| The conventional lithium ion batteries possess some safety risks limits large-scale applications due to flammable and leakage of organic electrolyte.The all-solid-state batteries employing solid electrolyte could fundamentally eliminate safety concerns and combined with lithium metal to provide higher energy density,which are considered as a promising next-generation energy storage technology.Compared with oxide and sulfide solid electrolytes,halide solid electrolytes have the following advantages:（1）the weak electrostatic attraction of halogen ions to lithium ions;（2）the high oxidation potential to match the high voltage cathodes;（3）good thermal stability.Hitherto,halide solid electrolyte with the hexagonal close-packed（hcp）structure exhibits low ionic conductivity(usually less than 0.5 m S cm-1).And halide solid electrolytes with the cubic close-packed（ccp）structure behavior as a superior conductor(above 1 m S cm-1),but its diffusion activation energy typically above 0.35e V,which is not conducive to transport Li+ions at low temperature.The halide electrolytes possessing high ionic conductivity with ccp structure are not suitable for commercial applications because it contains scarce precious metal elements.Therefore,it is necessary to develop halide electrolytes with fast ionic conductivity,low diffusion activation energy and low cost.This work focus on identifying potential ways to induced Li3YCl6 with hcp structure to transform into ccp structure with three-dimensional equivalent lithium ion transport channel by changing its lattice chemistry or doping its metal and halogen sites to obtain halide electrolytes with high ionic conductivity.（1）Here in this work,extensive first principles calculations were carried out to identifying novel candidates as highly attractive halide SSEs,and find that through tuning the lattice chemistry in the hexagonal Li3YCl6,one can open a new avenue in achieving three highly stable compounds with spinel-like cubic structures.The best two cubic compounds,Li2.125Y0.625Cl4 and Li2.5Y0.5Cl4,are able to offer very efficient three-dimensional diffusion channels for Li+transportation,with remarkable room-temperature Li+conductivities of 6.11 m S cm-1 and 8.42 m S cm-1 at low activation energies（0.247 e V and 0.244 e V）,respectively.In addition to ionic conductivities being several times higher than that of the pristine Li3YCl6 phase,they also have remarkably high oxidation potentials above 4.0 V desirable to accommodate high voltage cathode materials electrochemically.（2）Three halide electrolytes Li1.75Y0.75Cl4,Li2.125Y0.625Cl4 and Li2.5Y0.5Cl4theoretically designed in the previous work were synthesized.Further DSC and XRD characterization found that the components of these three electrolytes are mixed phases of ccp structure and hcp structure.The ionic conductivity of Li1.75Y0.75Cl4 at room temperature is 0.36 m S cm-1.The charge capacity of all solid-state batteries Li-In|Li6PS5Cl|Li1.75Y0.75Cl4|Li Co O2-Li1.75Y0.75Cl4 can reach 134.7 m Ah g-1 at the first cycle with 0.1 C and the Coulomb efficiency is 94.18%.（3）In order to obtain the halide electrolyte with ccp structure,further experiments were conducted to dop the metal and halogen sites of Li3YCl6 with Cr element and Br element at the same time to induced structure completely transformed from hcp structure to ccp structure.The ionic conductivity of Li2(Y0.7Cr0.3)2/3(Cl0.85Br0.15)4（0.3Cr-15%Br）,Li2(Y0.7Cr0.3)2/3(Cl0.8125Br0.1875)4（0.3Cr-18.75%Br）,Li2(Y0.7Cr0.3)2/3(Cl0.75Br0.25)4（0.3Cr-25%Br）were 0.738 m S cm-1,0.688 m S cm-1 and0.718 m S cm-1,respectively.Compared with the pristine Li3YCl6(0.0958 m S cm-1),the room temperature ionic conductivities of the three electrolytes are greatly improved.And the cheap metal elements Cr replaces part of the element Y reduced the cost of the electrolytes.The all-solid-state battery assembled with 0.3Cr-15%Br has excellent performance and cycling stability,and its capacity retention rate is 90% at the rate of 0.6 C for 200 cycles. |
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