Solid ion conductor, solid electrolyte and electrochemical device including the same, and method of preparing solid ion conductor
A solid ion conductor comprising a compound represented by Formula 1 having an orthorhombic crystal structure, and belonging to a Pnma space group or a Pnma-like space group: Li 3−x A x LuCl 6−y X y Formula 1 wherein, in Formula 1, A is a monovalent cation having an ionic radius of 76 picometers or greater, X is a monovalent anion, and 0≤x≤0.1, 0≤y≤1, and x+y>0.
1. A solid ion conductor comprising a compound represented by Formula 1 having an orthorhombic crystal structure, and belonging to a Pnma space group or a Pnma-like space group:
Li 3−x A x LuCl 6−y X y Formula 1
wherein, in Formula 1,
A is a monovalent cation having an ionic radius of 76 picometers or greater,
X is a monovalent anion, and
0<x≤0.1, 0≤y≤1, and x+y>0.
2. The solid ion conductor of claim 1 , wherein A is Na + , K + , Rb + , Cs + , Ag + , Au + , Cu + , Hg + , Tl + , or a combination thereof.
3. The solid ion conductor of claim 1 , wherein X is Br − , I − , or a combination thereof.
4. The solid ion conductor of claim 1 , wherein, in Formula 1, A is Na + , K + , Rb + , Cs + , Ag + , Au + , Cu + , Hg + , Tl + , or a combination thereof, X is Br − , I − , or a combination thereof, and 0<x≤0.1, and 0<y≤1.
5. The solid ion conductor of claim 1 , wherein the compound is represented by Formula 2:
Li 3−x A x LuCl 6 Formula 2
wherein, in Formula 2,
A is Na + , K + , Rb + , Cs + , Ag + , Au + , Cu + , Hg + , Tl + , or a combination thereof, and 0<x≤0.1.
6. The solid ion conductor of claim 1 , wherein the compound is Li 2.95 Na 0.05 LuCl 6 , Li 2.95 K 0.05 LuCl 6 , Li 2.95 Rb 0.05 LuCl 6 , Li 2.95 Cs 0.05 LuCl 6 , Li 2.95 Ag 0.05 LuCl 6 , Li 2.95 Au 0.05 LuCl 6 , Li 2.95 Cu 0.05 LuCl 6 , Li 2.95 Hg 0.05 LuCl 6 , Li 2.95 Tl 0.05 LuCl 6 , Li 2.95 Na 0.05 LuCl 5 Br, Li 2.95 K 0.05 LuCl 5 Br, Li 2.95 Rb 0.05 LuCl 5 Br, Li 2.95 Cs 0.05 LuCl 5 Br, Li 2.95 Ag 0.05 LuCl 5 Br, Li 2.95 Au 0.05 LuCl 5 Br, Li 2.95 Cu 0.05 LuCl 5 Br, Li 2.95 Hg 0.05 LuCl 5 Br, Li 2.95 Tl 0.05 LuCl 5 Br, Li 2.95 Na 0.05 LuCl 5 I, Li 2.95 K 0.05 LuCl 5 I, Li 2.95 Rb 0.05 LuCl 5 I, Li 2.95 Cs 0.05 LuCl 5 I, Li 2.95 Ag 0.05 LuCl 5 I, Li 2.95 Au 0.05 LuCl 5 I, Li 2.95 Cu 0.05 LuCl 5 I, Li 2.95 Hg 0.05 LuCl 5 I, Li 2.95 Tl 0.05 LuCl 5 I, or a combination thereof.
7. The solid ion conductor of claim 1 , wherein the compound has a centrosymmetric structure having a unit cell comprising
a first length in an x-axis direction, a second length in a y-axis direction, and a third length in a z-axis direction, and
eight inversion points,
wherein the x-axis direction, the y-axis direction, and the z-axis direction are perpendicular to one another, and the first length, the second length, and the third length are different from each other.
8. The solid ion conductor of claim 1 , wherein the compound has a unit cell comprising four 2 1 screw axes along each unit cell direction and two planes in a direction perpendicular to each unit cell axis.
9. The solid ion conductor of claim 1 , wherein in the crystal structure of the compound, LuCl 6 or LiX 6 octahedrons are positioned in an edge-sharing manner, wherein X is Cl or Br, and the A cation is positioned at a Li site.
10. The solid ion conductor of claim 1 , wherein the compound has a three-dimensional network of lithium ion transport channels within the orthorhombic crystal structure.
11. The solid ion conductor of claim 1 , wherein the compound has a network of lithium ion transport channels, which extend in an x-axis direction, a y-axis direction, and a z-axis direction, and
a spatial distribution of the lithium ion transport channels is determined by an ionic radius of the cation A or the monovalent anion X in the orthorhombic crystal structure.
12. The solid ion conductor of claim 1 , wherein the compound has an X-ray diffraction spectrum comprising a diffraction peak at 29°2θ to 32°2θ, 33°2θ to 35°2θ, and 34°2θ to 37°2θ, when analyzed with CuKα radiation.
13. The solid ion conductor of claim 12 , wherein the diffraction peaks of the compound are shifted to a smaller diffraction angle relative to diffraction peaks of Li 3 LuCl 6 .
14. The solid ion conductor of claim 1 , wherein the solid ion conductor has an ionic conductivity of about 1×10 −1 milliSiemens per centimeter to about 5×10 −1 milliSiemens per centimeter, when measured at 25° C.
15. The solid ion conductor of claim 1 , wherein the solid ion conductor has an interfacial resistance of about 1 ohm square centimeter to about 500 ohm square centimeters when contacted with lithium metal, when determined from an impedance spectrum of a lithium symmetric cell, in which the solid ion conductor is disposed between lithium metal electrodes, at 25° C., and a frequency range of 1 Hertz to 1×10 6 Hertz.
16. A solid electrolyte comprising the solid ion conductor according claim 1 .
17. A protected positive electrode comprising:
a positive electrode layer; and
a protection layer comprising the solid ion conductor of claim 1 on the positive electrode layer.
18. A protected negative electrode comprising:
a negative electrode layer; and
a protection layer comprising the solid ion conductor of claim 1 on the negative electrode layer.
19. An electrochemical device comprising:
a positive electrode layer;
a negative electrode layer; and
a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer, the solid electrolyte layer, the negative electrode layer, or a combination thereof comprises the solid ion conductor according to claim 1 .
20. The electrochemical device of claim 19 , wherein the solid electrolyte layer comprises the solid ion conductor.
21. The electrochemical device of claim 19 , further comprising a positive-electrode protection layer comprising the solid ion conductor on the positive electrode layer, a negative-electrode protection layer comprising the solid ion conductor on the negative electrode layer, or a combination thereof.
22. The electrochemical device of claim 20 , wherein the solid electrolyte layer has a thickness of about 10 micrometers to about 1 millimeter, and has a single-layer structure or a multilayer structure.
23. The electrochemical device of claim 20 , wherein the electrochemical device is an all-solid-state secondary battery or a metal air battery.
24. A method of preparing a solid ion conductor, the method comprising:
providing a precursor mixture; and
mechanically milling the precursor mixture to prepare the solid ion conductor,
wherein the solid ion conductor comprises a compound represented by Formula 1 having an orthorhombic crystal structure, and belonging to a Pnma space group or a Pnma-like space group:
Li 3−x A x LuCl 6−y X y Formula 1
wherein, in Formula 1,
A is a monovalent cation having an ionic radius of 76 pm or more,
X is a monovalent anion, and
0<x≤0.1, 0≤y≤1, and x+y>0.
25. The method of claim 24 , wherein the mechanical milling comprises ball milling, airjet milling, bead milling, roll milling, hand milling, planetary milling, stirred ball milling, vibrating milling, mechanofusion milling, shaker milling, attritor milling, disk milling, shape milling, nauta milling, high-shear mixing, or a combination thereof.
26. The method of claim 24 , wherein the mechanical milling comprises planetary milling, and is performed at a temperature of about 25° C.