JP2011081915A - Solid electrolyte, solid electrolyte film containing solid electrolyte and all solid lithium secondary battery using the solid electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte, a solid electrolyte film containing the solid electrolyte, and an all solid lithium secondary battery using the solid electrolyte. <P>SOLUTION: The solid electrolyte containing a first solid electrolyte and a spacer, includes a second solid electrolyte with a higher hardness than that of the first solid electrolyte and having ion conductivity as the spacer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a solid electrolyte, a solid electrolyte membrane containing the solid electrolyte, and an all-solid lithium secondary battery using the solid electrolyte.

  The secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge. In addition, the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge. A battery that can be stored (charged). Among secondary batteries, lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.

In the lithium secondary battery, when graphite (expressed as C ₆ ) is used as the negative electrode active material, the reaction of the formula (1) proceeds at the negative electrode during discharge.
C ₆ Li → C ₆ + Li ⁺ + e ⁻ (1)
The electrons generated by the equation (1) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated in the formula (1) move from the negative electrode side to the positive electrode side by electroosmosis in the electrolyte sandwiched between the negative electrode and the positive electrode.

Further, when lithium cobaltate (Li _0.4 CoO ₂ ) is used as the positive electrode active material, the reaction of the formula (2) proceeds at the positive electrode during discharge.
Li _0.4 CoO ₂ + 0.6 Li ⁺ + 0.6e ⁻ → LiCoO ₂ (2)
At the time of charging, the reverse reactions of the above formulas (1) and (2) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (C ₆ Li) into which lithium has entered by graphite intercalation is present in the positive electrode. Since lithium cobaltate (Li _0.4 CoO ₂ ) is regenerated, re-discharge is possible.

FIG. 4A shows a part of a conventional all-solid lithium secondary battery, which includes a solid electrolyte layer 21 made of a solid electrolyte 24 having lithium ion conductivity, and the solid electrolyte layer 21 as a pair of a positive electrode and a negative electrode. It is the figure which showed typically the cross section cut | disconnected in the lamination direction about the laminated body pinched | interposed by. Usually, the positive electrode has a positive electrode active material 25 and a positive electrode active material layer 22 mixed with a solid electrolyte 24 if necessary, and the negative electrode has a negative electrode active material 26 and, if necessary, a solid electrolyte 24 mixed. Each has a negative electrode active material layer 23.
FIG. 4B is a schematic cross-sectional view after applying a restraining pressure substantially perpendicular to the stacking direction to the stacked body. As shown in the broken line ellipse in FIG. 4B, in the all-solid lithium secondary battery of the prior art, when only the solid electrolyte with low hardness is used for the electrolyte layer, the electrolyte layer is damaged and opposed. There was a possibility that the electrodes, that is, the positive electrode and the negative electrode might come into contact with each other due to restraint pressure and short circuit.

  Techniques for preventing such breakage of the electrolyte layer and preventing a short circuit have been developed so far. Patent Document 1 discloses a technique of a solid electrolyte sheet that includes an electrolyte layer including a solid electrolyte and a spacer, and a first layer and a second layer that sandwich the electrolyte layer facing each other.

JP 2007-273436 A

In the technique relating to the solid electrolyte sheet disclosed in Patent Document 1, no consideration is given to the decrease in ion conductivity caused by adding a spacer to the electrolyte layer.
The present invention has been accomplished in view of the above circumstances, and an object thereof is to provide a solid electrolyte, a solid electrolyte membrane containing the solid electrolyte, and an all-solid lithium secondary battery using the solid electrolyte.

  The solid electrolyte of the present invention is a solid electrolyte including a first solid electrolyte and a spacer, and the spacer has a hardness higher than that of the first solid electrolyte and has an ionic conductivity. It has a solid electrolyte.

  The solid electrolyte having such a configuration is used in a solid electrolyte layer in an all-solid lithium secondary battery by having the second solid electrolyte having a hardness higher than that of the first solid electrolyte as a spacer. In this case, the thickness of the solid electrolyte layer can be maintained without damaging the solid electrolyte layer due to the restraining pressure applied from the outside of the battery. In addition, the solid electrolyte having such a configuration has ion conductivity when used in the solid electrolyte layer in the all-solid lithium secondary battery because the second solid electrolyte has ion conductivity. Compared with the case where a solid electrolyte layer having a conventional spacer that is not used is employed, high ion conductivity can be maintained.

  In the solid electrolyte of the present invention, it is preferable that the first solid electrolyte is a sulfide-based solid electrolyte, and the second solid electrolyte is an oxide-based solid electrolyte.

  The solid electrolyte having such a configuration can exhibit high lithium ion conductivity by employing a sulfide-based solid electrolyte as the first solid electrolyte. The solid electrolyte having such a configuration employs an oxide solid electrolyte having a hardness higher than that of the sulfide solid electrolyte as the second solid electrolyte, so that the solid electrolyte in the all-solid lithium secondary battery can be obtained. When used in the electrolyte layer, breakage of the electrolyte layer can be prevented in advance.

  In the solid electrolyte of the present invention, when the total content of the first solid electrolyte and the second solid electrolyte is 100% by volume, the content ratio of the first solid electrolyte is 40 to 99% by volume. It is preferable that

  Since the solid electrolyte having such a configuration includes the first solid electrolyte and the second solid electrolyte in an appropriate content ratio, the solid electrolyte layer in the all-solid lithium secondary battery has high ion conductivity. The effect of preventing breakage of the solid electrolyte layer when used inside can be efficiently achieved.

  The solid electrolyte membrane of the present invention is characterized by containing the solid electrolyte.

  An all solid lithium secondary battery of the present invention is an all solid lithium secondary battery having at least a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the solid electrolyte layer is The solid electrolyte is included.

  By including the solid electrolyte in the solid electrolyte layer, the all solid lithium secondary battery having such a configuration can simultaneously exhibit excellent power generation performance and the effect of preventing damage to the solid electrolyte layer. .

  According to the present invention, when the second solid electrolyte having a hardness higher than that of the first solid electrolyte is used as a spacer, the second solid electrolyte is used in the solid electrolyte layer in the all-solid lithium secondary battery. In addition, the thickness of the electrolyte layer can be maintained without damaging the electrolyte layer due to the restraining pressure applied from the outside of the battery. In addition, according to the present invention, the second solid electrolyte has ionic conductivity, so that when the second solid electrolyte is used in a solid electrolyte layer in an all-solid lithium secondary battery, it does not have ionic conductivity. Compared to the case where a solid electrolyte layer having a spacer is employed, high ion conductivity can be maintained.

It is the figure which showed typically the cross section cut | disconnected in the lamination direction about the laminated body which is a part of all the solid lithium secondary battery which concerns on this invention. A graph in which the vertical axis represents lithium conductivity, and the horizontal axis represents the volume ratio of the sulfide-based solid electrolyte when the total content of the sulfide-based solid electrolyte and the oxide-based solid electrolyte is 100% by volume. is there. It is a cross-sectional schematic diagram of the restraining jig for shape | molding the pellet of a solid electrolyte used in the Example. It is the figure which showed typically the cross section cut | disconnected in the lamination direction about the laminated body which is a part of the conventional all-solid-state lithium secondary battery.

1. Solid electrolyte The solid electrolyte of the present invention is a solid electrolyte including a first solid electrolyte and a spacer, and the spacer has a hardness higher than that of the first solid electrolyte and has ion conductivity. It has 2 solid electrolytes, It is characterized by the above-mentioned.

“Hardness” in the present invention refers to mechanical strength. Therefore, not only what is generally known as hardness (so-called scratch strength), such as so-called Mohs hardness and Vickers hardness, but also fracture strength (fracture energy), shear stress, yield stress, etc. are referred to as “hardness” in the present invention. include.
As described later, the “spacer” in the present invention is sandwiched between the positive electrode and the negative electrode in the battery when the solid electrolyte according to the present invention is used for the solid electrolyte layer in the all-solid lithium secondary battery. In order to prevent the solid electrolyte layer from being crushed, the distance between the positive electrode and the negative electrode is maintained and the thickness of the solid electrolyte layer is maintained.

As described above, in the all-solid lithium secondary battery of the prior art, when only a solid electrolyte having a low hardness such as a sulfide-based solid electrolyte is used for the electrolyte layer, the electrolyte layer is damaged, that is, the opposite electrode, There is a possibility that the positive electrode and the negative electrode are brought into contact with each other by a restraining pressure and short-circuited.
As a result of diligent efforts, the inventors have used, as a spacer, a second solid electrolyte having a hardness higher than that of the first solid electrolyte, and a solid electrolyte in which the first solid electrolyte and the second solid electrolyte are mixed. Can be used in the solid electrolyte layer in the all-solid-state lithium secondary battery, so that the thickness of the solid electrolyte layer can be maintained without damaging the solid electrolyte layer due to the restraining pressure applied from the outside of the battery. I found. The inventors have also found that the first solid electrolyte and the second solid electrolyte both have ionic conductivity, so that the solid electrolyte obtained by mixing these two kinds of solid electrolytes is an all-solid lithium secondary battery. When used in a solid electrolyte layer, it can maintain high ionic conductivity compared to the case of adopting a solid electrolyte layer having a conventional glass spacer or plastic spacer that does not have ionic conductivity. I found.

The spacer used in the present invention is not particularly limited as long as it is a solid electrolyte having higher hardness than the first solid electrolyte and having ion conductivity. The difference in hardness between the spacer and the first solid electrolyte is not particularly limited, but it is preferable that there is a difference of one order or more when the hardness is expressed in any unit of the mechanical strength described above. Specifically, the case where the fracture strength of the first solid electrolyte is on the order of less than 10 MPa while the fracture strength of the spacer is on the order of 100 MPa or more can be exemplified.
Specifically, from the viewpoint that the thickness of the electrolyte layer can be sufficiently maintained, it is particularly preferable that the fracture strength of the second solid electrolyte is 100 MPa or more as the spacer used in the present invention. In this case, as the breaking strength measurement test, a test method for measuring the breaking strength with respect to particles having a measured particle diameter of 5 μm is adopted by evaluation with a micro compression tester.
Specific examples of the fracture strength measurement test are as follows. First, a powder sample is prepared on a micro compression tester stage. Next, particles having a particle diameter of approximately 5 μm are selected by measuring the particle size. Subsequently, the diamond platen is lowered over the selected particles and the particles are compressed until failure. The test force when the particles are broken is the breaking strength of the particles, and the average of the breaking strength of several particles, usually about five, is the breaking strength of the powder sample.

From the viewpoint that both the high ion conductivity and the effect of preventing the damage of the solid electrolyte layer when used in the solid electrolyte layer in the all solid lithium secondary battery can be efficiently achieved, the first solid When the total content of the electrolyte and the second solid electrolyte is 100% by volume, the content ratio of the first solid electrolyte is preferably 40 to 99% by volume. If the content ratio of the first solid electrolyte is less than 40% by volume, sufficient ion conductivity cannot be exhibited. In addition, if the content ratio of the first solid electrolyte is a value exceeding 99% by volume, the content ratio of the second solid electrolyte is too small, so that the solid electrolyte layer in the all-solid lithium secondary battery contains When used, the solid electrolyte layer may be damaged by the restraining pressure applied from the outside of the battery.
In addition, it is especially preferable that the said content rate of a 1st solid electrolyte is 50-99 volume%, and it is most preferable that it is 60-99 volume%.

  It is preferable that the first solid electrolyte and the second solid electrolyte to be the spacer are both in the form of powder. In this case, the average particle diameter of the first solid electrolyte is preferably 0.01 to 500 μm, and the average particle diameter of the second solid electrolyte is preferably 0.1 to 500 μm. In addition, the average particle diameter of these solid electrolytes can be calculated | required by measuring and averaging the particle diameter of a fixed quantity of solid electrolyte observed, for example with a scanning electron microscope (SEM).

  It is preferable that the first solid electrolyte is a sulfide-based solid electrolyte, and the second solid electrolyte is an oxide-based solid electrolyte. By using different solid electrolytes in this way, (1) the sulfide-based solid electrolyte employed as the first solid electrolyte can exhibit high lithium ion conductivity, and (2) employed as the second solid electrolyte. The oxide-based solid electrolyte, which is generally harder than the sulfide-based solid electrolyte, effectively damages the electrolyte layer when used in the solid electrolyte layer in an all-solid lithium secondary battery. Two effects of being able to be prevented can be achieved simultaneously.

The sulfide-based solid electrolyte that can be used for the solid electrolyte according to the present invention is not particularly limited as long as it is a sulfide-based solid electrolyte that can be generally used for an all-solid lithium secondary battery. _{Specifically, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 3, Li 2 S-P 2 S 3 -P 2 S 5, Li 2 S-SiS 2, LiI-Li 2 S- _{P 2 S 5, LiI-Li} 2 S-SiS 2 -P 2 S 5, Li 2 S-SiS 2 -Li 4 SiO 4, Li 2 S-SiS 2 -Li 3 PO 4, Li 3 PS 4 -Li 4 _{GeS 4, Li 3.4 P 0.6 Si} 0.4 S 4, Li 3.25 P 0.25 Ge 0.76 S 4, Li 4-x Ge 1-x P x S 4, Li 7 P 3 can be exemplified S ₁₁ or the like.

The oxide-based solid electrolyte that can be used for the solid electrolyte according to the present invention is not particularly limited as long as it has a higher hardness than the above-described sulfide-based solid electrolyte. From the viewpoint of being chemically stable and thus difficult to react with the sulfide-based solid electrolyte, an oxide-based solid electrolyte containing a group 4 element (Ti, Zr, Hf, etc.) as a transition metal species is used. It is preferable.
In this case, examples of the “chemically stable” oxide-based solid electrolyte include an oxide-based solid electrolyte having a wide potential window.

Based on the above conditions, a specific example of the oxide-based solid electrolyte that can be used in the solid electrolyte according to the present invention is a garnet-type oxide-based solid electrolyte.
Examples of the garnet-type oxide-based solid electrolyte include an oxide-based solid electrolyte represented by Li _{3 + x} A _y G _z M _{2 -v} B _v O ₁₂ (hereinafter sometimes referred to as compound (I)). be able to. Here, A, G, M and B are metal cations. x preferably satisfies 0 ≦ x ≦ 5, and more preferably satisfies 4 ≦ x ≦ 5. y preferably satisfies 0 ≦ y ≦ 3, and more preferably satisfies 0 ≦ y ≦ 2. z preferably satisfies 0 ≦ z ≦ 3, and more preferably satisfies 1 ≦ z ≦ 3. v preferably satisfies 0 ≦ v ≦ 2, and more preferably satisfies 0 ≦ v ≦ 1. O may be partially or completely exchanged with a divalent anion and / or a trivalent anion, for example, N ³⁻ .
In compound (I), A is preferably an alkaline earth metal cation such as Ca, Sr, Ba and Mg, or a transition metal cation such as Zn. G is preferably a transition metal cation such as La, Y, Pr, Nd, Sm, Lu, or Eu. Moreover, M can mention transition metal cations, such as Zr, Nb, Ta, Bi, Te, Sb. B is preferably In, for example. In the present invention, M is preferably Zr. In particular, in the present invention, Li ₇ La ₃ Zr ₂ O ₁₂ is preferably used as the oxide solid electrolyte from the viewpoint of excellent Li ion conductivity as a bulk.
As the oxide-based solid electrolyte, in addition to the garnet-type oxide-based solid electrolyte, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , La _{0 .51} Li _0.34 TiO _0.74 , Li ₃ PO ₄ , Li ₂ SiO ₂ , Li ₂ SiO ₄ , Li _0.5 La _0.5 TiO ₃ , Li _1.5 Al _0.5 Ge _1.5 ( PO ₄ ) _{3 and the} like can be exemplified.

The lithium ion conductivity of the solid electrolyte according to the present invention is preferably 1.0 × 10 ⁻⁷ S / cm or more, and particularly preferably 1.0 × 10 ⁻⁶ S / cm or more. These ionic conductivities are determined by impedance measurement (measurement conditions: voltage amplitude of 30 mV, measurement frequency of 0.1 MHz to 1 MHz, measurement temperature of 25 ° C., constraint pressure of 6 N) of the solid electrolyte formed into a pellet shape with a jig or the like. The value to be measured.

2. Solid electrolyte membrane The solid electrolyte membrane of the present invention is characterized by containing the solid electrolyte.
The solid electrolyte membrane of the present invention is preferably composed only of the solid electrolyte, but may contain other components, for example, other solid electrolytes having lithium ion conductivity, binders for membrane formation, and the like. Good.
The solid electrolyte membrane of the present invention can be obtained by molding a raw material such as the above solid electrolyte using a conventional method.

3. All solid lithium secondary battery The all solid lithium secondary battery of the present invention is an all solid lithium secondary battery having at least a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode. The solid electrolyte layer includes the solid electrolyte according to the present invention.

The “all-solid lithium secondary battery” in the present invention refers to a lithium secondary battery in which each element is all solid. Therefore, for example, a lithium secondary battery using a liquid electrolyte as an electrolyte is not included in the present invention.
FIG. 1A shows a part of an all-solid lithium secondary battery according to the present invention, in which a solid electrolyte layer 11 and a laminate in which the solid electrolyte layer 11 is sandwiched between a pair of positive electrode and negative electrode are stacked in the stacking direction. It is the figure which showed typically the cross section cut | disconnected by. The solid electrolyte 14 includes at least a first solid electrolyte 14a and a second solid electrolyte 14b. Usually, a positive electrode active material 15 and a positive electrode active material layer 12 mixed with a solid electrolyte 14 if necessary are mixed as a positive electrode, and a negative electrode active material 16 and a solid electrolyte 14 as necessary are mixed as a negative electrode. Each negative electrode active material layer 13 is provided.
FIG. 1B is a schematic cross-sectional view after applying a restraining pressure substantially perpendicular to the stacking direction to the stacked body. As shown in FIG. 1 (b), in the all solid lithium secondary battery according to the present invention, the second solid electrolyte 14b has sufficient hardness, so that the solid electrolyte layer is damaged by the restraining pressure. It is not. In addition, since the first solid electrolyte 14a and the second solid electrolyte 14b in the solid electrolyte 14 both have lithium ion conductivity, the battery as a whole has high power generation performance.
Hereinafter, the positive and negative electrodes, the solid electrolyte layer, and other components (separator and the like), which are components of the all solid lithium secondary battery of the present invention, will be described separately.

3-1. Positive electrode and negative electrode Although the structure of the positive electrode used for the all solid lithium secondary battery of the present invention is not particularly limited, as a specific example, a structure having a positive electrode current collector and a positive electrode active material layer containing at least a positive electrode active material Can be mentioned. The configuration of the negative electrode used in the all solid lithium secondary battery of the present invention is not particularly limited, and specific examples include a configuration having a negative electrode current collector and a negative electrode active material layer containing at least a negative electrode active material. Can do.

Specific examples of the positive electrode active material used in the present invention include LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoMnO _4. , Li ₂ NiMn ₃ O ₈ , Li ₃ Fe ₂ (PO ₄ ) _3, Li ₃ V ₂ (PO ₄ ) _{3 and the} like. Among these, in the present invention, LiCoO ₂ is preferably used as the positive electrode active material.

  The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the all-solid lithium secondary battery or the like, but is preferably in the range of 10 μm to 250 μm, preferably 20 μm to 200 μm. It is particularly preferably within the range, and most preferably within the range of 30 μm to 150 μm.

  The average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 20 μm, and particularly preferably in the range of 3 μm to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because. The average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).

The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material included in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. For example, carbon black such as acetylene black and ketjen black Etc. Moreover, although content of the electrically conductive material in a positive electrode active material layer changes with kinds of electrically conductive material, it is in the range of 1 mass%-10 mass% normally.

  Examples of the binder included in the positive electrode active material layer used in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content of the binder is usually in the range of 1% by mass to 10% by mass.

  The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Among these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.

As the positive electrode electrolyte included in the positive electrode used in the present invention, a solid electrolyte is preferably used. As the solid electrolyte, specifically, the above-described sulfide-based solid electrolyte according to the present invention can be used.
After forming the positive electrode active material layer, the positive electrode active material layer may be pressed in order to improve the electrode density.

  The negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can occlude / release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, Examples thereof include metal nitrides and carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.

The negative electrode active material layer may contain a conductive material, a binder, and the like as necessary.
What was mentioned above can be used for the binder and the said electrically conductive material which can be used in a negative electrode active material layer. Moreover, it is preferable to select suitably the usage-amount of a binder and a electrically conductive material according to the use etc. of an all-solid-state lithium secondary battery. Further, the film thickness of the negative electrode active material layer is not particularly limited, but for example, it is preferably in the range of 10 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm.
As the negative electrode electrolyte included in the negative electrode used in the present invention, it is preferable to use a solid electrolyte. As the solid electrolyte, specifically, the sulfide-based solid electrolyte described above can be used.

As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.
As a manufacturing method of the negative electrode used in the present invention, a method similar to the manufacturing method of the positive electrode as described above can be adopted.

3-2. Solid electrolyte layer The solid electrolyte layer has at least the solid electrolyte according to the present invention described above.
The thickness of the solid electrolyte layer is preferably 2 to 500 μm, more preferably 2 to 200 μm, and particularly preferably 2 to 50 μm. If the thickness is less than 2 μm, a short circuit between the electrodes may occur when the battery is formed. On the other hand, if the thickness exceeds 500 μm, the resistance may increase and the performance of the battery may be deteriorated.
From the viewpoint that the above-described second solid electrolyte serves as a spacer that maintains the distance between the positive electrode and the negative electrode in the all-solid lithium secondary battery and maintains the thickness of the solid electrolyte layer, the average of the second solid electrolyte It is considered that the particle size and the content ratio of the second solid electrolyte to the entire solid electrolyte have some correlation with the binding pressure applied to the entire battery and the thickness of the solid electrolyte layer. That is, if the restraint pressure applied to the entire battery is constant, the solid electrolyte layer is expected to be thicker as the average particle size of the second solid electrolyte is larger or the content ratio of the second solid electrolyte is higher. it can. Therefore, the thickness of the desired solid electrolyte layer can be obtained by adjusting at least the content ratio and average particle diameter of the second solid electrolyte, and the binding pressure applied to the entire battery.

3-3. Other component As another component, a separator can be used for the all-solid-state lithium secondary battery of this invention. The separator is disposed between the positive electrode current collector and the negative electrode current collector described above, and usually has a function of preventing the contact between the positive electrode active material layer and the negative electrode active material layer and holding the solid electrolyte. Have. Furthermore, as for the separator, examples of the material of the separator include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among these, polyethylene and polypropylene are preferable. The separator may have a single layer structure or a multilayer structure. Examples of the separator having a multilayer structure include a separator having a two-layer structure of PE / PP and a separator having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric. Moreover, the film thickness of the said separator is not specifically limited, It is the same as that of the separator used for a general all solid lithium secondary battery.
Moreover, the battery case which accommodates the all-solid-state lithium secondary battery of this invention can also be used as another component. The shape of the battery case is not particularly limited as long as it can accommodate the above-described positive electrode, negative electrode, solid electrolyte, and the like. Specifically, a cylindrical shape, a square shape, a coin shape, a laminate shape, etc. Can be mentioned.

  The all solid lithium secondary battery according to the present invention can be manufactured by a method similar to the method of manufacturing a general lithium secondary battery. Specifically, in an inert atmosphere, a method of first storing a positive electrode, a negative electrode, and a separator in a battery case, then adding a solid electrolyte to the battery case, and finally sealing the battery case can be exemplified. .

1. Production of solid electrolyte [Example 1]
First, an oxide-based solid electrolyte was synthesized. Specifically, see Ramsaway Murgan et al. , “Fast Lithium Ion Conduction in Garnet-Type Li ₇ La ₃ Zr ₂ O ₁₂ ”, Angew. Chem. Int. Ed. Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO, garnet-type compound) was obtained by a method similar to the method described in 2007, 46, 7778-7781. In addition, Li ₇ La ₃ Zr ₂ O ₁₂ uses a material that has been confirmed to have a breaking strength of 100 MPa or more with respect to particles having a measured particle diameter of 5 μm by evaluation with a micro compression tester (manufactured by Shimadzu Corporation). It was.
Next, 75Li ₂ S · 25P ₂ S ₅ was prepared as a sulfide-based solid electrolyte.
Subsequently, Li ₇ La ₃ Zr ₂ O ₁₂ and 75Li ₂ S · 25P ₂ S ₅ were mixed so that the content ratio of 75Li ₂ S · 25P ₂ S ₅ was 40% by volume to obtain a raw material composition. . Next, the obtained raw material composition is placed inside a restraining jig as shown in FIG. 3 (position 10 in FIG. 3) and pressed under a pressure condition of 3 tons to obtain a pellet-shaped solid electrolyte. It was.

[Example 2]
The process is the same as that of Example 1 until Li ₇ La ₃ Zr ₂ O ₁₂ is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Next, Li ₇ La ₃ Zr ₂ O ₁₂ and 75Li ₂ S · 25P ₂ S ₅ were mixed so that the content ratio of 75Li ₂ S · 25P ₂ S ₅ was 31% by volume to obtain a raw material composition. . The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Example 3]
The process is the same as that of Example 1 until Li ₇ La ₃ Zr ₂ O ₁₂ is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Next, Li ₇ La ₃ Zr ₂ O ₁₂ and 75Li ₂ S · 25P ₂ S ₅ were mixed so that the content ratio of 75Li ₂ S · 25P ₂ S ₅ was 26% by volume to obtain a raw material composition. . The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Example 4]
The process is the same as that of Example 1 until Li ₇ La ₃ Zr ₂ O ₁₂ is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Next, Li ₇ La ₃ Zr ₂ O ₁₂ and 75Li ₂ S · 25P ₂ S ₅ were mixed so that the content ratio of 75Li ₂ S · 25P ₂ S ₅ was 22% by volume to obtain a raw material composition. . The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Example 5]
The process is the same as that of Example 1 until Li ₇ La ₃ Zr ₂ O ₁₂ is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Next, Li ₇ La ₃ Zr ₂ O ₁₂ and 75Li ₂ S · 25P ₂ S ₅ were mixed so that the content ratio of 75Li ₂ S · 25P ₂ S ₅ was 12% by volume to obtain a raw material composition. . The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Comparative Example 1]
First, 75Li ₂ S · 25P ₂ S ₅ was prepared as a sulfide-based solid electrolyte. Next, 75Li ₂ S · 25P ₂ S ₅ was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Comparative Example 2]
First, Al ₂ O ₃ (alumina) was prepared as an oxide-based solid electrolyte. Next, 75Li ₂ S · 25P ₂ S ₅ was prepared as a sulfide-based solid electrolyte.
Then, _Al 2 _{O 3} and 75Li _{2 S} · _{25P 2} S _5, and mixed as the content of 75Li 2 _S · _25P 2 S ₅ of 40 vol%, to obtain a raw material composition. The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Comparative Example 3]
It is the same as Comparative Example 2 until Al ₂ O ₃ (alumina) is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Next, Al ₂ O ₃ and 75Li ₂ S · 25P ₂ S ₅ were mixed so that the content ratio of 75Li ₂ S · 25P ₂ S ₅ was 30% by volume to obtain a raw material composition. The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Comparative Example 4]
It is the same as Comparative Example 2 until Al ₂ O ₃ (alumina) is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Then, _Al 2 _{O 3} and 75Li _{2 S} · _{25P 2} S _5, and mixed as the content of 75Li 2 _S · _25P 2 S ₅ is 20 vol%, to obtain a raw material composition. The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Comparative Example 5]
It is the same as Comparative Example 2 until Al ₂ O ₃ (alumina) is prepared as the oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ is prepared as the sulfide-based solid electrolyte.
Then, _Al 2 _{O 3} and 75Li _{2 S} · _{25P 2} S _5, the content ratio of 75Li 2 _S · _25P 2 S ₅ were mixed such that 15 vol%, to obtain a raw material composition. The obtained raw material composition was pressed in the same manner as in Example 1 to obtain a pellet-shaped solid electrolyte.

[Comparative Example 6]
The process is the same as in Example 1 until Li ₇ La ₃ Zr ₂ O ₁₂ is prepared as the oxide-based solid electrolyte. Next, Li ₇ La ₃ Zr ₂ O ₁₂ was pressed in the same manner as in Example 1 to obtain a pellet-shaped oxide solid electrolyte.

Impedance measurement was performed using the solid electrolytes obtained in Examples 1 to 5 and Comparative Examples 1 to 6. The impedance measurement conditions were a voltage amplitude of 30 mV, a measurement frequency of 0.1 MHz to 1 MHz, a measurement temperature of 25 ° C., and a constraint pressure of 6N. FIG. 2 shows the Li ion conductivity obtained from the impedance measurement.
FIG. 2 shows the volume ratio of the sulfide-based solid electrolyte when the vertical axis indicates lithium conductivity and the horizontal axis indicates the total content of sulfide-based solid electrolyte and oxide-based solid electrolyte as 100% by volume. It is a graph taken. FIG. 2 is a graph showing the results of a solid electrolyte containing Li ₇ La ₃ Zr ₂ O ₁₂ as an oxide-based solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ as a sulfide-based solid electrolyte (“LLZO + 75Li in the figure). ₂ S · 25P ₂ S ₅ ”) and a line graph (in the figure) showing the results of the solid electrolyte containing Al ₂ O ₃ as the oxide solid electrolyte and 75Li ₂ S · 25P ₂ S ₅ as the sulfide solid electrolyte “Al ₂ O ₃ + 75Li ₂ S · 25P ₂ S ₅ ”).
As can be seen from FIG. 2, Examples 1 to 5 containing Li ₇ La ₃ Zr ₂ O ₁₂ as the oxide-based solid electrolyte are compared when comparing examples containing 75Li ₂ S · 25P ₂ S ₅ with the same volume ratio. This solid electrolyte resulted in higher lithium conductivity than the solid electrolytes of Comparative Examples 2 to 5 containing Al ₂ O ₃ as the oxide-based solid electrolyte. This result shows that, in the comparative example, Al ₂ O ₃ having a spacer function does not have ionic conductivity, whereas in the example, Li ₇ La ₃ Zr ₂ O ₁₂ having a spacer function has ionic conductivity. caused by.
_The oxide-based solid electrolyte of Comparative Example 6 containing only _Li 7 _La 3 _Zr 2 _{O 12} free of 75Li 2 _S · _25P 2 S _5, of the experimental results shown in FIG. 2, the lowest lithium conductivity showed that. This indicates that the oxide solid electrolyte has a lower lithium ion conductivity than the sulfide solid electrolyte, and that the oxide solid electrolyte acting as a spacer alone cannot provide sufficient lithium ion conductivity. Show.
_The oxide-based solid electrolyte of Comparative Example 1 including only 75Li 2 _S · _25P 2 S _5, of the experimental results shown in FIG. 2, showing the highest lithium conductivity. However, when such a solid electrolyte is actually incorporated in a lithium ion secondary battery, it is expected to short-circuit due to a restraining pressure applied in the direction perpendicular to the plane.

DESCRIPTION OF SYMBOLS 10 Raw material composition arrange | positioned inside restraint jig 11 Solid electrolyte layer 12 Positive electrode active material layer 13 Negative electrode active material layer 14 Solid electrolyte 14a 1st solid electrolyte 14b 2nd solid electrolyte 15 Positive electrode active material 16 Negative electrode active material 21 Solid Electrolyte layer 22 Positive electrode active material layer 23 Negative electrode active material layer 24 Solid electrolyte 25 Positive electrode active material 26 Negative electrode active material

Claims (5)

A solid electrolyte comprising a first solid electrolyte and a spacer,
A solid electrolyte having a second solid electrolyte having hardness higher than that of the first solid electrolyte and having ion conductivity as the spacer.   The solid electrolyte according to claim 1, wherein the first solid electrolyte is a sulfide-based solid electrolyte, and the second solid electrolyte is an oxide-based solid electrolyte.   The content ratio of the first solid electrolyte is 40 to 99% by volume when the total content of the first solid electrolyte and the second solid electrolyte is 100% by volume. 2. The solid electrolyte according to 2.   A solid electrolyte membrane comprising the solid electrolyte according to any one of claims 1 to 3. An all-solid lithium secondary battery having at least a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode,
The said solid electrolyte layer contains the solid electrolyte as described in any one of the said Claims 1 thru | or 3, The all-solid-state lithium secondary battery characterized by the above-mentioned.