Preparation And Properties Of Coal-Based Carbon Anodes For Sodium/Potassium Ion Batteries

The slather of traditional energy resources leads to the worsening ecological environment,developing renewable clean energy systems is of great significance.Based on the abundant reserves and low cost of sodium and potassium elements,sodium ion batteries?SIBs?and potassium ion batteries?PIBs?have attracted great attention for scale energy storage device.However,the larger ionic size of Na and K compared with Li results in slow ion diffusion rate and large volume expansion during the process of charging and discharging,leads to poor rate performance and cycle stability.As a result,designing and preparing high-performance,low-cost anodes for SIBs and PIBs become an urgent task.In this paper,coal-based carbon anodes were synthesized with middle-rank bituminous coal and coal-based mesocarbon microbeads?MCMBs?as precursor by oxidation,carbonization,solvent extraction and KOH activation.We investigate the method of building pore structure and microstructure of coal-based carbon materials,meanwhile the structure-function relationship between the structure of coal-based carbon materials and their electrochemical energy storage performance was revealed.?1?Study on preparation and electrochemical properties of coal-based anodes for SIBs.In this paper,we used middle-rank bituminous coal as precursor to prepare novel coal-based carbon materials with a hierarchical pore structure and large carbon layer spacing by oxidation and carbonization technology,removed highly aromatic small molecules by solvent extraction,meanwhile the porous skeleton of macromolecules with high heteroatomic content was retained.The hierarchical pore structure and large carbon layer spacing can alleviate the volume variation,shorten the charge diffusion distance and improve the ion diffusion rate.The electrochemical performance of the coal-based carbon anodes has been improved obviously,which exhibits excellent cycling stability(92%capacity retention after 7000 cycles at 2 A g^-1),highly specific capacity(334 mAh g^-1 at 0.1 A g^-1)and impressive rate capability(79 mAh g^-1 at 10 A g^-1).?2?Study on modified coal-based MCMBs for potassium ion batteries.We improved potassium storage performance by using graphitized MCMBs as precursor through KOH activation at temperatures such as 850,950 and 1050 ^oC.The KOH controlled activation technique introduced a certain amount of pore defects while the high graphitization of raw materials was retained,which can shorten the ion/charge diffusion distance,improve the ion diffusion rate,reduce the volume variation,and retain the high voltage plateau.As a result,the high-performance coal-based anodes exhibit high reversible plateau capacity of 272 mAh g^-1(396-124 mAh g^-1 at 0.15 V)and impressive rate capability of 414 mAh g^-1 at 50 mA g^-1.