Lithium-ion conductor and lithium secondary battery using same

Abstract

The present invention provides a means capable of improving electrochemical stability in an LGPS type lithium-ion conductor, while maintaining high purity and lithium-ion conductivity. More specifically, provided is a lithium-ion conductor having a compound represented by the following formula: Li11.7-x-4y (Si0.9 Ge0.1)3-x+y Px S11.7-z Cl0.3 Oz (in the formula, x is 1.4 ≦ x ≦ 1.6, y is 0.05 ≦ y ≦ 0.15, and z is 1.65≦ z ≦ 1.8).

Description

Lithium ion conductor and lithium secondary battery using the same

[0001] The present invention relates to a lithium ion conductor and a lithium secondary battery using the same.

[0002] In recent years, research and development on all-solid-state lithium secondary batteries, which use lithium ion conductors (solid electrolytes) capable of conducting lithium ions in solids, has been actively pursued. All-solid-state lithium secondary batteries have the advantage that, in principle, they do not encounter the various problems associated with flammable organic electrolytes, as in conventional liquid-based lithium secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the battery's power density and energy density.

[0003] As a lithium ion conductor, an LGPS type having a composition of Li-MP-S-X (M=Ge, Si, Sn; X=Cl, O) is known. ９．５４ Si １．７４ P １．４４ S １１．７ Cl ０．３ (LSiPSCl) exhibits extremely high ionic conductivity. However, due to its low electrochemical stability, it has the problem of side reactions occurring at the interface between the solid electrolyte and the active material, resulting in increased resistance. Furthermore, LSiPSCl is prone to the formation of impurity phases, which causes a problem of reduced ionic conductivity.

[0004] To address these issues, Yuxiang Li et al., Oxygen Substitution for Li-Si-PS-Cl Solid Electrolytes toward Purified Li 10 GeP2S 12 In "Li-Type Phase with Enhanced Electrochemical Stabilities for All-Solid-State Batteries," Chem. Mater. 2020, 32, 8860-8867, some of the sulfur (S) in LSiPSCl was replaced with oxygen (O). ９．５４ Si １．７４ P１．４４ S １１．７－ｚ Cl ０．３ O ｚ (0<z≦0.6) (LSiPSClO ｚ ) discloses that such oxygen substitution improves electrochemical stability and purity.

[0005] However, according to the investigations of the present inventors, the LSiPSClO ｚ However, it has been found that even with this method, a lithium ion conductor having sufficient electrochemical stability may not be obtained.

[0006] Therefore, an object of the present invention is to provide a means for improving the electrochemical stability of an LGPS-type lithium ion conductor while maintaining high purity and lithium ion conductivity.

[0007] The present inventors have conducted extensive research to solve the above problems, and in the process have found that the above problems can be solved by incorporating germanium (Ge) and silicon (Si) as M and chlorine (Cl) and oxygen (O) as X in the Li-MP-S-X, and controlling the composition within a predetermined range, which has led to the completion of the present invention.

[0008] That is, the lithium ion conductor according to one embodiment of the present invention has the formula: Li １１．７－ｘ－４ｙ (Si ０．９ Ge ０．１ ) ３－ｘ＋ｙ P ｘ S １１．７－ｚ Cl ０．３ O ｚ The composition is characterized by having the following formula: (wherein x is 1.4≦x≦1.6, y is 0.05≦y≦0.15, and z is 1.65<z≦1.8).

[0009] Fig. 1 is a cross-sectional view showing a schematic overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. Fig. 2 shows X-ray diffraction patterns for the lithium ion conductors obtained in Comparative Example 4 and Example 6.

[0010] Hereinafter, embodiments of the present invention will be described, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. Note that the range "X to Y" means "X or more and Y or less."

[0011] <Lithium ion conductor> One embodiment of the present invention is a lithium ion conductor having the formula: Li １１．７－ｘ－４ｙ (Si ０．９ Ge ０．１ ) ３－ｘ＋ｙ P ｘ S １１．７－ｚ Cl ０．３ O ｚ (wherein x is 1.4≦x≦1.6, y is 0.05≦y≦0.15, and z is 1.65<z≦1.8). The lithium ion conductor according to this embodiment can improve the electrochemical stability of an LGPS-type lithium ion conductor while maintaining high purity and lithium ion conductivity. The mechanism by which the lithium ion conductor according to this embodiment exhibits the above-described effects has not been fully clarified, and the present invention is not bound by any theory, but the following mechanism is presumed. That is, the lithium ion conductivity according to this embodiment is higher than that of the Li ９．５４ Si １．７４ P １．４４ S １１．７－ｚ Cl ０．３ O ｚ Compared to the case where z is 0<z≦0.6, the amount of oxygen (O) substituting for sulfur (S) is large. The bond energy in the bond between Si or P and O (Si / P-O) is higher than the bond energy in the bond between Si or P and S (Si / P-S), so it is presumed that the electrochemical stability improves due to the increased amount of oxygen substitution. In addition, according to the above-mentioned literature, Li ９．５４ Si １．７４ P １．４４ S １１．７－ｚ Cl ０．３ O ｚIt is said that when the oxygen substitution amount is increased (when z = 0.9 or 1.5) in the above-mentioned lithium ion conductor, an impurity phase other than the LGPS phase is formed, resulting in a decrease in lithium ion conductivity. On the other hand, the lithium ion conductor according to the present embodiment has the specific composition represented by the above formula, and is therefore thought to further stabilize the LGPS phase. This is presumably why an impurity phase is less likely to be formed, resulting in a lithium ion conductor with high purity and lithium ion conductivity.

[0012] The lithium ion conductor according to the present embodiment has the formula: Li １１．７－ｘ－４ｙ (Si ０．９ Ge ０．１ ) ３－ｘ＋ｙ P ｘ S １１．７－ｚ Cl ０．３ O ｚ In the above formula, x is 1.4≦x≦1.6, y is 0.05≦y≦0.15, and z is 1.65<z≦1.8. If x is less than 1.4 or more than 1.6, y is less than 0.05 or more than 0.15, and / or z is more than 1.8, an impurity phase may be formed (reduced purity), and the lithium ion conductivity may decrease. If z is 1.65 or less, the effect of improving electrochemical stability may not be sufficiently obtained.

[0013] From the viewpoint of further improving the effects of the present invention, in the above formula, y preferably satisfies 0.1≦y≦0.15, more preferably 0.1≦y<0.15, and even more preferably 0.1. From the same viewpoint as above, z preferably satisfies 1.7≦z≦1.8, more preferably 1.75≦z≦1.8, and even more preferably 1.8.

[0014] To further improve the effects of the present invention, in the above formula, it is preferable that x is 1.4≦x≦1.6, y is 0.1≦y≦0.15, and z is 1.7≦z≦1.8; it is more preferable that x is 1.4≦x≦1.6, y is 0.1≦y<0.15, and z is 1.75≦z≦1.8; it is even more preferable that x is 1.5≦x≦1.6, y is 0.1, and z is 1.8; and it is most preferable that x is 1.6, y is 0.1, and z is 1.8.

[0015] The lithium ion conductor according to the present embodiment can be easily manufactured by a person skilled in the art by referring to the manufacturing method described in the above-mentioned document. ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ ) are weighed and mixed. The resulting mixture is mechanically pulverized using a pulverizer such as a planetary ball mill. The pulverized mixture is formed into pellets, heated to 673 to 748 K, and maintained at this temperature for approximately 8 hours to produce a lithium ion conductor.

[0016] <Lithium Secondary Battery> The lithium ion conductor has high purity and lithium ion conductivity, and is also excellent in electrochemical stability. Therefore, by using the lithium ion conductor as a solid electrolyte in a lithium secondary battery, it is possible to improve the capacity characteristics and / or high-rate characteristics of the battery. That is, according to another aspect of the present invention, a power generating element is provided, which includes a positive electrode having a positive electrode active material layer, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte. The positive electrode active material layer and / or the solid electrolyte layer contain the lithium ion conductor. A lithium secondary battery is provided.

[0017] Hereinafter, an embodiment of a lithium secondary battery according to one aspect of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0018] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power generating element 21, in which charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery outer casing. Here, the power generating element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 are disposed on the surface of the negative electrode current collector 11'. The positive electrode has a structure in which a positive electrode active material layer 15 are disposed on the surface of a positive electrode current collector 11". As a result, the negative electrode current collector 11', the negative electrode active material layer 13, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11" constitute one unit cell layer 19. Therefore, the stacked secondary battery 10a shown in FIG. 1 can be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27, which are electrically connected to the respective electrodes (negative and positive electrodes), are attached to the negative electrode current collector 11' and the positive electrode current collector 11", respectively, and are configured to be sandwiched between the ends of the laminate film 29 and extended to the outside of the laminate film 29. A restraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the power generation element 21 by a pressure member (not shown). Therefore, the volume of the power generation element 21 is kept constant.

[0019] The main components of the lithium secondary battery according to this embodiment will be described below.

[0020] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (negative electrode active material layer, positive electrode active material layer). There are no particular restrictions on the material that constitutes the current collector. Examples of materials that can be used for the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but an example is 10 to 100 μm.

[0021] [Negative Electrode Active Material Layer] The negative electrode active material layer contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but includes carbon materials, metal oxides, and metal active materials. Alternatively, a lithium-containing active material such as lithium metal or a lithium-containing alloy may be used as the negative electrode active material. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. When using lithium metal or a lithium-containing alloy as the negative electrode active material, the lithium secondary battery is preferably a so-called lithium deposition type in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during charging. The layer of lithium metal deposited on the negative electrode current collector during charging constitutes the negative electrode active material layer. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during full discharge, but in some cases, a negative electrode active material layer made of a certain amount of lithium metal may be present during full discharge.

[0022] The thickness of the negative electrode active material layer (in the case of a lithium deposition type, the thickness at full charge) differs depending on the configuration of the intended lithium secondary battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0023] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as a main component). The solid electrolyte contained in the solid electrolyte layer preferably contains the lithium ion conductor. When the solid electrolyte contained in the solid electrolyte layer contains the lithium ion conductor, the proportion of the lithium ion conductor in the solid electrolyte contained in the solid electrolyte layer is preferably 50% by mass or more and 100% by mass or more, more preferably 75% by mass or more and 100% by mass or more, even more preferably 90% by mass or more and 100% by mass or more, particularly preferably 95% by mass or more and 100% by mass or more, and most preferably 100% by mass, from the viewpoint of improving the capacity characteristics and / or high-rate characteristics of the battery.

[0024] Instead of or in addition to the lithium ion conductor, a material (lithium ion conductor) known in the art may be used as the solid electrolyte. ２ S-P ２ S ５ ), Li ６ P.S. ５ X (wherein X is Cl, Br or I), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S and Li ３ P.S. ４ Examples of the sulfide solid electrolyte include the following. One of these materials may be used alone, or two or more may be used in combination. Of course, materials other than those mentioned above may also be used.

[0025] The content of the solid electrolyte in the solid electrolyte layer is preferably 50% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99% by mass or less.

[0026] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The type of binder that can be used in the solid electrolyte layer is not particularly limited, and binders known in the art can be appropriately adopted. Examples include styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), and carboxymethyl cellulose (CMC). Among these, styrene-butadiene rubber, tetrafluoroethylene, and polyvinylidene fluoride are preferred, and tetrafluoroethylene and polyvinylidene fluoride are more preferred. These binders may be used alone or in combination of two or more.

[0027] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, preferably 10 to 40 μm.

[0028] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a solid electrolyte, a binder, and / or a conductive additive as necessary. The positive electrode active material layer is typically disposed on the surface of a positive electrode current collector as shown in Figure 1. However, if the positive electrode active material layer 15 itself has a certain degree of conductivity, the positive electrode active material layer itself can constitute the positive electrode without using a positive electrode current collector.

[0029] The type of positive electrode active material contained in the positive electrode active material layer is not particularly limited, but a lithium-containing metal oxide is preferred. Specific examples of lithium-containing metal oxides include LiCoO ２ , LiMnO ２ , LiNiO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ , LiVO ２ Among them, Li(Ni-Mn-Co)O ２ and those in which a part of these transition metals is substituted with other elements (NMC composite oxides) are preferably used as the positive electrode active material. These positive electrode active materials may be used alone or in combination of two or more.

[0030] In addition, a sulfur-based positive electrode active material is also one of the preferred embodiments. Examples of the sulfur-based positive electrode active material include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material can be used as long as it is capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0031] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle diameter (D ５０ ) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. ５０ The value of can be measured by a laser diffraction scattering method.

[0032] The content of the positive electrode active material is not particularly limited, but from the viewpoint of energy density, it is, for example, 50 to 99 mass %, preferably 70 to 99 mass %, and more preferably 80 to 99 mass %, relative to the total mass of the positive electrode active material layer.

[0033] The positive electrode active material layer may further contain a solid electrolyte, a binder and / or a conductive additive in addition to the positive electrode active material.

[0034] Here, the solid electrolyte that can be used in the positive electrode active material layer preferably contains the lithium ion conductor. When the solid electrolyte contained in the positive electrode active material layer contains the lithium ion conductor, the proportion of the lithium ion conductor in the solid electrolyte contained in the positive electrode active material layer is preferably 50% by mass or more and 100% by mass or more, more preferably 75% by mass or more and 100% by mass or more, even more preferably 90% by mass or more and 100% by mass or more, particularly preferably 95% by mass or more and 100% by mass or more, and most preferably 100% by mass or more, from the viewpoint of improving the capacity characteristics and / or high-rate characteristics of the battery. Instead of or in addition to the lithium ion conductor, a material (lithium ion conductor) known in the art may be used as the solid electrolyte. Such materials are the same as those described above for the solid electrolyte layer.

[0035] The binder that can be used in the positive electrode active material layer is the same as that described above for the solid electrolyte layer.

[0036] Examples of conductive additives that can be used in the positive electrode active material layer include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNT), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). In addition, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives.

[0037] The thickness of the positive electrode active material layer varies depending on the configuration of the intended lithium secondary battery, but is, for example, 0.1 to 1000 μm, preferably 30 to 300 μm, more preferably 50 to 200 μm, and even more preferably 70 to 150 μm.

[0038] [Positive current collector plate and negative current collector plate] The material constituting the current collector plate (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive current collector plate 27 and the negative current collector plate 25 may be made of the same material or different materials.

[0039] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collectors (11", 11') and the current collector plates (27, 25) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly adopted. Note that the portion removed from the exterior is preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like so as to prevent contact with peripheral devices or wiring, etc., causing electrical leakage and affecting products (for example, automobile parts, particularly electronic devices, etc.).

[0040] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element as shown in FIG. 1 can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable as the exterior material because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0041] The lithium secondary battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs.

[0042] The above describes an embodiment of the present invention, but the present invention is not limited to the configurations described in the above embodiment, and can be modified as appropriate based on the claims.

[0043] For example, the type of battery to which the lithium ion conductor according to the present invention can be applied includes a bipolar battery including a bipolar electrode having a positive electrode active material layer electrically bonded to one surface of a current collector and a negative electrode active material layer electrically bonded to the opposite surface of the current collector.

[0044] Furthermore, the lithium secondary battery according to the present embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferably an amount that allows the shape of the solid electrolyte layer formed by the solid electrolyte to be maintained and prevents leakage of the liquid electrolyte (electrolytic solution).

[0045] The following items are also included in the scope of the present invention: Item 1: Formula: Li １１．７－ｘ－４ｙ (Si ０．９ Ge ０．１ ) ３－ｘ＋ｙ P ｘ S １１．７－ｚ Cl ０．３ O ｚ Item 2: The lithium ion conductor according to Item 1, wherein y is 0.1≦y≦0.15 in the formula; Item 3: The lithium ion conductor according to Item 1, wherein y is 0.1 in the formula; Item 4: The lithium ion conductor according to any one of Items 1 to 3, wherein z is 1.8 in the formula; Item 5: A lithium secondary battery comprising a power generating element including a positive electrode having a positive electrode active material layer, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, wherein the positive electrode active material layer and / or the solid electrolyte layer contains the lithium ion conductor according to any one of Items 1 to 4.

[0046] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Note that the following operations were carried out in a glove box with an argon atmosphere at a dew point of -68°C or less. Furthermore, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0047] <Examples of Preparation of Lithium Ion Conductor> [Example 1] Li ２ S (purity>99.9%, manufactured by Mitsuwa Chemical Co., Ltd.), P ２ S ５(purity>99%, manufactured by Sigma-Aldrich), SiS ２ (purity >99%, manufactured by Mitsuwa Chemicals Co., Ltd.), LiCl (purity >99%, manufactured by Sigma-Aldrich), GeS ２ (purity >99.99%, manufactured by Kojundo Chemical Laboratory Co., Ltd.) and P ２ O ５ (purity > 99.99%, manufactured by Kojundo Chemical Laboratory Co., Ltd.) was weighed out in total 2 g of raw materials so that the molar ratio of Li:Si:Ge:P:S:Cl:O was 10.1:1.485:0.165:1.4:9.9:0.3:1.8 (in this example, Li ２ 0.8593g of S, ２ S ５ 0.2884 g of SiS ２ 0.5227 g, LiCl 0.0485 g, GeS ２ 0.0861 g of P ２ O ５ 0.195 g of the above was weighed out and mixed in a mortar for 15 minutes. The resulting mixture was placed in a zirconia pot containing zirconia balls (φ10 mm) and mechanically pulverized for 40 hours at 380 rpm using a planetary ball mill. The pulverized mixture was pressed into a disk (φ10 mm, thickness 1 mm), heated to 673-748 K over 3 hours, maintained at that temperature for an additional 8 hours, and then naturally cooled to 298 K. This yielded the lithium ion conductor of this example.

[0048] [Example 2] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.9:1.305:0.145:1.6:9.9:0.3:1.8.

[0049] [Example 3] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２and P ２ O ５ The lithium ion conductor of this example was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.7:1.575:0.175:1.4:9.9:0.3:1.8.

[0050] [Example 4] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this example was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.5:1.395:0.155:1.6:9.9:0.3:1.8.

[0051] [Example 5] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.9:1.53:0.17:1.4:9.9:0.3:1.8.

[0052] [Example 6] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this example was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.7:1.35:0.15:1.6:9.9:0.3:1.8.

[0053] [Example 7] Li ２ S, P ２ S ５ , SiS ２, LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.9:1.53:0.17:1.4:10:0.3:1.7.

[0054] [Comparative Example 1] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this comparative example was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=10:1.62:0.18:1.3:9.9:0.3:1.8.

[0055] [Comparative Example 2] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this comparative example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.6:1.26:0.14:1.7:9.9:0.3:1.8.

[0056] [Comparative Example 3] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this comparative example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=10.1:1.26:0.14:1.6:9.9:0.3:1.8.

[0057] [Comparative Example 4] Li ２ S, P ２ S ５ , SiS２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this comparative example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.6:1.71:0.19:1.3:9.9:0.3:1.8.

[0058] [Comparative Example 5] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this comparative example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.3:1.44:0.16:1.6:9.9:0.3:1.8.

[0059] [Comparative Example 6] Li ２ S, P ２ S ５ , SiS ２ , LiCl, GeS ２ and P ２ O ５ The lithium ion conductor of this comparative example was obtained in the same manner as in Example 1, except that the above components were weighed out so as to have a molar ratio of Li:Si:Ge:P:S:Cl:O=9.4:1.44:0.16:1.5:9.85:0.3:1.85.

[0060] <Evaluation of Lithium Ion Conductors> [X-ray Diffraction (XRD) Measurement] X-ray diffraction (XRD) measurements were performed on the lithium ion conductors obtained in the Examples and Comparative Examples. The measurements were performed under the following conditions: Measurement device: SmartLab (manufactured by Rigaku Corporation) Measurement angle range: 2θ = 10° to 60° Step width (2θ / θ): 0.01° Radiation source: CuKα (λ = 1.5418 Å).

[0061] FIG. 2 shows the X-ray diffraction patterns of the lithium ion conductors obtained in Comparative Example 4 and Example 6, respectively. As shown in FIG. 2, the diffraction patterns of the lithium ion conductors of Comparative Example 4 and Example 6 were similar to those of a known LGPS-type lithium ion conductor, although the peaks were slightly shifted. Comparing the diffraction patterns of Comparative Example 4 and Example 6, only peaks derived from the LGPS-type phase were observed in Example 6, whereas a peak derived from the argyrodite-type crystal structure (the peak indicated by a ■ symbol in FIG. 2 ) was observed near 2θ = 25° in Comparative Example 4. This indicates that the lithium ion conductor of Example 6 is a single phase consisting of the LGPS-type phase, whereas the lithium ion conductor obtained in Comparative Example 4 contains an argyrodite-type phase, which is an impurity phase, in addition to the LGPS-type phase. The diffraction patterns of the lithium ion conductors of the Examples and Comparative Examples were confirmed, and the purity was evaluated by assigning a ◯ to a pattern in which only a peak derived from a single phase consisting of the LGPS-type phase was observed, and an × to a pattern in which peaks derived from an impurity phase were observed in addition to the LGPS-type phase. The results are shown in Table 1 below.

[0062] [Measurement of Lithium Ion Conductivity] The lithium ion conductivity of the lithium ion conductors obtained in the Examples and Comparative Examples was measured. Specifically, Au powder / lithium ion conductor / Au powder was compression molded at a pressure of 570 MPa to prepare pellets (φ10 mm). The lithium ion conductivity (25°C) of the obtained pellets was measured by an AC impedance method. A frequency response analyzer (FRA) was used for the measurement, and the measurement conditions were an applied voltage of 0.01 V and a measurement frequency range of 1 to 10. ６ The results are shown in Table 1 below.

[0063] [Measurement of Oxidation Current] (Preparation of Test Cell) Test cells were prepared using the lithium ion conductors obtained in the Examples and Comparative Examples in a glove box in an argon atmosphere with a dew point of −68° C. or lower. A stainless steel cylindrical convex punch (10 mm diameter, working electrode) was inserted into one side of a cylindrical tube jig manufactured by Macor (tube inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and 100 mg of the measurement target (lithium ion conductor) was placed from the top of the cylindrical tube jig. Then, another stainless steel cylindrical convex punch was inserted to sandwich the measurement target, and the cylindrical tube jig was pressed at a pressure of 300 MPa for 1 minute using a hydraulic press to form a pellet of the measurement target with a diameter of 10 mm and a thickness of approximately 0.6 mm in the cylindrical tube jig. The lower stainless steel cylindrical convex punch was removed, and indium foil (9 mm diameter) and lithium foil (5 mm diameter, counter electrode / reference electrode) were inserted from the bottom of the cylindrical tube jig. The stainless steel cylindrical convex punch was then inserted again, and the jig was pressed at a pressure of 75 MPa for 10 seconds, thereby producing a test cell in which the working electrode (stainless steel), the object to be measured, and the counter electrode / reference electrode (lithium indium alloy) were stacked in this order.

[0064] (Cyclic Voltammetry (CV) Measurement) The oxidation current was measured using cyclic voltammetry. The test cell was placed in a thermostatic chamber set at 25°C, and after the cell temperature became constant, the cell was oxidized from the open circuit voltage (OCV) to 4.4 V vs. lithium indium alloy at a sweep rate of 10 mV / s, and then reduced to 1.6 V vs. lithium indium alloy. From the obtained cyclic voltammogram, the current value at the peak top of the oxidation peak present in the range of 3.17 to 3.39 V was read, and this value was taken as the oxidation current value. The results are shown in Table 1 below.

[0065]

[0066] As shown in Table 1, the present invention can improve electrochemical stability while maintaining high purity and lithium ion conductivity. Comparisons between Examples 1, 3, and 5, and between Examples 2, 4, and 6 show that when y is within the range of 0.1 to 0.15, the lithium ion conductivity is further improved.

[0067] 10a: laminated battery, 11': negative electrode current collector, 11'': positive electrode current collector, 13: negative electrode active material layer, 15: positive electrode active material layer, 17: solid electrolyte layer, 19: single cell layer, 21: power generating element, 25: negative electrode current collector, 27: positive electrode current collector, 29: laminate film.

Claims

1. Formula: Li １１．７－ｘ－４ｙ (Si ０．９ Ge ０．１ ) ３－ｘ＋ｙ P ｘ S １１．７－ｚ Cl ０．３ O ｚ A lithium ion conductor having a composition represented by the formula (wherein x is 1.4≦x≦1.6, y is 0.05≦y≦0.15, and z is 1.65<z≦1.8).

2. The lithium ion conductor according to claim 1, wherein in said formula, y is in the range of 0.1≦y≦0.

15.

3. The lithium ion conductor of claim 1, wherein y is 0.1 in said formula.

4. The lithium ion conductor of claim 1, wherein z is 1.

8.

5. A lithium secondary battery comprising a power generating element having: a positive electrode having a positive electrode active material layer; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, wherein the positive electrode active material layer and / or the solid electrolyte layer contains the lithium ion conductor according to claim 1.

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