycles more than 500 h at 175 mA g−1 with small capacity reduction, fast charged/discharged kinetics, and anti-freeze performance (below -20°C). By a series of ex situ characterizations, it is attested that the capacity originates mainly from Zn2+ insertion/removal of PTONQ without H+ incorporation, which also accounts for the formation of Znx(CF3SO3)y(OH)2x-y·nH2O by-products. This result benefits the understanding of the by-product formation mechanism of organic cathode and paves a new way to advance the aqueous Zn-organic batteries.

Inert Filler Selection Strategies in Li-Ion Gel Polymer Electrolytes.

Abstract: The main role of inert fillers in polymer electrolytes is to enhance ionic conductivity. However, lithium ions in gel polymer electrolytes (GPEs) conduct in liquid solvent rather than along the polymer chains. So far, the main role of inert fillers in improving the electrochemical performance of GPEs is still unclear. Here, various low-cost and common inert fillers (Al2O3, SiO2, TiO2, ZrO2) are introduced into GPEs to study their effects on Li-ion polymer batteries. It is found that the addition of inert fillers has different effects on ionic conductivity, mechanical strength, thermal stability, and, dominantly, interfacial properties. Compared with other gel electrolytes containing SiO2, TiO2, or ZrO2 fillers, those with Al2O3 fillers exhibit the most favorable performance. The high performance is ascribed to the interaction between the surface functional groups of Al2O3 and LiNi0.8Co0.1Mn0.1O2, which alleviates the decomposition of the organic solvent by the cathode, resulting in the formation of a high-quality Li+ conductor interfacial layer. This study provides an important reference for the selection of fillers in GPEs, surface modification of separators, and cathode surface coating.

Stable Continuous-Wave Lasing from Discrete Cesium Lead Bromide Quantum Dots embedded in a Microcavity

Abstract: All-inorganic cesium lead bromide (CsPbBr3) quantum dots (QDs) with high photoluminescence (PL) quantum efficiency have been reported as ideal gain materials for high-performance lasers. Nevertheless, isolated CsPbBr3 QDs have not...