Protection Of Zinc Anode And The Application In Zinc Batteries

Aqueous rechargeable batteries are considered as promising alternatives for Li-ion batteries because they contain aqueous electrolytes of flame-retardant,non-toxic,low cost and high ionic conductivity.Among them,aqueous zinc（Zn）metal batteries are highly competitive candidates due to their abundant Zn content,low overpotential（-0.762 V vs.standard hydrogen electrode）and high specific capacity(820 m Ah g^-1,5855 m Ah cm^-3).However,Zn anodes,similar to other metal anodes,inevitably face the problems of dendrite due to their host-free property and nonuniform exfoliation/plating,as well as other problems such as corrosion,passivation and hydrogen evolution in aqueous systems.These problems must be addressed or mitigated in order to better commercialize Zn batteries.Therefore,this paper explores the water-based rechargeable Zn metal battery from two aspects:the design of acid-base double electrolyte based Zn battery and the surface modification of Zn anode.The main research results are as follows:（1）Alkaline Zn-air batteries face many problems,such as low operating voltage,continuous side reactions of CO₂in alkaline electrolytes,etc.Acidic Zn-air battery systems can effectively address the above problems,but efficient catalysts and stable anodes in acidic solutions are still questionable.Thus,this study proposes an electrolyte decoupling strategy to assemble a novel aqueous Zn-air battery with an alkaline anolyte electrolyte and an acidic catholyte electrolyte separated by an ion-exchange membrane.Meanwhile,N-doped carbon（NC）shell-encapsulated Co particles embedded in highly porous NC nanocubes（NC@Co-HPNC）was prepared by directly calcining polydopamine-modified bimetallic Co/Zn-based zeolite imidazolate frameworks（ZIFs）precursors,and was further used as a cathode catalyst in acid-base double electrolyte Zn-air batteries.The NC@Co-HPNC exhibit excellent ORR/OER catalytic performance in acidic environment,even comparable to commercial catalysts.The construction of the acid-base dual electrolyte avoids the direct contact between the Zn anode and the acidic electrolyte,and improves the stability of the Zn anode.The NC@Co-HPNC-based Zn-air battery exhibits extremely high working potential（>2.1V）,extremely low polarization voltage（0.7 V）and good cycling stability（～197 h）when operating in acid-base dual electrolytes.An acid-base dual electrolyte Zn battery can effectively power a stopwatch due to its ultra-high voltage,while an ordinary Zn-air battery can hardly drive the stopwatch,highlighting the broad application potential of the acid-base dual electrolyte Zn-air battery.（2）Zn batteries with near-neutral electrolytes also face various challenges.The uneven nucleation and crystal growth during Zn electroplating/stripping tend to form rough coatings on the electrode surface,resulting in short-term battery failure,seriously hindering the practical applications of Zn batteries.The surface modification of Zn metal is a direct way to improve the uniformity of Zn coating.Herein,in this study,reduced graphene oxide（r GO）,Sn and Cu composite functional protective layer-modified Zn electrodes（r GO-Sn Cu/Zn）were prepared in situ on Zn foil using a simple one-pot method through electrochemical displacement reaction.The introduction of r GO,Sn and Cu metals with large specific surface areas and high electrical conductivity can provide balanced surface electric fields and low local current densities,thereby reducing the nucleation barrier of Zn and guiding uniform Zn deposition.In addition,Sn and Cu metals are also used as corrosion inhibitors for Zn electrodes,while the presence of r GO provides a flexible substrate to slow down the volume change of Zn anodes,and the synergistic effect of these three components further enhances the protection of Zn anodes.Therefore,compared with pure Zn anode,this novel r GO-Sn Cu/Zn anode can achieve extremely low voltage hysteresis（～29.8m V）and excellent rate capability,while exhibiting good stability over a cycling period of 3200 h.Furthermore,the corresponding Zn ion hybrid supercapacitors（AC||r GO-Sn Cu/Zn）can be stably cycled for 3000 cycles at a current density of 2 A g^-1.More interestingly,the r GO-Sn Cu/Zn anode was further coupled with the porous carbon cathode to assemble a neutral Zn-air battery,which also exhibited a long-term cycle life up to 200 h.The fundamental findings offer a better understanding of Zn metal surface chemistry and pave the way to developing practical Zn metal batteries with mild electrolyte.