The Preparation Of Nano-porous Tin-based Alloy/carbon Anode Material And Its Lithium Storage Behavior By Cyanide Glue Thermal Self-reduction Method

Owing to the higher capacity and enhanced safety,tin-based alloys(Sn-M,M = Fe,Ni,Co,and Cu)have been regarded as ideal anodic candidates to replace commercial carbon materials in lithium-ion batteries,but their practical utilization has been greatly hindered by the huge volume change-induced poor cycle life.Immobilization alloy nano-units within carbon matrices has proved to be the most effective strategy to improve their cycling stability since Li-Sn alloying and de-alloying reactions are confined within carbon nanoreactors.However,the particle sizes of the encapsulated alloys are generally larger than 10 nm and these particles often suffer from uneven size distribution and non-uniform dispersion within carbon matrices,causing appreciably local volume variations and considerable capacity decay upon repeated lithium insertion/extraction.To overcome these issues,in this thesis we propose a general gel-derived thermal-autoreduction methodology for uniformly immobilizing ultrasmall and homogeneous Sn-M alloys within nanoporous carbon networks,using cyano-bridged coordination polymer gels(cyanogels)as precursors.Specifically,three kinds of such nanoporous Sn-Fe alloy/carbon anodes,including Sn-Fe@C network,coral-like Sn-Fe@C framework,and 1D/3D hierarchical Sn-Fe@C framework,have been synthesized through cyanogel-derived thermal-autoreduction routes using citric acid(CA),polyethylene glycol(PEG),and chitosan gel hybridized Sn-Fe cyanogels as precursors,respectively.These nanoporous Sn-Fe alloy/carbon anodes possess unique structural and compositional superiorities toward lithium storage,and thus are able to manifest long cycle life,high specific capacities,and rate capability.The main innovative results are displayed as follows:(1)By using CA-hybridized Sn-Fe cyanogel as a precursor,Sn-Fe@C network has been fabricated via a thermal-autoreduction route.The uniform distribution of cyano-group,tin,and iron species at atomic scale in aerogel precursor favors the homogeneous embedding of Sn-Fe alloy nanocrystals within nanoporous carbon network,and moreover,the optimized CA source can further reduce the particle size of Sn-Fe alloys(?15.0 nm)and improve the dispersion between alloy and carbon components.These compositional and structural features make the Sn-Fe@C network manifest good cycle life(442 mA h g-1 after 100 cycles at 0.1 A g-1)and high rate capability(439 mA h g-1 at 1 A g-1).(2)By using PEG-hybridized Sn-Fe cyanogel as a precursor,coral-like Sn-Fe@C framework has been synthesized via a thermal-autoreduction route.PEG plays a critical role in reducing the Sn-Fe alloy size and improving the dispersion between alloy particles and carbon matrix,and the average size of Sn-Fe alloys in the optimized Sn-Fe@C framework is only 5.9 nm.These desirable features make the coral-like Sn-Fe@C framework exhibit good lithium-storage performance in terms of cycling life(371 mA h g-1 after 100 cycles at 0.1 A g-1)and rate capability(287 mA h g-1 at 1 Ag-1).(3)By using chitosan gel-hybridized Sn-Fe cyanogel as a precursor,1D/3D hierarchical Sn-Fe@C framework has been synthesized via a thermal-autoreduction route.The double-network nanostructured gel,consisting of three-dimensional(3D)intertwined inorganic Sn-Fe cyanogel and organic chitosan-glutaraldehyde gel,can realize 3D space confinement in molecular scale and thus obtain ultrafine Sn-Fe alloy particles(average size-2.7 nm)uniformly embedded in hierarchical 1D to 3D carbon framework.These unique compositional/structural features enable the hierarchical Sn-Fe@C framework to exhibit ultralong cycle life(516 mA h g-1 after 500 cycles at 0.1 A g-1)and ultrahigh rate capability(491 and 270 mA h g-1 at 1 and 10 A g-1,respectively).