| Currently,lithium ion batteries are attracting widespread interest and success in commercial electronics and electric vehicles due to their high energy density and reliable cycling performance.However,the low abundance and uneven distribution of lithium resources hinders its application to grid-scale electrochemical energy storage systems.Potassium has attracted particular attention due to its similar physicochemical properties to lithium and abundant reserves.And the exploration of potassium ion batteries has achieved groundbreaking technology and transformative advances.Carbon materials are widely studied for their low cost,good electrical conductivity,stable physical/chemical properties and environmental friendliness.However,the larger radius potassium ions suffer from sluggish diffusion kinetics during the embedding/de-embedding process,which causes structural distortions in the carbon material,resulting in rapidly decreasing energy density and power density.Coal pitch possesses a high carbon content and an easily tunable structure,which is considered to be a very economical and promising high-quality carbon precursor in the field of electrode materials.Based on this,this thesis uses coal pitch as a carbon precursor to prepare high performance anode materials.Through a simple and efficient synthesis route to optimize the microstructure of the carbon material.And build a relationship between structure and performance to explore potassium storage mechanisms.The main research content are as follows:（1）Regulating the microstructure of carbon materials for excellent electrochemical potassium storage.Direct preparation of structurally flexible and tunable coal pitch based soft carbon materials（SCs）using coal pitch as a carbon precursor by a high temperature solid phase method.By controlling the carbonization temperature not only can the crystallinity be regulated to alter the K+storage behaviour,but also the hindering effect of defects such as heteroatoms on the ordered lattice can be exploited to form turbo-layered structures with large layer spacing.SC-1100 is used for potassium ion battery anode materials which provide a reversible capacity of 119.5 m Ah g-1at a current density of 1.0 A g-1.（2）Reasonable construction of carbon hybrid structure for rapid and reversible potassium storage.Coal pitch was used as a carbon precursor,oxidized pitch carbon materials（OPCs）with nano-graphite domains and defects were prepared by a chemical oxidation method supplemented by a high temperature solid phase method.By controlling the time for chemical oxidation,a structural balance between ordered nano-graphite domains and disordered defects can be achieved.When OPC-6h is used as an anode material for potassium ion batteries,it provides a reversible capacity of219.6 m Ah g-1after 100 cycles at a current density of 0.05 A g-1.（3）Edge-oxidation-induced densification towards hybrid bulk carbon for high performance potassium storage.The hybrid bulk carbon is not only abundant in nano-graphite domains,which provide low potential potassium storage sites,but also possesses a well-developed defect network,which enhances K+diffusion kinetics.The hybrid carbon achieves a high reversible capacity at 1 V(248.8 m Ah g-1at 0.05 A g-1),a high ICE（68.2%）and a high rate(209.9 m Ah g-1at 1 A g-1).（4）Ball milling method for in-situ construction of composite carbon hybrid structures achieves low potential stable potassium storage.The high proportion of graphite in the composite carbon（G-HBC 7:3）provides high electrical conductivity,which enables fast electron transport.The hybrid carbon and oxygen-containing functional groups play a role in increasing the layer spacing,which improves the ion diffusion kinetics.The G-HBC 7:3 provides a reversible capacity of 305.5 m Ah g-1at a current density of 0.1 C when used in the anode of potassium ion batteries,and in particular a high reversible capacity of 213.9 m Ah g-1below 0.5 V.In this thesis,there are 83 figures,8 tables and 180 reference articles. |
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