MXene-Modified Conductive Framework as a Universal Current Collector for Dendrite-free Lithium and Zinc Metal Anode

Recent Advances in Current Collectors for Aqueous Zinc-ion Batteries

Aqueous zinc-ion batteries (AZIBs) are promising options for large-scale electrical energy storage because of their safety, affordability, and environmental friendliness. As an indispensable component of AZIBs, a current collector plays a crucial role in supporting electrode materials and collecting the accumulated electrical energy. Recently, some progress has been made in the study of current collectors for AZIBs; however, only few comprehensive reviews on this topic are available. In this review, the systematic summary and discussion of research progress on current collectors for AZIBs is presented. Furthermore, the main challenges and key prospects for the future development of current collectors for AZIBs are discussed.

Molecular Control Based on Electrostatically Driven Modification for Solid-State Lithium Metal Batteries

With the rapid development of energy vehicles, the demand for high-safety and high-energy-density battery systems, such as solid-state lithium metal batteries, is becoming increasingly urgent. Polyethylene oxide (PEO), as a commonly used electrolyte in solid-state batteries, has the advantages of easy processing and good interface compatibility but also faces the issue of poor ionic conductivity. In this study, we have enhanced the mechanical properties and ion conductivity of PEO electrolytes significantly, stabilizing electrochemical cycling, utilizing positively charged MXene as a modifying material for PEO solid electrolytes and leveraging stronger electrostatic forces. With these enhanced properties, the modified solid electrolyte in Li/Li cells demonstrates excellent cycling stability of over 430 h at 0.1 mA cm-2. Furthermore, the Li/LiFePO4 cells show excellent cycling performance, and the capacity retention rate is 92.1%.

In-Situ Ultrafast Construction of Zinc Tungstate Interface Layer for Highly Reversible Zinc Anodes

Constructing artificial solid electrolyte interface on the Zn anode surface is recognized as an appealing method to inhibit zinc dendrites and side reactions, whereas the current techniques are complex and time-consuming. Here, a robust and zincophilic zinc tungstate (ZnWO4) layer has been in situ constructed on the Zn anode surface (denoted as ZWO@Zn) by an ultrafast chemical solution reaction. Comprehensive characterizations and theoretical calculations demonstrate that the ZWO layer can effectively modulate the interfacial electric field distribution and promote the Zn2+ uniform diffusion, thus facilitating the uniform Zn2+ nucleation and suppressing zinc dendrites. Besides, ZWO layer can prevent direct contact between the Zn/water and increase the hydrogen evolution reaction overpotential to eliminate side reactions. Consequently, the in situ constructed ZWO layer facilitates remarkable reversibility in the ZWO@Zn||Ti battery, achieving an impressive Coulombic efficiency of 99.36 % under 1.0 mA cm-2, unprecedented cycling lifespan exceeding 1800 h under 1.0 mA cm-2 in ZWO@Zn||ZWO@Zn battery, and a steady and reliable operation of the overall ZWO@Zn||VS2 battery. The work provides a simple, low cost, and ultrafast pathway to crafting protective layers for driving advancements in aqueous zinc-metal batteries.

Copper Current Collector: The Cornerstones of Practical Lithium Metal and Anode-Free Batteries

Comparing with the commercial Li-ion batteries, Li metal secondary batteries (LMB) exhibit unparalleled energy density. However, many issues have hindered the practical application. As an element in lithium metal and anode-free batteries, the role of current collector is critical. Comparing with the cathode current collector, more requirements have been imposed on anode current collector as the anode side is usually the starting point of thermal runaway and many other risks, additionally, the anode in Li metal battery very likely determines the cycling life of full cell. In the review, we first give a systematic introduction of copper current collector and the related issues and challenges, and then we summarize the main approaches that have been mentioned in the research, including Cu current collector with 3D architecture, lithophilic modification of the current collector, artificial SEI layer construction on Cu current collector and carbon or polymer decoration of Cu current collector. Finally, we give a prospective comment of the future development in this field.

Working mechanism of MXene as the anode protection layer of aqueous zinc-ion batteries

In recent years, the research on intrinsically safe aqueous zinc-ion batteries (AZIBs) has gained significant attention. However, the commercialization of AZIBs is hindered because of the formation of dendrites in them and undesired hydrogen evolution reaction (HER) at their anode. MXene is a promising two-dimensional material that can inhibit dendrite growth and undesired HER at the anode when used as a protective layer for the anode in AZIBs. MXene's surface functional groups play a crucial role in this protective function. However, the working mechanisms of these surface functional groups have not been thoroughly understood. Based on first-principles calculations and molecular dynamics simulation, we investigated the mechanisms of MXene with nine surface functional groups, including oxygen and halogen elements, as an anode protection layer. We checked their structural stability, electronic structure, adsorption energy, HER reaction free energy, Zn2+ diffusion energy barriers, coordination number of Zn2+- H2O and diffusion coefficients of Zn2+. The MXene species with -S and -O functional groups exhibit good electrical conductivity and greatly adsorb Zn2+. Conversely, MXene species with halogen-functional groups significantly inhibit HER reactions. MXene materials with -Se functional group have the best desolvation effect (ΔCN = 0.31), while those with -I end group have the fastest ability to diffuse zinc ion. This research provides a theoretical guidance for the design of MXene based anode protection layers, which can help to develop dendrite-free and low side-reaction AZIBs.

Mechanochemical Pretreated Mn+1AXn (MAX) Phase to Synthesize 2D-Ti3C2Tx MXene Sheets for High-Performance Supercapacitors

Two-dimensional (2D) MXenes sheet-like micro-structures have attracted attention as an effective electrochemical energy storage material due to their efficient electrolyte/cation interfacial charge transports inside the 2D sheets which results in ultrahigh rate capability and high volumetric capacitance. In this article, Ti₃C₂T_x MXene is prepared by a combination of ball milling and chemical etching from Ti₃AlC₂ powder. The effects of ball milling and etching duration on the physiochemical properties are also explored, as well as the electrochemical performance of as-prepared Ti₃C₂ MXene. The electrochemical performances of 6 h mechanochemically treated and 12 h chemically etched MXene (BM-12H) exhibit an electric double layer capacitance behavior with an enhanced specific capacitance of 146.3 F g^-1 compared to 24 and 48 h treated samples. Moreover, 5000-cycle stability tested sample's (BM-12H) charge/discharge show increased specific capacitance due to the termination of the -OH group, intercalation of K⁺ ion and transformation to TiO₂/Ti₃C₂ hybrid structure in a 3 M KOH electrolyte. Interestingly, a symmetric supercapacitor (SSC) device fabricated in a 1 M LiPF₆ electrolyte in order to extend the voltage window up to 3 V shows a pseudocapacitance behavior due to Li on interaction/de-intercalation. In addition, the SSC shows an excellent energy and power density of 138.33 W h kg^-1 and 1500 W kg^-1, respectively. The ball milling pre-treated MXene exhibited an excellent performance and stability due to the increased interlayer distance between the MXene sheets and intercalation and deintercalation of Li⁺ ions.