Research On Preparation And Potassium Storage Properties Of Graphene-based Metal Compound Nanomaterials

In recent years,due to the rapid development of society,people's demand for energy has gradually increased,and it has become increasingly impractical and uneconomical to rely solely on expensive lithium-ion batteries.Rechargeable potassium-ion batteries,which have many advantages,such as low cost,high energy density,long cycle stability,and fast charge/discharge functions,have received extensive attention in recent years.Nevertheless,the research is still in the development stage and faces some scientific and engineering problems.For example,during the charging/discharging process,frequent insertion and extraction of potassium ions with a radius of 0.138 nm can easily damage the commonly used electrode materials for lithium-ion batteries and sodium-ion batteries,which results in low battery capacity,reduced rate performance,and poor cycle stability.Another significant issue is that the active material is relatively heavy,resulting in a low mass specific capacity of the battery.Therefore,there is an urgent need to figure down the structural and electrochemical properties of different electrodes explored for potassium-ion batteries,and then design/develop electrochemically active electrical materials with structurally robust to manufacture fully functional potassium-ion batteries.In response to the above challenges faced by potassium ion batteries,this paper mainly includes the following aspects:(1)We developed a simple and universal nanoconfinement strategy,and successfully prepared ultra-small BiOX(X=Cl,Br,I)nanoparticles with an average size about 6 nm uniformly anchored on graphene nanosheets.This strategy regulates the ionization degree of oxygen-containing functional groups on the surface of graphene oxide nanosheets by changing the p H value of the graphene oxide aqueous dispersion.At an appropriate p H value,the weakly stacked graphene oxide nanosheets not only provide a nucleation site for the growth of bismuth oxyhalide nanoparticles,but also a interlayer confinement nano-space that can control the overgrowth of crystals.(2)On the basis of the above work,the graphene-based ultra-small BiOCl nanocomposite can be evaluated as free-standing anode for potassium-ion battery and exhibited outstanding reversible capacity of 521 m Ah·g^-1 at 0.05 A·g^-1,along with excellent rate capability(205 m Ah·g^-1 at 5 A·g^-1)and extraordinary cycling stability.More importantly,a fully reversible potassium storage mechanism of BiOCl(BiOCl(?)Bi(?)K₃Bi)induced by the ultrasmall size effect was revealed for the first time by the operando X-ray diffraction and ex-situ transmission electron microscope,leading to a much higher accessible theoretical capacity of 618 m Ah·g^-1 for ultrasmall BiOCl nanocrystal in comparison with large BiOCl nanoparticles(308 m Ah·g^-1).Experimental results proved that BiOCl has great potential in the field of electrochemical energy storage.(3)A flexible porous material composed of FeCoP hollow nanoparticles uniformly embedded in the framework of three-dimensional interconnected graphene(3DG)was successfully prepared via a novel spatially confined one-step thermal transformation strategy using the exquisite 3DG wrapped metal organic framework(MOF)nanoparticles as precursor.The obtained FeCoP@3DG composite was directly used as a free-standing anode for potassium-ion battery and exhibited excellent potassium storage capability.It provides an ultra-high reversible capacity of 386 m Ah·g^-1 at a current density of 0.05 A·g^-1,outstanding rate performance(121 m Ah·g^-1 at 3 A·g^-1)and excellent cycle stability.