Research On The Energy-Storage Mechanism For Anode/Cathode-Free Aqueous Batteries

Aqueous batteries hold great promise in large-scale energy storage fields because of the merits of low cost,great safety,and environmental friendliness.Among various aqueous batteries,iron ion batteries（IIBs）have received widespread attention due to the overwhelming advantages of iron anode including abundant reserve,low cost,and high theoretical specific capacity（960 m Ah/g）.However,the IIBs still encounter issues including low iron plating/stripping efficiency and poor cycle life.Additionally,zinc-iodine batteries（ZIBs）also attract intensive research attention since zinc anode has high theoretical specific capacity（820 m Ah/g）and low redox potential（-0.76 V vs.SHE）.However,the by-products evolved from I₂ cathodes undergo shuttle effect during the redox reactions,leading to corrosions of zinc anodes and deteriorations of battery performances.Furthermore,both batteries utilize heavy metallic anodes,showing limited energy densities.To address these issues and optimize the performance of both batteries,we have proposed anode/cathode-free battery structure design and cooperatively utilize the electrolyte regulation strategy.The anode/cathode free battery configurations can effectively reduce the battery masses and thus evidently increase their energy densities.The iron plating/stripping efficiency is further enhanced through electrolyte regulation strategy,thus elevating the electrochemical performances of anode/cathode free IIBs.To improve the comprehensive performances of anode/cathode-free ZIBs,optimized current collectors are adopited to allivate the shuttle effect of polyiodides.The research details are listed as follows:1.Using the anode/cathode free design and electrolyte regulation strategies to construct high performance iron ion batteries:A novel anode/cathode free IIB is developed by using activated carbon with high specific surface area as both anodic/cathodic current collectors,with Fe SO₄ and NH₄Cl mixed aqueous solution as electrolyte.This battery adopts Fe²⁺in electrolyte as charge carriers,during the charge/discharge processes,Fe²⁺/Fe³⁺and Fe²⁺/Fe conversion reactions occur at the anode and cathode interfaces,respectively.The practical advantages of this battery are shown as follows:（I）The anode/cathode free configuration efficiently reduce the battery mass and increase the battery energy density,which is as high as 41.86 Wh/kg and nearly 27times higher than that of traditional IIBs.（II）NH₄Cl is adopted as the electrolyte additive,improving the plating/stripping efficiency of iron anode and hence prolonging the battery cyclic lifespan.The iron plating/stripping efficiency can reach 96.1%.Meanwhile,the Coulomb efficiency of the full battery is as high as 95.3%,and after 1000 cycles,this valuve can maitain more than 90%.（III）This IIBs are easily prepared,rather low-cost,and environmentally benign.This work provides a new thought for the research and development of IIBs with high energy density and long cycle life.2.Construct high-performance Zn-I₂ batteries using the anode/cathode free design:By using activated carbons@Polypyrrole（C@PPy）as the electrode current collectors,and Zn SO₄/Zn I₂ mixed solutions as the electrolyte,a novel type of anode/cathode free ZIBs has been developed.Zn²⁺and I^-in electrolyte are the charge carries for this ZIB.During charge/discharge processes,I^-/I₂ and Zn²⁺/Zn conversion reactions occur at the cathode/anode interfaces,respectively.There are several highlights for this battery system:（I）The light weight C@PPy is adopted as the electrode current collectors;therefore,the battery energy density can reach as high as 147 Wh/kg,far exceeding that for traditional ZIBs（72.6 Wh/kg）.（II）C@PPy can efficiently adsorb the polyiodides in the cathodic conversion reactions,inhibiting the adverse shuttle effects and thus enhancing the battery Coulomb efficiency.The Coulomb efficiency of our anode/cathode-free ZIBs can reach 99.8%;after 1000 times of cycling,the value still maintains as high as 99%.（III）The unique battery configuration can effectively simplify the battery manufacturing,and thus reducing the preparation cost.This work provides a scientific reference for the development of ZIBs with high efficiency and long life.