Boosting Electrochemical Performance Of Zinc Ion Energy Storage Device Via Manipulating Interfacial Structure

Wearable electronics,such as smart watches,health bracelets and physiological monitors,have been thrivingly developed in recent years,which have remarkably enriched and facilitated our daily lives.Electrochemical energy storage device play a unique role in its cruising capability as a crucial part of wearable electronics.Currently,lithium-ion battery is serving as the mainstream power source for portable electronics.However,lithium-ion batteries always suffer from the recent frequent safety risks due to the inflammability and explosivity of their organic electrolytes.Aqueous electrochemical energy storage systems are non-toxic and non-flammable,which are more feasible for wearable electronics in striking contrast with organic electrolyte electrochemical energy storage counterpart.Among various metal electrodes,zinc has unique merits in aqueous electrolytes,including superior ambient stability(zinc can be directly used as an anode),resource abundance,environmental friendliness,and divalent ions triggered prosperous charge storage.Thus,extensive efforts have been dedicated in aqueous zinc ion electrochemical energy storage system,with focusing on developing high-performance electrode materials and correlative integrated flexible wearable electronics.However,the aqueous electrolyte caused cathode active materials dissolution provoke severe capacity fading,which grievously limits the full battery practical application.In addition,the Zn ion uneven nucleation induced zinc dendrites and inevitable side reactions further diminish the interfacial stability during the long-term electrochemical cycles.Therefore,rational manipulating of the electrode/electrolyte interfacial structure is pivotal to improve the electrochemical performance of aqueous zinc ion energy storage devices.Focusing on the interfacial issues of zinc ion energy storage devices,the dissertation aims to manipulate the interfacial structure of zinc ion energy storage system from two aspects:(1)to improve the interfacial contact of the electrode and the electrolyte,and promote the pseudocapacitive charge contribution of carbon based cathodes;(2)to construct a superior stable electrode/electrolyte interface and facilitate the interfacial ionic transmission via utilizing bio-gel electrolyte.The main research contents of this dissertation are as follows:(1)Enhancement of the interfacial contact between the cathode and electrolyte.The oxygen functional groups of chemically reduced graphene oxide(rGO)has been systematically regulated to rationally enhance the interfacial compatibility between the rGO cathode and electrolyte,which effectively promoted the aqueous electrolyte-graphene cathode wettability.Zn-ion tends to adsorb onto oxygen functional group sites on carbon cathode,which accelerates the Zn ion transport kinetics.To further resolve the charge storage mechanism,a series of ex-situ or operando characterization techniques accompanied with theoretical computation,electrochemical dynamics study have been utilized to understand the interfacial electrochemical behavior.It verified that both the carboxyl and carbonyl play a critical role in enhancing the wettability and electrochemical performance of carbon based cathode in aqueous electrolyte.Owing to the negative charge of oxygen functional groups,the rGO cathode exhibits a desirable electrochemical performance,which leads to promoted pseudocapacitive redox activity and depressed Zn-ion adsorption energy.In addition,a quasi-solid-state flexible Zn-ion hybrid capacitor(ZHC)with a polyacrylamide gel electrolyte has been fabricated,which contains an adorable loading mass of 5.1 mg cm-2.The thus-fabricated quasi-solid-state ZHC also offers a superior areal capacitance and power density.(2)Building a stable electrode/electrolyte interface for efficient ion transport.The biogel electrolyte was prepared with a dominant component of keratin,which extracted from natural wool.By virtue of the proton-Zn ion coupling transport effect,the electrode/gel electrolyte interfacial Zn-ion transmission behavior has been regulated,with prominent enhancement of Zn-ion transport.It remarkably inhibits the Zn dendrite formation and associated side reactions,while improve the Zn-ion battery electrochemical stability.In this regard,the average coulombic efficiency of the zinc-ion battery with wool keratin bio-gel electrolyte system reaches 98%for 650 cycles.With the merits of the distinguishing interfacial ion transport behavior,the hybrid bio-gel based flexible zinc-ion battery delivers 99%capacity retention with excellent mechanical stability after a series of varied deformations(such as bending,folding,squeezing,rolling and compressing).