Modification Of Graphite Anode Materials For Potassium Ion Batteries

Aiming to solve large-scale intermit energy storage problem.electrochemical energy storage is the most promising one with low-cost and easy scale-up have attracted lots of attentions.The working principle potassium ion batteries with the same rocking-chair characterization as that of lithium ion batteries,a theoretical capacity of 279 mAhg-1 via forming KC8 and more abundant resources has attracted the much attention.However,the difficulties derived from larger K+have to be crossed.The potassium ion batteries graphite anodes would undergo dramatic volume expansion during forming KC8 from graphite by～61%resulting to the poor cycling performance.So the necessary protective measures must be taken for the electrode material.In response to the above situation,two Material modification methods,the Al2O3 film deposited by atomic layer deposition technique was used to coat the surface of graphite and obtained expanded graphite at different temperatures,were using to achieve performance optimization of potassium ion battery in this thesis.The paper mainly includes the following research contents:(1)Al2O3-atomic layer deposition process(ALD)was adopted to the surface modification of graphite.Electrochemical analysis shows that Al2O3-ALD araphite has an obvious improved cycling stability of 223 mAh/g at 50 mAg-1 after 50 cycles comparing to raw graphite anode of 92 mAh/g,improving 2.26 times.Ex-situ XRD.TEM and SEM characterizations combined with electrochemical analysis revealed that ultrathin Al2O3 coating is useful to form stable solid electrolyte interface film to buffer volume change and enhance performance of graphite anode in PIBs.(2)The flake graphite was expanded at different temperatures.properties of which were compared and studied.In comparison,the graphite materials after expansion at 800℃ shows a first charge and discharge specific capacity of 210.3 mAh/g and 476.9 mAh/g at a current density of 50 mA/g.Besides the first coulombic efficiency is 44%.After 50 cycles of electrochemical cycling,the reversible specific capacity of 120.6 mAh/g can still be maintained.Compared with the expanded graphite treated at 400℃ and 600℃,the potassium storage capacity is greatly improved.