Constructions And Li-storage Mechanisms Of Multinary Cation-disordered Ge-p-based Compounds

Due to the limited specific capacity(372 m A h g^-1)of graphite anodes,Ge-and P-based anode materials have attracted much attention due to the large Li-storage capacities and moderate working potentials.However,these alloy-type anodes will suffer poor electronic and Li-ionic conductance as well as large volume expansion during cycling,resulting in capacity attenuation.To resolve these problems,we designed and prepared cation-disordered Ge-P-based compounds with Sphalerite structure by a high energy mechanical ball milling by the mixed powders of Ge,P,Cu and Si.The main contents are as follows:The ternary cation-disordered CuGe₂P₃ compound is synthesized by ball milling from Cu powder,Ge powder and P powder,and its crystal structure was zinc blende structure by XRD refinement.The initial Coulombic efficiency of CuGe₂P₃ is 92%,and its specific capacity remained at 1260 m A h g^-1 after 100 cycles at low current density(100 m A g^-1).EIS,GITT,SEM and First Principles calculation confirm that the excellent electrochemical performance of cation-disordered CuGe₂P₃ can be attributed to its faster Li-ion transportation,electronic conduction and stronger resistance to electrode pulverization.The three-step Li-storage mechanism of cation-disordered CuGe₂P₃ was revealed by ex-XRD,ex-Raman and ex-XPS.When the first charging to 3V,its crystallinity was greatly reduced.Moreover,the faster charge transportation of ternary cation-disordered CuGe₂P₃ can be attributed to its endogenous mixed ion conductors（Li₂Cu P）,lithium ionic conductors（Li₃P）and electronic conductors(Li₁₅Ge₄,Cu).The quaternary cation-disordered CuGe Si P₃ with zinc blende structure is synthesized by a similar method considering the larger reversible capacity of Si.As anodes for Li-ion batteries,it delivers a reversible specific capacity 1459 m A h g^-1 at low current density(100 m A g^-1)and984 m A h g^-1 at high current density of 5000 m A g^-1.First Principles calculation confirm that quaternary cation disordered CuGe Si P₃ has better physical and chemical properties（lithium ion transportation,electronic conduction and resistance to electrode pulverization）than Ge.The bi-step Li-storage mechanisms of cation disordered CuGe Si P₃ was revealed by ex-XRD,ex-Raman,ex-XPS and ex-HRTEM.When the charged to 3V,the cation-disordered CuGe Si P₃become an amorphous state.Interestingly,similar to the ternary cation disordered CuGe₂P₃,the quaternary cation-disordered CuGe Si P₃ electrodes produced the electronic conductors(Cu,Li₁₅Ge₄,Li₂₁Si₈)and Li-ion conductors（Li₃P）during cycling,which can ensure the charge transportation during the whole charge and discharge process.