Preparation And Lithium Storage Property Investigation Of Transition Metal Oxide-modified Multi-dimensional Porous Carbon Composites

The non-renewable nature of fossil fuels and the problem of environmental pollution promote the sustained and fast growth of the new energy industry,and the energy storage system.Compared to other energy storage systems,lithium-ion battery（LIBs）is used in all aspects of people’s lives due to the advantages of high capacity,no memory effect,et.al.With these advantages and mature production lines,LIBs can be found in many fields,such as mobile electronic devices and new energy automobile industry.With social development,the demands for LIBs with high electrochemical performance are increasing.However,its capacity and cycle performance have been unable to meet people’s needs,which is an urgent to optimize the electrochemical performance of LIBs.Transition metal oxides（TMOs）are considered to be the star anode materials due to the characteristics of high theoretical capacity.However,the low conductivity and the volume expansion during the cycle are still the obstacle for its commercial application.Meanwhile,the carbon materials present relatively low theoretical capacity but high conductivity and outstanding cycling stability.Based on the above discussion,composite of transition metal oxides and carbon materials are expected to obtain electrodes materials with excellent electrochemical performance.In this paper,the porous carbon matrix originated from glucose decorated with different types of transition metal oxides was prepared by template method,freeze-drying method,and carbonization process,whose electrochemical properties are investigated.The specific works of this paper are as follows:Firstly,the single oxide modified carbon composites were explored.N-doped porous carbon composites modified with Co₃O₄ nanoparticles（Co₃O₄/N-C composites）were prepared by using Na Cl as a template.In this work,the introduction of nitrogen can optimize the electrochemical performance of Co₃O₄/N-C composites.The presence of graphite nitrogen in Co₃O₄/N-C composite can promote the conductivity of the composites,and the carbon matrix can prevent the volume expansion of Co₃O₄ in the cycle.Co₃O₄/N-C-6 composite displayed excellent electrochemical performance among the four composites with different contents.The capacity of 1323.2 m Ah g^-1 can be obtained after100 charging/discharging cycles at 0.05 A g^-1.The Co₃O₄/N-C-6 composite showed a high capacity of 766.2 m Ah g^-1 at 1.0 A g^-1,accompanied with a high coulomb efficiency over99.7%.This work provides an idea for exploring the preparation and electrochemical analysis of other transition metal oxides and carbon composites.Secondly,metallic element and oxide co-modified carbon composites were explored.Ni-Ni O/N-C composite were prepared by extracting the element of Ni from Ni（NO₃）₂·6H₂O.Besides N-doping,metallic Ni⁰ is introduced into the composite in this work.The presence of Ni⁰ can promote the further decomposition of Li₂O,provide conductive medium for electron transfer in the transformation process,and effectively improve the reversibility of composite materials.The Ni-Ni O/N-C-4 composite with excellent structure and electrochemical properties was obtained by adjusting the content of Ni（NO₃）₂.At 0.1 A g^-1,the Ni-Ni O/N-C-4 composite showed the high capacity of 1316.7m Ah g^-1 after 120 cycles,which exceeds its theoretical capacity.Meanwhile,the electrode revealed the excellent performance of rate with the capacity of 441.5 m Ah g^-1 at 20 A g^-1.This work offers a way to improve the electrochemical performance of electrode materials with metallic element doping.The last,the oxide-containing vacancy modified carbon composites were explored.（NH₄）₆Mo₇O·4H₂O was selected to extract the element of Mo to prepare N-doped ultra-small Mo O₂ nanoparticles embedded carbon composites with oxygen vacancy（Mo O₂/N-C）.The oxygen vacancy is introduced into the composites at high temperature in this work.By establishing the built-in local electric field,the charge imbalance effect promotes the Li⁺insert/disinsert to improve the reaction kinetics,thus improving the electrochemical performance.By adjusting the carbonization temperature,Mo O₂/N-C-6composite has the best performance.At 0.1 A g^-1,the Mo O₂/N-C-6 composite obtains relatively excellent electrochemical performance with the capacity of 918.2 m Ah g^-1 after130 cycles.The capacity of the electrode was 562.1 m Ah g^-1 after 1000 cycles at 1.0 A g^-1,with a coulomb efficiency close to 99.9%.This collaborative strategy of designing 3D porous structures and introducing nitrogen and oxygen vacancy into the matrix provides a new idea for the research of transition metal oxides and carbon composites with satisfactory electrochemical performance.