With the depletion of energy resources and escalating environmental issues, the development of new energy sources and advanced energy storage devices has become increasingly critical. Zinc-ion batteries have attracted significant attention due to their lower cost and safer chemistry. A major focus of zinc-ion battery research is the development of zinc anodes and electrolyte design. Zinc-free anodes have emerged as a promising strategy, offering higher zinc utilization compared to traditional zinc metal anodes (approximately 10%). Among many zinc-free anodes, Ti₃C₂Tx, a MXene (transition metal nitride/carbide layered material), stands out due to its lower lattice mismatch (~10%), higher conductivity, superior mechanical properties, and good hydrophilicity. However, the higher zinc utilization of zinc-free anodes presents challenges for the stable plating/stripping of zinc. Co-solvent engineering is a convenient and direct approach to improving the stability of zinc-free anodes.

In this study, we propose the use of PEG and IPA as co-solvents added to a 1M Zn(OTF)₂-H₂O electrolyte to enhance the stability of Ti₃C₂Tx zinc-free anodes. We found that the addition of PEG reduced the hydrogen evolution current by 0.42 mA (at -1.3 V vs. Ag wire), indicating suppression of the hydrogen evolution reaction. Furthermore, the addition of PEG in the electrolyte inhibits the 2D diffusion of zinc on the Ti₃C₂ surface and promotes zinc deposition along the (002) crystal direction, increasing the (002)/(001) ratio from 0.59 to 0.86, leading to more uniform zinc deposition. Consequently, the Ti₃C₂ zinc-free anode achieved a coulombic efficiency of 97.67% and a cycle life of 268 hours. Similarly, the addition of IPA reduced the hydrogen evolution current by 0.39 mA (at -1.3 V vs. Ag wire), indicating a weaker hydrogen evolution reaction. Moreover, the addition of IPA in the electrolyte inhibits 2D diffusion on the Ti₃C₂ surface and facilitates zinc deposition along the (002) crystal direction, increasing the (002)/(001) ratio from 0.59 to 0.87. The formation of an SEI containing ZnCO₃, ZnFx, and F-rich organics helps to homogenize the Zn ion gradient. Ultimately, the Ti₃C₂ zinc- free anode achieved a high coulombic efficiency of 98.95% and a cycle life of over 1200 hours in the IPA-containing electrolyte.

The high theoretical volumetric capacity, abundance of magnesium in the earth’s crust, and the relatively good safety features of Mg metal, have drawn great attention to developing Magnesium batteries as a follow-up to the success of Li-ion battery technology. However, the magnesium metal is incompatible with most electrolyte solvents and salts, which passivates the surface of magnesium and causes the battery failure. One of the crucial approaches to address this problem is to seek novel electrolytes which have good metallic Mg compatibility and subsequently improve the cycling performance.

In this research, the feasibility of combing PEO, Mg-alginate and MgCl2 to design a solid polymer electrolyte (SPE) for Mg-ion batteries has been assessed. The SPE membrane shows a conductivity of ~10-5 S·cm-1 at 60 °C and an increased value up to ~10-4 S·cm-1 at 80 °C and above. The XRD results have suggested there is no real interaction in between the two polymers which can cause reconstruction of the polymer structure. Moreover, this electrolyte material is highlighted with an excellent cycling stability of up to 150 hours. At last, a possible model which could explain the Arrhenius behavior of temperature-dependent ion conduction is proposed for this SPE material. Overall, this research demonstrates the potential application of Mg-alginate for Mg energy storage in terms of developing a polymer electrolyte, despite further modification in the future is needed.