JP2017139098A - Method for manufacturing laminate for all-solid battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a laminate for an all-solid battery, which enables formation of a chargeable/dischargeable interface while suppressing different phase formation in baking.SOLUTION: A method for manufacturing a laminate 20 for an all-solid battery comprises: an intermediate formation step of forming a negative electrode layer 2X, including a negative electrode active material including Si as a primary component and Zn as an assistant agent for interface formation, on a solid electrolyte layer 1X including an oxide solid electrolyte including elements of Li, La and Zr to form an intermediate 10; and a baking step of baking the intermediate 10 to bond the solid electrolyte layer 1X with the negative electrode layer 2X. In the baking step, a baking temperature is in a range of a melting point of Zn or higher but lower than 800°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an all-solid battery laminate capable of forming a chargeable / dischargeable interface while suppressing heterogeneous formation during firing.

  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 to make the battery completely solid does not use a flammable organic solvent in the battery, so the safety device can be simplified, and manufacturing costs and productivity can be reduced. It is considered excellent.

For example, Patent Document 1 includes a positive electrode layer, a solid electrolyte layer containing an oxide-based solid electrolyte, and a negative electrode layer, and at least one of the positive electrode layer or the negative electrode layer and the solid electrolyte layer are joined by sintering. An all-solid secondary battery and a method for manufacturing the same are disclosed. In this technique, by using a carbon material having a specific surface area of 1000 m ² / g or less as a conductive agent for the electrode layer (positive electrode layer or negative electrode layer), the combustion of the carbon material is suppressed in the sintering process. An all-solid-state secondary battery capable of sufficiently obtaining the effect that the conductive agent imparts electron conductivity to the electrode layer even when the electrode layer and the solid electrolyte layer are sintered and joined by increasing the ratio It is intended to provide.

  Patent Document 2 discloses a method for producing an electrode material for a lithium secondary battery made of powder containing Si as a main component. Specifically, Si fine particles having an optimum particle size and specific surface area are prepared, and a metal powder containing Si fine particles and at least one element selected from Sn, Al, Zn, In, Bi, Pb, and Mg. And carbon powder are dry-crushed and agglomerated by a ball mill to reduce the contact resistance between Si particles and produce an electrode material for a lithium secondary battery excellent in cycle characteristics. An object of this technique is to provide an electrode material for a lithium secondary battery having a large discharge capacity per volume and excellent charge / discharge cycle characteristics.

International Publication 2011/132627 JP 2006-216277 A

For example, when a solid electrolyte layer containing Li ₇ La ₃ Zr ₂ O ₁₂ and a negative electrode layer containing Si, for example, are integrally fired at a high temperature, the solid electrolyte and the material constituting the negative electrode layer react to form a different phase. There is a risk. On the other hand, if the firing temperature is lowered to suppress the formation of heterogeneous phases, there is a problem that the grain boundary resistance is increased and the battery does not function, and it is desired to solve these problems.

  The present invention has been made in view of the above circumstances, and mainly provides a method for producing a laminate for an all-solid-state battery capable of forming a chargeable / dischargeable interface while suppressing heterogeneous formation during firing. Objective.

  In order to solve the above-described problems, in the present invention, a negative electrode active material containing Si as a main component and an interface formation assistant are formed on a solid electrolyte layer containing an oxide solid electrolyte containing Li element, La element, and Zr element. Forming a negative electrode layer containing Zn as an agent, forming an intermediate, and firing the intermediate, and firing the solid electrolyte layer and the negative electrode layer. The manufacturing method of the laminated body for all-solid-state batteries characterized by the baking temperature in the said baking process being in the range more than melting | fusing point of Zn and less than 800 degreeC is provided.

  According to the present invention, by using Zn as an interface formation aid, the intermediate can be baked at a temperature lower than the temperature at which the solid electrolyte and Si react to form an interface. An all-solid battery laminate capable of forming a chargeable / dischargeable interface while suppressing formation can be obtained.

  The present invention produces an effect that it is possible to provide a method for producing a laminate for an all-solid-state battery capable of forming a chargeable / dischargeable interface while suppressing heterogeneous formation during firing.

It is process drawing which shows an example of the manufacturing method of the laminated body for all-solid-state batteries of this invention. It is a result of charging / discharging characteristic evaluation with respect to the battery for evaluation using the laminated body for all-solid-state batteries obtained in Example 1. FIG. It is a result of charging / discharging characteristic evaluation with respect to the battery for evaluation using the laminated body for all-solid-state batteries obtained by the comparative example 1. FIG. Results of X-ray diffraction (XRD) of the intermediate of the all-solid battery laminate obtained in Comparative Example 2, and results of XRD of the mixed powder of Si powder and LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder It is. It is a result of XRD of the intermediate body of the laminated body for all-solid-state batteries obtained in the comparative example 3. It is the result of evaluating the joining state of the intermediate | middle layers of the laminated body for all-solid-state batteries obtained by the comparative example 2. FIG.

  Hereinafter, the manufacturing method of the laminated body for all-solid-state batteries of this invention is demonstrated in detail.

FIG. 1 is a process diagram showing an example of a method for producing an all-solid battery laminate according to the present invention. First, as shown in FIGS. 1A to 1B, a negative electrode active material mainly composed of Si is formed on a solid electrolyte layer 1X containing an oxide solid electrolyte containing Li element, La element, and Zr element. Then, the negative electrode layer 2X containing Zn as an interface forming aid is formed to form the intermediate 10 (intermediate formation step). Next, as shown in FIGS. 1B to 1C, the intermediate body 10 is fired, and the solid electrolyte layer 1X and the negative electrode layer 2X are joined (firing step). Thereby, the laminated body 20 for all-solid-state batteries which has the solid electrolyte layer 1 and the negative electrode layer 2 in which the interface which can be charged / discharged was formed is obtained.
The present invention is greatly characterized in that the negative electrode layer contains Zn, and the firing temperature in the firing step is in the range from the melting point of Zn to less than 800 ° C.

  According to the present invention, by using Zn as an interface formation aid, the intermediate can be baked at a temperature lower than the temperature at which the solid electrolyte and Si react to form an interface. An all-solid battery laminate capable of forming a chargeable / dischargeable interface while suppressing formation can be obtained.

Conventionally, for example, an attempt was made to form an interface between a negative electrode layer containing Si as a negative electrode active material and a solid electrolyte layer containing Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) as a solid electrolyte by a powder coating firing method. In this case, it is necessary to perform the heat treatment at a temperature equal to or higher than the sintering temperature of the negative electrode active material or the sintering temperature of the solid electrolyte. There is a problem that a substance reacts to form a heterogeneous phase at the interface between the solid electrolyte layer and the negative electrode layer.
In order to suppress such a reaction, for example, when an interface forming aid such as a paste is introduced as an adhesive layer to form an interface, when the Li ion conductivity and electronic conductivity of the interface forming aid are low, There was a problem that the adhesive layer itself became a high resistance layer, and charging / discharging was hindered.
In addition, when the interface formation assistant exhibits a redox reaction at a higher potential than Si, there is also a problem that the potential as the negative electrode layer increases and the energy density of the battery decreases.

In order to solve the above-mentioned problem, the inventor of the present invention, as an interface formation aid added to the negative electrode layer, has a material having the following conditions, that is, a temperature at which Si and a solid electrolyte react to form a heterogeneous phase. Consider materials that have a melting point at a low temperature, have Li ion conductivity and electron conductivity, have no potential for charge / discharge at 1 V or less, or have a small potential for charge / discharge, or evaporate during firing. did.
In the present invention, Zn that satisfies all of the above conditions is added to the negative electrode layer as an interface forming aid, and the solid electrolyte layer and the negative electrode layer are at a temperature that is equal to or higher than the melting point of Zn and less than the temperature at which the heterogeneous phase is formed. By firing the intermediate, Zn functions as a paste, and the solid electrolyte layer and the negative electrode layer can be joined. Further, Zn has a low vapor pressure and evaporates to some extent during firing, so that the amount remaining in the negative electrode layer is small and the influence on the negative electrode potential is small. Thereby, it is guessed that the interface which can be charged / discharged can be formed, suppressing formation of a different phase at the time of baking.
Hereinafter, the manufacturing method of the laminated body for all-solid-state batteries of this invention is demonstrated for every process.

1. Intermediate Forming Process In the present invention, the intermediate forming process comprises a negative electrode active material containing Si as a main component and an interface forming aid on a solid electrolyte layer containing an oxide solid electrolyte containing Li element, La element and Zr element. This is a step of forming a negative electrode layer containing Zn as an agent.

(1) Negative electrode layer The negative electrode layer which comprises an intermediate body should just contain the negative electrode active material which has Si as a main component, and Zn as an interface formation adjuvant.

  The negative electrode active material in the present invention is not particularly limited as long as it contains Si as a main component. Specifically, Si alone or an alloy containing Si as a main component may be used. When the negative electrode active material is an alloy containing Si as a main component, for example, the Si content is 70% by weight or more, and preferably 80% by weight or more. On the other hand, the Si content may be 99% by weight or less and 90% by weight or less. As such an alloy element, at least one selected from the group consisting of Nb, V, Sn, Mo, W, Ti, Al, Zn and C can be used. Of these, Ti, Al, Zn and C are preferable.

The shape of the negative electrode active material in the present invention is, for example, powdery, and the average particle diameter (D ₅₀ ) is preferably in the range of 0.001 μm to 100 μm, and in the range of 0.01 μm to 10 μm. More preferably. If the average particle size is too large, it may be difficult to obtain a dense all-solid battery laminate after firing. If the average particle size is too small, it is difficult to produce a negative electrode active material. This is because there is a possibility of becoming. Incidentally, the average particle diameter can be defined by the D ₅₀ as measured by a particle size distribution meter.

The negative electrode layer in the present invention contains Zn as an interface forming aid. Zn may be in the form of particles or a thin film. When Zn is in the form of particles, for example, it may be mixed with other materials constituting the negative electrode layer. When Zn is in the form of a thin film, for example, an interface forming aid between the solid electrolyte layer and the negative electrode layer The thin film may be formed.
When Zn is in the form of particles, the average particle diameter (D ₅₀ ) of Zn is not particularly limited, but may be as large as the negative electrode active material from the viewpoint of being able to be uniformly mixed when forming the negative electrode layer. Preferably, for example, it is preferably in the range of 0.001 μm to 100 μm, and more preferably in the range of 0.01 μm to 10 μm.
In addition, when Zn is in the form of a thin film, the thickness of the Zn layer is in the range of 1 nm to 100 nm, and preferably in the range of 1 nm to 50 nm. The thickness of the Zn layer can be measured, for example, by observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

  The ratio (Zn / (Si + Zn)) of Zn to the total of the negative electrode active material containing Si as a main component and Zn is, for example, 1% by volume or more, may be 5% by volume or more, and may be 10% by volume or more. There may be. If the proportion of Zn is too small, the negative electrode layer and the solid electrolyte layer may not be sufficiently joined. On the other hand, Zn / (Si + Zn) is, for example, 50% by volume or less, and may be 40% by volume or less.

  In addition to the negative electrode active material, the negative electrode layer may contain at least one of a conductive agent, a solid electrolyte, and a binder (binder) as necessary. The negative electrode layer can improve the electroconductivity of a negative electrode layer by containing a electrically conductive agent. Examples of such a conductive agent include carbon fibers such as acetylene black, ketjen black, and VGCF, and graphite. The binder is not particularly limited as long as it is chemically and electrically stable, and examples thereof include cellulose, acrylic, polyvinyl alcohol, and polyvinyl butyral. . In addition, the solid electrolyte is not particularly limited as long as it has desired ionic conductivity, and examples thereof include an oxide solid electrolyte. The solid electrolyte will be described in detail in the section “(2) Solid electrolyte layer” described later.

  The content of the negative electrode active material in the negative electrode layer is preferably higher from the viewpoint of capacity, for example, in the range of 60% by volume to 99% by volume, particularly in the range of 70% by volume to 95% by volume. preferable. The thickness of the negative electrode layer varies greatly depending on the intended configuration of the all-solid battery, but is preferably in the range of 0.1 μm to 1000 μm, for example.

  Although the formation method of a negative electrode layer will not be specifically limited if it is a method which can obtain a desired negative electrode layer, For example, the slurry method can be mentioned. This is because the material of the negative electrode layer can be uniformly mixed and dispersed. In the slurry method, for example, a slurry containing a negative electrode active material containing Si as a main component, Zn as an interface formation aid, and a dispersion medium is formed, and the slurry contains a Li element, a La element, and a Zr element. It is applied on a solid electrolyte layer containing an oxide solid electrolyte and dried.

(2) Solid electrolyte layer The solid electrolyte layer in this invention contains the oxide solid electrolyte containing Li element, La element, and Zr element. The solid electrolyte layer may be a sintered body or a compacted body.
The solid electrolyte may be usually composed only of an oxide solid electrolyte containing Li element, La element and Zr element, or may be composed of an oxide solid electrolyte containing other elements. Examples of other elements contained in the solid electrolyte include Nb element, Al element, Ta element, and the like.
The total ratio of the Li element, La element, Zr element, and O element contained in the solid electrolyte is, for example, 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more.

The composition of the oxide solid electrolyte is not particularly limited. For example, the general formula Li _x La _y Zr _z Nb _w O ₁₂ (1 ≦ x ≦ 7, 2 ≦ y ≦ 4, 0 <z ≦ 3, 0 ≦ w ≦ 3), specifically, Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ La ₃ Zr _1.75 Nb _0.25 O ₁₂ , Li _6.75 La ₃ Zr _1.75 Nb _{0 .25} O ₁₂ can be mentioned.
In addition, the solid electrolyte layer may contain one kind of the oxide solid electrolyte, or may contain two or more kinds.

  The content of the oxide solid electrolyte in the solid electrolyte layer is not particularly limited, but is preferably larger from the viewpoint of suppressing the occurrence of a heterogeneous phase, specifically, 50% by volume or more. Preferably, it is 70% by volume or more, more preferably 90% by volume or more. The solid electrolyte layer may be a layer composed only of the oxide solid electrolyte.

  Further, the solid electrolyte layer may contain a binder as necessary. In addition, about a binder, it is the same as that used for the negative electrode layer mentioned above. The thickness of the solid electrolyte layer varies greatly depending on the type of solid electrolyte used and the configuration of the all-solid battery. For example, the thickness is in the range of 0.1 μm to 1000 μm, particularly in the range of 0.1 μm to 300 μm. It is preferable that

The shape of the oxide solid electrolyte is, for example, powder, and the average particle diameter (D ₅₀ ) is preferably in the range of 0.001 μm to 100 μm, and in the range of 0.01 μm to 10 μm. Is more preferable. If the average particle size is too large, it may be difficult to obtain a dense all-solid battery laminate after firing. If the average particle size is too small, it is difficult to produce a solid electrolyte. Because there is a possibility of becoming.

2. Firing step The firing step in the present invention is a step of sintering the intermediate and joining the solid electrolyte layer and the negative electrode layer.

  The firing temperature may be equal to or higher than the temperature at which Zn melts (the melting point of Zn). The melting point of Zn is 419.5 ° C. under atmospheric pressure. The firing temperature may be 420 ° C. or higher, 450 ° C. or higher, 500 ° C. or higher, or 600 ° C. or higher. When the firing temperature is too low, Zn does not melt, and there is a possibility that the solid electrolyte layer and the negative electrode layer cannot be joined. On the other hand, the sintering temperature may be less than the heterogeneous formation temperature at the interface between the solid electrolyte layer and the negative electrode layer, and is usually less than 800 ° C. and preferably 700 ° C. or less. When the firing temperature is too high, there is a possibility that the solid electrolyte and Si react to form a heterogeneous phase at the interface between the solid electrolyte layer and the negative electrode layer. Examples of the firing method include a method using a muffle furnace or an atmosphere control furnace.

  The firing time is not particularly limited as long as it can be formed by joining the solid electrolyte layer and the negative electrode layer. For example, the firing time is preferably within a range of 1 minute to 24 hours, and is preferably 10 minutes to 10 hours. More preferably within the range. The firing temperature and firing time are preferably selected as appropriate depending on the thickness of the intended laminate for an all-solid battery. Examples of the firing atmosphere include an inert atmosphere such as a nitrogen atmosphere.

  The porosity of the negative electrode layer obtained by the firing step is, for example, 15% or less, and preferably in the range of 5% to 10%. Moreover, the porosity of a solid electrolyte layer is 20% or less, for example, and it is preferable that it is 10% or less.

  Further, Zn added to the negative electrode layer only needs to be able to form a good interface between the negative electrode layer and the solid electrolyte layer, and Zn is evaporated at a predetermined rate by the baking step, and in the negative electrode layer after baking, It may be included to the extent that it does not affect the battery function. Specifically, the amount of Zn contained in the negative electrode layer after firing is, for example, 50 parts by weight or less, and may be 10 parts by weight or less, assuming that the amount of Zn added to the negative electrode layer is 100 parts by weight. It may be 5 parts by weight or less. Further, 0 part by weight, that is, Zn may not be present in the negative electrode layer after firing.

3. All-solid-state battery laminate In the present invention, an all-solid-state battery laminate is obtained by performing the above-described steps. In particular, in the firing step, Zn is added as an interface formation aid to the negative electrode layer, and fired at a temperature higher than the melting point of Zn and lower than the temperature at which the solid electrolyte and the negative electrode active material react to form a heterogeneous phase. By doing this, it is possible to form a chargeable / dischargeable interface while suppressing heterogeneous formation during firing.

  The all-solid-state battery laminate obtained by the present invention is formed by firing an intermediate. The intermediate body may have a structure having a solid electrolyte layer and a negative electrode layer, and may further have a structure having a positive electrode layer.

  Moreover, in this invention, it can also provide the manufacturing method of the all-solid-state battery characterized by having the laminated body for all-solid-state batteries mentioned above. For example, when the intermediate has a structure having a solid electrolyte layer and a negative electrode layer, it usually further includes a positive electrode layer forming step of forming a positive electrode layer. In addition, for example, when the intermediate has a structure having a solid electrolyte layer and a negative electrode layer and further having a positive electrode layer, an all-solid battery can be obtained without performing other steps.

  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.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Example 1]
(Intermediate formation process)
Si powder was used as an active material, Zn powder was used as an interface forming aid, and mixed at a volume ratio of Si: Zn = 75: 25. Next, an acrylic binder as a binder was mixed in a volume ratio of 20 by volume to the obtained mixture, and an appropriate amount of a dispersion medium (alcohol organic solvent) was added to prepare a slurry. Next, the obtained slurry was screen-printed on a Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as LLZ) solid electrolyte pellet and dried at 150 ° C. for 10 minutes to produce an intermediate.

(Baking process)
The obtained intermediate was fired at 500 ° C. for 1 hour in a nitrogen atmosphere to produce a laminate for an all-solid battery.

[Comparative Example 1]
A laminate for an all-solid-state battery was produced in the same manner as in Example 1 except that Sn was used instead of Zn as the interface forming aid.

[Evaluation]
Li was vapor-deposited as a counter electrode on the all-solid battery laminate obtained in Example 1 and Comparative Example 1 to produce an evaluation battery. The charge / discharge characteristics of the obtained evaluation battery were evaluated by a potential sweep measurement method (potential sweep range: within a range of 0 V to 2.5 V, sweep speed: 0.1 mV / s).
The results of Example 1 and Comparative Example 1 are shown in FIGS.

As shown in FIG. 2, in Example 1, since the redox peak of Si was seen and the redox peak other than Si was hardly seen, it was confirmed that the chargeable / dischargeable interface was formed. . On the other hand, as shown in FIG. 3, in Comparative Example 1, only the reduction peak of Sn was observed at a potential higher than that of Si, so that it was confirmed that Sn was hardly evaporated by firing.
In general, the melting point of Zn under atmospheric pressure is 419.5 ° C., and the boiling point is 907 ° C. Moreover, Sn has a melting point of 231.97 ° C. and a boiling point of 2270 ° C. Thus, since it is guessed that it is hard to evaporate so that the difference of a calcination temperature and a boiling point is large, it is thought that Sn hardly evaporated. Therefore, as shown in FIG. 3, when using a substance having a high boiling point such as Sn and causing a redox reaction at a potential more noble than Si as the negative electrode active material, the temperature is lower than the temperature at which a heterogeneous phase is generated (less than 800 ° C. Even if the negative electrode layer and the solid electrolyte layer can be joined in step), the substance remains in the negative electrode layer without evaporating and affects the potential of the negative electrode.

[Comparative Example 2]
A laminate for an all-solid-state battery was produced in the same manner as in Example 1 except that it was calcined at 600 ° C. for 1 hour without adding an interface forming aid.

[Comparative Example 3]
A laminate for an all-solid-state battery was produced in the same manner as in Comparative Example 2, except that firing was performed at 800 ° C. for 1 hour.

[Evaluation]
XRD measurement was performed on the all-solid battery laminate obtained in Comparative Examples 2 and 3. The results are shown in FIGS. Here, FIG. 4A shows the result of Comparative Example 2, and FIG. 4B shows the result of the mixed powder of Si powder and LLZ powder. Comparing FIG. 4A and FIG. 4B, since the same peak is obtained, in Comparative Example 2 (when Zn is not added and baking is performed at 600 ° C. for 1 hour), a heterogeneous phase is generated. Not confirmed. The firing temperature of Example 1 is 500 ° C., which is lower than the firing temperature of Comparative Example 2 (600 ° C.).

  On the other hand, when FIG. 5 and FIG. 4A are compared, in FIG. 5, the peaks near 2θ = 30.8 ° and 33.8 °, which are the main peaks of the cubic LLZ, become extremely small, and 2θ = 33 Since a peak around 0.0 ° was newly generated, it was confirmed that a heterogeneous phase was generated in Comparative Example 3 (when Zn was not added and baked at 800 ° C. for 1 hour).

  In addition, as shown in FIG. 6, when the all-solid-state battery laminate obtained in Comparative Example 2 was pinched with tweezers, the laminate collapsed. Therefore, without Zn, a temperature lower than the temperature at which the heterogeneous phase is formed, that is, It was confirmed that the negative electrode layer and the solid electrolyte layer were not joined even when fired at a temperature higher than the melting point of Zn and lower than 800 ° C. On the other hand, in Example 1, the negative electrode layer and the solid electrolyte layer were joined and the chargeable / dischargeable interface could be formed.

DESCRIPTION OF SYMBOLS 1X ... Solid electrolyte layer (in intermediate body) 2X ... Negative electrode layer (in intermediate body) 1 ... Solid electrolyte layer 2 ... Negative electrode layer 10 ... Intermediate body 20 ... Laminated body for all-solid-state battery

Claims (1)

On the solid electrolyte layer containing an oxide solid electrolyte containing Li element, La element and Zr element, a negative electrode active material containing Si as a main component and Zn as an interface forming aid is formed, An intermediate forming step for forming an intermediate;
Firing the intermediate, and joining the solid electrolyte layer and the negative electrode layer;
Have
A method for producing a laminate for an all-solid-state battery, wherein the firing temperature in the firing step is in the range of not less than the melting point of Zn and less than 800 ° C.