Design Of Doping Structure For Li₇P₃S₁₁solid-state Electrolyte Based On First-principles Calculations

Li₇P₃S₁₁,as a promising superionic conductor among sulfide-based solid electrolytes,has attracted wide publicity due to its advantages of excellent safety and considerable electrochemical properties.However,its ionic conductivity is still far from meeting the requirements and needs to be further improved.Ionic doping is an effective strategy to improve conductivity of materials.But random and uncertainty in the selection of doping cation still exist in experiment.Therefore,in order to design Li₇P₃S₁₁-based solid electrolytes with excellent properties,first-principles calculations were employed to systematically study the mechanism of ionic doping of Li₇P₃S₁₁ at the atomic and electronic scale in this paper.Moreover,it will provide important theoretical guidance to design a new generation of all-solid-state batteries.The specific content is as follows:（1）The effect of oxygen doping on the crystal structure of Li₇P₃S₁₁ has been studied.First,multi-concentration doping model of Li₇P₃S_11-xO_x（x=0.25、0.50、0.75 and 1）was constructed.The formation energies under different growth conditions are calculated.The results indicate that the doped structure with the best structural stability can be obtained as Li₂O₂ is picked to be the raw material for introducing oxygen in Li₇P₃S₁₁.Then,the quantitative relationship between energy barriers and band gaps of Li₇P₃S_11-xO_x（x=0、0.25、0.50、0.75 and 1）was analyzed to select the most desirable structure are simulated by performing AIMD approach.It is confirmed that Li₇P₃S_10.25O_0.75 has higher ionic conductivity(109 m S cm^-1)than Li₇P₃S₁₁(50 m S cm^-1).Moreover,the presence of Li vacancies is unlikely to alter the essence of inherent superionic conductor of Li_7-xP₃S_10.25O_0.75.Furthermore,Li₇P₃S_10.25O_0.75 still maintain good electrochemical stability and thermal stability.（2）The effect of selenium doping on the crystal structure of Li₇P₃S₁₁ has been studied.The formation energies of Li₇P₃S_11-xSe_x（x=0、0.25、0.50、0.75 and 1）under different growth conditions are analyzed and calculated,and it is found that the doped structure with the best structural stability can be synthesized under selenium-rich condition.Then we calculated the energy barriers and band gaps of Li₇P₃S_11-xSe_x（x=0.25、0.50、0.75 and 1）to select the most desirable structure(Li₇P₃S_10.25Se_0.75).The ionic conductivity of Li₇P₃S_10.25Se_0.75 was simulated to be 81 m S cm^-1 by performing AIMDapproach,which is higher than that of Li₇P₃S₁₁.Meanwhile,it is found that the presence of Li vacancies is unlikely to alter the essence of inherent superionic conductor of Li_7-xP₃S_10.25Se_0.75.And Li₇P₃S_10.25Se_0.75 still maintains good thermal stability.（3）The effect of chlorine doping on the crystal structure of Li₇P₃S₁₁ has been studied.The calculated results of formation energy demonstrate that doped structure with the best structural stability can be synthesized as SCl₂ is picked to be the raw material for introducing chlorine into Li₇P₃S₁₁.And Li_6.50P₃S_10.50Cl_0.50 was selected to be the most desirable structure due to the lowest diffusion barrier（0.18 e V）and poor electronic conductivity.AIMD simulation results demonstrate that Li_6.50P₃S_10.50Cl_0.50 has better ionic conductivity(140 m S cm^-1)than Li₇P₃S₁₁.In addition,Li_6.50P₃S_10.50Cl_0.50 has good thermal stability.（4）The effect of bromine doping on the crystal structure of Li₇P₃S₁₁ has been studied.PBr,as the raw material to introduce bromine into Li₇P₃S₁₁,can afford the optimal growth environment for the synthesis of doped structure.CI-NEB approach was implemented to calculated the diffusion barrier of Li_7-xP₃S_11-xBr_x（x=0、0.25 and 0.50）.It is found than Li_6.75P₃S_10.75Br_0.25has the lowest diffusion barrier（0.20 e V）among these three compounds.And it also possesses good electronic insulation.The ionic conductivity of Li_6.75P₃S_10.75Br_0.25 simulated by AIMD approach is(110 m S cm^-1),which is an order of magnitude greater than that of Li₇P₃S₁₁.Furthermore,Li_6.75P₃S_10.75Br_0.25possesses good thermal stability.