New insights into high-rate and super-stable aqueous zinc-ion batteries via the design concept of voltage and solvation environment coordinated control

As the great potential host materials, the application of low-valent vanadium-based compounds for aqueous zinc-ion batteries are usually suffered from the insufficient storage capability and cycle performance. In this work, a unique voltage and solvation environment coordinated control strategy was developed to unlock the MXene derived VNxOy/C heterostructure as robust host applied for aqueous zinc-ion batteries. As the results indicated, such VNxOy/C can be completely converted to the new phase of Zn3(OH)2V2O7·2H2O when the cut-off voltage was controlled at 0.2–2.0 V. Moreover, unlike the mechanism of H+/Zn2+ co-insertion/extraction accompanied with the by-product formation in the electrolyte of pure H2O system, it was demonstrated that the introduction of hydrophilic polyethylene glycol (PEG) into electrolyte enables tailoring the solvation environment, forming the proton shielding to eliminate the blocking effect of by-products on interfacial transport kinetics and storage reversibility of the electrode, thus realizing controllable Zn2+-dominant insertion/extraction mechanism. Unexpectedly, such low-valent VNxOy/C electrode under the coordinated control of voltage and solvation environment enables achieving a significantly enhanced rate capability and ultralong cycle lifespan, which can retain the specific capacities of 369.4 and 112.7 mAh g−1 after 2000 cycles at 0.5 A g−1 and 14,200 cycles at 10 A g−1, respectively. Such novel and efficient avenue for the development of low-valent cathode material is expected to deepen the understanding of the construction of efficient energy storage systems including but not limited to aqueous zinc-ion batteries.