JP2018073469A - Lithium all-solid battery - Google Patents

Abstract

A lithium all-solid-state battery having a higher discharge capacity than before is provided. In a lithium all-solid-state battery including a positive electrode current collector, a positive electrode active material layer, a separator, and a negative electrode current collector, a positive electrode active material layer and a positive electrode current collector are present on one surface of the separator in this order. A negative electrode current collector is present on the other surface of the positive electrode active material layer, the positive electrode active material layer contains a lithium compound, and a lithium ion conductive solid electrolyte, a lithium metal and lithium ion are provided between the separator and the negative electrode current collector. An all-solid lithium battery further comprising a mixture layer containing a non-reactive conductive powder. [Selection] Figure 2

Description

  The present invention relates to a lithium all solid state battery.

  With respect to an all-solid-state lithium battery, a technique that employs a predetermined negative electrode current collector is known for the purpose of preventing a short circuit during charging. For example, in Patent Document 1, the surface shape of the solid electrolyte layer facing the surface shape of the negative electrode current collector is formed so as to correspond to the surface shape of the negative electrode current collector, the surface of the negative electrode current collector on the solid electrolyte layer side, and the solid electrolyte layer A lithium solid state secondary battery is disclosed in which the ten-point average roughness on the surface on the negative electrode current collector side is within a predetermined range.

JP 2016-35867 A

  However, such a lithium all solid state battery has a problem that the discharge capacity is small. This is presumably because the lithium metal deposition reaction occurs only on the surface of the negative electrode current collector, so that the reaction area is small and the reaction does not proceed sufficiently.

  The present invention has been accomplished in view of the above-described circumstances regarding lithium all solid state batteries, and an object of the present invention is to provide a lithium all solid state battery having a higher discharge capacity than before.

  The lithium all solid state battery of the present invention is a lithium all solid state battery comprising a positive electrode current collector, a positive electrode active material layer, a separator and a negative electrode current collector, wherein the positive electrode active material layer and the positive electrode current collector are disposed on one side of the separator. The negative electrode current collector is present on the other surface of the separator, the positive electrode active material layer contains a lithium compound, and a lithium ion conductive solid electrolyte, lithium metal, and And a conductive layer that does not react with any of the lithium ions.

  According to the present invention, since the mixture layer including the lithium ion conductive solid electrolyte and the conductive powder is provided between the separator and the negative electrode current collector, lithium metal is deposited only on the surface of the negative electrode current collector. Compared with the conventional lithium all-solid battery, lithium metal can be deposited on the surface of the conductive powder, and as a result, the area of the reaction field where the lithium metal precipitation reaction occurs is widened. The discharge capacity can be increased.

It is a figure which shows an example of the layer structure of the lithium all-solid-state battery of this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. It is a bar graph which compares a relative discharge capacity about the lithium all-solid-state battery of Example 1 and Comparative Example 1.

  The lithium all solid state battery of the present invention is a lithium all solid state battery comprising a positive electrode current collector, a positive electrode active material layer, a separator and a negative electrode current collector, wherein the positive electrode active material layer and the positive electrode current collector are disposed on one side of the separator. The negative electrode current collector is present on the other surface of the separator, the positive electrode active material layer contains a lithium compound, and a lithium ion conductive solid electrolyte, lithium metal, and And a conductive layer that does not react with any of the lithium ions.

FIG. 1 is a diagram showing an example of a layer configuration of a lithium all solid state battery according to the present invention, schematically showing a cross section cut in a stacking direction. The lithium all-solid battery 100 includes a separator 1, a positive electrode active material layer 2, a positive electrode current collector 3, a negative electrode current collector 4, and a mixture layer 5. As shown in FIG. 1, the positive electrode active material layer 2 and the positive electrode current collector 3 exist in this order on one surface of the separator 1, and the mixture layer 5 and the negative electrode current collector 4 exist on the other surface of the separator 1. Exists in this order.
The lithium all solid state battery of the present invention is not necessarily limited to this example. For example, a positive electrode lead may be connected to a part of the positive electrode current collector 3, or a negative electrode lead may be connected to a part of the negative electrode current collector 4.

The positive electrode active material layer 2 contains a lithium compound. A lithium compound is usually used as a positive electrode active material. Lithium compounds include lithium alloys and lithium complexes. As the lithium compound, for example, Li ₂ S or the like can be used.
The positive electrode active material layer may contain a mixture of a lithium compound and other materials. For example, the positive electrode active material layer may include a mixture of Li ₂ S and S.

If necessary, the positive electrode active material layer further contains a conductive additive, a solid electrolyte, and the like as appropriate.
As a conductive support agent, what is normally used for lithium all-solid-state batteries, such as carbon materials, such as acetylene black, a metal material, can be used, for example.
As the solid electrolyte used for the positive electrode active material layer, for example, Li ₂ S · P ₂ S ₅ can be used. The solid electrolyte may be any of a solid electrolyte crystal, an amorphous solid electrolyte, and a solid electrolyte glass ceramic. In _the case of using Li 2 S _· P 2 _{S 5,} the content ratio of Li ₂ S and _P 2 _{S 5} is not particularly limited.

The positive electrode mixture used for forming the positive electrode active material layer is prepared by appropriately mixing a lithium compound, a conductive additive, a solid electrolyte, and the like. The mixing ratio is not particularly limited, and examples thereof include lithium compound: conductive auxiliary agent: solid electrolyte = 1: 1: 2 (mass ratio).
The method for preparing the positive electrode mixture is not particularly limited, and examples thereof include a method in which the material for the positive electrode active material layer is mixed by mechanical milling such as a ball mill.

  The material of the positive electrode current collector 3 is not particularly limited as long as it is normally used for a lithium all solid state battery, and examples thereof include aluminum.

The mixture layer 5 includes a lithium ion conductive solid electrolyte 5a and a conductive powder 5b. Although FIG. 1 shows a state in which the conductive powder 5b is uniformly dispersed in the lithium ion conductive solid electrolyte 5a, the present invention is not necessarily limited to this mode.
The lithium ion conductive solid electrolyte used for the mixture layer is not particularly limited as long as it is a solid electrolyte having a function of mediating the exchange of lithium ions between the positive electrode active material layer and the mixture layer. Examples of the lithium ion conductive solid electrolyte include Li ₂ S · P ₂ S ₅ based solid electrolyte, Li ₃ PO ₄ , Li ₃ PS ₄ , LiPON, LiBH _{4, and the} like.

As the conductive powder in the mixture layer, a material that does not react with either lithium metal or lithium ions is used. Here, “a material that does not react with either lithium metal or lithium ion” means that the composition of the material itself is changed by contact with lithium metal and / or lithium ion, or other materials containing lithium element by contact. It means a material that does not generate. The property inert to lithium metal and lithium ions is important as a condition for depositing lithium metal on the surface of the conductive powder.
The conductive powder is not particularly limited as long as it does not react with lithium metal and lithium ions and is conductive. For example, SUS powder, copper powder, titanium powder, iron powder, nickel powder, gold powder, etc. Can be mentioned.
As described above, since the mixture layer in which the lithium ion conductive solid electrolyte and the conductive powder are mixed is used, a wide contact area between these two kinds of materials can be ensured. As a result, lithium metal is deposited on the surface of the negative electrode current collector. Compared with the prior art which has been used, the area of the reaction field where the precipitation reaction of lithium metal occurs can be increased. In addition, since the conductive powder does not react with either lithium metal or lithium ions, there is no possibility of impairing lithium ion conductivity in the resulting mixture layer.

The average particle diameter of the conductive powder is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and further preferably 1 to 3 μm. When the average particle size of the conductive powder is less than 0.1 μm, handling may be difficult. On the other hand, when the average particle size of the conductive powder exceeds 10 μm, the surface area per unit volume of the conductive powder is reduced, and as a result, a high discharge capacity may not be obtained.
In addition, the average particle diameter of electroconductive powder is calculated | required by measuring the particle diameter of 200-500 electroconductive powder observed, for example with a scanning electron microscope (SEM), and averaging the result.

  The mixing ratio of the lithium ion conductive solid electrolyte and the conductive powder is preferably lithium ion conductive solid electrolyte: conductive powder = 90% by mass: 10% by mass to 10% by mass: 90% by mass, and more preferably. Is lithium ion conductive solid electrolyte: conductive powder = 85% by mass: 15% by mass to 15% by mass: 85% by mass, and more preferably lithium ion conductive solid electrolyte: conductive powder = 80% by mass: 20 % By mass to 20% by mass: 80% by mass. If the lithium ion conductive solid electrolyte is less than 10% by mass, lithium ion conduction between the positive electrode active material layer and the mixture layer may be insufficient. If the conductive powder is less than 10% by mass, the amount of lithium metal deposited on the surface of the conductive powder is reduced, and as a result, a sufficiently high discharge capacity may not be obtained.

The average thickness of the mixture layer is preferably 1 to 500 μm, more preferably 2 to 300 μm, and further preferably 3 to 200 μm. When the average thickness of the mixture layer is less than 1 μm, a sufficient discharge capacity may not be obtained. On the other hand, when the average thickness of the mixture layer exceeds 500 μm, the resistance becomes too high, and as a result, the discharge capacity may decrease.
In addition, the average thickness of a mixture layer is calculated | required by measuring the thickness of 3-10 places of a mixture layer, for example using an optical microscope, a caliper, etc., and averaging the result.

The relative density of the mixture layer is preferably 70 to 99%, more preferably 75 to 90%, and further preferably 80 to 85%. When the relative density of the mixture layer is less than 70%, the conductivity and lithium ion conductivity in the mixture layer may be inferior. On the other hand, when the relative density of the mixture layer exceeds 99%, a sufficient discharge capacity cannot be ensured in the mixture layer, so that a high discharge capacity may not be obtained.
The relative density of the mixture layer is a value obtained by dividing the absolute density obtained from the mass and volume of the mixture layer by the true density of the mixture layer obtained from the true density of each material constituting the mixture layer based on the mass ratio. .

The method for forming the mixture layer is not particularly limited. As an example of the method for forming the mixture layer, a mixture containing a lithium ion conductive solid electrolyte and a conductive powder is mixed by a stirring means such as an ultrasonic homogenizer, and the composition of the mixture is made uniform. A method of placing the mixture on a surface and pressing it can be mentioned.
In the mixture, a dispersion medium such as water or an organic solvent may be appropriately added in order to uniformly mix the lithium ion conductive solid electrolyte and the conductive powder. As the lithium ion conductive solid electrolyte and the conductive powder are uniformly mixed and the mutual contact area increases, the reaction field where lithium metal can be dissolved and precipitated in the battery reaction increases, and the discharge capacity of the battery can be increased.
Examples of the dispersion medium that can be used for preparing the mixture include heptane.

  The material of the negative electrode current collector 4 is not particularly limited as long as it is normally used for a lithium all solid state battery, and examples thereof include copper.

The separator 1 is a layer that exists between the positive electrode active material layer 2 and the mixture layer 5. Ions are conducted between the positive electrode active material layer 2 and the mixture layer 5 through the separator 1.
Material of the separator is not particularly limited as long as it is usually used in a lithium all solid state battery, for example, Li ₃ PS ₄ and the like.

An example of a method for producing a lithium all solid state battery will be described below. First, a positive electrode active material layer is formed on one surface of the separator, and a mixture layer is formed on the other surface of the separator. Next, with respect to the obtained laminate, a positive electrode current collector is disposed on the side facing the positive electrode active material layer, and a negative electrode current collector is disposed on the side facing the mixture layer, thereby completing a lithium all solid state battery. To do.
You may use a lithium all-solid-state battery in the state accommodated in exterior bodies, such as a glass container. The lithium all solid state battery is preferably stored and used in an inert atmosphere such as argon or nitrogen so as not to be exposed to the air.

1. Production of Lithium All Solid Battery [Example 1]
(1) Synthesis of lithium ion conductive solid electrolyte Li ₂ S (manufactured by Nippon Kagaku Kogyo Co., Ltd.) and P ₂ S ₅ (manufactured by Aldrich Co.) are in a molar ratio of Li ₂ S: P ₂ S ₅ = 3: 1 These were weighed and mixed in an agate mortar for 5 minutes. To this mixture, dehydrated heptane (manufactured by Kanto Chemical Industry Co., Ltd.) was added, and mechanical milling was performed for 40 hours using a planetary ball mill to obtain a lithium ion conductive solid electrolyte (Li ₃ PS ₄ ).

(2) Preparation of positive electrode composite material 0.25 g of Li ₂ S (lithium compound), 0.25 g of acetylene black (AB, conductive additive), 0.50 g of Li ₃ PS ₄ (solid electrolyte) were weighed, and these were ball milled pot (capacity: 45mL, ZrO made ₂₎ was placed in. Further, 160 ZrO ₂ balls (φ5 mm) were placed in this ball mill pot. The ball mill pot was set in a ball mill and mixed at 370 rpm for 5 hours. After completion of the ball mill, the mixture was taken out from the ball mill pot and used as a positive electrode mixture.

(3) Preparation of lithium ion conductive solid electrolyte mixture layer material was prepared Li ₃ PS _4. SUS powder (average particle diameter: 1 μm) was prepared as a conductive powder that does not react with either lithium metal or lithium ions. Further, dehydrated heptane (manufactured by Kanto Chemical Co., Inc.) was prepared as a dispersion medium for these materials.
Li ₃ PS ₄ 0.30 g, SUS powder 0.075 g, and dehydrated heptane 0.70 g were weighed and added to a container. The materials were mixed using an ultrasonic homogenizer (manufactured by SMT, model number: UH-50). The obtained slurry was transferred to a petri dish and dried at 100 ° C. for 1 hour or longer to prepare a mixture layer material.

(4) Preparation of lithium all-solid battery 100 mg of the above lithium ion conductive solid electrolyte (Li ₃ PS ₄ ) was added to a ceramic mold (cross-sectional area: 1 cm ² ), and the separator was pressed by pressing at 4 ton / cm ^2. Formed. The positive electrode active material layer was formed by adding 10 mg of the positive electrode mixture to one side of the separator and pressing at 1 ton / cm ² . 40 mg of the mixture layer material was added to the separator on the side opposite to the positive electrode active material layer, and the mixture layer was formed by pressing at 6 ton / cm ² . From the mass of the material for the mixture layer and the volume of the mixture layer, the absolute density of the mixture layer is determined as follows.
Absolute density = (40 * 10 ⁻³ [g]) / (1 [cm ² ] × 210 * 10 ⁻⁴ [cm])
= 1.90 [g / cm ³ ]
Moreover, the true density of the mixture layer calculated | required based on mass ratio from the true density of each material which comprises a mixture layer is 2.35 [g / cm < ³ >].
Accordingly, the relative density is determined as follows.
Relative density = absolute density / true density = (1.90 [g / cm ³ ] /2.35 [g / cm ³ ]) * 100 [%]
= 81 [%]
Further, a positive electrode current collector (aluminum foil) was disposed on the positive electrode active material layer side, and a negative electrode current collector (copper foil) was disposed on the mixture layer side, whereby the lithium all solid state battery of Example 1 was obtained.
The lithium all solid state battery of Example 1 was sealed in a glass container under an argon atmosphere so as not to be exposed to the atmosphere.

[Comparative Example 1]
In Example 1 above, “(3) Preparation of mixture layer material” was not carried out, and “(4) Preparation of lithium all solid state battery” was carried out without forming a mixture layer, A lithium all-solid battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the negative electrode current collector (copper foil) was directly disposed on the opposite side.

2. Charging / discharging test About the lithium all-solid-state battery of Example 1 and Comparative Example 1, 1 cycle charging / discharging was performed on the following conditions, and the discharge capacity was measured.
Measurement temperature: 25 ° C
Voltage range: Range from 0.0V to 3.0V Measurement current: 0.133mA

FIG. 2 is a bar graph comparing the relative discharge capacities of the lithium all solid state batteries of Example 1 and Comparative Example 1. The relative discharge capacity in FIG. 2 was calculated with the discharge capacity of Comparative Example 1 being 100%.
From FIG. 2, the relative discharge capacity of Example 1 is 110%. Therefore, it can be seen that the lithium all solid state battery of Example 1 including the mixture layer has a discharge capacity increased by 1.1 times compared to the lithium all solid state battery of Comparative Example 1 having no mixture layer.

DESCRIPTION OF SYMBOLS 1 Separator 2 Positive electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Mixture layer 5a Lithium ion conductive solid electrolyte 5b Conductive powder 100 Lithium all solid state battery

Claims (1)

In a lithium all solid state battery comprising a positive electrode current collector, a positive electrode active material layer, a separator and a negative electrode current collector,
A positive electrode active material layer and a positive electrode current collector are present in this order on one side of the separator,
A negative electrode current collector is present on the other side of the separator;
The positive electrode active material layer contains a lithium compound;
Between the separator and the negative electrode current collector,
A lithium ion conductive solid electrolyte;
Conductive powder that does not react with either lithium metal or lithium ions;
A lithium all-solid battery, further comprising a mixture layer comprising:

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