Preparation And Properties Of Functional Gel Electrolytes For Aqueous Zinc-based Energy Storage Devices

With the rapid development of wearable electronics,there arises an urgent need to exploit flexible,bendable,and even self-reparative energy storage devices.Meanwhile,these devices are anticipated to possess large energy/power densities,long life span,high safety,and low cost.Flexible aqueous zinc-based energy storage devices are promising to satisfy the abovementioned demands.One of the key components of aqueous zinc-based energy storage devices is the gel electrolyte.Therefore,it is emerging to develop high-performance gel electrolytes.The main work of this dissertation is to prepare multifunctional gel electrolytes,assemble flexible aqueous quasi-solid-state zinc-based energy storage devices,investigate the electrochemical performances of these devices systematically,and explore the effect and mechanism of gel electrolytes in inhibiting zinc dendrites and side reactions.The main research contents include:（1）A zinc-salt-containing borax-crosslinked polyvinyl alcohol/nanocellulose hydrogel electrolyte is developed,and shows great mechanical properties,intriguing self-healing feature,and high ionic conductivity.To demonstrate the feasibility of this hydrogel electrolyte,a flexible quasi-solid-state zinc-ion hybrid supercapacitor is assembled from this hydrogel electrolyte,activated carbon cathode（AC-paper）,and zinc metal anode.The obtained device exhibits high specific capacity(56.1 m Ah g^-1,504.9 m F cm^-2,and 224.4μAh cm^-2 at 0.5 m A cm^-2),great rate capability(22.1 m Ah g^-1 at 10 m A cm^-2),and excellent cyclability（95.3%capacity retention over5000 cycles）.It can also be folded,bent,compressed,and even self-healed while sacrificing only a small portion of its capacity.（2）A borax-crosslinked polyvinyl alcohol（PVA）/glycerol gel electrolyte is developed,in which glycerol can strongly interact with PVA chains with the assistance of borax,thus effectively prohibiting the formation of ice crystals within the whole gel network.Thanks to that,the freezing point of this gel electrolyte is below-60°C,which allows it to work at extremely cold environment.Even at–35°C,it still exhibits high ionic conductivity of 10.1 m S cm^-1 and great mechanical properties.On the basis of this anti-freezing gel electrolyte,a flexible quasi-solid-state aqueous Zn-Mn O₂ battery is assembled and realizes an impressive energy density of 46.8 m Wh cm^–3(1330μWh cm^–2)at a power density of 96 m W cm^–3(2.7 m W cm^–2)at 25°C,outperforming nearly all the reported aqueous zinc-ion batteries.More importantly,when the temperature is reduced to–35°C,a rather high energy density(25.8 m Wh cm^–3,732μWh cm^–2)can still be achieved.This battery also shows excellent cycling durability（around 90%capacity retention over 2000 cycles）when the temperature is down to–35°C.（3）A facile and cost-effective method is developed to construct an all-round hydrogel electrolyte by using cotton as the raw material,tetraethyl orthosilicate as the crosslinker,and glycerol as the anti-freezing agent.The obtained hydrogel electrolyte has high ionic conductivity,excellent mechanical properties（e.g.,high tensile strength and elasticity）,ultralow freezing point,good self-healing ability,high adhesion,and good heat-resistance ability.Remarkably,to the best of our knowledge,this hydrogel electrolyte can provide a record-breaking high ionic conductivity of 19.4 m S cm^–1 at–40°C compared with previously reported zinc-based aqueous electrolytes.In addition,this hydrogel electrolyte can significantly inhibit the zinc dendritic growth and parasitic side reactions from–40 to 60°C.With this hydrogel electrolyte,a flexible quasi-solid-state Zn-Mn O₂ battery is assembled and shows remarkable energy densities from–40 to 60°C.The battery also exhibits outstanding cycling durability and has high endurance under various harsh conditions.