Structure Control And Energy Storade Performance Of Coal-based Needle Coke

With the rapid development of society,the consumption of large-scale energy storage devices has greatly increased.Due to the shortcomings of lithium-ion batteries such as limited lithium reserves and rising prices,it is necessary to find new alternative energy storage technologies.As a promising alternative technology,potassium ion batteries with abundant reserves and high voltage and energy density have attracted widespread attention.In this thesis,coal-based needle coke is used as the anode material of potassium ion battery.After its acid cleaning and purification,the electrolyte configuration of the anode material of potassium ion half-cell is explored.In the ether electrolyte solvent DME,the rate performance of the needle coke anode and the cycle performance is poor.However,the reversible capacity is 275 mAh g-1 at 0.05 A g-1 in 0.5 MKPF6-EC/DEC electrolyte,and the capacity is 115 mAh g-1 after 500 cycles of 0.5 A g-1,the capacity retention rate is 77%.Needle coke anode has the best potassium storage performance at low current in low-concentration KPF6 salt electrolyte,high concentration has better performance at large current,while the high concentration of KFSI electrolyte salt under high current,needle coke has reflects relatively good performance as negative electrode,and the concentration has little effect on the performance at a small current density.Using KMnO4 and KOH to heat-treat needle coke to activate pores.By controlling the mass ratio and type of activator,the results show that the typical etchant KOH has no obvious effect on needle coke-based soft carbon materials,while KMnO4 can affect needle coke.The coke has a good hole-making effect.The layer spacing increased from about 0.345nm to about 0.350nm,and a layered structure with mesopores and macropores coexisting was formed,and the specific surface area reached 6.6 m2 g-1.When the mass ratio of KMnO4 to needle coke reaches 4,the potassium storage performance of the activated negative electrode material is improved most obviously,the first lap coulombic efficiency reaches.51.6%,and the reversible capacity reaches 74 mAh g-1 at 2 A g-1.After 500 cycles at 0.5 A g-1,it still has a reversible capacity of 139 mAh g-1.The innovative method of "expansion+doping" is used to adjust the needle coke layer spacing and doping atoms,and the improved Hummer method is used to oxidize the needle coke.Needle coke is thermally reduced and oxidized at temperature,and nitrogen and phosphorus sources are introduced at the same time,so that nitrogen and phosphorus atoms are incorporated into the carbon structure.The needle coke layer distance obtained by the method of "expansion+doping" reaches about 0.368nm,and the specific surface area reaches 21.2 m2 g-1.By controlling the temperature of the oxidized needle coke,the needle coke obtained by reduction at 500℃exhibits excellent rate performance and still has a reversible capacity of 87 mAh g-1 at 5 A g-1.At the same time,it is reduced at 900℃.The capacity retention rate of the needle coke is as high as 96%after being circulated 500 cycles at 1 A g-1,showing excellent cycle performance.