Ion Migration Regulation Of Ternary Halide Solid Electrolyte

All-solid-state li-ion batteries have attracted worldwide attention due to their high energy density,strong safety and long cycle life.The development of all-solid-state li-ion batteries with high energy density requires the development of solid electrolytes with good stability and high Li⁺conductivity.However,after years of exploration,solid electrolyte materials with multiple excellent properties are still scarce.Halogenated electrolytes have attracted widespread attention due to their high Li⁺conductivity and high oxidation stability.Although there are many studies on halide solid electrolytes in recent years,the effects of different factors on the transport of ternary halide ions are not fully studied,especially the effects of Li concentration and strain on ternary halide electrolytes.In this paper,the effects of Li⁺concentration and strain on the electronic structure and ion transport of ternary halides are studied by first-principles calculations.The main research results of this work are as follows:1)The structures,electronic properties and ion transport of Li_xYCl_3+x（x=2.14,3.00,4.20）and Li_xYBr_3+x（x=1.80,3.00,5.00）materials were systematically studied.Firstly,the ground state structures of Li_xYCl_3+x（x=2.14,3.00,4.20）and Li_xYBr_3+x（x=1.80,3.00,5.00）were systematically searched at 0 K.It is worth noting that CALYPSO software was used to search the ground state structures of Li_2.14YCl and Li_4.2YCl with more configurations,and then we calculated the obtained ground state structures.The result of the electronic properties shows that among all the considered halides,Li₃YCl₆（LYC）and Li₃YBr₆（LYB）have larger band gaps,indicating that they is the wider theoretical electrochemical window.For Li_xYCl_3+x（x=2.14,3.00,4.20）and Li_xYBr_3+x（x=1.80,3.00,5.00）structures,the NEB calculation further shows that LYC and LYB with 75%Li⁺concentration show the lowest migration energy barriers of 0.19 e V and 0.24 e V,respectively.These results show that LYC and LYB materials with 75%Li⁺concentration exhibit the best Li⁺and Li vacancy balance,showing the best performance.2)The effects of strain for LYC and LYB were studied.The effects of strain for the electronic structures and Li⁺transport of ternary halide materialswere investigated by applying 2%-6%compressive strain and tensile strain to LYC and LYB,respectively.The results show that the band gap of LYC with 2%tensile strain is the largest（5.45 e V）.When the strain is not enough large,the strain has little effect on the band gap,and the band gap of all strains is 5.41-5.45 e V.In addition,the strain has a great influence on the migration energy barrier of LYC.The lowest migration energy barrier is 0.12 e V for LYC with 2%tensile strain,which is lower than the migration energy barrier of 0.19 e V for LYC without strain,and the tensile strain greater than 2%will increase the migration energy barrier.All compressive strains will increase the migration energy barrier of Li⁺in LYC,thereby reducing the conductivity of the material.For LYB,the strain has little effect on its electronic structures.In the considered strain range,the band gap varies between 4.35-4.71 e V.Among them,the band gap of LYB with 2%tensile strain is the largest,which is 4.71 e V.In addition,the migration barrier of LYB with 4%tensile strain is the lowest（0.20 e V）,which is lower than the migration barrier of 0.24 e V without strain LYB.These results show that the ion conductivity of the material is significantly improved by applying 2%and4%tensile strain energy to LYC and LYB,respectively.