The Lithium Storage Performance Of Cobalt Oxide/Carbon Nanocomposites Anode Materials

Rechargeable lithium-ion batteries have been regarded as one of the most promising energy storage systems.Due to its light weight,high energy,and good performance characteristics,scientific resources have been increasingly invested in this area.Lithium ion anode is an important part of the battery structure,although the lithium ion battery anode materials are varied and complex,the choice of anode materials is very important for lithium ion battery performance.The current commercial lithium batteries are mostly apply graphite as anode materials with the theoretical capacity of only 372 mAh g^-1,limiting the development of lithium-ion batteries.Many researchers endeavored to develop new electrode materials to meet the demands for the ever-increasing cycle life and higher energy density.Co₃O₄ is a transition metal oxide own high redox capacitance,excellent physical properties,high chemical purity and large particle size distribution and can be widely used in LIBs.In addition,Co₃O₄ has significant advantages of almost the highest reversible capacity in LIBs,and each formulation unit can store 8 lithium atoms.However,transition metal oxide are tend to swelling resulting in structure collapsing and capacity fading during the charge/discharge process.Therefore,synthesizing nanoscale cobalt oxide or cobalt oxide/carbon composite materials to prepare anode materials for lithium-ion batteries has attracted more and more attention.This thesis is mainly contributed to fabricate nanoscale cobalt oxide/carbon composites as anode materials for lithium-ion batteries.The releated research content mainly includes the following four works:1.The preparation of Co₃O₄@porous carbon nanomaterials from MOF-5 and its application for anode materials for lithium ion batteries.Metal-organic frameworks?MOFs?-derived hierarchically porous carbon?MDPC?was obtained by calcining MOF-5 at high temperature.The Co₃O₄ NPs@MDPC nanocomposites was obtained through the loading of nano-sized cobalt tetroxide on the surface and internal pores of MDPC.During charge and discharge process,the vast micro/mesopores of MDPC provided an effective channel for the transport of Li⁺.And the MDPC matrix prevented Co₃O₄ NPs from agglomerating effectively.When used as anode materials for lithium ion batteries,the as-prepared nanocomposites manifested outstanding capability of 650 mAh g^-1 at 2 A g^-1 and when the current density was back to 0.1 A g^-1,the specific capacity was 1500 mAh g^-1,apparently superior to that of other Co₃O₄NPs@PC.The high capacity especially at high current density and exceptional rate capability of Co₃O₄ NPs@MDPC manifest that it is a promising anode material for LIBs.2.The preparation of hollow Co-Co₃O₄@CNT nanocomposites from ZIF-67 and its application for anode materials for lithium ion batteries.The ZIF-67 cube was used as scacrificial template to calcining in a reducing atmosphere along with in-situ growth of carbon nanotubes,followed by calcination under air to construct a cubic structure composed of hollow Co₃O₄ spheres.After cycling 200 cycles at a current density of 0.2 A g^-1,the reversible capacity was still maintained at 806.7 mAh g^-1.Excellent cycle stability and lithium storage capacity might be due to the construction of hollow structures and the encapsulation of carbon nanotubes to relieve the volume expansion and contraction of Co₃O₄.Meanwhile,the increased specific surface area could effectively improve the storage of lithium ions.Therefore,the hollow Co-Co₃O₄@CNT nanocomposites have potential applications in lithium batteries.3.The preparation of CF@Co-Co₃O₄/CNT nanocomposites from melamine foam and its application for anode materials for lithium ion batteries.The three-dimensional macroporous carbon framework surrounded by carbon nanotubes was obtained by calcining an easily accessible,low-cost melamine foam pre-soaked in cobalt nitrate solution for some time under a nitrogen atmosphere.And cobalt oxide nanoparticles were successfully loaded on the carbon substrate through oxidizing part of the metal cobalt to obtain CF@Co-Co₃O₄/CNT composite.Among them,metal cobalt,carbon nanotubes,and its own three-dimensional carbon framework ensured excellent electrical conductivity.In addition,the presence of cobalt oxide nanoparticles effectively increased the lithium storage capacity.At the same time,the three-dimensional carbon framework surrounded by carbon nanotubes can also relieve the volumetric deformation of cobalt xide to some extent.When applied for negative electrode material of lithium ion battery,the current density was 0.5 A g^-1,the material can exhibited a reversible capacity of about 500 mAh g^-1,which was much higher than the theoretical capacity of graphite.The synthesis method is simple and convenient for large-scale production.