Purification Of Manganese Based Materials And Synthesis And Mechanism Research Of Electrocatalyst

The Li-air batteries are focused for the high capacity with the rapid development of the new energy materials industry.However,the sluggish ORR and OER process hinder the realize of great performance in Li-air batteries.Mn-based materials have been considered as one of the most competitive electrocatalysts due to the structural characteristics and resource advantages.Due to the much impact on electrocatalytic properties of Mn-based materials from the impurities,this paper studies the purification process of Mn-based materials based on the solubility products control of metal cation in different solutions from the low grade of manganese ore in China,which provides the Mn-source materials for Mn-based electrocatalysts.The repeated leaching process concentrates the MnSO4 solution(from 19.4 to 72.3 g L-1)and improves the utilization of sulfuric acid.Meanwhile,the dissolution rates of calcium and magnesium were reduced by 76.68 and 65.33%,respectively.The coupling purification was carried out with Ba(OH)2 and NH4HCO3 as purifications in the positive and negative direactions.The recovery rate of Mn reached 96.54 and 99.2%,respectively.The synthesized high pure MnSO4 meets the requirements of"HG/T 4823-2015".LCA shows that the consumption of energy and sulfuric acid was dividually reduced more than 70%and 36%with 59%CO2 emission compared with the traditional method.For the effects of surface structure and electronic structure in Mn-based electrocatalytic activity,this paper synthesized the composite material ofδ-MnO2@MWCNTs with 34 wt%MnO2 wrapped on the surface of MWCNTs in form of monomolecular layer.The dominated(002)facet and abundant oxygen vacancies of δ-MnO2 layer accelerate the adsorption of O2 and elongate the O-O bond.And the oriented growth of Li2O2 ensures the stable reaction zone in the cathode with sufficient charge transfer and oxygen diffusion channel.So the Li-O2 batteries with δ-MnO2@MWCNTs as cathode catalysts demonstrate the high discharge capacity of 28517 mAh g-1 with the overpotential of 0.14 V(100 mA g-1)and the excellent electrochemical reversibility with 20 cycles under a limited discharge depth of 1000 and 4000 mAh g-1,respectively.The Mn-based electrocatalysts was synthesized with excellent ORR and OER electrocatalytic properties through the imported Fe into the δ-MnO2@MWCNTs materials.The Fe-optimized materials demonstrate the shortened bond length of Mn-O and much higher d-band center than the δ-MnO2@MWCNTs materials,which enhanced the binding energy between the electrocatalyst and LiO2.So the the Li-O2 batteries with Fe-optimized Mn-based materials demonstrate the lower charge overpotential and higher electrochemical reversibility,which run 270 cycles with 1000 mAh g-1(100 mA g-1)and 35 cycle with 4000 mAh g-1(1000 mA g-1).