CVD Design Of Carbonaceous Materials For Potassium Battery And Study On Their Performance

Carbonaceous materials dominated by sp2 hybridization have the advantages of good electrical conductivity and environmental friendliness,which play an important role in potassium batteries.In potassium-ion batteries,larger K+ radius leads to sluggish reaction kinetics and higher irreversibility.Nitrogen-doped carbon anode material can enhance K+storage performance by virtue of its enhanced adsorption ability.As for potassium metal batteries,in consideration of the fact that potassium metal cannot be deposited uniformly and orderly on traditional substrates,carbonaceous materials can be used as modified materials to regulate electrode interface reactions to manage the nucleation-growth behavior of potassium metal.Despite the multifarious virtues carbonaceous materials hold,there still exists many problems in the domain of rational design,precise preparation and efficient modification of carbon materials.The prevailing fabrication method is plagued by the fact that considerable variations in the total N-doping concentration occur in the course of regulating the type of nitrogen dopants,incapable of distinguishing the certain roles of them under similar conditions.In addition,the introduction strategy of carbon-modified materials also faces bottlenecks such as large material dose,uneven modification,and low bonding strength.In view of the above problems,this thesis realized the rational design and precise preparation of nitrogen-doped carbon by means of chemical vapor deposition(CVD)technology.Simultaneously,an efficient modification strategy for potassium metal deposition substrates using olefinic carbon materials was also developed.(1)The precise preparation of high edge-N doped carbon(HENC)and high graphitic-N doped carbon(HGNC)was achieved by CVD technology.XPS characterization results show that HENC and HGNC harness basically identical N-doping levels(5.78 at%for HENC;5.07 at%for HGNC).Throughout roll-to-roll CVD setup,commercial Al foils are decorated with ultrathin graphene modified layer(Al@G)harnessing strong adhesion(10.52 N m-1)and high surface energy(66.6 mJ m-2).(2)Using electrochemical test methods such as galvanostatic charge-discharge,cyclic voltammetry scanning and galvanostatic intermittent titration,combined with DFT theoretical calculations,the specific roles of different nitrogen doping configurations in potassium ion storage were decoupled.Edge-N species possess enhanced ion adsorption owing to its advanced binding energy for K+,contributing to enhanced capacity,fast reaction kinetics and elongated cyclic life-span.However,such merits are compromised by the higher capacity implemented mostly at the high voltage(vs.K+/K)range,which in fact weakens the application potential of HENC as a practical high-energy PIB anode.With respect to graphitic-N,it equips carbon network with higher conductivity but harvests weaker adsorption of K+,even inferior to that of bare graphitic carbons.Meanwhile,the potassium storage mechanism of nitrogen-doped carbon was traced by in-situ Raman,ex-situ XRD and ex-situ XPS.This work offers a feasible avenue to identify the specific effects of nitrogen dopants toward the rational design of high-performance carbonaceous anodes.(3)The electrochemical performance of Al@G under various operating conditions is evaluated in detail.Al@G manages to maintain an elongated lifespan up to 1000 h at 0.5 mA cm-2 with 99%CE,and even sustains stable cycling for 750 h under periodic current fluctuations of 0.1 to 2 mA cm-2.Furthermore,guided by the thin film growth model,the melt wettability and electrochemical wettability of Al@G to potassium metal were tested,and the structure-activity relationship between the substrate surface energy and potassium metal affinity was obtained:higher surface energy conferred better potassium metal affinity of the substrate.Meanwhile,the evolution of SEI composition during potassium metal plating/stripping was revealed by XPS.Finally,Al@G was paired with pre-potassiated FeS2 to study its performance in the harsh application scenario in anode-free potassium metal battery.