Research On Electrolytes Of Aqueous Zinc Batteries And Zinc Air Batteries

Aqueous zinc batteries have drawn a growing attention over the recent years,because of their intrinsic merits,such as the high ionic conductivity,low cost,high security,and environmental benignity of aqueous electrolytes,as well as the cheapness and high theoretical capacity of zinc anode(820 m Ah g^-1 and 5855 m Ah cm^-3).These appealing features render the aqueous zinc batteries extremely favorable for large-scale energy-storage systems that require batteries with low cost and inherent safety.To this end,various aqueous zinc batteries prototypes,e.g.,Zn//Mn O2 batteries,Zn//V2O5 batteries,Zn-air batteries,hybrid zinc-ion capacities,etc.,are emerging rapidly,which have made great progresses on both material designs and cell performances but suffer from common challenges originated from notorious aqueous electrolyte（e.g.,dendritic zinc growth,anode corrosion,anode passivation,hydrolysis reaction,cathode dissolution and capacity degeneration）.In this thesis,a series of electrolyte strategies are applied to solve these issues by means of the regulation of electric double layer（EDL）structure,electrolyte additives and decoupling neutral and acidic electrolyte.To this end,the efforts of this thesis are focused on the following aspects:（1）During the study of the most common aqueous Zn SO4 electrolyte,I reveal the phenomenon of high reversibility of aqueous zinc batteries at high current densities through theoretical and experimental methods.I confirm that the reconstructed EDL with a Zn²⁺ion-enriched electrode surface and compressed thickness contribute to the dense and compact zinc deposits and corrosion-resistant electrodeposition behavior.This new understanding discloses the mechanisms of highly reversible aqueous zinc batteries at high current densities,which will provide a new approach to guide the regular nucleation and growth of zinc from the perspective of EDL structure regulation.Importantly,we further verify the feasibility of this mechanism for practical applications in Zn//V2O5 batteries using the common aqueous Zn SO4 electrolyte,which exhibits a long lifespan（1800 cycles）and a high cumulate areal capacity(2.46 A h cm^-2).（2）Based on the above previous work,I further develop a grain refinement strategy to regulate the zinc deposition behavior and suppress the side reactions of electrode and electrolyte.Smooth and dense zinc deposition behavior is achieved by introducing trace amounts of Pb²⁺additive into the aqueous Zn SO4 electrolyte.Owing to the strong adsorption ability of Pb²⁺ions on the zinc crystal,the strongly positively-charged Pb²⁺ions are tightly absorbed on the typical crystal planes of initially-formed zinc nuclei,which suppressed the subsequent absorption and electroreduction of Zn²⁺ions.As a result,the Pb²⁺ions-containing electrolyte that is endowed with“grinding effect”for electrodeposits refines the zinc grain size from 7.43-7.87μm to 0.88-2.26μm,thereby forming smooth Zn electrodeposits.Meanwhile,the tight adsorption of Pb²⁺inhibits the zinc corrosion and hydrogen evolution reaction to a certain extent.Importantly,the grain-refined zinc anode affords a high reversibility of Zn plating/stripping behavior with a high Coulombic efficiency of 99.9%over1000 cycles and enables the aqueous Zn//V2O5 battery with durable lifespan over 2000 cycles.This work will provide a novel strategy to realize the compact and stable metal anodes by refining the grain size of electrodeposits via introducing the adsorbable ion with“grinding effect”.（3）To overcome the severe electrochemical irreversibility of conventional Zn-air batteries originating from strong alkaline electrolytes,I design a hybrid Zn-air battery with an acidic air cathode to prevent detrimental side reactions of carbonate and its subsequent precipitations,a neutral Zn anode to permit highly reversible Zn stripping/plating behavior,and develop a dual-hydrophobic membrane to give full play to the advantages of decoupling neutral-acidic system.Using this hybrid Zn-air battery as an example,the dual-hydrophobic membrane effectively prevents the crossover of protons and selectively transport hydrophobic anions to maintain charge balance inside the hybrid battery.As a result,the hybrid Zn-air battery exhibits a high working voltage of 1.5 V and long-term cycling performance of 2000 h.（4）Based on the above hybrid Zn-air battery,to overcome the limitations of voltage and lifespan of Zn//Mn O2 batteries,I further design a hybrid Zn//Mn O2 battery,in which the acidic Mn O2 cathode and neutral Zn anode are decoupled by a dual-hydrophobic-induced hydrophilic-ion-shielding and hydrophobic-ion-conducting membrane.This strategy avoids the common cross-contamination in hybrid systems and ensures the optimal reaction mechanisms for both the cathode and anode,e.g.,the high-voltage and high-energy two-electron reaction of Mn O2/Mn²⁺solid-liquid conversion in acidic electrolyte and highly reversible zinc plating/stripping behavior in neutral electrolyte.As a result,based on the decoupling neutral-acidic electrolyte system,the hybrid Zn//Mn O2 battery exhibits a high working voltage（2.05 V）,large discharge capacity(18 m Ah cm^-2),and long-term cycling stability（2275 h,2000 cycles）.