Solid electrolyte including halide, method of preparing the same, and secondary battery including the same

Abstract

To provide a novel halide-based solid electrolyte composition exhibiting improved ion conductivity, a method for producing the same, and a secondary battery including the same.SOLUTION: In the solid electrolyte composition containing a lithium yttrium halide having a hexagonal close-packed structure, when the number occupied by metal ions in the number of metal ion sites in two continuous layers constituting a unit cell of the hexagonal close-packed structure is defined as the occupancy of the metal ions, the sum of the occupancies of the metal ions in the two layers is 0.888 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a halide-containing solid electrolyte, and more particularly to a novel halide-based solid electrolyte exhibiting improved ionic conductivity, a method for producing the same, and a secondary battery including the same. [Background technology]

[0002] There is growing interest and research in semi-solid or all-solid-state batteries, in which some or all of the liquid electrolyte is replaced with a solid electrolyte.

[0003] However, the solid electrolyte is required to have excellent interfacial properties between the electrolyte layer containing it and the active material layer, as well as excellent contact properties between the solid electrolyte and the active material particles, and is also required to have excellent lithium ion conductivity comparable to that of a liquid electrolyte.

[0004] To meet these requirements, various solid electrolytes have been studied, and for example, sulfide-based solid electrolytes, oxide-based solid electrolytes, and halide-based solid electrolytes have been proposed.

[0005] Sulfide-based solid electrolytes have the advantage of being more flexible than oxide-based solid electrolytes, making it easier to induce close contact between the solid electrolyte and active material particles and thus having relatively excellent lithium ion conductivity. However, they have the disadvantage of being less stable when exposed to moisture or oxygen in the air, making the battery manufacturing process difficult. Furthermore, oxide-based solid electrolytes have the disadvantage of being difficult to ensure good contact characteristics between the solid electrolyte and the active material, resulting in insufficient ion conductivity.

[0006] In recent years, in order to solve the drawbacks of the sulfide-based or oxide-based solid electrolytes, halide-based solid electrolytes have been proposed, which exhibit excellent stability and a certain level of ionic conductivity.

[0007] Most halide-based solid electrolytes have a layered structure, a rock-salt structure, or a similar structure. Among them, hcp-Li3YCl6-based solid electrolytes in particular have various compositions, with various components being substituted or added, including Zr and lanthanum.

[0008] It is known that such halide-based solid electrolytes exhibit high levels of ionic conductivity through mechanochemical synthesis, but the underlying mechanism has not been fully elucidated, and it has not yet been possible to control the ionic conductivity of halide-based solid electrolytes or freely design halide solid electrolytes with high ionic conductivity. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2023-0092885 [Patent Document 2] Japan Special Publication No. 2023-519758 Summary of the Invention [Problem to be solved by the invention]

[0010] In order to solve the above-mentioned problems of the prior art, an object of the present invention is to provide a novel halide composition that optimizes the ionic conductivity of a halide-based solid electrolyte.

[0011] Another object of the present invention is to provide a chloride composition in which trivalent metal ions are substituted with tetravalent metal ions while suppressing the loss of lithium in a hexagonal close-packed halide (lithium yttrium chloride).

[0012] Another object of the present invention is to provide a halide (lithium yttrium chloride) that limits the occupancy of metal ions within layers in a halide with a hexagonal close-packed structure.

[0013] Another object of the present invention is to provide a lithium secondary battery containing the above-mentioned halide as a solid electrolyte. [Means for solving the problem]

[0014] In order to achieve the above technical objectives, the present invention provides a solid electrolyte composition containing a lithium yttrium halide having a hexagonal close-packed structure, wherein, when the metal ion occupancy is defined as the number of metal ions out of the total number of metal ion sites in two consecutive layers constituting a unit cell of the hexagonal close-packed structure, the sum of the metal ion occupancies in the two layers is 0.888 or less.

[0015] In the present invention, it is preferable that each of the layers has a metal ion occupancy rate of 0.444 or less.

[0016] The halide has the composition formula Li 3-a (Y 1-(4-4x) A 3-3x+(a / 4) The present invention provides a solid electrolyte composition containing a halide having a hexagonal close-packed structure expressed as: )Cl6 (A is a tetravalent cation, x = 0.75 to (0.888 - a / 4), a = 0 to 0.552).

[0017] In the present invention, A may contain at least one element selected from the group consisting of Ti, Zr, Hf, and Rf.

[0018] In the present invention, the halide may contain (1-x) moles of vacancies in its crystal structure.

[0019] In order to achieve the above-mentioned other technical object, the present invention provides a lithium secondary battery containing the above-mentioned solid electrolyte composition in an electrolyte layer. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a halide-based solid electrolyte composition having high ionic conductivity.

[0021] Furthermore, the present invention can provide a halide having an expanded lithium ion conduction path by limiting the metal occupancy rate within the layers in a halide having a hexagonal close-packed structure. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1(a) is a diagram showing the crystal structure of hcp-Li3YCl6, and FIG. 1(b) is a diagram for explaining possible arrangement models depending on the arrangement type of metal in the crystal structure of hcp-Li3YCl6. [Figure 2] 1A is a diagram illustrating the ordering of metal ions in each arrangement model, and FIG. 1B is a diagram for explaining the diffusion path of lithium at each site. [Figure 3] FIG. 1(a) is a graph showing the calculation results of the activation barrier due to the metal ion arrangement rule, and (b) to (d) are diagrams for explaining the difference in the ion conduction path due to the metal ion arrangement rule. [Figure 4] FIG. 2 is a diagram for explaining a design rule for a halide composition according to an embodiment of the present invention. [Figure 5] FIG. 2 is a diagram illustrating the metal ion occupancy rate of each layer in a halogenated composition having a hexagonal close-packed structure and the ion conduction pathways depending on the occupancy rate. [Figure 6] 1 is a graph plotting calculated layer occupancy rates in a unit cell of a hexagonal close-packed structure of a target composition according to an embodiment of the present invention; [Figure 7] 7 is a table summarizing the compositions and sources of the prior art documents plotted in FIG. 6. [Figure 8]1 is a graph showing the results of X-ray diffraction analysis of a halide sample prepared according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Please note that in the following description, only the parts necessary for understanding the embodiments of the present invention will be described, and descriptions of other parts may be omitted so as not to obscure the gist of the present invention.

[0024] The terms and phrases used in the following specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of terms to best describe his own invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely preferred embodiments of the present invention, and do not represent the entire technical idea of ​​the present invention. Therefore, it should be understood that various equivalents and modifications may exist as of the time of filing this application.

[0025] In the following description, a compound defined by its constituent elements may include a compound containing an element that replaces part of the referred element or that is in addition to the referred element. When a compound name is referred to by its constituent elements, for example, lithium yttrium chloride (LYC) does not only refer to a ternary compound composed of lithium, yttrium, and chlorine, but also includes a quaternary or higher compound that contains one or more other elements that substitute for part of the metal ion or that further contains other intersitial elements in the crystal structure.

[0026] The present invention will now be described in detail with reference to the drawings.

[0027] <A. Halide solid electrolyte>

[0028] [A-1. Crystal structure of hcp-Li3YCl6]

[0029] Figure 1(a) shows the crystal structure of hcp-Li3YCl6 (hereinafter referred to as hcp-LYC), and Figure 1(b) shows two possible arrangement models in the hcp-LYC structure depending on the metal arrangement type, namely, the ααα model and the αββ model.

[0030] Referring to FIG. 1(a), in the exemplary structure of hcp-LYC, two layers, Layer 1 and Layer 2, are arranged in succession, so that Cl - The ions form a hexagonal closed packed structure, and Cl - Lithium ions and metal ions are arranged in the octahedral site formed by the ions.

[0031] As shown in Figure 1(a), there are two sites in each layer where metal ions can enter. One site is the 1a site located at the vertex of the unit cell, and the other site is the 2d site located in the center of each layer.

[0032] A-2. Layer structure modeling and optimization of hcp-Li3YCl6

[0033] To understand the ionic conductivity change due to the number and arrangement of metal ions, two models can be established based on the location of the metal ions within the 2d site. One model includes an ααα layer in which metal ions coexist within the 2d site and the 1a site, as shown in Figure 1(b). The other model includes an αββ layer in which ions are separated into layers within the 2d site and the 1a site, as shown in Figure 1(c). The latter structure may be the most stable arrangement in the hcp-LYC structure.

[0034] For both models, we performed ionic conductivity calculations for the overall structure and the ab-plane / c-axis conductivity, which are shown in Figure 1(d). The ionic conductivity was calculated using AIMD (ab initio molecular dynamics) simulations, using the Vienna ab-initio Simulation Package (VASP) software.

[0035] Referring to FIG. 1(d), it can be seen that the conductivity of the αββ model has a higher value.

[0036] It is noteworthy that in the ααα model, although the c-axis diffusion rate is faster than that of the αββ model, the diffusion rate in the ab plane is slower than that of the αββ model, resulting in a lower overall ionic conductivity. This suggests that ab plane diffusion determines the overall ionic conductivity in this structure. Therefore, it is necessary to explain the effect of metal arrangement on ab plane diffusion.

[0037] Figure 2(a) illustrates the ordering of metal ions in each model. As shown in Figure 2(a), the ααα model allows Y-free ordering and Y-3 ordering, while the αββ model allows Y-1 ordering and Y-2 ordering. Here, the number following Y indicates the number of metal atoms contained in the unit cell on the ab plane.

[0038] By separating the layers of each model individually and examining the sites where Li can exist in the ab plane, it can be seen that in the cases of Y-free ordering, where there are no metal ions, and Y-1 ordering, where there is only one metal ion in total, an environment in which Li can percolate can be created overall, while in the cases of Y-2 ordering and Y-3 ordering, Li is isolated between metal ions, creating an environment in which ion diffusion is difficult.

[0039] FIG. 2(b) is a diagram for explaining the diffusion path of lithium at each site.

[0040] Referring to Figure 2(b), it can be seen that in order for lithium ions to move, they must pass through intermediate tetrahedral sites that are face-shared with octahedral sites that can be occupied by metal ions. In this case, the diffusion path when metal ions are in the octahedral sites is called T Y The diffusion path when the octahedral site is vacant is T V Then, T Y In the case of , the repulsive force of metal ions is strong, making it difficult for lithium ions to pass through, while in the case of T where there are no metal ions, V In this case, it can be understood that the environment is such that lithium ions can easily pass through the tetrahedral sites.

[0041] The energy required for metal ions to pass through tetrahedral sites and the hopping rate were simulated depending on whether the metal ions occupy the octahedral sites or not. The energy was calculated using VASP, and the hopping rate in the simulation results was analyzed using the MATLAB program.

[0042] 2(d) and (e) are graphs showing the simulation results. Referring to the figures, when metal ions exist on both lithium migration paths (i.e., T Y T Y ), the energy required for the passage is very high, making it difficult for lithium to move, and therefore, a low hopping rate was observed. V T Y ) contains high-energy T Y Instead, low energy T VIt was also confirmed that when there are no metal ions in either of the two, lithium ions can pass through both pathways.

[0043] Uniquely, there are no metal ions in the lithium pathway. V T V Compared to T, which has one metal ion V T Y or T Y T V It can be seen that the diffusion of lithium ions is faster in the case of . This phenomenon can be explained as follows.

[0044] When comparing a Y-free ordered layer, which has no metal ions in a single layer, with a Y-1 ordered layer, which has one metal ion in a single layer, the biggest difference in lithium conduction is that the width of the most important path in plane diffusion (i.e., the interlayer distance) varies depending on the number of metal ions.

[0045] To investigate the effect of the interlayer distance on diffusion, T v T v The activation barrier was calculated by varying the interlayer distance in each case. The activation barrier was calculated using Nudged Elastic Band (NEB) simulation software, VASP.

[0046] Figure 3(a) shows the T v T v 1 is a graph showing the activation barrier calculation results. The T v T v It can be seen that the activation barrier changes in the same way. It can also be seen that the activation barrier for diffusion decreases as the interlayer distance increases.

[0047] On the other hand, the effect of the Y occupancy on the interlayer spacing was calculated, and the results are shown in Figure 3(d). The interlayer spacing was calculated by analyzing the results of first-principles calculations. The software used was VASP.

[0048] Referring to FIG. 3(d), it can be seen that the occupancy of Y increases until it reaches 0.166 and then saturates.

[0049] In other words, it was found that the difference in the diffusion degree between Y-free ordering and Y-1 ordering without metal ions is due to the difference in the interlayer distance, and that when there are 0.166 or more metal ions, the lithium ion pathways become wider to a certain extent.

[0050] Furthermore, as shown in Figure 3(c), it can be calculated that when Y is present in the lithium diffusion path, distortion of the intermediate site occurs, and it can be seen that such elongation of the tetrahedral site also affects the expansion of the interlayer distance.

[0051] On the other hand, Figure 3(b) shows that the distance between adjacent Y ions is significantly shorter in the Y-1 layer (7.19 Å) than in the Y-free layer (8.83 Å), so the c-axis repulsion component between adjacent planar Y ions becomes stronger, which increases the interlayer spacing from 5.97 to 6.17 Å.

[0052] B. Composition of halide solid electrolyte

[0053] As mentioned above, diffusion in the ab plane can proceed quickly when the interlayer distance is large enough to allow lithium ions to percolate within the layers. While a small number of metal ions within a layer is favorable for percolation, the interlayer distance can only be large if there is an appropriate number of metal ions.

[0054] The range satisfying both of these conditions may be specified as follows. The occupancy of metal ions in each layer is preferably equal to or greater than a predetermined lower limit to ensure sufficient interlayer distance and equal to or less than a predetermined upper limit to provide permeation in each layer. Preferably, in the present invention, the lower limit may be 0.166 and the upper limit may be 0.444.

[0055] In the present invention, the upper limit may be determined as follows.

[0056] Referring to FIG. 4(a), when a hexagonal unit cell is set based on metal ions, the condition for lithium ion penetration is that all lithium ions in the hexagonal unit cell are T V T Y or T V T V To achieve this state, the central metal ion must be vacant, and the two metal ions at the corners of the unit cell must be vacant. At occupancy rates above this, lithium ions cannot pass through the unit cell.

[0057] Figure 4(a) explains and illustrates a method for calculating the occupancy threshold for percolating to occur. A hexagonal unit cell contains one central metal ion site and six vertex sites. However, the vertex site is shared by two adjacent unit cells, resulting in a total of three metal ion sites per unit cell. Therefore, the maximum number of metal ions in a unit cell in the critical state where percolating is possible, in which the central metal ion is vacant and the two metal ions at the vertices of the unit cell are vacant, is (4 * 1 / 3), and the metal ion occupancy can be calculated as ((4 * 1 / 3) / 3 = 4 / 9 ≒ 0.444).

[0058] Based on these results, design rules for the state in which lithium can penetrate can be determined.

[0059] As mentioned above, the hcp-LYC structure consists of two consecutive layers. In a composition where the metal to anion ratio is 1:6, there are a total of six metal ion sites in the two layers, and a total of three metal ions. In a composition where the metal to anion ratio is 1:6, it is possible for all metal ion sites in one layer to be occupied by metal ions (e.g., Y-3 ordering), which can be expressed as an occupancy of 1. On the other hand, in this case, all metal ion sites in the adjacent layer may be vacant (e.g., Y-free ordering), which can be expressed as an occupancy of 0. Therefore, in the hcp-LYC structure, each layer may have an occupancy value ranging from 0 to 1. If the occupancy of one layer is k, the occupancy of the adjacent layer can be expressed as 1-k. In other words, the sum of the occupancies of two consecutive layers should be 1.

[0060] Figure 5(a) shows the Y ion sites in a hexagonal unit cell. As shown, there is one Y ion site at the center and six Y ion sites at the corners.

[0061] In Figure 5(b), CASE I shows the occupancy rate k of Y ions depending on whether each vertex is occupied or not when the central Y ion site is occupied by a Y ion, and CASE II shows the occupancy rate k of Y ions depending on whether each vertex is occupied or not when the central Y ion site is vacant.

[0062] FIG. 5(c) is a diagram showing the penetration path of Li depending on the occupancy rate k of Y ions.

[0063] As mentioned above, the critical value of the occupancy rate of a layer through which ions can permeate is 0.444. If one of two adjacent layers has a metal ion occupancy rate of k=0.444, the occupancy rate of the other adjacent layer, 1-k, must be 0.556 (=1-0.444). In this case, the number of metal ions in the other layer exceeds the critical value, so it must become a non-percolating layer.

[0064] For example, in order for an hcp-LYC solid electrolyte to have high ionic conductivity, the maximum value of the metal ion occupancy in the structure is 0.444, so the sum of the occupancies of two adjacent layers should be designed to be 0.444*2=0.888 or less.

[0065] Based on this finding, the inventors of the present invention have designed a composition that can realize high ionic conductivity without varying the number of Li atoms in the unit cell, while maintaining the sum of the metal occupancies of two consecutive layers at 0.888 or less.

[0066] That is, the present invention provides an hcp-LYC-based solid electrolyte composition in which the number of metal ions contained in the hcp-LYC-based solid electrolyte composition is reduced, and the metal ion occupancy of each individual layer is 0.444 or less, and the sum of the metal ion occupancies of the two layers is 0.888 or less.

[0067] FIG. 6 is a graph plotting the calculated occupancy rates of Layer 1 and Layer 2 in a unit cell for the target composition of the present invention and compositions reported in the prior art. Referring to FIG. 6, it can be seen that in the case of the prior composition, the metal content is relatively high outside the target region of the present invention. In the formula of FIG. 6, Li a M x Cl b In the formula, M represents a trivalent or tetravalent ion such as Y, Ho, Er, or Zr that forms a hcp-trigonal structure.

[0068] FIG. 7 is a table summarizing the literature compositions and sources plotted in FIG.

[0069] The composition of the present invention can be expressed by the following composition formula:

[0070] (compositional formula 1) Li3(Y 1-(4-4x) A 3-3x )Cl6 (A is a tetravalent cation and x = 0.75 to 0.888.)

[0071] In the present invention, A contains at least one element selected from the group consisting of Ti, Zr, Hf and Rf.

[0072] In the present invention, the range of x values ​​may be calculated as follows:

[0073] Here, 1 - (4 - 4x) is reduced to 4x - 3, but 4x - 3 ≥ 0 must be satisfied, so x ≥ 0.75. Meanwhile, in composition formula 1, the number of atoms, 4x - 3 + 3 - 3x, becomes x, which is twice the percolation threshold of each layer, 0.167 to 0.444, and is limited to a minimum of 0.333 and a maximum of 0.888. Therefore, the value of x that satisfies both of these conditions is 0.75 ≤ x ≤ 0.888.

[0074] As in formula 1, trivalent ions are replaced with higher tetravalent ions (A4+ ) and the resulting vacancies are reflected in the formula:

[0075] (compositional formula 2) Li3(Y 1-(4-4x) A 3-3x □ (1-x)) Cl6 (where □ is a vacancy and x = 0.75 to 0.888)

[0076] Meanwhile, in consideration of the case where vacancies are formed corresponding to some of the substituted tetravalent ions and the number of lithium ions is reduced corresponding to the remaining substituted ions to maintain charge balance, the composition formula of the present invention may be more generally expressed as follows:

[0077] (compositional formula 3) Li 3-a (Y 1-(4-4x) A 3-3x+(a / 4) )Cl6 (A is a tetravalent cation, x = 0.75 to (0.888-a / 4), a = 0 to 0.552)

[0078] The composition formula reflecting the generated vacancies is as follows:

[0079] (compositional formula 4) Li 3-a (Y 1-(4-4x) A 3-3x+(a / 4) □(1-x))Cl6 (A is a tetravalent cation, x=0.75~(0.888-a / 4), a=0~0.552)

[0080] In the composition formulas 3 and 4, when a, which indicates the reduction ratio of lithium ions, is set to 0, the composition formulas are the same as the composition formulas 1 and 2.

[0081] Illustrative experimental examples of the present invention will now be described.

[0082] <Experimental Example 1>

[0083] To obtain the composition shown in Table 1 below, LiCl, YCl3, and ZrCl4 were weighed out according to the molar ratios of Li, Y, Zr, and Cl in the formula, and then the composition was synthesized by mechanochemical synthesis using a ball mill. The mechanochemical synthesis conditions for this synthesis were a Fritsch Pulverisette 7PL at 800-900 rpm, a ball-to-powder ratio of 25:1, and 10 g of 10 mm ZrO2 balls and 15 g of 5 mm ZrO2 balls. Each step consisted of 15 minutes of milling and a 5 minute rest, for a total of 12 steps, totaling 4 hours.

[0084] The composition formula of this experiment is shown in Figure 6: Li a M x Cl b In the composition formula expressed as follows, x, which indicates the molar ratio of metal ions (M), corresponds to the region where x is 0.8 to 0.888.

[0085] To measure the ionic conductivity of the synthesized composition, a symmetrical cell with a SUS / solid electrolyte / SUS structure was used, which can prevent electrodeposition and desorption of ions in the electrolyte. The solid electrolyte was compressed to form a pellet at 254 MPa, and AC impedance measurements were performed at frequencies from 3 MHz to 100 MHz using Biologic's VMP3 under a pressure of 75 MPa.

[0086] Table 1 shows the ionic conductivity of each composition.

[0087] [Table 1]

[0088] Figure 8 is a graph showing the results of X-ray diffraction analysis for sample #3. For comparison, the XRD data for Li3YCl6 (i.e., x = 1) is also shown. From Figure 8, it was confirmed that sample #3 has the same structure as the comparative example, Li3YCl6. In addition, Zr 4+The diffraction pattern shifted to the right due to the introduction of Zr, which has a small ionic radius and induces the generation of vacancies. 4+ This result indicates that the lattice constant is reduced by the addition of

[0089] <Experimental Example 2>

[0090] To obtain a composition having the composition formula shown in Table 2 below, starting materials were weighed according to the molar ratios of Li, Y, Zr, and Cl in the composition formula, and then the composition was synthesized. a M x Cl b In the composition formula expressed as follows, the region where x, which indicates the molar ratio of metal ions (M), is 0.9 or more.

[0091] The ionic conductivities of the synthesized compositions were measured and are shown in Table 2.

[0092] [Table 2]

[0093] <Experimental Example 3>

[0094] To obtain a composition satisfying the formula in Table 3, where the metal ion ratio is 0.8, the starting materials were weighed according to the molar ratios of Li, Y, Zr, and Cl in the formula, and then the composition was synthesized. The value of a in formula 3 was calculated and shown in Table 3.

[0095] The ionic conductivities of the synthesized compositions were measured and are shown in Table 3.

[0096] [Table 3]

[0097] <Experimental Example 4>

[0098] To obtain a composition satisfying the formula in Table 4, where the metal ion ratio is 0.85, the starting materials were weighed according to the molar ratios of Li, Y, Zr, and Cl in the formula, and then the composition was synthesized. The value of a in formula 3 was calculated and shown in Table 4.

[0099] The ionic conductivities of the synthesized compositions were measured and are shown in Table 4.

[0100] [Table 4] <Experimental Example 5> To obtain a composition that satisfies the formula in Table 5, in which the ratio of metal ions is 0.88, the starting materials were weighed according to the molar ratios of Li, Y, Zr, and Cl in the formula, and then the composition was synthesized. The ionic conductivities of the synthesized compositions were measured and are shown in Table 5. [Table 5]

[0101] B. Secondary battery containing a halide solid electrolyte

[0102] In the present invention, the lithium secondary battery may include a negative electrode, a positive electrode facing the negative electrode, and an electrolyte layer between the negative electrode and the positive electrode. In the secondary battery of the present invention, when the electrolyte layer includes a liquid electrolyte, the electrolyte layer may be provided with a separator. In addition, in the present invention, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the negative electrode, the positive electrode, and the electrolyte layer, and a sealing member that seals the battery container.

[0103] In the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0104] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and may be made of, for example, aluminum, stainless steel, nickel, titanium, plastic carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and may have fine irregularities formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material.

[0105] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder onto the positive electrode current collector.

[0106] In the present invention, the positive electrode active material may include a lithium metal oxide capable of electrochemically inserting or desorbing lithium through an oxidation-reduction reaction.

[0107] For example, the positive electrode active material powder of the present invention may be a lithium-containing cobalt-based compound, a lithium-containing nickel-based compound, or a lithium-containing manganese-based compound. In this application, the term "lithium-containing cobalt-based compound" encompasses compounds that are composed of binary cations, as well as compounds that contain ternary cations or higher multi-component cations that further include other metal components such as Ni or Mn.

[0108] In the present invention, the core particle composition is a layered structure containing four-component cations. x Ni y Co 1-z Mn 1-y-z O2 (0.95≦x≦1.1). NCMs with a layered structure have the advantages of high capacity and high thermal stability.

[0109] In the present invention, the positive electrode active material may be a multi-component composition having a layered structure, further containing one or more elements selected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, Bi, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, and W in addition to NCM.

[0110] Meanwhile, in the present invention, the conductive material may be a conductive material that has been conventionally known to be usable in lithium secondary batteries, etc., and for example, graphene, carbon nanotubes, Ketjenblack, activated carbon, powder-type Super p carbon, rod-type Denka, vapor grown carbon fiber (VGCF), etc. may be suitably used.

[0111] In the lithium secondary battery of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0112] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, plastic carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material.

[0113] The negative electrode active material layer includes a negative electrode active material. The negative electrode active material may be a material capable of electrochemically inserting or extracting lithium through an oxidation-reduction reaction. For example, the negative electrode active material may be metallic lithium, or a LiAl-based, LiAg-based, LiPb-based, LiSi-based, or LiIn-based alloy that is alloyed with lithium. The negative electrode active material may also be a common carbon material such as soft graphitized carbon obtained by plasticizing graphite or resin, easily graphitized carbon obtained by heat-treating coke, or fullerene. Alternatively, the negative electrode active material may be silicon, its alloy, silicon oxide, or various other materials.

[0114] The conductive material is used to impart conductivity to the electrode, and examples thereof include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0115] Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0116] In the present invention, the electrolyte layer may contain the above-mentioned halide solid electrolyte.

[0117] In this case, the solid electrolyte of the embodiment contained in the electrolyte layer may be contained in a content of, for example, 10 to 100 volume % or 50 to 100 volume % based on the volume of the entire electrolyte layer.

[0118] The thickness of the electrolyte layer may be, for example, 0.1 to 1000 μm, or 0.1 to 300 μm. For example, the electrolyte layer may be prepared by compression molding the solid electrolyte of the embodiment, or by mixing the solid electrolyte with a binder and a solvent, coating the mixture as a slurry, and then drying the mixture.

[0119] The secondary battery of the above-described other embodiment may be in the form of an all-solid-state secondary battery or a semi-solid-state secondary battery depending on whether or not an additional liquid or gel electrolyte is included. By including the solid electrolyte of one embodiment, the secondary battery of such other embodiment may not only ensure excellent safety but also exhibit improved ionic conductivity, capacity characteristics, and cycle life characteristics.

[0120] On the other hand, the embodiments disclosed in this specification and the drawings are merely specific examples presented to aid in understanding, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art to which the present invention pertains that other modifications based on the technical concept of the present invention can be implemented in addition to the embodiments disclosed herein.

Claims

1. A solid electrolyte composition comprising a lithium yttrium halide having a hexagonal close-packed structure, The halide is A solid electrolyte composition, wherein the sum of the metal ion occupancies of two consecutive layers constituting a unit cell of a hexagonal close-packed structure is 0.888 or less, where the metal ion occupancy is defined as the number of metal ion sites occupied by metal ions out of the total number of metal ion sites in the two consecutive layers constituting the unit cell of a hexagonal close-packed structure.

2. The solid electrolyte composition according to claim 1 , wherein each of the layers has a metal ion occupancy rate of 0.444 or less.

3. The halide has the composition formula Li ３－ａ (Y １－（４－４ｘ） A ３－３ｘ＋（ａ／４） ) Cl ６ (A is a tetravalent cation, x = 0.75 to (0.888 - a / 4), a = 0 to 0.552). The solid electrolyte composition according to claim 1, comprising a halide having a hexagonal close-packed structure expressed as follows:

4. 2. The solid electrolyte composition according to claim 1, wherein A comprises at least one element selected from the group consisting of Ti, Zr, Hf, and Rf.

5. 2. The solid electrolyte composition according to claim 1, wherein the halide contains (1-x) moles of vacancies in its crystal structure.

6. A lithium secondary battery comprising an electrolyte layer comprising the solid electrolyte composition according to any one of claims 1 to 5.

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