JP2015076324A - Solid electrolytic material and all-solid battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reliable solid electrolytic material of NASICON structure including Ti or Zr which makes possible to prevent the worsening of the performance of a solid battery owing to the decrease in ion conductivity as a result of reduction; and an all-solid battery arranged by use of such a solid electrolytic material.SOLUTION: A solid electrolytic material has a crystalline structure of NASICON type or similar to NASICON type. The solid electrolytic material has a composition expressed by the following general formula: LiM1R(PO)(where M1 represents an element larger than Li in ion radius; R represents Ti or Zr; a=0.50-1.79; and b=0.01-1.00). In the composition, M1 is an alkali metal other than Li; Na is used as M1. The composition may be arranged to meet the condition that R is Ti, part of which is substituted with another element M2, and M2 is at least one element selected from a group consisting of Mg, Ca, Sr, Al, Ga, In, Ge, Sn and Sb. Used as M2 is an element smaller than Zr in ion radius.

Description

  The present invention relates to an electrolyte material and a battery, and more particularly to a solid electrolyte material and an all-solid battery using the same.

  In recent years, various batteries (secondary batteries) have been widely used for mobile phones and portable computers. In a battery that has been widely used conventionally, a liquid electrolyte (electrolytic solution) such as an organic solvent is generally used as a medium for moving ions.

  However, in a battery using a liquid electrolyte (electrolytic solution), problems such as leakage of the electrolytic solution may occur, and there is a point to be improved regarding reliability. Moreover, the organic solvent etc. which are generally used for electrolyte solution are combustible substances, and there exists a problem that it is unpreferable on safety.

  For this reason, it has been proposed to use a solid electrolyte instead of the electrolytic solution, and the development of a solid secondary battery in which a solid electrolyte is used as the electrolyte and the other components are also made of solid is being promoted. .

  Patent Document 1 discloses various compositions of a compound having a NASICON structure using various cations as conductors as a solid electrolyte constituting an all-solid battery.

  However, as a result of investigations by the inventors of the present application, when a solid electrolyte having a NASICON structure containing Ti disclosed in Patent Document 1 is reduced, the ionic conductivity of the solid electrolyte may be reduced. all right. In other words, when a solid electrolyte having a NASICON structure containing Ti as a central metal is used as the electrolyte of a solid battery, the ionic conductivity is reduced by reducing the solid electrolyte having a NASICON structure containing Ti by the potential of the negative electrode. As a result, it was confirmed that the performance of the solid battery was remarkably deteriorated.

JP 2007-258165 A

  The present invention solves the above-mentioned problems, and uses a solid electrolyte material with high reliability capable of preventing reduction in ion conductivity due to reduction and deterioration in performance of a solid battery and the same. An object is to provide an all-solid-state battery.

The inventors of the present invention studied solid electrolyte materials in order to solve the above problems. As a result, it has been found that a solid electrolyte having a composition of LiZr (PO ₄ ) ₃ easily forms various crystal systems, and thus it is difficult to obtain a single phase.
Based on this knowledge, various experiments and examinations were further performed, and regarding the solid electrolyte having a NASICON structure, a part of Li constituting the solid electrolyte having a LiZr (PO ₄ ) ₃ composition was replaced with another element, which was excellent. Knowing that charge / discharge characteristics may be exhibited, the inventors further studied and completed the present invention.

The solid electrolyte material of the present invention is
A solid electrolyte material having a crystal structure similar to NASICON type or NASICON type,
General formula: Li _a M1 _b R ₂ (PO ₄ ) ₃ (M1 is an element having an ionic radius larger than Li, and R is Ti or Zr, a = 0.50 to 1.79, b = 0.01 to 1 .00).

  In the solid electrolyte material of the present invention, the M1 is preferably an alkali metal other than Li.

When M1 is an alkali metal that is the same monovalent cation as Li, the solid electrolyte material exhibits higher ionic conductivity.
When M1 is an element other than an alkali metal, the valence is larger than monovalent, so even if the amount of M1 is the same (the value of the coefficient b of M1 is the same), the valence is neutral. If it tries to hold | maintain, compared with the case where it substitutes with an alkali metal, the quantity of Li will fall (namely, the value of the coefficient a of Li will become small), and there exists a tendency for ion conductivity to fall.
Therefore, it is preferable to use an alkali metal which is a monovalent cation as M1, and by using a monovalent alkali metal as M1, a solid electrolyte material exhibiting higher ionic conductivity can be obtained.

  The M1 is preferably Na.

  By using Na as M1, it becomes possible to obtain a solid electrolyte material exhibiting higher ionic conductivity. In addition, it has been found that Na forms a solid solution most easily. In this respect, the greatest effect can be obtained when Na is used.

Further, R is Ti, and is represented by a composition of (Li _a M1 _b ) (Ti _2−c M2 _c ) (PO ₄ ) ₃ in which a part of Ti is substituted with another element M2, and a = 0. It is preferable to satisfy the requirements of 50 to 1.79, b = 0.01 to 0.50, and c ≦ 0.8 (0 is not included).

  By setting it as the said structure, the solid electrolyte material which shows high ion conductivity more reliably can be obtained.

  The amount of Li should just be neutral valence, and if the Li coefficient a is 0.5 or more, it is preferable. Furthermore, the Li amount (Li coefficient a) is preferably in the range of 0.5 to 1.79.

Further, M1, which replaces a part of Li and has a larger ionic radius than Li, is much less likely to conduct ions compared to Li, so that the ionic conductivity decreases as the amount of M1 (the value of the coefficient b of M1) increases. Tend to. Therefore, only the minimum amount necessary for the reduction reaction of Ti ⁴⁺ → Ti ³⁺ to be less likely to occur is used for M1, and the coefficient b of M1 is in the range of 0.01 to 0.50. More preferably, the range is most preferably in the range of 0.01 to 0.10.

In addition, the Li amount and the M1 amount (that is, the Li coefficient a and the M1 coefficient b) are as described above in order to maintain the neutrality of the positive charge and the negative charge in the NASICON type or NASICON type similar crystal. It is preferable to adjust appropriately within the range (a = 0.50-1.79, b = 0.01-0.50).
Further, the amount of M2 (the coefficient c of M2) is preferably in the range of 0.8 or less (excluding 0), and the total amount of Ti and substitution elements is preferably 2.0.

  The M2 is preferably at least one selected from the group consisting of Mg, Ca, Sr, Al, Ga, In, Ge, Sn, and Sb.

  By using at least one selected from the group consisting of Mg, Ca, Sr, Al, Ga, In, Ge, Sn, and Sb as typical metal elements or metalloid elements as M2, an even greater effect can be obtained. Can do.

  The element M2 may be any element as long as it can form a NASICON type or a NASICON type-like crystal structure even if it is replaced with Ti. For example, Sc, Y, Hf, Nb, Cr, Fe, Ru Co, Al, La, Lu, Ni, Mn, Co, Fe, Cu, Ag, or the like can be used.

The R is Zr, and is represented by a composition of (Li _a M1 _b ) (Zr _2−c M2 _c ) (PO ₄ ) ₃ in which a part of Zr is substituted with another element M2, and a = 0. It is preferable to satisfy the requirements of 50 to 1.49, b = 0.01 to 0.50, and c ≦ 1.0 (not including 0).

  Substituting Zr, which is the central metal, with another element M2, facilitates the formation of rhombohedral crystals. The amount of M2 (the value of the coefficient c of M2) may be an amount necessary for stabilizing the rhombohedral crystal, and the coefficient c of M2 is in the range of 1.0 or less (not including 0). It is preferable to do.

  The M2 is preferably an element having an ionic radius smaller than that of Zr.

  By making the element M2 replacing Zr an element having an ionic radius smaller than that of Zr, a rhombohedral crystal having a high ion conduction phase is more easily formed, and a high ion conductivity can be obtained.

  The M2 is preferably at least one selected from the group consisting of Mg, Al, Ti, Cu, Ga, Ge, Ag, and Sn.

  By using at least one of Mg, Al, Ti, Cu, Ga, Ge, Ag, and Sn as M2, a greater effect can be obtained with respect to ion conductivity.

The all solid state battery of the present invention is
A laminate in which a positive electrode green sheet and a negative electrode green sheet are stacked is sintered through an electrolyte green sheet formed using the solid electrolyte material of the present invention.

The all solid state battery of the present invention is
The solid electrolyte material of the present invention is included in at least one of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

The solid electrolyte material of the present invention is a solid electrolyte material having a crystal structure similar to NASICON type or NASICON type, and has a general formula: Li _a M1 _b R ₂ (PO ₄ ) ₃ (M1 is an element having an ionic radius larger than that of Li) And R is represented by Ti or Zr, a = 0.50-1.79, b = 0.01-1.00). It is possible to obtain a solid electrolyte material in which the degree does not decrease.
In addition, by using the solid electrolyte material of the present invention as an electrolyte, it is possible to obtain a highly reliable all solid state battery whose performance is unlikely to deteriorate.

  Moreover, the all solid state battery of the present invention is obtained by sintering a laminate in which a positive electrode green sheet and a negative electrode green sheet are laminated through an electrolyte green sheet formed using the solid electrolyte material of the present invention. Alternatively, since the solid electrolyte material of the present invention is included in at least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer, a solid battery having more excellent charge / discharge characteristics can be obtained.

  For example, an all-solid battery is manufactured by firing in a state where a solid electrolyte having a crystal structure similar to NASICON or NASICON is mixed with an active material, a sintering aid, or other additives. It is also possible to obtain the solid electrolyte material of the present invention as described above by causing some element diffusion between the substance, sintering aid and other additives and the solid electrolyte.

It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Examples 1-4 of this invention, and the comparative example 1. FIG. It is a figure which shows the colle-core plot of the sample of Example 1 of this invention obtained by impedance measurement. It is a figure which shows the charging / discharging curve about the sample of Examples 1-4 obtained by measuring reduction current, and the sample of the comparative example 1, (a) is a relationship between an electric potential and an electric current, (b) is a capacity | capacitance. It is a figure which shows the relationship of an electric potential. It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Examples 5-8 and the comparative example 2 of this invention. It is a figure which shows the charging / discharging curve about the sample of Examples 5-8 obtained by measuring reduction current, and the sample of the comparative example 2, (a) is a relationship between an electric potential and an electric current, (b) is a capacity | capacitance. It is a figure which shows the relationship of an electric potential. It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Examples 9-13 of this invention. It is a figure which shows the charging / discharging curve about the sample of Examples 9-13 obtained by measuring a reduction current, (a) is a relationship between an electric potential and an electric current, (b) is a figure which shows a relationship between a capacity | capacitance and an electric potential. It is. It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Examples 14-18 of this invention. It is a figure which shows the charging / discharging curve about the sample of Examples 14-18 obtained by measuring reduction current, (a) is a relationship between an electric potential and an electric current, (b) is a figure which shows a relationship between a capacity | capacitance and an electric potential. It is. It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Examples 21-25 of this invention, and the comparative example 3. FIG. It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Examples 26-30 of this invention. It is a figure which shows the result of the XRD measurement about the sample (solid electrolyte material) of Example 31 and 32 of this invention. It is a figure which shows the charging / discharging curve (relationship between an electric potential and an electric current) about the sample of Example 26. It is a figure which shows the charging / discharging curve (relationship between an electric potential and an electric current) about the sample of Example 31.

  Embodiments of the present invention will be described below to describe the features of the present invention in more detail.

[Embodiment 1]
Samples of Examples 1 to 18 and Samples of Comparative Examples 1 and 2 shown in Table 1A and Table 1B were prepared by the method described below.

The samples of Examples 1 to 18 are samples (solid electrolytes) in which the Li site of the material represented by the general formula (Li _a M1 _b ) (Ti _{2 -c} M2 _c ) (PO ₄ ) ₃ is replaced with M1. Material).
In addition, the samples of Examples 5 to 8 in Table 1A and 14 to 18 in Table 1B are samples (solid electrolyte materials) in which the Ti site is replaced with M2 in addition to the Li site being replaced with M1. .
Moreover, the samples of Comparative Examples 1 and 2 in Table 1A are samples (solid electrolyte materials) in which the Li site is not replaced with M1.

In Tables 1A and 1B, the unit of ion radius is angstrom.
The ionic radii in Tables 1A and 1B were referred to the following paper, and the ionic radii having a coordination number of 6 were used as a reference.
Structural Crystallography and Crystal Chemistry Volume 25, Part 5 (May 1969)

<Synthesis of solid electrolyte material>
The solid electrolytes of Examples 1 to 18 and Comparative Examples 1 and 2 were prepared according to the procedure described below.
First, as raw materials, lithium carbonate Li ₂ CO ₃ , titanium oxide TiO ₂ , ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ , sodium carbonate Na ₂ CO ₃ , silver oxide AgO, aluminum oxide Al ₂ O ₃ , calcium carbonate CaCO _3. Potassium carbonate K ₂ CO ₃ was prepared.

  This was weighed appropriately, sealed in a 500 ml polyethylene polypot and rotated on a pot rack at 150 rpm for 16 hours to mix the raw materials. Then, the mixture was baked in an air atmosphere at 500 ° C. for 1 hour and at 800 ° C. for 6 hours to remove volatile components.

  Next, it was enclosed in a 500 ml polyethylene polypot together with water and φ5 mm cobblestone, and pulverized by rotating on a pot rack at 150 rpm for 16 hours. Thereafter, moisture was removed on a hot plate at 120 ° C.

  Firing was performed at 1200 ° C. for 20 hours in an air atmosphere to obtain powders (samples) of solid electrolyte materials having the compositions of Examples 1 to 18 and Comparative Examples 1 and 2 in Table 1A and Table 1B.

<Evaluation of crystal structure of solid electrolyte material>
Samples of Examples 1 to 18 and Comparative Examples 1 and 2 (solid electrolyte material powder) were subjected to XRD (X-ray diffractometer) at a scan rate of 4.0 ° / min at 25 ° C. and a measurement range of 10 ° to 60 °. ) To examine the crystal structure (see FIGS. 1, 4, 6, and 8).

In each figure,
(A) a pattern of rhombohedral LiTi ₂ (PO ₄ ) ₃ JCPDS (Joint Committee on Powder Diffraction Standards) card (No. 01-072-6140);
(B) a pattern of orthorhombic AlPO ₄ JCPDS card (No. 01-074-3255);
(C) a pattern of rhombohedral NaTi ₂ (PO ₄ ) ₃ JCPDS card (No. 01-084-2009);
(D) a pattern of rhombohedral KTi ₂ (PO ₄ ) ₃ JCPDS card (No. 00-025-0691);
(E) Related patterns of monoclinic KTiP ₂ O ₇ JCPDS card (No. 00-052-0302) are also shown.

<Evaluation of ionic conductivity of solid electrolyte material>
For the samples of Examples 1 to 18 and Comparative Examples 1 and 2, the ionic conductivity was measured by the following method.

(1) Production of sintered tablet The solid electrolyte material, polyvinyl acetal resin, and alcohol produced as described above were weighed at a weight ratio of 98: 15: 140 and mixed thoroughly, and then heated at 80 ° C. The alcohol was removed on the plate to obtain a solid electrolyte material powder coated with a polyvinyl acetal resin as a binder.

For the sample of Comparative Example 1 and Example 1～4,9～13 containing no element M2, the Li ₂ O as a sintering aid, the solid electrolyte material powder: the sintering aid = 98: 2 in weight ratio Added.

Next, the solid electrolyte material powder to which the sintering aid was added was pressed into a tablet by pressing at 90 MPa using a tablet molding machine.
Then, the solid electrolyte material molded into a tablet shape was sandwiched between two porous setters and then fired to produce a sintered tablet.
Baking is performed at a temperature of 1000 ° C. in a nitrogen gas atmosphere after removing the polyvinyl acetal resin by baking (debinding) in a nitrogen gas atmosphere containing 1% by volume of oxygen at a temperature of 500 ° C. As a result, a sintered tablet was obtained. Table 2 shows the mass, thickness, and diameter of the obtained sintered tablet.

(2) Measurement of ion conductivity After forming a platinum (Pt) layer to be a current collector layer by sputtering on one side of the sintered tablet produced as described above, the sintered tablet was dried at 100 ° C. Water was removed.

  After applying PMMA gel electrolyte (gel electrolyte containing electrolyte) on metallic lithium as the counter electrode, the surface of the sintered tablet that does not form the current collector layer is in contact with the application surface. The sintered tablet and metallic lithium were laminated and sealed with a 2032 type coin cell. And about the cell after sealing, ion conductivity was computed by alternating current impedance measurement. Hereinafter, this ionic conductivity is referred to as “ionic conductivity in an open circuit state”.

Thereafter, the platinum side serving as a current collector layer was scanned to a potential of 1.0 V vs Li ⁺ / Li with respect to metallic lithium serving as a counter electrode, and the reduction current was measured.
Thereafter, the platinum side serving as the current collector layer was held at a potential of 1.0 V vs Li ⁺ / Li for 30 minutes, and then the ionic conductivity was calculated by AC impedance measurement in a state where the platinum side was held. Hereinafter, this ionic conductivity is referred to as “ionic conductivity in the reduced state”.

  The AC impedance measurement was performed using a Solartron frequency response analyzer (FRA) under conditions of a frequency range of 0.1 to 1 MHz and an amplitude of ± 10 mV.

The ionic conductivity was calculated from the following equation: (1) by obtaining the resistance of each solid electrolyte (the sum of the particle and grain boundary resistance) from a coll-coll plot obtained from AC impedance measurement.
Ionic conductivity = (t / A) × (1 / R) (1)
t: thickness of sample, A: area of electrode, R: resistance of solid electrolyte.

The reduction current was measured using a Solartron potentio / galvanostat, and cyclic voltammetry (CV) measurement was performed using a scanning potential range: 1.0 V vs Li ⁺ / Li to an open circuit potential, scanning speed: 0.1 mV / Carried out in seconds.
All tests were conducted at 25 ° C.

  Tables 3A and 3B show the crystal phases detected from the XRD measurements of the samples of Examples 1 to 18 and the samples of Comparative Examples 1 and 2, the ionic conductivity in the open circuit state, and the ionic conductivity in the reduced state. .

<Evaluation 1>
Moreover, the result of the XRD measurement about the sample of Examples 1-4 and the sample of the comparative example 1 is shown in FIG. FIG. 1 shows a pattern of (a) rhombohedral LiTi ₂ (PO ₄ ) ₃ JCPDS (Joint Committee on Powder Diffraction Standards) card (No. 01-072-6140) and (d) rhombohedral crystal. The pattern of KTi ₂ (PO ₄ ) ₃ JCPDS card (No. 00-025-0691) and the pattern of (e) monoclinic KTiP ₂ O ₇ JCPDS card (No. 00-052-0302) are combined. Show.

  FIG. 2 shows a colle-coll plot of the sample of Example 1 obtained by impedance measurement.

  Furthermore, the charging / discharging curve about the sample of Examples 1-4 obtained by measuring a reduction current and the sample of the comparative example 1 to FIG. 3 (a), (b) is shown.

In the case of the non-substituted sample (LiTi ₂ (PO ₄ ) ₃ ) that is not substituted with M1 or M2 for any of the Li site and Ti site in Comparative Example 1, the crystal phase detected from the XRD measurement is rhombohedral. It was confirmed to match the card pattern of crystalline LiTi ₂ (PO ₄ ) ₃ .

Further, in the sample of Comparative Example 1, as a result of the charge / discharge test, a peak current due to the redox of Ti was confirmed at about 2.5 V (FIG. 3A). Further, in the case of the sample of Comparative Example 1, the ionic conductivity of OCV (ionic conductivity in an open circuit state) was 4.0 × 10 ⁻⁴ S / cm, but 1.0V vs Li ⁺ / Li ion The conductivity (reduced state ionic conductivity) was found to be significantly reduced to 1.1 × 10 ⁻⁶ S / cm.

Further, in the case of the samples in which a part of Li in Examples 1 to 4 was replaced, the crystal phase detected from the XRD measurement may be consistent with the rhombohedral LiTi ₂ (PO ₄ ) ₃ card pattern. confirmed.

Further, only a slightly different phase was confirmed in the sample of Example 4 in which the Li site was replaced with K (M1). The heterogeneous phase was consistent with the KTi ₂ (PO ₄ ) ₃ and KTiP ₂ O ₇ card patterns. This is because the ionic radius of the substituting element K is larger than the ionic radii of the substituting elements (Ag, Ca, Na) in Examples 1 to 3, and the entire amount could not be dissolved.

  Further, the value at the end of the right end of the arc in the colle-core plot (FIG. 2) was defined as the resistance of the sample of Example 1 (the sum of the grain and grain boundary resistance).

As shown in Table 3A, the ionic conductivity in the open circuit state (OCV) of the samples of Examples 1 to 4 is 1.2 × 10 ^{−4 to} 4.1 × 10 ⁻⁴ S / cm, both of which are compared. It was equivalent to the sample of Example 1 (unsubstituted LiTi ₂ (PO ₄ ) ₃ ).

Furthermore, as shown in Table 3A, the ionic conductivity in the reduced state of 1.0 V vs Li ⁺ / Li of the samples of Examples 1 to 4 is 1.0 × 10 ^{−4 to} 2.8 × 10 ⁻⁴ S. / Cm, both of which are only slightly lower than the ionic conductivity in the open circuit state, and the rate of decrease compared to the sample of Comparative Example 1 (unsubstituted LiTi ₂ (PO ₄ ) ₃ ) Was confirmed to be small.

Further, from the charge / discharge curves of FIGS. 3A and 3B, a part of Li in Examples 1 to 4 is replaced as compared with the sample of Comparative Example 1 (unsubstituted LiTi ₂ (PO ₄ ) ₃ ). In each of the samples, the peak current value due to Ti redox (Ti ⁴⁺ → Ti ³⁺ reduction reaction) of about 2.5 V vs. Li ⁺ / Li is small (FIG. 3A). It was also confirmed that the integrated value (charge capacity) of the peak current value representing the total amount of redox was small (FIG. 3B).

These results, LiTi ₂ (PO _{4) 3} composition of the solid electrolyte, Ti ⁴⁺ by replacing a large ionic radius of the element M1 part than the ion radius 0.90Å of Li ⁺ of Li → Ti ³⁺ It was confirmed that the reduction reaction of Ti was less likely to occur, and the decrease in Li ion conductivity was suppressed.

  In particular, it was confirmed that the greatest effect was obtained when a part of Li was replaced with Na. This is considered to be because the decrease in the number of Li ions could be suppressed by substitution with alkali metal (Na), which is the same monovalent cation as Li.

  It should be noted that the ionic conductivity of the sample of Example 4 in which a part of Li was substituted with K, which is an alkali metal having an ionic radius larger than that of Na, was smaller than the ionic conductivity of the sample of Example 3 substituted with Na. It is considered that this is because it is difficult to obtain a single phase and a mixed phase including different phases is obtained.

<Evaluation 2>
Further, a sample of Examples 5 to 8 in Table 1A in which a part of Li was replaced with M1 and a part of Ti was replaced with M2, and a sample of Comparative Example 2 in which a part of Ti was replaced with M2 (Al) Was evaluated.

In FIG. 4, the result of the XRD measurement about the sample of Examples 5-8 and the sample of the comparative example 2 is shown. FIG. 4 shows (a) a rhombohedral LiTi ₂ (PO ₄ ) ₃ JCPDS (Joint Committee on Powder Diffraction Standards) card (No. 01-072-6140) pattern, and (b) an oblique pattern. A pattern of crystal AlPO ₄ JCPDS card (No. 01-074-3255), a pattern of (d) rhombohedral KTi ₂ (PO ₄ ) ₃ JCPDS card (No. 00-025-0691), (E) A pattern of a monoclinic KTiP ₂ O ₇ JCPDS card (No. 00-052-0302) is also shown.

  Furthermore, the charging / discharging curve about the sample of Examples 5-8 and the sample of the comparative example 2 which were obtained by measuring a reduction current in Fig.5 (a), (b) is shown.

  Table 3A shows the crystal phases detected from the XRD measurement of the samples of Examples 5 to 8 and the sample of Comparative Example 2, and the ionic conductivity in the open circuit state and the reduced state.

In the case of Li _1.3 Ti _1.7 Al _0.3 (PO ₄ ) ₃ in Comparative Example 2, it was confirmed that the crystal phase detected from the XRD measurement coincided with the rhombohedral LiTi ₂ (PO ₄ ) ₃ card pattern. .

Moreover, in the case of the sample of the comparative example 2, the peak current resulting from the redox of Ti was confirmed to be about 2.5 V as a result of the charge / discharge test (FIG. 5A).
Furthermore, if the sample of Comparative Example 2, but ion conductivity of OCV (ionic conductivity of the open-circuit state) was 4.0 × 10- ⁴ S / cm, the 1.0V vs Li ⁺ / Li-ion It was found that the conductivity (the ionic conductivity in the reduced state) was significantly reduced to 1.7 × 10 ⁻⁶ S / cm.

Also, in the case of the solid electrolyte material in which a part of Li in Examples 5 to 8 was substituted, the crystal phase detected from the XRD measurement was consistent with the rhombohedral LiTi ₂ (PO ₄ ) ₃ card pattern. It was confirmed.

Further, only a slightly different phase was confirmed in the sample of Example 8 in which the Li site was replaced with K (M1). The heterogeneous phase was consistent with the KTi ₂ (PO ₄ ) ₃ and KTiP ₂ O ₇ card patterns. This is because the ionic radius of the substituting element K is larger than that of the substituting elements (Ag, Ca, Na) of Examples 5 to 7, and the entire amount could not be dissolved.

The ionic conductivity in the open circuit state (OCV) of the samples of Examples 5 to 8 was 3.0 × 10 ^{−4 to} 8.1 × 10 ⁻⁴ S / cm.
Furthermore, the ionic conductivity in the reduced state of 1.0 V vs Li ⁺ / Li is 1.0 × 10 ^{−4 to} 8.2 × 10 ⁻⁴ S / cm, which is compared with the ionic conductivity in the open circuit state. All were only slightly decreased, and it was confirmed that the degree of decrease was small compared to the sample of Comparative Example 2 (unsubstituted LiTi ₂ (PO ₄ ) ₃ ) (see Table 3A).

Also, from the charge / discharge curves of FIGS. 5A and 5B, compared to the sample of Comparative Example 2 (unsubstituted Li _1.3 Ti _1.7 Al _0.3 (PO ₄ ) ₃ in which a part of Li is not substituted). In each of the samples obtained by substituting a part of Li in Examples 5 to 8 with M1, the peak current caused by Ti redox (Ti ⁴⁺ → Ti ³⁺ reduction reaction) of about 2.5 V vs Li It was confirmed that the value was small (FIG. 5A) and the integrated value (charge capacity) of the peak current value representing the total amount of Ti redox was also small (FIG. 5B).

By examining these results, even when a part of Ti is substituted with another element (Al), a part of Li is made to have an ionic radius of Li ⁺ of 0, as in the samples of Examples 5 to 8. By substituting with an element larger than 90 例 え ば (for example, Ag, Ca, Na, K), Ti ⁴⁺ → Ti ³⁺ Ti reduction reaction is less likely to occur, and the decrease in Li ion conductivity is suppressed. confirmed.

<Evaluation 3>
In addition, in the sample in which a part of Li was replaced with Na, the samples of Examples 9 to 13 in Table 1B in which the substitution amount of the substitution element Na was changed were evaluated.
In FIG. 6, the result of the XRD measurement about the sample of Examples 9-13 is shown. FIG. 6 shows a pattern of (a) rhombohedral LiTi ₂ (PO ₄ ) ₃ JCPDS (Joint Committee on Powder Diffraction Standards) card (No. 01-072-6140), and (b) orthorhombic crystal. A pattern of an AlPO ₄ JCPDS card (No. 01-074-3255) and a pattern of a (c) rhombohedral NaTi ₂ (PO ₄ ) ₃ JCPDS card (No. 01-084-2009) are shown together. .

Furthermore, the charging / discharging curve about the sample of Examples 9-13 obtained by measuring a reduction current to Fig.7 (a), (b) is shown.
Table 3B shows the crystal phases detected from the XRD measurements of the samples of Examples 9 to 13, and the ionic conductivity of the open circuit state and the reduced state.

In the case of the samples of Examples 9 to 13 in which a part of Li was substituted with Na, the crystal phase detected from the XRD measurement was a rhombohedral LiTi ₂ (PO ₄ ) ₃ card regardless of the substitution amount. It was confirmed to match the pattern.

Further, in the case of the samples of Examples 12 and 13 with a large amount of Na, a pattern of NaTi ₂ (PO ₄ ) _{3 was} partially confirmed.

Furthermore, the ionic conductivity in the reduced state of 1.0 V vs Li ⁺ / Li of the samples of Examples 9 to 13 is 0.8 × 10 ^{−4 to} 4.7 × 10 ⁻⁴ S / cm, It was confirmed that none of the ionic conductivity in the open circuit state almost decreased (see Table 3B).

  In addition, among the samples of Examples 9 to 13, the sample with the Na substitution amount of 0.01 to 0.50 (the samples of Examples 9 to 12) is ion-conducted in both the reduced state and the open circuit state. It was confirmed that the sample showed a particularly high value in the samples with the Na substitution amount of 0.01 to 0.10 (samples of Examples 9 to 11).

  Further, as in the sample of Sample No. 13, it was confirmed that when the amount of Na substitution exceeded 0.5, the ionic conductivity was lowered in both the reduced state and the open circuit state (Table 3B).

<Evaluation 4>
In addition, evaluation was performed on samples of Examples 14 to 18 in Table 1B in which a part of Li was substituted with Na, a part of Ti was substituted with Al, and the substitution amount of the substitution element Na was changed.
In FIG. 8, the result of the XRD measurement about the sample of Examples 14-18 is shown. FIG. 8 shows a pattern of (a) rhombohedral LiTi ₂ (PO ₄ ) ₃ JCPDS (Joint Committee on Powder Diffraction Standards) card (No. 01-072-6140), and (b) orthorhombic crystal. A pattern of an AlPO ₄ JCPDS card (No. 01-074-3255) and a pattern of a (c) rhombohedral NaTi ₂ (PO ₄ ) ₃ JCPDS card (No. 01-084-2009) are shown together. .

Furthermore, the charging / discharging curve about the sample of Examples 14-18 obtained by measuring a reduction current is shown to Fig.9 (a), (b).
Table 3B shows the crystal phases detected from the XRD measurement and the ionic conductivities in the open circuit state and the reduced state of the samples of Examples 14 to 18.

In the case of the samples of Examples 14 to 18 in which a part of Li was replaced with Na, a part of Ti was replaced with Al, and the amount of the substitution element Na was changed, the crystal phase detected from the XRD measurement was Li Regardless of the amount of Na replaced by Na, it was confirmed that both coincided with the rhombohedral LiTi ₂ (PO ₄ ) ₃ card pattern.
Further, in the case of the samples of Examples 17 and 18 with a large amount of Na, a pattern of NaTi ₂ (PO ₄ ) _{3 was} partially confirmed.

Further, in the case of the samples of Examples 14 to 18, the ionic conductivity in the reduced state of 1.0 V vs Li ⁺ / Li is 1.2 × 10 ^{−4 to} 8.2 × 10 ⁻⁴ S / cm, and the open state is open. It was confirmed that none of the ionic conductivity in the circuit state almost decreased (see Table 3B).

  Further, among the samples of Examples 14 to 18, the sample in which the Na substitution amount is in the range of 0.01 to 0.50 (the samples of Examples 14 to 17) is in either the reduced state or the open circuit state. In addition, it was confirmed that the sample showed a particularly high value in the sample in which the substitution amount of Na was in the range of 0.01 to 0.10 (samples of Examples 14 to 16).

  Further, as in the sample of sample number 18, when the Na substitution amount exceeded 0.5, it was confirmed that the ionic conductivity was lowered in both the reduced state and the open circuit state (Table 3B).

  Moreover, it was confirmed that the charging / discharging curve (FIG. 9 (a), (b)) about the sample of Examples 14-18 is similar to the case of the sample of above-mentioned Examples 1-4.

[Embodiment 2]
The samples of Examples 21 to 32 shown in Table 4 and the sample of Comparative Example 3 were produced by the method described below.

The samples of Examples 21 to 25 are samples ((Li _a M1 _b ) Zr ₂ (PO ₄ ) _{3 in} which the Li site of the material represented by the general formula LiZr ₂ (PO ₄ ) ₃ is replaced with M1. A solid electrolyte material represented by
Samples of Examples 26 to 32 in Table 4 are samples in which the Zr site was replaced with M2 in addition to the Li site replaced with M1 (general formula (Li _a M1 _b ) (Zr _2-c M2 _c ) (PO ₄ ) ₃ ).
In addition, the sample of Comparative Example 3 in Table 4 is a sample (solid electrolyte material) in which neither Li site nor Zr site is subjected to element substitution with M1 or M2.

In addition, the ionic radius in Table 4 was referred to the following paper, and the ionic radius having a coordination number of 6 was used as a reference.
Structural Crystallography and Crystal Chemistry Volume 25, Part 5 (May 1969)

<Synthesis of solid electrolyte material>
The samples of Examples 21 to 32 and the sample of Comparative Example 3 (solid electrolyte material) were prepared by the following procedure.
First, as raw materials, lithium carbonate Li ₂ CO ₃ , zirconium oxide ZrO ₂ , ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ , sodium carbonate Na ₂ CO ₃ , silver oxide AgO, aluminum oxide Al ₂ O ₃ , titanium oxide TiO ₂ , germanium oxide GeO ₂ , calcium carbonate CaCO ₃ , potassium carbonate K ₂ CO ₃ were prepared.

  This was weighed appropriately, sealed in a 500 ml polyethylene polypot and rotated on a pot rack at 150 rpm for 16 hours to mix the raw materials. Then, the mixture was baked in an air atmosphere at 500 ° C. for 1 hour and at 800 ° C. for 6 hours to remove volatile components.

Next, it was enclosed in a 500 ml polyethylene polypot together with water and φ5 mm cobblestone, and pulverized by rotating on a pot rack at 150 rpm for 16 hours. Thereafter, moisture was removed on a hot plate at 120 ° C.
Firing was performed at 1200 ° C. for 20 hours in an air atmosphere to obtain powders (samples) of solid electrolyte materials having the compositions of Examples 21 to 32 and Comparative Example 3 in Table 4.

<Evaluation of crystal structure of solid electrolyte material>
The samples of Examples 21 to 32 and Comparative Example 3 (solid electrolyte material powder) were scanned at 25 ° C. at a scan rate of 4.0 ° / min and at an angle measurement range of 10 ° to 60 ° by XRD (X-ray diffractometer). The crystal structure was examined (see FIGS. 10 to 12).

In each figure,
(A ′) the pattern of rhombohedral LiZr ₂ (PO ₄ ) ₃ JCPDS (Joint Committee on Powder Diffraction Standards) card (No. 01-072-7742);
(B ′) a pattern of a triclinic LiZr ₂ (PO ₄ ) ₃ JCPDS card (No. 01-074-2562);
(C ′) a pattern of a monoclinic LiZr ₂ (PO ₄ ) ₃ JCPDS card (No. 01-070-5819);
(D ′) Related patterns of rhombohedral KZr ₂ (PO ₄ ) ₃ JCPDS card (No. 01-070-1905) are also shown.
That is, FIG. 10 shows the patterns (a ′) to (d ′) together, and FIGS. 11 and 12 show the patterns (a ′) to (c ′) together. Showed.

<Evaluation of ionic conductivity of solid electrolyte material>
For the samples of Examples 21 to 32 and Comparative Example 3, the ionic conductivity was measured by the following method.

(1) Production of Sintered Tablet The solid electrolyte material, polyvinyl acetal resin, and alcohol produced as described above were weighed in a weight ratio of 100: 15: 140 and mixed sufficiently, and then heated at 80 ° C. The alcohol was removed on the plate to obtain a solid electrolyte material powder coated with a polyvinyl acetal resin as a binder.
Next, the solid electrolyte material powder was pressed into a tablet by pressing at 90 MPa using a tablet molding machine.

  Then, the solid electrolyte material molded into a tablet shape was sandwiched between two porous setters, and then fired to produce a sintered tablet. Baking is performed at a temperature of 1000 ° C. in a nitrogen gas atmosphere after removing the polyvinyl acetal resin by baking (debinding) in a nitrogen gas atmosphere containing 1% by volume of oxygen at a temperature of 500 ° C. By doing this, the sintered tablet concerning Examples 21-32 and the comparative example 3 was obtained. Table 5 shows the mass, thickness, and diameter of the obtained sintered tablet.

(2) Measurement of ion conductivity After forming the platinum (Pt) layer used as a collector layer by sputtering on both surfaces of the sintered tablet produced as described above, the sintered tablet was dried at 100 ° C. Water was removed. Then, the sintered tablet was sealed with a 2032 type coin cell.

  And the alternating current impedance measurement was carried out at room temperature (25 degreeC) in the range of 0.1-1 MHz (± 100 mV) for the sintered tablet formed using each solid electrolyte material, and the ionic conductivity (in an open circuit state) Ionic conductivity) was evaluated.

<Evaluation 1>
In FIG. 10, the result of the XRD measurement about the sample of Examples 21-25 and the sample of the comparative example 3 is shown.
Table 6 shows the crystal phases detected from the XRD measurement of the samples of Examples 21 to 25 and the sample of Comparative Example 3, and the ionic conductivity in the open circuit state.

As shown in Table 6, in the case of the unsubstituted sample (LiZr ₂ (PO ₄ ) ₃ ) in which neither the Li site nor the Zr site was substituted in Comparative Example 3, in addition to the rhombohedral crystal, a triclinic crystal And monoclinic crystals were mixed. Moreover, it was confirmed that the ionic conductivity in an open circuit state is 1.1 × 10 ⁻⁶ S / cm.

In addition, in the case of the samples of Examples 21 to 25 in which a part of Li was replaced with M1, the crystal phases detected from the XRD measurement must all match the rhombohedral LiZr ₂ (PO ₄ ) ₃ card pattern. Was confirmed.

Further, only a slightly different phase was confirmed in the sample of Example 25 in which the Li site was replaced with K. The heterogeneous phase was consistent with the KZr ₂ (PO ₄ ) ₃ card pattern. This is because the ionic radius of the substitution element K of the sample of Example 25 was larger than the ionic radius of the substitution elements (Ag, Ca, Na) of Examples 21 to 24, and the entire amount could not be dissolved. It is because.

Moreover, the ionic conductivity of the open circuit state of the samples of Examples 21 to 25 forming rhombohedral crystals was the same as that of the non-substituted Comparative Example 3 in which neither the Li site nor the Zr site was substituted (LiZr). ₂ (PO ₄ ) ₃ ) (Table 6).

From these results, a solid electrolyte having a composition of LiZr ₂ (PO ₄ ) ₃ is obtained by substituting a part of Li with an element M1 having an ionic radius larger than the ionic radius of Li ⁺ of 0.90Å, thereby reducing Ti (Ti ^{4 +} → Ti ³⁺ ) is less likely to occur, and a decrease in Li ion conductivity is suppressed.

  In particular, the greatest effect could be obtained when a part of Li was replaced with Na. This is because the decrease in the number of Li ions could be suppressed by substitution with alkali metal (Na), which is the same monovalent cation as Li.

In the sample in which a part of Li was substituted with K, which is an alkali metal having an ion radius larger than that of Na (the sample of Example 25), the ion conductivity was LiZr ₂ (PO ₄ ) ₃ ion substituted with Na. Although it became smaller than the conductivity, it is considered that this is because it was difficult to obtain a single phase and a mixed phase including different phases was obtained.

<Evaluation 2>
In FIG. 11, the result of the XRD measurement about the sample of Examples 26-30 is shown.
Table 7 shows the crystal phase detected from the XRD measurement of the samples of Examples 26 to 30 and the ionic conductivity in the open circuit state.

As shown in Table 7, in the case of the samples of Examples 26 to 30, in which a part of Li was replaced with Na and a part of Zr was replaced with an element (Al) having an ionic radius smaller than Zr, It was confirmed that both coincided with the rhombohedral LiZr ₂ (PO ₄ ) ₃ card pattern.

  In addition, the ionic conductivity in the open circuit state of the samples of Examples 26 to 30 is the sample in which the ratio of the element M1 (Na) substituted for Li is 0.01 to 0.50 (sample numbers 26 to 29). It was confirmed that the sample showed a high value and the sample in the range of 0.01 to 0.10 (sample Nos. 26 to 28) showed a higher value.

  Moreover, when the ratio of the element M1 (Na) substituted with Li was more than 0.5 like the sample of Example 30, it was confirmed that the ionic conductivity of an open circuit state will become low (Table 7). .

<Evaluation 3>
FIG. 12 shows XRD measurement results for the samples of Examples 31 and 32 in which a part of Li was replaced with Na and a part of Zr was replaced with an element (Ti, Ge) having an ionic radius smaller than that of Zr. Results are shown.
Table 8 shows the crystal phase detected from the XRD measurement of the samples of Examples 31 and 32 and the ionic conductivity in the open circuit state.
Table 8 shows a sample of sample number 26 (a sample in which a part of Li is replaced with Na and a part of Zr is replaced with Al) and a comparative example in which neither Li nor Zr is substituted. 3 shows the crystal phase detected from the XRD measurement and the ionic conductivity of the three samples.

As shown in Table 8, in the samples of Examples 31 and 32, a part of Li was replaced with Na, and a part of Zr was replaced with an element (Ti or Ge) having an ionic radius smaller than Zr. The crystal phases detected from the XRD measurement were confirmed to coincide with the rhombohedral LiTi ₂ (PO ₄ ) ₃ card pattern.

  In each of Examples 26, 31, and 32, each sample in which a part of Li was replaced with Na and a part of Zr was replaced with an element having an ionic radius smaller than that of Zr was obtained for both Li and Zr. It was confirmed that the ion conductivity was higher than that of the sample of Comparative Example 3 that was not substituted (see Table 8).

Moreover, about the sample of Example 26 and the sample of Example 31, the reduction current was measured and the charging / discharging curve was obtained.
In obtaining the charge / discharge curve by measuring the reduction current, first, a part of Li was replaced with Na, and a part of Zr was replaced with a typical metal element with Al which is a non-transition metal element. Sputtering was applied to one side of each sintered tablet formed using the electrolyte material and the solid electrolyte material of Example 31 in which part of Li was replaced with Na and part of Zr was replaced with Ti as a transition metal element. A platinum (Pt) layer to be an electric layer was formed. Then, after drying the sintered tablet at 100 ° C. to remove moisture, Li foil is pasted on the other surface via a gel electrolyte containing an electrolyte and sealed with a 2032 type coin cell. did.

Then, this sintered tablet was subjected to a charge / discharge test at room temperature (25 ° C.) in the range of 0.1 mV / second and 0.0 to 3.0 V vs Li ⁺ / Li. At this time, the potential was held at 0.0 V vs Li ⁺ / Li, and AC impedance measurement was performed in the range of 0.1 to 1 MHz (± 100 mV) to evaluate ion conductivity.
FIG. 13 shows the charge / discharge curve of the sample of Example 26, and FIG. 14 shows the charge / discharge curve of the sample of Example 31.

  Table 9 shows the ionic conductivity of the samples of Example 26 and Example 31.

  As is clear from FIG. 13 and FIG. 14, in the case of the sample of Example 31 in which a part of Zr was substituted with the transition metal element Ti, the occurrence of charge / discharge reaction due to the Ti reds was confirmed (FIG. 14). However, in the case of the sample of Example 26 in which a part of Zr was replaced with Al which is a non-transition metal element with a typical metal element, the occurrence of charge / discharge reaction was not confirmed (FIG. 13).

  Therefore, in the case of the all-solid-state battery using the material of Example 31, it is necessary to use it in a range where the charge / discharge reaction due to the Ti Reds does not occur, and the usage conditions are restricted. There is no such restriction in the case of a sample. Therefore, from this point, it is found that it is desirable to use Al as an element (M2) that substitutes Zr when Ti and Al are compared.

  In addition, for example, a green body for a positive electrode and a green sheet for a negative electrode are formed through the electrolyte green sheet formed using the solid electrolyte material of the present invention, and a laminate is formed and sintered. As a result, an all-solid battery having good characteristics can be obtained.

  Moreover, the all-solid-state battery of this invention can also be set as the structure which contains the above-mentioned solid electrolyte material of this invention in at least any one layer of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

  The present invention is not limited to the above embodiment, and various applications and modifications can be made within the scope of the invention.

Claims (10)

A solid electrolyte material having a crystal structure similar to NASICON type or NASICON type,
General formula: Li _a M1 _b R ₂ (PO ₄ ) ₃ (M1 is an element having an ionic radius larger than Li, and R is Ti or Zr, a = 0.50 to 1.79, b = 0.01 to 1 .00). A solid electrolyte material characterized by   2. The solid electrolyte material according to claim 1, wherein M1 is an alkali metal other than Li.   The solid electrolyte material according to claim 2, wherein M1 is Na. R is Ti, and is represented by a composition of (Li _a M1 _b ) (Ti _2−c M2 _c ) (PO ₄ ) ₃ in which a part of Ti is substituted with another element M2, a = 0.50 The solid electrolyte according to claim 1, wherein the solid electrolyte satisfies the requirements of 1.79, b = 0.01 to 0.50, and c ≦ 0.8 (0 is not included). material.   6. The solid electrolyte material according to claim 5, wherein the M2 is at least one selected from the group consisting of Mg, Ca, Sr, Al, Ga, In, Ge, Sn, and Sb. R is Zr, and is represented by a composition of (Li _a M1 _b ) (Zr _2−c M2 _c ) (PO ₄ ) ₃ in which a part of Zr is substituted with another element M2, a = 0.50 The solid electrolyte according to claim 1, wherein the solid electrolyte satisfies the requirements of 1.49, b = 0.01 to 0.50, and c ≦ 1.0 (not including 0). material.   7. The solid electrolyte material according to claim 6, wherein M2 is an element having an ionic radius smaller than that of Zr.   7. The solid electrolyte material according to claim 6, wherein the M2 is at least one selected from the group consisting of Mg, Al, Ti, Cu, Ga, Ge, Ag, and Sn.   It is what sintered the laminated body by which the green sheet for positive electrodes and the green sheet for negative electrodes were laminated | stacked through the electrolyte green sheet formed using the solid electrolyte material in any one of Claims 1-8. All-solid battery featuring.   An all-solid battery comprising the solid electrolyte material according to claim 1 in at least one of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

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