Preparation And Electrochemical Performance Study Of Manganese-Based Cathode Materials For Aqueous Zinc-Ion Batteries

Due to the shortage of lithium resources and potential safety hazards such as combustion and explosion,there is an urgent need to develop new energy storage systems to adapt the development and progress of society.Because of the advantages of high safety,low cost,and environmental friendliness,zinc-ion batteries(ZIBs)are one of the ideal choices for forming a complementary energy storage system with lithium-ion batteries.Benefiting from the abundant resources,low toxicity and high energy density,manganese-based materials are considered to be one of the most potential cathode materials for water-based ZIBs.Among them,manganese monoxide has a wide range of sources and low price.It has been widely used in many fields such as catalysis and metallurgy.However,due to low reversible capacity and unclear reaction mechanism,compared with traditional manganese dioxide cathodes,manganese monoxide has been less studied in water-based ZIBs.This paper focuses on manganese monoxide research.Through structural design,morphology control,composite conductive materials and electrochemical activation,a high-performance manganese-based cathode material is obtained.In this paper,the carbon-coated manganese monoxide composite material(MnO@C-L)was first prepared by multi-steps strategy of co-precipitation reaction,dopamine polymerization coating and high-temperature pyrolysis.Thanks to the high electronic conductivity of the carbon and the higher specific surface area of the composite,the MnO@C-L achieves a reversible Zn²⁺storage.Compared to the commercial MnO,the MnO@C-L delivers a significant improvement in the discharge ratio capacity and cycle stability.A discharge capacity over 190 m Ah g^-1 can be realized at 0.1 A g^-1,corresponding to the energy density with 247 Wh kg^-1.After cycling 1000 cycles at 1 A g^-1,the MnO@C-L still exhibits a discharge capacity of119 m Ah g^-1.In order to further improve the specific capacity and rate performance of the MnO,a yolk-shell structural carbon-coated MnO nanometer composite(MnO@C-Y-S)was synthesized.The yolk-shell structure contains a large number of cavities and pores,which effectively alleviates the volume change problem caused by the deintercalation of Zn²⁺.In addition,the carbon shell and porous structure can also improve the electron transport and ion conduction processes.This material exhibits excellent comprehensive electrochemical performance.The MnO@C-Y-S has a discharge capacity of 270 m Ah g^-1 at a 0.1 A g^-1,corresponding to the high energy density of335.4 Wh kg^-1.Moreover,MnO@C-Y-S also achieves good cycling stability with a high capacity retention rate of 97%after 1000 cycles.At the current density 5 A g^-1,the MnO@C-Y-S can still offer 113 m Ah g^-1.Finally,the electrochemical activation process and zinc storage mechanism were studied with the ex-situ physics and morphology characterization.After the initial MnO conversion process to of the during the charge and discharge cycle,the MnO@C-Y-S is transformed into MnO_2-x·n H2O completely.In the subsequent cycle process,the MnO_2-x·n H2O realizes the reaction mechanism of Zn²⁺/H⁺co-(de)intercalation.Such a synergistic strategy by structural design and electrochemical activation strategy can provide reference to other manganese-based materials for ZIBs.