High-Capacity and Ultra-Long-Life Mg-Metal Batteries Enabled by Intercalation-Conversion Hybrid Cathode Materials.

The advancement of rechargeable Mg-metal batteries (RMBs) is severely impeded by the lack of suitable cathode materials. Despite the good cyclic stability of intercalation-type compounds, their specific capacity is relatively low. Conversely, the conversion-type cathodes can deliver a higher capacity but often suffer from poor cycling reversibility and stability. Herein, a WSe2/Se intercalation-conversion hybrid material with elemental Se uniformly distributed into WSe2 nanosheets is fabricated via a simple solvothermal method for high-performance RMBs. The uniformly introduced Se confined in WSe2 nanosheets can not only efficiently improve the conductivity of the hybrid cathodes, facilitating the fast electron transport and ion diffusion, but also provide additional specific capacity. Besides, the WSe2 can effectively inhibit the detrimental Se dissolution and polyselenide shuttle, thereby activating the activity of Se and improving its utilization. Consequently, the synergy of intercalation and conversion mechanisms endows WSe2/Se hybrids with superior reversible capacity of 252 mAh g-1 at 0.1 A g-1 and ultra-long cyclability of up to 5000 cycles at 2.0 A g-1 with capacity retention of 78.1%. This work demonstrates the feasibility of the strategy by integrating intercalation and conversion mechanisms for developing high-performance cathode materials for RMBs.

Structural Transformation by Crystal Engineering Endows Aqueous Zinc-Ion Batteries with Ultra-long Cyclability.

Manganese oxide is a promising cathode material for aqueous zinc batteries. However, its weak structural stability, low electrical conductivity, and sluggish reaction kinetics lead to rapid capacity fading. Herein, a crystal engineering strategy is proposed to construct a novel MnO2 cathode material. Both experimental results and theoretical calculations demonstrate that Al-doping plays a crucial role in phase transition and doping-superlattice structure construction, which stabilizes the structure of MnO2 cathode materials, improves conductivity, and accelerates ion diffusion dynamics. As a result, 1.98% Al-doping MnO2 (AlMO) cathode shows an incredible 15 000 cycle stability with a low capacity decay rate of 0.0014% per cycle at 4 A g-1 . Additionally, it provides superior specific capacity of 311.2 mAh g-1 at 0.1 A g-1 and excellent rate performance (145.2 mAh g-1 at 5.0 A g-1 ). To illustrate the potential of 1.98%AlMO to be applied in actual practice, flexible energy storage devices are fabricated and measured. These discoveries provide a new insight for structural transformation via crystal engineering, as well as a new avenue for the rational design of electrode material in other battery systems.

Ordered Mesoporous Graphitic Carbon/Iron Carbide Composites with High Porosity as a Sulfur Host for Li-S Batteries.

The lithium-sulfur battery (LSB) is a promising candidate for future energy storage but faces technological challenges including the low electronic conductivity of sulfur and the solubility of intermediates during cycling. Additionally, current host materials often lack sufficient conductivity and porosity to raise the sulfur loading to over 80 wt %. Here, ordered mesoporous graphitic carbon/iron carbide nanocomposites were prepared via an evaporation-induced self-assembly process using soluble resol, prehydrolyzed tetraethyl orthosilicate (TEOS), and iron(III) chloride as the carbon, silica (SiO2), and iron precursors, respectively. Graphitization and SiO2 etching were conducted simultaneously via Teflon-assisted, solid-state decomposition at high temperature. A high surface area (∼3100 m2 g-1), large pore volume (∼3.3 cm3 g-1), and graphitized carbon frame were achieved, giving a high sulfur loading (85 wt %) while tolerating volumetric expansion during discharge. Electrochemical testing of a LSB containing the composite/sulfur cathode exhibited a superior reversible capacity exceeding 1300 mAh g-1 at a moderate current (C/10) and a low decay in capacity of 9% after 500 cycles at C/5. The interaction between mesoporous graphitic carbon and sulfur is proposed.

Textile Inspired Lithium-Oxygen Battery Cathode with Decoupled Oxygen and Electrolyte Pathways.

The lithium-air (Li-O2 ) battery has been deemed one of the most promising next-generation energy-storage devices due to its ultrahigh energy density. However, in conventional porous carbon-air cathodes, the oxygen gas and electrolyte often compete for transport pathways, which limit battery performance. Here, a novel textile-based air cathode is developed with a triple-phase structure to improve overall battery performance. The hierarchical structure of the conductive textile network leads to decoupled pathways for oxygen gas and electrolyte: oxygen flows through the woven mesh while the electrolyte diffuses along the textile fibers. Due to noncompetitive transport, the textile-based Li-O2 cathode exhibits a high discharge capacity of 8.6 mAh cm-2 , a low overpotential of 1.15 V, and stable operation exceeding 50 cycles. The textile-based structure can be applied to a range of applications (fuel cells, water splitting, and redox flow batteries) that involve multiple phase reactions. The reported decoupled transport pathway design also spurs potential toward flexible/wearable Li-O2 batteries.