The Synthesis Of Porous Carbon And Its Nano-Composite For Application In High-Power Electrochemical Energy Storage

With the increasingly serious environmental problems and the crisis of non-renewable resources,developing new energy structure is a major strategic choice to improve the living environment and reduce the dependence on non-renewable resources.The clean energy sources are included of solar energy,wind energy,tidal energy,geothermal energy and nuclear fusion energy.However,due to the distributed dispersion,intermittent supply,and low efficiency of clean energy sources,efficient energy storage and conversion devices are urgently needed to achieve centralized,intelligent and efficient management and application.Electrochemical energy storage devices are one of the essential devices.Porous carbon materials have been widely used in electrochemical energy storage devices,such as lithium ion batteries（LIBs）and supercapacitors（SCs）,due to their stable structure,economic source and various types.Studies have shown that the specific surface area,pore size distribution,surface wettability,microscopic morphology,heteroatoms-doped and the combination with nanomaterials have a great influence on the electrochemical properties of porous carbon.At present,graphite is faced with the problems of low reversible capacity and poor rate performance as negative electrode materials for LIBs,which widely limited the application in large-scale energy storage equipment.In addition,activated carbon（AC）,as electrode material of SCs,has been commercialized.But the poor conductivity and semi-closed micropores with slow infiltrating of electrolyte,make AC difficult to efficiently charge and discharge.Therefore,there is a need to find new types of porous carbon and hybrid composites with low cost and high performance.Based on the above problems,this dissertation focuses on the application of porous carbon and graphene composites with TiO₂ in LIBs,modified by structure and composition to obtain high electrochemical performance.From the aspects of conductivity and the force between the electrolyte and surface of electrode material,porous carbon catalyzed by different transition metal ion for SCs is studied.The main research contents are as follows:To begin with,hybrid materials of inorganic（Magadiite）-organic（polyaniline,phytic acid/oxalic acid）can be formed by electrostatic force between Magadiite and aniline with a surface rich in silicon-hydroxyl（-OH）.With this hybrid material as the precursor,homogeneous and dispersed N and P co-modified ultra-thin two-dimensional porous carbon materials（NPHC）can be obtained by high-temperature heat treatment.Phytic acid is uniformly doped in polyaniline structure as an acid catalyst and surfactant and heteroatom surface functionalization due to its high stability at the high temperature.The NPHC,synthesized via a layered Magadiite surface-induced strategy,possesses dispersed ultra-thin layers（1.5-5 nm）,high specific surface area(457.9 m² g^-1),wide Pore size distribution（0.55-100 nm）and high heteroatom content.The structure is beneficial to increase the surface lithium storage active sites.When applied as an anode for Li-ion batteries,the NPHC delivers a superior rate capability of 146.6 mAh g^-1 at 8000 mA g^-1 and cycle performance with the retention of 83%after 1000 cycles at 2000 mA g^-1.Secondly,a novel strategy is reported for the nanographitic domains（sp²carbon）distributed in porous carbon（NCF（M））via transition metal acetate(Fe²⁺,Co²⁺,Ni²⁺,Fe³⁺)assistance and in situ N-doping during the KOH activation process with glucose and pyrrole as C and N sources,respectively.Compared to NCF（M）,NCF（Fe）exhibits a higher degree of graphitization,pyrrole-N,specific surface area(2630 m² g^-1)and a broad pore size distribution.The Fe（OH）_x（CO₃）_0.5（2-x）nanoparticles（NPs）formed by Fe²⁺can effectively catalyze the surrounding sp³amorphous carbon to sp² graphitized carbon at the high temperature.The graphitization process,along with reduction reaction of Fe NPs to produce CO₂,physically activate porous carbon,further increase specific surface area and broaden pore size distribution.Thanks to the above advantages,NCF（Fe）,as a three-electrode material in 6 M KOH,even at 10 A·g^-1,the reversible capacity could also reach 200.5 F·g^-1.In a two-electrode system（1 M TEABF₄/AN）,a symmetric supercapacitor composed of NCF（Fe）can achieve energy density of 25.9 Wh·kg^-1.Even at a power density of 6.26 kW·kg^-1,the high energy density of 21.4 Wh·kg^-1can be achieved.Finally,mesoporous graphene oxide-based TiO₂ composites（TiO₂（B）@GO）are synthesized by one-step reflux self-assembly.And they can be further converted into mesoporous reduced graphene based multiple TiO₂（anatase/bronze）heterogeneous compounds（TiO₂（AB）@rGO）through 350°C heat treatment.This temperature treatment can not only reduce GO,but also make the composite rich in heterogeneous interfaces.The TiO₂（AB）@rGO exhibits sheet-like structure constructed of small size（¹0 nm）nanocrystalline connecting with graphene by Ti-O-C bond.Enriching of the interface,porous structure and graphene conductive network can help improve the electronic conductivity and ion diffusion of the composites.Consequently,the TiO₂（AB）@rGO displays excellent rate capacity(103.2 mAh·g^-1 at 7.08 C)and cycling stability over 1000 cycles at 3.54 C rate with90%capacity retention.Detailed kinetic analysis confirm that the electrochemical redox reaction is mainly determined by surface capacitance behavior.