Efficient Preparation And Microstructure Control Of Graphene-Based Materials For Energy Storage Applications

Due to their two-dimensional characteristics,single-atom-layer thickness,exceptional electrical,thermal,mechanical,and optical properties,and flexible structural tunability,graphene-based materials possess unique advantages for utilization as electrochemical interfaces in constructing high-energy electrochemical energy storage devices.However,graphene’s potential remains far from fully realized,owing to limited control over surface properties,microstructure,and assembly,as well as an insufficient understanding of the structure-performance relationship in electrochemical energy storage.To address these challenges,directed design and precise control of graphene-based materials at each stage,from preparation and assembly to application,are crucial for achieving high-performance energy storage.In this context,the present dissertation concentrates on three aspects:efficient and controllable preparation of graphene oxide,precise tailoring of graphene’s surface pore structure,and optimization of Li nucleation and early growth via a periodic mesoporous interface,as discussed in detail below:Firstly,the traditional Hummers method,currently employed in batch-style preparation in kettle reactors,suffers from low reaction efficiency,nonuniform product quality,and safety concerns.This work proposes a microfluidic strategy for preparing graphite oxide.By using a microchannel reactor,the oxidation reaction time is reduced to 1.2-4.0 minutes,while the resultant graphene oxide exhibits a higher oxidation degree and an increased number of epoxy groups.Adjusting the microchannel configuration,retention time,and flow rate provides the opportunity to precisely control the oxidation degree,oxygen-containing functional groups,and lateral size of graphene oxide,with a tunable C/O ratio of 1.80-2.89.Notably,in-situ Raman spectroscopy has been employed to monitor the time-evolution of G bands during graphite oxidation,enabling the dynamic identification of oxidation percentage and kinetic parameters.Based on this,the effects of flow rate,lateral size,and oxygen content of raw graphite have been quantitatively compared with corresponding reaction rate constants.Furthermore,the continuous-flow preparation of graphene is demonstrated through the assembly and reduction of graphene oxide in microchannels.Secondly,top-down and bottom-up approaches have been developed to tailor the in-plane pores of graphene-based materials.Utilizing the top-down strategy,nickel metal nanoparticles with controllable size and areal density are introduced into the interlamellar space of graphene and employed as etchers to create in-plane throughholes,leveraging their high carbon solubility.By adjusting the growth kinetics of nickel nanoparticles,the resulting pore distribution can be effectively controlled within a range of 10-40 nm.In the bottom-up approach,iron oleate complexes are uniformly introduced into the interlayer space of graphene oxide,which subsequently transform into self-growing metal oxide templates covered with surface carbon layers on the substrate graphene during calcination.Consequently,an ordered carbon structure,comprising graphene decorated with in-plane mesoporous grids,is obtained.By further controlling the crystallinity and growth kinetics of template particles or introducing doping post-treatment,mesoporous grids can be precisely tailored with sizes ranging from 10 to 17 nm,pore shapes varying from round to square,and adjustable chemical components.Notably,these two methods provide straightforward solutions for the directional design of in-plane structures in graphene-based materials.Lastly,the finely-controllable ordered carbon decorated with open periodic mesoporous grids can serve as an ideal model material to elucidate the effects of interfacial architecture on electrochemical properties.When the size of the mesoporous grid approaches the thermodynamic critical size of lithium nuclei under classical nucleation theory,nucleation and early growth of lithium metal on ordered mesoporous graphene substrates transition to a uniform,dense,full-coverage mode,as opposed to the typical spherical crown-like lithium nuclei observed on flat graphene substrates.The favorable deposition morphology is attributed to the highly curved carbon layer and the inorganic-rich solid electrolyte interphase(SEI).More interestingly,layer-bylayer deposition is observed on ordered mesoporous graphene,which resembles the’Frank-van der Merwe’ mode.By reducing the size of mesoporous grids to 10 nm,the obtained Li metal anode exhibits favorable cycling stability of over 1100 cycles at 2 mA cm-2 and 1 mAh cm-2 in a symmetric cell.When paired with a lithium iron phosphate cathode,the assembled full cell demonstrates a capacity stability of over 200 cycles with a retention of 93%and a capacity of 116 mAh g-1 at 5 C.The unique nucleation and early growth of lithium in restricted constructs,as revealed in this study,offers a new strategy for constructing high-performance lithium metal anodes.