Solid electrolyte, method for manufacturing solid electrolyte, and battery

Abstract

This solid electrolyte: contains, as a main component, a component expressed by a composition formula of Naa+dMbXcAeOf by using values a to f larger than 0 (where M represents an element that becomes a trivalent cation, X represents a halogen element, and A represents a sulfur element or a phosphorus element); and satisfies 0.8c≤(a+3b)≤1.2c and 1.6f≤(d+n×e)≤2.4 (where, when A represents a sulfur element, n is 4 or 6, and when A represents a phosphorus element, n is 5). Accordingly, a solid electrolyte having high ion conductivity can be provided.

Description

Solid electrolyte, method for manufacturing solid electrolyte, and battery

[0001] The present invention relates to a solid electrolyte and a battery.

[0002] In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as their power sources has expanded significantly. Batteries used for such applications have traditionally used organic electrolytes, in which an electrolyte is dissolved in a flammable organic solvent, as a medium for ion transfer. Batteries containing organic electrolytes may pose safety issues. Therefore, to ensure essential safety, development of all-solid-state batteries that use solid electrolytes instead of organic electrolytes is underway. Since the electrolyte in all-solid-state batteries is a non-flammable material, high safety is realized.

[0003] Furthermore, in response to the recent rapid changes in social conditions toward achieving carbon neutrality, demand is rapidly increasing for decarbonized electric vehicles (EVs) and large lithium-ion batteries that ensure a stable supply of renewable energy. In addition to the scarce elements Co and Ni, supply concerns and rising costs of Li have also become an issue.

[0004] Therefore, Japanese Patent Laid-Open No. 2023-48155 (Document 1) and Japanese Patent No. 7230772 (Document 2) disclose solid electrolytes that are Na ion conductors. ｘ M １ ２－（ｙ＋Ｚ） M ２ ｙ M ３ ｚ (A.O. ４ ) ３ and M １ , M ２ and M ３ are each independently Hf, Mg, Sc, In, Y, Ca or Zr, and A is P, Si, S or a combination thereof. In the production of the solid electrolyte in Document 2, a Na source, a Y source and a Si source are mixed and fired to obtain Na ５ YSi ４ O １２ The sintered body is molded and then sintered.３ YSi ３ O ９ In addition, in International Publication No. WO2022 / 210482 (Reference 3), the composition formula is Li ａ＋ｄ M ｂ X ｃ A ｅ O ｆ In this composition formula, M is an element that becomes trivalent as a cation, X is a halogen element, and A is sulfur element or phosphorus element.

[0005] However, the production of the solid electrolytes described in References 1 and 2 requires high-temperature sintering (heat treatment) for densification and other purposes. In battery production, when a pre-sintered solid electrolyte is mixed with a positive electrode active material or a negative electrode active material and sintered, the solid electrolyte may react with the active material to increase its resistance. Therefore, there is a need for a novel Na-ion solid electrolyte that can be densified by press molding or other methods and has high ionic conductivity.

[0006] The present invention is directed to a solid electrolyte, and aims to provide a solid electrolyte having high ionic conductivity.

[0007] The invention of aspect 1 is a solid electrolyte, and the composition formula is Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ (wherein M is an element that becomes trivalent as a cation, X is a halogen element, and A is sulfur element or phosphorus element), and 0.8c≦(a+3b)≦1.2c and 1.6f≦(d+n×e)≦2.4f (wherein when A is sulfur element, n is 4 or 6, and when A is phosphorus element, n is 5) are satisfied.

[0008] According to the present invention, a solid electrolyte having high ionic conductivity can be provided.

[0009] A second aspect of the present invention is the solid electrolyte of the first aspect, wherein the composition formula satisfies 0<e / (c+e)≦0.5.

[0010] A third aspect of the present invention is the solid electrolyte of the first or second aspect, wherein, in the composition formula, A is a sulfur element and 0.8d≦2e≦1.2d is satisfied, or A is a phosphorus element and 0.8d≦e≦1.2d is satisfied.

[0011] A fourth aspect of the present invention is the solid electrolyte according to any one of the first to third aspects, wherein in the composition formula, A is a sulfur element and n is 6.

[0012] A fifth aspect of the present invention is the solid electrolyte according to any one of the first to fourth aspects, wherein in the composition formula, M is an aluminum element and X is a fluorine element.

[0013] A sixth aspect of the present invention is the solid electrolyte according to any one of the first to fifth aspects, wherein, in measurement with an X-ray diffractometer using CuKα radiation, the half-width of a peak detected in a 2θ range of 31 to 35° is 0.4° or more.

[0014] A seventh aspect of the present invention is a method for producing a solid electrolyte, the method comprising: a) forming a solid electrolyte having a composition formula of Na using values ​​a to f that are greater than 0; ａ M ｂ X ｃ and Na ｄ A ｅ O ｆ (wherein M is an element that becomes trivalent as a cation, X is a halogen element, A is sulfur element or phosphorus element, a to f satisfy 0.8c≦(a+3b)≦1.2c and 1.6f≦(d+n×e)≦2.4f, and when A is sulfur element, n is 4 or 6, and when A is phosphorus element, n is 5); and b) preparing compounds represented by the formula: ａ M ｂ X ｃ and Na ｄ A ｅ O ｆ and a step of mechanically milling the mixture, ａ M ｂ X ｃ Amount of substance and Na ｄ A ｅ O ｆ The amount of Na in the total amount of ｄ Aｅ O ｆ The ratio of the amount of substance is 85% or less.

[0015] The invention of aspect 8 is a method for producing a solid electrolyte, comprising: a) mixing a first compound which is NaX and a second compound which is MX ３ and a third compound consisting of Na, A, and O (where X is a halogen element, M is an element that becomes trivalent as a cation, and A is sulfur element or phosphorus element); and b) a step of mechanically milling the first compound, the second compound, and the third compound, wherein in the step a), when the substance amount ratios of Na, M, and X in the mixture of the first compound and the second compound, and Na, A, and O in the third compound are expressed as a:b:c:d:e:f using values ​​a to f that are greater than 0, the following conditions are satisfied: 0.8c≦(a+3b)≦1.2c; and 1.6f≦(d+n×e)≦2.4f (where n is 4 or 6 when A is sulfur element, and n is 5 when A is phosphorus element), and further 0<e / (c+e)≦0.5 are satisfied.

[0016] A ninth aspect of the invention is the method for producing a solid electrolyte according to the seventh or eighth aspect, wherein A is a sulfur element and 0.8d≦2e≦1.2d is satisfied, or A is a phosphorus element and 0.8d≦e≦1.2d is satisfied.

[0017] A tenth aspect of the present invention is the method for producing a solid electrolyte according to any one of the seventh to ninth aspects, wherein A is a sulfur element and n is 6.

[0018] An eleventh aspect of the invention is the method for producing a solid electrolyte according to any one of the seventh to tenth aspects, wherein M is an aluminum element and X is a fluorine element.

[0019] A twelfth aspect of the invention is a battery comprising a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, wherein the solid electrolyte according to any one of the first to sixth aspects is contained in at least one of the positive electrode, the negative electrode, and the electrolyte layer.

[0020] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings.

[0021] 1 is a longitudinal sectional view showing an all-solid-state secondary battery; FIG. 2 is a diagram showing a flow of manufacturing a solid electrolyte; FIG. 3 is a diagram showing an X-ray diffraction pattern obtained from the solid electrolyte; ２ SO ４ 1 is a graph showing the relationship between the ratio of the amount of Na and the ionic conductivity at room temperature. ２ SO ４ 1 is a diagram showing the relationship between the ratio of the amounts of substances and the ionic conductivity at 120° C. FIG. 2 is a diagram showing the flow of another example of producing a solid electrolyte.

[0022] FIG. 1 is a longitudinal cross-sectional view showing an all-solid-state sodium ion secondary battery 1 (hereinafter simply referred to as "all-solid-state secondary battery 1"). The all-solid-state secondary battery 1 has, from top to bottom in FIG. 1 , a positive electrode 11, a solid electrolyte layer 13, and a negative electrode 12. That is, the solid electrolyte layer 13 is located between the positive electrode 11 and the negative electrode 12. The solid electrolyte layer 13 also serves as a separator layer. The positive electrode 11 includes a current collector 111 and a positive electrode layer 112. The positive electrode layer 112 includes a positive electrode active material. The negative electrode 12 includes a current collector 121 and a negative electrode layer 122. The negative electrode layer 122 includes a negative electrode active material.

[0023] An example of the positive electrode active material of the positive electrode layer 112 is Na(Fe, Mn)O ２ Another example of the positive electrode active material is a layered compound, NaCoO ２ , NaNiO ２ , NaMnO ２ , Na(Ni,Co,Mn)O ２ , NaFeO ２ , Na(Ni, Mn, Fe, Ti)O ２ Spinel-type NaMn ２ O ４ Polyanion type Na ３ V ２ (P.O. ４ ) ３ , Na ２ Fe ２ (SO ４ ) ３ , Na ２ Mn ２ (SO４ ) ３ , NaFePO ４ , NaMnPO ４ , Na ４ Fe ７ (P.O. ４ ) ６ , Na ３ V (PO ３ ) ３ N, sodium pyrophosphate ２ MnP ２ O ７ , Na ２ FeP ２ O ７ The positive electrode layer 112 includes a solid electrolyte, which will be described later, in addition to a positive electrode active material. The positive electrode layer 112 may further include an electron conduction aid (carbon black, etc.). An example of the positive electrode layer 112 is one in which these materials are integrated by applying pressure or the like.

[0024] An example of the negative electrode active material of the negative electrode layer 122 is hard carbon. Other examples of the negative electrode active material include metals such as Na, In, Sn, and Sb, alloys of these metals with Na, graphite, SiO, and TiO. ２ , Fe ２ O ３ , Na ４／３ Ti ５／３ O ４ , Na ２ Ti ６ O １３ , Na ０．６６ [Li ０．２２ Ti ０．７８ ]O ２ , Na ３ V ２ (P.O. ４ ) ３ , SnO, Li ４ Ti ５ O １２ The anode layer 122 includes a solid electrolyte, which will be described later, in addition to the anode active material. The anode layer 122 may further include an electron conduction aid (carbon black, etc.). One example of the anode layer 122 is one in which these materials are integrated by applying pressure or the like.

[0025] The configurations and materials of the positive electrode 11 and the negative electrode 12 of the all-solid-state secondary battery 1 are not limited to those described above, and various other configurations and materials can be adopted.

[0026] The solid electrolyte layer 13 is made of or includes a solid electrolyte according to one embodiment of the present invention (hereinafter also referred to as "the present solid electrolyte"). The present solid electrolyte is a sodium ion conductive material. The present solid electrolyte is, for example, a mixture (or synthesis) of a compound containing sodium element (Na), an element (M) that becomes a trivalent cation, and a halogen element (X), and a compound containing sodium element, sulfur (S) or phosphorus (P), and oxygen element (O). As will be described later, the present solid electrolyte has a composition formula of Na, where a to f are values ​​greater than 0. ａ＋ｄ M ｂ X ｃ A ｅ O ｆ (wherein M is an element that becomes trivalent as a cation, X is a halogen element, and A is sulfur element or phosphorus element), and 0.8c≦(a+3b)≦1.2c and 1.6f≦(d+n×e)≦2.4f (wherein when A is sulfur element, n is 4 or 6, and when A is phosphorus element, n is 5) are satisfied. This solid electrolyte has high ionic conductivity (typically, sodium ionic conductivity). It is also non-flammable and chemically stable.

[0027] A preferred example of the solid electrolyte is a Na solid electrolyte containing sodium, aluminum, and fluorine. ３ AlF ６ (sodium hexafluoroaluminate) and Na, an inorganic salt containing sodium and sulfur or phosphorus. ２ SO ４ (sodium sulfate) or NaPO ３ It is a mixture of Na ３ AlF ６ And Na ２ SO ４ or NaPO ３ In the present solid electrolyte containing ３ AlF ６ The reason for this is unclear, but one possible reason is that the mechanical milling process, as described below, allows the Na ３ AlF ６And Na ２ SO ４ or NaPO ３ It is believed that an interfacial layer with high ionic conductivity is formed at the particle interface between the solid electrolyte and the ionic conductivity. Furthermore, the present solid electrolyte maintains high ionic conductivity even at a high temperature range, for example, 120°C. In other words, the present solid electrolyte achieves high temperature stability.

[0028] FIG. 2 is a diagram showing the flow of manufacturing the solid electrolyte. ３ AlF ６ and Na ２ SO ４ The process for producing the present solid electrolyte will be described below. ３ AlF ６ and NaPO ３ The same applies to the case where the present solid electrolyte is produced by mixing Na ３ AlF ６ powder and Na ２ SO ４ The powders are prepared (step S11). ３ AlF ６ In preparing the powder, for example, commercially available NaF (sodium fluoride) powder and commercially available AlF ３ (aluminum fluoride) powder is weighed and mixed. The resulting mixture is then heat-treated (for example, at 1050°C) and then pulverized to obtain Na ３ AlF ６ The powder obtained is Na ３ AlF ６ The powder may be produced by other methods. ２ SO ４ The powder is commercially available (NaPO ３ The same applies to powders of Na. ２ SO ４ powder may be produced by known techniques (NaPO ３ The same applies to the powder of Na ａ M ｂ X ｃ and Na ｄ A ｅ O ｆ This is the process of preparing the above.

[0029] Next, Na ３ AlF ６ powder and Na ２ SO ４ The powder is mixed with the powder of Na, and then subjected to mechanical milling (step S12). Here, in one example of mechanical milling, a planetary ball mill is used. In a planetary ball mill, the pot rotates on its axis while the stage on which the pot is placed revolves, making it possible to generate very high impact energy. The mechanical milling may also be performed using other types of grinders. By the mechanical milling, the powder of the present solid electrolyte to be used for the positive electrode layer 112, the negative electrode layer 122, or the solid electrolyte layer 13 is obtained. In this processing example, the mechanical milling is performed at room temperature, but the conditions such as temperature may be changed as appropriate. In step S12, Na ａ M ｂ X ｃ and Na ｄ A ｅ O ｆ This is a process of mechanical milling.

[0030] In step S12, Na ３ AlF ６ Amount of substance and Na ２ SO ４ The amount of Na in the total amount of ２ SO ４ It is preferable that the ratio of the amount of substance of is greater than 0% and not more than 85%. This makes it possible to increase the ionic conductivity of the present solid electrolyte to Na at both room temperature and high temperatures (e.g., 120°C). ３ AlF ６ As will be shown in the experimental example below, ３ AlF ６ and Na ２ SO ４ In the present solid electrolyte containing ２ SO ４ The ratio of the amount of substance is 15 to 85%, so that the ionic conductivity at 120°C is approximately 1.0 × 10 －５ To further increase the ionic conductivity of this solid electrolyte, Na２ SO ４ The ratio of the amount of substance is preferably 20 to 75%. ２ SO ４ Instead of NaPO ３ The same applies when using

[0031] 3 is a diagram showing an X-ray diffraction (XRD) pattern obtained by measuring the present solid electrolyte by powder X-ray diffraction method. ２ SO ４ The solid electrolyte obtained by mechanical milling (Experimental Example 4 described later) has a material amount ratio of 50%. In this measurement, CuKα radiation is used as the radiation source of the X-ray diffractometer. In FIG. 3, the peak marked with R1 is a peak due to Si powder, which is an internal standard sample. As shown in FIG. 3, in the solid electrolyte produced by mechanical milling, all peaks in the X-ray diffraction pattern are broad (Na ３ AlF ６ and NaPO ３ This is because the very high impact energy of the mechanical milling process allows the Na ３ AlF ６ and Na ２ SO ４ It is thought that the particles become finer, some become amorphous, and the crystal structure is disturbed due to strain or dislocation within the crystal, and that this phenomenon occurs particularly significantly at the particle interfaces, which is why the ionic conductivity of the present solid electrolyte is thought to be high. Therefore, in order to increase the ionic conductivity of the present solid electrolyte, it is preferable that the half-width of the peak detected in the 2θ range of 31 to 35° in the X-ray diffraction pattern is 0.4° or more (Na ３ AlF ６ and NaPO ３ The same applies to solid electrolytes containing the above.) The upper limit of the half-value width is not particularly limited, but is, for example, 3.0°. The solid electrolyte may be amorphous.

[0032] Next, experimental examples of solid electrolytes will be described. The following experiments were carried out in a glove box or a dry room with a dew point of −40° C. or lower.

[0033] (Experimental Example 1) Commercially available NaF (sodium fluoride) powder and commercially available AlF were used as raw materials. ３ (aluminum fluoride) powder was prepared. The raw materials were NaF:AlF ３ The mixture was heated at 1050°C and then pulverized in a mortar to obtain Na ３ AlF ６ A powder was obtained. ３ AlF ６ The powder was subjected to mechanical milling using a planetary ball mill to obtain Na ３ AlF ６ A solid electrolyte powder containing only powder was obtained.

[0034] (Experimental Example 2) ３ AlF ６ In addition to powder, commercially available Na ２ SO ４ Powder was prepared. ３ AlF ６ : Na ２ SO ４ were weighed out so that the ratio of the amounts of the substances was 80:20, and mechanically milled using a planetary ball mill to obtain Na ３ AlF ６ -Na ２ SO ４ The powder was obtained as a solid electrolyte powder.

[0035] (Experimental Example 3) Na ３ AlF ６ : Na ２ SO ４ The same treatment as in Experimental Example 2 was carried out, except that the amounts were weighed out so that the ratio of the amounts of the substances was 60:40, to obtain a solid electrolyte powder.

[0036] (Experimental Example 4) Na ３ AlF ６ : Na ２ SO ４ The same treatment as in Experimental Example 2 was carried out, except that the amounts were weighed out so that the ratio of the amounts of the substances was 50:50, to obtain a solid electrolyte powder.

[0037] (Experimental Example 5) Na ３ AlF６ : Na ２ SO ４ The same treatment as in Experimental Example 2 was carried out, except that the amounts were weighed out so that the ratio of the amounts of the substances was 40:60, to obtain a solid electrolyte powder.

[0038] (Experimental Example 6) Na ３ AlF ６ : Na ２ SO ４ The same treatment as in Experimental Example 2 was carried out, except that the amounts were weighed so that the ratio of the amounts of the substances was 30:70, to obtain a solid electrolyte powder.

[0039] (Experimental Example 7) Na ３ AlF ６ : Na ２ SO ４ The same treatment as in Experimental Example 2 was carried out, except that the amounts were weighed so that the ratio of the amounts of the substances was 20:80, to obtain a solid electrolyte powder.

[0040] (Experimental Example 8) The above Na ３ AlF ６ In addition to the powder, commercially available NaPO ３ Powder was prepared. ３ AlF ６ : NaPO ３ were weighed out so that the ratio of the amounts of substances was 50:50, and mechanically milled using a planetary ball mill to obtain Na ３ AlF ６ -NaPO ３ The powder was obtained as a solid electrolyte powder.

[0041] <Measurement of ionic conductivity> A solid electrolyte powder was placed in a mold consisting of a resin sleeve and upper and lower punches made of stainless steel (SUS), and uniaxial press molding was performed under a pressure of 150 MPa. Lead wires were connected to the upper and lower punches, and impedance measurements were performed at room temperature to 120°C to calculate the ionic conductivity.

[0042] <Powder X-ray Diffraction Measurement> The solid electrolyte powder was analyzed using an X-ray diffractometer (XRD) using CuKα radiation to obtain an X-ray diffraction pattern. The obtained X-ray diffraction pattern was subjected to automatic fitting using XRD data analysis software JADE, and the half-width of the peak was calculated.

[0043] Table 1 shows the Na content in the solid electrolytes of Experimental Examples 1 to 8. ３ AlF ６ and Na ２ SO ４ or NaPO ３ The ratio of the amount of substance to the amount of Na, the ionic conductivity at room temperature, and the ionic conductivity at 120°C are also shown. Also shown are some of the half-widths of the strongest peaks in the range of 31 to 35° obtained by X-ray diffraction measurement. In Table 1, Experimental Examples 2 to 8 are examples of the present invention, and Experimental Example 1 is a comparative example. Figures 4 and 5 show the results of the analysis of Na ３ AlF ６ and Na ２ SO ４ The proportion of Na in the total amount of substances ２ SO ４ 4 shows the relationship between the ratio (mol %) of the amount of substance of the ionic conductivity and the ionic conductivity at room temperature, and FIG.

[0044]

[0045] Na ２ SO ４ The solid electrolyte powders of Experimental Examples 2 to 7 containing NaPO ３ The solid electrolyte powder of Experimental Example 8 containing Na had higher ionic conductivities at room temperature and 120°C than the solid electrolyte powder of Experimental Example 1 not containing Na. ３ AlF ６ Amount of substance and Na ２ SO ４ The amount of Na in the total amount of ２ SO ４ When the ratio of the amount of substance is relatively low (for example, in the range of 50% or less), Na ２ SO ４ As the ratio of the amount of Na increased, the ionic conductivity at room temperature and 120°C also increased. ２ SO ４ However, as the ratio of the amount of Na increased, the ionic conductivity decreased. ２ SO ４Even in Experimental Example 7, in which the ratio of the amount of substance of Na was 80%, the ionic conductivity was sufficiently higher than that of the solid electrolyte powder of Experimental Example 1. ２ SO ４ It is believed that a higher ionic conductivity than that of the solid electrolyte powder of Experimental Example 1 can be ensured by setting the ratio of the amount of substance of to be greater than 0% and equal to or less than 85%.

[0046] Also, Na ２ SO ４ In Experimental Example 2, in which the ratio of the amount of substance of is 20%, the ionic conductivity at room temperature is 3.7 × 10 －７ S / cm, and the ionic conductivity at 120°C is 4.7 × 10 －５ S / cm. Na ２ SO ４ In Experimental Example 7, in which the ratio of the amount of substance of is 80%, the ionic conductivity at room temperature was 1.8 × 10 －７ S / cm, and the ionic conductivity at 120°C is 1.9 × 10 －５ S / cm. ２ SO ４ If the ratio of the amount of substance is 15 to 85%, the ionic conductivity at room temperature is approximately 1.0 × 10 －７ S / cm or more, and the ionic conductivity at 120°C can be approximately 1.0 x 10 －５ It is believed that the ionic conductivity can be increased to 5 S / cm or more. ２ SO ４ The ratio of the amount of substance of is preferably 20 to 75%. Furthermore, the solid electrolyte powders of Experimental Examples 2 to 8 maintained high ionic conductivity even when held at 120°C for a certain period of time, for example, 15 hours. Thus, the solid electrolyte powders of the examples of the present invention were stable at high temperatures.

[0047] In addition, the solid electrolyte powders of Experimental Examples 2 to 5 had X-ray diffraction patterns with very broad peaks, with the half-width of the strongest peak detected in the range of 31 to 35° being 0.89° to 0.98°.

[0048] <Fabrication of all-solid-state battery> Na(Fe,Mn)O ２A positive electrode active material powder, a solid electrolyte powder, and an electron conduction additive powder were weighed and mixed to obtain a positive electrode blended powder. A negative electrode active material powder, a hard carbon, a solid electrolyte powder, and an electron conduction additive powder were weighed and mixed to obtain a negative electrode blended powder. The solid electrolyte powder was placed in a mold consisting of a PEEK resin sleeve and SUS upper and lower punches, and uniaxially pressed under a pressure of 150 MPa. The positive electrode blended powder was placed on top of the pressed solid electrolyte powder and integrated under a pressure of 150 MPa. The negative electrode blended powder was placed on the pressed solid electrolyte powder opposite the positive electrode and integrated under a pressure of 150 MPa. This produced a battery consisting of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer.

[0049] <Charge-Discharge Test> After connecting the lead wires to the upper and lower punches, the battery was placed in a thermostatic chamber at 120°C and subjected to a cc-cv (Constant Current-Constant Voltage) charge-discharge test. In the charge-discharge test, a cc current density of 300 μA / cm was used. ２ , cv current density 30μA / cm ２ The cutoff voltage was set to 4.25-1.50 V. In the battery using the solid electrolyte powder of Experimental Example 1 (Comparative Example), the discharge capacity was 0 mAh / g per positive electrode active material. In other words, the resistance was high and charging and discharging were not possible. In the battery using the solid electrolyte powder of Experimental Example 4 (Example), the discharge capacity was 25 mAh / g per positive electrode active material.

[0050] In the above embodiment, Na ３ AlF ６ And Na ２ SO ４ or NaPO ３ The present solid electrolyte can be obtained by mechanical milling an inorganic salt of the formula: Na (Na), but the present solid electrolyte may also be produced by mixing any compound containing sodium (Na), an element that becomes a trivalent cation, and a halogen element with any inorganic salt containing sodium and sulfur or phosphorus. In this case, the compound has a composition formula of Na (Na), where M is aluminum (Al) or another element that becomes a trivalent cation (typically, a metal element) and X is fluorine (F) or another halogen element. ａ Mｂ X ｃ (where a to c are all greater than 0). Here, Na, M, and X are monovalent cations, trivalent cations, and monovalent anions, respectively, so the compound can be expressed as Na ３ MX ６ It is expressed as: Na ３ MX ６ In this case, a + 3b = c and a = 3b are satisfied. ３ AlF ６ In addition, for example, Na ３ YF ６ , Na ３ LaF ６ , Na ３ GaF ６ , Na ３ YCl ６ , Na ３ YBr ６ , Na ３ InCl ６ , Na ３ LaI ６ etc.

[0051] Similarly, the inorganic salt has the composition formula Na ｄ A ｅ O ｆ (where d to f are all values ​​greater than 0). Here, when A is elemental sulfur, Na, A, and O are monovalent cations, tetravalent or hexavalent cations, and divalent anions, respectively, so d+4e=2f or d+6e=2f must be satisfied. When A is elemental phosphorus, Na, A, and O are monovalent cations, pentavalent cations, and divalent anions, respectively, so d+5e=2f must be satisfied. In other words, d+n×e=2f must be satisfied (where n is 4 or 6 when A is elemental sulfur, and n is 5 when A is elemental phosphorus). Na ２ SO ４ or NaPO ３ The inorganic salts other than those mentioned above include, for example, Na ２ SO ３ (Sodium sulfite), Na ３ P.O. ４(sodium orthophosphate), etc.

[0052] In this way, using values ​​a to f that are all greater than 0, a compound consisting of sodium element (Na), an element that becomes a trivalent cation (M), and a halogen element (X) is called Na ａ M ｂ X ｃ and inorganic salts containing sodium and sulfur or phosphorus are represented as Na ｄ A ｅ O ｆ When expressed as above, the composition formula of the present solid electrolyte obtained by mixing the two is Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ In addition, the above-mentioned conditions a + 3b = c, a = 3b, and d + n × e = 2f (where n is 4 or 6 when A is elemental sulfur, and n is 5 when A is elemental phosphorus). Taking into account measurement errors, etc., it is sufficient that 0.8c ≦ (a + 3b) ≦ 1.2c, 0.8a ≦ 3b ≦ 1.2a, and 1.6f ≦ (d + n × e) ≦ 2.4f are satisfied. Preferably, 0.9c ≦ (a + 3b) ≦ 1.1c, 0.9a ≦ 3b ≦ 1.1a, and 1.8f ≦ (d + n × e) ≦ 2.2f are satisfied. In the case where the composition formula is Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ The present solid electrolyte represented by the formula (I) has high ionic conductivity. As a result, it is possible to provide an all-solid-state secondary battery with high output. As will be described later, the compound Na ａ M ｂ X ｃ If no α-α is generated, 0.8a≦3b≦1.2a does not need to be satisfied.

[0053] Among solid electrolytes, sulfide-based materials are widely known to react with water to generate hydrogen sulfide gas. Meanwhile, oxide-based solid electrolytes that do not generate gases like hydrogen sulfide are also being widely developed. However, these typically require densification by high-temperature sintering to increase ionic conductivity, which can lead to problems with reaction with active materials during battery fabrication, resulting in high resistance. In contrast, the present solid electrolyte is nonflammable and chemically stable, making it possible to provide an essentially safe ion battery. Furthermore, the present solid electrolyte can be densified by press molding pressure rather than sintering, thereby preventing reaction with active materials during battery fabrication. Furthermore, anodes capable of stable charge and discharge can be formed even when using anode active materials with low operating potentials, such as graphite. The present solid electrolyte uses sodium, an inexpensive and resource-free element, making it possible to provide all-solid-state secondary batteries that are inexpensive and can be supplied in large quantities.

[0054] As mentioned above, Na ３ AlF ６ Amount of substance and Na ２ SO ４ The amount of Na in the total amount of ２ SO ４ If the ratio of the amount of substance is 85% or less, Na ３ AlF ６ This relationship is more reliably achieved by increasing the ionic conductivity than that of the simple substance. ａ＋ｄ M ｂ X ｃ A ｅ O ｆ The same is thought to be true for the solid electrolytes of the above inorganic salts (Na ２ SO ４ When the ratio of the amount of substance of the above-mentioned composition formula Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ In this case, e / (c+e) is 0.49. Therefore, the composition formula Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆBy satisfying 0<e / (c+e)≦0.5, in the present solid electrolyte, Na ａ M ｂ X ｃ As mentioned above, a to f are values ​​greater than 0, and the solid electrolyte is Na ｄ A ｅ O ｆ Depending on the ionic conductivity required in the solid electrolyte, e / (c+e) may be greater than 0.5.

[0055] In order to increase the ionic conductivity by setting the ratio of the amount of substance of the inorganic salt to 15 to 85%, the composition formula Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ It is preferable that the ratio of the amount of substance of the inorganic salt is set to 20 to 75% and the ionic conductivity is further increased by using the composition formula Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ It is preferable that the relationship 0.04≦e / (c+e)≦0.33 is satisfied.

[0056] Preferably, Na ｄ A ｅ O ｆ is Na ２ SO ４ or NaPO ３ This makes it possible to more reliably achieve high ionic conductivity. ｄ A ｅ O ｆ Na ２ SO ４ When the formula is Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ In the formula, A is a sulfur element and d=2e is satisfied. Taking into consideration measurement errors, etc., it is sufficient that 0.8d≦2e≦1.2d is satisfied, and preferably 0.9d≦2e≦1.1d is satisfied. ｄ A ｅ O ｆ NaPO３ When the formula is Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ In the formula, A is a phosphorus element and d=e is satisfied. Taking into consideration measurement errors, etc., it is sufficient that 0.8d≦e≦1.2d is satisfied, and preferably 0.9d≦e≦1.1d is satisfied. Also, preferably, Na ａ M ｂ X ｃ is Na ３ AlF ６ In other words, the composition formula Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ In the above formula, M is an aluminum element and X is a fluorine element, thereby more reliably realizing high ionic conductivity.

[0057] As mentioned above, the composition formula of this solid electrolyte is Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ For example, Na ３ AlF ６ and Na ２ SO ４ When mixing, the composition formula is Na ａ＋ｄ Al ｂ F ｃ S ｅ O ｆ Also, Na ３ AlF ６ and NaPO ３ When mixing, the composition formula is Na ａ＋ｄ Al ｂ F ｃ P ｅ O ｆWhen confirming whether an unknown solid electrolyte is the present solid electrolyte, chemical analysis of the unknown solid electrolyte is performed to confirm whether the constituent elements are Na, M, X, A, and O (wherein M is an element that becomes trivalent as a cation, X is a halogen element, and A is sulfur or phosphorus element). When the constituent elements are Na, M, X, A, and O, if the values ​​a to f of the substance amount ratios of the constituent elements are all greater than 0 and satisfy 0.8c≦(a+3b)≦1.2c and 1.6f≦(d+n×e)≦2.4f (wherein n is 4 or 6 when A is sulfur element, and n is 5 when A is phosphorus element), the unknown solid electrolyte can be said to be the present solid electrolyte. Furthermore, if 0<e / (c+e)≦0.5 is satisfied, the unknown solid electrolyte can be said to be the present solid electrolyte. ３ AlF ６ etc.) and the amount of the above inorganic salts (Na ２ SO ４ The ratio of the amount of the inorganic salt to the total amount of the other inorganic salts is 85% or less.

[0058] For example, Na, Al, S, and P can be quantified using an ICP-emission spectrometer. F can be quantified using an ion chromatograph. O can be quantified by oxygen-nitrogen gas analysis. When the present solid electrolyte contains an element M other than Al and an element X other than F, a measurement method capable of quantifying element M and element X is appropriately selected.

[0059] In the above processing example, NaF and AlF ３ and Na were mixed in a substance ratio of 3:1. ３ AlF ６ After generating Na ３ AlF ６ and Na ２ SO ４ (or NaPO ３ ) and mechanical milling treatment was explained, but Na ３ AlF ６ Without generating NaF, AlF ３ and Na ２ SO ４ (or NaPO ３) can also be subjected to mechanical milling.

[0060] 6 is a diagram showing the flow of another example of manufacturing the solid electrolyte. In this manufacturing example, NaF powder and AlF ３ powder and Na ２ SO ４ (or NaPO ３ ) powder is prepared (step S21). ３ powder and Na ２ SO ４ (or NaPO ３ ) powder is mixed and then subjected to mechanical milling (step S22).

[0061] At this time, NaF and AlF ３ The ratio of the amount of NaF to the amount of AlF may be other than 3:1. ３ Amount of substance and Na ２ SO ４ The ratio of the amount of NaF to the total amount of AlF is, for example, 10% or more and 80% or less, and preferably 30% or more and 70% or less. ３ The ratio of the amount of substance of is, for example, 5% or more and 60% or less, and preferably 10% or more and 50% or less. ２ SO ４ The ratio of the amount of the substance is, for example, 2% or more and 50% or less, and preferably 10% or more and 40% or less. By the above treatment, a powder of the present solid electrolyte having high ionic conductivity is obtained. ２ SO ４ Instead of NaPO ３ The same applies when using

[0062] Here, NaF and AlF prepared in step S21 ３ The ratio of the amounts of Na, Al, and F in the mixture when only Na, Al, and F are mixed is expressed as a:b:c (where a to c are values ​​greater than 0). In this case, Na, Al, and F are monovalent cations, trivalent cations, and monovalent anions, respectively, so a+3b=c is satisfied. Taking into account measurement errors, etc., 0.8c≦(a+3b)≦1.2c is satisfied. On the other hand, Na ３ AlF６ Unlike the case where NaF and AlF are pre-generated, ３ The ratio of the amounts of substances is not limited to 3:1, so a = 3b is not necessarily satisfied. In other words, even when 0.8a ≦ 3b ≦ 1.2a is not satisfied, it is possible to obtain the present solid electrolyte having high ionic conductivity (and high-temperature stability).

[0063] In the production of the solid electrolyte shown in FIG. 6, as described above, NaF, AlF ３ and Na ２ SO ４ The solid electrolyte is obtained by mechanical milling. The raw materials for the solid electrolyte are NaF and AlF. ３ and Na ２ SO ４ (or NaPO ３ The present solid electrolyte is a compound of a first compound NaX, where X is any halogen element, M is any element that becomes trivalent as a cation, and A is sulfur or phosphorus element, and MX ３ and a third compound consisting of Na, A, and O. In this case, in step S21 of Fig. 6, the first compound, the second compound, and the third compound are prepared. In step S22, the first compound, the second compound, and the third compound are subjected to a mechanical milling treatment to obtain the present solid electrolyte.

[0064] When the ratios of the amounts of Na, M, and X in the mixture of the first and second compounds and Na, A, and O in the third compound are expressed as a:b:c:d:e:f using values ​​a to f greater than 0, the mixture satisfies 0.8c≦(a+3b)≦1.2c as described above. Furthermore, the third compound satisfies 1.6f≦(d+n×e)≦2.4f as described above (where n is 4 or 6 when A is elemental sulfur, and n is 5 when A is elemental phosphorus). The first compound NaX can be, in addition to NaF, NaCl, NaBr, or the like. The second compound MX ３ is AlF ３ Besides, for example, YF ３ , LaF ３ , GaF ３ etc. Third compound Naｄ A ｅ O ｆ is Na ２ SO ４ or NaPO ３ In addition, for example, Na ２ SO ３ (lithium sulfite), Na ３ P.O. ４ (lithium orthophosphate), etc.

[0065] The solid electrolyte of FIG. 6 was also produced using the composition formula Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ The solid electrolyte can be obtained with high ionic conductivity. It is also preferable that 0<e / (c+e)≦0.5 is satisfied, which can more reliably achieve high ionic conductivity. ３ The mixing ratio of is not particularly limited, but in order to more reliably obtain high ionic conductivity, it is preferable that 0.1a≦3b≦10a be satisfied.

[0066] The present solid electrolyte, the method for producing the present solid electrolyte, and the battery can be modified in various ways.

[0067] The solid electrolyte may contain impurities and has a composition formula of Na ａ＋ｄ M ｂ X ｃ A ｅ O ｆ The component represented by the formula (I) may be contained as a main component. The main component is the component having the largest mass ratio among the components contained in the solid electrolyte. The mass ratio of the main component in the solid electrolyte is preferably 80 mass% or more, more preferably 90 mass% or more. The solid electrolyte may be mixed with other substances (which may contain Na) and used as an electrolyte material. The mass ratio of the solid electrolyte in the electrolyte material is preferably 50 mass% or more, more preferably 60 mass% or more, and even more preferably 70 mass% or more.

[0068] In an X-ray diffraction pattern obtained from the present solid electrolyte, the half-width of a peak detected in a diffraction angle 2θ range of 31 to 35° may be less than 0.4°.

[0069] The solid electrolyte layer 13 may contain a substance other than the present solid electrolyte. The present solid electrolyte used in the all-solid-state secondary battery 1 does not necessarily need to be contained in all of the positive electrode 11, the negative electrode 12, and the solid electrolyte layer 13, but may be contained in at least one of the positive electrode 11, the negative electrode 12, and the solid electrolyte layer 13. The present solid electrolyte may be used in batteries other than all-solid-state secondary batteries and may be used for applications other than batteries. The present solid electrolyte may be produced by a method other than mechanical milling.

[0070] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0071] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0072] 1 All-solid-state sodium ion secondary battery 11 Positive electrode 12 Negative electrode 13 Solid electrolyte layer S11, S12, S21, S22 Step

Claims

1. A solid electrolyte having a composition formula of Na with values ​​a to f greater than 0. ａ＋ｄ M ｂ X ｃ A ｅ O ｆ (wherein M is an element which becomes trivalent as a cation, X is a halogen element, and A is elemental sulfur or elemental phosphorus), and the following conditions are satisfied: 0.8c≦(a+3b)≦1.2c, and 1.6f≦(d+n×e)≦2.4f (wherein, when A is elemental sulfur, n is 4 or 6, and when A is elemental phosphorus, n is 5).

2. A solid electrolyte according to claim 1, wherein in said composition formula, 0<e / (c+e)≦0.5 is satisfied.

3. A solid electrolyte according to claim 1, wherein, in the composition formula, A is a sulfur element and 0.8d≦2e≦1.2d is satisfied, or A is a phosphorus element and 0.8d≦e≦1.2d is satisfied.

4. A solid electrolyte according to claim 1, wherein in the composition formula, A is a sulfur element and n is 6.

5. A solid electrolyte according to claim 1, wherein in the composition formula, M is an aluminum element and X is a fluorine element.

6. The solid electrolyte according to claim 1, wherein in measurement with an X-ray diffractometer using CuKα radiation, the half-width of a peak detected in the 2θ range of 31 to 35° is 0.4° or more.

7. A method for producing a solid electrolyte, comprising the steps of: a) forming a solid electrolyte having a composition formula of Na using values ​​a to f greater than 0; ａ M ｂ X ｃ and Na ｄ A ｅ O ｆ (wherein M is an element which becomes trivalent as a cation, X is a halogen element, A is elemental sulfur or elemental phosphorus, a to f satisfy 0.8c≦(a+3b)≦1.2c and 1.6f≦(d+n×e)≦2.4f, and when A is elemental sulfur, n is 4 or 6, and when A is elemental phosphorus, n is 5); and b) preparing a compound represented by the formula: ａ M ｂ X ｃ and Na ｄ A ｅ O ｆ and subjecting the mixture to mechanical milling. ａ M ｂ X ｃ Amount of substance and Na ｄ A ｅ O ｆ The amount of Na in the total of ｄ A ｅ O ｆ The method for producing a solid electrolyte, wherein the ratio of the amount of substance is 85% or less.

8. A method for producing a solid electrolyte, comprising: a) mixing a first compound, which is NaX, and a second compound, which is MX ３ and a third compound consisting of Na, A and O (wherein X is a halogen element, M is an element that becomes trivalent as a cation, and A is elemental sulfur or elemental phosphorus); and b) a step of subjecting the first compound, the second compound and the third compound to a mechanical milling treatment, wherein in the step a), when the substance amount ratios of Na, M, and X in the mixture of the first compound and the second compound, and Na, A, and O in the third compound are expressed as a:b:c:d:e:f using values ​​a to f greater than 0, 0.8c≦(a+3b)≦1.2c and 1.6f≦(d+n×e)≦2.4f (wherein n is 4 or 6 when A is elemental sulfur, and n is 5 when A is elemental phosphorus), are satisfied, and 0<e / (c+e)≦0.5 is further satisfied.

9. A method for producing a solid electrolyte according to claim 7 or 8, wherein A is a sulfur element and 0.8d≦2e≦1.2d is satisfied, or A is a phosphorus element and 0.8d≦e≦1.2d is satisfied.

10. A method for producing a solid electrolyte according to claim 7 or 8, wherein A is elemental sulfur and n is 6.

11. A method for producing a solid electrolyte according to claim 7 or 8, wherein M is an aluminum element and X is a fluorine element.

12. A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer provided between the positive electrode and the negative electrode, wherein the solid electrolyte according to any one of claims 1 to 6 is contained in at least one of the positive electrode, the negative electrode, and the electrolyte layer.

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