An Investigation Of The Effect Of Bi-MOF And Its Derivative For Regulating The MnO₂deposition Process And Its Application In Aqueous Zinc-ion Batteries

MnO₂is considered as the most promising cathode for zinc-ion batteries（ZIB）due to its high energy density,abundance of earth resources,environmental friendliness and low cost.In order to improve the poor cycling stability of MnO₂,pre-adding Mn²⁺into the electrolyte is a mainstream strategy to effectively inhibit the dissolution of MnO₂.However,the electrodeposition reaction(Mn²⁺→MnO₂)associated with the Mn²⁺additive during the charging process is considered to be an adverse reaction affecting the performance of zinc-mn batteries and should be suppressed.This work adopts the strategy of"using instead of suppressing",which controls the deposition rate of MnO₂and stabilizes the MnO₂deposite using Bi MOF and its derivatives as the deposition interface,resulting in the construction of a"cathode-free"zinc ion battery with high cycling stability.A Bi-MOF material（Bi-PYDC）is prepared by a hydrothermal method and casting on the surface of carbon paper cathode to construct a deposition interface（Bi MOF-CP）.Bi MOF-CP is assembled with Zn anode to form a cathode-free zinc ion battery（Zn//Bi MOF-CP）.The electrochemistry test of Zn//Bi MOF-CP shows a significantly improved cycling life span of over 10000 cycles under a high current density of 1 m Ah cm^-2by regulating the Mn²⁺electrodeposition reaction.The triple functions of Bi MOF-CP are verified by various testing methods such as SEM,contact angle,and ICP.Firstly,Bi MOF-CP can effectively control the Mn²⁺deposition at a moderate rate,avoiding the consumption of Mn²⁺in the electrolyte and preventing rapid cycling degradation.Secondly,as a Bi³⁺reservoir,Bi MOF-CP can slowly release Bi³⁺to stabilize the deposited R-MnO₂structure.Thirdly,Bi MOF-CP can also accommodate the insertion/extraction of H⁺ions,providing additional contributions to the capacity of the battery.A range of MOF-derived carbon materials（Bi PYDC-X,X represents the carbonization temperature）is obtained by carbonizing the Bi-PYDC metal-organic framework at different temperatures.These materials are used as the Mn²⁺deposition interface to construct a cathode-free zinc ion battery（Zn//Bi PYDC-X）.Characterization tests,including SEM,EDS,and XRD,shown that all Bi PYDC-X products were Bi-C composites with MOF morphology,and the Bi content of the materials decreased with increasing temperature.Electrochemical tests indicate that the cycle performance and specific capacity of the battery varied significantly depending on the carbonization temperature.The best long cycle performance and rate performance are observed when using MOF-derived material Bi PYDC-900 as the deposition interface,with Zn//Bi PYDC-900 reaching a capacity as high as 0.055 m Ah cm^-2at a current density of 1 m A cm^-2,and cycling stably for 6000 cycles.Using MOF-derived carbon materials to construct the cathode interface of zinc ion batteries is an extension of the"MOF as electrochemical deposition surface"strategy.In addition to achieving deposition control and stability,this approach further enhances the electrode’s electrochemical performance,such as its conductivity and rate capability.