First-principles Study On The Adsorption Behavior Of Li₂S_x On The Transition Metal Nb And Zr Doped TiN?001? Surface

The estimated value of the energy density of the lithium-sulfur battery is2600Wh·kg^-1,and the highest specific capacity is 1675mAh·g^-1.The raw materials containing S have little pollution to the environment and the acquisition cost is not high,which makes the"lithium-sulfur battery"a very potential energy storage system for development.However,the problems in the lithium-sulfur battery,such as the safety problem of the metal negative electrode,the volume expansion problem of the lithium-sulfur battery,the shuttle effect,and the poor conductivity of the active material S and the discharge product result in a relatively low utilization rate,which prevents the"lithium-sulfur battery"from further Commercial development.The method currently concerned by researchers is to change the material of the separator,and this method is more likely to succeed.The transition metal nitride TiN is selected as the anchoring material for Li₂S_x,and the first-principle method is used to calculate the four positions of lithium polysulfide Li₂S_x?x=1-8?on the surface of TiN?001?:N atom top position,Ti Atomic top position,N-Ti bridge position,N-Ti core position stable adsorption configuration,adsorption energy,charge transfer?Bader?and partial wave state density?PDOS?,etc.The results show that the TiN?001?surface has a strong adsorption effect on the short-chain lithium polysulfide Li₂S_x?x=1-4??maximum adsorption energy 2.739eV?,which can effectively suppress the dissolution of lithium polysulfide during discharge,Less active material is lost in the electrolyte in the area of the positive and negative electrodes,and it will not prevent the electrochemical reaction from continuing due to excessive adsorption.Calculations have shown that TiN has a higher adsorption energy for long-chain lithium polysulfide Li₂S_x?x=5-8??maximum adsorption energy 3.957eV?,which not only has a limited adsorption effect on lithium polysulfide.At the same time,TiN?001?surface has a certain catalytic effect on the decomposition of long-chain lithium polysulfide Li₂S_x?x=5-8?.The long-chain lithium polysulfide Li₂S₇ at the OT-N adsorption position on the TiN?001?surface is decomposed into short-chain lithium polysulfide Li₂S₄,which reduces the loss of active substances Li and S while suppressing the shuttle effect.In order to improve the adsorption and dissociation of lithium polysulfide on the TiN surface,the surface modification was carried out.The bare Ti atoms in the TiN?001?surface were selected to replace and dope Nb atoms and Zr atoms,respectively,to obtain a stable doped surface structure.The adsorption evolution structure and energy of lithium polysulfide at four positions?OT-N,OT-Ti,BR_N-Ti,HL_N-Ti?on the surface of doped TiN?001?were calculated and analyzed.The results show that the energy of the short-chain lithium polysulfide is TiN_pure<TiN_Nb<TiN_Zr.For long-chain lithium polysulfide,the adsorption energy of doped TiN to adsorb lithium polysulfide is slightly stronger than that of pure TiN,and the stable evolution of adsorption shows a stronger catalytic dissociation effect than pure TiN to long-chain lithium polysulfide.At the BR adsorption site on the Zr-doped TiN?001?surface,the long-chain lithium polysulfide Li₂S₇is completely decomposed into the short-chain lithium polysulfide Li₂S₄.The doping of Nb atoms and Zr atoms improves the binding strength and catalytic performance of TiN to lithium polysulfide.