The First-principles Study Of Metal-doped Hexagonal Boron Nitride In Lithium-sulfur Batteries

As mobile phones,electric vehicles and other electronic devices are increasingly widely used in daily life,energy storage is becoming the most promising research direction.At present,commercial lithium ion batteries are the most widely used and successful energy storage technology,but the inherent theoretical capacity hinders further development.Therefore,it is imperative to develop new energy storage technologies.Lithium-sulfur batteries are seen as the one of the most promising energy batteries to replace lithium ion batteries due to the theoretical capacity(1675m Ah g-1).However,the shuttle effect of lithium polysulfides(Li PSs)and slow reaction kinetics lead to the reduction of their cycle life.To address these problems,researchers constructed cathedo/separator modification materials with excellent anchoring and catalytic properties to improve battery performance.In this paper,the first-principles study was used to construct the structures of single/dual-atom catalysts by doping 3d transition metal into hexagonal boron nitride(h-BN).The anchoring and catalytic effect of single/dual-atom catalysts on Li PSs was analyzed,and its internal mechanism was further researched.The main contents are as follows:(1)TM-BN was constructed by replacing B atoms in h-BN with 3d transition metal atoms(TM = Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn).Compared with pure h-BN,TMBN exhibits the better anchoring properties for Li PSs,especially the anchoring effect of Ti-BN,V-BN and Cr-BN structures are the best.Bader charge analysis,states of density,charge density difference and other electronic structure information was adopted to prove that the strength of S-TM bond increases as the d-band center of TMBN gets closer to the Fermi level,while the bond strength of Li-N bond decreases gradually.Obviously,there is a trade-off effect between the S-TM bond and Li-N bond,which affects the anchoring effect of TM-BN.The implicit solvation model simulated by VASP-sol module was used to evaluates the solvent effect,which has little influence on the anchor energy of Ti-BN,V-BN and Cr-BN.The method of climbing-image nudged elastic band shows that TM atom can activate Li2 S molecule and thus reduce its dissociation energy barrier,and the dissociation energy barrier decreases with increasing activity of TM atom.The anchoring and catalytic properties of Ti-BN indicate that Ti-BN has great potential for lithium-sulfur batteries application.(2)The dual-atom catalyst of Ti TM(BN-C)was constructed by doping two 3d transition metals(TM = Ti,Fe,Co,Ni,Cu,Zn)atoms into h-BN substrate and modifing C atoms on its plane edge to enhance its electronic conductivity.The anchor effect of Ti Cu(BN-C)for Li PSs was researched and compared with TM-BN,the results show Ti Cu(BN-C)showed better anchoring strength.The van der Waals force contributed more significantly to weakly polar molecules for different Li PSs.Moreover,the results of implicit solvent model show that Ti Cu(BN-C)in the electrolyte could still anchor Li PSs effectively in the electrolyte and inhibit its shuttle effect.The catalytic performance of Ti Cu(BN-C)was analysed and shows that the decomposition energy barrier of Li2 S and thermodynamic reaction energy barrier on the Ti Cu(BN-C)surface was lower than TM-BN.In conclusion,the application of dual-atom catalysts(Ti Cu(BN-C))in lithium-sulfur batteries is expected to show more excellent anchoring and catalysis effect and has great potential to improve battery performance.