Study On The Preparation And Modification Of LiMn₂O₄ With Spent Zn-Mn Batteries As Manganese Source

The spent Zn-Mn batteries will hurt the environment a lot in term of the heavy mental content and toxic chemicals when abandoned casually.The impact on the environment and human body has urged the development of green and commercially feasible technologies.The spinel LiMn₂O₄ powders act as a promising cathode material for lithium ion batteries because its high specific capacity,low cost and non-toxicity.However,bare LiMn₂O₄ powders have a poor cycling performance when charged/discharged.In order to overcome this capacity fading problem,two methods can be employed,one way is substitution of heterogeneous atom into the host LiMn₂O₄ structure of cathode materials and the other is surface modification.In this study,two different products of MnO₂ and KMnO4 have been recycled from spent Zn-Mn batteries and have been selected as manganese source to synthesize LiMn₂O₄ powders by salt molten method and one-step hydrothermal method,respectively.The structure,morphology,and electrochemical properties of prepared LiMn₂O₄ were characterized by X-ray diffraction,scanning electron microscope,galvanostatic charge/discharge.The γ-MnO₂ and β-MnO₂ with regular particle size was recycled by redox reactions using H2C2O4 and Na2S2O8;the KMnO4 was recycled from the Zn-Mn batteries using KOH and KClO3 as row materials.Spinel LiMn₂O₄ synthesized by salt molten method uses γ-MnO₂ and β-MnO₂ and Li₂CO₃ as raw materials,powders calcined at 770 °C using β-MnO₂ as manganese source have better performance than others.LiMn₂O₄ surface modification has enhanced the cycling performance obviously,MgO-coated LiMn₂O₄ has showed the best electrochemically performance of all,with an initial capacity of 104.2 mAh g^-1 and retained 95.8% after 150 cycles at a current density of 200 uA·cm^-2,the capacity raised by 7.4% compared with the bare LiMn₂O₄ after 150 cycles,at a higher current density of 400 uA cm^-2,MgO-coated LiMn₂O₄ has performed an initial capacity of 95.6 mAh g^-1 and has retained 99.5%after 100 cycles,the capacity raised by 19%compared with the bare LiMn₂O₄ after 100 cycles.The excellent electrochemical performance shows that surface modification intends to be an attractive method to improve the cycling ability of LiMn₂O₄.LiMn₂O₄ synthesized by one-step hydrothermal method using KMnO4 and LiOH as raw materials.The undoped LiMn₂O₄ shows a relative poor electrochemical performance,Co-doping treatment was carries out,which resulted in a significant enhancement of the electrochemical properties.The Co-doped LiMn1.9Co0.1O4 had an initial discharge capacity of 102.7 and 90.1 mAh g^-1 and with a capacity retention of91% and 98.8% at the current densities of 200 and 400 uA cm^-2 after 150 cycles,the capacity raised by 15.3% and 37.8% compared with undoped LiMn₂O₄ after 150 cycles,respectively,whose performance was enhanced distinctly compared to that of the un-doped LiMn₂O₄.