Anode-free aqueous zinc metal batteries (AZMBs) offer significant potential for energy storage due to their low cost and environmental benefits. Ti₃C₂T_x MXene provides several advantages over traditional metallic current collectors like Cu and Ti, including better Zn plating affinity, lightweight, and flexibility. However, self-freestanding MXene current collectors in AZMBs remain underexplored, likely due to challenges with Zn deposition reversibility. This study investigates the combination of a Ti₃C₂T_x self-freestanding film with advanced electrolyte engineering, specifically examining the effects of Li-salt and propylene carbonate (PC) as additives on Zn plating reversibility. While using Li⁺ ions as an additive alone facilitates uniform Zn deposition on bulk metals through the electrostatic shielding effect, the addition of Li-salt negatively impacts Zn plating uniformity on Ti₃C₂T_x. Meanwhile, using PC additive alone forms an organic SEI layer on Ti₃C₂T_x and causes Zn agglomeration. The use of both additives together results in a ZnF₂-containing hybrid SEI layer with improved interfacial kinetics, promoting more uniform Zn deposition. This approach achieves an average Coulombic efficiency (CE) of 96.8% over 150 cycles (a maximum CE of 97.8%). The study highlights the strategic difference in electrolyte design, emphasizing the need for tailored approaches to optimize Zn deposition on MXenes, contrasting with traditional metallic current collectors.

MXenes, a thriving class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, demonstrate considerable potential in diverse electrochemical energy storage applications. To leverage MXenes for high-performance sulfur-based batteries, researchers have employed various strategies to modify their properties, aiming to tackle challenges such as the notorious shuttle effect induced by soluble polysulfides, sluggish redox reaction kinetics, and substantial volume expansion during the lithiation process. This review article offers an overview of MXene modification strategies, emphasizing their significant potential in adjusting the composition, surface chemistry, and morphology to address one or more challenges specially in sulfur cathodes. We first discuss internal regulation methods of MXene, including surface group engineering, heteroatom doping, and high-entropy MXene synthesis, which have been demonstrated to enhance MXene-polysulfide interactions and facilitate polysulfide conversion. Subsequently, we provide a summary of the recent design methods and advancements made in MXene-derived and MXene-based composites, with a particular emphasis on electronic structure reconstruction at the heterointerface and their synergistic roles in Li-S batteries. Following this, we outline the utilization of MXenes to address the challenges encountered in metal-sulfur batteries beyond Li-S batteries. Concluding the review, we offer prospects for the future development of utilizing MXenes in practical sulfur-based batteries.

Limited Li resources, high cost, and safety risks of using organic electrolytes have stimulated a strong motivation to develop non-Li aqueous batteries. Aqueous Zn-ion storage (ZIS) devices offer low-cost and high-safety solutions. However, their practical applications are at the moment restricted by their short cycle life arising mainly from irreversible electrochemical side reactions and processes at the interfaces. This review sums up the capability of using 2D MXenes to increase the reversibility at the interface, assist the charge transfer process, and thereby improve the performance of ZIS. First, they discuss the ZIS mechanism and irreversibility of typical electrode materials in mild aqueous electrolytes. Then, applications of MXenes in different ZIS components are highlighted, including as electrodes for Zn²⁺ intercalation, protective layers of Zn anode, hosts for Zn deposition, substrates, and separators. Finally, perspectives are put forward on further optimizing MXenes to improve the ZIS performance.