Solid ion conductor compound, solid electrolyte comprising the same, electrochemical cell comprising the solid ion conductor compound, and preparation method thereof
A solid ion conductor compound includes a compound represented by Formula 1: Li 6−w Hf 2−x M x O 7−y Z y Formula 1 where, in Formula 1, M is an element having an oxidation number of a and a is 5, 6, or a combination thereof, Z is an element having an oxidation number of −1, and 0<x<2, 0≤y≤2, and 0<w<6 and w=[(a−4)×x]+y.
1. A solid ion conductor compound represented by Formula 1:
Li 6−w Hf 2−x M x O 7−y Z y Formula 1
wherein in Formula 1,
M is an element having an oxidation number of a, wherein a is 5, 6, or a combination thereof,
Z is an element having an oxidation number of −1, and
0<x<2, 0≤y≤2, and 0<w<6, wherein w=[(a−4)×x]+y.
2. The solid ion conductor compound of claim 1 , wherein M is a Group 5 element, a Group 15 element, or a combination thereof.
3. The solid ion conductor compound of claim 1 , wherein M is Ta, Nb, V, Sb, As, or a combination thereof.
4. The solid ion conductor compound of claim 1 , wherein M is a Group 6 element, a Group 16 element, or a combination thereof.
5. The solid ion conductor compound of claim 1 , wherein M is W, Se, Te, Mo, or a combination thereof.
6. The solid ion conductor compound of claim 1 , wherein Z is F, Cl, Br, I, or a combination thereof.
7. The solid ion conductor compound of claim 1 , wherein 0<x≤0.25, 0≤y≤0.25, and 0<w≤0.75.
8. The solid ion conductor compound of claim 1 , wherein in the compound represented by Formula 1, M is Ta, Nb, V, Sb, or As,
Z is F, Cl, Br, I, or a combination thereof, and
0<x≤0.25, 0≤y≤0.25, and 0<w≤0.5.
9. The solid ion conductor compound of claim 1 , wherein in the compound represented by Formula 1 M is W, V, Se, Te, or Mo,
Z is F, Cl, Br, I, or a combination thereof, and
0<x≤0.25, 0≤y≤0.25, and 0<w≤0.75.
10. The solid ion conductor compound of claim 1 , wherein the solid ion conductor compound represented by Formula 1 has an ion conductivity of about 1×10 −3 millisiemens per centimeter or more at 27° C.
11. The solid ion conductor compound of claim 1 , wherein the solid ion conductor compound represented by Formula 1 has an electron conductivity of about 1×10 −5 millisiemens per centimeter or less at 27° C.
12. The solid ion conductor compound of claim 1 , wherein a mole ratio of the lithium atoms to the oxygen atoms is equal to or less than about 0.9.
13. The solid ion conductor compound of claim 1 , wherein the solid ion conductor compound represented by Formula 1 has a monoclinic crystal structure.
14. The solid ion conductor compound of claim 13 , wherein the solid ion conductor compound represented by Formula 1 belongs to a C2/c space group.
15. The solid ion conductor compound of claim 1 , wherein the solid ion conductor compound represented by Formula 1 has a rock-salt crystal structure, and
a unit cell of the rock-salt-type crystal structure has an ordered oxygen deficiency,
wherein the lithium atoms are each coordinated by 5 oxygen atoms in a square pyramid form, and at least one atom of Hf and M is coordinated by 6 oxygen atoms in an octahedral form in the unit cell of the rock-salt-type crystal structure.
16. The solid ion conductor compound of claim 1 , wherein the energy above hull of the solid ion conductor compound represented by Formula 1 is about 25 millielectron volts per atom, or less.
17. A solid electrolyte comprising:
the solid ion conductor compound according claim 1 .
18. The solid electrolyte of claim 17 , wherein the solid electrolyte further comprises an additional phase.
19. The solid electrolyte of claim 18 , wherein the additional phase comprises of Li a M b O c wherein 1.0≤a≤4.0, 0.5≤b≤1.5, 2.0≤c≤5.0, and M is Ta, Nb, V, Sb, As, W, Se, Te, or Mo, Li a Hf b O c wherein 5.0≤a≤7.0, 1.5≤b≤2.5, and 6.0≤c≤8.0, La d Hf e O f wherein 7.5≤d≤8.5, 0.5≤e≤1.5, and 0.5≤f≤6.5, La h Hf i O j wherein 1.5≤h≤2.5, 0.5≤i≤1.5, and 2.5≤j≤3.5, Li 2 O, LiF, LiCl, LiBr, LiI, or a combination thereof.
20. An electrochemical cell comprising:
a positive electrode,
a negative electrode, and
an electrolyte disposed between the positive electrode and the negative electrode,
wherein at least one of the positive electrode, the negative electrode, or the electrolyte comprises the solid ion conductor compound according to claim 1 .
21. The electrochemical cell of claim 20 , wherein a protective layer comprising the solid ion conductor compound is disposed on a surface of at least one of the positive electrode, the negative electrode, or the electrolyte.
22. The electrochemical cell of claim 20 , wherein the negative electrode comprises lithium metal, a lithium metal alloy, or a combination thereof.
23. The electrochemical cell of claim 20 , wherein the negative electrode comprises a negative active material, wherein the negative active material comprises:
a core comprising lithium metal, a lithium metal alloy, or a combination thereof, and
a protective shell disposed on a surface of the core,
wherein the protective shell comprises the solid ion conductor compound.
24. The electrochemical cell of claim 20 , wherein the electrochemical cell is an all-solid-state lithium battery, a lithium battery including a liquid electrolyte, or a lithium air battery.
25. A method of preparing a solid ion conductor compound, the method comprising:
contacting a lithium compound, a tetravalent cationic element-containing compound, and at least one of a pentavalent cationic element-containing compound and a hexavalent cationic element-containing compound to provide a mixture; and
heat-treating the mixture in an oxidizing atmosphere to provide a solid ion conductor compound of Formula 1,
Li 6−w Hf 2−x M x O 7−y Z y Formula 1
wherein in Formula 1,
M is an element having an oxidation number of a, wherein a is 5, 6, or a combination thereof,
Z is an element having an oxidation number of −1, and
0<x<2, 0≤y≤2, and 0<w<6, wherein w=[(a−4)×x]+y.
26. The method of claim 25 , wherein the heat treating of the mixture comprises heat-treating at a temperature less than about 1000° C. for about 1 hour to about 36 hours.
27. The method of claim 25 , further comprising:
pulverizing the solid ion conductor compound of Formula 1,
molding the solid ion conductor compound to prepare a molded product; and
heat-treating the molded product in an oxidizing atmosphere to prepare a sintered product.
28. The method of claim 27 , wherein heat-treating of the molded product comprises heat-treating for about 1 hour to about 36 hours at a temperature which is less than about 1000° C. and greater than the temperature of the heat-treating of the mixture.