Study On Controllable Synthesis Of Nano-manganese Composites And Electrode Performance

Lithium-ion batteries?LIBs?are widely used in various electronic products,large-scale energy storage power stations,and pure?hybrid?electric vehicles,etc.,due to their high energy density,long cycle life,and safety and reliability.Because the lower theoretical specific capacity of traditional graphite lithium negative electrode(372 mAh g^-1)has greatly restricted the development of advanced LIBs,it is imminent to develop a high-performance anode material.However,owing to the large volume change during the conversion reaction,slow reaction kinetics,and inherently low conductivity,the rate performance and cycle performance of MnO have been greatly affected.Aiming at the defects of MnO,this paper uses MnO and carbon materials to composite,and chooses the simplest and most effective carbon coating method.One-dimensional nanomanganese-based compounds?MnOOH nanowires,MnO₂ nanorods?are used as precursors.After KNO₃ treatment,one-dimensional KMn₈O₁₆6 is obtained as a self-template,and an N-doped carbon layer is formed by in-situ polymerization and simple annealing,and the core is a one-dimensional nano-core-shell structure of MnO?MnO@C?.This structure has many advantages in energy storage,such as continuous directional electron transfer and short lithium ion diffusion paths,what's more,the carbon layer can prevent MnO from agglomerating,reducing side reactions and volume expansion,and maintaining electrode structure stability.By comparing the electrochemical performance and material structure characterization of MnO@C treated with KNO₃ and without KNO₃,the MnO@C treated with KNO₃ has a higher degree of graphitization and has a partially amorphous nature.This is the decisive factor for superior electrochemical performance of KNO₃-treated MnO@C.Because the KNO₃-treated MnO@C has better conductivity and lower Gibbs free energy,making it more excellent in delithiating/intercalating lithium.In addition,the volume expansion during the charge and discharge process is smaller than that of crystalline materials.The extra active sites caused by defects and vacancies and the rapid ion diffusion are all conducive to electrochemical charge storage.Therefore,using MnOOH nanowires as precursors,KNO₃-treated MnO@C has excellent rate performance.At 0.1,0.5,1 and 3 A g^-1,the capacity is 867,690,585 and 384 mAh g^-1,even at 5 A g^-1,the capacity can reach 238 mAh g^-1;moreover,the capacity reaches 666 mAh g^-1 after 600cycles under a large current density of 1 A g^-1,and the capacity has almost no attenuation,showing good cycling performance.In addition,when MnO₂ nanorods are used as precursors,KNO₃-treated MnO@C has higher performance characteristics.At 0.1 A g^-1,the ultra-high rate reversible capacity reached 1105 mAh g^-1,even at a high current density of 5 A g^-1,the capacity can be as high as 471 mAh g^-1;and it circulates 400 times at a current density of 0.5 A g^-1,with a capacity of up to 1128 mAh g^-1 and a retention rate of up to 112%.