Study On The Flexible Zinc Ion Batteries Based On Mn₂O₃@PPy Cathode And H₂Ti₃O₇·xH₂O Anode

Among many aqueous batteries,zinc ion batteries feature the advantages of high specific capacity,high stability,rich zinc resources and low cost.Thus,flexible zinc ion batteries have become the next generation of the promising energy storage devices for portable wearable electronics.However,the development of flexible aqueous ZIBs is still in the early stage,which is suffering from some problems including the poor cyclability of electrode materials and difficult balance between mechanical properties and electrochemical properties.Therefore,it is urgent to deeply develop the strategies and methods to achieve the reliable flexible ZIBs.In this research,we focus on the construction of high-performance flexible zinc ion batteries.The Mn₂O₃@PPy cathode material and H₂Ti₃O₇·xH₂O anode material were prepared,which possess the long lifespan.The Mn₂O₃@PPy//H₂Ti₃O₇·xH₂O flexible quasi-solid-state ZIBs were constructed using the pomelo peel cellulose（PPC）as substrate and PPC hydrogel as electrolyte.This flexible ZIB exhibits the improved electrochemical performance and mechanical stability.Aiming at the poor cycle performance of manganese oxide cathode materials with high capacity and high voltage,polypyrrole coated Mn₂O₃ porous micro-boxes materials（Mn₂O₃@PPy）were prepared through the phase conversion and in-situ polymerization methods using Mn CO₃ micro-boxes materials as the precursor.It was proved that PPy coating can effectively improve the cycling life of Mn₂O₃ materials(2000 cycles,178 m Ah g^-1,0.4 A g^-1)and the porous structure endows micrometer-scale Mn₂O₃@PPy materials with good rate performance(75.6 m Ah g^-1,2.0 A g^-1).The ex-situ analysis revealed that the electrode reaction of Mn₂O₃@PPy composite is related on zinc ions and hydrogen ions in the electrolyte.Because the dendrites are generated on the metal zinc anode during cycling and the metal zinc anode is not suitable for flexible batteries,H form titanate H₂Ti₃O₇·xH₂O was synthesized as the anode material for ZIBs via the cation exchange process of Na₂Ti₃O₇precursor.The H₂Ti₃O₇·xH₂O features the interlayer crystalline water and large lattice spacing.The existence of crystal water in the material was proved by solid-state ¹H NMR,FTIR and thermogravimetry.The content of crystal water in the H₂Ti₃O₇·xH₂O material is determined to be 8.85%.Compared with the H₂Ti₃O₇ material without crystalline water,the（200）crystal plane spacing of H₂Ti₃O₇·xH₂O material is increased by 0.4?.H₂Ti₃O₇·xH₂O cathode material exhibits the low working potential(0-0.4 V vs.Zn²⁺/Zn)and long-term cycling life(4000 cycles,0.6 A g^-1).The study of ion diffusion kinetics proves that the large lattice spacing and interlayer crystalline water jointly endow the H₂Ti₃O₇·xH₂O electrode with the fast mass transfer.The ex-situ characterizations（XRD,SEM and TEM）demonstrate that the electrochemical reaction process of H₂Ti₃O₇·xH₂O electrode needs the participation of zinc ions and hydrogen ions in the electrolyte.The free-standing sandwich-type Mn₂O₃@PPy flexible cathode was prepared by using sheet-like PPC as the substrate material,carbon nanotubes as the conductive additive and Mn₂O₃@PPy composites as the active material,in which the sheet-like PPC substrate features the property of ion transport.The study about the performance of flexible half-cell proves that the Mn₂O₃@PPy flexible electrode exhibits good rate and cycle performance as well stable electrochemical performance under different bending states.The free-standing sandwich-type H₂Ti₃O₇·xH₂O flexible anode was synthesized with the substrate of PPC,the conductive additive of carbon nanotubes and the active material of H₂Ti₃O₇·xH₂O.The maximum tensile strength of H₂Ti₃O₇·xH₂O flexible anode can be up to 13.2 MPa,revealing the excellent mechanical behavior.This flexible electrode shows stable resistance under the bending state.It is demonstrated that the flexible H₂Ti₃O₇·xH₂O anode delivers the low redox potential,high rate and cycling performance.Under different bending states,the flexible H₂Ti₃O₇·xH₂O anode shows the high-capacity retention of 99%.The PPC/Zn SO₄ quasi-solid-state electrolyte is prepared using PPC film as the gel-electrolyte matrix,which exhibits a high ionic conductivity(24 m S cm^-1).A Mn₂O₃@PPy//H₂Ti₃O₇·xH₂O flexible quasi-solid-state ZIB containing the PPC-based hydrogel electrolyte,flexible Mn₂O₃@PPy cathode and H₂Ti₃O₇·xH₂O anode was obtained.The related experiments show that the synthesized flexible ZIB can deliver the high energy density(62.7 Wh kg^-1,based on the total mass of active materials),long lifespan(88%,1000 cycles,1.0 A g^-1)and stable specific capacity under different bending states.