Design And Performance Of Anode Materials For Li/Na-Ion Batteries

Tin-based materials have attracted great attention in the development of high-performance Li-ion batteries（LIBs）and Na-ion batteries（NIBs）due to the high theoretical capacity.However,the weak electric conductivity and huge volume expansion in the cycling process severely hinder the practical application of the electrode.Herein,we focus on the structural design and a series of composites combined tin-based materials with carbon were fabricated to obtain excellent electrochemical performances of LIBs and NIBs.In addition,Na-storage properties of low-cost carbon material and transition metal phosphides with high theoretical capacity were also primarily investigated based on the similar design concept.Firstly,hollow structured SnO₂/C core-shell fibers were facilely synthesized by coaxial electrospinning process.SnO₂ nanoparticles（NPs）were observed to be attached on the inner shell of the carbon fibers and sufficient hollow voids filled in the surrounding area.The unique porous structure and conductive carbon shell make the electrode high cycling stability and enhanced rate capacity.When used as anodes for LIBs,it delivers high capacity retention of 750 mAh g^-1 at 100 mA g 1 and excellent rate capability of 267 mAh g 1 at 3000 mA g^-1.To avoid the formation of unstable SEI film which resulted by the direct exposure of SnOx with electrolyte in the traditional graphene/SnOx composite,carbon confined porous graphene/SnOx frameworks were fabricated via a silica template assisted nanocasting approach followed by a carbon coating method.In detail,porous SnOx NPs were anchored on the surface of 3D graphene surface and then coated by a carbon layer.The structural design effectively avoids the direct contact between SnOx and electrolyte and stable SEI film can be formed on the surface of the electrode.When used as anodes for LIBs,the composite suggests stable cycling performance with a discharge capacity of 555 mAh g^-1 after 400 cycles at 1000 mAg^-1.Novel 3D porous graphene-encapsulated CNT@SnO₂ composite was constructed using a facile two-step hydrothermal method,and the lithium and sodium storage performances were investigated.Benefiting from the synergistic roles of CNT,graphene and SnO₂ NPs associated with unique 3D porous framework architecture,the composite suggests improved discharge capacity of 947 mAh g^-1 after 100 cycles at 100 mA g^-1,and enhanced rate capability of 281 mAh g^-1 at 3000 mA g^-1 in LIBs.In addition,Na storage testing suggests that a high discharge capacity of 323 mAh g^-1 after 100 cycles at 25 mA g^-1 was achieved.Next,well-dispersed Sn NPs were embedded in the porous N-doped graphene-like carbon network by a one-step thermal reaction using low cost raw materials as precursors.The as-prepared Sn/C composite possesses not only improved electrical conductivity,but also sufficient pores to alleviate volume expansion of Sn NPs and keep the structural integrity,which leads to enhanced Li/Na storage performances.Moreover,the approach is simple,low-cost and versatile for the scalable fabrication.In order to improve the specific capacity of carbon anode materials in SIBs,we referred the structural design in chapter four and 3D porous carbon-coated graphene composite was obtained using silica as the porous template combined with a carbon coating method.Through constructing highly conductive and sufficient Na-storage networks,the resultant carbon anode suggests high reversible capacity,excellent cyclability and remarkable rate capability.Lastly,Co2P NPs were encapsulated in 3D porous carbon nanosheet networks（3D-PNC）as anode for NIBs,using a cobalt nitrate-induced polyvinylpyrrolidone（PVP）-blowing method combined with an in-situ phosphidation process.The unique structural design method can not only accommodate the volume variation of Co2P NPs during cycling process,leading to efficient Na-storage,but also achieve controllable synthesis for the anode material.