Preparation And Electrochemical Properties Of Pitch-based Carbon Anode Materials For Potassium Ion Batteries

In recent years,potassium ion batteries have shown great potential in the field of large-scale electrical energy storage due to their abundant resource reserves.One of the key factors to determine its electrochemical performance lies in the creation of carbon anode materials for large radius potassium ion storage.China’s rich reserves of coal pitch,mainly composed of tricyclic and above polycyclic aromatic hydrocarbons and their derivatives,and its derived carbon materials have highly adjustable carbon crystallinity and carbon layer spacing,which makes coal pitch become one of the preferred raw materials for secondary battery cathode materials.However,the effect of pitch-based structure on the microstructure of its derivative carbon materials and the storage mechanism of potassium are rarely reported.If the structural characteristics of the polycyclic aromatic hydrocarbons molecules in coal pitch can be fully utilized to synthesize anode materials for storage and transport of large radius potassium ions from the bottom-up,and the storage and transport mechanism of potassium ions can be fully understood and revealed,it will open up a new way for the development of coal pitch in the field of potassium ion battery anode materials.On this basis,using quinoline rich in coal tar as structural unit,quinoline oligomers were synthesized by catalytic polymerization of Al Cl₃-catalyzed polymerization,and combined with heteroatomic sulfur doping and template method to construct high-performance potassium ion battery anode materials.Details of the research are as follows:（1）The fractions of toluene soluble（TS）,quinoline soluble（QS）and quinoline insoluble（QI）were obtained by solvent separation to explore the structural composition of the coal tar pitch components.In addition,these three fractions were carbonized separately to study the potassium storage properties.The TS sample has the lowest molecular weight and the worst thermal stability,with a weight loss rate of84.1%,and its carbonized products are mainly in the form of laminar structure with a layer spacing about 0.35 nm.QS sample has relatively large molecular weight,and the weight loss rate is 32.3%.Most of the carbonized products are stacked with lamellar layers,and the layer spacing is about 0.35 nm.QI sample has the largest molecular weight and excellent thermal stability,with a weight loss rate of only 11.2%.Its carbonized products are mainly spherical particles of different sizes,with a large carbon layer spacing of about 0.38 nm.The reversible capacities of TS,QS and QI carbonized products were 257,333 and 271 m Ah g^-1at 0.05 A g^-1,respectively.Furthermore,the cyclic properties of TS,QS and QI carbonized products were 12,70 and 97 m Ah g^-1at2 A g^-1 after charging and discharging 1000 times,respectively.（2）The sulfur-doped quinoline oligomers were synthesized by Al Cl₃-catalyzed polymerization of coal tar-rich quinoline as structural units,and the sulfur-doped quinoline oligomer soft carbon nanosheets were prepared by combining heteroatomic sulfur doping and template-interface induction strategies.The soft carbon nanosheets have a large carbon layer spacing（0.396 nm）with moderate defects and relatively ordered carbon layer structure,which can not only alleviate the volume expansion,but also help to enhance the diffusion rate of potassium ions and enhance the potassium storage capacity.When used as the anode material for potassium ion batteries,the reversible capacity can be as high as 456 m A h g^-1 at 0.05 A g^-1,and the cycle performance is 188.9 m A h g^-1 after 1000 cycles at 2 A g^-1,indicating excellent reversible capacity and cycle performance.