JP2019033053A - Lithium solid battery and manufacturing method thereof - Google Patents

Abstract

To provide a lithium solid battery suppressing occurrence of a short circuit caused by dendrite.SOLUTION: A lithium solid battery 10 includes a negative electrode current collector 1, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5 in this order, and a Li occlusion layer 2 is provided between the negative electrode current collector 1 and the solid electrolyte layer 3, and the porosity of the Li occlusion layer 2 is less than 60 to 100%, preferably 78 to 86%. Preferably, in a Li solid battery 10, the Li occlusion layer 2 contains a carbon material, and more preferably, Ketjen black.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a lithium solid state battery.

With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

Since lithium batteries currently on the market use an electrolyte solution containing a flammable organic solvent, a safety device for preventing a temperature rise at the time of a short circuit and a structure for preventing a short circuit are required. In contrast, a lithium battery in which the electrolyte is changed to a solid electrolyte layer and the battery is completely solidified is
Since no flammable organic solvent is used in the battery, it is considered that the safety device can be simplified and the manufacturing cost and productivity are excellent.

In the field of lithium batteries, the occurrence of short circuits due to dendrites is known. In the short circuit, lithium deposited on the negative electrode active material layer during charging grows in the direction of the positive electrode active material layer,
This is caused by physical contact between the negative electrode active material layer and the positive electrode active material layer. In order to prevent a short circuit due to dendrite growth, several studies have been made. For example, Patent Document 1 discloses a lithium secondary battery including a negative electrode made of a mixture of metallic lithium, carbon black, and a solid electrolyte. On the other hand, in Patent Document 2, in a lithium secondary battery in which the negative electrode reaction is a deposition / dissolution reaction of metallic lithium,
A lithium secondary battery is disclosed that includes a first electrode (copper foil) that causes melting and a second electrode (Li _x TiO ₂ ) that prevents dendrite precipitation of metallic lithium.

JP 2006-100088 A JP-A-10-302794

Even in the prior art, the dendrite growth is not sufficiently suppressed, and further suppression of dendrite growth is required. The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide a lithium solid state battery in which dendrite growth is suppressed.

In order to solve the above-described problem, in the present disclosure, a negative electrode current collector, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector are provided in this order, and the negative electrode current collector and the solid electrolyte layer are provided in this order. The present invention provides a lithium solid state battery having a Li storage layer in which the porosity of the Li storage layer is 60% or more and less than 100%.

According to the present disclosure, a Li storage layer is provided between the negative electrode current collector and the solid electrolyte layer, and Li
When the occlusion layer has a predetermined porosity, metallic lithium can be dispersed and precipitated in the Li occlusion layer, and a lithium solid state battery in which dendrite growth caused by the precipitation of metallic lithium is suppressed can be obtained.

Moreover, the short circuit of the battery resulting from a dendrite growth can also be suppressed by providing Li storage layer and suppressing the dendrite growth resulting from precipitation of metallic lithium.

  In the above disclosure, the porosity of the Li storage layer may be 78% or more and 86% or less.

  In the above disclosure, the Li storage layer may contain a carbon material.

In the above disclosure, the carbon material used for the Li storage layer may further contain ketjen black.

  In the above disclosure, the Li storage layer may contain a solid electrolyte.

In the above disclosure, the Li storage layer may have a weight ratio of the solid electrolyte to the carbon material of 0.5 or less.

The lithium solid state battery of the present disclosure has an effect that dendrite growth of metallic lithium can be suppressed.

It is a schematic sectional drawing which shows the comparison form of the lithium solid battery of this indication. It is a schematic sectional drawing which shows an example of the lithium solid battery of this indication. It is a figure which shows the reversible capacity | capacitance ratio with respect to the porosity of the Li occlusion layer of an Example and a comparative example. It is a figure which shows the reversible capacity | capacitance ratio with respect to the weight ratio of the solid electrolyte which comprises the Li occlusion layer of an Example and a comparative example, and a carbon material.

Hereinafter, the lithium solid state battery of the present disclosure and the method for producing the lithium solid state battery will be described in detail. However, the present invention is not limited to the following embodiment. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

Lithium solid state battery First, the lithium solid state battery of the present disclosure can be roughly classified into two forms. Hereinafter, the lithium solid state battery of the present disclosure will be described separately for the embodiment and the comparative example.

1. Comparative Form FIG. 1 is a schematic cross-sectional view showing a lithium solid state battery of a comparative form.

As shown in FIG. 1, a lithium solid battery 11 of a comparative form includes a negative electrode current collector 1, a solid electrolyte layer 3, a positive electrode active material layer 4 and a positive electrode current collector 5 in this order. No Li storage layer is provided between the negative electrode current collector 1 and the solid electrolyte layer 3.

2. Embodiment FIG. 2 is a schematic sectional view showing an example of the lithium solid state battery of the embodiment.

As shown in FIG. 2, the lithium solid battery 10 of the embodiment includes a negative electrode current collector 1, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5 in this order. A Li storage layer 2 is provided between the solid electrolyte layers 3. The solid electrolyte layer 3 contains a solid electrolyte.
The present disclosure is characterized in that the porosity of the Li storage layer 2 is in the range of 60% or more and less than 100%.

According to the embodiment, the Li occlusion layer having voids is formed between the negative electrode current collector and the solid electrolyte layer, and further, the porosity of the Li occlusion layer is 60% or more and less than 100%. Thus, a lithium solid state battery with suppressed dendrite growth can be obtained.

The reason why the dendritic growth of metallic lithium can be suppressed is presumed as follows. First,
When the Li storage layer is not provided between the negative electrode current collector and the solid electrolyte layer (corresponding to a comparative form), lithium ions are conducted from the positive electrode active material layer, and electrons are conducted from the negative electrode current collector. The interface of the electric conductor becomes the deposition point of metallic lithium, and metallic lithium is deposited. It is estimated that the deposited metal lithium grows along the voids of the solid electrolyte layer toward the positive electrode active material layer, the metal lithium dendrite grows up to the positive electrode active material layer side, and a short circuit of the battery occurs. On the other hand, a Li storage layer is provided between the negative electrode current collector and the solid electrolyte layer, and the porosity of the Li storage layer is
In the case of 60% or more and less than 100% (corresponding to the embodiment), the precipitated metallic lithium can be deposited in the voids in the Li storage layer, and therefore, dendrite is prevented from growing to the positive electrode active material layer side. Can do. Furthermore, since it can suppress that a dendrite grows to the positive electrode active material layer side, it is estimated that generation | occurrence | production of the short circuit resulting from a dendrite can also be suppressed.

When the porosity of the Li storage layer is 60% or less, there are few voids for depositing lithium metal,
Precipitated metallic lithium is deposited in the space other than the Li occlusion layer, for example, in the solid electrolyte layer, and suppresses dendrite growth on the positive electrode active material layer particularly when charging at a high current density at which metallic lithium is likely to precipitate. It is estimated that the dendrite grows significantly from the Li storage layer to the positive electrode active material layer side.

More preferably, the porosity of the Li storage layer is 78% or more and 86% or less. In addition to suppressing dendrite growth of metallic lithium, it is possible to reversibly dissolve the metal deposited on the Li storage layer. The reason is presumed as follows. When the porosity of the Li occlusion layer is 86% or more, there are many voids for depositing metallic lithium, so that metallic lithium is dispersed and deposited in the voids of the Li occlusion layer, and dendrite growth on the positive electrode active material layer can be suppressed. . However, since the contact point between the metal lithium and the solid electrolyte acting as a lithium ion conduction path is reduced by the gap, the metal lithium deposited in the gap during charging becomes difficult to dissolve during discharge,
It is estimated that the reversible capacity of the battery will decrease.

On the other hand, it can suppress that a dendrite grows to the positive electrode active material layer side because the porosity of a Li occlusion layer is 78% or more and 86% or less. Moreover, it is estimated that the lithium metal which can be reversibly deposited / dissolved increases and the reversible capacity of the battery can be increased as compared with the case where the porosity of the Li storage layer is 86% or more. Thus, in the embodiment, it is possible to achieve both suppression of dendrite growth and increase in reversible capacity of the battery.
Hereinafter, the lithium solid state battery will be described for each configuration.

(1) Negative electrode current collector The material of the negative electrode current collector is preferably a material that does not alloy with Li, for example, SUS,
Examples thereof include copper and nickel. Examples of the form of the negative electrode current collector include a foil shape and a plate shape. The shape of the negative electrode current collector in plan view is not particularly limited,
For example, a circular shape, an elliptical shape, a rectangular shape, an arbitrary polygonal shape, and the like can be given. Moreover, although the thickness of a negative electrode collector changes with shapes, it is in the range of 1 micrometer-50 micrometers, for example, and it is preferable that it exists in the range of 5 micrometers-20 micrometers.

(2) Li storage layer The Li storage layer is a carbon material or a mixture composed of a carbon material and a solid electrolyte.
In the present disclosure, the porosity of the Li storage layer determined by the calculation method described below is
Usually, it is preferably 60% or more and less than 100%, more preferably 78% or more and 86% or less. Specifically, by using the method described in the examples described later,
The porosity of the Li storage layer can be determined.

(2-1) Carbon material Examples of the carbon material include ketjen black (KB), vapor grown carbon fiber (VGCF), acetylene black (AB), activated carbon, furnace black, carbon nanotube (CNT), graphene and the like. Can be mentioned. As a carbon material to be used,
Ketjen black (KB) is preferred. In the case of ketjen black, since lithium ions are not easily inserted between the layers, charging / discharging is unlikely to proceed at a potential higher than the deposition / dissolution potential of metallic lithium, which is preferable for improving the energy density of the battery.

The average particle diameter (D ₅₀ ) of the carbon material is preferably in the range of 10 nm to 10 μm, for example, and more preferably in the range of 15 nm to 5 μm. The average particle diameter may be a value calculated by a laser diffraction particle size distribution meter or a value measured based on image analysis using an electron microscope such as SEM.

(2-2) Solid electrolyte If the solid electrolyte in Li storage layer can be used for an all-solid-state lithium ion battery,
Although there is no restriction | limiting in particular, For example, inorganic solid electrolytes, such as sulfide solid electrolyte and oxide solid electrolyte, are mentioned. Examples of the sulfide solid electrolyte include Li ₂ S—P ₂ S ₅ and Li ₂ S—P ₂ S _{5.
-LiI, Li 2 S-P 2} S 5 -LiI-LiBr, Li 2 S-P 2 S 5 -Li 2 O, Li 2 S
_{-P 2 S 5 -Li 2 O-} LiI, Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S
_{-SiS 2 -LiBr, Li 2 S-} SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -Li
_{I, Li 2 S-SiS 2} -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z m S
_n (where m and n are positive numbers. Z is any one of Ge, Zn, and Ga), Li ₂ S—GeS
₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ —Li _x MO _y (where x, y
Is a positive number. M is any one of P, Si, Ge, B, Al, Ga, and In. ) And the like.
Examples of the oxide solid electrolyte include Li ₂ O—B ₂ O ₃ —P ₂ O ₃ and Li ₂ O—Si.
_{O 2, Li 5 La 3 Ta} 2 O 12, Li 7 La 3 Zr 2 O 12, Li 6 BaLa 2 Ta 2 O 12, Li
₃ PO _{(4-3 / 2w)} N _w (w <1), Li _3.6 Si _0.6 P _0.4 O _{4 and the} like. The description of “Li ₂ S—P ₂ S ₅ ” means a sulfide solid electrolyte using a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. .

In particular, the sulfide solid electrolyte preferably includes an ionic conductor containing Li, A (A is at least one of P, Si, Ge, Al, and B), and S. further,
The ionic conductor has an anion structure having an ortho composition (PS ₄ ^3- structure, SiS ₄ ^4- structure, Ge
S ₄ ^4- structure, AlS ₃ ^3- structure, BS ₃ ^3- structure) is preferably used as the main component of the anion. This is because a sulfide solid electrolyte having high chemical stability can be obtained. The ratio of the anion structure of the ortho composition is 70 mol% with respect to the total anion structure in the ionic conductor.
The above is preferable, and 90 mol% or more is more preferable. The ratio of the anion structure of the ortho composition can be determined by Raman spectroscopy, NMR, XPS or the like.

The sulfide solid electrolyte may contain lithium halide in addition to the ionic conductor. Examples of the lithium halide include LiF, LiCl, LiBr, and Li
I can be mentioned, among which LiCl, LiBr and LiI are preferable. The ratio of LiX (X = I, Cl, Br) in the sulfide solid electrolyte is, for example, 5 mol% to 30 m.
It is in the range of ol%, and may be in the range of 15 mol% to 25 mol%.

The solid electrolyte may be a crystalline material or an amorphous material. The solid electrolyte may be glass or crystallized glass (glass ceramics).
Examples of the shape of the solid electrolyte include a particulate shape.

The average particle diameter (D ₅₀ ) of the solid electrolyte is preferably in the range of ₅₀ nm to 10 μm, for example, and preferably in the range of 100 nm to 5 μm. The average particle diameter may be a value calculated by a laser diffraction particle size distribution meter or a value measured based on image analysis using an electron microscope such as SEM.

The ratio of the carbon material and the solid electrolyte in the Li storage layer is related to the weight ratio of these two types of materials.
Carbon material: solid electrolyte = 1: 1 to 10: 0 is preferable, and carbon material: solid electrolyte = 2: 1 to 10: 0 is more preferable.

Examples of the method for producing a mixture composed of a carbon material and a solid electrolyte include hand-mixing using a mortar and pestle, a homogenizer, and mechanical milling. The mechanical milling may be dry mechanical milling or wet mechanical milling.

Mechanical milling is not particularly limited as long as it is a method of mixing a carbon material and a solid electrolyte while imparting mechanical energy, and examples thereof include a ball mill, a vibration mill, a turbo mill, a mechanofusion, a disk mill, and the like. Among these, a ball mill is preferable, and a planetary ball mill is particularly preferable.

The liquid used when preparing the mixture using a homogenizer preferably has an aprotic property that does not generate hydrogen sulfide, specifically, a polar aprotic liquid, And aprotic liquids such as aprotic liquids.

The Li occlusion layer in the present disclosure is characterized in that the porosity of the Li occlusion layer determined by the calculation method described below is within the above-described range.

(3) Solid electrolyte layer The solid electrolyte layer is a layer formed between the positive electrode active material layer and the negative electrode current collector. Further, the solid electrolyte layer contains at least a solid electrolyte, and may further contain a binder as necessary. About the solid electrolyte used for a solid electrolyte layer, since it is the same as that of the content described in said "(2-2) solid electrolyte", description here is abbreviate | omitted. The solid electrolyte used for the solid electrolyte layer may be the same solid electrolyte as the Li storage layer, or may be a solid electrolyte different from the Li storage layer.

The solid electrolyte content in the solid electrolyte layer is, for example, in the range of 10 wt% to 100 wt%, and may be in the range of 50 wt% to 100 wt%. The thickness of the solid electrolyte layer is, for example, in the range of 0.1 μm to 1 mm, and may be in the range of 0.1 μm to 700 μm.

(4) Positive electrode active material layer The positive electrode active material layer is a layer containing at least a positive electrode active material, and may contain at least one of a solid electrolyte, a conductive material, and a binder as necessary. . The positive electrode active material is usually
Li is contained. Examples of the positive electrode active material include an oxide active material. Specifically, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn
Rock salt layered active materials such as _1/3 O ₂ , spinel active materials such as LiMn ₂ O ₄ and Li (Ni _0.5 Mn _1.5 ) O ₄ , LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCuPO _{4 and the} like Olivine type active material and the like. Further, Si-containing oxides such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ may be used as the positive electrode active material, and sulfides such as Li ₂ S and lithium polysulfide may be used as the positive electrode active material. The average particle diameter (D ₅₀ ) of the positive electrode active material is, for example, 10 nm.
It is preferably within a range of ˜50 μm, more preferably within a range of 100 nm to 30 μm, and even more preferably within a range of 1 μm to 20 μm. The average particle diameter may be a value calculated by a laser diffraction particle size distribution meter or a value measured based on image analysis using an electron microscope such as SEM.

In addition, a coating layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte (can be suppressed. Examples of the Li ion conductive oxide include LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , and Li ₃ PO ₄ . The thickness is, for example, in the range of 0.1 nm to 100 nm, and 1 nm to 2
It may be in the range of 0 nm. The coverage of the coat layer on the surface of the positive electrode active material is, for example,
It is 50% or more, and may be 80% or more.

The positive electrode active material layer may further contain a solid electrolyte. Although the kind of solid electrolyte is not specifically limited, For example, a sulfide solid electrolyte can be mentioned. As the sulfide solid electrolyte, the same material as the sulfide solid electrolyte described above can be used.

The positive electrode active material layer may further contain a conductive material. By adding a conductive material, the conductivity of the positive electrode active material layer can be improved. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. The positive electrode active material layer may contain a binder. Examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). Moreover, it is preferable that the thickness of a positive electrode active material layer exists in the range of 0.1 micrometer-1000 micrometers, for example.

(5) Positive Electrode Current Collector A lithium solid battery usually has a positive electrode current collector that collects current from the positive electrode active material layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. The thickness, shape, and the like of the positive electrode current collector are preferably selected as appropriate according to the use of the battery.

(6) Other configurations In the present disclosure, a lithium solid state battery in which a negative electrode active material layer is provided between the Li storage layer and the negative electrode current collector during assembly, or between the Li storage layer and the negative electrode current collector during assembly. It may be a lithium solid state battery in which metallic lithium is deposited as a negative electrode active material by charging after the negative electrode active material layer is not provided. In addition, the lithium metal deposited between the negative electrode current collector and the solid electrolyte layer after the initial charge is used as a negative electrode active material.

(7) Lithium Solid Battery The lithium solid battery of the embodiment is not particularly limited as long as it has a negative electrode current collector, a solid electrolyte layer, a positive electrode active material layer, a positive electrode current collector, and a Li storage layer. . The all solid state battery may be a primary battery or a secondary battery, but among them, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Examples of the shape of the all solid state battery include a coin type, a laminate type, a cylindrical type, and a square type.

In the present disclosure, it is also possible to provide a method for manufacturing an all-solid battery having a pressing step of arranging and pressing the positive electrode active material layer or the solid electrolyte layer described above. The press pressure is not particularly limited, but is, for example, 1 ton / cm ² or more, 4 ton
/ Cm ² or more.

In addition, since a comparative form is the content substantially the same as each structure of embodiment mentioned above, description by each is abbreviate | omitted.

In addition, this indication is not limited to the said embodiment. The above-described embodiment is an exemplification, and the present invention has the same configuration as the technical idea described in the claims of the present disclosure and has the same function and effect regardless of the present embodiment. It is included in the technical scope of the disclosure.

[Example 1]
(Preparation of sulfide solid electrolyte)
Li ₂ S (manufactured by Rockwood Lithium) 0.550 g, P ₂ S ₅ (manufactured by Aldrich) 0.887 g, LiI (manufactured by Aldrich) 0.285 g, and LiBr (manufactured by High Purity Chemical Laboratory) 0.277 g Were weighed and mixed in an agate mortar for 5 minutes. To this mixture, 4 g of dehydrated heptane (manufactured by Kanto Chemical Co., Inc.) was further added, and mechanically milled using a planetary ball mill for 40 hours to obtain a sulfide solid electrolyte.

(Preparation of positive electrode material)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nichia Corporation) was used as the positive electrode active material. This positive electrode active material is subjected to a surface treatment of LiNbO ₃ in advance. As the positive electrode active material and conductive material carbon, VGCF (manufactured by Showa Denko KK) and the above-mentioned sulfide solid electrolyte in a weight ratio of 85.
The mixture was weighed so as to be 3: 1.3: 13.4, and the resulting mixture was used as a positive electrode material as a positive electrode active material.

(Preparation of Li storage layer material)
Ketjen Black as a carbon material (E made by Lion Specialty Chemicals)
_{CP600JD: KB,} and D 50 = 34 nm), using a solid electrolyte (SE) as the sulfide solid electrolyte _(D 50 = _0.5μm), KB in a weight ratio: SE = 2: were weighed to be 1,
After mixing by hand, add heptane and homogenizer (SMT Co., Ltd., UH-50)
A mixture of 3 minutes was used to obtain a Li storage layer material which is a material of the Li storage layer.

(Production of lithium solid state battery)
A solid electrolyte layer was formed by weighing 101.7 mg of the sulfide solid electrolyte into a ceramic mold (cross-sectional area: 1 cm ² , using a cylindrical container) and pressing it at 1 ton / cm ² . Add 31.3 mg of the positive electrode material to one side of the solid electrolyte layer, and add 6 ton / c
A positive electrode active material layer was formed by pressing at m ² . 2 mg / cm ² of the Li storage layer material was added to the solid electrolyte layer on the side opposite to the positive electrode active material layer. In addition, a positive electrode current collector (aluminum foil) is disposed on the positive electrode active material layer side, and a negative electrode current collector (SUS foil) is disposed on the negative electrode layer side. A lithium solid state battery of Example 1 was obtained. In addition, all the operations using the sulfide solid electrolyte were performed in a glove box in a dry Ar atmosphere.

[Example 2]
A lithium solid state battery was obtained in the same manner as in Example 1 except that the weight ratio of ketjen black (KB) used for the Li storage layer and the solid electrolyte (SE) was changed to KB: SE = 4: 1.

[Example 3]
A lithium solid state battery was obtained in the same manner as in Example 1 except that the weight ratio of ketjen black (KB) used for the Li storage layer and the solid electrolyte (SE) was changed to KB: SE = 9: 1.

[Example 4]
A lithium solid state battery was obtained in the same manner as in Example 1 except that the weight ratio of ketjen black (KB) used for the Li storage layer and the solid electrolyte (SE) was changed to KB: SE = 10: 0.

[Comparative Example 1]
A lithium solid state battery was obtained in the same manner as in Example 1 except that no Li storage layer was provided between the negative electrode current collector and the solid electrolyte layer.

[Comparative Example 2]
A lithium solid state battery was obtained in the same manner as in Example 1 except that the weight ratio of ketjen black (KB) used for the Li storage layer and the solid electrolyte (SE) was changed to KB: SE = 1: 2.

[Evaluation]
(Calculation method of porosity of Li storage layer)
For each of the Li storage layers of Examples 1 to 4 and Comparative Example 2, the porosity of the Li storage layer was calculated by the method described below.

First, a negative electrode current collector and a sulfide solid electrolyte were placed in a cylindrical container and pressed at 1 ton / cm ² to form a solid electrolyte layer. The positive electrode material is added to one side of the solid electrolyte layer, and the positive electrode active material layer is formed by pressing at 6 ton / cm ² , and there is no Li storage layer between the negative electrode current collector and the solid electrolyte layer. A lithium solid state battery (cell) was produced. After restraining the produced lithium solid battery at 0.2 N, using a micrometer, the height of the cell relative to the stacking direction in which each current collector, positive electrode active material layer and solid electrolyte layer constituting the cell are stacked (H
₁ ) was measured.

The weight (w) of the Li storage layer material of the Li storage layer provided between the negative electrode current collector and the solid electrolyte layer is weighed, and the Li storage layer material is disposed between the negative electrode current collector and the solid electrolyte layer, and 4 ton / Li storage layer is formed by pressing at cm ² . After constraining the cell with 0.2 N, the cell height (H ₂ ) was measured with a micrometer in the same manner as the cell height measurement method described above for the cell in which the Li storage layer was formed. It was then calculated thickness (d) from the difference between the _{H 2} and _{H 1 (H} 2 -H ₁₎ with respect to the stacking direction of Li storage layer.

From the above-described weight (w) of the Li storage layer, the true density of the ketjen black that is the carbon material used for the Li storage layer, and the true density of the solid electrolyte used, the occupied volume of the Li storage layer material in the Li storage layer (V ₁ ) was calculated.

From the product of the thickness (d) of the Li storage layer and the bottom area of the cell, the actual volume (V ₂ ) of the Li storage layer material in the Li storage layer was calculated. The volume value obtained by subtracting V ₁ from V ₂ is expressed as the spatial volume (V ₃ =
V ₂ −V ₁ ) was calculated, and the porosity (%) of the Li storage layer was calculated by multiplying 100 by the value of V ₂ for the denominator and V ₃ for the numerator.

Table 1 is a table showing the weight ratio, porosity, and reversible capacity ratio of the Li storage layers of Examples and Comparative Examples. As shown in Table 1, it was confirmed from the results of Examples 1 to 4 and Comparative Example 2 that the porosity of the Li storage layer increases as the ratio of ketjen black increases.

(Charge / discharge measurement)
Using the lithium solid state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 2, charge and discharge measurements were performed after leaving in a constant temperature bath at 60 ° C. for 3 hours in advance. Measurement conditions were 25 ° C., a current density of 8.7 mA / cm ² , and constant current charging. When the charging capacity reached 4.35 mAh / cm ² , the charging was terminated and the battery was suspended for 10 minutes. Then, 25 ° C, current density 0.435
When mA / cm ² , CC discharge was performed and the lower limit voltage reached 3.0 V, the discharge was terminated. In addition,
Charge corresponds to lithium deposition on the negative electrode current collector, discharge corresponds to lithium dissolution on the negative electrode current collector,
The lithium solid state battery of the present disclosure starts from charging.

The results are shown in FIG. 3 and FIG. The reversible capacity ratio of the battery was as described above in Comparative Example 2.
When the value of the discharge capacity is 100, the value of the discharge capacity ratio (reversible capacity ratio) of Example 1-4 and Comparative Example 1-2 is shown. In FIG. 3, the above-mentioned reversible capacity ratio is plotted against the porosity of the Li storage layer. In FIG. 5, the solid electrolyte (SE) with respect to Ketjen black (KB).
It is the graph which plotted the reversible capacity | capacitance ratio with respect to the weight ratio.

When a short circuit due to dendritic growth of metallic lithium occurs, the positive electrode active material causes self-discharge on the positive electrode active material layer side. Therefore, the discharge capacity at the time of the above-described discharge, that is, the reversible capacity is reduced. From FIG. 3, Examples 1 to 4 having the Li storage layer between the negative electrode current collector and the solid electrolyte layer had a reversible capacity ratio larger than that of Comparative Example 1. From this, by providing the Li storage layer between the negative electrode current collector and the solid electrolyte layer, short circuit caused by dendrites was suppressed, and self-discharge of the positive electrode active material on the positive electrode active material layer side was suppressed. confirmed.
In addition, Examples 1 to 4 showed a value with a larger reversible capacity than Comparative Example 2. from this result,
It was also confirmed that the short circuit caused by the dendrite can be suppressed even when the porosity of the Li storage layer is within a specific value range.

4, when Example 1 to Example 4 and Comparative Example 2 are compared, the weight ratio of the solid electrolyte (SE) to the ketjen black (KB) is specific between the negative electrode current collector and the solid electrolyte layer. By providing a Li storage layer having a value, short circuit caused by dendrite is suppressed,
It was confirmed that self-discharge of the positive electrode active material on the positive electrode active material layer side was suppressed.

DESCRIPTION OF SYMBOLS 1 ... Negative electrode collector 2 ... Li occlusion layer 3 ... Solid electrolyte layer 4 ... Positive electrode active material layer 5 ... Positive electrode collector 10,11 ... Lithium solid state battery

Claims (6)

A negative electrode current collector, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector are provided in this order, and a Li storage layer is provided between the negative electrode current collector and the solid electrolyte layer. A lithium solid state battery having a porosity of 60% or more and less than 100%. 2. The lithium solid state battery according to claim 1, wherein a porosity of the Li storage layer is not less than 78% and not more than 86%. The lithium solid state battery according to claim 1, wherein the Li storage layer contains a carbon material. 4. The lithium solid state battery according to claim 3, wherein the carbon material used for the Li storage layer includes ketjen black. 5. The lithium solid state battery according to any one of claims 1 to 4, wherein the Li storage layer contains a solid electrolyte. 6. The lithium solid state battery according to claim 3, wherein the Li storage layer has a weight ratio of a solid electrolyte to a carbon material of 0.5 or less.

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