JP7180419B2 - All-solid battery - Google Patents

Description

The present application discloses an all-solid-state battery.

Patent Literature 1 discloses an all-solid battery including a positive electrode active material having a rock salt layered structure capable of intercalating and deintercalating lithium ions. Patent document 2 includes an intermediate layer between a positive electrode layer and a solid electrolyte layer, and the intermediate layer contains monoclinic LiMO ₃ (where M represents Ti or Mn) for an all-solid-state battery. A laminate is disclosed. Patent Document 3 uses a particulate positive electrode active material selected from a layered positive electrode active material, a spinel type positive electrode active material, or an olivine type positive electrode active material, and the positive electrode layer contains two or more types of particulate positive electrode active materials having different average particle sizes. Cathode bodies containing materials are disclosed. Patent Document 4 discloses a method in which a first active material powder having a spinel-type crystal structure that expands during discharge and shrinks during charge, and a second active material powder that has a layered rock salt-type crystal structure that shrinks during discharge and expands during charge are combined into It discloses cathodes mixed from 1:2 to 2:1 by %.

JP 2014-146458 A JP 2014-110149 A Japanese Patent No. 5262143 JP 2012-248454 A

In an all-solid-state battery, when a positive electrode active material having a spinel crystal structure is used as the positive electrode active material, reaction unevenness is large. This is because the potential difference between the high SoC (State of Charge) positive electrode active material and the low SoC positive electrode active material is small, and the positive electrode active material on the solid electrolyte layer side reacts preferentially.

Accordingly, an object of the present application is to provide an all-solid-state battery in which reaction unevenness is suppressed.

As a result of intensive studies, the present inventors have found that, in the positive electrode active material layer of an all-solid-state battery, the first positive electrode layer and the second positive electrode layer disposed between the first positive electrode layer and the positive electrode current collector are In addition, the first positive electrode layer contains more layered positive electrode active material than the spinel-type positive electrode active material, and the second positive electrode layer contains more spinel-type positive electrode active material than the layered positive electrode active material, thereby solving the above problems. I found that it can be done, and completed the present invention.

That is, as one means for solving the above problems, the present application provides an all-solid battery comprising a positive electrode current collector, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector in this order, wherein the positive electrode layer is comprising a layered positive electrode active material and a spinel-type positive electrode active material, wherein the positive electrode layer comprises a first positive electrode layer and a second positive electrode layer disposed between the first positive electrode layer and the positive electrode current collector; An all-solid-state battery is disclosed in which the first cathode layer comprises more layered cathode active material than the spinel-type cathode active material, and the second cathode layer comprises more spinel-type cathode active material than the layered cathode active material.

According to the all-solid-state battery of the present disclosure, reaction unevenness can be suppressed.

1 is a schematic cross-sectional view of an all-solid-state battery 100; FIG. 3 is an enlarged cross-sectional view focusing on the positive electrode layer 20. FIG. This is the case where only the second positive electrode layer is used as the positive electrode layer. A cross-sectional view focusing on the second positive electrode layer is shown in the upper part, and the potential curve of the LNMO is shown in the lower part. This is the case where only the first positive electrode layer is used as the positive electrode layer. A cross-sectional view focusing on the first positive electrode layer is shown in the upper part, and the potential curve of the NCM is shown in the lower part. This is the case where the positive electrode layer of the present disclosure is used for the positive electrode layer. The upper part shows a cross-sectional view focusing on the positive electrode layer of the present disclosure, and the lower part shows the potential curve of the positive electrode layer divided into the first positive electrode layer and the second positive electrode layer. FIG. 5 is a diagram showing the results of Examples 1 to 5 and Comparative Examples 1 and 2;

[All-solid battery]
An all-solid-state battery of the present disclosure will be described with reference to an all-solid-state battery 100 that is one embodiment.
The all-solid-state battery 100 includes a positive electrode current collector 10, a positive electrode layer 20, a solid electrolyte layer 30, a negative electrode layer 40, and a negative electrode current collector 50 in this order. "Provided in this order" means that each layer is arranged in this order, and does not interfere with a form in which another layer is arranged between each layer. In other words, it includes a mode in which each layer is directly arranged in this order, and a mode in which another layer is arranged between each layer and indirectly arranged in this order.
FIG. 1 shows a schematic cross-sectional view of an all-solid-state battery 100. As shown in FIG.

(Positive electrode layer 20)
The positive electrode layer 20 contains at least a positive electrode active material. The positive electrode active material includes a layered positive electrode active material and a spinel-type positive electrode active material. FIG. 2 shows an enlarged cross-sectional view focusing on the positive electrode layer 20 .
As shown in FIG. 2 , the cathode layer 20 comprises a first cathode layer 21 and a second cathode layer 22 interposed between the first cathode layer 21 and the cathode current collector 10 . The first positive electrode layer 21 contains more layered positive electrode active material than the spinel-type positive electrode active material, and the second positive electrode layer 22 contains more spinel-type positive electrode active material than the layered positive electrode active material. .

As shown in FIG. 2, the second positive electrode layer 22 is laminated on one side surface of the positive electrode current collector 10, the first positive electrode layer 21 is laminated on one side surface of the second positive electrode layer 22, A solid electrolyte layer 30 is laminated on one surface of the first positive electrode layer 21 .
However, in the all-solid-state battery of the present disclosure, the positive electrode layer may include the second positive electrode layer and the first positive electrode layer in this order from the positive electrode current collector side to the solid electrolyte layer side. In other words, in the all-solid-state battery of the present disclosure, the positive electrode layer may be two or more layers, between the positive electrode current collector and the second positive electrode layer, between the second positive electrode layer and the first positive electrode layer , another layer may be provided between the first positive electrode layer and the solid electrolyte layer.

In addition, the above-mentioned "the first positive electrode layer 21 contains more layered positive electrode active material than the spinel-type positive electrode active material" means that the first positive electrode layer 21 is the positive electrode active material, and the spinel-type positive electrode active material It means a state in which the layered positive electrode active material is contained in a larger amount than the spinel type positive electrode active material, and the spinel type positive electrode active material may not be contained. In other words, the first positive electrode layer 21 contains at least the layered positive electrode active material as the positive electrode active material, and when the first positive electrode layer 21 contains the spinel-type positive electrode active material and the layered positive electrode active material as the positive electrode active material, means that the layered positive electrode active material is contained more than the spinel positive electrode active material. Preferably, the positive electrode active material contained in the first positive electrode layer 21 is a layered positive electrode active material, or the positive electrode active material contained in the first positive electrode layer 21 contains a spinel-type positive electrode active material and a layered positive electrode active material. In this case, the spinel-type positive electrode active material and the layered positive electrode active material are contained at a weight ratio of 0:10 to 3:7.

“The second cathode layer 22 contains more spinel-type cathode active material than the layered cathode active material” means that the second cathode layer 22 contains more spinel-type cathode active material than the layered cathode active material on a weight basis. It means a state in which a large amount of active material is contained, and the layered positive electrode active material may not be contained. In other words, the second positive electrode layer 22 contains at least a spinel-type positive electrode active material as the positive electrode active material. As a standard, it means that the spinel-type positive electrode active material is included more than the layered positive electrode active material. Preferably, the positive electrode active material contained in the second positive electrode layer 22 is a spinel-type positive electrode active material, or the positive electrode active material contained in the second positive electrode layer 22 is a spinel-type positive electrode active material and a layered positive electrode active material. When it is included, it is included at a weight ratio of spinel-type positive electrode active material:layered positive electrode active material=10:0 to 7:3.

As the layered positive electrode active material, LiCoO ₂ , LiNiO ₂ , Li _1+x Ni _a Co _b Mn _1-ab O ₂ (0.05≦x≦0.3, 0.24≦a≦0.26, 0.24≦a≦0.26, 24≦b≦0.26) (which may be referred to as “NCM” in this specification). NCM is preferred.
Examples of spinel-type positive electrode active materials include LiMn ₂ O ₄ , LiCoMnO ₄ , and LiNi _x Mn _2-x O ₄ (0≦x≦0.5) (in this specification, x=0.5 is referred to as “LNMO”). There is a thing called this.) etc. can be mentioned. LNMO is preferred.

The reason why the positive electrode layer 20 includes the first positive electrode layer 21 and the second positive electrode layer 22 in the above-described predetermined order is as follows.
First, consider the case where only the second positive electrode layer is used as the positive electrode layer. A cross-sectional view focusing on the second positive electrode layer is shown in the upper portion of FIG. 3, and a potential curve (vertical axis: potential, horizontal axis: capacity) of a spinel-type positive electrode active material (LNMO) is shown in the lower portion. This represents Comparative Example 1, which will be described later. 3 and the arrows indicating the relationship between the upper and lower parts of FIG. 3 are added for convenience in order to visually explain the following. The same applies to FIGS. 4 and 5 below.
As shown in FIG. 3, LNMO has a small potential difference between the high SoC positive electrode active material and the low SoC positive electrode active material. Therefore, the positive electrode active material on the solid electrolyte layer side continues to react preferentially. As a result, the positive electrode active material on the solid electrolyte layer side becomes high SoC, and the potential rises to reach the upper limit voltage. On the other hand, the positive electrode active material on the positive electrode current collector side remains low SoC. Therefore, the positive electrode layer using only the spinel-type positive electrode active material has a large reaction unevenness, and there is a problem that the energy cannot be extracted sufficiently.

Next, consider the case where only the first positive electrode layer is used as the positive electrode layer. A cross-sectional view focusing on the first positive electrode layer is shown in the upper portion of FIG. 4, and a potential curve (vertical axis: potential, horizontal axis: capacity) of the layered positive electrode active material (NCM) is shown in the lower portion. This represents Comparative Example 2, which will be described later.
As shown in FIG. 4, the NCM has a large potential slope with respect to the SoC, so charging unevenness in the thickness direction (lamination method) is small. However, since the layered positive electrode active material (NCM) has a higher resistance than the spinel type positive electrode active material (LNMO), there is a problem that short-term output is disadvantageous.

Finally, consider the case of using the positive electrode layer of the present disclosure. The upper part of FIG. 5 shows a cross-sectional view focusing on the positive electrode layer of the present disclosure, and the lower part shows the potential curve of the positive electrode layer (vertical axis: potential, horizontal axis: capacity) divided into the first positive electrode layer and the second positive electrode layer. Indicated. NCM was used as a positive electrode active material for the first positive electrode layer, and LNMO was used as a positive electrode active material for the second positive electrode layer. This represents Examples 1 to 5 below. As shown in FIG. 5, the NMC has a capacity around the reaction potential of the LNMO and also has a large potential slope with respect to the SoC, so charging unevenness in the thickness direction is small. In addition, the positive electrode active material on the positive electrode current collector side has less unevenness in the thickness direction than that on the solid electrolyte layer side. Therefore, such a positive electrode layer will have sufficient charge energy density.

Therefore, according to the positive electrode layer 20, by providing the first positive electrode layer 21 and the second positive electrode layer 22 in a predetermined order, the reaction unevenness of the positive electrode layer 20 as a whole can be reduced, and the charge energy density can be improved. can.
In addition, when the arrangement order of the first positive electrode layer 21 and the second positive electrode layer 22 is reversed, the above effect cannot be obtained. Since unevenness in reaction is particularly likely to occur on the solid electrolyte layer side, if the order of arrangement of the first positive electrode layer 21 and the second positive electrode layer 22 is reversed, the spinel-type positive electrode active material with large reaction unevenness will cause uneven reaction. This is because it is arranged on the solid electrolyte layer side, which is likely to occur, and it becomes more difficult to obtain the charging energy density.

Further, when the total weight of the layered positive electrode active material and the spinel-type positive electrode active material contained in the entire positive electrode layer 20 is 1, the weight ratio x of the spinel-type positive electrode active material is 0.7≦x<1. preferable. As a result, the charging energy density can be improved, and the decrease in output for a short time can be suppressed, that is, the resistance can also be suppressed.
Such a weight ratio can be calculated from the true density by judging each positive electrode active material particle from the SEM-EDX image of the cross section of the positive electrode, regarding the area ratio as the mixed particle volume ratio, and then calculating the true density.

The positive electrode layer 20 can optionally contain a solid electrolyte, a binder, a conductive aid, and the like, in addition to the positive electrode active material described above. The solid electrolyte that can be contained in the positive electrode layer 20 is preferably an inorganic solid electrolyte. This is because the ionic conductivity is higher than that of organic polymer electrolytes. Moreover, it is because it is excellent in heat resistance compared with an organic polymer electrolyte. Preferred inorganic solid electrolytes include oxide solids such as lithium lanthanum zirconate, LiPON, Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ , Li—SiO glass, Li—Al—S—O glass, and the like. Electrolyte; Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Si ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ —LiI—LiBr , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ -GeS ₂ and other sulfides A solid electrolyte can be exemplified. In particular, a sulfide solid electrolyte is preferred, a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ is more preferred, and a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ -LiI-LiBr is even more preferred. Examples of binders that can be contained in the positive electrode layer 20 include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), polyvinylidene fluoride (PVdF), and the like. Examples of binders that can be contained in the positive electrode layer 20 include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), polyvinylidene fluoride (PVDF), and the like. Conductive agents that can be contained in the positive electrode layer 20 include carbon materials such as acetylene black, ketjen black, and vapor grown carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel.

The content of each component in the positive electrode layer 20 may be the same as the conventional one. The shape of the positive electrode layer 20 may also be the same as the conventional one. In particular, a sheet-shaped positive electrode layer is preferable from the viewpoint that the all-solid-state battery 100 can be easily configured. In this case, the thickness of the positive electrode layer 20 is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 150 μm or less. The thicknesses of the first positive electrode layer 21 and the second positive electrode layer 22 are also appropriately set.

(Solid electrolyte layer 30)
Solid electrolyte layer 30 includes at least a solid electrolyte. The solid electrolyte layer 30 can optionally contain a binder in addition to the solid electrolyte. The solid electrolyte is preferably an inorganic solid electrolyte. This is because the ionic conductivity is higher than that of organic polymer electrolytes. Moreover, it is because it is excellent in heat resistance compared with an organic polymer electrolyte. Preferred inorganic solid electrolytes include oxide solids such as lithium lanthanum zirconate, LiPON, Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ , Li—SiO glass, Li—Al—S—O glass, and the like. Electrolyte; Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Si ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ —LiI—LiBr , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ -GeS ₂ and other sulfides A solid electrolyte can be exemplified. In particular, a sulfide solid electrolyte is preferred, a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ is more preferred, and a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ -LiI-LiBr is even more preferred. Binders similar to the binders described above can be appropriately selected and used. The content of each component in the solid electrolyte layer 30 may be the same as the conventional one. The shape of the solid electrolyte layer 30 may also be the same as the conventional one. In particular, a sheet-like solid electrolyte layer is preferable from the viewpoint that the all-solid-state battery 100 can be easily constructed. In this case, the thickness of the solid electrolyte layer 30 is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 100 μm or less.

(Negative electrode layer 40)
The negative electrode layer 40 contains at least a negative electrode active material. In addition to the negative electrode active material, the negative electrode layer 40 can optionally contain a solid electrolyte, a binder, a conductive agent, and the like. A known negative electrode active material may be used as the negative electrode active material. For example, when constructing a lithium ion battery, silicon-based active materials such as Si, Si alloys and silicon oxides as negative electrode active materials; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate. Substance: metal lithium, lithium alloy, or the like can be used. The solid electrolyte that can be contained in the negative electrode layer 40 is preferably an inorganic solid electrolyte. This is because the ionic conductivity is higher than that of organic polymer electrolytes. Moreover, it is because it is excellent in heat resistance compared with an organic polymer electrolyte. Preferred inorganic solid electrolytes include oxide solids such as lithium lanthanum zirconate, LiPON, Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ , Li—SiO glass, Li—Al—S—O glass, and the like. Electrolyte; Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Si ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ —LiI—LiBr , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ -GeS ₂ and other sulfides A solid electrolyte can be exemplified. In particular, a sulfide solid electrolyte is preferred, a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ is more preferred, and a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ -LiI-LiBr is even more preferred. Examples of binders that can be contained in the negative electrode layer 40 include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), polyvinylidene fluoride (PVDF), and the like. Conductive agents that can be contained in the negative electrode layer 40 include carbon materials such as acetylene black, ketjen black, and vapor grown carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel. The content of each component in the negative electrode layer 40 may be the same as the conventional one. The shape of the negative electrode layer 40 may also be the same as the conventional one. In particular, a sheet-like negative electrode mixture layer is preferable from the viewpoint that the all-solid-state battery 100 can be easily configured. In this case, the thickness of the negative electrode layer 40 is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 150 μm or less. However, it is preferable to determine the size (area and thickness) of the negative electrode layer 40 so that the capacity of the negative electrode is larger than the capacity of the positive electrode.

(Positive electrode current collector 10, negative electrode current collector 50)
The positive electrode current collector 10 and the negative electrode current collector 50 may be made of metal foil, metal mesh, or the like. Metal foil is particularly preferred. Examples of metals forming the positive electrode current collector 10 and the negative electrode current collector 50 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. Cu and Al are particularly preferred. The positive electrode current collector 10 and the negative electrode current collector 50 may have some kind of coating layer on their surfaces for adjusting resistance. The thickness of each of the positive electrode current collector 10 and the negative electrode current collector 50 is not particularly limited. For example, it is preferably 0.1 μm or more and 1 mm or less, more preferably 1 μm or more and 100 μm or less.

As described above, the all-solid-state battery of the present disclosure has been described using the all-solid-state battery 100 . According to the all-solid-state battery of the present disclosure, reaction unevenness can be suppressed.

The all-solid-state battery of the present disclosure can be manufactured by a known method. For example, it can be produced by stacking separately produced positive electrode layer, solid electrolyte layer, and negative electrode layer and pressing them. The positive electrode current collector or the negative electrode current collector may be arranged in the positive electrode layer or the negative electrode layer before lamination thereof, or may be arranged after lamination thereof. The positive electrode layer is formed by coating a base material or a positive electrode current collector with a slurry containing a component that constitutes the second positive electrode layer and drying it, and further applying a slurry containing a component that constitutes the first positive electrode layer and drying it. , can be produced by pressing them.

Hereinafter, the all-solid-state battery of the present disclosure will be further described using examples.
The nonpolar solvent described below is heptane, butyl butyrate, or a mixture thereof.

[Fabrication of all-solid-state battery]
<Example 1>
(Preparation of positive electrode)
An _active material (LNMO) and a sulfide solid electrolyte (LiI-- _Li.sub.2O -- _{Li.sub.2SP.sub.2S.sub.5} ) were weighed in a weight ratio of _85:15 . Further, 1.5 parts of the binder (PVDF) and 3.0 parts of the conductive additive (VGCF) were weighed with respect to 100 parts of the active material. Then, using a non-polar solvent, they were mixed so that the weighed solid content rate was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a positive electrode layer slurry 1. . The produced positive electrode layer slurry 1 was applied to an aluminum foil (positive electrode current collector) and dried by heating.

Next, the active material (NCM) and the sulfide _solid electrolyte (LiI-- _Li.sub.2O -- _{Li.sub.2SP.sub.2S.sub.5} ) were weighed so that the weight ratio was _75:25 . Further, 1.5 parts of the binder (PVDF) and 3.0 parts of the conductive additive (VGCF) were weighed with respect to 100 parts of the active material. Then, using a non-polar solvent, they were mixed so that the weighed solid content was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a positive electrode layer slurry 2. . The prepared positive electrode slurry 2 was applied onto the dried positive electrode mixture layer and dried by heating.
Then, the obtained laminate was pressed at 25° C. and a linear pressure of 1 ton/cm to obtain a positive electrode in which the positive electrode current collector and the positive electrode layer were laminated.

From the SEM-EDX image of the cross section of the positive electrode obtained using a SEM-EDX apparatus (manufactured by Hitachi High-Technologies), particles containing Ni, Mn or Ni, Mn, Co are each discriminated, and the area ratio is the mixed particle volume ratio. considered. Then, the mixed particle weight ratio (LNMO ratio) of LNMO was calculated from the true densities of LNMO and NCM. Table 1 shows the results.

(Preparation of negative electrode)
An _active material (lithium titanate: LTO) and a sulfide solid electrolyte (LiI-- _Li.sub.2O -- _{Li.sub.2SP.sub.2S.sub.5} ) were weighed at a weight ratio of _58:42 . Also, 1.5 parts of the binder (PVDF) and 5.0 parts of the conductive additive (VGCF) were weighed with respect to 100 parts of the active material. Then, a non-polar solvent was used to mix the weighed solids so that the solid content was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare negative electrode layer slurry 1. . The prepared negative electrode layer slurry 1 was applied to a Ni foil (negative electrode current collector) and dried by heating. Then, the obtained laminate was pressed at 25° C. and a linear pressure of 1 ton/cm to obtain a negative electrode in which a negative electrode current collector and a negative electrode layer were laminated.
The coating was adjusted so that the positive/negative electrode capacity ratio was 1:1.

(Fabrication of all-solid-state battery)
After laminating so that the positive electrode and the negative electrode face each other with a solid electrolyte layer (LiI—Li ₂ O—Li ₂ SP ₂ S ₅ ) interposed therebetween, the all solid state according to Example 1 is obtained by pressing at a linear pressure of 5 tons. got a battery.

<Examples 2 to 5>
The positive electrode layer was prepared by adjusting the two-layer coating so that the mixed particle weight ratio of LNMO in the positive electrode was the value shown in Table 1. , all-solid-state batteries according to Examples 2 to 5 were obtained.

<Comparative Example 1>
An all-solid-state battery according to Comparative Example 1 was obtained in the same manner as the all-solid-state battery according to Example 1, except that the positive electrode layer was made using only the first positive electrode slurry.

<Comparative Example 2>
An all-solid-state battery according to Comparative Example 2 was obtained in the same manner as the all-solid-state battery according to Example 1, except that the positive electrode layer was made using only the second positive electrode slurry.

<Comparative Example 3>
(Preparation of positive electrode)
The active material (LNMO), the binder (PVDF), and the conductive aid (VGCF) were weighed so that the binder was 1.5 parts and the conductive aid was 3.0 parts with respect to 100 parts of the active material. Then, using a non-polar solvent, they were mixed so that the weighed solid content rate was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a positive electrode layer slurry 3. . The produced positive electrode layer slurry 3 was applied to an aluminum foil (positive electrode current collector) and dried by heating.
The laminate thus obtained was pressed so that the voids were 20 vol % to obtain a positive electrode in which the positive electrode current collector and the positive electrode layer were laminated.

(Preparation of negative electrode)
The active material (LTO), the binder (PVDF), and the conductive aid (VGCF) were weighed so that the binder was 1.5 parts and the conductive aid was 5.0 parts with respect to 100 parts of the active material. Then, a non-polar solvent was used to mix the weighed solids so that the solid content was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare negative electrode layer slurry 2 . . The prepared negative electrode layer slurry 2 was applied to a Ni foil (negative electrode current collector) and dried by heating. Then, the obtained laminate was pressed at 25° C. and a linear pressure of 1 ton/cm to obtain a negative electrode in which a negative electrode current collector and a negative electrode layer were laminated.

(Production of liquid-based battery)
After laminating so that the positive electrode and the negative electrode face each other with a separator made of polymer (polypropylene or polycarbonate) sandwiched therebetween, an electrolytic solution (1.0 M LiPF ₆ , EC (ethylene carbonate):DMC (dimethyl carbonate) = 1:1) is added. A battery according to Comparative Example 3 was obtained by injecting and sealing.

<Comparative Example 4>
A battery according to Comparative Example 4 was obtained by manufacturing in the same manner as the method for manufacturing the battery of Comparative Example 3, except that a positive electrode manufactured as follows was used.

(Preparation of positive electrode)
The active material (LNMO), the binder (PVDF), and the conductive aid (VGCF) were weighed so that the binder was 1.5 parts and the conductive aid was 3.0 parts with respect to 100 parts of the active material. Then, using a non-polar solvent, they were mixed so that the weighed solid content rate was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a positive electrode layer slurry 3. . The produced positive electrode layer slurry 3 was applied to an aluminum foil (positive electrode current collector) and dried by heating.

The active material (NCM), the binder (PVDF), and the conductive additive (VGCF) were weighed so that the binder was 1.5 parts and the conductive additive was 3.0 parts with respect to 100 parts of the active material. Then, using a non-polar solvent, they were mixed so that the weighed solid content rate was 63 wt %, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a positive electrode layer slurry 4. . The prepared positive electrode layer slurry 4 was applied onto the dried positive electrode mixture layer and dried by heating.
The laminate thus obtained was pressed so that the voids were 20 vol % to obtain a positive electrode in which the positive electrode current collector and the positive electrode layer were laminated.

The method for calculating the mixed particle weight ratio of LNMO is the same as described above. Table 1 shows the results.

[evaluation]
In a constant temperature bath at 25° C., the batteries prepared as described above were CCCV charged (1/500 Cut) to 3.5 V at 1/10 C to obtain the charge capacity of each battery. Also, the charge energy density was calculated from the product of the capacity per weight and the average voltage.
Next, the battery was adjusted to 50% SoC and subjected to 10 sec constant power discharge to obtain a 10 sec discharge output value up to 1.5 V cut. The conditions for the 10 sec constant power discharge were set according to each battery.

These results are shown in Table 1. The results of Examples 1 to 5 and Comparative Examples 1 and 2 are expressed as ratios to the charge energy density and 10-sec discharge output value of Comparative Example 1, which are both 1.00. Further, the results of Comparative Examples 3 and 4 are expressed as a ratio to the charge energy density and 10-sec discharge output value of Comparative Example 3, which are each assumed to be 1.00.
Further, FIG. 6 shows the relationship between the LNMO ratio and the charge energy density ratio or the 10 sec discharge output value ratio in Examples 1 to 5 and Comparative Examples 1 and 2.

From Table 1 and FIG. 6, it was found that the charging energy densities of Examples 1-5 were higher than those of Comparative Examples 1 and 2. The charging energy density can also be said to be a parameter representing reaction unevenness. Therefore, it was found that reaction unevenness was suppressed by using a positive electrode layer including a first positive electrode layer containing NMC as a positive electrode active material and a second positive electrode layer containing LNMO as a positive electrode active material.

Here, the charging energy density results of Examples 1 to 5 and Comparative Examples 1 and 2 are further examined. The reason why the charging energy density is improved when the LNMO ratio is 1 to 0.7 is considered to be that reaction unevenness is suppressed and a capacity close to the theoretical value can be obtained. On the other hand, the reason why the LNMO ratio decreases from 0.7 to 0 is that the ratio of NMC with a low average potential increases.

Next, the results of the 10 sec discharge output value will be examined. Since the resistance of the NCM is higher than that of the LNMO, it is considered that the output decreases for a short time as the NMC content increases.
In Examples 1 to 3, the 10-sec discharge output value did not decrease so much, but when the LNMO ratio was less than 0.7, the 10-sec discharge output value decreased sharply. From this, it is considered that when the LNMO ratio is less than 0.7, the properties of NCM begin to appear strongly. This is also consistent with the charge energy density beginning to decrease when the LNMO ratio becomes less than 0.7.
Therefore, it can be seen that the LNMO ratio is preferably 0.7 or more and less than 1 in order to improve the charge energy density and suppress the decrease in short-time output.

In addition, according to Comparative Examples 3 and 4 in Table 1, even if the LNMO ratio was set to 0.8 in the liquid-based battery, it was found that the effect was not so strong. This is thought to be because, in Comparative Examples 3 and 4, liquid-based batteries were used, and in the electrolytic solution, reaction unevenness appeared due to diffusion rate control of counter ions, and the effect of forming two layers of the positive electrode was limited. be done. As in Examples 1 to 5 and Comparative Examples 1 and 2, when a solid electrolyte is used, the Li ion transport rate is 1, and the influence of diffusion in the electrolyte is small, so it can be inferred that the above effects were obtained.

10 positive electrode current collector 20 positive electrode layer 21 first positive electrode layer 22 second positive electrode layer 30 solid electrolyte layer 40 negative electrode layer 50 negative electrode current collector 100 all-solid battery

Claims (1)

In an all-solid battery comprising a positive electrode current collector, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector in this order,
The positive electrode layer includes a layered positive electrode active material and a spinel-type positive electrode active material,
The positive electrode layer includes a first positive electrode layer and a second positive electrode layer disposed between the first positive electrode layer and the positive electrode current collector,
The first positive electrode layer contains more of the layered positive electrode active material than the spinel-type positive electrode active material,
The second positive electrode layer contains more spinel-type positive electrode active material than the layered positive electrode active material,
When the total weight of the layered positive electrode active material and the spinel-type positive electrode active material contained in the entire positive electrode layer is 1, the weight ratio x of the spinel-type positive electrode active material is 0.7 ≤ x < 1.
All-solid battery.

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