Preparation And Electrochemical Properties Of N-doped Porous Carbon And The Composites

As a predominant power source for portable electronic devices and electric vehicles,lithium-ion batteries(LIBs)have gained increasing popularity because of their high energy density and environmental benignity.Commercial LIBs are usually based on graphite anode,which cannot meet the increasing demand for LIBs with high power due to the limited theoretical capacity of graphite(372 mAh/g).To further increase the capacity of lithium-ion battery,variety of anode materials are committed.The development of high-capacity anode materials is generally divided into two approaches.One is the development of various nanomaterials,high specific surface area carbon materials such as carbon nanotubes,graphene,porous carbon materials and carbon nanospheres.Among them,porous carbon materials have attracted much attention because of their high specific surface area and controllable pore structure,which can provide fast mass transfer.The other one is looking for new types of anode materials,such as metal oxides,silicon-based anode materials.Among them,the nanostructured ZnO has attracted much intensive exploration due to its high theoretical capacity(978 mAh/g),high Li ion diffusion coefficient,and nontoxicity.In this paper,nitrogen-doped porous carbon(N-PC)was prepared by a template method where the silica as the template,dicyandiamide as the nitrogen source and phenolic resin as a carbon source.The N-PC has a three-dimensionally ordered interconnected macroporous structure(? 290 nm),which can effectively enhance mass transfer.There are small mesoporous structure on the wall of macropore,which can enhance the electrochemistry performance by providing a high specific surface area and increasing the active site of embedding lithium ion.The nitrogen element in carbon can increase the conductivity,capacity of lithium storage and transmission rate of carbon,which can improve its electrochemical performance.In the lithium-ion battery,N-PC shows reversible capacity of 394 mAh/g after 100 cycles at a current density of 100 mA/g,showing good capacity and cycle stability.Compared with commercial graphite anode materials,N-PC has a higher capacity,however,it still cannot meet needs for high capacity lithium-ion batteries.Therefore,the ZnO/N-doped porous carbon composite is prepared by sol-gel method.The distribution of ZnO particle in nitrogen-doped porous carbon can be controlled by the dropping rate of potassium hydroxide solution during the reaction process.The content of ZnO can be controlled by the quantity of zinc acetate.The formation mechanism and electrochemical reaction process are studied by the morphology and structure characterization.It can be seen from a series of characterizations that the prepared composite with a 30 wt.% content has the most excellent electrochemical performance,which has a capacity of 942 mAh/g after 250 cycles at a current density of 0.1 C.This high performance of reversible capacity and good cycle stability show a good prospects for the development of lithium-ion batteries.