Bidirectional Tandem Electrocatalysis Manipulated Sulfur Speciation Pathway for High-Capacity and Stable Na-S Battery

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Unleashing the high energy potential of zinc-iodide batteries: high-loaded thick electrodes designed with zinc iodide as the cathode

The realization of high energy is of great importance to unlock the practical potential of zinc-iodine batteries. However, significant challenges, such as low iodine loading (mostly less than 50 wt%), restricted iodine reutilization, and severe structural pulverization during cycling, compromise its intrinsic features. This study introduces an optimized, fully zincified zinc iodide loaded onto a hierarchical carbon scaffold with high active component loading and content (82 wt%) to prepare a thick cathode for enabling high-energy Zn-I2 batteries. The synergistic interactions between nitrogen heteroatoms and cobalt nanocrystals within the porous matrix not only provide forceful chemisorption to lock polyiodide intermediates but also invoke the electrocatalytic effects to manipulate efficient iodine conversion. The ZnI2 cathode could effectively alleviate continuous volumetric expansion and maximize the utilization of active species. The electrochemical examinations confirm the thickness-independent battery performance of assembled Zn-I2 cells due to the ensemble effect of composite electrodes. Accordingly, with a thickness of 300 μm and ZnI2 loading of up to 20.5 mg cm-2, the cathode delivers a specific capacity of 92 mA h gcathode-1 after 2000 cycles at 1C. Moreover, the Zn-I2 pouch cell with ZnI2 cathode has an energy density of 145 W h kgcathode-1 as well as a stable long cycle life.

Bidirectional Confined Redox Catalysis Manipulated Quasi-Solid Iodine Conversion for Shuttle-Free Solid-State Zn-I2 Battery

Electrochemically reversible conversion of I2/I- redox couple in a controllable iodine speciation manner is the eternal target for practical metal-iodine batteries. This contribution demonstrates an advanced polyiodide-free Zn-I2 battery achieved by the bidirectional confined redox catalysis-directed quasi-solid iodine conversion. A core-shell structured iodine cathode is fabricated by integrating multiporous Prussian blue nanocubes as a catalytic mediator, and the polypyrrole sheath afforded a confinement environment that favored the iodine redox. The zincate Znx+1FeIII/II[Fe(CN)6]y has substantially faster zinc-ion intercalation kinetics and overlapping kinetic voltage profiles compared with the I2/ZnI2 redox, and behave as a redox mediator that catalyze reduction of polyiodides via chemical redox reactions during battery discharging and an exemplary reaction is Zn(I3)2+2Znx+1FeII[Fe(CN)6]y=3ZnI2+2ZnxFeIII[Fe(CN)6]y,ΔG=-19.3 kJ mol-1). During the following recharging process, the electrodeposited ZnI2 can be facially activated by iron redox hotspots, and the ZnxFe[FeIII/II(CN)6]y served as a cation-transfer mediator and spontaneously catalyze polyiodides oxidation (Zn(I3)2+2ZnxFe[FeIII(CN)6]y=3I2+2Znx+1Fe[FeII(CN)6]y,ΔG = -7.72 kJ mol-1), manipulating the reversible one-step conversion of ZnI2 back to I2. Accordingly, a flexible solid-state battery employing the designed cathode can deliver an energy density of 215 Wh kgiodine -1.

Binary Atomic Sites Enable a Confined Bidirectional Tandem Electrocatalytic Sulfur Conversion for Low-Temperature All-Solid-State Na-S Batteries

The broader implementation of current all-solid-state Na-S batteries is still plagued by high operation temperature and inefficient sulfur utilization. And the uncontrollable sulfur speciation pathway along with the sluggish polysulfide redox kinetics further compromise the theoretical potentials of Na-S chemistry. Herein, we report a confined bidirectional tandem electrocatalysis effect to tune polysulfide electrochemistry in a novel low-temperature (80 °C) all-solid-state Na-S battery that utilizes Na3 Zr2 Si2 PO12 ceramic membrane as a platform. The bifunctional hollow sulfur matrix consisting binary atomically dispersed MnN4 and CoN4 hotspots was fabricated using a sacrificial template process. Upon discharge, CoN4 sites activate sulfur species and catalyze long-chain to short-chain polysulfides reduction, while MnN4 centers substantially accelerate the low-kinetic Na2 S4 to Na2 S directly conversion, manipulating the uniform deposition of electroactive Na2 S and avoiding the formation of irreversible products (e.g., Na2 S2 ). The intrinsic synergy of two catalytic centers benefits the Na2 S decomposition and minimizes its activation barrier during battery recharging and then efficiently mitigate the cathodic passivation. As a result, the stable cycling of all-solid-state Na-S cell delivers an attractive reversible capacity of 1060 mAh g-1 with a high CE of 98.5 % and a high energy of 1008 Wh kgcathode -1 , comparable to the liquid electrolyte cells.