Controllable Synsthesis And Electrochemical Performance Of Carbon Materials As Anode Materials For Potassium Ion Batteries

Potassium ion batteries（PIBs）are expected to be substitute devices for lithium ion batteries in the field of large-scale energy storage.Carbon materials are considered as good anode materials for PIBs due to their high chemical stability,good electrical conductivity,and other advantages.In this thesis,we chose the carbon anode materials as the research object,firstly studied the roles of crystal structure and N-doping strategies in achieving high capacity potassium storage,and on that basis developed a high capacity graphitic carbon anode material.The specific research contents are as follows:1. Two phenolic resin spheres with the same morphology are synthesized according to extensional St?ber method.The main difference between the two types of resin spheres prepared here is whether N-doped or not.After carbonization at different temperatures,two series of carbon spheres with different nitrogen contents and without N-doping are prepared.The electrochemical performance of two carbon spheres as anode materials for PIBs are detailed studied and compared.The results show that there is no obvious relationship between the storage capacity of potassium ions and nitrogen content,while the storage capacity of potassium ions increases as the（002）lateral size of the carbon materials（L_a）increases.Kinetic analysis reveals that N-doping changes the potassium storage mechanism though affecting the ion diffusion process,but the total capacity still depends on L_a.Therefore,we conclude that the crystal structure instead of N-doping mainly determines the storage capacity of potassium ions for carbon materials.NCS-600 with L_a of 8.32 nm exhibits better storage capacity of potassium ions and rate performance.It exhibits a reversible capacity of 241 m Ah g^-1 at 25 m A g^-1,and the specific capacity can still reach 121 m Ah g^-1 after 100 cycles at 100 m A g^-1.2. Based on the conclusion that the storage capacity of potassium ions increases as L_a increases in the previous chapter,we graphitize the commercial carbon molecular sieve（CMS）to make the crystal plane fully grows,and obtain a new graphitic carbon material（G-CMS）.The change of carbon structure and its effect on the potassium storage performance and mechanism are symmetrically studied.Comparatively,the potassium storage capacity of CMS increases from 208 m Ah g^-1 of CMS to 248 m Ah g^-1 at 25 m A g^-1.Although G-CMS has been graphitized,it still shows good cycle stability.After 650 cycles at 100 m A g^-1,a high specific capacity of 210 m Ah g^-1 is remained.Moreover,G-CMS shows good rate performance,giving a specific charge capacity of 191 m Ah g^-1 at 9 A g^-1.Kinetics analysis indicates that the potassium storage of G-CMS is mainly controlled by the diffusion process,while CMS is mainly controlled by the capacitive process.In-situ Raman spectroscopy is also used to verify the different potassium storage mechanisms of the two materials during the discharge process.And the phase transition of graphite intercalation compound can be observed in G-CMS,while the ion adsorption process dominates CMS.Due to the lower potassiation platform and higher capacity,the energy density in full cells with G-CMS as the anode increases by 14.7%compared that with CMS when using the same cathode material of PTCDA.