Electrolyte Additive Design And Application In Zn-based Energy Storage Devices

Rechargeable Zn-based energy storage devices are often considered as a replacement for lithium metal batteries in large-scale energy storage applications due to their low redox potential(-0.762 V vs.standard hydrogen electrode),high volume capacity(5585 mA h cm-3),low toxicity,affordability,and safety.However,the practical application of Zn-based energy storage devices still faces many challenges,such as Zn dendrite formation,poor electrochemical performance at low temperatures,and irreversibility of cathode materials.This dissertation aims to address these key issues by using electrolyte additives to achieve high electrochemical stability of Zn-based energy storage devices.The main research results of this dissertation are summarized below:(1)The modified electrolyte,consisting of 1 M ZnSO4 and 0.1 M NaF,effectively inhibits the growth of Zn dendrites.The Zn//Zn symmetric cell with NaF additive shows a battery cycle-life of 368 h.Moreover,the full batteries with NaF exhibit a higher specific capacity of 146.94 mA h g-1 and a higher capacity retention of 83.2%.(2)The modified electrolyte,which includes 1 M ZnCl2 and a 40%volume fraction of ethylene glycol(EG)organic solvent,can suppress side reactions and dendrite growth on the surface of the Zn anode.Additionally,EG improves the energy storage efficiency of the ZnCl2 electrolyte at low temperatures.The Zn//Zn symmetric cell and Cu//Zn half cell with the modified ZnCl2 electrolyte can exhibit a cycle-life of over 570 h and 1600 h at-20℃,respectively.Moreover,the hybrid capacitors with the modified ZnCl2 electrolyte exhibit an average capacity of 42.68 mA h g-1 in 10000 cycles at-20℃.(3)The modified electrolyte,which includes 0.5 M Na2SO4 and 2.1 M glycerol(Gl)and 1 M Zn(ClO4)2,can enhance the cycle stability of the Zn anode by regulating the growth direction of Zn dendrites.The Zn//Zn symmetric cell with the modified electrolyte achieves a stable cycle-life of 2930 h.Furthermore,even at-10℃,the capacity retentions of the full battery and the hybrid capacitor with Gl after 30000 and 3000 cycles are 95.37%and 62.48%,respectively.(4)The modified electrolyte including 1.3 M Zn(CF3SO3)2 and 50%volume fraction trifluoroethanol(TFEA)can suppress the growth of Zn dendrites and the solidification of electrolyte at low temperatures,and alleviate V2O5 dissolution effectively,thus achieving stable and high-performance full batteries.The Zn//Zn symmetric cell with TFEA can provide a long cycle-life of 782 h at a current density of 5 mA cm-2 and an area capacity of 2 mA h cm-2,far exceeding the cycle-life of the symmetric cell without TFEA.In addition,the V2O5//Zn full battery achieves an initial capacity of 264.05 mA h g-1 and a capacity retention of up to 93.44%after 1000 cycles at room temperature.Even if the temperature drops to-25℃,the initial capacity of the full battery is still 116.78 mAh g-1,and they can still maintain 87.72%capacity after 2000 cycles.