JP7304578B2 - All-solid battery - Google Patents

Description

The present disclosure relates to a positive electrode layer, a negative electrode layer, a solid electrolyte layer, and an all-solid battery using the same.

2. Description of the Related Art In recent years, the development of reusable secondary batteries has been demanded due to the reduction in weight and cordlessness of electronic devices such as personal computers and mobile phones. Secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, lead-acid batteries, and lithium-ion batteries. Among these, lithium-ion batteries are attracting attention due to their features such as light weight, high voltage and high energy density.

Lithium ion batteries are composed of a positive electrode layer, a negative electrode layer, and an electrolyte disposed therebetween. Or a solid electrolyte is used. Lithium-ion batteries, which are currently in wide use, are flammable because they use electrolytes containing organic solvents. Therefore, there is a need for materials, structures and systems to ensure the safety of lithium-ion batteries. On the other hand, by using a nonflammable solid electrolyte as the electrolyte, it is expected that the above-mentioned materials, structures and systems can be simplified, and the energy density can be increased, the manufacturing cost can be reduced, and the productivity can be improved. It is possible. A lithium-ion battery using a solid electrolyte is hereinafter referred to as an "all-solid battery".

Solid electrolytes can be roughly divided into organic solid electrolytes and inorganic solid electrolytes. The organic solid electrolyte has an ionic conductivity of about 10 ⁻⁶ S/cm at 25° C., which is extremely low compared to the ionic conductivity of the electrolytic solution, which is about 10 ⁻³ S/cm. Therefore, it is difficult to operate an all-solid-state battery using an organic solid electrolyte in an environment of 25°C. Inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. The ionic conductivity of these materials is about 10 ⁻⁴ to 10 ⁻³ S/cm, which is relatively high. Oxide-based solid electrolytes have high grain boundary resistance. Therefore, sintering the powder and thinning the film have been investigated as a means of lowering the grain boundary resistance. Due to mutual diffusion, it is difficult to obtain sufficient characteristics. Therefore, all-solid-state batteries using oxide-based solid electrolytes are mainly studied in thin films. On the other hand, since sulfide-based solid electrolytes have lower grain boundary resistance than oxide-based solid electrolytes, good characteristics can be obtained only by compression molding of powder, so research has been actively promoted in recent years. there is

Under such circumstances, all-solid-state batteries, for example, as batteries for vehicles, are required to have a higher battery capacity. However, there is a problem that the cracks due to expansion and contraction due to charging and discharging become conspicuous and the durability of the all-solid-state battery decreases.

On the other hand, in Patent Document 1, as shown in FIG. The porosity of the positive electrode mixture layer 212 increases from the solid electrolyte layer 240 interface side to the positive electrode current collector 211 interface side of 212, and the porosity in the positive electrode mixture layer 212 is closer to the positive electrode current collector 211 interface side from the solid electrolyte layer 240 interface side. An all-solid-state battery 300 is disclosed that is becoming larger.

JP 2012-104270 A

However, in the configuration of the conventional all-solid-state battery, it is difficult to achieve both high durability and high battery capacity of the all-solid-state battery. Therefore, the present disclosure provides an all-solid-state battery with high battery capacity and improved durability.

In order to solve the above problems, an all-solid-state battery in the present disclosure includes a positive electrode current collector and a positive electrode layer formed on the positive electrode current collector and including a positive electrode mixture layer containing at least a positive electrode active material and a solid electrolyte. a negative electrode current collector; and a negative electrode layer comprising a negative electrode mixture layer formed on the negative electrode current collector and containing at least a negative electrode active material and a solid electrolyte; the positive electrode mixture layer and the negative electrode mixture layer; a solid electrolyte layer disposed between and containing at least a solid electrolyte having ionic conductivity; The active material volume ratio, which is the volume ratio, increases in the thickness direction of the positive electrode mixture layer as it approaches the positive electrode current collector interface side from the solid electrolyte layer interface side of the positive electrode mixture layer. In the thickness direction of the positive electrode mixture layer, the porosity of the agent layer decreases as the positive electrode mixture layer approaches the positive electrode current collector interface side from the solid electrolyte layer interface side.

According to the present disclosure, it is possible to provide an all-solid-state battery with high battery capacity and improved durability.

FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery in this embodiment. FIG. 2 is a schematic diagram of the roll-pressing step of the positive electrode mixture layer when the volume ratio of the active material in the second positive electrode mixture layer is 0.5 or more in the present embodiment. FIG. 3 is a schematic diagram of the roll-pressing step of the positive electrode mixture layer when the volume ratio of the active material in the second positive electrode mixture layer is less than 0.5 in the present embodiment. FIG. 4 is a schematic cross-sectional view showing an example of an all-solid-state battery in a modified example of the present embodiment. FIG. 5 is a schematic cross-sectional view showing an example of a conventional all-solid-state battery.

(Knowledge leading to this disclosure)
In the conventional technique of Patent Document 1, in particular, in order to increase the battery capacity of an all-solid-state battery, the active material concentration in the electrode active material layer such as the positive electrode mixture layer (active material volume / [active material volume + solid electrolyte volume]) is greater than 0.7, the ratio of the solid electrolyte that exhibits the function of maintaining the shape of the electrode active material layer by connecting the active materials and securing the ion conduction path is becomes very low. Furthermore, since the electrode active material layer has a structure in which the porosity increases as it gets closer to the current collector interface containing more active material, the voids have the function of maintaining the shape of the electrode active material layer and the ion conduction path. There is a problem that the function to ensure is further hindered, and the durability and battery capacity are lowered.

The present disclosure has been made based on such findings, and provides an all-solid-state battery with high battery capacity and improved durability.

An all-solid-state battery in one aspect of the present disclosure includes a positive electrode current collector, a positive electrode layer formed on the positive electrode current collector and including a positive electrode mixture layer containing at least a positive electrode active material and a solid electrolyte, and a negative electrode current collector. and a negative electrode layer formed on the negative electrode current collector and including a negative electrode mixture layer containing at least a negative electrode active material and a solid electrolyte, and disposed between the positive electrode mixture layer and the negative electrode mixture layer. and a solid electrolyte layer containing at least a solid electrolyte having ionic conductivity, wherein the ratio of the volume of the positive electrode active material to the sum of the volume of the positive electrode active material and the volume of the solid electrolyte in the positive electrode mixture layer is The volume ratio of the active material increases in the thickness direction of the positive electrode mixture layer as it approaches the positive electrode current collector interface side from the solid electrolyte layer interface side of the positive electrode mixture layer, and the voids in the positive electrode mixture layer In the thickness direction of the positive electrode mixture layer, the ratio decreases as the positive electrode mixture layer approaches the positive electrode current collector interface side from the solid electrolyte layer interface side.

In the present disclosure, “in the thickness direction of the positive electrode mixture layer, it becomes larger as it approaches the positive electrode current collector interface side from the solid electrolyte layer interface side of the positive electrode mixture layer” means that the active material volume ratio is It means increasing from the solid electrolyte layer interface side of the mixture layer toward the positive electrode current collector interface side, more specifically, the local active material volume ratio of two different parts in the positive electrode mixture layer When compared, it means that the local active material volume ratio in the portion closer to the positive electrode current collector in the positive electrode mixture layer is higher than the local active material volume ratio in the portion closer to the solid electrolyte layer. The increase in the active material volume ratio in this case includes a continuous increase such as a gradient increase, a linear increase, and an intermittent increase such as a stepwise increase.

In addition, "the porosity of the positive electrode mixture layer becomes smaller as it approaches the positive electrode current collector interface side from the solid electrolyte layer interface side of the positive electrode mixture layer" means that the porosity of the positive electrode mixture layer decreases from the solid electrolyte layer interface side of the positive electrode mixture layer to the positive electrode layer interface side. It means that it decreases toward the current collector interface side, and more specifically, when comparing the local porosity of two different parts in the positive electrode mixture layer, the positive electrode collector It means that the local porosity of the portion closer to the electrode is smaller than the local porosity of the portion closer to the solid electrolyte layer. The porosity reduction in this case includes continuous reduction such as gradient reduction and linear reduction, and intermittent reduction such as stepwise reduction.

According to the present disclosure, the volume ratio of the active material in the positive electrode mixture layer increases toward the interface side between the positive electrode mixture layer and the positive electrode current collector, and the porosity of the positive electrode mixture layer increases with the positive electrode mixture layer. It becomes smaller as it approaches the interface side with the positive electrode current collector. As a result, even in a positive electrode mixture layer having a composition for high battery capacity in which the active material volume ratio of the positive electrode active material is large, the portion of the positive electrode mixture layer near the positive electrode current collector, in which the active material volume ratio is particularly high, does not Since the positive electrode active materials are close to each other in the mixture layer, the expansion and contraction of the positive electrode active materials are mutually restrained, thereby obtaining the effect of suppressing damage such as cracks in the positive electrode mixture layer. be done. In addition, since the porosity is relatively high in the portion of the positive electrode mixture layer near the solid electrolyte layer, where the influence of the expansion and contraction of the positive electrode active material is likely to become apparent, the influence of the expansion and contraction of the positive electrode active material is suppressed by the voids. can be absorbed.

Furthermore, the solid electrolyte maintains the shape of the electrode by connecting the positive electrode active materials, and exhibits the function of securing the ion conduction path. Even in the positive electrode mixture layer, the porosity is small in the portion of the positive electrode mixture layer near the positive electrode current collector, where the volume ratio of the solid electrolyte is particularly small. is not lost due to the influence of voids, and an ionic conduction path can be secured. In addition, since the volume ratio of the solid electrolyte is relatively large in the portion of the positive electrode mixture layer near the solid electrolyte layer, an ion conduction path to the solid electrolyte layer is easily secured.

Therefore, even when a positive electrode mixture layer having a composition for high battery capacity is provided, the durability of the all-solid-state battery can be improved, and the all-solid-state battery has a high battery capacity and improved durability. becomes.

Further, for example, in the all-solid-state battery, the solvent contained in at least one layer selected from the group consisting of the positive electrode mixture layer, the negative electrode mixture layer, and the solid electrolyte layer has a concentration of 50 ppm or less, and , the concentration of the binder may be 100 ppm or less.

As a result, at least one layer selected from the group consisting of the positive electrode mixture layer, the negative electrode mixture layer, and the solid electrolyte layer contains almost no solvent or binder, so that deterioration of the solid electrolyte due to the influence of the solvent can be suppressed. , battery capacity is improved by not containing a binder that does not contribute to battery characteristics. Therefore, an all-solid-state battery with higher battery capacity and improved durability is obtained.

Further, for example, in the all-solid-state battery, the active material volume ratio of a portion of the positive electrode mixture layer near the positive electrode current collector may be greater than 0.7.

As a result, the active material volume ratio of the positive electrode active material in the portion close to the positive electrode current collector increases, so that the amount of lithium ions in the positive electrode mixture layer can be increased, resulting in an all-solid-state battery with a higher battery capacity.

Further, for example, in the all-solid-state battery, the active material volume ratio of a portion near the solid electrolyte layer in the positive electrode mixture layer may be 0.5 or more.

As a result, the active material volume ratio of the positive electrode active material in the portion close to the solid electrolyte layer increases, so that the amount of lithium ions in the positive electrode mixture layer can be increased, resulting in an all-solid battery with a higher battery capacity.

Further, for example, in the all-solid-state battery, the positive electrode mixture layer includes a first positive electrode mixture layer disposed on the positive electrode current collector side and a second positive electrode mixture layer disposed on the solid electrolyte layer side. , wherein the material volume ratio in the first positive electrode mixture layer is higher than the active material volume ratio in the second positive electrode mixture layer, and the porosity of the first positive electrode mixture layer is It may be smaller than the porosity of the two positive electrode mixture layers.

Accordingly, since the positive electrode mixture layer has a plurality of layers, the active material volume ratio and the porosity can be set for each layer, so that the all-solid-state battery can be easily manufactured.

Further, for example, in the all-solid-state battery, the volume ratio of the active material in the first positive electrode mixture layer may be greater than 0.7.

As a result, the active material volume ratio of the positive electrode active material in the first positive electrode mixture layer close to the positive electrode current collector increases, so the amount of lithium ions in the positive electrode mixture layer can be increased, and the all-solid-state battery with a higher battery capacity. becomes.

Further, for example, in the all-solid-state battery, the first positive electrode mixture layer may have a porosity of 0.05% or more and 8% or less.

As a result, since the porosity of the first positive electrode mixture layer is in a small range, the electric resistance in the positive electrode mixture layer due to the voids is reduced, resulting in an all-solid-state battery with a higher battery capacity.

Further, for example, in the all-solid-state battery, the volume ratio of the active material in the second positive electrode mixture layer may be 0.5 or more.

As a result, the active material volume ratio of the positive electrode active material in the second positive electrode mixture layer close to the solid electrolyte layer increases, so the amount of lithium ions in the positive electrode mixture layer can be increased, and an all-solid-state battery with a higher battery capacity can be obtained. Become. Further, in the second positive electrode mixture layer, the positive electrode active material with low fluidity and high hardness occupies the majority. By maintaining the shape of the layer, the force of the press is transmitted to the entire positive electrode mixture layer, and the solid electrolyte and the positive electrode active material are further adhered to each other. It becomes an all-solid-state battery with improved characteristics.

Further, for example, in the all-solid-state battery, the porosity of the second positive electrode mixture layer may be 5% or more and 35% or less.

As a result, since the porosity of the first positive electrode mixture layer is within an appropriate range, the effect of expansion and contraction of the positive electrode active material is absorbed by the voids while suppressing an increase in electrical resistance in the positive electrode mixture layer due to the voids. Therefore, it becomes an all-solid-state battery that achieves both high battery capacity and improved durability.

Further, for example, in the all-solid-state battery, the positive electrode layer may further include a positive electrode junction layer that is disposed between the positive electrode current collector and the positive electrode mixture layer and that contains at least a conductive agent.

As a result, the positive electrode current collector and the positive electrode mixture layer are bonded through the positive electrode bonding layer. The positive electrode mixture layer cuts into the positive electrode bonding layer, which has a lower hardness than the positive electrode active material, and the adhesive strength between the positive electrode bonding layer and the positive electrode mixture layer increases. Further, when the positive electrode bonding layer contains a small amount of binder, the bonding strength of the binder increases the bonding strength between the positive electrode bonding layer and the positive electrode current collector. Therefore, by bonding the positive electrode current collector and the positive electrode mixture layer through the positive electrode bonding layer, the adhesive strength between the positive electrode current collector and the positive electrode mixture layer is increased without impairing the electronic conductivity. It becomes an all-solid-state battery with improved durability.

Hereinafter, all-solid-state batteries according to embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the following embodiments all show one specific example of the present disclosure, and the numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of the constituent elements, etc. are examples, and do not limit the present disclosure. not something to do. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in independent claims representing the highest concept of the present disclosure will be described as optional constituent elements.

In addition, each figure is a schematic diagram that has been appropriately emphasized, omitted, or adjusted in proportion to show the present disclosure, and is not necessarily strictly illustrated, and the actual shape, positional relationship, and ratio may differ. In each figure, substantially the same configurations are denoted by the same reference numerals, and redundant description may be omitted or simplified.

Also, in this specification, terms that indicate the relationship between elements such as parallel, terms that indicate the shape of elements such as rectangles, and numerical ranges are not expressions that express only strict meanings, but substantially It is an expression that means to include a difference in an equivalent range, for example, a few percent difference.

In this specification, "plan view" means the case of viewing the all-solid-state battery along the stacking direction of the all-solid-state battery. is the length of the direction.

Also, in this specification, the terms “top” and “bottom” in the configuration of the all-solid-state battery do not refer to the upward direction (vertically upward) and the downward direction (vertically downward) in absolute spatial recognition, but It is used as a term defined by a relative positional relationship based on the stacking order in the configuration. Also, the terms "above" and "below" are used only when two components are spaced apart from each other and there is another component between the two components, as well as when two components are spaced apart from each other. It also applies when two components are in contact with each other and are placed in close contact with each other.

Further, in this specification, a cross-sectional view is a view showing a cross section when the central portion of the all-solid-state battery is cut in the stacking direction.

(Embodiment)
[A. All-solid-state battery]
FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery in this embodiment. The all-solid-state battery 100 in FIG. 1 includes a positive electrode current collector 11 and a positive electrode mixture layer 12 formed on the positive electrode current collector 11 and containing at least a positive electrode active material 1 and a solid electrolyte 2. A positive electrode layer 20, a negative electrode current collector 13, and a negative electrode layer 30 including a negative electrode mixture layer 14 formed on the negative electrode current collector 13 and containing at least the negative electrode active material 3 and the solid electrolyte 2, and a positive electrode mixture A solid electrolyte layer 40 disposed between the layer 12 and the negative electrode mixture layer 14 and containing at least a solid electrolyte 2 having ionic conductivity. Furthermore, the positive electrode layer 20 includes a positive electrode bonding layer 5 that is arranged between the positive electrode current collector 11 and the positive electrode mixture layer 12 and contains at least a conductive agent.

The positive electrode layer 20 may not include the positive electrode bonding layer 5, and the positive electrode mixture layer 12 and the positive electrode current collector 11 may be formed in contact with each other.

Further, in the all-solid-state battery 100, the active material volume ratio, which is the ratio of the volume of the positive electrode active material 1 to the sum of the volume of the positive electrode active material 1 and the volume of the solid electrolyte 2 in the positive electrode mixture layer 12, is In the thickness direction of the positive electrode mixture layer 12, the porosity increases from the solid electrolyte layer 40 interface side of the positive electrode mixture layer 12 toward the positive electrode current collector 11 interface side, and the porosity of the positive electrode mixture layer 12 in the thickness direction of the positive electrode mixture layer 12 is , becomes smaller as it approaches the positive electrode current collector 11 interface side from the solid electrolyte layer 40 interface side of the positive electrode mixture layer 12 . The active material volume ratio is the ratio of the volume of the positive electrode active material 1 to the total volume of the positive electrode active material 1 and the volume of the solid electrolyte 2, and the active material volume ratio = positive electrode active material volume / (positive electrode active material volume + solid electrolyte volume).

In FIG. 1, the positive electrode mixture layer 12 has a first positive electrode mixture layer 12a and a second positive electrode mixture layer 12b. The second positive electrode mixture layer 12 b is arranged on the side closer to the positive electrode current collector 11 in the layer 12 , and the second positive electrode mixture layer 12 b is arranged on the side closer to the solid electrolyte layer 40 in the positive electrode mixture layer 12 . The first positive electrode mixture layer 12a and the second positive electrode mixture layer 12b both contain the positive electrode active material 1 and the solid electrolyte 2, and the active material volume ratio of the first positive electrode mixture layer 12a (the positive electrode active material volume /[positive electrode active material volume + solid electrolyte volume]) is a1, the porosity of the first positive electrode mixture layer 12a (the ratio of the voids 4 in the positive electrode mixture layer 12) is b1, and the activity of the second positive electrode mixture layer 12b is When the material volume ratio is a2 and the porosity of the second positive electrode mixture layer 12b is b2, the relationships a1>a2 and b1<b2 are satisfied. That is, the active material volume ratio represented by the volume ratio of the positive electrode active material 1 in the first positive electrode mixture layer 12a is the active material volume ratio represented by the volume ratio of the positive electrode active material 1 in the second positive electrode mixture layer 12b. The porosity of the first positive electrode mixture layer 12a is larger than the volume ratio, and the porosity of the second positive electrode mixture layer 12b is lower than that of the second positive electrode mixture layer 12b.

According to the present embodiment, the solid electrolyte 2 maintains the shape of the positive electrode mixture layer 12 by connecting the positive electrode active materials 1, and exhibits a function of securing an ion conduction path. Even in the positive electrode mixture layer 12 having a composition for high battery capacity with a very small ratio, the porosity of the positive electrode mixture layer 12 is particularly small in a portion near the positive electrode current collector 11 side where the volume ratio of the solid electrolyte 2 is small. Therefore, the structural strength capable of maintaining the shape of the positive electrode mixture layer 12 is not lost due to the effect of the voids, and the ionic conduction paths in the positive electrode mixture layer 12 can be secured.

In addition, in the case of an all-solid-state battery for high battery capacity having the positive electrode mixture layer 12 having a composition with a very large volume ratio of the positive electrode active material 1, the positive electrode active materials 1 are close to each other in the positive electrode mixture layer 12. Since the expansion and contraction of the positive electrode active material 1 are mutually restrained, damage due to cracks or the like is suppressed inside the positive electrode mixture layer 12 . Although the influence of the expansion and contraction of the positive electrode active material 1 becomes apparent at the interface with the solid electrolyte layer 40, according to the present embodiment, in the thickness direction of the positive electrode mixture layer 12, the positive electrode mixture layer Since the porosity in the positive electrode mixture layer increases from the positive electrode current collector 11 interface side of 12 to the solid electrolyte layer 40 interface side, the positive electrode materialized at the interface between the positive electrode mixture layer 12 and the solid electrolyte layer 40 The effect of expansion and contraction of the active material 1 can be absorbed by the existence of the voids, and the durability of the all-solid-state battery 100 can be improved.

Further, in the all-solid-state battery 100, at least one layer selected from the group consisting of the positive electrode mixture layer 12, the negative electrode mixture layer 14, and the solid electrolyte layer 40 has a solvent concentration of 50 ppm or less, and The concentration of the binder contained in at least one layer selected from the group consisting of the agent layer 12, the negative electrode mixture layer 14, and the solid electrolyte layer 40 may be 100 ppm or less.

Hereinafter, the all-solid-state battery 100 according to the present embodiment will be described for each configuration.

[B. Positive electrode layer]
First, the positive electrode layer 20 in this embodiment will be described. Positive electrode layer 20 in the present embodiment includes positive electrode current collector 11 and positive electrode mixture layer 12 formed on positive electrode current collector 11 and containing positive electrode active material 1 and solid electrolyte 2 .

Furthermore, the positive electrode layer 20 includes a positive electrode bonding layer 5 that is arranged between the positive electrode current collector 11 and the positive electrode mixture layer 12 and contains at least a conductive agent.

[B-1. Positive electrode mixture layer]
Positive electrode mixture layer 12 in the present embodiment is a layer containing at least positive electrode active material 1 and solid electrolyte 2, and may further contain a conductive aid as necessary.

[B-1-2. Positive electrode active material]
In the positive electrode active material 1 of the present embodiment, metal ions such as lithium (Li) are inserted into or removed from the crystal structure at a potential higher than that of the negative electrode layer 30, and oxidation occurs as the metal ions such as lithium are inserted or removed. or a substance to be reduced. The type of the positive electrode active material 1 may be appropriately selected according to the type of the all-solid-state battery 100, and examples thereof include oxide active materials and sulfide active materials.

For example, an oxide active material (lithium-containing transition metal oxide) is used as the positive electrode active material 1 in the present embodiment. Examples of oxide active materials include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiNiPO ₄ , LiFePO ₄ , LiMnPO ₄ , and by substituting transition metals of these compounds with one or two different elements. The obtained compound etc. are mentioned. Compounds obtained by substituting one or two different elements for the transition metal of the above compounds include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 Known materials such as O ₂ and LiNi _0.5 Mn _1.5 O ₂ are used. One type of positive electrode active material may be used, or two or more types may be used in combination.

Examples of the shape of the positive electrode active material include particulate and thin film. When the positive electrode active material is particulate, the average particle diameter (D ₅₀ ) of the positive electrode active material is, for example, preferably in the range of 50 nm or more and 50 μm or less, and more preferably in the range of 1 μm or more and 15 μm or less. When the average particle size of the positive electrode active material is 50 nm or more, the handleability tends to be improved. . The "average particle diameter" in the present specification is the volume-based average diameter measured by a laser analysis and a scattering particle size distribution analyzer.

The surface of the positive electrode active material may be covered with a coat layer. The reason for providing the coat layer is that the reaction between the positive electrode active material (eg, oxide active material) and the solid electrolyte (eg, sulfide-based solid electrolyte) can be suppressed. Examples of materials for the coat layer include Li ion conductive oxides such as LiNbO3, Li3PO4 and LiPON. The average thickness of the coat layer is preferably, for example, within the range of 1 nm or more and 10 nm or less.

[B-1-2. Solid electrolyte]
The solid electrolyte in this embodiment will be described below.

As shown in FIG. 1 , positive electrode mixture layer 12 in the present embodiment contains positive electrode active material 1 and solid electrolyte 2 . The solid electrolyte 2 may be appropriately selected according to the conductive ion species (for example, lithium ion), and can be broadly divided into, for example, sulfide-based solid electrolytes and oxide-based solid electrolytes.

_The type of sulfide-based solid _electrolyte in the present embodiment is _not particularly limited _{. 2SP 2} S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ and Li ₂ SP ₂ S ₅ , especially lithium ion conductive It is preferable to contain Li, P and S because the is excellent. The sulfide-based solid electrolytes may be used singly or in combination of two or more. Moreover, the sulfide-based solid electrolyte may be crystalline, amorphous, or glass-ceramics. The above description of "Li ₂ SP ₂ S ₅ " means a sulfide-based solid electrolyte using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to other descriptions. .

In the present embodiment, one form of the sulfide-based solid electrolyte is sulfide glass-ceramics containing Li ₂ S and P ₂ S ₅ , and the ratio of Li ₂ S and P ₂ S ₅ is Li ₂ S:P ₂ S ₅ =70:30 to 80:20, preferably Li ₂ S:P ₂ S ₅ =75:25 to 80:20. The reason why the ratio within this range is preferable is that a crystal structure with high ion conductivity is obtained while maintaining the lithium concentration that affects the battery characteristics.

The shape of the sulfide-based solid electrolyte in the present embodiment includes, for example, particle shapes such as spherical and ellipsoidal shapes, and thin film shapes. When the sulfide-based solid electrolyte material is in the form of particles, the average particle size (D ₅₀ ) of the sulfide-based solid electrolyte is not particularly limited. The following are preferable.

The oxide-based solid electrolyte in this embodiment will be described. Although the _{type of} oxide-based solid electrolyte _is not particularly limited, LiPON, _{Li3PO4 , Li2SiO2} , _{Li2SiO4 , Li0.5La0.5TiO3 , Li1.3Al0.3Ti 0.7} ( _{PO4 ) 3} , _{La0.51Li0.34TiO0.74} , _{Li1.5Al0.5Ge1.5} ( _PO4 ) _{3 and the} like _. One type of oxide-based solid electrolyte may be used, or two or more types may be used in combination.

Further, the type and particle size of the solid electrolyte contained in each layer of the positive electrode mixture layer 12, the negative electrode mixture layer 14, and the solid electrolyte layer 40 may be different for each layer.

[B-1-3. binder]
The binder in this embodiment will be described below.

The binder is used between the positive electrode active materials 1 in the positive electrode mixture layer 12, between the positive electrode active material 1 and the solid electrolyte 2, between the solid electrolytes 2, between the positive electrode mixture layer 12 and the positive electrode current collector 11, and Although it plays a role of binding between the positive electrode mixture layer 12 and the solid electrolyte layer 40, it does not directly contribute to the battery characteristics, so the concentration of the binder contained in the positive electrode mixture layer 12 should be 100 ppm or less. is desirable. By setting the concentration of the binder to 100 ppm or less, it becomes possible to contain more positive electrode active material 1 in the positive electrode mixture layer 12, which leads to a higher battery capacity. In addition, it is possible to prevent an increase in the internal electrical resistance of the all-solid-state battery 100 due to the binder blocking the ion-conducting path and the electron-conducting path, thereby improving the charge-discharge characteristics of the all-solid-state battery 100 .

In the present specification, concentration is weight-based concentration unless otherwise specified.

Specific examples of binders include butadiene rubber, isoprene rubber, styrene-butadiene rubber (SBR), styrene-butadiene-styrene copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), ethylene - Synthetic rubbers such as propylene rubber, butyl rubber, chloroprene rubber, acrylonitrile-butadiene rubber, acrylic rubber, silicone rubber, fluororubber and urethane rubber, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer ( PVDF-HFP), polyimide, polyamide, polyamideimide, polyvinyl alcohol and chlorinated polyethylene (CPE).

[B-1-4. Conductive agent]
The conductive additive in the present embodiment will be described below.

In all-solid-state battery 100 according to the present embodiment, positive electrode mixture layer 12 may contain a conductive aid.

By adding a conductive aid, the electron conductivity in the positive electrode mixture layer 12 can be increased, so that the electron conduction path in the positive electrode mixture layer 12 can be secured, and the inside of the all-solid-state battery 100 resistance can be lowered. This increases the amount of current that can be conducted through the electron conduction path, thereby improving the charge/discharge characteristics of the all-solid-state battery 100 .

The conductive aid in the present embodiment is not particularly limited as long as it improves the electron conductivity of the positive electrode mixture layer 12. Examples include acetylene black, Ketjenblack (registered trademark), carbon black, graphite, A carbon fiber etc. are mentioned. One type of conductive aid may be used, or two or more types may be used in combination.

[B-2. Positive electrode current collector]
The positive electrode current collector 11 is made of, for example, aluminum, gold, platinum, zinc, copper, SUS, nickel, tin, titanium, or an alloy of two or more of these foil-shaped, plate-shaped, or mesh-shaped bodies. A body is used.

Moreover, the thickness and shape of the positive electrode current collector 11 may be appropriately selected according to the application of the all-solid-state battery.

As for the adhesion between the positive electrode mixture layer 12 and the positive electrode current collector 11 containing a binder having a concentration of 100 ppm or less, the positive electrode mixture layer 12 is pressed after forming the positive electrode mixture layer 12 in the manufacturing process described below. The agent layer 12 bites into the positive electrode current collector 11 to obtain adhesive strength. Here, although the details of the manufacturing process will be described later, in order to further increase the adhesion between the positive electrode mixture layer 12 and the positive electrode current collector 11, as shown in FIGS. On the positive electrode current collector 11 on the side where the agent layer 12 is formed, a positive electrode junction mainly composed of a conductive carbon material such as carbon, which has conductivity and has lower hardness than the positive electrode active material 1. It is desirable to form layer 5 . As a result, as shown in FIG. 2(b), when the positive electrode mixture layer 12 is pressed by the roll 7, the positive electrode mixture layer 12 is promoted to bite into the positive electrode bonding layer 5, and the positive electrode bonding layer The adhesive strength between 5 and the positive electrode mixture layer 12 is increased. In addition, since the positive electrode bonding layer 5 contains a small amount of binder, the adhesive strength of the binder increases the adhesive strength between the positive electrode bonding layer 5 and the positive electrode current collector 11 . Therefore, by bonding the positive electrode current collector 11 and the positive electrode mixture layer 12 through the positive electrode bonding layer 5, the adhesive strength between the positive electrode current collector 11 and the positive electrode mixture layer 12 is maintained without impairing the electron conductivity. can be raised.

[B-3. Positive electrode bonding layer]
The positive electrode bonding layer 5 is mainly composed of a conductive agent and also contains a binder. The role of the positive electrode bonding layer 5 is to bond the positive electrode current collector 11 and the positive electrode mixture layer 12 via the positive electrode bonding layer 5 .

Conductive agents include, for example, conductive carbon materials such as acetylene black, Ketjenblack (registered trademark), carbon black, graphite, and carbon fiber. One type of conductive agent may be used, or two or more types may be used in combination.

As the binder, the above-described binder may be used, so the description is omitted here.

[C. Negative electrode layer]
The negative electrode layer 30 in this embodiment will be described with reference to FIG.

The negative electrode layer 30 in the present embodiment includes, for example, a negative electrode current collector 13 made of metal foil and a negative electrode mixture layer 14 formed on the negative electrode current collector 13 .

[C-1. Negative electrode mixture layer]
The negative electrode mixture layer 14 is a film including at least the negative electrode active material 3 and the solid electrolyte 2 .

The negative electrode mixture layer 14 preferably has a binder concentration of 100 ppm or less. Further, the negative electrode mixture layer 14 may contain a conductive aid. The details of the binder and conductive aid are the same as those of the positive electrode mixture layer.

[C-1-1. Negative electrode active material]
The negative electrode active material 3 in this embodiment will be described below.

The negative electrode active material is a material in which metal ions such as lithium are inserted into or removed from the crystal structure at a potential lower than that of the positive electrode mixture layer 12, and oxidized or reduced as the metal ions such as lithium are inserted or removed. be.

Examples of the negative electrode active material 3 in the present embodiment include metals that are easily alloyed with lithium such as lithium, indium, tin, and silicon; carbon materials such as hard carbon and graphite; or Li ₄ Ti ₅ O ₁₂ and SiO _x . A known material such as an oxide active material such as is used. As the negative electrode active material 3, a composite or the like obtained by appropriately mixing the above-described negative electrode active materials may also be used.

The ratio of the negative electrode active material and the solid electrolyte contained in the negative electrode mixture layer 14 is in the range of 0.67 or more and 19 or less when the weight ratio of the negative electrode active material/solid electrolyte is calculated in terms of weight. is preferably within the range of 1 or more and 5.67 or less. The reason why the weight ratio is preferably within this range is to secure both the ion conduction path and the electron conduction path in the negative electrode mixture layer 14 .

[C-1-2. Solid electrolyte]
For solid electrolytes, see [B. Positive Electrode Layer], the solid electrolyte described above may be used, so the description is omitted here.

[C-1-3. binder]
Regarding binders, see [B. Positive Electrode Layer], the binder described above may be used, so the description is omitted here.

[C-1-4. Conductive agent]
Regarding the conductive aid, see [B. Positive Electrode Layer], the conductive aid described above may be used, so the description is omitted here.

[C-2. Negative electrode current collector]
The negative electrode current collector 13 is, for example, a foil-shaped body, a plate-shaped body, a mesh-shaped body, or the like made of SUS, gold, platinum, zinc, copper, nickel, titanium, tin, or an alloy of two or more of these. is used.

Moreover, the thickness and shape of the negative electrode current collector 13 may be appropriately selected according to the application of the all-solid-state battery.

[D. Solid electrolyte layer]
Solid electrolyte layer 40 in the present embodiment will be described with reference to FIG.

Solid electrolyte layer 40 in the present embodiment includes at least solid electrolyte 2 having ion conductivity. Since the binder does not directly contribute to the battery characteristics, the concentration of the binder contained in the solid electrolyte layer 40 is desirably 100 ppm or less. As a result, it is possible to prevent an increase in the internal electric resistance of the all-solid-state battery 100 due to the binder interfering with the ion conduction path, and the charge-discharge characteristics of the all-solid-state battery 100 are improved.

[D-1. Solid electrolyte]
For solid electrolytes, see [B. Positive Electrode Layer], the solid electrolyte described above may be used, so the description is omitted here.

[D-2. binder]
For the binder, see [B. Positive Electrode Layer], the binder described above may be used, so the description is omitted here.

[E. Other configurations]
In the all-solid-state battery 100 according to the present embodiment, although not shown, a terminal (metal positive electrode lead) may be attached by welding to the surface of the positive electrode current collector 11 opposite to the positive electrode mixture layer 12. A terminal (metal negative electrode lead) may be attached by welding to the surface of the negative electrode current collector 13 opposite to the negative electrode mixture layer 14 . The all-solid-state battery obtained by attaching the terminals in this manner, or the battery group obtained by connecting a plurality of the above-mentioned all-solid-state batteries, is housed in a battery case, and the positive electrode lead and the negative electrode lead are outside the battery case. It may be an all-solid-state battery constructed so that the battery case is sealed.

The above is the description of the all-solid-state battery 100 in the present embodiment.

[F. Production method]
[F-1. Method for manufacturing all-solid-state battery]
The method for manufacturing the all-solid-state battery 100 according to the present embodiment includes, for example, a film formation step of preparing the positive electrode layer 20 having the positive electrode mixture layer 12, the negative electrode layer 30 having the negative electrode mixture layer 14, and the solid electrolyte layer 40. Then, the prepared positive electrode layer 20, negative electrode layer 30, and solid electrolyte layer 40 are aligned or laminated such that the solid electrolyte layer 40 is disposed between the positive electrode mixture layer 12 and the negative electrode mixture layer 14. 1, a lamination step of obtaining a laminated structure; and a pressing step of pressing the obtained laminated structure from above and below in the lamination direction.

[F-2. Film formation process of positive electrode layer]
The film forming step of the positive electrode layer 20 in the present embodiment is a step of forming the positive electrode mixture layer 12 on the positive electrode current collector 11 . In the film forming process of the positive electrode layer 20, for example, a positive electrode mixture obtained by mixing a solid electrolyte 2 in a powder state (not slurried), a positive electrode active material 1, and a conductive aid as necessary on a positive electrode current collector 11. and a powder pressing step of pressing the laminate obtained by the powder laminating step.

On the other hand, as another method for manufacturing the positive electrode layer 20, the positive electrode active material 1, the solid electrolyte 2, and if necessary, a binder and a conductive aid are dispersed in an organic solvent to prepare a slurry, and the obtained slurry is used as a positive electrode collector. A coating step of applying to the surface of the current collector 11, a drying and baking step of heating and drying the obtained coating film to remove the organic solvent, and a coating of pressing the dried coating film formed on the positive electrode current collector 11. It may be manufactured by a film forming process including a film pressing process. Since the binder does not directly contribute to battery characteristics, it is desirable that the positive electrode mixture does not contain a binder. Alternatively, the concentration of the binder contained in the positive electrode mixture is desirably 100 ppm or less.

In the case of slurrying with an organic solvent, the ionic conductivity of the solid electrolyte may be lowered due to the influence of the organic solvent remaining in the positive electrode mixture layer 12, and a huge drying facility is required to remove the organic solvent. Since the initial investment cost of equipment and the running cost due to energy consumption are very large, a method of forming a film without using an organic solvent using the above-mentioned material in a powder state that is not slurried, or a positive electrode synthesis method. It is preferable to use a very small amount of solvent so that the concentration of the solvent contained in the agent layer 12 is 50 ppm or less.

Further, as a method for forming a positive electrode mixture layer having a composition distribution in which the local active material volume ratio intermittently increases from the solid electrolyte layer interface side of the positive electrode mixture layer toward the positive electrode current collector interface side, For example, a plurality of positive electrode mixture layers are formed by press-molding a positive electrode mixture containing the positive electrode active material 1 and the solid electrolyte 2 at different volume ratios, and the obtained positive electrode mixture layers are bonded together. a method of overcoating the positive electrode mixture layer forming ink containing the positive electrode active material 1 and the solid electrolyte 2 at different volume ratios; A method of stacking the positive electrode mixture contained in (1) by CVD vapor deposition, PVD vapor deposition, or the like can be mentioned. At this time, as the ink for forming the positive electrode mixture layer, a slurry obtained by dispersing the positive electrode mixture in a solvent may be used. In order to avoid an increase in cost due to this, a method of forming a film without using an organic solvent, or a positive electrode mixture containing a small amount of solvent so that the concentration of the solvent contained in the positive electrode mixture layer 12 is 50 ppm or less is used. method is preferred.

Further, as a method for forming a positive electrode mixture layer having a composition distribution in which the local active material volume ratio continuously increases from the solid electrolyte layer interface side of the positive electrode mixture layer toward the positive electrode current collector interface side, For example, a method of forming a positive electrode mixture layer by a sputtering method, an inkjet method, or the like so that the volume ratio of the positive electrode active material 1 and the solid electrolyte 2 has a continuous gradient, or a positive electrode current collector (eg, aluminum foil, etc.) A positive electrode mixture in which the positive electrode active material 1 and the solid electrolyte 2 are uniformly mixed is applied to the surface, and a magnetic force is applied to move the positive electrode active material 1, so that the positive electrode active material 1 is abundant at the interface where the positive electrode mixture is applied. A method of forming such that At this time, when using a slurry obtained by dispersing the positive electrode mixture in a solvent, the organic solvent is not used in order to avoid deterioration of battery characteristics due to the influence of the organic solvent and an increase in cost due to the drying equipment as described above. or a method of forming a film using a positive electrode mixture containing a very small amount of solvent so that the concentration of the solvent contained in the positive electrode mixture layer is 50 ppm or less.

Here, the method for measuring the organic solvent is not particularly limited, and examples thereof include gas chromatography, mass change method, and the like.

Further, when the positive electrode layer 20 includes the positive electrode bonding layer 5, before forming the positive electrode mixture layer 12, a paste containing a conductive agent and a binder is applied onto the positive electrode current collector 11 and dried. Thus, the positive electrode bonding layer 5 is formed. Then, the positive electrode mixture layer 12 is formed on the positive electrode bonding layer 5 formed on the positive electrode current collector 11 by the method described above.

After forming the positive electrode mixture layer 12 , the positive electrode mixture layer 12 is formed in order to improve the density of the positive electrode mixture layer 12 and to increase the adhesiveness between the positive electrode mixture layer 12 and the positive electrode current collector 11 . You may press from the top and bottom of the lamination direction.

Positive electrode mixture layer 12 in the present embodiment may have a single-layer structure consisting of one layer, or may have a multilayer structure consisting of two or more layers as shown in FIG. Further, the thickness of the positive electrode mixture layer 12 is, for example, preferably in the range of 1 μm or more and 300 μm or less, and more preferably in the range of 20 μm or more and 200 μm or less. By setting the thickness of the positive electrode mixture layer 12 to 1 μm or more, it is easy to obtain a sufficient electric capacity, and by setting the thickness of the positive electrode mixture layer 12 to 300 μm or less, it is difficult to increase the electric resistance, and the battery is improved. Output characteristics are less likely to deteriorate. In addition, when the positive electrode mixture layer 12 consists of a plurality of layers, the thickness of the positive electrode mixture layer 12 is the total thickness of each positive electrode mixture layer.

When positive electrode mixture layer 12 in the present embodiment has a two-layer structure, for example, as shown in FIG. A positive electrode mixture layer 12 made of the second positive electrode mixture layer 12b arranged closer to the electrolyte layer 40 is used.

The ratio of the thickness of the first positive electrode mixture layer 12a to the thickness of the positive electrode mixture layer 12 (thickness of the first positive electrode mixture layer 12a/thickness of the positive electrode mixture layer 12) is, for example, 0.3 or more and 0.9 or less. is within the range of By setting the ratio of the thickness of the first positive electrode mixture layer 12a to the thickness of the positive electrode mixture layer 12 to 0.3 or more, the thickness of the first positive electrode mixture layer 12a containing a large proportion of the positive electrode active material 1 is ensured. sufficient capacity can be obtained. The ratio of the thickness of the first positive electrode mixture layer 12a to the thickness of the positive electrode mixture layer 12 is 0.9 or less (that is, the ratio of the thickness of the second positive electrode mixture layer 12b to the thickness of the positive electrode mixture layer 12 is 0.1 or more. ), the thickness of the second positive electrode mixture layer 12b containing a relatively large proportion of the solid electrolyte 2 is ensured, so that a sufficient ion conduction path by the solid electrolyte 2 can be ensured.

In the first positive electrode mixture layer 12a on the positive electrode current collector 11 side in the positive electrode mixture layer 12, the content of the positive electrode active material 1 in the first positive electrode mixture layer 12a is The total volume of the positive electrode active material 1 contained is preferably larger than the total volume of the solid electrolyte 2 contained in the first positive electrode mixture layer 12a. Active material volume+solid electrolyte volume]) is preferably greater than 0.5, more preferably greater than 0.7. The reason why the total volume of the positive electrode active material 1 contained in the first positive electrode mixture layer 12a is preferably larger than the total volume of the solid electrolyte 2 contained in the first positive electrode mixture layer 12a is that the positive electrode mixture This is because the amount of lithium ions in the layer 12 can be increased, and an all-solid-state battery with a high battery capacity can be realized.

Also, in the second positive electrode mixture layer 12b on the solid electrolyte layer 40 side in the positive electrode mixture layer 12, the total volume of the positive electrode active materials 1 included in the second positive electrode mixture layer 12b is equal to the second positive electrode mixture layer 12b. It is preferably equal to or greater than the total volume of the solid electrolyte 2 contained in the agent layer 12b, that is, the active material volume ratio (positive electrode active material volume/[positive electrode active material volume + solid electrolyte volume]) is 0.5 or more. is preferred, and greater than 0.5 is more preferred. In addition, in the second positive electrode mixture layer 12b, the active material volume ratio is preferably 0.85 or less in order to secure an ion conduction path by the solid electrolyte 2. As shown in FIG.

In particular, the solid electrolyte 2 maintains the shape of the positive electrode mixture layer 12 by connecting the positive electrode active materials 1, and exhibits a function of securing an ion conduction path. In the positive electrode mixture layer 12 having a composition for high battery capacity with a very small volume ratio of the solid electrolyte such that the concentration of the binder that does not directly contribute to the is 100 ppm or less and the volume ratio of the active material is greater than 0.7 is desirable to press the positive electrode mixture layer 12 after forming the positive electrode mixture layer 12 . As a result, the solid electrolyte 2 softer than the positive electrode active material 1 is pressed against the positive electrode active material 1, and the sintering of the solid electrolyte 2 is promoted, thereby making it possible to press and harden the positive electrode mixture layer 12. It becomes possible to maintain the shape of the positive electrode mixture layer 12 .

For the powder pressing process and the coating film pressing process, for example, a roll press capable of continuous processing is desirable in consideration of productivity.

2 and 3 are schematic diagrams showing the process of roll-pressing the positive electrode material mixture layer formed on the positive electrode current collector. 2 shows the positive electrode mixture layer 12 having the first positive electrode mixture layer 12a and the second electrode mixture layer 12b, and FIG. 3 shows the first positive electrode mixture layer 12c and the second positive electrode mixture layer 12c. A positive electrode mixture layer 22 having an agent layer 12d is shown. 2 shows the case where the active material volume ratio is 0.5 or more in the second positive electrode mixture layer 12b, and FIG. 3 shows the case where the active material volume ratio is 0.5 in the second positive electrode mixture layer 12d. If less than 5 is indicated.

FIG. 2(a) shows a cross section of a state in which the positive electrode mixture layer 12 is laminated on the positive electrode current collector 11 with the positive electrode bonding layer 5 interposed therebetween, and FIG. A cross section of the laminate of FIG. 2(a) during roll pressing is shown. In addition, FIG. 3(a) shows a cross section of a laminate in which the positive electrode mixture layer 22 is laminated on the positive electrode current collector 11 at the start of roll pressing, and FIG. ) shows a cross section of the laminate of FIG. 3(a) during roll pressing.

In the second positive electrode mixture layer 12b directly pressed by the roll 7, when the active material volume ratio is 0.5 or more, as shown in FIG. Since the positive electrode active material 1 with low fluidity and high hardness occupies the majority, the force applied by roll pressing is arranged on the side closer to the positive electrode current collector 11 in the positive electrode mixture layer 12 without diffusing. is sufficiently transmitted to the first positive electrode mixture layer 12a. Therefore, since the entire positive electrode mixture layer 12 is uniformly pressed and compacted, the positive electrode mixture layer has a binder concentration of 100 ppm or less and a composition for high battery capacity in which the volume ratio of the solid electrolyte 2 is very small. 12 as well, the shape of the positive electrode mixture layer 12 can be maintained. That is, as shown in (a) and (b) of FIG. 2, even if the positive electrode mixture layer 12 is roll-pressed, the shape hardly changes. In addition, the force applied by the roll press is sufficiently transmitted to the first positive electrode mixture layer 12a disposed closer to the positive electrode current collector 11 in the positive electrode mixture layer 12 without diffusing. In the first positive electrode mixture layer 12a, the solid electrolyte 2 having fluidity can be sufficiently spread into the gaps between the positive electrode active materials 1, and the minimum amount of the solid electrolyte 2 can sufficiently separate the positive electrode active materials 1. It is possible to secure an ion conducting path and reduce the porosity of the first positive electrode mixture layer 12a.

On the other hand, in the second positive electrode mixture layer 12d directly pressed by the roll 7 on the solid electrolyte layer 40 side during the roll pressing, when the active material volume ratio is less than 0.5, (a ) and (b), the solid electrolyte 2 with high fluidity occupies the majority, and the flow of the solid electrolyte 2 spreads the second positive electrode mixture layer 12d outward in the plane direction. As a result, the force applied by the roll press is diffused and is not sufficiently transmitted to the first positive electrode mixture layer 12 c located closer to the positive electrode current collector 11 in the positive electrode mixture layer 22 . Therefore, it becomes difficult to sufficiently spread the solid electrolyte 2 in the first positive electrode mixture layer 12c into the gap between the positive electrode active materials 1, and the solid electrolyte 2 in the first positive electrode mixture layer 12c is pressed and solidified. As a result, it becomes difficult to maintain the shape of the positive electrode mixture layer 12 .

Moreover, it is more desirable to apply heat during the roll pressing, since the effect of further improving the fluidity of the solid electrolyte 2 and promoting sintering can be obtained.

In addition, the porosity of the positive electrode mixture layer 12 may decrease as the positive electrode mixture layer 12 approaches the collector interface side from the solid electrolyte layer interface side. Also at the location of , it is preferably within the range of 0.05% or more and 35% or less, and more preferably within the range of 0.1% or more and 15% or less.

Here, the porosity will be described in the case where the positive electrode mixture layer 12 in the present embodiment has a two-layer structure composed of the first positive electrode mixture layer 12a and the second positive electrode mixture layer 12b.

In general, when the porosity of the positive electrode mixture layer is too small, the voids cannot sufficiently absorb the mechanical displacement due to the expansion and contraction of the positive electrode active material, and the positive electrode mixture layer 12 warps, warps, cracks, and the like. may occur, and if the porosity of the positive electrode mixture layer 12 is too large, the electrical resistance of the positive electrode mixture layer 12 may increase.

However, the concentration of the binder contained in the positive electrode mixture layer 12 that does not directly contribute to the battery characteristics is 100 ppm or less, and the volume ratio of the solid electrolyte is very small, such as the volume ratio of the active material being greater than 0.7. In the first positive electrode mixture layer 12a on the positive electrode current collector 11 side, which has a composition for high battery capacity, the function of connecting the positive electrode active materials 1 is likely to be impaired by voids, and the shape of the first positive electrode mixture layer 12a is It is desirable to reduce the porosity because it is likely to be difficult to hold. Here, the positive electrode current collector 11 side has a composition for high battery capacity with a very small solid electrolyte volume ratio such that the binder concentration is 100 ppm or less and the active material volume ratio is greater than 0.7. In the first positive electrode mixture layer 12a, since the positive electrode active materials 1 are close to each other, the expansion and contraction of the positive electrode active material 1 are mutually constrained, so that in the first positive electrode mixture layer 12a An effect of suppressing damage due to cracks or the like can be obtained. Therefore, when the active material volume ratio of the first positive electrode mixture layer 12a is greater than 0.7, the positive electrode active material is less active than when the active material volume ratio of the first positive electrode mixture layer 12a is 0.7 or less. Since the number of voids to absorb the displacement due to the expansion and contraction of the substance 1 may be small, the void ratio may be set small.

On the other hand, the influence of the expansion and contraction of the positive electrode active material 1 becomes apparent at the interface of the positive electrode mixture layer 12, which has a relatively small active material volume ratio, on the solid electrolyte layer 40 side. The second positive electrode material mixture layer 12 b on the solid electrolyte layer 40 side in 1 needs to have sufficient voids to absorb mechanical displacement due to expansion and contraction of the positive electrode active material 1 .

Therefore, according to the present embodiment, the first positive electrode mixture layer 12a on the positive electrode current collector 11 side has a composition for high battery capacity, which contains a large amount of the positive electrode active material 1 and has a very small volume ratio of the solid electrolyte 2. , it is desirable to reduce the porosity and provide the second positive electrode mixture layer 12b having a higher porosity than the first positive electrode mixture layer 12a on the solid electrolyte layer 40 side of the first positive electrode mixture layer 12a. As a result, even in the positive electrode mixture layer 12 that contains a large amount of the positive electrode active material 1 and has a composition for high battery capacity in which the volume ratio of the solid electrolyte 2 is very small, the positive electrode mixture layer 12 has structural strength that can maintain its shape. is not lost due to the influence of voids, and sufficient ionic conduction paths can be secured, and the influence of the expansion and contraction of the positive electrode active material 1 that becomes apparent at the interface between the positive electrode mixture layer 12 and the solid electrolyte layer 40 is It can be absorbed by the voids of the two positive electrode mixture layers 12b. Therefore, since the positive electrode mixture layer 12 contains a large amount of the positive electrode active material 1, it is possible to improve the durability of the all-solid-state battery 100 having a high battery capacity. The porosity of the first positive electrode mixture layer 12a is, for example, preferably in the range of 0.05% or more and 8% or less, and more preferably 0.1% or more and 5% or less. The porosity of the second positive electrode mixture layer 12b is within a range in which the porosity is higher than that of the first positive electrode mixture layer 12a, for example, preferably in the range of 5% to 35%, and 8% to 15%. % or less is more preferable.

The porosity of the positive electrode mixture layer 12 is the ratio of the volume occupied by voids in the positive electrode mixture layer 12 to the apparent volume of the positive electrode mixture layer 12 . It can be obtained by calculating from the total volume of each material calculated from the weight and density of each material contained in positive electrode mixture layer 12 and the actual apparent volume of positive electrode mixture layer 12 . That is, the porosity is
Porosity (%) = (apparent volume - total volume of each material) x 100/apparent volume.

Moreover, the porosity of the positive electrode mixture layer 12 can be adjusted when the positive electrode mixture layer 12 is formed. Also, it can be adjusted by the pressing temperature, the degree of dispersion of the material constituting the positive electrode mixture layer 12, and the like.

[F-3. Film formation process of negative electrode layer]
The film forming process of the negative electrode layer 30 in the present embodiment is basically the same as the film forming process of the positive electrode layer 20 except that the active material used is changed to the negative electrode active material 3. Description is omitted.

[F-4. Formation process of solid electrolyte layer]
In the film formation process of the solid electrolyte layer 40 in the present embodiment, the material to be used is changed to a solid electrolyte without using an active material or a conductive agent, and the positive electrode layer 20, the negative electrode layer 30, and another Since the process for forming the positive electrode layer 20 is basically the same except that the positive electrode layer 20 is formed on at least one of the substrates, the description thereof is omitted here.

[F-5. Lamination process and press process]
In the stacking step, the positive electrode layer 20 , the negative electrode layer 30 , and the solid electrolyte layer 40 obtained in the film forming step are stacked so that the solid electrolyte layer 40 is arranged between the positive electrode mixture layer 12 and the negative electrode mixture layer 14 . to obtain a laminated structure. In the pressing step, the laminated structure obtained in the laminating step is pressed from the outer side of the positive electrode current collector 11 and the negative electrode current collector 13 in the stacking direction to obtain the all-solid-state battery 100 .

The purpose of the pressing step is to increase the density (filling rate) of the positive electrode mixture layer 12 , the negative electrode mixture layer 14 and the solid electrolyte layer 40 . By increasing the density (filling rate), the lithium ion conductivity and electron conductivity can be improved in the positive electrode mixture layer 12, the negative electrode mixture layer 14, and the solid electrolyte layer 40, and good battery characteristics can be obtained. be done.

(Modification)
A modification of the embodiment will be described below with reference to FIG. In addition, in the following description of the modified example, the differences from the embodiment will be mainly described, and the description of the common points will be omitted or simplified.

FIG. 4 is a schematic cross-sectional view of an all-solid-state battery 200 in a modified example of the embodiment. FIG. 4 shows the case where the positive electrode mixture layer 112 is one layer in the positive electrode layer 120 . When the positive electrode mixture layer 112 is one layer, the active material volume ratio of the portion of the positive electrode mixture layer 112 near the positive electrode current collector 11 is preferably, for example, 0.7 or more. In addition, the porosity of the portion of the positive electrode mixture layer 112 near the positive electrode current collector 11 is, for example, preferably in the range of 0.05% or more and 8% or less, and is 0.1% or more and 5% or less. is more preferable. Here, “a portion of the positive electrode mixture layer 112 close to the positive electrode current collector 11” means the positive electrode mixture layer 112 and the positive electrode junction layer 5 (if the positive electrode junction layer 5 is not provided, A region within 1/10 of the thickness of the positive electrode mixture layer 112 (the region indicated by A in FIG. 4) is defined as the distance from the interface with the conductor 11).

Further, the active material volume ratio of the portion of the positive electrode mixture layer 112 near the solid electrolyte layer 40 is within a range where the active material volume ratio is smaller than that of the portion of the positive electrode mixture layer 112 near the positive electrode current collector 11. For example, It is preferably 0.5 or more. Further, the porosity of the portion of the positive electrode mixture layer 112 close to the solid electrolyte layer 40 is within a range where the porosity is higher than that of the portion of the positive electrode mixture layer 112 close to the positive electrode current collector 11, for example, 5% or more. It is preferably within the range of 35% or less, and more preferably within the range of 8% or more and 15% or less. Here, “a portion of the positive electrode mixture layer 112 close to the solid electrolyte layer 40” means that the distance from the interface between the positive electrode mixture layer 112 and the solid electrolyte layer 40 in the stacking direction is the thickness of the positive electrode mixture layer 12. The area within 1/10 (the area indicated by B in FIG. 4) shall be indicated.

(Other embodiments)
As described above, the all-solid-state battery according to the present disclosure has been described based on the embodiments, but the present disclosure is not limited to these embodiments. As long as it does not deviate from the gist of the present disclosure, various modifications that a person skilled in the art can think of are applied to the embodiments, and other forms constructed by combining some of the constituent elements of the embodiments are also within the scope of the present disclosure. included.

For example, in the above-described embodiment, the all-solid-state battery includes a positive electrode mixture layer having two layers of a first positive electrode mixture layer and a second positive electrode mixture layer. A positive electrode mixture layer having a positive electrode mixture layer having the same composition may be used. In addition, the active material volume ratio of the positive electrode mixture layer locally increases from the solid electrolyte layer interface side of the positive electrode mixture layer toward the current collector interface side within a range that does not interfere with the effects of the present disclosure. The positive electrode mixture layer may have a portion where the porosity of the positive electrode mixture layer does not decrease from the solid electrolyte layer interface side toward the current collector interface side.

The positive electrode layer, negative electrode layer, solid electrolyte layer, and all-solid-state battery using the same according to the present disclosure are expected to be applied to various batteries such as power sources for portable electronic devices and automotive batteries.

1 positive electrode active material 2 solid electrolyte 3 negative electrode active material 4 void 5 positive electrode bonding layer 7 roll 11 positive electrode current collectors 12, 112 positive electrode mixture layer 12a first positive electrode mixture layer 12b second positive electrode mixture layer 13 negative electrode current collector 14 negative electrode mixture layers 20, 120 positive electrode layer 30 negative electrode layer 40 solid electrolyte layers 100, 200 all-solid battery

Claims (10)

a positive electrode layer comprising a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector and containing at least a positive electrode active material and a solid electrolyte;
a negative electrode layer comprising a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector and containing at least a negative electrode active material and a solid electrolyte;
a solid electrolyte layer disposed between the positive electrode mixture layer and the negative electrode mixture layer and containing at least a solid electrolyte having ionic conductivity;
with
The active material volume ratio, which is the ratio of the volume of the positive electrode active material to the sum of the volume of the positive electrode active material and the volume of the solid electrolyte in the positive electrode mixture layer, in the thickness direction of the positive electrode mixture layer is becomes larger as it approaches the positive electrode current collector interface side from the solid electrolyte layer interface side of the agent layer,
The porosity of the positive electrode mixture layer decreases as the positive electrode mixture layer approaches the positive electrode current collector interface side from the solid electrolyte layer interface side in the thickness direction of the positive electrode mixture layer.
All-solid battery. At least one layer selected from the group consisting of the positive electrode mixture layer, the negative electrode mixture layer, and the solid electrolyte layer has a solvent concentration of 50 ppm or less and a binder concentration of 100 ppm or less.
The all-solid-state battery according to claim 1. In the positive electrode mixture layer, the active material volume ratio of a portion near the positive electrode current collector is greater than 0.7,
The all-solid-state battery according to claim 1 or 2. In the positive electrode mixture layer, the active material volume ratio of a portion near the solid electrolyte layer is 0.5 or more.
The all-solid-state battery according to any one of claims 1 to 3. The positive electrode mixture layer has a first positive electrode mixture layer arranged on the positive electrode current collector side and a second positive electrode mixture layer arranged on the solid electrolyte layer side,
the volume ratio of the active material in the first positive electrode mixture layer is greater than the volume ratio of the active material in the second positive electrode mixture layer;
The porosity of the first positive electrode mixture layer is smaller than the porosity of the second positive electrode mixture layer.
The all-solid-state battery according to claim 1 or 2. the volume ratio of the active material in the first positive electrode mixture layer is greater than 0.7;
The all-solid-state battery according to claim 5. The first positive electrode mixture layer has a porosity of 0.05% or more and 8% or less.
The all-solid-state battery according to claim 5 or 6. The volume ratio of the active material in the second positive electrode mixture layer is 0.5 or more.
The all-solid-state battery according to any one of claims 5-7. The porosity of the second positive electrode mixture layer is 5% or more and 35% or less.
The all-solid-state battery according to any one of claims 5-8. The positive electrode layer further includes a positive electrode bonding layer disposed between the positive electrode current collector and the positive electrode mixture layer and containing at least a conductive agent.
The all-solid-state battery according to any one of claims 1 to 9.

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