JP6946836B2 - Lithium solid-state battery and manufacturing method of lithium solid-state battery - Google Patents

Description

The present disclosure relates to a lithium solid state battery.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones, and communication devices in recent years, the development of batteries used as their power sources has been emphasized. In addition, the automobile industry and the like are also developing high-output and high-capacity batteries for electric vehicles or hybrid vehicles. Currently, among various batteries, lithium batteries are attracting attention from the viewpoint of high energy density.

Since the lithium battery currently on the market uses an electrolytic solution containing a flammable organic solvent, it is necessary to attach a safety device that suppresses a temperature rise at the time of a short circuit and a structure for preventing the short circuit. On the other hand, a lithium battery in which the electrolyte is changed to a solid electrolyte layer and the battery is completely solidified is used.
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.

Further, 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, and the short circuit occurs.
It is generated by the physical contact between the negative electrode active material layer and the positive electrode active material layer. Several studies have been made to prevent short circuits due to the growth of dendrites. For example, Patent Document 1 discloses a lithium secondary battery including a negative electrode composed 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 precipitation / dissolution reaction of metallic lithium, the precipitation / dissolution of metallic lithium is performed.
A lithium secondary battery including a first electrode (copper foil) in which dissolution occurs and a second electrode (Li _x TiO _{2) for preventing dendrite precipitation of metallic lithium is disclosed.}

Japanese Unexamined Patent Publication No. 2016-100088 Japanese Unexamined Patent Publication No. 10-302794

Even in the prior art, the growth of dendrites 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 an object of the present disclosure is to provide a lithium solid-state battery in which dendrite growth is suppressed.

In order to solve the above problems, 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 between the negative electrode current collector and the solid electrolyte layer. Provided is a lithium solid-state battery having a Li storage layer and having a void ratio of 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 storage layer has a predetermined void ratio, metallic lithium can be dispersed and precipitated in the Li storage layer, and a lithium solid-state battery in which dendrite growth caused by precipitation of metallic lithium is suppressed can be obtained.

Further, by providing the Li storage layer and suppressing the dendrite growth caused by the precipitation of metallic lithium, the short circuit of the battery due to the dendrite growth can also be suppressed.

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 of suppressing the growth of dendrites of metallic lithium.

It is the schematic sectional drawing which shows the comparative form of the lithium solid-state battery of this disclosure. It is the schematic sectional drawing which shows an example of the lithium solid-state battery of this disclosure. It is a figure which shows the reversible volume ratio with respect to the porosity of the Li storage layer of an Example and a comparative example. It is a figure which shows the reversible volume ratio with respect to the weight ratio of the solid electrolyte which constitutes the Li storage layer of an Example and a comparative example, and a carbon material.

Hereinafter, the lithium solid-state battery of the present disclosure and a method for manufacturing the lithium solid-state battery will be described in detail. However, the present invention is not limited to the following embodiments. In addition, the following description and drawings have been simplified as appropriate to clarify the description.

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 embodiments and comparative embodiments.

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

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

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

As shown in FIG. 2, the lithium solid-state 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, and includes the negative electrode current collector 1 and the negative electrode current collector 5. A Li storage layer 2 is provided between the solid electrolyte layers 3. Further, the solid electrolyte layer 3 contains a solid electrolyte.
A major feature of the present disclosure is that the porosity of the Li storage layer 2 is within the range of 60% or more and less than 100%.

According to the embodiment, a Li storage layer having voids is formed between the negative electrode current collector and the solid electrolyte layer, and the void ratio of the Li storage layer is 60% or more and less than 100%, whereby metallic lithium is formed. It is possible to obtain a lithium solid-state battery in which the growth of occlusion is suppressed.

The reason why the dendrite 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 the comparative form), lithium ions are conducted from the positive electrode active material layer and electrons are conducted from the negative electrode current collector, and the solid electrolyte layer and the negative electrode collection are conducted. The interface of the electric body serves as a precipitation point of metallic lithium, and metallic lithium is deposited. It is presumed that the deposited metallic lithium grows dendrites of metallic lithium toward the positive electrode active material layer along the voids of the solid electrolyte layer, the dendrites grow to the positive electrode active material layer side, and the battery is short-circuited. 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 increased.
When it is 60% or more and less than 100% (corresponding to the embodiment), the precipitated metallic lithium can be precipitated in the voids in the Li storage layer, so that dendrites are suppressed from growing to the positive electrode active material layer side. Can be done. Furthermore, since it is possible to suppress the growth of dendrites to the positive electrode active material layer side, it is presumed that the occurrence of short circuits due to dendrites can also be suppressed.

When the porosity of the Li storage layer is 60% or less, there are few voids for precipitating metallic lithium.
The precipitated metallic lithium precipitates in the voids of the solid electrolyte layer other than the voids of the Li storage layer, for example, and suppresses the growth of dendrite on the positive electrode active material layer especially when charging at a high current density where metallic lithium tends to precipitate. Is insufficient, and it is presumed that dendrite grows remarkably from the Li occlusion layer to the positive electrode active material layer side.

Further, more preferably, the porosity of the Li storage layer is 78% or more and 86% or less. Not only can it suppress the dendrite growth of metallic lithium, but it can also reversibly dissolve the metal deposited in the Li occlusion layer. The reason is presumed as follows. When the void ratio of the Li storage layer is 86% or more, there are many voids for precipitating metallic lithium, so that metallic lithium is dispersed and precipitated in the voids of the Li storage layer, and the growth of dendrite in the positive electrode active material layer can be suppressed. .. However, since the contact points between the metallic lithium and the solid electrolyte acting as a lithium ion conduction path are reduced by the voids, it becomes difficult for the metallic lithium deposited in the voids during charging to dissolve during discharge.
It is presumed that the reversible capacity of the battery will decrease.

On the other hand, when the porosity of the Li storage layer is 78% or more and 86% or less, it is possible to suppress the growth of dendrites to the positive electrode active material layer side. Further, it is presumed that the amount of metallic lithium that can be reversibly precipitated and dissolved increases and the reversible capacity of the battery can be increased as compared with the case where the void ratio of the Li storage layer is 86% or more. As described above, in the embodiment, it is possible to suppress the growth of dendrites and increase the reversible capacity of the battery at the same time.
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.
Copper, nickel and the like can be mentioned. Examples of the form of the negative electrode current collector include a foil shape and a plate shape. The plan-view shape of the negative electrode current collector is not particularly limited, but
For example, a circular shape, an elliptical shape, a rectangular shape, an arbitrary polygonal shape, or the like can be mentioned. The thickness of the negative electrode current collector varies depending on the shape, but is preferably in the range of, for example, 1 μm to 50 μm, and preferably in the range of 5 μm to 20 μm.

(2) Li storage layer The Li storage layer is a carbon material or a mixture composed of a carbon material and a solid electrolyte.
Further, in the present disclosure, the porosity of the Li storage layer obtained by the calculation method described below is determined.
Usually, it is preferably 60% or more and less than 100%, and more preferably 78% or more and 86% or less. Specifically, by using the method described in 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. The carbon material used is
Ketjen Black (KB) is preferred. In the case of Ketjen Black, since lithium ions are less likely to be inserted between layers, charging / discharging is less likely to proceed at a potential noble than the precipitation / dissolution potential of metallic lithium, which is preferable for improving the energy density of the battery.

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

(2-2) Solid electrolyte If the solid electrolyte in the Li storage layer can be used for an all-solid-state lithium-ion battery,
The present invention is not particularly limited, and examples thereof include inorganic solid electrolytes such as sulfide solid electrolytes and oxide solid electrolytes. Examples of the sulfide solid electrolyte include Li ₂ SP ₂ S ₅ and Li ₂ SP 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 -Li I, 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 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 (however, x, y
Is a positive number. M is any of P, Si, Ge, B, Al, Ga, and In. ) Etc. can be mentioned.
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
Examples thereof include ₃ PO _{(4-3 / 2w)} N _w (w <1), Li _3.6 Si _0.6 P _0.4 O _4. The above description of "Li ₂ SP ₂ S ₅ " means a sulfide solid electrolyte made by 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 comprises an ionic conductor containing Li, A (A is at least one of P, Si, Ge, Al and B), and S. Moreover,
The ion conductor is an anion structure _(PS ^{4 3-} structure ortho-composition, _SiS ^{4 4-structure,} Ge
It is preferable to have S ₄ ^4- structure, AlS ₃ ^3- structure, BS ₃ ^3- structure) as the main component of the anion. This is because it can be a sulfide solid electrolyte having high chemical stability. The ratio of the anion structure of the ortho composition is 70 mol% with respect to the total anion structure in the ionic conductor.
It is preferably 90 mol% or more, and more preferably 90 mol% or more. The proportion of anionic structure in the ortho composition can be determined by Raman spectroscopy, NMR, XPS and the like.

The sulfide solid electrolyte may contain lithium halide in addition to the above-mentioned ionic conductor. Examples of lithium halide include LiF, LiCl, LiBr and Li.
I can be mentioned, and among them, 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. Further, the solid electrolyte may be glass or crystallized glass (glass ceramics).
Examples of the shape of the solid electrolyte include particulate matter.

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

The ratio of carbon material to solid electrolyte in the Li storage layer is the weight ratio of these two materials.
The carbon material: solid electrolyte = 1: 1 to 10: 0 is preferable, and the 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 manual mixing using a mortar and a pestle, a homogenizer, and mechanical milling. The mechanical milling may be a dry mechanical milling or a 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 applying mechanical energy, and examples thereof include a ball mill, a vibration mill, a turbo mill, a mechanofusion, and a disc mill. Of these, ball mills are preferable, and planetary ball mills are particularly preferable.

The liquid used when preparing the mixture using the homogenizer preferably has an aprotic property that does not generate hydrogen sulfide. Specifically, a polar aprotic liquid or a non-polar liquid. An aprotic liquid such as the aprotic liquid of the above can be mentioned.

The Li storage layer in the present disclosure is characterized in that the porosity of the Li storage layer obtained by the calculation method described below is within the above 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 may contain at least a solid electrolyte, and may further contain a binder, if necessary. The solid electrolyte used in the solid electrolyte layer is the same as that described in "(2-2) Solid electrolyte" above, and thus the description thereof is omitted here. As the solid electrolyte used for the solid electrolyte layer, the same solid electrolyte as the Li storage layer may be used, or a solid electrolyte different from the Li storage layer may be used.

The content of the solid electrolyte in the solid electrolyte layer is, for example, in the range of 10% by weight to 100% by weight, and may be in the range of 50% by weight to 100% by weight. 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, if necessary. .. Positive electrode active material is usually
Contains Li. Examples of the positive electrode active material include an oxide active material, and specifically, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn.
Rock salt layered active material such as _1/3 O ₂ , spinel type active material such as _{LiMn 2} O ₄ , Li (Ni _0.5 Mn _1.5 ) O _{4 , LiFePO 4} , LiMnPO ₄ , LiNiPO ₄ , LiCuPO _4, etc. Olivin type active material and the like can be mentioned. _Further, may be used _{Li 2 FeSiO 4, Li 2 MnSiO} Si -containing oxide such as ₄ as the positive electrode active material, it may be used Li ₂ S and polysulfides sulfides such as lithium as the positive electrode active material. The average particle size (D ₅₀ ) of the positive electrode active material is, for example, 10 nm.
It is preferably in the range of ~ 50 μm, more preferably in the range of 100 nm to 30 μm, and even more preferably in the range of 1 μm to 20 μm. As the average particle size, a value calculated by a laser diffraction type particle size distribution meter or a value measured based on image analysis using an electron microscope such as SEM can be used.

Further, a coat 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 (because it can be suppressed. Examples of the Li _{ion conductive oxide include LiNbO 3 , Li 4} Ti ₅ O ₁₂ , and Li ₃ PO ₄ of the coat layer. 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. The type of the solid electrolyte is not particularly limited, and examples thereof include a sulfide solid electrolyte. 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 the conductive material, the conductivity of the positive electrode active material layer can be improved. Examples of the conductive material include acetylene black, ketjen black, carbon fiber and the like. Further, the positive electrode active material layer may contain a binder. Examples of the type of binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). The thickness of the positive electrode active material layer is preferably in the range of, for example, 0.1 μm to 1000 μm.

(5) Positive Electrode Current Collector A lithium solid-state battery usually has a positive electrode current collector that collects electricity from the positive electrode active material layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon. It is preferable to appropriately select the thickness and shape of the positive electrode current collector according to the application of the battery and the like.

(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 at the time of assembly, or between the Li storage layer and the negative electrode current collector at the time of assembly. A lithium solid-state battery in which the negative electrode active material layer is not provided and metallic lithium is precipitated as the negative electrode active material by charging thereafter may be used. Further, after the initial charging, the metallic lithium precipitated between the negative electrode current collector and the solid electrolyte layer is used as the negative electrode active material.

(7) Lithium solid-state battery The lithium solid-state 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. .. Further, the all-solid-state battery may be a primary battery or a secondary battery, but a secondary battery is preferable. This is because it can be charged and discharged repeatedly and is useful as an in-vehicle battery, for example. Examples of the shape of the all-solid-state battery include a coin type, a laminated type, a cylindrical type, and a square type.

Further, in the present disclosure, it is also possible to provide a method for producing an all-solid-state battery having a pressing step of arranging and pressing the positive electrode active material layer or the solid electrolyte layer described above so as to overlap each other. The press pressure is not particularly limited, but is, for example, 1 ton / cm ² or more and 4 ton.
It may be / cm ^{2 or more.}

Since the comparative form has almost the same contents as each configuration of the above-described embodiment, the description of each is omitted.

The present disclosure is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present disclosure and exhibiting the same effect and effect is the present invention. 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 Weighed and mixed in an agate mortar for 5 minutes. Further, 4 g of dehydrated heptane (manufactured by Kanto Chemical Industry Co., Ltd.) was added to this mixture, and mechanical milling was performed for 40 hours using a planetary ball mill 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. The positive electrode active material is previously subjected to surface treatment of _{LiNbO 3.} As the positive electrode active material, the conductive material carbon, VGCF (manufactured by Showa Denko KK) and the above-mentioned sulfide solid electrolyte were used in a weight ratio of 85.
Weighed so as to have a ratio of 3: 1.3: 13.4, and the mixture was used as a positive electrode material to be a positive electrode active material.

(Preparation of Li storage layer material)
Ketjen Black as a carbon material (manufactured by Lion Specialty Chemicals Co., Ltd. E)
CP600JD: KB, D ₅₀ = 34 nm) and the above-mentioned sulfide solid electrolyte (D ₅₀ = 0.5 μm) as the solid electrolyte (SE) were used, and weighed so that the weight ratio was KB: SE = 2: 1.
After mixing by hand, add heptane and homogenizer (manufactured by SMT Co., Ltd., UH-50).
The Li storage layer material, which is the material of the Li storage layer, was obtained by mixing the mixture for 3 minutes.

(Manufacturing of lithium solid-state battery)
A solid electrolyte layer was formed by weighing 101.7 mg of the sulfide solid electrolyte in a ceramic mold (cross-sectional area: 1 cm ^{2 , using a cylindrical container) and pressing at 1 ton / cm 2.} 31.3 mg of the above positive electrode material was added to one side of the solid electrolyte layer, and 6 ton / c.
A positive electrode active material layer was formed by pressing with ^{m 2. 2 mg / cm 2} of the above Li storage layer material was added to the solid electrolyte layer on the side opposite to the positive electrode active material layer. Further, by arranging a positive electrode current collector (aluminum foil) on the positive electrode active material layer side and a negative electrode current collector (SUS foil) on the negative electrode layer side, and restraining the produced lithium solid-state battery with 0.2N. , The lithium solid-state battery of Example 1 was obtained. 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 the Li storage layer was not 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 pressed at 6 ton / cm 2} to form a positive electrode active material layer, 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 manufactured. After restraining the produced lithium solid-state battery with 0.2N, using a micrometer, the height of the cell with respect to the stacking direction in which each current collector, the positive electrode active material layer, and the solid electrolyte layer constituting the cell are laminated (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 placed between the negative electrode current collector and the solid electrolyte layer, and 4 ton / A Li occlusion layer is formed by pressing with ^{cm 2.} _{After restraining the cell at 0.2 N, the cell height (H 2} ) of the cell on which the Li storage layer was formed was measured by a micrometer in the same manner as the above-mentioned method for measuring the cell height. Then, the thickness (d) of the Li storage layer with respect to the stacking direction was calculated from the difference between _{H 2} and H _{1 (H 2-} H _1).

Based on the weight (w) of the Li storage layer described above, the true density of Ketjenblack, which is a carbon material used for the Li storage layer, and the true density of the solid electrolyte used, the volume occupied by the Li storage layer material in the Li storage layer. (V ₁ ) was calculated.

_{The actual volume (V 2} ) of the Li storage layer material in the Li storage layer was calculated from the product of the thickness (d) of the Li storage layer and the bottom area of the cell. The value of the volume obtained by subtracting V ₁ from V _{2 is the spatial volume (V 3} =
V _2- V ₁ ) was calculated, and the porosity (%) of the Li storage layer was calculated by multiplying the value _{of V 2} for the denominator and V _{3 for the numerator by 100.}

Table 1 is a table showing the weight ratio, porosity and reversible volume ratio of the Li storage layers of Examples and Comparative Examples. As shown in Table 1, from the results of Examples 1 to 4 and Comparative Example 2, it was confirmed that the larger the proportion of Ketjen black, the larger the porosity of the Li occlusion layer.

(Charge / discharge measurement)
Using the lithium solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 2, the charge / discharge measurement was performed after leaving the batteries in a constant temperature bath at 60 ° C. for 3 hours in advance. The measurement conditions were 25 ° C., current density 8.7 mA / cm ² , constant current charging, and when the charging capacity reached 4.35 mAh / cm ² , charging was terminated and the battery was allowed to rest for 10 minutes. Then, at 25 ° C, the current density is 0.435.
The discharge was completed at mA / cm ² , CC, and when the lower limit voltage reached 3.0 V. note that,
Charging corresponds to lithium precipitation on the negative electrode current collector, and discharging 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 FIGS. 3 and 4. The reversible capacity ratio of the battery is as described above in Comparative Example 2.
When the value of the discharge capacity of is 100, the value of the discharge capacity ratio (reversible capacity ratio) of Examples 1-4 and Comparative Example 1-2 is shown. In addition, in FIG. 3, the above-mentioned reversible volume ratio is plotted with respect to the porosity of the Li storage layer, and in FIG. 5, the solid electrolyte (SE) with respect to Ketjen black (KB) is plotted.
It is a graph which plotted the reversible volume ratio with respect to the weight ratio of.

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

Further, from FIG. 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) between the negative electrode current collector and the solid electrolyte layer is specific. By providing the Li storage layer having a value, the short circuit caused by the dendrite is suppressed, and the short circuit is suppressed.
It was confirmed that the self-discharge of the positive electrode active material on the positive electrode active material layer side was suppressed.

1 ... Negative electrode current collector 2 ... Li storage layer 3 ... Solid electrolyte layer 4 ... Positive electrode active material layer 5 ... Positive electrode current collectors 10, 11 ... Lithium solid-state battery

Claims (5)

A negative electrode current collector, an inorganic 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 inorganic solid electrolyte layer, and the Li storage layer is provided. A lithium solid-state battery characterized in that the void ratio of the layer is 78% or more and 86% or less. The lithium solid-state battery according to claim 1, wherein the negative electrode current collector has a foil shape or a plate shape. The lithium solid-state battery according to claim 1 or 2 , wherein the Li storage layer contains a carbon material. The lithium solid-state battery according to any one of claims 1 to 3 , wherein the Li storage layer contains an inorganic solid electrolyte. The Li storage layer contains a carbon material and contains
The Li storage layer contains an inorganic solid electrolyte, and the Li storage layer contains an inorganic solid electrolyte.
The lithium solid-state battery according to claim 1 or 2 , wherein the Li storage layer has a weight ratio of the inorganic solid electrolyte to the carbon material of 0.5 or less.

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