Construction And Potassium Storage Properties Of Pitch-based Carbon Microspheres Anodes

The clear vision of“dual carbon”aims to accelerate the energy transformation from high carbon to low carbon or even zero carbon.As one of the“post-lithium-ion batteries”,potassium ion batteries（PIBs）have great potential in the field of large-scale energy storage because of its abundant resource reserves.One of the key factors determining its electrochemical performance is to create carbon anode materials for large radius potassium ion storage.China’s coking industry is huge.As the main by-product of coking industry,coal tar pitch（CTP）is a heavy component after distillation of high temperature coal tar.Current CTP deep processing technology is relatively backward,low value-added products,resulting in serious waste of resources and ecological damage.On the other hand,CTP is mainly composed of three or more polycyclic aromatic hydrocarbons and their derivatives,and its derived carbon materials have highly tunable carbon crystallinity and carbon layer spacing,which makes coal tar pitch one of the preferred raw materials for secondary battery anode materials.In this paper,CTP was used as raw material,based on physical and chemical methods,the chemical composition and molecular structure of raw materials were designed and controlled.Combined with emulsification,oxidation and heteroatom doping technology,a new type of pitch-based carbon microspheres anode material with controllable structure and composition was developed.Details are as follows:（1）Without template,oxidized pitch-based microspheres are successfully obtained by coordinated pre-oxidation and emulsification method with coal tar pitch as the precursor,assisted by surfactant and dispersion medium.The influence of emulsification temperature on the morphology of microspheres is explored,and 280°C is determined as the optimal emulsifying temperature.The prepared pitch-based carbon microspheres present better electrochemical performance:The O-CMs-750 possess initial discharge capacity of 310 m A h g^-1 at 0.05 A g^-1,and 102 m A h g^-1 at 2 A g^-1,and the discharge capacity of 230 m A h g^-1 still achieves as the current density recovers to0.05 A g^-1.Importantly,long-term cyclability remains 108 m A h g^-1 after 1000 cycles at 1 A g^-1.Its excellent potassium storage performance is due to the fact that the cross-linking structure formed by low-temperature pre-oxidation can realize the structural evolution from order to disorder.Moreover,the introduction of oxygen-containing groups not only makes the precursor molecules cross-linked at the spatial level,ensuring the structural stability during electrochemical de-/intercalation,but produces abundant vacancies and defects,and thereby increasing potassium storage sites.（2）The oxidized pitch-based carbon microspheres and sodium hypophosphite with mass ratio of 1/10 are co-carbonized to prepare P/O co-doped pitch-based carbon microspheres.In situ generated PH₃ not only etched the surface of microspheres,resulting in a large number of defects,but act as phosphorus source,evenly doped in the material,doped P content up to 4.0 at.%.P/O-CMs shows excellent potassium storage capacity when used as anode materials for potassium ion batteries,i.e.The anode delivers considerable discharge capacity of 352 m A h g^-1 at 0.05 A g^-1,impressive rate capacity of 114 m A h g^-1 at 5 A g^-1,and long lifespan of 181 m A h g^-1 at 1 A g^-1after 1000 cycles,with a capacity retention of 86.2%.In addition,P/O-CMs//KPB presents high specific discharge capacity of 154 m A h g^-1 at 0.05 A g^-1,and the reversible capacity of 22 m A h g^-1 is still maintained at 2 A g^-1.The full cell can maintain82 m A h g^-1 after 100 cycles at 0.1 A g^-1.