Research On The Application Of Organic Microporous Polymers And Silicon Nanoparticles In Lithium-ion Batteries

Rechargeable batteries have been widely applied in portable electronic equipment,instruments and electric vehicles.Among all kinds of secondary batteries,lithium-ion batteries(LIBs)have become the most promising candidateas high efficiency rechargeable batteries because of their high specific energy density,low self-discharge,long cycle life and excellent cycle performance.The energy crisis and environmental issues caused by the utilization of fossil fuels promote the exploitation of green and renewable energy systems.The popularization of various types of electronic products and the gradual elimination of fuel-powered vehicles make the LIBs-based electric-powered vehicles great opportunities.The electrode materials of LIBs play the key role since the properties of the electrode materials have a big influence on the electrochemical performance of LIBs.However,traditional anode materials are facing with some severe problems,such as low specific capacity and poor cycling stability.Therefore,it is highly desirable to develop novel anode materials with high capacity,high performance,high energy density and good safety.Microporous organic polymers(MOPs),as a kind of advanced porous materials,show great potentials in the areas such as catalysis,absorption and energy storage due to their high specific surface area,good physicochemical and thermal stability,low skeletondensity,insolubility in common organic solvents and synthetic diversity.Recent studies revealed that MOPs could be also applied as electrode materials for LIBs.One big advantage of MOPs is that the electrochemical performance of LIBs could be efficiently improved by controlling the polymer structure and electronic structure.As thus,MOPs have attracted much attention as electrode materials for LIBs.Owing to the high theoretical capacity(4200 mAh g-1),low working potential and abundance of Si in nature,Si has been considered as one of the most promising anode materials for LIBs.However,the huge volume change of Si-based electrodes during charging and discharging process limited its further application.Therefore,through modifying silicon materials to improve their electrochemical properties has become one of the key issues in this field.Provious studies have demonstrated that many strategies could be used to improve the electrochemical properties of Si-based LIBs,which mainly include reducing the particle size of Si,preparing Si-based composite,surface coating and synthesizing Si materials with special morphology.With this in mind,two types of microporous organic polymers with high specific surface area and one kind of Si nanoparticle were designed and synthesized in this dissertation.The physical properties of the materials and the electrochemical performance of LIBs from these materials as anode materials were comprehensively studied.The work of this dissertation mainly includes the following three parts:(1)A series of conjugated microporous polymers with high specific surface area was synthesized by Suzuki polymerization from 1,4-benzenediboronic acid with two kinds of nitrogen-containing monomers,respectively.The results showed that polymer SP-CMP6 exhibited the highest specific surface area of 1087 m2 g-1,and the gas adsorption results showed that SP-CMP6 had a maximum carbon dioxide adsorption capacity of 3.85 mmol g-1 with a methane adsorption amount of 1.24 mmolg-1 at 273 K/1.13 bar.All the polymers exhibited prominent electrochemical performance when they were applied as the anode material for LIBs.Among of them,SP-CMP6 showed the best performance with a specific capacity of 793 mAh g-1 after 150 cycles at a current density of 100 mAg-1.(2)Two kinds of hyper-crosslinked polymers with different morphologies were prepared by Friedel-Crafts alkylation reaction using 1,2-triphenylene and hexabenzobenzene as monomers.Among of them,HCP-1 showed the higher specific surface area of 661 m2 g-1 Both materials exhibited excellent electrochemical performance as the anode material for LIBs,while HCP-1 with porous morphology exhibited better electrochemical performance.After 200 cycles at a current density of 200 mAg-1 HCP-1 based LIBs could still retain a high capacity of 1050 mAh g-1.(3)Si nanoparticle with size between 200-300 nm was obtained from bulk silicon and hydrogen chloride gas reacted with copper-based catalyst on fixed-bed equipment.This reaction is the main production reaction of organic Si monomer in chemical industry.The obtained nano-Si particles exhibited excellent electrochemical performance as the anode material for LIBs,and the electrochemical performance was greatly improved compared with the raw material.The obtained Si nanoparticle could maintain a capacity of 636 mAh g-1 after 50 cycles at a current density of 50 mA g-1.