Halide solid electrolyte, method for manufacturing same, and secondary battery including same

Abstract

The present invention relates to a halide solid electrolyte, a method for manufacturing the halide solid electrolyte, and a secondary battery including the halide solid electrolyte, the halide solid electrolyte exhibiting more improved ionic conductivity and exhibiting excellent stability, flexibility, and the like. The halide solid electrolyte may be represented by the following formula: Li (6-4a + b) MaX6-bSb.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2022-0130017 filed on October 11, 2022, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a halide solid electrolyte exhibiting more improved ionic conductivity, excellent stability, flexibility, and the like, a method for producing the halide solid electrolyte, and a secondary battery including the halide solid electrolyte. Background Art

[0004] Industrial fields requiring lithium secondary batteries have recently expanded from power sources for small mobile devices to medium and large electric vehicles and energy storage systems (ESS).

[0005] In particular, people's interest in electric vehicles has been growing rapidly, and major automobile companies around the world regard electric vehicles as the next-generation growth technology and are accelerating technology development. In the case of medium and large lithium secondary batteries used for this purpose, not only is the operating environment harsh, unlike small batteries, but also because large lithium secondary batteries include large-capacity batteries, safety must be ensured. Accordingly, people's interest in the safety issues of lithium secondary batteries is greatly increasing.

[0006] Conventional lithium secondary batteries include a liquid electrolyte containing a non-aqueous solvent, and therefore have problems such as low thermal stability, fire, and leakage. In fact, explosion accidents involving products to which the batteries are applied are being reported, and therefore, there is an urgent need to solve these problems.

[0007] For this reason, there is an increasing interest and research in semi-solid or all-solid batteries that replace part or all of the liquid electrolyte with a solid electrolyte. By the way, the solid electrolyte is required to have excellent interface properties between the electrolyte layer containing it and the active material layer, and further excellent contact properties between the solid electrolyte and the active material particles. In addition, excellent lithium ion conductivity comparable to that of the liquid electrolyte is required.

[0008] In order to meet these requirements, various solid electrolytes have been studied in the past. For example, sulfide-based solid electrolytes, oxide-based solid electrolytes, or halide-based solid electrolytes have been proposed.

[0009] Among them, the advantages of sulfide-based solid electrolytes are that they are softer than oxide-based solid electrolytes, easily cause close contact between the solid electrolyte and the active material particles, and have relatively excellent lithium ion conductivity. However, the disadvantage is that their stability is low when exposed to moisture and oxygen in the air, making the battery manufacturing process difficult. In addition, the disadvantage of oxide-based solid electrolytes is that it is difficult to ensure excellent contact characteristics between the solid electrolyte and the active material, and the ion conductivity is insufficient.

[0010] In recent years, in order to solve the disadvantages of sulfide-based or oxide-based solid electrolytes, halide solid electrolytes that exhibit excellent stability and a specific level of ion conductivity have been proposed. However, the previously proposed halide solid electrolytes also do not exhibit sufficient lithium ion conductivity, and therefore, these points need to be further supplemented. Summary of the Invention

[0011]

Technical Problem

[0012] An object of the present disclosure is to provide a halide solid electrolyte that exhibits improved ion conductivity, excellent stability, flexibility, etc., and a method for manufacturing a halide solid electrolyte.

[0013] Another object of the present disclosure is to provide a secondary battery including a halide solid electrolyte and thus exhibiting excellent safety and capacity characteristics.

[0014]

Technical Solution

[0015] According to one aspect of the present disclosure, there is provided a halide solid electrolyte represented by the following formula 1:

[0016] [Formula 1]

[0017] Li (6-4a+b) M a X 6-b S b

[0018] Wherein in Formula 1, M is a tetravalent transition metal element, X is a halogen element, 0 < a < 1.5, and 0 < b < 6.

[0019] According to another aspect of the present disclosure, there is provided a method for manufacturing the halide solid electrolyte of Formula 1, the method including reacting a mixture of lithium halide, Group 4 transition metal M halide, and lithium sulfide under the application of mechanical force.

[0020] According to still another aspect of the present disclosure, there is provided a secondary battery including:

[0021] a positive electrode;

[0022] a negative electrode; and

[0023] An electrolyte layer is formed between the positive and negative electrodes,

[0024] At least one of the positive electrode, the negative electrode or the electrolyte layer comprises a halide solid electrolyte of Formula 1.

[0025]

Beneficial Effects

[0026] The solid electrolyte disclosed in the present invention is a solid electrolyte in the form of a lithium transition metal halide, in which part of the halogen element is substituted and doped with sulfur. This solid electrolyte disclosed in the present invention can further increase the content ratio of lithium in the structure because part of the halogen element is substituted and doped with sulfur, which is a -2 valent element. Therefore, it has been confirmed that this solid electrolyte can exhibit improved lithium ion conductivity compared to conventionally known halide solid electrolytes.

[0027] In addition, the solid electrolyte can control the substitution rate of sulfur or the like, thereby maintaining the excellent crystal stability and structural stability of the alkaline halide solid electrolyte, and therefore, can exhibit excellent stability even when exposed to air or oxygen, etc. Further, due to the substitution of sulfur, the solid electrolyte exhibits excellent flexibility, which makes it easy to ensure excellent contact characteristics between the solid electrolyte and the active material particles.

[0028] Therefore, the solid electrolyte of the present disclosure can greatly contribute to replacing existing liquid electrolytes and provide a secondary battery with excellent safety and high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of a secondary battery 100 to which a halide solid electrolyte according to an embodiment of the present disclosure is applied;

[0030] Figure 2 For Example 2 (Li 2.1 ZrCl 5.9 S 0.1 )、Example 4 (Li 2.2 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 )’s X-ray diffraction analysis (XRD) spectrum of the halide solid electrolyte.

[0031] Figure 3a For the use of Comparative Example 1 (Li 2 ZrCl 6 ) and Example 2 (Li 2.1 ZrCl 5.9 S0.1 ) of the voltage-capacity graph of the initial charge / discharge cycle of a secondary battery fabricated using a solid electrolyte, and Figure 3b a graph showing the discharge capacity of each cycle of such a secondary battery; and

[0032] Figure 4a For Comparative Example 1 (Li 2 ZrCl 6 ), Example 2 (Li 2.1 ZrCl 5.9 S 0.1 ), and Example 4 (Li 2.2 ZrCl 5.8 S 0.2 ), X-ray diffraction analysis (XRD) spectra of the solid electrolytes after storage in an oxygen atmosphere for 3 weeks, and Figure 4b For Comparative Example 1 (Li 2 ZrCl 6 ), and Example 2 (Li 2.1 ZrCl 5.9 S 0.1 ), X-ray diffraction analysis (XRD) spectra of the solid electrolytes after storage in air for 1 day. DETAILED DESCRIPTION

[0033] A halide solid electrolyte, a method for manufacturing a halide solid electrolyte, and a secondary battery including the halide solid electrolyte will now be described in detail according to specific embodiments of the present disclosure.

[0034] According to an embodiment of the present disclosure, there is provided a halide solid electrolyte represented by the following Formula 1:

[0035] [Formula 1]

[0036] Li (6-4a+b) M a X 6-b S b

[0037] Wherein in Formula 1, M is a tetravalent transition metal element, X is a halogen element, 0 < a < 1.5, and 0 < b < 6.

[0038] The present inventors continued their research and developed a halide solid electrolyte which, compared with previously known solid electrolytes, not only exhibits improved ionic conductivity, but also exhibits excellent structural stability and chemical stability even when exposed to moisture or oxygen in air, and also exhibits excellent flexibility, and thus enables excellent contact characteristics between the solid electrolyte and the active material particles, as well as further excellent interfacial characteristics between the solid electrolyte layer and the active material layer.

[0039] During such research, the present inventors found that a halide solid electrolyte of Formula 1 based on a lithium transition metal halide bonded to a Group 4 transition metal and in which part of the halogen element in the halide is substituted and doped with sulfur can meet industrial requirements, and completed the present disclosure.

[0040] The halide solid electrolyte of Formula 1 may have a higher lithium content ratio in its structure because part of the halogen element forming the monovalent anion is replaced by the sulfur element forming the divalent anion, which allows more lithium ions to be formed in the electrolyte. Therefore, compared with previously known halide solid electrolytes, etc., the solid electrolyte of one embodiment may exhibit improved ionic conductivity.

[0041] Further, the solid electrolyte of one embodiment replaces part of the halogen element with sulfur having an element size similar to chlorine (Cl) (chlorine is a typical halogen element), while adjusting the substitution rate of sulfur, etc. As a result, it has been confirmed that the solid electrolyte can maintain the excellent structural stability of the alkaline halide and can also exhibit excellent stability when used in a high voltage environment or exposed to moisture or oxygen in the air, etc.

[0042] In addition, due to the substitution of sulfur, the solid electrolyte exhibits excellent flexibility similar to existing sulfide-based solid electrolytes, which makes it easy to ensure excellent contact characteristics between the solid electrolyte and the active material particles, and further excellent interface characteristics between the electrolyte layer and the active material layer.

[0043] Therefore, the solid electrolyte of one embodiment can contribute to replacing the existing liquid electrolyte and thus provide excellent safety and high energy density for lithium secondary batteries and the like.

[0044] On the other hand, in the solid electrolyte of one embodiment, M in Formula 1 may be a transition metal element having a tetravalent oxidation state, for example, a transition metal element belonging to Group 4 of the periodic table, and specifically, it may be one or more tetravalent transition metal elements selected from the group consisting of zirconium (Zr), hafnium (Hf) and titanium (Ti). Among them, M may be zirconium (Zr), so that the solid electrolyte can form a stable crystal structure.

[0045] In a more specific example, from the perspective 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 include 60 mol% or more, 80 mol% or more, or 80 mol% to 100 mol% of zirconium (Zr), and may include the remaining amount of hafnium (Hf) or titanium (Ti).

[0046] Further, X in Formula 1 may be any halogen element, for example, one or more halogen elements selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). In particular, X may be chlorine (Cl), in consideration of the excellent ionic conductivity of the solid electrolyte and its excellent stability when part of the electrolyte is replaced by sulfur.

[0047] In a more specific example, considering the excellent ionic conductivity of the solid electrolyte, etc., based on 100 mol% of the total content of the halogen element X contained in the solid electrolyte, X may include 60 mol% or more, or 80 mol% or more, or 80 mol% to 100 mol% of chloride (Cl), and may include the remaining amount of bromine (Br), iodine (I) or fluorine (F).

[0048] In a more specific example, considering the excellent ionic conductivity and structural stability of the solid electrolyte, X consists only of chlorine (Cl), or X may contain 60 mol% to 99 mol% or 80 mol% to 90 mol% of chlorine (Cl) and 1 mol% to 40 mol% or 10 mol% to 20 mol% of bromine (Br).

[0049] On the other hand, in the solid electrolyte of Formula 1, in order to further enhance the effect of improving ionic conductivity and flexibility due to partial sulfur substitution while maintaining the structural stability and crystal stability of the alkaline lithium transition metal halide, b which defines the degree of sulfur substitution and a which defines the content ratio of the tetravalent transition metal M can be adjusted to an appropriate range.

[0050] For example, 6-4a+b defining the content ratio of lithium in Formula 1 may be adjusted within a range of greater than 2 and 3.3 or less, or 2.05 to 2.80 or 2.10 to 2.40. By adjusting the range of 6-4a+b in this manner, the content ratio of lithium may be increased, thereby further improving ionic conductivity while maintaining excellent stability of the solid electrolyte.

[0051] Moreover, considering the excellent stability of the solid electrolyte and the appropriate range of the lithium content ratio 6-4a+b, a corresponding to the content ratio of the tetravalent transition metal M may satisfy the range of 0.8 to 1.0, 0.95 to 1.0, or 0.98 to 1.0. In addition, b defining the substitution and doping ratio of sulfur may satisfy the range of greater than 0 and 0.5 or less, or 0.05 to 0.4, or 0.1 to 0.25, or 0.15 to 0.25.

[0052] Since the molar ratio of a and b satisfies the above range, the solid electrolyte of one embodiment can show more improved ionic conductivity and flexibility, and can also show excellent stability comparable to the stability of alkali halides. However, if the range of b is too large or the range of a is too small, etc., the ionic conductivity or stability of the solid electrolyte may be reduced.

[0053] The solid electrolyte of one embodiment mentioned above may basically have a stable triangular crystal structure or a hexagonal crystal structure. This crystal structure can be stably maintained even in the case of partial sulfur substitution and doping. The solid electrolyte of one embodiment having such a stable crystal structure can also exhibit excellent stability even when driven at a high voltage or exposed to moisture or oxygen in the air, etc.

[0054] The shape of the halide solid electrolyte is not particularly limited, and may have, for example, a needle-like, spherical, or ellipsoidal particle shape. Alternatively, such particles may be formed to have a pellet or plate shape.

[0055] Further, when the solid electrolyte has a spherical or ellipsoidal particle shape, for example, the solid electrolyte particle may have a D 50 At this time, D 50 D may mean a particle size when the cumulative volume of the volume-based particle size distribution corresponds to 50%, and the corresponding volume-based particle size distribution and D may be measured using a laser particle size analyzer or the like. 50 .

[0056] Since the particle size 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 and the like can be achieved.

[0057] The solid electrolyte of one embodiment described above can be produced by a method including, for example, reacting a mixture of lithium halide, Group 4 transition metal M halide, and lithium sulfide under application of mechanical force.

[0058] More specifically, lithium halide LiX, halide of Group 4 transition metal M MX are mixed in a molar ratio of (6-4a-b):a:b corresponding to each raw material according to the equivalent ratio. 4 and lithium sulfide Li 2 S, and this mixture can react under the application of mechanical force to produce a solid electrolyte of Formula 1.

[0059] At this time, each raw material may be mixed in a solid phase in a powder state, and this solid phase mixing and reaction step may be mechanically ground using any one of a ball mill, a vibration mill, a turbo mill, a mechanofusion mill, a disk mill, or the like.

[0060] At this time, the mechanical grinding may be performed at a rotation speed of 300 rpm to 700 rpm or 400 rpm to 600 rpm, and may be performed for 10 hours to 30 hours or 12 hours to 24 hours.

[0061] By such a mechanical milling method or the like, the above-mentioned raw materials may be mixed and reacted according to an equivalent ratio to manufacture a halide solid electrolyte of one embodiment.

[0062] On the other hand, according to another embodiment of the present disclosure, there is provided a secondary battery 100 including the solid electrolyte of the above-described one embodiment. Figure 1 A schematic diagram of such a secondary battery 100 is shown. The secondary battery 100 of another 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, wherein at least one of the positive electrode 10, the negative electrode 30 and the electrolyte layer 50 includes the halide solid electrolyte of the above one embodiment.

[0063] The positive electrode 10 may include an active material layer including a positive active material, and may further include a solid electrolyte, a conductive material, and a binder in addition to the positive active material. At this time, the positive electrode 10 may include a solid electrolyte, for example, may include a solid electrolyte of one embodiment.

[0064] At this time, the proportion of the solid electrolyte of one embodiment included in the positive electrode 10 varies depending on the type of battery, but for example, based on the volume of the entire active material layer, the solid electrolyte can be included in a proportion of 0.1 volume % to 80 volume %, 1 volume % to 60 volume %, or 10 volume % to 50 volume %.

[0065] Further, the positive electrode active material may be in the form of a lithium metal oxide capable of electrochemically inserting and extracting lithium through a redox reaction. The type of such a positive electrode active material is not particularly limited, but examples thereof may include lithium cobalt composite oxides (such as LiCoO 2 ), lithium nickel composite oxides (such as LiNiO 2 ), lithium manganese composite oxides (such as LiMn 2 O 4 ), lithium vanadium composite oxides (such as LiV 2 O 5 ), lithium iron composite oxide or phosphorus oxide, or a composite oxide represented by the following formula 2 or formula 3:

[0066] [Formula 2]

[0067] LiNi x Co y Mn z O 2 (x+y+z=1)

[0068] [Formula 3]

[0069] LiNi x Co y Mn z M a O 2 (x+y+z+a=1)

[0070] Wherein 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.

[0071] In addition, as the conductive material, a conductive material other than previously known conductive materials that can be used for lithium secondary batteries, etc. can be used, and for example, graphene, carbon nanotubes, Ketjen black, activated carbon, powdered Superp carbon, rod-shaped Denka, and vapor grown carbon fiber (VGCF) can be appropriately used.

[0072] Further, the positive electrode 10 can be formed by forming an active material layer on a current collector using a composition containing the above-mentioned positive electrode active material, a solid electrolyte (such as a solid electrolyte of one embodiment), a conductive material, a binder, a solvent, etc. At this time, some of the solid electrolyte, solvent, conductive material, binder, etc. may be omitted or used depending on the shape of the battery.

[0073] On the other hand, the negative electrode 30 includes an active material layer containing a negative electrode active material.

[0074] The negative electrode active material may be a material that can electrochemically embed or deintercalate lithium through a redox reaction. For example, the negative electrode active material may be metallic lithium, or a LiAl alloy, a LiAg alloy, a LiPb alloy, a LiSi alloy, or a LiIn alloy alloyed with lithium. Further, as the negative electrode active material, conventional carbon materials (such as difficult graphitizable carbon obtained by sintering and carbonizing graphite or resin, graphitizable carbon obtained by heat treating coke, and fullerene) may be used, or silicon, its alloys or silicon oxide may be used, or various other materials may be used.

[0075] In addition to the negative electrode active material, the active material layer of the negative electrode 30 may further include a solid electrolyte, a conductive material, and a binder. At this time, the negative electrode 30 may include a solid electrolyte, for example, may include a solid electrolyte of one embodiment.

[0076] On the other hand, a solid electrolyte that can be used for the negative electrode 30 , its content, the type of conductive material, etc., and a manufacturing process of the negative electrode 30 are the same as those described for the positive electrode 10 , and therefore, further explanation thereof will be omitted.

[0077] The electrolyte layer 50 is a layer formed between the positive electrode 10 and the negative electrode 30, and if necessary, it may be a solid electrolyte layer containing only a solid electrolyte, or a semi-solid electrolyte layer further containing some liquid or gel electrolyte. Further, depending on the battery shape, etc., the electrolyte layer 50 may have a stacked structure including a plurality of electrolyte layers, each of which contains a solid electrolyte having a different composition from each other. In addition to the electrolyte layer 50, a separator including a porous polyolefin resin substrate, etc. may be further stacked.

[0078] However, according to one example, the electrolyte layer 50 may be a solid electrolyte layer containing a halide solid electrolyte of one embodiment.

[0079] At this time, the proportion of the solid electrolyte of one embodiment included in the electrolyte layer 50 may be contained in an amount of, for example, 10 volume % to 100 volume % or 50 volume % to 100 volume % based on the volume of the entire electrolyte layer.

[0080] The thickness of the electrolyte layer 50 may be, for example, 0.1 μm to 1000 μm or 0.1 μm to 300 μm, and, for example, it may be manufactured by a method of press-molding the solid electrolyte of one embodiment, or may be manufactured by a method of mixing the solid electrolyte with a binder and a solvent, etc., applying a slurry, and then drying it.

[0081] Depending on whether an additional liquid or gel electrolyte is included, the secondary battery of the other embodiments described above may be in the form of an all-solid secondary battery or a semi-solid secondary battery, etc. Since the secondary battery of such other embodiments includes the solid electrolyte of one embodiment, it can exhibit improved ion conductivity, capacity characteristics, and life characteristics while ensuring excellent safety.

[0082] Hereinafter, preferred embodiments are presented for a better understanding of the present invention, but the following embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various variations and modifications may be made without departing from the scope and technical spirit of the present invention, and it goes without saying that such variations and modifications fall within the scope of the claims.

[0083] Examples 1 to 19 and Comparative Example 1: Preparation of Halide Solid Electrolyte

[0084] Referring to the composition formula shown in Table 1 below, LiCl, LiBr, ZrCl 4 and Li 2 Each raw material of S is charged into the ball mill bowl at a molar ratio of (6-4a-bx):x:a:b. For reference, the charging ratio of each raw material takes into account the composition formula of the following formula 1a of the solid electrolyte to be finally manufactured, and can be calculated based on the a, b and x values ​​of each embodiment and comparative example listed in Table 1 below.

[0085] Subsequently, the raw material mixture was reacted under mechanical milling for 12 hours while ball milling at 400 to 600 rpm, and milled for 15 minutes and left standing for 15 minutes to prepare a solid electrolyte having a composition formula of Formula 1a summarized in Table 1 below.

[0086] [Formula 1a]

[0087] Li (6-4a+b) Zr a Cl 6-b-x Br x S b

[0088] Wherein in Formula 1a, a, b and x are summarized in Table 1 below.

[0089] [Table 1]

[0090]

[0091] Preparation Example: Production of Secondary Battery

[0092] Using the halide solid electrolyte of the aforementioned Example or Comparative Example, each lithium secondary battery was manufactured by the following method.

[0093] The positive electrode is manufactured by applying a dry mixing process. Specifically, single crystal LiNi 0.8 Mn 0.1 Co 0.1 O 2 As a positive electrode active material, one of the solid electrolytes of Examples or Comparative Examples was used as a solid electrolyte. Further, carbon nanofibers (CNF) were used as a conductive material.

[0094] The positive electrode active material: solid electrolyte: conductive material were mixed in a ratio of 80:20:3 (parts by weight) to produce an active material layer and a positive electrode.

[0095] The electrolyte layer was manufactured by press-molding a sulfide-based solid electrolyte, and then further press-molding a halide solid electrolyte selected in the example or the comparative example. 6PS 5 Cl is used as a sulfide-based solid electrolyte.

[0096] A secondary battery was manufactured using a Li-In alloy as a negative electrode together with this positive electrode and an electrolyte layer. In the electrolyte layer, a sulfide solid electrolyte was placed toward the positive electrode, and a halide solid electrolyte was placed facing the positive electrode.

[0097] Test example: Evaluation of characteristics of solid electrolytes or secondary batteries

[0098] (1) X-ray diffraction measurement and stability evaluation

[0099] First, the solid electrolytes in Examples or Comparative Examples were subjected to X-ray diffraction analysis within 2θ of 10° to 70°, thereby confirming the crystal structure of each solid electrolyte.

[0100] For reference, in Figure 2 Example 2 (Li 2.1 ZrCl 5.9 S 0.1 )、Example 4 (Li 2.2 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 )’s solid electrolyte.

[0101] refer to Figure 2 , it was confirmed that the solid electrolyte of the example exhibited crystallinity, and the intensity of each peak tended to decrease with the increase of S substitution and doping amount.

[0102] Furthermore, in order to evaluate the stability of the solid electrolytes of the embodiments and comparative examples, Comparative Example 1 (Li 2 ZrCl 6 )、Example 2 (Li 2.1 ZrCl 5.9 S 0.1 ) and Example 4 (Li 2.2 ZrCl 5.8 S 0.2 ) was stored in an oxygen atmosphere for 3 weeks, and then subjected to X-ray diffraction analysis (XRD), and its spectrum is shown in Figure 4a In. Figure 4b Comparative Example 1 (Li 2 ZrCl 6 ) and Example 2 (Li 2.1ZrCl 5.9 S 0.1 ) after being stored in air for 1 day.

[0103] refer to Figure 4a and Figure 4b , it was confirmed that the solid electrolyte of the example stably maintained the crystal structure even when exposed to air or oxygen, and exhibited stability comparable to that of Comparative Example 1.

[0104] (2) Measurement of ionic conductivity

[0105] The ionic conductivity of the solid electrolytes produced in Examples and Comparative Examples was measured at 30° C. by the method described below, and the measurement results are summarized in Table 2 below.

[0106] First, in a glove box with an argon atmosphere, an appropriate amount of sample was weighed, placed in a polyetheretherketone tube (PEEK tube, inner diameter 10 mm, outer diameter 30 mm, height 20 mm), and inserted between powder molding jigs containing SUS304 from the top and bottom.

[0107] Next, it was pressed using a single screw press at an indicated pressure of 2 tons to form pellets having a diameter of 10 mm and an arbitrary thickness. Then, SUS foils were placed on both sides of the pellets and further molded at an indicated pressure of 2 tons. The resulting pellets were placed in a closed electrochemical cell capable of maintaining an argon atmosphere.

[0108] For the ionic conductivity measurement, a Potensiostat (VSP300) manufactured by Biologic was used as a frequency response analyzer (FRA), and a small environmental tester was used as a constant temperature device. The measurement was started in the high frequency range under the conditions of an AC voltage of 10 mV to 100 mV, a frequency range of 1 Hz to 10 MHz, an integration time of 0.2 seconds, and a temperature of 30° C. EC-lab was used for measurement and analysis software.

[0109] [Table 2]

[0110] Examples / Comparative Examples Ionic conductivity (mS / cm) Comparative Example 1 0.360 Example 1 0.606 Example 2 0.734 Example 3 0.849 Example 4 0.834 Example 5 0.890 Example 6 0.530 Example 7 0.604 Example 8 0.876 Example 9 0.963 Example 10 0.909 Embodiment 11 0.866 Example 12 0.436 Example 13 0.700 Embodiment 14 0.770 Embodiment 15 0.854 Example 16 0.661 Embodiment 17 0.665 Embodiment 18 0.621 Embodiment 19 0.685

[0111] Referring to Table 2, it is confirmed that the solid electrolyte of Example exhibits very excellent ion conductivity compared with Comparative Example 1.

[0112] (3) Charge / discharge characteristics of secondary batteries

[0113] The charge / discharge characteristics of the secondary battery produced in Preparation Example were evaluated by the following method.

[0114] After charging at a constant current until the voltage reached 4.0 V relative to Li, charging of the battery was terminated. The battery was discharged at a constant current of up to 2.4 V. Further, during such a test, charging / discharging was performed at 0.1 C, and the characteristics of the secondary battery were evaluated while the cycle was repeated.

[0115] Figure 3a For the use of Comparative Example 1 (Li 2 ZrCl 6 ) and Example 2 (Li 2.1 ZrCl 5.9 S 0.1 ) of a secondary battery made with a solid electrolyte having an initial charge / discharge cycle voltage-capacity diagram, and Figure 3b Graph showing the discharge capacity per cycle of the secondary batteries manufactured in Comparative Example 1 and Example 2.

[0116] refer to Figure 3a It was confirmed that the secondary battery manufactured using the solid electrolyte of the embodiment exhibited similar characteristics to the secondary battery manufactured in the comparative example in the initial cycle. Figure 3b It was confirmed that the secondary battery manufactured in the example exhibited a more excellent discharge capacity than the secondary battery manufactured in the comparative example as the charge / discharge cycle was repeated.

Claims

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

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

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

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

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

6. The halide solid electrolyte according to claim 1, which satisfies the range of 2 < 6 - 4a + b ≤ 3.3 in Formula 1.

7. The halide solid electrolyte according to claim 6, which satisfies the range of 2.10 ≤ 6 - 4a + b ≤ 2.40 in Formula 1.

8. The halide solid electrolyte according to claim 1, which satisfies the range of 0.8 ≤ a ≤ 1.0 in Formula 1.

9. The halide solid electrolyte according to claim 8, which satisfies the range of 0.95 ≤ a ≤ 1.0 in Formula 1.

10. The halide solid electrolyte according to claim 1, which satisfies the range of 0 < b ≤ 0.5 in Formula 1.

11. The halide solid electrolyte according to claim 10, which satisfies the range of 0.1 ≤ b ≤ 0.25 in Formula 1.

12. A method for manufacturing the halide solid electrolyte according to claim 1, comprising: reacting a mixture of lithium halide, a Group 4 transition metal M halide, and lithium sulfide under the application of mechanical force.

13. The method according to claim 12, wherein the reaction comprises reacting LiX, MX 4 and Li 2 S mixture to react.

14. The method according to claim 12, wherein the reaction is carried out while mechanically grinding the mixture.

15. A secondary battery, comprising: a positive electrode; a negative electrode; and an electrolyte layer formed between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, or the electrolyte layer includes the halide solid electrolyte according to claim 1.

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