KR20220139218A - Lithium halide-based solid electrolyte, manufacturing method thereof and all-solid-state battery comprising the lithium halide-based solid electrolyte - Google Patents

Abstract

The present invention relates to a lithium halide-based solid electrolyte, a manufacturing method thereof, and an all-solid-state battery including the lithium halide-based solid electrolyte. More specifically, since the lithium halide-based solid electrolyte, in which heteroatoms are substituted, is formed by heat-treating a precursor mixture including lithium halide, M1 metal halide, and M2 metal halide such that phase transition to monoclinic and orthorhombic II crystal structures are performed, higher lithium ion conductivity and lower activation energy than those of conventional solid electrolytes are provided, thereby providing excellent electrochemical stability. In addition, when applied to an all-solid-state battery, the lithium halide-based solid electrolyte has high charge and discharge performance, thereby significantly increasing lifespan characteristics and capacity retention rate of a battery. The lithium halide-based solid electrolyte comprises a compound represented by Li_(3 - x)M1_(1 - x)M2_xX_6, wherein x is 0.2 ≤ x ≤ 0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.

Description

Lithium halide-based solid electrolyte, manufacturing method thereof, and all-solid-state battery comprising the lithium halide-based solid electrolyte

The present invention relates to a lithium halide-based solid electrolyte, a manufacturing method thereof, and an all-solid-state battery comprising the lithium halide-based solid electrolyte.

Lithium-ion batteries (LIBs) have revolutionized the electrification of transportation, but they have limitations in terms of safety and energy density, and thus a breakthrough is needed. Lithium-ion batteries have a method of using a solid electrolyte (SE) in which the electrolyte is solidified with a non-flammable inorganic superion conductor to increase stability and energy density. Therefore, the development of a new solid electrolyte (SE) that can meet various requirements of high ionic conductivity, mechanical sinterability and electrochemical stability is the key to practical all-solid-state Li batteries (ASLBs).

Among the solid electrolytes, oxide-based solid electrolytes have Li ⁺ conductivity of 10 ^-4 to 10 ^-3 S/cm, and despite having excellent electrochemical stability, in order to be applied to integrated bulk ASLB, it is necessary to use a harmful high-temperature sintering process or Hybridization is required.

In addition, the sulfide-based solid electrolyte can be mechanically sintered and has a high conductivity of up to 10 ^-2 S/cm, but has a disadvantage in that the electrochemical instability is large. In addition, sulfide-based solid electrolytes emit toxic H ₂ S gas when exposed to ambient air, and have a low inherent electrochemical oxidation stability limit of 2 to 3V (vs. Li/Li ⁺ ). In particular, the uncoated layered LiMO ₂ anode material paired with the sulfide-based solid electrolyte has poor electrochemical performance due to its large interfacial resistance.

In addition, borohydride-based solid electrolytes are another type of superionic conductor that exhibits mechanical sinterability, but there are problems in that complicated synthesis protocols, expensive precursors, and limited anode stability have to be solved.

Therefore, there is a need for research on new solid electrolytes that can improve hybridization, ionic conductivity, interfacial resistance, and electrochemical stability of existing oxide-based, sulfide-based, and boron-hydride-based solid electrolytes with polymer electrolytes.

Korean Patent Publication No. 2021-0054129

In order to solve the above problems, the present invention provides a lithium halide-based solid electrolyte having high lithium ion conductivity and low activation energy in which a metal element having an oxidation number of +3 is substituted with a metal element having an oxidation number of +4. Its purpose is to provide

Another object of the present invention is to provide a method for preparing the lithium halide-based solid electrolyte.

Another object of the present invention is to provide an all-solid-state battery including the lithium halide-based solid electrolyte.

Another object of the present invention is to provide a device including the all-solid-state battery.

Another object of the present invention is to provide a method for preparing a lithium halide-based solid electrolyte.

The present invention provides a lithium halide-based solid electrolyte comprising a compound represented by the following formula (1).

[Formula 1]

Li _3-x M1 _1-x M2 _x X ₆

(In Formula 1, x is 0.2≤x≤0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.)

In addition, the present invention is an anode layer; cathode layer; and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, wherein at least one of the positive electrode layer, the negative electrode layer and the solid electrolyte layer includes the lithium halide-based solid electrolyte of the present invention. provides

The present invention also provides a device comprising an all-solid-state battery, wherein the device is a transportation device or an energy storage device.

In addition, the present invention comprises the steps of preparing a precursor mixture by solid-phase mixing of lithium halide, M1 metal halide and M2 metal halide as a precursor under an inert gas atmosphere; and heat-treating the precursor mixture to prepare a lithium halide-based solid electrolyte comprising a compound represented by the following formula (1).

[Formula 1]

Li _3-x M1 _1-x M2 _x X ₆

(In Formula 1, x is 0.2≤x≤0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.)

The lithium halide-based solid electrolyte of the present invention is obtained by heat-treating a precursor mixture including lithium halide, M1 metal halide and M2 metal halide, so that a metal element having an oxidation number of +3 is converted to a metal element having an oxidation number of +4. By forming a substituted solid electrolyte, the phase is changed to monoclinic and orthorhombic II crystal structures, which has high lithium ion conductivity compared to conventional oxide, sulfide, or boron hydride solid electrolytes, and at the same time shows low activation energy and excellent electrochemical stability. There is an advantage.

In addition, the lithium halide-based solid electrolyte of the present invention has high charge/discharge performance when applied as an all-solid-state battery, and can significantly improve battery life characteristics and capacity retention.

The effects of the present invention are not limited to the above-mentioned effects. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 shows (a, b) trigonal Li ₃ MCl ₆ (M = Y, Tb-Tm), (c, d) orthorhombic Li ₃ MCl ₆ ( M = Yb, Lu), (e, f) unit cells for orthorhombic Li _2.5 M _0.5 Zr _0.5 Cl ₆ (M = Y, Er) and (g, h) monoclinic Li ₃ lnCl ₆ and corresponding The Li ⁺ substructure outlines the crystal structure.
2 is a high-resolution synchrotron radiation x-ray Rietveld for Li _3-x Yb _1-x Zr _x Cl ₆ (x = 0) (Li ₃ YbCl ₆ ) prepared in Examples 1-1 and 2-1 according to the present invention; A tablet profile (a) and an Arrhenius plot (b) of Li ⁺ conductivity are shown.
3 is (a) 30 ℃ according to the change in heat treatment temperature for Li _2.5 Y _0.5 Zr _0.5 Cl ₆ prepared in Comparative Examples 1-1 and 1-2 and Examples 1-5 and 2-5 according to the present invention; Li ⁺ conductance and activation energy graph in (b) Li _2.5 Y _0.5 Zr _0.5 Cl ₆ XRD pattern result graph at various temperatures.
4 shows Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 and Examples 4-1 to 4-6 according to the present invention at (a) 400° C. and ( b) XRD pattern graph of Li _3-x Yb _1-x Hf _x Cl ₆ heat treated at 500 °C for 6 hours, (c) Li _3-x Yb _1-x Hf _x Cl ₆ prepared at 400 °C or 500 °C A schematic diagram showing the phase change according to (d) Li ⁺ conductivity graph at 30 °C, and (e) activation energy graph for Li _3-x Yb _1-x Hf _x Cl ₆ .
5 shows Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 according to the present invention (a) Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ heat-treated at 400 ° C. Nyquist plot graphs at various temperatures and (b) Arrhenius plot graphs of Li ⁺ conductivity of Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ heat treated at 400 °C.
6 shows the time current of Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ prepared at 400° C. with respect to Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 according to the present invention; Chronoamperometry (CV) results graph.
7 shows Li _3-x Yb _1-x Zr _x Cl ₆ prepared in Examples 1-4, 1-6 and 1-7 according to the present invention, Li 3- _x having a monoclinic structure measured by HRXRD; Lattice parameter graph for Yb _1-x Zr _x Cl ₆ (0.4 ≤ x ≤ 0.8).
8 is Li _3-x Yb prepared in Examples 1-1, 1-2, 1-5 to 1-7 and Examples 2-1, 2-2, 2-5 to 2-7 according to the present invention; Li _3-x Yb _{1 -x} Zr _x Cl ₆ (0.4 ≤ x ≤ 0.8) heat treated at (a) 400 °C and (b) 500 °C for 1-x Zr _x Cl ₆ (0 ≤ x ≤ 0.8) XRD pattern graph, (c) Li ⁺ conductivity for Li _3-x Yb _1-x Zr _x Cl ₆ at 30 °C, and (d) activation energy graph for Li _3-x Yb _1-x Zr _x Cl ₆ . .
9 shows Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-4 and 4-4 according to the present invention heat-treated at (a) 400 ° C. and (b) 500 ° C. Observed and calculated high-resolution synchrotron radiation x-ray Rietveld purification profile graph for _2.60 Yb _0.60 Hf _0.40 Cl ₆ . The Bragg position in FIG. 9(b) represents an orthorhombic II phase with different lattice parameters.
10 is 200 ℃, 300 ℃, 400 ℃ for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in 3-4, 4-4 and Comparative Examples 2-1 and 2-2 according to the present invention; It is an XRD pattern graph of Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ prepared by ball milling according to whether heat treatment was performed at 500° C. or not.
11 is an SEM image of cold-pressed pellets at (a) high magnification and (b) low magnification for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Example 3-4 according to the present invention.
12 shows a single NCA88 electrode using Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Example 3-4 according to the present invention (a) at 0.5 C (0.64 mA/cm ² ) and 30° C. A graph of the cycling performance of a single NCA88 electrode in a single NCA88/Li-In all-solid-state battery and (b) a graph of the corresponding charge/discharge voltage profile.

Hereinafter, the present invention will be described in more detail by way of an embodiment.

The present invention relates to a lithium halide-based solid electrolyte, a manufacturing method thereof, and an all-solid-state battery comprising the lithium halide-based solid electrolyte.

As described above, conventional oxide-based, sulfide-based or boron-hydride-based solid electrolytes have problems in that it is difficult to hybridize with the electrolyte, and the electrochemical stability is poor due to low ionic conductivity and large interfacial resistance.

1 shows (a, b) trigonal Li ₃ MCl ₆ (M = Y, Tb-Tm), (c, d) orthorhombic Li ₃ MCl ₆ ( M = Yb, Lu), (e, f) unit cells for orthorhombic Li _2.5 M _0.5 Zr _0.5 Cl ₆ (M = Y, Er) and (g, h) monoclinic Li ₃ lnCl ₆ and corresponding The Li ⁺ substructure outlines the crystal structure. 1 (a, b), the trigonal structure (space group: P 3 m 1) is a hexagonal closed packing (hcp) anion framework in which the octahedral region is occupied by Li ⁺ ions, metal ions and pores. Based on this, it exhibits a 1D preferential 3D Li ⁺ diffusion pathway along the c-axis through a face-shared octahedron.

In addition, the new composition based on the above Li ₃ MCl ₆ (M = Y, Er) is monoclinic Li ₃ InCl ₆ (2 mS/cm), orthorhombic Li _3-x M _1-x Zr _x Cl ₆ (M = Y, Er, up to ~1.4 mS/cm), superionic conductors with spinel Li ₂ Sc ₂ /3Cl ₄ (1.5 mS/cm) and monoclinic Li _x ScCl _3+x (up to 3 mS/cm) and triangular There are several halide superionic conductors including crystalline Fe ³⁺ substituted Li ₂ ZrCl ₆ (up to ~1 mS/cm).

The lithium ion conductivity of such a lithium halide-based solid electrolyte may have characteristics that vary greatly depending on various factors such as a crystal structure and a synthesis protocol. In the case of the Li ₃ MCl ₆ (M = Y, Er), in order to have much higher lithium ion conductivity, the disordered form of the M site, which widens the diffusion channel of lithium ions (Li ⁺ ), is compared to the high-crystalline heat-treated solid electrolyte. is required In particular, when forming a monoclinic structure ( C2 /m) in which Li ⁺ channels are formed through an octahedral-tetrahedral-octahedral region like the Li ₃ InCl ₆ , the cubic closed packing shown in (g) and (h) of FIG. 1 . By forming a 3D Li ⁺ diffusion channel in (cubic closed-packed, ccp), it can have high lithium ion conductivity.

On the other hand, monoclinic Li ₂ ZrCl ₆ heat-treated at 260 ° C. showed poor Li ⁺ conductivity of 5.7 x 10 ^-6 S/cm, resulting in a mechanochemically derived trigonal phase (4 x 10 ^-4 S/cm) of the same composition. in stark contrast to This case reflects the complexity of factors affecting Li ⁺ migration in lithium halide-based solid electrolytes. Several factors, including anion lattice structure, M-site disorder, Li content, tetrahedral Li occupancy, concentration and distribution of metal ions, can affect lithium ion migration in lithium halide-based solid electrolytes.

Accordingly, in the present invention, a lithium halide-based solid electrolyte by substituting a metal element having an oxidation number of +3 with a metal element having an oxidation number of +4 for an existing solid electrolyte having an orthorhombic I crystal structure by heat treatment. By producing a phase change to monoclinic and orthorhombic II crystal structures, it can have high lithium ion conductivity compared to conventional oxide-based, sulfide-based or boron-hydride-based solid electrolytes. have. In addition, when it is applied as an all-solid-state battery, it is possible to significantly improve the battery life characteristics and capacity retention while having high charge/discharge performance.

Specifically, the present invention provides a lithium halide-based solid electrolyte comprising a compound represented by the following formula (1).

[Formula 1]

Li _3-x M1 _1-x M2 _x X ₆

(In Formula 1, x is 0.2≤x≤0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.)

In the lithium halide-based solid electrolyte, M1 includes a metal element having an oxidation number of +3, and the metal element having an oxidation number of +3 has a characteristic of forming Cl ^- 6 and octagonal polyhedron MCl ₆ . Specific examples of M1 may be at least one selected from the group consisting of Yb, Sc, Y, In, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu. and preferably Yb or Er, and most preferably Yb.

In the lithium halide-based solid electrolyte, M2 includes a metal element having an oxidation number of +4, and the metal element having an oxidation number of +4 has abundant reserves compared to the metal having an oxidation number of +3, so it is easy to obtain and , has the advantage of low unit price. Due to this, the manufacturing cost can be reduced compared to the conventional solid electrolyte, and there is an advantage that mass production is possible. Specific examples of M2 may be at least one selected from the group consisting of Hf, Zr and Ti, preferably Hf or Zr, and most preferably Hf.

The lithium halide-based solid electrolyte can significantly improve lithium ion conductivity when M1, which is a metal element having an oxidation number of +3, and M2, which is a metal element, having an oxidation number of +4 are used together. The chemical stability can be increased and the mixing ratio can be selected by controlling the cost.

X may be a halogen element F, Cl or Br, preferably Cl or Br, and most preferably Cl. The halogen element is advantageous in that ion conduction is well made, and the electrochemical oxidation stability and deformability are simultaneously improved.

In Formula 1, x may be in the range of 0.2≤x≤0.8, preferably 0.3≤x≤0.6, and most preferably 0.4≤x≤0.5. At this time, when x is less than 0.2, the lithium halide-based solid electrolyte forms a trigonal crystal structure, so that lithium ions cannot reside in a tetrahedral site. However, it has a smaller lattice size, and lithium ion conductivity may be rapidly reduced. Conversely, when x is greater than 0.8, activation energy is greatly increased, so electrochemical stability is lowered, and the material may be decomposed during the heat treatment process.

Preferably, in Formula 1, x may be 0.3≤x≤0.6, M1 may be Yb or Er, M2 may be Hf or Zr, and X may be Cl or Br.

Most preferably, in Formula 1, x may be 0.4≤x≤0.5, M1 may be Yb, M2 may be Hf or Zr, and X may be Cl.

The lithium halide-based solid electrolyte is monoclinic and orthorthombic II by heat treatment of a precursor mixture containing lithium halide, M1 metal halide, and M2 metal halide by aliovalent substitution. Or it may have a crystal structure consisting of a mixture thereof. Preferably, it may have a crystal structure consisting of a mixture of monoclinic and orthorhombic II.

That is, the lithium halide-based solid electrolyte is a metal having an oxidation number of +4 by replacing M1, which is a metal having an oxidation number of +3, with M2, a metal having an oxidation number of +4, through the mixed use of the M1 metal halide and M2 metal halide and heat treatment. A phase change may occur from the trigonal and orthorthombic I crystal structures to the monoclinic and orthorthombic II crystal structures. The crystal structure of the monoclinic or orthorhombic system II has much more favorable ion transport than the trigonal or orthorhombic system I, so that the lithium ion conductivity can be improved, and on the contrary, the activation energy can be lowered to increase the electrochemical stability. Furthermore, when this is applied to an all-solid-state battery, it can have excellent charge/discharge performance.

The heat treatment may be performed at a temperature of 300 to 600 ° C for 3 to 8 hours, preferably at a temperature of 350 to 550 ° C for 4 to 7 hours, and most preferably at a temperature of 400 to 500 ° C for 5.5 to 6.5 hours. have.

The lithium halide-based solid electrolyte may have a lithium ion conductivity of 1 to 3 mS/cm, an activation energy of 0.1 to 0.5 eV, and preferably a lithium ion conductivity of 1.3 to 1.5 mS/cm, and an activation energy of 0.26 to 0.35. eV.

In addition, the present invention is an anode layer; cathode layer; and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, wherein at least one of the positive electrode layer, the negative electrode layer and the solid electrolyte layer includes the lithium halide-based solid electrolyte of the present invention. provides

Further, the present invention provides a device including an all-solid-state battery, wherein the device is a transportation device or an energy storage device.

In addition, the present invention comprises the steps of preparing a precursor mixture by solid-phase mixing of lithium halide, M1 metal halide and M2 metal halide as a precursor under an inert gas atmosphere; and heat-treating the precursor mixture to prepare a lithium halide-based solid electrolyte comprising a compound represented by the following formula (1).

[Formula 1]

Li _3-x M1 _1-x M2 _x X ₆

(In Formula 1, x is 0.2≤x≤0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.)

The lithium halide may be at least one selected from the group consisting of LiCl, LiBr, LiI and LiF, preferably LiCl.

The M1 metal halide is at least one M1 selected from the group consisting of Yb, Sc, Y, In, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu. It may include a metal, preferably Yb or Er, and most preferably Yb.

The M2 metal halide may include one or more M2 metals selected from the group consisting of Hf, Zr and Ti, preferably Hf or Zr, and most preferably Hf.

The precursor mixture contains the lithium halide, M1 metal halide and M2 metal halide in a molar ratio of 2 to 3.3: 0.1 to 1.5: 0.1 to 1.2, preferably 2.4 to 2.8: 0.4 to 0.8: 0.2 to 0.6, most preferably For example, it may be mixed in a molar ratio of 2.5 to 2.7: 0.5 to 0.7: 0.3 to 0.5. In this case, when the molar ratio of the M1 metal halide or M2 metal halide does not satisfy the above range, heterovalent substitution is not performed properly, so that the compound of Formula 1 cannot be formed, and an appropriate compound cannot be formed and lithium ion conductivity This low mixture state can be erroneously synthesized.

The inert gas may be at least one selected from the group consisting of argon, helium, neon and nitrogen, preferably argon or nitrogen, and most preferably argon.

The solid-phase mixing may be performed by any one mechanical milling selected from the group consisting of a ball mill, a vibration mill, a turbo mill, a mechanofusion and a disk mill, preferably a ball mill or a vibration mill, and most preferably a ball mill. can be performed by

The mechanical milling may be performed at a rotation speed of 400 to 800 rpm for 7 to 15 hours, preferably 500 to 700 rpm, 8 to 13 hours, most preferably 550 to 650 rpm, and 9 to 11 hours.

In the step of preparing the lithium halide-based solid electrolyte, a heteroatom is substituted for M1, a metal having an oxidation number of +3, with M2, a metal element having an oxidation number of +4 by heat-treating the precursor mixture to obtain a compound represented by Formula 1 It is possible to form a lithium halide-based solid electrolyte comprising.

The heat treatment may be performed at a temperature of 300 to 600 ° C for 3 to 8 hours, preferably at a temperature of 350 to 550 ° C for 4 to 7 hours, and most preferably at a temperature of 400 to 500 ° C for 5.5 to 6.5 hours. have. At this time, when the heat treatment temperature is less than 300 ° C. or the heat treatment time is less than 3 hours, heterovalence substitution is not performed properly, so that the phase change into the crystal structures of monoclinic and orthorthombic II may not occur, and thus As a result, lithium ion conductivity may be significantly reduced. Conversely, when the heat treatment temperature is more than 600° C. or the heat treatment time is more than 8 hours, some of the precursor materials may not be stably synthesized in the powder and sublimate to change the composition.

The lithium halide-based solid electrolyte is a mixture of the M1 metal halide and the M2 metal halide, and satisfies all of the conditions for performing heat treatment. It may have a crystal structure, and preferably may have a crystal structure consisting of a mixture of monoclinic and orthorhombic II.

If the M1 metal halide and the M2 metal halide are not mixed, or the precursor mixture is synthesized by mechanical milling without heat treatment and heterovalent substitution is made, crystalline form cannot be formed and the lithium ion conductivity does not reach the expected level. Not only that, but also the durability is not good.

In particular, although not explicitly described in the following Examples or Comparative Examples, in the method for preparing a lithium halide-based solid electrolyte according to the present invention, an all-solid to which a lithium halide-based solid electrolyte prepared under the following 11 conditions is applied. A battery was prepared. The manufactured all-solid-state battery was charged and discharged 1500 times by a conventional method, and then durability, oxidation stability, charge/discharge capacity, battery life characteristics, and capacity retention were tested.

As a result, it was confirmed that the durability and oxidation stability of the all-solid-state battery were excellent due to the strong bonding force between the electrode and the solid electrolyte even after 1500 charge/discharge cycling when all of the following conditions were satisfied, unlike in other conditions and other numerical ranges. In addition, it was confirmed that the charge/discharge capacity of the all-solid-state battery was maintained at a high level for a long time, the output density decrease rate after 1500 charge/discharge was as low as about 16% or less, and the capacity retention rate was maintained as high as 80.5%.

① the x is 0.4≤ x ≤ 0.5, ② the M1 is Yb, ③ the M2 is Hf or Zr, ④ the X is Cl, ⑤ the precursor mixture is the lithium halide, M1 metal halide and M2 metal halide is mixed in a molar ratio of 2.5 to 2.7: 0.5 to 0.7: 0.3 to 0.5, ⑥ the inert gas is argon, ⑦ the solid phase mixing is performed by mechanical milling of a ball mill, ⑧ the mechanical milling is 550 to It is carried out for 9 to 11 hours at a rotation speed of 650 rpm, ⑨ the heat treatment is performed at a temperature of 400 to 500 ° C. for 5.5 to 6.5 hours, ⑩ the lithium halide-based solid electrolyte is monoclinic and orthorhombic II (orthorthombic II), ⑪ the lithium halide-based solid electrolyte may have a lithium ion conductivity of 1.3 to 1.5 mS/cm and an activation energy of 0.26 to 0.35 eV.

However, when any one of the above 11 conditions is not satisfied, some loss of solid electrolyte occurs after 900 charge/discharge cycling, so that the durability or oxidation stability of the all-solid-state battery is rapidly reduced, and the power density after 1500 charge/discharge cycles The reduction ratio was as high as about 40% or less, and the capacity retention rate was also very low, about 50% or less.

As described above, the lithium halide-based solid electrolyte according to the present invention satisfies the mixed use and heat treatment temperature conditions of the M1 metal halide and M2 metal halide. As a result, it may have high lithium ion conductivity and low activation energy.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

Example 1-1: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0)

LiCl, YbCl _{3 ,} and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were added in a molar ratio of 3: 1: 0, and 15 ZrO ₂ balls (φ = 10 mm) were used in Ar atmosphere using Pulverisette 7 PL (Fritsch GmbH). Precursor mixture powder was prepared by mechanically milling in a 50 ml ZrO ₂ vial at 600 rpm for 10 hours with Then, the milled precursor mixture powder was sealed in a quartz ampoule under vacuum, and then heat treated at 400 °C for 6 hours at a heating rate of 5 °C/min, and then naturally cooled at room temperature to Li _3-x Yb _1-x Zr _x Cl ₆ (x=0) was prepared.

Example 1-2: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0.1)

LiCl, YbCl _3, and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in a molar ratio of 2.9: 0.9: 0.1, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Zr _x Cl ₆ (x=0.1) was prepared.

Example 1-3: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0.25)

LiCl, YbCl ₃ and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in a molar ratio of 2.75: 0.75: 0.25, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Zr _x Cl ₆ (x=0.25) was prepared.

Example 1-4: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0.4)

LiCl, YbCl _3, and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in the same manner as in Example 1-1 except that 2.6: 0.4: 0.6 molar ratio was mixed with Li _3-x Yb _{1- x} Zr _x Cl ₆ (x=0.4) was prepared.

Example 1-5: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0.5)

LiCl, YbCl _3, and ZrCl ₄ as precursors (99.99%, Sigma Aldrich) were mixed in a molar ratio of 2.5:0.5:0.5, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Zr _x Cl ₆ (x=0.5) was prepared.

Example 1-6: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0.6)

LiCl, YbCl _3, and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in the same manner as in Example 1-1 except for mixing in a mole ratio of 2.4:0.4:0.6 Li _3-x Yb _{1- x} Zr _x Cl ₆ (x=0.6) was prepared.

Example 1-7: Li heat-treated at 400 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0.8)

LiCl, YbCl _3, and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in the same manner as in Example 1-1 except that 2.2: 0.2: 0.8 molar ratio was mixed with Li _3-x Yb _{1- x} Zr _x Cl ₆ (x=0.8) was prepared.

Examples 2-1 to 2-7: Li heat-treated at 500 °C _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x = 0, 0.1, 0.25, 0.4, 0.5, 0.6, 0.8)

After forming the precursor mixture powder in the same manner as in Examples 1-1 to 1-7, heat treatment was performed at 500° C. for 6 hours at a heating rate of 5° C./min, followed by natural cooling at room temperature. At this time, according to the x value of Li _3-x Yb _1-x Zr _x Cl ₆ Example 2-1 (x = 0), Example 2-2 (x = 0.1) Example 2-3 (x = 0.25) , Example 2-4 (x=0.4), Example 2-5 (x=0.5), Example 2-6 (x=0.6), Example 2-7 (x=0.8).

Example 3-1: Li heat-treated at 400 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0)

As precursors, LiCl (99.99%, Sigma Aldrich), YbCl ₃ (99.9%, Alfa Aesar) and HfCl ₄ (99%, Alfa Aesar) were added in a molar ratio of 3: 1: 0 and milled in a molar ratio of Example 1- In the same manner as in 1, Li _3-x Yb _1-x Hf _x Cl ₆ (x = 0) was prepared.

Example 3-2: Li heat-treated at 400 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0.1)

LiCl, YbCl _3, and HfCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in a molar ratio of 2.9: 0.9: 0.1, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Hf _x Cl ₆ (x=0.1) was prepared.

Example 3-3: Li heat-treated at 400 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0.25)

LiCl, YbCl _3, and HfCl ₄ as precursors (99.99%, Sigma Aldrich) were mixed in a molar ratio of 2.75: 0.75: 0.25, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Hf _x Cl ₆ (x=0.25) was prepared.

Example 3-4: Li heat-treated at 400 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0.4)

LiCl, YbCl _3, and HfCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in a molar ratio of 2.6:0.6:0.4, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Hf _x Cl ₆ (x=0.4) was prepared.

Example 3-5: Li heat-treated at 400 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0.6)

LiCl, YbCl _3, and HfCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in a molar ratio of 2.4:0.4:0.6 in the same manner as in Example 1-1, except that Li _3-x Yb _{1- x} Hf _x Cl ₆ (x=0.6) was prepared.

Example 3-6: Li heat-treated at 400 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0.8)

LiCl, YbCl _3, and HfCl ₄ (99.99%, Sigma Aldrich) as precursors were mixed in a molar ratio of 2.2: 0.2: 0.8, and in the same manner as in Example 1-1, Li _3-x Yb _{1- x} Hf _x Cl ₆ (x=0.8) was prepared.

Examples 4-1 to 4-6: Li heat-treated at 500 °C _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x = 0, 0.1, 0.25, 0.4, 0.6, 0.8)

As precursors, LiCl (99.99%, Sigma Aldrich), YbCl ₃ (99.9%, Alfa Aesar) and HfCl ₄ (99%, Alfa Aesar) were added in a molar ratio of 3-x : 1-x : x, and milled and milled in Example 2- Li _3-x Yb _1-x Hf _x Cl ₆ (0≤x≤0.8) was prepared in the same manner as in Examples 3-1 to 3-6, except that the heat treatment was performed at 500 °C in the same manner as in 1. did. At this time, according to the x value of Li _3-x Yb _1-x Hf _x Cl ₆ Example 4-1 (x = 0), Example 4-2 (x = 0.1) Example 4-3 (x = 0.25) , Example 4-4 (x=0.4), Example 4-5 (x=0.6), Example 4-6 (x=0.8).

Comparative Examples 1-1 and 1-2: Li _3-x Yb _1-x Zr _x Cl ₆ Preparation of (x=0.5)

LiCl, YbCl ₃ and ZrCl ₄ (99.99%, Sigma Aldrich) as precursors were added in a molar ratio of 3-x: 1-x: x, mixed and milled at 200 °C (Comparative Example 1-1), 300 °C (Comparative Example) 1-2), except that each heat treatment was carried out in the same manner as in Example 1-5, Li _2.5 Y _0.5 Zr _0.5 Cl ₆ was prepared.

Comparative Examples 2-1 and 2-2: Li _3-x Yb _1-x Hf _x Cl ₆ Preparation of (x=0.4)

LiCl, YbCl ₃ and HfCl ₄ (99.99%, Sigma Aldrich) as precursors were added in a molar ratio of 3-x: 1-x: x, mixed and milled at 200 °C (Comparative Example 2-1), 300 °C (Comparative Example) Except for the heat treatment in 2-2), Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ was prepared in the same manner as in Example 2-4.

Experimental Example 1-1: X-ray diffraction (HRXRD) and AC impedance analysis

For the Li _3-x Yb _1-x Zr _x Cl ₆ (x = 0) (Li ₃ YbCl ₆ ) prepared in Examples 1-1 and 2-1, the crystal structure according to the heat treatment (HT) temperature change was confirmed. To do this, high-resolution X-ray diffraction (HRXRD) analysis was performed, and the Li ⁺ conductivity of Li ₃ YbCl ₆ was measured by the AC impedance method using a Li ⁺ blocking Ti/SE/Ti symmetric cell with a diameter of 6 mm. In addition, a control experiment was performed using Li _2.5 Y _0.5 Zr _0.5 Cl ₆ , which crystallizes from a trigonal to an orthorhombic structure as the HT temperature rises. The results are shown in FIGS. 2 and 3 and Tables 1 to 3.

Specific powder XRD patterns (laboratory scale) were performed using a Rigaku MiniFlex600 diffractometer with Cu Kα radiation (λ = 1.5406 Å). XRD cells containing hermetically sealed solid electrolyte samples with beryllium windows were mounted on an XRD diffractometer and measured at 40 kV and 15 mA. High-resolution synchrotron radiation X-ray data were collected using monochromatic X-rays (λ = 1.5220 Å) at the 9B beamline of the Pohang Accelerator Laboratory (PAL, Korea). Quantitative structural information was obtained by the Rietveld purification method using the FullProf Suite software package.

2 is a high-resolution synchrotron radiation x-ray Rietveld purification profile for Li _3-x Yb _1-x Zr _x Cl ₆ (x=0) (Li ₃ YbCl ₆ ) prepared in Examples 1-1 and 2-1 ( A) and an Arrhenius plot (b) of Li ⁺ conductivity are shown.

Referring to FIG. 2(a), in the case of Li ₃ YbCl ₆ heat-treated at 400° C. of Example 1-1, it has an hcp trigonal structure such as Li ₃ MCl ₆ (M = Y, Er). Crystallized, and in the case of Li ₃ YbCl ₆ heat-treated at 500 °C in Example 2-1, an orthorhombic I structure was formed. These results show that the formation energy of the orthorhombic phase I is slightly lower than the formation energy of the orthorhombic phase.

In addition, (b) of FIG. 2 shows an Arrhenius plot graph of Li ⁺ conductivity and the corresponding activation energy, and the activation of Example 1-1 (400 ° C., Li ₃ YbCl ₆ ) having a trigonal structure (0.47 eV) The energy was lower than that of Example 2-1 (500 °C, Li ₃ YbCl ₆ ) having an orthorhombic I structure (0.53 eV). Also, the Li ⁺ conductivity of Li ₃ YbCl ₆ was slightly higher than that of Example 1-1 (400° C.) (0.19 mS/cm) compared to Example 1-2 (500° C.) (0.14 mS/cm). . These results indicate that the orthorhombic phase is superior to the orthorhombic I phase for Li ₃ YbCl ₆ considering that it leads to higher crystallinity and lower grain-boundary resistance when the heat treatment temperature is 400 °C. Could know.

Through this, it was confirmed that the Li ₃ YbCl ₆ exhibits high Li ⁺ conductivity and low activation energy by forming different crystal structures through heat treatment (HT) at temperatures of 400 and 500 °C. The Li ₃ YbCl ₆ exhibited trigonal (0.19 mS/cm and 0.47 eV) and orthorhombic I (0.14 mS/cm and 0.53 eV) phases when heat treated at 400 and 500° C., respectively. Accordingly, it was found that the Li ₃ YbCl ₆ is a good material for isolating the influence of the crystal structure on the Li ⁺ conductivity.

3 is a graph showing Li _2.5 Y _0.5 Zr _0.5 Cl ₆ prepared in Comparative Examples 1-1 and 1-2 and Examples 1-5 and 2-5 according to the change in heat treatment temperature (a) Li ⁺ conductivity at 30° C. and (b) Li _2.5 Y _0.5 Zr _0.5 Cl ₆ XRD pattern result graph at various temperatures.

Referring to FIG. 3 , Li _2.5 Y _0.5 Zr _0.5 Cl ₆ prepared at 200° C. of Comparative Example 1-1 showed a trigonal structure, but evolved into an orthorhombic II structure as the HT temperature increased. In particular, in the case of Examples 1-5 and 2-5, as the heat treatment temperature increased, the Li ⁺ conductivity slightly decreased, and the activation energy increased. These results show that the orthorhombic II phase has a more advantageous structure than the trigonal phase.

Through this, it can be seen that when a hetero atom is substituted for Yb ³⁺ of Li ₃ YbCl ₆ with a tetravalent metal ion of Hf ⁴⁺ or Zr ⁴⁺ , a sudden phase transition to monoclinic and orthorhombic II occurs, respectively, 0.26 It was confirmed that the Li ⁺ conductivity reached 1.54 mS/cm with an activation energy of eV (Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ ). In particular, it was found that a distinctly different phase transition occurred between the samples annealed at 400 °C and 500 °C, leading to high Li ⁺ conductivity and low activation energy.

Experimental Example 1-2: Crystalline data and Rietveld purification analysis

Crystallographic data and crystallinity data and Rietveld purification analysis by high-resolution X-ray diffraction (HRXRD) analysis data of Experimental Example 1-1 for Li ₃ YbCl ₆ prepared in Examples 1-1 and 2-1 The results are shown in Tables 1 and 2 below.

According to the results of Tables 1 and 2, Li ₃ YbCl ₆ having a trigonal structure prepared in Example 1-1 (400 ° C.) is Li ₃ YCl ₆ (655.723 Å ³ ) or Li ₃ ErCl ₆ (660.350 Å) ³ ) compared to M2-M3 site disorder of 3.6% and a slightly smaller lattice size (645.100 Å ³ ) was confirmed. It was found that the heat-treated solid electrolyte sample had high crystalline properties and a smaller ionic radius Yb ³⁺ (87 pm) than Y ³⁺ (90 pm) or Er ³⁺ (89 pm).

Experimental Example 2-1: X-ray diffraction (XRD), chronological current (CV), ion conductivity and activation energy analysis

Structural evolution according to heat treatment (HT) temperature change for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 and Examples 4-1 to 4-6, Li ⁺ In order to confirm the conductivity and activation energy, ion conductivity and activation energy were measured by X-ray diffraction (XRD) analysis and the same method as in Experimental Example 1. In addition, typical Nyquist plots and Arrhenius plots of Li ⁺ conductance at different temperatures were analyzed. The results are shown in FIGS. 4 to 6 .

4 is (a) 400 ° C. and (b) 500 for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 and Examples 4-1 to 4-6; XRD pattern graph of Li _3-x Yb _1-x Hf _x Cl ₆ heat treated at °C for 6 hours, (c) Phase according to Li _3-x Yb _1-x Hf _x Cl ₆ prepared at 400 °C or 500 °C Schematic showing the change, (d) Li ⁺ conductivity graph at 30 °C, and (e) activation energy graph for Li _3-x Yb _1-x Hf _x Cl ₆ .

4 (a), (b) and (c), in the case of Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 (400 ° C.) , the trigonal structure was preserved up to x = 0.10. However, further substitution of x > 0.10 resulted in a sharp phase transition, and the monoclinic evolution observed in Li ₃ InCl ₆ began to evolve at x = 0.25. For 0.40 ≤ x ≤ 0.60, the main reflection of the XRD pattern belonged to monoclinic.

In addition, in the case of Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 4-1 to 4-6 (500° C.), it is represented as an orthorhombic II phase, which is the Li _3-x Yb _1-x It was observed when prepared with Hf _x Cl ₆ (x≥0.25, Fig. 4b). A pure monoclinic phase was obtained at x=0.80. In Examples 4-1 to 4-6 (500° C.) Li _3-x Yb _1-x Hf _x Cl ₆ , the orthorhombic I structure was maintained at x ≤ 0.10. More substitutions (x ≥ 0.25) resulted in an orthorhombic II structure, which is isostructural with the orthorhombic phase of Li _3-x M _1-x Zr _x Cl ₆ (M = Y, Er, 0.367 < x < 0.6). formed. At x=0.80, the HfCl ₄ precursor was detected at the expense of the reflection of the orthorhombic II phase, indicating a solid-solution limit of x < 0.80.

In addition, referring to FIGS. 4 (d) and (e), the x value increases in Examples 3-1 to 3-6 (400° C.) and Examples 4-1 to 4-6 (500° C.) Li ⁺ conductivity also increased, and it was confirmed that the best Li ⁺ conductivity was exhibited when x=4 and then decreased. On the contrary, the activation energies of Examples 3-1 to 3-6 (400° C.) and Examples 4-1 to 4-6 (500° C.) gradually decreased as the value of x increased, and then reached the highest when x=4. After showing a low activation energy, it was confirmed that there was a slight increase.

5 is a view showing various temperatures for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 (a) Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ heat-treated at 400 ° C. Nyquist plot graphs and (b) Arrhenius plot graphs of Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ of Li ⁺ conductivity heat-treated at 400 °C.

6 is a chronoamperometry of Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ prepared at 400 ° C. with respect to Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-1 to 3-6 CV) is the result graph.

5 and 6, in the case of Li _2.60 Hf _0.40 Yb _0.60 Cl ₆ heat-treated at 400 ° C., it was confirmed that it had a low electronic conductivity of 4.5 x 10 ^-9 S/cm, and thus it could act as a good solid electrolyte. knew that it could be Also, regardless of the HT temperature, the Li _3-x Yb _1-x Hf _x Cl ₆ has the highest Li ⁺ conductivity (1.5 and 1.3 mS/cm) and opposite forms of activation energies corresponding to the lowest activation energies (0.26 and 0.35 eV). This type of behavior is equally observed in many superionic conductors, where the charge carrier concentration of the ion or void dominates the overall ionic conductivity.

Experimental Example 2-2: Ion conductivity and activation energy analysis

Li _3-x Yb _1-x Zr _x Cl prepared in Examples 1-1, 1-2, 1-5 to 1-7 and Examples 2-1, 2-2, 2-5 to 2-7 ₆ , ion conductivity and activation energy were measured in the same manner as in Experimental Example 1 to confirm Li ⁺ conductivity and activation energy according to temperature change in heat treatment (HT). For the experiment, LiCl, YbCl _3, and ZrCl ₄ were mixed at 400 °C and 500 °C, respectively, and the case where x was 0.2 and 0.3 in Li _3-x Yb _1-x Zr _x Cl ₆ was added and analyzed. The results are shown in FIGS. 7 and 8 .

7 shows Li _3-x Yb _1-x Zr _x Cl ₆ prepared in Examples 1-4, 1-6 and 1-7, monoclinic Li _3-x Yb _1- as measured by HRXRD; A graph of lattice parameters for _x Zr _x Cl ₆ (0.4 ≤ x ≤ 0.8).

8 shows Li _3-x Yb _1-x prepared in Examples 1-1, 1-2, 1-5 to 1-7 and Examples 2-1, 2-2, 2-5 to 2-7; XRD pattern graph of Li _3-x Yb _1-x Zr _x Cl ₆ (0.4 ≤ x ≤ 0.8) heat treated at (a) 400 °C and (b) 500 °C for Zr _x Cl ₆ (0 ≤ x ≤ 0.8) and (c) Li ⁺ conductivity for Li _3-x Yb _1-x Zr _x Cl ₆ at 30 °C and (d) activation energy for Li _3-x Yb _1-x Zr _x Cl ₆ .

7 and 8 , the activation energy, structural evolution tendency and Li ⁺ conductivity for the Li _3-x Yb _1-x Zr _x Cl ₆ (Li ₃ YbCl ₆ substituted with Zr ⁴⁺ ) are the above-described Hf It was the same as the result of Li ₃ YbCl ₆ substituted with ⁴⁺ . It can be seen that this is a predictable result when considering a similar ionic radius (Zr ⁴⁺ : 72 pm, Hf ⁴⁺ : 71 pm). In particular, the monoclinic phase crystallized at 400 °C showed higher Li ⁺ conductivity and lower activation energy over the entire composition range compared to the orthorhombic II phase crystallized at 500 °C.

These results indicate that the monoclinic structure is more favorable for Li ⁺ diffusion in Li _3-x Yb _1-x Zr _x Cl ₆ than the orthorhombic structure, and the only contribution of the crystal structure to the Li ⁺ conductivity can be confirmed. It was confirmed that the monoclinic structure with ccp anion arrangement is more advantageous in ionic conductivity than the hcp-based orthorhombic structure. This has better ion conductivity by the 3D channel, which is the ion migration path for the ccp monoclinic structure, and contrasts with the anisotropic ion migration path for the hcp structure, such as trigonal and orthorhombic phases. In addition, Li ⁺ diffusion was more favorable when Li ⁺ ions were present in the tetrahedral sites. Accordingly, compared with Li _3-x Yb _1-x Zr _x Cl ₆ of the orthorhombic II phase heat treated at 500 °C, the results for monoclinic Li _3-x Yb _1-x Zr _x Cl ₆ heat treated at 400 °C It was found to have higher Li ⁺ conductivity despite the low HT temperature.

Through this, in the case of Li _3-x Yb _1-x Hf _x Cl ₆ prepared at 400 °C and 500 °C, the initial structures of trigonal and orthorhombic I have the highest conductivity and lowest activation energy at x = 0.40, respectively. It can be seen that the phase change has occurred in completely different structures of monoclinic and orthorhombic II. The average value of the metal ion radius of Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ (80.6 pm) was close to that of In ³⁺ (80 pm) or Li _2.5 Y _0.5 Zr _0.5 Cl ₆ (81 pm) in the case of Li ₃ InCl ₆ . This means that the monoclinic or orthorhombic II structure is an evolved structure for Li _3-x Yb _1-x Hf _x Cl ₆ . The critical temperature for the evolution of a particular structure was configuration-dependent, specifically, Li _3-x Yb _1-x Hf _x Cl ₆ and Li _3-x Y _1-x Zr _x Cl ₆ had different temperatures of 400 to 400, respectively. It was crystallized into an orthorhombic II phase at 500 °C and 300 to 400 °C, and it was found that the HT protocol as well as the size of metal ions were decisive factors for the phase transition.

Experimental Example 3: X-ray diffraction (XRD), ion conductivity and activation energy analysis

Rietveld purification profile was analyzed for HRXRD pattern for in-depth analysis of Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-4, 4-4 and Comparative Examples 2-1 and 2-2 did. The results are shown in FIGS. 9 and 10 and Tables 3 to 6 .

9 is a view showing Li _2.60 Yb _0.60 heat-treated at (a) 400° C. and (b) 500° C. for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-4 and 4-4. Observed and calculated high-resolution synchrotron radiation x-ray Rietveld purification profile graph for Hf _0.40 Cl ₆ . The Bragg position in FIG. 9(b) represents an orthorhombic II phase with different lattice parameters.

10 is 200 ℃, 300 ℃, 400 ℃, 500 for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Examples 3-4, 4-4 and Comparative Examples 2-1 and 2-2 It is an XRD pattern graph of Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ prepared by ball milling according to whether or not heat treatment was performed at ℃.

According to the results of FIGS. 9 and 10 and Tables 3 and 4, in the case of Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ heat treated at 400 ° C., it was confirmed that the monoclinic and orthorhombic II phases accounted for 70.5% and 29.5%, respectively. From these results, it was assumed that the Li ⁺ conductivity of the pure monoclinic phase was slightly higher than the measured value (1.5 mS/cm). In addition, a pure monoclinic phase of Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ was not obtained through HT at a lower temperature. Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ heat-treated at less than 400° C. exhibited orthorhombic II phase properties and poor crystallinity, thereby preventing purification ( FIG. 10 ).

According to the results of FIGS. 9, 10 and Tables 5 and 6, the HRXRD pattern for Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ of Example 4-4 (500° C.) is orthorhombic in the same space group with different lattice parameters. It was confirmed that two phases belonging to the II structure were formed. That is, it was found that each crystallized into two phases with different lattice sizes in the orthorhombic II structure. In general, multiphase regions have been reported to appear during the synthesis of NaMO ₂ (M = Fe, Co) negative electrode materials stacked via HT or charge-discharge processes. In addition, the lattice parameters of crystalline solid electrolyte materials can vary depending on the degree of heat treatment, where the separated regions with different phases formed at low temperatures (e.g., 400 °C) evolved into the same orthorhombic II phase, but with an increase of 500 °C. It was confirmed that they had different lattice parameters at different temperatures.

Experimental Example 4: SEM and charge/discharge performance analysis

For Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Example 3-4, SEM analysis and charging/discharging cycling performance of cold-pressed pellets according to high and low magnifications were analyzed to confirm the cross-sectional area of the solid electrolyte. did. At this time, the applied pressure for cold pressing was 370 MPa. In addition, the compatibility of the optimal composition Hf ⁴⁺ substituted Li ₃ YbCl ₆ (Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ ) showing the highest Li ⁺ conductivity (1.5 mS/cm, prepared at 400 °C) for a single NCA88 negative electrode material was 0.5C , 30 °C and a voltage range of 3.0–4.3V (vs. Li/Li + ) were evaluated using a half-cell. The results are shown in FIGS. 11 and 12 .

11 is an SEM image of the cold-pressed pellets at (a) high magnification and (b) low magnification for Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Example 3-4.

12 shows a single NCA88 electrode using Li _3-x Yb _1-x Hf _x Cl ₆ prepared in Example 3-4 (a) 0.5 C (0.64 mA/cm ² ) and a single NCA88/ A graph of the cycling performance of a single NCA88 electrode in a Li-In all-solid-state battery and (b) a graph of the corresponding charge/discharge voltage profile.

11 and 12, the deformability of the Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ confirmed the flat surface of the cold-pressed pellets at an applied pressure of 370 MPa. As a result of checking the cycling performance and the corresponding charge-discharge voltage profile at 2, 150, 500, and 1000 cycles, the all-solid-state battery had a high discharge capacity (188 mAh/g) and a coulombic efficiency (84.8%) in the initial cycle. showed In addition, it was confirmed that the capacity retention rate at 1000 cycles was maintained at a high level of 83.6%.

As described above, the structural evolution of Li ₃ YbCl ₆ substituted with Hf ⁴⁺ or Zr ⁴⁺ through Examples 1 to 4 and the corresponding Li ⁺ conductivity were at two different HT temperatures of 400 ° C and 500 ° C. It was confirmed that it depends on Unsubstituted Li ₃ YbCl ₆ was trigonal and orthorhombic, respectively, with slightly higher Li ⁺ conductivity (0.19 vs. 0.15 mS/cm) and lower activation energy (0.47 vs. 0.53 eV) when annealed at 400 °C and 500 °C. Crystallized differently with a crystalline I structure. In addition, upon heterovalent substitution with Hf ⁴⁺ or Zr ⁴⁺ , the Li ⁺ conductivity was maximally increased to 1.5 mS/cm (0.26 eV), and a rapid phase transition was confirmed. In particular, it was confirmed that crystallization from orthorhombic I to orthorhombic II was observed for HT at 500 °C from trigonal to monoclinic at 400 °C.

In particular, Li _3-x Yb _1-x Hf _x Cl ₆ (Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ ) annealed at a low temperature of 400 °C showed higher Li ⁺ conductivity and lower activation energy, which is a halide type It was confirmed that the only effect of the crystal structure on Li ⁺ diffusion in the solid electrolyte was. That is, the monoclinic structure was more advantageous than the orthorhombic structure. Specifically, it has the highest Li ⁺ conductivity of 1.5 mS/cm in intrinsic electrochemical oxidation and optimum composition Li _2.60 Yb _0.60 Hf _0.40 Cl ₆ . It showed good capacity retention of 83.6% in two cycles. These results confirmed that they are important not only in terms of practical applicability to all-solid-state batteries, but also in terms of the design principle of a new halide superionic conductor.

Claims (22)

A lithium halide-based solid electrolyte comprising a compound represented by the following formula (1).
[Formula 1]
Li _3-x M1 _1-x M2 _x X ₆
(In Formula 1, x is 0.2≤x≤0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.)
According to claim 1,
wherein M1 is at least one lithium halide selected from the group consisting of Yb, Sc, Y, In, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu based solid electrolyte.
According to claim 1,
wherein M2 is at least one selected from the group consisting of Hf, Zr and Ti.
According to claim 1,
Wherein X is F, Cl or Br of lithium halide-based solid electrolyte.
According to claim 1,
Wherein x is 0.3≤x≤0.6,
Wherein M1 is Yb or Er,
M2 is Hf or Zr,
Wherein X is Cl or Br. Lithium halide-based solid electrolyte.
6. The method of claim 5,
wherein x is 0.4≤x≤0.5,
wherein M1 is Yb,
M2 is Hf or Zr,
Wherein X is Cl. Lithium halide-based solid electrolyte.
According to claim 1,
The lithium halide-based solid electrolyte is monoclinic, orthorthombic II, or a mixture thereof by heat-treating a precursor mixture including lithium halide, M1 metal halide, and M2 metal halide to obtain heterovalent substitution. A lithium halide-based solid electrolyte having a crystal structure consisting of
8. The method of claim 7,
The heat treatment is a lithium halide-based solid electrolyte that is performed at a temperature of 300 to 600 ℃ for 3 to 8 hours.
According to claim 1,
The lithium halide-based solid electrolyte has a lithium ion conductivity of 1 to 3 mS/cm and an activation energy of 0.1 to 0.5 eV.
anode layer; cathode layer; and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, comprising:
At least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer is an all-solid-state battery comprising the lithium halide-based solid electrolyte of any one of claims 1 to 9.
11. A device comprising the all-solid-state battery of claim 10, comprising:
The device is a transport device or an energy storage device.
preparing a precursor mixture by solid-phase mixing lithium halide, M1 metal halide and M2 metal halide as precursors in an inert gas atmosphere; and
preparing a lithium halide-based solid electrolyte including a compound represented by the following Chemical Formula 1 by heat-treating the precursor mixture;
A method for producing a lithium halide-based solid electrolyte comprising a.
[Formula 1]
Li _3-x M1 _1-x M2 _x X ₆
(In Formula 1, x is 0.2≤x≤0.8, M1 is a metal element having an oxidation number of +3, M2 is a metal element having an oxidation number of +4, and X is a halogen element.)
13. The method of claim 12,
Wherein the lithium halide is at least one selected from the group consisting of LiCl, LiBr, LiI and LiF.
13. The method of claim 12,
The M1 metal halide is at least one M1 selected from the group consisting of Yb, Sc, Y, In, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu. A method for producing a lithium halide-based solid electrolyte which is an M1 metal halide containing a metal.
13. The method of claim 12,
The M2 metal halide is an M2 metal halide comprising at least one M2 metal selected from the group consisting of Hf, Zr and Ti.
13. The method of claim 12,
In the precursor mixture, the lithium halide, M1 metal halide and M2 metal halide are mixed in a molar ratio of 2 to 3.3: 0.1 to 1.5: 0.1 to 1.2.
13. The method of claim 12,
The method for producing a lithium halide-based solid electrolyte, wherein the inert gas is at least one selected from the group consisting of argon, helium, neon and nitrogen.
13. The method of claim 12,
The solid-phase mixing is performed by any one mechanical milling selected from the group consisting of a ball mill, a vibration mill, a turbo mill, a mechanofusion, and a disk mill.
19. The method of claim 18,
The method for producing a lithium halide-based solid electrolyte, wherein the mechanical milling is performed for 7 to 15 hours at a rotation speed of 400 to 800 rpm.
13. The method of claim 12,
The method for producing a lithium halide-based solid electrolyte wherein the heat treatment is performed at a temperature of 300 to 600 ℃ for 3 to 8 hours.
13. The method of claim 12,
The lithium halide-based solid electrolyte is a method of manufacturing a lithium halide-based solid electrolyte having a crystal structure consisting of monoclinic, orthorthombic II, or a mixture thereof.
13. The method of claim 12,
wherein x is 0.4≤x≤0.5,
M1 is Yb,
M2 is Hf or Zr,
wherein X is Cl,
The precursor mixture is a mixture of the lithium halide, M1 metal halide and M2 metal halide in a molar ratio of 2.5 to 2.7: 0.5 to 0.7: 0.3 to 0.5,
The inert gas is argon,
The solid-phase mixing is performed by mechanical milling of a ball mill,
The mechanical milling is performed for 9 to 11 hours at a rotation speed of 550 to 650 rpm,
The heat treatment is carried out at a temperature of 400 to 500 °C for 5.5 to 6.5 hours,
The lithium halide-based solid electrolyte has a crystal structure consisting of a mixture of monoclinic and orthorthombic II,
The lithium halide-based solid electrolyte has a lithium ion conductivity of 1.3 to 1.5 mS/cm and an activation energy of 0.26 to 0.35 eV.

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