JP7119214B2 - All-solid secondary battery and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to an all-solid secondary battery and a manufacturing method thereof.

A lithium-ion secondary battery has a negative electrode, a positive electrode, and an electrolyte sandwiched between the negative electrode and the positive electrode, and is a storage battery that can be charged and discharged by reciprocating lithium ions between the two electrodes. . Organic electrolytic solutions have been conventionally used as electrolytes in lithium ion secondary batteries. However, organic electrolytes tend to leak, and there is also a risk of short-circuiting inside the battery due to overcharge or overdischarge, and further improvements in reliability and safety are required.
Under such circumstances, the development of all-solid secondary batteries using nonflammable inorganic solid electrolytes instead of organic electrolytes is underway. An all-solid secondary battery consists of a negative electrode, an electrolyte, and a positive electrode, all of which are solid, and can greatly improve safety and reliability, which are problems of batteries using organic electrolytes, and also enable longer life. It is said that

In general, a secondary battery that reciprocates metal ions between both electrodes usually has an irreversible capacity. In the case of batteries, the amount of lithium) may decrease (leading to loss of discharge capacity), and the desired battery capacity may not be achieved.
As one of the countermeasures against the decrease in the amount of metal due to the above-described first charge, there is a technique of replenishing corresponding metal ions separately from the active material forming the negative electrode active material layer or the positive electrode active material layer. For example, in Patent Document 1, in a lithium ion secondary battery using a non-aqueous electrolytic solution, for a laminate consisting of a positive electrode precursor containing a positive electrode active material and a specific lithium compound, a negative electrode, and a separator, A method for pre-doping lithium ions into the negative electrode by decomposing the lithium compound by applying a voltage under specific conditions between the positive electrode precursor and the negative electrode in the presence of a non-aqueous electrolyte is described. In this method, in addition to the pre-doping of lithium ions, the high-load charge-discharge cycle characteristics of the lithium-ion secondary battery can be improved by retaining the non-aqueous electrolyte in the pores generated by the decomposition of the lithium compound. Have been described.

Japanese Patent No. 6251452

However, in an all-solid secondary battery, since the electrolyte is also solid, it is difficult to retain or fill the pores generated in the positive electrode active material layer with the solid electrolyte layer as in Patent Document 1. On the other hand, increasing the pre-doping amount of metal ions in order to compensate (cover) the decrease in the amount of metal (the amount of loss in discharge capacity) leads to a decrease in energy density.

An object of the present invention is to provide an all-solid secondary battery that achieves not only high battery capacity but also high energy density, and a method for manufacturing the same.

The present inventors prepared a laminate of a positive electrode active material layer containing a negative electrode active material precursor and a solid electrolyte layer, charged the laminate, and then compressed the positive electrode active material layer, thereby increasing the battery capacity and We have found that an all-solid secondary battery with higher energy density can be produced. The present invention has been completed through further studies based on these findings.

That is, the above problems have been solved by the following means.
<1> A method for manufacturing an all-solid secondary battery having a solid electrolyte layer containing an inorganic solid electrolyte and a positive electrode active material layer on one surface of the solid electrolyte layer,
forming a positive electrode active material layer on one surface of the solid electrolyte layer using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor;
charging a laminate including a positive electrode active material layer and a solid electrolyte layer;
A step of compressing at least the positive electrode active material layer after the step of charging;
A method for manufacturing an all-solid secondary battery.
<2> The method for producing an all-solid secondary battery according to <1>, wherein the laminate is pressurized at a pressure of 10 to 1000 MPa in the compressing step.
<3> The method for producing an all-solid secondary battery according to <2>, wherein the pressure is 80 MPa or more.
<4> The method for producing an all-solid secondary battery according to any one of <1> to <3>, wherein the charging step is performed while the laminate is pressed and constrained in the stacking direction.
<5> The method for producing an all-solid secondary battery according to any one of <1> to <4>, wherein the compressing step is performed without applying a voltage to the laminate.
<6> Any one of <1> to <5>, wherein the negative electrode active material precursor is at least one compound selected from carbonates, oxides and hydroxides of alkali metals or alkaline earth metals. 1. The manufacturing method of the all-solid-state secondary battery as described in 1 above.
<7> The method for producing an all-solid secondary battery according to any one of <1> to <6>, wherein the all-solid secondary battery has a negative electrode active material layer on the other surface of the solid electrolyte layer.
<8> The all-solid secondary according to <7>, which has a step of forming a negative electrode active material layer using a negative electrode composition containing silicon or an alloy containing a silicon element before the step of charging. Battery manufacturing method.
<9> An all-solid secondary battery obtained by the method for producing an all-solid secondary battery according to any one of <1> to <8> above.

According to the method for producing an all-solid secondary battery of the present invention, an all-solid secondary battery exhibiting high battery capacity and high energy density can be produced. The all-solid secondary battery of the present invention exhibits high battery capacity and high energy density.
The above and other features and advantages of the present invention will become more apparent from the following description, with appropriate reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view schematically showing a preferred embodiment of the all-solid secondary battery of the present invention.

In the description of the present invention, a numerical range represented using "-" means a range including the numerical values described before and after "-" as lower and upper limits.

[All-solid secondary battery]
First, an all-solid secondary battery (also referred to as an all-solid secondary battery of the present invention) produced by the method for producing an all-solid secondary battery of the present invention will be described.
The all-solid secondary battery of the present invention has a positive electrode active material layer, a negative electrode active material layer facing the positive electrode active material layer, and a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer. In the all-solid secondary battery of the present invention, the positive electrode active material layer, the solid electrolyte layer and the negative electrode active material layer are preferably adjacent to each other.
In the present invention, unless otherwise specified, the negative electrode active material layer is a layer of metal deposited by charging ( negative electrode active material layer in a form in which the negative electrode active material layer is not formed in advance).
In the present invention, each layer constituting the all-solid secondary battery may have a single layer structure or a multilayer structure as long as it exhibits a specific function.
The all-solid secondary battery of the present invention is not particularly limited to other configurations as long as it has the above-described configuration (solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer). A known configuration for secondary batteries can be employed.

FIG. 1 is a cross-sectional view schematically showing the lamination state of each constituent layer constituting the battery in one embodiment of an all-solid secondary battery. The all-solid secondary battery 10 of the present embodiment has a negative electrode current collector 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5, which are laminated in this order when viewed from the negative electrode side. It has a structure in which adjacent layers are in direct contact with each other.
The charging and discharging of the all-solid secondary battery of the present invention having such a structure is the same as that of a normal all-solid secondary battery, except for the pre-doping of metal ions, and will be briefly described below.
That is, during charging, electrons (e ⁻ ) are supplied to the negative electrode side, and at the same time, the alkali metal or alkaline earth metal constituting the positive electrode active material is ionized, passes (conducts) through the solid electrolyte layer 3, and flows to the negative electrode side. It migrates and accumulates (reduced) ions of alkali metals or alkaline earth metals. For example, in the case of a lithium ion secondary battery, lithium ions (Li ⁺ ) are accumulated in the negative electrode.
In addition, although the details will be described later, when the all-solid secondary battery is first charged after manufacturing, the negative electrode active material precursor in the positive electrode active material layer is (oxidized) decomposed, and alkali metal or alkaline earth metal ions (all In the case of a solid lithium ion secondary battery, lithium ions) are generated, and these ions pass through the solid electrolyte layer, move to the negative electrode side, and are replenished (doped). This supplementation of ions is performed before use of the all-solid-state secondary battery, so it is also called pre-doping to distinguish it from supplementation of ions during use.
On the other hand, during discharge, the metal ions accumulated in the negative electrode are returned (moved) to the positive electrode side, and electrons generated at the negative electrode are supplied to the operating portion 6 and reach the positive electrode. In the illustrated example of the all-solid secondary battery, a light bulb is adopted as the operating portion 6, and is designed to be lit by discharging.

In the all-solid secondary battery of the present invention, the negative electrode active material layer can take various forms.
Examples of forms that can be taken as the negative electrode active material layer include, for example, a negative electrode active material layer containing a negative electrode active material described later, especially a negative electrode active material layer containing a silicon material or a silicon-containing alloy exhibiting high battery capacity (also referred to as a Si negative electrode). ), a form in which a solid electrolyte layer and a negative electrode current collector are laminated without having a lithium metal layer or a negative electrode active material layer (a form in which a negative electrode active material layer is not formed in advance), and the like. In the all-solid-state secondary battery of the present invention, the form of the negative electrode active material layer can be appropriately selected according to required characteristics, manufacturing conditions, and the like.

In an all-solid-state secondary battery in which a negative electrode active material layer is not formed in advance, metal ions (alkali metal ions) belonging to group 1 of the periodic table or group 2 of the periodic table accumulated in the negative electrode current collector during charging Some of the metal ions (alkaline earth metal ions) belonging to ) is used to form the negative electrode active material layer. That is, the all-solid-state secondary battery of this form causes the metal deposited on the negative electrode current collector to function as a negative electrode active material layer. For example, lithium metal is said to have a theoretical capacity ten times or more that of graphite, which is commonly used as a negative electrode active material. Therefore, a layer of lithium metal can be formed by depositing lithium metal on the negative electrode current collector. It becomes possible to realize a further improved all-solid secondary battery.
Thus, the all-solid-state secondary battery in which the negative electrode active material layer is not formed in advance has an uncharged state (a state in which the negative electrode active material is not deposited) and a charged state (a state in which the negative electrode active material is deposited). It includes both aspects. In the present invention, the all-solid-state secondary battery in which the negative electrode active material layer is not formed in advance means that the negative electrode active material layer is not formed in the layer forming step in battery production. The material layer is formed on the negative electrode current collector by charging.

<Solid electrolyte layer>
The solid electrolyte layer 3 includes an inorganic solid electrolyte having ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table (when in the form of particles, it is also referred to as inorganic solid electrolyte particles), and the effects of the present invention. It contains the components described later within a range that does not impair the , and usually does not contain the positive electrode active material and / or the negative electrode active material.
This solid electrolyte layer is a layer that functions as a separator that exhibits electronic insulation while exhibiting the above-described ionic conductivity, and can be applied without particular limitation to the solid electrolyte layer provided in a conventional all-solid secondary battery. . This solid electrolyte layer is formed of particles of the inorganic solid electrolyte.
The content of the inorganic solid electrolyte and the like in the solid electrolyte layer is the same as the content in 100% by mass of the solid content of the solid electrolyte composition described later.

<Positive electrode active material layer>
The positive electrode active material layer contains an inorganic solid electrolyte having ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, a positive electrode active material, and components described later within a range that does not impair the effects of the present invention. contains. In addition, it is one of preferred embodiments that the all-solid secondary battery contains a negative electrode active material precursor, which will be described later, in the initial uncharged state. The inorganic solid electrolyte, positive electrode active material, negative electrode active material precursor, etc. will be described later.
The contents of the positive electrode active material, the inorganic solid electrolyte, the negative electrode active material precursor, and the like in the positive electrode active material layer are the same as the contents of 100% by mass solid content in the positive electrode composition described later.

When the positive electrode active material layer contains the negative electrode active material precursor, ions of a metal element can be replenished (doped) without using a highly active material (for example, lithium metal) when manufacturing an all-solid secondary battery. , the battery capacity can be improved. Furthermore, by compressing the positive electrode active material layer after the decomposition reaction (crushing the voids generated by the decomposition), the positive electrode active material layer is made thinner and the (volume) energy density of the all-solid secondary battery is increased. can be done.
The positive electrode active material layer containing the negative electrode active material precursor is preferably applied to the above-described form in which the Si negative electrode or the negative electrode active material layer is not formed in advance. When a Si negative electrode is employed as the negative electrode active material layer, the silicon material or silicon-containing alloy has a large irreversible capacity, and the capacity (amount of movable lithium ions) is greatly reduced during the first charge. In addition, even in the case where the negative electrode active material layer is not formed in advance, the decrease in capacity due to the first charge is large, as in the case of the Si negative electrode. However, in an all-solid secondary battery having a Si negative electrode and an all-solid secondary battery in which the negative electrode active material layer is not formed in advance, the positive electrode active material layer contains the negative electrode active material precursor, and the decomposition reaction occurs during the first charge. It is possible to replenish the reduced metal ions (metal ions are occluded in the Si negative electrode). In addition, when the positive electrode active material layer contains the negative electrode active material precursor, expansion due to absorption of metal ions during charging or expansion due to metal deposition (volumetric expansion of the negative electrode active material layer) can be absorbed by the negative electrode active material layer. can be canceled by the voids generated by the decomposition reaction of the precursor, the breakage of the solid electrolyte layer can be prevented, and the arrival of dendrites to the positive electrode (occurrence of short circuit) can be suppressed. Moreover, by crushing the voids, the energy density can be improved.

<Negative electrode active material layer>
As described above, the negative electrode active material layer is a layer containing a negative electrode active material, optionally an inorganic solid electrolyte having ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and further components described later. , a lithium metal layer, or the like. An inorganic solid electrolyte, a negative electrode active material, etc. are mentioned later.
A lithium metal layer that can constitute a negative electrode active material layer means a layer of lithium metal, and specifically includes a layer formed by depositing or molding lithium powder, a lithium foil, a lithium deposition film, and the like.
In the present invention, the negative electrode active material layer is preferably a negative electrode active material layer containing a carbonaceous material in that volume expansion and volume contraction due to charging and discharging are small. On the other hand, from the standpoint of battery capacity, a configuration in which the negative electrode active material layer is not formed in advance is preferable, and a Si negative electrode is preferable from the viewpoint that a high battery capacity can be achieved and the occurrence of a short circuit can be effectively prevented. When the negative electrode active material layer is in a form in which the Si negative electrode or the negative electrode active material layer is not formed in advance, metal ions can be replenished by the initial charge, and the advantages of the Si negative electrode and the above forms are utilized, while the battery capacity and energy density are improved. can be improved.
The contents of the negative electrode active material, the inorganic solid electrolyte, and the like in the negative electrode active material layer are the same as the contents in 100% by mass of the solid content in the negative electrode composition described later.

<Thicknesses of Negative Electrode Active Material Layer, Solid Electrolyte Layer, and Positive Electrode Active Material Layer>
The thicknesses of the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer are not particularly limited. The thickness of each layer is preferably 10 to 1,000 μm, more preferably 20 μm or more and less than 500 μm. The thickness of the negative electrode active material layer in the form in which the negative electrode active material layer is not formed in advance varies depending on the amount of metal deposited by charging, and is not uniquely determined. In the all-solid secondary battery, the thickness of at least one of the positive electrode active material layer, the solid electrolyte layer and the negative electrode active material layer is more preferably 50 μm or more and less than 500 μm. When a lithium metal layer is employed as the negative electrode active material layer, the thickness of this lithium metal layer can be, for example, 0.01 to 100 μm regardless of the thickness of the negative electrode active material layer.

<Current collector>
The positive electrode current collector 5 and the negative electrode current collector 1 are preferably electronic conductors.
In the present invention, either one of the positive electrode current collector and the negative electrode current collector, or both of them may simply be referred to as the current collector.
Examples of materials for forming the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel and titanium, as well as aluminum or stainless steel surfaces treated with carbon, nickel, titanium or silver (thin films are formed). ) are preferred, and among them, aluminum and aluminum alloys are more preferred.
Materials for forming the negative electrode current collector include aluminum, copper, copper alloys, stainless steel, nickel and titanium, and the surface of aluminum, copper, copper alloys or stainless steel is treated with carbon, nickel, titanium or silver. and more preferably aluminum, copper, copper alloys and stainless steel.

As for the shape of the current collector, a film sheet is usually used, but a net, a punched one, a lath, a porous body, a foam, a molded body of fibers, and the like can also be used.
Although the thickness of the current collector is not particularly limited, it is preferably 1 to 500 μm.
It is also preferable that the surface of the current collector is roughened by surface treatment.

In the present invention, a functional layer or member is appropriately interposed or disposed between or outside each layer of the negative electrode current collector, the negative electrode active material layer, the solid electrolyte layer, the positive electrode active material layer, and the positive electrode current collector. You may Further, each layer may be composed of a single layer or may be composed of multiple layers.

<Case>
The all-solid secondary battery manufactured by the method for manufacturing an all-solid secondary battery of the present invention may be used as an all-solid secondary battery with the above structure depending on the application. It is also preferable to enclose it in a suitable housing for use. The housing may be made of metal or resin (plastic). When using a metallic one, for example, an aluminum alloy and a stainless steel one can be used. It is preferable that the metal casing be divided into a positive electrode side casing and a negative electrode side casing and electrically connected to the positive electrode current collector and the negative electrode current collector, respectively. It is preferable that the housing on the positive electrode side and the housing on the negative electrode side are joined and integrated via a gasket for short-circuit prevention.

The all-solid secondary battery manufactured by the manufacturing method of the present invention exhibits high battery solubility and high (volumetric) energy density. That is, in the all-solid secondary battery of the present invention, the negative electrode active material layer is pre-doped with metal ions by the first charge, and the negative electrode active material formed using a silicon material or a silicon-containing alloy having a large irreversible capacity as the negative electrode active material. Sufficient battery characteristics are exhibited even when the material layer is provided, or when the negative electrode active material layer is not formed in advance. In addition, since the positive electrode active material layer is provided in which the voids formed by the initial charging are crushed, the volume becomes smaller than that before the initial charging, and thus high energy density is exhibited.
Furthermore, even if the constituent layers of the all-solid secondary battery are formed of solid particles, and even if the (rapid) charging and discharging of the all-solid secondary battery are repeated, the occurrence of short circuits can be suppressed. Such suppression of the occurrence of a short circuit can also be realized by adopting a layer made of graphite and a lithium metal layer as the negative electrode active material layer.
The all-solid-state secondary battery of the present invention exhibiting the above-described excellent characteristics is used in a state in which the constituent layers are pressed and constrained in the lamination direction of the constituent layers (the stacking direction of the constituent layers, usually the thickness direction of the constituent layers). is preferred. As a result, even if the amount of the negative electrode active material decreases during discharge, the contact between the solid electrolyte layer and the negative electrode active material is maintained. can reduce the amount of metal deactivation (amount of isolated metal) due to charging and discharging, suppressing the decrease in battery capacity due to charging and discharging, and also exhibits excellent cycle characteristics.

<Application of all-solid secondary battery>
The all-solid secondary battery of the present invention can be applied to various uses. There are no particular restrictions on the mode of application, but for example, when installed in electronic equipment, notebook computers, pen-input computers, mobile computers, e-book players, mobile phones, cordless phone slaves, pagers, handy terminals, mobile faxes, mobile phones, etc. Copiers, portable printers, headphone stereos, video movies, liquid crystal televisions, handy cleaners, portable CDs, minidiscs, electric shavers, transceivers, electronic notebooks, calculators, portable tape recorders, radios, backup power sources, memory cards, etc. Other consumer products include automobiles (electric vehicles, etc.), electric vehicles, motors, lighting equipment, toys, game devices, road conditioners, clocks, strobes, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). . Furthermore, it can be used for various military applications and space applications. It can also be combined with a solar cell.

[Method for producing all-solid secondary battery of the present invention]
Next, the manufacturing method of the all-solid secondary battery of the present invention (also referred to as the manufacturing method of the present invention) will be described.
The manufacturing method of the present invention performs the following steps in order.
Step of forming (positive electrode active material layer): Using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor, a positive electrode active material layer is formed (laminated) on one surface of the solid electrolyte layer. Step of charging (the laminate): charging the laminate including the positive electrode active material layer and the solid electrolyte layer Compressing (the positive electrode active material layer): after the charging step, at least the positive electrode active material layer is Process of compressing under pressure

The production method of the present invention also preferably includes the following forming step.
Step of forming a (solid electrolyte layer): A step of forming a solid electrolyte layer using a solid electrolyte composition containing a solid electrolyte. It can be performed before or after the step of forming the material layer, and the order of each forming step can be appropriately determined according to the form and forming method of each layer to be formed.

The manufacturing method of the present invention may have the following discharging step.
Step of discharging (laminate): Step of discharging the laminate In the production method of the present invention, the discharging step may or may not be provided after the compressing step, and before the compressing step. It is preferable not to have a step of discharging.

When the all-solid secondary battery is of a form in which the negative electrode active material layer is formed in advance, the manufacturing method of the present invention preferably includes the following forming step.
Step of forming (a negative electrode active material layer): Using a negative electrode active material, preferably a carbonaceous material as the negative electrode active material, or a negative electrode composition containing silicon or an alloy containing silicon element, Step of Forming Material Layer This step of forming is preferably performed before the step of charging.

In the present invention, "performing the steps in order" means the temporal precedence of performing a certain process and another process, and another process (resting process) is performed between a certain process and another process. including.) is also included. In addition, the embodiment in which a certain step and another step are performed in order also includes an embodiment in which the time, place, or performer is appropriately changed.

In the manufacturing method of the present invention, a solid electrolyte layer, a positive electrode active material layer and a negative electrode active material layer are formed respectively. Each layer may be formed alone, or two or more layers may be collectively or sequentially formed as a laminate. Each layer is usually shaped into a sheet or plate, and may be provided with a base material, other layers, and the like.
The base material is not particularly limited as long as it can support the solid electrolyte layer, and examples thereof include sheets (plates) of materials such as the materials described above for the current collector, organic materials, and inorganic materials. Examples of organic materials include various polymers, and specific examples include polyethylene terephthalate, polypropylene, polyethylene, cellulose, and the like. Examples of inorganic materials include glass and ceramics.
Other layers include, for example, a protective layer (release sheet), a current collector, a coat layer, and the like. The solid electrolyte layer used in the form in which the negative electrode active material layer is not formed in advance preferably has a negative electrode current collector on its surface.
In the present invention, a sheet containing a solid electrolyte layer and not having a positive electrode active material layer and a negative electrode active material layer is a solid electrolyte sheet, a sheet containing a negative electrode active material layer is a negative electrode sheet, and a sheet containing a positive electrode active material layer is a positive electrode sheet. called.
The layer thickness of each layer is the same as the layer thickness of each layer described in the all-solid secondary battery of the present invention.

When manufacturing an all-solid secondary battery, a solid electrolyte layer, a positive electrode active material layer, and, if the all-solid secondary battery has a negative electrode active material layer in advance, a negative electrode active material layer are formed (prepared). .

<Step of Forming Solid Electrolyte Layer>
In carrying out this step, a solid electrolyte composition is prepared.
The solid electrolyte composition contains an inorganic solid electrolyte, and further optionally contains a binder, a dispersion medium, a conductive aid to be described later, and other components.
The solid electrolyte composition is preferably a non-aqueous composition. In the present invention, the non-aqueous composition includes not only a form containing no water but also a form having a water content (also referred to as water content) of 200 ppm or less. The water content of the solid electrolyte layer is preferably 150 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less. The water content indicates the amount of water contained in the solid electrolyte composition (mass ratio to the solid electrolyte composition). The water content can be obtained by filtering the solid electrolyte composition through a 0.45 μm membrane filter and performing Karl Fischer titration.

Components contained in the solid electrolyte composition and components that can be contained in the solid electrolyte composition are described below.

- Inorganic solid electrolyte -
In the present invention, the inorganic solid electrolyte means an inorganic solid electrolyte, and the solid electrolyte means a solid electrolyte in which ions can move. Since the main ion-conducting materials do not contain organic substances, organic solid electrolytes (polymer electrolytes typified by polyethylene oxide (PEO), etc., organic electrolytes typified by lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), etc.) electrolyte salt). Moreover, since the inorganic solid electrolyte is solid in a steady state, it is not usually dissociated or released into cations and anions. In this respect, it is also clearly distinguished from electrolytes or inorganic electrolyte salts in which cations and anions are dissociated or released in a polymer (LiPF ₆ , LiBF ₄ , LiFSI, LiCl, etc.). The inorganic solid electrolyte is not particularly limited as long as it has ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and generally does not have electronic conductivity.

The inorganic solid electrolyte has ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table. As the inorganic solid electrolyte, a solid electrolyte material applicable to this type of product can be appropriately selected and used. Examples of inorganic solid electrolytes include (i) sulfide-based inorganic solid electrolytes, (ii) oxide-based inorganic solid electrolytes, (iii) halide-based inorganic solid electrolytes, and (iv) hydride-based solid electrolytes. A sulfide-based inorganic solid electrolyte is preferred in terms of high ionic conductivity and ease of interfacial bonding between particles. In the present invention, as the inorganic solid electrolyte, an inorganic solid electrolyte material applicable to this type of product can be appropriately selected and used.
When the all-solid secondary battery of the present invention is an all-solid lithium ion secondary battery, the inorganic solid electrolyte preferably has ion conductivity of lithium ions.

(i) Sulfide-based inorganic solid electrolyte The sulfide-based inorganic solid electrolyte contains sulfur atoms, has the ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is electronically insulating. A compound having a property is preferred. The sulfide-based inorganic solid electrolyte preferably contains at least Li, S and P as elements and has lithium ion conductivity. element may be included.

Examples of sulfide-based inorganic solid electrolytes include lithium ion conductive sulfide-based inorganic solid electrolytes that satisfy the composition represented by the following formula (1).

L _a1 M _b1 P _c1 S _d1 A _e1 Formula (I)

In the formula, L represents an element selected from Li, Na and K, with Li being preferred. M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al and Ge. A represents an element selected from I, Br, Cl and F; a1 to e1 indicate the composition ratio of each element, and a1:b1:c1:d1:e1 satisfies 1-12:0-5:1:2-12:0-10. a1 is preferably 1 to 9, more preferably 1.5 to 7.5. b1 is preferably 0-3, more preferably 0-1. d1 is preferably 2.5 to 10, more preferably 3.0 to 8.5. e1 is preferably 0 to 5, more preferably 0 to 3.

The composition ratio of each element can be controlled by adjusting the compounding ratio of the raw material compounds when producing the sulfide-based inorganic solid electrolyte, as described below.

The sulfide-based inorganic solid electrolyte may be amorphous (glass), crystallized (glass-ceramics), or only partially crystallized. For example, Li--P--S type glass containing Li, P and S, or Li--P--S type glass ceramics containing Li, P and S can be used.
Sulfide-based inorganic solid electrolytes include, for example, lithium sulfide (Li ₂ S), phosphorus sulfide (e.g., diphosphorus pentasulfide (P ₂ S ₅ )), elemental phosphorus, elemental sulfur, sodium sulfide, hydrogen sulfide, and lithium halides (e.g., LiI, LiBr, LiCl) and sulfides of the element represented by M (eg, SiS ₂ , SnS, GeS ₂ ) are reacted with at least two raw materials.

The ratio of Li ₂ S and P ₂ S ₅ in the Li—P—S type glass and Li—P—S type glass ceramics is Li ₂ S:P ₂ S ₅ molar ratio, preferably 60:40 to 90:10, more preferably 68:32 to 78:22. By setting the ratio of Li ₂ S and P ₂ S ₅ within this range, the lithium ion conductivity can be increased. Specifically, the lithium ion conductivity can be preferably 1×10 ⁻⁴ S/cm or higher, more preferably 1×10 ⁻³ S/cm or higher. Although there is no particular upper limit, it is practical to be 1×10 ⁻¹ S/cm or less.

Examples of combinations of raw materials are shown below as specific examples of sulfide-based inorganic solid electrolytes. For example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiCl, Li ₂ SP ₂ S ₅ -H ₂ S, Li ₂ SP ₂ S ₅ -H ₂ S-LiCl, Li ₂ S—LiI—P ₂ S ₅ , Li ₂ S—LiI—Li ₂ OP ₂ S ₅ , Li ₂ S—LiBr—P ₂ S ₅ , Li ₂ S—Li ₂ OP ₂ S ₅ , Li ₂ S—Li ₃ PO ₄ —P ₂ S ₅ , Li ₂ SP ₂ S ₅ —P ₂ O ₅ , Li ₂ SP ₂ S ₅ —SiS ₂ , Li ₂ SP ₂ S ₅ —SiS ₂ -LiCl, Li2SP2S5 _- SnS, Li2SP2S5 _{- Al2S3} , _{Li2S - GeS2} , _{Li2S - GeS2 -} ZnS _{, Li2S -} Ga _2S3 , _Li2S -- _GeS2 -- _Ga2S3 , _Li2S -- _GeS2 -- _P2S5 , _{Li2S -- GeS2 -- Sb2S5} , _{Li2S -- GeS2 -- Al2S 3} , Li ₂ S—SiS ₂ , Li ₂ S—Al ₂ S ₃ , Li ₂ S—SiS ₂ —Al ₂ S ₃ , Li ₂ S—SiS ₂ —P ₂ S ₅ , Li ₂ S—SiS ₂ —P 2S5-LiI, _{Li2S - SiS2} -LiI, _{Li2S - SiS2 - Li4SiO4 , Li2S - SiS2 - Li3PO4} , _Li10GeP2S12 and the like. However, the mixing ratio of each raw material does not matter. An example of a method for synthesizing a sulfide-based inorganic solid electrolyte material using such a raw material composition is an amorphization method. Amorphization methods include, for example, a mechanical milling method, a solution method, and a melt quenching method. This is because the process can be performed at room temperature, and the manufacturing process can be simplified.

(ii) Oxide-Based Inorganic Solid Electrolyte The oxide-based inorganic solid electrolyte contains oxygen atoms, has the ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is electronically insulating. compounds having the properties are preferred.
The ion conductivity of the oxide-based inorganic solid electrolyte is preferably 1×10 ⁻⁶ S/cm or more, more preferably 5×10 ⁻⁶ S/cm or more, and 1×10 ⁻⁵ S/cm or more. /cm or more is particularly preferable. Although the upper limit is not particularly limited, it is practically 1×10 ⁻¹ S/cm or less.

Specific compound examples include Li _xa La _ya TiO ₃ [xa=0.3 to 0.7, ya=0.3 to 0.7] (LLT), Li _xb La _yb Zr _zb M ^bb _mb O _nb (M ^bb is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, xb satisfies 5≦xb≦10, and yb is 1≦yb ≦4, zb satisfies 1≦zb≦4, mb satisfies 0≦mb≦2, and nb satisfies 5≦nb≦20.), Li _{xc Byc} M ^cc _zc O _nc (M ^cc is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, where xc satisfies 0<xc≦5, yc satisfies 0<yc≦1, and zc satisfies 0<zc≦ 1 and nc satisfies 0 < nc ≤ 6.), Li _xd (Al, Ga) _yd (Ti, Ge) _zd Si _ad P _{md Ond} (where 1 ≤ xd ≤ 3, 0 ≤ yd ≤ 1 , 0 ≤ zd ≤ 2, 0 ≤ ad ≤ 1, 1 ≤ md ≤ 7, 3 ≤ nd ≤ 13), Li _(3-2xe) M ^ee _xe D ^ee O (xe is a number from 0 to 0.1 and M ^ee represents a divalent metal atom, D ^ee represents a halogen atom or a combination of two or more halogen atoms), Li _xf Si _yf O _zf (1≦xf≦5, 0<yf≦3 , 1≦zf≦10), Li _{xg SygO zg} (1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ₃ BO ₃ —Li ₂ SO ₄ , Li ₂ OB ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li ₃ PO _(4-3/2w) N _w (w is w<1), LISICON (Lithium superionic conductor ) type crystal structure, La _0.55 Li _0.35 TiO ₃ having a perovskite type crystal structure, and _{LiTi 2} P ₃ having a NASICON ₍ Natrium _superionic conductor) type crystal structure. O ₁₂ , Li _1+xh+yh (Al, Ga) _xh (Ti, Ge) _2-xh Si _yh P _3-yh O ₁₂ (where 0 ≤ xh ≤ 1, 0 ≤ yh ≤ 1), Li having a garnet crystal structure _{7La3Zr _ 2} O ₁₂ (LLZ) and the like. Phosphorus compounds containing Li, P and O are also desirable. For example, lithium phosphate (Li ₃ PO ₄ ), LiPON in which part of the oxygen in lithium phosphate is replaced with nitrogen, LiPOD ¹ (D ¹ is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr , Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.). LiA ¹ ON (A ¹ is at least one selected from Si, B, Ge, Al, C, Ga, etc.) and the like can also be preferably used.

(iii) Halide-Based Inorganic Solid Electrolyte The halide-based inorganic solid electrolyte contains halogen atoms, has the ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is electronically insulating. compounds having the properties are preferred.
Examples of the halide-based inorganic solid electrolyte include, but are not limited to, compounds such as LiCl, LiBr, LiI, and Li ₃ YBr ₆ and Li ₃ YCl ₆ described in ADVANCED MATERIALS, 2018, 30, 1803075. Among them, Li ₃ YBr ₆ and Li ₃ YCl ₆ are preferable.

(iv) Hydride-Based Inorganic Solid Electrolyte The hydride-based inorganic solid electrolyte contains hydrogen atoms, has the ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is electronically insulating. compounds having the properties are preferred.
The hydride-based inorganic solid electrolyte is not particularly limited, but examples thereof include LiBH ₄ , Li ₄ (BH ₄ ) ₃ I, 3LiBH ₄ --LiCl and the like.

The inorganic solid electrolyte is preferably particles. In this case, the particle size (volume average particle size) of the inorganic solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.1 μm or more. The upper limit is preferably 100 μm or less, more preferably 50 μm or less. The particle size of the inorganic solid electrolyte is measured by the following procedure. A 1% by mass dispersion of inorganic solid electrolyte particles is prepared by diluting it in a 20 mL sample bottle with water (heptane for water-labile substances). The diluted dispersion sample is irradiated with ultrasonic waves of 1 kHz for 10 minutes and immediately used for the test. Using this dispersion sample, using a laser diffraction/scattering particle size distribution analyzer LA-920 (trade name, manufactured by HORIBA), data was taken 50 times using a quartz cell for measurement at a temperature of 25 ° C. Obtain the volume average particle size. For other detailed conditions, etc., refer to the description of JIS Z 8828:2013 "Particle Size Analysis-Dynamic Light Scattering Method" as necessary. Five samples are prepared for each level and the average value is adopted.
An inorganic solid electrolyte may be used individually by 1 type, and may use 2 or more types.
The content of the inorganic solid electrolyte in the solid electrolyte composition is not particularly limited, but in terms of dispersibility, reduction of interfacial resistance, and binding properties, it is preferable that the solid content is 100% by mass and 50% by mass or more. It is preferably 70% by mass or more, and particularly preferably 90% by mass or more. The upper limit is not particularly limited and may be 100% by mass, but from the same viewpoint, it is preferably 99.99% by mass or less, more preferably 99.95% by mass or less, and 99 0.9% by mass or less is particularly preferred.
In the present invention, the solid content (solid component) refers to a component that does not disappear by volatilization or evaporation when the solid electrolyte composition is dried at 130° C. for 6 hours under a pressure of 1 mmHg and a nitrogen atmosphere. . Typically, it refers to components other than the dispersion medium described below.

- Binder -
The solid electrolyte composition may contain a binder that binds solid particles such as an inorganic solid electrolyte.
Examples of binders include organic polymers, and known organic polymers used in the production of all-solid secondary batteries can be used without particular limitations. Examples of such organic polymers include fluorine-containing resins, hydrocarbon thermoplastic resins, acrylic resins, polyurethane resins, polyurea resins, polyamide resins, polyimide resins, polyester resins, polyether resins, polycarbonate resins, cellulose derivative resins, and the like. are mentioned. Preferably, the binder is particulate. A binder may be used individually by 1 type, or may use 2 or more types. When the solid electrolyte composition contains a binder, the content of the binder in the solid content of the solid electrolyte composition is not particularly limited, but is preferably 0.1 to 10% by mass, more preferably 1 to 10% by mass. , 2 to 5 mass % is more preferable.

- Dispersion medium -
The solid electrolyte composition of the present invention also preferably contains a dispersion medium.
The dispersion medium should just disperse each component contained in the solid electrolyte composition. In the present invention, the dispersion medium is preferably a non-aqueous dispersion medium containing no water, and is usually selected from organic solvents. In the present invention, the expression that the dispersion medium does not contain water includes not only the embodiment in which the content of water is 0% by mass, but also the embodiment in which the content is 0.1% by mass or less. However, the water content in the solid electrolyte composition is preferably within the above range (non-aqueous composition).
Examples of organic solvents include, but are not limited to, alcohol compounds, ether compounds, amide compounds, amine compounds, ketone compounds, aromatic compounds, aliphatic compounds, nitrile compounds, ester compounds, and the like.
The dispersion medium contained in the solid electrolyte composition may be of one type or two or more types.
The content of the dispersion medium in the solid electrolyte composition is not particularly limited, and is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and particularly preferably 40 to 60% by mass.

- Other ingredients -
The solid electrolyte composition may contain other components.
Other components include, but are not limited to, various additives.
Examples of the above additives include thickeners, cross-linking agents (such as those that undergo a cross-linking reaction by radical polymerization, condensation polymerization, or ring-opening polymerization), polymerization initiators (such as those that generate acid or radicals by heat or light), Antifoaming agents, leveling agents, dehydrating agents, antioxidants and the like can be contained.
The content of other components in the solid electrolyte composition is not particularly limited and is set as appropriate.

- Preparation of solid electrolyte composition -
The solid electrolyte composition can be prepared, for example, as a solid mixture or a slurry by mixing an inorganic solid electrolyte, an appropriate binder, a dispersion medium, other components, and the like, for example, with various commonly used mixers. .
The mixing method is not particularly limited, and can be performed using a known mixer such as a ball mill, bead mill, disc mill, and the like. Also, the mixing conditions are not particularly limited. The mixed atmosphere may be air, dry air (with a dew point of −20° C. or less), inert gas (eg, argon gas, helium gas, nitrogen gas), or the like. Since the inorganic solid electrolyte reacts with moisture, mixing is preferably performed under dry air or in an inert gas.

- Formation of solid electrolyte layer -
The solid electrolyte layer is not particularly limited, but can be formed by a molding method in which a solid electrolyte composition is pressure-molded, or a coating drying method in which a solid electrolyte composition (slurry) containing a dispersion medium is coated and dried, and then preferably pressed, or the like. can be produced by
The method for molding the solid electrolyte composition may be any method as long as the solid electrolyte composition can be molded into a layer or film, and various known molding methods can be applied. press molding) is preferred. The pressure during molding is not particularly limited, but is usually set preferably in the range of 50 to 1500 MPa, more preferably set in the range of 150 to 600 MPa, and set in the range of 100 to 300 MPa. is more preferred. The molding (pressing) time may be short (for example, within several hours) or long (one day or longer).
Although heating may be performed simultaneously with pressurization of the solid electrolyte composition, in the present invention, preforming without heating is preferred. The atmosphere during molding is preferably dry air or inert gas.

Examples of the coating method of the solid electrolyte composition (slurry) include wet coating methods such as spin coating, dip coating, slit coating, stripe coating and bar coating. Although the drying temperature is not particularly limited, for example, 30 to 300°C is preferable, and 60 to 250°C is more preferable.
It is preferable to apply pressure to the dried layer of the solid electrolyte composition. The pressurizing method and pressure are not particularly limited, and for example, the same method and pressure as those of the solid electrolyte composition molding method and pressure can be appropriately employed. This pressurization can also be performed, for example, after laminating an active material layer or the like.

<Step of Forming Negative Electrode Active Material Layer>
When the all-solid-state secondary battery is of a form in which the negative electrode active material layer is formed in advance, the step of forming the negative electrode active material layer is performed in the manufacturing method of the present invention.
When implementing this process, the composition for negative electrodes is prepared.
The negative electrode composition contains a negative electrode active material, preferably an inorganic solid electrolyte and a conductive aid, and further optionally contains a binder, a dispersion medium, a lithium salt and other components. This negative electrode composition may be the negative electrode active material itself, and is preferably a non-aqueous composition.
The inorganic solid electrolyte, binder, dispersion medium and other components that can be used in the negative electrode composition are as described above. Lithium salts used in all-solid secondary batteries can be used without particular limitations.

- Negative electrode active material -
The negative electrode active material used in the present invention is a material capable of inserting and releasing ions of metal elements belonging to Group 1 or Group 2 of the periodic table. The negative electrode active material is preferably one capable of reversibly intercalating and deintercalating lithium ions. The material is not particularly limited as long as it has the above properties, carbonaceous material, metal or metalloid element oxide (including composite oxide), elemental lithium, lithium alloy, or lithium and alloy negative electrode active materials capable of forming an alloy with lithium, and the like. Among them, from the viewpoint of reliability, carbonaceous materials, metalloid element oxides, metal composite oxides, and elemental lithium are preferable. A negative electrode active material that can be alloyed with lithium is preferable from the viewpoint that the capacity of an all-solid secondary battery can be increased.

A carbonaceous material used as a negative electrode active material is a material substantially composed of carbon. For example, petroleum pitch, carbon black such as acetylene black (AB), graphite (natural graphite, artificial graphite such as vapor-grown graphite, etc.), and various synthetics such as PAN (polyacrylonitrile)-based resin or furfuryl alcohol resin A carbonaceous material obtained by baking a resin can be mentioned. Furthermore, various carbon fibers such as PAN-based carbon fiber, cellulose-based carbon fiber, pitch-based carbon fiber, vapor growth carbon fiber, dehydrated PVA (polyvinyl alcohol)-based carbon fiber, lignin carbon fiber, vitreous carbon fiber and activated carbon fiber. , mesophase microspheres, graphite whiskers and tabular graphite.
These carbonaceous materials can be classified into non-graphitizable carbonaceous materials (also referred to as hard carbon) and graphitic carbonaceous materials according to the degree of graphitization. The carbonaceous material preferably has the interplanar spacing or density and crystallite size described in JP-A-62-22066, JP-A-2-6856 and JP-A-3-45473. The carbonaceous material may not be a single material, and a mixture of natural graphite and artificial graphite described in JP-A-5-90844, graphite having a coating layer described in JP-A-6-4516, etc. can be used. can also
As the carbonaceous material, hard carbon or graphite is preferably used, and graphite is more preferably used.

The oxide of a metal or metalloid element that is applied as a negative electrode active material is not particularly limited as long as it is an oxide that can occlude and release lithium. Examples include oxides, composite oxides of metal elements and metalloid elements (collectively referred to as metal composite oxides), and oxides of metalloid elements (semimetal oxides). As these oxides, amorphous oxides are preferable, and chalcogenite, which is a reaction product of a metal element and an element of Group 16 of the periodic table, is also preferable. In the present invention, the metalloid element refers to an element that exhibits intermediate properties between metal elements and non-metalloid elements, and usually includes the six elements boron, silicon, germanium, arsenic, antimony and tellurium, and further selenium. , polonium and astatine. In addition, the term "amorphous" means one having a broad scattering band with an apex in the region of 20° to 40° in 2θ value in an X-ray diffraction method using CuKα rays, and a crystalline diffraction line. may have. The strongest intensity among the crystalline diffraction lines seen at 2θ values of 40° to 70° is 100 times or less than the diffraction line intensity at the top of the broad scattering band seen at 2θ values of 20° to 40°. is preferable, more preferably 5 times or less, and it is particularly preferable not to have a crystalline diffraction line.

Among the compound group consisting of the above amorphous oxides and chalcogenides, amorphous oxides of metalloid elements or the above chalcogenides are more preferable, and elements of groups 13 (IIIB) to 15 (VB) of the periodic table (for example, , Al, Ga, Si, Sn, Ge, Pb, Sb and Bi) are particularly preferable. Specific examples of preferred amorphous oxides and chalcogenides include Ga ₂ O ₃ , GeO, PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₂ O ₄ , Pb ₃ O ₄ , Sb ₂ O ₃ and Sb ₂ . _{O4 , Sb2O8Bi2O3 , Sb2O8Si2O3 , Sb2O5} , _Bi2O3 , _{Bi2O4 , GeS , PbS , PbS2 , Sb2S3 or Sb2 S5} is preferred.
Examples of negative electrode active materials that can be used in combination with amorphous oxides mainly composed of Sn, Si, and Ge include carbonaceous materials capable of absorbing and/or releasing lithium ions or lithium metal, elemental lithium, lithium alloys, and lithium. and a negative electrode active material that can be alloyed with.

From the viewpoint of high current density charge/discharge characteristics, the oxides of metals or semimetals, especially metal (composite) oxides and chalcogenides, preferably contain at least one of titanium and lithium as a constituent component. Examples of lithium-containing metal composite oxides (lithium composite metal oxides) include composite oxides of lithium oxide and the above metal (composite) oxides or chalcogenides, more specifically Li ₂ SnO ₂ . mentioned.
The negative electrode active material, for example, a metal oxide, preferably contains a titanium element (titanium oxide). Specifically, Li ₄ Ti ₅ O ₁₂ (lithium titanate [LTO]) exhibits excellent rapid charge-discharge characteristics due to its small volume fluctuation during lithium ion occlusion and desorption, suppressing electrode deterioration and promoting lithium ion secondary It is preferable in that the life of the battery can be improved.

The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy normally used as a negative electrode active material for secondary batteries, and examples thereof include lithium aluminum alloys.

The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is commonly used as a negative electrode active material for secondary batteries. Such an active material expands and contracts significantly during charging and discharging of an all-solid secondary battery. Examples of the active material include negative electrode active materials (alloys) containing silicon element or tin element, and metals such as Al and In. substance) is preferable, and a silicon element-containing active material having a silicon element content of 50 mol % or more of all constituent elements is more preferable.
In general, negative electrodes containing these negative electrode active materials (Si negative electrodes containing silicon element-containing active materials, Sn negative electrodes containing active materials containing tin elements, etc.) are used as carbon negative electrodes (graphite, acetylene black, etc.). In comparison, more Li ions can be occluded. That is, the amount of Li ions stored per unit mass increases. Therefore, the battery capacity can be increased. As a result, there is an advantage that the battery driving time can be lengthened.
Silicon element-containing active materials include, for example, silicon materials such as Si and SiOx (0<x≦1), and silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, lanthanum, etc. (for example, LaSi ₂ , VSi ₂ , La—Si, Gd—Si, Ni—Si) or organized active materials (e.g. LaSi ₂ /Si), as well as elemental silicon and elemental tin such as SnSiO ₃ , SnSiS ₃ and active materials containing In addition, SiOx itself can be used as a negative electrode active material (semimetal oxide), and since Si is generated by the operation of the all-solid secondary battery, the negative electrode active material that can be alloyed with lithium (the can be used as a precursor substance).
Examples of negative electrode active materials containing tin include Sn, SnO, SnO ₂ , SnS, SnS ₂ , active materials containing silicon and tin, and the like. In addition, composite oxides with lithium oxide, such as Li ₂ SnO ₂ can also be mentioned.

In the present invention, the above-described negative electrode active material can be used without any particular limitation. , the above silicon materials or silicon-containing alloys (alloys containing elemental silicon) are more preferred, and silicon (Si) or silicon-containing alloys are even more preferred.

Although the shape of the negative electrode active material is not particularly limited, it is preferably particulate. The particle size (volume average particle size) of the negative electrode active material is preferably 0.1 to 60 μm. A conventional pulverizer or classifier is used to obtain a predetermined particle size. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a whirling current jet mill, a sieve, and the like are preferably used. At the time of pulverization, wet pulverization can also be performed in which water or an organic solvent such as methanol is allowed to coexist. Classification is preferably carried out in order to obtain a desired particle size. The classification method is not particularly limited, and a sieve, an air classifier, or the like can be used. Both dry and wet classification can be used. The average particle size of the negative electrode active material particles can be measured by the same method as the method for measuring the volume average particle size of the inorganic solid electrolyte described above.

In the present invention, the chemical formula of the compound obtained by the calcination method can be calculated by inductively coupled plasma (ICP) emission spectrometry as a measurement method, or from the difference in mass of the powder before and after calcination as a simple method.

The surface of the negative electrode active material may be surface-coated with another metal oxide. Examples of surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, lithium niobate-based compounds, and specific examples include Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ and LiTaO ₃ . , _LiNbO3 , _LiAlO2 , _{Li2ZrO3 , Li2WO4 , Li2TiO3 , Li2B4O7 , Li3PO4 , Li2MoO4 , Li3BO3 , LiBO2 , Li2CO 3} , Li ₂ SiO ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , B ₂ O ₃ and the like.
Moreover, the surface of the electrode containing the negative electrode active material may be surface-treated with sulfur or phosphorus.
Furthermore, the surface of the particles of the negative electrode active material may be surface-treated with actinic rays or an active gas (such as plasma) before and after the surface coating.

The negative electrode active materials may be used singly or in combination of two or more.
When the negative electrode active material layer is formed, the mass (mg) (basis weight) of the negative electrode active material per unit area (cm ² ) of the negative electrode active material layer is not particularly limited. It can be determined appropriately according to the designed battery capacity.

- Conductive agent -
The negative electrode composition preferably contains a conductive aid, and it is particularly preferred that the silicon element-containing active material as the negative electrode active material is used in combination with the conductive aid.
There is no particular limitation on the conductive aid, and any commonly known conductive aid can be used. For example, electronic conductive materials such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black and furnace black, amorphous carbon such as needle coke, vapor grown carbon fiber or carbon nanotube. Carbon fibers such as carbon fibers such as graphene or fullerene may be used, metal powders such as copper and nickel, metal fibers may be used, and conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives may be used. may be used.
In the present invention, when an active material and a conductive aid are used in combination, among the above conductive aids, a conductive aid that does not cause insertion and release of Li during charging and discharging of the battery and does not function as an active material. and Therefore, among the conductive aids, those that can function as an active material in the active material layer during charging and discharging of the battery are classified as active materials rather than conductive aids. Whether or not it functions as an active material when the battery is charged and discharged is not univocally determined by the combination with the active material.
The shape of the conductive aid is not particularly limited, but is preferably particulate.
1 type may be used for a conductive support agent, and 2 or more types may be used for it.

The content of the negative electrode active material in the negative electrode composition is not particularly limited. More preferably, it is up to 80% by mass.
When the negative electrode composition contains an inorganic solid electrolyte, the total content of the inorganic solid electrolyte and the negative electrode active material in the negative electrode composition is preferably 5% by mass or more with respect to 100% by mass of solid content, It is more preferably 10% by mass or more, particularly preferably 15% by mass or more, even more preferably 50% by mass or more, particularly preferably 70% by mass or more, and 90% by mass or more. Most preferably there is. The upper limit is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and particularly preferably 99% by mass or less.
The content of the conductive aid in the negative electrode composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, based on 100 parts by mass of the solid content.
The contents of the binder and the dispersion medium in the negative electrode composition are not particularly limited, and can be, for example, the above contents in the solid electrolyte composition.
In addition, the contents of the lithium salt and other components in the negative electrode composition are not particularly limited, and can be appropriately set, for example, to the above contents in the solid electrolyte composition.

- Preparation of negative electrode composition -
The negative electrode composition can be prepared in the same manner and under the same conditions as in the preparation of the solid electrolyte composition.

- Formation of negative electrode active material layer -
The negative electrode active material layer is not particularly limited, but can be prepared by the same method and conditions as those for forming the solid electrolyte layer. In forming the negative electrode active material layer, the applied and dried negative electrode composition may be heated at the same time as being pressurized. Although the heating temperature is not particularly limited, it is generally in the range of 30 to 300°C.
The method for forming the negative electrode active material layer on the surface of the solid electrolyte layer opposite to the positive electrode active material layer (the other side) is not particularly limited, and a normal method can be applied. For example, a method of forming a solid electrolyte layer and a negative electrode active material layer and stacking both layers, and a method of forming a negative electrode active material layer or a solid electrolyte layer on the surface of the solid electrolyte layer or the negative electrode active material layer can be mentioned.
The method for laminating both layers is not particularly limited, and examples thereof include a method of pressure lamination, a method of placing the negative electrode active material on the surface of the solid electrolyte layer and applying pressure, and a method of bonding.
The method of laminating under pressure is not particularly limited, but for example, a method of placing (arranging) the negative electrode active material layer on the surface of the solid electrolyte layer and then pressing. In the method of pressure-bonding lamination and the method of pressing the negative electrode active material on the surface of the solid electrolyte layer, the method and conditions for pressure-bonding lamination or pressure are not particularly limited as long as both layers can be pressure-bonded. The pressure may be any pressure that allows the negative electrode active material layer to be pressure-bonded. For example, it can be set to 1 MPa or more, preferably 1 to 150 MPa, more preferably 5 to 60 MPa. Although pressure lamination or pressurization may be carried out under heating, in the present invention, it is preferably carried out without heating, for example, it is more preferably carried out at an ambient temperature of 0 to 50°C. The atmosphere for pressure lamination or pressurization is the same as the atmosphere for preparing the solid electrolyte composition.
The method of bonding is not particularly limited, and for example, a method of placing (arranging) the negative electrode active material layer after applying the electrolytic solution to the surface of the solid electrolyte layer can be mentioned. The electrolytic solution to be used is not particularly limited.

The method for directly forming the negative electrode active material layer or the solid electrolyte layer on the surface of the solid electrolyte layer or the negative electrode active material layer is not particularly limited. Alternatively, a method of coating and drying the solid electrolyte composition may be used. The coating and drying method and conditions are not particularly limited, and for example, the coating and drying method and conditions for the solid electrolyte composition can be applied.

When the all-solid-state secondary battery is of a form in which the negative electrode active material layer is not formed in advance, the negative electrode active material layer is formed by the charging step described below. In this case, instead of the negative electrode active material, a compound that generates ions of a metal belonging to Group 1 or Group 2 of the periodic table (such as a positive electrode active material) is used. A negative electrode active material layer can be formed by combining ions generated from this compound with electrons on or in the vicinity of the negative electrode current collector and depositing them as metal.

<Step of Forming Positive Electrode Active Material Layer>
When performing the step of forming the positive electrode active material layer, a positive electrode composition is prepared.
The positive electrode composition contains a positive electrode active material, a negative electrode active material precursor, preferably an inorganic solid electrolyte and a conductive aid, and further optionally contains a binder, a dispersion medium, a lithium salt and other components. This positive electrode composition is preferably a non-aqueous composition.
The inorganic solid electrolyte, conductive aid, binder, dispersion medium, lithium salt and other components that can be used in the positive electrode composition are as described above.

- Positive electrode active material -
The positive electrode active material used in the present invention is a material capable of inserting and releasing ions of metal elements belonging to Group 1 or Group 2 of the periodic table. A metal oxide (preferably a transition metal oxide) is preferable as the positive electrode active material.

The positive electrode active material is preferably one capable of reversibly intercalating and deintercalating lithium ions. The material is not particularly limited as long as it has the above properties, and may be a transition metal oxide, an element that can be combined with Li such as an organic substance or sulfur, or a composite of sulfur and a metal.
Among them, it is preferable to use ^a transition metal oxide as the positive electrode active material. things are more preferred. Further, the transition metal oxide may contain an element M ^b (an element of group 1 (Ia) of the periodic table of metals other than lithium, an element of group 2 (IIa) of the periodic table, Al, Ga, In, Ge, Sn, Pb, elements such as Sb, Bi, Si, P or B) may be mixed. The mixing amount is preferably 0 to 30 mol % with respect to the amount (100 ^mol %) of the transition metal element Ma. More preferred is one synthesized by mixing so that the Li/M ^a molar ratio is 0.3 to 2.2.
Specific examples of the transition metal oxide include (MA) a transition metal oxide having a layered rock salt structure, (MB) a transition metal oxide having a spinel structure, (MC) a lithium-containing transition metal phosphate compound, (MD ) lithium-containing transition metal halide phosphate compounds and (ME) lithium-containing transition metal silicate compounds.

(MA) Specific examples of transition metal oxides having a layered rocksalt structure include LiCoO ₂ (lithium cobalt oxide [LCO]), LiNi ₂ O ₂ (lithium nickel oxide), LiNi _0.85 Co _0.10 Al 0.5 _{. 05O2 (} lithium nickel cobalt aluminum oxide [NCA]), LiNi1 _{/ 3Co1} / _3Mn1 / _{3O2 (} lithium nickel manganese cobaltate [NMC]) and _{LiNi0.5Mn0.5O2 (} lithium manganese nickelate).
(MB) Specific examples of transition metal oxides having a spinel structure include LiMn ₂ O ₄ (LMO), LiCoMnO ₄ , Li ₂ FeMn ₃ O ₈ , Li ₂ CuMn ₃ O ₈ , Li ₂ CrMn ₃ O ₈ and Li _{2NiMn3O8 . _}
Examples of (MC) lithium-containing transition metal phosphate compounds include olivine-type iron phosphate salts such as LiFePO ₄ and Li ₃ Fe ₂ (PO ₄ ) ₃ , iron pyrophosphates such as LiFeP ₂ O ₇ , and LiCoPO ₄ . and monoclinic Nasicon-type vanadium phosphates such as Li ₃ V ₂ (PO ₄ ) ₃ (lithium vanadium phosphate).
Examples of (MD) lithium-containing transition metal halogenated phosphate compounds include iron fluorophosphates such as Li ₂ FePO ₄ F, manganese fluorophosphates such as Li ₂ MnPO ₄ F, and Li ₂ CoPO ₄ F. and other cobalt fluoride phosphates.
(ME) Lithium-containing transition metal silicate compounds include, for example, Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ and Li ₂ CoSiO ₄ .
In the present invention, transition metal oxides having a (MA) layered rocksalt structure are preferred, and LCO or NMC is more preferred.

Although the shape of the positive electrode active material is not particularly limited, it is preferably particulate. The volume average particle size (average particle size in terms of spheres) of the positive electrode active material is not particularly limited. For example, it can be 0.1 to 50 μm. An ordinary pulverizer or classifier may be used to make the positive electrode active material have a predetermined particle size. The positive electrode active material obtained by the calcination method may be washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent before use. The average particle size of the positive electrode active material particles can be measured by the same method as the method for measuring the volume average particle size of the inorganic solid electrolyte described above.

The surface of the positive electrode active material may be surface-coated with another metal oxide, similar to the negative electrode active material.
The positive electrode active material may be used alone or in combination of two or more.
When the positive electrode active material layer is formed, the mass (mg) (basis weight) of the positive electrode active material per unit area (cm ² ) of the positive electrode active material layer is not particularly limited. It can be determined appropriately according to the designed battery capacity.

- Negative electrode active material precursor -
The negative electrode active material precursor is a compound that generates (releases) ions (metal ions) of a metal element belonging to Group 1 or Group 2 of the periodic table in the positive electrode active material layer by the charging step described later. . The generated metal ions reach the negative electrode active material layer and the like by charging the all-solid secondary battery and pre-dope the negative electrode active material layer. When the all-solid-state secondary battery is in a form in which the negative electrode active material layer is not formed in advance, metal ions reach the negative electrode current collector and combine with electrons to precipitate as metal and pre-dope the negative electrode active material layer.
The negative electrode active material precursor is not particularly limited as long as it has such properties or functions, and examples include compounds containing the above metal elements. It is different from salt in that it decomposes by releasing lithium ions during the initial charge and does not contribute to the release of lithium ions during the next charge. As described above, the negative electrode active material precursor is a compound different from the above-described positive electrode active material in that lithium ions cannot be reversibly intercalated and released by charging and discharging.

The negative electrode active material precursor is preferably an inorganic compound containing the above metal element, more preferably an inorganic salt that generates the above metal ion and anion, and a carbonate or oxidation of the above metal element (alkali metal or alkaline earth metal). more preferred are compounds or hydroxides, particularly preferred are compounds selected from carbonates. The inorganic salt is not particularly limited, but is preferably one that generates gas by decomposition at normal temperature and normal pressure, preferably in a charging environment. For example, carbonates generate metal element ions and carbonate ions through oxidative decomposition. The generated ions of the metal element become constituent materials of the negative electrode active material layer, and the carbonate ions change to carbon dioxide gas and are discharged (disappeared) from the positive electrode active material layer to the outside. Therefore, the carbonate, including decomposition products, does not remain in the positive electrode active material layer, and deterioration of battery characteristics (energy density) due to carbonate inclusion can be avoided.
When the all-solid secondary battery is an all-solid lithium ion secondary battery, the metal element forming the negative electrode active material precursor is preferably lithium.
Examples of negative electrode active material precursors include inorganic salts such as carbonates, oxides, hydroxides, and halides of the above metal elements, and organic salts such as carboxylates (eg, oxalates) of the above metal elements. mentioned. Specific examples of the compound containing lithium element (lithium salt) as the negative electrode active material precursor include, for example, lithium carbonate, lithium oxide, lithium hydroxide, lithium fluoride, lithium chloride, lithium oxalate, lithium iodide, Lithium nitride, lithium sulfide, lithium phosphide, lithium nitrate, lithium sulfate, lithium phosphate, lithium oxalate, lithium formate, lithium acetate, etc., and lithium carbonate, lithium oxide or lithium hydroxide are preferred. Lithium carbonate is more preferable because it can be handled safely (low hygroscopicity).

The positive electrode composition may contain one type of negative electrode active material precursor, or may contain two or more types.
The average particle size of the negative electrode active material precursor is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.1 to 1 μm. The average particle size is a value measured in the same manner as the average particle size of the inorganic solid electrolyte particles described above.

The content of the positive electrode active material in the positive electrode composition is not particularly limited. 55 to 80 mass % is particularly preferred.
When the positive electrode composition contains an inorganic solid electrolyte, the total content of the inorganic solid electrolyte and the positive electrode active material in the positive electrode composition is preferably 5% by mass or more with respect to 100% by mass of solid content, It is more preferably 10% by mass or more, particularly preferably 15% by mass or more, even more preferably 50% by mass or more, particularly preferably 70% by mass or more, and 90% by mass or more. Most preferably there is. The upper limit is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and particularly preferably 99% by mass or less.
The content of the negative electrode active material precursor in the positive electrode composition varies depending on the amount of ions of the metal element to be replenished, etc., and is not uniquely determined. is preferred, more preferably 5 to 30% by mass, even more preferably 7 to 20% by mass. The total content of the positive electrode active material and the negative electrode active material precursor in the positive electrode composition is not particularly limited, and is preferably 70 to 90% by mass.
The content of the conductive aid in the positive electrode composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, based on 100 parts by mass of the solid content.
The contents of the binder and the dispersion medium in the positive electrode composition are not particularly limited, and can be, for example, the above contents in the solid electrolyte composition.
The content of the other components in the positive electrode composition is not particularly limited, and can be set as appropriate, and can be, for example, the content described above for the solid electrolyte composition.

- Preparation of positive electrode composition -
The positive electrode composition can be prepared in the same manner and under the same conditions as in the preparation of the solid electrolyte composition.

- Formation of positive electrode active material layer -
The positive electrode active material layer is not particularly limited, but can be prepared by the same method and conditions as those for forming the solid electrolyte layer. In forming the positive electrode active material layer, it is preferable to heat the applied and dried positive electrode composition simultaneously with pressurization. Although the heating temperature is not particularly limited, it is generally in the range of 30 to 300°C.
The method for forming the positive electrode active material layer on the surface of the solid electrolyte layer on the opposite side (one side) of the solid electrolyte layer from the negative electrode active material layer is not particularly limited, and an ordinary method can be applied. For example, a method of forming a solid electrolyte layer and a positive electrode active material layer and stacking both layers, and a method of forming a positive electrode active material layer or a solid electrolyte layer on the surface of the solid electrolyte layer or the positive electrode active material layer can be used.
As a method for forming the positive electrode active material layer on one surface of the solid electrolyte layer, a positive electrode active material, a positive electrode active material layer, or a positive electrode composition is used instead of the negative electrode active material, the negative electrode active material layer, or the negative electrode composition. Other than that, the same method as the method of forming the negative electrode active material layer on the other surface of the solid electrolyte layer can be used.

As described above, the step of forming the solid electrolyte layer and the positive electrode active material layer is performed to produce a laminate including the positive electrode active material layer and the solid electrolyte layer. Further, when the all-solid secondary battery is in a mode in which a negative electrode active material layer is formed in advance, a step of forming a negative electrode active material layer is further performed, and a laminate including a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer Create a body.
The laminate thus obtained is an all-solid secondary battery before initial charging and compression, and is also called an all-solid secondary battery precursor.

<Step of charging the laminate>
In the manufacturing method of the present invention, the step of charging the obtained laminate is then performed.
The charging conditions may be any conditions as long as the negative electrode active material precursor in the positive electrode active material layer can be oxidatively decomposed, and examples thereof include the following conditions.
Current: 0.05-1mA/ ^cm2
Voltage: 4.2-4.5V
Charging time: 1-20 hours Temperature: 25-60°C
The step of charging releases the anions (compounds generated from) of the precursor of the negative electrode active material to the outside of the laminate, so it is preferable to perform the step in the open rather than sealing the laminate. The atmosphere at this time is the same as in the preparation of the solid electrolyte composition.
It is preferable that the step of charging is performed while pressurizing and constraining the stack in the stacking direction. This makes it possible to suppress problems due to volume fluctuation of the negative electrode active material layer (for example, damage to the solid electrolyte layer). The pressure at this time is not particularly limited, but is preferably 0.05 MPa or more, more preferably 1 MPa. The upper limit may be any pressure that does not compress the positive electrode active material layer, and is preferably less than 10 MPa, more preferably 8 MPa or less, for example.
In this step, charging may be performed once or multiple times.

By this charging step, the negative electrode active material precursor in the positive electrode active material layer is oxidatively decomposed to generate metal ions and anions. The generated metal ions move to or near the negative electrode active material layer and dope the negative electrode active material layer. On the other hand, although the anions may remain in the positive electrode active material layer, they are preferably changed to gas and released to the outside of the laminate. Thus, in the production method of the present invention, pre-doping can be performed safely and simply without using lithium metal or the like.
Thus, when charging is completed, voids originating from the oxidatively decomposed negative electrode active material precursor are generated in the positive electrode active material layer.
The porosity of the positive electrode active material layer after charging (the porosity of the total voids including the voids derived from the negative electrode active material precursor) depends on the type or particle size of the positive electrode active material, conditions for forming the positive electrode active material layer, and the negative electrode active material. Since it varies depending on the type, particle size, content, etc. of the precursor, it is not unambiguously determined, but it can be, for example, 5 to 30%, preferably 15 to 25%.
The porosity of the positive electrode active material layer is measured by the following method. That is, an arbitrary cross section of the positive electrode active material layer is observed with a scanning electron microscope (SEM), the obtained SEM photograph is taken at a magnification of 30,000 times, and the area of the void in a field of view of 3 μm × 2.5 μm is obtained, It is calculated as a value (percentage) obtained by dividing this area by the visual field area (7.5 μm ² ).

In all-solid-state secondary batteries in which a negative electrode active material layer is not formed in advance, a negative electrode current collector or the like that can serve as a scaffold for depositing ions of metals belonging to Group 1 or Group 2 of the periodic table can be appropriately used. . By this charging step, not only the dope due to the decomposition of the negative electrode active material precursor but also the negative electrode active material layer is formed.

<Step of discharging laminate>
In the production method of the present invention, a step of discharging the laminate can also be performed.
Discharge conditions are not particularly limited, and include, for example, the following conditions.
Current: 0.05-1mA/ ^cm2
Voltage: 2.5-3.0V
Charging time: 1-20 hours Temperature: 25-60°C
The step of discharging is preferably carried out with the laminate open, in that the negative ions of the precursor of the negative electrode active material can be released to the outside of the laminate. The atmosphere at this time is the same as in the preparation of the solid electrolyte composition.
The step of discharging is preferably performed while pressurizing and constraining the stack in the stacking direction. Thereby, the adhesion between the current collector and the electrode layer can be maintained. The pressure at this time is not particularly limited, and can be set within the above pressure range in the charging step, and may be the same as or different from the pressure in the charging step.
In this step, discharging may be performed once or multiple times.

By this discharging step, metal ions are generated from the negative electrode active material layer or its vicinity and reach the positive electrode active material layer. However, the positive electrode active material incorporating metal ions and further metal ions does not completely fill the voids derived from the negative electrode active material precursor, and the positive electrode active material layer has voids that are crushed in the compression step described later. (remaining).
The porosity of the positive electrode active material layer after discharge is not particularly limited, but can be, for example, 10% or more, preferably 20% or more.
In the all-solid-state secondary battery in which the negative electrode active material layer is not formed in advance, the metal deposited by the charging step is ionized and moves to the positive electrode active material layer (the negative electrode active material layer is reduced in volume). or disappear).
In the present invention, charging by the charging step is called initial charging, and discharging by the discharging step is called initial discharging. The initial charge and the initial discharge are collectively referred to as initialization, and the initialization may be performed for one cycle or a plurality of cycles, with one initial charge and one initial discharge as one cycle.

<Step of Compressing Positive Electrode Active Material Layer>
In the manufacturing method of the present invention, the step of pressurizing and compressing the positive electrode active material layer is then performed.
Through this step, voids formed in the positive electrode active material layer after charging or voids remaining in the positive electrode active material layer after discharging are crushed (crushed), and the positive electrode active material layer is thinned (densified). do. As a result, the total thickness (volume) of the all-solid secondary battery is reduced, and the energy density is improved.
In the compressing step, it is sufficient that at least the positive electrode active material layer can be compressed. It is preferred to compress the material layer.

The method of pressurizing and compressing the positive electrode active material layer is not particularly limited, and various known pressurization methods can be applied, and pressurization (for example, pressurization using a hydraulic cylinder press) is preferable. The pressure in this step is not particularly limited as long as it is a pressure that can crush the voids, and is preferably higher than the pressure restraint in the charging step. The pressure is appropriately determined depending on the type or content of the positive electrode active material, the amount of voids, etc., and is preferably set in the range of 10 to 1000 MPa, for example. The lower limit of the pressure is more preferably 40 MPa or higher, more preferably 50 MPa or higher, particularly preferably 60 MPa or higher, most preferably 80 MPa or higher, and the upper limit is more preferably 1000 MPa or lower, and further preferably 750 MPa or lower. The pressing time is not particularly limited, and may be short (for example, within several hours) or long (one day or longer).
Although the positive electrode active material layer may be heated at the same time as being pressurized and compressed, in the present invention, it is preferable to pressurize and compress without heating. For example, it is preferable to pressurize and compress at an ambient temperature of 10 to 50°C. . The atmosphere during compression is not particularly limited, and includes a mixed atmosphere of the solid electrolyte composition.

The compressing step is preferably performed without applying voltage (not charging/discharging) to at least the positive electrode active material layer, usually the all-solid secondary battery precursor. In the present invention, "no voltage is applied" includes not only a mode in which no voltage is applied to the positive electrode active material layer, etc., but also a mode in which a voltage of 2.5 to 3.0 V corresponding to the final voltage of the initial discharge is applied. do.

The compression of the positive electrode active material layer is performed until the porosity of the positive electrode active material layer after compression becomes smaller than the porosity of the positive electrode active material layer after charging. Ideally, this compression is performed until the voids derived from the negative electrode active material precursor are completely crushed (until the porosity of the positive electrode active material layer before charging is reached), but in reality, it is performed before charging. up to the vicinity of the porosity of the positive electrode active material layer. For example, it is compressed to a porosity higher than the porosity of the positive electrode active material layer before charging by 1.5%, preferably 1%, more preferably 0.5%.
This compressing step compresses the positive electrode active material layer (crushing the voids), and is different from pressure restraint preferably applied when using an all-solid secondary battery.

In general, when producing an all-solid secondary battery, a laminate (all-solid secondary battery precursor) having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer depending on the form of the all-solid secondary battery is It does not press with such pressure that the layer is compressed. This is because if voids exist in the negative electrode active material layer and the positive electrode active material layer, cracks or cracks will occur in the solid electrolyte layer existing between both layers, and the secondary battery will not function sufficiently.
However, in the manufacturing method of the present invention, since the step of compressing the positive electrode active material layer is performed after the step of charging, voids derived from the negative electrode active material precursor are formed in the positive electrode active material layer of the laminated body to be compressed. The number of voids in the negative electrode active material layer has hardly increased after the formation of the negative electrode active material layer. In the manufacturing method of the present invention, in which the void amount is set for the positive electrode active material layer and the negative electrode active material layer and the laminate is pressurized, the positive electrode active material layer can be formed without causing cracks or cracks in the solid electrolyte layer. Can be compressed. The occurrence of cracks and the like in the solid electrolyte layer can be more effectively suppressed by not performing the discharging step immediately before the compressing step (performing the charging step and the compressing step without intervening the discharging step). .

As described above, the compression step is performed to manufacture an initially charged, preferably initialized, all-solid secondary battery. This all-solid secondary battery exhibits high battery capacity and high energy density as described above.

The present invention will be described in more detail below based on examples. In addition, this invention is not limited and interpreted by this. "Parts" and "%" representing compositions in the following examples are based on mass unless otherwise specified.

<Synthesis Example 1: Synthesis of sulfide-based inorganic solid electrolyte Li—P—S-based glass>
As a sulfide-based inorganic solid electrolyte, T.I. Ohtomo, A.; Hayashi, M.; Tatsumisago, Y.; Tsuchida, S.; Hama, K.; Kawamoto, Journal of Power Sources, 233, (2013), pp231-235; Hayashi, S.; Hama, H.; Morimoto, M.; Tatsumisago, T.; Minami, Chem. Lett. , (2001), pp872-873, Li-P-S based glass was synthesized.

Specifically, in a glove box under an argon gas atmosphere (dew point −70° C.), 2.42 g of lithium sulfide (Li ₂ S, manufactured by Aldrich, purity >99.98%), diphosphorus pentasulfide (P ₂ S ₅ , manufactured by Aldrich, purity >99%) (3.90 g) was weighed, put into an agate mortar, and mixed for 5 minutes using an agate pestle. The mixing ratio of Li ₂ S and P ₂ S ₅ was Li ₂ S:P ₂ S ₅ =75:25 in terms of molar ratio.
Sixty-six zirconia beads with a diameter of 5 mm were put into a 45 mL zirconia container (manufactured by Fritsch), and then the entire mixture of lithium sulfide and phosphorus pentasulfide was added, and the container was sealed under an argon gas atmosphere. This container is set in a planetary ball mill P-7 (trade name) manufactured by Fritsch, and mechanical milling is performed at a temperature of 25 ° C. and a rotation speed of 510 rpm for 20 hours to obtain a yellow powdery sulfide-based inorganic solid electrolyte (Li-P- S-based glass) 6.20 g was obtained. The ionic conductivity was 0.28 mS/cm. The particle size of the Li—P—S glass measured by the above measurement method was 1 μm.

Example 1
In this example, an all-solid secondary battery having a positive electrode active material layer containing a negative electrode active material precursor and a Si negative electrode (negative electrode active material layer) was manufactured.
<Preparation of solid electrolyte sheet>
100 mg of the synthesized sulfide-based inorganic solid electrolyte was placed in a Macor (registered trademark) cylinder with an inner diameter of 10 mm and pressed for 1 minute under an argon gas atmosphere at 25° C. and a pressure of 180 MPa. Thus, a solid electrolyte sheet made of a sulfide-based inorganic solid electrolyte (thickness: 600 μm) was obtained.

<Production of negative electrode sheet>
- Preparation of negative electrode composition -
66 zirconia beads with a diameter of 5 mm were put into a zirconia 45 mL container (manufactured by Fritsch), 9.0 g of the Li—P—S glass synthesized in Synthesis Example 1 above, and modified polyvinylidene fluoride resin (PVDF) as a binder. After adding 1.3 g of particles of (4500-20 (trade name), manufactured by Arkema) and 12 g of diisobutyl ketone as a dispersion medium, this container was set in a planetary ball mill P-7 (trade name, manufactured by Fritsch), Stirring was continued for 2 hours at a temperature of 25° C. and a rotation speed of 300 rpm.
Further, 9.0 g of Si powder (Silicon Powder, average particle size 1 to 5 μm according to the above measurement method, manufactured by Alfa Aesar) and 0.9 g of acetylene black as a conductive agent were added, and 5 g of diisobutyl ketone was added. was set in a planetary ball mill P-7 (trade name, manufactured by Fritsch), and stirring was continued for 5 minutes at a temperature of 25° C. and a rotation speed of 150 rpm. Thus, a negative electrode composition (slurry) was prepared.
- Formation of negative electrode active material layer -
The prepared negative electrode composition was wet-coated on a copper foil having a thickness of 8 μm at a basis weight of 2 mg/diameter of 10 mm, dried at 100° C., and temporarily pressed at 180 MPa to form a Si negative electrode active material layer. .
Thus, a negative electrode sheet having a copper foil and a Si negative electrode active material layer (thickness: 30 μm) was produced.

<Lamination of Solid Electrolyte Sheet and Negative Electrode Sheet>
A disc-shaped negative electrode sheet having a diameter of 10 mm was punched out from the prepared negative electrode sheet so that the Si negative electrode active material layer of the disc-shaped negative electrode sheet was in contact with the surface of the disc-shaped solid electrolyte sheet which was punched out from the solid electrolyte sheet into a disc shape having a diameter of 10 mm. The negative electrode sheet was laminated on the solid electrolyte sheet, and pressure-bonded in an argon gas atmosphere at 25° C. and a pressure of 24 MPa for 1 minute. In this way, a negative electrode sheet laminated with a solid electrolyte layer was produced.

<Preparation of positive electrode sheet>
Next, a positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer was produced.
- Preparation of positive electrode composition -
66 zirconia beads with a diameter of 5 mm were added to a zirconia 45 mL container (manufactured by Fritsch), and 2.0 g of the Li—P—S glass synthesized in Synthesis Example 1 above and styrene-butadiene rubber (product code 182907, Aldrich Co., Ltd.) and 22 g of octane as a dispersion medium were added. After that, this container was set in a planetary ball mill P-7 manufactured by Fritsch, and stirred at a temperature of 25° C. and a rotation speed of 300 rpm for 2 hours. After that, 7.11 g of a positive electrode active material LiNi _0.85 Co _0.10 Al _0.05 O ₂ (lithium nickel cobalt aluminum oxide) and Li ₂ CO ₃ (lithium carbonate, average particle size 1 μm) as a negative electrode active material precursor. 0.79 g was put into the container, and the container was again set in the planetary ball mill P-7, and the mixing was continued for 15 minutes at a temperature of 25° C. and a rotation speed of 100 rpm. Thus, a positive electrode composition (slurry) containing the negative electrode active material precursor was obtained.
Next, on an aluminum foil having a thickness of 20 μm as a current collector, the positive electrode composition obtained above is applied with a basis weight of 15 mg / diameter 10 mm with a baker applicator, heated at 80 ° C. for 2 hours, and the positive electrode The composition for drying was dried. Then, using a heat press, the positive electrode layer composition dried to a predetermined density was heated (120° C.) and pressurized (600 MPa, 1 minute). Thus, a positive electrode sheet having an aluminum foil and a positive electrode active material layer (thickness: 110 μm) was produced.

<Production of all-solid secondary battery>
- Production of laminate -
A positive electrode active material layer of a disk-shaped positive electrode sheet punched out from the prepared positive electrode sheet into a disk shape with a diameter of 10 mm is laminated with a solid electrolyte layer. It was attached by applying a liquid mixed with polyethylene oxide (PEO). Thus, a disk-shaped laminate (all-solid secondary battery precursor) composed of the Si negative electrode current collector, the Si negative electrode active material layer, the solid electrolyte layer, the positive electrode active material layer, and the positive electrode current collector was obtained. .
- Charging process (initial charging) -
The resulting disk-shaped laminate was constrained in the lamination direction with a confining pressure of 8 MPa, and was initially charged under conditions of a current of 0.09 mA/cm ² , a voltage of 4.2 V, a charging time of 20 hours, and a temperature of 25°C. Due to this initial charge, lithium ions generated from lithium carbonate were doped into the Si negative electrode active material layer as a lithium alloy, and carbon dioxide gas was released to the outside of the battery. When the positive electrode active material layer after the initial charge was observed, the porosity (according to the above measurement method) increased by 7% to 15% compared to the positive electrode active material layer before the initial charge.
- Compression process -
After initial charging, the disk-shaped laminate was released from restraint, a pressure of 100 MPa was applied between the positive electrode current collector and the Si negative electrode current collector, and the disk-shaped laminate after the initial charge was pressed in the stacking direction. , compressed the positive electrode active material layer. This compression was performed using a heat press at room temperature (25° C.) for 1 hour without applying voltage (charging and discharging) to the disk-shaped laminate.
When this positive electrode active material layer was observed, it was found that the porosity of the positive electrode active material layer before initial charging was increased by 1% (a state in which the voids corresponding to the porosity of 6% in the positive electrode active material layer before initial charging were crushed). ) was compressed (thinned).
Thus, an all-solid secondary battery having the layer structure shown in FIG. 1 was manufactured.

Comparative example 1
An all-solid secondary battery was manufactured in the same manner as in Example 1, except that the pressure in the compressing step was set to 8 MPa. The positive electrode active material layer in this all-solid secondary battery had a porosity of 7% and was not compressed (thinned) before and after the compression step.

Comparative example 2
In this example, an all-solid secondary battery having a positive electrode active material layer containing no negative electrode active material precursor and a Si negative electrode (Si negative electrode active material layer) was manufactured.
In the method for producing an all-solid secondary battery of Example 1, the following positive electrode composition was used (the positive electrode sheet was prepared in the same manner as in Example 1), and the compression step was not performed. An all-solid secondary battery having a positive electrode active material layer containing no negative electrode active material precursor was produced in the same manner as in the production of the all-solid secondary battery of Example 1.
- Preparation of positive electrode composition -
66 zirconia beads with a diameter of 5 mm were added to a zirconia 45 mL container (manufactured by Fritsch), and 2.0 g of the Li—P—S glass synthesized in Synthesis Example 1 above and styrene-butadiene rubber (product code 182907, Aldrich Co., Ltd.) and 22 g of octane as a dispersion medium were added. After that, this container was set in a planetary ball mill P-7 manufactured by Fritsch, and stirred at a temperature of 25° C. and a rotation speed of 300 rpm for 2 hours. After that, 7.9 g of the positive electrode active material LiNi _0.85 Co _0.10 Al _0.05 O ₂ (lithium nickel-cobalt aluminum oxide) was put into the container, and the container was again set in the planetary ball mill P-7 and heated to 25°C. C. and 100 rpm, mixing was continued for 15 minutes. Thus, a positive electrode composition was obtained.

<Evaluation: Charge-discharge cycle characteristic test>
Before conducting the charge-discharge cycle characteristic test, each all-solid secondary battery prepared above was constrained in the stacking direction with a confining pressure of 8 MPa, 0.09 mA / cm ² , final voltage 2.5 V, charging time 18 hours. Initial discharge was performed at a temperature of 25° C. for initialization.
Next, using each all-solid secondary battery, (rapid) charging and discharging were performed under the following conditions, and a charge-discharge cycle characteristics test (severe accelerated conditions) was carried out.
(conditions)
A charge/discharge cycle of charging to 4.25 V at a current density of 2.2 mA/cm ² and discharging to 2.5 V at a current density of 2.2 mA/cm ² was set as one cycle, and seven cycles were repeated.

The charge-discharge cycle characteristics were evaluated by measuring the charge capacity and discharge capacity for each cycle and obtaining the charge-discharge efficiency from the following formula.

Formula: charge and discharge efficiency (%) = [discharge capacity / charge capacity] × 100

The results of the charge/discharge cycle characteristic test are shown below.
Example 1
The all-solid secondary battery of Example 1 had a 7-cycle discharge capacity equivalent to that of Comparative Example 2 using 7.9 g of the positive electrode active material NCA (with the same basis weight of the positive electrode active material). As a result, it was confirmed that this all-solid secondary battery exhibited a discharge capacity equivalent to that of Comparative Example 2, and that the battery volume was reduced due to the thinning of the positive electrode active material layer, and the volumetric energy density was improved. .
Moreover, the charging/discharging efficiency of all 7 cycles was stable at 99%. It can be seen that this can suppress the occurrence of a short circuit. Moreover, interfacial peeling between the negative electrode active material layer and the solid electrolyte layer due to volume expansion and contraction of the negative electrode active material layer can be prevented, and a high discharge capacity is maintained.
When the cross section of the solid electrolyte layer was observed by SEM after ion beam milling, no cracks or cracks were observed.

Comparative example 1
In the all-solid secondary battery of Comparative Example 1, since the positive electrode active material layer was not compressed, no improvement in volumetric energy density could be confirmed.
Comparative example 2
In the all-solid secondary battery of Comparative Example 2, since the positive electrode active material layer does not contain the negative electrode active material precursor, it is not possible to compensate for the decrease in the amount of lithium metal in the Si negative electrode active material layer, and the discharge capacity is reduced. Not enough. Moreover, since the thickness of the positive electrode active material layer was constant (unchanged), no improvement in the volumetric energy density could be confirmed.

While we have described our invention in conjunction with embodiments thereof, we do not intend to limit our invention in any detail to the description unless specified otherwise, which is contrary to the spirit and scope of the invention as set forth in the appended claims. I think it should be interpreted broadly.

This application claims priority based on Japanese Patent Application No. 2019-060215 filed in Japan on March 27, 2019, the contents of which are incorporated herein by reference. taken in as a part.

1 negative electrode current collector 2 negative electrode active material layer 3 solid electrolyte layer 4 positive electrode active material layer 5 positive electrode current collector 6 operating part 10 all-solid secondary battery

Claims (9)

A method for manufacturing an all-solid secondary battery having a solid electrolyte layer containing an inorganic solid electrolyte and a positive electrode active material layer on one surface of the solid electrolyte layer,
forming a positive electrode active material layer on one surface of the solid electrolyte layer using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor;
charging a laminate including the positive electrode active material layer and the solid electrolyte layer;
a step of pressurizing and compressing at least the positive electrode active material layer after the charging step;
After the compressing step, a step of discharging at least the laminated body in which the positive electrode active material layer is compressed;
A method for manufacturing an all-solid secondary battery. 2. The method for manufacturing an all-solid secondary battery according to claim 1, wherein in said compressing step, said laminate is pressurized with a pressure of 10 to 1000 MPa. 3. The method for manufacturing an all-solid secondary battery according to claim 2, wherein said pressure is 80 MPa or higher. 4. The method for producing an all-solid secondary battery according to claim 1, wherein the charging step is performed while the laminate is pressurized and constrained in the stacking direction. The method for manufacturing an all-solid secondary battery according to any one of claims 1 to 4, wherein the compressing step is performed without applying a voltage to the laminate. 6. The negative electrode active material precursor according to any one of claims 1 to 5, wherein the negative electrode active material precursor is at least one compound selected from carbonates, oxides and hydroxides of alkali metals or alkaline earth metals. A method for manufacturing an all-solid secondary battery. The method for producing an all-solid secondary battery according to any one of claims 1 to 6, wherein said all-solid secondary battery has a negative electrode active material layer on the other surface of said solid electrolyte layer. The all-solid secondary battery according to claim 7, which has a step of forming the negative electrode active material layer using a negative electrode composition containing silicon or an alloy containing silicon element before the charging step. manufacturing method. An all-solid secondary battery obtained by the method for producing an all-solid secondary battery according to any one of claims 1 to 8.

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