3D assembly of MXene-stabilized spinel ZnMn₂O₄ for highly durable aqueous zinc-ion batteries

Although spinel ZnMn₂O₄ (ZMO) has been regarded as a potential cathode material for aqueous zinc-ion batteries (ZIBs), the unsatisfactory long-term cycling stability seriously restricts its commercial applications. To overcome this obstacle, it is urgent to clarify the energy storage mechanism and cycling degradation reason of spinel ZMO upon Zn²⁺ insertion/extraction. Herein, the phase and structure evolutions of spinel ZMO are deeply probed by means of in-situ and ex-situ investigations, which is closely related to the reversible phase transformation between spinel ZMO and MnO₂ during charging-discharging, while irreversible formation of inactive ZnO byproduct could cause the capacity fading after repeated cycles. Guided by the clear electrochemical mechanism, a 3D assembly of Ti-MXene (Ti₃C₂T_x)-stabilized ZMO nanoparticles has been designed and synthesized, in which high-conductive Ti₃C₂T_x scaffold can effectively inhibit the irreversible structural degradation and side reaction of spinel ZMO. As a result, the ZMO@Ti₃C₂T_x composite cathode exhibits a large reversible specific capacity, excellent rate capability and long-term cyclic stability (capacity retention of ~92.4% after 5000 cycles), superior than previously reported ZMO-based cathodes in aqueous ZIBs. For real applications, a kind of flexible aqueous ZIBs are fabricated and represent stable electrochemical performance at various deformation states, indicating their potential applications in portable/wearable electronics.