Preparation Of Composite Solid Electrolytes And Applications For Rechargeable Metal Batteries

The issues of increasing crisis in fossil energy and environmental pollutions and rapid development of portable electronic devices and electromobiles jointly evoke the extensive attention in exploiting energy storage devices with high energy density.Representative secondary batteries that utilize metallic lithium and zinc as anode own an ultra-high theoretical specific capacity.However,the dendrites,low Coulombic efficiency,and safety issues caused by electrolyte leakage,fires and even explosions seriously restrict the further their development.On this basis,this thesis encompasses the safety and stability of the rechargeable metal batteries,prepares composite solid electrolytes with high ion transference number and superior compatibility with electrode materials,and reduces the polarization during charge transfer process and addresses the safety problems caused by non-uniform metal-ion deposition after building stale electrode-electrolyte interfaces,realizing dendrite-free and working-stable rechargeable metal batteries with high coulombic efficiency.The main contents are as follows:（1）Preparation and properties of symmetrical percolating composite electrolyte membraneThe polyethylene（PE）substrate was functionalized by attapulgite with rich inner pores to construct a symmetric electrolyte membrane with ion percorlating structure.The electrolyte membrane acts as a"natural reservoir"and improve the absorption and retention rates toward electrolyte by nearly 4 times.The rich internal ion transport channels promotes the migration of lithium ions with an ion transference number of 0.80,which realizes dendrite-free Li deposition.In addition,the symmetric layer shows high thermal stability and improving the safety of batteries.Pairing the obtained electrolyte with LiFeO₄ cathode,the obtained Li metal batteries operate stably for 400 cycles（up to half a year）with 84%capacity retention at 0.2C rate and exhibit an average coulombic efficiency of 99.97%with no dendrite formation.In addition,the electrolyte also enables Li/LiCoO₂ batteries to work under a voltage of 4.3V and release a capacity of 80mAhg^-1 at 5C rate.（2）Preparation and properties of hierarchically conducting composite electrolyte and electrode.A two-dimensional composite electrolyte composed of chitosan and ethylene carbonate was prepared by low-temperature self-polymerization,corresponding zinc-ion transference number is as high as 0.72.Meanwhile,the vanadium pentoxide cathode that grows on the three-dimensional conductive substrate is further coated with a polypyrrole as secondary conductive network by electrochemical polymerization.Assembling this electrolyte with positive vanadium pentoxide cathode,the zinc metal batteries show excellent cycling reversibility and small polarization,acquire a discharge capacity of 501.2mAhg^-1 at 0.3Acm^-2 and a discharge capacity of 309.2mAhg^-1 even at 10Acm^-2.Above results certify the significance of design for hierarchically conductive composite electrolyte-electrode structure that guarantees battery with good rate performance and cycling stability.