Room‐temperature sodium–sulfur (RT Na–S) batteries, as promising next‐generation energy storage candidates, are drawing more and more attention due to the high energy density and abundant elements reserved in the earth. However, the native downsides of RT Na‐S batteries (i.e., enormous volume changes, the polysulfide shuttle, and the insulation and low reactivity of S) impede their further application. To conquer these challenges, hierarchical porous hollow carbon polyhedrons embedded with uniform Mo2C nanoparticles are designed deliberately as the host for S. The micro‐ and mesoporous hollow carbon indeed dramatically enhances the reactivity of the S cathodes and accommodates the volume changes. Meanwhile, the highly conductive dispersed Mo2C has a strong chemical adsorption to polysulfides and catalyzes the transformation of polysulfides, which can effectively inhibit the dissolution of polysulfides and accelerate the reaction kinetics. Thus, the as‐prepared S cathode can display a high reversible capacity (1098 mAh g−1 at 0.2 A g−1 after 120 cycles) and superior rate performance (483 mAh g−1 at 10.0 A g−1). This work provides a new method to boost the performance of RT Na–S batteries.

A High‐Efficiency Mo2C Electrocatalyst Promoting the Polysulfide Redox Kinetics for Na–S Batteries

The practical application of Na-S batteries is largely hindered by their low mass loading, inferior rate capability, and poor cycling performance. Herein, we report a design strategy for encapsulation of sodium polysulfides using Ti3C2Tx MXene. Porous nitrogen-doped Ti3C2Tx MXene microspheres have been synthesized by a facile synthesis method. Porous nitrogen-doped Ti3C2Tx MXene microspheres contain abundant pore structures and heteroatom functional groups for structural and chemical synergistic encapsulation of sodium polysulfides. Sodium-sulfur batteries, based on the as-proposed cathode, demonstrated outstanding electrochemical performances, including a high reversible capacity (980 mAh g-1 at 0.5 C rate) and extended cycling stability (450.1 mAh g-1 at 2 C after 1000 cycles at a high areal sulfur loading of 5.5 mg cm-2). This MXene-based hybrid material is a promising cathode host material for polysulfide-retention, enabling high-performance Na-S batteries.

Porous Heteroatom-Doped Ti3C2Tx MXene Microspheres Enable Strong Adsorption of Sodium Polysulfides for Long-Life Room-Temperature Sodium-Sulfur Batteries.

Heteroatom doping can endow MXenes with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of MXenes materials and their potential for a spectrum of applications. This article comprehensively and critically discusses the syntheses, properties, and emerging applications of the growing family of heteroatom-doped MXenes materials. First, the doping strategies, synthesis methods, and theoretical simulations of high-performance MXenes materials are summarized. In order to achieve high-performance MXenes materials, the mechanism of atomic element doping from three aspects of lattice optimization, functional substitution, and interface modification is analyzed and summarized, aiming to provide clues for developing new and controllable synthetic routes. The mechanisms underlying their advantageous uses for energy storage, catalysis, sensors, environmental purification and biomedicine are highlighted. Finally, future opportunities and challenges for the study and application of multifunctional high-performance MXenes are presented. This work could open up new prospects for the development of high-performance MXenes.

Element-Doped Mxenes: Mechanism, Synthesis, and Applications.

Room‐temperature sodium–sulfur (RT‐Na/S) batteries are emerging as promising candidates for stationary energy‐storage systems, due to their high energy density, resource abundance, and environmental benignity. A better understanding of RT‐Na/S batteries in the view of the whole battery components is of essential importance for fundamental research and practical applications. In particular, the components other than sulfur cathodes in preventing the migration of polysulfides and accelerating the reaction kinetics have been greatly overlooked. Such a biased research trend is also adverse to the broader applications for RT‐Na/S batteries, which have long been ignored in previous reviews. Herein, approaches to the historical progress toward practical RT‐Na/S batteries through a “teamwork” perspective are comprehensively summarized, and balanced research trends are encouraged to enable practical RT‐Na/S batteries. In the meantime, the persisting issues, promising solutions, and practical applications of advanced sulfur host design, Na metal anode protection, electrolyte optimization, separator modification, and binder engineering are clearly emphasized. Finally, the device‐scale evaluation in practical parameters and advanced characterization tools are thoroughly provided. This review aims to provide the “teamwork” perspective on the whole‐cell design and fundamental guidelines that can shed light on research directions for practical RT‐Na/S batteries.

The Future for Room‐Temperature Sodium–Sulfur Batteries: From Persisting Issues to Promising Solutions and Practical Applications

Room‐temperature sodium–sulfur (RT‐Na/S) batteries possess high potential for grid‐scale stationary energy storage due to their low cost and high energy density. However, the issues arising from the low S mass loading and poor cycling stability caused by the shuttle effect of polysulfides seriously limit their operating capacity and cycling capability. Herein, sulfur‐doped graphene frameworks supporting atomically dispersed 2H‐MoS2 and Mo1 (S@MoS2‐Mo1/SGF) with a record high sulfur mass loading of 80.9 wt.% are synthesized as an integrated dual active sites cathode for RT‐Na/S batteries. Impressively, the as‐prepared S@MoS2‐Mo1/SGF display unprecedented cyclic stability with a high initial capacity of 1017 mAh g−1 at 0.1 A g−1 and a low‐capacity fading rate of 0.05% per cycle over 1000 cycles. Experimental and computational results including X‐ray absorption spectroscopy, in situ synchrotron X‐ray diffraction and density‐functional theory calculations reveal that atomic‐level Mo in this integrated dual‐active‐site forms a delocalized electron system, which could improve the reactivity of sulfur and reaction reversibility of S and Na, greatly alleviating the shuttle effect. The findings not only provide an effective strategy to fabricate high‐performance dual‐site cathodes, but also deepen the understanding of their enhancement mechanisms at an atomic level.

Atomically Dispersed Dual‐Site Cathode with a Record High Sulfur Mass Loading for High‐Performance Room‐Temperature Sodium–Sulfur Batteries

Alkali metal anodes have been regarded as an ideal candidate for next generation high-energy electrode couples due to their ultrahigh specific capacity and the lowest redox potential. However, their real-world application has been severely hampered by their highly uncontrollable chemical reactivity, which directly dictates metal dendrite growth behavior during cycling, low coulombic efficiency, and even safety concerns. Crystallographic optimization based on metal anode materials provides a fundamental solution for suppressing dendrite growth and enabling a stable metal anode, which has attracted extensive attention. In this perspective, we summarize the recent advances in the crystallographic optimization for dendrite prevention and suppression and highlight the recent progress of crystallographic optimization for a new generation of rechargeable batteries, including lithium metal batteries, sodium metal batteries, potassium metal batteries, zinc metal batteries and magnesium metal batteries. The challenges and prospects for the future development of crystallographic optimization are discussed to shed light on the future research of crystallographic optimization for boosting the performances of rechargeable batteries.

Chengfei Qian

Papers

Porous Heteroatom-Doped Ti3C2Tx MXene Microspheres Enable Strong Adsorption of Sodium Polysulfides for Long-Life Room-Temperature Sodium-Sulfur Batteries.

Stable alkali metal anodes enabled by crystallographic optimization-A review