Preparation And Properties Of Mn(Sn) Compound/Carbon Composites For Lithium-Ion Storage

As environmentally friendly secondary battery,lithium ion batteries(LIBs)have gradually emerged from the field of electrochemical storage.The anode materials with high selectivity and great fabrication play an important role in LIBs.To overcome the low capacity,poor rate and short cycle life of anode materials,Mn-based or Sn-based compounds with high theoretical capacity and carbon materials with great conductivity are combined for efficient lithium ion storage while rational structure design and controllable morphology promote the electrochemical property.The specific contents are as follows:(1)The MnO nanoparticles wrapped in double carbon layers(HNC@MnO@NC)are designed to a multi-layer buffer structure by in-situ polymerization and hydrothermal methods.The presence of hollow N-doped carbon(HNC)inside can not only increase the electron migration rate of the composite material,but also prevent the MnO nanoparticles from gathering together and losing the active sites of lithium ions.In addition,HNC@MnO@NC protected by N-doped carbon(NC)outside with stable physical structure achieves ultrahigh discharge capacity of 820 m Ah/g after 1000 cycles at 1 A/g.(2)The pea chains containing the heterostructured MnO-Sn(MnO-Sn@CNF)confined by N-doped carbon nanofibers(CNF)are prepared by electrospinning and high-temperature reduction methods,which exhibit high reversible capacity(1 A/g,98%capacity retention after1000 cycles)and outstanding rate performance(447 m Ah/g at 5 A/g).Carbon nanofibers are not only used as high-speed channels for ion transfer and electron conduction but also overcome the volume change of MnO-Sn during charge/discharge process.In addition,the stable interface area of heterostructured MnO-Sn alleviates the structural change of tin-based materials and improves the electron migration rate.(3)The hollow CoSnO_x necklace-like chains(CoSnO_x@CNF)are synthesized by electrospinning and one-step carbonization.The ultra-thin carbon fibers on the outer layer,which shorten the diffusion distance of lithium ions,are tightly wrapped on the surface of the CoSnO_x cubes with ultra-high theoretical capacity.The one-dimensional core-shell structure of compounds not only promotes the reaction kinetics of lithium ions,but also limits the microstructure change of CoSnO_x during the reaction process.By controlling the temperature,CoSnO_x@CNF-400 at 400?can maintain a discharge specific capacity of 733 m Ah/g after800 cycles at 1 A/g.