Halide solid electrolyte, method for producing the same and secondary battery including the same

Abstract

The present invention relates to a halide solid electrolyte that exhibits improved ionic conductivity and excellent stability and flexibility, a method for producing the same, and a secondary battery including the same. (6-4a+b) M a X 6-b S b It can be represented by the chemical formula:

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0130017 dated October 11, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a halide solid electrolyte that exhibits improved ionic conductivity and excellent stability and flexibility, a method for producing the same, and a secondary battery including the same. [Background technology]

[0003] Recently, the industrial fields requiring lithium secondary batteries have expanded from small mobile device power sources to medium and large electric vehicles and energy storage systems (ESS).

[0004] In particular, interest in electric vehicles is growing rapidly, and major automakers around the world are accelerating their technological development, recognizing electric vehicles as a next-generation growth technology. Unlike small-sized batteries, medium- to large-sized lithium secondary batteries are required to operate in harsh environments and contain large-capacity batteries, making safety essential. Therefore, interest in the safety of lithium secondary batteries is increasing significantly.

[0005] Existing lithium secondary batteries contain liquid electrolytes that contain non-aqueous solvents, which causes problems such as low thermal stability, flammability, and leakage. In fact, there have been a series of reports of explosions in products that use these electrolytes, making it urgent to resolve these issues.

[0006] Therefore, interest in and research into semi-solid or all-solid-state batteries, in which a part or all of the liquid electrolyte is replaced with a solid electrolyte, is continuously increasing. However, the solid electrolyte is required to have excellent interfacial properties between the electrolyte layer containing the solid electrolyte and the active material layer, as well as excellent contact properties between the solid electrolyte and the active material particles. In addition, the solid electrolyte is required to have excellent lithium ion conductivity comparable to that of a liquid electrolyte.

[0007] Research into various solid electrolytes to meet these demands has been ongoing, and for example, sulfide-based solid electrolytes, oxide-based solid electrolytes, and halide-based solid electrolytes have been proposed.

[0008] Among these, sulfide-based solid electrolytes have advantages over oxide-based solid electrolytes, such as superior flexibility and ease of inducing close contact between the solid electrolyte and active material particles, and relatively excellent lithium ion conductivity, but have disadvantages such as poor stability when exposed to moisture or oxygen in the air, making the battery manufacturing process difficult. Furthermore, oxide-based solid electrolytes have disadvantages such as difficulty in ensuring good contact characteristics between the solid electrolyte and the active material, and insufficient ion conductivity.

[0009] Recently, halide solid electrolytes have been proposed to overcome the shortcomings of sulfide-based or oxide-based solid electrolytes, as they exhibit excellent stability and a certain level of ionic conductivity. However, the previously proposed halide solid electrolytes also have difficulty in exhibiting sufficient lithium ion conductivity, so additional solutions are needed. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, an object of the present invention is to provide a halide solid electrolyte that exhibits improved ionic conductivity and excellent stability and flexibility, and a method for producing the same.

[0011] Another object of the present invention is to provide a secondary battery that contains the above-mentioned halide solid electrolyte and exhibits excellent safety and capacity characteristics. [Means for solving the problem]

[0012] Therefore, the present invention provides a halide solid electrolyte represented by the following chemical formula 1. [Chemical formula 1] Li (6-4a+b) M a X 6-b S b In the formula 1, M is a tetravalent transition metal element, X is a halogen element, and 0 <a<1.5であり、0<b<6である。

[0013] The present invention also provides a method for preparing the halide solid electrolyte of Formula 1, which comprises reacting a mixture of lithium halide, a halide of a Group 4 transition metal M, and lithium sulfide under the application of a mechanical force.

[0014] The present invention also provides a cathode; negative electrode; and an electrolyte layer formed between the positive electrode and the negative electrode; At least one of the positive electrode, the negative electrode, and the electrolyte layer includes the halide solid electrolyte of Formula 1. [Effects of the Invention]

[0015] The solid electrolyte of the present invention has a lithium transition metal halide-type solid electrolyte in which some of the halogen elements are substituted and doped with sulfur. The solid electrolyte of the present invention can further increase the lithium content in its structure by substituting and doping some of the halogen elements with sulfur, a divalent element. Therefore, it has been confirmed that the solid electrolyte can exhibit improved lithium ion conductivity compared to previously known halide solid electrolytes.

[0016] In addition, the solid electrolyte can maintain the excellent crystallographic and structural stability of the basic halide solid electrolyte by controlling the sulfur substitution ratio, etc., and therefore exhibits excellent stability even when exposed to air or oxygen, etc. Furthermore, the solid electrolyte exhibits excellent flexibility due to the sulfur substitution, and it is easy to ensure excellent contact characteristics between the solid electrolyte and the active material particles.

[0017] Therefore, the solid electrolyte of the present invention can significantly contribute to providing a secondary battery having excellent safety and high energy density in place of existing liquid electrolytes. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of a secondary battery 100 to which a halide solid electrolyte according to an embodiment of the present invention is applied. [Figure 2] 1 shows X-ray diffraction analysis (XRD) spectra of the halide solid electrolytes of Example 2 (LiZrClS0.9S0.1), Example 4 (LiZrClS0.8S0.2), Example 6 (LiZrClS0.7S0.3), and Example 7 (LiZrClS0.6S0.4). [Figure 3a] 1 is a voltage-capacity graph of the initial charge-discharge cycle of secondary batteries manufactured using the solid electrolytes of Comparative Example 1 (LiZrCl) and Example 2 (LiZrCl5.9S0.1), respectively. [Figure 3b] 1 is a graph showing the discharge capacity by cycle of secondary batteries manufactured using the solid electrolytes of Comparative Example 1 (Li2ZrCl6) and Example 2 (Li2.1ZrCl5.9S0.1), respectively. [Figure 4a] 1 shows X-ray diffraction analysis (XRD) spectra of the solid electrolytes of Comparative Example 1 (LiZrCl), Example 2 (LiZrCl5.9S0.1), and Example 4 (LiZrCl5.8S0.2) after storage in an oxygen atmosphere for 3 weeks. [Figure 4b]1 shows X-ray diffraction analysis (XRD) spectra of the solid electrolytes of Comparative Example 1 (LiZrCl) and Example 2 (LiZrCl5.9S0.1) after storage in air for 1 day. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a halide solid electrolyte, a method for producing the same, and a secondary battery including the same according to specific embodiments of the invention will be specifically described.

[0020] According to one embodiment of the present invention, there is provided a halide solid electrolyte represented by the following chemical formula 1: [Chemical formula 1] Li (6-4a+b) M a X 6-b S b

[0021] In the formula 1, M is a tetravalent transition metal element, X is a halogen element, and 0 <a<1.5であり、0<b<6である。

[0022] The present inventors have conducted extensive research to develop a halide solid electrolyte that exhibits improved ionic conductivity compared to previously known solid electrolytes, while also exhibiting excellent structural and chemical stability even when exposed to moisture, oxygen, and the like in the air, and that exhibits excellent flexibility to achieve excellent contact properties between the solid electrolyte and active material particles, as well as excellent interfacial properties between the solid electrolyte layer and the active material layer.

[0023] During this research process, we discovered that a halide solid electrolyte of Chemical Formula 1, based on a lithium transition metal halide bonded with a Group 4 transition metal, in which some of the halogen elements in the halide are replaced with sulfur and doped, can meet the needs of the industry, and thus completed the invention.

[0024] The halide solid electrolyte of Formula 1 may have a higher lithium content in its structure because some of the halogen atoms forming monovalent anions are replaced with sulfur atoms forming divalent anions, thereby allowing more lithium ions to be formed in the electrolyte. Therefore, the solid electrolyte of this embodiment may exhibit improved ionic conductivity compared to previously known halide solid electrolytes.

[0025] In addition, in the solid electrolyte of one embodiment, some halogen elements are substituted with sulfur, which has an element size similar to that of chlorine (Cl), a typical halogen element, while adjusting the sulfur substitution ratio, etc. As a result, it has been confirmed that the solid electrolyte can maintain the excellent structural stability of the basic halide and exhibit excellent stability even when used in a high-voltage environment or exposed to moisture or oxygen in the air.

[0026] In addition, the solid electrolyte exhibits excellent flexibility similar to existing sulfide-based solid electrolytes due to the substitution of sulfur, and excellent contact characteristics between the solid electrolyte and the active material particles, as well as excellent interfacial characteristics between the electrolyte layer and the active material layer, can be easily ensured.

[0027] Therefore, the solid electrolyte of the embodiment can contribute to providing lithium secondary batteries and the like that have excellent safety and high energy density in place of existing liquid electrolytes.

[0028] Meanwhile, in the solid electrolyte of one embodiment, M in Chemical Formula 1 may be a transition metal element having a tetravalent oxidation number, for example, a transition metal element belonging to Group 4 of the periodic table, specifically, one or more tetravalent transition metal elements selected from the group consisting of zirconium (Zr), hafnium (Hf), and titanium (Ti). Among these, M may be zirconium (Zr) so that the solid electrolyte can form a stable crystal structure.

[0029] In a more specific example, in terms of excellent stability and ionic conductivity of the solid electrolyte, based on 100 mol% of the total content of the transition metal M contained in the solid electrolyte, M may comprise 60 mol% or more, 80 mol% or more, or 80 to 100 mol% of zirconium (Zr), with the remainder being hafnium (Hf) or titanium (Ti).

[0030] Furthermore, X in Formula 1 may be any halogen element, for example, at least one halogen element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Among these, X may be chlorine (Cl) in consideration of the excellent ionic conductivity of the solid electrolyte and the excellent stability when partially substituted with sulfur.

[0031] In a more specific example, taking into consideration the excellent ionic conductivity of the solid electrolyte, based on 100 mol% of the total content of halogen element X contained in the solid electrolyte, X may comprise 60 mol% or more, 80 mol% or more, or 80 to 100 mol% of chlorine (Cl), with the remainder being bromine (Br), iodine (I), or fluorine (F).

[0032] In a more specific example, in consideration of the excellent ionic conductivity and structural stability of the solid electrolyte, X may consist of chlorine (Cl) alone, or may contain 60 to 99 mol % or 80 to 90 mol % of chlorine (Cl) and 1 to 40 mol % or 10 to 20 mol % of bromine (Br).

[0033] Meanwhile, the solid electrolyte of Formula 1 maintains the structural and crystallographic stability of the basic lithium transition metal halide while further enhancing the effects of partial sulfur substitution on ionic conductivity and flexibility. In this regard, b, which defines the degree of sulfur substitution, and a, which defines the content ratio of the tetravalent transition metal M, may be adjusted to appropriate ranges.

[0034] For example, 6-4a+b, which defines the lithium content in Formula 1, may be adjusted to be greater than 2 and less than 3.3, or 2.05 to 2.80, or 2.10 to 2.40. By adjusting the range of 6-4a+b in this manner, the lithium content can be increased to further improve ionic conductivity while maintaining excellent stability of the solid electrolyte.

[0035] In addition to the appropriate range of the lithium content ratio 6-4a+b, taking into consideration the excellent stability of the solid electrolyte, a, which corresponds to the content ratio of the tetravalent transition metal M, can be in the range of 0.8 to 1.0, or 0.95 to 1.0, or 0.98 to 1.0. Furthermore, b, which defines the sulfur substitution and doping ratio, can be in the range of more than 0 but not more than 0.5, or 0.05 to 0.4, or 0.1 to 0.25, or 0.15 to 0.25.

[0036] When the molar ratios of a and b satisfy the above ranges, the solid electrolyte of one embodiment can exhibit improved ionic conductivity and flexibility, and can exhibit excellent stability comparable to that of the basic halide. However, if the range of b is excessively large or the range of a is excessively small, the ionic conductivity or stability of the solid electrolyte may actually decrease.

[0037] The solid electrolyte of the embodiment described above may have a stable trigonal or hexagonal crystal structure, and such a crystal structure may be stably maintained even with partial substitution and doping of sulfur. The solid electrolyte of the embodiment having such a stable crystal structure may exhibit excellent stability even when operated at a high voltage or exposed to moisture or oxygen in the air.

[0038] The shape of the halide solid electrolyte is not particularly limited, and may be, for example, a particle shape such as a needle, sphere, or oval sphere. Alternatively, the particles may be formed into a pellet or plate shape.

[0039] Furthermore, when the solid electrolyte has a spherical or ellipsoidal particle shape, the solid electrolyte particles may have a D50 of 0.1 to 100 μm or 0.5 to 10 μm. Here, D50 refers to the particle size when the cumulative volume of the volume-based particle size distribution corresponds to 50%, and the volume-based particle size distribution and D50 can be measured using a laser particle size analyzer, etc.

[0040] When the particle diameter of the solid electrolyte particles satisfies the above range, the dispersibility of the solid electrolyte can be improved, and excellent contact characteristics with the active material particles can be achieved.

[0041] The solid electrolyte of one embodiment described above can be produced, for example, by a method including a step of reacting a mixture of lithium halide, a halide of a Group 4 transition metal M, and lithium sulfide under the application of a mechanical force.

[0042] More specifically, the raw materials, lithium halide LiX, halide MX of a Group 4 transition metal M, and lithium sulfide LiS, are mixed in a molar ratio of (6-4a-b):a:b according to the equivalent ratio, and the mixture is reacted under the application of mechanical force to produce the solid electrolyte of Formula 1.

[0043] In this case, each raw material may be solid-phase mixed in a powder state, and such solid-phase mixing and reaction step may be performed by mechanical milling using a ball mill, a vibration mill, a turbo mill, a mechanofusion mill, a disc mill, or the like.

[0044] In this case, the mechanical milling can be carried out at a rotation speed of 300 to 700 rpm, or 400 to 600 rpm, for 10 to 30 hours, or 12 to 24 hours.

[0045] The above-described raw materials can be mixed and reacted according to an equivalent ratio through such a mechanical milling method or the like to produce the halide solid electrolyte of one embodiment.

[0046] Meanwhile, according to another embodiment of the present invention, a secondary battery 100 including the solid electrolyte of the above-described embodiment is provided. Figure 1 shows a schematic diagram of such a secondary battery 100. The secondary battery 100 of the other embodiment includes a positive electrode 10, a negative electrode 30, and an electrolyte layer 50 formed between the positive electrode 10 and the negative electrode 30, and at least one of the positive electrode 10, the negative electrode 30, or the electrolyte layer 50 may include the halide solid electrolyte of the above-described embodiment.

[0047] The positive electrode 10 includes an active material layer containing a positive electrode active material, and may further include a solid electrolyte, a conductive agent, a binder, etc. In this case, the positive electrode 10 may include a solid electrolyte, for example, the solid electrolyte of one embodiment.

[0048] At this time, the ratio of the solid electrolyte of the embodiment contained in the positive electrode 10 varies depending on the type of battery, but may be, for example, 0.1 to 80 volume %, 1 to 60 volume %, or 10 to 50 volume % based on the volume of the entire active material layer.

[0049] The positive electrode active material may be in the form of a lithium metal oxide capable of electrochemically inserting or extracting lithium through an oxidation-reduction reaction. The type of the positive electrode active material is not particularly limited, and may be, for example, a lithium-cobalt composite oxide such as LiCoO2, a lithium-nickel composite oxide such as LiNiO2, a lithium-manganese composite oxide such as LiMn2O4, a lithium-vanadium composite oxide such as LiV2O5, a lithium-iron composite oxide or phosphate oxide, or a composite oxide represented by the following chemical formula 2 or 3: [Chemical formula 2] LiNixCoyMnzO2(x+y+z=1) [Chemical formula 3] LiNixCoyMnzMaO2 (x+y+z+a=1)

[0050] M is 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.

[0051] In addition, the conductive agent may be any conductive agent other than those conventionally known to be usable in lithium secondary batteries, etc. For example, graphene, carbon nanotubes, Ketjenblack, activated carbon, powder-type Super p carbon, rod-type Denka, or vapor grown carbon fiber (VGCF) may be suitably used.

[0052] The cathode 10 may be formed by forming an active material layer on a current collector using a composition including the above-described cathode active material, a solid electrolyte such as the solid electrolyte of one embodiment, a conductive agent, a binder, and a solvent. In this case, the solid electrolyte, solvent, conductive agent, binder, etc. may be partially or completely omitted depending on the battery configuration.

[0053] Meanwhile, the negative electrode 30 includes an active material layer containing a negative electrode active material.

[0054] 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 non-graphitizable carbon obtained by carbonizing graphite or resin, easily graphitizable carbon obtained by heat-treating coke, or fullerene. Silicon, its alloys, or silicon oxides may also be used, as well as various other materials.

[0055] The active material layer of the negative electrode 30 may further include a solid electrolyte, a conductive agent, a binder, etc. in addition to the negative electrode active material. In this case, the negative electrode 30 may include a solid electrolyte, for example, the solid electrolyte of an embodiment.

[0056] Meanwhile, the solid electrolyte usable for the negative electrode 30, its content, the type of conductive agent, etc., and the manufacturing process for the negative electrode 30 are the same as those described for the positive electrode 10, and therefore further description thereof will be omitted.

[0057] The electrolyte layer 50 is a layer formed between the cathode 10 and the anode 30, and may be a solid electrolyte layer containing only a solid electrolyte, or a semi-solid electrolyte layer further containing a liquid or gel electrolyte, as needed. Depending on the battery configuration, the electrolyte layer 50 may have a laminated structure including multiple electrolyte layers each containing a solid electrolyte of a different composition, and a separator including a porous polyolefin resin substrate may be further laminated on the electrolyte layer 50.

[0058] However, according to one example, the electrolyte layer 50 may be a solid electrolyte layer including a halide solid electrolyte in one embodiment.

[0059] In this case, the ratio of the solid electrolyte of the embodiment contained in the electrolyte layer 50 may be, for example, 10 to 100% by volume, or 50 to 100% by volume, based on the volume of the entire electrolyte layer.

[0060] The thickness of the electrolyte layer 50 may be, for example, 0.1 to 1000 μm, or 0.1 to 300 μm, and the electrolyte layer 50 may be produced, for example, by compression molding the solid electrolyte of the embodiment, or by mixing the solid electrolyte with a binder and a solvent, applying the mixture to form a slurry, and then drying the mixture.

[0061] The secondary battery of the other embodiments described above may be in the form of an all-solid-state secondary battery, a semi-solid-state secondary battery, etc., 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 the other embodiments may exhibit improved ionic conductivity, capacity characteristics, and life characteristics while ensuring excellent safety. [Example]

[0062] Below, preferred examples are presented to help understand the invention. However, the following examples are merely illustrative of the invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the invention and technical idea. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0063] Examples 1 to 19 and Comparative Example 1: Production of halide solid electrolyte The raw materials LiCl, LiBr, ZrCl4, and Li2S were charged into a ball milling bowl in a molar ratio of (6-4a-bx):x:a:b, with reference to the composition formulas shown in Table 1. For reference, the charging ratio of the raw materials is determined in consideration of the composition formula of the final solid electrolyte to be produced, which is shown in Chemical Formula 1a below, and can be calculated from the a, b, and x values ​​of each example and comparative example shown in Table 1.

[0064] Thereafter, the raw material mixture was subjected to a reaction under mechanical milling for 12 hours while being ball milled at 400 to 600 rpm for 15 minutes on and 15 minutes off, to produce solid electrolytes having the composition formula of Chemical Formula 1a, each of which is summarized in Table 1 below. [Chemical formula 1a] Li (6-4a+b) Zr a Cl 6-b-x Br x S b

[0065] In the formula 1a, a, b, and x are as summarized in Table 1 below.

[0066] [Table 1]

[0067] Manufacturing example: Secondary battery manufacturing Using the halide solid electrolyte of the above Examples or Comparative Examples, each lithium secondary battery was manufactured by the following method.

[0068] The positive electrode was manufactured using a dry mixing process. Specifically, single-crystal LiNi was used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 O2 was used, one of the solid electrolytes in the examples or comparative examples was used as the solid electrolyte, and carbon nanofibers (CNF) were used as the conductive agent.

[0069] The positive electrode active material, solid electrolyte, and conductive agent were mixed in a ratio (parts by weight) of 80:20:3 to prepare an active material layer and a positive electrode.

[0070] The electrolyte layer was fabricated by press-molding a sulfide-based solid electrolyte and then press-molding a halide solid electrolyte selected from the examples or comparative examples. The sulfide-based solid electrolyte used was Li6PS5Cl.

[0071] A secondary battery was fabricated using a Li-In alloy as the negative electrode, together with the positive electrode and electrolyte layer. In the electrolyte layer, the sulfide solid electrolyte was oriented toward the negative electrode, and the halide solid electrolyte was oriented toward the positive electrode.

[0072] Test example: Characterization of solid electrolyte or secondary battery (1) X-ray diffraction measurement and stability evaluation First, the solid electrolytes in the examples and comparative examples were subjected to X-ray diffraction analysis over a 2θ range of 10 to 70°, thereby confirming the crystal structure of each solid electrolyte.

[0073] For reference, Example 2 (Li 2.1 ZrCl 5.9 S 0.1 ), Example 4 (Li2.2 ZrCl 5.8 S 0.2 ), Example 6 (Li 2.3 ZrCl 5.7 S 0.3 ) and Example 7 (Li 2.4 ZrCl 5.6 S 0.4 The X-ray diffraction (XRD) spectrum of the solid electrolyte is shown in FIG.

[0074] Referring to FIG. 2, it was confirmed that the solid electrolyte of the example exhibited crystallinity, and that the intensity of each peak tended to decrease as the amount of S substitution and doping increased.

[0075] In addition, in order to evaluate the stability of the solid electrolytes of the above examples and comparative examples, Comparative Example 1 (LiZrCl) and Example 2 (Li 2.1 ZrCl 5.9 S 0.1 ) and Example 4 (Li 2.2 ZrCl 5.8 S 0.2 The solid electrolyte of Comparative Example 1 (Li2ZrCl6) and Example 2 (Li2ZrCl6) were stored in an oxygen atmosphere for 3 weeks and then subjected to X-ray diffraction analysis (XRD). The resulting spectrum is shown in FIG. 2.1 ZrCl 5.9 S 0.1 The X-ray diffraction (XRD) spectrum of the solid electrolyte (A) after storage in air for 1 day is shown in Figure 4b.

[0076] 4a and 4b, it was confirmed that the solid electrolyte of the example stably maintained its crystalline structure even when exposed to air or oxygen, and exhibited stability equivalent to that of Comparative Example 1. (2) Measurement of ionic conductivity

[0077] The ionic conductivity of the solid electrolytes produced in the above Examples and Comparative Examples was measured at 30° C. by the following method, and the measurement results are summarized in Table 2 below.

[0078] First, in a glove box under an argon atmosphere, an appropriate amount of sample was weighed and placed in a polyether ether ketone tube (PEEK tube, inner diameter 10 mm, outer diameter 30 mm, height 20 mm), and then inserted between powder molding jigs containing SUS304 from above and below.

[0079] Next, a uniaxial press was used to press the pellets at a pressure of 2 tons to form pellets of 10 mm diameter and desired thickness. Next, SUS foil was placed on both sides of the pellets, and additional molding was performed at a pressure of 2 tons. The resulting pellets were placed in a sealed electrochemical cell capable of maintaining an argon atmosphere.

[0080] To measure ionic conductivity, a Biologic potentiostat (VSP300) was used as a frequency response analyzer (FRA), and a small environmental test chamber was used as a thermostatic device. Measurements were started in the high-frequency range under the following conditions: AC voltage 10 mV to 100 mV, frequency range 1 Hz to 10 MHz, integration time 0.2 seconds, and temperature 30°C. EC-lab was used for measurement and analysis software.

[0081] [Table 2]

[0082] Referring to Table 2, it was confirmed that the solid electrolyte of the example exhibited much better ionic conductivity than that of Comparative Example 1.

[0083] (3) Charge and discharge characteristics of secondary batteries The secondary batteries manufactured in the manufacturing examples were used to evaluate the charge / discharge characteristics in the following manner. The battery was charged at a constant current until the voltage reached 4.0 V vs. Li, and then terminated. The battery was discharged at a constant current until the voltage reached 2.4 V. During this test, charging and discharging were performed at 0.1 C, and the cycle was repeated to evaluate the characteristics of the secondary battery.

[0084] FIG. 3a shows Comparative Example 1 (LiZrCl) and Example 2 (Li 2.1 ZrCl 5.9 S 0.1 3a and 3b show voltage-capacity graphs of the initial charge-discharge cycles of secondary batteries fabricated using the solid electrolytes of Comparative Example 1 and Example 2, respectively, and FIG. 3b shows a graph showing the discharge capacity of the secondary batteries fabricated in Comparative Example 1 and Example 2 according to the cycle.

[0085] 3a, it was confirmed that the secondary battery prepared using the solid electrolyte of the Example exhibited similar characteristics to the secondary battery prepared in the Comparative Example in the initial cycle, and FIG. 3b, it was confirmed that the secondary battery prepared in the Example exhibited superior discharge capacity compared to the secondary battery prepared in the Comparative Example through repeated charge-discharge cycles.

Claims

1. A halide solid electrolyte represented by the following chemical formula 1. [Chemical formula 1] Li （６－４ａ＋ｂ） M ａ X ６－ｂ S ｂ (In the above formula 1, M is a tetravalent transition metal element, X is a halogen element, 0<a<1.5, and 0<b<6.)

2. M contains one or more tetravalent transition metal elements selected from the group consisting of zirconium (Zr), hafnium (Hf), and titanium (Ti), 2. The halide solid electrolyte according to claim 1, wherein zirconium (Zr) is contained in an amount of 60 mol % or more based on the total content of M.

3. 2. The halide solid electrolyte of claim 1, wherein M is zirconium (Zr).

4. X contains one or more halogen elements selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I), 2. The halide solid electrolyte according to claim 1, wherein chlorine (Cl) is contained in an amount of 60 mol % or more based on the total content of X.

5. 5. The halide solid electrolyte according to claim 4, wherein X consists solely of chlorine (Cl), or contains 60 to 99 mol% chlorine (Cl) and 1 to 40 mol% bromine (Br).

6. The halide solid electrolyte according to claim 1, wherein in Chemical Formula 1, the range of 2<6-4a+b≦3.3 is satisfied.

7. The halide solid electrolyte according to claim 6, wherein in Chemical Formula 1, the range of 2.10≦6−4a+b≦2.40 is satisfied.

8. The halide solid electrolyte according to claim 1 , wherein in Chemical Formula 1, a satisfies the range of 0.8≦a≦1.

0.

9. The halide solid electrolyte according to claim 8 , wherein in Chemical Formula 1, a satisfies the range of 0.95≦a≦1.

0.

10. The halide solid electrolyte according to claim 1 , wherein in Chemical Formula 1, b satisfies the range of 0<b≦0.

5.

11. The halide solid electrolyte according to claim 10, wherein in Chemical Formula 1, the range of 0.1≦b≦0.25 is satisfied.

12. 10. The method of claim 1, comprising reacting a mixture of lithium halide, a halide of a Group 4 transition metal M, and lithium sulfide under the application of a mechanical force.

13. The reaction step is LiX, MX ４ and Li ２ The method for producing a halide solid electrolyte according to claim 12, comprising reacting a mixture containing S in a molar ratio of (6-4a-b):a:b.

14. The method for producing a halide solid electrolyte according to claim 12 , wherein the reacting step is carried out while mechanically milling the mixture.

15. positive electrode; a negative electrode; and an electrolyte layer formed between the positive electrode and the negative electrode; 10. The secondary battery according to claim 1, wherein at least one of the positive electrode, the negative electrode, and the electrolyte layer comprises the halide solid electrolyte.

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