JP2021128857A - All-solid battery negative electrode - Google Patents

Abstract

To provide an all-solid battery negative electrode capable of suppressing an increase in internal resistance even when Si coated with a solid electrolyte is used as a negative electrode active material.SOLUTION: An all-solid battery negative electrode includes coated particles formed by coating a negative electrode active material containing Si with a sulfide solid electrolyte, and a composite particle composed of a negative electrode active material and a sulfide solid electrolyte and containing five or more negative electrode active materials, and the aspect ratio of the composite particles is 2.0 or less, and the long side is 38.3 μm or less.SELECTED DRAWING: Figure 1

Description

The present application relates to a negative electrode for an all-solid-state battery.

Si is attracting attention as a negative electrode active material for solid-state batteries. This is because Si has a high theoretical capacity and is effective in increasing the energy density of the battery. However, on the other hand, the volume change due to charging and discharging is large, and the contact with the conductive material such as the solid electrolyte and carbon is cut off, and the resistance tends to increase.

On the other hand, conventionally, it has been considered that the volume change due to charging and discharging can be suppressed by coating Si with a solid electrolyte. For example, Patent Document 1 discloses a technique for coating an active material with a sulfide solid electrolyte, and further, Si, a carbon material, and the like are listed as negative electrode active materials in the same document. Further, Patent Documents 2 and 3 do not specifically disclose the use of Si as the negative electrode active material, but disclose a technique for coating the negative electrode active material with a sulfide solid electrolyte.

Japanese Unexamined Patent Publication No. 2016-207418 Japanese Unexamined Patent Publication No. 2015-22016 JP-A-2017-68929

As described above, it is considered that the volume change can be suppressed by coating Si, which is the negative electrode active material, with a solid electrolyte. On the other hand, when Si coated with a solid electrolyte is used, there is a problem that the internal resistance is significantly increased as compared with the case where Si without coating is used.

In view of the above circumstances, an object of the present application is to provide a negative electrode for an all-solid-state battery capable of suppressing an increase in internal resistance even when Si coated with a solid electrolyte is used as a negative electrode active material.

As one means for solving the above problems, the present application is composed of coated particles obtained by coating a negative electrode active material containing Si with a sulfide solid electrolyte, a negative electrode active material and a sulfide solid electrolyte, and is composed of a negative electrode active material. Discloses a negative electrode for an all-solid-state battery, which comprises a composite particle containing 5 or more particles, and the composite particle has an aspect ratio of 2.0 or less and a long side of 38.3 μm or less.

According to the negative electrode for all-solid-state batteries of the present disclosure, even if Si coated with a solid electrolyte is used as the negative electrode active material, an increase in internal resistance can be suppressed.

It is the schematic of the negative electrode 100 for an all-solid-state battery. 6 is an SEM image of an example of the coated particles 10 and the composite particles 20. It is a flowchart of the manufacturing method 200 of the negative electrode for an all-solid-state battery. It is an SEM image of the composite particle of Comparative Example 1. It is an SEM image of the composite particle of Comparative Example 2. It is an SEM image of the composite particle of Example 1. It is an SEM image of the composite particle of Example 2. 3 is an SEM image of the composite particles of Example 3. This is the result of the internal resistance evaluation test.

The negative electrode for an all-solid-state battery of the present disclosure is composed of coated particles formed by coating a negative electrode active material containing Si with a sulfide solid electrolyte, and a negative electrode active material and a sulfide solid electrolyte, and contains 5 or more negative electrode active materials. It is characterized in that the composite particles containing the composite particles include, and the aspect ratio of the composite particles is 2.0 or less and the long side is 38.3 μm or less.

Conventionally, by coating a negative electrode active material containing Si with a solid electrolyte, expansion and contraction of Si due to charging and discharging can be suppressed, but by coating with a solid electrolyte, the electrical resistance is higher than that of an uncoated negative electrode active material. Is known to decrease. It was considered that this is because when the solid electrolyte is coated with the negative electrode active material, the crystallinity of the solid electrolyte is lowered and the Li ion conductivity of the solid electrolyte is deteriorated. However, as a result of diligent studies by the present inventor, it has been found that the deterioration of the electric resistance is not only due to the above reason but also due to the presence of the negative electrode active material-solid electrolyte composite particles. Such composite particles have a form in which the solid electrolyte becomes like bean paste and a plurality of negative electrode active materials or coated negative electrode active materials are incorporated, and the conductive auxiliary agent added at the time of coating is added. Since it contained almost no electrons, it was considered that the electron conductivity was insufficient. Therefore, it was speculated that the presence of such composite particles hindered the electron conduction path in the electrode and increased the electrical resistance in the electrode.

Therefore, the present inventor has found that by adjusting the aspect ratio and the major axis of the composite particles as described above, it is possible to suppress a decrease in internal resistance due to the presence of the composite particles, and the all-solid state of the present disclosure. The negative electrode for the battery was completed.

[Negative electrode 10 for all-solid-state battery]
Hereinafter, the negative electrode for an all-solid-state battery of the present disclosure will be described using the negative electrode 100 for an all-solid-state battery, which is one embodiment. FIG. 1 shows a schematic view of the negative electrode 100 for an all-solid-state battery.

As shown in FIG. 1, the negative electrode 100 for an all-solid-state battery includes coated particles 10, composite particles 20, a second solid electrolyte 30, and a conductive auxiliary agent 40. FIG. 2 shows an SEM image of an example of the coated particles 10 and the composite particles 20.

(Coated particles 10)
The coated particles 10 are formed by coating the negative electrode active material 11 containing Si with the first solid electrolyte 12 (sulfide solid electrolyte). “Coated” means that the coverage of the first solid electrolyte 12 with respect to the surface of the negative electrode active material 11 is at least 50% or more. The coverage is preferably 70% or more, more preferably 90% or more, still more preferably 100%. By coating the negative electrode active material 11 containing Si with the first solid electrolyte 12, the expansion and contraction of the negative electrode active material due to charging and discharging is suppressed.

The negative electrode active material containing Si is not particularly limited as long as it contains Si in the composition, but is preferably Si alone. The first solid electrolyte 12 is a sulfide solid electrolyte. As the sulfide solid electrolyte, a known sulfide solid electrolyte can be used. For example, 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 S-P} 2 S 5, LiI-Li 2 S-P 2 O 5, LiI-Li 3 PO 4 -P 2 S 5, Li 2 S-P 2 include the S 5 -GeS _2, etc. Can be done.

The average particle size of the negative electrode active material 11 contained in the coated particles 10 is not particularly limited, but is preferably 600 nm or more and less than 2.6 μm. Here, the "average particle size" is the particle size calculated by the laser diffraction particle size distribution measurement when the cumulative frequency is 50%, counting from the smallest particle size.

(Composite particle 20)
The composite particle 20 is composed of the negative electrode active material 11 and the first solid electrolyte 12, and contains 5 or more negative electrode active materials. Further, the composite particles 20 substantially do not contain a conductive auxiliary agent. "Substantially free of conductive auxiliary agent" means that only when the conductive auxiliary agent is inevitably contained is allowed, and further, the content of the conductive auxiliary agent in the composite particles 20 is 3% by mass. It means that it is as follows. The content of the conductive auxiliary agent in the composite particles 20 is preferably 2% by mass or less, more preferably 1% by mass or less. The lower part of FIG. 2 shows an SEM image of an example of the composite particle compounded particles 20 when a coating active material (a mixture of the coated particles 10 and the composite particles 20 and the like) is prepared by adding a conductive auxiliary agent. .. It can be seen that the conductive auxiliary agent is not present in the composite particles 20 of the image.

Further, the composite particle 20 has an aspect ratio of 2.0 or less, which is the ratio of the long side to the short side, and the long side is 38.3 μm or less. The lower limit of the aspect ratio is not particularly limited, but it is preferable that the aspect ratio is 1.1 or more. The lower limit of the long side of the composite particle 20 is not particularly limited, but the long side is preferably 17.7 μm or more. Here, the ferret diameter is used for the short side and the long side. The long side and the short side of the composite particle 20 can be measured by an electron emitting scanning electron microscope (FE-SEM) or the like. The negative electrode 100 for an all-solid-state battery contains only the composite particles 20 included in the above range, in other words, the negative electrode 100 for an all-solid-state battery does not contain coarse composite particles not included in the above range. It is possible to suppress an increase in the internal resistance of the negative electrode.

The ratio of the number of particles of the composite particles 20 to the total number of particles of the coated particles 10 and the composite particles 20 is not particularly limited, but may be 1% to 20%.

(Second solid electrolyte 30)
The second solid electrolyte 30 is an optional component and is not particularly limited as long as it is a solid electrolyte applicable to the negative electrode for an all-solid-state battery. For example, an oxide solid electrolyte or a sulfide solid electrolyte can be used. A sulfide solid electrolyte is preferable. Examples of the oxide solid electrolyte include lithium lanthanozylconate, LiPON, Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ , Li-SiO glass, Li-Al-SO glass and the like. can. The sulfide solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Si 2 S-P 2 S 5, Li 2 S-P _{2 S 5 -LiI-LiBr, LiI} -Li 2 S-P 2 S 5, LiI-Li 2 S-P 2 O 5, LiI-Li 3 PO 4 -P 2 S 5, Li 2 S-P 2 S 5 -GeS _{2 and the} like can be mentioned.

Here, in the negative electrode 100 for an all-solid-state battery, the ratio of the weight of the first solid electrolyte 12 to the total weight of the first solid electrolyte 12 and the second solid electrolyte 30 is in the range of 46% by weight to 100% by weight. Is preferable. When the weight ratio of the first solid electrolyte 12 is 100% by weight, it means that the second solid electrolyte 30 is not contained in the negative electrode 10 for an all-solid-state battery. This is because the second solid electrolyte 30 is an optional component. The first solid electrolyte 12 and the second solid electrolyte 30 may use the same type of solid electrolyte.

(Conductive aid 40)
The conductive auxiliary agent 40 is an optional component and is not particularly limited as long as it is a conductive auxiliary agent applicable to the negative electrode for an all-solid-state battery. For example, carbon material and metal material can be mentioned. Examples of the carbon material include spherical carbon, acetylene black, Ketjen black, VGCF (gas phase carbon fiber), graphite and the like. Examples of the metal material include nickel, aluminum, stainless steel and the like. One type of such conductive auxiliary agent may be used, but two or more types may be used. The content of the conductive auxiliary agent is preferably in the range of 1.0% by weight to 2.5% by weight with respect to the content of the negative electrode active material.

(Other optional ingredients)
The negative electrode 100 for an all-solid-state battery may contain an optional component such as a binder in addition to the above. Examples of the binder include a fluorine-based binder such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), a rubber-based binder such as styrene-butadiene rubber (SBR), polypropylene (PP), and polyethylene (PE). ) And other olefin-based binders, and cellulose-based binders such as carboxymethyl cellulose (CMC). The content of other optional components in the negative electrode 100 is not particularly limited as long as it can exert the effect of suppressing an increase in internal resistance.

Further, the negative electrode 100 for an all-solid-state battery may include a negative electrode current collector. Examples of the metal constituting the negative electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. Especially Cu and Al are preferable. The negative electrode current collector may have some coating layer on its surface for adjusting the resistance. The thickness of the negative electrode current collector is not particularly limited.

(shape)
The shape of the negative electrode 100 for an all-solid-state battery is not particularly limited, but it is preferably in the form of a sheet. In this case, the thickness of the negative electrode 100 for an all-solid-state battery 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, the thickness can be appropriately set depending on the capacity of the negative electrode 100 for the all-solid-state battery and the like.

(Use)
The negative electrode 100 for an all-solid-state battery is suitable as a negative electrode for an all-solid-state battery, and is more suitable for a negative electrode for a lithium-ion all-solid-state battery.

[Manufacturing method of negative electrode for all-solid-state battery]
The method for manufacturing the negative electrode for an all-solid-state battery of the present disclosure is not particularly limited, and for example, it can be manufactured by the following manufacturing method 200 for the negative electrode 100 for an all-solid-state battery. FIG. 3 shows a flowchart of a method 200 for manufacturing the negative electrode 100 for an all-solid-state battery.

As shown in FIG. 3, the manufacturing method 200 of the negative electrode 100 for an all-solid-state battery includes a coating step S1, a mixing step S3, and a forming step S4. Further, a removal step S2, which is an optional step, may be provided between the coating step S1 and the mixing step S3.

(Coating step S1)
The coating step S1 is a step of coating the negative electrode active material 11 containing Si with the first solid electrolyte 12. At this time, the conductive auxiliary agent 40 may be added as needed. The coating step S1 can be performed by a known method using, for example, a particle compounding device or the like. The conditions of the device are also set as appropriate according to the purpose.

(Removal step S2)
After the coating step S1 and before the mixing step S2, the obtained coating active material (mixture of coated particles 10, composite particles 20, etc.) has an aspect ratio of more than 2.0 and a long side. When coarse composite particles exceeding 38.3 μm are present, the step is to classify the coarse composite particles by a sieve and remove the coarse composite particles. The removal step S2 is an arbitrary step. The mesh size of the sieve is not particularly limited, but is preferably 45 μm or less, more preferably 32 μm or less, and further preferably 20 μm or less. In the removal step S2, two or more types of open sieves may be used in combination.

(Mixing step S3)
The mixing step S3 is performed after the coating step S1 or the removing step S2, and is a step of mixing the coating active material obtained by these steps with the second solid electrolyte 30 or the like which is an optional component. The mixing method is not particularly limited, and may be a dry type or a wet type. For example, the material constituting the negative electrode 100 for an all-solid-state battery may be dispersed in an organic dispersion medium to form a slurry. Alternatively, the materials constituting the negative electrode 100 for an all-solid-state battery may be mixed in a dry manner. Since these mixing methods are known, they are omitted here. It is known by the present inventor that the composite particles 20 are not crushed in the mixing step S3.

(Formation step S4)
The forming step S4 is a step of forming the mixture obtained in the mixing step S3 on the negative electrode 100 for an all-solid-state battery. When the materials constituting the negative electrode 100 for an all-solid-state battery are mixed in a wet manner as described above to form a slurry, the slurry is applied to a base material or a negative electrode current collector and dried to obtain the negative electrode 100 for an all-solid-state battery. Can be formed. When mixed by a dry method, the negative electrode 100 for an all-solid-state battery can be formed by press-molding the mixed mixture.

As described above, the negative electrode 100 for an all-solid-state battery can be manufactured by the method 200 for manufacturing a negative electrode for an all-solid-state battery. However, the method 200 for manufacturing the negative electrode 100 for an all-solid-state battery is an embodiment of the method for manufacturing a negative electrode for an all-solid-state battery of the present disclosure, and the method for manufacturing a negative electrode layer for an all-solid-state battery of the present disclosure is limited to this. is not it.

Hereinafter, the negative electrode layer for an all-solid-state battery of the present disclosure will be further described with reference to Examples.

[Manufacturing of evaluation battery]
As follows, the evaluation batteries according to Examples 1 to 3 and Comparative Examples 1 and 2 were produced.

<Comparative example 1>
(Preparation of negative electrode structure)
A coating active material was prepared using a particle composite lowering device (NOB-MINI, manufactured by Hosokawa Micron Co., Ltd.). First, the negative electrode active material (Si particles), the sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ )), which is the first solid electrolyte, and the average particle size are placed in the processing container of the apparatus. 0.5 μm) and the conductive auxiliary agent (spherical carbon, specific surface area 93 m ² / g) were added at the ratio shown in Table 1 below so as to have a total of 30 g. Next, the distance between the rotary splash (blade) of the compression shear rotor and the inner wall of the processing vessel is set to 1 mm, the pressure is set to 100 Pa, the blade peripheral speed is set to 26.4 m / s, and the processing time is set to 12.5 minutes. The treatment was carried out to obtain a coating active material.

The obtained coating active material, a sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ), an average particle size of 0.5 μm), which is a second solid electrolyte, and a conductive auxiliary agent ( VGCF) and binder (PVdF) are prepared, and these are weighed in a weight ratio so that the negative electrode active material: sulfide solid electrolyte: conductive auxiliary agent: binder = 53: 41: 4: 2, and the dispersion medium (heptane) is used. Mixed with. The obtained mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a negative electrode slurry.

The obtained negative electrode slurry was applied onto a negative electrode current collector (copper foil) and dried under the conditions of 100 ° C. for 30 minutes. Then, ^{by punching to a size of 1 cm 2} , a negative electrode structure having a negative electrode layer and a negative electrode current collector was obtained. The thickness of the negative electrode layer was 31 μm.

(Preparation of positive electrode structure)
Positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ), average particle size 0 .5 μm), conductive auxiliary agent (VGCF), binder (PVdF) are prepared, and these are positive electrode active material: sulfide solid electrolyte: conductive auxiliary agent: binder = 85: 13: 1: 1 by weight ratio. Weighed and mixed with a dispersion medium (heptane). The obtained mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a positive electrode slurry.

The obtained positive electrode slurry was applied onto a positive electrode current collector (aluminum foil) and dried under the conditions of 100 ° C. for 30 minutes. Then, ^{by punching to a size of 1 cm 2} , a positive electrode structure having a positive electrode layer and a positive electrode current collector was obtained. The thickness of the positive electrode layer was 50 μm.

(Manufacturing of evaluation battery)
A sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ), average particle size 0.5 μm) was placed in a tubular plastic having an inner diameter and cross-sectional area of 1 cm ^{2 and 4 ton / cm 2} A solid electrolyte layer (thickness 15 μm) was obtained by pressing with.
The positive electrode structure and the negative electrode structure were arranged so as to sandwich the obtained solid electrolyte layer, and pressed at ^{4 ton / cm 2.} Then, stainless steel rods were placed on the positive electrode side and the negative electrode side, respectively, and restrained at 5 MPa to obtain an all-solid-state battery (evaluation battery).

<Comparative Example 2, Examples 1 to 3>
The evaluation batteries according to Comparative Examples 2 and 1 to 3 were produced in the same manner as the evaluation batteries according to Comparative Example 1 except that the following changes were made. Table 1 shows the average particle size of the negative electrode active material (Si particles), the opening of the sieve used, the ratio of the weight of the first solid electrolyte to the weight of the first solid electrolyte and the second solid electrolyte, and the coating step. The negative electrode active material (Si particles), the sulfide solid electrolyte (first solid electrolyte), and the weighed values of the conductive auxiliary agent used in the above are shown respectively.

-Change 1: In Comparative Example 2, a negative electrode slurry was prepared using a coating active material that had passed through a sieve having a mesh opening of 42 μm. In Example 2, a negative electrode slurry was prepared using a coating active material which was sequentially passed through a sieve having a mesh size of 45 μm and 32 μm. In Example 3, a negative electrode slurry was prepared using a coating active material which was sequentially passed through a sieve having a mesh size of 45 μm and 20 μm.
-Change 2: In Comparative Example 2 and Examples 1 to 3, the negative electrode active material: sulfide solid electrolyte: conductive auxiliary agent: binder = 62: 32: 5: 1 in the negative electrode active material: sulfide solid electrolyte: conductive auxiliary agent by weight ratio of each material at the time of preparing the negative electrode slurry. Mixed in proportion.

[evaluation]
<Cross-section observation>
A field emission scanning electron microscope (FE-SEM) was applied to the coating active materials obtained in Examples 1 to 3 and Comparative Examples 1 and 2 (passed through a sieve for Examples 2, 3 and Comparative Example 2). Observed using. At the time of observation, after embedding the coated particles in the ABR resin, a cross section was obtained by cross-section polisher (CP) processing. Among the observed composite particles, the aspect ratio (long side / short side) and the length of the long side were measured for the composite particles having the longest side. The results are shown in Table 2, FIGS. 4 to 8.

<Internal resistance evaluation>
The internal resistance of the evaluation batteries according to Examples 1 to 3 and Comparative Examples 1 and 2 was evaluated by the DC-IR method. Specifically, the OCV of the evaluation battery was adjusted to 3.7V, then discharged at 17.2 mA for 10 seconds, and the voltage during that period was measured. Then, the internal resistance was obtained from the change in the voltage. For comparison, the internal resistance of the battery not coated with the negative electrode active material was set to 100%. The results are shown in Table 2 and FIG.

From Table 2 and FIG. 9, in Examples 1 to 3 having no coarse composite particles, the increase in the internal resistance of the battery was reduced as compared with Comparative Examples 1 and 2 in which the coarse composite particles were present. rice field. From this result, it is considered that when the aspect ratio of the composite particles is 2.0 or less and the long side is 38.3 μm, the increase in the internal resistance of the battery can be suppressed.

Comparing Example 1 and Comparative Example 2, the length of the long side and the aspect ratio of the composite particles are smaller in Example 1 which has not been passed through a sieve. It is considered that this is because the ratio of the first solid electrolyte in Example 1 is smaller than that in Comparative Example 2, and the amount of glue forming the composite particles is small.

10 Coated particles 11 Negative electrode active material 12 First solid electrolyte 20 Composite particles 30 Second solid electrolyte 40 Conductive aid 100 Negative electrode for all-solid-state battery 200 Method for manufacturing negative electrode for all-solid-state battery

Claims (1)

Coated particles formed by coating a negative electrode active material containing Si with a sulfide solid electrolyte,
Containing composite particles composed of the negative electrode active material and the sulfide solid electrolyte and containing 5 or more particles of the negative electrode active material.
The aspect ratio of the composite particles is 2.0 or less, and the long side is 38.3 μm or less.
Negative electrode for all-solid-state batteries.

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