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EP-4044309-B1 - NOVEL SOLID ELECTROLYTE, AND METHOD FOR PRODUCING SAME

EP4044309B1EP 4044309 B1EP4044309 B1EP 4044309B1EP-4044309-B1

Inventors

  • JO, Vin-Na
  • HAN, HYEA-EUN
  • LYOO, Je-Yne
  • HONG, SEUNG-TAE

Dates

Publication Date
20260506
Application Date
20210318

Claims (11)

  1. A sulfide-based solid electrolyte having a novel crystal structure satisfying the following conditions (a)-(c): (a) a space group that belongs to P 3 1m (No. 162); (b) unit cell parameters of a = 6.03 ± 0.5 Å and c = 6.59 ± 0.5 Å; and (c) crystallographic coordinates of cations occupying 2c, 2d and 2e coordinates in a unit cell with a site occupancy of each coordinate of larger than 0 and equal to or less than 1, and a crystallographic coordinate of anions occupying 6k coordinate in a unit cell with a site occupancy of 6k of larger than 0 and equal to or less than 1, wherein each of the coordinates represents the following: 2c (1/3, 2/3, 0); 2d (1/3, 2/3, 1/2); 2e (0, 0, z), wherein 0.30 ≤ z ≤ 0.33; and 6k (x, 0, z), wherein 0.325 ≤ x ≤ 0.35 and 0.23 ≤ z ≤ 0.28, and wherein said sulfide-based solid electrolyte comprises a compound represented by the following Chemical Formula 1: [Chemical Formula 1] Li x Zn y P z S 6 wherein 1 ≤ x ≤ 4, 0 < y ≤ 2, and 0 < z ≤ 3.
  2. The sulfide-based solid electrolyte according to claim 1, which comprises a compound represented by the following Chemical Formula 2: [Chemical Formula 2] Li 2+2k Zn 1-k P 2 S 6 wherein 0 ≤ k < 1.
  3. The sulfide-based solid electrolyte according to claim 1, which shows peaks at the following positions, as analyzed by powder X-ray diffractometry (XRD) using Cu-Kα rays with an X-ray wavelength of 1.5406 Å and 1.5444 Å: 2 θ = 12 − 14 ° ; 2 θ = 16 − 18 ° ; 2 θ = 25 − 26 ° ; 2 θ = 30 − 33 ° ; 2 θ = 39 − 41 ° ; and 2 θ = 50 − 53 °
  4. The sulfide-based solid electrolyte according to claim 1, which has the same crystal structure as Li 4 P 2 S 6 .
  5. The sulfide-based solid electrolyte according to claim 2, wherein k is 0-0.75, and the sulfide-based solid electrolyte has an ion conductivity of 1 X 10 -6 to 15 X 10 -6 S/cm.
  6. A method for preparing a sulfide-based solid electrolyte which comprises a compound represented by the following Chemical Formula 1: [Chemical Formula 1] Li x Zn y P z S 6 wherein 1 ≤ x ≤ 4, 0 < y ≤ 2, and 0 < z ≤ 3 said method comprising the steps of: (S1) mixing lithium sulfide (Li 2 S), zinc sulfide (ZnS), a phosphorus (P) compound and a sulfur (S) compound to obtain a mixture; and (S2) heat treating the mixture to obtain a crystalline or vitreous solid electrolyte.
  7. The method for preparing a sulfide-based solid electrolyte according to claim 6, wherein lithium sulfide and zinc sulfide are used at a molar ratio of 2 + 2k : 1 - k wherein 0 ≤ k < 1.
  8. The method for preparing a sulfide-based solid electrolyte according to claim 7, wherein k is 0-0.75, and the sulfide-based solid electrolyte has an ion conductivity of 1 X 10 -6 to 15 X 10 -6 S/cm.
  9. The method for preparing a sulfide-based solid electrolyte according to claim 6, which further comprises a step of pelletizing the mixture between step (S1) and step (S2).
  10. The method for preparing a sulfide-based solid electrolyte according to claim 6, which is carried out under vacuum or under inert gas atmosphere.
  11. An all-solid-state battery comprising: a positive electrode; a negative electrode; and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode and the electrolyte layer includes the sulfide-based solid electrolyte as defined in any one of claims 1 to 5.

Description

TECHNICAL FIELD The present disclosure relates to a solid electrolyte and a method for preparing the same. Particularly, the present disclosure relates to a sulfide-based solid electrolyte. The present application claims priority to Korean Patent Application No. 10-2020-0039967 filed on April 1, 2020 in the Republic of Korea. BACKGROUND ART Importance of lithium secondary batteries has been increased, as the use of vehicles, computers and portable terminals has been increased. Particularly, there is a need for developing lithium secondary batteries having a low weight and capable of providing high energy density. Such lithium secondary batteries may be provided as lithium-ion batteries by interposing a separator between a positive electrode and a negative electrode and injecting a liquid electrolyte thereto, or as all-solid-state batteries by interposing a solid electrolyte membrane between a positive electrode and a negative electrode. Among such lithium secondary batteries, lithium-ion batteries using a liquid electrolyte have a structure including a negative electrode and a positive electrode divided by a separator. Therefore, when the separator is damaged by deformation or external impact, a short-circuit may occur, resulting in risks, such as overheating or explosion. On the contrary, all-solid-state batteries using a solid electrolyte show enhanced battery safety and can prevent electrolyte leakage, and thus provide improved battery reliability. The present disclosure relates to a solid electrolyte having a novel crystal structure. More particularly, the present disclosure relates to a sulfide-based solid electrolyte having a channel facilitating ion conduction by virtue of crystallographic specificity derived from the ordering of metal ion sites and metal ion defects in a unit cell, and an electrochemical device including the same. Solid electrolytes may be classified depending on crystal structures, as shown in FIG. 1 (P. Lian, B. Zhao, L. Zhang, N. Xu, M. Wu and X. Gao, J. Mater. Chem. A, 2019). Although all of the materials in FIG. 1 have a potential as solid electrolytes, each of them has an advantage and disadvantage depending on the applications using them. It is thought that this is because different ion conductivities and physicochemical properties are provided as a function of temperature depending on the unique properties of the materials, such as the crystal structure or ion defect structure of each material. The solid electrolytes used for such all-solid-state batteries may be classified broadly into oxide-based solid electrolytes and sulfide-based solid electrolytes. Particularly, sulfide-based solid electrolytes show high ion conductivity as compared to oxide-based solid electrolytes. US8697292 describes a sulfide solid electrolyte material. Among such sulfide-based solid electrolytes, Li-P-S type solid electrolytes are representative next-generation materials having high ion conductivity. DISCLOSURE Technical Problem Such Li-P-S type sulfide-based solid electrolytes include non-crystalline Li2S-P2S5 type glass ceramics or crystalline Li-Ge-P-S (LGPS) type solid electrolytes. Particularly, the Li2S-P2S5 type glass ceramics show increased lithium-ion conductivity by adding a halogenated compound thereto, but are disadvantageous in that they have a difficulty in handling due to the presence of a halogen compound. In addition, the LGPS type compounds have disadvantages in terms of cost-efficiency and commercialization due to the high cost of germanium (Ge). Under these circumstances, the present disclosure is directed to providing a novel sulfide-based solid electrolyte which is free from a halogenic element or germanium and has excellent electrochemical stability. The present disclosure is also directed to providing a novel sulfide-based solid electrolyte prepared by mixing a zinc element, and having a novel crystal structure that has not been known to date and lithium-ion conductivity derived from such a novel crystal structure. These and other objects and advantages of the present disclosure may be understood from the following detailed description and will become more fully apparent from the exemplary embodiments of the present disclosure. Also, it will be easily understood that the objects and advantages of the present disclosure may be realized by the means shown in the appended claims and combinations thereof. Technical Solution In one aspect of the present disclosure, there is provided a novel sulfide-based solid electrolyte according to any one of the following embodiments. According to the first embodiment, there is provided a sulfide-based solid electrolyte having a novel crystal structure satisfying the following conditions (a)-(c): (a) a space group that belongs to P31m (No. 162);(b) unit cell parameters of a = 6.03 ± 0.5 Å and c = 6.59 ± 0.5 Å; and(c) crystallographic coordinates of cations occupying 2c, 2d and 2e coordinates in a unit cell with a site occupancy of each coord