Flexible Carbon/Manganese Oxide Integrated Electrode For Aqueous Zinc Ion Battery

The ever-growing development of wearable electronics puts forward the demand of advanced flexible energy storage devices.However,the electrodes of flexible batteries should not only have high energy density and excellent stability,but also have mechanical properties and flexibility to withstand different bending conditions.The rational construction of high-performance integrated flexible electrodes is the key to promote the development of flexible batteries.The rechargeable Zn-MnO2 system has the advantages of high specific capacity,abundant resources,low cost,high safety and materials easy to manufacture,which is expected to be applied to wearable electronics.The cathodes prepared by pasting MnO2 powder with binder will detached from the current collector under repeated bending forces.In addition,pure MnO2 with low electronic conductivity usually suffers from Mn dissolution in electrolytes during the process of charge/discharge,resulting in structural collapse of the electrode experienced in flexible Zn-MnO2 system.Furthermore,commercial zinc plates are usually applied directly to the negative electrode,but it has a high quality,low utilization rate and the growth of zinc dendrites during the process of charge and discharge,especially its limited flexibility is far from enough to satisfy the demand of wearable applications,which severely limits the development in flexible ZIB.To solve above problems,this paper proposes to optimize the mechanism of zinc ion insertion/extraction by regulating the composition of the manganese oxide phase,and to develop an idea for constructing the integrated cathodes and anodes for high-performance flexible zinc ion batteries.First,the work of this paper adopts the carbon nanosheet arrays(C-NSAs)as the substrate to construct hierarchical MnOx/C-NSAs.What's more,a cathode material ultrathin film(MnO2-UTF)is first modified on the surface of the carbon cloth as active sites for the in situ nucleation and directed epitaxial growth of metal Zn.As a result,the CC@MnO2-UTF@Zn anode can be cycled in aqueous electrolyte and maintain stable cycling performance during repeated Zn deposition/stripping processes,and the construction of flexible device is realized finally.The specific research contents are as follows:(1)Study on the Integrated Manganese Oxide/Carbon Nanosheet Arrays(MnOx/C-NSAs)Cathode for Zinc-Ion Batteries:In order to construct high performance flexible aqueous Zn ion battery cathodes,we prepared the carbon nanosheet arrays with the large specific surface area and high conductivity by using layered double hydroxides(LDH)as the self-sacrificing template and ZIF-67 as carbon source and calcination and acid etching on a flexible carbon cloth substrate,on which ?-MnO2 was in situ grown.Then,in order to regulate the phase composition,C-NSAs was used as a reductant for secondary calcination reduction,and part of the layered MnO2 was reduced to the face-centered cubic MnO phase to adjust the Mn2+balance.The Zn//MnOx/C-NSAs battery assembled with the electrode has an initial capacity of202 mAh g-1 at a high current density of 1 A g-1,and the coulombic efficiency of the battery has remained above 99.7%with a capacity retention rate of up to 91.2%,and still maintain the capacity of 184.3 mAh g-1 over 1000 cycles,showing the good reversibility and cycle stability under high current density.In this work,we construct a three dimensional C-NSAs to improve the transmission of ions and electrons.Furthermore,MnO was introduced to the bulk phase to inhibit the dissolution of manganese and adjust the balance of Mn2+ so as to reduce the loss of active materials quickly at different current rates.To demonstrate its application in flexible wearable devices,we successfully fabricated flexible solid-state batteries.Thanks to the high energy density and flexibility of MnOx/C-NSAs electrodes,two flexible zinc-ion batteries can be connected in series to light a LED and bent at different bending angles,which illustrates its application prospects in flexible devices.(2)Study on Highly Reversible Zinc Anode Enhanced by Ultrathin MnO2 Cathode Material Film for Zinc-Ion Batteries:In order to solve the problems of zinc anode,such as high quality,difficult bending,and dendrite generation in the cycling process,in this work,MnO2 cathode material is first used as functional atomic matrix to control the initial homogeneous nucleation of Zn.MnO2 ultrathin film(MnO2-UTF)with the thickness about 10 nm was synthesized by controlling of reaction time precisely,which greatly lower the nucleation overpotential and thereby enhance the reversibly Zn plating/striping.The prepared CC@MnO2-UTF@Zn was assembled into a symmetrical battery.The CC@MnO2-UTF@Zn anode exhibited a stable cycling performance and much lower overpotential for up to 550 h at a current density of 0.5 mA cm-2.Moreover,the full cells with CC@MnO2-UTF@Zn anode and CC@MnO2 cathode delivered a high Coulombic efficiency of about 100%and a specific capacity of 186 mAh g-1 after 300 cycles at 1 A g-1.Surprisingly,the flexible solid-state ZIB batteries with the CC@MnO2-UTF@Zn anode pouch cell also exhibits superior stability and excellent power/energy density(465 Wh kg-1/1 46.23 W kg-1),which is superior to the reported results so far.In summary,we introduced MnO2-UTF to significantly improve the reversibility and stability of zinc anode during plating/striping process,and the dendrite problem of zinc anode was alleviated.Besides,the CC@MnO2-UTF@Zn anode can deposit zinc quantitatively according to demand,greatly improving the utilization of zinc.The excellent performance of the prepared CC@MnO2-UTF@Zn electrode in the flexible zinc ion battery can provide a new strategy for the preparation of the flexible zinc anode.