Surface Modification Of 3d Matrix For Preparation And Electrochemical Performance Study Of Lithium Metal Anode

Due to its low density,the lowest redox potential and the highest specific capacity,lithium metal becomes an idea anode for the next-generation lithium batteries.However,severe safety issues and bad cycling performance always restrict its practical application.One aspect,lithium dendrites can penetrate through the separator to cause the short circuit of batteries,thus creating security risks.On the other aspect,lithium dendrites can easily detach from two-dimensional elelctrode,and lost electrical connection with current collectors because of insulation of solid electrolyte interface(SEI)film,which forms large amount of “dead Li”,leading to capacity loss of batteries.Through surface modification of 3D matrix,this paper can decrease the lithium nucleation overpotential,relieve infinite volume expansion,increase the binding energy between lithium and matrix,enhance the lithium distribution uniformity,suppress the growth of lithium dendrites,thus improving the electrical performance of lithium metal anode.Meanwhile,the related lithiophilic mechanism for matrix and the mechanism of reflowing modification are also discussed and studied.Through hydrothermal method and high-temperature carbonization to prepare nitrogen-doped graphene aerogels(NGA),which is coated on the surface of 2D copper foil to construct 3D NGA lithophilic matrix.The 3D structure of NGA can increase the specific surface areas of electrode,and decrease the effective current density of electrode;Nitrogen doping can enhance the binding energy between matrix and lithium,thus guiding lithium to nucleate and grow on the matrix.Porous structure of NGA could provide storage spaces for lithium,and alleviate problems of the “hostless” problems and “infinite volume change” during the processes of lithium plating/stripping.Therefore,3D NGA lithophilic matrix could suppress the growth of lithium dendrites,and improve the electrochemical performance of lithium metal anode.Through one-step hydrothermal method,3D nitrogen-doped graphene/nickel foam(NGNF)lithiophilic matrix was prepared by lithiophilic nitrogen-doped graphene coating on the scaffold of nickel foam with poor lithiophilicity.Relative physical characterization and electrochemical analysis confirm 3D structure and lithiophilic modification could decrease the lithium nucleation overpotential on the matrix,inhibit lithium dendrites growth to some extent,and guide lithium metal to nucleate and grow on the matrix uniformly.No matter used in half cells or full cells,3D NGNF shows excellent electrochemical performance.Combined with density function theory,pyridinic N,pyrrolic N,and pyridine-N oxides of nitrogen doping for graphene own strong binding energy,which are helpful for free-state lithium to nucleate at N sites,thus guiding lithium to uniformly deposite on the 3D matrix.Lithium was electrodeposited on the lithiophilic matrix,then it was treated by reflowing modification because of low melting point of lithium.The lithiophilic modification of matrix is helpful to improve the distribution uniformity of electrodeposited lithium;Thermal motion of Li atoms increases greatly under high temperature,so reflowing treatment could destroy crystal faces of electrodeposited lithium.Through physical characterization and electrochemical analysis,this method can enhance uniform distribution of lithium on the electrode,improve surface roughness of electrode,suppress lithium dendrites,and improve the electrochemical performance of batteries.First-principles molecular dynamics simulations confirmed that crystal faces easy to grow lithium dendrites have been destroyed after reflowing modification,which would generate new nuclei due to lack of crystal growth faces,thus inhibiting the growth of lithium dendrites.Slight oxidation of copper foam(SOCF)matrix was used to adsorb molten lithium to prepare 3D composite lithium metal anode.The surface of 3D copper foam was oxidized into Cu O in air,which adsorbs molten lithium to prepare 3D composite lithium metal anode through reaction of Cu O with Li to form Li2 Cu O2.In consideration of low specific capacity of present cathode materials of lithium-ion batteries,it is hard to match with the high specific capacity of lithium metal anode.Therefore,highperformance sulfur cathode with bi-confinement effect of polysulfide was prepared,and used to assemble high-performance lithium-sulfur batteries matched with 3D composite lithium metal anode.Under 0.2 C,0.5 C,1 C,2 C,and 5 C rate,the r GO@S/NCP/CNTs-Li/SOCF batteries could show an average discharge specific capacity of 1081.7,813.7,702.2,612.7,and 471.9 m Ah g-1,respectively,which are much better than those of batteries using 2D lithium foil anode.