Study On The Sodium Storage Performance And Mechanism Of Nano MnO And MnSe Materials

Since the first commercial lithium-ion battery（LIB）came out in 1991,lithium-ion batteries have developed rapidly and are widely used in many aspects of our society to cope with the energy and environmental crisis caused by the over consumption of fossil fuels.However,the limited reserves of lithium resources have aroused the urgent need to find new alternatives.The ubiqutous distribution of sodium makes sodium ion batteries（SIBs）become one of the potential alternatives.However,due to the problems such as the large radius of sodium ions and sluggish insertion/extraction during charge/discharge,SIBs are still in the research stage.Designing high-performance anode materials for SIBs is one of the effective ways to achieve commercial applications.Conversion electrode materials have become one of the important directions due to their higher theoretical specific capacity.However,their distinct problems such as large volume expansion during Na⁺insertion/extraction,poor rate performance and inferior cycling stability need to be carefully addressed.Inspired by this,this thesis designs and prepares manganese-based conversion materials,mainly by regulating their unique nanostructures or chemical compositions to inhibit structural variation or enhance Na⁺transport,thus improving the cycling stability optimizing the electrochemical performance.The main research contents are as follows:Firstly,we synthesized two manganese-based oxides with thorn ball-like nanostructures.The Mn O sample showed a high reversible capacity of 261 m Ah g^-1 at the current density of 0.2 A g^-1 after 200 cycles,and a stable capacity of around 100m Ah g^-1 at a high current density of 5 A g^-1 for 2000 cycles.While the Mn₂O₃counterpart showed much lower capacities of only 176 and 58 m Ah g^-1at 0.2 and 5 A g^-1,respectively.More strikingly,because of the unique double-shell hollow structures,the integrity of the nanospheres could be perfectly retained even after 200 cycles at 0.5 A g^-1,highlighting the superior robustness of the current double-shell architecture.The subsequent density functional theory（DFT）theoretical calculations also show that sodium atoms have larger adsorption energy and lower migration energy in Mn O materials comparing with Mn₂O₃ materials,which leads to Mn O materials show better performance.Subsequently,we explored another high-performance anode material,-Mn Se.It exhibits excellent capacity under low current density(416 m Ah g^-1 at a current density of 0.2 A g^-1),highly rate performance(270 m Ah g^-1 at a current density of 20 A g^-1)and stable cycling performance(a reversible specific capacity of 275 m Ah g^-1 after 2000cycles at 10 A g^-1,and the loss per cycle is only 0.138‰)in SIBs.At the same time,in the subsequent full cell test,it still has a capacity of 153 m Ah g^-1 after 100 cycles at a current density of 0.2 A g^-1,showing its potential for application in rechargeable SIBs.