Organic Cathode for Aqueous Zn-Ion Batteries: Taming a Unique Phase Evolution toward Stable Electrochemical Cycling

Aqueous zinc ion batteries are highly attractive for large-scale storage applications because of their inherent safety, low cost, and durability. Yet, their advancement is hindered by a dearth of positive host materials (cathode) due to sluggish diffusion of Zn 2+ inside solid inorganic frameworks. Here, we report on a novel organic host, tetrachloro-1,4-benzoquinone (also called: p-chloranil), which due to its inherently soft crystal structure can provide reversible and efficient Zn 2+ storage. It delivers a high capacity of ≥200 mAh g –1 with a very small voltage polarization of 50 mV in a flat plateau around 1.1 V, which equate to an attractive specific energy of >200 Wh kg –1 at an unparalleled energy efficiency (∼95%). As unraveled by density functional theory (DFT) calculations, the molecular columns in p-chloranil undergo a twisted rotation to accommodate Zn 2+, thus restricting the volume change (−2.7%) during cycling. In-depth characterizations using operando X-ray diffraction, electron microscopy, and impedance analysis reveal a unique phase evolution, driven by a phase transfer mechanism occurring at the boundary of solid and liquid phase, which leads to unrestricted growth of discharged/charged phases. By confining the p-chloranil inside nanochannels of mesoporous carbon CMK-3, we can tame the phase evolution process, and thus stabilize the electrochemical cycling.